critical thinking questions about earthquakes

Questions and answers on the subject of earthquakes

Faqs on the subject of earthquakes are answered by researchers from the helmholtz-gemeinschaft (helmholtz association)..

1. What are earthquakes and what causes them? 2. How many earthquakes occur annually worldwide? 3. What equipment is used to record and measure earthquakes? 4. Where do earthquakes occur most frequently? 5. Is it possible to predict earthquakes? 6. Why are the values published on the magnitude of an earthquake sometimes slightly different? 7. Where can I obtain information on current and past earthquakes? 8. How can I protect myself during an earthquake? 9. How much energy is released by an earthquake? 10. How large is the risk of an earthquake in Germany? 11. What was the strongest earthquake ever recorded in Germany? 12. What does epicentre mean? 13. What is the intensity of an earthquake? 14. What is "earthquake magnitude"? 15. What is a Richter scale? 16. What was the strongest earthquake ever recorded? 17. Which magnitude values can be distinguished from each other? 18. Are earthquake-proof building structures possible? 19. Why can the ground liquefy due to an earthquake?

  FAQ Earthquakes download   online view

1. What are earthquakes and what causes them?

Earthquakes are rupturing processes in the Earth's crust that lead to vibrations on the sur­face layer of the planet. Most of the damaging earthquakes so far have been tectonic in origin (tectonic quakes).  They are caused by a sudden displacement along a fracture face in the Earth's crust and by the resulting release of accumulated elastic energy. These fault zones are predominantly located along plate boundaries. However, there are other reasons than tectonics for the occurrence of earthquakes.

2. How many earthquakes occur annually worldwide?

Very strong earthquakes with magnitudes of 8 and higher occur once a year on a global average. On average, 15 quakes ranging in magnitude between 7 and 8 strike on an annual basis. Quakes with magnitudes greater than 7 can have devastating effects on people and the environment. Up to 1,300 moderate quakes on a scale of 5 to 6 take place worldwide every year, smaller quakes with magnitudes of 3 to 4 occur, roughly speaking, 130,000 times a year. Magnitude 3 earthquakes are usually still noticed by people if they are in the vicinity of the epicentre, but in most cases they do not cause any damage.

3. What equipment is used to record and measure earthquakes?

Earthquakes are usually measured by seismometers. Seismometers are installed on the Earth's surface around the globe in particularly "quiet places", generally in seismological observatories. These may be old tunnels, basements in remote buildings or specifically dedicated buildings on their own piece of land. The best-known seismological observatories in Germany are located in the Black Forest (BFO station near Schlitach), in Bavaria (WET station near Wetzell) and in Thuringia (MOX station near Jena). The Deutsches GeoForschungsZentrum (German Research Centre for Geosciences — GFZ) operates seismological stations in cooperation with research institutions in other countries around the world. All observatories record their data on a standardised time basis (Coordinated Universal Time, UTC), so that the data of a recorded earthquake can be collected in one place and jointly analysed.  In addition to the traditional observatories, seismometers are now being operated on the sea floor, at active volcanoes, on ice floes, in glaciers, and even temporarily on the moon.

4. Where do earthquakes occur most frequently?

The uppermost layers of the earth are made up of many rigid plates (tectonic plates) that either slide towards or away from each other or over and under each other. The strongest earthquakes usually occur along the plate boundaries. Severely affected regions include, for example, the west coast of North and South America, Indonesia, Japan, Central Asia and parts of China and Turkey, and in Europe, Italy, Greece and Iceland in particular, where strong quakes are recurrent.

5. Is it possible to predict earthquakes?

No, the precise date, place and magnitude of an earthquake cannot be predicted. However, seismologists nowadays develop seismic hazard maps in which the probability of the occurrence of strong ground tremors due to tectonic quakes can be indicated for a specific period.

6. Why are the values published on the strength of an earthquake sometimes slightly different?

One reason may be that different "strength scales" are being cited. For example, there are several different magnitude scales for earthquakes that are based on different types of data and analyses. Other reasons could be that just after an earthquake has struck, the various services and observatories can initially only access different monitoring stations and are not yet able to share or analyse all the data completely. This may be one of the reasons for slightly different results for one and the same magnitude scale. The first early statements about the strength of an earthquake are associated with greater uncertainties due to the still small amount of data. Over the course of time, more and more data is analysed by an increasing number of monitoring stations, so that the statements about the strength of an earthquake become more accurate.

7. Where can I obtain information on current and past earthquakes?

The GFZ in Potsdam operates a global network of stations consisting of over 100 stations in which seismometers detect ground tremors. All in all, there are only a few of these global networks, but they all work closely together. The denser the monitoring network, the faster the location of the epicentre and the magnitude of the earthquake can be determined. GEOFON stands for GEOFOrschungsNetzwerk (Geosciences Research Network). You can find current global earthquake reports at www.gfz-potsdam.de/portal/gfz/Services .

8. How can I protect myself during an earthquake?

If you are inside a building:

There is no specific protection against earthquakes as they cannot yet be predicted. However, the GFZ has published a list of rules of conduct: Stay calm! Do not panic! Do not jump out of the window or from the balcony! Seek immediate protection beneath a heavy, sturdy piece of furniture (for example a table) and hold on tight to something as long as the tremors persist, even if the furniture moves. If this is not possible, take refuge under a sturdy door frame or lie down on the floor near to a load-bearing interior wall away from windows and protect your head and face with crossed arms. Stay in the building as long as the earthquake tremors persist! The most dangerous thing you can do is to try and leave the building during the quake. You can be injured by falling objects or broken glass. Exception: When the earthquake begins, you are on the ground floor and near to an exit door that leads directly to the outside (garden or open square, not a narrow street). Do not use the stairs! Do not use the elevator!

If you are outdoors:

Go as quickly as possible to an open area, far away from buildings, street lamps and utility lines. Stay there until the tremors have stopped. If you are in a car, drive immediately to the side of the road, away from buildings, trees, flyovers and utility lines. Stay in the car as long as the earthquake tremors persist! Turn on the radio. Do not drive over bridges, cross-roads or below flyovers! When the quake has subsided, continue to drive with the utmost caution (avoid bridges and ramps that could have been damaged by the event) or leave the car parked where it is. If you are at the foot of a steep slope when the tremors begin, move immediately away from it (risk of landslides or falling rocks!). If you feel earth­quake tremors along a flat coastline, run as fast as you can inland to the highest point possi­ble. An earthquake can trigger extreme (up to 30 m high) ocean waves (tsunami). These waves sometimes hit the shoreline long after the quake tremors have subsided. A second wave can also follow a lot later. For this reason, do not leave your elevated place of refuge until the official tsunami all-clear has been given.

9. How much energy is released by an earthquake?

A magnitude 3 earthquake, which people can feel under favourable conditions, releases a seismic energy of approximately two billion joules, which corresponds to 555.6 kilowatt hours (kWh). With every added increment of magnitude, the energy increases by a factor of 30. In 2010, the average energy consumption of a private household was 66 GJ, which corresponds to 18,335 MWh and an earthquake magnitude of 4. A highly destructive magnitude 7 quake releases an energy volume of 450 gigawatt hours, which is ten per cent of the annual electrical energy volume provided by the block of a modern coal-fired power plant. In 2011, the total consumption of all private households in Germany added together came to 2194 PJ (source: Arbeitsgemeinschaft Energiebilanzen [Working Group on Energy Balances] 10/2012), which corresponds roughly to a magnitude 9 earthquake.

10. How large is the risk of earthquakes in Germany?

The risk of earthquakes in Germany is relatively low in global terms, but still not negligible. Smaller quakes occur quite frequently in particular in the area of the Rhine, the Swabian Alb, in eastern Thuringia and western Saxony, including the earthquake swarm area of Vogtland. However, clearly perceptible or even destructive quakes are rare events in Germany.

11. What was the strongest earthquake in Germany so far?

The strongest historically documented quake with an estimated magnitude of roughly 6.1 occurred on 18 February 1756 in the German region of the Lower Rhine Basin in the Cologne-Aachen-Düren area.  One person was killed. If an earthquake of similar magnitude to the one in 1756 occurred today in the same location, the impact would be much more grievous due to the greater population density. In 1750, Cologne, for example, with less than 50,000 inhabitants, had almost one-twentieth of its current population. One of the strongest earthquakes in recent history hit Germany in the early morning hours of 13 April 1992 in the German-Dutch border area. The epicentre was located four kilometres to the southwest of Roermond in the Netherlands. The quake's hypocentre with a magnitude of 5.9 was located at a depth of 18 kilometres. In North Rhine-Westphalia, more than 30 people were injured, mainly by falling roof slates and chimneys.

12. What does epicentre mean?

The epicentre is located on the Earth's surface directly above an earthquake's hypocentre. This is the place in the Earth's crust where the fracture begins to spread across the fracture face.

13. What is the intensity of an earthquake?

Earthquake research uses two scales to classify earthquakes and earthquake tremors. They are often confused. The magnitude scale is a measure of the energy released during the fracture process at the quake's hypocentre. In contrast to this, the intensity scale classifies the shocks/vibrations at any given location on the Earth's surface according to the type of vibration as perceived by people and the degree of earthquake damage. This intensity scale (sometimes also abbreviated according to its authors' names to MSK or MM or - in the latest version for Europe - to EMS98) divides earthquakes into 12 classes. An intensity of 12 on this scale corresponds to total destruction. If the corresponding maximum vibrations do not apply for an indefinite distance from the quake's hypocentre but rather for the area directly above the hypocentre, at the so-called epicentre, then one speaks of the so-called I0 epicentral intensity. As a rule, it is the greatest intensity observed in an earthquake. Because of its spatial nature, the earthquake intensity scale is comparable to the Beaufort wind force scale, which also consists of 12 classes - from "Calm" to "Hurricane force".

14. What is "earthquake magnitude"?

Magnitude is the logarithmic measure of the seismic energy released by an earthquake at its hypocentre. To determine the magnitude, the ground movements must be recorded as seismograms using seismometers. An increase in magnitude of one unit corresponds to an increase in ground movement by a factor of 10 and increase in energy roughly to the power of thirty. Whereas the magnitude is a measure of the energy released in the earthquake's hypocentre, the intensity classifies the vibrations at any given location on the Earth's surface.

15. What is a Richter scale?

It is a magnitude scale designed by the American seismologist Charles Francis Richter in 1935 for California. It ranks the ground motion of the primary waves measured with a spe­cial seismograph (Wood Anderson seismograph) on a logarithmic scale. The Richter scale was originally defined for stations at a distance of a few hundred kilometres. In the following years further magnitude scales were developed to include stations at greater distances and sometimes analyse other wave types.

16. What was the strongest earthquake ever recorded?

The Shaanxi earthquake in China in 1556 is considered the most devastating quake in human history, with a death toll of approximately 830,000 and an estimated magnitude of 8. The strongest quake in the last hundred years took place in Chile on 22 May 1960 with a (moment) magnitude of 9.5. On 28 March 1964, a magnitude 9.1 quake shook the Prince William Sound in Alaska. Further strong quakes occurred on 26 December 2004 off the north-eastern coast of Indonesia in the Indian Ocean with a magnitude of 9.2, and on 11 March 2010 in the Pacific Ocean off the east coast of Japan with a magnitude of 9.0. All four events took place below the sea and triggered devastating tsunamis.

17. Which magnitude values can be distinguished from each other?

Local earthquake magnitude (ML) is determined on the basis of the primary waves from only relatively close stations. Normally this magnitude scale applies to distances of up to several hundred kilometres between the earthquake and the station. In contrast to this, the body wave magnitude (mb) uses seismic waves travelling through the deep interior of the Earth that are recorded by stations at distances of over 2,000 km. This magnitude is always determined very quickly. However, for strong earthquakes (> 6 mb), the bodywave magnitude is considered to be saturated, so that the magnitude hardly increases, even though the quake was a great deal stronger. Surface waves travel relatively slowly across the surface of the earth (velocities of some 3-4 km/s compared with 8-14 km/s for the body waves in the Earth's interior), but they can still be measured well at large distances from the hypocentre. The surface-wave magnitude (MS) determined from these waves only saturates during stronger events and was used for a long time to characterise strong quakes. However, the slow propagation speed means that the MS only becomes available some time after the event. Nowadays, earthquakes and stronger quakes are characterised primarily by the moment magnitude (Mw) that no longer saturates and can be linked directly with the physical parameters of the hypocentre. To determine this magnitude, theoretical seismograms are usually computed for the Earth and compared with observations. In the case of strong quakes, surface waves are mostly compared with each other, which is why the Mw value also cannot be made available immediately after the event.

18. Are earthquake-proof building structures possible?

The use of steel beams in construction work in earthquake hazard regions has distinct ad­vantages. However, complete protection from earthquakes does not exist. Nevertheless, suitable construction measures help to considerably reduce the danger of a structure col­lapsing, even in the event of strong earthquakes. There are no worldwide standards, but at least for Europe the requirements on the design of earthquake-resistant structures have been summarised (EUROCODE 8). Safety standards have been defined for high-rise build­ings, bridges, pipelines, towers and stacks.

19. Why can the ground liquefy due to an earthquake?

Soil liquefaction is a physical phenomenon related to a complete loss of shear resistance.

Granular loose material like sand undergoes a rapid compaction when shaken. If this material is saturated, in the compaction leads to a rapid pore pressure increase. As a result the water attempts to flow out from the soil towards the ground surface. The deformation associated with liquefaction goes from being very limited to huge lateral displacements and vertical disruptions.  Liquefaction mainly affects young geological formations, poorly consolidated deposits such as alluvial and littoral formations and also man-made landfills.

The effect of liquefaction can be reproduced, for example, by kicking a couple of times the sand close to the shoreline making this mechanically stressed area flabby. Experts call this liquefaction, thixotropy.

Even a strong (although not Major Great) earthquake like the 6.2 quake in 2011 in Christchurch, New Zealand caused an enormous damage by ground liquefactions. Some buildings collapsed or were uninhabitable due to the invading mudflow.

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Investigating earthquakes – question bank.

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An inquiry approach is a method often used in science education. This question bank provides a list of questions about earthquakes and places where their answers can be found.

The questions are in three groups:

Earthquakes in general

Base isolation.

The article Investigating earthquakes – introduction has links to further resources and student activities.

This question bank asks general questions about earthquakes.

Q. We can't see through solid rock, so where's the evidence for how earthquakes work?

• Inside the Earth
• Plate tectonics
• Moulding the Earth

Q. Why does the earth shake so far away from where an earthquake starts?

Q. can i see earthquake waves.

• Seismic waves

Q. Who is talking about this?

• Keith Machin

Q. What are New Zealand scientists doing about this?

• The Alpine Fault
• Squishy rocks and earthquakes
• Seismic engineering at Canterbury University

Q. How long have we known about this?

• Earthquakes – timeline

This question bank focuses on the form of earthquakes known as slow slips.

Q. How can slow slips help us understand earthquakes?

• What are slow slips?
• Dr Laura Wallace

Q. Where can we find out about this?

• GNS Science Limited

A group of questions focuses on the technology of base isolation.

Q. How do I know which buildings are the safest?

• Strengthening Parliament House
• Seismic engineering

Q. How can base isolators be tested without being in an earthquake?

• How do base isolators work?
• Dr Bill Robinson
• Robinson Seismic Limited

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Multiple Choice Questions for Earthquakes - Chapter 16

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Discussion questions, lesson 4 "earthquakes-the rolling earth"  , thought and discussion questions .

1. Describe in your own words what a  fault  is. 2. How is a strike-slip boundary different from a convergent and divergent boundary? 3. What is a tsunami? 4. How does a tsunami form? Hyperstudio Questions 1. How are earthquake waves produced? 2. What does a Richter Scale show? 3. What are the differences between compression, shear, and surface   waves? Lesson #5 Volcanoes Discussion Questions #5 1. What caused the death of so many people during the second eruption of Vesuvius? 2. What is a pyroclastic flow? Hyper Studio Questions #5 1. Where do volcanoes form? 2. What are the two definitions for the term volcano. 3. Write definitions in your own word for the following terms: a) Active Volcano- b) Dormant Volcano- c) Extinct Volcano-

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Effect of critical thinking disposition on household earthquake preparedness

• Original Paper
• Published: 11 December 2015
• Volume 81 , pages 807–828, ( 2016 )

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• Yoshinori Nakagawa 1  

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Critical thinking is a form of open-minded thinking that aims to gain insight into how to improve things. The focus is on criticism and applicability of the resultant knowledge. Despite the existence of theories linking the critical thinking disposition and hazard adjustment adoption, there have been no previous studies examining the association between this disposition and household earthquake preparedness. The present study intends to identify this association. Data were collected from 598 respondents through a questionnaire survey. Household earthquake preparedness was measured by the number of adjustments adopted in the household. In regression analysis, taking into account interactions between the considered variables, it was found that logical thinking awareness, a subconstruct of the critical thinking disposition, was a significant predictor of household preparedness. Furthermore, inquisitiveness, another subconstruct of critical thinking disposition, was found to moderate the association between risk perception and earthquake preparedness. This finding suggests that people who have the motivation to tackle challenging situations actually do so in the context of earthquake preparedness. The practical implications of the findings are also discussed.

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Acknowledgments

The author acknowledges support from the Watanabe Memorial Foundation for the Advancement of New Technology (#H26-351). The author is also grateful to Professor Ryo Kimura (Director of Research Department, Kochi University of Technology) for his varied support.

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Nakagawa, Y. Effect of critical thinking disposition on household earthquake preparedness. Nat Hazards 81 , 807–828 (2016). https://doi.org/10.1007/s11069-015-2107-x

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DOI : https://doi.org/10.1007/s11069-015-2107-x

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Chapter 1: Plate Tectonics

The 2 nd edition is now available click here., learning objectives.

The goals of this chapter are to:

• Identify types of plate boundaries and compare their characteristic earthquake and volcanic activities
• Assess the basic lines of evidence supporting plate tectonics
• Explain how ancient plate boundaries affect modern topography

1.1 Introduction

Plate tectonics is the grand unifying theory in geology. It gets that title because many topics in geology can be explained, in some way, by the movement of tectonic plates. Tectonic plates are composed of Earth’s crust and the uppermost, rigid portion of the mantle. Together they are called the lithosphere . Earth’s crust comes in 2 “flavors”: oceanic and continental (Table 1.1).

Lithospheric plates move around the globe in different directions and come in many different shapes and sizes. Their movement rate is millimeters to a few centimeters per year, similar to the rate that your fingernails grow. Motion between tectonic plates can be divergent , convergent , or transform . In divergent boundaries, plates are moving away from each other; in convergent boundaries, plates are moving toward each other; and in transform boundaries, plates are sliding past each other. The type of crust on each plate determines the geologic behavior of the boundary (Figure 1.1).

Exercise 1.1 – Reconstructing Positions of Continents Using Wegener’s Evidence

When Alfred Wegener came up with his continental drift hypothesis in the early 1900s, he used several lines of evidence to support his idea. He also proposed that 200 million years ago, all continents were together in a single supercontinent called Pangea. In this exercise, you will use the fit of the continents and matching fossil evidence to piece together Pangea. This exercise is adapted from “ This Dynamic Planet ” by the USGS.

• Label the landmasses of each continent in Figure 1.2.
• Color the fossil areas to match the legend below.
• Cut out each of the continents along the edge of the continental shelf (the outermost dark line).
• Try to logically piece the continents together so that they form a giant supercontinent.
• When you are satisfied with the fit of the continents, discuss the evidence with your classmates and decide if the evidence is compelling or not. Explain your decision and reasoning on the evidence.
• Pangea began to break apart about 200 Ma resulting in the formation of the Atlantic Ocean. Using the map in Figure 1.3, calculate the spreading rate of the Mid-Atlantic Ridge in mm/yr. (Hint: measure the distance from the easternmost tip of South America to the inside curve of western Africa). ____________________

1.2 Plate Tectonics, Earthquakes, and Volcanoes

Plate tectonic boundaries are often associated with earthquakes and volcanic activity. By looking at maps for the distribution of earthquakes and volcanoes worldwide (Figures 1.4-1.5), you can interpret the boundaries between the major tectonic plates. Generally, divergent plate boundaries are characterized by shallow earthquakes and some volcanism. Convergent boundaries have a range of earthquake depths from shallow to deep, and many have volcanoes as a result of subduction . Subduction occurs in convergent boundaries where the denser, oceanic plate descends into the mantle beneath the overriding plate. Convergent boundaries also tend to produce linear and curved mountain belts . Transform boundaries typically have shallow earthquakes and no volcanoes.

Exercise 1.2 – Modern Examples of Plate Tectonic Boundaries

Each type of plate boundary has distinct earthquake and volcanic patterns. Using observational and critical thinking skills, answer the following questions:

• Observe the patterns amongst the earthquake and volcano location maps (Figures 1.4-1.5). Hypothesize where you think the major plate boundaries exist and draw those boundaries on the blank map in Figure 1.6 using three different colors to identify the type of motion for each boundary (example: red for divergent boundaries, blue for convergent boundaries, and green for transform boundaries).
• Which type of boundary (divergent, convergent, or transform) is the most abundant? ______________________________________
• Continent-Continent Convergence (CCC)
• Ocean-Ocean Convergence (OOC)
• Continent-Ocean Convergence (COC)
• Continent-Continent Divergence (CCD)
• Ocean-Ocean Divergence (OOD)
• Continent-Continent Transform (CCT)
• What type of plate boundary is associated with most of the deep earthquakes?______________________

Earthquake locations can tell you more about an area than what type of plate boundary is there. For example, in subduction zones, most earthquakes occur along the boundary between the subducting slab and the overriding slab. The angle of subduction is not always constant and can vary from one boundary to the next and can even vary along the same boundary. When a plate subducts at a low angle, it is called flat-slab subduction. The effects of flat-slab subduction are many, including shallower earthquakes, uplifting of mountains, and the location and activity of volcanoes.

Exercise 1.3 – Interpreting Subduction Angle from Earthquake Data

The Western margin of South America is a tectonically active region where the Nazca Plate subducts under the South American Plate (Figure 1.7), creating the Andes Mountains . Even though the entire coast is part of the same subduction zone, the subduction process doesn’t look the same throughout. Tables 1.3 and 1.4 contain earthquake data from two different locations of the subduction zone, one from central Chile and another near the Chile-Peru border. The location data are the distance each earthquake was from the trench and how deep within the Earth it was.

• Using the graph paper provided by your instructor, plot the distance of the earthquake foci (hypocenters) from the trench on the horizontal axis and the depth of the earthquakes on the vertical axis; the recommended scale is 1 cm = 10 km. Connect the plotted points to create an approximate cross-section of the subduction zone at the two locations.
• Look at the graph you made, which region has a steeper subduction angle, the Chile-Peru border or central Chile? ____________________

1.3 Plate Tectonics and Topography

Geologists can observe most of the processes occurring at plate tectonic boundaries today (earthquakes, volcanoes, mountain building, etc.). However, understanding the plate tectonic activity of the geologic past is more difficult because the events have already happened. Hence, geologists use processes that occur in the present to interpret processes that occurred in the past. This is known as uniformitarianism . One way geologists can interpret ancient plate tectonic activity is to look at the topography of an area. Topography is the study of shapes and features of the land surface. When studying features on the seafloor, the topography is instead referred to as bathymetry because this data is referencing how deep a feature is. There are numerous ways of looking at the topography of Earth’s surface, including satellite imagery, topographic maps, shaded relief maps, and digital elevation models.

Exercise 1.4 – Interpreting Plate Boundaries from Topographic Profiles

Below are five topographic profiles showing different plate boundary configurations. A topographic profile is a graph that shows elevation changes as you walk from one point on the Earth to another. These are all made with vertical exaggeration (length/elevation) of 50:1. This overemphasizes the changes in topography. In all of these profiles, the 0 value on the vertical axis is at sea level.

• For the topographic profiles in Table 1.4, identify what types of plate boundaries are shown using the names from Figure 1.1. Pay close attention to the y-axis versus x-axis.
• On each profile, draw the location of the boundary between the two plates. You can show this as a single line.
• For each profile, label features such as oceanic and/or continental crust, mid-ocean ridges, volcanoes, mountain belts, and trenches.
• Indicate which direction each tectonic plate is moving (you can use arrows for this).

Geologists can use topography to get a broad sense of the tectonic history of an area. Generally speaking, plate tectonic activity tends to produce elevation changes at or near the plate boundary, especially in convergent settings. The collision of two plates leads to suturing ; the two plates become one when the collision ends. Evidence of these ancient boundaries is most commonly in the form of linear mountain belts that are not currently near a plate tectonic boundary. For example, an eroded, linear mountain belt in the middle of a continent would indicate that area was part of a convergent boundary deep in the geologic past and likely a continent-continent collision. The Ural Mountains in Russia fit this description (Figure 1.8). They formed during an orogeny 240 to 300 million years ago and now serve as the boundary between Europe and Asia.

Exercise 1.5 – Interpreting Ancient Plate Tectonic Boundaries

• Look at the topographic map for part of North America (Figure 1.9). Mark two areas that you think have been through major convergence of tectonic plates.

When most people think about tectonic plate boundaries, they often visualize parallel, symmetric lines separating the plates. This is not always the case in the real world as many plate boundaries are curved or segmented; this is because Earth is a sphere. Think about this: if you had a ball and tried to wrap it with a flat sheet of paper, would the paper wrap around it perfectly smooth? The answer is no; the paper will want to fold in some places and tear in other places. The tectonic plates behave similarly to the paper. Of course, other factors affect the shape of a boundary. Evidence of these plate boundaries is also contained in the topography of continents because not all mountain belts are straight lines.

Exercise 1.6 – Ancient Plate Boundaries in Texas, Oklahoma, New Mexico, and Northeastern Mexico

Below is a topographic map of Texas, Oklahoma, New Mexico, and northeastern Mexico (Figure 1.11). This area is not near an active plate tectonic boundary today; the closest boundary is in the Gulf of Mexico. However, there is evidence in this topography to indicate it was part of a plate tectonic boundary at least twice in the geologic past.

• Based on the topography, mark two areas that have been part of a plate tectonic boundary in the geologic past. Topographic changes do not need to be symmetric as some tectonic processes are not symmetric.
• One of these boundaries is older than the other. Label the old and young boundaries.

As tectonic plates move, they ride over stationary “ hotspots ” of heat from the mantle . Hotspots are still a poorly understood geologic phenomenon, but they allow extremely hot mantle material to rise close to the surface. Hotspots are marked by volcanoes, which come from melting of the mantle and crust directly above a hotspot. If they occur under oceanic crust, they produce basalts. On the other hand, if they are under continental crust, they form both basalts and rhyolites, often called bimodal volcanism. Under North America, there are two hotspots: The Yellowstone hotspot, which is currently under Yellowstone National Park in Wyoming and Montana, and the Anahim hotspot in central British Columbia, Canada. As the North American Plate moves over these hotspots, calderas form from volcanic activity; one of the largest volcanic eruptions ever occurred when the Gray’s Landing volcanics erupted 8.72 million years ago above the Yellowstone hotspot. One of the controversies is whether the hot spot is still capable of supereruptions or whether the volume of eruptive material is waning.

Exercise 1.7 – Tracking North American Hotspots

Use Figure 1.12 to answer the following questions about North American hotspots.

• Angle for Yellowstone: ____________________
• Angle for Anahim: ____________________
• Rate of plate motion for Yellowstone: ____________________
• Rate of plate motion for Anahim: ____________________
• Are these the same for the two hotspots? ____________________

The answer may not be apparent as we don’t often move things around on a sphere. Instead, we think of motion as a straight line from point a to point b. These hotspots are on the North American plate which means the plate rotates around a point in the middle of northern Quebec. Since they rotate around a point on a sphere, different locations on the plate move at dissimilar speeds and directions. Geoscientists call this an Euler pole .

Additional Information

Exercise contributions.

Daniel Hauptvogel, Virginia Sisson, Carlos Andrade, Melissa Hansen

Knott, T.R., Branney, M.J., Reichow, M.K., Finn, D.R., Tapster, S., and Coe, R.S., 2020, Discovery of two new super-eruptions from the Yellowstone hotspot track (USA) Is the Yellowstone hotspot waning? Geology, v. 48, p. 934-938. doi.org/10.1130/G47384.1 

Martinod, J.,  Husson, L., Roperch, P., Guillaume, B., and Espurt, N., 2010, Horizontal subduction zones, convergence velocity and the building of the Andes. Earth and Planetary Science Letters, v. 299, pp. 299-309. DOI:10.1016/j.epsl.2010.09.010 .

Google Earth Locations

the uppermost layer of the Earth as defined by physical properties. It is composed of the crust and uppermost, rigid part of the mantle.

a linear feature where two plate boundaries move apart from each other

a plate boundary where two plates move towards each other

a plate boundary where two plate boundaries move horizontally beside each other

the hypothesis proposed by Alfred Wegener in 1915 that stated the continents were moving

the climate during some past geological time

an ancient landmass of almost all of the continental crust or supercontinent that formed in the late Paleozoic

a process that occurs at convergent plate boundaries where one plate descends beneath another into Earth's mantle.

an aligned group of mountain ranges that form from the same cause, usually an orogeny or convergent plate boundary

a topographic depression of the sea floor, relatively narrow in width, but very long usually associated with convergent plate boundaries

the theory that the same natural laws and processes that operate in our present-day scientific observations have always operated in the universe in the past and apply everywhere in the universe. It is sometimes referenced as "The present is the key to the past".

the zone where two continental plates meet during convergence

a mountain-building event typically resulting from a convergent tectonic boundary

linear volcanic regions that are probably fed by underlying mantle that is anomalously hot compared with the surrounding mantle

a layer in the Earth or a planet that is between the core and crust

The Story of Earth: An Observational Guide Copyright © by Daniel Hauptvogel & Virginia Sisson is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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Experts Answer Your Biggest Questions About Earthquakes

Early Wednesday morning, a big earthquake shook several Italian towns and cities to the ground. At least 120 people are dead. It all happened in a region where seven years ago, another earthquake of similar magnitude shook several Italian cities to the ground, killing several hundred people. The latter earthquake became famous, not for the death and damage it caused, but for the trial that followed. Italy's most prominent seismologists were taken to court, accused of recklessly addressing the public about the danger of a quake in the region---a week before the big one hit.

The L'Aquila earthquake became the most tangible proxy for a phenomenon that happens after every major quake: People—intelligent, educated, thoughtful—ponder questions like why didn't science see this one coming? And that question is itself a concise way of saying that a lot of intelligent, educated, and thoughtful people don't understand squat about earthquakes.

And I'm not being condescending here. I have written about quakes many times, and yet I still wound up Googling what seem to be some very basic questions. After the quake, my editors and I found ourselves asking each other all sorts of very basic questions. To wit: I legit had to Google whether there was a link between earthquake activity and Earth's circadian patterns. So, with the help of some seismologists, here is WIRED's guide to some common earthquake questions.

A firefighter walks through San Pellegrino, in Perugia province, southeast of Norcia, after the 6.2-magnitude earthquake hit central Italy.

No, but they can forecast them. If that sounds like splitting hairs, think of it this way: Meteorologists know that during certain months of the year—say, summer—New York City is more likely to experience thunder storms. In fact, they can be pretty damn sure that during the fourth week of August, Manhattan will have at least one day of soggy weather. However, even up until the third week of August or later, it is pretty much impossible for them to say which day the sky will open up.

Like in meteorology, seismologists use a combination of historical records and sprawling computer programs to figure out their forecasts. "We use models of the whole Earth to think about how fast different plates are moving with respect to each other, so then we can say, 'OK, over the long term we have an inch or so a year of movement and that will be concentrated on San Andreas fault or wherever," says Simon Klemperer , a geophysicist at Stanford University. They compare these models to the historical record—not just the past 100 years or so, but 1,000, 10,000 years—to see the last time those faults released their strain.

Right. So, scientists have those models, their historical data, and also some pretty good maps of where all the world's fault lines lie. But in order to predict, you need to know the precise physical characteristics of the rocks making up those plates and faults. "If I take a wooden pencil in my hands and start to bend it, I know it's going to break at some point in time," says Klemperer. "But it is very hard to predict the exact millisecond when it will snap." This is because, even though he knows the pencil is made out of cedar and graphite, he has no idea how the grain looks, whether the graphite is uniformly dense, if there's any pre-existing stress on the pencil, and so on.

This gets way trickier with rocks. Even though scientists have done a hell of a job mapping all the different rock types making up the Earth's geology, they still don't have super granular understanding of all those rocks' specific properties.

OK, let's assume you started funding seismology like it was, I dunno, the Apollo moon mission or the US Marine Corps. "It might be theoretically possible to build up enough knowledge to predict earthquakes," says Klemperer. But that would take many, many geologists observing each fault zone for decades upon decades. "So it's not a practical task in terms of the scale of human lives."

The tides exert a very small effect on the shape of the planet, including rocks along fault lines. "They do change the stress a tiny amount," says Klemperer, "but it's nothing compared to the stress required to trigger the quake." So while the time of day can certainly impact the devastation caused by an earthquake---daytime quakes can injure and kill more people as they're out and about---it doesn't make them more or less likely.

Depends on the size of the quakes and the distances between them. For instance, in the time between when I was assigned this article and when you are reading it, a 6.8 magnitude quake struck Myanmar . Based on the geophysical properties of how earthquakes propagate energy through the Earth, it's pretty much impossible for energy from the Italian quake to have propagated thousands of miles to trigger the quake in Myanmar.

If the timing between the two quakes seems too coincidental for you to hang up your tin hat, spend a few days watching the USGS's earthquake map . Big quakes happen all the time, all over the world. You just don't hear about all of them because they happen in places where no people live.

Before the 2009 L'Aquila earthquake, one of the Italian scientists who got in trouble said in an offhand way that the cluster of small quakes the region had been experiencing were probably evidence that the fault was letting off steam. This is not true. (That scientists was a hydrologist, not a seismologist. Also, his comments were taken slightly out of context.) "The key is to remember that what everyone uses the a logarithmic scale to measure earthquakes ," says Klemperer. Let's say you have a magnitude 4 quake, which is preceded by a weak 1 magnitude quake. Even if a hundred teeny temblors struck, each would only be about 1/10,000 the intensity of the moderately big one. "That’s why the small earthquakes don’t matter very much in terms of relieving pressure," says Klemperer.

In practical terms, seismology is useful primarily for informing earthquake-prone regions how to survive their fates. More succinctly: Building codes. "It’s humbling to a seismologist, but in the end, it’s the structural engineers who save lives," says Klemperer.

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Frequently Asked Questions about Earthquakes (FAQ)

FAQ - Glossary

Table of contents

What is an "earthquake", what causes earthquakes, how do earthquakes cause damage, does the earth open up during an earthquake, where do earthquakes occur, what is the relationship between volcanoes and earthquakes, will more shocks be felt after a strong earthquake, can earthquakes be predicted, does the rate of earthquakes increase during the cold weather, are there certain months of the year that are more seismically active than others, what is the intensity of an earthquake, can people cause earthquakes.

• What is an "anthropogenic" seismic event?

Does a small earthquake mean that a larger earthquake is coming?

What is the "magnitude" of an earthquake, what is the difference between the "magnitude" and the "intensity" of an earthquake, what it is the difference between magnitudes m l and m n , certain earthquakes have a negative magnitude, is this an error, is there a maximum magnitude for an earthquake, at what magnitude do earthquakes begin to be felt when does damage start do to be observed, do several magnitude scales exist, how often do earthquakes occur, where can i find information on the world's earthquakes, are earthquakes really on the increase, what was the greatest earthquake in world history, how often do earthquakes occur in canada, where do earthquakes occur in canada, do damaging earthquakes occur in canada, what is the largest earthquake ever recorded in canada, how often do earthquakes occur in western canada, have there been damaging earthquakes in western canada, why are there so many earthquakes in western canada, what are some important studies that tell us about earthquake hazards in western canada, how often do megathrust earthquakes occur, how big can they be, where do megathrust earthquakes occur, how do we know that megathrust earthquakes have occurred, how do we know that we will have another one in the future.

• If the shaking of a magnitude 7 is 10 times greater than a magnitude 6 and 100 times greater

If a magnitude 6.9 earthquake can devastate Kobe, Japan, what would a magnitude 9 megathrust earthquake do to Vancouver?

Will vancouver island sink when a megathrust earthquake occurs, are megathrust earthquakes our biggest earthquake hazard, why do megathrust earthquakes cause tsunamis, is all of coastal bc vulnerable to tsunamis from a megathrust earthquake, what do the different tsunami messages mean ( warning / watch / advisory / information ), if we have lots of little earthquakes will they relieve the stress building up for a megathrust earthquake, where can i find information on canadian earthquakes, in canada, how many casualties were caused by earthquakes, can we record nuclear explosions, where can i find information on the faults and the geology of my area, what is a seismograph, what do seismic waves look like, is it possible to build your own seismograph, help on the "see the shaking" seismogram viewer, can buildings be designed to withstand earthquakes, are buildings designed to withstand earthquakes in canada, where can i find information on seismic hazards in canada, where can i find seismic hazard maps for canada, what is the safest type of structure, where can i get more information on earthquake engineering, what should you do during an earthquake, what should you do after a strong earthquake, what causes damage, can houses withstand earthquakes, what is a seismologist, what do scientists do after an earthquake, seismic sources - earthquakes, nuclear blasts, mining events.

An earthquake occurs when rocks break and slip along a fault in the earth. Energy is released during an earthquake in several forms, including as movement along the fault, as heat, and as seismic waves that radiate out from the "source" in all directions and cause the ground to shake, sometimes hundreds of kilometers away.

Earthquakes are caused by the slow deformation of the outer, brittle portions of "tectonic plates", the earth's outermost layer of crust and upper mantle. Due to the heating and cooling of the rock below these plates, the resulting convection causes the adjacently overlying plates to move, and, under great stress, deform. The rates of plate movements range from about 2 to 12 centimeters per year. Sometimes, tremendous energy can build up within a single, or between neighbouring plates. If the accumulated stress exceeds the strength of the rocks making up these brittle zones, the rocks can break suddenly, releasing the stored energy as an earthquake.

Most earthquake damage is caused by ground shaking. The magnitude or size (energy release) of an earthquake, distance to the earthquake focus or source, focal depth, type of faulting, and type of material are important factors in determining the amount of ground shaking that might be produced at a particular site. Where there is an extensive history of earthquake activity, these parameters can often be estimated. In general, large earthquakes produce ground motions with large amplitudes and long durations. Large earthquakes also produce strong shaking over much larger areas than do smaller earthquakes. In addition, the amplitude of ground motion decreases with increasing distance from the focus of an earthquake. The frequency content of the shaking also changes with distance. Close to the epicenter, both high (rapid) and low (slow)-frequency motions are present. Farther away, low-frequency motions are dominant, a natural consequence of wave attenuation in rock. The frequency of ground motion is an important factor in determining the severity of damage to structures and which structures are affected.

No! A common misconception is that of a hole in the ground that opens during an earthquake to swallow up unfortunate victims. This has nothing to do with reality but is Hollywood's version of earthquakes. After a strong earthquake, some cracks may be seen on the ground or in basements. These are not faults, nor are they crevasses ready to close up again. Theses cracks are probably due to soil settlement caused by the ground shaking.

Earthquakes occur all over the world; however, most occur on active faults that define the major tectonic plates of the earth. 90% of the world's earthquakes occur along these plate boundaries (that represent about 10% of the surface of the earth). The "Ring of Fire" circling the Pacific Ocean, and including Canada's west coast, is one of the most active areas in the world.

The earthquake activity of numerous volcanoes is closely monitored to provide warning signs of an imminent eruption. Large volcanic eruptions, especially the explosive type, can release huge amounts of energy that can be recorded by seismographs even far from the source.

Recent volcanic activity in Canada has been experienced in BC and the Yukon . Worldwide, the majority of volcanoes and earthquakes are located in the same areas. This relationship is explained through a geological model called plate tectonics. You can find additional explanations on plate tectonics:

• IRIS - Tectonic Plates, Earthquakes & Volcanoes

In Eastern and Northern Canada, earthquakes are not related to volcanic processes. Although volcanic rocks exist in many regions (sometimes as old as 2 billions years of age) and magmatic bodies can be found (the Monteregian Hills of Quebec are 60 million year old intrusives), these magmatic events are just too old to have any relationship with current earthquake occurrences. No volcanic or magmatic activity is currently underway in these parts of Canada.

For more information on volcanoes in Canada, see Volcanoes Canada .

For several hours, or even days, after a strongly felt earthquake, it is quite possible that people may feel more shocks. This possibility always exists, but keep in mind these four facts:

• In most cases, these shocks (called aftershocks) will be smaller; therefore, the vibrations will be weaker.
• Aftershocks do not mean that a stronger earthquake is coming.
• Aftershocks are normal; they show that the earth's crust is readjusting after the main earthquake.
• The number of felt aftershocks is quite variable and thus cannot be predicted. There might be several per day, or only several per week.

It is impossible to predict either the number or the magnitude of aftershocks that might occur. These vary greatly from one region to another, according to many factors which are poorly understood.

With the present state of scientific knowledge, it is not possible to predict earthquakes and certainly not possible to specify in advance their exact date, time and location, although scientists have carried out research on a wide variety of attempted prediction methods.

However, the rates of earthquakes in particular regions, expressed in terms of probabilities, can be usefully estimated . Canada, along with other countries, is working to minimize damage and injuries through the implementation of modern earthquake-resistant standards so people will be protected whenever and wherever an earthquake occurs.

Although cold temperatures greatly affect the ground near the surface, it has no effect at greater depths. Near the surface, freeze and thaw cycles can weaken and break rock due to high water pressure. However, this is a phenomenon limited to near surface soil.

Consider a mine: the temperature inside the mine will be influenced by surface temperature only for about the first 50 m. Deeper in the mine the temperature will be influenced by the internal heat of the earth - a temperature that is relatively constant throughout the year.

The hypocentre (the place where displacement occurs along a rock fracture) of an earthquake is generally located several km below the surface (on average, between 5-30 km in Eastern Canada), where the surface temperature would have no influence. For example, the hypocentre of the 1988 Saguenay earthquake occurred at a depth of 28 km where the temperature is approximately constant at 300°C year round.

Furthermore, the principle causes of earthquakes (movement of tectonic plates, volcanoes, etc.) are large scale phenomena, unrelated to surface temperature.

However, close to lakes and rivers, when the ambient temperature drops below -20°C many little microseisms may be heard and are sometimes felt. These microseisms are not earthquakes as they are caused by cracking ice and movements of ice blocks one against another. They are cryoseisms, also known as frost quakes, and can only be felt close to the body of water from which they originate. Such ice cracks can sometimes be detected by a seismograph if it is located close to the body of water.

Seismic trace of a typical frost quake recorded on the vertical component of the seismic station in Sadowa, Ontario, near Georgian Bay (SADO), January 18, 2000 at 6:55 pm, a very cold night (12 frost quakes were recorded within 2 hours that night). A seismologist immediately recognizes the nature of such an event by the single frequency contained in the record.

No, there are no months that have more earthquakes than others. Examining the list of Canadian or global earthquakes, there isn't a season that stands out as having an increased number of earthquakes.

The explanation for this can be found by considering that the mechanisms that cause earthquakes are independent of seasonal temperature changes ( see effects of cold temperatures on earthquakes ), and independent of the changes in position of the Earth in the solar system at different times of the year. It is internal geological forces that play the most important role in generating earthquakes.

Most large earthquakes are as a result of immense continental plates, called tectonic plates, that move, one with respect to another. The driving force for this movement is found in the Earth's mantle in the form of convective currents. These currents carry the tectonic plates around the Earth generating earthquakes and volcanic eruptions. The movement of the plates creates strain which is then accumulated in faulted areas causing earthquakes. Both the movement of the plates and the accumulation of strain along faults are continual processes independent of the time of year.

Since the distance between the Earth and Sun changes throughout the year due to the elliptical trajectory of the Earth around the Sun, it seems possible that the attractive gravitational forces between the two bodies might cause extra strain in the Earth's crust. However, strain models have shown that this extra force is insignificant compared to the tectonic force present.

Since the temperature and gravitational forces are the only forces changing with the seasons, seasonal effects can be eliminated as a factor in influencing the frequency of earthquakes.

See the Modified Mercalli Intensity Scale.

Yes! Minor earthquakes have been triggered by human activities such as mining (rockbursts and cavity collapse), the filling of reservoirs behind large dams, and the injection of fluids into wells for oil recovery or waste disposal. Large dams hold back enormous quantities of water. Some of this water may penetrate into cracks in the underlying rock, and sometimes this may trigger small earthquakes under or very near the reservoir.

Following an underground nuclear explosion, small earthquakes have often been recorded near the test site. These are due to the collapse of the cavity created by the explosion.

Man-made earthquakes always occur close to the site of the activity. There is no link between human activities like these and earthquakes occurring hundreds or thousands of kilometres away.

What is an “anthropogenic” seismic event?

The word “anthropogenic” means that something originates in human activities. Anthropogenic seismic events include those that are induced or triggered by human activities (see above), but it also includes phenomena such as explosions, from quarry and construction blasts to nuclear tests. The main purpose of the National Earthquake Database is to catalogue earthquakes in Canada. Anthropogenic events tend to enter the database when they are difficult to distinguish from earthquakes, are of interest to mine operators, or have research value. Ripple-fired blasts, in particular, are relatively easy to distinguish from earthquakes, based on their waveform characteristics, and are not comprehensively catalogued. It can also be noted that there are some rarer types of “natural” seismic events, other than tectonic earthquakes, such as large landslides and meteorite impacts.

No, except for very rare exceptions. Every year, hundreds of earthquakes occur in Canada. Only a very tiny minority of these precede a larger earthquake.

Although a large earthquake may be preceded by a foreshock (the Saguenay earthquake of November 1988 is an example), the occurrence of a small earthquake is not in itself a typical sign. Hundreds of small earthquakes occur every year in Canada, whereas major earthquakes have occurred only a few times in this century.

A small earthquake, however, provides an ideal opportunity to offer reminders about safety measures to take before, during and after an earthquake.

Magnitude is a measure of the amount of energy released during an earthquake. It is frequently described using the Richter scale. To calculate magnitude, the amplitude of waves on a seismogram is measured, correcting for the distance between the recording instrument and the earthquake epicentre. Since magnitude is representative of the earthquake itself, there is only one magnitude per earthquake.

Taking the Saguenay QU earthquake of November 25, 1988 as an example, one could not therefore speak of magnitude 6 at Quebec City and magnitude 4 to 5 at Montreal. The effects (or intensities) experienced at different places were different, but the magnitude of the earthquake is unique; in this example, it was 6 on the Richter scale. Magnitude thus has more to do with the effects of the earthquake overall.

The magnitude scale is logarithmic. This means that, at the same distance, an earthquake of magnitude 6 produces vibrations with amplitudes 10 times greater than those from a magnitude 5 earthquake and 100 times greater than those from a magnitude 4 earthquake. In terms of energy, an earthquake of magnitude 6 releases about 30 times more energy than an earthquake of magnitude 5 and about 1000 times more energy than an earthquake of magnitude 4.

It is very unlikely that an earthquake of magnitude less than 5 could cause any damage.

The Intensity scale is designed to describe the effects of an earthquake, at a given place, on natural features, on industrial installations and on human beings. The intensity differs from the magnitude which is related to the energy released by an earthquake.

Without going into the seismological details, the magnitude defined by Charles Richter is the source of all magnitude scales. Over the years however, it was realized that the magnitude that Richter had defined for California (M L means local magnitude), did not apply to Eastern North America where the seismic waves attenuate differently. Otto Nuttli, a seismologist at the University of Saint-Louis in the United States, developed a magnitude formula which corresponded better to the reality of Eastern America. One of the formulas which Nuttli derived is used to measure the seisms of Eastern Canada. The formulation used is called Magnitude Nuttli or m N . In order to simplify communication with the public, Canadian seismologists will often refer to the Richter magnitude whereas strictly speaking the seisms that occur in Eastern Canada are measured according to the Nuttli magnitude. An exception exists for the very small earthquakes of the Charlevoix Region, where the Richter scale is used. Around the world other scales of magnitude exist according to the source conditions of the earthquakes (depth), the conditions of attenuation, the type of measured wave, etc. More and more, seismologists describe earthquakes according to the magnitude of the moment scale (M W or M).

No, it is not an error. As magnitude calculations are based on a logarithmic scale, a ten-fold drop in amplitude decreases the magnitude by 1. Let us assume that on a seismogram:

• an amplitude of 20 millimetres corresponds to a magnitude 2 earthquake.
• 10 times less (2 millimetres) corresponds to a magnitude of 1;
• 100 times less (0.2 millimetres) corresponds to magnitude 0;
• 1000 times less (0.02 millimetres) corresponds to magnitude -1.

Naturally, a negative magnitude is found only for very small events, which are not felt by humans.

Though theoretically there is no mathematical limit with the magnitude calculation, physically there is a limit. The magnitude is related to the surface area of the blocks of rock which rub together and in doing so give rise to seismic waves. Since the tectonic plates have finite dimensions, the magnitude must therefore also reach a maximum. It is believed that the greatest earthquakes can reach magnitude 9.5, which corresponds to the magnitude of the Chilean earthquake described below.

This is difficult to answer absolutely. According to past earthquakes , one can however draw up some general information for Eastern Canada .

Though seismologists generally refer to magnitude on the Richter scale, several magnitude scales do exist.

Distribution and frequency of Earthquakes

Global Frequency of Earthquakes

In addition to the international networks which can detect earthquakes of magnitude 5.0 and greater, the majority of the countries have their own national network.

No, earthquakes occur at more or less at the same rate every year. For more info: USGS web site

The greatest earthquake of recent history is the Chilean earthquake of May 22, 1960 , which is estimated at magnitude 9.5. According to the USGS , this earthquake caused the death of more than 2000 people in Chile, in addition to generating a tsunami which propagated around the Pacific, adding several hundreds of victims to the assessment. The greatest world earthquakes since 1900 are described on the USGS site.

On average, the Geological Survey of Canada (GSC) records and locates over 4000 earthquakes in Canada each year . That is about 11 per day! Of these 4000, only about 50 (1/week) are generally felt.

Earthquakes occur across much of Canada . Most earthquakes occur along the active plate boundaries off the British Columbia coast, and along the northern Cordillera (southwestern corner of the Yukon Territory and in the Richardson Mountains and Mackenzie Valley) and arctic margins (including Nunavut and northern Quebec). Earthquakes also occur frequently in the Ottawa and St. Lawrence Valleys, in New Brunswick, and the offshore region to the south of Newfoundland.

• The province in Canada least likely to experience an earthquake is Manitoba.
• The province in Canada most likely to experience an earthquake is British Columbia.

Yes! Some of the world's largest earthquakes have occurred here (see next question).

The largest earthquake recorded (during historic times) in Canada was a magnitude 8.1 event that struck just off the Haida Gwaii on Canada's west coast on August 22, 1949. This earthquake (larger than the 1906 San Francisco earthquake) ruptured a 500-km-long segment of the Queen Charlotte fault and was felt over almost all of British Columbia, and as far north as the Yukon Territory and as far south as Oregon State.

Although not recorded by seismographs, the largest earthquake ever to strike Canada was undoubtedly the giant megathrust (subduction zone) earthquake of 1700 off the west Coast of Vancouver Island.

Earthquakes in Western Canada

Every day! Scientists at the Geological Survey of Canada office near Sidney, B.C. record and locate approximately 1000 earthquakes each year in western Canada.

Yes! Some of the world's largest earthquakes have occurred in western Canada. Click here to see the 5 most significant .

Western Canada is the most seismically active region in Canada. It consists of several discrete areas of intense earthquake activity each corresponding to a particular plate tectonic regime. The most seismic of these regions is offshore, west of Vancouver Island. More than 100 earthquakes with a magnitude of 5 or greater have occurred here in the past 70 years. Most of the seismicity occurs in areas of fractured oceanic crust, which mark boundaries of small plates known as the Explorer and Juan de Fuca plates

Earthquake activity is also high in the Cascadia Subduction Zone. Here, the Juan de Fuca Plate dips below the easterly neighbouring North American plate. Thus, both deep (dipping plate) and shallow (overriding plate) earthquakes occur in this zone, though no earthquakes occur at the interface of the plates. Another region of high seismicity is defined by a zone of plate breakage or "faulting" immediately west of the Haida Gwaii ("the Queen Charlotte fault"). Earthquakes of magnitude 7 occurred here in May of 1929 and June of 1970.

The St. Elias Mountains, southwest Yukon Territory and the extreme northwest of B.C., too, is a highly seismic region. This is because of plate margin deformation between two converging plates in the area (the "Pacific" to the west and "North American" to the east.) Finally, the Canadian Cordillera typically shows intense seismicity north of 60 degrees in a broad zone through the Mackenzie and Richardson Mountains. The largest earthquake recorded here, with magnitude of 6.9, occured in the Mackenzie Mountains in December, 1985. South of 60 N, seismicity drops off markedly away from the coast to a low level through much of the Cordillera, though it is slightly higher in the Coast Mountains from southern British Columbia to the Yukon Border.

Understanding earthquake hazards involves many types of studies: monitoring earthquakes, monitoring crustal deformation; mapping the marine environment for evidence of offshore earthquake activity; studying wave propagation; mapping earth structure; understanding local geological conditions; and looking for geological evidence of prehistoric earthquakes.

Many different types of studies are conducted by scientists at the Pacific Geoscience Centre of the Geological Survey of Canada to better improve our understanding of earthquake hazards in western Canada.

• Click here for details on monitoring crustal deformation in western Canada
• Click here for details on earthquake-related marine studies

The recurrence time varies from subduction zone to subduction zone. In the Cascadia subduction zone 13 megathrust events have been identified in the last 6000 years, an average one every 500 to 600 years. However, they have not happened regularly. Some have been as close together as 200 years and some have been as far apart as 800 years. The last one was 300 years ago.

Megathrust earthquake are the world's largest earthquakes. The last Cascadia earthquake is estimated at magnitude 9. A megathrust earthquake in Chile in 1960 was magnitude 9.5, and one in Alaska in 1964 was magnitude 9.2.

The Cascadia fault, on which megathrust earthquakes occur, is located mostly offshore, west of Vancouver Island, Washington, and Oregon, although it does extend some distance beneath the Olympic Peninsula of Washington State. The large distance between the Cascadia fault and the urban centres limits the level of shaking that the urban areas are exposed to.

The sudden submergence of the outer coast when a megathrust earthquake occurs kills vegetation which can be dated. Megathrust earthquakes also cause underwater landslides off the continental shelf into the deep ocean. The landslide deposits can be recognized in core samples taken from the ocean floor.

The deformation of the crust in a predictable pattern can be detected by very careful geodetic measurements using Global Positioning Satellites, precise levelling, micro-gravity measurements and changing distance measurements using laser technology.

If the shaking of a magnitude 7 is 10 times greater than a magnitude 6 and 100 times greater than a magnitude 5, is the shaking from a magnitude 9 100 times greater than a magnitude 7

No. Earthquake shaking, in the frequencies that damage buildings, increases to a maximum between a magnitude 7 and 8 earthquake, then the shaking simply involves a bigger area. However, the duration of shaking for a megathrust earthquake is much longer. It can be several minutes. This long duration can result in damage to some types of buildings that might not be damaged at the same strength of shaking produced by a smaller earthquake.

The Kobe earthquake was right beneath the city and the megathrust earthquake will be about 150 kilometres from Vancouver. The damage pattern would be very different. We can get a good example of the kinds of damage Vancouver can expect to experience if we look at what happened to Anchorage, Alaska, during the 1964 magnitude 9.2 megathrust earthquake. Anchorage is about the same distance from the Alaska subduction fault. Small buildings generally had little or no damage, unless they were affected by landsliding. Almost all the damage involved large buildings or large structures such as bridges.

No. Vancouver Island is part of the North American plate. The fact that there is water between Vancouver Island and the mainland is function of the current position of sea level. However, the west coast of Vancouver Island will drop as much as a metre or two when the next megathrust earthquake occurs.

No. Inland earthquakes, which are not as big but can be much closer to our urban areas and occur much more frequently, are our biggest earthquake hazard.

The thrusting motion of megathrust earthquake causes large vertical movement on the sea floor and this displaces a large volume of water which travels away from the undersea motion as a tsunami .

No. Just the coast exposed to the open Pacific is vulnerable to damaging tsunamis waves. The areas vulnerable to tsunamis are indicated in the red-tabbed pages of the telephone books published for the coastal communities of British Columbia.

Data from selected NRCan seismometers are forwarded to the National (United States) Oceanic and Atmospheric Administration’s (NOAA) National West Coast and Alaska Tsunami Warning Centre (NTWC) in Palmer, Alaska. This information is integrated with other seismic, tide gauge, and deep ocean buoy system data to produce tsunami information statements, alerts, watches, or warnings for all North American coastlines (including the Atlantic and Arctic). NTWC distributes these messages to Emergency Measures Organizations (EMO) and other clients 5 to 15 minutes after a potentially tsunamigenic earthquake has occurred and provide updates at regular intervals.

NTWC product definitions are provided here .

No. It takes many, many small earthquakes to release the amount of energy equivalent to a large earthquake. The amount of energy released increases about 40 times every time there is an increase of one unit on the magnitude scale. Thus, if we consider a small earthquake at the felt level, about magnitude 2, there would have to be 40x40x40x40x40x40x40 of these earthquakes to release the amount of energy as one magnitude 9 event. That is about one million small earthquakes a day, every day, for 500 years. That level of earthquake activity is not observed.

This Earthquakes Canada site is the authoritative source of information on Canadian eathquakes. Available here, among other things:

• A list of events within the last 30 days
• Access to the National Earthquake Database of earthquakes since 1980
• A description of the seismic zones of Canada
• A link to the Pacific Geoscience Centre's Geodynamics prgogram

No casualities were ever directly related to Canadian earthquakes. In fact, Canadian earthquakes have never caused the collapse of a building. Only some injuries were caused by the fall of objects.

Although it has been reported that a yound girl was killed during the 1732 Montreal earthquake , it has never been substanciated by independent sources.

In Canada, the only loss of life related to an earthquake, although indirectly, were those caused by the tsunami created by the 1929 Grand Banks earthquake .

Nuclear Explosions

Yes! While there are differences between the recordings of an earthquake and a nuclear explosion, the same basic instrumentation and measurement techniques apply. Being geographically the second largest country in the world, Canada plays an important role in nuclear explosion monitoring .

Geology (faults, landslides, etc)

If you live in the East or the North of Canada, the presence of faults in your area is not indicative of a higher probability earthquakes. In these areas, the faults represent very old geological movements. The Geological Survey of Canada has produced maps for certain areas of Canada. You can consult what is available in the GEOSCAN database .

Instruments and networks

How we record earthquakes - Seismographs

How we record earthquakes - Seismic Waves

Building your own seismograph is possible, but it requires time and materials. If your project is due tomorrow, forget about it! If you have a little more time here is a reference:

• " The Amateur Scientist", Scientific American, July 1957 and July 1979: BASIC principles and how to build a simple seismograph.

The 1979 article is reproduced on the Redwood City (California) Public Seismic Network site.

The seismogram viewer is a display of vertical component seismic data recorded by a selection of our seismograph stations. It is intended to provide qualitative information for the general public.

The time shown is Coordinated Universal Time (UTC) . The plots are delayed by about 5 minutes which is the time it takes to acquire the data and process it.

A pink display indicates that there is no data available for that station at that time.

The vertical scale has been adjusted to a level intended to suppress most local noise and emphasize Canadian earthquakes. There is no simple correspondence between amplitude on the real-time seismogram viewer and earthquake magnitude, as it depends on the distance to the earthquake and other factors. Some recordings which can look quite large are actually just noise such as wind or human activity close to the seismograph station. See Interpreting Seismograms .

If you require detailed technical information, you can download waveforms from our waveform archive ; however, using and interpreting the data may require specialized seismological software and expertise.

To find the magnitude of events, you can look at our recent significant earthquake reports and at the the last 30 days of Canada earthquakes .

Seismic Hazard and Earthquake Engineering

Yes! Engineers can, and are, designing earthquake-resistant structures.

The first seismic hazard maps for use in Canada have been in use since 1953. This initial hazard map was a subjective assessment based on historical seismicity. In 1970 the first modern maps were developed using probabilistic methods. In 1985 two maps were produced, "acceleration" - suitable for use when designing small structures, and "velocity" - suitable for use when designing large structures.

• Maps and publications
• Seismic Hazard Calculations

Seismologists at the Geological Survey of Canada produce seismic hazard maps for use in the National Building Code of Canada.

• For more details, to see the maps, or for a detailed reference to the National Building Code of Canada, click here: Earthquake Hazard

The safest type of structure is a modern, well-designed, and well-constructed building. Generally, wood-frame houses perform very well during an earthquake. However, even these structures are prone to damage from soil failure, chimneys may be damaged or collapse, windows may break, interior walls may crack, and those houses not securely bolted to their foundation may fail at or near ground level. For more information on your home and earthquakes, click here . For some examples of damage to typical wood-frame houses during the M=7.3 Vancouver Island earthquake of 1946, click below:

• chimney damage
• foundation damage

Unreinforced masonary structures (those not seismically upgraded) are generally more vulnerable to earthquake damage. For some photos of damage caused to unreinforced masonary structures during the M=7.3 Vancouver Island earthquake of 1946, click below:

• masonary failure
• masonary failure and broken windows
• Ottawa Carleton Earthquake Engineering Research Centre
• Pacific Earthquake Engineering Research Center - UC Berkeley
• Multidisciplinary Centre for Earthquake Engineering Research

Facing Earthquakes

Falling objects pose the greatest danger during a major earthquake. In Canada, no house has ever collapsed during an earthquake. However, many types of objects may fall and cause damage or injuries. Of prime concern, therefore, is protection from falling objects such as framed pictures, light fixtures, plaster from ceilings or the upper part of walls, or chimneys which may fall outside or through the roof into the house.

Here is what to do:

• Stay calm - don't panic.
• If you are indoors, stay there. Do not run outside: you could be hit by flying debris or bits of glass. Take cover under, and hold on to a sturdy desk, a table, or a bed - or stand in a doorframe. Never use the elevators (they may have been damaged and/or the power may fail).
• If you are outdoors, stay there. Keep away from power lines and buildings. (House chimneys are likely to topple during a strong earthquake).
• If you are in a vehicle, stop and park away from buildings, bridges and overpasses.

To learn more about earthquake preparedness, follow the links at Preparing for earthquakes .

• Help the injured, if any. Speak calmly with family members, especially children about what has just happened, in order to relieve stress.
• Stay tuned to the radio and follow instructions.
• Use the telephone only in an emergency.
• Do not enter damaged buildings.
• To prevent fire, check the chimneys or have them checked before using the furnace or fireplace. Check all gas lines.
• Earthquakes can trigger huge ocean waves called tsunamis . The best warning is the earthquake itself and residents in tsunami risk areas should be prepared to evacuate to higher ground immediately (at least 10 metres above sea level) in the case of a large undersea earthquake. Stay tuned to your radio during a disaster.

For more information on earthquake preparedness and what to do during and after earthquakes, follow the links at Preparing for earthquakes .

Most earthquake damage is caused by ground shaking. The magnitude or size of an earthquake, distance to the earthquake focus or source, type of faulting, depth, and type of material are important factors in determining the amount of ground shaking that might be produced at a particular site. Where there is an extensive history of earthquake activity, these parameters can often be estimated.

The magnitude of an earthquake, for instance, influences ground shaking in several ways. Large earthquakes usually produce ground motions with large amplitudes and long durations. Large earthquakes also produce strong shaking over much larger areas than do smaller earthquakes. In addition, the amplitude of ground motion decreases with increasing distance from the focus of an earthquake. The frequency content of the shaking also changes with distance. Close to the epicenter, both high (rapid)and low (slow)-frequency motions are present. Farther away, low-frequency motions are dominant, a natural consequence of wave attenuation in rock. The frequency of ground motion is an important factor in determining the severity of damage to structures and which structures are affected.

Generally speaking, Canadian wood-frame houses are well able to withstand vibrations generated by earthquakes - even very large ones. Moreover, modern buildings must be designed according to national or provincial building code standards, which are intended to minimize the probability of building collapse in major earthquakes.

However, building codes do not prevent certain types of non-structural damage. Thus, it is possible that cracks may be seen on some walls. Unreinforced masonry (e.g. brick walls and chimneys) has little resistance to strong horizontal shaking and may collapse. Vibrations may also cause ground settlement under a house. Sometimes this may cause small cracks in the basement or warping of walls. These are indirect effects that do not indicate that a fault lies near the house.

For more on the effects of earthquakes on buildings, see section 4 above, "Seismic Hazards and Earthquake Engineering." See also How would your home stand up?

Seismologists

FAQ - What is a seismologist?

In the hour immediately following a relatively large earthquake, GSC Seismologists locate the earthquake and measure its magnitude. They use data supplied by the national seismograph network , which feeds continuous data 24 hours per day to the Ottawa and Sidney, BC offices. They pass this information on to the federal Office of Critical Infrastructure Protection and Emergency Preparedness, Provincial Emergency Program offices, to the news media - and, in Quebec, to the Quebec Provincial Police and to Hydro-Quebec.

During the following hours, the seismologists decide whether it would be feasible to conduct a field survey to learn more about the geological environment where the earthquake occurred, and to record any aftershocks that might occur in the ensuing hours and days.

In a field survey, seismologists set up portable seismographs to measure any further release of energy through small earthquakes. This information is analyzed in the weeks and months after the main earthquake and permits scientists to better understand the phenomenon of earthquakes in Canada. In the short term, this information cannot be used to predict earthquakes. In the long term, it will provide the basis for a more comprehensive understanding of seismic activity in the region.

Also, if the earthquake was large, other scientists specializing in surface deposits (clay, sand) may join the field survey team. Engineers may also come to inspect buildings to better determine the effects of the earthquake. Some of these specialists may return again after several months to gather additional data.

Order Your Almanac Today!

Earthquake Questions and Answers

Shake, rattle, and roll! In this short article, we answer common earthquake questions and answers to give you a basic understanding of this disruptive event.

What is an earthquake? 

What determines that an earthquake is really an aftershock, read next, remembering the 1906 san francisco earthquake, famous earthquakes in history.

• Worst Hurricanes in American History (Part II )

Where was the largest-magnitude earthquake in the 50 states, and when was it?

The strongest recorded earthquake in the United States was near Prince William Sound, Alaska, on March 27, 1964. It measured a 8.4 on the Richter scale and killed 131 people. It also caused a 50-foot tsunami that traveled 8,445 miles at 450 miles per hour. This earthquake’s tremors were felt in California, Hawaii, and Japan.

However, the New Madrid (Missouri) Earthquake, which was not recorded, is considered by many to have been the most severe in U.S. history. This series of earthquakes started in December 1811 and lasted until March 1812. It shook more than two-thirds of the United States and was felt in Canada. It changed the level of the land by as much as 20 feet, altered the course of the Mississippi River, and created new lakes west of Mississippi and Tennessee. Because the area was so sparsely populated, there was no known loss of life.

How often do severe earthquakes occur on the West Coast?

The states of California and Nevada experience the most earthquakes. More than 300,000 earthquakes have been recorded in these two states since 1836, including 10 of the 15 largest earthquakes in the contiguous United States.

The largest earthquake in California, and the second largest in the United States, registered 7.9 on the Richter scale and occurred along the San Andreas Fault in Fort Tejon in 1857. One person was killed, and the earthquake caused significant property damage.

Here are some more recent examples of severe earthquakes in that area:

• A 1933 quake in Long Beach, California, registered 6.3, killed 115 people, and caused $40 million in damage.
• A 1952 quake in Kern County registered 6.1, killed 12 people, and caused $60 million in damage.
• The famous Loma Prieta quake of 1989—watched by many during the World Series—registered 7.1, killed 63 people, injured more than 3,700, and caused $6 billion in damage.
• The Northridge quake of 1994, which happened in a densely populated area of Los Angeles, registered 6.8, killed 57 people, seriously injured more than 1,500, and resulted in $20 billion in damage, including several important Los Angeles freeways. For many days after the earthquake, thousands of homes were without gas and electricity, and 49,000 homes had no water, making this one of the biggest earthquakes in terms of disruption of life.

What have been the most recent earthquakes and where were they?

In April 2009, one earthquake struck central Italy, registering a 6.3. The next day, a 4.9–magnitude aftershock hit the same area.

So far, in 2010, there have been six recent earthquakes. Four were in January: a 6.5–magnitude quake off the shore of Northern California, 4.3–magnitude quake in Southern California, a 7.0–magnitude quake approximately 16 miles from Haiti’s capital city of Port-au-Prince, and a 6.1–magnitude aftershock again in Haiti. One was in February in central Chile; it registered an 8.8. One other quake was in April; it registered a 7.2 and struck just south of the U.S. border near Mexicali.

Where does the seismograph come from?

The American scientist John Winthrop (1714-1779) was one of the first to make scientific studies of earthquakes and is known as the founder of seismology. However, we cannot say that he was the inventor of the seismograph, as it is quite likely that various versions of this “machine” had already been constructed by his time. We do know that Zhang Heng invented an earthquake detector in China around A.D. 132. It consisted of a copper-domed urn with dragons’ heads—each containing a bronze ball—around the outside. Inside the dome was a pendulum that would swing when the earth shook and knock a ball from the mouth of a dragon into the mouth of a bronze toad waiting below. The ball made a loud noise and signaled the occurrence of an earthquake.

Michael Steinberg

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Worst Hurricanes in American History (Part II)

Worst Hurricanes in American History (Part I)

Earthquake Weather: Do Earthquakes Affect Weather?

Worst Hurricanes in American History (Part III)

What causes the Boom of an earthquake, the sudden noise? Is it the actual ledges way underground shifting? Out in the country where there are not other bldgs, it cannot be the noise of bldgs moving. So please explain the noise(s) that occur as a quake is happening or about to happen. The rattleing can continue without more noise. How come?

Good question, watani, and not an easy answer. This is a topic on which there is not a lot known. One of the best studies—in fact, the first to record earthquake sounds—dates to 1986! Many factors contribute to the “sound” that an earthquake makes. In brief, yes, the boom emanates from the ground shifting. (Again, simply put), quakes generate P waves first that move back-and-forth, and followed by S waves that move with more of a sideways motion. The P waves, which travel fastest, create the sound. The stronger S waves, follow within seconds and vibrate more slowly. BTW, in very strong earthquakes, both waves may be felt; in small quakes, usually only the S wave/s may be felt—but the sound of the P wave may be heard. Note, too, that P and S waves refer underground effects; these are not waves that travel on Earth’s surface.

Fostering Sustainable, Healthy & Safe Behaviors

Critical thinking is a form of open-minded thinking that aims to gain insight into how to improve things. The focus is on criticism and applicability of the resultant knowledge. Despite the existence of theories linking the critical thinking disposition and hazard adjustment adoption, there have been no previous studies examining the association between this disposition and household earthquake preparedness. The present study intends to identify this association. Data were collected from 598 respondents through a questionnaire survey. Household earthquake preparedness was measured by the number of adjustments adopted in the household. In regression analysis, taking into account interactions between the considered variables, it was found that logical thinking awareness, a subconstruct of the critical thinking disposition, was a significant predictor of household preparedness. Furthermore, inquisitiveness, another subconstruct of critical thinking disposition, was found to moderate the association between risk perception and earthquake preparedness. This finding suggests that people who have the motivation to tackle challenging situations actually do so in the context of earthquake preparedness. The practical implications of the findings are also discussed.

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This Week: Turkish Earthquake, Board Meeting, RSR Bridge

7:50 AM PDT on June 24, 2024

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Here is a list of events this week.

• Tuesday Earthquake Recovery in Türkiye . Why did the earthquake cause so much damage in Türkiye? Where is Türkiye now in the recovery timeline and how are leaders thinking about housing recovery and “building back better”? Join SPUR panelists as they answer these questions and consider lessons for the Bay Area. Tuesday, June 25, 12:30-1:30 p.m. Register for Zoom link .
• Tuesday San Francisco Bicycle Coalition Board Meeting . All members are invited to join via Zoom or phone. Tuesday, June 25, 6-8 p.m. Register for Zoom link  and more information.
• Wednesday Save the Richmond-San Rafael Bridge Path . Join Bike East Bay to learn more about the current status of the RSR Bridge and MTC’s plans to convert the multi-use path into a roadway shoulder. Wednesday, June 26, 6 p.m. Register for Zoom link .
• Thursday Film Screening: Fault Lines and the San Francisco Housing Crisis . From directors Nate Houghteling (American Pathogen, State of Pride) and Yoav Attias (Brick City, Chicagoland) comes this documentary about the San Francisco housing crisis. Join this SPUR screening of the film. Thursday, June 27, 5-8:30 p.m., SPUR Urban Center, 654 Mission Street, S.F.
• Thursday Seamless Bay Area Happy Hour . Join Seamless at Shotwell's Saloon in the Mission District of San Francisco. They'll be joined by the Overhead Wire's Jeff Wood, who produces the "Talking Headways" podcast , interviewing advocates, elected officials, researchers and others about cities and sustainable transportation. Thursday, June 27, 5:30 p.m. Shotwell's Saloon, 3349 20th Street, S.F.
• Friday Pride Ride . Join the San Francisco Bicycle Coalition for a bike tour of sites with historic significance to the LGBTQ+ movement. Friday, Jun 28, 4 p.m. Starts at the Hellman Hollow Picnic Area in Golden Gate Park, S.F.
• Saturday Family Learn to Ride . In partnership with San Francisco Safe Routes to School, Excelsior Collaborative, Excelsior Bike Club, Casa de Apoyo, and Excelsior Strong, the San Francisco Bicycle Coalition is holding a multilingual family bike fair. Saturday, June 29, 10 a.m.-1 p.m. Monroe Elementary, 260 Madrid Street, S.F.

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