Earthquakes often strike without warning, causing great destruction and, sometimes, loss of life. One example is the earthquake that occurred in Indonesia in May 27, 2006; measuring a magnitude of 6.3, this earthquake killed over 6000 people, injured over 20,000, and left over 200,000 homeless.

Earthquakes occur when massive amounts of stored energy are released from the earth. When this energy is released, it travels through the surrounding geological structures in waves; it is these waves that literally "move the Earth". As you have probably have already learned in Geology, the Earth's surface is made up of crustal plates that move naturally, as a result of underlying convection (http://pubs.usgs.gov/gip/dynamic/dynamic.html). When these plates meet and rub against each other they produce heat and friction.

Did You Know?
The earth's crust is made up of many crustal plates that are in constant movement

Earthquake-causing energy is released when a block of rocks (i.e., a crustal plate) rapidly moves past another block along a fault, a fracture, or a "zone of fracture" that exists between the two blocks (http://pasadena.wr.usgs.gov/shake/).

Did You Know?
Rapid movement of rocks along a fault results in the release of massive amounts of stored energy

Today's magnitude scale, similar to the original Richter magnitude measurement system, is actually a measure of energy released from the earth at the time of the quake. Each unit is an increase of approximately thirty times the energy from the previous unit — i.e., a magnitude 6 earthquake has approximately thirty times more energy than a magnitude 5 event. Most geological faults produce repeated displacements over time, so regions of potential earthquake hazard are relatively well-known by scientists

Did You Know?
The magnitude scale that is used to measure an earthquake is a measure of the energy released at the time of the quake

While earthquakes can occur almost anywhere in the world, the majority take place on the "Ring of Fire", which is a horseshoe-shaped geological feature that almost completely circles the Pacific Ocean. The Ring of Fire is simply an area where a series of these crustal plates converge and display elevated levels of tectonic activity, resulting in seismic events. Approximately 90% of the world's earthquake events occur within the Ring of Fire! The largest of these events are subduction earthquakes, in which one slab of rock pushes below an overriding plate.

Did You Know?
A subduction earthquake is one of the largest of the seismic events and is caused when one tectonic plate moves underneath another one

A small earthquake that occurs in the middle of the Pacific Ocean might not have significant consequences. However, a large earthquake near a major urban centre in Canada could result in damages in the multi-billion dollar range and in thousands of deaths. The most active seismic region in Canada lies on the west coast, within the Ring of Fire, where the coastal region of southwestern B.C. is subject to these large crustal and subduction earthquakes.

Earthquake damage is a direct result of: i) the level of shaking that is induced by the event and ii) the type and quality of the structures that it shakes. While the shaking that an earthquake produces is a physical property of the earthquake itself (i.e., a function of the quake's magnitude and geometry), the type of structure that is shaken is controlled by the local government building codes.

Earthquake engineers can build structures that minimize the damage from a large event. However, such a task is expensive and can be difficult to accomplish in poorer regions of the world. For example, the recent Indonesian earthquake killed more than 6000 people, yet it was only a moderate event of magnitude 6.3. Ironically, similar earthquakes that occur in areas such as Japan or California, where the construction is built to modern building codes, cause less damage and minimal-to-no loss of life.

Did You Know?
Earthquake engineers design buildings and structures that can withstand earthquake activity

Earthquake losses are greatly reduced through knowledge of earthquake risk. Much of the concern comes from an inability to accurately predict exactly where and how often earthquakes will occur. Many scientists are studying earthquakes and seismic waves, as well as techniques for predicting when earthquakes will happen. This research should help us better understand these events so that we can reduce the hazards associated with earthquakes and prevent tragedies similar to the one experienced in Indonesia.

Learn More About Earthquakes:

Earthquakes Canada

http://earthquakescanada.nrcan.gc.ca/

U.S. Geological Survey:

http://pubs.usgs.gov/gip/dynamic/dynamic.html

Research at the University of Western Ontario:

www.uwo.ca/earth/Tiampo.html

www.uwo.ca/earth/Eaton.html

Dr. Kristy Tiampo is a professor of geophysics who studies earthquakes and volcanoes. She grew up in the United States where she got her degree first as an engineer and then as a scientist. She currently lives in London, Ontario. While she has been in two earthquakes big enough to feel: one in California and one in Montreal, she was in an elevator for the second one and so didn't even experience that one.

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