Lesson: Earthquakes (corresponding to Chapter 12: BC SCIENCE 10) On December 26, 2003, the Iranian city of Bam was virtually leveled by an earthquake. The estimated 30,000 deaths could have been reduced greatly if better construction techniques were used. Earthquakes are one of nature’s deadliest natural disasters.

Prince William Sound Earthquake, 1964. 9.2 Magnitude- largest recorde earthquake in N. America

Sendai, Japan earthquake, March 2011 Magnitude 9.0

Port au Prince, Haiti, January 2010 7.0 Magnitude

Impact of Earthquakes A. distance to epicenter B. geology of the area C. magnitude of earthquake

Earthquake Hazards An old saying among geologists is that “earthquakes don’t kill people, buildings do”. The vast majority of deaths in earthquakes occur when ground shaking from earthquake waves (particularly S-waves and surface waves) causes buildings or other structures collapse, killing the people inside. Most damage and collapse of structures like buildings, bridges, and roads occurs due to sideways movement of the ground from earthquake waves.

Other Hazards Liquefaction of soil Landslides Fire Tsunamis

Fires Fires- commonly break out during quakes due to ruptured gas lines or downed electrical lines. In some urban quakes, fires have caused more damage than the ground shaking itself. The photograph shows an uncontrolled fire in San Francisco after the 1989 Loma Prieta quake.

Liquefaction Liquefaction- occurs in water-saturated soils. The shaking of earthquake waves causes the soil to turn into a weak, fluid-like mass. Structures built on areas that liquify may simply fall over, as shown in this photo from the 1964 Niigata, Japan, quake. This is also thought to be what will happen in Richmond, BC.

Tsunamis Tsunamis- waves generated by physical disturbances of the ocean. Shifting of the sea floor during an earthquake is the most common cause. Undersea volcanic eruptions, landslides, or even meteorite impacts can also cause tsunamis.

In deep water, tsunamis are very low, fast-moving waves that are nearly undetectable. But as the leading waves of a tsunami approach a shoreline, friction with the sea floor slows the waves down, allowing the waves behind to catch up. This process of waves coming together and stacking up is called shoaling, and it builds up the height and steepness of the waves. The waves surge onto shore typically as a rapidly rising flood of water with great destructive power. The aftermath of the tsunami in Aceh Indonesia.

Sumatra-Andaman Tsunami- Dec 26, 2004 An 9.2 Magnitude earthquake occurred when the India plate subducted under the Burma micro-plate (part of the larger Sunda plate)

Most destructive tsunamis occur in Pacific Ocean Most destructive tsunamis occur in Pacific Ocean. This is clearly related to plate tectonics: the borders of the Pacific Ocean are dominated by active subduction zones that produce frequent violent earthquakes (as well as undersea volcanic eruptions and landslides). Hawaii, with its central location, is vulnerable to tsunamis coming from several different areas of subduction.

1. Tsunami warning systems issue warnings based on the locations of earthquakes. (Recall the method for locating earthquakes presented earlier in this lesson.) When a large, potentially tsunami-producing earthquake is located, warnings are issued for coastal areas. Unfortunately, since many earthquakes do not make tsunamis, this system has a ~75% false alarm rate, which has lead many communities to distrust the system! There was no such warning system in the Indian Ocean where the December 2004 tsunami occurred.

Mitigation (reduction) of hazards 4. Seismic joints: areas of flexible material, like rubber, form connections between different parts of a building. These allow the separate areas of the building to shake independently. Shear walls: diagonal braces or plywood sheeting built into the walls, to keep the building from deforming during base shear. 2. Bolting to the foundation, so the building does not slide off. Base isolation: putting the building on large rubber pads, rolling wheels, or slippery Teflon plates.