They are common in California along the San Andreas fault. The best known strike-slip earthquake is the Loma Prieta earthquake that disrupted the 1989 World Series in Oakland, California.
Thrust Earthquakes These earthquakes occur on faults that separate converging plates. They are also called subduction earthquakes. They are common off the coast of B.C., Washington, and Oregon. These earthquakes are the strongest on Earth (some are larger than M9) and can produce tsunamis.
Normal Fault Earthquakes These earthquakes occur on faults associated with divergent plate boundaries. They are common along the Mid-Atlantic Ridge. Most are located under oceans and are generally smaller than M6. (Tsunamis need at least a M7)
Intraplate Earthquakes Definition: An earthquake on a fault in the interior of a continent, far from a plate boundary. These earthquakes are typically smaller than plate boundary earthquakes. However, damage could be considerable due to lack of preparedness.
Intraplate Earthquakes Because of dense continental bedrock, these earthquakes are felt over large areas. There are two relatively active intraplate zones in North America: Central Mississippi River Valley and St. Lawrence River Valley The New Madrid earthquakes in Missouri (1811-12) were over M7.5 and felt over the entire continent. The recurrence interval in this area is likely several hundred year. RI: The time between consecutive events
Earthquake Hazard Map
Effects of Earthquakes Several different effects related to earthquakes contribute to deaths and property destruction. Primary effects: ground shaking, surface rupture Secondary effects: liquefaction, land-level change, landslides, fire, tsunamis
Ground Rupture Displacement along faults causes cracks in the surface. During strong earthquakes, fault scarps (photo) can be produced that extend for hundreds of kilometres. Figure 3.20
Ground Rupture Ground rupture can uproot trees, collapse buildings, and destroy bridges, tunnels, and pipelines.
Liquefaction Definition: The transformation of water-saturated sediment from solid to liquid. This may occur during strong earthquakes when water pressure becomes high enough to suspend particles of sediment within the soil. Once the pressure decreases, the sediment compacts and regains its strength.
Liquefaction Watery sand and silt may flow upward along fractures in the overlying solid material. This effect can cause extensive damage. Figure 3.22 Figure 3.24
Landslides Ground motion produced by an earthquake can cause rock and sediment to move downslope. A single earthquake in a mountainous area can cause thousands of landslides.
Fires Ground shaking and rupture can sever power and gas lines, starting fires. Appliances may topple over causing gas leaks that ignite. (Huge problem in urban areas) 80% of the damage during the 106 San Fran earthquake was caused by fire. (Buildings fall, firetrucks can’t get through the city) The earthquake doesn’t necessarily cause the major damage, it’s the SECONDARY EFFECTS.
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