San Andreas Fault/ Earthquakes

The above picture (credit USNP) is of the Carrizo Plain in which the San Andreas fault (think San Francisco earthquake of 1906) runs through this area. Using this area let's review some of the terms that pertain to earthquakes.

• a fault is where Earth movement has occurred due to a release of elastic rebound energy.
• the spot inside the Earth where the earthquake started is the focus, while the area directly above the focus on the Earth's surface is the epicenter.

The energy from an earthquake propagates as waves and can move the ground surface in any direction. There are three types of earthquake waves:

• surface waves- act like water waves and are the most destructive, slowest wave.
• p-waves- travel the fastest, push-pull (compressional) travel through solids and liquids.
• s-waves- slower than p-waves, transverse, can only go through solids.

Tsunamis are large ocean waves produces by movement of the ocean floor.
An earthquake's position can be determined by 3 seismic stations that contain an instrument called a seismograph. Scientists use the moment magnitude scale for measuring the strength of earthquakes.