Earthquakes and Seismic Waves  Caused by pressures generated through plate tectonics. Plates try to move but cannot. As pressure increases rock breaks along a fault generating an earthquake.

Location of Earthquake  Focus The point in the earth’s interior where the rocks break and release energy. Origin of earthquake.  Epicenter The point on the earth’s surface directly above the focus.

Seismic Waves  Seismic Waves are a release of energy in the earths crust due to stress.  All seismic waves leave at the same time.

Seismic Wave Animation  ce/terc/content/visualizations/es1002/es1002 page01.cfm?chapter_no=visualization ce/terc/content/visualizations/es1002/es1002 page01.cfm?chapter_no=visualization

Primary Waves  Called P-waves  First to arrive  Travel through earth’s core  Travel fastest 6-7 Km/sec  Cause ground to compress and stretch.

Secondary Waves  Called S-waves  Second to arrive  Cannot travel through earth’s core  Slightly slower about 3.5 Km/sec  Cause ground to move up and down.

Video: Seismic Waves

Surface Waves  Called L-waves  Last to arrive  Only travel on surface/cause the most damage  Slowest about 2.5 Km/sec  Cause ground to move in a rolling motion. See Wave Simulation

Locating an Epicenter  P,S, and L waves do not travel at the same speed.  As the waves travel the distance between the P and S waves increases.  The time interval between the P and S waves is converted to distance on a graph.  Doing this in three locations allows you to triangulate the earthquakes epicenter.

How to find the Epicenter of an Earthquake html

Measuring Earthquakes  Magnitude A measure of the energy released by an earthquake. Richter scale often used An increase in one is 10 times the ground motion An increase in one is 32 times the energy released.

Seismic Activity in our Area  INFO_GENERAL/eqhazards.html INFO_GENERAL/eqhazards.html