1. Locating Earthquakes Earthquake occurs when there is a rupture in the rock or when the strain builds up enough to cause movement along a fault. 3 waves that are formed during an earthquake are: P waves-1 st to arrive S waves-2 nd to arrive Surface Waves-last to arrive: cause the most damage

2. Locating Earthquakes Seismograph: instrument that measures seismic waves Seismogram: paper record of a seismic event

3. Locating Earthquakes By studying seismic waves, scientists can determine how far away an earthquake is from a seismograph station. By studying seismic waves, scientists can determine how far away an earthquake is from a seismograph station.

4. Locating Earthquakes

6. Scientists use readings from multiple seismograph stations to help try and determine the location of an earthquake. You need at least 3 to determine the location by using a method called triangulation. Scientists use readings from multiple seismograph stations to help try and determine the location of an earthquake. You need at least 3 to determine the location by using a method called triangulation.

7. Locating Earthquakes Earthquakes are described by their distance from a seismograph: Earthquakes are described by their distance from a seismograph: Local Events: less than 100 km away Local Events: less than 100 km away Regional Events: 100 km-1400 km away Regional Events: 100 km-1400 km away Teleseismic Event: greater than 1400 km away Teleseismic Event: greater than 1400 km away

8. Locating Earthquakes Scientists also use seismic waves to determine what the interior of Earth looks like. Scientists also use seismic waves to determine what the interior of Earth looks like. What relationship exists between density of materials as you get closer to the center of the Earth? What happens to the speed of seismic waves as they pass through denser material?

9. Locating Earthquakes Shadow Zone - area of 105 O – 140 O from the earthquake focus where no seismic waves are recorded.

10. Mapping Earth’s Internal Structure As you descend further down into the crust and into the top of the mantle the density __increases___. Therefore, the speed of the seismic waves will __ increase___. This area is known as the Mohorovicic discontinuity (Moho). The waves continue until they reach the asthenosphere, the semi liquid state of the mantle. Here the seismic waves __ decrease __ in speed.

11. After they pass through the asthenosphere, the mantle then becomes solid again and the speed of the waves __ increases __. The core of the Earth is divided into 2 layers: a liquid outer core and a solid inner core. As seismic waves reach the outer core, P waves _ slow _ in speed, but then _ increase ___when they reach the inner core. S waves _ cannot _pass through the outer core.