Locating Locating EarthquakesEarthquakes

•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-1st to arrive

•S waves-2nd to arrive

•Surface Waves-last to arrive: cause the most damage

Locating EarthquakesLocating EarthquakesSeismograph:

instrument that measures seismic waves

Seismogram:

paper record of a seismic event

Locating EarthquakesLocating Earthquakes

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

Locating EarthquakesLocating Earthquakes

Locating EarthquakesLocating Earthquakes Scientists use readings from multiple seismograph stations to help Scientists use readings from multiple seismograph stations to help

try and determine the location of an earthquake. You need at least try and determine the location of an earthquake. You need at least 3 to determine the location by using a method called 3 to determine the location by using a method called triangulationtriangulation..

Locating EarthquakesLocating Earthquakes

Earthquakes are described by their Earthquakes are described by their distance from a seismograph:distance from a seismograph:

Local Events:Local Events: less than 100 km away less than 100 km away

Regional Events:Regional Events: 100 km-1400 km away 100 km-1400 km away

Teleseismic EventTeleseismic Event: greater than 1400 km : greater than 1400 km awayaway

Locating EarthquakesLocating Earthquakes Scientists also use seismic waves to determine Scientists also use seismic waves to determine

what the interior of Earth looks like.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?

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

Mapping Earth’s Internal StructureAs 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.

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.