Earthquakes

An earthquake is… …the shaking of the earth’s crust caused by a release of energy. Earthquakes can be caused by: 1. Eruption of a volcano 2. Collapse of a cavern 3. Impact of a meteorite 4. Strain built up along boundaries between tectonic plates

A fault is… …a break in the lithosphere along which movement has occurred. Most earthquakes occur in this way. The elastic rebound theory states that friction between plates prevents them from moving, so strain builds up. Eventually, the strain becomes great enough that the rock moves, and returns to normal shape.

Terminology Focus: the point at which the rock first breaks and moves in an earthquake. The focus is below the surface. Epicenter: the point on the earth’s surface directly above the focus.

Seismic Waves Primary waves (P waves) Secondary waves (S waves) The energy released in an earthquake travels in waves. There are three types: Primary waves (P waves) Secondary waves (S waves) Surface waves

Primary Waves Compression waves – they exert a Push and Pull force. Can travel through any material - solid, liquid, or gas. Travel the fastest

Secondary Waves They have a Side to Side movement. Can travel only through solid material. Travel at about half the speed of P waves

Surface Waves Seismic waves that travel along Earth’s Surface. When P and S waves reach the surface of the Earth, they make Surface waves. These bad boys cause all of the damage.

Locating Earthquakes Because P waves and S waves travel at different speeds, the difference in their arrival times can be used to determine the distance away an earthquake occurred.

Locating Earthquakes If you know the distance an earthquake occurred from at least three different seismic stations, you can locate the epicenter. Using the S-P time interval data from 3 stations to determine the epicenter

Earthquake Hazards Fire: causes the most damage in an earthquake, some utility lines and roads get damaged Liquefaction: when the ground turns to quicksand due to the shaking Tsunamis: caused by underwater earthquakes that cause water movement