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 plates

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

Focus: the point at which the rock first breaks and moves in an earthquake. 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 (Love and Rayleigh)

Primary Waves Called P waves Compression waves- squeeze and stretch rock (Push and Pull) Can travel through any material- solid, liquids, and gases Travel the fastest

Secondary Waves S waves Side to Side movement. Can travel only through solid material, not liquids or gases Travel a little more than half the speed of P waves

Surface Waves Seismic waves that travel along Earth’s Surface When P and S waves reach the surface, they make Surface waves There are two types, Love waves and Rayleigh waves Cause lots of damage

Measuring Earthquakes Seismograph: Instrument used to measure an Earthquake Seismogram: The paper record of the Earthquake data (shaking) is called a seismogram

The S-P Time Interval is the time between the start of the p wave and the s wave.

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

Earthquake Magnitude: strength measured by the amount of released energy Richter Scale by Charles Richter Each increase in number represents 10x an increase in power. Example: a 4.0 is ten times stronger than a 3.0

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: Are caused by underwater earthquakes that make a big wave.