An earthquake is… • The shaking of the earth’s crustcaused by arelease of energy. • Earthquakes can be caused by: • 1. Eruptionof avolcano • 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 • 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 tomeasure an Earthquake • Seismogram: The paper record of the Earthquake data (shaking) is called a seismogram
The S-P Time Interval is thetime 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 • 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.