Chapter 12 Section 2 Earthquakes

What is an earthquake? Earthquake- The shaking that results from the movement of rock beneath the Earth’s surface

Types of stress Shearing- stress that pushes a rock in two separate directions Tension- stretches rock, causing it to become thinner in the middle Compression- pushes the two plates together until they either fold or break

Types of stress

Kinds of Faults 1 Fault – crack where movement was Strike Slip Faults- from shearing Normal Faults- Footwall rises above hanging wall Reverse Faults- Hanging wall rises above footwall

Normal Fault Reverse Fault Strike-Slip Fault

Strike-slip faults

FOCUS & EPICENTER 2-3 Focus- The point beneath the Earth’s surface where rock breaks under stress and causes an earthquake Epicenter- The point on the Earth’s surface directly above an earthquake’s focus

Triangulation to find the epicenter

Epicenters on a larger scale

3 Types of Earthquake Waves 57 (P)rimary waves- push pull waves (S)econdary waves- side to side waves (L) Surface waves- up and down rolls Seismic Waves- Earthquake waves that are compressional and transverse.

1. Primary waves (P-waves) – arrive at a given point before any other type of seismic wave.   (fastest of the three)

2. Secondary Waves (S-waves) – arrive at a given point after the P wave. (second fastest)

 3. Surface waves (L-waves) –  slowest moving seismic waves. Arrives last. Most destructive!

Seismographs We use a seismograph to measure/ detect seismic waves

Modern day seismographs

Ways we measure earthquakes Mercalli scale- relies on eyewitness accounts Richter scale- measures ground movement Moment Magnitude scale- uses both eyewitness accounts and ground movement

Major continental U.S. earthquakes

How earthquakes cause damage Loose soil Can cause landslides or mudslides

Liquefaction Soil and the water that is in it become separated Because the soil is heavier, it sinks pushing the water to the surface

Mudslide and landslide

San Andreas Fault

Why earthquakes in Japan?

Building damaged by liquefaction

Earthquake damage

San Francisco 1906 Earthquake

Los Angeles 1994

San Francisco 1989

Crack in the surface

Faults in California

Movement along a fault

Buildings in Japan after earthquake

Aftershocks Movement along a fault that occurs after a larger earthquake along that same fault

Tsunamis Tidal waves that can reach upwards to 115 feet Caused by Earthquakes that happen deep under water

2004 Sumatra tsunami

Tsunami travel time

Tsunami height

Tsunami in Bangladesh

Tsunami damage

Days before tsunami Few minutes before tsunami During tsunami

During an earthquake, how do you protect yourself? Go under a table Go under a doorway Go under steps

Earthquake Hazards

Earthquake prone areas in the Midwest U.S.

How do we monitor movements in the faults? Creep meters Laser-ranging devices Tilt meters Satellite monitors

Creep Meter

Fault detecting laser

Tilt meter