Ch 15 Earthquakes

I. Earthquake – the shaking of Earth’s crust caused by a release of energy; vibrations made from rocks breaking

II. Forces Inside the Earth

Elastic Rebound Theory

1. friction prevents movement

2. stress deforms plates

3. stress overcomes friction & plates move suddenly because rocks have bent & stretched until they have broken

Results : plates snap back to shape but at new locations; Earthquake

B. Fault

Surface along which rocks break

Rocks move in different directions on either side of a fault

http://www.thirteen.org/savageearth/earthquakes/html/sidebar1.html

C. Focus – place inside the Earth where the quake actually occurs

D.Epicenter - pt. on Earth’s surface directly above the focus of the quake

E. 3 Forces Rocks Experience

1.1. CompressionCompression – stress that squeezes compacts

2.2. TensionTension – stress that causes stretching & elongation

3.3. ShearShear – force that causes slippage & the rocks on either side to move past each other

III. Earthquake Information

A. Seismic waves - energy waves that move outward from the earthquake focus & make the ground quake

B. 3 Types of Seismic Waves

1.1. Primary wavePrimary wave (P-wave)

2.2. Secondary waveSecondary wave (S-wave)

3.3. Surface waveSurface wave (L-wave)

a. Love

b. Rayleigh

C. Primary waves

Compressional, travel through any material: solid rock, magma, ocean water, & air

Compaction & stretching of rock  Fastest wave 2 x speed of S waves

D. Secondary wave

Shear, travel through solids, not through liquids or gases

E. Surface waves (Longitudinal waves)

- Waves that travel like ripples on a pond across Earth's surface

Travel out from the epicenter Particles move in an elliptical motion,

as well as back & forth Cause the most destruction Slowest waves Two types: Rayleigh & Love waves

Surface Waves

Rayleigh Waves

III. Locating an Earthquake Seismograph - instrument that detects &

records earthquakes Readings from 3 seismograph stations are

needed to locate the epicenter P-waves travel the fastest The more time between the P & S waves,

the farther away the epicenter is Damaged area increases as focus depth

increases

The difference in arrival times between the P & S waves (from 3 different stations) is used to find the distance to that earthquake.

The difference in arrival times is ___

A. Richter Scale - the measure of the amount of energy (magnitude) released by a quake, each # is 32 x greater in energy

B. Moho Discontinuity - boundary between the crust & the mantle

seismic waves speed up because they are passing through a denser region

Moho Discontinuity

Seismograph – instrument used to record seismic waves

Tsunami – ocean waves generated by earthquakes

Seismology – the study of earthquakes

Seismologist – person who studies earthquakes & seismic waves

Cove where Tsunami Hit in 1964

Height of Tsunami Wave

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