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 kes/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. Compression 1. Compression – stress that squeezes compacts 2. Tension 2. Tension – stress that causes stretching & elongation 3. Shear 3. Shear – 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.Primary wave 1.Primary wave (P-wave) 2.Secondary wave 2.Secondary wave (S-wave) 3.Surface wave 3.Surface 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

`