Earthquakes Chapter 6

Elastic Rebound Theory Rocks on either side of a fault move slowly When locked, stress builds…until fault ruptures Rocks fracture and slip to new position releasing vibrations - create seismic waves

RelaxedStressedReleased

What are faults A fault is a crack in the Earth's crust along which movement has occurred. Occur at plate boundaries or within a plate Consists of a hanging wall (HW) and a foot wall (FW)

3 types of faults Normal: –at divergent boundaries, HW moves down, FW moves up

Reverse (or thrust fault): –at convergent boundaries: HW moves up, FW moves down

Strike-slip faults: –At transform boundaries; movement is horizontal

San Andreas Fault From shuttle (above) From air (at right) Strike-slip fault

More San Andreas

Earthquake Vocab Focus: area along fault where slippage 1 st occurs Epicenter: point on surface directly above the focus

Major EQ Zones – 1. Ring of Fire

2. Mid-Ocean Ridges

3. Eurasian-Melanesian Mts Boundary of Eurasian-Indian-African plates

4. Fault Zones Faults along plate boundaries – San Andreas strike-slip fault Faults within plates – in middle of US New Madrid, Missouri EQ New England, too? Nov NH – 1.2

Recording EQs Seismograph: instrument used to record EQs Seismogram: printout from a seismograph

Types of Seismic Waves Primary “P” Secondary “S” Surface Waves –Rayleigh “R” –Love “L”

Primary “P” waves “push-pull” waves Fastest seismic waves; 1 st to be recorded Compression waves (like sound) Cause movement in the same direction as the wave motion Rocks vibrate backwards and forwards, P waves can travel through liquids and solids

Secondary “S” waves Shake or shear waves Second to be recorded Slower and more destructive than P waves Rocks are moved from side to side as the wave passes, moving at right angles to the direction of wave motion Transverse waves, like water waves Move through solid only

Surface, “L” waves L for “Love” waves Slowest of the three EQ wave types L waves take the longer surface route around the earth Have a rolling motion, side to side Cause great damage Behaves most like waves in a pond or on the sea

Other surface waves Rayleigh waves Rolls along the ground, moving ground up and down Animation:

Power and ground type The type of rock will determine how fast the wave travels, and will thus affect amplitude of the waves Animation:

Using Seismic Waves to determine Earth’s Interior P waves travel through solids, liquids and gases S waves travel through solids only Outer core must be liquid (no S waves pass)

Earthquakes, Tsunami and animals

Homework Read and take notes – pp Answer questions #1-4, pg 102 and #3-5, pg 105