EARTHQUAKES: WHY? AND HOW?

EARTHQUAKES sudden movement or shaking of the Earth Caused by plate tectonic stresses releases stored Energy! Located at plate boundaries Resulting in breakage of the Earth’s brittle crust

Elastic Rebound Theory Stresses build on both sides of a fault. When stresses become too great, the rocks break and move. This releases the built up energy and creates an earthquake. Video Clip

3 Types of Stress Compression- occurs at convergent boundaries (plates move toward each other) Tension- occurs at divergent boundaries (plates move away from each other) Shear- occurs at transform boundaries (plates are sliding past each other)

PLATE TECTONIC STRESSES Plate boundaries and faults (= cracks where plate sections are moving in different directions) cause friction as plates move Plates in a fault zone have STICK-SLIP motion Periods of no movement (stick) and fast movement (slip) Energy stored as plates stick Energy released as plates slip

3 Types of Faults Normal Fault Reverse Fault Strike-Slip Fault

Normal Fault Result of plates moving apart. The hanging wall moves downward in relation to the footwall.

Normal Fault: Tetons in Wyoming

Reverse Fault Result of plates moving together. The hanging wall moves upward in relation to the footwall.

Reverse Fault: Sierra Madre

Strike-Slip Fault Result of plates sliding past each other. The displacement is horizontal

Strike-Slip: San Andreas Fault

Parts of a Wave Energy is transmitted in waves

EARTHQUAKE WAVES FOCUS = place deep within the Earth and along the fault where rupture occurs EPICENTER = geographic point on surface directly above focus SEISMIC WAVES produced by the release of energy move out in circles from the point of rupture (focus) 2 types of Seismic Waves: surface & body (travel inside & through earth’s layers) http://earthquake.usgs.gov/learning/animations/

2 Types of Body Waves Body waves travel faster than surface waves. P waves: back and forth movement of rock; travel thru solid, liquid, gas S waves: sideways movement of rock; travel thru solids only

2 Types of Surface Waves Travel along the ground, outward from an earthquake’s epicenter. Slowest of the seismic waves Do most of the damage Two Types of Surface Waves: Love Wave Rayleigh Wave

Tsunami Deadly ocean waves most often caused by undersea earthquakes. Tsunami Awareness NOAA DART