Earthquakes

Page
1

Slide 1

What are Earthquakes?

The shaking or trembling caused by the sudden release of energy

Usually associated with faulting or breaking of rocks

Continuing adjustment of position results in aftershocks

Slide 2

What is the Elastic Rebound Theory?

Explains how energy is stored in rocks

Rocks bend until the strength of the rock is exceeded

Rupture occurs and the rocks quickly rebound to an undeformed shape

Energy is released in waves that radiate outward from the fault

Slide 3

The Focus and Epicenter of an Earthquake

The point within Earth where faulting begins is the focus, or hypocenter

The point directly above the focus on the surface is the epicenter

Slide 4

Seismographs record earthquake events

At convergent boundaries, focal depth increases along a dipping seismic zone called a Benioff zone

Slide 5

Where Do Earthquakes Occur and How Often?

~80% of all earthquakes occur in the circum-Pacific belt

most of these result from convergent margin activity

~15% occur in the Mediterranean-Asiatic belt

remaining 5% occur in the interiors of plates and on spreading ridge centers

more than 150,000 quakes strong enough to be felt are recorded each year

Slide 6

The Economics and Societal Impacts of EQs

Damage in Oakland, CA, 1989

Building collapse

Fire

Tsunami

Ground failure

Slide 7

What are Seismic Waves?

Response of material to the arrival of energy fronts released by rupture

Two types:

Body waves

P and S

Surface waves

R and L

Slide 8

Body Waves: P and S waves

Body waves

P or primary waves

fastest waves

travel through solids, liquids, or gases

compressional wave, material movement is in the same direction as wave movement

S or secondary waves

slower than P waves

travel through solids only

shear waves - move material perpendicular to wave movement

Slide 9

Surface Waves: R and L waves

Surface Waves

Travel just below or along the ground’s surface

Slower than body waves; rolling and side-to-side movement

Especially damaging to buildings