Chapter 16 Earthquakes

Circum-Pacific Belt

the most important concentration of earthquakes that encircles the rim of the Pacific Ocean

Moment magnitude

the most objective way of measuring the energy released by a large earthquake

Seismogram

the paper record of Earth vibration

Epicenter

the point on the Earth's surface directly above the focus

Seismic Waves

waves of energy produced by an earthquake

Benioff Zones

zones of inclined seismic activity

Focus

the point within the Earth where seismic waves first originate

Elastic Rebound theory

the sudden release of progressively stored strain in rocks, causing movement along a fault. Deep-seated internal forces act on a mass of rock over many decades. Initially the rock bends but does not break. More and more energy is stored in the rock as the bending becomes more severe. Eventually the energy stored in the rock exceeds the breaking strength of the rock, and the rock breaks suddenly, causing an earthquake.

Surface Waves

Seismic waves that travel on Earth's surface away from the epicenter, like ripples from a pebble thrown into a pond.

Intensity

measure of an earthquakes effect on people and buildings

Magnitude

measure of the energy released during the earthquake

Love waves

most like S waves that have no vertical displacement

Richter Scale

numerical scale of magnitudes

Seismograph

recording device that produces a permanent record of Earth motion detected by a seismometer

Body Waves

seismic waves that travel through the Earth's interior, spreading outward from the focus in all directions

S Wave

slower, transverse wave that travels through near surface rock that is propagated by a shearing motion much like that in a stretched shaken rope. The rock vibrates perpendicular to the direction of wave propagation, that is, crosswise to the direction the waves are moving. Cannot pass through liquid

Aftershocks

small earthquakes that follow the main shock

Earthquake

trembling or shaking of the ground caused by the sudden release of energy stored in the rocks beneath the Earth's surface

Tsunami

(Seismic Sea Waves)Sudden movement of the sea floor upward or downward during a submarine earthquake can generate very large sea waves.

Fire aftershock Tsunami Ground Failure Ground Motion

5 Earthquake Hazards

Island Arc

Benioff zones slope under a continent or a curved line of islands

depth of focus

Distance between the focus and the epicenter

Mercalli Scale

Earthquake intensity scale that describes effect on people and buildings

Liquefaction

Water-saturated soil turns from solid to liquid as a result of shaking

Rayleigh Waves

behave like rolling ocean waves

P wave

compressional (or longitudinal) wave in which rock vibrates back and forth parallel to the direction of wave propagation. Very fast and is always the first wave to arrive at recording station following an earthquake. Can pass through liquid