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