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Earthquakes and Earth's Interior Quiz Part 1

Chapter 14 Essentials of Geology by Pearson
STUDY
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Earthquake
The vibration of Earth produced by the rapid release of energy
Focus
The source of the energy that radiates in all directions from here in the form of waves
Faults
Large fractures in the Earth's crust that are associated with movements that produce earthquakes
Plate Tectonics Theory
Most of the motion along faults can be explained by this
Seismology
The study of earthquake waves; dates back to the Chinese almost 2000 years ago
Seismologists
People who study earthquakes and their characteristics
H.F. Reid
First explained mechanism for earthquakes
Mechanism for earthquakes
Rocks on either side of fault are deformed by tectonic forces, bend and store elastic energy, frictional force is overcome
Elastic rebound
Slippage at the weakest point (the focus) occurs; vibrations occur as the deformed rock "springs back" to its original shape
Focus
Point at the depth where the rocks ruptured to produce earthquakes; place where quake waves originate
Aftershocks
smaller quakes produced after a major quake caused by rocks shifting to new positions
Foreshocks
small earthquakes that come before a major earthquakes
San Andreas
Most studied fault system
Fault creep
Slow gradual displacement of some portions of fault
50 to 200 years
Great earthquakes should occur about
Seismograph
Instruments that record seismic waves
Large hollow jar
Chinese used this to measure seismic activity with suspended free motion mass
Seismograms
Records obtained from seismographs
Types of seismic waves
Surface, Body
Surface waves
Travel along the Earth's surface; cause greatest destruction; slow & great
Two kinds of body waves
Primary (P) and Secondary (S)
Body waves
Travel through Earth's interior; two types
Primary (P) waves
travel 1.7 times faster than S waves; travel through whole interior; motion is back & forth
Secondary (S) waves
shaking motion at right angles; travels only through solids; slower velocity than P waves; slightly greater amplitude than P waves
Waves
Wavelength, crest, trough and amplitude
Epicenter
location on the surface directly above the focus; located using the difference in velocities of P & S waves
Three
At least this many station recordings needed to locate an epicenter
Travel-time graph
used to determine each station's distance to the epicenter
Locating the epicenter
a circle with radius equal to distance to epicenter drawn around each station; point where all 3 circles intersect is epicenter
95%
percent of energy released by earthquakes; originates in a few relatively narrow zones that wind around the globe
Major earthquake zones
Circum-Pacific belt, Mediterranean Sea region to Himalayan complex & oceanic ridge system (underwater mountains)
5 to almost 700 km
Range of depths of earthquakes
Types of earthquakes
Shallow, Intermediate & Deep Focus
Shallow
surface to 70 km; occur along oceanic ridge system; nearly all damaging quakes originate at this depth; not much room so more damage
Intermediate
between 70to 300 km
Deep Focus
over 300 km; almost all occur in circum-pacific belt
90%
Percent of all earthquakes occur at depths of less than 100 km
Two measurements of earthquake size
Intensity and Magnitude
Intensity
a measure of the degree of quake shaking at a given locale based on amount of damage
Magnitude
estimates the amount of energy released at the source of the quake
Modified Mercalli Intensity Scale
developed using CA buildings; drawback not true measure of quakes actual severity; Guiseppe Mercalli; 1-12 in Roman numerals; I - least; XII - most; used after quake