Environmental Engineering Reference
In-Depth Information
11
Earthquakes
11.1
Introduction
11.1.1
General
The Hazard
Earthquakes
are the detectable shaking of the Earth's surface resulting from seismic waves
generated by a sudden release of energy from within the Earth. Surface effects can include
damage to or destruction of structures; faults and crustal warping, subsidence and lique-
faction, and slope failures offshore or onshore; and tsunamis and seiches in water bodies.
Seismology
is the science of earthquakes and related phenomena (Richter, 1958). The
Chinese began keeping records of earthquakes about 3000 years ago, and the Japanese
have kept records from about 1600
A
.
D
. Scientific data, however, were lacking until the first
seismographs were built in the late 1800s. Strong-motion data, the modern basis for aseis-
mic design, did not become available until the advent of the accelerograph, the first of
which was installed in Long Beach, California, in 1933.
Engineering Aspects
Objectives of engineering studies are to design structures to resist earthquake forces,
which may have a wide variety of characteristics requiring prediction and evaluation.
Important elements of earthquake studies include:
Geographic distribution and recurrence of events
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Positions as determined by focus and epicenter
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Force as measured by intensity or magnitude
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Attenuation of the force with distance from the focus
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Duration of the force
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Characteristics of the force as measured by: (1) amplitude of displacement
in terms of the horizontal and vertical acceleration due to gravity and (2) its
frequency component, i.e., ground motion
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Response characteristics of engineered structures and the ground
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Earthquake damage factors
to be considered include:
Magnitude, frequency content, and duration of the event
●
Proximity to populated areas
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Local geologic conditions
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Local construction practices
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