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Earthquake SeismologyGEO 335
BU: Bahria University
Department of Earth and Environmental Sciences
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Seismology
• Seismology is the study of generation,
propagation and recording of elastic waves or
seismic waves in the Earth (and other celestial
bodies) and of the source, which produces
them.
• The sources can be natural earthquakes or
man-made sources of deformational energythat generate the seismic waves.
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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
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CLASSIFICATION OF EARTHQUAKES
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FREQUENCY-MAGNITUDE RELATION
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What is the Elastic Rebound Theory?
• Explains how energy isstored in rocks
– Rocks bend until thestrength of the rock
is exceeded – Rupture occurs and
the rocks quicklyrebound to anundeformed shape
–
Energy is released inwaves that radiateoutward from thefault
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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
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TYPES OR CAUSES OF EARTHQUAKES
• Tectonic Earthquakes
– Subduction Zone Earthquakes
– Collision Zone Earthquakes
– Divergent and Transcurrent Plate Boundary
Earthquakes
– Intraplate Earthquakes
• Volcanic Earthquakes
• Induced Earthquakes
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9
Strike-Slip- TRANSFORM P.B.
Normal- DIVERGENT Plate Boundry
Reverse/Thrust- CONVERGENT P.B.
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TECTONIC PLATES
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Seismographs recordearthquake events
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The Economics and Societal Impacts of EQs
Damage in Oakland, CA, 1989
• Building collapse• Fire
• Tsunami
• Ground failure
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TELESEISMIC, REGIONAL AND LOCAL
EARTHQUAKES
• The earthquakes, which are recorded by aseismograph station at a greater distance, arecalled teleseismic earthquakes. These are very
often called teleseisms.• The earthquakes, which occur beyond say 500 km
but within 1000 km of a seismograph station, arecalled regional earthquakes.
• Earthquakes occurring within a distance of fewhundred km, say 500 km, from a seismic stationare called local earthquakes.
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FORESHOCKS, AFTERSHOCKS AND
EARTHQUAKE SWARMS
• A larger shock is likely to be preceded by a few
smaller shocks; these are called foreshocks.
• There are, almost certain, to be many shocks
after a main shock, which are called
aftershocks.
• On the other hand, a long series of small shocks
with no main event is frequently recorded incertain localities; these sequences are called
earthquake swarms.
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EARTHQUAKE MAGNITUDE, INTENSITY
AND ENERGY
• Magnitude is one of the basic and important
parameters of an earthquake. It defines the
size of an earthquake.
• Intensity of an earthquake is a measure of its
effect, i.e. degree of damage; for example
broken windows, collapsed houses etc.
produced by an earthquake at a particularplace.
E th k S i l d th I t i f
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Earthquake Seismology and the Interior of
the Eartth• The 3 major layers in the Earth, from outside in, are the
crust, mantle, and core.
• The crust is very thin, averaging about 30 km thick in the
continents and 5 km thick in the oceans
•The mantle is 2900 km thick, almost halfway to thecentre of the Earth. It is made of dark, dense, ultramafic
rock material (peridotite).
• Core is divided into two parts, outer and the inner core.
• The outer core is 2300 km thick and is made of a mixture
liquid iron (90%) and nickel (10%)
• The inner core is at the centre of the Earth and has a
1200 km radius; it's made of solid iron (90%) and nickel
(10%)
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