Earthquake Seismology - week 1.pptx

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Earthquake SeismologyGEO 335

BU: Bahria University

Department of Earth and Environmental Sciences



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.



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



CLASSIFICATION OF EARTHQUAKES



FREQUENCY-MAGNITUDE RELATION



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



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



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



9

Strike-Slip- TRANSFORM P.B.

Normal- DIVERGENT Plate Boundry

Reverse/Thrust- CONVERGENT P.B.



10

TECTONIC PLATES



Seismographs recordearthquake events



The Economics and Societal Impacts of EQs

Damage in Oakland, CA, 1989

• Building collapse• Fire

• Tsunami

• Ground failure



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.



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.



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



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%)

Earthquake Seismology - week 1.pptx

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