Seismology: Fundementals 1

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Ali [email protected] of Earth Sciences

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Introduction to Seismology

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The What, Where and How of Earthquakes

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Parks and Plates©2005 Robert J. Lillie

Types of Plate Boundaries

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Mid-Atlantic ridge

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Internal heat

engine

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Measuring plate motions

From: McClusky et al., 2003, GJI, 155, 126–138

Velocities of the Arabian Platewith respect to the Eurasian Plate

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BSSA, Vol 70, 70, No. 6, pp. 2291-2293, December 1980Intr

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IN THE TIHAMAT-ASIR REGION

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From: AMBRASEYS andMELVILLE, 1989, BSSA, Vol. 79

Crustal Earthquakes in NW Arabia

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Mw=5.0March 11

2002

From: Rodgers et al., 2006, Tectonophysics, 415 (2006) 57–64Intr

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Lillie, Figure 7.1Intr

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Elastic Rebound (H.F.Reid, 1906)

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LOCATION OF EARTHQUAKE

FocusActual point of rupture within the Earth.EpicenterPoint on Earth’s surface directly above the focus.An asperityis the roughness on the fault surface. It is a region of high shear strength.

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Release of Accumulateenergy

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Lillie, Fig. 7.4Intr

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How to determine Distances ?

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http://www.geol.binghamton.edu/faculty/jones/eqlocate.html

Ali [email protected] of Earth Sciences

KFUPM

Introduction to Seismology

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•Measure log (A) in mm

•Measure S-P in second

•Measure Distance in km

•Estimate Magnitude

Richter’s Local Magnitude

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Earthquake Magnitude

ML - Local (Richter) magnitude

MW - Seismic Moment magnitude

MS - Surface wave magnitude

MB- Body wave magnitude

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Magnitude Saturation

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What Causes Saturation?The rupture process.

Small earthquakes rupture small areas.Large earthquakes rupture large areas.

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Are mb and Ms still useful?

YES!

Many (most) earthquakes are small enoughthat saturation does not occurEmpirical relations between energy releaseand mb and Ms exist The ratio of mb to Ms can indicate whethera given seismogram is from an earthquakeor a nuclear explosion (verificationseismology)

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What is the better estimate of M?

The seismic moment – Mo

Invented in the 1960s to circumvent magnitude limitationsHas physical units of energy (Nm, cal, J)Is the product of three factors thatindicate the size of the earthquake:Mo = (shear modulus) x (rupture area) x (slip offset)

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Moment Magnitude

Moment-Magnitude ScaleSeismic Moment = Strength of Rock x Fault Area x Total amount of Slip along Rupture

M0 = µ A D

Moment Magnitude Mw = 2/3 x [log10M0(dyne-cm) –16]

Measurement Analysis requires Time

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STRENGTH OF EARTHQUAKEMagnitude

Relates to the amount of energy released by the earthquake.

IntensityRelates to the effects (damage) observed at the surface.


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Logarithmic (not linear) scale.

Increase 1 order of magnitude means:The seismic waves are 10 times as large.

Parks and Plates©2005 Robert J. Lillie

Question:Compare M=6 EQ to M=7 EQ?

Logarithmic (not linear) scale.Increase 1 order of magnitude

means:The seismic waves are 10 times as

large.30 times as much seismic energy

was released by the earthquake.

Respond:Seismic waves 10 times as big. 30 times more energy.


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Next Question:An M=8 EQ is equivalent how many M=6 EQ going off at the same time?

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Start with a magnitude 6 earthquake.

A magnitude 7 earthquake releases 30 times the amount of seismic energy as a magnitude 6 earthquake.

A magnitude 8 earthquake releases 30 times the amount of energy as a magnitude 7 earthquake.

30 x 30 = 900

It would take about 900 magnitude 6 earthquakes going off at the same time to pack the same wallop as a magnitude 8 earthquake!


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Seismic Energy900 times as big.

Seismic waves100 times as big.

This figure was produced in cooperation with the US Geological Survey, and the University of Memphis private foundations

Magnitude -Energy Correlation

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http://www.geol.binghamton.edu/faculty/jones/eqlocate.html

web.ics.purdue.edu/~braile/edumod/eqlocate/tutorial.pdf

For Tutorial and Download

Assignment: Estimate Location of One Earthquake Due to Next Wednesday

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I played zooming and keys of arrow and arranged the location of above map. Good luck for rest of exercise.In

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Seismogram

Seismogram in one window

Step 3

Technology

Seismology: Fundementals 1