Department of Earth SciencesKFUPM

Introduction to Seismology

Earthquake Occurrence 2

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Ali Onceloncel@kfupm.edu.

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Previous Lecture

•Magnitude Occurrence •The Gutenberg-Richter Law •Difficulties in practice due to Lack of seismicity Data •Earthquake occurrence: Poisson Process and Probability •Earthquake Catalogues:  Desirable Properties

•Homogeneity •Completeness •Duration •Source Material

•Online Data

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Recall: MAGNITUDE OCCURRENCEThe Gutenberg and Richter (1944) cumulative frequency-magnitude law. The number of earthquakes in a region decreases exponentially with magnitude or:

log10 Nc(m>M) = a - bm

4

3

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1

4 5 6 7 8

log10 Nc

Magnitude m

This is a whole process distribution, that means we use all the earthquakes in the data set or catalogue (not aftershocks)

The magnitude of the quake expected to be largest in a year is:

m1 = a/b [i.e. Nc = 1]

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b=βx log e log e=0.4343

Seismicity of Stable Cratonic Cores (SCC)

Fenton, Adams, Halchuk, 2006

Earthquake catalogue completeness

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Magnitude-Frequency (per 50.7 x 106 km2) plot for the worldwide SCC seismicity data set

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Stable Craton

Once a decade a M6.5

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Once a decade a M6.5Once a decade a M6.5Once a decade a M6.5

log10 Nc(m) = 3.68 – 0.947 m

Worldwide rates of stable cratonic core seismicity

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2002Plattsburgh

NY

stablewest east

stablewesteast

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There are several online catalogs of earthquakes. In this exercise, you will need to access one of these. For earthquakes any place in the world, a good place to start is: http://wwwneic.cr.usgs.gov/neis/epic/epic.html A catalog of focal mechanisms (CMT Solutions) is at the Harvard seismology site: http://www.seismology.harvard.edu/ You will need to use an Excel spreadsheet to solve some of these problems.

Homework on Earthquake Search due May, 3

1. How many earthquakes occurred for the Saudi Arabia and vicinity since 1973

a) with magnitude 6.0 or larger.

b) with magnitude 5.0 or larger.

c) with magnitude 4.0 or larger.2. Present your data, giving the average number of earthquakes per year and establish Log N= a – b M.3. By consulting the Harvard catalog of moment tensors, for the largest of the events in this region, infer the main tectonic process in this region. Explain the reasoning behind your response.In

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Quiz 4

m

(3)

(1)

(2)

(1) Explain the physical meaning of above graph?(2) What you think might be a reason for observing

roll-off at lower (3) and higher (1) magnitudes.

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Log N