Fault Mechanism

Department of Earth SciencesKFUPM

Introduction to Seismology

Fault Mechanism

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Ali [email protected].

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http://www.learninggeoscience.net/free/00071/index.html

Previous Lecture

•Faulting Stresses •Radiation Patterns •First Motions and Azimuth •Compiling Data: Example from 2004 Sumatra Earthquake •What types of Earthquake Software for solutions of Focal Mechanisms? •What are the sources of Seismic Data? •Downloading Seismological Data: Example from IRISH Channel •Problem in Defining Fault Strike •What is the Focal Sphere and how it is projected? •Fault-Plane Solution derived Cross sections of Dip-Slip Faults

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What type of faulting?

A normal faulting mechanism.

Which plane do you think is the fault plane ? A reverse faulting mechanism. Which plane do you think is the fault plane ?

Strike-slip faulting. Which strike?

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Select your area by cursorThen, click on button “submit”Then, click on “Show Data Set”From Geophysics, select “CMT Focal Mechanism”Then, Click on “Submit Data Set”

Select your data of Focal Mechanism via the Interactive

Database

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Focal Mechanism MapIn

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Now, you can download the map under different options.

JPG is easy to download but *.PS is good if making up

for picture is needed.

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Now, just click on the option “JPG” and see the map of focal mechanisms.

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What is CMT?In

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Homework due March, 28

Through the Interactive Data Module which is explained so farhttp://atlas.geo.cornell.edu/ima.html Prepare the focal mechanism map of the area for your term project as file *.jpg, send it to me via e-mail due next lecture. Also, try to provide a discussion about one paragraph on types of the faulting deformation through the region.

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Pla

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Parks and Plates©2005 Robert J. Lillie

a) Shallow earthquakes at divergent and transform

boundaries are present;

b) Shallow, intermediate, and deep earthquakes occur where plates converge.In

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Large Earthquakes (5 yr)

The boundaries of plates are evident from the pattern of earthquake activity.

Parks and Plates©2005 Robert J. Lillie

Earth Dynamic Systems

1995, Hamblin and Christiansen

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Active vs. Passive Continental Margins

Earthquakes lie mostly along the boundaries of moving plates.

Parks and Plates©2005 Robert J. Lillie

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Active vs. Passive Continental Margins

Parks and Plates©2005 Robert J. Lillie

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The nearest plate boundary to the U. S. East Coast is the Mid-Atlantic Ridge.

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Active vs. Passive Continental Margins

Parks and Plates©2005 Robert J. Lillie

The U. S. West Coast lies along a convergent plate boundary, and is thus an ACTIVE CONTINENTAL MARGIN.

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Active vs. Passive Continental Margins

The U. S. East Coast is far from a plate boundary, and is thus a PASSIVE CONTINENTAL MARGIN.

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Parks and Plates©2005 Robert J. Lillie

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Axis of the oceanic ridge is offset by transform (strike-slip) faults which produce lateral displacement. Ridges and rifts indicate movement.

Earthquakes at Mid-Ocean Ridge System

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Transcurrent Fault Model

1. Strike-lip earthquakes occur between the ridges and on the fracture zones extending beyond the ridge

2. No earthquakes occur on the ridge axes

3. For the specific example, earthquake on the transcurrent fault have right-lateralIn

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Transform Fault Model

1. Strike-slip earthquakes occur only between the ridge segments; not on the fracture zones beyond the ridge segments;

2. Normal fault earthquakes occur on the ridges axes;

3. For the specific example, the strike-slip earthquakes on the transform fault have left-lateral motions.

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Fig 7.22 of LillieIntr

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