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Fault

Advances In Fault Studies

Our understanding of how faults move has improved greatly with modern technology and mapping. Laser survey equipment and satellite photogrammetry (measurements made with highly accurate photographs) have helped measure minute movements on faults that may indicate significant patterns and imminent earthquakes. Seismic gaps have been identified along plate boundaries. Through detailed mapping of tiny earthquakes, zones where strains in the earth have been relieved are identified; similarly, seismic gap areas without those strain-relieving motions are studied as the most likely zones of origin of coming earthquakes.


Resources

Books

Erickson, Jon. "Quakes, Eruptions, and Other Geologic Cataclysms." The Changing Earth Series. New York: Facts on File, 1994.

Halacy, D. S., Jr. Earthquakes: A Natural History. Indianapolis, IN: The Bobbs-Merrill Company, Inc., 1974.

Keller, Edward. Environmental Geology. Upper Saddle River, NJ: Prentice-Hall, Inc., 2000.

Japanese Geotechnical Society. Soils and Foundations: Special Issue on Geotechnical Aspects of the January 17, 1995, Hyogoken-Nambu Earthquake. Tokyo: Japanese Geotechnical Society, January 1996.

Verney, Peter. The Earthquake Handbook. New York: Paddington Press Ltd., 1970.

Walker, Bryce and the Editors of Time-Life Books. Planet Earth: Earthquake. Alexandria, VA: Time-Life Books, 1982.


Gillian S. Holmes

KEY TERMS


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Continental drift

—A theory that explained the relative positions and shapes of the continents, and other geologic phenomena, by lateral movement of the continents. This was the precursor to plate tectonic theory.

Core

—The molten center of the earth.

Crust

—The outermost layer of the earth, situated over the mantle and divided into continental and oceanic crust.

Dip

—The angle of inclination (measured from the horizontal) of faults and fractures in rock.

Footwall

—The block of rock situated beneath the fault plane.

Graben

—A block of land that has dropped down between the two sides of a fault to form a deep valley.

Hanging wall

—The block of rock that overlies the fault plane.

Horst

—A block of land that has been pushed up between the two sides of a fault to form a raised plain or plateau.

Mantle

—The middle layer of the earth that wraps around the core and is covered by the crust. The mantle consists of semi-solid, partially melted rock.

Normal fault

—A fault in which tension is the primary force and the footwall moves up relative to the hanging wall.

Plate tectonics

—The theory, now widely accepted, that the crust of the earth consists of about twelve massive plates that are in motion due to heat and motion within the earth.

Reverse fault

—A fault resulting from compressional forces and the hanging wall moves up relative the footwall.

Seismic gap

—A length of a fault, known to be historically active, that has not experienced an earthquake recently and may be storing strains that will be released as earthquake energy.

Strike-slip fault

—A fault at which two plates or rock masses meet and move lateral or horizontally along the fault line and parallel to the compression.

Subduction

—In plate tectonics, the movement of one plate down into the mantle where the rock melts and becomes magma source material for new rock.

Thrust fault

—A low-angle reverse fault in which the dip of the fault plane is 45° or less and displacement is primarily horizontal.

Additional topics

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