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Southern California as an Earthquake Laboratory
| Article
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16198 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
6 / 1989 |
4,029 Words |
| Author
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Egill Hauksson
Egill Houksson is research assistant professor of geological
sciences at the University of Southern California. |
Southern California is an ideal earthquake laboratory. Easy access to earthquake faults makes it possible for earth scientists to map the faults' configuration. Earthquake monitoring instruments have been placed along faults to monitor their movement in detail. The results from experiments carried out in this natural laboratory provide new information about the earthquake history of the region and permit us to map previously unrecognized faults. Scientists are also using the data to develop new methods for earthquake prediction.
To understand why damaging earthquakes occur in southern California, we need to understand the motion of the earth's lithosphere--the rigid, outer layer of the earth--in this region. Southern California straddles the boundary between two pieces of the lithosphere, the North America Plate and the Pacific Plate. The generally northward movement of the Pacific Plate against the North America Plate along the San Andreas Fault is the ultimate cause of all earthquakes in the region.
While the San Andreas Fault is clearly the main dividing boundary line between the plates, a significant part of the motion occurs away from it, as the 1971 San Fernando and 1987 Whittier Narrows earthquakes demonstrated. These earthquakes also illustrate how a whole series of ridges and valleys, the Transverse Ranges, are being simultaneously pushed into the earth's mantle as well as being folded and uplifted.
The coexistence of earthquakes both along as well as away from the San Andreas Fault greatly complicates earthquake prediction. Most scientists have abandoned methods based on physical models as the only approach to earthquake prediction. These methods consisted of monitoring radon or water level changes and identifying characteristic anomalies. The most recent developments in earthquake prediction are based on applying probabilistic methods along with a quantitative description of past earthquake history to predict the future. As our understanding of the earthquake process improves, the probabilistic methods will lead to fewer false alarms and fewer missed earthquakes.
The Los Angeles metropolitan area has a population of about 13 million. My colleagues and I have focused our earthquake hazards research in southern California on mitigating the effects of future damaging earthquakes in this region. This effort consists of identifying active faults, estimating their earthquake potential, and inferring how different geological areas of southern California may respond to strong ground shaking.
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