Broadband study of the 1989 Loma Prieta earthquake
The authors determined the source characteristics of the Oct. 18, 1989 Loma Prieta, California, earthquake using teleseismic data. The solution from body waves gives a mechanism with dip=70{degree}, rake=138{degree}, and strike=128{degree}, and a seismic moment of 3{times}10{sup 26} dyne-cm (M{sub w}=6.9). The body wave form suggests a depth of about 15 km. The effective duration of the source is 6 sec, which suggests a fault length of 30 km and 15 km for bilateral and unilateral faulting, respectively. Considering the extent of the aftershock area, they used 35 km as an estimate of the total rupture length. The strike-slip and the thrust components of the coseismic slip are 177 and 159 cm, respectively. If the Loma Prieta earthquake is a characteristic earthquake with a recurrence interval of about 100 years, the 159 cm displacement implies a long term uplift rate of about 1 cm/year, which appears too large for this region. Three hypotheses for reconciling this apparent conflict are: (1) the geometry of plate motion along the Santa Cruz Mountain segment changes over a time scale of several thousand years to that the coseismic displacement has not accumulated enough to produce high topographic relief; (2) the coseismic slip direction varies from event to event; (3) the slip plane of the 1989 Loma Prieta earthquake is different from the major boundary between the Pacific and the North American plates. The surface slip of about 1 m for the 1906 San Francisco earthquake is one of the key data in long-term forecasting. No surface slip was observed for the 1989 Loma Prieta earthquake, even if the horizontal slip at depth is as large as 1.8 m. This points to a risk of relying too heavily on surface observations for long-term seismic risk analysis.
- OSTI ID:
- 6148215
- Journal Information:
- Geophysical Research Letters (American Geophysical Union); (USA), Vol. 17:8; ISSN 0094-8276
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CALIFORNIA
EARTHQUAKES
SEISMIC SOURCES
AFTERSHOCKS
DEPTH
EARTHQUAKE MAGNITUDE
EPICENTERS
FORECASTING
GEOLOGIC FAULTS
GEOLOGIC MODELS
LENGTH
PLATE TECTONICS
ROCK MECHANICS
RUPTURES
SEISMIC WAVES
SLIP
TIME DEPENDENCE
WAVE FORMS
DIMENSIONS
FAILURES
FEDERAL REGION IX
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
MECHANICS
NORTH AMERICA
SEISMIC EVENTS
TECTONICS
USA
580000* - Geosciences