Oroville earthquakes: a study of source characteristics and site effects

Journal Article · Thu Jun 10 04:00:00 EDT 1982 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB087iB06p04585· OSTI ID:5101333

Cohn, S N; Hong, T; Helmberger, D V

Half-space modeling, in the time domain, of broadband seismic records from the Oroville aftershock sequence demonstrates that these events have simple sources. Systematic scaling between the far-field source duration and seismic moment for the aftershocks studied here and other California earthquakes confirms Brune's (1970) source model and shows that the stress drops for California earthquakes range between 10 and 100 bars. These events also show no trend in stress drop as a function of size for 3.0< or =M/sub L/< or =6.4. Analysis of the static deformation associated with the main shock shows that the slip occurred on a fault 81 km/sup 2/ in area corresponding to the zone defined by the first 3 days of aftershocks. Teleseismic studies indicate that the seismic source area was 50 km/sup 2/, corresponding to a zone completely free of aftershocks in the middle of the aftershock zone. Both results imply a stress drop of 29--39 bars and seismic moment between 5.7 and 8.7 x 10/sup 24/ dyn cm. The evidence suggests that faulting occurred seismically on the central portion of the fault and propagated out slowly, enlarging the fault plane. Complicated waveforms recorded for the same events at nearby sites on alluvium indicate the critical role that propagation through complex structure plays in determining the character of the observed seismic signal at close-in stations. Modeling of these records show that dipping structure may account for the observed waveform complexities.

• Research Organization: Seismological Laboratory, California Institute of Technology, Pasadena, California 91125
• OSTI ID: 5101333
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 87:B6; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580201* -- Geophysics-- Seismology &amp; Tectonics-- (1980-1989)
AFTERSHOCKS
DEFORMATION
EARTHQUAKE MAGNITUDE
EARTHQUAKES
FORESHOCKS
SEISMIC EVENTS
SLIP
STRESS ANALYSIS
WAVE FORMS
WAVE PROPAGATION