| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
DEPARTMENT OF GEOSCIENCES UNIVERSITY OF ARIZONA, TUCSON, ARIZONA 85721
RICHTER SEISMOLOGICAL LABORATORY AND INSTITUTE OF TECTONICS UNIVERSITY OF CALIFORNIA, SANTA CRUZ, SANTA CRUZ, CALIFORNIA 95064
Abstract
Analysis of regional and teleseismic broadband body waves and long-period surface waves from the 1989 Loma Prieta earthquake demonstrates that a fairly simple average fault model explains most characteristics of seismic wave radiation over a broad period range (1 to 300 sec), but there are some systematic period-dependent characteristics that are not yet understood. Determinations of the preferred point source focal mechanism are consistent for different seismic waves, as long as optimal source-time functions and depths are chosen for each wavetype. The major double couple orientation compatible with the entire period range has a strike = 128 ± 3°, dip = 67 ± 5°, and rake = 133 ± 8°. While this source mechanism consistency is encouraging and indicates that the average source process is quite simple, there are some systematic discrepancies in the source parameter estimates from different period waves. The source duration estimated from the principal body-wave ground motions is 8 ± 2 sec, compatible with the duration of near-field strong-motion vibrations, but the surface waves indicate total durations of 18 to 30 sec, depending on the earth model selected for computing propagation corrections. The model dependence of the surface-wave results suggests that it may be possible to reconcile the duration estimates with improved earth models, but the discrepancy is quite large. There is some complexity in the source-time function, comprised of three subevents at different depths, but this complexity is only manifested in short-period signals and does not explain the duration discrepancy. Changes of fault geometry or slip direction during rupture, as suggested by recent finite-fault inversions, are unlikely to cause a bias in source duration estimates. The centroid depth determined from our body-wave analysis is 10 to 12 km, consistent with the finite-fault models, which indicate rupture extending from 5 to 18 km. Surface-wave centroid depth estimates (15 to 30 km) vary substantially for different choices of global Q model and lithospheric structure in the source region, but they do tend to be deeper than the body-wave results. It is again not clear whether this depth discrepancy is due to the source process or inadequate earth models. The body-wave and surface-wave seismic moment estimates are also not fully consistent; the moment from our body-wave inversions is 2.4 ± 0.3 x 1019 N-m, while our surface-wave analysis gives 3.2 ± 0.5 x 1019 N-m. It is not known whether reasonable changes of the earth models can bring the moment estimates into full agreement. The systematic discrepancies in source duration, centroid depth, and seismic moment, despite the consistency in source orientation, raise the possibility of a deep, relatively slow co-seismic slip component, but trade-offs with modeling assumptions preclude us from confirming this hypothesis at present.
This article has been cited by other articles:
|
|
 |
|
  F. Pettenati and L. Sirovich Validation of the Intensity-Based Source Inversions of Three Destructive California Earthquakes Bulletin of the Seismological Society of America, October 1, 2007; 97(5): 1587 - 1606. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Parsons Seismic-reflection evidence that the Hayward fault extends into the lower crust of the San Francisco Bay area, California Bulletin of the Seismological Society of America, October 1, 1998; 88(5): 1212 - 1223. [Abstract] [PDF]
|
|
|
|
|
|
M. Guatteri and M. Cocco On the variation of slip direction during earthquake rupture: Supporting and conflicting evidence from the 1989 Loma Prieta earthquake Bulletin of the Seismological Society of America, December 1, 1996; 86(6): 1935 - 1951. [Abstract] [PDF]
|
|
|
|
|
|
P. Bodin and J. N. Brune On the scaling of slip with rupture length for shallow strike-slip earthquakes: Quasi-static models and dynamic rupture propagation Bulletin of the Seismological Society of America, October 1, 1996; 86(5): 1292 - 1299. [Abstract] [PDF]
|
|
|
|
|
|
S. P. Jarpe and P. W. Kasameyer Validation of a procedure for calculating broadband strong-motion time histories with empirical Green's functions Bulletin of the Seismological Society of America, August 1, 1996; 86(4): 1116 - 1129. [Abstract] [PDF]
|
|
|
|
|
|
Kamal and L. Mansinha The triggering of aftershocks by the free oscillations of the earth Bulletin of the Seismological Society of America, April 1, 1996; 86(2): 299 - 305. [Abstract] [PDF]
|
|
|
|
|
|
S. Horton A fault model with variable slip duration for the 1989 Loma Prieta, California, earthquake determined from strong-ground-motion data Bulletin of the Seismological Society of America, February 1, 1996; 86(1A): 122 - 132. [Abstract] [PDF]
|
|
|
|
|
|
M. KIKUCHI and M. ISHIDA Source retrieval for deep local earthquakes with broadband records Bulletin of the Seismological Society of America, December 1, 1993; 83(6): 1855 - 1870. [Abstract] [PDF]
|
|
|
|
|
|
J. H. STEIDL, R. J. ARCHULETA, and S. H. HARTZELL Rupture history of the 1989 Loma Prieta, California, earthquake Bulletin of the Seismological Society of America, October 1, 1991; 81(5): 1573 - 1602. [Abstract] [PDF]
|
|
|
|
|
|
T. C. HANKS and H. KRAWINKLER The 1989 Loma Prieta earthquake and its effects: Introduction to the special issue Bulletin of the Seismological Society of America, October 1, 1991; 81(5): 1415 - 1423. [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
