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Rupture model of the 1989 Loma Prieta earthquake from the inversion of strong-motion and broadband teleseismic data

Wald, David J. and Helmberger, Donald V. and Heaton, Thomas H. (1991) Rupture model of the 1989 Loma Prieta earthquake from the inversion of strong-motion and broadband teleseismic data. Bulletin of the Seismological Society of America, 81 (5). pp. 1540-1572. ISSN 0037-1106.

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We have used 24 broadband teleseismic and 48 components of local strong motion velocity records of the 1989 Loma Prieta earthquake in a formal inversion to determine the temporal and spatial distribution of slip. Separate inversions of the teleseismic data (periods 3-30 sec) or strong motion data (periods 1-5 sec) result in similar models. The data require bilateral rupture with relatively little slip in the region directly updip from the hypocenter. Slip is concentrated in two patches; one centered 6 km northwest of the hypocenter at a depth of 12 km and with a maximum slip of 350 cm, and the other centered about 5 km southeast of the hypocenter at a depth of 16 km and with a maximum slip of 460 cm. The bilateral nature of the rupture results in large amplitude ground motions at sites located along the fault strike, both to the northwest and the southeast. However, the northwestern patch has a larger moment and overall stress drop and is, consequently, the source of the largest ground motion velocities, consistent with the observed recordings. This bilateral rupture also produces relatively modest ground motion amplitudes directly updip from the hypocenter, which is in agreement with the velocity ground motions observed at Corralitos. There is clear evidence of a foreshock (magnitude between 3.5 and 5.0) or a slow rupture nucleation about 2 seconds before the main part of the rupture; the origin time implied by strong motion trigger times is systematically 2 seconds later than the time predicted from the high-gain regional network data. The seismic moment obtained from either of the separate data sets or both sets combined is about 3.0 x 10^(26) dyne-cm and the potency is 0.95 km^3.

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Heaton, Thomas H.0000-0003-3363-2197
Additional Information:© 1991 by the Seismological Society of America. Manuscript received 18 October 1990. Reviews of Hiroo Kanamori, Paul Somerville, and Lisa Wald improved the original manuscript. We thank Steve Hartzell for useful discussions and advice on the use of his inversion software. This work was supported by the U.S. Geological Survey under contracts 14-08-0001-21912 and 14-08-0001-G1832. Contribution No. 4935, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California.
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USGS14-08- 0001-G1832
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Caltech Division of Geological and Planetary Sciences4935
Issue or Number:5
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ID Code:35981
Deposited On:20 Dec 2012 22:32
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