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Faulting process of the May 17, 1976 Gazli, USSR earthquake

Hartzell, Stephen (1980) Faulting process of the May 17, 1976 Gazli, USSR earthquake. Bulletin of the Seismological Society of America, 70 (5). pp. 1715-1736. ISSN 0037-1106.

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The May 17, 1976 Gazli earthquake (m_b = 6.2, M_s = 7.0) has both seismological and engineering importance. Waveform modeling of long-period IDA Rayleigh waves, and WWSSN long- and short-period body waves indicates a thrust mechanism with strike N40°E, dip 54°SE, and rake of 78°. The moment is estimated to be 1.6 × 10^(26) dyne-cm; the fault area, 150 km^2; the average dislocation, 3.3 meters; and the average stress drop, 200 bars. Strong directivity effects due to a propagating rupture are present in both the long- and short-period teleseismic P waves. The data are not adequately explained by a simple point source, and require a three-dimensional, finite-source model. The relative amplitudes of P and pP at both long and short periods are used to deduce that the rupture started at a depth of 15 km and propagated almost entirely unilaterally upward, with an average rupture velocity of 2.0 to 2.5 km/sec. Simultaneous deconvolution of long- and short-period P waves reveals a complex, azimuthally dependent, source-time function. Finite-source models further suggest that a major part of the faulting was concentrated at depth, below 7 km. The strong-ground motion within 10 km of the fault is characterized by unusually high-amplitude (1300 cm/sec^2), high-frequency (10 Hz) accelerations and low-amplitude (10 cm), low-frequency (0.8 Hz) displacements. Synthetic Wood-Anderson records computed from the accelerograms give a local magnitude, M_L, of 6.35. The duration and character of the strong-ground motion is consistent with a rupture propagating upward in the general direction of the station.

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Additional Information:© 1980, by the Seismological Society of America. Manuscript received March 17, 1980. The author benefited greatly from discussions with Donald Helmberger, Tom Heaton, Gordon Stewart, and John Ebel. Computer programs were used which were written in part or totally by Donald Helmberger, Tom Heaton, Hiroo Kanamori, and Larry Burdick. Gordon Stewart assisted greatly with the surface-wave analysis, as did Tom Heaton with the body-wave analysis. This research was supported by the Earth Sciences Section, National Science Foundation Grant PFR 7808813 and by the Advanced Research Projects Agency of the Department of Defense and was monitored by the Air Force Office of Scientific Research under Contract F49620-77-C-0022.
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NSFPFR 7808813
Advanced Research Projects Agency (ARPA)UNSPECIFIED
Air Force Office of Scientific Research (AFOSR)F49620-77-C-0022
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Caltech Division of Geological and Planetary Sciences3423
Issue or Number:5
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Official Citation:Stephen Hartzell Faulting process of the May 17, 1976 Gazli, USSR earthquake Bulletin of the Seismological Society of America, October 1980, v. 70, p. 1715-1736
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49198
Deposited By: Ruth Sustaita
Deposited On:03 Sep 2014 23:50
Last Modified:03 Oct 2019 07:11

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