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Source spectra of great earthquakes: Teleseismic constraints on rupture process and strong motion

Houston, Heidi and Kanamori, Hiroo (1986) Source spectra of great earthquakes: Teleseismic constraints on rupture process and strong motion. Bulletin of the Seismological Society of America, 76 (1). pp. 19-42. ISSN 0037-1106.

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Short-period body waves recorded at teleseismic distances from great earthquakes provide information about source rupture processes and strong motions. First, we examine mostly WWSSN records of 19 earthquakes of moment magnitude M_w of 6.5 to 9.5. Four parameters are measured from the short-period P-wave train: the maximum amplitude; the period at maximum amplitude; the time between the first arrival and when the maximum amplitude is attained; and coda length. An extension, m_b, of the teleseismic magnitude, m_b, is defined using the maximum amplitude of the entire short-period P-wave rather than the amplitude achieved in the first few P-wave cycles. A least-squares fit to the data yields the following relationship between m_b and M_w: m_b = 0.53 M_w + 2.70 for M_w 6.5 to 9.5. The time from the first arrival until the maximum amplitude is achieved and the coda length are roughly proportional to M_w, but are further interpreted by a simple asperity model of the rupture process. These data support that short-period waves are, on average, generated preferentially in the same regions of the fault plane as long-period waves (with periods of 10 to 50 sec). We analyze the spectra of short- and intermediate-period teleseismic GDSN records for seven earthquakes with M_w's of 6.4 to 7.8 and hand-digitized short-period WWSSN records of the 1971 San Fernando earthquake. Significant differences exist between the spectra of different events, due partly to variations in tectonic setting or seismic coupling. Using the digital data, we also investigate the relationship between time-domain amplitude and spectral amplitude for short-period P waves. From our empirical relation between spectral amplitude and time-domain amplitude, we estimate the spectral amplitudes implied by the m_b data. We compare our results to the ω^(−2) and Gusev spectral models. Neither model can completely represent the data. Nevertheless, we consider the ω^(−2) model a useful reference model for comparing different events. The average source spectrum of six large events with M_w 7.4 to 7.8 does not have the spectral structure suggested by Gusev. An application to strong motion modeling is presented in which a 1971 San Fernando teleseismic short-period record is summed up to simulate teleseismic records produced by five great earthquakes. The summation procedure matches the moment of the event to be simulated, and includes rupture propagation, fault plane roughness, and randomness. The m_b data provide an important constraint on the summation procedures. Thus constrained, this summation procedure can be more confidently used with near-field strong motion records as Green's functions to predict strong motions from great earthquakes.

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Additional Information:© 1986, by the Seismological Society of America. Manuscript received 29 May 1985. We thank Dave Boore for encouragement and helpful discussions and a review of an early version of this paper. We also had helpful discussions with Doug Coats. Steve Hartzell made the Pasadena Benioff 1-90 records and spectra readily available. Inez Cifuentes sent us copies of short-period records of the 1960 Chilean earthquake. Jia-Jun Zhang helped us to read SRO tapes written before 1980. C. Langston provided digitized teleseismic records of the 1971 San Fernando earthquake. M. Kikuchi provided the results of his deconvolutions of moment release. Allen Olson, Art Frankel, and John Vidale reviewed the manuscript. This research was supported by Exxon Production Research, Agreement PR-7373 and U.S. Geological Survey Grant 14-08-0001-G-979.
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Exxon Production ResearchPR-7373
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Caltech Division of Geological and Planetary Sciences4228
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Official Citation:Heidi Houston and Hiroo Kanamori Source spectra of great earthquakes: Teleseismic constraints on rupture process and strong motion Bulletin of the Seismological Society of America, February 1986, v. 76, p. 19-42
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48517
Deposited By: Ruth Sustaita
Deposited On:13 Aug 2014 20:51
Last Modified:13 Aug 2014 20:51

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