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Estimation of strong ground motions from hypothetical earthquakes on the Cascadia subduction zone, Pacific Northwest

Heaton, Thomas H. and Hartzell, Stephen H. (1986) Estimation of strong ground motions from hypothetical earthquakes on the Cascadia subduction zone, Pacific Northwest. U.S. Geological Survey open-file report. No.86-328. U.S. Dept. of the Interior, Geological Survey , Denver, CO.

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Strong ground motions are estimated for the Pacific Northwest assuming that large shallow subduction earthquakes, similar to those experienced in southern Chile, southwestern Japan, and Colombia, may also occur on the Cascadia subduction zone. Fifty-six strong motion recordings from twenty-five subduction earthquakes of M_S ≥ 7.0 are used to estimate the response spectra that may result from earthquakes M_w < 8 1/4 Large variations in observed ground motion levels are noted for a given site distance and earthquake magnitude. When compared with motions that have been observed in the western United States, large subduction zone earthquakes produce relatively large ground motions at surprisingly large distances. An earthquake similar to the 22 May 1960 Chilean earthquake (M_w 9.5) is the largest event that is considered to be plausible for the Cascadia subduction zone. This event has a moment which is two orders of magnitude larger than the largest earthquake for which we have strong motion records. The empirical Green's function technique is used to synthesize strong ground motions for such giant earthquakes. Observed teleseismic P-waveforms from giant earthquakes are also modeled using the empirical Green's function technique in order to constrain model parameters. The teleseismic modeling in the period range of 1.0 to 50 sec strongly suggests that fewer Green's functions should be randomly summed than is required to match the long-period moments of giant earthquakes. It appears that a large portion of the moment associated with giant earthquakes occurs at very long periods that are outside the frequency band of interest for strong ground motions. Nevertheless, the occurrence of a giant earthquake in the Pacific Northwest may produce quite strong shaking over a very large region.

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Heaton, Thomas H.0000-0003-3363-2197
Additional Information:© 1986 U. S. Geological Survey. We thank Hiroo Kanamori and C. B. Grouse for helpful discussions and we thank C. B. Grouse for his help in collection of the digitized strong motion data used in this report. We thank Bob Page, Bill Joyner, and Heidi Houston for their comments on this manuscript. This work was partially supported by the United States Nuclear Regulatory Commission.
Group:Division of Geological and Planetary Sciences
Funding AgencyGrant Number
Nuclear Regulatory Commission (NRC)UNSPECIFIED
Series Name:U.S. Geological Survey open-file report
Issue or Number:86-328
Record Number:CaltechAUTHORS:20121127-084238485
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35655
Deposited By: Tony Diaz
Deposited On:11 Feb 2013 23:16
Last Modified:15 Nov 2022 21:35

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