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Lg and Rg Waves on the California Regional Networks From the December 23, 1985 Nahanni Earthquake

Wald, Lisa A. and Heaton, Thomas H. (1991) Lg and Rg Waves on the California Regional Networks From the December 23, 1985 Nahanni Earthquake. Journal of Geophysical Research B, 96 (B7). pp. 12099-12125. ISSN 0148-0227. doi:10.1029/91JB00920.

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We investigate Lg and Rg propagation in California using the central and southern California regional networks. Approximately 550 stations constitute these two short-period networks providing a dense coverage of almost the entire state. The waveforms recorded from the December 23, 1985, Nahanni, Canada, earthquake are used to construct three profiles along the propagation path (almost N-S) and three perpendicular to the propagation path (almost E-W) to look at the nature of propagation of these two types of surface waves. Groups of records from stations in various geological and tectonic provinces in California are also examined in order to establish regional characteristics of the surface waves. We find that the propagation characteristics of Lg differ from those of Rg across California; Lg waves are apparently more sensitive to crustal heterogeneities. The most striking observations are the similarity of coda for both the Lg and the Rg waves within geologic provinces and the marked difference in coda between regions. These differences are seen in the amplitudes, coda duration, shape of the energy envelope, frequency content, and sharpness of the phase initiation. In general, a decrease in the Moho depth near the Pacific Coast is correlated with a decrease in the surface wave amplitude, especially at higher frequencies (0.15–0.2 Hz). Most interesting is the association of the San Andreas fault with abrupt changes in the wave train amplitudes. The surface waves are amplified in the vicinity of the fault zone and then decrease in amplitude after the zone is crossed. In the Coast Ranges, amplitudes are low and waveform coherence is poor. The Rg phase dominates the record in the Sierra Nevada, and both surface waves are amplified by the thick sedimentary sequence of the Great Valley.

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Heaton, Thomas H.0000-0003-3363-2197
Additional Information:© 1991 American Geophysical Union. Received 25 May 1990; revised March 11, 1991; accepted 22 March 1991. We would like to acknowledge Bob Somera at the USGS in Menlo Park for digitizing the FM analog tape and Jerry Eaton, also in Menlo Park, for providing gain information for the Central California Netwoik stations. We would also like to thank Toshiro Tanimoto and Dave Harlaider of Caltech for providing helpful comments and suggestions. David Hill, Rufus Catchings, David Wald, and two anonymous reviewers provided reviews which greatly improved this document.
Group:UNSPECIFIED, Division of Geological and Planetary Sciences
Issue or Number:B7
Record Number:CaltechAUTHORS:20121121-104344746
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Official Citation: Wald, L. A. and T. H. Heaton (1991), Lg and Rg waves on the California Regional Networks from the December 23, 1985 Nahanni Earthquake, J. Geophys. Res., 96(B7), 12,099–12,125, doi:10.1029/91JB00920.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35604
Deposited By: Ruth Sustaita
Deposited On:21 Nov 2012 19:06
Last Modified:09 Nov 2021 23:16

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