Impact of Broadband Seismology on the Understanding of Strong Motions
Abstract
Most analyses of strong motion attenuation assume simple whole-space type geometrical spreading, namely (1/R) or its modified form e^(−kR/R). However, broadband data presently becoming available suggests a more complex behavior with substantial crustal effects. Events such as the Sierra Madre event, M = 5.8, triggered the strong motion channels at all of the TERRAscope stations allowing for 0.01-sec sampling of the wavefield. We find that most of the well-defined crustal bodywave arrivals defined and modeled in the 1 to 0.1-hz bandpass also contain high-frequency energy. By comparing the triggered channels with the continuous channels we see that several of the more distant stations triggered on the depth phase sP_(m)P. These phases as well as the depth phase sS_(m)S are obvious in velocity and quite apparent in accelerations. Our best models for Southern California contain a relatively thick low-velocity layer at the surface, roughly 5 km thick with shear velocities below 3 km/sec. This layer or zone, because it appears to vary considerably, controls the wavefield at nearly all frequencies out to about 60 km and yields attenuation decay faster than (1/R). At large ranges the lower crustal triplications dominate and the attenuation curve flattens. Adding random scatters to these layered models adds additional complexity but does not alter the basic flat-layer predictions.
Additional Information
© 1993 The Seismological Society of America. Manuscript received 18 August 1992. This research was supported by U.S.G.S. contract 14-08-001-G1872 and contribution No. 5143, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125.Attached Files
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Additional details
- Eprint ID
- 48051
- Resolver ID
- CaltechAUTHORS:20140806-091536952
- 14-08-001-G1872
- USGS
- Created
-
2014-08-06Created from EPrint's datestamp field
- Updated
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2023-10-17Created from EPrint's last_modified field
- Caltech groups
- Division of Geological and Planetary Sciences
- Other Numbering System Name
- Caltech Division of Geological and Planetary Sciences
- Other Numbering System Identifier
- 5143