Multi-mode analysis of Rayleigh-type Lg. Part 2. Application to southern California and the northwestern Sierra Nevada
Abstract
The UC diagram technique described in the companion paper (Part 1), is applied to nine sets of Lg phases recorded through the CEDAR system in southern California, and two sets of Lg phases recorded along the northwestern margin of the Sierra Nevada. A clear image of the signal is obtained in time-frequency-wavenumber space, and we discuss in particular observations at 2.5-sec period, for events 200 to 300 km outside the profiles. From the gross features of UC diagrams we conclude that a representation of Lg as a single coherent multi-mode wave train is oversimplified in the case of southern California but is more appropriate for the Sierra block. In southern California, peaks observed at group velocities smaller than 3.2 km/sec are not predicted by realistic crustal models of the area, and are probably due to lateral heterogeneities effects such as mode conversion and multipathing. On the other hand, for group velocities between 3.2 and 3.6 km/sec, peaks observed in either area can generally be interpreted in terms of overtones excited at the source and propagating through spatially averaged structures, although care must be taken to monitor the stability of the algorithm on actual short-period records.
Additional Information
© 1981 Seismological Society of America. Manuscript received July 16, 1980. We thank the staff of the Seismological Laboratory and C. Johnson for considerable help m manipulating CEDAR data. D. G Harkrider kindly provided computer programs to compute synthetics. G. Eaton and G. Poupinet were very helpful in selecting and digitizing CALNET data. This research was supported by the U.S. Geological Survey under Contracts 14-08-0001-18331 and 14-08-0001-19270 and the Advanced Research Projects Agency of the Department of Defense, and was monitored by the Air Force Office of Scientific Research under Contracts F49620-77-C-0022 and F49620-81-C-0008. M. Cara was supported by a CNRS-NSF fellowship (French-U S convention).Attached Files
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Additional details
- Eprint ID
- 49171
- Resolver ID
- CaltechAUTHORS:20140903-081929697
- 14-08-0001-18331
- USGS
- 14-08-0001-19270
- USGS
- Advanced Research Projects Agency (ARPA)
- F49620-77-C-0022
- Air Force Office of Scientific Research (AFOSR)
- F49620-81-C-0008
- Air Force Office of Scientific Research (AFOSR)
- CNRS-NSF Fellowship
- Created
-
2014-09-03Created from EPrint's datestamp field
- Updated
-
2019-10-03Created from EPrint's last_modified field
- Other Numbering System Name
- Caltech Division of Geological and Planetary Sciences
- Other Numbering System Identifier
- 3476