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A slow seismic event recorded in Pasadena

Kanamori, Hiroo (1989) A slow seismic event recorded in Pasadena. Geophysical Research Letters, 16 (12). pp. 1411-1414. ISSN 0094-8276. doi:10.1029/GL016i012p01411.

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A prominent long-period wave with a duration of 2000 sec or longer was recorded with a very-broadband system in Pasadena on June 18, 1988. This wave was not observed elsewhere, and is considered of local origin. The acceleration amplitude is 2.5×10^(−5) cm/sec² in the northwest direction, with the vertical component less than 10% of the horizontal. The horizontal acceleration can be interpreted as due to a tilt of the ground of 2.5×10^(−8) radians to the northwest. A slowly propagating pressure wave with an amplitude of about 15 mbars could be the cause of the tilt; however, there were no reports suggesting such pressure changes. A more likely cause is a slow tectonic event near Pasadena. The required magnitude of such a slow event is M_w=0, 2, and 4, for a distance of 0.1, 1, and 10 km respectively. This event could be part of a tectonic episode associated with the larger earthquakes which occurred in southern California around this time, especially the December 3, 1988, Pasadena earthquake (M_L=4.9) which occurred six months later within 4 km of the Pasadena station.

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Kanamori, Hiroo0000-0001-8219-9428
Additional Information:Copyright 1989 by the American Geophysical Union. (Received August 1, 1989; revised October 20, 1989; accepted October 23, 1989.) Paper number 89GL03370. I thank Bruce Bolt and Duncan Agnew for sending me long-period records from Berkeley and Piñon Flats Observatories, respectively. Duncan Agnew also suggested to me the possibility that a slowly moving pressure wave was a possible cause of title. Ehrling Wang, at California State University, Northridge, kindly sent me the barograph data for June, 1988, which turned out to be the only atmospheric pressure data available in the Los Angeles basin. Helpful suggestions given to me during coffee break discussions at the Seismological Laboratory provided the strong encouragement that enabled me to transform the seemingly nebulous data into this manuscript. This research was supported by U.S. Geological Survey grant number 14-0-001-G1354. Contribution number 4776 from the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.
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Caltech Division of Geological and Planetary Sciences4776
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ID Code:51054
Deposited By: George Porter
Deposited On:30 Oct 2014 17:34
Last Modified:10 Nov 2021 19:05

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