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Focal process of the great Chilean earthquake May 22, 1960

Kanamori, Hiroo and Cipar, John J. (1974) Focal process of the great Chilean earthquake May 22, 1960. Physics of the Earth and Planetary Interiors, 9 (2). pp. 128-136. ISSN 0031-9201. doi:10.1016/0031-9201(74)90029-6.

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Long-period strain seismogram recorded at Pasadena is used to determine the focal process of the 1960 Chilean earthquake. Synthetic seismograms computed for various fault models are matched with the observed strain seismogram to determine the fault parameters. A low-angle (∼ 10°) thrust model with rupture length of 800 km and rupture velocity of 3.5 km/sec is consistent with the observed Rayleigh/Love wave ratio and the radiation asymmetry. A seismic moment of 2.7 · 10^(30) dyn · cm is obtained for the main shock. This value, together with the estimated fault area of 1.6 · 10^5 km^2, gives an average dislocation of 24 m. The strain seismogram clearly shows unusually long-period (300–600 sec) wave arriving at the P time of a large foreshock which occurred about 15 minutes before the main shock, suggesting a large slow deformation in the epicentral area prior to the major failure. A simple dislocation model shows that a dislocation of 30 m, having a time constant of 300–600 sec, over a fault plane of 800 × 200 km^2 is required to explain this precursory displacement. The entire focal process may be envisaged in terms of a large-scale deformation which started rather gradually and eventually triggered the foreshocks and the “main” shock. This mechanism may explain the large premonitory deformations documented, but not recorded instrumentally, for several Japanese earthquakes. The moments of the main shock and the precursor add to 6 · 10^(30) dyn · cm which is large enough to affect the earth's polar motion.

Item Type:Article
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URLURL TypeDescription
Kanamori, Hiroo0000-0001-8219-9428
Additional Information: © 1974 Published by Elsevier B.V. Accepted 27 August 1974, Available online 25 October 2002. We thank Don Anderson for kindly reading the manuscript, and Frank Press for kindly suggesting to us the use of the Benioff 1-90 system for the calibration of the strain instrument. Francis Lehner provided us with useful information concerning the instrument characteristics. This research was partially supported by National Science Foundation grant GA 40752 and the Advanced Research Projects Agency of the Department of Defense and was monitored by the Air Force Office of Scientific Research under contract No. F44620-72-C-0078.
Group:UNSPECIFIED, Division of Geological and Planetary Sciences
Funding AgencyGrant Number
NSFGA 40752
Advanced Research Projects Agency (ARPA)UNSPECIFIED
Air Force Office of Scientific Research (AFOSR)F44620-72-C-0078
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Caltech Division of Geological and Planetary Sciences2509
Issue or Number:2
Record Number:CaltechAUTHORS:20150218-070604055
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Official Citation:Hiroo Kanamori, John J. Cipar, Focal process of the great Chilean earthquake May 22, 1960, Physics of the Earth and Planetary Interiors, Volume 9, Issue 2, 1974, Pages 128-136, ISSN 0031-9201, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:54902
Deposited By: Ruth Sustaita
Deposited On:18 Feb 2015 15:42
Last Modified:10 Nov 2021 20:39

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