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Bulletin of the Seismological Society of America; June 1984; v. 74; no. 3; p. 863-873
© 1984 Seismological Society of America
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Are reservoir-induced earthquakes of magnitude greater double equals 5.0 at Koyna, India, preceded by pairs of earthquakes of magnitude greater double equals 4.0?

HARSH K. GUPTA* and H. M. IYER

U.S. GEOLOGICAL SURVEY, 345 MIDDLEFIELD ROAD, MAIL STOP 77, MENLO PARK, CALIFORNIA 94025

Abstract

Foreshocks of Koyna, India, earthquakes of magnitude greater double equals 5.0 are investigated using data from the Poona WWSSN Seismic Station situated at a distance of 120 km from Koyna. Schemes for estimating earthquake magnitude on the SPZ component seismogram at Poona have been developed. These schemes are applicable to earthquakes of magnitude greater double equals 2.0 occurring in the Koyna region.

Earthquakes of magnitude greater double equals 5 on 13 September 1967, 10 December 1967, and 17 October 1973 in the Koyna region were each preceded by two earthquakes of magnitude greater double equals 4.0 occurring within the preceding 15 days. In comparison, the activity of September 1980 was different. An earthquake of magnitude greater double equals 5.0 occurred on 2 September and two more greater double equals 5.0 earthquakes occurred on 20 September. These earthquakes were not preceded by pairs of greater double equals 4.0 events. All events of magnitude greater double equals 4.0 during 1974 through 1976 were singular (no two such events occurred within 15 days of one another). There appears to be a 50 per cent probability of occurrence of a magnitude greater double equals 5.0 earthquake if two earthquakes of magnitude greater double equals 4.0 are closely spaced in time (within 15 days) in the Koyna region.

Footnotes

* Present address: Director, Centre for Earth Science Studies, P. B. No. 2235, Sasthamangalam, Trivandrum 695010, India.




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H. K. GUPTA
Are ris events of M greater double equals 5 preceded by a couple of foreshocks of M greater double equals 4?
Bulletin of the Seismological Society of America, February 1, 1992; 82(1): 517 - 520.
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