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Published March 1, 1996 | Published
Journal Article Open

Intermediate depth earthquakes beneath the India-Tibet collision zone


We report on three intermediate depth earthquakes in the India‐Tibet collision zone, two under the Himalayan Thrust Belt (HTB) and one beneath the Indus Zangbo suture. The mb magnitudes of these three events are from 4.3 to 4.9, and are too small to be well located by conventional means. However, from modeling their broadband waveforms recorded at near‐regional distances on a temporary PASSCAL array, we can confidently confine the sources to be below the crust, between 70 and 80 km deep. The existence of these intermediate depth earthquakes in this area suggests relatively low temperatures in the mantle lithosphere. The two events under the HTB display strike‐slip mechanisms with some normal faulting component; this is quite different from the shallow thrust events typical of the same area. The principal P and T axes of all 3 fault plane solutions show roughly NS compression and EW extension, consistent with a regional stress field produced by the indenting of the India continent.

Additional Information

© 1996 American Geophysical Union. Received 5 June 1995; accepted 19 December 1995. We thank 3 anonymous reviewers, L. Burdick, C. Scrivner, T. Melbourne, and X. Song for their helpful comments on the manuscript. This work has been supported by the Department of Defense as monitored by the Air Force Office of Scientific Research under contract F49620-92-J-0470. Contribution No. 5556, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California.

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