Broadband Seismic Studies In Southern Asia

We are continuing efforts to develop 3-D velocity models for southern Asia through the collection and analysis of broadband waveform data acquired on the Indian subcontinent. The geology of India is diverse, but can be divided into three main regions: the Himalayas, the Indo-Gangetic plain, and the...

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Bibliographic Details
Main Authors: Priestley, Keith, Gaur, Vinod K, Rai, S S, Bonner, Jessie L, Lewkowicz, James F
Format: Report
Language:English
Subjects:
BROADBAND
EARTH MANTLE
EARTHQUAKES
GANGES RIVER
Geology, Geochemistry and Mineralogy
HIMALAYA MOUNTAINS
INDIA
INDIAN SHIELD
INDO-GANGETIC PLAIN
LITHOSPHERE
PHASE VELOCITY
SEISMIC DATA
SEISMIC WAVES
Seismology
SHILLONG PLATEAU
SOUTH ASIA
STRUCTURAL GEOLOGY
SURFACE WAVES
SYMPOSIA
WAVE PROPAGATION
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Summary:We are continuing efforts to develop 3-D velocity models for southern Asia through the collection and analysis of broadband waveform data acquired on the Indian subcontinent. The geology of India is diverse, but can be divided into three main regions: the Himalayas, the Indo-Gangetic plain, and the Indian Shield. Our initial focus has been on the southern Indian shield, and we have also completed studies in the trans-Himalayas and the Shillong Plateau. The goal of our work is to determine the crust and upper mantle velocity and attenuation structure and to characterize regional seismic waveform propagation of the Indian subcontinent. Teleseismic receiver function data, S-to-P conversions, and short-period surface wave phase velocity data have been interpreted for seismograms recorded along a 700-km north-south profile of the southern Shield. These data show that the shield velocity structure is extremely uniform, simple, and consists of a surface wave velocity of approximately 3.45 km/sec and a moderate gradient of 0.20 km/sec/km with the Moho at 35-1 km depth. To the south of the shield in the granulite terrain, the crust is both thicker (44?1 km deep) and more complicated, with a mid-crustal discontinuity at approximately 25-km depth. We constrain the upper mantle structure with phase velocity measurements of long-period surface waves; these show that the seismic lithosphere is approximately 150 km thick and underlain by a weak low-velocity zone. We have also modeled the regional waveforms of a moderate earthquake that occurred near Koyna, India, in September 2000 and of the 26 January 2001 Bhuj main shock and its aftershocks to calibrate paths to the regional stations. Presented at the Seismic Research Review: Worldwide Monitoring of Nuclear Explosions (23rd) held in Jackson Hole, WY on 2-5 October 2001. Published in the Proceedings of the Seismic Research Review: Worldwide Monitoring of Nuclear Explosions (23rd), p100-109, 2001.