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Seismotectonics of the Himalayan collision zone; geometry of the underthrusting Indian Plate beneath the Himalaya



Seismotectonics of the Himalayan collision zone; geometry of the underthrusting Indian Plate beneath the Himalaya



JGR Journal of Geophysical Research



Epicenters of events along the Himalayan Arc (between 1961 and 1981) are concentrated in a narrow zone, about 50 km wide, lying between the northerly dipping Main Boundary (MBT) and Main Central (MCT) thrusts. Events with accurately determined depths obtained from identification of surface-reflected phases define a simple, planar zone from about 10-km and 20-km depth, with an apparent dip of about 15 degrees . Focal mechanisms of events within this zone indicate shallow, north dipping thrusts. This shallow, north dipping zone apparently defines a part of the detachment that separates the underthrusting Indian Plate from the Lesser Himalayan crustal block. The MBT and nearby subsidiary surface and blind thrusts, rather than the MCT, are currently the most active structures of the Himalayan Arc. Suggestion that the great Himalayan earthquakes occur along the same detachment surface as defined by the thrust-type medium-sized events. The above results suggest that the Indian continental plate is underthrusting the Himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones. The November 19, 1980, earthquake that occurred near the MCT shows a predominantly strike-slip focal mechanism; this predominantly left-lateral mechanism indicates a possible genetic relationship between transverse structural features in the underthrusting Indian Plate and Upper Himalayan blocks and Tibet.--Modified journal abstract.

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Accession: 019995719

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DOI: 10.1029/jb089ib02p01147


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