Nonuniform subduction of the Indian crust beneath the Himalayas.

Himalayan tectonic activity is triggered by downward penetration of the Indian plate beneath the Asian plate. The subsurface geometry of this interaction has not been fully investigated. This study presents novel constraints on this geometry provided by two newly obtained, deep seismic reflection profiles. The profiles cover 100- and 60-km transects across the Yarlung-Zangbo suture of the Himalaya-Tibet orogen at c. 88°E. Both profiles show a crustal-scale outline of the subducting Indian crust. This outline clearly shows Indian understhrusting southern Tibet, but only to a limited degree. When combined with a third seismic reflection profile of the western Himalayas, the new profiles reveal progressive, eastward steepening and shortening in the horizontal advance of the subducting Indian crust.