The 3-D geometry of the seismicity in Hindu Kush-Pamir-western China region has been defined by seismic records for 1975-1999 from the National Earthquake Information Center, the U. S. Geological Survey, and over 16, 000 relocated earthquakes since 1975 recorded by the Xinjiang seismic network of China. The results show that most Ms≥5. 0 hypocenters in the area are confined to a major intracontinental seismic shear zone (MSSZ). The MSSZ. which dips southwards in Pamir has a north-dipping counterpart in the Hindu Kush to the west; the two tectonic realms are separated by the sinistral Chaman transform fault of the India-Asia collisional zone. The authors demonstrate that the MSSZ constitutes the upper boundary of a south-dipping, actively subducting Pamir continental plate. Three seismic concentrations are recognized just above the Pamir MSSZ at depths between 45~65 km, 95~120 km, and 180~220 km, suggesting different structural relationships where each occurs.
