Magnitude 6.6 HINDU KUSH REGION, AFGHANISTAN
2004 April 05 21:24:04 UTC
Preliminary Earthquake Report
U.S. Geological Survey, National Earthquake Information Center
World Data Center for Seismology, Denver
This earthquake resulted from the release of stresses that accumulated during the ongoing collision between the Indian and Eurasian plates. In this area, known geologically as the Pamir-Hindu Kush region, the two plates are converging at a rate of about 4.4 cm per year. On average, there are four magnitude 5 or greater earthquakes per year whose epicenters are within 60 km of this event. Earthquake depths in this region range from the surface to depths of 380 km. Generally, earthquakes at depths greater than 70 km do not occur at the boundary of two continental plates as they do in the Pamir-Hindu Kush region. The sub-crustal seismicity in the region forms an "S" shaped pattern (see figure).
It is generally believed that the Indian plate is subducting beneath the Eurasian plate west of about 71.5 degrees longitude and that the sense of subduction changes such that the Eurasian plate subducts beneath the Indian plate near the Afghanistan-Tajikistan border east of about 71.5 degrees longitude. This earthquake likely occurred in the subducted Indian plate.