MAPPING AFGHANISTAN'S PROBABLE AND SUSPECT QUATERNARY FAULTS

The USGS has completed an inventory and map of probable and possible active faults in Afghanistan and the bordering regions by reviewing published information and systematically inspecting Landsat, Quickbird, and IKONOS imagery. Mapped features show continuous expression of offset landforms, but were not confirmed by field studies. In the digital database that accompanies the map, faults are characterized by 1) geomorphic expression; 2) relative-age of offset deposits; 3) style of fault slip; and 4) lateral offset of stream channels, shutter ridges, and other landforms (where possible), all of which can be expanded as more data are collected.

Previously recognized faults were mapped in greater detail, and new zones of active faulting were identified. Eight tectonic domains were defined on the basis of deformation styles, and slip rates were categorized based on comparing the surface expression and characteristics of active faults of known slip rates in similar geomorphic settings. These eight newly defined tectonic domains and slip-rate categories help to constrain Quaternary deformational models of the Alpine-Himalayan orogenic belt by providing kinematic data within a poorly understood region.

The general patterns, types, and orientations of faults in Afghanistan are kinematically consistent with historical seismicity. The Chaman fault (a plate boundary, left-lateral, strike-slip fault) likely has the highest slip rate in the country. In northeastern Afghanistan, slip is partitioned into a complex array of thrust, normal, and strike-slip faults within a transpressional tectonic setting. North-central Afghanistan is marked by north-verging thrust faults, whereas regions of western and central Afghanistan are dominated by extensional deformation where strike-slip fault zones transition into normal faults. Based on historical and contemporary seismicity and mapped faults, the greatest seismic hazards occur along the Chaman fault and extend north-northeast into the Hindu Kush. In addition, probable Quaternary faulting has occurred within regions with little historical seismicity.