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Thrusting of the Hindu Kush over the Southeastern Tadjik Basin, Afghanistan: Evidence from two large earthquakes
Author(s) -
Abers Geoffrey,
Bryan Carol,
Roecker Steven,
McCaffrey Robert
Publication year - 1988
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/tc007i001p00041
Subject(s) - geology , seismology , structural basin , fault (geology) , thrust fault , subduction , basement , basin and range topography , focal mechanism , magnitude (astronomy) , tectonics , paleontology , geography , physics , archaeology , astronomy
We infer from the mechanisms and depths of two large earthquakes that the Hindu Kush is actively thrusting northwest over the Tadjik basin and that the basin is closing rather than being displaced to the west. Teleseismic body waves were used to determine focal mechanisms and depths for the two largest shallow earthquakes on the southern edge of the basin. The two earthquakes, on June 24, 1972 (m b =6.0), and December 16, 1982 (m b =6.2), have seismic moments of 2 × 10 18 N‐m and 6 × 10 18 N‐m, respectively. Focal mechanisms of both events indicate almost pure thrust faulting with nodal planes striking northeast‐southwest. The inferred fault planes dip southeast, at 20° for the first event and 50° for the second. The P axes for both events are oblique to the direction of relative motion between India and Asia, suggesting that the Pamir is overthrusting the basin to the west. Depths for both earthquakes are between 20 and 25 km and place them well below the Tadjik basin sediments. The depths and steep fault planes suggest that these earthquakes represent a downdip extension within the basement of shallow folding and thrusting seen in the sediments northwest of the events. Thus convergence in Afghanistan between India and Eurasia is taken up along southeast dipping thrust faults north of the Hindu Kush as well as by northward subduction under the southern part of the range.