Spatial distribution and focal mechanisms of mantle earthquakes in the Hindu Kush–Pamir region: A contorted Benioff zone

Seismic imaging of subducting continental lower crust beneath the Pamir

“…There is a long standing debate whether the geometry of the seismic zone results from a single originally northward dipping subduction interface, which was contorted and overturned under the eastern Pamir (Billington et al, 1977;Pegler, and Das, 1998;Pavlis and Das, 2000), or if it is the result of two subduction zones, one dipping to the north beneath the Hindu Kush and one dipping to the south beneath the Pamir (Burtman and Molnar, 1993;Chatelain et al, 1980;Fan et al, 1994;Negredo et al, 2007). Recent high resolution earthquake locations from the local TIPAGE network (see next paragraph) show the seismicity in the Pamir as a curviplanar arc dipping to the south in the eastern Pamir and bending to an eastward dipping direction beneath the south-western Pamir, while the separated seismic zone beneath the Hindu Kush is a more complex structure striking east-west and dipping subvertically north to north-west (Sippl et al, 2013).…”

Geometry of the Pamir‐Hindu Kush intermediate‐depth earthquake zone from local seismic data

“…There are essentially two prevailing lines of interpretation in the literature: (1) Both Pamir and Hindu Kush slabs belong to a single slab of Indian origin which is torn, contorted and overturned in its southdipping Pamir part [Billington et al, 1977;Pegler and Das, 1998;Pavlis and Das, 2000]. (2) Pamir and Hindu Kush are two distinct slabs subducting in opposite directions next to each other, where the Pamir slab is made up of Eurasian material and the Hindu Kush slab is of Indian provenance [Burtman and Molnar, 1993;Fan et al, 1994].…”

“…Lithospheric deformation is accompanied by vigorous intermediate-depth (up to nearly 300 km depth) earthquake activity [Billington et al, 1977;Pegler and Das, 1998], which is, with the possible exception of Vrancea, Romania [Ismail-Zadeh et al, 2012], globally unique within a continental collision zone far from any active oceanic subduction. Tibet, in comparison, is essentially aseismic at depths greater than 80 or 90 km (uppermost mantle).…”

“…However, comparison of these models to nature is difficult because of a lack of observations, not least because of the generally aseismic nature of orogenic mantle deformation, with the apparent exception of the Pamir-Hindu Kush. A variety of models attempting to explain the Pamir-Hindu Kush zone's peculiar geometry (along-strike overturning of dip) and dynamics have been proposed, but fundamental questions, e.g., whether it is related to subduction [e.g., Billington et al, 1977] or exists due to a mantle drip [Koulakov, 2011], whether continental [Roecker, 1982;Burtman and Molnar, 1993] or oceanic material [Chatelain et al, 1980;Pegler and Das, 1998] hosts these earthquakes, or whether Pamir and Hindu Kush form one single [Billington et al, 1977;Pegler and Das, 1998;Pavlis and Das, 2000] or two separate structures [Chatelain et al, 1980;Burtman and Molnar, 1993;Fan et al, 1994] outlined by seismic activity, have not been conclusively solved.…”

The Soviet-American exchange in earthquake prediction

“…To the east, the Darvaz-Kara-Kul fault separates the depression from the Pamir Mountains. Both shallow and intermediate depth seismicity here and to the south of the depression are related to subduction in the Hindu Rush and Pamirs (Billington et al, 1977;Chatelain et al, 1980).…”