Imagingb‐Value Variation beneath the Pamir–Hindu Kush Region

Abstract

The frequency–magnitude distribution ( b ‐value) for the seismicity of the Pamir–Hindu Kush region from August 2008 to June 2010 is analyzed. We used a very precisely located earthquake dataset containing 9532 events with a magnitude of completeness of 2.9. We attempted both 1D and 2D approaches to resolve the b ‐value variation as a function of depth. Several pockets of high b ‐value were detected during the cross‐sectional analysis that may reflect the changes in the physical properties of the subducting slab with depth. Under the Hindu Kush sector, a high b ‐value (>1.2) is identified at the depth of 150 km, but under Pamir this zone ( b >0.9) is apparent at shallower depth. An earlier detailed seismic tomography study revealed a low‐velocity zone beneath Hindu Kush where the high b ‐value is imaged in the present study. This observation is corroborated by the existence of fluid due to the dehydration and increase in pore pressure within the lower portion of the Indian lithosphere. The relatively high b ‐value at shallower depth could be associated with the higher slab temperature, as caused by the slower subduction under Pamir.