3D Scattering and Absorption Imaging of the Jammu and Kashmir Himalaya

The NW Himalayan "seismic gap" spanning the meisoseismal zone of the 1555-Kashmir earthquake, is located between the rupture zones of the 1905 and 2005 earthquakes. Knowledge of the lateral variation in seismic attenuation across this orogenic belt is crucial to estimate ground shaking from future earthquakes. To this end, we use recordings from the Jammu and Kashmir Seismological NETwork to compute the 3D S-wave attenuation (through coda-normalization) and, jointly separate and map the frequency dependent seismic absorption (from coda quality factors) and scattering (from peak delay times) contributions. Our findings reveal strong variations in these parameters throughout the region which are controlled by the differences in crustal structure and rheology. Maps at shallow depths show patches of both high and low attenuation throughout the Sub-Himalaya and the Lesser Himalaya relating to differences in sediment thicknesses or rheology. The regions adjoining the reentrants of MFT south of the Reasi Thrust, and those of the MBT and MCT, SW and SE of the Kishtwar Window display high absorption characteristics, conspicuous across all frequencies and this pattern does alter significantly as depth increases (~20 km). The Kishtwar window, hosting crystalline rocks, is marked by lower attenuation overall but higher attenuation in patches to the south and north, as we go deeper. Surprisingly, high absorption of energy is visible throughout the window across all frequencies. SW of the window, near the MCT reentrant, a broad patch of high absorption coincides with the lateral ramp of the MHT and continues all through in the SE direction. The Kashmir Valley, where sedimentary rocks overlie the crystalline basement shows lateral variations of low and high Q and Qc (absorption), with the Pir Panjal Ranges to its south showing high S-wave attenuation, low absorption and high scattering. At greater depths however this entire zone is marked by high attenuation, high absorption but low scattering which may be a signature of the structure of the top of the underthrusting Indian Plate and/or the frontal-lateral ramps on the MHT.