P-Wave Attenuation Tomography of the 'Seismic Gap' in the Jammu and Kashmir Himalaya

Jammu and Kashmir (J&K) Himalaya lies between the rupture zones of the 1905 (Mw 7.9) Kangra and 2005 (Mw 7.6) Muzafarrabad earthquakes. It straddles the meisoseismal zone of the 1555 (Mw 8.0) Kashmir earthquake and is known to be a "seismic gap" in the NW Himalaya. This region is replete with small-to-moderate earthquakes, recorded by the recently deployed Jammu And Kashmir Seismological NETwork (JAKSNET). Shallow-depth local-earthquake P-waveforms from JAKSNET are used to study the P-wave attenuation characteristics (Qp-1) of the J&K Himalaya. P-waveform spectra for each earthquakes, recorded at multiple stations, are inverted using a spectral curve-fitting technique to estimate source parameters (M0 and fc) along with path-averaged attenuation operator (t∗) at frequencies between 1 and 20 Hz. Qp is calculated for each earthquake-station path from the t∗. This yielded a total of 466 earthquake-station Qp measurements, with error weighted average Qp of 410 ± 19. These measurements have been regionalised using a tomographic formulation and the resolution in lateral variations computed using a standard checkerboard test. The 2D variation map of Qp reveals lower values associated with the frontal and lateral ramps on the Main Himalayan Thrust, beneath the Lesser-Higher Himalaya. The Kashmir Valley shows lateral variation in Qp with higher values in the east compared to the west. Highest Qp values are associated with the Tethyan Himalaya and the Reasi Thrust reentrant in the Shiwalik Himalaya.