Seismic Coda-Wave Attenuation Tomography of the Jammu and Kashmir Himalaya

Lateral variation in seismic attenuation of the Jammu and Kashmir Himalaya has been studied from local-earthquake coda waves using 588 single-trace measurements and back-projection tomography of coda quality factor (Q(c)(f)). Single-trace measurements are performed for a range of lapse time and coda-window length, and a final choice of 2t(s) and 90 s, respectively, have been made based on an unbiased distribution of Q(0) as a function of epicentral distance. These choices ensure coda start time beyond transient arrivals and satisfies the assumption of coda-wave generation through multiple forward-scattering. From single-traces we obtain Q(c)(f) = 231 +/- 21f(0.93 +/- 0.05), with a negative correlation between Q(0) and eta. Q(c)(f) tomography are presented as 2D-anomaly maps computed from Q(mean) at every f, and as absolute Q(0) and eta maps. These reveal strong frequency-dependent lateral variations in attenuation. At f = 3-5 Hz, the central Shiwalik Himalaya, Jammu-Kishtwar Higher Himalaya, Zanskar Ranges, and eastern Kashmir Valley have similar to 10% positive Q(c) anomaly; and high Q(0) (270-300) and low eta (0.8-0.85), indicating low absorption of seismic energy. The Kishtwar Window region, the reentrant of the Main Boundary and Main Central thrusts, and the western Kashmir Valley have similar to 10% negative Q(c) anomaly, low-to-intermediate Q(0) (210-250) and high eta (0.9-1.0), revealing strong attenuation at structural heterogeneities. At f = 8-14 Hz, the lateral variation in Q(c) anomaly between the western Kashmir Himalaya (positive) and eastern Jammu-Kishtwar Himalaya (negative), possibly arises from the crustal thickness variations and steep-to-shallow NE dipping Moho from east-to-west.