Coda Q estimation for Kinnaur region and surrounding part of NW Himalaya

摘要

Spatial variation of coda wave attenuation is obtained for the Kinnaur Himalaya using the single backscattering model based on the data of 376 local earthquakes ranging in magnitude from 1.5 to 4.5. A frequency-dependent S-coda wave quality factor, Qc = 69f(1.0) (Qc = Q(0)f(n)), is obtained at eight central frequencies between 1.5 and 24Hz for epicenter distance 30km. The n values are found to vary highly, maximum in the tectonically and seismically active High Himalaya, intermediate in the seismically active Kaurik-Chango region, and least in the Spiti valley. Q(0) (Qc at 1Hz) is high in the High Himalaya, with values ranging from 87 to 109 which matches with already published works. It decreases towards NNE, the value is lowest in the Tethys Himalaya which varies between 49 and 55. To investigate attenuation with increasing depth, the Qc is estimated at eight coda wave window lengths between 20 and 90s. With increasing window length, equivalent to increasing lapse times, the Q(0) increases from 46 +/- 3 to 493 +/- 34 and n value decreases from 1.07 to 0.58. Further by dividing the entire coda wave data into four groups of epicenter distances, i.e., 0-25, 26-50, 51-75, and 76-100km, Qc relations are estimated to vary as 111f(0.93), 183f(0.80), 264f(0.73), and 296f(0.71), respectively, for four groups. The increase of Qc with increasing lapse time is interpreted as a decrease of heterogeneity with depth. The data is reasonably fit in the power-law decay of turbidity.