Source parameters of the deadly M-w 7.6 kashmir earthquake of 8 october, 2005

摘要

During the last six years, National Geophysical Research Institute, Hyderabad has established a semi-permanent seismological network of 5-8 broadband seismographs and 10-20 accelerographs in the Kachchh seismic zone, Gujarat with a prime objective to monitor the continued aftershock activity of the 2001 M-w 7.7 Bhuj mainshock. The reliable and accurate broadband data for the 8 October M-w 7.6 2005 Kashmir earthquake and its aftershocks from this network as well as Hyderabad Geoscope station enabled us to estimate the group velocity dispersion characteristics and one-dimensional regional shear velocity structure of the Peninsular India. Firstly, we measure Rayleigh-and Love-wave group velocity dispersion curves in the period range of 8 to 35 sec and invert these curves to estimate the crustal and upper mantle structure below the western part of Peninsular India. Our best model suggests a two-layered crust: The upper crust is 13.8 km thick with a shear velocity (Vs) of 3.2 km/s; the corresponding values for the lower crust are 24.9 km and 3.7 km/sec. The shear velocity for the upper mantle is found to be 4.65 km/sec. Based on this structure, we perform a moment tensor (MT) inversion of the bandpass (0.05-0.02 Hz) filtered seismograms of the Kashmir earthquake. The best fit is obtained for a source located at a depth of 30 km, with a seismic moment, Mo, of 1.6 x 10(27) stop dyne-cm, and a focal mechanism with strike 19.5 degrees, dip 42 degrees, and rake 167 degrees. The long-period magnitude (M-A similar to M-w) of this earthquake is estimated to be 7.31. An analysis of well-developed sPn and sSn regional crustal phases from the bandpassed (0.02-0.25 Hz) seismograms of this earthquake at four stations in Kachchh suggests a focal depth of 30.8 km.