Determination and identification of focal mechanism solutions for Himalayan earthquakes from waveform inversion employing ISOLA software

摘要

ISOLA software has been used to determine moment tensor solutions by using the single-station three-component seismogram data. This will be useful and worthwhile for analysis of the earthquakes occurred in Himalayan region, where well azimuthal coverage data are not available. Two earthquakes occurred in Garhwal Himalaya on 21 September 2009 (M (w) 5.2) near Uttarkashi and on 3 May 2010 (M (w) 4.1) near Ghansali with known fault plane solutions from polarity inversion have been used to identify and verify the obtained moment tensor solutions from waveform inversion. The focal mechanism solutions of 21 September 2009 and 3 May 2010 estimated by two different independent schemes, i.e. single- and multiple-station waveform inversion and polarity inversion, have been found in agreement. Also the magnitude estimated by waveform inversion agrees with the report by various agencies. The inversion has been performed by using maximum azimuthal coverage data as well as using only single-station data. The frequency bands used for inversion of 21 September 2009 and 3 May 2010 are 0.02-0.11 and 0.08-0.20 Hz, respectively. These bands correspond to the maximum signal-to-noise ratio. The solutions estimated by polarity inversion, maximum-station data and single-station data have almost similar focal mechanism parameters. This infers that if an accurate crustal velocity structure, hypocentre location and a proper frequency band have been used, then moment tensor solutions can be estimated by single-station waveform data.