Estimation of quality factor, seismic moment, and stress drop of local earthquakes along the MCT in Chamoli region, India

In the present study, 149 local earthquakes (0.6≤ML≤5.1), those that occurred in the Chamoli region of the Garhwal Himalaya and are recorded by a 12-station digital telemetry seismological network around the Tehri region, have been analyzed to estimate source parameters using Brune’s (1970) point source circular model and the quality factor Qc, adopting the single back-scattering model given by Aki and Chouet (1975). Two data sets comprised of 86 local earthquakes (data set 1) in the magnitude range (0.6≤ML≤3.3) recorded during January 2009 to December 2014 and 63 local earthquakes (data set 2) in the magnitude range (0.7≤ML≤5.1) recorded during January–December 2017 have been used for this purpose. The source parameters, viz., seismic moment (Mo), source radii (r), and stress drop (∆σ), have been computed from the displacement spectra of SH-component of the S-wave, whereas the quality factor Qc has been estimated from the coda waves of 30-s window length of vertical component seismograms for giving the frequency-dependent attenuation relation for the region. Mo, r, and ∆σ vary from 1.2˟1011 to 7.9˟1013 Nm, 132 to 317 m, and 0.05 to 42.9 bars, respectively, for data set 1 and from 2.5˟1011 to 2.1˟1015 Nm, 45.7 to 365m, and 0.2 to 149 bars, respectively, for the data set 2. Low stress drops have been obtained for the majority of events of both the data sets. However, high stress drops, i.e., 307 bars and 480 bars, have also been observed for two small size earthquakes of the second data sets having a magnitude of ML~5.1 and ~4.9, respectively. The estimation of quality factor Qc has provided the frequency-dependent average attenuation relations, Qc=137f0.87 and Qc=120f0.99, for data set 1 and 2, respectively, for the region.