The 2011 Sikkim earthquake ([formula omitted] 6.9) of the Himalaya: Estimates of earthquake source parameters and representability of attenuation characteristics

Abstract

The empirical accelerograms of the September 18, 2011, Sikkim earthquake (MW=6.9) have been used in the present study to estimate its source parameters and to identify a representative relation for the attenuation of peak ground acceleration with distance. The spectra of high energy packets observed in the SH waves (approximated by transverse components of accelerograms) has been modeled using Brune’s model. A two-step procedure has been adopted for this purpose. The estimated source parameters of the 2011 Sikkim earthquake have been found to be as - corner frequency (fc): 0.09 Hz, seismic moment (M0): (2.43 ± 0.5) × 1026 dyne-cm, stress drop (Δσ): 50.4 ± 9.28 bars, and the moment magnitude (MW): 6.87 ± 0.05. These estimated values have been found to be consistent with those of reported values obtained using different data sets and procedures. The high-frequency earthquake ground motions are governed by stress drop at the source. Therefore a value of stress drop estimated here is useful for the simulation of earthquake strong ground motions in the region. The attenuation characteristics of observed peak ground acceleration as a function of distance have been compared with those of obtained using five empirical relations. It has been found that a relation given by McGuire (1978) represents the attenuation characteristics of peak ground acceleration is relatively better. This relation may be used for estimating the peak ground acceleration of similar magnitude for future earthquakes in the region. This relation is also useful for the simulation of earthquake strong ground motions in the region using envelope technique. The outcome of the present study is useful for the estimation of the seismic hazard of the Sikkim region of the Himalaya.