The 18th September 2011 Sikkim Earthquake (Mw 6.8) and its aftershocks recorded in Adampool Seismic Observatory

摘要

On 18th September 2011, an earthquake of magnitude Mw 6.8 occurred 84 km northwest of Adampool Seismic Observatory near Gangtok, in the mountainous region of northeast India in Sikkim-Nepal border region. The source parameters for this earthquake have been estimated using record of the event in the observatory. The spectral analysis of waveform on transverse component of the three-component seismograms is performed. The estimated seismic moment (Mo), source radius (R), stress drop (Δσ) and magnitude (Mw) for this earthquake are 1.99×10~(19) Nm, 10.17 km, 83.24 bar and 6.8 respectively. The present study elucidates the seismicity of the region before and after the occurrence of mainshock with recorded earthquakes especially also with those events (M< 3.0) that are not recorded by distant observatories of the national network and local seismic network. The data recorded in the observatory for the period before the occurrence of this earthquake do not show any noticeable or anomalous precursory activity close to the mainshock except the background seismicity. To show the variation of seismic moment with corner frequency, source radius and stress drop, 19 well-recorded aftershocks (5.0 > Mw > 2.7) are selected in this study. The estimated seismic moment, source radius and stress drop of these aftershocks range from 1.58 x 1013 Nm to 4.27 x 1016 Nm, 0.24 km to 0.98 km and 0.9 bar to 294.2 bar respectively.