Abstract
Fault plane solutions of the September 18, 2011 Sikkim Himalaya earthquake Mw 6.9 and its four aftershocks (Mw>4.0) are studied by waveform inversion using the local broadband network data. The solutions show pure strike-slip mechanisms; one aftershock show thrust faulting with strike-slip component. Strike-slip mechanisms indicate predominant transverse tectonics in Sikkim, in the eastern Himalaya region, unlike predominant thrust tectonics in the western Himalaya. The 2011 main shock occurred at a much deeper depth (~47 km) compared to the shallower (<20 km) thrust events in the western Himalaya. Further, analysis of ground acceleration spectra reveals low stress drop (14-38 bars) in agreement with the relatively long source duration and small co-seismic slip of the main shock as well as the aftershocks. We interpret the low stress drop in terms of lower energy release due to reactivation of the Tista fault in opposite sense to that of the Himalayan thrust tectonics. The low stress drop also indicates a pre-existing brittle zone or fault zone at deeper depth or mantle depth.
Highlights
A powerful destructive earthquake of Mw 6.9 at a depth of ~47 km (GCMT report), struck on September 18, 2011 in north-west Sikkim, at the border between India and Nepal (Figure 1)
This model suggested that in the Himalayan Seismic Belt (HSB), earthquakes between the Main Boundary Thrust (MBT) and Main Central Thrust (MCT) are confined above the plane of detachment
The Moho in the Sikkim Himalaya has been interpreted by de la Torre et al [2007] to lie at 40–80 km depth
Summary
A powerful destructive earthquake of Mw 6.9 at a depth of ~47 km (GCMT report), struck on September 18, 2011 in north-west Sikkim, at the border between India and Nepal (Figure 1). We have determined fault plane solutions of the 2011 main shock and its four small aftershocks (Mw 3.9-4.5) by waveform inversion using the local broadband data of the IMD national network. We have critically examined these fault plane solutions of the main shock and the four selected aftershocks using the IMD permanent broadband network data, and we have estimated the source parameters of these events by spectral analysis. These results, with their tectonic implications are presented here. Monsalve et al [2006] reported deeper (30-60 km) source zones of earthquakes in the foothills region; these results were based on permanent digital network data of Nepal, central Himalaya. Unlike the 1988 foothills earthquake, the 2011 Sikkim Himalaya earthquake provided local broadband network data that may shed new light to our understanding of the eastern Himalaya earthquakes at the Himalaya Seismic Belt (HSB) zone
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
