Active fault beneath the Tehri dam, Garhwal Himalaya - seismological evidence

摘要

We present here seismological evidence for an active fault beneath the Tehri dam based on mapping of the earthquake distribution in the Kumaon-Garhwal Himalaya using 40 broadband digital seismographs operated over a period of 39 months during 2005-2008. The earthquake distribution shows two well-defined bands: (i) following the surface trace of the Munsiari Thrust and (ii) a significant EW trend in the Lower Himalaya following the Tons Thrust Fault in the west and the Ramgarh Thrust in the east. The Tehri dam is in close proximity of the south-dipping Tons Thrust Fault. We also recorded over 20 earthquakes (M 1.6-2.8) in 20 km radius of the dam site. Most of these earthquakes have a thrust mechanism. The tectonic loading on this active Tons Fault due to local seismicity coupled with the reservoir loading and unloading may generate earthquake(s) and cause additional seismic risk in this critically stressed region.