Introduction

The federal democratic republic of Nepal is located at the boundary between Indian and Tibetan tectonic plates and therefore lies in a seismically active region. Historical data evidence the occurrence of destructive great earthquakes in the past. Mitigation of earthquake risk can be made only with adequate assessment of seismic hazard which should be based on the evaluation of seismotectonic and geological process prevailing in this part of the world.

 

Microseismic monitoring is a very fast and efficient tool to understand the seismotectonics of the region. It is an instrument for seismic surveillance allowing a fast post earthquake rescue operation. For regional and global earthquake location and related seismological studies it provides a valuable database.

 

Microseimic monitoring in Nepal started in November, 1978 by Department of Mines and Geology (DMG), Ministry of Industry, government of federal democratic republic of Nepal in collaboration with Laboratoire de Geophysique Appliquee, Paris University, France with the installation of first short period vertical seismic station Phulchoki(PKI) hilltop in the south of Kathmandu. The number of stations were augmented gradually to create the National Network consisting of 21 short period seismic stations in 1998 and 7 accelerometer stations in 2012. The network is operated in collaboration with Department of Analysis & Surveillance of Environment (DASE), France. The 21 short period seismic stations and 7 accelerometer stations occupy the Lesser Himalaya and Sub Himalayan terrain of Nepal Himalaya uniformly.

 

The recording is carried out at two centres Birendranagar Regional Seismological Centre (RSC), Surkhet and National Seismological Centre (NSC), Lainchour, Kathmandu. RSC records 9 stations of mid western and farwestern Nepal while NSC records the remaining 12 stations from Puthan to Taplejung. The stations are operated in two sensitivity channels allowing a dynamic range of 110 db. The signals are digitized centrally acquired using JADE software of DASE. The location is made with ONYX software of DASE since April, 2001. Before this ISIS software of DASE was used for acquisition & processing.

 

Since earthquake is caused by sudden release of elastic energy stored in the active geological faults inside the earth which causes movement in the crust. In order to monitor the crustal shortening because of continuous movement of Indian Plate towards the north, NSC/DMG installed 29 GPS Stations in technical collaboration with Caltech/USA and DASE/France across the Nepal Himalaya.

 

By the end of 2012, 151667 earthquakes have been recorded by the centre out of which 51053 are local and regional and 100814 are teleseisms.



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