Seismicity and source parameters of local earthquakes in Bilaspur region of Himachal Lesser Himalaya
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ORIGINAL PAPER
Seismicity and source parameters of local earthquakes in Bilaspur region of Himachal Lesser Himalaya Ashwani Kumar & Arjun Kumar & S. C. Gupta & A. K. Jindal & Vandana Ghangas
Received: 10 October 2012 / Accepted: 15 March 2013 # Saudi Society for Geosciences 2013
Abstract The pattern of local seismicity (110 events) and the source parameters of 26 local events (1.0≤Mw≤2.5) that occurred during May 2008 to April 2009 in Bilaspur region of Himachal Lesser Himalaya were determined. The digital records available from one station have been used to compute the source parameters and fmax based on the Brune source model (1970) and a high-frequency diminution factor (Boore 1983) above fmax. The epicentral distribution of events within 30 km of local network is broadly divided into three clusters of seismic activity: (1) a cluster located to the south of the Jamthal (JAMT) station and falls to the north of the Main Boundary Thrust (MBT) which seems to reflect the contemporary local seismicity of the segment of the MBT, (2) an elongated zone of local seismicity NE–SW trending, delineated NE of JAMT station that falls in the Lesser Himalaya between the MBT and the Main Central Thrust, and (3) NE–SW trending zone of local seismic activity located at about 10 km east of NHRI station and about 15 km northeast of NERI station and extending over a distance of about 20 km. Majority of events occur at shallow depths up to 20 km, and the maximum number of events occurs in the focal depth range between 10 and 15 km. The entire seismic activity is confined to the crust between 5 and 45 km. The average values of these source parameters range from 3.29×1017 to 3.73×1019 dyne-cm for seismic moment, 0.1 to 9.7 bars for stress drops, and 111.78 to 558.92 m for source radii. The average value of fmax for these events varies from 7 to 18 Hz and seems to be source dependent. A. Kumar : A. Kumar (*) : S. C. Gupta : A. K. Jindal : V. Ghangas Department of Earthquake Engineering, Indian Institute of Technology, Roorkee 247667 Uttarakhand, India e-mail: [email protected]
Keywords Source parameters . fmax . Stress drop . Bilaspur . Himachal Lesser Himalaya
Introduction The nature of seismicity and source parameters provide an opportunity to study the ongoing faulting processes and regional stresses operating in the study area. The Bilaspur region of Himachal Pradesh is located in Lesser Himalaya, is highly seismically active, and lies in seismic zone V (IS: 1893–2002 (Part l): General Provisions and Buildings) as shown in Fig. 1 (index). This region has a great potential for hydropower generation, and a number of small- to largescale hydropower projects are either in operation or are under construction. Several tectonic features of local and regional scales have been mapped in the region around. Many moderate- to large-sized earthquakes have occurred in this region. Five prominent earthquakes have occurred around the study area during the last more than 100 years. The nature of seismicity and source parameters will obviously be
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