CIGN, A Strong‐Motion Seismic Network in Central Indo‐Gangetic Plains, Foothills of Himalayas: First Results

Abstract

Online Material: Table of PGAs and PGVs during the 21 May 2014 ( M w 6.1) Bay of Bengal earthquake at Central Indo‐Gangetic Plains network (CIGN) stations. The arcuate shape Himalayan collision zone is one of the most seismically active regions of the world. Five M ∼8 earthquakes have occurred in the last 120 years: 1897 Meghalaya, 1905 Kangra, 1934 Bihar–Nepal border, 1950 Arunachal Pradesh, and 2015 Gorkha. Several workers (e.g., Bilham et al. , 2001; Lave et al. , 2005; Hough and Bilham, 2008) recomputed magnitudes of the older earthquakes in the Himalayas, estimated present‐day seismic moment deficit, and reported earthquakes of M w∼8.8 along the arc in the past. These earthquakes have caused extensive damage in the region (Ambraseys, 2000). Seismicity along the Himalayan collision zone is due to the movement of the Indian plate in a north‐northeast direction at a rate of ∼5 cm/yr of which 2 cm/yr is accommodated through stick and slip manner on a seismically active detachment under the outer and lesser Himalayas (Molnar, 1990; Bilham et al. , 1997; Seeber and Armbruster, 1981). The Indo‐Gangetic Plains (IGP) is a foredeep basin that follows the trend of the Himalayan collision zone. The basin is filled with thick alluvium deposits of varying degrees of compaction overlying the basement faults, ridges, and other tectonic features, obliterating their surface expression. Estimates of sediment thickness in the IGP, varying between 0.5 and 3.9 km, have been reported from gravity and borehole data (Sastri et al. , 1971; Rao, 1973; Srivatsava, 2001) and receiver function analysis (Srinivas et al. , 2013), with maximum thickness observed along the foothills of Himalayas. The near‐surface geologic structures, especially soft soils in basins, are known to dramatically amplify seismic waves and cause great damage and deaths, even at sites relatively far from the epicenter …