Indian Strong Motion Instrumentation Network

Abstract

The Indian subcontinent is prone to earthquakes in both interplate and intraplate regions. Areas that have been identified as severe seismic regions include the Himalayan belt in the north from Kashmir to Manipur; Gujarat in the west; and the Andaman and Nicobar Islands in the southeast. The faults in these areas are capable of generating large-magnitude earthquakes that would subject neighboring areas to significant ground shaking. Thus, seismic hazard assessment is of prime importance in India. The relative velocity of the Indian plate with respect to the Eurasian plate near Delhi is about 5 cm/yr in the direction of N13° E (NUVEL-1A model of De Mets et al. 1994). The collision of these continental plates results in crustal shortening along the northern edge of the Indian plate. This process has given rise to three major thrust planes: the main central thrust (MCT), the main boundary thrust (MBT), and the main frontal thrust (MFT) (see, for example, Gansser 1964; Molnar and Chen 1982). The region has experienced several great earthquakes in the past hundred years or so (1897 Assam, 1905 Kangra, 1934 Bihar-Nepal, 1950 Assam). The Himalayan geodynamics and the occurrence of great earthquakes are well summarized by Seeber and Armbruster (1981), Khattri (1999), and Bilham and Gaur (2000). During the last episode of strain release, a 750-km-long segment, which lies between the eastern edge of the 1905 rupture zone and the western edge of the 1934 earthquake, remained unbroken (Figure 1). This segment, called the central seismic gap, continues to be under high strain ( e.g. , Singh et al. 2002). Large earthquakes occurred in this seismic gap in 1803 and 1833, but the magnitudes of these earthquakes were less than 8, and, hence, they were not gap-filling events (Khattri 1999; Bilham 1995). Based on these considerations and on …