806 Seismological Research Letters Volume 79, Number 6 November/December 2008 doi: 10.1785/gssrl.79.6.806 INTRODUCTION he 26 January 2001 (Mw 7.7) Bhuj earthquake, in the Kachchh region of Gujarat, India, caused 13,819 deaths, U.S. $10 billion in economic losses and damaged more than 1 million houses (Gupta, Purnachandra Rao, et al. 2001, Gupta, Harinarayana, et al. 2001; Rastogi et al. 2001). he city of Bhuj and neighbor- ing villages were most afected. he damage can be seen as far as Ahmedabad, 240 km from the epicenter, where 69 reinforced buildings collapsed (Department of Earthquake Engineering, University of Roorkee 2001). Gujarat and the adjoining region falls under all four seismic zones—V, IV, III, and II—of the seis- mic zoning map of India (Bureau of Indian Standards 2002), with likely earthquakes of magnitude 8, 7, 6, and 5, respectively. It is one of the most seismic-prone intracontinental regions in the world. It has experienced two large earthquakes of magni- tude M w 7.8 (Johnston and Kanter 1990) and 7.7, in 1819 and 2001, respectively, and seven earthquakes of magnitude M ≥ 6.0 (Figure 1) during the past two centuries (Quittmeyer and Jacob 1979; Rastogi 2001, 2004). he intense atershock activity of the 2001 Bhuj earthquake is still continuing. hrough March 2008, 14 atershocks with M 5.0–5.8, about 200 atershocks with M 4.0–4.9, about 1,600 atershocks with M 3.0–3.9, and several thousand atershocks with M < 3 have been recorded (Mandal and Johnston 2006; Mandal 2007). Regional seismic- ity has also increased with M ≤ 5 earthquakes and associated foreshock-atershock sequences. At the time of the earthquake, the Kachchh region had only one seismic observatory at Bhuj operated by the India Meteorological Department (IMD), the primary agency in the country for routinely monitoring earth- quakes through its national seismological network. In the past, a few analog seismic recorders and strong-motion accelerographs have been operated by irrigation projects in the northeastern, central, and southern parts of the state of Gujarat. A three-sta- tion network was operated around Kadana in the northeastern part of Gujarat, and one station each was operated at Vadodara, Kevadia, and Ukai in the central and southern part of Gujarat. Ater the 2001 Bhuj earthquake, a network of stations (19 strong-motion accelerographs, 11 broadband seismographs, and one short-period seismograph) has been operated by the National Geophysical Research Institute (NGRI), Hyderabad, conined to the atershock zone of the 2001 Bhuj earthquake. Even this network is not enough to enable more detailed studies needed to develop proper mitigation strategies, such as regional hazard assessment, microzonation of critical areas, early warn- ing systems, and synthetic shake maps. he Gujarat region is at the tri-junction of three failed rits: Kachchh, Cambay, and Narmada, with several active faults (Biswas 1987, 2005; Talwani and Gangopadhyay 2001). hese rits were formed by riting along major Precambrian trends. he riting occurred at successive stages during the northward move- ment of the Indian plate ater the breakup from Gondwanaland in the Late Triassic or Early Jurassic. he riting developed around the Saurashtra horst. he Kachchh riting took place in the Late Triassic–Early Jurassic, Cambay riting in Early Cretaceous, and Narmada riting in the Late Cretaceous (Biswas 1987). he rit- ing ceased in the Late Cretaceous era during the pre-collision stage of the Indian plate. he Kachchh rit basin became a shear zone during the post-collision compressive regime of the Indian plate, with strike-slip movements along subparallel rit faults. he Kachchh mainland fault along the rit axis became the active principal fault (Figure 1). he eastern part of this fault, where it overhangs the South Wagad fault, is the most strained region (Biswas 2005). he epicenter of the 2001 Bhuj earth- quake and its atershocks are located in this zone. Presently, this zone is most active. Yet in spite of its being a high seismic hazard zone, the Gujarat region has not been studied adequately from the point of view of seismic hazard and risk. To rectify this situation, the Department of Science and Technology (DST), Government of Gujarat, India, established the Institute of Seismological Research (ISR) and a network of seismic stations with funding from the Asian Development Bank and World Bank through the Gujarat State Disaster Management Authority. In July 2006, the Gujarat Engineering Research Institute (GERI) and ISR installed a network of 22 broadband seismographs and 43 strong-motion accelerographs throughout the state of Gujarat to monitor earthquake activity. he network was further strengthened in April 2008 with the addition of 23 broadband seismographs and six strong-motion accelerographs. In this article, we describe the Gujarat Seismic The Gujarat (India) Seismic Network Sumer Chopra, R. B. S. Yadav, Hardik Patel, Santosh Kumar, K. M. Rao, B. K. Rastogi, Abdul Hameed, and Sanjay Srivastava Sumer Chopra, R. B. S. Yadav, Hardik Patel, Santosh Kumar, K. M. Rao, and B. K. Rastogi Institute of Seismological Research, Gandhinagar (Gujarat), India Abdul Hameed, Sanjay Srivastava Gujarat Engineering Research Institute, Vadodara (Gujarat), India