RESEARCH ARTICLE CURRENT SCIENCE, VOL. 80, NO. 11, 10 JUNE 2001 1397 The 2001 Kutch (Bhuj) earthquake: Coseismic surface features and their significance Kusala Rajendran* ,# , C. P. Rajendran*, Mahesh Thakkar † and Martitia P. Tuttle ‡ *Centre for Earth Science Studies, P.B. No. 7250, Akkulam, Thiruvananthapuram 695 031, India † Department of Geology, R.R.Lalan College, Bhuj, 370 001, India ‡ M. Tuttle & Associates, Tibbetts Lane, Georgetown, ME 04548, USA The Mw 7.7, 2001 Kutch (Bhuj) earthquake that occurred in the northwestern fringes of the Indian craton is the most damaging earthquake during the recent history. Although the main fault rupture did not reach the surface, the epicentral area is characterized by the development of secondary features, including flexures and folds that are related to compressional deformation, in a wide area of the Banni Plain. Based on the spatial distribution of these structures and their inferred mechanics, we propose that the earthquake originated on an imbricate blind thrust, located north of the Kutch mainland fault. Besides surface deforma- tion, the earthquake also induced widespread lique- faction, leading to ground failure including lateral spreading. Although a large earthquake had occurred in the Rann of Kutch in 1819, preliminary assessment based on ancient monuments and temples in the region indicates that the source of the 2001 earthquake may not have experienced similar size events at least since 9th century A.D. Occurrences of this and the 1819 earthquake underscore the need for recognizing hidden faults in the Kutch–Saurashtra region and assessing their seismogenic potential. THE 26 January 2001 Bhuj earthquake (Mw 7.7) that occurred in Gujarat is the most disastrous earthquake in India’s recent history. While the actual figures of death and injury remain uncertain, at least 20,000 people are feared dead and more than 200,000 injured. Nearly 400,000 houses were destroyed and twice as many dam- aged. Although damage of such proportion is astonishing, the occurrence of the event itself is not surprising, con- sidering the geologic and seismic history of the region. Two damaging earthquakes are known to have struck the Kutch Peninsula during the last two centuries, namely, the 1819 earthquake that killed more than 2000 people and wiped out several centres of human settlements in the Rann and the more recent event in 1956 that killed 115 people and damaged a large part of the town of Anjar. The 2001 earthquake has attracted tremendous attention from the national and international research community. Several study teams arrived within a week to study differ- ent aspects of this earthquake including the damage pat- tern, response of structures, field effects and aftershock activity. Uniqueness of its tectonic regime, especially the influence of an active plate boundary on the stress field and analogies with other intraplate earthquakes associated with ancient rift basins are issues that generated interest among the scientific community (see http://clifty.com/ hazard/archives.html). One aspect that adds to the uniqueness of the Bhuj event is its location in a region considered to be part of a stable continental region (SCR) that had generated an Mw 7.5 earthquake in 1819. Occurrence of another earth- quake of similar size within a short interval of time gives a rare opportunity to compare its effects with those gener- ated by the previous event. Such data are useful not only for the seismic hazard assessment in western India, but also in other regions of analogous geologic settings. Because of its exceptional geologic significance, a special session on this earthquake was organized at the 2001 Annual Meeting of the Seismological Society of America (San Francisco) and another one is planned for the spring meeting of the American Geophysical Union. The Kutch region is underlain by a Mesozoic rift system 1 . Faults within such rift systems are known to have the potential to generate large earthquakes 2 . In fact, the 1819 earthquake has been cited as one of the classic examples of SCR earthquakes in an ancient rift 2 . In a recent paper, Rajendran 3 noted that the Kutch rift can be differentiated from other SCR palaeorifts by its relative proximity to an active plate boundary, an important factor that influences its level of seismicity. In a forthcoming paper, Bendick et al. 4 have made some preliminary observations about the strain changes following this earthquake. In this paper we do not deal with these issues, but restrict our discussion to the post-seismic field observations and their implications on the mechanism of the earthquake. Tectonic setting and past seismicity The Kutch aulocogen owes its origin to Mesozoic tectonic events initiated during the break-up of Gondwanaland and the northward drift of the Indian plate. The rift basin evolved as a consequence of this break-up and was con- trolled by a series of normal faults, which are still # For correspondence. (e-mail: kusala@vsnl.com) RESEARCH ARTICLE