Geoseismological investigation of the January 26, 2001 Bhuj earthquake in western peninsular India

Abstract

Of the intraplate seismic events, the January 26, 2001 Bhuj earthquake (Mw 7.7) would be remembered as one of the deadliest, in which 13,805 human lives were lost, 0.177 million injured and a total of 1,205,198 houses were fully or partly damaged in 16 districts of Gujarat state with an estimated overall loss of Rs. 284, 23 million. The brunt of the calamity was borne by five districts, namely Kachchh, Ahmadabad, Rajkot, Jamnagar and Surendranagar, where 99 % of the total casualties and damage occurred. In the neighbouring parts of Sindhh Province of Pakistan, 40 human casualties were reported, and some buildings cracked in the Karachi city as well. In the Kachchh district of Gujarat state, the telecommunication links and power supply were totally disrupted, road and rail links partially impaired and water supply snapped at many places. The Bhuj airbase had to be closed for some time due to damage to the infrastructure. The macroseismic survey carried out by the Geological Survey of India in an area as large as 1.2 million sq km indicated an epicentral intensity as high as X on the MSK scale in an area of 780 sq km in the central part of Kachchh rift basin. Apart from damages to civil structures, the January 26 earthquake induced conspicuous terrain deformation in the form of liquefaction features, structural ground deformation and low-order slope failures that were mainly prevalent within the higher intensity isoseists. Liquefaction occurred in an area of about 50,000 sq km. The extensive plains of Rann of Kachchh, the marshy tracts of the Little Rann and the shallow groundwater table zones of Banni Land provided the most conducive geotechnical environments for the development of seismites. The liquefaction activity was profuse in seismic intensity zones X and IX, widespread in intensity VIII, subdued in intensity VII and stray in intensity VI. The common forms of liquefaction were sand blows/boils, ground fissures, craters, lateral spreading and slumping. Ground deformation of tectonic origin was witnessed in the epicentral tract. Such features, though much less subdued in comparison with the 1819 large earthquake (Mw 7.8) in region, occurred along the Kachchh Mainland fault (KMF) and along a transverse lineament, referred to as Manfara–Kharoi fault. The manifestations were in the form of fractures, displacement of strata, linear subsidence, upheaval, formation of micro-basins/micro-ridges, ripping off of rock surface, and at places violent forms of liquefaction. The localities where coseismic deformations were observed include Bodhormora, Sikra, Vondh, Chobari, Manfara and Kharoi. The 2001 event has demonstrated the role of local geology in influencing the ground motion characteristics and, therefore, the hazard estimation.