A database on occurrence patterns of unusual geological incidents in southwest Peninsular India and its implication on future seismic activity

Singh, N. H. and Mathai, J. and Neelakandan, V. N. and Shankar, D. and Singh, V. P. (2005) A database on occurrence patterns of unusual geological incidents in southwest Peninsular India and its implication on future seismic activity. Acta Geodaetica et Geophysica Hungarica, 40 (1). pp. 69-88. ISSN 1217-8977

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Abstract

A series of unusual geological incidents have occurred throughout the Kerala State (southwest Peninsular India) during the year 2001 mainly in two active phases i.e. February to March, and June to November 2001. In the beginning during February-March 2001, oscillations and rise in water levels, wavy formations and spouting up of water in the open wells, cracks in the buildings, perceptible ground fissures, shaking of trees/bushes and enhanced microearthquake activity have occurred. Collapse of shallow open wells, draining of water, lowering of water level, land subsidence, ground fissures etc., and further increased microearthquake activity were the dominant incidents in various parts of the State during June to November 2001. Interestingly, no such incidents had occurred in the past in this region. The frequency of all the above incidents, including microearthquakes activity, reduced drastically to background level beyond November 2001 except a few earthquakes during 2002 and 2003. The incidents are distributed in a vast area irrespective of geology and topography right from coastal stretch to hinterlands in the Western Ghats of India. This chain of incidents was preceded by two moderate size earthquakes of M ~ 5 on 12 December 2000 and 7 January 2001 which were not capable to trigger such widespread incidents in the region. The temporal patterns of these incidents clearly indicate the phenomenon of rapid ground vibrations at several occasions possibly due to movement of crustal block along certain active fault. This geological process perhaps lead to uplift and tilt of the ground giving rise to several underground water related anomalies and incidents of land deformations. The temporal patterns of individual incident also did not show any clear inter-relationships indicating that all these incidents were caused by a single internal geological process possibly due to converging trend of tectonic stress through the process of redistribution. It is inferred that these incidents constitute a well defined patterns of precursory sequence to a future large seismic activity in the southwest part of Peninsular India. The existence of the present chain of events can be explained by dilatancy diffusion model. Using the spatial distribution of these incidents including microearthquake activity and past significant earthquakes, an east-west trending potential area (10.7-10.9°N; 76.0-76.8°E) is delineated in the central Kerala region as the preparatory zone for the location of future earthquake.

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