Browsing by Author "V.N. Neelakandan"

Now showing 1 - 2 of 2

A database on occurence patterns of unusual geological incidents in southwest Peninsular India and its implication on future seismic activity
(2005) N.H. Singh; J. Mathai; V.N. Neelakandan; D. Shankar; V.P. Singh
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 p henomenon 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. © 2005 Akadémiai Kiadó, Budapest.
Distribution patterns of natural radioactivity and delineation of anomalous radioactive zones using in situ radiation observations in Southern Tamil Nadu, India
(2007) H.N. Singh; D. Shanker; V.N. Neelakandan; V.P. Singh
In situ radiation measurements in the beach sectors and adjacent hinterlands and along rivers in the interiors of southern peninsular India were carried out using a portable radiation survey meter. A very high intrinsic anomalous radioactivity >26 μGy/h has been observed in the hinterlands within a fresh quarry and weathered boulders in the syenite rock body around Puttetti in the western Kanyakumari district of southern Tamil Nadu. Over the weathered hillocks in the hinterlands adjacent to the coast around Inayam, Kurumpanai and Midalam, the in situ radiation measurements have also exhibited high radioactivity ranging from 4 to 22 μGy/h which is significantly higher than the radiation exposure rates (RER) observed along the beach sectors at various locations from Chavara to Tuticorin (1-14 μGy/h). The observed radiation levels are presumably the highest concentration in southern India and it is the first time that such a high intrinsic radiogenic source in the hinterlands is reported in southwest coast of India. It is also observed based on the laboratory analysis of samples and in situ radiation data that the rivers/channels in this region contain insignificant level of radioactivity concentration and hence they do not contribute much to the placer deposits on the beaches. The placer deposits associated with significant RER (both in situ observations as well as laboratory estimates from samples) in the beach sectors from Kadiapattanam to Inayam are inferred to be derived through the country rocks/weathered hillocks in the immediate hinterlands. © 2006 Elsevier B.V. All rights reserved.