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Strong anomalies in the concentration of helium, radon and gamma were observed in gases at the geochemical monitoring station, Bakreswar, West Bengal, India, about two weeks before the 7.9 M earthquake at Sichuan, China. The distance between the epicenter of the earthquake and the monitoring site is about 1800 km. This long distance preseismic observation indicates that the radius of influence of large magnitude earthquakes may be substantially large and may cut across plate boundaries. This paper presents the observed geochemical anomalies for the Sichuan earthquake and discusses empirical postulates between earthquake magnitude and its radius of influence.

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Acta Geodaetica et Geophysica Hungarica
Authors: H. Chaudhuri, D. Ghose, R. Bhandari, P. Sen, and B. Sinha

Helium was first observed in the sun and subsequently much later on the earth. Starting from the early days of its discovery, helium continues to be entwined with the Indian scientific scenario in more ways than one. The element thus has a special charm and significance to the currently emerging situation where it is applied to solve problems in the exceptionally challenging field of tracing the formation of earthquakes and anticipating its occurrence. The present article delves into some of the broader aspects of the problem through a historical approach. The paper also deals with the statistical analysis of the pre-seismic geochemical (He and 222Rn) anomalies recorded at our existing field site laboratories ahead of some major earthquakes that occurred in and around India. A description of the experimentally recorded geochemical (He, F, Cl, SO 4 −− , and B) and geophysical (temperature, pH, conductivity) characteristics of some thermal springs of north and north-east India is included. A dedicated mass spectrometer analyzed intensities of 3He and 4He in air sample made in our laboratory and implication of the pre-seismic enhancement of 3He/4He ratios measured in thermal spring gases is briefly discussed.

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