Chemical and Noble Gas Isotope Compositions of Formation Gases from a 3 km Deep Scientific Borehole in the Koyna Seismogenic Zone, Western India
(a) Map of the Koyna region showing the locations of the 1967 6.3 Koyna earthquake (red star) and the pilot borehole KFD1. The trace of the Donichawadi fissure zone (dashed lines), formed during 1967 earthquake [31, 40], and the study area (square) where the soil-helium surveys were conducted during 1996-1997 are also shown. Inset shows the location of Koyna within the Deccan Traps province (shaded green) on the outline map of India. (b) Map showing the coincidence of the helium anomalies established by soil-helium measurements along 12 traverses (AA, BB,…, LL) with coseismic en echelon fissures (thick lines) from the 1967 earthquake (Gupta et al. ).
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