43rd IAH Congress, Montpellier, France, 25 - 29 September 2016, pp.1973
The 23 October 2011 Van earthquake (Mw: 7.2) and aftershocks are the latest manifestations of active tectonics in the eastern Anatolian region, Turkey, that has been prevailing since the Miocene. In this study, we examine the relationship between the 2011 Van earthquake and temporal changes in CO2/3He and R/RA (R=(3He/4He)sample and RA= (3He/4He)atmosphere) values of geothermal waters in eastern Anatolia for the period of 2009-2011. For all samples, the difference between measured and air-corrected 3He/4He ratios is only minor (±0.1 RA). Air-corrected R/RA values of waters selected for the comparison are in the range of 0.93-6.36 for 2009 and 0.84-6.37 for 2011. Waters with high R/RA values are mostly discharged from geothermal springs around historically active/dormant volcanoes and major tectonic lines. Based on three-component mixing model for mantle, atmosphere and crust end-members, mantle-helium contributions to waters from the vicinity of Nemrut crater, Çaldıran fault zone and Diyadin region are 46-81%, 6-53% and 2-23%, respectively. Post-earthquake R/RA values and the proportion of mantle-He remained unchanged for samples around the Nemrut crater whilst those for Çaldıran springs increased and Diyadin waters decreased. CO2/3He ratios of most samples (ranging from 4.9 × 1010 to 6.8 × 1013) behaved in a more ambiguous manner possibly due to hydrothermal-related fractionation processes. Our findings show that the 2011 Van earthquake resulted in a change in the hydrogeologic system of the region along the Çaldıran fault zone at a distance of 58–60 km from the epicenter. The energy released by the 2011 earthquake facilitated reopening of fracture systems and formation of new fractures in the region which gave rise to volatile transfer from asthenospheric melts to the surface.