Post-earthquake anomalies in He–CO2 isotope and relative abundance systematics of thermal waters: The case of the 2011 Van earthquake, eastern Anatolia, Turkey

We report the helium and carbon isotope (He-3/He-4, delta C-13) and relative abundance (CO2/He-3) characteristics of hydrothermal gases from eastern Anatolia sampled similar to 1 month after the October 23, 2011 Van earthquake (Mw: 7.2, focal depth: 19 km). Seven sites were sampled which comprise three localities along the Caldiran Fault Zone, at a distance of 58-66 km to the epicenter (Group I), two localities north of the Caldiran Fault, about 90-113 km from the epicenter (Group II), and two localities in the vicinity of the historically-active Nemrut Caldera at a distance of 110-126 km from the epicenter (Group III). All sites were previously sampled for their He-CO2 systematics in 2009 (Mutlu et al., 2012) facilitating direct comparison with the post-earthquake dataset. The post-earthquake values cover a wide range of He-3/He-4, delta C-13 and CO2/He-3 ratios, from 0.84 to 6.37 RA (where RA = air He-3/He-4), -5.30 to + 0.49% (vs. VPDB), and 4.9 x 10(10) to 6.85 x 10(13), respectively. Group I samples show a consistent post-earthquake increase in He-3/He-4 whereas both Group II localities decreased in He-3/He-4. No change was recorded for the two Group III localities. He isotope variations are consistentwith simple changes in the proportions of mantle and crustal volatiles, with all Group I sites showing an increase in the mantle He contribution. We hypothesize that the enhanced mantle He signal is derived from asthenospheric melts intruded into the crust, with seismic perturbations responsible for bubble formation and growth leading to overpressure and gas loss. The strike-slip Caldiran Fault Zone provides the permeable pathway for the liberated volatiles to reach hydrothermal systems at shallow levels of the crust and the surface. Release of crustal He dominates the He mass balance of Group II samples as locations are further from the earthquake epicenter. Group III samples are even further away from the earthquake and show no perturbations in He isotopes. Whereas binary mixing dominates the He isotope systematics, CO2 shows additional effects involving the hydrothermal system. Consequently, changes in the balance between mantle and crustal CO2 are masked and more difficult to discern. The results emphasize the sensitivity of He isotopes to seismic perturbations in the crust and illustrate how location of sampling sites - on permeable segments of faults - and distance from seismic events influence resulting changes involving gas chemistry

Examination of the kinematic structures in İzmir (Western Anatolia) with repeated GPS observations (2009, 2010 and 2011)

The Western Anatolia and the Aegean Sea regions are one of the most significant seismically active and rapidly deforming fields in the world. Generally, seismic activities cause deformations and these deformations are monitored with Global Positioning System (GPS) /Global Navigation System (GNSS). In this context, GPS data were used to determine the deformation of Izmir and its surrounding to estimate the relative plate motions. In this study, the kinematic structures of the faults, which control the seismic hazard in Izmir and its surroundings, processing results of the three-year (2009, 2010 and 2011) episodic GPS observations and the estimation of displacements for 21 GPS stations were presented. The aim of this study is to examine interplate motion of the stations and their relations with the tectonic structures, seismicity and paleomagnetism and additionally, to interprete the motions of the study area relative to different block motions. Consequently, the mean motion of the study area was found approximately 25 mm/yr (towards the SSW) in the Eurasia fixed frame solution. The Aegean block fixed frame and the Anatolian block fixed frame solutions were computed relative to Euler vectors. In Aegean and Anatolian block solutions it was determined that the stations move separately, not as a group. In Euler pole solution, some stations are separated from each other and meanwhile some stations are grouped by considering the differences and similarities of the station motions. According to this solution three lines and two regions were described in the study area. The relations between seismicity and paleomagnetic studies and the kinematic structures determined in Anatolian block fixed frame and Euler pole solution were also investigated. When the Anatolian block fixed frame solution and the earthquakes occurred between the years 1973 and 2011 were evaluated together, it was found that in the high seismically active region especially near to Sigacik bay, the motions of GPS stations were different even though their locations were close to each other. As a result of this, the relationship between the vector directions and active tectonism was determined. Additionally, in the Euler pole solution directions of the motion were found to be coherent with the paleomagnetic results, particularly in Urla and its surroundings. Here, the block fixed frame and Euler pole solutions and additionally, relations of them with seismicity and tectonism were mentioned as difference from previous studies. Besides, in this study, high importance was given to locate each station in main geological formations of the study area. (C) 2016 Elsevier Ltd. All rights reserved

Slip distribution and source parameters of the 20 July 2017 Bodrum-Kos earthquake (Mw6.6) from GPS observations

© 2017 The Author(s). Greek-Turkish boundary near the cities Kos and Bodrum has been shaken on July 20, 2017 by a Mw6.6 earthquake. The mainshock is located offshore and did not generate an on-land surface rupture. Analyzing pre- and post-earthquake continuous/survey-type static GPS observations, we investigated co-seismic surface displacements at 20 sites to characterize source parameters and slip-distribution of the mainshock. Fault plane solutions as well as co-seismic slip distribution have been acquired through the inversion of co-seismic GPS displacements modeling the event as elastic dislocations in a half space. Fault plane solution shows a southward dipping normaltype fault segment extending a depth down to ~12 km, which remains within the brittle upper crust. Results from the distributed slip inversion show that the mainshock activated a ~65 km fault section, which has three high slip patches, namely western, central and eastern patches, where the coseismic slips reach up to 13, 26, and 5 cm, respectively. This slip pattern indicates that the pre-earthquake coupling, which is storing the slip deficit, occurred on these three patches