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Ankara, Turkey

Duman T.Y.,General Directorate of Mineral Research and Exploration | Can T.,Cukurova University | Emre O.,Fugro | Kadirioglu F.T.,AFAD | And 15 more authors.
Bulletin of Earthquake Engineering | Year: 2016

Turkey is located in one of the most seismically active regions in the world. Characterizing seismic source zones in this region requires evaluation and integration of geological, geophysical, seismological and geodetical data. This first seismotectonic database for Turkey presented herein was prepared, under the framework of the National Earthquake Strategy and Action Plan—2023. The geographic information system (GIS)-based database includes maps of active faults, catalogues of instrumental and historical earthquakes, moment tensor solutions and data on crustal thickness. On the basis of these data, 18 major seismotectonic zones were delineated for Turkey and the surrounding region. The compilation and storage of the seismotectonic data sets in a digital GIS will allow analyses and systematic updates as new data accrete over time. © 2016 Springer Science+Business Media Dordrecht

Woith H.,Helmholtz Center Potsdam | Parolai S.,Helmholtz Center Potsdam | Boxberger T.,Helmholtz Center Potsdam | Picozzi M.,University of Naples Federico II | And 4 more authors.
Journal of Applied Geophysics | Year: 2014

We report on the application of seismic noise investigations, including H/V (horizontal to vertical) spectral ratio and array techniques, to a shallow gas-rich geothermal reservoir in Heybeli, southwestern Turkey. Fundamental resonant frequencies were determined to estimate the sediment thickness. Using small-scale seismic arrays, phase velocity dispersion curves were derived by correlating noise recordings according to the extended spatial autocorrelation method. Improved shear wave velocity profiles were estimated by combining Rayleigh wave dispersion curves and horizontal to vertical spectral ratios in a joint inversion. We found that the velocities obtained for the reservoir site are higher than those for a location outside the reservoir. In addition to the fundamental resonant peaks in the spectra, a clear 6-Hz-signal could be identified originating from the center of the geothermal field, repeatedly observed in 2010 and 2011. It had been claimed that low frequency (1-10. Hz) seismic signal anomalies were correlated with the occurrence of hydrocarbons. One of the physical mechanisms under consideration to explain these tremor-like signals above such reservoirs is resonant amplification due to the oscillation of bubbles. Based on the signal similarity with volcanic tremors, it is not a priori given that the liquid phase must be oil for resonance effects to occur. We therefore applied array techniques to identify potential noise originating from the Heybeli reservoir. In fact, the frequency-wavenumber (f- k) method clearly indicated a noise source coming from the main production well of the reservoir. In 2011, as part of our assessment, the operators of the spa facility stopped the extraction of thermal water for 2. h: the 6-Hz-signal disappeared after the pump had been stopped and reappeared after the pump began operating again. Thus, the 6-Hz-signal is likely of artificial origin. In addition, no natural noise source inside the reservoir could be identified. © 2014 Elsevier B.V.

Akca I.,Ankara University | Ozturk Akca C.,AFAD
8th Congress of the Balkan Geophysical Society, BGS 2015 | Year: 2015

An adaptive model parameterization methodology is used to develop a two dimensional inversion scheme for the direct current resistivity data. Adaptation is realized by a two stage inversion algorithm. The inverted model after the first stage of inversion is clustered to distinguish the target anomalies and the background. In the second stage a new parameter grid is formed by refining the model cells corresponding to the target bodies or structures. This methodology is well suited for the targets such as archaeological ruins, embedded bodies (tanks, bunkers) and cavities. A test with a synthetic data set is carried out to demonstrate the efficiency of the developed method. Results showed that algorithm is able to recover the subsurface image with more detail in comparison with the inversion results of the regular model mesh.

Prevedel B.,Helmholtz Center Potsdam | Bulut F.,Helmholtz Center Potsdam | Bulut F.,TUBITAK - Marmara Research Center | Bohnhoff M.,Helmholtz Center Potsdam | And 5 more authors.
International Journal of Earth Sciences | Year: 2015

Downhole sensors of different types and in various environments provide substantial benefit to signal quality. They also add the depth dimension to measurements performed at the Earths’ surface. Sensor types that particularly benefit from downhole installation due to the absence of near-surface noise include piezometers, seismometers, strainmeters, thermometers, and tiltmeters. Likewise, geochemical and environmental measurements in a borehole help eliminate near-surface weathering and cultural effects. Installations from a few hundred meter deep to a few kilometer deep dramatically reduce surface noise levels—the latter noticeably also reduces the hypocentral distance for shallow microearthquakes. The laying out of a borehole network is always a compromise of local boundary conditions and the involved drilling costs. The installation depth and procedure for a long-term downhole observatory can range from time limited installations, with a retrieval option, to permanently cemented sensors. Permanently cemented sensors have proven to be long-term stable with non-deteriorating coupling and borehole integrity. However, each type needs to be carefully selected and planned according to the research aims. A convenient case study is provided by a new installation of downhole seismometers along the shoreline of the eastern Marmara Sea in Turkey. These stations are being integrated into the regional net for monitoring the North Anatolian Fault Zone. Here we discuss its design, installation, and first results. We conclude that, despite the logistical challenges and installation costs, the superior quality of downhole data puts this technique at the forefront of applied and fundamental research. © 2015, The Author(s).

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