Acoustic evidence for shallow gas accumulations in the sediments of the Eastern Black Sea*

ABSTRACT The Black Sea contains immense gas accumulations. Exploration of gas accumulations is geologically and economically important because migration of methane in sediments may cause massive slope failures and the methane seeps may indicate deeper hydrocarbon reservoirs. Human activity both in and on the seafloor (oil industry) and natural activity (earthquakes, cyclones) trigger mechanisms for seafloor failure and gas release that may have a local and possibly global environmental impact. Recently, sonar and high‐resolution seismic surveys were carried out to obtain information about the effects of gas and gas‐filled sediments throughout the Turkish margin of the Eastern Black Sea, and shallow gas was detected on the subbottom profiler records. It continues about 25–65 m below the sea floor and is marked by bright and cloudy spots, sometimes pockmarks and acoustic voids. The lower section of the Turkish shelf is an extensive pockmarked plateau. The pockmarks are seen as circular structures with high backscattering on the sonar records.     

Modelling strain localization in granular materials using micropolar theory: numerical implementation and verification

Implementation and applications for a constitutive numerical model on F‐75 silica sand, course silica sand and two sizes of glass beads compressed under plane strain conditions are presented in this work. The numerical model is used to predict the stress versus axial strain and volumetric strain versus axial strain relationships of those materials; moreover, comparisons between measured and predicted shear band thickness and inclination angles are discussed and the numerical results compare well with the experimental measurements. The numerical model is found to respond to the changes in confining pressure and the initial relative density of a given granular material. The mean particle size is used as an internal length scale. Increasing the confining pressure and the initial density is found to decrease the shear band thickness and increase the inclination angle. The micropolar or Cosserat theory is found to be effective in capturing strain localization in granular materials. The finite element formulations and the solution method for the boundary value problem in the updated Lagrangian frame (UP) are discussed in the companion paper. Copyright © 2006 John Wiley & Sons, Ltd.     

Development of a three-dimensional basin model to evaluate the site effects in the tectonically active near-fault region of Gölyaka basin,Düzce,Turkey

Natural Hazards - The high seismicity and tectonic activity of the study area located in a near-fault region in Gölyaka, Düzce, results in a bedrock geometry highly complex in the sense...     

Correlations of SMR-Qslope Data in Stability Classification of Discontinuous Rock Slope: A Modified Relationship Considering the Iranian Data

Geotechnical and Geological Engineering - The preliminary responses on stability assessment are very effective in discontinuous rock slope stabilisations, which geo-mechanical empirical...     

PSHA of Van province for performance assessment using spectrally matched strong ground motion records

Within the framework of the performance based earthquake engineering, site specific earthquake spectra for Van province has been obtained. It is noteworthy that, in probabilistic seismic hazard assessment, as a first stage data from geological studies and records from the instrumental period were compiled to make a seismic source characterization for the study region. The probabilistic seismic hazard curves were developed based on selected appropriate attenuation relationships, at rock sites, with a probability of exceedance 2, 10 and 50% in 50 yrs period. The obtained results are compared with the spectral responses proposed for seismic evaluation and retrofit of building structure in Turkish Earthquake Code (2007), section 7. The acceleration response spectrums obtained from probabilistic seismic hazard analysis are matched to adjust earthquake accelerograms recorded during the 2011 Van earthquakes by using SeismoMatch v2.0 software. The aim of this procedure is to obtain a set of reasonable earthquake input motions for the seismic evaluation of existing buildings.     

Spatiotemporal patterns of sediment transport rate and beach–ocean profile for multi-hazard risk management

Natural Hazards - Many parameters, interacting differently in time and space, affect a long-shore hydrological and marine ecosystem model, and the water resource management advancement is highly...     

GIS based analysis of doline density on Taurus Mountains,Turkey

The Taurus Mountain is one of the most important karstic region of the world and dolines are characteristics landforms of this area. However, the number and distribution of doline are unknown in the study area. The aims of this study are to explain the total number of dolines, distribution of doline density, effects of slope conditions and the change of doline orientation in the Taurus Mountains. According to the 1/25000 scale topographic maps utilized in this study, a total of 140,070 dolines were determined in a 13,189 km² area on eleven high karstic plateaus bordered by steep slopes and deep gorges. These plateaus are substantially affected by highly-faulted and jointed systems and about 80% of each plateau is covered with neritic limestone. The dolines are located at an elevation between 10 and 2870 m. Average elevation of all dolines is 1842 m. 90% of dolines are located between 1300 and 2270 m and only 5% of dolines found under 1330 m. According to this results, the densest doline zone corresponds to the alpine and periglacial zone above the treeline. Doline density reaches?>?100 doline/km² on Mt. Anamas and the Seyran, Geyik and Akda? ranges as well as the Ta?eli plateau. Maximum density (187 doline/km²) is found on the Akda? Mountains. However, 66% of the study area is characterized by low density, 29.9% with moderate density, 3.4% with high density and 0.7% with very high density. The highest doline densities are seen on gentle slopes (15°–25°/km²) and steep slopes (>?35°/km²) are limited doline distribution. According to the rose diagram formed by the azimuths of the long axis of the dolines at the Central Taurus, two direction are dominant in doline orientations (NW–SE and NE–SW). However, dominant directions are NE-SW at eastern, NE–SW and NW–SE at central and NW-SE at western part of the Central Taurus. According to this elongations, doline orientations are formed an arc which is formed by tectonic evolution of the Central Taurus.     

Re-evaluations of seismic hazard of Iraq

In recent years, Iraq has experienced an increase in seismic activity, especially, near the east boundary with Iran. Previous studies present their results in terms of PGA and for return periods of 500 years and less, and other studies not continued to include the whole PSHA process whereas some recent studies continued to include the whole PSHA process using earthquakes data till 2009 including dependent events. This study includes two main stages, the first is collecting the earthquakes records including the recent events till the end of March 2016 and applying data processing to get the net catalog to independent events. The second stage is applying the steps of PSHA method. Matlab programs have been built to execute these two stages and to convert the results of PSHA computations into contours of 5% damping PGA and spectral accelerations at 0.2 and 1.0 s for a return period of 2475 years, and for rock sites. Also, spectral acceleration against period has been presented for main cities. Also, the PGA map, for a return period of 475 years, has been plotted and then prepared together with similar maps of neighbor countries in one map for comparison. In general, this comparison indicates the similarity in behavior but, the values reveal a relative agreement and they are between Turkish and Iranian values.     

Paleoproterozoic Nb-enriched meta-gabbros in the Quanji Massif,NW China:Implications for assembly of the Columbia supercontinent

Diverse models have been proposed for the role of the Tarim Craton within the Paleoproterozoic Columbia supercontinent assembly. Here we report a suite of-1.71 Ga Nb-enriched meta-gabbro lenses in the eastern Quanji Massif, within the Tarim Craton in NW China. The meta-gabbroic rocks have Nb contents of 11.5-16.4 ppm with Nb/La ratios varying from 0.84 to 1.02((Nb/La)_N = 0.81-0.98) and Nb/U ratios from 38.0 to 47.2. They show low SiO_2(45.1-48.5 wt.%) and MgO(5.96-6.81 wt.%) and Mg#(Mg# = Mg/(Mg + Fe) = 43.5-47.7), high FeO~t(13.0-15.7 wt.%) and moderate Ti02(1.70-2.51 wt.%).with tholeiitic affinities. These rocks possess low fractionated REE patterns without obvious Eu anomalies(Eu/Eu~* = 0.87-1.02). Their primitive mantle-normalized elements patterns display significant Zr-Hf troughs, positive Nb anomalies, weak negative Ti and P anomalies, and high contents of Rb and Ba,resembling Nb-enriched basalts generated in arc-related tectonic settings. Their arc-like geochemical signatures together with whole rock εNd(t) values of 0.4-2.1 and corresponding old T_(DM)(2.22-2.37 Ga)as well as(~(143)Nd/~(144)Nd)_t and(~(87)Sr/~(86)Sr)t(t = 1712 Ma) values of 0.5104-0.5105 and 0.7030-0.7058,respectively, suggest that their precursor magma originated from mantle wedge peridotite metasomatised by subduction-derived melts. The results from our study reveal subduction along the eastern periphery of the Tarim Craton and marginal outgrowth continuing to ~1.7 Ga within the Columbia supercontinent.     

Formation of the Upper Pleistocene terraces of Lake Van (Turkey)

Sedimentological and geomorphological studies of terraces around Lake Van (1647 m) provided a preliminary framework for lake‐level variations. The elevations of terraces and past lake level were measured with a differential global positioning system. A chronology is developed using ²³⁴U/²³⁰Th dating of travertines, ³⁹Ar/⁴⁰Ar dating of pyroclastites and ¹⁴C dating of organic matter. Facies and stratigraphic correlations identify four transgressions (C1′, C1″, C2′ and C2″), each followed by a regression which ended with low lake levels that caused river incision and terrace formation. Evidence of the oldest transgression (C1′) is found in the uppermost reaches of valleys up to 1755 m, an altitude higher than the present lake threshold (1736 m). This C1′ transgression may be related to pyroclastic flows which dammed an outlet located in the western part of the lake basin and which is dated to before 105 ka. After 100 ka, a second transgression (C1″) reached 1730/1735 m, possibly related to a younger ignimbrite flow, in association with high water inflow (warm and/or wetter conditions). The two younger transgressions reached 1700–1705 m. The first one (C2′) is dated to 26–24.5 cal. ka BP and the second one (C2″) to 21–20 cal. ka BP. Available data suggest that the long‐term lake‐level changes responded mainly to climate oscillations. Additional events such as river captures caused by volcanic falls filling valleys, tectonism, erosion and karstic diversion may have impacted these long‐term lake‐level changes. Copyright © 2010 John Wiley & Sons, Ltd.