Assessment of rock slope stability with the effects of weathering and excavation by comparing deterministic methods and slope stability probability classification (SSPC)

Cut slopes are prone to fail due to the disturbance on original geometry and strength. In addition, because of these disturbances and stress relief, natural apertures which increase the weathering effects widen in engineering time. Owing to these reasons, slope stability assessment has a prominent role on these road cuts. Generally, slope stabilities are assessed by deterministic approaches with a significant engineering judgment. Because of this reason the reputation of probabilistic approaches is increasing. In this study, 20 road cuts located in North West Black Sea region of Turkey were evaluated using slope stability probability classification (SSPC). Considering this probabilistic approach, rock strength parameters and failure mechanisms were determined. Furthermore, slope mass rating (SMR) classification was applied for each road cut in order to compare with the results obtained from SSPC. These overall results were then evaluated with the field observations considering rockslope deterioration assessment (RDA) and Falling Rock Hazard Index (FRHI) for the disturbed/weathered zones, and failure mechanisms. According to these, SSPC is found to be more accurate for surficial degradations (raveling and fall) using samples taken from the disturbed/weathered zones rather than using relatively fresh samples beyond the disturbed zone. Moreover, despite strength differences between weathered and relatively fresh zones, SMR classification is identified to reveal the same stable probabilities. It is found that SSPC shows more detailed probabilistic results than SMR. Lastly, rockfall and raveling mechanisms determined by RDA and rockfall risk by FRHI were found to be coherent with SSPC and field observations.     

Upper Palaeozoic subduction/accretion processes in the closure of Palaeotethys: Evidence from the Chios Melange (E Greece), the Karaburun Melange (W Turkey) and the Teke Dere Unit (SW Turkey)

During Late Palaeozoic time a wide ocean, known as Palaeotethys, separated the future Eurasian and African continents. This ocean closed in Europe in the west during the Variscan orogeny, whereas in Asia further east it remained open and evolved into the Mesozoic Tethys, only finally closing during Late Cretaceous–Early Cenozoic.Three Upper Palaeozoic lithological assemblages, the Chios Melange (on the Aegean Greek island), the Karaburun Melange (westernmost Aegean Turkey) and the Teke Dere Unit (Lycian Nappes, SW Turkey) provide critical information concerning sedimentary and tectonic processes during closure of Palaeotethys. The Chios and Karaburun melanges in the west are mainly terrigenous turbidites with blocks and dismembered sheets of Silurian–Upper Carboniferous platform carbonate rocks (shallow-water and slope facies) and poorly dated volcanic rocks. The Teke Dere Unit to the southeast begins with alkaline, within-plate-type volcanics, depositionally overlain by Upper Carboniferous shallow-water carbonates. This intact succession is overlain by a tectonic slice complex comprising sandstone turbidites that are intersliced with shallow-water, slope and deep-sea sediments (locally dated as Early Carboniferous). Sandstone petrography and published detrital mineral dating imply derivation from units affected by the Panafrican (Cadomian) and Variscan orogenies.All three units are interpreted as parts of subduction complexes in which pervasive shear zones separate component parts. Silurian–Lower Carboniferous black cherts (lydites) and slope carbonates accreted in a subduction trench where sandstone turbidites accumulated. Some blocks retain primary depositional contacts, showing that gravitational processes contributed to formation of the melange. Detached blocks of Upper Palaeozoic shallow-water carbonates (e.g. Chios) are commonly mantled by conglomerates, which include water-worn clasts of black chert. The carbonate blocks are restored as one, or several, carbonate platforms that collided with an active margin, fragmenting into elongate blocks that slid into a subduction trench. This material was tectonically accreted at shallow levels within a subduction complex, resulting in layer-parallel extension, shearing and slicing. The accretion mainly took place during Late Carboniferous time.Alternative sedimentary-tectonic models are considered in which the timing and extent of closure of Palaeotethys differ, and in which subduction was either northwards towards Eurasia, or southwards towards Gondwana (or both). Terrane displacement is also an option. A similar (but metamorphosed) accretionary unit, the Konya Complex, occurs hundreds of kilometres further east. All of these units appear to have been assembled along the northern margin of Gondwana by Permian time, followed by deposition of overlying Tauride-type carbonate platforms. Northward subduction of Palaeotethys beneath Eurasia is commonly proposed. However, the accretionary units studied here are more easily explained by southward subduction towards Gondwana. Palaeotethys was possibly consumed by long-lived (Late Palaeozoic) northward subduction beneath Eurasia, coupled with more short-lived (Late Carboniferous) southward subduction near Gondwana, during or soon after closure of Palaeotethys in the Balkan region to the west.     

Lutetian arc-type magmatism along the southern Eurasian margin: New U-Pb LA-ICPMS and whole-rock geochemical data from Marmara Island, NW Turkey

The rocks of Turkey, Greece and Syria preserve evidence for the destruction of Tethys, the construction of much of the continental crust of the region and the formation of the Tauride orogenic belt. These events occurred between the Late Cretaceous and Miocene, but the detailed evolution of the southern Eurasian margin during this period of progressive continental accretion is largely unknown. Marmara Island is a basement high lying at a key location in the Cenozoic Turkish tectonic collage, with a Palaeogene suture zone to the south and a deep Eocene sedimentary basin to the north. North-dipping metamorphic thrust sheets make up the island and are interlayered with a major metagranitoid intrusion. We have dated the intrusion by Laser Ablation ICP-MS analysis of U and Pb isotopes on zircon separates to 47.6?±?2 Ma. We also performed major- and trace-elemental geochemical analysis of 16 samples of the intrusion that revealed that the intrusion is a calc-alkaline, metaluminous granitoid, marked by Nb depletion relative to LREE and LIL-element enrichment when compared to ocean ridge granite (ORG). We interpret the metagranitoid sill as a member of a mid-Eocene magmatic arc, forming a 30 km wide and more than 200 km long arcuate belt in NW Turkey that post-dates suturing along the ?zmir-Ankara-Erzincan Suture zone. The arc magmatism was emplaced at the early stages of mountain building, related to collision of Eurasia with the Menderes-Taurus Platform in early Eocene times. Orogenesis and magmatism loaded the crust to the north creating coeval upward-deepening marine basins partially filled by volcanoclastic sediments.     

Magnetic susceptibility and VLF-R investigations for determining geothermal blowout contaminated area: a case study from Alaşehir (Manisa/Turkey)

Western Turkey is one of the most spectacular regions of widespread, active continental extension in the world. The most prominent structures of this region are E–W trending Gediz and Büyük Menderes Grabens. Geothermal activity around city of Manisa in Gediz Graben has been investigated by many researchers and many geothermal boreholes were drilled in order to produce electricity. In the middle of May 2012, a geothermal blowout occurred 150 m away from the deep drilling (depth 1,100 m), in Alkan village of Ala?ehir resort in city of Manisa. After that, four big blowouts took place at the same area and thermal water had been diverted to Alkan stream for almost 4 months. The boron (B) and Fe levels of thermal water are 87 and 11.2 ppm where the background B and Fe values of topsoil vary between 0.2–1.5 ppm and 3.08–5.63 ppm, respectively. The objective of this study was to utilize joint magnetic susceptibility and VLF-R investigations to determine possibly contaminated area with B, related to high Fe level on the topsoil and thermal water in the subterranean layers. It is observed that magnetic susceptibility values vary between 500 and 790 cgs (×10^?6) in the vicinity of blowouts and 150–340 cgs (×10^?6) at a distance of 50 m around, where the background average value is 20 cgs (×10^?6), by using the data collected at 346 stations. Besides, the VLF-R studies were carried out along 18 profiles at three different frequencies. Laterally constrained two-layer inversion was applied to each station; in addition to the inversion of all profiles for each frequency, all lines were stacked, 2-D resistivity maps were obtained, and the contaminated area was determined approximately as 35,000 m². The results show not only satisfactory agreement between magnetic susceptibility and VLF-R data, but also provide fast and valued interpretation of geochemical and geophysical properties of the geothermal contaminated area.     

Radio frequency interference measurements in Indonesia

We report the first measurements of radio frequency spectrum occupancy performed at sites aimed to host the future radio astronomy observatory in Indonesia. The survey is intended to obtain the radio frequency interference (RFI) environment in a spectral range from low frequency 10 MHz up to 8 GHz. The measurements permit the identification of the spectral occupancy over those selected sites in reference to the allocated radio spectrum in Indonesia. The sites are in close proximity to Australia, the future host of Square Kilometre Array (SKA) at low frequency. Therefore, the survey was deliberately made to approximately adhere the SKA protocol for RFI measurements, but with lower sensitivity. The RFI environment at Bosscha Observatory in Lembang was also measured for comparison. Within the sensitivity limit of the measurement equipment, it is found that a location called Fatumonas in the surrounding of Mount Timau in West Timor has very low level of RFI, with a total spectrum occupancy in this measured frequency range being about 1 %, mostly found at low frequency below 20 MHz. More detailed measurements as well as a strategy for a radio quiet zone must be implemented in the near future.     

Seasonal variations in methane concentrations and diffusive fluxes in the Curonian and Vistula lagoons,Baltic Sea

Expected seasonal variations in methane concentrations and diffusive fluxes from surficial sediments into near-bottom waters were investigated in autumn 2012 and winter 2013 in the Curonian and Vistula lagoons of the Baltic Sea, expanding on earlier findings for summer 2011. Methane concentrations in bottom sediments (upper ca. 2 cm) generally ranged from ca. 1 to 1,000 μmol/dm³, and in near-bottom waters from ca. 0 to 1 μmol/l. Highest concentrations were found in the Curonian Lagoon, plausibly explained by the influence of freshwater conditions and finer-grained, organic-rich sediments. Vistula Lagoon methane concentrations and fluxes are dampened by periodic saline water inflow from the open sea, intensifying sulphate reduction. Calculated diffusive methane fluxes from the upper sediment layer (usually 0–5 cm, i.e. excluding any fluffy layer) into near-bottom waters were highest—2.48 mmol/(m² day)—in clayey silts of the Curonian Lagoon in autumn (September) 2012, contrasting strongly with the minimum value of 0.002 mmol/(m² day) observed there in February 2013 under ice-covered conditions. Seasonal and even weekly variations in methane dynamics can be largely explained by two main drivers, i.e. wind and temperature, operating at various spatiotemporal scales via, for example, wind wave-induced resuspension of bottom sediments, and involving regional weather patterns including autumnal low-pressure zones over the Gulf of Gdansk.     

Discrete fracture model for simulating waterflooding processes under fracturing conditions

In our study, we develop a model for simulating fracturing processes in a poroelastic medium. The proposed approach combines the discrete fracture model enriched with contact plane mechanics. The model captures mechanical interactions of fractures and a deformable medium, fluid, and heat transfer in fractures and in a porous medium. Both effects of poroelasticity and thermoelasticity are accounted in our model. Mass and heat conservation equations are approximated by the finite volume method, and mechanical equilibrium equations are discretized by means of the Galerkin finite element approach. Two‐dimensional grid facets between 3‐dimensional finite elements are considered as possible fracture surfaces. Most of these facets are inactive from the beginning and are activated throughout the simulation. A fracture propagation criterion, based on Irwin's approach, is verified on each nonlinear iteration. When the criterion is satisfied, additional contact elements are added into finite element and discrete fracture model formulations respectively. The proposed approach allows modeling of existing natural and artificially created fractures within one framework. The model is tested on single‐ and multiple‐phase fluid flow examples for both isothermal and thermal conditions and verified against existing semianalytical solutions. The applicability of the approach is demonstrated on an example of practical interests where a sector model of an oil reservoir is simulated with different injection and production regimes.     

Erratum to: New paleomagnetic results from Upper Cretaceous arc-type rocks from the northern and southern branches of the Neotethys ocean in Anatolia

International Journal of Earth Sciences -     

CSAMT investigations of the Caferbeyli (Manisa/Turkey) geothermal area

Journal of Earth System Science - Western Turkey is one of the most remarkable regions of very active continental extension in the world. The most significant structures of this region are...