The Manyas fault zone (southern Marmara region,NW Turkey): active tectonics and paleoseismology

The Manyas fault zone (MFZ) is a splay fault of the Yenice Gönen Fault, which is located on the southern branch of the North Anatolian Fault System. The MFZ is a 38 km long, WNW–ESE-trending and normal fault zone comprised of three en-echelon segments. On 6 October 1964, an earthquake (Ms = 6.9) occurred on the Salur segment. In this study, paleoseismic trench studies were performed along the Salur segment. Based on these paleoseismic trench studies, at least three earthquakes resulting in a surface rupture within the last 4000 years, including the 1964 earthquake have been identified and dated. The penultimate event can be correlated with the AD 1323 earthquake. There is no archaeological and/or historical record that can be associated with the oldest earthquake dated between BP 3800 ± 600 and BP 2300 ± 200 years. Additionally, the trench study performed to the north of the Salur segment demonstrates paleoliquefaction structures crossing each other. The surface deformation that occurred during the 1964 earthquake is determined primarily to be the consequence of liquefaction. According to the fault plane slip data, the MFZ is a purely normal fault demonstrating a listric geometry with a dip of 64°–74° to the NNE.     

Evaluation of andesite source as armourstone for a rubble mound breakwater (Hisarönü, Turkey)

Black Sea coast line is a hazardous region especially in winter due to the dominant wave action. Therefore, rubble mound breakwaters protected with armourstone used as ship shelters are vital structures especially for the fishermen. The deterioration of the armourstone with time in the form of abrasion and disintegration may result in the failure of the breakwater. In this study, the properties of the armourstone taken from an andesite quarry and used in the Hisarönü rubble mound breakwater were studied both in field and laboratory in order to assess their qualities and long-term durabilities. Based on the in situ observations and laboratory tests, the andesite is found to be generally marginal rock. CIRIA/CUR, RDI_s, RERS and Wet-Dry strength ratio classifications are in good agreement with the in situ observations and the results of the laboratory tests. However, RDI_d, Average Pore Diameter and Saturation Coefficient classifications cannot correctly predict long-term durability of the armourstone. Field studies reveal that block size of the andesite in the quarry increases with depth due to the increase in spacing of the cooling joints of the rock.     

A probabilistic seismic hazard assessment for the Turkish territory—part I: the area source model

The seismic zoning map of Turkey that is used in connection with the national seismic design code (versions issued both in 1997 and 2007) is based on a probabilistic seismic hazard assessment study conducted more than 20 years ago (Gülkan et al. in En son verilere göre haz?rlanan Türkiye deprem bölgeleri haritas?, Report No: METU/EERC 93-1, 1993). In line with the efforts for the update of the seismic design code, the need aroused for an updated seismic hazard map, incorporating recent data and state-of-the-art methodologies and providing ground motion parameters required for the construction of the design spectra stipulated by the new Turkish Earthquake Design Code. Supported by AFAD (Disaster and Emergency Management Authority of Turkey), a project has been conducted for the country scale assessment of the seismic hazard by probabilistic methods. The present paper describes the probabilistic seismic hazard assessment study conducted in connection with this project, incorporating in an area source model, all recently compiled data on seismicity and active faulting, and using a set of recently developed ground motion prediction equations, for both active shallow crustal and subduction regimes, evaluated as adequately representing the ground motion characteristics in the region. The area sources delineated in the model are fully parameterized in terms of maximum magnitude, depth distribution, predominant strike and dip angles and mechanism of possible ruptures. Resulting ground motion distributions are quantified and presented for PGA and 5 % damped spectral accelerations at T = 0.2 and 1.0 s, associated with return periods of 475 and 2475 years. The full set of seismic hazard curves was also made available for the hazard computation sites. The second part of the study, which is based on a fault source and smoothed seismicity model is covered in Demircioglu et al. in Bull Earthq Eng, (2016).     

Rockfall hazard analysis for an historical Castle in Kastamonu (Turkey)

The Kastamonu Castle located on a sandstone hill with Eocene age is one of the most historical and touristic places in Kastamonu city center. The settlement of the city expanded towards the hill of the Kastamonu Castle and adversely affected by rockfalls in the past. The rockfall problems around the castle could be related to jointing, weathering, freezing-thawing and earthquake effects or a combination. In this study, the rockfall hazard at the castle is evaluated by two-dimensional rockfall analyses along 17 profiles selected in different orientations. Different size of rock blocks and various types of movements are taken into consideration in the analyses. Fall-out distance, bounce height, kinetic energy and velocity of the sandstone blocks are separately evaluated. The obtained data are used to define the possible rockfall hazard zones. Finally, the areas having potential rockfall risks are distinguished. Based on the evaluation of the data, rock bolting after removing of unstable blocks and supporting the area with the protective fences are suggested.     

Polyphase strain caps

Strain caps are one of a series of microstructures that typically form during deformation of a softer matrix around hard objects. However??in contrast to other microstructures around porphyroblasts, for example pressure shadows??strain caps are rarely described in the literature. Here we describe strain caps with particular focus on strain caps associated with growth of a new phase, not elsewhere present in the paragenesis. Examples from foliated, amphibolite facies, metapelitic schists from Alaska, Sinai and Bhutan are discussed. All examples show chlorite growth exclusively in strain caps formed around porphyroblasts. Porphyroblasts around which the strain caps grow are muscovite, staurolite and garnet, respectively. In all of these examples strain caps formed synkinematically, but the chlorite grew statically at a later stage. Three mechanisms can explain the formation of new phases in the strain cap region: (a) the strain cap region may have experienced different P-T conditions from the matrix; (b) the strain cap region has a different effective bulk composition from the surrounding matrix; (c) fluid flow that is preferentially focused parallel to the foliation planes causing only local adjustment to retrograde metamorphism in the strain cap region. We show that the third hypothesis is the most preferable mechanism. Indeed, the absence of chlorite outside the strain cap region allows a quantification of the amount of fluid that infiltrated the rock. It is shown that for Bhutan sample about 8.5 mole% more water must have been added to the rock during fluid infiltration to cause the strain cap formation.     

Predicting rainfall intensity using a genetic algorithm approach

A genetic algorithm rainfall intensity (GARI) model has been developed and used to predict the intensities for given return period. It is a one‐step solution procedure that may not require any mathematical transformation. The problem formulation is given and the genetic algorithm solution of the problem is presented. The results show that the proposed GARI model can be used to solve the rainfall intensity–duration–frequency relations with lowest mean‐squared error between measured and predicted intensities. Predicted intensities are in good agreement between measured and predicted values for given return periods. Copyright © 2006 John Wiley & Sons, Ltd.     

A newly developed seismic microzonation model of Erbaa (Tokat, Turkey) located on seismically active eastern segment of the North Anatolian Fault Zone (NAFZ)

A methodology to model seismic microzonation maps is required in the hazard mitigation decision plans of the earthquake prone areas. The stage of disaster preparedness for new residential places is of great importance for detailed seismic microzonation models. The effects of local geological and geotechnical site conditions were considered in order to establish site characterization as the initial stage of the models in this study. Dynamic soil properties based on the empirical correlations between shear wave velocity (V _s) and standard penetration test blow counts were taken into account in order to define representative soil profiles extending down to the engineering bedrock. One-dimensional site response analyses were performed to analyze earthquake characteristics on the ground surface. The layers for soil classification, geology, depth to groundwater level, amplification, distance to fault, slope and aspect, and liquefaction-induced ground deformation potential of the study area were prepared in seismic microzonation models. The study area, Erbaa, is placed along the seismically active North Anatolian Fault Zone. Final seismic microzonation map of the study area was evaluated applying different GIS-based Multi-Criteria Decision Analysis (MCDA) techniques. Two of the MCDA techniques, simple additive weighting and analytical hierarchical process (AHP), are considered during the evaluation step of the final seismic microzonation map. The comparison is made in order to distinguish two different maps based on these MCDA techniques. Eventually, AHP-based seismic microzonation map is more preferable for the seismic design purposes in this study.     

Spatial Prediction of Lateral Variability of a Laterite-Type Bauxite Horizon Using Ancillary Ground-Penetrating Radar Data

Tropical laterite-type bauxite deposits often pose a unique challenge for resource modelling and mine planning due to the extreme lateral variability at the base of the bauxite ore unit within the regolith profile. An economically viable drilling grid is often rather sparse for traditional prediction techniques to precisely account for the lateral variability in the lower contact of a bauxite ore unit. However, ground-penetrating radar (GPR) offers an inexpensive and rapid method for delineating laterite profiles by acquiring fine-scale data from the ground. These numerous data (secondary variable) can be merged with sparsely spaced borehole data (primary variable) through various statistical and geostatistical techniques, provided that there is a linear relation between the primary and secondary variables. Four prediction techniques, including standard linear regression, simple kriging with varying local means, co-located cokriging and kriging with an external drift, were used in this study to incorporate exhaustive GPR data in predictive estimation the base of a bauxite ore unit within a lateritic bauxite deposit in Australia. Cross-validation was used to assess the performance of each technique. The most robust estimates are produced using ordinary co-located cokriging in accordance with the cross-validation analysis. Comparison of the estimates against the actual mine floor indicates that the inclusion of ancillary GPR data substantially improves the quality of the estimates representing the bauxite base surface.     

Real Option Identification Framework for Mine Operational Decision-Making

Natural Resources Research - Identification of opportunities for applying real options (RO) in mining operations is a major challenge to decision-makers. In order to make optimal decisions in...     

Geotechnical assessment of a landslide along a natural gas pipeline for possible remediations (Karacabey-Turkey)

A new natural gas pipeline with a 0.90-m diameter is under construction to provide a gas connection between Turkey and Greece as well as to create a gas ring for southern Europe. The new pipeline route lies next to an existing small diameter gas pipeline broken by a landslide that occurred in February 2006 near Karacabey (Bursa). Although the existing pipeline has been temporarily repaired, either the pipeline route should be relocated or the landslide should be stabilized. The geological survey conducted in the study area reveals that relocation is not feasible due to the existence of other landslides in close vicinity to the site. In order to investigate the causes of the landslide and to suggest possible remedial measures, geotechnical investigations including surface geological mapping, trial pitting, drilling with field tests, inclinometer measurements, laboratory testing, and limit equilibrium analyses were conducted. The investigation revealed that the unconsolidated clayey soil slid on claystone along a non-circular failure surface. Based on the gathered data, possible remedial measures including partial removal of landslide material and construction of toe buttresses, slope flattening, lowering the pipeline, and surface drainage systems were evaluated. These are suggested to prevent the reactivation of the landslide, and thus to establish a safe route for both the existing and the new pipelines.