Crustal velocity and Vp/Vs structures beneath central Anatolia from local seismic tomography

We applied a seismic tomography technique to arrival time data generated by local crustal earthquakes in central Anatolia in order to study the three-dimensional velocity and Vp/Vs structures and their relation with the complex tectonic processes and seismic activity occurring in the study region. The relatively equal and large number of both P- and S-wave arrival times comprising a total of 51,650 arrivals and the relatively uniform distribution of the recording stations imply that the obtained velocity anomalies are reliable features down to a depth of 40 km. This is also evident from the results of the checkerboard resolution test, hit count, and the ray-path coverage. The inversion results indicate the existence of strong lateral heterogeneities in the crust and uppermost mantle beneath central Anatolia. Prominent low-velocity anomalies are clearly imaged at all layers especially beneath existing volcanoes and the active fault segments. Higher-than-average Vp/Vs ratios are widely distributed, indicating the possible existence of over-pressurized fluids that may be responsible for the triggering of the large crustal earthquakes along the north and east Anatolian fault zones. We noticed that the seismic activity occurs mainly at the low-velocity areas and to a lesser extent in some high-velocity zones, perhaps because of the complex tectonics and geological structures. These observations imply that all the zones with velocity anomalies—either low or high—are potential sites for strain energy accumulation and subsequent release. The obtained velocity and Vp/Vs models are consistent with previous geophysical measurements conducted beneath central Anatolia and give much deeper understanding of the current seismotectonic processes occurring in the region.     

GIS-based DRASTIC, Pesticide DRASTIC and the Susceptibility Index (SI): comparative study for evaluation of pollution potential in the Nabeul-Hammamet shallow aquifer, Tunisia

Three vulnerability index models were applied to assess the pollution potential of Nabeul-Hammamet shallow aquifer, Tunisia: DRASTIC, Pesticide DRASTIC and the Susceptibility Index (SI). An output map layer of each one was obtained using a geographic information system (GIS). The SI layer was overlain with DRASTIC and Pesticide DRASTIC and the percentage areas of agreement and divergence in vulnerability categories were extracted. DRASTIC results suggest the aquifer has mostly low vulnerability. Pesticide DRASTIC and SI identify three vulnerability categories (low, moderate, high) in the aquifer. Published data on current chemical groundwater composition indicate that parts of the aquifer are highly contaminated, revealing that DRASTIC underestimates the risk of pollution; Pesticide DRASTIC and SI reflect this risk better. Agreement in vulnerability categories between the two last models is found for 64 % of the aquifer area. To help manage land-use allocation and prevent Nabeul-Hammamet-aquifer contamination, DRASTIC is not recommended. Pesticide DRASTIC and SI are recommended but for slightly different applications. SI helps in the monitoring of current vulnerable areas and, thus, in contamination prevention. Pesticide DRASTIC could better intervene as a criterion in a multi-criteria analysis to select the best sites for specific on-the-ground practice or future land use.     

Study of a Neogene basin dynamics: The “Bizerte basin”, northeastern Tunisia: relevance to the global Messinian Salinity Crisis

The Messinian sediments of northeastern Tunisia were deposited under an active tectonic setting. They are organized in sequences indicating a transitional deposit from margin – littoral to lacustrine – continental facies. These series unconformably overlie the Serravallian–Tortonian silty clays packages, and are overlain by the transgressive Early Pliocene marl (Zanclean). The presence of evaporitic strata points out to the Messinian Salinity Crisis described in the peripheral basins of the western Mediterranean. The Messinian sedimentation was found to have been closely controlled by transtensive tectonics and differential subsidence at a large spatio-temporal scale. It is organized in sequences typical of a depositional environment controlled by eustatism, tectonic and maybe by climate changes. Despite the existence of some local specific sedimentological characteristics, our results corroborate previous findings that pointed out to the Messinian times as a singular period all around the Mediterranean Basin. Field and subsurface seismic profile data helped reconstructing either the sedimentary or tectonic unconformities existing between the studied Messinian series and older Neogene successions.     

The role of geophysical and seismological data in evaluating the subsurface structures and tectonic trends of Nile Delta, Egypt

In the present study, the Bouguer, aeromagnetic, and seismological data analysis for Nile Delta including the Greater Cairo region and its surroundings was used to examine and trace the tectonic framework for some deep-seated faults (mostly normal faults with a small strike–slip component) and their orientation, on which most earthquakes have occurred. The new tilt derivative (TDR) geophysical map and Euler deconvolution presented here can be used to trace the structural relationships and their depth investigations across the entire region. Generally, most of the Euler deconvolution results especially from the gravity map were well coincided with the location of contacts derived by TDR particularly NNW to NS, EW, and NE trended structures. The depths to the gravity or magnetic sources, and the locations of the contacts of density contrast were estimated. Results of the Euler deconvolution method suggested that, in the southeastern part of the area, the basement could be observed to be shallow and has become deeper beneath the northern part. Furthermore, the resulting structural map of this study is well correlated with previous geological and seismological data analyses. At least two sets of predominant faults are suspected, faults with a NNW strike (Clysmic trend) which are particularly felt in the southern portion of the Delta, and some of them give it the shape of a “graben like structure.” Another parallel set of faults, having NE–SW strike (Pelusium trend), was also obvious in the southern part between Cairo and Suez cities (at Abu Zabal area). The evaluated trending faults (NNW–SSE or NE–SW) are intersecting with predominant major WNW–ESE to E–W (Tethys trend) striking faults. These intersections may generate more additional seismic pulses and consequently increase the seismic activity for these structures. However, minor NW (Najd Fault System) is obvious in the TDR magnetic map, whereas less attendance NS (East African trend) structural trends are evident in the TDR gravity map. Moreover, it could be said that the southeastern portion of the Nile Delta (especially the eastern portion of Greater Cairo) is affected by highly tectonic fault systems. Finally, a new tectonic map was also evaluated from the resulting structural map, which helps to quantify different structural patterns (faults and/or contacts), and their relations with the regional tectonic trends are discussed.     

Trace and REE element geochemistry of fluorite and its relation to uranium mineralizations,Gabal Gattar Area,Northern Eastern Desert,Egypt

Uranium mineralizations occur and form in a broad range of geologic setting and age, including magmatic to surfacial conditions, and there are numerous controls on their transportation and deposition, such as redox, pH, ligand concentration, complexation, and temperature. These temporal and spatial variations have caused a range of ore deposit mineral assemblages. Consequently, understanding their conditions of formation is still in its infancy. This research reports rare earth elements (REE) and trace elements of fluorite associated with hexavalent uranium mineralizations and tests of genetic models for the deposits. These data contribute to a better understanding of the variables controlling fluorite formation and uranium ore composition through understanding the evolution of these ore-forming hydrothermal systems. Fluorite in Gabal Gattar granite occurs as disseminations and/or thin veinlets and encrustations filling some uranium mineralized fissures and fractures along the northern margin of host granite mass. In the U-poor samples, fluorite forms well-developed large crystals that are commonly zoned. The zones are represented by alternating colorless and violet zones, and the outer zones are frequently dark violet. In the U-rich samples, fluorite is usually anhedral, unzoned, and has a dark violet color. The results of analysis of REE and trace element contents of fluorites using laser ablation inductively coupled plasma mass spectrometry indicate that total REE in the anhedral unzoned fluorite are elevated compared to the well developed zoned fluorite, and also total REE in dark violet zones of zoned fluorite are elevated with respect to the colorless zones. The fluorites and host granite are generally characterized by strongly negative Eu anomalies and slightly negative or chondritic Ce anomalies. Accordingly, REE patterns of the fluorite and host granite are roughly alike, indicating that the source of REE and trace elements of hydrothermal fluids is the host granite leached by fluids. Y/Y*, Ce/Ce,* and Eu/Eu* patterns show that fluorite clearly records the compositional evolution of the hydrothermal solutions that have transferred trace and REE from host granite during the fluid–wall rocks interactions. The high uranium contents of fluorite in Gabal Gattar granite suggest that parent fluids bearing fluorine have interacted with host granite to leach uranium from the accessory minerals of granite and tetravalent uranium minerals in reduced or weakly oxidized zones.     

A study of the effect of driving on pre‐bored piles

A finite element model for pile‐driving analysis is developed and used to investigate the behaviour of pre‐bored piles, which are then driven the last 1.25 or 2.25 m to their final design depth. The study was conducted for the case of saturated clays. The model traces the penetration of the pile into the soil and accommodates for large deformations. The non‐linear behaviour of the clay in this study is predicted using the bounding‐surface‐plasticity model, as applied to isotropic cohesive soils. The details of the 3‐D numerical modelling and computational schemes are presented. A significant difference was observed in the pile displacement during driving, and in the computed soil resistance at the pile tip, particularly at the earliest driving stages. No difference in soil resistance at the soil pile interface along the pile shaft was detected between the pre‐bored piles whether driven 1.25 or 2.25 m. Copyright © 2002 John Wiley & Sons, Ltd.     

Effect of nonextensive electron and ion on dust acoustic rogue waves in dusty plasma of opposite polarity

Propagation of nonlinear dust-acoustic waves in a magnetized collisionless plasma having positively, negatively charged dust grains and nonextensive distributed electrons and ions has been investigated. A reductive perturbation method is used to obtain a nonlinear Korteweg-de Vries (KdV) equation describing the model. The dynamics of the modulational instability gives rise to the formation of rogue waves that is described by a nonlinear Schrödinger equation. The dependence of rogue waves profiles on positive and negative charged dust cyclotron frequencies, nonextensive parameters of electrons and ions is investigated numerically. The result of the present investigation may be applicable to some plasma environments, such as cometary tails and upper mesosphere.     

Expansion of Cavities Embedded in Cohesionless Elastoplastic Half-Space and Subjected to Anisotropic Stress Field

Cavity expansion theories are employed in a wide range of geotechnical applications including interpretation of pressure meter tests, evaluation of shaft capacity of piles, and pulling forces for horizontal directional drilling. Most of these theories assume infinite medium and isotropic stress field, which may not be justified for many applications. The main objectives of this paper are two folds: to investigate the effects of the free surface, stress gradient, and in situ stress anisotropy on the displacements during the expansion phase of cavities embedded in dilatant sands; and to establish correction factors to account for these effects. The investigation was conducted using two-dimensional finite element analyses. It was found that the cavity expansion theory due to Yu and Houlsby (Geotechnique 41:173–183, 1991) can be used reliably for cases subjected to an initial isotropic stress and embedment depth to diameter ratio of 20 or higher. However, it becomes inaccurate for shallow embedment depth and/or stress anisotropy conditions. An analytical procedure to account for the effects of embedment and/or stress anisotropy was proposed. The applicability of the proposed procedure was demonstrated for a wide range of soil properties and geometrical configurations. The results obtained confirmed its ability to estimate the cavity pressures within 10?% of the values obtained using FEA calculations.     

Reliability-based design of spread footings on clays reinforced with aggregate piers

ABSTRACT

The economical and safe design of footings supported on aggregate-pier-reinforced clay could benefit from the implementation of a reliability-based approach that incorporates the different sources of uncertainty. Monte Carlo simulations are conducted to quantify the probability distribution of the ultimate bearing capacity for practical design scenarios. A reliability analysis is then conducted to propose design charts that yield the required factor of safety as a function of the major input parameters. The novelty in the proposed methodology is the incorporation of a lower bound shear strength that is based on the remoulded undrained shear strength in the reliability analysis.     

Mineralogical and geochemical characterization of listwaenite from the Semail Ophiolite, Oman

The late Cretaceous-lower Tertiary hydrothermal alteration of serpentinized peridotite in the Semail ophiolite has formed two distinct types of listwaenite. Type I is characterized by the presence of calcite (Type IA) or dolomite (Type IB)+fuchsite±spinel. Type II is dominated by silicate minerals (quartz, chlorite, fuchsite)±calcite+dolomite±magnetite±apatite±plagioclase. Most listwaenites occur as veins along thrust fault zones within the ophiolite mélange. High Cr and Ni contents, abundant occurrence of Cr-spinel within a matrix of red-brown ferruginous carbonates within a micro-vein network of goethite, and the relics of mesh texture indicate an ultramafic protolith. Type I and II listwaenites represent different stages of hydrothermal alteration. The mineralogical and chemical distinctions of both types are the response to the extent of the reactions between the protoliths and the solutions leading to different stages of metasomatic replacement. The hydrothermal fluids involved in the formation of Type I listwaenite were enriched in Ca, Mg, and CO₂, whereas Type II listwaenite bodies were formed from a hydrothermal fluid enriched in SiO₂. REE and trace elements in both listwaenite types were extracted in part from adjoining peridotite. No Au anomaly in the study areas has been detected.