Showing papers in "Geosciences Journal in 2016"

A comparative study of landslide susceptibility maps using logistic regression, frequency ratio, decision tree, weights of evidence and artificial neural network

Abstract: For the purpose of comparing susceptibility mapping methods in Mizunami City, Japan, the landslide inventory was partitioned into three groups as various training and test datasets to identify the most appropriate method for creating a landslide susceptibility map. A total of fifteen landslide susceptibility maps were produced using frequency ratio, logistic regression, decision tree, weights of evidence and artificial neural network models, and the results were assessed using existing test landside points and areas under the relative operative characteristic curve (AUC). The validation results indicated that the logistic regression model could provide the highest AUC value (0.865), and a relatively high percentage of landslide points fell in the high and very high landslide susceptibility classes in this study. Furthermore, the paper also suggested that the model performances would be increased if appropriate landslide points were used for the calculation.

The 12 September 2016 Gyeongju earthquakes: 1. Observation and remaining questions

Abstract: Two earthquakes (M L 5.1 and 5.8) ruptured branches of the Yangsan Fault System in Gyeongju, S. Korea on September 12, 2016. After the M L 5.8 earthquake, aftershock earthquakes continued to occur, including two notable earthquakes (M L 4.3 and 4.5) on September 12 and 19, 2016. This paper details the early reports of the Yangsan Fault System in the Gyeongsang Basin from various geological and geophysical/seismological perspectives. Based on a review and an initial seismological analysis of the results of the three earthquakes (M L 5.1, 5.8, and 4.5), we present and discuss the following topics: (1) the tectonic setting and the geophysical/seismic structure of the Yangsan Fault System, (2) historical seismicity and inferred seismic hazard from historical (literature) data, and (3) source mechanisms of the three earthquakes. In the end, we highlight some of the outstanding issues with regard to earthquakes and future research topics.

Oil-oil correlation by FTIR spectroscopy of asphaltene samples

Abstract: In this paper, a new technique with easy interpretation, low cost, and reliable results is presented for oil-oil correlation purpose. In this technique, the structural characterization of asphaltene, because of its structural similarity with kerogene and resistance to secondary processes (e.g., migration, biodegradation, thermal maturity, and so on), was considered as a correlation parameter and asphaltenes structure similarity in different oil samples is the basis of geochemical correlation. FTIR spectroscopy was applied to detect and compare asphaltene structures with each other. The four oil samples from different oil fields in the Iranian sector of the Persian Gulf were investigated by FTIR spectroscopy and introduced indexes that represent structural characteristic of asphaltenes enabled us to perform geochemical correlation. To validation of this technique, the other common geochemical techniques (e.g., stable carbon isotope and biomarkers) were applied to geochemical correlation. These techniques completely supported and complemented the results of the asphaltene FTIR spectroscopy technique. The results of these three techniques show genetic relationships among these 4 oil samples and indicated that these oil samples belong to two distinct oil families. The First oil family originated from carbonate rich source rock and the second oil family was sourced from calcareous shale source rock.

The 12 September 2016 Gyeongju earthquakes: 2. Temporary seismic network for monitoring aftershocks

Abstract: The ML 5.8 earthquake in Gyeongju, southeastern Korea, on September 12, 2016 11:32:54 (UTC) was the largest earthquake on the Korean Peninsula since instrumental monitoring began in 1978. It was preceded by an ML 5.1 foreshock and is being followed by numerous aftershocks. Within an hour of the mainshock, the first temporary seismic station to monitor aftershocks was installed at about 1.5 km east of the announced epicenter. The current temporary seismic network consists of 27 stations equipped with broadband sensors covering an area of ∼38 × 32 km in the mainshock region. This is the first high-density aftershock monitoring array in the Korean Peninsula. Initial results, using data from both the regional seismic networks and the aftershock monitoring array, indicate that earthquakes during the first 10 days following the mainshock are related to the Yangsan Fault System. Establishment of an official rapid-response team to monitor aftershocks of major earthquakes is advised.

X-Ray CT scanning imaging for the Nubia sandstone as a tool for characterizing its capillary properties

Abstract: The Nubia sandstone is among the most important aquifers/reservoirs system in and around the Gulf of Suez province in Egypt. It is composed of very fine to coarse siliceous highly porous sandstone. It can be differentiated into four formations, named Araba, Naqus, Abu Durba and Malha. The capillary imbibition properties of the Nubia sandstone have been studied using two different techniques: 1) Increasing mass against time and 2) X-Ray CT scanning imaging. Both methods are valuable in characterizing the different capillary properties of the studied rocks, i.e., the coefficient of capillary ‘C’ (measured in g/(cm2.s1/2) using the first method and the capillary parameter ‘A’ (measured in cm/s1/2) using the second one. In addition, porosity (17.7 to 23.5%) was measured using two techniques: 1) Water saturation under vacuum, and 2) mercury injection ‘MICP’ under high pressure. The mercury injection test indicated homogeneity in the pore throat distribution of the studied samples. Liquid permeability (41.6 to 374.2 md) was measured using water flow; it is very good to excellent and mostly controlled by the rock porosity and average pore throat diameter. Both capillary parameters ‘A’ and ‘C’ show a positive correlation with permeability. On a limited set of samples the anisotropy linked to pore fabric could be estimated.

Numerical analysis on scale effect of elasticity, strength and failure patterns of jointed rock masses

Abstract: It is of great importance to study the failure process and scale effect of jointed rock mass in the field of rock mechanics and mining engineering. In the present paper, initially the uniaxial compression test on granite was performed and acoustic emission (AE) sequence was acquired during the compression process in laboratory. Results from numerical simulations using the particle flow code in two dimensions (PFC2D) were presented, and compared with experimental measurements. It was observed that the approach was reasonably good in predicting the real response of granite rock samples. The mechanical parameter of joint model was then calibrated based on PFC2D model with experimental results. Finally the mechanical properties of complex rocks with discrete fracture network (DFN) were studied and scale effects on the elasticity and strength were then investigated. The result showed that the failure pattern was similar when the ratio of joint contact bond strength (both shear and normal) to rock contact bond strength was in the range of 3~9%. The elastic modulus and strength parameters were changed with the sizes of rock sample for DFN models. Moreover, the variation of rock failure pattern under different sizes was also studied and finally the representative elementary volume (REV) size of the considered rock mass was estimated to be 9 × 9 m. It is suggested that the failure pattern analysis should be considered in the REV study of jointed rock mass.

Effects of intersection and dead-end of fractures on nonlinear flow and particle transport in rock fracture networks

Abstract: Fluid flow tests were conducted on three artificial rock fracture network models to visually investigate the behaviors of fluid flow and solute transport within the fracture intersections, by using the visualization techniques with a CCD camera. Numerical simulations by solving the Navier-Stokes equations were performed to simulate the fluid flow and solute transport based on the experimental models, and to extensively estimate the effects of fracture intersection and dead-end in fracture networks. The results show that for the crossed fracture models, when the Reynolds number (Re) of the inlet is larger than 1, a nonlinear flow regime starts to appear where the proportion of the flow rates in the two outlets change nonlinearly. When calculating the fluid flow in discrete fracture network (DFN) models, it is found that the critical condition of applying the local cubic law to model fluid flow in each single fracture in DFNs is J ≤ 10–5, where J is the hydraulic gradient. Beyond this value, the deviation of applying the cubic law increases remarkably with increasing hydraulic gradient. The effects of dead-ends of fractures on fluid flow are negligible, however, they have a strong impact on the breakthrough curves of particles in DFNs with the relative time deviation rate in the range of 5–35%.

Indirect estimation of deformation modulus of an in situ rock mass: an ANFIS model based on grid partitioning, fuzzy c-means clustering and subtractive clustering

Abstract: Deformability of rock masses influencing their behavior is an important geomechanical property for the rock structures design. Due to the problems in determining the deformability of jointed rock masses at the laboratory-scale, various in situ test methods such as plate loading tests, dilatometer etc. have been developed. Although these methods are currently the best techniques, they are expensive and time consuming, and present operational problems. Furthermore, the influence of the test volume on modulus of deformation depending on the technique used is also important. For these reasons, in this paper, the adaptive network-based fuzzy inference system (ANFIS) was used to build a prediction model for the indirect estimation of deformation modulus of a rock mass. Three ANFIS models were implemented by grid partitioning (GP), subtractive clustering method (SCM) and fuzzy c-means clustering method (FCM). The estimation abilities offered using three ANFIS models were presented by using field data of achieved from road and railway construction sites in Korea. In these models, rock mass rating (RMR), depth, uniaxial compressive strength of intact rock (UCS) and elastic modulus of intact rock (Ei) were utilized as the input parameters, while the deformation modulus of a rock mass was the output parameter. Various statistical performance indexes were utilized to compare the performance of those estimation models. The results achieved indicate that the ANFIS-SCM model has strong potential to indirect estimation of deformation modulus of a rock mass with high degree of accuracy and robustness.

High spatial resolution trace element determination of geological samples by laser ablation quadrupole plasma mass spectrometry: implications for glass analysis in volcanic products

Abstract: Increasing the spatial resolution of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is a challenge in microanalysis of geological samples. Smaller sizes for the laser beam will allow for (1) high resolution determination of trace element compositions, (2) accurate estimation of crystal/melt partition coefficients, (3) detailed characterization of diffusion profiles, and (4) analysis of fine volcanic glasses. Here, we report about the figures of merit for LA-ICP Quadrupole MS down to a spatial resolution of 5 μm. This study highlights the possibility to achieve suitable limits of detection, accuracy and precision for geological samples even at spatial resolutions of the order of 5 μm. At a beam size of 15 μm, precision (measured as one sigma) and accuracy (expressed as relative deviation from the reference value) are of the order of 10%. At a smaller beam size of 8 um, precision decreases to 15% for concentration above 1.7 μg g–1. As the beam size is decreased to ∼5 μm, precision declines to about 15% and 20% for concentrations above 10 μg g–1 using 42Ca and 29Si as internal standard, respectively. Accuracy is better or equal to 10% and 13% at beam sizes of 15 and 10 μm, respectively. When the spatial resolution is increased to 8 μm, accuracy remains better than 15% and 20% for 42Ca and 29Si as internal standard, respectively. We employed such high-resolution techniques to volcanic glasses in ash particles of the 2010 Eyjafjallajokull eruption. Our results are well consistent with the previously reported data obtained at lower spatial resolution, supporting the reliability of the method.

Implication of the chemical index of alteration as a paleoclimatic perturbation indicator: an example from the lower Neoproterozoic strata of Aksu, Xinjiang, NW China

Abstract: The Neoproterozoic successions in the Aksu region, NW China, which lies unconformably on the Precambrian Aksu Group basement, comprises the Qiaoenbrak, Yuermeinak, Sugetbrak, and Chigebrak formations (from bottom to top). The two lowermost units include two distinct glacial diamictites, which indicate distinct episodes of glaciations. We report the major and trace element (including rare earth element) data for the Qiaoenbrak, Yuermeinak, and Sugetbrak formations to identify the paleoclimatic perturbations. The chemical index of alteration (CIA) values show variations from Qiaoenbrak to Yuermeinak, then Sugetbrak formations. The diamictites have relatively lower chemical index of alteration values (45.23–59.64) than inter-, post- and non-glacial sediments (48.28–66.96). This result supported the condition that the diamictites underwent relatively weak chemical weathering from a dry-cold sedimentary environment, which is associated with the sedimentary facies description. The lower Neoproterozoic successions recoded at least two glaciations, one is Qiaoenbrak glaciation and the other is Yuermeinak glaciation.

Shallow groundwater system monitoring on controlled CO2 release sites: a review on field experimental methods and efforts for CO2 leakage detection

Abstract: Carbon dioxide capture and sequestration (CCS) is a promising alternative for reduction of greenhouse gas emission. However, injected CO2 in deep formation has potential to leak into a shallow aquifer. Thus, although it is challenging, development of detection technologies in a shallow aquifer region is essential to assure the long term safety of a CCS project. Recently, field scale experiments were carried out around the world to identify CO2 leakage and to investigate effects on groundwater quality in shallow aquifers. From the literature, 8 controlled CO2 release test sites and 9 experimental cases were identified. In those sites, CO2 was artificially injected around the shallow aquifer region as CO2-infused groundwater phase or gas phase for identifying environmental effects caused by CO2 injection. This paper reviews the hydraulic heterogeneity, mineral compositions, monitoring systems, and environmental parameters required for leakage detection at each site. For constructing a controlled test bed, inclined wells, horizontal wells, and multiple injection wells were identified as reliable injection components. It was also identified that the injected CO2 migration and its effects were monitored through the constructed monitoring networks. The previous operation cases show that continuous monitoring of pH, electrical conductivity (EC), Ca and Mg concentrations is the most basic and important factor for leakage detection. Trace elements and isotopes were also widely used to determine the CO2 leakage. The Korea CO2 Storage Environmental Management (K-COSEM) research center is going to construct an environmental impact test (EIT) facility for developing CO2 leakage detection methods in a shallow aquifer region in Korea. The challenging issues will include the fate and transport of CO2 from the fractured zone to the saturated zone and to the unsaturated soil. Based on the lessons learned from the previous tests, environmental monitoring technologies will be developed through the analysis of the time series data of hydrogeochemical parameters for the planned EIT facility in Korea.

Estimating groundwater recharge in the humid and semi-arid African regions: review.

Abstract: Reliable estimation of groundwater recharge rate is crucial for the assessment of groundwater resource potential in Africa. In this study, we reviewed existing studies on groundwater recharge, especially in the semi-arid and humid regions of Africa. After the assessment of the main advantages and disadvantages of each method, we strongly agree that among the distinct existing methods, Water-Table Fluctuations (WTF), Recession-Curve Displacement, and Chloride Methods can be used with a better certainty of improved estimation of groundwater recharge in these regions. In addition, the features of existing studies on groundwater recharge are outlined. The major challenge of these regions on recharge study is the lack of basic data. Therefore, this paper suggests methods for dealing with this limitation and also the future outlook using recently developed technologies such as Remote Sensing (RS) and Geographical Information System (GIS). Watershed hydrologic modeling, which is a robust method for recharge estimation that is widely applied around the world, should also be applied for future perspective by solving the problems of its use and data requirements to find a better result. Strictly speaking, the key to the successful estimation of groundwater recharge lies in the utilization of a variety of independent methods. Therefore, by bringing together the advantages, limitations, and cost of each method, the study of the recharge estimation in different climatic environments of African regions can enter a new era.

Diffuse flow characteristics and their relation to hydrochemistry conditions in the Petoyan Spring, Gunungsewu Karst, Java, Indonesia

Abstract: This study was conducted on the Petoyan Spring, one of the most important springs in the western part of Gunung Sewu Karst, Java, Indonesia. The main purpose of the study is to define the diffuse flow characteristics of the spring. It also focuses on identifying the relationship between the diffuse flow proportion and several hydrochemical parameters to provide a better aquifer characterization. Water-level monitoring and discharge measurements were conducted over an eight months period in order to define the discharge hydrograph. The calculation of recession constants, including the diffuse flow (Kb), fissure flow (Ki), and conduit flow (Kc), was done by selecting several flood hydrograph events. Furthermore, the base flow-separation analysis was conducted to determine the diffuse flow proportion throughout the research period. Water sampling for hydrogeochemical analysis was taken every week and every hour for two selected flood events. A bivariate plot analysis between the diffuse flow proportion and certain hydrochemical parameters was made in order to describe the hydrogeochemical processes. The results showed that the diffuse- flow significantly dominates the spring discharge during non-flooding and flooding recession periods. Conversely, during the rising limb period, the diffuse proportion decreased drastically due to the conduit flow supply. This fact was also supported by the high Kb and short Tp (time to peak) and Tb (time to base flow) values. Hydrogeochemically the correlation between the diffuse flow proportion and major dissolved elements during the flood recession periods was strong because the conduit flow domination was replaced by the diffuse flow, causing the domination of water-rock interaction. According to the diffuse flow and its relation to its hydrochemistry, it is apparent that small fractures in the Petoyan Spring aquifer still provide good storage for the diffuse flow, even though the conduit fracture has already been developed.

How much information can soil solute profiles reveal about groundwater recharge

Abstract: The unsaturated zone is an important link between groundwater and the land surface, and can provide storage capacity for both water and contaminants. Consequently, the solute profile of the unsaturated zone can provide much information on groundwater recharge using tracers. This study takes a rain-fed agricultural area (Luochuan loess plain) in the Chinese Loess Plateau as an example to demonstrate how much recharge information in the thick unsaturated zone can be obtained from the solute profile. The results show that the recharge rate is 36–67 mm yr–1 and infiltration rate is 0.19 to 0.30 m yr–1, as obtained using three methods, i.e., evaluating the Cl-peak, chloride mass balance, and nitrate levels. The amount of time needed for annual precipitation to reach the water table is 133–316 years, and the groundwater is tritium free. The nitrate introduced by human activities is mainly distributed in the upper unsaturated zone (above 6 m), and the groundwater nitrate content (3.7 to 9.6 mg l–1 as NO3) remains at baseline level. The storage capacity of the unsaturated zone is found to delay the entrance of pollutants into the aquifer.

Experimental and numerical investigations on the shear behavior of a jointed rock mass

Abstract: The original forming process of the earth crust is companied with internal in situ stress, which gradually complicates while the earth crust evolves with geological conformation movements, leading to the generation of large amounts of faults, joints and fissures. These structural planes, to some extent, remarkably reduce the strengths of rock mass, including the shear behavior. In this paper, the authors report a physical model test on jointed rock mass under direct shear stress state and also adopt a numerical method, Discontinuous Deformation Analysis for Rock Failure (DDARF), to simulate the shear failure process, the variation of stresses and displacements of some key monitoring points. The comparative analysis demonstrates that the numerical results are favorable with those obtained in the physical model test. Therefore, it is concluded that the method of DDARF could effectively simulate the shear behavior of jointed rock mass. Furthermore, other than the original physical model test, the numerical models with echelon joints under different axial loadings are also simulated. The crack initiation, extension, coalescence, and the ultimate shear failure are totally investigated, after which the shear behavior of numerical models in different cases are comparatively analyzed.

Landslide susceptibility mapping at Gongliu county, China using artificial neural network and weight of evidence models

Abstract: The aim of this study was to apply and to verify the use of artificial neural network (ANN) and weight of evidence (WoE) models to landslide susceptibility mapping in the Gongliu county, China, using a geographic information system (GIS). For this aim, in this study, a landslide inventory map was prepared using earlier reports and aerial photographs as well as by carrying out field surveys. A total of 163 landslides (70% out of 233 detected landslides) were randomly selected for model training, and the remaining 70 landslides (30%) were used for the model validation. Then, a total number of twelve landslide conditioning factors, such as slope angle, slope aspect, general curvature, plan curvature, profile curvature, altitude, distance to rivers, distance to roads, lithology, rainfall, normalized difference vegetation index (NDVI), and sediment transport index (STI), were used in the analysis. Landslide hazardous areas were analyzed and mapped using the landslide-occurrence factors by ANN and WoE models. Finally the output maps were validated using the area under the curve (AUC) method. The validation results showed that the ANN model with a success rate of 82.51% and predictive accuracy of 77.31% performs better than WoE (success rate, 79.82%; predictive accuracy, 74.59%) model. Overall, both models showed almost similar results. Therefore, the two landslide susceptibility maps obtained were successful and can be useful for preliminary general land use planning and hazard mitigation purpose.

Effect of particle shape on the shear strength of fault gouge

Abstract: The shear strength of fault gouge plays an important role in the dynamic behavior of faults, ranging from small-scale displacements to severe earthquakes. The characteristics and interactions of constituent materials in fault gouge are the main determinants of shear strength. Assessing the shear strength of fault gouge by means of experiments, however, requires time-consuming procedures, including sampling, shear testing, and reliability checking; consequently, simple and indirect methods to assess shear strength in terms of the characteristics of fault gouge fragments have been investigated. This study focuses on the influence of the shape of fault gouge particles on the shear strength of gouge. We introduce a novel technique to obtain shape parameters of particles using Xray computed tomography (CT), and then show the effects of particle shape on the friction angle of the fault gouge. Samples collected from fault zones developed in various parent rock materials were tested in laboratory experiments to characterize their shear strengths. After shear testing, the particles in the fault gouge were collected, scanned by X-ray CT, and then analyzed for shape characterization. We successfully determined the shape parameters (sphericity, elongation, flatness, and slenderness) of the fault gouge fragments, and found that the parameters are well correlated with the friction angle of the gouge.

Distribution of diagenetic alterations within depositional facies and sequence stratigraphic framework of fan delta and subaqueous fan sandstones: evidence from the Lower Cretaceous Bayingebi Formation, Chagan sag, China–Mongolia frontier area

Abstract: Linking siliciclastic diagenesis to sequence stratigraphy allows a better understanding of the parameters controlling the spatial and temporal distribution of diagenetic alterations. A study of the subaqueous fan and fan delta sandstones of the Bayingebi Formation, Lower Cretaceous, Chagan sag (China), reveals that the distribution of diagenetic alterations can be constrained within a sequence stratigraphic framework. Eogenetic alterations, which were encountered in the sandstones of subaqueous fan and fan delta, include: (1) replacement of detrital silicates and mud matrix by kaolinites in sandstones of the late highstand systems tract (HST) and the lowstand systems tract (LST). The formation of kaolinites is attributed to the influx of meteoric water when the base level fell and the channels migrated laterally on preexisting floodplains or channel deposits. (2) Infiltrated clays, which rim around detrital grains, mainly occur in channel sandstones of the LST due to the percolation of mud-rich surface waters. (3) Calcite I (δ18OVPDB = −20.19‰ to −3.64‰ and δ13CVPDB = −0.67‰ to −3.1‰), Calcite II (δ18OVPDB = −14‰ to −18.28‰ and δ13CVPDB = −2.2‰ to −3.60‰), dolomite (δ18OVPDB = −17.91‰ to −21.04‰ and δ13CVPDB = −0.46‰ to −1.66‰) and ankerite (δ18OVPDB = −15.02 to −20.42‰ and δ13CVPDB = −0.074 to −1.43‰), which are associated with palaeosol horizons mainly developed on top of overbank and channel sandstones of transgressive systems tract (TST) and early stage of the HST. Such extensive eogenetic calcite cements may act as potential layers for the formation of reservoir compartments for underlying sandstones. Mesogenetic alterations include: (1) abundant quartz overgrowths in the overbank sandstones of subaqueous fan in the LST and pro-fan-delta sandstones in the HST, in which early carbonate cements are lacking and grain-coats are thin. (2) Illite, chlorite and albitized feldspars, which occur in small amounts, are most common in the LST and late stage of the HST sandstones. Such cementation by calcite, dolomite, quartz overgrowths and formation of illite led to porosity and permeability deterioration during mesodiagenesis. This study revealed the importance of integration of diagenesis with sequence stratigraphy of subaqueous fan and fan delta sandstones in improving our ability to predict the spatial and temporal distribution of eogenetic alterations and their subsequent impact on mesogenetic alterations, and thus on reservoir quality modifications.

Integrated resistivity and water chemistry for evaluation of groundwater quality of the Gulf of Aqaba coastal area in Saudi Arabia

Abstract: The most productive lands in the coastal area of Saudi Gulf of Aqaba lie in Wadi Humeidah, where irrigation relies predominantly on groundwater. Crop yields have been lately reduced due to increased salinity of groundwater and have led to abandonment of some wells adjacent to the Gulf area. Geophysical and geochemical investigations were combined to assess seawater-contaminated zones in the shallow coastal groundwater aquifer and to identify subsurface geologic formation. The prevalence of Ca2+, Na+, Cl– and SO 4 2– suggests that weathering of surrounding rocks is potentially the major source of ions. Characterization of aquifer conditions up to a depth of 60 m showed that the groundwater aquifer is composed of three zones with vertically different resistivity values. The surface layer with resistivity of 30–1000 ohm-m, represents the alluvial sand and gravel. The second layer with lower resistivity values ranging from 0.6 to 70 ohm-m, indicates saline-to-brackish-to-slightly fresh water saturated rocks. The third layer extending up to a depth of 60 m is dominated by resistivity values of several hundred to several thousand ohm-meters, reflecting the basement rocks. While the groundwater is generally brackish, the salinity content varied spatially with TDS values that decreased in the northeast direction. The variations in TDS are related to multiple sources and primarily dependent on dissolution of saltbearing sediments, exploitation rate, over-irrigation with salty water, aquifer-bearing strata and the location of wells. Groundwater aquifers in the vicinity of the coastline were found to have been impacted by saline water. The central east area has a type of groundwater that is relatively less brackish.

U-Pb zircon systematics of the Mansehra Granitic Complex: implications on the early Paleozoic orogenesis in NW Himalaya of Pakistan

Abstract: Mansehra Granitic Complex (MGC) lies in the NW Himalaya of Pakistan. The MGC magmatic rocks are peraluminous, calc-alkaline S-type granitoids. Prior to this study the Mansehra Granite had produced ages of 83 Ma by K/Ar, 215 Ma using Ar/Ar on biotite, and 516 ± 16 Ma, using the whole rock Rb/Sr method. The Susalgali Granite Gneiss, a sheared facies of the Mansehra Granite previously regarded as older than the Mansehra Granite, was dated at 79 Ma using K/Ar on biotite. Hakale Granite, which is intrusive into the Mansehra Granite, had yielded K/Ar muscovite age of 165 Ma. The age of the leucogranites was not reported before this contribution. We have presented the revised geochronology of the MGC magmatic bodies, employing SHRIMP and LA-ICP-MS U-Pb zircon chronometry, to constraint precise crystallization ages and tectonic setting of the NW Himalaya, Pakistan. Dates of emplacement of the Mansehra Granite, leucogranites and Hakale Granite are ca. 478, 475 and 466 Ma, respectively. These new ages are comparable to U-Pb zircon and Rb/Sr dates of other granites and granite gneisses in the Lesser Himalaya to the east, in India, Nepal, south Tibet and SW China. The age components of ca. 1900–1300, 985–920, 880–800 and 690–500 Ma are interpreted as inherited grains. Geochronological and field evidence suggest that the MGC of the NW Himalaya are the product of an Andean-type Cambro-Ordovician accretional orogenesis with continental-continental settings along the northen margin of east Gondwana. On the basis of new age data of the MGC plutonic rocks it is inferred that Cambro-Ordovician accretional event commenced from SW China and extends at least up to NW Pakistan along the northern margin of east Gondwana. However, granitic rocks of Pan African affiliation prevail in central Iran and Turkey along northern and western margins of Gondwana.

Seismic and well log driven structural and petrophysical analysis of the Lower Goru Formation in the Lower Indus Basin, Pakistan

Abstract: The Sinjhoro concession is prolific gas-producing block situated on the eastern limb of the Lower Indus Basin in Pakistan. It contains several development and production (D & P) leases, which are producing gas from Cretaceous rocks. The present study aimed to evaluate the structural and petrophysical properties of the Lower Goru Formation using a 2D seismic and well-driven integrated study. A seismic driven time structure map of the Lower Goru Formation was generated, which depicted horst and graben structures oriented predominantly in a NNW-SSE direction. These normal faults are deep seated and potentially provide a vertical primary migration pathway to hydrocarbon flow. A prospective lead of 20 ms was identified in the northwestern portion of the structural map, which could be explored further. Besides this, a RMS amplitude map was generated within the target reservoir level to show the general sand body distribution within the reservoir. Our study revealed that the reservoir quality sands are deposited in the eastern portion of the study area. The identified lead is also located on a fair to good level of sand body which is producing from the well drilled to the south of the prospective area. Additionally, it is strongly recommended to conduct an infill seismic survey over and around the newly identified prospect in order to validate its existence and aerial outspreads. Well correlation, petrophysical data logs (PDLs) and cross-plot techniques were adopted to predict the petrophysical properties of the reservoir level. During the petrophysical study, two prospective zone were identified, with Zone-II showing more promising results for hydrocarbon presence than Zone-I. The present research has shown that integration of seismic attributes with petrophysical calculations can help to identify new prospective leads even in cases where there is less seismic data coverage.

Induced seismicity: the potential hazard from shale gas development and CO2 geologic storage

Abstract: We present an overview of the current status of unconventional energy development, particularly of shale gas, and underground CO2 storage as a measure to mitigate greenhouse gas increase in the atmosphere We review their potential to induce seismicity, which has caused debates among related energy enterprises, engineers, researchers, and environmental and public communities regarding their potential hazards Studies show that fracking can be a problem in that it consumes abundant water, but the seismicity induced by fracking has not yet been observed to induce many felt earthquakes However, massive wastewater injection, a part of the unconventional energy development process has caused M50+ earthquakes in the past as well as several recent and ongoing cases of induced seismicity Large-scale CO2 injection as a part of carbon sequestration efforts in the near future has a high risk of inducing large earthquakes Therefore, injection operations related to both unconventional energy development and carbon sequestration should be optimized and managed to mitigate the likelihood of an induced seismic event

Mineralogy and geochemistry of three weathered Lower Cambrian black shale profiles in Northeast Chongqing, China

Abstract: This paper reports a geochemical study on the mineralogy and major elements of mid-ridge (A), near mountaintop (B), and valley (C) profiles developed in the Lower Cambrian black shale in Northeast Chongqing, China. The primary objective was to understand the elemental mobility, mineralogical transformation, and weathering progression during black shale chemical weathering in a subtropical climate. Profiles A, B, and C are characterized as weak, weak to moderate, and moderate to intense in terms of weathering intensity, respectively, by the Chemical Index of Alteration (CIA). Results indicate that most elements were mobilized by acidic solutions produced during the oxidation of pyrite and organic matter (OM). Among the major elements, Si was slightly enriched in profile A, but depleted through desilication in profile B and C. Al was enriched in the regolith zone in profile A and C, and Fe was enriched at the oxic front because of secondary clay and sesquioxide formation. The addition and depletion of major elements and the depth of the oxic front increased with the degree of weathering. Gypsum and Fe- (hydro-) oxides were observed to form and re-precipitate in the saprock and fractured shale zones. Clay minerals formed from dissolution of plagioclase and the transformation of other labile clay minerals during weathering. The progressive changes in mineralogical composition of weathered material from profile A to C showed the sequence of mineral decomposition with degree of weathering: first, oxidation of pyrite and OM; then Ca and Mg were removed during dissolution of carbonatite; followed by removal of Na from dissolution of plagioclase; lastly, transformation of clay minerals during weathering; meanwhile, desilication occurs at moderate to intense weathering stages.

Exploration geochemistry data-application for anomaly separation based on discriminant function analysis in the Parkam porphyry system (Iran)

Abstract: There are several statistical methodologies presented for separating anomalous values from background leading to determination of anomalous areas. These methods range from simple approaches to complicated ones. A common objective method for anomaly detection in geochemical exploration is target delineation by discriminant function analysis. Discriminant analysis (DA) is a multivariate statistical technique that classifies each observation into a specific group based on observed predictor variables and predefined groups. In the present study, to achieve this target, two populations of anomaly and background were determined using combination of Mahalanobis distance (MD) and median absolute deviation (MAD) method, using borehole data set. For this purpose, in the first step, Mahalanobis distance values should be determined and then MAD method should be applied on Mahalanobis distance values of boreholes data (grade of copper and molybdenum). Thus for separating anomaly from background of surface samples and determining anomaly areas, algorithm of DA method is applied on grade of Cu and Mo (surface samples). Results show that samples indicated by the DA methods as anomalous are more regular; less dispersed and are more accurate than other multivariate methods (e.g., MD method) and other univarite methods since anomalous samples are determined based on several variables. Finally, bivariate lithogeochemical map of the study area is provided for copper and molybdenum which has been prepared using DA method. In this map, the delineated Cu-Mo mineralization is closely associated with the defined zone of potassic alteration, which is also consistent with the field and microscopic observation of the Cu mineralization in this alteration zone. Moreover, it is associated with the phyllic alteration and is spatially conformable with the zone defined for it.

Assessing floods and droughts in ungauged small reservoirs with long term Landsat imagery

Abstract: Small reservoirs have developed across semi-arid areas as a low cost solution for millions of rural small holders to harvest scarce water resources. Studies have highlighted limited agricultural water use and low water availability on individual reservoirs, but no information exists on the drought patterns of multiple small reservoirs. Their small size and dispersion prevents individualised hydrological monitoring, while hydrological modelling suffers from rainfall variability and heterogeneity across data sparse catchments and reservoirs. A semi-automated original approach exploiting free, archive Landsat satellite images is developed here for long-term monitoring of multiple ungauged small water bodies. Adapted and tested against significant hydrometric time series on three lakes, the method confirms its potential to monitor water availability on the smallest water bodies (1–10 ha) with a mean RMSE of 20,600 m3 (NRMSE = 26%). Uncertainties from the absence of site-specific and updated surface-volume rating curves were here contained through a power relationship adapted over time for silting based on data from 15 surrounding lakes. Applied to 51 small reservoirs and 546 images over 1999–2014, results highlight the ability of this transposable method to shed light on flood dynamics and allow inter annual and inter lake comparisons of water availability. In the Merguellil upper catchment, in Central Tunisia, results reveal the significant droughts affecting over 80% of reservoirs, confirming the need for small reservoirs to maintain a supplementary irrigation objective only.

Internal structure and materials of the Yangsan fault, Bogyeongsa area, Pohang, South Korea

Abstract: The internal structure and materials of a fault are crucial to understanding its mechanical and fluid flow behaviors because they are interrelated. The Yangsan fault is a major strikeslip fault in SE Korea, and its possible reactivation has been an issue of great interest and debate. However, the internal structure of the fault has not been extensively studied; one reason for this is the scarcity of the fault outcrop. Based on field observations and materials analysis, here we report the characteristics of the internal structure and the materials of the fault in the Bogyeongsa area, where a new outcrop showing the entire section of the fault is found. The fault is composed of a core zone (9−10 m in thickness) and surrounding damage zones (>200 m in thickness). The core zone has two subzones: one is an ~8–9-m thick alternating blue and purple gouge zone (BPZ) and the other is an ~0.5-m thick brown gouge zone (BZ). The former exhibits large fractured lenses and anastomosing gouges, and the latter has a strong network of foliation. Given the smaller content and size of clasts in the BZ than in the BPZ, it follows that larger fault displacement was accommodated in the BZ than in the BPZ. The damage zones around the core zone are characterized by dense fractures and veins and subsidiary faults of multiple generations. According to an analysis of the materials, the core zone gouges are clay-rich (>50 wt%). The BPZ is enriched in illite and chlorite, whereas the BZ is enriched in smectite, which has a notably low frictional strength when wet. Given the occurrence of the Quaternary slip faults in the damage zone of the Yangsan fault in other areas, further studies of the materials and mechanical properties on both the main core zone and the subsidiary faults in the damage zones are necessary to determine which is likely to be reactivated seismogenically under the current stress field.

Experimental and theoretical investigations into the formation of ice lenses in deformable porous media

Abstract: The aim of this paper is to increase the understanding of ice lens initiation and growth in freezing soil. A model describing the growth process of ice lenses in soils has been established. The model presented here, which considers a series of processes, including heat transfer, water migration, phase change, ice lens formation, soil deformation, is solved by the use of a transient finite element. The simulated results agree with the experimental data. Results show that: (1) Negative pore water pressure occurs in unfrozen areas, this result in the water transfers from the unfrozen zone to the frozen zone and substantial water was stored in the frozen zone which results in oscillation with in water content distributions. (2) Few segregation ice lenses appeared in the fast freezing section, several thin and discontinuous segregation ice lenses appeared in the transitional section, and thick ice lenses appeared in the third phase when the freezing front tended to be stable. (3) Both the consolidation process and the expansion process are in progress during the freezing process, due to the migration of unfrozen water. (4) The frost heave model is composed of two aspects: the coupled heat-mass transport and the growth of ice lens. Numerical modeling is able to represent the development of both the thermal field and ice segregation observed in the physical models.

Estimating shear wave velocities in oil fields: a neural network approach

Abstract: In this study, we applied the back-propagation Artificial Neural Network (ANN) technique to test the shear-velocity for the two wells from an oil field in southeastern region of Turkey estimated from an empirical relationship. The input to the neural network includes neutron porosity, density, true resistivity, P-wave velocity and gamma-ray logs which are known to affect the shearwave velocity. The correlation between the shear-wave velocity from the empirical relationship and that from the neural network is close to one in both the training and testing stages. Thus, the ANN technique can be used to predict shear-wave velocity from other well log data.

Spectral characteristics of minerals associated with skarn deposits: a case study of Weondong skarn deposit, South Korea

Abstract: This study examined the spectral characteristics of minerals occurring at Weondong skarn deposit located in South Korea and assessed the effectiveness of VNIR-SWIR spectroscopic approaches in zone definition characterizing skarn deposits based on XRD, XRF, and petrographic studies. The spectroscopic analyses identified intrusive rock, garnet-clinopyroxene skarn, clinopyroxene-garnet skarn, W-ore, and host rock zones. The assessment results for VNIR-SWIR spectroscopy in skarn exploration illustrated that the spectral approaches would be very useful for attaining skarn mineral information such as calcite, chlorite, clinopyroxene, garnet, scapolite, vesuvianite, and wollastonite and clay minerals. Furthermore, the rock-forming minerals such as K-feldspar, plagioclase, quartz, fluorite, and tungsten-bearing minerals like scheelite may require supplementary mineral analysis. A combined analysis of spectrometry, XRD, XRF, UV lamp scanning, and petrographic studies reveals that the skarn mineralization of the study area related to W mineral of the study core is defined as proximal endoskarn to proximal exoskarn, which could be defined by spectroscopic approaches.

GIS-based evaluation of geomorphic response to tectonic activity in Makran Mountain Range, SE of Iran

Abstract: This paper investigates the impact of active tectonics on the geomorphic processes and landscape evolution of Makran Mountain range at southeastern of Iran using spatial analysis of geomorphic indices. We documented how topography and morphology are influenced by active tectonic deformation. Quantitative analysis of the geomorphological response to active tectonics within the study area have been done using drainage basin asymmetry factor (Af), drainage basin shape index (Bs), drainage density index (Dd), hypsometric integral (Hi), mean axial slope of the channel (MASC), topographic roughness (STD), mountain-front sinuosity (Smf) and valley floor width-valley height ratio (Vf). The obtained results from these indices were combined to yield an index of active tectonics (Iat). The indicative values of this index are consistent with the landforms and geology of the study area. The morphometric data (quantitative analysis of geomorphic indices) provides evidence of relative variation in the tectonic activity of the study area and related landforms. The utilization of geomorphic parameters exhibits decrease in the geomorphic response of the landforms from north to south. Also, the Ghasr-e-Ghand fault, based on the front-based indices has an important role in uplift of the middle part of the study area. Based upon the results of this study we suggest a southward tectonic vergence for the Makran Mountain Range.