Geological Variables Research Articles

Coastal vulnerability assessment using GIS-Based multicriteria analysis of Alexandria-northwestern Nile Delta, Egypt

This study intends to map the relative coastal vulnerability index (CVI) for the administrative governorates of Alexandria and adjacent Behera in the northwestern coastal margin of the Nile delta. In addition to other common environmental stresses, these governorates are under threat due to accelerated sea level rise induced from climate change. Of special interest is that the coastal margin of the study area is characterized by markedly constructing geology, morpho-dynamics and land surface topography that varies from low-lying (−3 m below MSL) to high land (~20 m height). Therefore, nine physical and geological variables influencing the vulnerability of the coast are used in this study, including land elevation, seabed/beach composition, beach type (dissipative to reflective), relative sea level, historical shoreline change, tidal range, significant wave height, shore protection measures, and land cover. Results obtained from performing multi-criteria analysis of GIS indicates that about 16.58%, 15.45, 42.03%, 18.16 and 7.78% of the shoreline is under very high, high, moderate, low and very low vulnerability respectively. Of great concern is that although the low-lying broad depression (−1 to −3 m below MSL) east and southeast of Alexandria is protected now by a combination of natural shore-parallel elevated ridges (up to 10 m) and artificial shore-parallel detached structures, it is likely to be accidently flooded by unexpected extreme storm or tsunami events at the lowest waterfront points.

A wind-albedo-wind feedback driven by landscape evolution

The accurate characterization of near-surface winds is critical to our understanding of past and modern climate. Dust lofted by these winds has the potential to modify surface and atmospheric conditions as well as ocean biogeochemistry. Stony deserts, low dust emitting regions today, represent expansive areas where variations in surficial geology through time may drastically impact near-surface conditions. Here we use the Weather Research and Forecasting (WRF) model over the western Gobi Desert to demonstrate a previously undocumented process between wind-driven landscape evolution and boundary layer conditions. Our results show that altered surficial thermal properties through winnowing of fine-grained sediments and formation of low-albedo gravel-mantled surfaces leads to an increase in near-surface winds by up to 25%; paradoxically, wind erosion results in faster winds regionally. This wind-albedo-wind feedback also leads to an increase in the frequency of hours spent at higher wind speeds, which has implications for dust emission potential.

Common pattern of distribution for Mesoamerican Triatoma dimidiata suggest geological and ecological association

The phylogeny of the Triatoma dimidiata complex has been widely assessed with different genetic and morphological data, which has allowed to reach the consensus that the complex consists of at least three taxonomic units. However, these taxonomic units seem to have a distribution related to geography throughout Mesoamerica, with different groupings depending on the source of information used. In the present study, we aimed to determine if there is a common biogeographical, genetic and phenetic distribution pattern among the T. dimidiata species in Mesoamerica and if this pattern is related to ecological and geological variability of the region. We found that panbiogeographical analysis showed three generalized tracks that coincide with genetic/phenetic data which showed a general pattern of distribution in two big clusters to the north and south of Mesoamerica. We also found that these clusters were significantly related to geological tectonic plates and ecotypes. We conclude that the geological history may be a plausible explanation for the greater differentiation observed in the T. dimidiata complex, but that the current ecological characteristics of the morphotectonic units or ecotypes may be responsible for the additional variation observed and therefore differential control strategies for each cluster considering geological history and ecotype should be used. Further, more detailed biogeographical and landscape genetic analyses are necessary with the goal to elucidate T. dimidiata differentiation related with ecological and geological variables in the region and the possible epidemiological and evolutionary consequences.

Hydrological responses in equatorial watersheds indicated by Principal Components Analysis (PCA) – study case in Atrato River Basin (Colombia)

ABSTRACT The Atrato river basin is located in the Pacific fringe of Colombia, region with one of the highest precipitation rates in the world. The main purpose of this study is to determine the dominant processes in the hydrological responses along 17 sub-basins within the basin using principal component analysis. Watersheds located at the headwater presented a fast or medium response to the precipitation events, while higher flow homogeneity was observed in watersheds located at the lower portions of the basin. Three principal components were responsible for explaining 85.18% of the total variance. The component PC1 revealed the largest contributions for low flow behavior, being associated to precipitation, characteristic discharge values, compactness index, soil coverage and soil coarse textures. The component PC2 was assigned to the geological variables, fine and average texture soil and the average basin slope. Finally, the component PC3 has shown to be related to high flow patterns (maximum characteristic discharge values Q5 and Q1), igneous rocks and length of the basin. Highest specific discharge was associated to alluvial deposits and forest cover, whereas the slope was considered determinant for the run-off generation.

Plotting Ternary Diagrams by R Library ggtern for Geological Modelling

Selecting proper methods of data modelling is crucial in geosciences, as effective data visualization enables better understanding of complex geological phenomena: processes, structure and dynamics. Various approaches of the data analysis by R language include both traditional methods of linear charts and other approaches to data visualization: ternaries, circular and radar charts. Using ternaries for triple correlations between variable can be seen in applied geological analysis which proves it to be important method for data modelling. Visualizing geological variables by ternaries enables to highlight correlation between variables in a triangle, how data are dependent and affected. In this study, several geologic, tectonic and geomorphic variables, such as sediment thickness, tectonic plates, volcanic areas, steepness and depths, were tested using R based modelling in {ggtern} library. Other graphs include radar charts and circular diagrams. Visualizing attributes as a triple component correlation by ternaries gives a better insight to the geological factors. Traditional techniques for visualization of pairwise linear correlations are not sufficient to show triple variations. Ternaries approach identifies data correlations by triple factors. Additional graphical models include circular and Euler-Venn diagrams of quantitative and qualitative geospatial data modelling. The study is supported by 7 R code listings and 9 figures.

Multi-scale characteristics of remote sensing lineaments

Lineaments whose dominant azimuth reflects the basic framework of regional structure are mainly related to faults, but their spatial morphology and characteristics are different at different scales. The changing characteristics of multi-scale lineaments extracted by wavelet edge detection are quantitatively analyzed through image characteristics, azimuth characteristics, histogram, box-plot and paired-samples T test. As the result, the difference of “proportion of NE structure” in different areas becomes more and more significant with the increasing of wavelet transformation scale. Three geological variables extracted based on wavelet edge image of Level 3, “proportion of NE structure”, “density of NE structure” and “entropy”, are synthesize by factor analysis, then the results show that the distribution of the values referring to the “dominance of NE structure” are basically consistent with the structure framework of Huize lead-zinc mine area, that is, the dominant position of NE lineaments in the triangular region enclosed by the large main faults such as Kuangshanchang Fault and Qilinchang Fault is the most obvious. The potential relation between remote sensing lineaments and actual geological structure can be found through multi-scale edge detection and characteristics analysis.

Rational Way of Estimating Liquefaction Severity: An Implication for Chattogram, the Port City of Bangladesh

Earthquake-induced liquefaction is responsible for the extensive damage to the infrastructures in both developed and developing cities. Chattogram, the second largest city of Bangladesh and one of the vital port city in the south Asian region is situated in the active seismic region, and the frequency of recent small magnitude earthquakes around the city reveals that a significant earthquake of probable magnitude 7.0 or higher is due. Therefore, liquefaction severity at different locations of Chattogram Metropolitan Area is estimated based on the in situ parameters. Two widely used liquefaction assessment procedures has been applied to estimate the liquefaction susceptibility at the selected locations. Later, geospatial techniques are applied to prepare a hazard map based on liquefaction potential of discrete locations. The flat tidal part of the city is identified as extremely liquefy prone areas, while the small hillocks and nearby areas at the central part of city are safe against liquefaction hazard. Geological variation of parameter in all directions are also taken into account to prepare the hazard map. Predicted liquefaction potential is then compared with a second data set and the linear regression between the observed and predicted liquefaction potential portray consistent approximation in all cases. Case studies and practical experience also justify the developed hazard map. Therefore, the developed hazard map can be a useful tool for the disaster mitigation policy of Bangladesh Government.

Facies classification with different machine learning algorithm – An efficient artificial intelligence technique for improved classification

Accurate and precise identification of lithological facies is vital to understand geological variation in a proven reservoir. Four specific different machine learning (ML) classification algorithms...

Parameterization of A Priori Geological Knowledge in Seismic Inversion

Abstract—An approach to parameterization of prior geological knowledge concerning the changes in depositional environment in space and geological time for their quantitative use in the workflow of seismic inversion is presented. The idea is to describe the observed or expected facies diversity in terms of a few statistically independent factors (generalized geological variables). The topology and metrics of the model are determined by the set of basic depositional environments and the statistics of facies transitions. The introduced parameters make it possible to estimate the occurrence probability of different facies at each model point. The proposed technique can be applied for regions with various degree of detail of the existing geological knowledge and amount of available well logging data.

Regional relative tectonic activity of structures in the Pampean flat slab segment of Argentina from 30 to 32°S

The Pampean flat slab segment of the Central Andes in Argentina is a broad, active deformation zone subject to both plate boundary-related and intraplate deformation. To the west, plate boundary-related deformation is dominated by thin-skinned fold-and-thrusts of the Precordillera, while to the east, intraplate deformation involves thick-skinned reverse faults of the Sierras Pampeanas. GPS data and absolute dating of displaced geomorphic features suggest that most of the active permanent deformation occurs between these two regions at the Andean orogenic front and that there is a west-to-east trend of decreasing shortening rates. However, GPS stations and sites with geomorphic slip rate measurements are currently too sparse and cover too short a time period to make reliable inferences about the longer-term distribution and relative rates of deformation. Mountain range-scale geomorphic indices, on the other hand, reflect tectonic activity since at least the Pleistocene. In this study, we measured geomorphic indices (hypsometric integral and curves, basin elongation ratio, basin volume-to-area-ratio, valley floor width-to-height ratio, mountain front sinuosity, and normalized steepness indices of rivers) from 10 different N-S striking, range-bounding faults that span both the Precordillera and Sierras Pampeanas regions from west to east. We use these data to assess the regional relative tectonic activity of major Quaternary deformation features in the Pampean segment of the Central Andes. Even when variations in climate and geology are considered, mean values for each geomorphic index suggests uplift rates for the 10 mountain-range bounding faults display local trends that are closely associated with the structural style and tectonic evolution of these structures. Although vertical uplift rates vary little, horizontal shortening rates are higher for the Precordillera fold-and-thrusts in the west than the thick-skinned reverse faults of the Sierras Pampeanas in the east, due to shallower fault dips for Precordilleran structures. The similarity with decadal slip rate gradients from GPS studies could possibly indicate that the stress-field has been constant since at least the Pleistocene, but further slip rate studies over broader time intervals in the late Quaternary are necessary to confirm this. Variations observed in relative uplift rates along each fault point to sites that warrant further detailed study of slip rates and evaluation of associated seismic hazards.

Detecting riparian habitat preferences in "savanna" chimpanzees and associated Fauna with strontium isotope ratios: Implications for reconstructing habitat use by the chimpanzee-human last common ancestor.

Riparian or gallery forests are critical habitats for numerous plants and animals today. Paleoanthropologically, reliance on such habitats informs behavioral and ecological reconstructions; for example, gallery forest habitats likely played a critical role in the transition from ape to hominin in the early Pliocene and may represent a preferred habitat for the last common ancestor of chimpanzees and humans. Direct indicators for gallery forest habitats preference are lacking. The objective of this article is to assess whether strontium isotope ratios are a reliable indicator of habitat preference for fauna living in and around gallery forests. We report bioavailable strontium isotope ratios from the Mugiri River, its tributaries, and its gallery forest (Toro-Semliki Wildlife Reserve, southwestern Uganda), and compare them to surrounding savanna-grassland values. We compare these environmental values to strontium isotopes ratios in faunal tooth enamel to determine if habitat preferences are accurately reflected. Gallery forest and savanna-grassland vegetations have significantly different strontium isotope ratio profiles. We trace these isotopic differences to the influence of the Mugiri tributaries, which originate on Paleoproterozoic gneiss deposits on top of the surrounding escarpments. These isotopic differences in vegetation are mirrored in the tissues of fauna with habitat preferences for either the gallery forest or the surrounding grasslands. This research demonstrates the potential of strontium isotope ratios to identify habitat preferences in modern or fossil fauna under proper geologic variability. It provides a methodological model for future studies seeking to reconstruct habitat preferences in early hominins.

Geologic and geomorphic controls on rockfall hazard: how well do past rockfalls predict future distributions?

Abstract. To evaluate the geospatial hazard relationships between recent (contemporary) rockfalls and their prehistoric predecessors, we compare the locations, physical characteristics, and lithologies of rockfall boulders deposited during the 2010–2011 Canterbury earthquake sequence (CES) (n=185) with those deposited prior to the CES (n=1093). Population ratios of pre-CES to CES boulders at two study sites vary spatially from ∼5:1 to 8.5:1. This is interpreted to reflect (i) variations in CES rockfall flux due to intra- and inter-event spatial differences in ground motions (e.g., directionality) and associated variations in source cliff responses; (ii) possible variations in the triggering mechanism(s), frequency, flux, record duration, boulder size distributions, and post-depositional mobilization of pre-CES rockfalls relative to CES rockfalls; and (iii) geological variations in the source cliffs of CES and pre-CES rockfalls. On interfluves, CES boulders traveled approximately 100 to 250 m further downslope than prehistoric (pre-CES) boulders. This is interpreted to reflect reduced resistance to CES rockfall transport due to preceding anthropogenic hillslope de-vegetation. Volcanic breccia boulders are more dimensionally equant and rounded, are larger, and traveled further downslope than coherent lava boulders, illustrating clear geological control on rockfall hazard. In valley bottoms, the furthest-traveled pre-CES boulders are situated further downslope than CES boulders due to (i) remobilization of pre-CES boulders by post-depositional processes such as debris flows and (ii) reduction of CES boulder velocities and travel distances by collisional impacts with pre-CES boulders. A considered earth-systems approach is required when using preserved distributions of rockfall deposits to predict the severity and extents of future rockfall events.

Description of three new velvet geckos (Diplodactylidae: Oedura) from inland eastern Australia, and redescription of Oedura monilis De Vis.

Inland eastern Australia has a complex array of habitats, driven by variation in topography, geology and moisture. This broad region is relatively poorly surveyed compared to coastal eastern Australia and likely contains significant numbers of undescribed reptiles. Oedura monilis is found through much of this region but has been shrouded in taxonomic uncertainty since its original description. Here I assess variation across the range of 'O. monilis' and show that it consists of two species: a widespread species in the northern half of the range and a widespread species in the southern half of the range. These two species are readily diagnosed by colour pattern and aspects of shape and scalation. I show that the name O. monilis applies to the northern species. I also show that the name O. attenboroughi Wells Wellington applies to the northern populations, making it a junior synonym of O. monilis. I describe the southern widespread species as Oedura elegans sp. nov.. I also describe two new, highly localised species from inland eastern Queensland that are allied to O. monilis: Oedura picta sp. nov. from a rocky range in the Moranbah-Dysart region, and Oedura lineata sp. nov. from brigalow forest remnants in the Arcadia Valley. These two species are distinct for colour pattern and aspects of size, shape and scalation. Oedura lineata sp. nov. has a very small and fragmented range, and is restricted to a highly threatened habitat type. It therefore warrants conservation attention. I also provide more detailed diagnoses for O. coggeri Bustard and O. tryoni De Vis, and demonstrate that the name O. ocellata Boulenger is a junior synonym of O. tryoni.

Bayesian artificial intelligence for geologic prediction: Fracture case study, Horn River Basin

AbstractA Bayesian Belief Network (BN) has been developed to predict fractures in the subsurface during the early stages of oil and gas exploration. The probability of fractures provides a first-order proxy for spatial variations in fracture intensity at a regional scale. Nodes in the BN, representing geologic variables, were linked in a directed acyclic graph to capture key parameters influencing fracture generation over geologic time. The states of the nodes were defined by expert judgment and conditioned by available datasets. Using regional maps with public data from the Horn River Basin in British Columbia, Canada, predictions for spatial variations in the probability of fractures were generated for the Devonian Muskwa shale. The resulting BN analysis was linked to map-based predictions via a geographic information system. The automated process captures human reasoning and improves this through conditional probability calculations for a complex array of geologic influences. A comparison between inferred high fracture intensities and the locations of wells with high production rates suggests a close correspondence. While several factors could account for variations in production rates from the Muskwa shale, higher fracture densities are a likely influence. The process of constructing and cross-validating the BN supports a consistent approach to predict fracture intensities early in exploration and to prioritize data needed to improve the prediction. As such, BNs provide a mechanism to support alignment within exploration groups. As exploration proceeds, the BN can be used to rapidly update predictions. While the BN does not currently represent time-dependent processes and cannot be applied without adjustment to other regions, it offers a fast and flexible approach for fracture prediction in situations characterized by sparse data.

Erosion Hazard Model Mapping for Orlu Zone, Imo State, Nigeria Using GIS

Soil erosion is a significant environmental issue of common concern in the world today. For the past five decades, the study area (Orlu Zone) in Imo State, Nigeria has been experiencing environmental degradation and loss of properties due to soil erosion. Impact of soil erosion on man and his environment is natural and as old as the time of Earths creation. It has been supported that a number of factors combined in contributing to soil erosion and its negative environmental consequences ranging from social, economic and property losses of which serious runoff and soil loss has become one of the main factors restraining local economic developments. The aim of this study is therefore, to produce an erosion hazard model map that identifies areas of high and low risks for erosion. Study identified seven susceptibilities factors (soil characteristics, variation in elevation, slope, land use, geology, population density and drainage density) of soil erosion, converted them to grid format and reclassified each factor into five potential after assigning erosion risk values based on acceptable hazard potential of each factor. Thereafter, weighed on Arc GIS version 10.2 software weighted overlay toolbox to produce erosion risk map showing Orlu Zone lands classified into various hazard potentials. Result showed that highest vulnerable land areas to soil erosion occurred in the Northern part of the study area while the lowest vulnerable areas occurred on the Southern counterpart.

How Local Economic Conditions Affect School Finances, Teacher Quality, and Student Achievement: Evidence from the Texas Shale Boom

AbstractWhether improved local economic conditions lead to better student outcomes is theoretically ambiguous and will depend on how schools use additional revenues and how students and teachers respond to rising private sector wages. The Texas boom in shale oil and gas drilling, with its large and localized effects on wages and the tax base, provides a unique opportunity to address this question that spans the areas of education, labor markets, and public finance. An empirical approach using variation in shale geology across school districts shows that the boom reduced test scores and student attendance, despite tripling the local tax base and creating a revenue windfall. Schools spent additional revenue on capital projects and debt service, but not on teachers. As the gap between teacher wages and private sector wages grew, so did teacher turnover and the percentage of inexperienced teachers, which helps explain the decline in student achievement. Changes in student composition did not account for the achievement decline but instead helped to moderate it. The findings illustrate the potential value of using revenue growth to retain teachers in times of rising private sector wages.

GIS Modeling of Earthquake Damage Zones Using ETM Data and Remote Sensing- Bojnoord, Khorasan Province.

The devastating earthquake that occurred in Khorasan Shomali Province, Iran, on the 12th May 2008, caused widespread damage and devastation to rural communities and economy. The terrain of the entire region has been weakened and is now highly susceptible to long-term slope instability that will trouble this region for many years to come. Methodology: However, the actual intensity caused by the earthquake ranged between VIII and XI. The seismic intensity map is practical for regional guidance but lacks the detail to provide an adequate representation of the true damage level, in terms of current status and future potential in such a seismically active and populated region, especially when the hazards and risks are likely to be multiple and cascading in high relief areas. Results: This paper presents a GIS-based approach to earthquake damage zone modeling using satellite remote sensing and DEM data. The novelty is to take into account the coseismic ground deformation as an important modulating factor in modeling the susceptibility of earthquake-related geohazards, together with conventional multicriteria factors which draw on geological and topographical variables such as rock competence, slope, proximity to drainage, and fracture density. The modulating effect of the earthquake greatly enhances the susceptibility in the areas where the majority of the ensuing landslides and debris-flows actually took place. Conclusion: When this susceptibility model is further modulated by the mapped surface disruption caused by the earthquake, it is directly linked to seismic intensity and we call it “earthquake damage”. The output earthquake damage map represents both the current damage status as well as the future damage (hazard) potential.

Magnetic and radar surveys at Locri Epizephyrii: A comparison between expectations from geophysical prospecting and actual archaeological findings

Abstract In recent years, geophysical methods have been increasingly applied as a preliminary mapping tool to guide archaeological excavations. Despite the reported growing case histories of geophysical prospections for archaeological purposes, direct comparison between expectations arising from the geophysical results and actual findings is not always systematically performed. A critical comparison between pre-excavation geophysical-guided hypotheses and post-excavation archeological evidences is proposed in this work. A test site within the archaeological area of Locri Epizephyrii (Calabria, southern Italy) was chosen for this purpose. An unsurveyed rectangular area (31 × 26 m) was investigated with high-density ground-penetrating radar (GPR) and magnetic profiles. Several anomalous alignments, both compatible and oblique with respect to the orientation of the Greek-Roman city plan, were preliminarly observed in the geophysical results. The use of two different techniques allowed for comparison of anomalous areas, enhancing the likelihood of finding features of significance. Two archaeological soundings were later carried out in the areas showing the most peculiar geophysical anomalies. Several structures revealing the same orientation of the ancient city plan and belonging to at least two different building phases were unearthed from a depth of 15–25 cm below the ground surface. A systematic comparison between geophysical and archeological results was then carried out. In general, walls showing different construction typologies (opus testaceum, opus incertum or opus caementicium) were found to generate similar radar anomalies. Artifacts made with materials similar to the background sandy alluvial deposits were not identified by both geophysical techniques, as in the case of an unearthed channel bank, made of local sandstone blocks. GPR was globally observed to detect buried structures better than the magnetic method, probably due to background geological variables linked to the presence of Fe-rich minerals within the background sediments, generating noisier and scattered magnetic gradient maps.

Seismic graph analysis to aid seismic interpretation

During the seismic interpretation process, geoscientists rely on their experience and visual analysis to assess the similarity between seismic sections. However, evaluating all of the seismic sections in a 3D survey can be a time-consuming task. When interpreters are working on a data set, a common procedure is to divide the cube in increasingly finer grids until they are satisfied with the result of the interpretation. We have developed a method based on graph theory and image texture in which we represent a seismic data set as a complete weighted undirected graph — which we call a seismic graph. The vertices of this graph represent the seismic sections, and the weight of the edges represents the distance between the texture feature vectors of the vertices they connect, allowing for a powerful yet concise representation of potentially large data sets. We have investigated the potential of graph analysis to build an adaptive grid that is more likely to capture the underlying structures present in a survey, providing a tool for a faster and more precise interpretation. The main idea is that such a grid would be finer in regions with more geologic variations and coarser otherwise. To demonstrate the capabilities of our technique, we apply it on a public data set called Netherlands F3. Using our method, we suggest which seismic sections — key sections — should be considered in the interpretation process. The results of our experiments indicate that our methodology has great potential to aid the seismic interpretation process.

Applications of supervised deep learning for seismic interpretation and inversion

Recent advances in machine learning and its applications in various sectors are generating a new wave of experiments and solutions to solve geophysical problems in the oil and gas industry. We present two separate case studies in which supervised deep learning is used as an alternative to conventional techniques. The first case is an example of image classification applied to seismic interpretation. A convolutional neural network (CNN) is trained to pick faults automatically in 3D seismic volumes. Every sample in the input seismic image is classified as either a nonfault or fault with a certain dip and azimuth that are predicted simultaneously. The second case is an example of elastic model building — casting prestack seismic inversion as a machine learning regression problem. A CNN is trained to make predictions of 1D velocity and density profiles from input seismic records. In both case studies, we demonstrate that CNN models trained from synthetic data can be used to make efficient and effective predictions on field data. While results from the first example show that high-quality fault picks can be predicted from migrated seismic images, we find that it is more challenging in the prestack seismic inversion case where constraining the subsurface geologic variations and careful preconditioning of input seismic data are important for obtaining reasonably reliable results. This observation matches our experience using conventional workflows and methods, which also respond to improved signal to noise after migration and stack, and the inherent subsurface ambiguity makes unique parameter inversion difficult.