Anomalous Zones Research Articles

Understanding the behaviour of seismically derived Poisson's ratio in near-surface characterization

Near-surface characterization is often challenging using a single geophysical technique. We show that seismic refraction is an effective tool by combining P- and S-wave velocity models in the form of V P / V S and Poisson's ratio ( σ ) to detect buried targets along with electrical resistivity imaging (ERI). We acquired vertical and horizontal component seismic data along a 2D profile over two known targets. The first is a water pipe of c . 0.8 m diameter located c . 1.5 m below the surface and the second is a storm drainage pipe (SDP) of c . 1 m diameter at c . 2 m depth. The first arrival times of vertical and horizontal component data were picked and inverted using grid-based tomography. The resulting velocity models have smoothly varying structures and could not identify any of the target features. However, when combined as V P / V S and Poisson's ratio models, the features clearly appeared as anomalous zones. A collocated 2D electrical resistivity model shows the presence of anomalies around the same locations. Our study suggests that anomalous V P / V S and Poisson's ratio values derived from seismic velocities are indicative of the relative changes owing to the disturbances in the soil because of construction with respect to the background instead of the anomaly.

Deciphering the low-frequency seismic signals in the Weiyuan Shale gas field: implications for reservoir and structural heterogeneity

SUMMARY Hydraulic fracturing (HF) often stimulates the local earthquake productivity which provides a unique opportunity to characterize the crustal heterogeneities, reservoir properties and fluid injection effects. However, the velocity models acquired solely based on the arrival time records are often undermined due to the seismic network coverage and interpolation techniques. Instead, we adopt the waveform-based approach to apprehend; (1) structural heterogeneities, (2) reservoir distribution and (3) signatures of the injected fluid in the Weiyuan shale gas field. We categorize the waveforms into dominant high and low frequencies based on the qualitative inspection and frequency index analysis of the seismic waveforms. We first inspect the waveform to access the potential controlling mechanisms (source, site and path effects) at both single and multiple stations in different azimuthal orientations. As a result, we find the path effect as a dominant factor to influence the waveform characteristics, for example S-wave amplitude, and frequency. Subsequently, to localize the path effect, we conduct an in-depth examination of events within 10 km of each seismic station and classify the waveform records using their frequency indices. Notably, certain stations record a significant proportion of low-frequency waveforms (LFWs, up to 20 per cent), while others have limited occurrences (∼1 per cent) indicating suspected anomalous zones. Afterward, we identify two suspected anomalous zones based on LFWs intensity and ray tracing map. Both zones are in close proximity to fault zones and preserved reservoirs with no HF activities, where fault damage zones or the fluid-rich reservoir may contribute to our observed LFWs.

Three-dimensional fine crust-mantle structure imaging and structural characteristics of Bohai Sea

This study used the consistency-constrained double-difference tomography method to invert 3D fine structure models of Vp, Vs, Vp/Vs at depths above 60 km, and precise relocation parameters of earthquakes in the Bohai Sea. According to the results, the velocity structures of P-wave and S-wave in the Bohai Sea area were highly similar and demonstrated noticeable lateral non-uniformity. The crust beneath the Tanlu Fault displayed a clear stratification structure, with a continuous velocity transition in the middle of the crust. The intricate crustal structure beneath the Zhangpeng Fault displayed high-velocity bodies in the crust and low-velocity anomalous zones connected to the top of the mantle in the lower section of the crust. The structural pattern in the deep crust of the Bohai Sea controls the occurrence characteristics of the Zhangpeng Fault and the Tanlu Fault. The earthquakes in the Bohai Sea area were concentrated mainly in the southern part near the Zhangpeng Fault. There is a good correspondence between the relocated earthquakes and velocity structure. There are many significant differences in crustal structure between the north and south of the Bohai Strait, and there are obvious velocity anomalies in the middle and upper crust. The distribution shape of high Vp/Vs value indicates that mantle material migration has occurred at the bottom of the crust. This paper provided important reference for further research on the relationship between deep tectonic features and tectonic activity in the North China Craton.

Оценка параметров источника гравитационной аномалии методом роя частиц

An algorithm for solving a nonlinear inverse problem of gravity exploration using the particle swarm optimization for a two-dimensional horizontal prism is considered. After a relatively small number of iterations, the size and depth of the disturbing object were determined. Three options were used to adjust the speed of movement of the swarm during the optimization process. The interpretation results are presented in the form of a geodensity model that corresponds to the minimum discrepancy between the observed and theoretical fields, as well as a vertical isoline map of the localization function. A quantitative interpretation of the gravity force of the Berezovskiy anomalous zone (Perm region) was carried out. It is concluded that the use of swarm intelligence is highly promising for assessing the parameters of gravitational anomalies sources.

Energy Consumption of Methods for Pattern Recognition using Microcontrollers

This paper presents the study of energy consumption of the methods for recognizing patterns/anomalies in numerical series, namely, the light sensor values in a smart home system. Methods for analyzing time series, identifying anomalous zones, and testing anomaly recognition algorithms are presented, and the smart system is prototyped. The energy consumption of correlation, comparison, and recognition methods using NNs is measured and analyzed. The case study has confirmed that the most resistant to signal changes and interference is the correlation analysis method. A methodology for applying recognition algorithms for different strategies for using optimal energy consumption is presented.

Structural and tectonic features of the Transcarpathian trough according to gravity and magnetic data

Based on the analysis and interpretation of gravity and magnetic field anomalies, we studiedthe peculiarities of fault tectonics, structural-tectonic structure (including salt dome tectonics) of the Transcarpathian trough. We identified signs of the manifestation of deep faults and other large structural-tectonic elements in anomalies of gravity and magnetic fields. We then traced these structural-tectonic units by comparing the morphology, intensity, dimensions, and directions of the typical anomalous zones in the gravitational and magnetic fields with the tectonic structure of the region.
 We used digital maps of gravitational and magnetic fields; averaging transforms and relief-shadow images, we mapped local gravimagnetic anomalies. Analysis of the spatial structure of the original gravimagnetic fields and their transforms and structural-tectonic maps yielded a reflection of large tectonic elements of fault tectonics, anticlinal and salt dome structures in the gravimagnetic fields. Based on gravimagnetic data, the tectonic structure of the Transcarpathian trough was clarified, and the boundaries of tectonic zones and microplates were traced. The zone of the Transcarpathian deep fault is identified as a tectonic zone traced by a band of intense local positive anomalies of the gravity field along the Flysch Carpathians to the border of the Marmarosh massif. It is limited by high gradients from the southwest and northeast and is a reflection of the Pieniny and Marmarosh rock zones. The zone of the Transcarpathian deep fault is considered a suture zone of the Inner and Flysch Carpathians. In the structure of the anomalous gravity field of the Transcarpathian trough, a number of local anomalies associated with salt stocks, as well as individual anomalies, expected to be connected to salt-bearing deposits, werefound.
 We confirmed the effectiveness of gravimagnetic methods in the geological conditions of the Transcarpathian trough to detect anticlinal structures, basement protrusions, which create favorable conditions for oil and gas traps in sedimentary strata. Interpreting anomalous gravimagnetic fields in combination with geological and tectonic materials is an important condition for the integral process of studying the geological and tectonic structure of the Earth’s crust in the Transcarpathian region.

A Short Review on The Application of Potential Field Methods for Geothermal Energy Exploration

There is quite a long history in Nigeria of Geothermal energy exploration. Geothermal energy resources are available in every part of Nigeria beneath the subsurface. The resources, however, vary in concentration in all the geological parts of the country. This paper reviewed the prospects of geothermal energy exploration by using the potential field (magnetic and gravity) technique for the exploration activities. The potential field data is capable to provide information on the subsurface structures after some filtering techniques (in case of magnetic) or data corrections (in case of gravity) have been applied to the raw field data. The processed data is capable to scan the lateral and vertical extent of anomalous zones beneath the surface. Geothermal energy, if properly exploited would contribute to the generation of clean energy in Nigeria for domestic and industrial purpose.

Недеструктивно археологическо проучване в местността „Долната чатма“ при село Велино, Шуменско

In the late autumn of 2022, a non-destructive archaeological survey was carried out in the territory of Velino village, Shumen municipality. The survey went through several stages: 1) collection of preliminary information on the names of localities and toponyms in the area of the survey; 2) conducting a field survey during which accumulations of large unprocessed stones and a relatively large concentration of fragmented Old Bulgarian household ceramics were registered; 3) aerial photogrammetric survey of the terrain, as a result of which a digital elevation model and an ortho-photo plan of the area designated for study were produced. The contours of linear structures of artificial origin were clearly visible; 4) geophysical survey in four zones, which confirmed the proposals for the presence of anomalous zones; 5) vertical electric sounding with the aim of studying the stratigraphy of the object during which it was established that the structures probably develop at a depth of 0.80-1.00 m from the contemporary terrain. The results of the non-destructive archaeological survey in Dolnata Chatma locality, near the village of Velino, Shumen region show that linear stone structures develop on the flat terrace east of the village, probably part of a presumed archaeological object. At this stage, its scope, chronology and character are not clarified, and this remains a task for the team in future exploratory and subsequently regular archaeological surveys.

Fine Detection and Analysis of Hidden Karst in Wellsite with Quasi-Three-Dimensional TDEM Based on Lateral Constraint

Considering that karst caves, underground rivers, and dissolution fractures in shallow carbonate formation in the Sichuan Basin are extremely developed, leakage, failure and plugging difficulties are easy to occur in the drilling process. The TDEM was used to carry out the exploration of hidden karst geological bodies in well QM2, and the quasi-three-dimensional inversion based on lateral constrain was used to invert the TDEM data. Three NW trending anomalous bands were identified in the lower Triassic Jialingjiang Formation within the range of drilling, consisting of seven relatively low-resistivity anomalous zones. Under the guidance of TDEM quasi-three-dimensional inversion resistivity data, the low-resistivity karst development area is avoided, and the specific drilling location of well QM2 is determined. No karst cave and underground river were drilled in the later drilling process of well QM2, as well as no instability phenomenon occurred. It indicates that the TDEM detection results are consistent with the actual drilling, and the quasi-three-dimensional TDEM inversion interpretation data based on lateral constraints is reliable and can accurately detect the buried karst in the wellsite.

Tectonic geomorphology of Türkiye and its insights into the neotectonic deformation of the Anatolian Plate

Quantitative geomorphic analyses are usually powerful in identifying active tectonics across global orogenic belts. Our present study will focus on the Anatolian Plate which hosts a lot of recent catastrophic earthquakes in Türkiye. Six geomorphic indices for 100 sub-basins around Türkiye have been computed including local relief, slope, normalized steepness index (kSn)), hypsometric curve and integral (HI), transverse topographic symmetry factor (Tf), and the basin asymmetry factor (Af). The averaged kSn and Af values have shown four high-value anomalous zones, suggesting relatively high uplift rates featured by high river incision and regional tilting. The values of 0.35 ​≤ ​HI ​< ​0.6 for basins with S-shaped curves imply intensive tectonic activities along the eastern part of the North Anatolian Fault Zone (NAFZ), the Northeast Anatolian Fault Zone (NEAFZ), the East Anatolian Fault Zone (EAFZ), and the Central Anatolian Fault Zone(CAFZ). All results of the geomorphic indices analysis suggest a relatively high degree of tectonic activity in the following four areas, the Isparta Angle, the Eastern Black Sea Mountains, the South-eastern Anatolia Region, and the Central Anatolian fault zone. We further suggest that the eastern part of the NAFZ, NEAFZ, EAFZ, and CAFZ will be more active in tectonic activities, with a greater potential for strong earthquake occurrence.

Mapping Leachate Pathways in Aging Mining Tailings Pond Using Electrical Resistivity Tomography

Mining activities often leave behind a legacy of environmental challenges, with aging tailings ponds representing a significant concern due to their potential for leachate formation and subsequent contaminant release. Thus, this study employs Electrical Resistivity Tomography (ERT) to investigate the intricate pathways of leachate within an aging mining tailings pond, addressing the pressing environmental and human health concerns associated with potential contaminant release. Ten 2D ERT profiles were acquired at the El Mochito mine waste site, covering an area of approximately half a square kilometer. These profiles, ranging in length from 104 to 363 m, provided insights into subsurface conditions down to a maximum depth of 60 m. The subsurface mapping of the ERT data showed three different geoelectric layers. The uppermost layer, with a thickness of approximately 2.5 m and resistivity values ranging from 60 to 100 Ohm.m, was identified as a dry tailing/soil zone. Beneath it, the second layer exhibited moderately resistive values (30–60 Ohm.m) with varying thicknesses of 10–20 m, signifying a percolation/leaching zone (semi-saturated zone). The third layer, characterized by substantially low resistivity (1–30 Ohm.m), indicated saturation and the presence of conductive materials, strongly suggesting active leaching. Based on these findings, this study recommends further investigation through geochemical analysis of subsurface samples and more advanced geophysical imaging techniques to validate the distribution of anomalous zones and delineate remediation pathways. This study lays the foundation for future comprehensive research that will integrate geophysical surveys with geochemical analysis and establish 4D modeling techniques to monitor pollutant penetration over time, with a particular focus on mine waste tailings mapping. Plus, this study contributes valuable insights into the characterization of leachate pathways within mining tailings ponds, offering a foundation for informed environmental management and remediation strategies.

“Safe Legal Pathways” or New Colonial Frontiers? A Critical Analysis of European Intervention in the Sahel and the Creation of Anomalous Legal Zones

Abstract This article critiques the increasingly popular concept of the “safe legal pathway” in refugee politics, policy and law, using European engagement and intervention in the Sahel as its primary case study. It draws upon neo-colonial studies, necropolitics, border studies and the legal literature on sovereignty and extraterritoriality to explore the function, structure, and import of the “safe legal pathway”, and its compatibility with contemporary understandings of international legal history and argumentation. Divided into four sections, the article focuses on the drivers behind Europe’s migration-development-security objectives in the Sahelout of which the pathways discourse emerges, the EU’s concomitant insistence on criminalising the illusive “people smuggling business model”, and the role which the traditional tropes of sovereignty, territory, and civilisation play in determining policy parameters. Noting the multidirectional nature and multifunctional purposes of pathways, and focusing on the policing of migrant communities both within and outside Europe, this article provides a comprehensive and critical overview of the nature, structure, function, and regulation of the pathway, its susceptibility to being leveraged for the commodification, extraction, discipline and transformation of non-European bodies and narratives, and its place in the creation of differentiated, suspended, and anomalous legal zones for the transfer and manipulation of global norms.

Density and magnetic susceptibility of major rock types within the Abitibi greenstone belt: a compilation with examples of its use in constraining inversion

Geophysical inversions give non-uniqueness solutions and unless constrained by appropriate initial values and geological constraints can give unrealistic results. One of the critical constraints can be the physical property values of different lithologies. We have compiled a density and magnetic susceptibility database consisting of thousands of measurements collated from different organisations and/or projects across the Abitibi greenstone belt. Statistical tools (histograms, quantile-quantile probability plots and boxplots) are applied to characterise systematically major and minor lithologies. We observed that the magnetic susceptibility frequently has a bimodal distribution, while density is typically unimodal. Our results are summarized in a table that includes the representative mean (or median) and a range of acceptable values. These values can be used to better understand the regional geology, but in this paper, we used the tabulated properties in a geophysical/petrophysical inversion of gravity data from the Chicobi area in the Abitibi subprovince to show the level of improvements that the petrophysical constraints can add to an unconstrained model. When our density database is used to seed the initial guess in a gravity inversion, an anomalous zone becomes apparent that was less evident on an unconstrained inversion.

VERY LOW FREQUENCY ELECTROMAGNETIC (VLF-EM) SURVEY FOR GROUNDWATER DEVELOPMENT IN BICHI/BAGWAI AREA, NORTH WESTERN NIGERIA

Abstarct&#x0D; Detailed Very Low Frequency Electromagnetic (VLF-EM) hydrogeophysical survey was undertaken to identify conductive zones and recommend potential areas for possible groundwater development in the Bichi area of Kano state northwestern Nigeria. Geologically, the area is characterized by porphyritic granite, coarse grained granite and medium to fine grained granite. The VLF-Electromagnetic method was adopted as a fast reconnaissance tool to map possible linear fractures. During the survey, measurements were taken at a station interval of 20 m along each profile line ranging from 0 – 420 m, making a total of six VLF-EM traverses which were mapped in the study area. The filtered components for both real and imaginary parts of the VLF-EM data were plotted against distance for each profile using the Karous–Hjelt filter® computer software to interpret and identify the top of linear fractures. The Very Low frequency (VLF) normal and filtered component anomalies identified ten (10) major geological interfaces suspected to be faults/fractured zones (f1 – f10). These suspected zones were marked as targets for future groundwater development in the area since these anomalous zones are areas of high conductivity and this parameter is one of the physical characteristics of water saturated zones. Therefore, this work has proven that VLF method is robust in tying down good locations for groundwater development in rural areas.&#x0D; Keywords: Electromagnetic, Hydrogeophysical, Groundwater Development, Conductive Zones, Fault, Fractures.

Optimization of electrical resistivity survey utilizing modified harmony search algorithm to predict anomalous zone ahead of tunnel faces

Predicting anomalies ahead of a tunnel face is essential to ensure construction safety and efficiency during tunneling. This study proposes an optimization system to estimate the characteristics of anomalies ahead of a tunnel face. The developed system can estimate the location, the thickness and the electrical resistivity of the anomaly using inverse analysis based on the modified harmony search algorithm with resistivity measurement. To verify the efficacy of the developed system, laboratory chamber tests were conducted by simulating ground formations with faults. The experimental results indicated that the developed system had substantial prediction performance with a short data analysis time. Notably, the location of an anomaly was relatively well predicted compared to the other properties, which is crucial information that can prevent potential risks. Therefore, the system could predict anomaly characteristics and enable the appropriate management of potential risks.

New Insights into the Gold Mineralization in the Babaikundi–Birgaon Axis, North Singhbhum Mobile Belt, Eastern Indian Shield Using Magnetic, Very Low-Frequency Electromagnetic (VLF-EM), and Self-Potential Data

The North Singhbhum Mobile Belt (NSMB) in the eastern Indian shield is an excellent example of a diverse lithological domain with multiphase shear/fracture zones. It is a well-acknowledged prospective region known for various mineralizations, e.g., Cu, Au, U, and Fe. The present study was conducted in the Babaikundi–Birgaon Axis (a shear and fracture zone within NSMB) within Babaikundi village. The study suggests that anomalous zones are possibly related to gold-associated sulfide mineralization using photomicrography and geophysical methods such as magnetic, self-potential (SP), and very low-frequency (VLF) electromagnetic (EM) methods. Photomicrography on quartz samples and Scanning Electron Microscope (SEM) Backscattered-Electron (BSE) images show that gold particles are present in the quartz reef vein in Babaikundi. Magnetic data are presented in the total magnetic intensity (TMI), upward continuation, and analytical signal maps. VLF-EM data were analyzed using different processing techniques to delineate anomalous auriferous zones. Furthermore, the SP data were inverted using the Particle Swarm Optimization (PSO), Very Fast Simulated Annealing (VFSA), and Genetic Algorithm (GA) approaches for comparative study of the resultant model parameters and their suitability considering a 2D inverted resistivity section derived using VLF-EM. The photomicrography study indicates the existence of gold/ pyrite/pyrrhotite within the Babaikundi–Birgaon axis, which corresponds to a low magnetic anomaly based on a magnetic study; a high current density, a high Fraser value, and a low resistivity based on the VLF-EM study; and a negative SP value was found based on the SP study. The combined study generally supports mapping auriferous zones and demarcates the Babaikundi–Birgaon axis within the Babaikundi–Birgaon area.

Формирование хемоземов в условиях длительного воздействия аэропромышленных выбросов горно-металлургического комбината

Introduction. The mining and processing industry, as one of the complex, high energy-consuming production processes is the most problematic from an environmental point of view. As a result of processing raw materials from ore, a huge amount of waste of practically all types, solid, liquid and gaseous, is generated. In some areas, tones of slag dumps and tailings are stored, which in one way or another are exposed to external impact and are transported by Aeolian streams to the adjacent environment. Hydrogenic surface runoff is also formed from the surface of dumps and the territory of enterprises with atmospheric precipitation, and gas-dust emissions flying into the atmosphere are deposited on the nearby landscapes. In aggregate, all the above mentioned technogenic flows carry pollutants, including heavy metals, which accumulate in the depositing environments, changing them in one way or another. Thus, for more than 100 years, in the Soymanovskaya Valley of the Chelyabinsk Region, as a result of the Karabashmed Copper Smelting Plant, soils and other landscape components have been undergoing changes under the influence of anthropogenic flows. Research methods and materials. As a result of this work, in order to study the impact of air-industrial emissions of the plant on the soil cover, soil samples were taken both from the adjacent landscapes in the vicinity of the plant and at a distance of more than 20 km from the source of gas-dust emissions. In the selected soil samples, the determination of the main physical and chemical parameters of soils was carried out: pH, Sorg content, exchangeable calcium and magnesium cations. To identify the degree of contamination of the territory, the gross content of Zn, Cd, Pb, Cu, Ni, Mn was determined by atomic adsorption spectroscopy. According to the obtained data of heavy metals content in the surface layer of soils, the total pollution coefficient was calculated. Research results. In the course of works, it was determined that in the lower illuvial horizons of soils of natural and anthropogenic landscapes the concentrations of heavy metals are practically at the same level. In the upper layers of soils, a significant difference with excess of heavy metal concentrations in soils of anthropogenic landscapes in comparison with soils of background areas was recorded, which may indicate the entry of pollution from the surface. Soils with a small thickness of profile (up to 45 cm), located near the mill, have a fully contaminated profile, from the surface to the lower horizons, as a result of which these soils are transformed into chemozems. With the distance from the mill a sharp decrease of concentrations to values close to background was revealed, even within the city limits. The obtained calculations of the total pollution coefficient Zc, indicate that all chemozems have skillfully dangerous and extremely dangerous category of pollution. Background soils have acceptable category of pollution. When comparing background soils and chemozems located in the zone of intensive anthropogenic load, it is established that there is no influence of bedrock on soil profile modification and transformation. In the lower horizons of such soils, both in chemozems and background soils, physico-chemical parameters practically do not change. Comparative analysis of the upper soil stratum showed significant exceedances of concentrations in comparison with clark and background content. Exceedances relative to these values are 50 times for Cd, 40 times for Cu, 45 times for Pb and 30 times for Zn. Conclusions. As a result of the conducted researches it was proved that the influence of air-industrial emissions of the combine on the transformation of native soils and formation of chemozems from them. This circumstance occurs for more than 100 years, as a result of the Karabash area, anomalous zones with high concentrations of heavy metals are formed, which directly changes the regional background. The results of the research can be useful in adjusting the regional geochemical background of heavy metals, making geochemical maps of the degree of soil contamination, as well as can serve as a basis for the development of measures to eliminate the degree of soil contamination.

Structure and genesis of the Achimov olistostromic strata of Western Siberia

The question of the genesis of the anomalous Bazhen-Achimov zones remains to be one of the most controversial problems in Western Siberia. By now, about dozen hypotheses of the sedimentary environment of this specific formation have been proposed. However, none of these hypotheses is generally accepted. All hypotheses have been classified by genesis and their critical analysis is given in the article. The solution is closely related with experience of the geological exploration works, since the prospects of oil and gas are associated with these deposits. The article highlights the key features of the structure of the anomalous section’s zones based on drilling and seismic data. The classification of the hypotheses is given and the features of sedimentation in the Bazhenov and Achimov times are highlighted. An accumulated data has allowed us to substantiate the olistostromous genesis of the anomalous section. Based on a set of data, including paleogeographic, sedimentological, paleotectonic reconstructions, a principal detailed model of the sedimentary environment of olistostromes is proposed for the first time. The proposed model seems to be the most logical, supported by the actual data known to date, is the most universal and fits into the paleogeographic situation and tectonic regime that prevailed in the Achimov time.

Geological conditions and controls on accumulation of tight sandstone gas, deep part of the Shengbei sub-sag, Turpan-Hami basin, NW China

With the further exploration of the Jurassic strata in the Turpan-Hami Basin, the targets for hydrocarbon exploration have been gradually shifted from the tectonic belts around sags to the proximal lithological zones of deep sags. Based on the systematic coring of the first exploration well (well Qintan-1) in the center Shengbei sub-sag, this study conducted experiments of organic carbon, pyrolysis, gas chromatography (GC), nuclear magnetic resonance (NMR), and low-temperature nitrogen adsorption. Then, this study systematically analyzed the geological conditions and major controlling factors for the accumulation of tight sandstone gas in the deep part of the Shengbei sub-sag. The results show that: (1) Multiple sets of coal-measure source rocks have developed in the Jurassic strata in the center Shengbei sub-sag, providing plenty of gas sources for multilayered hydrocarbon accumulation; (2) Tight sandstones have poor physical properties and complex pore structures. However, high-permeability zones and anomalous zones of nano-scale pores have developed in the deep part, providing favorable spaces for the accumulation and preservation of tight oil and gas in the deep part; (3) Compaction and late carbonate cementation are key factors in reservoir densification. The microscopic storage space and connectivity of the tight sandstone reservoirs in the Shengbei sub-sag were improved due to the dissolution of fluids in coal measure strata. The occurrence of high-quality reservoirs in the Shengbei sub-sag is significantly controlled by source rocks, and both the former and the latter are characterized by adjacent sources and reservoirs and short-distance migration and accumulation. Furthermore, the special geological phenomena of chert cementation, abnormally high homogenization temperatures of fluid inclusions, and abnormal pyrolysis parameters confirm the presence of low-temperature hydrothermal activity in the deep part of the target strata. Therefore, the center Shengbei sub-sag has geological conditions for the large-scale accumulation of primary gas and, thus, is a key area for future hydrocarbon exploration.

Shear wave crustal velocity structure in the Garhwal-Kumaon Himalaya based on noise cross-correlation of Rayleigh wave

The tectonics of the Garwal-Kumaon Himalaya is characterized by thrusts, tectonic windows, and klippen. We investigate crustal shear wave velocity variations using ambient noise cross-correlation tomography. The studied region encompasses the Kali River valley in the east to Satluj valley in the west, with the adjoining Indo-Gangetic Plain in the south covering the northern part of the Delhi-Haridwar ridge. The fundamental mode group velocities of Rayleigh waves are extracted from cross-correlation data of 33 broadband seismological stations from a regional seismic network. A total of 374 dispersion curves with a period range of 4–29 s show a group velocity variation between ∼2.3 and ∼ 3.4 km/s. The shear wave velocity structure of the uppermost lithosphere down to ∼50 km obtained by non-linear inversion of the Rayleigh wave dispersion data provides new insight into the geometry of the crust. A large variation in Vs in the range of ∼2.8 to ∼4.7 km/s corresponds to a variety of changes in the tectonic deformation, structure, and crustal thickness of the Himalayan wedge. Thick low-velocity sedimentary formations are identified beneath the Indo-Gangetic Plain and the frontal Himalaya. Anomalous low Vs zones are also observed in the mid-crust beneath the higher Himalaya and southern Tibet, indicating partial melting or the presence of aqueous fluid zones. The high-velocity anomalies may be correlated with duplex structures beneath the Lesser Himalaya and with lithospheric flexure.