Buried Source Research Articles

A mathematical model for a buried source in the layered reduced micropolar half-space

A mathematical model for a buried source in the layered reduced micropolar half-space

Probing a planet from the subsurface to the atmosphere with infrasound data

The analysis of infrasound waves has a significant potential for retrieving a range of geophysical parameters across various scales, such as atmospheric structures, characteristics of surface and buried sources, and seismic velocity structures. This potential was recently showcased in infrasound studies that illustrated the ability to retrieve Earth's shallow velocities and Mars' near-surface atmospheric winds from remote acoustic observations. Consequently, infrasound is becoming an essential component of planetary missions, providing insights into the interiors and atmospheres of other terrestrial planets in the solar system. However, utilizing infrasound data requires efficient forward wave simulation techniques and an accurate description of waveform sensitivity to source and medium parameters. Even under ideal conditions, many inverse problems associated with infrasound-based probing are inherently ill-posed, necessitating regularization or other approaches to ensure reliable results. In this contribution, we highlight recent seismo-acoustic research findings, addressing atmospheric probing at both smaller and global scales, as well as innovative methods to accelerate infrasonic wave propagation modeling.

Distribution of magmatic intrusions and key petroleum system elements in the Pliocene–Holocene Pangani Rift Basin, Northeastern Tanzania

The sedimentary fills in the Pangani rift basin (PRB) of northeastern Tanzania have not yet been studied in detail and their petroleum potential is poorly understood. This study aims at assessing distribution of magmatic intrusions and key petroleum system elements in the PRB based on 2D seismic, remote sensing, and aeromagnetic data interpretations. Results show that evolution of the basin fill was influenced by sediment supply, magmatism, and tectonics. The PRB contains Pliocene–Holocene clastic, magmatic, and volcaniclastic deposits. The clastic sediment was sourced from the north-northeast and east-southeast of the PRB. The magmatic and volcaniclastic rocks were formed during Pleistocene–Holocene and are increasing in frequency toward the north and northeast of the basin. Tectonics and faulting created depocenters and magma conduits; magmatic intrusions and fault systems form potential petroleum traps. Seismic interpretation has shown that PRB contains potential reservoir and seal rocks for possible petroleum accumulations. Fault systems dissecting the PRB provided petroleum migration pathways from deep buried source rocks to potential reservoirs. For the first time, this study has shown that the PRB contains key petroleum system elements for petroleum accumulations to occur. Our results will be of interest to researchers working in different East African Rift basins.

A Note on Exact Closed-Form Solutions for Lamb’s Problem with an Arbitrary Poisson’s Ratio

Abstract Lamb’s Problem, a cornerstone in theoretical seismology, investigates the displacement of an elastic half-space due to surficial or buried point sources. Although the exact closed-form solution for surface displacements from surficial sources is well established, the solutions for buried sources in the 3D case have remained limited, either confined to integral forms or applicable only for certain Poisson’s ratios. This study addresses this gap by generalizing the existing closed-form solutions to accommodate Poisson’s ratio for buried sources. Our solutions are expressed in terms of elementary algebraic expressions, elliptic integrals, and Gauss hypergeometric functions. The derived solution is validated by numerical tests. With the newly derived solution, we also explore the properties of the leaking mode, which stems from the complex conjugate roots of the Rayleigh equation.

Improved Approaches for 3D Gravity and Gradient Imaging Based on Potential Field Separation: Application to the Magma Chamber in Wudalianchi Volcanic Field, Northeastern China

The gravity and gradient anomalies contain valuable information about the underground geological structures at various depths. Deep and shallow buried source bodies are able to be identified through multi-scale field separation processes, and visual comprehensions of geological structures can be obtained via 3D density inversion techniques. In this study, we propose an improved 3D imaging strategy based on gravitational field separation using the preferential continuation filter. This strategy incorporates the relationship between spectral features and buried depths of source bodies, allowing for a one-step transformation from planar gravity and full-tensor gradient field observations to a 3D density structure in the wave-number domain. Synthetic tests validate the effectiveness and robustness of the gravity and gradient imaging approaches, highlighting their advantages in high vertical resolution and low computational requirements. Nonetheless, it should be noted that the imaging effects of horizontal gradients Γxx and Γyy are unsatisfactory due to their weak noise resistance. Thus, they are not suitable for real data applications. The other imaging approaches are further applied to recover the subsurface 3D density structure beneath the Weishan cone in Wudalianchi Volcanic Field, Northeastern China. Our results provide insights into the possible location and shape of the low-density magma chamber. Also, the potential presence of partial melts is inferred and supported from a gravity perspective. The primary advantage of these approaches is their ability to generate a reasonable geological model in scenarios with limited prior information and physical property constraints. As a result, they have significant practical value in the field of applied geophysics, including mineral exploration and volcanology studies.

Exploring a planet with infrasound: Challenges in probing the subsurface and the atmosphere

Infrasound waves have shown great potential to retrieve a range of geophysical parameters across scales, such as atmospheric structures, surface and buried source characteristics, and seismic velocity structures. In particular, infrasound generated by seismic waves coupling to the atmosphere can provide unique insight into a planet's interior. However, utilizing infrasound data require efficient forward wave simulation techniques and an accurate description of waveform sensitivity to source and medium parameters. Even under idealized conditions, many of the inverse problems associated with infrasound-based probing are inherently ill-posed, requiring regularization or other approaches to yield reliable output. In this contribution, we highlight recent research results from our group and collaborators, tackling atmospheric probing at smaller and global scales, as well as innovative approaches to speed up infrasonic wave propagation modeling. We also call attention to the objectives and early results from a newly launched project focusing on the feasibility of exploring the interior of Venus using infrasound recorded from balloon platforms.

Field Testing of a Mixed Potential IoT Sensor Platform for Methane Quantification

Emissions of CH4 from natural gas infrastructure must urgently be addressed to mitigate its effect on global climate. With hundreds of thousands of miles of pipeline in the US used to transport natural gas, current methods of surveying for leaks are inadequate. Mixed potential sensors are a low cost, field deployable technology for remote and continuous monitoring of natural gas infrastructure. We demonstrate for the first time a field trial of a mixed potential sensor device coupled with machine learning and internet-of-things platform at Colorado State University’s Methane Emissions Technology Evaluation Center (METEC). Emissions were detected from a simulated buried underground pipeline source. Sensor data was acquired and transmitted from the field test site to a remote cloud server. Quantification of concentration as a function of vertical distance is consistent with previously reported transport modelling efforts and experimental surveys of methane emissions by more sophisticated CH4 analyzers.

Numerical simulation of ground temperature field changein underground heat transfer zone of ground sourceheat pump under different groundwater runoff conditions

The heat transfer capacity of ground and soil energy sources is the key factor that affects the performance of the ground source heat exchanger. The heat storage capacity of soil is related to various factors. The author proposes a multi-component heat pump system which combines solar energy, waste heat, and air, and designs a new type of dual channel finned tube evaporator for defrosting. Based on different weather conditions, the operation mode of the system was provided, and performance tests were conducted on the system under no light conditions and with or without waste heat utilization. The results show that the seepage speed of buried tube ground source heat pump system geographic tube heat exchanger and soil heat transfer influence is larger, the groundwater seepage speed of 15 m per annual, running 3-4 years later, the heat transfer well area of the soil temperature field will be stable, which can judge in the groundwater seepage is sufficient area, the buried tube ground source heat pump conditional soil winter and summer heat balance.

Comprehensive Evaluation of Adaptability Zoning for Shallow Geothermal Energy Development and Utilization: Case of Nantong City, East Coast of China

The development of green energy sources, such as shallow geothermal energy, is one of the most important measures to reduce the environmental pollution caused by the use of traditional energy sources. At present, coastal cities in the east of the Yangtze River Delta, China, have favorable conditions for the development of shallow geothermal energy because of their abundant geothermal resources. However, the development and utilization of shallow geothermal energy are still in their infancy, and adaptability zoning is yet to be fully carried out. The study area is Nantong City, which is in the eastern coast of the Yangtze River Delta. A comprehensive analysis of the conditions of shallow geothermal energy is carried out based on the analysis of the regional geological, hydrogeological, and environmental geological conditions. The adaptability zoning index system of the groundwater source heat pump and buried pipe ground source heat pump system is then constructed, and the weight of evaluation factors is determined according to analytic hierarchy process. Finally, the adaptability zoning of shallow geothermal energy development and utilization mode is obtained by using the spatial analysis function of geographic information. The results showed that the areas with good suitability and better suitability account for 98.24% of the study area and those with good economy and better economy account for 99.67% of the study area. This method can provide reference suggestions for the orderly development and sustainable utilization of shallow geothermal energy in coastal cities in plain areas.

Characteristics of limited flow and soil water infiltration boundary of a subsurface drip irrigation emitter in silty loam soil

The accurate estimation of the infiltration boundary of a buried point source is required in the hydraulic design of a subsurface drip irrigation (SDI) system, as well as in the numerical simulation of soil water movement. In this study, an experiment was conducted to measure the variation in emitter flow rate and soil back pressure in silty loam soil. The infiltration cavity was observed, and the radius was estimated by matching the measured emitter flow rate and soil back pressure using HYDRUS-2D simulations. The relationship between the cavity radius, emitter flow rate, and soil back pressure, as affected by the soil bulk density, working pressure, and nominal emitter flow rate, are discussed. The results indicate that the infiltration cavity formed rapidly during irrigation with an irregular shape. The surface area increased as nominal emitter flow rate increased and soil bulk density increased. The variation of flow rate as a function of time had no necessary relationship with that of soil back pressure, due to the formation of the cavity. When the infiltration process became stable, higher soil bulk density resulted in increase in soil back pressure and decrease in emitter flow rate. However, the effects of working pressure and nominal emitter flow rate on soil back pressure were unclear. The emitter flow rate and back pressure, solved by an existing analytical model using estimated radius, demonstrated satisfactory agreement with the measured data, with the minimum root-mean-square error (RMSE), compared with those using a constant radius. When the infiltration boundary was taken as a constant head, the soil back pressure and cavity both significantly affected the simulated soil wetting patterns. The effect of cavity radius on the wetting front could be neglected for the constant flux boundary.

Sound pressure and particle motion calculations considering pile skin friction

Modelling sound propagation over seabeds where the seabed cannot be approximated as an equivalent fluid due to limestone layers with high shear wave speeds is a common underwater acoustic propagation modelling problem for Australian shallow marine environments. With the increase in prospective areas for offshore windfarm development across Australia, construction operations across large regions of the continental shelf area are set to increase. Windfarm construction will require the installation of a large number of foundation piles near potentially sensitive marine habitat areas. Predicting the underwater noise from these activities requires suitable models. This paper investigates the modelling approaches for including a full elastic parameterisation of the seabed when conducting numerical predictions of pile driving sound emissions. The approach considers buried sources and the excitation of shear waves via a skin friction model for the stress–strain relation at the pile-seabed boundary. Shear waves are considered in the source model and in the propagation model. Sound pressure level metrics and particle motion metrics are considered as part of the numerical predictions.

Two-sided fault parameter assessment through the utilization of a particle swarm optimizer to different gravity horizontal gradients-orders with application to various cases studies

Metaheuristic methods are increasingly being implemented to source parameter estimation of gravity anomalies. These approaches have become popular in the geophysical community because of their superior advantages. We emphasize the application of the particle swarm optimizer (PSO), which is motivated by the birds’ behaviors, to elucidate gravity anomalies. Besides, using different horizontal derivative orders for the observed data is valuable in reducing the regional field effect. The current inversion algorithm applied to other synthetic models (a two-sided dipping fault with a third-order regional, a two-sided dipping fault model interfered by a spherical structure model with and without 10% noise, and two neighboring two-sided dipping faults models with and without 10% noise) as well as two real-world cases from the United States and Tunisia. The usefulness of applying these techniques together was demonstrated by providing stable results in executing the buried source parameters and eradicating the regional field effect. Therefore, we recommend the application of these techniques in the model parameter estimation studies performed with potential field anomalies due to mineralized zones.

Past Earthquake Simulations Using Ambient Seismic Noise in Vrancea, Romania

Abstract The Vrancea seismic zone (VSZ), located in Romania, at the sharp bend of the southeast Carpathians, is an anomalous intraplate seismic nest releasing the largest strain in continental Europe. The last powerful earthquake in Vrancea occurred in 1977 causing significant damage to the densely populated cities in southeast Romania. The seismic infrastructure was underdeveloped at that time and the earthquake was not well recorded locally. Using ambient seismic noise recorded at modern broadband seismic stations around Vrancea in the year 2020, and the approximate moment tensor solutions of significant earthquakes Mw>6 since 1977, we reconstruct ground-motion waveforms recorded by modern seismometers decades after their occurrence. The virtual earthquake approach uses empirical Green’s functions from ambient noise cross correlations between pairs of seismic stations and adds the signatures of a model earthquake: double couple mechanism, buried source, and a realistic earth model in the epicentral area. Ambient noise data capture the signatures of complex subsurface structures and the 3D path effects, providing a more physically accurate representation of the seismic wavefield than purely synthetic data. Our new results demonstrate the viability of this innovative method and provide a unique opportunity for more accurate seismic hazard analysis in intraplate seismic zones with insufficient instrumental data.

A multiple scattering formulation to design meta-trenches for mitigating low-frequency ground-borne vibrations induced by surface railways and subways

We propose a multiple scattering formulation to investigate the performance of meta-trenches. The meta-trench is a novel device, composed of an array of resonant units buried in the ground in a proper arrangement, aimed at reducing the railway and/or subway induced ground motion by exploiting its scattering and resonant properties. Compared to classical open trenches, the resonators contribute to improving the wave mitigation performance of the trench in the low-frequency regime.The proposed formulation allows to consider the wave source anywhere in the half-space and a generic distribution of resonators in terms of number and position. The incident wave field generated by the source, such as a train or subway, along with the scattered wave fields produced by the resonant units that constitute the meta-trench, are modeled via Green’s functions. The multiple scattering formulation enables the solution of coupled wave problems by determining the amplitudes of scattered wave fields at various frequencies. Through comparison with finite element simulations, we demonstrate that in both buried source (i.e., subway) and surface-located source (i.e., ground railway) scenarios, our analytical formulation is able to properly model the dynamics of the coupled problems with a noticeable computational cost saving. Opening to fast and reliable parametric simulations, our formulation allows for a deeper knowledge of the wave interaction processes, resulting thus in a reliable tool for predicting the coupled wave field under both bulk and Rayleigh waves.

Enhanced meta-heuristic optimization of resource efficiency in multi-relay underground wireless sensor networks.

Achieving a balanced energy and spectral resource utilization is an interesting key design to extend the lifetime of underground wireless sensor networks (UWSNs) where sensor nodes are equipped with small limited energy batteries and communicate through a challenging soil environment. In this article, we apply an improved meta-heuristic algorithm, based on the Salp Swarm Algorithm (SSA), for multi-relay UWSNs where cooperative relay nodes amplify and forward sensed data, received from the buried source nodes, to the aboveground base station. Hence, the optimal nodes transmission powers, maximizing the network resource efficiency, are obtained and used to select beneficial relay nodes. The algorithm enhances the standard SSA by considering the chaotic map for salps population initialization and the uniform crossover technique for salps positions updates. Simulation results show that the proposed algorithm significantly outperforms the SSA in resource efficiency optimization and network lifetime extension. The obtained gain increases when the number of cooperative relay nodes increases. Furthermore, simulations prove the efficiency of the proposed algorithm against other meta-heuristic algorithms.

The effect of free‐surface reflections on depth images for acquisition with buried sources and receivers: Investigation through the point spread function#

AbstractIn reverse time migration, if sources or receivers are buried at certain depths, the interference between the primary wave and the free‐surface reflection causes losing spectral contents in seismic data. If they are not properly compensated, errors will be carried to the target during the reverse time migration and cause a distorted image by so‐called ghost image. By invoking the point spread function, we investigate how distorted seismic data are mapped to the subsurface. Quantitative relations between the free‐surface parameters (i.e. source/receiver depth, free‐surface incident angle and near‐surface velocity) and wavenumber‐domain illumination can be created, which map missing frequency contents in seismic data to missing wavenumber contents in the point spread function. After transformed back to the space domain, we can investigate its effect on the image distortion. Numerical calculations expand the above approach to handle complex overburden structures and more realistic acquisition geometries. The proposed method provides us with a useful tool to investigate deghosting related problems, for example optimizing parameters of acquisition geometry, evaluating capabilities of existing acquisition systems and data processing technologies in suppressing the free‐surface reflection effect in the depth image, or developing new deghosting approaches.

A reconnaissance study for tracing and ordering new mineralisation zones using integrated remote sensing, GIS, and aeromagnetic techniques, west Allaqi-Heiani-Suture,Egypt

ABSTRACT Reducing expenses is a critical aspect of natural resource explorations, especially in the reconnaissance stage. Accordingly, GIS algorithms using the free remote sensing data were used to rank the probable mineralised zones before any future implementations of the high-cost drilling and/or detailed geophysical programmes. Geological and tectonic settings, and being a historical mineral resource were motivations to choose the Allaqi-Heiani Suture (AHS), Upper Egypt, as a study area. Remote sensing data were processed for tracing the probably mineralised alteration zones, determining fractures and dominating structural systems, and mapping different geological units. Various alteration minerals including hydroxyls–carbonates, ferrous and ferric iron oxides were detected over different rock units using band ratio (BR) and Crosta techniques. Different geological units were distinguished using false colour composite (FCC) images. Moreover, an intense fractured system, demonstrating the area, was revealed by tracing lineaments using informative, spatially enhanced remote-sensed images. Fractures within the altered rocks represent 35% of the total fracturing system in the AHS to indicate a structural system controlling mineralisation occurrences. The processing of magnetic data suggested a deep/buried nature of these remotely detected lineaments/structures. Reduced to pole (RTP) and tilt derivative (TDR) maps detected the buried magnetic sources, whereas zero contours of TDR, Euler deconvolution, analytic signal and source parameter imaging (SPI) techniques traced buried contacts/structures and estimated their depths. A GIS strategy depending on the intensity of the fracturing system and the presence of more than one type of alteration was applied to potential-rank the prospective mineralised occurrences over AHS. The correlation between ranked zones with the old/known mines showed encouraging evaluation.

A Novel Enhanced Total Gradient (ETG) for Interpretation of Magnetic Data

Edge detection techniques identify the horizontal extents of the underground geological bodies and work well in association with magnetic as well as seismic data. Even though the detected edges might not be a lithological contact, they offer first-hand information regarding various rocks that ultimately offers an extra argument for existing tectonics. Most of the edge enhancement techniques depend either on the horizontal gradient or total gradient of the potential fields. As of now, no single edge detection filter performance is best in all conditions. The study proposes a novel edge detection filter called “ETG-Enhanced Total Gradient” that combines the derivatives of the analytic signal (AS) (in the third dimension). The maximum amplitude of the AS is less dependent of the direction of magnetization and is critical in mapping the borders of the buried magnetic sources beneath the Earth. As the ETG filter is based on the total gradient of the field, there is no need to apply reduction to the pole process on the magnetic data. One limitation of the method is that the filter is unable to perform better at the corners where the other conventional methods miserably failed. The filter’s behavior is examined and validated using 2D and 3D synthetic magnetic data. The reliability of the ETG filter is examined by applying it to the magnetic data of the Seattle uplift region, USA. A new structural map of the region is generated by using the proposed ETG filter. The observed peak response of the ETG filter is well correlated with major tectonic features such as the Seattle Fault Zone (SFZ), Hood Canal Fault (HCF), and Dewatto Fault (DF).

Impact of natural weathering on source rocks: Organic and inorganic geochemical evidence from the Triassic Chang 7 outcrop profile in Tongchuan of the Southern Ordos Basin (China)

Exposure of buried source rocks at or near the surface causes organic matter (OM) to be subjected to loss through weathering impacts. A detailed organic and inorganic investigation of the natural weathering of the Triassic Chang 7 Yishicun Profile in Tongchuan City of the Ordos Basin revealed pronounced changes in bulk, molecular, mineral, and elemental compositions. In this study, systematic and visible variations caused by natural weathering were shown in the amount and composition of both organic (kerogen and extractable organic matter [EOM]) and inorganic matter (minerals and elements). The results indicate that natural weathering could substantially affect the characteristics of source rocks at a depth of 2 m from the surface, resulting in a 41% decrease in total organic carbon (TOC) and a 75% loss of EOM. Furthermore, changes were noted in kerogen elemental compositions, fractional compositions of EOM, and some geochemical parameters from Rock-Eval pyrolysis. The mineral and major, trace, and rare earth element (REE) compositions of the outcrop samples were also analysed and compared. The weathering of source rocks was mainly due to the influence of surface water leaching and biodegradation of the OM. This resulted in the oxidation of kerogen and the preferential depletion of low-carbon-number n-alkanes and low-molecular-weight high-water-solubility biomarkers. This has led to bias in petroleum geochemical interpretation based on these organic geochemical parameters. The major elemental composition indicated that the outcrop profile was moderately weathered. Moreover, some commonly used palaeoenvironmental geochemical proxies, including U/Th, AU, Mo, Sr/Ba, Sr/Cu, and P/Ti, display varying degrees of weathering-related alteration. However, other palaeoenvironmental proxies such as V/(V + Ni), Ni/Co, V/Cr, δU, and Ceanom experienced little variation and remained reliable for environmental interpretation. Thus, petroleum resource evaluation and sedimentary environmental analysis of source rocks based on outcrop samples should consider the effects of natural weathering.

Detrital zircon U-Pb provenance analysis of Precambrian and Paleozoic strata from southwestern Brazil: Assessment of potential Grenvillian sediment input and Amazonian-Laurentian tectonic interaction

Southwest Amazonia is proposed to have collided with southeast Laurentia during the Grenville orogeny. In Laurentia, the collision produced a continental-scale late Mesoproterozoic to early Neoproterozoic clastic wedge dominated by detrital zircon (DZ) sourced from Grenvillian magmatic rocks (major Geon 11 and 10, with minor Geon 13, 12, and 9 ages: the “Great Grenvillian Sedimentation Episode”). New DZ ages in clastic units from southwestern Brazil permit testing the hypothesis that Grenvillian sediment from southeast Laurentia spilled onto western Amazonia during Rodinian assembly. Late Mesoproterozoic arenites are dominated by Geons 18, 17, 15, 14, and 13 ages sourced from Amazonia basement provinces. Two samples exhibit major Geon 12 and 11 ages with minor Geon 18–13 ages. Geon 12 and 11 correspond to a conspicuous age gap in Amazonian magmatic events. Latest Neoproterozoic samples exhibit minor Geon 13 to 9 ages interpreted to be sourced from the Rondônia-San Ignacio or Sunsás provinces of western Amazonia. Late Neoproterozoic and Devonian age spectra exhibit multiple Amazonian age modes ∼2500 to 500 Ma but with no dominant modes. The age distributions for all samples indicate a lack of Laurentian Grenville sediment influx to southwest Amazonia during Rodinian assembly and breakup. The enigmatic Geon 12 ages are interpreted to correspond to a buried Andean source or the southwestern Grenville province in Laurentia. In contrast to exposed basement in southwestern Amazonia, Andean basement clastic sequences and Pleistocene to Recent Amazon River sediments exhibit Grenville dominance of DZ ages, strikingly similar to eastern Laurentia clastic systems. The Andean Grenville dominance may be accounted for by extensive Grenvillian crust beneath the Andean clastic wedge containing a major component of Geons 12, 11 and 10 magmatic rocks, and which was not being fully exhumed until the Neoproterozoic, similar to Laurentian Grenville.