Subsurface Structure Research Articles

Locating Potential Groundwater Pathways in a Fringing Reef Using Continuous Electrical Resistivity Profiling

Groundwater discharge from high tropical islands can have a significant influence on the biochemistry of reef ecosystems. Recent studies have suggested that a portion of groundwater may underflow the reefs to be discharged, either through the reef flat or toward the periphery of the reef system. Understanding of this potential discharge process is limited by the characterization of subsurface reef structures in these environments. A geophysical method was used in this study to profile the reef surrounding the high volcanic island of Mo’orea, French Polynesia. Boat-towed continuous resistivity profiling (CRP) revealed electrically resistive features at about 10–15 m depth, ranging in width from 30 to 200 m. These features were repeatable in duplicate survey lines, but resolution was limited by current-channeling through the seawater column. Anomalous resistivity could represent the occurrence of freshened porewater confined within the reef, but a change in porosity due to secondary cementation cannot be ruled out. Groundwater-freshened reef porewater has been observed near-shore on Mo’orea and suggested elsewhere using similar geophysical surveys, but synthetic models conducted as part of this study demonstrate that CRP alone is insufficient to draw these conclusions. These CRP surveys suggest reefs surrounding high islands may harbor pathways for terrestrial groundwater flow, but invasive sampling is required to demonstrate the role of groundwater in terrestrial runoff.

Joint Inversion of Gravity and Magnetic Anomalies to Image Salt–Basement Structures Offshore Abu Dhabi, UAE, Using Deep Neural Networks

Summary By using a deep neural network (DNN), a novel technique is developed for a 2.5D joint inversion of gravity and magnetic anomalies to model subsurface salts and basement structures. The joint application of gravity and magnetic anomalies addresses the inherent nonuniqueness problem of geophysical inversions. Moreover, DNN is used to conduct the nonlinear inverse mapping of gravity and magnetic anomalies to depth-to-salt and depth-to-basement. To create the training data set, a three-layer forward model of the subsurface is designed indicating sediments, salts, and the basement. The length and height of the model are determined based on the dimensions of the target area to be investigated. Several random parameters are set to create different representations of the forward model by altering the depth and shape of the layers. Given the topography of the salts and basement layers as well as their predefined density and susceptibility values, the gravity and magnetic anomalies of the forward models are calculated. Using multiprocessing algorithms, thousands of training examples are simulated comprising gravity and magnetic anomalies as input features and depth-to-salt and depth-to-basement as labels. The application of the proposed technique is evaluated to interpret the salt–basement structures over hydrocarbon reservoirs in offshore United Arab Emirates (UAE). Correspondingly, a DNN model is trained using the simulated data set of the target region and is assessed by making predictions on the random actual and noise-added synthetic data. Finally, gravity-magnetic anomalies are fed into the DNN inverse model to estimate the salts and basement structures over three profiles. The results proved the capability of our technique in modeling the subsurface structures.

Subsurface structure regulates water storage in the alpine critical zone on the Qinghai-Tibet Plateau

The subsurface critical zone (CZ) structure in alpine regions has a profound influence on water storage that is not well understood due to a lack of available accurate spatiotemporal measurements. This work is to reveal that the organic layer (A), leaching-deposit layer (B), saprolite layer (C) and freeze–thaw processes regulate changes in subsurface liquid water storage (CSWS). We performed in situ field surveys, ground-penetrating radar (GPR) and electrical resistivity tomography (ERT) along an elevation gradient (4221–3205 m) in the Qinghai Lake Basin Critical Zone Observatory (QLBCZO) on the Qinghai-Tibet Plateau. The results showed that the saprolite layer (thickness of 0.84–41.85 m) and the liquid water storage (SWS) increased along the decreasing elevation. The saprolite layer was the main subsurface liquid water storage reservoir, with average value of 595.49 ± 729.87 mm, which occupied 76.10 % of the total water storage of layers A, B and C. The SWS of the saprolite layers increased the most, by 39.41 mm and 45.88 mm in the thawing and nonfreezing periods, respectively, and that of layer B decreased maximally by 52.50 mm in the freezing period. The subsurface layer and elevation had the contribution to SWS at 68.07 % during the nonfreezing period. Comparing other climate and environmental factors, the seasonal frozen thickness (SFT) and precipitation contributed most to CSWS during the thawing and freezing period (27.95 % and 19.87 %), respectively. This study contributes to advancing the mechanistic understanding of the interactions between the subsurface CZ structure and water storage processes and provides high-quality data with which coupled ecohydrological models can be developed.

An upper-crust lid over the Long Valley magma chamber.

Geophysical characterization of calderas is fundamental in assessing their potential for future catastrophic volcanic eruptions. The mechanism behind the unrest of Long Valley Caldera in California remains highly debated, with recent periods of uplift and seismicity driven either by the release of aqueous fluids from the magma chamber or by the intrusion of magma into the upper crust. We use distributed acoustic sensing data recorded along a 100-kilometer fiber-optic cable traversing the caldera to image its subsurface structure. Our images highlight a definite separation between the shallow hydrothermal system and the large magma chamber located at ~12-kilometer depth. The combination of the geological evidence with our results shows how fluids exsolved through second boiling provide the source of the observed uplift and seismicity.

Investigation of Subsurface and Geological Structures Contributing to Collapse Sinkholes in Covered Karst Terrain, Northeast Thailand

This study focuses on covered karst terrain situated in Phu Pha Man District, Khon Kaen Province, Northeast Thailand, where records of collapse sinkholes are limited. Here, we investigate the subsurface characteristics and potential causes of sinkhole formation within this area using geophysical methods, hydrogeological techniques, and precipitation analysis. We collected field data by measuring groundwater levels, and conducting electrical resistivity tomography (ERT) surveys. We identified eight cover-collapse sinkholes of various shapes and sizes. Analysis of the groundwater flow indicated that the predominant flow direction runs from north to southeast. Examination of rainfall data showed a progressive increase in total rainfall on a yearly basis, with a significant precipitation event preceding the initial occurrence of sinkholes. The ERT results revealed the presence of highly resistive bedrock, water-saturated layers, and potential cavities. Notably, the tomograms indicated variations in resistivity values, suggesting the presence of irregular surfaces of limestone bedrock and weathered zones as characteristics of karst settings. Intense precipitation is a possible dominant trigger for the formation of the sinkholes. This study contributes to understanding sinkhole formation in karst environments and provides key information for hazard mitigation, not only in the Phu Pha Man District but also in areas with similar geological settings.

Multi-Scale Seismic Measurements for Site Characterization and CO2 Monitoring in an Enhanced Oil Recovery/Carbon Capture, Utilization, and Sequestration Project, Farnsworth Field, Texas

To address the challenges of climate change, significantly more geologic carbon sequestration projects are beginning. The characterization of the subsurface and the migration of the plume of supercritical carbon dioxide are two elements of carbon sequestration that can be addressed through the use of the available seismic methods in the oil and gas industry. In an enhanced oil recovery site in Farnsworth, TX, we employed three separate seismic techniques. The three-dimensional (3D) surface seismic survey required significant planning, design, and processing, but produces both a better understanding of the subsurface structure and a three-dimensional velocity model, which is essential for the second technique, a timelapse vertical seismic profile, and the third technique, cross-well seismic tomography. The timelapse 3D Vertical Seismic Profile (3D VSP) revealed both significant changes in the reservoir between the second and third surveys and geo-bodies that may represent the extent of the underground carbon dioxide. The asymmetry of the primary geo-body may indicate the preferential migration of the carbon dioxide. The third technique, cross-well seismic tomography, suggested a strong correlation between the well logs and the tomographic velocities, but did not observe changes in the injection interval.

Evidence of Widespread Volcanic Activity near Hebrus Valles on Mars Revealed by SHARAD

Hebrus Valles is an outflow channel system in the plain-forming terrains of southeastern Utopia Planitia, Mars. These terrains may have formed through a combination of liquid water and volcanic processes, yet their nature, subsurface structure, and composition remain unclear. We investigate these terrains by mapping subsurface reflectors across 540 Shallow Radar (SHARAD) profiles and applying two complementary loss tangent inversion techniques. We find moderate loss tangent values across some subregions of Granicus Valles and Hyblaeus Fossae (tan δ = 0.0162 ± 0.0004 and tan δ = 0.019 ± 0.002, respectively), suggesting the presence of basaltic lava flows. We interpret non-detections in the other flows in Granicus Valles to be due to the presence of radar-lossy materials formed through aqueous processes, which supports the hypothesized occurrence of lahars in this region. A small area near Hebrus Valles exhibits subsurface reflectors with low to moderate loss tangents (tan δ = 0.010 ± 0.003), suggesting the presence of pristine lava flows or sedimentary materials capped by lava flows. We also find a widespread occurrence of very low-loss tangent materials near Hyblaeus Dorsa (tan δ = 0.0045 ± 0.0002), which may represent a lobe of the Medusae Fossae Formation or similar high-porosity materials buried underneath a lava flow. Together, these findings suggest that volcanic activity played a central role in the formation of terrains across the broader Hebrus Valles region.

A high-resolution, 3D groundwater-surface water simulation of the contiguous US: Advances in the integrated ParFlow CONUS 2.0 modeling platform

Large-scale, high-resolution hydrologic modeling is an important tool to address questions of water quantity, availability, and potential recharge. Continental-to-Global scale models, particularly those that include groundwater, are growing in number. However, many of these approaches simplify aspects of the system and the connections between surface water and groundwater. The ParFlow CONUS modeling platform is a large-scale, hyper-resolution, hydrologic model that relies on the integrated solution of 3D partial differential equations that describe groundwater, soil, and 2D surface water flow. The prior version, ParFlow CONUS 1.0, was the first large-scale hydrologic model that included an explicit treatment of lateral groundwater flow for the contiguous US (CONUS). Here, we present the ParFlow CONUS 2.0 integrated hydrologic model. This model extends to the coastlines and contributing basins for CONUS and is consistent with the NOAA National Water Model. Here we document the roughly five years of technical development of this platform, present steady-state simulation results, rigorously compare these results to the prior ParFlow CONUS 1.0 simulations, and evaluate the model performance based on observations. Simulated water table depth and streamflow were evaluated using more than 635 K observations from USGS monitoring wells, other compiled groundwater datasets, and NHD and USGS streamflow gauges. Our results demonstrate improvement in both groundwater and surface water simulations over the prior generation model for all USGS Hydrologic Unit Code (HUC) basins. These results suggest that this current generation hydrologic model has good to excellent streamflow performance over the entire CONUS, with almost half of the HUC subbasins exhibiting excellent performance based on normalized root-square error (RSR). These results suggest that the current generation model approaches good performance for water table depth over the CONUS, a metric not usually compared directly at all in large-scale studies, with good-to-excellent performance exhibited over some HUC regions. We also delineate two regions that influence model performance, one where microtopography around streams dominates (D2), and another where a mix of subsurface heterogeneity and topographic gradients dominate (D1). Improvements in topography from CONUS1 to CONUS2 generally result in better streamflow and water table depth performances. Advancements in the subsurface depth and structure also produce better water table estimates.

The utilization of ghost reflections retrieved by seismic interferometry for layer‐specific characterization of the shallow subsurface

AbstractSeismic interferometry (SI) retrieves the Green function between two receiver locations using their recordings from a boundary of sources. When using sources and receivers only at the surface, the virtual‐source gathers retrieved by SI contain pseudo‐physical reflections as well as ghost (non‐physical) reflections. These ghost reflections are the results of the cross‐correlation or auto‐correlation (AC) of primary reflections from two different depth levels, and they contain information about the seismic properties of specific layers in the subsurface. We investigated the application of ghost reflections for layer‐specific characterization of the shallow subsurface using SI by AC. First, we showed the technique's potential using synthetic data for a subsurface model with a lateral change in velocity, a gradient in depth for velocity, a thickness change and a velocity change of the target layer. Then, we applied the technique to shallow subsurface field data. We also focused on improving the retrieval of ghost reflections by removing the free‐surface multiples and muting undesired events in active‐source gathers before applying SI. Our results demonstrate that the ghost reflections can be used advantageously to characterize the layer that causes them to appear in the results of SI. Consequently, they can also provide valuable information for imaging and monitoring shallow subsurface structures.

Three-dimensional magnetotelluric imaging of the Edough massif and its overlying formations (Northeast Algeria)

The Edough massif (NE Algeria) is the easternmost coastal crystalline massif of the Maghrebide belt, whose current structural position remains poorly known. Magnetotelluric (MT) data from 15 stations were collected along three profiles across the Edough massif and its neighboring formations in the period range of 0.001–1000 s to assess the deep electrical resistivity structure. A phase tensor dimensionality analysis indicates that the measured data are dominated by 3-D effect of underlying geological structure, thus revealing a complex subsurface structure. A 3-D inversion model was obtained using the full impedance tensor and the vertical magnetic field transfer function including bathymetry and topography. Our preferred 3-D geo-electrical model shows heterogeneous electrical structures and are related to the known geological features of the region. We mainly observe a clear resistivity contrast characterizing the upper/middle crust. The Edough massif appears generally as a homogenous resistive structure. The shallow conductive structures are associated with the Mio-Plio-Quaternary deposits and Flysch units. Most of conductive bodies are likely related to the iron/magnetic anomaly. These may likely correspond to the suture zone. Under the Neogene basin, the high resistivities with a north dipping strong angle may correspond to the African basement.

Dispersion inversion for P- and S-wave velocities based on guided P and Scholte waves

Inversion based on dispersion curves is widely used for the estimation of subsurface velocity structures. However, conventional surface-wave dispersion inversion usually uses normal modes, and only the S-wave velocities are retrieved. To retrieve P-wave velocities, the dispersion of guided P waves should be considered. We develop an inversion scheme that uses the guided-P-wave and Scholte-wave modes to implement an integrated inversion for P- and S-wave velocity structures of shallow marine sediments. The forward modeling of dispersion curves is based on the spectral-element method and the perfectly matched layer technique. A quantitative sensitivity analysis of guided P modes is then carried out, which not only confirms the capability of guided P modes for estimating the P-wave velocity but also indicates that guided P modes can be combined with Scholte modes to better constrain the S-wave velocity. Based on the Levenberg-Marquardt algorithm, a joint inversion scheme that uses guided P and Scholte modes is developed. The validity of the inversion scheme is assessed by testing synthetic and field ocean-bottom seismometer data obtained in shallow marine environments. The results demonstrate the effectiveness of the joint inversion for retrieving the P- and S-wave velocity structures of shallow marine sediments.

IDENTIFIKASI AKUIFER DI DAERAH RAWAN BANJIR DENGAN METODE VERTICAL ELECTRICAL SOUNDING DI KECAMATAN MUARA BANGKAHULU (Identification of Aquifers in Flood-Prone Areas using the Vertical Electrical Sounding Method in Muara Bangkahulu sub-district)

Muara Bangkahulu Subdistrict is a flood-prone area in Bengkulu City, Bengkulu Province. This study aims to identify the depth of aquifers in flood-prone areas. Flood-prone areas in the Muara Bangkahulu sub-district were analyzed using the Vertical Electrical Sounding (VES) method with Schlumberger configuration of as many as 40 VES points in residential areas. Data acquisition was carried out using the Geoelectric IP Meter MAE X612-EM. The obtained data was then processed using Progress 3.0 software to get a 1D Resistivity Log cross-section. The log data was then modelled using Voxler 4 software to find an overview of the distribution of aquifers and subsurface structures in 3D. The distribution of resistivity values at depths of 2, 5, 10, 15, 30, and 40 meters using ArcGIS 10.8 are mapped to see the distribution of aquifers. The aquifers in the Muara Bangkahulu sub-district are sand and gravel with a value of 0-25 Ω.m. The intrusion of seawater influences this value. Flood-prone areas are located at shallow aquifer, namely depths of 2-5 m in the villages of Rawa Makmur, Rawamakmur Permai, and Bentiring Permai.

3D Visualization of Geothermal System Structure Based on Inversion Model of Gravity Data. Case Study: Mt. Salak Region, West Java

The geothermal power plant located in Gunung Salak plays a crucial role in increasing the electricity supply transmitted to the Java-Bali region, as the energy demand continues to rise. The objective of this research is to determine the 3D subsurface structure of Gunung Salak, specifically the distribution of the reservoir as the target for geothermal energy using the Gravity method. Gravity data, including gravity disturbance (gd), geoid, and Digital Elevation Model (DEM), were obtained from the ICGEM website with a total of 48740 data each. Based on the results of the residual anomaly map, the low anomalies beneath Gunung Salak have values from -5.15 to -1.88 mGal, which are suspected to be associated with the magma chamber. The high anomalies beneath the manifestations have values from 0.92 to 5.01 mGal, indicating andesitic basalt intrusive rocks believed to be the reservoir rock. Through the 3D inversion modeling of the subsurface structure of the Gunung Salak geothermal system, a clay cap with a density from 2.47 to 2.5 g/cc at depths of 0 to 700 m and andesitic basalt rock as the reservoir with a density from 2.74 to 2.91 g/cc at depths of 700 to 3000 m have been identified.

Geophysical and geological exploration of the Aurus clay pan as an archive of the long-term climatic and environmental history of the Namib Desert

The Namib Desert is one of the oldest deserts on Earth. Whilst the history of the desert during the last glacial-interglacial cycle is relatively well understood, information on the older Pleistocene and Neogene history is very scarce, because longer-term records such as those in lakes and caves have not been formed due to the aridity. Here, we investigate the potential of the sedimentary record in the Aurus clay pan in the Sperrgebiet Domain in the southern Namib Desert, Namibia, for longer-term paleoclimate research. For this purpose, we conducted a multi-disciplinary geophysical site survey along with initial sedimentological investigations. We used a combination of transient electromagnetic (TEM), seismic and magnetic data, that allows us to derive information with respect to tectonic features as well as the deeper sedimentary architecture of the Aurus clay pan. TEM and seismics were applied along two perpendicular transects. The data obtained reveal a three- to four-layered subsurface structure with a maximum sedimentary thickness between 31 and 65 m overlaying resistive bedrock. The aeromagnetic data show a fault zone cutting the southwestern corner of the clay pan that correlates with deep conductive anomalies visible in the TEM data. Radiocarbon ages of plant remains from the sediment surface evidence modern deflation, probably due to a particularly dry climate. The composition of a 4-m-long sediment core, which probably reflects the depositional history from 3400 to 23,000 cal. yr BP, however, suggests that most of the Holocene was characterized by a relatively high humidity, whereas the latest Pleistocene again was much dryer. According to an extrapolation of the sedimentation rates in the upper 4 m to the base of the sedimentary infill the record in Aurus clay pan penetrates in the order of 340,000 cal. yr BP. This would be longer than most other paleoclimate records in the Namib, but much less then recently recovered in the Atacama Desert in Chile. A comparison of the geophysical and geological data from Aurus with comparable data and two drill cores from clay pans in the Atacama furthermore shows that the physical parameter in all cases allow to decipher the sediment thickness and general architecture, but alone provides limited information on the sediment composition.

Subsurface structures of solution dolines inferred from electrical resistivity tomography: A hypothesis on the evolutionary process of solution dolines at the Akiyoshi-dai Plateau, southwest Japan

The evolution of solution dolines is regulated by carbonate dissolution mediated by water and CO2. The subsurface structure influences the evolutionary pattern of the dolines. Despite the significant effects of enlarged joints or shafts on the development of solution dolines, a few studies have identified the subsurface structures of multiple solution dolines. To this end, we utilized 2-D electrical resistivity tomography (ERT) at 15 dolines and an outcrop in the Akiyoshi-dai Plateau, Japan, which is composed of massive and fractured limestone lithology. The results of ERT exhibited the following: (i) a similar range for electrical resistivity in parallel to the topographic relief; (ii) an increase in resistivity with depth, and; (iii) a low resistivity zone characterized by <400 Ωm, at shallow areas. Some electrical resistivity distributions exhibited high resistivity zones that were vertically split by low or intermediate resistivity zones. Our results and interpretation revealed that the main shafts, which play a substantial role in the evolution of solution dolines, can be formed around the doline bottoms rather than in their central sectors. We propose a hypothesis that can better account for the subsurface structures and the development of dolines in Akiyoshi-dai. Our hypothesis suggests that the role of main shafts in the evolution of solution dolines can be superseded by another influential joint system with a potential shaft during their evolution, resulting in the ubiquity of main shafts beneath the doline bottoms. This hypothesis would further our understanding of the intricate role of shafts in the evolution of karst systems involving solution dolines.

Terrain analysis and hydrogeomorphic investigation of the Sita-Swarna river basin, Udupi, SW India: Insights from remote sensing methods

Hydrogeomorphic characteristics of the Sita-Swarna river basin, Western Ghats, India, are investigated to understand the influence of lithology, structure and geological control on the channel morphology. For preliminary investigation, remote sensing, geomorphic and morphometric analysis was carried out, producing slope, aspect and lineament maps from a 30 m resolution Digital Elevation Model (DEM) with the help of GIS. Remote sensing analysis inferred a steep south-to-southwest slope with dominant lineaments trending NW and ENE to E in the middle reaches of the Sita-Swarna river basin. These lineaments are deduced to have possibly been instigated by faults, shear zones, dyke ridges, or subsurface structures that influence the surficial topography. Upland and pediment geomorphic zone were identified, inferring Western Ghats Escarpment (WGE) and gently coastward W-sloping dissected pediment surface. A comprehensive morphometric analysis is performed using various linear, areal, and relief parameters for basin characterization. The linear parameters infer that the basin is structurally controlled and shows moderate to high permeability and flood susceptible areas downstream. The calculated morphometric parameters for basin characterization reveals that the Sita-Swarna river basin is at the mature stage of development and highly asymmetrical with the westward tilt, which indicates a possible influence of paleo tectonism. Rapid runoff is observed due to the steep escarpment leading to less infiltration and flash flood possibility during heavy rainfall. The present study mainly establishes the potential application of remote sensing methods to quantify the hydrogeological aspects, basin morphometry and landscape evaluation in the tropical climatic zone.

Receiver Function Adjoint Tomography for Three‐Dimensional High‐Resolution Seismic Array Imaging: Methodology and Applications in Southeastern Tibet

AbstractA new technique for P‐wave receiver function (PRF) inversion, within the framework of wave equation‐based adjoint tomography and referred to as receiver function adjoint tomography (RFAT), has been developed to obtain models of Vp, Vs, and density. This innovative technique fits the synthetic PRFs with observed PRFs and can better image the lateral variations of Vs from the crust to the uppermost mantle than traditional 1‐D PRF inversion. We utilized RFAT to perform high‐resolution imaging beneath a dense seismic array in Southeastern Tibet, revealing low‐velocity zones extending from the uppermost mantle to the crust, as well as an eastward dipping Moho under the Red River Fault (RRF). Our inversion results provide direct evidence for the existence of a distinct asthenospheric upwelling channel beneath the RRF, and further highlight the effectiveness of RFAT for accurately imaging subsurface structures.

Advancing ocean subsurface thermal structure estimation in the Pacific Ocean: A multi-model ensemble machine learning approach

Estimation of the ocean subsurface thermal structure (OSTS) is important for understanding thermodynamic processes and climate variability. In the present study, a novel multi-model ensemble machine learning (Ensemble-ML) model is developed to retrieve subsurface thermal structure in the Pacific Ocean by integrating sea surface data with Argo observations. The Ensemble-ML model integrates four individual machine learning models to enhance estimation accuracy and reliability. Our results exhibit good agreement between the satellite sea surface temperature (SST) and sea surface salinity (SSS) data and Argo observations, providing validation for the utilization of these datasets in the Ensemble-ML model. The Ensemble-ML model exhibits better performance compared to individual machine learning models, with an average root mean square error (RMSE) of 0.3273 °C and an average coefficient of determination (R²) of 0.9905. Notably, incorporating geographical information as input variables enhance model performance, emphasizing the importance of considering spatial context in OSTS estimation. The Ensemble-ML model accurately captures the spatial distribution of OSTS across depths and seasons in the Pacific Ocean, effectively reproducing critical temperature features while maintaining strong agreement with Argo observations. Nevertheless, its performance shows relative weakness within the thermocline layer and the equatorial Pacific region (spanning from 10°S to 10°N latitude), which are characterized by complex circulation systems. Despite these challenges, the Ensemble-ML model effectively reproduces the spatial distribution of OSTS of the Pacific Ocean. This indicates the potential of machine learning models, particularly ensemble models, for enhancing OSTS estimation in the Pacific Ocean and other regions, offering valuable insights for future research and applications in physical oceanography.

Tectonic transition revealed by upper mantle heterogeneities and anisotropy of the SE margin of the Tibetan Plateau: Insights into the Cenozoic intraplate volcanisms

The SE margin of the Tibetan Plateau is a key channel for understanding the plateau's evolution. However, the links between mantle dynamics, surface deformation, and associated intraplate volcanism remain elusive. Here, 3D radially anisotropic seismic structures of the upper mantle beneath the SE margin of the Tibetan Plateau are presented based on adjoint waveform tomography using dense arrays. The seismic image shows a prominent tectonic transition along 26°N, characterized by strong heterogeneities. In the north of 26°N, lithospheric delamination is revealed by high-velocity anomalies between the Tibetan Plateau and the Yangtze Craton at the 150–250 km depth, which may drive the early Cenozoic potassic volcanism. In the south of 26°N, asthenospheric flow is suggested by significantly low velocity and positive radial anisotropy at the uppermost mantle, which probably accounts for the late Cenozoic sodic volcanism. We propose that such upper mantle dynamics shape the surface expression of plateau uplift and intraplate volcanism. Plain language summaryThe mechanism controlling the growth and volcanism of the Tibetan Plateau remains ambiguous. We present clues from subsurface structures using earthquake seismology. We observe strong heterogeneities of velocity and anisotropy in the upper mantle of the SE margin of the Tibetan Plateau. The results suggest that lithospheric delamination and asthenospheric flow control the generation of the early Cenozoic K-rich volcanism and late Cenozoic Na-rich volcanism, respectively. Our study indicates that tectonic transition might exist in the subsurface of the SE margin of the Tibetan Plateau.

Unveiling Accurate Seismic Imaging through the Advanced Target-Oriented Kirchhoff Migration Method

A major challenge for the oil and gas industry is expediting the exploration geophysics activity. It is necessary to produce fast and accurate image of the targeted hydrocarbon reservoir, yet it involves extensive dataset due to the target location lies in deeper subsurface. Therefore, target-oriented oil and gas-reservoir imaging is currently seen as more attractive than conventional full-volume migration, in terms of computation efficiency. Through the integration of seismic redatuming with Kirchhoff migration, we presented a target-oriented imaging workflow that can effectively reduce computational cost while simultaneously enhancing the accuracy of the migrated image. Kirchhoff migration is renowned for being one of the simplest and flexible migration techniques, making it straightforward to implement. However, this migration approach is typically avoided in the presence of complex geology, as it tends to introduce artifacts in the images, thereby disrupting the interpretation beneath the complex overburden. Therefore, this paper highlighted the advantages of utilizing seismic redatuming to retrieve data beneath the overburden, followed by the utilization of the redatumed data as input for Kirchhoff migration. With an improved signal to noise ratio, the primary reflection events were amplified, providing clearer representation of the subsurface structure within the hydrocarbon reservoir or targeted area. Additionally, we utilized the benefits of Kirchhoff migration and explored the feasibility of performing patch-based migration in several areas of interest beneath the salt layer. This approach aimed to reduce both the turnaround time and the associated seismic migration costs. The developed workflow then was subsequently put to the test and applied to both a sub-salt SEG Advanced Modeling (SEAM) model and field data situated in East Malaysia. Based on the outcomes of the target-oriented migration, the proposed methodology demonstrated its capability to generate better quality and instant migrated images within the designated region. Furthermore, the feasibility of target-oriented imaging with Kirchhoff migration was substantiated through the integration of seismic redatuming, resulting in significant benefits towards seismic processing, imaging, and interpretation.