This study combines terrestrial gravity observations with the XGM2019e_2159 global gravity field model using the Least-Squares Collocation (LSC) technique to investigate the geological structures of the Mount Cameroon region and its surroundings. The complete Bouguer gravity anomaly dataset was processed through regional–residual anomaly separation, followed by the application of edge detection filters to enhance residual gravity signatures associated with shallow geological structures. Both conventional and advanced edge detection techniques, including the total horizontal derivative (THDR), Tilt Angle of the Horizontal Gradient (TAHG), Horizontal Derivative of the Tilt Angle (HDR_TA), Improved Logistic (IL), and Softsign (SF) filters, were employed to delineate structural boundaries across the study area. Euler deconvolution was subsequently applied to the residual gravity anomalies to estimate the depth distribution and spatial extent of the identified geological structures. The complete Bouguer anomaly map reveals significant lateral density variations within the subsurface, with anomaly values ranging from −47 to 129 mGal. The structural map derived from the SF filter indicates that most geological boundaries are predominantly oriented NNE–SSW, ENE–WSW, and NE–SW. Several previously mapped structures, including the Bokosso, Tiko, Ekona, Bao, and Bomona faults, were successfully identified. Additional lineaments revealed by the analysis exhibit orientations consistent with the regional tectonic framework of the Cameroon Volcanic Line (CVL). Euler deconvolution results reveal a multilevel distribution of geological discontinuities at different depths and indicate that the study area has been affected by a regional fault system trending NE–SW to ENE–WSW. The mapped structures are inferred to play a major role in controlling both the gravitational spreading of the volcanic flanks and the volcanic activity of Mount Cameroon, suggesting that magma ascent is facilitated through a network of active and reactivated fault systems.
Earthquake rupture is a spatially extended, time-dependent process governed by the interplay between rupture kinematics and energy partitioning along the fault. Although kinematic source models and energetic formulations are widely used, their local physical consistency is typically not enforced explicitly. Here, a physical–mathematical framework is introduced that links rupture geometry, kinematic fields, and local energy balance within a unified spatial–temporal–energetic description of extended seismic sources. Rupture propagation is described through a spatially defined rupture-time field, from which rupture-front velocity is derived as the inverse gradient of rupture time. Local energy consistency is imposed through a balance between energy release rate, fracture energy, and radiated energy, leading to a formulation in which rupture velocity and radiative efficiency are locally constrained by a common energy balance. Within this framework, kinematic rupture models can be interpreted as implicitly defining a local energy budget. A synthetic diagnostic example demonstrates that not all kinematically admissible rupture-time fields correspond to energetically plausible configurations, and that strongly heterogeneous rupture-velocity patterns may imply violations of local energy-balance conditions. The proposed formulation does not provide direct constraints for inversion, but establishes necessary conditions for physical admissibility that are independent of specific constitutive laws or numerical implementations. By making explicit the energetic assumptions embedded in kinematic descriptions, this framework provides a physically grounded basis for interpreting rupture heterogeneity, radiated energy variability, and source-process observations.
Geotechnical investigations have traditionally relied on invasive methods, such as boreholes and laboratory tests. However, these techniques can be time-consuming, expensive and spatially limited, often resulting in discontinuous subsurface characterisation that fails to capture the full extent of soil heterogeneity. Geophysical methods are becoming increasingly integrated into conventional geotechnical investigations to overcome these spatial and economic constraints. This review examines how seismic, electrical resistivity and electromagnetic surveys provide rapid, nondestructive and spatially continuous subsurface data that can be used to infer geotechnical information across a range of shallow infrastructure and environmental applications, typically within the upper 30 m of the subsurface, at site-specific scale. Methods such as multichannel analysis of surface waves (MASW) estimate shear-wave velocity profiles, which can be related to soil stiffness and small-strain shear modulus through appropriate constitutive assumptions and site-specific calibration. Electrical resistivity tomography (ERT) is well suited to mapping moisture content distributions and detecting seepage anomalies in embankments and slopes. A key finding of this review is that the reliability of geophysical–geotechnical correlations is strongly parameter-dependent: Relationships grounded in physical theory, such as that between shear-wave velocity and small-strain shear modulus, are more robust and transferable than empirical correlations such as those between resistivity and SPT-N values, which tend to be highly site-specific. In all cases, reliability depends on integration with complementary geophysical methods and calibration against direct geotechnical measurements, since soil heterogeneity and environmental conditions can make interpretation ambiguous. Advanced data fusion approaches, including belief function theory and geostatistical interpolation, show practical potential for combining heterogeneous datasets and managing spatial uncertainty. Emerging techniques such as machine learning and Full waveform inversion (FWI) offer further possibilities for quantitative parameter estimation, though their routine application remains constrained by computational demands and the current lack of standardised field validation datasets. This review identifies current knowledge gaps and outlines directions for developing more reliable, quantitative frameworks for geophysical–geotechnical integration in infrastructure assessment and environmental applications.
This study was conducted in the district of Perma, in northwestern Benin, in the department of Atacora. This region of Precambrian crystalline bedrock is known for its gold potential, which is exploited using artisanal and semi-industrial methods. The use of mercury and cyanide has serious repercussions on soil and water, mainly due to acid mine drainage (AMD). The main objective of this study is to characterize AMD associated with gold mining in Perma using magnetic methods and electrical resistivity tomography. Four mining sites were studied, including two alluvial sites (Perma-Centre and Perma-Koka) and two vein sites (Gnagnamou and Koussigou Montagne). The magnetic data show that AMD is stored in the bed of the Perma River at the alluvial sites, with a total magnetic field intensity varying between 33,337.0 and 33,360.8 nT at Perma-Centre and 33,429.2 and 33,443.5 nT at Perma-Koka. At the vein sites, the AMD is stored in fractures and galleries created by gold miners, with magnetic intensity varying between 33,434.7 and 33,446.2 nT at Gnagnamou and 33,437.4 and 33,470.7 nT at Koussigou Montagne. These magnetic data guided the choice of profiles for ERT section acquisition. ERT data show that resistivities at the alluvial sites range from 114 to 10,121 Ωm at Perma-Centre and from 45.4 to 7967 Ωm at Perma-Koka. The AMD, with resistivity ranging from 199 to 402 Ωm, infiltrates the riverbed to a depth of 30 m at Perma-Centre and 15 m at Perma-Koka and circulates in the gravel. At the vein sites, resistivities vary between 655 and 47,180 Ωm at Koussigou Montagne and between 2181 and 134,398 Ωm at Gnagnamou. The AMD flows toward depressions and accumulates in fractures, sometimes reaching depths of more than 40 m. These variations in resistivity confirm the differentiated impact of the AMD.
