Geophysical Journal International

SummaryThe response of porous rocks to fluid flow and external loads is critical to a wide range of geophysical and geotechnical problems, and is described by the long-established theory of poroelasticity. Despite the wealth of literature existing on the subject, little investigation has been devoted to the analysis of the state of stress and pore pressure regimes within porous media under the action of gravity force. Here, we present analytical solutions for the effective stress and pore pressure in gravitationally loaded porous rocks, in both drained and undrained conditions, and compare them with results from Finite Element numerical models. We also apply our models to a ground deformation episode observed in the Campi Flegrei caldera, Italy. We find that the numerical results accurately reproduce our analytical solutions and show how accounting for gravity-induced stress and pore pressure regimes is critical to model stress and deformation in poroelastic media accurately. Specifically, we highlight how failing to assign realistic initial conditions, or neglecting gravity altogether, may lead to misleading results and interpretations of geophysical observables, such as ground deformation and rock failure.

SummaryPrecursory spurious arrivals, commonly observed in ambient noise correlations, are generated by near-field noise sources. We have developed an inversion method to evaluate the noise source distribution based on the precursory waves. This method is applied to the BASIN experiment in Los Angeles, revealing that the noise sources show coherent patterns with features like faults and structure boundaries. Our spectral analysis indicates that the energy of the noise source in generating the precursory signal is predominant at higher frequencies, suggesting a shallow source(<200m). We conclude that near-field noise is primarily produced by scattering from geological structures with significant velocity contrasts, such as faults at shallow depths. This method offers a new way to map faults using ambient noise correlations.

SummaryThere are currently few studies in the literature on source and background seismic noise power distribution in Italy. In this research, the seismic noise recorded by 233 broadband (BB) seismic stations of the Italian Seismic Network (ISN), operating continuously between 2015 - 2018, was investigated. Starting from the average Power Spectral Density (PSD) calculated for each selected station, the seismic noise powers in four subsets from 0.025 to 30 Hz frequency bands were analysed. Using the Inverse Distance Weighted (IDW) interpolation method, the background noise distribution in the entire Italian territory was observed, producing noise interpolation maps for each of the four frequency bands. Furthermore, regional seismic noise models and local anomalies for each subset of the frequency bands were found by applying 2D moving average spatial filtering techniques. In addition, in this research, a first attempt of linear regression analysis is performed to discover possible relationships between seismic noise powers and geographical parameters (elevation site and minimal station-coast distance) and the role of meteorological parameters such as rainfall. The large dataset obtained allowed for the assessment of the main characteristics and sources of seismic noise at all sites. One can thus know the distribution of noise levels in the Italian territory and in particular study their main sources related to natural and anthropic ambient vibrations. To improve the analysis, a comparison between the seismic noise maps and the completeness magnitude map was carried out, which showed the effectiveness of the national seismic network.

SummaryThe Seoul Mega City (SMC), one of the most densely populated regions in the world, has experienced an increase in seismic activity, raising concerns about the potential presence of concealed faults that could trigger clustered earthquakes in the Seongbuk area (SB), located in the central part of the SMC. This study aims to identify such a fault through the interpretation of terrestrially measured gravity field. By employing dip-curvature analysis and the first vertical derivative calculation of the gravity field, supported by S-wave velocity models, reflection seismic profiles, geological data, and borehole data analyses, we provide compelling evidence for the existence of a deeply buried NS-trending fault (DF0) associated with the Dongducheon Fault system. This fault is likely responsible for the clustered seismic activities observed in the SB. The confirmation of DF0’s presence highlights the critical need for further geophysical investigations to better understand seismic risks in the SMC, which has a history of significant seismic events.

SummaryThe Lamb problem stands as a classic issue in theoretical seismology aimed at obtaining solutions for the Green's functions of point sources in elastic half-spaces. It serves as the foundation for studying vibrational signals from many sources such as walking and driving, bearing significant theoretical and practical value. While the analytical solutions exist for the Lamb problem when both excitation and reception occur on the ground, the presence of singularity makes the numerical stability of calculating the Green's functions from these analytical solutions a challenge. In this study, we propose a stable algorithm that circumvents the impact of time singularity in the analytical solutions of the Lamb problem by introducing a tiny time parameter perturbation and judiciously selecting the starting position for time discretization sampling. This means that the zero time point (i.e. the excitation time of the source pulse) and the starting time of discretization sampling may not be coincident. The advantages of this method lie in its stability, simplicity, and practical accuracy, with the calculation results aligning consistently with the theoretical geometric decay of surface waves. Additionally, analysis of field data demonstrates that our stable algorithm effectively captures the amplitude characteristics of measured footstep responses and vehicle signals. Building upon the foundation of obtaining stable discrete solutions, we further elaborate on the process of transforming the discrete sampling starting point to approach the actual zero time point infinitely, even though this tiny time parameter perturbation does not affect the simulation results.

SummaryThe cross-correlation of the ambient noise recordings, also known as noise correlation functions (NCFs), can converge to Green’s functions (GFs) which describe wave propagation between a pair of stations. However, the NCFs are often biased from the true GFs due to the presence of random noise and spurious arrivals arising from non-diffuse wavefields. Additionally, the limited spatial and temporal coverage of recording stations can lead to large data gaps in the retrieved virtual shot gathers, particularly at large inter-station distances (far offsets). Both these factors impose great challenges to retrieving high-quality NCFs and conducting reliable subsurface imaging. In this study, we propose a multi-dimensional (4D) reconstruction method to compensate for the insufficient station coverage and simultaneously attenuate incoherent noise in the NCFs. We test the feasibility of the proposed method using a dense seismic array deployed in western Canada. Our results demonstrate that the reconstructed virtual common mid-point gather (VCMG) can greatly improve the stability and reliability of the surface-wave dispersion measurements and subsequent shear velocity inversions compared to the conventional approaches. The proposed ambient noise processing framework enables us to construct accurate 3D velocity model of the subsurface.

SummaryThis paper describes a refined version of the point acceleration approach, referred to as the refined acceleration approach, which makes use of K-band range-acceleration observations to derive high-precision monthly gravity field solutions. For overcoming shortcomings of the conventional approach, several refinements are made as follows. (1) The inter-epoch correlated errors caused by numerical differentiation are decorrelated by a decorrelation operator. (2) The satellite velocity is transformed into a function of satellite positions and dynamic parameters. (3) The effect of satellite position error is taken into consideration while building the range-acceleration observational equation. (4) An autoregression (AR) model is used for modelling the high-frequency error of K-band range-acceleration observations. Applying the proposed approach, GRACE-FO observation data spanning the period from January 2019 to December 2022 were processed and a time series of monthly gravity field solutions, referred to as SSM-ACC-GFO, was derived. This time series is comprehensively compared with three official time series, i.e. CSR RL06, JPL RL06 and GFZ RL06, both in spectral and spatial domain. Comparison results demonstrate that SSM-ACC-GFO performs comparably with JPL RL06 and GFZ RL06 indicating that the refined acceleration approach has the ability of deriving high-precision monthly gravity field solutions.

AbstractUnderstanding the mechanical behavior of a fractured geothermal reservoir during its operation phase, when a sustained circulation of fluid is taking place, is of crucial importance for the appraisal of this technology. This knowledge is also essential for understanding natural fault systems that exhibit fluid-induced seismicity, as the geothermal reservoir serves as a small-scale analog to these systems. Here we analyze the seismicity of a geothermal reservoir in France, which has been the primary target for heat exploitation over the last 8 years. Fluid circulation in the granite has been maintained along a main fractured zone through pathways with enhanced permeability thanks to the continuous injection of fluid from a single well. We show that the seismicity occurring during the operation of this reservoir exhibits a progressive expansion outpacing the zone initially activated during the hydraulic stimulation. We also show that most recorded earthquakes are clustered in time within discrete bursts that activate different portions of the fault system. The migration of the events included in these bursts indicates that they are likely related to aseismic transients developing over the creeping fault interfaces. It therefore demonstrates that the intermittency of the seismic activity characterizing earthquake swarms can arise naturally as the complex hydro-thermo-mechanical response of a system under continuous forcing conditions.

SummaryThe configuration of the Earth's magnetic field during the Middle Devonian (394.3–378.9 Ma) is poorly understood. The magnetic signals in Middle Devonian rocks are often overprinted during the Kiaman reverse superchron, obscuring their primary remanence. In other cases, available palaeomagnetic data are ambiguous, conflicting with tectonic reconstructions or dipolar geomagnetic field behaviour. Here, we study the palaeomagnetic signal of Middle Devonian pillow basalts from the Rhenish Massif in Germany. Our rock-magnetic experiments show that the pillow basalts can store and retain magnetisations over time. However, the pillow basalts have a somewhat low initial natural remanent magnetisation (NRM), which is not expected based on their magnetite content. The palaeomagnetic directions determined from alternating field demagnetisation, thermal demagnetisation, and a combination of both, fail to cluster around a common mean. Great circle analyses of these palaeomagnetic directions reveal traces of both Kiaman and present-day field overprints. Our palaeointensity measurements have a very low success rate of < 2 per cent, with only one sample yielding a result of 5.9 µT. This low intensity might explain the low initial NRM of the samples and the lack of interpretable directional data in this study. However, given the very low success rate, this result does not convincingly represent the palaeointensity of the Middle Devonian field. All together, the lack of signal in our Middle Devonian pillow lavas could be a sign of an (ultra-)low, or non-dipolar, or possibly even absent geomagnetic field during the time of formation.

SummaryThe dip angle is one of the fault parameters that most affect fault-related hazard analyses (ground shaking, tsunami) because it not only influences the inference of other fault parameters (e.g., down-dip width, earthquake maximum magnitude based on fault scaling relations) but also and most importantly, the dip angle controls: a) the fault-to-site distance values of ground motion estimates based on predictive models (Ground Motion Models); b) the ground shaking predicted by physics-based simulations; and c) the vertical component of static surface displacement, which determines the initial conditions for tsunami simulations when the seafloor is displaced. We present the results of a global survey of earthquake-fault dip angles (G-DIP, short for Global Dip) and analyse their empirical distribution for various faulting categories (normal, reverse, transcurrent crustal faulting, and subduction-interface reverse faulting). These new empirical statistics are derived from an extensive and homogeneous dataset of 597 uniquely determined fault plane dip angles corresponding to 269 individual earthquakes. As such, our statistics of fault dip occurrences separated by fault types at a global scale improve previous fault dip-angle distributions. We found significant differences between the average empirical fault dip-angle distributions and the values usually assumed based on Anderson's theory. Dip-slip crustal faults show the same mode at 40-50° for both normal and reverse mechanisms, whereas transcurrent faults have a large spread of values below the mode at 80-90°. Regarding reverse crustal faults, our result became evident after separating them from subduction interface faults, which show significantly lower dip values, with a mode at 10-20°. We remark on the importance of documented uniquely determined fault planes to develop dip-angle statistics. We also suggest that our results can effectively be used as distribution priors for characterising the geometry of poorly known seismogenic faults in earthquake hazard analyses and earthquake-fault modelling experiments.

SummaryThe development of reliable operational earthquake forecasts is dependent upon managing uncertainty and bias in the parameter estimations obtained from models like the Epidemic-Type Aftershock Sequence (ETAS) model. Given the intrinsic complexity of the ETAS model, this paper is motivated by the questions: “What constitutes a representative sample for fitting the ETAS model?” and “What biases should we be aware of during survey design?”. In this regard, our primary focus is on enhancing the ETAS model’s performance when dealing with short-term temporally transient incompleteness, a common phenomenon observed within early aftershock sequences due to waveform overlaps following significant earthquakes. We introduce a methodological modification to the inversion algorithm of the ETAS model, enabling the model to effectively operate on incomplete data and produce accurate estimates of the ETAS parameters. We build on a Bayesian approach known as inlabru, which is based on the Integrated Nested Laplace Approximation (INLA) method. This approach provides posterior distributions of model parameters instead of point estimates, thereby incorporating uncertainties. Through a series of synthetic experiments, we compare the performance of our modified version of the ETAS model with the original (standard) version when applied to incomplete datasets. We demonstrate that the modified ETAS model effectively retrieves posterior distributions across a wide range of mainshock magnitudes and can adapt to various forms of data incompleteness, whereas the original model exhibits bias. In order to put the scale of bias into context, we compare and contrast further biases arising from different scenarios using simulated datasets. We consider: (1) sensitivity analysis of the modified ETAS model to a time binning strategy; (2) the impact of including and conditioning on the historic run-in period; (3) the impact of combination of magnitudes and trade-off between the two productivity parameters K and α; and (4) the sensitivity to incompleteness parameter choices. Finally, we explore the utility of our modified approach on three real earthquake sequences including the 2016 Amatrice earthquake in Italy, the 2017 Kermanshah earthquake in Iran, and the 2019 Ridgecrest earthquake in the US. The outcomes suggest a significant reduction in biases, underlining a marked improvement in parameter estimation accuracy for the modified ETAS model, substantiating its potential as a robust tool in seismicity analysis.

SummaryThis study investigates the longitudinal (T1) to transverse (T2) relaxation time ratios in unconsolidated geological materials to determine how they vary across different geological units. Assessing the T1/T2 ratio can inform about the validity of the presumed relationship between T1 and T2 relaxation times in steady-state surface NMR modeling (i.e. T1/T2 ratio is assumed to be constant and equal to one). The T1/T2 ratio investigation is conducted by two-dimensional T1-T2 correlation data using laboratory and borehole NMR measurements at a Larmor frequency of 2 MHz and 430 kHz, respectively. Laboratory NMR measurements were performed on 73 sediment samples from 9 sites in Denmark and Germany, and borehole NMR measurements were conducted at 59 selected depth intervals in unconsolidated geological units across 8 sites in the same countries. Volumetric magnetic susceptibility of the laboratory samples was measured to evaluate the effects of magnetic susceptibility on the T1/T2 ratio. Our results indicate that the T1/T2 ratios in mineral soils and sediments are pretty similar for borehole NMR and lab NMR datasets, regardless of the geological unit. In these geological materials, the mean value of the T1/T2 ratios is 1.64 in lab-NMR and 1.82 in borehole NMR datasets. In contrast, in our in-situ borehole NMR measurements in organic peat soils, the mean value of the T1/T2 ratios was higher (i.e. 2.77), exhibiting a broader distribution ranging from 1 to 4.8. Moreover, we observed that magnetic susceptibility did not have a significant effect on the T1/T2 ratio in the investigated samples. More importantly, the findings in this study can be adopted in the modeling of steady-state surface NMR modeling routines where a constant ratio of 1 for T1/T2 is assumed when solving the Bloch equations. It is expected that updating the T1/T2 ratio can improve the accuracy of water content and relaxation time estimations derived from steady-state surface NMR measurements.

SummaryIn this study, the microseismicity and damage-zone characteristics of a locked fault are investigated on a major left-lateral strike slip fault segment north of the Dead Sea Lake, the Jericho Fault (JF). The JF was observed as seismically silent for ${M}_w > 2$ earthquakes during recent decades, although it has generated significant earthquakes in the past. We extend seismological observations towards the microseismic range by deploying nine strong motion accelerometers directly on the inferred surface trace. From one year of continuous recordings (06/22–06/23) we found 61 seismic events in the range of 0.9 < ${M}_w$< 2.4, that are below the detection threshold of the permanent regional network. Most of these events are located west of the fault zone and represent activity on other smaller faults, with only three events located along the JF zone itself. We also found that the JF is more seismically quiescent than an analogous segment of the San Jacinto Fault (California)—the Anza gap, indicating that the JF is a particularly quiet fault segment even for microseismic activity and therefore, may be accumulating significant elastic strain energy along the locked-creeping boundary. The JF segment shows a characteristic earthquake distribution behaviour that could reasonably cause an earthquake of ${{\rm{M}}}_{\rm{w}}$ ∼ 7–7.4 if all strain energy, accumulated since the last major earthquake in 1033 AD, is released seismically in a single event. We also provide a new observational-based approach to characterise fault zone properties from trapped waves’ delay-times. Here we emphasise the damage zone velocity as the endmember on a continuum of discrete velocity values that progressively decrease towards the fault. This approach can be applied to other fault zones assisting in characterising rupture zone properties of fault segments. We report the first trapped waves observations at the Dead Sea Transform, caused by waves propagating along a damaged segment of the JF fault zone. We introduce a new trapped-waves inversion scheme, solely data driven, that does not make use of synthetic seismograms and model-based pre-assumptions. The JF coherently trends northwards from the Dead Sea Lake, showing a fault zone trapped-wave velocity estimation of 0.95 -1.15 ${\rm{km\ }}{{\rm{s}}}^{{\rm{ - 1}}}$ with $\~$35 per cent reduction from the surrounding host rock to the fault's damaged rock. A significant velocity drop is observed at the Jericho Escarpment reflecting a geological transfer from hard rock to soft sedimentary layers, towards the Jericho Fault. The trapped-waves inversion indicates ∼16 km of coherently damaged rock trending northwards from the Dead Sea Lake; this serves as a minimum estimate of the JF length, and appears to coincide with the silent section of the JF, rather than extending coherently further north.

SummaryThis study presents the results of an interlaboratory test designed to evaluate the accuracy of Spectral Induced Polarization (SIP) measurements using controlled electrical test networks. The study, conducted in Germany since 2006, involved 12 research institutes, six different impedance measurement devices, and four types of electrical test networks specifically designed to evaluate phase shift errors in SIP measurements. The test networks, with impedances ranging from 100 kΩ to 150 kΩ, represent high-impedance samples with different phase characteristics, and pose the measurement challenges typical of such samples, including high contact impedances and parasitic capacitances. Four key findings emerged from the study: (1) Impedance measurements across all devices showed deviations within 1% over a wide frequency range (0.001 Hz - 1000 Hz); (2) phase errors remained below 1 mrad up to 100 Hz for most devices, but increased at higher frequencies due to parasitic capacitances and electromagnetic coupling effects; (3) lab-specific instruments have lower phase errors than field instruments when used in a laboratory environment, primarily due to the effects of long cables and too low input impedances of the field instruments; and (4) short cables and driven shielding technology effectively minimized parasitic capacitance and improved measurement accuracy. The study highlights the usefulness of test networks in assessing the accuracy of SIP measurements and raises awareness of the various factors influencing the quality of SIP data.

SummaryGas-bearing sediments in shallow-water environments have recently attracted attention from the perspectives of energy resources, potential geohazards, and climate change. Our laboratory measurements demonstrate the potential for gas-bubble manipulation in gas-bearing sands via radiating repeated pulse signals. By monitoring the temporal changes in the waveform of repeated ultrasonic pulse irradiation with a dominant frequency of 100 kHz transmitted through gas-bearing sand, we observe energy amplification and a frequency shift toward the dominant frequency in the recorded waveforms over 880 h. These results imply that gas bubbles may deform or move autonomously to propagate irradiated ultrasonic waves most efficiently and thereby minimize the energy loss of the transmitted waves. Gas bubbles larger than sand grains detected using three-dimensional X-ray computed tomography cannot explain the phenomena of energy amplification and frequency shifts, indicating the need for a higher spatial resolution to capture the behavior of smaller gas bubbles.

SummaryAirborne magnetotelluric (AirMT) systems generate transfer function data from magnetic fields measured in the air and either electric or magnetic fields measured at a base station. AirMT anomalies are fundamentally controlled by the anomalous magnetic fields within the survey region. While AirMT data acquired using a magnetic field base station are not directly sensitive to the conductivity at the base station, AirMT data acquired using an electric field base station are scaled by the inverse square root of the conductivity at the base station. The transfer function data collected by various AirMT systems have different sensitivity functions. Consequently, the inversion of AirMT data for different acquisition systems may not recover the same conductivity model for the same set of inversion parameters. In this paper, we aim to characterize the fundamental similarities and differences between AirMT inversion for data collected using a magnetic field base station, and for data collected using an electric field base station. We adopt an unconstrained, smoothest model inversion approach to characterize the structures that are naturally recovered by inverting AirMT data when the base station is far away and located on the surface of a homogeneous quarter-space. Our work shows that when a-priori knowledge of the host conductivity within the survey region is available, AirMT inversion effectively recovers conductive and resistive structures within the survey region, regardless of whether the data are collected using an electric or magnetic base station. We show that a single ground magnetotelluric station might provide enough information about the host conductivity to construct a suitable starting model for AirMT inversion, and we discuss the impact of jointly inverting AirMT data and ground magnetotelluric data for a single station.

SummaryThe global oceans are a noisy environment with characteristic acoustic and seismic soundscapes. The enclosed, sea ice-covered Arctic Ocean constitutes a particular noise environment that is rapidly changing. Here, we present a first, comprehensive description of the seismic soundscape of the Arctic Ocean recorded by ocean bottom seismometers especially equipped for the operation in sea ice. They were deployed at 4 km water depth in the Laptev Sea near the sea ice edge in September 2018 and recovered one year later. Analysis of the spectral power between 20 s and 60 Hz demonstrates that ambient noise levels are generally very low compared to other ocean bottom seismic records. Distinct noise bands at high frequencies (>6 Hz) characterize the winter time and are likely caused by the deformation of sea ice emitting seismic signals recordable at the ocean bottom over tens of kilometers. Sea ice noise decays suddenly in May while sea ice concentration is still 100 per cent, but freezing stops and compressional stresses decrease. It only gradually develops in autumn as sea ice becomes thicker, brittle and internally stressed. Microseisms with frequencies of 0.2-2 Hz appear with open water on the Laptev Shelf. Swell events in autumn cause large microseisms and high-frequency noise although ice-noise is not yet present in this season. Ice concentration decreases following the swell events, showing the impact of swell on the sea ice. Ocean bottom seismic records thus represent a powerful tool to monitor the interplay between wave action in the emerging Arctic Ocean and the physical state of its sea ice cover.

SummaryGeologically, Europe consists of a combination of Phanerozoic and Precambrian terranes. Our research focuses on understanding the collision and suture zones between these terranes by imaging the lithosphere-asthenosphere boundary (LAB) and the mid-lithospheric discontinuity (MLD) using seismic S-to-P converted waves. The amount of available data from permanent broadband stations and temporary deployments has significantly increased in recent years. This development allows us to resolve new details regarding continental collisions in Europe.We interpret the new data to show that the Scandinavian MLD extends southward beneath the Caledonides and Variscides, reaching as far as the Bohemian Massif. We have also identified a west-dipping seismic phase extending from the East European Platform (EEP) to the centre of the Pannonian Basin. This phase could represent the MLD of the EEP, akin to the collision between Scandinavia and Phanerozoic Europe in the north. To support these novel findings, geodynamic modelling is required to explain the processes leading to such a structure, which is beyond the scope of this paper. Below the Alps, we confirm earlier observations of the European plate subducting below the Adriatic lithosphere.

SummaryFault Zone Head Waves (FZHW) are a key diagnostic tool to identify bimaterial interfaces along fault zones. We detect and analyze FZHW recorded in the waveforms from the local MONGAN (MONitoring of the GANos Fault) seismic network along the Ganos section of the North Anatolian Fault Zone, northwestern Türkiye, between October 2017 and July 2019. MONGAN covers the Ganos fault with different inter-station distances ranging from 25 m to ∼4 km. To detect FZHW, an automatic detector is used as a preliminary analysis method followed by manual revision and particle-motion analyses to distinguish between FZHW and direct P waves. FZHWs are predominantly detected at the southern side of the fault. The observed FZHWs have a moveout (∆t) with respect to the direct P arrivals, increasing with distance traveled along the fault and indicating a deep bimaterial interface down to the bottom of the seismogenic crust. The average velocity contrast is estimated to be 5.9% across the fault. Near fault-recordings indicate that the Ganos Fault is offset by ∼250 m with respect to the surface trace obtained from literature. To a lesser extent, FZHW are also observed in the northern stations from the fault, indicating a shallow wedge-shaped low-velocity portion constituted by highly fractured material to either side along the southwestern section of the Ganos Fault between the fast Eocene block to the north and the slow Miocene block to the south. The seismic velocity contrast and geological complexity have important implications for the rupture evolution during future earthquakes on the Ganos fault in that they would progress predominantly westward, away from Istanbul and Tekirdağ. Furthermore, an asymmetric aftershock distribution skewed to the northern block can be expected, with subsequent implications for site-dependent risk there. Our results allow to revise focal mechanism solutions by separating FZHW from direct-P wave for previous Sea of Marmara earthquakes.

SummaryBorehole breakout (BO) has increasingly been utilised to estimate in-situ stress magnitudes given the importance of the stress field in subsurface activities and the limitations of conventional stress measurement techniques. In this study, a new backpropagation neural network model is developed to estimate both maximum and minimum horizontal stress magnitudes from multi-scale BO data. A total of 150 experimental data points from pre-stressed true-triaxial laboratory tests and 44 field data from a mine site in Australia and the literature are collected and employed for model development and validation. Compared to previous studies, the collected dataset is significantly enhanced in both quantity and quality. To address discrepancies in stress magnitudes between experimental and field data, the three principal stresses are normalised by borehole wall strength (BWS). Overall, the model achieves mean absolute percentage errors of below 8% for the maximum horizontal stress and below 20% for the minimum horizontal stress, significantly outperforming the previous model developed for this purpose. Furthermore, these error rates fall within the typical error range (10-20%) of conventional stress measurement techniques, indicating the model's sufficient accuracy for practical applications. Moreover, the effectiveness and generalisability of the model are verified using 166 additional BOs from two mine sites, which are independent of those used in model development. Continuous and detailed stress profiles are established based on these BOs, covering greater depth intervals than the stress measurements from the overcoring method. The results of this study demonstrate that the proposed model can provide reliable and accurate stress estimation, utilising input parameters that can be readily obtained from borehole geophysical logs.