Near‐fault severe seismic activity is frequently observed when excavating deep underground during various engineering projects. The present study elaborates a method to simulate the heterogeneous, complex stress state inside fractured rock mass in a fault damage zone, based on the concept of equivalent elastic compliance tensor and boundary traction method. After verifying the method with the discrete element method, the stress state of the fault damage zone composed of millions of fractures was analyzed. It is then demonstrated that the method is capable of simulating stress anomalies that could be the cause for severe seismic activity. The quantitative analysis indicates that the discrepancy between local and regional fracture densities is one of the dominant factors that produce an intensely stressed region, suggesting the use of local‐to‐regional fracture density ratio as an index to evaluate the potential for stress anomalies and its degree. Furthermore, a model parametric study on fracture properties was carried out to provide insight into the discrepancy in the likelihood of abnormal stress state between jointed host rock and fault damage zone. Lastly, b‐value was computed from thousands of possible seismic events identified in the model, by assuming seismic efficiency and scaled energy. The computed b‐value was found to fall within a reasonable range estimated from induced seismicity in deep underground mines. These results imply that the proposed method may be used to obtain a first‐order approximation of the complex rock mass stress state in fault damage zones and to evaluate the severity of seismic activity.

Artisanal and small-scale gold mining (ASGM) is a serious growing concern in Sub-Saharan Africa. In Mauritania, recent gold discoveries in the north and northwest have led to an increase in ASGM centers, reflecting trends across the region and posing considerable risks of mercury (Hg) contamination. Notwithstanding this fact, the extent of mercury contamination in the region remains unclear due to insufficient knowledge on the mechanisms of Hg dispersion in hyper-arid regions. In light of this, the present study aimed to acquire fundamental knowledge to elucidate the dispersion mechanism of mercury through conducting soil and groundwater sampling in and around Chami town, Mauritania, where ASGM activities have intensified. We analyzed 180 soil samples and 5 groundwater samples for total mercury (total Hg) using cold vapor atomic absorption spectrometry (CVAAS) and atomic fluorescence spectrometry (AFS) methods. The total Hg levels in soil samples ranged from 0.002 to 9.3 ppm, with the highest concentrations found at ASGM sites. Groundwater samples exhibited low total Hg levels (0.25–1.25 ng/L). The total Hg content in soil and groundwater samples was below Japanese standards, yet soil samples from hotspot points exceeded other international standards. Our study emphasizes the Hg dispersion patterns around Chami town, suggesting a gradual decrease in total Hg with increasing distance from ASGM sites and a potential influence of wind dynamics. The knowledge accumulated in this study provides essential insights into the Hg dispersion mechanisms in Chami town, laying the foundation for establishing a predictive model of Hg contamination in hyper-arid regions.

Induced seismicity is strongly related to various engineering projects that cause anthropogenic in-situ stress change at a great depth. Hence, there is a need to estimate and mitigate the associated risks. In the past, various simulation methods have been developed and applied to induced seismicity analysis, but there is still a fundamental difference between simulation results and field observations in terms of the spatial distribution of seismic events and its frequency. The present study aims to develop a method to simulate spatially distributed on-fault seismicity whilst reproducing a complex stress state in the fault zone. Hence, an equivalent continuum model is constructed, based on a discrete fracture network within a fault damage zone, by employing the crack tensor theory. A fault core is simulated at the center of the model as a discontinuous plane. Using the model, a heterogeneous stress state with stress anomalies in the fault zone is first simulated by applying tractions on the model outer boundaries. Subsequently, the effective normal stress on the fault plane is decreased in a stepwise manner to induce slip. The simulation result is validated in terms of theb-value and other seismic source parameters, hence demonstrating that the model can reproduce spatially and temporally distributed on-fault seismicity. Further analysis on the parameters shows the variation of frequency-magnitude distribution before the occurrence of large seismic events. This variation is found to be consistent with field observations, thus suggesting the potential use of this simulation method in evaluating the risk for seismic hazards in various engineering projects.