Ground Surface Deformation Research Articles

Updating model parameters and predictions in SEM tunnelling using a surrogate-based Bayesian approach

This paper presents a surrogate-based Bayesian approach for updating the ground parameters within an application of the observational method in sequential excavation method (SEM) construction. A three-dimensional (3D) finite-difference model is used in the forward analysis to simulate SEM construction explicitly considering 3D multi-face excavation effects and ground–structure interaction. The polynomial-chaos Kriging (PCK) method was employed to provide a surrogate for the 3D finite-difference model to alleviate the cost of probabilistic analysis. The uncertain geotechnical parameters are updated during SEM construction through a progressive Bayesian updating procedure. Time-series observations of multiple types of measurements are used to form the likelihood function. The posterior distributions of the uncertain parameters are derived from the affine invariant ensemble sampling (AIES) algorithm. The proposed framework is illustrated through application to data from the Regional Connector Transit Corridor (RCTC) crossover cavern project constructed in downtown Los Angeles. The uncertainties of the geotechnical parameters were substantially reduced. The posterior estimations indicate higher elastic modulus and cohesion of the Fernando formation than what was assumed before the construction. The updated predictions of the ground surface, subsurface and structural deformations showed improvement in agreement with the field measurements through the continuous updating process.

Semi-Analytical Prediction of Ground Surface Heave Induced by Shield Tunneling Considering Three-Dimensional Space Effect

The ground surface deformation induced by shield tunnels passing through enclosure structures of existing tunnels is a particular underground construction scenario that has been encountered in Wuhan Metro Line 12 engineering cases in China. Timely ground deformation prediction is important to keep shield tunneling safe. However, the classic ground deformation theory is difficult to accurately predict for this ground deformation. This paper develops a semi-analytical method to predict ground heave considering the space effect in this engineering condition. Based on the improved ground deformation theory, a novel deformation prediction method for the ground and enclosure structure is derived and combined with Kirchhoff plate theory. Comparing with field deformation measurements, the maximum difference between the measured and calculated deformation is 14.6%, which demonstrates that the proposed method can be used to predict the ground heave induced by shield tunnels passing through the enclosure structure of existing tunnels. The parameters of the underground diaphragm wall used in Wuhan Metro Line 12 are further studied in detail. The results show that the ground heaves have a positive correlation with the embedded ratio of the diaphragm wall, but a negative correlation with its elastic modulus and thickness. However, the thickness and embedded ratio have a limited effect on ground heaves. This study provides a technical reference for optimizing the setting of enclosure structures in order to protect existing buildings.

Assessment and mapping of landslides in steep mountainous terrain using PS-InSAR: A case study of Karimabad Valley in Chitral

Assessing and mapping landslides in rugged, mountainous terrain presents considerable challenges due to the high cost, risk, and complexity involved. High-resolution assessments of landslides are essential for mitigating landslide-relevant damage and understanding landslide kinematics. Recent studies have utilized satellite-based Synthetic Aperture Radar Interferometry (InSAR) to achieve millimeter-scale detection of ground surface deformation. Among these InSAR techniques, Persistent Scatterers Interferometry (PS-InSAR) is particularly useful in identifying landslide-prone areas, offering a means to map and detect slope movements and characterize the stability of potentially unstable slopes. This study focuses on the slow-moving unstable hillslopes of Karimabad Valley in Chitral. We conducted an analysis using Sentinel-1 SLC data over a three-year period, obtained in interferometric wide swath mode with vertical-vertical polarization. Our results, derived from both ascending and descending satellite passes, reveal that the hillslopes of Karimabad Valley exhibit an average velocity of −25 to +28 mm/yr. Based on the deformation pattern identified, we detected seven deformation zones, with particular concern for the Beshgram village area. To better understand terrain steepness, four topographic profile lines (AA', BB', CC', and DD') were extracted and correlated with the deformation time series. Furthermore, the deformation time series were examined in relation to rainfall, earthquake, and snowfall data. These analyses highlight the complex interplay of multiple factors contributing to the observed variations in deformation, including the region's topography characterized by steep slopes, the freezing and thawing of snow, and seismic events.

Prediction Parameters for Mining Subsidence Based on Interferometric Synthetic Aperture Radar and Unmanned Aerial Vehicle Collaborative Monitoring

Coal mining induces surface subsidence, making rapid and precise monitoring of this subsidence a key area of current research. To address the limitations of D-InSAR technology in capturing large-gradient deformations in the central subsidence basin and the challenges facing UAVs in accurately monitoring small deformations at the basin’s edge, we propose a method for inverting the expected parameters of surface subsidence by synergistically integrating InSAR and UAV monitoring. We determined the cumulative subsidence of monitoring points along the dip and strike observation line of the Banji 110,801 working face between 10 April 2021 and 28 June 2022, employing D-InSAR and UAV techniques. By leveraging the complementary strengths of both monitoring techniques, we fused the two types of monitoring data and verified the error of the fusion data to be within 10 cm through leveling data verification. Simulation experiments utilizing the probability integration method and the Broyden–Fletcher–Goldfarb–Shanno (BFGS) optimization algorithm confirmed that the 10 cm data source error remains within the required limits for probability integration parameter inversion. Finally, the BFGS algorithm was employed to invert the parameters of the probability integration method based on the fusion data results. Subsequently, these inversion parameters were used to predict the subsidence at the monitoring point and were compared with the level measured data. The results demonstrate that the use of collaborative InSAR and UAV monitoring technology for inverting the expected parameters of surface subsidence in the mining area yields superior results, aligning with the actual patterns of ground surface movement and deformation. This study addresses the global need for unmanned monitoring of mining-related subsidence. It employs InSAR and UAV technologies in a synergistic approach to monitor surface subsidence in mining regions. This approach harnesses the strengths of multiple data sources and presents a novel concept for the unmanned monitoring of surface subsidence in mining areas, contributing to environmental protection efforts.

A surrogate model for predicting ground surface deformation gradient induced by pressurized fractures

Fast and reliable estimation of engineered fracture geometries is a key factor in controlling undesirable fractures and enhancing stimulation design. Measuring the surface deformation gradient (tilt) for engineered fractures in shallow depths (<1000 m) has been proven a reliable source of data to infer fracture geometry, thanks to the impressive resolution of tiltmeter units (in the order of nano-radians). However, solving the inverse problem requires reliable and fast forward models. In this study, we present a fast and reliable machine-learned surrogate model to estimate the ground surface tilt induced by pressurised fractures. The proposed surrogate model, based on Conditional Generative Adversarial Networks (cGAN), receives a fracture aperture map in XY and XZ planes as input and predicts the corresponding surface tilts (in X and Y directions). The surrogate model with Wasserstein loss and gradient penalty has been trained using 11,000 samples and tested for a range of input parameters such as depth, dip angles, elastic properties, fluid pressures and fracture shapes. The testing results show excellent performance of the surrogate model compared with the forward finite element model for both single and multiple pressurised fractures, while running hundreds to potentially thousands of times faster.

A parametric study on deformation behaviour for design of braced excavation in soft clay

ABSTRACT Adequate prediction of surrounding ground movement during braced excavation is critically important as excessive soil movement damages adjacent structures. The magnitudes and patterns of ground movement and wall deflection largely depend on excavation parameters like thickness of diaphragm wall, wall embedment depth, strut locations and soil parameters such as soil strength, compressibility and creep parameter. In the present paper a thorough, parametric study has been conducted using finite element (FE) analysis to address the influence of various parameters on deformation characteristics of braced excavation in soft clayey deposits. The importance of correct estimation of soil parameters for braced excavation design is also documented. The analysis of typical braced excavations in soft clay is carried out using PLAXIS 2D software where soft soil creep constitutive model is used. On the basis of numerical study a handy design guideline is recommended. Further multivariate regression models are developed incorporating various important excavation parameters for the adequate prediction of maximum wall and ground displacement along with wall and ground surface deformation profile. Here large numbers of data reported in case histories and generated artificially from FE analysis are used for formation of regression equations. The proposed model is validated comparing results from literatures not used for the development of the model.

Performance of parallel double pipelines under non-uniform seismic excitation

This paper investigates the structural safety of parallel double-buried pipelines under non-uniform seismic excitation considering the soil-pipeline interaction. A three-dimensional nonlinear numerical model has been established to study the effects of seismic wave propagation and ground motion intensity, as well as the pipeline internal pressure and spacing between the pipelines on their structural safety. The dynamic response of the parallel double buried pipelines was evaluated in terms of the acceleration amplification, settlement of ground surface, and strain, displacement, and elliptical deformation of the pipeline. The results demonstrate that the seismic response of buried pipelines under non-uniform excitation has obvious nonlinear characteristics, especially when the loading intensity is high. It is found that the internal pressure has virtually no effect on the site acceleration response, but it amplifies the settlement of the ground surface. Meawhile, it inhibits the elliptic deformation of the pipeline. Furthermore, the variation of the elliptic deformation of parallel buried pipelines is found to be the same for different pipeline spacings considered in this study. On the other hand, the pipelines spacing has a significant influence on their seismic response as the interaction between the two pipelines gradually decreases with the increase in the spacing.

Mitigation of reverse faulting in foundation soils using geosynthetic-encased granular columns

In this study, a series of reduced model tests was conducted on soil foundations reinforced by Geosynthetic-Encased Granular Columns (GECs) placed across a reverse fault. These tests aimed at evaluating the effectiveness, reinforcing mechanism and optimal GEC horizontal spacing to mitigate the ground surface deformation associated with reverse faulting. For comparison, reduced model tests were also performed on unreinforced and Geosynthetic-Reinforced Soil (GRS) foundations. The reduced model tests were conducted to simulate a prototype 3-m-thick foundation layer subjected to a reverse fault displacement of 0.9 m. Digital Image Analysis (DIA) techniques were adopted to determine the surface displacement profile, angular distortion and shear rupture propagation considering various reverse fault offsets. Test results revealed that the GEC foundation can considerably reduce the fault-induced angular distortion at the ground surface. A reduction of 23.3% on the maximum angular distortion at the ground surface was observed as the fault displacement reached 30% of the foundation height (S/H = 30%), indicating the GEC foundation can mitigate the risk of surface fault hazards associated with large reverse fault movement. Two mechanisms, shear rupture diffusion and diversion effects, were identified for the GEC foundation, depending on the magnitude of the fault displacement and the system stiffness of the GEC foundation. Because of complex mechanisms between diversion and diffusion of the shear rupture in the GEC foundations, an optimal GEC spacing of Sh/dc = 3.3 was observed, which exhibited the most significant reduction in βmax at large fault offsets.

Forecasting landslides using community detection on geophysical satellite data.

As a result of extreme weather conditions, such as heavy precipitation, natural hillslopes can fail dramatically; these slope failures can occur on a dry day, due to time lags between rainfall and pore-water pressure change at depth, or even after days to years of slow motion. While the prefailure deformation is sometimes apparent in retrospect, it remains challenging to predict the sudden transition from gradual deformation (creep) to runaway failure. We use a network science method-multilayer modularity optimization-to investigate the spatiotemporal patterns of deformation in a region near the 2017 Mud Creek, California landslide. We transform satellite radar data from the study site into a spatially embedded network in which the nodes are patches of ground and the edges connect the nearest neighbors, with a series of layers representing consecutive transits of the satellite. Each edge is weighted by the product of the local slope (susceptibility to failure) measured from a digital elevation model and ground surface deformation (current rheological state) from interferometric synthetic aperture radar (InSAR). We use multilayer modularity optimization to identify strongly connected clusters of nodes (communities) and are able to identify both the location of Mud Creek and nearby creeping landslides which have not yet failed. We develop a metric, i.e., community persistence, to quantify patterns of ground deformation leading up to failure, and find that this metric increased from a baseline value in the weeks leading up to Mud Creek's failure. These methods hold promise as a technique for highlighting regions at risk of catastrophic failure.

Thaw-Season InSAR Surface Displacements and Frost Susceptibility Mapping to Support Community-Scale Planning in Ilulissat, West Greenland

In permafrost regions, ground surface deformations induced by freezing and thawing threaten the integrity of the built environment. Mapping the frost susceptibility of the ground at a high spatial resolution is of practical importance for the construction and planning sectors. We processed Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) data from thawing seasons 2015 to 2019, acquired over the area of Ilulissat, West Greenland. We used a least-squares inversion scheme to retrieve the average seasonal displacement (S) and long-term deformation rate (R). We secondly investigated two different methods to extrapolate active layer thickness (ALT) measurements, based on their statistical relationship with remotely sensed surface characteristics. A generalized linear model (GLM) was first implemented, but the model was not able to fit the data and represent the ALT spatial variability over the entire study domain. ALT were alternatively averaged per vegetation class, using a land cover map derived by supervised classification of Sentinel-2 images. We finally estimated the active layer ice content and used it as a proxy to map the frost susceptibility of the ground at the community scale. Fine-grained sedimentary basins in Ilulissat were typically frost susceptible and subject to average seasonal downward displacements of 3 to 8 cm. Areas following a subsiding trend of up to 2.6 cm/yr were likely affected by permafrost degradation and melting of ground ice below the permafrost table. Our approach enabled us to identify frost-susceptible areas subject to severe seasonal deformations, to long-term subsidence induced by degrading permafrost, or to both. Used in combination with traditional site investigations, InSAR maps provide valuable information for risk management and community planning in the Arctic.

Ground Surface Deformation Caused by Pipe Jacking Construction in a Soft Soil Area: An Experiment-Based Study

Soft soil has the characteristics of high compressibility, large void ratio, and strong structure. Therefore, it is more likely to cause surface subsidence or even surface cracking and collapse when laying oil and gas pipelines in soft soil areas through the pipe jacking method. In this study, test soil was pressurized using a flexible loading bladder, and variable formation losses brought on by pipe jacking were mimicked by varying the loading bladder’s water injection level. The surface deformation brought on by pipe jacking construction is related to the four parameters of stratum loss rate, overburden load, soil disturbance, soil tension fissures, and horizontal deformation. The findings demonstrate that the surface deformation brought on by the excavation gradually reduces and starts to stabilize after the thickness of the overlying soil layer on the pipe jacking surpasses 1.5 times the diameter of the pipe jacking. The constructed settling tank is broader the deeper the jacking pipe is submerged. Further ground surface settling will be exacerbated by the weight above the jacking pipe. The maximum ground surface deformation value will decrease with an increase in the overlying load when the overlying load is high (0.018 MPa).

Evaluation of ground surface deformation in discontinuous permafrost regions along the China-Russia Crude Oil Pipelines in Northeast China using InSAR and ground surveys

Adequately and timely measuring and evaluating the ground surface deformation (GSD) are keys to the prudent mitigation of frost hazards of foundation soils and thus to the safe and cost-effective operation of oil pipelines in permafrost regions. Thus, it is crucial to accurately evaluate the GSD along the route of China-Russia Crude Oil Pipelines (CRCOPs) for a better understanding of frequent and substantial (differential) frost heave and thaw settlement of pipeline foundation soils in permafrost regions. In this study, GSDs along the CRCOPs from Xiufeng town to Jinsong town, northern Heilongjiang Province were monitored in discontinuous permafrost regions in the northern Da Xing'anling Mountains, Northeast China. The Sentinel-1B images from 2017 to 2021 and the Small Baseline Subset Interferometric Synthetic Aperture Radar (SBAS-InSAR) technology were used in combination with the Geographical Detector (GeoDetector) for identifying the drivers for GSDs and with ground survey data for validation analysis of GSD at chosen sites (e.g., MDX304 and others). InSAR results show that most of the annual GSD rates along the CRCOPs range from −10 to 0 mm/a, with larger deformation rates in Ta’he, Cuigang, and Jinsong. GeoDetector analysis shows that latitude and soil types are the most important contributors to GSDs along the CRCOPs, and; GSDs are closely related to elevation, ground temperature at the depth of 1 m (GT1m), normalized difference vegetation index (NDVI), annual precipitation (AP), and slope aspects. Analyses of ground and oil-flow temperatures and survey results of electrical resistivity tomography (ERT) show that permafrost along CRCOPs has been degrading and thawing, resulting in thaw settlement, consolidation, and deformation of pipeline foundation soils and underlying/lateral permafrost layers and subsequently, the ground surface subsidence. This study provides key deformation data for the assessment and mitigation of frost hazards along the CRCOPs.

Ground Deformation and Permafrost Degradation in the Source Region of the Yellow River, in the Northeast of the Qinghai-Tibet Plateau

The source region of the Yellow River (SRYR) is situated on the permafrost boundary in the northeast of the Qinghai-Tibet Plateau (QTP), which is an area highly sensitive to climate change. As a result of increasing global temperatures, the permafrost in this region has undergone significant degradation. In this study, we utilized Sentinel-1 to obtain ground surface deformation data in the SRYR from June 2017 to January 2022. We then analyzed the differences in terrain deformation under various environmental conditions. Our findings indicated an overall subsidence trend in the SRYR, with a long-term deformation velocity of −4.2 mm/a and seasonal deformation of 8.85 mm. Furthermore, the results showed that terrain deformation varied considerably from region to region, and that the Huanghe’ yan sub-basin with the highest permafrost coverage among all sub-basins significantly higher subsidence rates than other regions. Topography strongly influenced ground surface deformation, with flat slopes exhibiting much higher subsidence rates and seasonal deformation. Moreover, the ground temperature and ground ice richness played a certain role in the deformation pattern. This study also analyzed regional deformation details from eight boreholes and one profile line covering different surface conditions, revealing the potential for refining the permafrost boundary. Overall, the results of this study provide valuable insights into the evolution of permafrost in the SRYR region.

Tunnelling-induced ground deformation subjected to the behavior of tail grouting materials

The deformation of tail grouting plays an essential role in the settlement control of shield tunnelling, which has not been visualized in construction. The conventional methods can only evaluate the quality of tail grouting by the calculating deformation of ground surface, and the mechanism of grouts deformation under the earth pressure is not yet understood in construction. In this study, a novel lab apparatus is designed to explore the mechanism of grouts deformation in respect to the behavior of grouting materials. The purpose of lab tests is to visually analyze the behavior of grouting materials and to investigate the mechanism of grout consolidation induced by varying proportions of grouts and earth pressure. The XRD (X-ray diffraction) and SEM (Scanning Electron Microscope) analysis is used to reveal the micromechanics of the deformation and strength of grouts. Based on laboratory tests results, the parameters of the displacement convergence method are calibrated to optimize numerical analysis. The comparison of results of the proposed method with those obtained by analytical methods and equivalent layer method shows the high performance of the proposed method. The parameters of the proposed numerical method are derived through laboratory tests as opposed to empirical estimations, which could result in more accurate predictions of ground deformation. By comparing the predicted surface settlement to measured data, the Beijing Metro Line 12 project verifies the adaptability of the proposed method.

RESEARCH AND APPLICATION OF U-BIT CONSTRUCTION METHOD IN SUBWAY STATION ENGINEERING LOCATED IN SATURATED SOFT SOIL AREA

In order to solve the problems existing in the construction of underground structures located in the downtown of saturated soft soil area, such as insufficient construction site, complex adjacent structures and great impact on the surrounding environment, the construction method of underground bundled integrate tunnel(U-BIT) is proposed. In this method, after steel pipes jacking completed, concrete is filled into the pipes, and prestress is tensioned to make each independent pipe combined to form a whole bearing structure, so as to achieve the purpose of reducing the size of structural components, improving the structural stiffness and bearing capacity. Based on the structural mechanical properties test and the project of Wuding Road Station of Shanghai Metro Line 14, the failure mechanism of bundled integrate structure, the tension technology of prestressed tendons in narrow space and the variation rules of ground surface subsidence are systematically studied. The research shows that structural seam sections will be destroyed before pipe sections, so ensuring the mechanical performance of seam sections is very important to make sure the structural safety. Since each independent pipe is combined to form an overall stable structure under the prestress effect, the subsequent soil excavation has little influence on the tension of prestressed tendons and ground surface deformation. Therefore, the above construction method can control the ground surface subsidence effectively and reduce the influence of underground engineering construction on the surrounding environment.

Geomechanical Modeling of Ground Surface Deformation Associated with Thrust and Reverse-Fault Earthquakes: A Distinct Element Approach

ABSTRACTWe seek to improve our understanding of the physical processes that control the style, distribution, and intensity of ground surface ruptures on thrust and reverse faults during large earthquakes. Our study combines insights from coseismic ground surface ruptures in historic earthquakes and patterns of deformation in analog sandbox fault experiments to inform the development of a suite of geomechanical models based on the distinct element method (DEM). We explore how model parameters related to fault geometry and sediment properties control ground deformation characteristics such as scarp height, width, dip, and patterns of secondary folding and fracturing. DEM is well suited to this investigation because it can effectively model the geologic processes of faulting at depth in cohesive rocks, as well as the granular mechanics of soil and sediment deformation in the shallow subsurface. Our results show that localized fault scarps are most prominent in cases with strong sediment on steeply dipping faults, whereas broader deformation is prominent in weaker sediment on shallowly dipping faults. Based on insights from 45 experiments, the key parameters that influence scarp morphology include the amount of accumulated slip on a fault, the fault dip, and the sediment strength. We propose a fault scarp classification system that describes the general patterns of surface deformation observed in natural settings and reproduced in our models, including monoclinal, pressure ridge, and simple scarps. Each fault scarp type is often modified by hanging-wall collapse. These results can help to guide both deterministic and probabilistic assessment in fault displacement hazard analysis.

EZ-InSAR: An easy-to-use open-source toolbox for mapping ground surface deformation using satellite interferometric synthetic aperture radar

Satellite Interferometric Synthetic Aperture Radar (InSAR) is a space-borne geodetic technique that can map ground displacement at millimetre accuracy. Via the new era for InSAR applications provided by the Copernicus Sentinel-1 SAR satellites, several open-source software packages exist for processing SAR data. These packages enable one to obtain high-quality ground deformation maps, but still require a deep understanding of InSAR theory and the related computational tools, especially when dealing with a large stack of images. Here we present an open-source toolbox, EZ-InSAR (easy-to-use InSAR), for a user-friendly implementation of InSAR displacement time series analysis with multi-temporal SAR images. EZ-InSAR integrates the three most popular and renowned open-source tools (i.e., ISCE, StaMPS, and MintPy), to generate interferograms and displacement time series by using these state-of-art algorithms within a seamless Graphical User Interface. EZ-InSAR reduces the user’s workload by automatically downloading the Sentinel-1 SAR imagery and the digital elevation model data for the user’s area of interest, and by streamlining preparation of input data stacks for the time series InSAR analysis. We illustrate the EZ-InSAR processing capabilities by mapping recent ground deformation at Campi Flegrei (> 100 mm·yr−1) and Long Valley (~ 10 mm·yr−1) calderas with both Persistent Scatterer InSAR and Small-Baseline Subset approaches. We also validate the test results by comparing the InSAR displacements with Global Navigation Satellite System measurements at those volcanoes. Our tests indicate that the EZ-InSAR toolbox provided here can serve as a valuable contribution to the community for ground deformation monitoring and geohazard evaluation, as well as for disseminating bespoke InSAR observations for all.

InSAR-Based Early Warning Monitoring Framework to Assess Aquifer Deterioration

Aquifer surveillance is key to understanding the dynamics of groundwater reservoirs. Attention should be focused on developing strategies to monitor and mitigate the adverse consequences of overexploitation. In this context, ground surface deformation monitoring allows us to estimate the spatial and temporal distribution of groundwater levels, determine the recharge times of the aquifers, and calibrate the hydrological models. This study proposes a methodology for implementing advanced multitemporal differential interferometry (InSAR) techniques for water withdrawal surveillance and early warning assessment. For this, large open-access images were used, a total of 145 SAR images from the Sentinel 1 C-band satellite provided by the Copernicus mission of the European Space Agency. InSAR processing was carried out with an algorithm based on parallel computing technology implemented in cloud infrastructure, optimizing complex workflows and processing times. The surveillance period records 6-years of satellite observation from September 2016 to December 2021 over the city of Chillan (Chile), an area exposed to urban development and intensive agriculture, where ~80 wells are located. The groundwater flow path spans from the Andes Mountain range to the Pacific Ocean, crossing the Itata river basin in the Chilean central valley. InSAR validation measurements were carried out by comparing the results with the values of continuous GNSS stations available in the area of interest. The performance analysis is based on spatial analysis, time series, meteorological stations data, and static level measurements, as well as hydrogeological structure. The results indicate seasonal variations in winter and summer, which corresponds to the recovery and drawdown periods with velocities &gt; −10 mm/year, and an aquifer deterioration trend of up to 60 mm registered in the satellite SAR observation period. Our results show an efficient tool to monitor aquifer conditions, including irreversible consolidation and storage capacity loss, allowing timely decision making to avoid harmful exploitation.

Influences of across-strike heterogeneous viscosity on the earthquake cycle in a three-dimensional strike-slip fault model

Geodetic observations have shown that there exist large differences in the viscosity of the deep lithosphere across many large strike-slip faults. Heterogeneity in lithospheric viscosity structure can influence the efficiency of stress transfer and thus may have a significant effect on the earthquake cycle. Until now, how the lateral viscosity variation across strike-slip faults affects the earthquake cycles is still not well understood. Here, we investigate the effects of across-strike viscosity variation on long-term earthquake behaviors with a three-dimensional strike-slip fault model. Our model is a quasi-static model which is controlled by the slip-weakening friction law and power-law rheology. By comparing with the reference case, we find that low viscosity on one side of the fault results in a smaller rupture area but with a higher Coulomb stress drop on the ruptured fault region. In addition, low viscosity also leads to a small Coulomb stress accumulation rate. These combined effects increase the earthquake recurrence interval by approximately 10% and the earthquake moments by about 30% when the low viscosity is related to a geothermal gradient of 30 ​K/km. In addition, across-strike viscosity variation causes asymmetric interseismic ground surface deformation rate. As the viscosity contrast increases, the difference in the interseismic ground surface deformation rate between the two sides of the fault gradually increases, although the asymmetric feature is not pronounced. This asymmetry of interseismic ground deformation rate across a strike-slip fault is supposed to result in asymmetric coseismic deformation if the long-term plate motion velocity is invariant. As a result, this kind of asymmetry of interseismic deformation may influence the evaluation of potential earthquake hazards along large strike-slip faults with lateral viscosity contrast.

Ground Surface Deformation Analysis Integrating InSAR and GPS Data in the Karstic Terrain of Cheria Basin, Algeria

Karstic terrains are usually dominated by aquifer systems and/or underground cavities. Overexploitation of groundwater in such areas often induces land subsidence and sometimes causes sinkholes. The Cheria basin in Algeria suffers from severe land subsidence issues, and this phenomenon has been increasing in recent years due to population expansion and uncontrolled groundwater exploitation. This work uses GPS data and persistent scatterer interferometry synthetic aperture radar (PS-InSAR) techniques to monitor the land subsidence rate by employing Sentinel-1 satellite data for the period from 2016 to 2022. Our results demonstrate that the Cheria basin experiences both uplift and subsidence in places, with an overall substantial change in the land surface. The total cumulative subsidence over 6 years reached a maximum of 500 mm. Comparison of land deformation between PSI and GPS showed root mean square error (RMSE) values of about 2.83 mm/year, indicating that our analyzed results are satisfactorily reproducing the actual changes. Nonetheless, these results can be used to extract the susceptible zones for vertical ground displacement and evaluate the surface deformation inventory map of the region for reducing damages (e.g., human losses, economic impact, and environmental degradation) that may occur in the future (e.g., sinkholes) and can be further utilized in perspective for a sinkhole early warning system.