Retrieving Three-Dimensional Large Surface Displacements in Coal Mining Areas by Combining SAR Pixel Offset Measurements with an Improved Mining Subsidence Model

Interferometric synthetic aperture radar (InSAR) technology can obtain one-dimensional surface displacements in the radar line of sight (LOS). In the field of mining subsidence, large 3D movements often occur at the same time, and hence InSAR derived one-dimensional LOS displacements can hardly reflect the actual surface motion in mining areas. To realize the monitoring of three-dimensional large surface displacements in mining areas, a method for monitoring three-dimensional large surface displacements in mining areas that combines SAR pixel offset tracking (OT) and an improved mining subsidence model is proposed in this article. First, a new functional relationship between surface subsidence and horizontal movement combined with the characteristics of the overburden rock stress and the deformation characteristics of the fractured rock mass in coal mining areas is established. Then, a three-dimensional surface deformation model is established based on the proposed relationship between surface subsidence and horizontal movement and the radar projection equation, and finally, the optimal parameters of the deformation model are inverted iteratively using LOS deformation results obtained by OT method to retrieve the three-dimensional large displacements of the surface. The significant advantage of the method proposed in this article is that it can accurately acquire the 3D large surface displacements using only two SAR amplitude images with the same imaging geometry. To verify the accuracy and reliability of the proposed algorithm, two scenes of high-resolution spotlight TerraSAR-X images are used in this paper to conduct a three-dimensional surface displacement monitoring experiment on a working panel in the Daliuta mining area in Shaanxi Province, China, based on the proposed method. Experimental monitoring results show that the maximum surface subsidence is approximately 4.5 m, and the maximum horizontal movements in the strike and dip directions are approximately 1.4 m and 1.2 m, respectively. Using GPS measurements to verify the monitoring results, the root mean square error (RMSE) of vertical subsidence is 6.8 cm, and the RMSE of horizontal movement is 7.1 cm. Compared with those in the original mining subsidence model, the accuracies of vertical subsidence and horizontal movement in the proposed model are increased by 28.2% and 37.5%, respectively, which proves the reliability and accuracy of the proposed method.

Integration of InSAR and LiDAR Technologies for a Detailed Urban Subsidence and Hazard Assessment in Shenzhen, China

Spaceborne interferometric synthetic aperture radar (InSAR) methodology has been widely successfully applied to measure urban surface micro slow subsidence. However, the accuracy is still limited by the spatial resolution of currently operating SAR systems and the lacking precision of geolocation of the respective scatters. In this context, high-precision urban models, as provided by the active laser point cloud methodology through light detection and ranging (LiDAR) techniques, can assist in improving the geolocation quality of InSAR-derived permanent scatters (PS) and provide the precise contour of buildings for hazard analysis. This paper proposes to integrate InSAR and LiDAR technologies for an improved detailed analysis of subsidence levels and a hazard assessment for buildings in the urban environment. By the use of LiDAR data, most building contours in the main subsidence area were extracted and SAR positioning of buildings via PS points was refined more precisely. The workflow for the proposed method includes the monitoring of land subsidence by the TS-InSAR technique, the geolocation improvement of InSAR-derived PS, and building contour extraction by LiDAR data. Furthermore, a reasonable hazard assessment system of land subsidence was developed. Significant vertical subsidence of −40 to 12 mm per year was detected by the analysis of multisensor SAR images. The land subsidence rates in the Shenzhen District obviously follow certain spatial patterns. Most stable areas are located in the middle and northeast of Shenzhen except for some areas in Houhai, the Qianhai Bay, and the Wankeyuncheng. An additional hazard assessment of land subsidence reveals that the subsidence of buildings is mainly caused by the construction of new buildings and some by underground activities. The research results of this paper can provide a useful synoptic reference for urban planning and help reducing land subsidence in Shenzhen.

Deformation Behavior of Mining beneath Flat and Sloping Terrains in Mountainous Areas

Slope structures and surface terrains are two significant factors affecting the deformation behavior of mining slopes in mountainous areas. This research is aimed at investigating the deformation characteristics of a mining slope wielding Particle Flow Code (PFC), with 9 different mining configurations (i.e., horizontal distance from extracted panel center to slope shoulder, D = −200 m, −150 m, −100 m, −50 m, 0 m, 50 m, 100 m, 150 m, and 200 m). A representative slope in Faer Town, Liupanshui City, Guizhou Province, China, was selected, which was characterized by soft and hard interbedded rock strata. The results indicated that the overlying rock mass tended to move towards the sloping surface with mining beneath sloping terrain, which brought an asymmetrical subsidence funnel, and formed a wider relative disturbance range on the slope surface. With the vertical subsidence increasing additionally, the stability of the overall slope deteriorated. A safe mining range should be proposed based on evaluating the time-dependent deformation behavior at the slope shoulder and the overall slope stability.

Ground Displacement in East Azerbaijan Province, Iran, Revealed by L-band and C-band InSAR Analyses

Iran, as a semi-arid and arid country, has a water challenge in the recent decades and underground water extraction has been increased because of improper developments in the agricultural sector. Thus, detection and measurement of ground subsidence in major plains is of great importance for hazard mitigation purposes. In this study, we carried out a time series small baseline subset (SBAS) interferometric synthetic aperture radar (InSAR) analysis of 15 L-band PALSAR-2 images acquired from ascending orbits of the ALOS-2 satellite between 2015 and 2020 to investigate long-term ground displacements in East Azerbaijan Province, Iran. We found that two major parts of the study area (Tabriz and Shabestar plains) are subsiding, where the mean and maximum vertical subsidence rates are −10 and −98 mm/year, respectively. The results revealed that the visible subsidence patterns in the study area are associated with either anthropogenic activities (e.g., underground water usage) or presence of compressible soils along the Tabriz–Shabestar and Tabriz–Azarshahr railways. This implies that infrastructure such as railways and roads is vulnerable if progressive ground subsidence takes over the whole area. The SBAS results deduced from L-band PALSAR-2 data were validated with field observations and compared with C-band Sentinel-1 results for the same period. The C-band Sentinel-1 results showed good agreement with the L-band PALSAR-2 dataset, in which the mean and maximum vertical subsidence rates are −13 and −120 mm/year, respectively. For better visualization of the results, the SBAS InSAR velocity map was down-sampled and principal component analysis (PCA) was performed on ~3600 randomly selected time series of the study area, and the results are presented by two principal components (PC1 and PC2).

The enigma of the Albian Gap: spatial variability and the competition between salt expulsion and extension

The Albian Gap is a uniquely large (up to 65 km wide and >450 km long), enigmatic salt-related structure in the Santos Basin, offshore Brazil. It is located near the basin margin and trends NE (i.e. subparallel to the Brazilian coastline). The gap is characterized by a near-complete absence of Albian strata above depleted Aptian salt. Its most remarkable feature is an equivalently large, equally enigmatic, basinward-dipping, supra-salt rollover that contains a post-Albian sedimentary succession that is up to 9 km thick. Owing to its unique geometry, size and counter-regional aspect, the origin and evolution of the Albian Gap has been the centre of debate for >25 years. This debate revolves around two competing models; that is, did it form as a result of thin-skinned (i.e. supra-salt) extension, or progradational loading and salt expulsion? The extension-driven model states that the Albian Gap (and overlying rollover) formed as a result of post-Albian gravity-driven extension accommodated by slip on a large, counter-regional, listric normal fault (the Cabo Frio Fault). Conversely, the expulsion-driven hypothesis states that the Albian Gap was established earlier, during the Albian, and that post-Albian deformation was controlled by differential loading, vertical subsidence and basinward salt expulsion in the absence of significant lateral extension. This study utilizes a large (c. 76 000 km2), dense (4–8 km line spacing), depth-migrated, 2D seismic dataset that fully covers and thus permits, for the first time, a detailed, quasi-3D structural analysis of the entire Albian Gap. In this study we focus on (1) the evolution of base-salt relief and the original salt thickness variations and (2) the geometry of the post-Albian rollover, and its related faults and salt structures. To constrain the kinematics of the Albian Gap, and how this relates to the evolution of the base-salt relief, we also apply novel structural restoration workflows that incorporate flexural isostasy, in addition to a detailed, sequential reconstruction of the intra-gap rollover sequences. Our results show that the geometry and kinematics of the Albian Gap vary along-strike, and that both post-Albian extension and expulsion play a significant role in its evolution. Basinward-dipping growth wedges, salt rollers and listric normal faults record extension, whereas sigmoidal wedges, halokinetic sequences and upturned near-diapir flaps, the latter two associated with large diapirs bounding the downdip edge of the gap, record basinward salt expulsion and inflation. Where the Albian Gap is relatively wide (>50 km), these processes alternate and operate at approximately equal proportions. Our results are consistent with the amount of basinward translation inferred from the analysis of ramp–syncline basins located downdip on the São Paulo Plateau. Our results seemingly reconcile one of the longest-running debates in salt tectonics, as well as having more general implications for understanding the regional kinematics and dynamics of salt-related structures in other salt basins, in particular the controls on the development of large, counter-regional faults.Supplementary material: Uninterpreted versions of the seismic sections are available at https://doi.org/10.6084/m9.figshare.c.5023088

The enigma of the Albian Gap: spatial variability and the competition between salt expulsion and extension

<p>The Albian Gap is an enigmatic salt-related feature in the Santos Basin, offshore Brazil. It is a uniquely large, up to 65 km wide and >450 km long structure, located in the updip portion of the basin and trending NE (i.e. sub-parallel to the coast). The gap is characterized by the near-complete absence of Albian strata above depleted Aptian salt. Its most remarkable feature is an equivalently large, post-Albian seaward-dipping rollover that is up to 9 km thick. Due to its unique geometry, size, and counter-regional aspect, the Albian Gap has been the centre of debate for >25 years. This debate revolves around two competing models for its origin and evolution; i.e. did it form due to thin-skinned extension, or progradation loading and expulsion? The extension-driven model invokes that the rollover and the Albian Gap formed due to post-Albian gravity-driven extension associated with a large, counter-regional, listric normal fault, the Cabo Frio Fault. Conversely, the expulsion-driven hypothesis suggests that the Albian Gap was established earlier, during the Albian, and that post-Albian deformation was controlled by differential loading, vertical subsidence, and basinward salt expulsion without significant lateral extension. This study utilizes a large (c. 76,000 km<sup>2</sup>) and dense depth-migrated, 2D seismic dataset that covers and which thus permit a detailed, 3D structural analysis of the entire Albian Gap, focusing on i) base-salt relief and original salt thickness variations and ii) the geometry of the post-Albian rollover, and its related faults and salt structures. We also apply novel structural restoration workflows incorporating flexural isostasy, along with a detailed sequential reconstruction of the rollover sequences, to constrain the kinematics of the Albian Gap, and how this relates to base-salt relief. Our results show that the geometry and kinematics of the Albian Gap vary along-strike and that both post-Albian extension and expulsion play a significant role on its evolution. Seaward-dipping growth wedges, salt rollers and normal listric faults evidence extension, whereas sigmoidal wedges, halokinetic sequences, and upturned near-diapir flaps, the latter two associated with inflated diapirs bounding the downdip edge of the gap, indicate basinward salt expulsion and inflation. Where the Albian gap is relatively wide (>50 km), these processes alternate and operate at approximately equal proportions. Our results are consistent with the observed amount of basinward translation further downdip within ramp basins in the Sao Paulo Plateau and seemingly reconciles one of the longest-running debates in salt tectonics. Our results have implications for understanding the regional kinematics and dynamics of salt-related structures in other salt basins, in particular, the controls on the development of large, salt-detached, counter-regional faults.</p>

Surface deformation of Asama volcano, Japan, detected by time series InSAR combining persistent and distributed scatterers, 2014‒2018

Asama volcano is one of the most active volcanoes in Japan. Spatially dense surface deformation at Asama volcano has rarely been documented because of its high topography and snow cover around the summit. This study presents the first interferometric synthetic aperture radar (InSAR) observation of ground deformation at Asama volcano with 120 Sentinel-1 SAR images from both ascending and descending tracks and 20 descending ALOS-2 images acquired between 2014 and 2018. We exploited both persistent and distributed scatterers to overcome decorrelation of SAR signals and applied a three-dimensional unwrapping method to retrieve the displacement time series efficiently. Our observations reveal an asymmetric deformation around the volcano with two main deformation regions on the northeast and southeast flanks, respectively. The northeast flank (NEF) exhibits line-of-sight (LOS) extensions in all the three SAR datasets with maximum velocities of − 14, − 10, and − 12 mm/year for the descending ALOS-2, ascending, and descending Sentinel-1 measurements, respectively. The southeast flank (SEF) shows LOS extensions in the ascending observations and LOS shortening in the descending observations with velocities between − 12 and 9 mm/year. Decomposition of the LOS displacements reveals nearly pure subsidence at the NEF, while the SEF exhibits a substantial eastward component as well as subsidence. Comparisons of the vertical subsidence at two continuous GNSS stations near the summit crater with our InSAR observations indicate small discrepancies smaller than 4 mm/year. We interpreted that the subsidence at the NEF of Asama is primarily due to the hydrothermal activity, while the deformation at SEF is plausibly due to flank instability. We highlight that efforts should be taken to monitor the slope instability at Asama volcano in the future.

Identifying the Design Alternatives and Flow Interference of Tuna Purse Seine by the Numerical Modelling Approach

Dynamic responses of tuna purse seine to currents were numerically studied with regard to the vertical subsidence and global load distribution, and determinant attributes were identified. We rebuilt the submerged geometry of a purse seine net using the lumped mass method with hydrodynamic coefficients obtained from measurements of the prototype material, as well as a mesh grouping method, which corrects the twine diameter and netting material density for the equivalent net by introducing the compensation coefficient. Uneven tension distribution showed that it was vulnerable to high loads in the bunt area at shooting and along the lead line at pursing. High loads were present at the convex sections of net circles in the direction of the current. Higher shooting speeds resulted in well-balanced sinking, while a reduced hanging ratio of netting panels was beneficial to faster sinking. While large mesh sizes reduce water resistance and increase sinking velocity, extensive use should be cautioned in terms of the sensibility to stress. Comparing two options of different proportions of large-mesh panels, mesh sizes doubled for 15 strips versus 5 strips, suggesting that the 15 strip option would pose a higher risk of strand vulnerability, while the 5 strip option may be a more balanced alternative with a lower mesh density and a lower mesh stress.

Strata Movement and Fracture Propagation Characteristics due to Sequential Extraction of Multiseam Longwall Panels

Multiseam longwall mining-induced strata deformation and fracture propagation patterns are different from those of single-seam mining. This difference is due to interaction of the caved zones as a result of longwall mining activity at different coal seams, which severely impacts formation of subsidence and permeability of the strata after multiseam mining. Understanding this phenomenon is of great importance in order to predict the multiseam subsidence reliably, evaluate the risk of water inrush and take suitable preventive measures, and determine suitable locations for placing gas drainage boreholes. In this study, scaled physical modelling techniques are utilised to investigate strata deformation, fracture propagation characteristics, and vertical subsidence above multiseam longwall panels. The results show that magnitude of the incremental multiseam subsidence increases significantly after multiseam extraction in comparison with single-seam mining. This increase occurs to different extent depending on the multiseam mining configuration. In addition, interstrata fractures above the abutment areas of the overlapping panels propagate further towards the ground surface in multiseam extractions compared with single-seam extractions. These fractures increase the risk of water inrush in presence of underground/surface water and create highly permeable areas suitable for placing gas drainage boreholes.

Cratonic basins and the Wilson cycle: a perspective from the Parnaíba Basin, Brazil

Cratonic basins appear to occupy a specific place in the Wilson cycle, initiating after continental collision and supercontinent development, but before rifting and continental break-up. They do not result directly from the horizontal plate motions characteristic of the Wilson cycle, but from localized, long-lived subsidence. Covering c. 10% of the Earth's continental crust, most of the preserved cratonic basins developed in the Early Paleozoic after the formation of Gondwana and Laurentia. Recent investigation of the Parnaíba cratonic basin of Brazil has shown that this basin, and potentially cratonic basins in general, are characterized by six features: (1) formation on thickened lithosphere (>150 km); (2) a pronounced basal unconformity; (3) a sub-circular outline and large area of 0.5 × 105 to 2 × 106 km2; (4) long-lived (100–300 myr) quasi-exponential tectonic subsidence of shallow marine and terrestrial sediments; (5) no major extensional strain features, such as rifts, crustal or lithospheric thinning or Moho elevation; and (6) dense, high velocity and conductive lower crust and upper mantle. These characteristics indicate basin initiation and development by purely vertical subsidence of the lithosphere, either thermally or mechanically driven. Thermal subsidence may be related to orogenic thickening, radiogenic heating and erosion associated with supercontinent assembly, whereas mechanical subsidence may be a result of the emplacement in the lower crust or upper mantle of a dense igneous body related to plume activity during the lifetime of a supercontinent.