Inferring subsidence characteristics in Wuhan (China) through multitemporal InSAR and hydrogeological analysis

Wuhan (China) is facing severe consolidation subsidence of soft soil and karst collapse hazards. To quantitatively explore the extent and causes of land subsidence in Wuhan, we performed multitemporal interferometry (MTI) analysis using synthetic aperture radar (SAR) data from the TerraSAR-X satellite from 2013 to 2017 and the Sentinel-1A satellite from 2015 to 2017. MTI results reveal four major subsidence zones in Wuhan, namely, Hankou (exceeding −6 cm/yr), Xudong-Qingshan (−3 cm/yr), Baishazhou-Jiangdi (−3 cm/yr), and Jianshe-Yangluo (−2 cm/yr). Accuracy assessment using 106 levelling benchmarks and cross-validation between the two InSAR-based results indicate an overall root-mean-square error (RMSE) of 2.5 and 3.1 mm/yr, respectively. Geophysical and geological analyses suggest that among the four major subsiding zones, Hankou, Xudong-Qingshan, and Jianshe-Yangluo are located in non-karstic soft soil areas, where shallow groundwater (< 30 m) declines driven by engineering dewatering and industrial water depletion contribute directly to soft soil compaction. Subsidence in the Baishazhou-Jiangdi zone develops in the karst terrain with abundant underground caves and fissures, which are major natural factors for gradual subsidence and karst collapse. Spatial variation analysis of the geological conditions indicates that the stage of karst development plays the most important role in influencing kart subsidence, followed by municipal construction, proximity to major rivers, and overlying soil structure. Moreover, land subsidence in this zone is affected more via coupling effects from multiple factors. Risk zoning analysis integrating subsidence horizontal gradient, InSAR deformation rates, and municipal construction density show that the high-risk areas in Wuhan are mainly distributed in the Tianxingzhou and Baishazhou-Jiangdi zone, and generally spread along the metro lines. © 202

Automatic Detection of Volcanic Unrest Using Blind Source Separation with a Minimum Spanning Tree Based Stability Analysis

Repeated synthetic aperture radar (SAR) acquisitions can be utilized to produce measurements of ground deformations and associated geohazards, such as it can be used to detect signs of volcanic unrest. Existing time series algorithms like permanent scatterer analysis and small baseline subset are computationally demanding and cannot be applied in near real time to detect subtle, transient, and precursory deformations. To overcome this problem, we have adapted a minimum spanning tree based spatial independent component analysis method to automatically detect sources related to volcanic unrest from a time series of differential interferograms. For a synthetic dataset, we first utilize the algorithm's capability to isolate signals of geophysical interest from atmospheric artifacts, topography, and other noise signals, before monitoring the evolution of these signals through time in order to detect the onset of a period of volcanic unrest, in near real time. In this article, we first demonstrate our approach on synthetic datasets having different signal strengths and temporal complexities. Second, we demonstrate our approach on a couple of real datasets, one acquired in 2017-2019 over the Colima volcano, Mexico, showing the occurrence of previously unrecognized short-term deformation events and the other over Mt. Thorbjorn in Iceland acquired over 2020. This shows the strength of the deep learning application to differential interferometric SAR measurements, and highlights that deformation events occurring without eruptions, which may have previously been undetected

Depth-Varying Friction on a Ramp-Flat Fault Illuminated by ∼3-Year InSAR Observations Following the 2017 Mw 7.3 Sarpol-e Zahab Earthquake

We use interferometric synthetic aperture radar observations to investigate the fault geometry and afterslip evolution within 3 years after a mainshock. The postseismic observations favor a ramp-flat structure in which the flat angle should be lower than 10°. The postseismic deformation is dominated by afterslip, while the viscoelastic response is negligible. A multisegment, stress-driven afterslip model (hereafter called the SA-2 model) with depth-varying frictional properties better explains the spatiotemporal evolution of the postseismic deformation than a two-segment, stress-driven afterslip model (hereafter called the SA-1 model). Although the SA-2 model does not improve the misfit significantly, this multisegment fault with depth-varying friction is more physically plausible given the depth-varying mechanical stratigraphy in the region. Compared to the kinematic afterslip model, the mechanical afterslip models with friction variation tend to underestimate early postseismic deformation to the west, which may indicate more complex fault friction than we expected. Both the kinematic and stress-driven models can resolve downdip afterslip, although it could be affected by data noise and model resolution. The transition depth of the sedimentary cover basement interface inferred by afterslip models is ∼12 km in the seismogenic zone, which coincides with the regional stratigraphic profile. Because the coseismic rupture propagated along a basement-involved fault while the postseismic slip may activate the frontal structures and/or shallower detachments in the sedimentary cover, the 2017 Sarpol-e Zahab earthquake may have acted as a typical event that contributed to both thick- and thin-skinned shortening of the Zagros in both seismic and aseismic ways

Elevation Change Detection for Quantification of Extensive Permafrost Thaw Subsidence in East Siberian Coastal Lowlands

Permanently frozen ground in the Arctic is being destabilized by continuing permafrost degradation, an indicator of climate change in the northern high latitudes. Accelerated coastal erosion due to sea ice reduction and an increased intensity of ground settlement through ground ice melt caused by rising summer air temperatures result in widespread geomorphological activity. The objective of our study is to analyze time series of repeat terrestrial laser scanning (rLiDAR) for quantification of extensive land surface lowering through thaw subsidence, which is the main unknown in terms of recent landscape development in the vast but neglected coastal lowlands of the East Siberian Arctic. These in-situ data provide the basis for calibration and validation of large scale surface change assessments using very high resolution space-borne elevation data with high precision. Complementing our surveys, we conducted botanical mapping. This allows us to relate elevation differences to specific surface conditions and enhances our capabilities to extrapolate our local observations to larger areas through land-cover classifications of multispectral remote sensing data such as Sentinel-2. Additionally, highly detailed digital elevation models (DEMs) with sub-metre accuracy have been photogrammetrically derived from satellite stereo data. These DEMs contain valuable terrain height information for 3D change detection, in case of DEMs representing the state of a study area at different points in time. The results show that elevation differences are almost always negative. When calculated as rates over time, land surface lowering in the ground-ice-rich Siberian coastal lowlands permafrost amounts to 3-10 cm per year

Ground displacement measurement of the 2013 M7.7 and M6.8 Balochistan Earthquake with TerraSAR-X ScanSAR data

This paper addresses the November 2013 Balochistan Earthquake. A co-seismic TerraSAR-X pair acquired in wide-swath ScanSAR mode has been used to derive two-dimensional deformation measurements (radar line-of-sight and azimuth direction) of the eastern part of the main M7.7 earthquake and the large M6.8 aftershock by correlating SAR amplitude images. Atmospheric and solid Earth tide corrections have been considered to achieve accuracy in the order of several centimeters. Correlation measurements from Landsat-8 images have been additionally estimated. The intention is to isolate vertical and horizontal components in order to obtain three-dimensional deformation measurements. Interferometric processing issues of ScanSAR data for non-stationary scenarios, specifically co-registration, are additionally discussed

Spatial and temporal patterns of land subsidence and sinkhole occurrence in the Konya endorheic basin, Turkey

The endorheic Konya Basin is a vast aggradational plain in Central Anatolia, Türkiye. It occupies a significant portion of Konya Province, covering approximately 50,000 km2. The basin is subjected to intense groundwater withdrawal and extensive agricultural activities with excessive irrigation. These activities have led to human-induced hazards, such as sinkholes and regional land subsidence. Although sinkhole occurrence mainly occurs in the Karapınar area, land subsidence is primarily observed in the central sector of Konya city, with 2 million inhabitants, as well as in various parts of the basin. This study focuses on determining the extent and rate of land subsidence throughout the basin, understanding sinkhole formation, and unraveling their relationship with anthropogenic activities. For this purpose, Interferometric Synthetic Aperture Radar (InSAR) analysis of Sentinel-1 data from 2014 to 2022 was conducted to identify and assess land subsidence. We also used the land cover data and groundwater-level information to better understand the spatial and temporal patterns of land subsidence and sinkhole occurrence. Additionally, the land cover data were used to resolve spatial–temporal variations in the cultivated area and urbanization, which are the main factors governing groundwater exploitation in the region. Our study identified widespread subsidence zones with rates as high as 90 mm/y. Groundwater overexploitation to sustain extensive agricultural operations is the main cause of the high rate of land subsidence. Additionally, it was discovered that the number of sinkholes has substantially increased due to anthropogenic influences, currently amounting to as many as 660

Land subsidence in Jakarta and Semarang Bay - The relationship between physical processes, risk perception, and household adaptation

Sea level rise (SLR) is among the most pressing challenges for urban coastal areas. While geocentric (eustatic) SLR receives widespread attention in politics and media, relative SLR at the coast, mainly caused by land subsidence, is still comparatively under-researched despite much higher rates. This paper introduces a combined natural and social science study to bring subsidence more to the forefront of coastal hazard research. We use data from radar altimetry, GNSS controlled tide gauge stations, and InSAR mapping to characterize regional and relative SLR at Jakarta and Semarang Bay, and focus-group discussions and a standardized household survey to analyze risk perceptions and adaptation. Our analysis of InSAR, radar altimetry, and corrected tide gauges clearly identifies subsidence as the major coastal threat in our study areas. The InSAR analysis for Semarang shows stable trends of subsidence up to -100 mm/a. For Jakarta, our analysis reveals more complex spatial and temporal patterns with rates around 60 mm/a; revealing significant changes to previous studies. Our analysis of radar altimetry data since 1993 shows a moderate regional SLR of 2.1 mm/a off Semarang and 3.2 mm/a off Jakarta. The InSAR data are integrated into our statistical analysis of household responses towards subsidence. We found, that in contrast to fast-onset events, constantly proceeding subsidence becomes normalized in peoples' perceptions and responses are integrated into day-to-day habits. Thus, risk perception is a far lesser determinant of responses towards subsidence than it is for fast-onset events. Hence, our results relativize former assumptions that risk perception and not actual exposure lead to action. Moreover, we found that local people are not willing to vacate highly exposed areas. Their views need to be included in municipal disaster risk reduction, the urgency of which clearly lies on mitigating subsidence effects rather than on building protection against regionally rising sea levels

Depth‐Varying Friction on a Ramp‐Flat Fault Illuminated by ∼3‐Year InSAR Observations Following the 2017 Mw 7.3 Sarpol‐e Zahab Earthquake

We use interferometric synthetic aperture radar observations to investigate the fault geometry and afterslip evolution within 3 years after a mainshock. The postseismic observations favor a ramp‐flat structure in which the flat angle should be lower than 10°. The postseismic deformation is dominated by afterslip, while the viscoelastic response is negligible. A multisegment, stress‐driven afterslip model (hereafter called the SA‐2 model) with depth‐varying frictional properties better explains the spatiotemporal evolution of the postseismic deformation than a two‐segment, stress‐driven afterslip model (hereafter called the SA‐1 model). Although the SA‐2 model does not improve the misfit significantly, this multisegment fault with depth‐varying friction is more physically plausible given the depth‐varying mechanical stratigraphy in the region. Compared to the kinematic afterslip model, the mechanical afterslip models with friction variation tend to underestimate early postseismic deformation to the west, which may indicate more complex fault friction than we expected. Both the kinematic and stress‐driven models can resolve downdip afterslip, although it could be affected by data noise and model resolution. The transition depth of the sedimentary cover basement interface inferred by afterslip models is ∼12 km in the seismogenic zone, which coincides with the regional stratigraphic profile. Because the coseismic rupture propagated along a basement‐involved fault while the postseismic slip may activate the frontal structures and/or shallower detachments in the sedimentary cover, the 2017 Sarpol‐e Zahab earthquake may have acted as a typical event that contributed to both thick‐ and thin‐skinned shortening of the Zagros in both seismic and aseismic ways.Plain Language Summary: The 2017 Mw 7.3 Sarpol‐e Zahab earthquake is the largest instrumentally recorded event to have ruptured in the Zagros fold thrust belt. Although much work has been conducted for a better understanding of the relationship between crustal shortening and seismic and aseismic slip of the earthquakes in the Zagros, active debate remains. Here, we use interferometric synthetic aperture radar observations to study the fault geometry and afterslip evolution within 3 years after the 2017 Mw 7.3 Sarpol‐e Zahab earthquake. For postseismic deformation sources, afterslip and viscoelastic relaxation are considered to be possible causes of postseismic deformation. Our results show that the kinematic afterslip model can spatiotemporally explain the postseismic deformation. However, the mechanical afterslip models tend to underestimate the earlier western part of the postseismic deformation, which may indicate a more complex spatial heterogeneity of the frictional property of the fault plane. We find that there is deep afterslip downdip of coseismic slip from both the kinematic and stress‐driven afterslip models, although it could be affected by data noise and model resolution. We additionally find that the viscoelastic response is negligible. Postseismic slip on more complex geological structures may also be reactivated and triggered, combined with geodetic inversions, geological cross‐section data and local structures in the Zagros.Key Points: The Spatiotemporal evolution of postseismic observations favors a ramp‐flat structure in which the flat angle should be lower than 10°, Depth‐varying friction is required to better simulate the rate‐strengthening afterslip evolution. Downdip afterslip can be resolved by afterslip models, although it relies on data accuracy and model resolution.National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809China Scholarship Council http://dx.doi.org/10.13039/501100004543Ministry of Science and Technology in Taiwanhttps://www.asf.alaska.edu/http://irsc.ut.ac.ir/https://www.globalcmt.org/https://doi.org/10.5281/zenodo.711307