During the past three decades, thousands of sinkholes were formed along the Dead Sea (DS) shorelines in Israel and Jordan, due to dissolution of subsurface salt by undersaturated groundwater. The sinkholes are associated with gradual subsidence preceding their collapse by periods ranging from a few days to almost 5 years. To determine the factors controlling this precursory subsidence, we examine tens of subsidence‐sinkhole sequences along the DS shorelines in Israel. The duration and magnitude of the precursory subsidence are determined by Interferometric Synthetic Aperture Radar (InSAR) measurements and simulated by viscoelastic damage rheology models. Longer periods of precursory subsidence are found in the cemented alluvial fans and in simulations of higher‐viscosity sediments. While surface subsidence accelerates during the precursory period, the widths of the subsiding areas remain uniform, suggesting that during this period upward propagation of damage from the subsurface cavity is not accompanied by upward migration of the actual cavity. Our observations and simulations are used to constrain the viscosity of the sediments along the DS and to reduce sinkhole hazards by assessing the precursory times of future sinkholes in the different sedimentary environments.
During the past three decades, the Dead Sea (DS) water level has dropped at an average rate of ~1 m/year, resulting in the formation of thousands of sinkholes along its coastline that severely affect the economy and infrastructure of the region. The sinkholes are associated with gradual land subsidence, preceding their collapse by periods ranging from a few days to about five years. We present the results of over six years of systematic high temporal and spatial resolution interferometric synthetic aperture radar (InSAR) observations, incorporated with and refined by detailed Light Detection and Ranging (LiDAR) measurements. The combined data enable the utilization of interferometric pairs with a wide range of spatial baselines to detect minute precursory subsidence before the catastrophic collapse of the sinkholes and to map zones susceptible to future sinkhole formation. We present here four case studies that illustrate the timelines and effectiveness of our methodology as well as its limitations and complementary methodologies used for sinkhole monitoring and hazard assessment. Today, InSAR-derived subsidence maps have become fundamental for sinkhole early warning and mitigation along the DS coast in Israel and are incorporated in all sinkhole potential maps which are mandatory for the planning and licensing of new infrastructure.
The Ridgecrest earthquake pair ruptured a previously unknown orthogonal fault system in the eastern California shear zone. The stronger of the two, an Mw 7.1 earthquake that occurred on 6 July 2019, was preceded by an Mw 6.4 foreshock that occurred 34 hr earlier. In this study, distinct final slip distributions for the two earthquakes are obtained via joint inversion of Interferometric Synthetic Aperture Radar (InSAR), optical imagery, and Global Positioning System (GPS) measurements. Special attention is paid to the merging of dense (e.g., InSAR and optical imagery) and sparse geodetic (e.g., GPS) datasets. In addition, a new approach is introduced for data and model discretization through intermittent model- and data-space reconditioning that stabilizes the inversion, thus ensuring that small changes in the data space do not cause disproportionate large changes to the model space. Although the coseismic slip of the Mw 6.4 earthquake was complex, involving three distinct asperities distributed among an intersecting orthogonal set of faults, the coseismic slip of the Mw 7.1 earthquake was limited to the main northwest-striking fault. In addition to the Mw 7.1 earthquake, that northwest-striking fault plane also hosted one of the Mw 6.4 asperities. Slip on this coplanar foreshock asperity increased the shear stress at the future site of the Mw 7.1 hypocenter, and triggered a vigorous aftershock activity on the main northwest fault that culminated in its rupture. This, in turn, reactivated the coplanar foreshock asperity. In addition to failing twice within 34 hr, we find that the reruptured asperity slipped about six times more during the Mw 7.1 than during the Mw 6.4 earthquake. This repeated failure is indicative of an incomplete stress drop and premature rupture arrest during the Mw 6.4 foreshock, requiring an efficient frictional strengthening and emphasizing the causal link between highly rate-dependent friction, dynamic frictional restrengthening, and partial stress drop that has been observed in numerical studies of frictional sliding.
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