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Abstract The shallow portion of a megathrust represents the zone of first contact between two colliding plates, and its rheological properties control the seismic and tsunami hazards generated by the fault. The high cost of underwater geodetic data collection results in sparse observations, leading to limited constraints on the interseismic behavior of megathrusts. The Rakhine‐Bangladesh megathrust offers a unique opportunity to probe the behavior of the shallow megathrust as it is the only ocean‐continent subduction zone where the near‐trench region is fully accessible on land. Here, we use observations from ALOS‐2 wide‐swath imagery spanning 2015 to 2022 to conduct an InSAR timeseries analysis of the overriding plate within Bangladesh and the Indo‐Myanmar Ranges. We identify a narrow pattern of alternating uplift and subsidence associated with mapped anticlines but show that it cannot be explained by slip on the megathrust or other fault structures. Instead, we argue that the deformation is likely caused by active aseismic folding within the wedge above a shallow decollement. We show that estimates of the decollement depth derived from a viscous folding model and the observed anticline spacing are in agreement with previous seismic observations of the decollement depth across the fold belt. We suggest that the role of ductile deformation in the overriding plate in subduction zones may be more important than previously recognized. 

ABSTRACT The Mw 7.5 earthquake that struck central Papua New Guinea in 2018 was the largest event ever recorded in the region with modern seismic instruments. The ground motions associated with this event also triggered widespread landslides and affected more than 500,000 people. However, due to the absence of a local seismic and Global Positioning System network in the vicinity, the fault location, system, and slip distribution of this earthquake are not well documented. In this study, we use the subpixel offset method on the Copernicus Sentinel-1 Synthetic Aperture Radar (SAR) images to calculate the 3D coseismic displacement of the 2018 Papua New Guinea earthquake. The results show clear fault traces that suggest coseismic slip on the Mubi fault and the Mananda fault that triggered landslides that spread out in a more than 260  km2 region. Finite-source inversions based on the subpixel offset measurements show up to 4.1 and 6.5 m coseismic slip on the Mubi and Mananda faults, respectively. Despite higher data uncertainty (∼0.4–0.8  m) of the subpixel offset data, synthetic resolution tests show resolvable slip above 8 km in depth. The lack of shallower slip on the west side of the Mananda fault could be due to an inflated geothermal gradient near the dormant volcano, Mount Sisa, as a slip barrier. The result of the coulomb stress change suggests possible southeastward slip propagation from the Mananda fault to the Mubi fault. Our work successfully resolves 3D coseismic displacement in highly vegetated terrains and demonstrates the feasibility of using the subpixel offset on SAR images to help our understanding of regional active tectonic systems. 

Abstract Factors driving freshwater salinization syndrome (FSS) influence the severity of impacts and chances for recovery. We hypothesize that spread of FSS across ecosystems is a function of interactions among five state factors:human activities,geology,flowpaths,climate, andtime. (1)Human activitiesdrive pulsed or chronic inputs of salt ions and mobilization of chemical contaminants. (2)Geologydrives rates of erosion, weathering, ion exchange, and acidification‐alkalinization. (3)Flowpathsdrive salinization and contaminant mobilization along hydrologic cycles. (4)Climatedrives rising water temperatures, salt stress, and evaporative concentration of ions and saltwater intrusion. (5)Timeinfluences consequences, thresholds, and potentials for ecosystem recovery. We hypothesize that state factors advance FSS in distinct stages, which eventually contribute to failures in systems‐level functions (supporting drinking water, crops, biodiversity, infrastructure, etc.). We present future research directions for protecting freshwaters at risk based on five state factors and stages from diagnosis to prognosis to cure.