Spatiotemporal deformation of existing sinkholes and the surrounding region in Wink, TX are probed using time-series interferometric synthetic aperture radar (InSAR) methods with radar images acquired from the Sentinel-1A satellite launched in April 2014. The two-dimensional deformation maps, calculated using InSAR observations from ascending and descending tracks, reveal that much of the observed deformation is vertical. Our results indicate that the sinkholes are still influenced by ground depression, implying that the sinkholes continue to expand. Particularly, a region 1 km northeast of sinkhole #2 is sinking at a rate of up to 13 cm/year, and its aerial extent has been enlarged in the past eight years when compared with a previous survey. Furthermore, there is a high correlation between groundwater level and surficial subsidence during the summer months, representing the complicated characteristics of sinkhole deformation under the influence of successive roof failures in underlying cavities. We also modeled the sinkhole deformation in a homogenous elastic half-space with two dislocation sources, and the ground depression above cavities could be numerically analyzed. Measurements of ongoing deformation in sinkholes and assessments of the stability of the land surface at sinkhole-prone locations in near real-time, are essential for mitigating the threat posed to people and property by the materialization of sinkholes.

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Magma intrusion rate is a key parameter in eruption triggering but is poorly quantified in existing geodetic studies. Here we examine two episodes of rapid inflation in this context. Two noneruptive microseismic swarms were recorded at Semisopochnoi Volcano, Alaska in 2014-2015. We use differential SAR techniques and TerraSAR-X images to document surface deformation from 2011 to 2015, which comprises island-wide radial inflation totaling~25 cm (+/−1 cm) line of sight displacement in 2014-2015. Multiple source geometries are tested in an inversion of the deformation data, and InSAR data are best fit by a spheroid trending to the northeast and plunging to the southeast, with a major axis of~4 km and minor axes of~1 km, directly under the central caldera of Semisopochnoi. In 2014, a modeled influx of 0.043 km 3 of magma caused line of sight displacement of~17 cm. This magma was stored at a depth of~8 km, until 2015 when 0.029 km 3 was added. Along with the definition of inflation source parameters, the recorded seismic events are relocated using differential travel times. These relocated events outline a linear aseismic area within a larger zone of shallow (<10 km) seismicity. This aseismic region aligns with the centroid of the deformation model. Based on these geodetic and seismic models, the plumbing system at Semisopochnoi is interpreted as a spheroidal magma storage zone at a depth of˜8 km below a linear feature of partial melt. The observed deformation and seismicity appear to result from rapid injection into this main storage region.

No abstract

Glacial isostatic adjustment (GIA), resulting from the Pleistocene loading of the Laurentide and Cordilleran ice sheets, is frequently associated with positive vertical velocities, or uplift. In Northern and Western Alaska, thousands of kilometers from the center of these ice sheets, vertical motion is primarily negative, or subsidence. Previously, no regional Earth structure model has been estimated for these areas using GIA modeling techniques, and the contribution of GIA processes to the observed subsidence signal has not been studied. We compare the vertical motion rates from 54 campaign and continuous GPS sites in Northern and Western Alaska to the predictions of the ICE‐5G and ICE‐6G GIA models, and to a suite of models that vary with four adjustable parameters defining the lithospheric thickness, asthenospheric thickness and viscosity, and upper mantle thickness and viscosity with the ICE‐3G loading model of Tushingham and Peltier (1991, https://doi.org/10.1029/90JB01583). The best overall fit with the ICE‐3G loading model and Earth model parameters were 120‐km lithosphere over a 100‐km asthenosphere with a viscosity of 2.5 × 1019 Pa/s, overlying a 450‐km‐thick upper mantle with a viscosity of 1.5 × 1021 Pa/s. These values are for a fixed lower mantle viscosity of 3 × 1021 Pa/s in a one‐dimensional Earth model that uses a linear Maxwell rheology. The GIA estimates are found to fit the GPS observations well and can be used to more accurately interpolate between measurement sites in a region where there is sparse spatial and temporal coverage of tectonic vertical velocities.