Antarctic ice shelves play a key role in regulating the rate of ice flow in tributary ice streams. Temporal variations in the associated ice-shelf buttressing stress are observed to impact ice flow in glaciers and ice streams. Ephemeral grounding induced by tides is an important mechanism for modulating the buttressing stress. Here, we develop an approach to inferring variations in 3-D surface displacements at an ice-shelf-stream system that explicitly accounts for ephemeral grounding. Using a temporally dense nine-month-long synthetic-aperture radar image acquisition campaign collected over Rutford Ice Stream, West Antarctica, by the 4-satellite COSMO-SkyMed constellation, we infer the ephemeral grounding zones and the spatiotemporal variation of the fortnightly ice-flow variability. We find ephemeral grounding zones along the western ice-shelf margin as well as a few prominent ephemeral grounding points in the central trunk and in the vicinity of the grounding zone. Our observations provide evidence for tide-modulated buttressing stress and the temporally asymmetric response of ice-shelf flow to tidal forcing. Long-term oceanic warming and ice-shelf thinning will cause the loss of ephemeral grounding and decrease in ice-shelf buttressing stress.

The 4 July 2019 Mw 6.4 Earthquake and 5 July Mw 7.1 Earthquake struck near Ridgecrest, California. Caltech-Jet Propulsion Laboratory Advanced Rapid Imaging and Analysis (ARIA) project automatically processed synthetic aperture radar (SAR) images from Copernicus Sentinel-1A and -1B satellites operated by the European Space Agency, and products were delivered to the US and California Geological Surveys to aid field response. We integrate geodetic measurements for the three-dimensional vector field of coseismic surface deformation for thee two events and measure the early postseismic deformation, using SAR data from Sentinel-1 satellites and the Advanced Land Observation Satellite-2 (ALOS-2) satellite operated by Japanese Aerospace Exploration Agency. We combine less precise large-scale displacements from SAR images by pixel offset tracking or matching, including the along-track component, with the more precise SAR interferometry (InSAR) measurements in the radar line-of-sight direction and intermediate-precision along-track InSAR to estimate all three components of the surface displacement for the two events together. InSAR coherence and coherence change maps the surface disruptions due to fault ruptures reaching the surface. Large slip in the Mw 6.4 earthquake was on a NE-striking fault that intersects with the NW-striking fault that was the main rupture in the Mw 7.1 earthquake. The main fault bifurcates towards the southeast ending 3 km from the Garlock Fault. The Garlock fault had triggered slip of about 15 mm along a short section directly south of the main rupture. About 3 km NW of the Mw 7.1 epicenter, the surface fault separates into two strands that form a pull-apart with about 1 meter of down-drop. Further NW is a wide zone of complex deformation. We image postseismic deformation with InSAR data and point measurements from new GPS stations installed by the USGS. Initial analysis of the first InSAR measurements indicates the pull-apart started rebounding in the first weeks and the main fault had substantial afterslip close to the epicenter where the largest coseismic slip occurred. Slip on a NE-striking fault near the northern end of the main rupture in the first weeks, in the same zone as large and numerous aftershocks along NE-striking and NW-striking trends shows complex deformation.