A document by Jiahui Wang. Click on the document to view its contents.

Slow-moving landslides are hydrologically driven. Yet, landslide sensitivity to precipitation, and in particular, precipitation extremes, is difficult to constrain because landslides occur under diverse hydroclimatological conditions. Here we use standardized open-access satellite radar interferometry data to quantify the sensitivity of 38 landslides to both a record drought and extreme rainfall that occurred in California between 2015 and 2020. These landslides are hosted in similar rock types, but span more than ~2 m/yr in mean annual rainfall. Despite the large differences in hydroclimate, we found these landslides exhibited surprisingly similar behaviors and hydrologic sensitivity, which was characterized by faster (slower) than average velocities during wetter (drier) than average years, once the impact of the drought diminished. Our findings may be representative of future landslide behaviors in California where precipitation extremes are predicted to become more frequent with climate change.

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.

Located at the meeting point between the Red Sea Ridge, the East African Rift and the Aden Ridge, the Afar Depression is characterized by contrasting modes of deformation with focused extension across recently activated magmatic segments and broadly distributed faults. InSAR data spanning over two decades reveal stable and evolving patterns in the deformation field of Central Afar, including (1) a 120 km-wide belt of horizontal extension, extending from west to east between the Manda-Hararo and Asal-Ghoubbet rifts and accommodating ~12 mm/yr of the Arabia-Somalia plate motion, (2) broad zones of subsidence aligned with the axial volcanic ridges marking the major diverging segments propagating into Afar, (3) accelerated opening and uplift across the Manda-Hararo Rift subsequent to the 2005-2010 diking sequence, and (4) a series of four micro-faulting events, which occurred between 2001 and 2005 on an alignment of north-northeast trending rifts between the Afdera and Gad Elu volcanoes. These observations suggest that different modes of deformation take place in the shallow and deeper parts of the crust, which are mechanically decoupled. Major magmatic segments steadily opening into the deep part of the crust between diking episodes, produce focused extension and plate thinning at intermediate depth, resulting in localized subsidence along axial ridges. The horizontal diverging movement across the segments is transformed by creep in a detachment fault at the base of the brittle crust, which deforms by distributed faulting. Episodic emplacements of dikes above deep-seated diverging segments compensate for inter-diking subsidence, also accommodating extension in the shallow crust.