Mobile laser scans of vine rows deformed by the South Napa earthquake record shallow fault slip that does not breach the surface.

Deformation associated with plate convergence at subduction zones is accommodated by a complex system involving fault slip and viscoelastic flow. These processes have proven difficult to disentangle. The 2010 Mw 8.8 Maule earthquake occurred close to the Chilean coast within a dense network of continuously recording Global Positioning System stations, which provide a comprehensive history of surface strain. We use these data to assemble a detailed picture of a structurally controlled megathrust fault frictional patchwork and the three-dimensional rheological and time-dependent viscosity structure of the lower crust and upper mantle, all of which control the relative importance of afterslip and viscoelastic relaxation during postseismic deformation. These results enhance our understanding of subduction dynamics including the interplay of localized and distributed deformation during the subduction zone earthquake cycle.

Abstract:We describe a prototype compact mobile laser scanning system that may be operated from a backpack or unmanned aerial vehicle. The system is small, self-contained, relatively inexpensive, and easy to deploy. A description of system components is presented, along with the initial calibration of the multi-sensor platform. The first field tests of the system, both in backpack mode and mounted on a helium balloon for real-world applications are presented. For both field tests, the acquired kinematic LiDAR data are compared with highly accurate static terrestrial laser scanning point clouds. These initial results show that the vertical accuracy of the point cloud for the prototype system is approximately 4 cm (1σ) in balloon mode, and 3 cm (1σ) in backpack mode while horizontal accuracy was approximately 17 cm (1σ) for the balloon tests. Results from selected study areas on the Sacramento River Delta and San Andreas Fault in California demonstrate system performance, deployment agility and flexibility, and potential for operational production of high density and highly accurate point cloud data. Cost and production rate trade-offs place this system in the niche between existing airborne and tripod mounted LiDAR systems.

The Mw 6.4 and Mw 7.1 Ridgecrest earthquake sequence occurred on 4 and 5 July 2019 within the eastern California shear zone of southern California. Both events produced extensive surface faulting and ground deformation within Indian Wells Valley and Searles Valley. In the weeks following the earthquakes, more than six dozen scientists from government, academia, and the private sector carefully documented the surface faulting and ground-deformation features. As of December 2019, we have compiled a total of more than 6000 ground observations; approximately 1500 of these simply note the presence or absence of fault rupture or ground failure, but the remainder include detailed descriptions and other documentation, including tens of thousands of photographs. More than 1100 of these observations also include quantitative field measurements of displacement sense and magnitude. These field observations were supplemented by mapping of fault rupture and ground-deformation features directly in the field as well as by interpreting the location and extent of surface faulting and ground deformation from optical imagery and geodetic image products. We identified greater than 68 km of fault rupture produced by both earthquakes as well as numerous sites of ground deformation resulting from liquefaction or slope failure. These observations comprise a dataset that is fundamental to understanding the processes that controlled this earthquake sequence and for improving earthquake hazard estimates in the region. This article documents the types of data collected during postearthquake field investigations, the compilation effort, and the digital data products resulting from these efforts.

Afterslip hazard map of the Browns Valley neighborhood and surrounding area. A detailed map explanation is presented on the following page. vi Caption for map on previous page: Levels of Afterslip Hazard for the Browns Valley Neighborhood, City of Napa, California: All fault traces shown on this map face potential future earthquake fault surface rupture hazard and other earthquake-related hazards such as shaking, liquefaction, and landslides; these hazards are treated separately in other publications and maps from CGS and USGS (with preliminary updates provided in this report). For all levels of afterslip hazard, the afterslip amount that is measured 90 days after the earthquake can be expected to as much as double by 10 years after the earthquake (less than double is also possible). Red Fault Trace-High level of afterslip hazard; very likely to experience more than 15 cm of afterslip during the 3 years after the earthquake. (Red is intentionally included, even though none is indicated on this map.) Yellow Fault Trace-Moderate level of afterslip hazard; likely to experience less than 15 cm, but more than 5 cm, of afterslip during the 3 years after the earthquake. (Additional afterslip accumulation is likely to gradually accumulate an additional 5 cm during the 10 years after the earthquake and an additional 5 cm 30 years after the earthquake.) Green Fault Trace-Low level of afterslip hazard; very unlikely to experience more than 5 cm of afterslip during the 3 years after the earthquake. (Faults that experienced <10 cm of coseismic offset and <5 cm of afterslip within the 3 months after the earthquake are included in this category. Some faults or lineaments shown as green had no measurable coseismic slip or afterslip associated with the August 24, 2014, earthquake. Faults and lineaments of several categories are shown for completeness. Some are previously mapped strands (U.S. Geological Survey and California Geological Survey, 2006); others represent preliminary mapping based on a combination of imagery interpretation and field mapping that has taken place since the August 24, 2014, earthquake. All of the faults and/or imagery lineaments shown as heavy green lines on this map may be considered to have a low level of afterslip hazard. Subsequent ongoing mapping, that is, work still in progress, may reveal that certain lineaments shown here are not actually faults.) Map orientation: North direction is toward top of map.