USING THE STRABOSPOT2 FIELD DATA APP AND DATABASE SYSTEM, A TEST CASE PROJECT: DETAILED GEOLOGIC MAPPING TO DETERMINE THE TOTAL SLIP OF SEISMOGENIC FAULTS IN THE 2019 RIDGECREST (CALIFORNIA, USA) EARTHQUAKES

The NSF-funded StraboSpot2 app (SS2)—free for iOS and Android devices—is a powerful field tool for all-digital, georeferenced geologic mapping. The app is supported by a web-based interface and archival storage. To highlight and test the abilities of this app and database, a field geologic map project covering 650 km² was undertaken in an area of limited previous study. This project required detailed field mapping of bedrock features combined with mapping of subtle, low-relief Plio-Pleistocene features from aerial photos and LiDAR data. The mapper has 20+ years of digital field geologic mapping experience using a field laptop running GIS and was involved in the design and testing of the app and database. The SS2 app is an ideal tool for this study with its compass functionality, stereonets, notes, photos, and georeferenced point, line, and polygons at all scales.

The field area is the Spangler Hills of eastern California, where the 2019 M7.1 and M6.4 Ridgecrest earthquakes resulted in slip on previously unrecognized faults. This is in the active dextral oblique Walker Lane belt and is adjacent to the sinistral slip Garlock fault. Geologic mapping was done to examine the previously unstudied rock units and structures and to constrain the total slip on seismogenic faults.

The main NNW-striking fault scarp of the southern end of the 2019 fault scarps is found to have ~200 m of right-lateral offset based on offset of bedrock features and Pleistocene shorelines. Other right-lateral faults with 2019 slip occur farther west with up to 600 m of total slip. Older faults farther west have ~1200 m of right-lateral offset, showing that dextral faulting has migrated eastward. Another set of 2019 seismogenic faults have left-lateral offset, these were found to have offsets of 200 to 700 m and showed that the locus of activity on these faults migrated northward. The mapping data thus illustrates the complications and changing geometries in an incipient fault system.

The SS2 app and the office desktop mode performed well for this task. Best practices using the app were experimented with. The biggest problem encountered was that the iOS tablet did not work in air temperatures hotter than 37ºC. Several steps were taken to mitigate this by keeping the tablet out of the sun and using it in short bursts of time. An android cellular phone with this app was also carried, this device was not as affected by the heat.