Most SCEC scientists were preparing for 4th of July celebrations when the M6.4 Ridgecrest earthquake occurred. Numerous industry, academic, and agency geologists responded quickly to capture ephemeral data, following earthquake rapid response protocols developed with SCEC participation. They began to document the left-lateral ~NE-SW trending surface rupture and secondary effects. Just 34 hours later, the M7.1 earthquake occurred along a nearly orthogonal, NW-SE trending right lateral system, cutting largely through the China Lake Naval Weapons Station, and dramatically disrupting the dinner hour and response coordination meeting of responding geologists in nearby Ridgecrest, California. Due to access constraints, US Geological Survey and California Geological Survey personnel worked closely with the US Navy to document surface rupture on the base, while the academic and industry scientists focussed their effort off the base.

Earthquake geology observations, collected in July Mojave desert heat, included documentation of offsets and mapping of the complex ground ruptures, as well as fragile geologic features that constrained strong ground motions. Field observations are augmented with a variety of  remote mapping technology, including high-resolution  photogrammetry, airborne and terrestrial laser scanning, and image and topographic differencing. 

The earthquake geology results are being published in numerous peer-reviewed venues including dedicated sections of the Seismological Research Letters and Bulletin of the Seismological Society of America. The scientific response demonstrated a well coordinated effort among many geologists from numerous institutions, including many within the SCEC collaboration. SCEC also coordinated an effort to jointly support lidar data acquisition, field geology, and geodesy efforts via an NSF RAPID award.

The M6.4 rupture was about 18 km long and had mean left-lateral displacement of 0.3-0.5 m with a maximum of 0.7-1.6 m (Figure 1). The right lateral M7.1 ground ruptures were ~50 km long with mean displacement of 1.2-1.7 m and maxima of 4.3-7.0 m. The peak displacement occurred along a 12 km portion of the rupture near the epicenter. More than 650 field-based surface displacement measurements are summarized by DuRoss, et al., 2020. Airborne laser scanning (Hudnut, et al., 2020 available at OpenTopography) and photogrammetry (Pierce, et al., 2020 and Donnellan, et al., 2020) were collected immediately after the earthquakes and provide the basis for rupture mapping, offset reconstructions, and topographic differencing.

Figure 1. Ridgecrest earthquake sequence (orange lines; from DuRoss, et al., 2020) within the California fault network (other lines from USGS Qfaults database). Red lines indicate historic earthquake ruptures: notably the 1872 M7.5 Owens Valley earthquake to the NW and the 1992 M7.3 Landers and 1999 M7.1 Hector Mine earthquake. These events illustrate the activity of the Eastern California Shear Zone, which is dominated today by right-lateral strike-slip faulting. The upper right 0.25 m per pixel lidar-derived hillshade illuminated from the NE shows the ground rupture along the southern portion of the M7.1 rupture. The lower right shows SCEC scientists including Rich Koehler (UNR) and Alana WIlliams (ASU) working along the rupture (photograph by Ian Pierce; Oxford University).

	Ramon Arrowsmith is a professor in the School of Earth and Space Exploration at Arizona State University. His research focuses on the earthquake geology, paleoseismology, and geomorphology of fault zones. He is currently co-leader of the San Andreas Fault Systems group of the Science Planning Committee and co-founder and co-PI of the OpenTopography effort.
	Michael Oskin is a professor in the Earth and Planetary Sciences Department at the University of California, Davis. His research focuses on active crustal deformation and its relationships to surface processes and topography. He has been the co-leader of the Earthquake Geology working group of the Science Planning Committee since 2007.