Poster #216, Ground Motions

Displaced rocks as an indicator of ground motion during the 4 July 2019 M6.4 Ridgecrest earthquake

Malinda G. Zuckerman, Colin B. Amos, Christopher M. Madugo, Austin J. Elliott, Albert R. Kottke, Christine A. Goulet, Xiaofeng Meng, & Jacqueline Caplan-Auerbach
Poster Image: 

Poster Presentation

2020 SCEC Annual Meeting, Poster #216, SCEC Contribution #10624
Fragile geologic features, including rocks or rock formations displaced or toppled during earthquakes, provide insight into spatial extent and intensity of strong ground shaking. This study focuses on individual pebble and cobble sized clasts displaced and disturbed during the July 4, 2019 M6.4 Ridgecrest, California earthquake. The goal of this study is to use these data as a primary input for models of near-fault strong ground motion. In the fall of 2019, we collected measurements of displaced rocks at 170 sites in orthogonal transects along the southern 8 km portion of rupture. Displaced rocks were identified primarily based on the presence of empty soil sockets on the nearby ground surfa...ce. We developed a rubric and GIS routine to measure, locate, and describe displaced rock measurements in the field. At each measurement site, we recorded clast dimensions, displacement type, magnitude and azimuth, substrate type, slope gradient and aspect, and location relative to the surface rupture trace. Preliminary results suggest that the prevalence of displaced rocks strongly depends on substrate type, rock size and density, fault complexity, local topography, and proximity to the rupture. These results suggest ground motion clearly attenuates on a meter scale moving away from the fault.