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

Published August 14, 2020, SCEC Contribution #10624, 2020 SCEC Annual Meeting Poster #216 (PDF)

Poster Image: 
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 surface. 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.

Key Words
Ridgecrest, Ground Motion, Fragile Geologic Features, Displaced Rocks

Citation
Zuckerman, M. G., Amos, C. B., Madugo, C. M., Elliott, A. J., Kottke, A. R., Goulet, C. A., Meng, X., & Caplan-Auerbach, J. (2020, 08). Displaced rocks as an indicator of ground motion during the 4 July 2019 M6.4 Ridgecrest earthquake. Poster Presentation at 2020 SCEC Annual Meeting.


Related Projects & Working Groups
Ground Motions