Fault slip distribution along the southern 15 km of the M7.1 Ridgecrest earthquake surface rupture

Salena E. Padilla, Sinan O. Akciz, Alexandra E. Hatem, James F. Dolan, & Ridgecrest Rupture Mapping Group

Submitted August 15, 2019, SCEC Contribution #9817, 2019 SCEC Annual Meeting Poster #219

A pair of large earthquakes struck the Searles Valley, California area on July 4 and 5, 2019. The July 5, M7.1 earthquake northeast of Ridgecrest, CA, ruptured bilaterally along an ~50 km long, right-lateral, fault zone striking NW-SE. We followed the main rupture trace from Highway 178 southeastwards, making field observations of fault orientations, slip of sense, fault zone width, surface deformation patterns, and displacement measurements where piercing lines were available. Here is a summary of our field observations: (1) Maximum horizontal separation measured immediately south of Highway 178 along the main trace is 105±5 cm. Vertical separations here along W-side-down scarps reach ~40 cm; (2) Slip along this main strand rapidly decreases to <2cm within one km south of Highway 178 and to the south is expressed mainly as discontinuous fractures; (3) At this one-km mark, rupture steps left across a 500-m-wide zone, before consolidating farther south along a dominantly left-stepping zone of en-echelon faults and fault splays, with a typical total fault-zone width of ~ 20-50 m; (4) South of the one-km left step area, surface fracturing with measurable offsets occurred along three sub-parallel faults. Maximum horizontal separation measured along the eastern strand is 115±5 cm. Vertical separations along W-side-down scarps along this strand reach nearly 50 cm; (5) A local minimum in horizontal slip along this eastern strand 9-10 km south of Highway 178 is picked up by right-lateral slip along the central strand, which in this reach has maximum horizontal displacements reaching 30 cm; (6) Slip along the eastern strand extended to within 500 m of the southern end of the rupture trace, which is characterized by a >650-m-wide zone of complicated cross-fracturing that extended to within 5 km of the Garlock fault to the south.

Padilla, S. E., Akciz, S. O., Hatem, A. E., Dolan, J. F., & Mapping Group, R. (2019, 08). Fault slip distribution along the southern 15 km of the M7.1 Ridgecrest earthquake surface rupture. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Ridgecrest Earthquakes