Detailed fracture map and orthophoto of the southern portion of the M7.1 2019 Ridgecrest Earthquake

Ian Pierce, Alana M. Williams, Rich D. Koehler, Sinan O. Akciz, Colin Chupik, & Jayne M. Bormann

Published August 14, 2019, SCEC Contribution #9587, 2019 SCEC Annual Meeting Poster #218

An M7.1 earthquake struck on July 5, 2019, near Ridgecrest, California, and ruptured bilaterally. An M6.4 event preceded this earthquake on July 4. Between July 5 and July 9, more than 20,000 low altitude aerial photos were acquired along ~12 km of the M7.1 and ~8 km of the M6.4 Ridgecrest earthquake sequence surface ruptures south of CA 178. Structure-from-motion (SfM) was used to produce georeferenced orthophoto mosaics (~2-20 cm/pixel) along the M7.1 rupture. This basemap was used to map the details of the surface trace at scales ranging from 1:40 to 1:150 (depending on the resolution of the orthophoto) and plot the locations of the lateral offset measurement locations. The maximum observed right-lateral displacement on this section of the rupture was 115 cm. The overall surface rupture pattern consists of a prominent mole track with a maximum vertical height of ~20 cm, and left-stepping en-echelon faults with steps ranging from a few to hundreds of meters. The rupture width varies from <10 m to >100 m. Locally, the fault exhibits both compressional and extensional features such as grabens, vertical scarps, and thrusts. The fracture patterns are highly variable with several conjugate faults and structural complexities such as horsetail splays, releasing bends, and restraining bends. The pattern of faulting at the southern rupture termination forms a complex series of conjugate faults and stepovers. Evidence such as preexisting vertical scarps and laterally offset drainages suggest that this section of the M7.1 rupture did not occur along a new fault, but rather along an unnamed fault that ruptured in the Holocene or Late Pleistocene.

Key Words
Ridgecrest, surface rupture, sfm, fault mapping

Citation
Pierce, I., Williams, A. M., Koehler, R. D., Akciz, S. O., Chupik, C., & Bormann, J. M. (2019, 08). Detailed fracture map and orthophoto of the southern portion of the M7.1 2019 Ridgecrest Earthquake . Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Ridgecrest Earthquakes