RECENTLY MAPPED FAULTING IN THE SAN BERNARDINO MOUNTAINS, CALIFORNIA

Miles H. Wagner, & Frank F. Jordan Jr.

Published September 10, 2023, SCEC Contribution #13245, 2023 SCEC Annual Meeting Poster #086 (PDF)

Fault mapping through the San Bernardino Mountains (SBM) has been conducted as part of a Masters thesis in progress as CSUSB. Mapping of primarily high-angle strike-slip faults using review of mosaicked aerial imagery available on the Google Earth Pro (GE) platform identified numerous faults not recognized on geologic maps of the SBM and several digital fault databases issued by USGS, CGS, and San Bernardino County. The faults were identified on several years of aerial imagery draped over the digital elevation model employed by GE. The geomorphic features indicative of faulting were enhanced using the 3-dimensional, vertical exaggeration tool available on GE, combined with the GE rotation and tilt features. The faults identified were mapped directly onto GE imagery using the path mapping tool. In general, the faults identified for the thesis were not included in the digital fault databases reviewed for this mapping effort. The faults identified in the SBM provide potential pathways for transferring right-lateral, strike-slip plate motion from the Salton Trough spreading center through the SBM to the Eastern California Shear Zone (ECSZ). Although fault databases previously issued by the USGS and CGS categorized their faults by age, no attempt was made via the thesis mapping to age date the newly mapped faults. Faults previously mapped by the USGS are color coded with respect to Historic, Holocene, and Pleistocene latest ground surface offsets. Faults with evidence of Historic or Holocene-age latest ground surface offset are included within Alquist-Priolo Earthquake Fault Zones by CGS. The California Building Code (CBC) modified the definition of active faulting in CA to include faults that generate earthquakes or have the potential to generate earthquakes. Earthquake epicenters included in the Caltech database were added to the map of faults found in the SBM. Epicenters correlate well with strike-slip faulting associated with the 1992 Landers and Big Bear earthquakes. Other earthquake epicenters appear to have the potential to be associated with the faults mapped for the thesis. Considering the pivotal location of faulting identified in the SBM between the Salton Trough and the ECSZ, and the revised definition of active faulting found in the CBC, faults identified in the SBM are considered to represent active faults. San Bernardino County may include these faults in Fault Hazard Zones in a revision of the County’s Hazard Mitigation Plan.

Key Words
faulting, San Bernardino Mountains, California Building Code, eastern California Shear Zone, earthquake database, fault databases

Citation
Wagner, M. H., & Jordan Jr., F. F. (2023, 09). RECENTLY MAPPED FAULTING IN THE SAN BERNARDINO MOUNTAINS, CALIFORNIA. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology