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Withdrawn: Multi-phase History of Strands of the San Andreas Fault Through the San Gorgonio Pass Region, Southern California

The San Gorgonio Pass region (SGPr) is a locus of extensive deformation within a multi-strand section of the San Andreas Fault Zone (SAF). We define and evaluate two fault-bounded blocks in the SGPr that are characterized by extensive crystalline bedrock outcrops with similar bedrock lithologies and separated by the San Bernardino strand (SBS) of the SAF. Morphometric variables (local relief, slope, slope distribution and surface roughness) demonstrate distinctions between the bedrock upland regions of the two blocks. Quaternary units differ between the two blocks, reflecting the different surficial processes active in each block. The morphology highlights a lineament within the eastern block that we informally name the Lion Canyon lineament (LCL). The LCL more clearly differentiates the two regions, as compared to the mapped SBS, and may represent a previously active strand or bounding structure in this section. The distinctions in morphology and surficial processes lead to our interpretation that the two blocks have experienced different uplift histories. This further leads us to conclude that the SBS, broadly defined, was at some point in the past contiguous with the Banning strand to the south, allowing for through-going rupture along the fault system. This connectivity may have occurred along the Burro Flats section of the SBS or the LCL, though the fault connection along the mapped trace of the SBS is not currently evident at the surface, suggesting that the integration has been disrupted. We propose this is due to intervals of N-S compression in the region, manifest as slip along other local faults. We present evidence for lateral displacement along the SBS and Banning strand and propose a sequence of fault activity, including multiple phases of activity along the SBS and Banning strand pathway, to account for the structural complexity and lack of surficial fault continuity. This fault history leads to a better understanding of potential earthquake ruptures.

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Presentation Time: Pacific

Presenting Author: Katherine Kendrick

Student Presenter: No

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