Abstract

We examine hypocenter patterns, geomorphic features, total slip determinations, and slip-rate information to define the active elements of the southern and central portions of the right-lateral Elsinore fault zone in southern California. In addition to the Elsinore fault, the seismicity patterns define a continuous fault between about 33°N and 33.5°N, 7 to 12 km east of the Elsinore fault, that corresponds to the Aguanga, Agua Tibia, and Earthquake Valley faults. This part of the fault zone is double stranded. Total slip and current slip rate are apparently distributed between the two strands. Slip transfer between the strands occurs at the ends of the eastern strand over two steps with topographic signatures reflecting the step geometries in a right-lateral fault zone: a contractional left step occupied by Palomar mountain, and an extensional right step within the Vallecito-Fish Creek basin. We suggest that the two strands of the double-stranded portion of the fault zone have different ages, and the proportion of slip carried by each strand may have changed through time. Hypocenter patterns define several northeast-striking faults within the fault zone; we attribute a 1940 ML 5.1 earthquake to one of them.

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