Abstract

Examination of 11 adjacent, large-diameter boreholes reveals evidence for at least one, and possibly two surface ruptures on the Hollywood fault during the past ∼22,000 years. Bulk-soil radiocarbon ages recovered from a faulted, buried soil at 7-8 m depth, and overlying unfaulted alluvial units indicate that the most recent surface rupture occurred during early to mid-Holocene time, between ∼6,000 and 11,000 years ago, with a preferred time span of ∼7,000 to ∼9,500 years ago. Less well-constrained evidence for at least one separate, inferred fault splay that may cut an older buried soil, but not the youngest faulted soil, implies the occurrence of at least one earlier surface rupture between ∼10,000 and ∼22,000 years ago. These data suggest a very long recurrence interval for the fault and confirm that the Hollywood fault is active and capable of producing damaging earthquakes large enough to cause surface rupture beneath the northern edge of the densely urbanized Los Angeles basin. Comparison with published paleoseismologic data from the Santa Monica fault, along strike to the west, suggests that these faults, although they are part of the same oblique reverse-left-lateral fault system, probably did not rupture together during the most recent Hollywood fault surface rupture.

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