Style, Activity, and Uplift Rate of the Hollywood Fault in Hollywood and West Hollywood, California
S. C. Lindvall1, T. K. Rockwell2, G. Kasman3, and J. G. Helms1
1William Lettis & Associates, Inc, Valencia, CA
2Department of Geological Sciences, San Diego State Univ, San Diego, CA
3Law/Crandall, Los Angeles, CA
The activity and styles of deformation on the Hollywood fault differ significantly between range-front sites in Hollywood and West Hollywood. Near the Highland/Franklin Avenue intersection in Hollywood, a transect of borings revealed ground water barriers, stratigraphic mismatches, and truncations of buried soils that we interpret as evidence for up to 4 steeply north-dipping fault strands. These features are considered active as they appear to extend upward into deposits as young as latest Holocene age. To the west, the zone of active faulting appears to step away from the crystalline range front from where the Hollywood fault was previously mapped. Extensive investigations near the intersection of Sunset and La Cienega Boulevards in West Hollywood have revealed several inactive secondary fault strands that displace a newly-discovered buried marine abrasion platform. These faults include both north-dipping, pure dip-slip structures, and more common south-southeast-dipping strands that exhibit a south-side-down normal and lateral (?) sense of slip. These structures displace the abrasion platform and associated marine sands that are estimated to be 400–900 ka, based on age assessment of the sequence of overlying soils and their associated alluvial fan deposits. Unfaulted, late Pleistocene soil horizons constrain the cessation of faulting on most strands as >100 ka. The active Hollywood fault zone is presumed to be located south of these hanging-wall structures. The alignment of bedrock outcrops along Sunset Boulevard was previously interpreted to be the location of the main Hollywood fault, but now appears to be a paleo-seacliff. Using the present elevation of the abrasion platform shoreline (~110 m), we calculate a long-term uplift rate of 0.12 to 0.28 mm/yr for the Hollywood Hills. Quinn et al (2000) document an uplift rate of 0.14 mm/yr for the footwall block in the La Brea Plain to the south based on subsurface mapping of the 320 ka Stage 9 marine terrace. This yields a differential long-term uplift rate across the Hollywood fault of 0 to 0.14 mm/yr.
AAPG Search and Discovery Article #90904©2001 AAPG Pacific Section Meeting, Universal City, California