High-Angle
Oblique-Slip Faults in the Southern Eel River Basin: Forearc Deformation at Migrating Triple Junction
Yun, Janet1, J.
Casey Moore2, N. Driscoll3, Danny O;Shea4,
Leah Hogarth3 (1) Chevron Energy Technology Company, Houston, TX (2)
UC Santa Cruz, Santa Cruz, CA (3) Scripps Institute of Oceanography, UCSD, La
Jolla, CA (4) Humboldt State University, Arcarta, CA
T
wo young, east-west
trending, south-dipping, high-angle deformation zones are observed in nearshore seismic reflection profiles north of Cape Mendocino in the southern
offshore Eel River basin. These deformation
zones exhibit possible left-lateral up-to-the-south oblique-slip and are the
youngest structures on the continental shelf. Deformation
along these high-angle faults likely initiated in the late Pleistocene, with
some deformation continuing into the present. Projected onshore, these
deformation zones appear to influence onshore topography. The high-angle
deformation represents one of at least two types of structures in the southern Eel River basin. On the continental
shelf, deformation appears to have changed from northwest-southeast trending
broad anticline/syncline pairs that were active in the mid-Pleistocene, to
east-west trending high-angle faults that appear active in the late Pleistocene
to Holocene. The south-dipping high-angle faults are in a location where
north-dipping reverse and thrust faults are mapped onshore. Known gas venting
along the trend of one of the high-angle structures suggests that slip may be
facilitated by overpressured fluids within the fault
zone. The change in deformation type and structural trend may be related to the
northward migration of the Pacific plate and the Mendocino triple junction.