Late Cenozoic Displacement Along the San Clemente Fault, Offshore Southern California

M. R. Legg¹, C. Goldfinger², J. D. Chaytor³, and V. Wong-Ortega^4
1Legg Geophysical, Inc., Huntington Beach, CA, [email protected]
²Oregon State University, Corvallis, OR, [email protected]
³Woods Hole Oceanographic Inst., Woods Hole, MA, [email protected]
⁴CICESE, Ensenada, Baja California, MX, [email protected]

Combination of high-resolution bathymetry, seismic reflection, and sub-bottom profiles allows identification of piercing points offset by late Cenozoic strike-slip along the San Clemente fault offshore southern California. Along the San Clemente Island escarpment, slope gullies show dextral offsets exceeding 140 m. The seafloor morphology resembles the Carrizo Plain along the San Andreas fault, and the most distinct gullies may be active since the 18-ka glacial lowstand. Offshore northern Baja California, high-stand submarine fans are disrupted and offset up to 4.6 km by right-slip on the San Isidro fault. Age estimates of the Banda fan, based upon regional sedimentation rates from radiocarbon-dated piston cores, suggest late Quaternary offset younger than about 700 ka. A large restraining bend linking the San Clemente and San Isidro faults produced seafloor uplift of 420 m and structural relief of 750 m. Acoustically transparent hemipelagic drape that records the bulk of this uplift is estimated at 200 ka to 530 ka. Local pull-apart basins and a fault-sliver pop-up along the principal displacement zone in this restraining bend show maximum offsets of 3.0 km to 6.4 km during the period of bend uplift. Folding and faulting induced by basement block uplift in the bend may be offset by 14 km to 18 km. The western rim of a large sub-circular crater with central uplift at Emery Knoll is offset about 60 km since the middle Miocene when widespread volcanism occurred throughout the Inner Borderland Rift and adjacent region. Basalt flows within the Rosarito Beach Formation, derived from offshore sources along the northern Baja California coast, show Ar-Ar ages of 15-16 Ma. The long-term slip-rate appears comparable to the late Quaternary slip-rate, but confirmation of piercing point age and character is necessary to quantify the displacement history.

AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009