Time-Invariant Late Quaternary Slip Rates Along the Agua Blanca Fault, northern Baja California, Mexico

Peter O. Gold

Submitted July 23, 2019, SCEC Contribution #9240

Fault slip rates are useful for testing models of strain accumulation and release, which over geologic time scales may be variable or constant depending on multiple factors such as structural complexity and proximity to other faults. In this study, we present a Late Pleistocene-Holocene geologic slip history for the Agua Blanca Fault, the most prominent of several faults that transfer ~14% of San Andreas-related Pacific-North American dextral plate motion across the Peninsular Ranges of northern Baja California. We measured time-averaged slip rates of 2.8 +0.8/-0.6 mm/a since ~65.1 ka, 3.0 +1.4/-0.8 mm/a since ~21.8 ka, 3.2 +1.0/-0.6 mm/a since ~12.5 ka, and 3.5 +5.1/-2.0 mm/a since ~1.6 ka and three sites, however, the actual slip rate may be closer to 4 mm/a when factoring in slip on secondary fault strands. Significantly, although the Agua Blanca Fault is more similar in length, net offset, and slip rate to variable slip rate faults, the most straightforward age and offset interpretations suggest constant slip over ~10 kyr time scales. This suggests that fault interaction, or lack thereof, may be the most important factor controlling whether slip rates are constant along this fault, although variations over shorter time scales cannot be ruled out without additional measurements. The new rates account for over half of the slip transferred across the Peninsular Ranges, clarifying transfer kinematics and strain partitioning at this latitude, and will be a useful contribution to updated seismic forecasting models for the southern San Andreas Fault system.

Citation
Gold, P. O. (2019). Time-Invariant Late Quaternary Slip Rates Along the Agua Blanca Fault, northern Baja California, Mexico. Tectonics, (submitted).