Abstract
AbstractFault slip rates inform models of strain accumulation and release, which over geologic time may vary or remain constant depending on factors like structural complexity, fault strength, deformation rates, and proximity to other faults. In this study, we present a Late Pleistocene–Holocene slip history based on four new geologic slip rates for the Agua Blanca Fault (ABF), which transfers Pacific‐North American dextral plate boundary motion across the Peninsular Ranges of northern Baja California. Time‐averaged slip rates from three sites are 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 ~1.4 ka; however, the actual slip rate may be closer to 4 mm/a when off‐fault slip and age interpretation uncertainties are considered. Significantly, although the ABF has more in common in terms of length, net offset, and slip rate with known variable slip rate faults, the most straightforward age and offset interpretations for the ABF suggest constant slip rates over ~10 kyr time scales. As with other constant slip rate faults, comparable neighboring faults that might modulate the ABF slip rate are absent, suggesting that fault interaction, or lack thereof, may be a more significant factor controlling fault behavior on this and potentially other faults. The new rates indicate that the ABF accommodates at least half of total slip across the Peninsular Ranges, clarifying strain partitioning for seismic forecasting models that previously lacked modern geologic slip rate constraints for this domain of the plate boundary.
Highlights
Earthquakes occur when locked faults surpass a critical elastic strain threshold after a period of loading by tectonic plate motion
We present a Late Pleistocene–Holocene slip history based on four new geologic slip rates for the Agua Blanca Fault (ABF), which transfers Pacific‐North American dextral plate boundary motion across the Peninsular Ranges of northern Baja California
The new rates indicate that the ABF accommodates at least half of total slip across the Peninsular Ranges, clarifying strain partitioning for seismic forecasting models that previously lacked modern geologic slip rate constraints for this domain of the plate boundary
Summary
Earthquakes occur when locked faults surpass a critical elastic strain threshold after a period of loading by tectonic plate motion. Gold et al, 2013; Kirby et al, 2006; Onderdonk et al, 2015, 2018), proximity to ephemeral surface loads (e.g., lakes, glaciers) (e.g., Hetzel & Hampel, 2005), variations in fault strength (e.g., Chery & Vernant, 2006; Dolan et al, 2007; Oskin et al, 2008), and orientation with respect to principal stress directions (e.g., Fletcher et al, 2020) Varying these parameters is likely to result in a wide range of fault behaviors, so a practical goal is to determine whether different categories of faults that share several common characteristics are more or less likely to exhibit constant or variable slip over geologic time scales. We evaluate the strengths and limitations of the new slip rates, compare the new rates to previous estimates, reassess regional strain partitioning and slip transfer across the Peninsular Ranges, and discuss factors that may control slip variability in strike slip faults, and the evidence for and against long‐term slip rate variations on the ABF
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