Abstract

We estimate a renewal time for large earthquakes on the southernmost San Andreas fault (SAF) of 260 ± 100 years based on new paleoseismological data and a 34 millennia slip rate of 5–8 mm/yr. Our mean recurrence interval, 260 ± 100, is longer and its variance is smaller than the 160 + 240/–93 estimate for a M ≥7 earthquake used by the Working Group on California Earthquake Probabilities (WGCEP, 1995). A smaller creep rate than on contiguous 12-km fault segments is explained by Global Positioning System data that reveals 2–4 mm/yr of creep on the recently discovered Witbaard fault that bypasses the 12-km-long North Shore strand of the SAF. Geomorphic features near an archaeological site that cross the fault allow us to measure displacements of 155 ± 25 cm based on right-lateral gully offsets by the most recent earthquake (e.g., 1690). An Indian stone ring, straddling the fault trace, is currently offset 142 ± 12 cm. The ring lies on the 12-km-long North Shore segment of the SAF that has accumulated a minimum of 30 mm of triggered slip and aseismic creep since 1969. Contrasting slip rates of 23–35 mm/yr near Indio and 5–14 mm/yr on the southernmost SAF suggest that the Coachella Valley strand may be comprised of two distinct segments. Smaller long-term strain accumulation along the southernmost segment probably reduces earthquake potential for that area.

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