The Greenville fault: Preliminary estimates of its long-term creep rate and seismic potential

Abstract

Once assumed to be locked, we show that the northern third of the Greenville fault (GF) creeps at 2 mm=yr, based on 47 yr of trilateration net data. This northern GF creep rate equals its 11 ka slip rate, suggesting a low strain accumulation rate. In 1980, the GF, easternmost strand of the San Andreas fault system east of San Francisco Bay, produced an Mw 5.8 earthquake with a 6 km surface rupture and dextral slip growing to ≥ 2 cm on cracks over a few weeks. Trilateration shows a 10 cm post-1980 transient slip ending in 1984. Analysis of 2000-2012 crustal velocities on continuous Global Positioning System stations, allows creep rates of ~2 mm=yr on the northern GF, 0-1 mm=yr on the central GF, and ~0 mm=yr on its southern third. Modeled depth ranges of creep along the GF allow 5%-25% aseismic release. Greater locking in the southern two-thirds of the GF is consistent with paleoseismic evidence there for large late Holocene ruptures. Because the GF lacks large (> 1 km) discontinuities likely to arrest higher (~1 m) slip ruptures, we expect full-length (54 km) ruptures to occur that include the northern creeping zone. We estimate sufficient strain accumulation on the entire GF to produce Mw 6.9 earthquakes with a mean recurrence of ~575 yr. While the creeping 16 km northern part has the potential to produce an Mw 6.2 event in 240 yr, it may rupture in both moderate (1980) and large events. These two-dimensional-model estimates of creep rate along the southern GF need verification with small aperture surveys.