Behavior of Repeating Earthquake Sequences in Central California and the Implications for Subsurface Fault Creep

Abstract

Repeating earthquakes (REs) are sequences of events that have nearly identical waveforms and are interpreted to represent fault asperities driven to failure by loading from aseismic creep on the surrounding fault surface at depth. We

Estimates of aseismic slip associated with small earthquakes near San Juan Bautista, CA

“…Two of these postseismic moment ratios are larger than those observed here, but they were estimated over years, not 1.5 days. If we assume that afterslip following the small earthquakes analyzed here continues at a rate proportional to time −1 for rate for 4 months, a time period more than 10% of the several year recurrence intervals [e.g., Nadeau and Johnson , ; Nadeau et al , ; Templeton et al , ], we would predict postseismic to coseismic moment ratios of 2 to 3, comparable to the ratios observed for the 1998 San Juan Bautista, 2004 Parkfield, and 2007 Alum Rock earthquakes [ Langbein et al , ; Freed , ; Barbot et al , ; Murray‐Moraleda and Simpson , ; Taira et al , ].…”

“…One might imagine that some property of repeating earthquake patches facilitates larger postseismic slip than observed in most earthquakes. However, in section 6.3 we isolated the strain associated with some of the repeating earthquakes identified by Templeton et al []. The postseismic strain of these repeaters is moderate—less than twice the coseismic strain—and similar to that observed for the entire earthquake set.…”

Widespread Fault Creep in the Northern San Francisco Bay Area Revealed by Multistation Cluster Detection of Repeating Earthquakes

“…More intriguingly, the shallower REs in the area, located at depths of 1-5 km, define a subvertical trend that projects to the surface ∼ 5 km NE of the main Maacama surface trace, suggesting that there is a subvertical shallow splay fault at this location that may also be creeping (profile A3-B3; Figure 4). This structure is variously referred to as the "East Willits fault" (Prentice et al, 2014) or the "East Valley fault" (Woolace, 2005) and was recognized in the 1970s (Simon et al, 1978). This structure is variously referred to as the "East Willits fault" (Prentice et al, 2014) or the "East Valley fault" (Woolace, 2005) and was recognized in the 1970s (Simon et al, 1978).…”

Crustal Deformation Studies using Synthetic Aperture Interferometry

“…Thus the asperity is not located at a transition zone between locked seismic rupture and steady creep, as, for example, occurs in subduction zones or near the base of the high Himalaya. The process is similar to that associated with repeating earthquakes on asperities on creeping faults in central California and elsewhere (Templeton et al, 2008). Creep processes apparently permit the plateau to stream around basal asperities, with strain developing upstream and along their sides.…”