Variability of fault slip behavior along the San Andreas Fault in the San Juan Bautista Region

Abstract

An improved understanding of the time history of fault slip at depth is an essential step toward understanding the underlying mechanics of the faulting process. Using a waveform cross-correlation approach, we document spatially and temporally varying fault slip along the northernmost creeping section of the San Andreas Fault near San Juan Bautista (SJB), California, by systematically examining spatiotemporal behaviors of characteristically repeating earthquakes (CREs). The spatial distribution of pre-1998 SJB earthquake (1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998) fault slip rate inferred from the CREs reveals a~15 km long low creep or partially locked section located near the 1998 M w 5.1 SJB earthquake rupture. A finite-fault slip inversion reveals that the rupture of the 1998 SJB earthquake is characterized by the failure of a compact~4 km 2 asperity with a maximum slip of about 90 cm and corresponding peak stress drop of up to 50 MPa, whereas the mean stress drop is about 15 MPa. Following the 1998 earthquake, the CRE activity was significantly increased in a 5-10 km deep zone extending 2-7 km northwest of the main shock, which indicates triggering of substantial aseismic slip. The postseismic slip inferred from the CRE activity primarily propagated to the northwest and released a maximum slip of 9 cm. In this 5-10 km depth range, the estimated postseismic moment release is 8.6 × 10 16 N m, which is equivalent to M w 5.22. The aseismic slip distribution following the 1998 earthquake is not consistent with coseismic stress-driven afterslip but represents a triggered, long-lasting slow earthquake.

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

“…The SAF near San Juan Bautista may be especially prone to such large afterslip. As noted above, large postseismic slip has been observed for three M 5–6 earthquakes on creeping sections of the San Andreas and Calaveras Faults: 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 , ]. Small earthquakes on other faults may have smaller afterslip.…”

Long‐term acceleration of aseismic slip preceding the Mw 9 Tohoku‐oki earthquake: Constraints from repeating earthquakes

“…Repeating earthquakes have nearly identical waveforms, magnitudes, and source locations and have been found in a number of tectonic settings including the San Andreas Fault, California, [ Bufe et al , ; Vidale et al , ; Nadeau and Johnson , ; Schaff et al , ; Bürgmann et al , ] and the Japan Trench [ Igarashi et al , ; Uchida et al , ; Uchida and Matsuzawa , ]. Sequences of repeating earthquakes respond to large nearby earthquakes with decreasing recurrence intervals that gradually recover to premainshock rates, consistent with their being driven by frictional afterslip [ Schaff et al , ; Nadeau and McEvilly , ; Uchida et al , ; Chen et al , ; Taira et al , ; Uchida et al , ]. Additionally, variations in recurrence intervals were correlated with independent geodetic measurements of fault creep [ Nadeau and McEvilly , ].…”

Spatiotemporal variations of characteristic repeating earthquake sequences along the Middle America Trench in Mexico

“…Equation provides the slip at the interface, whereas a piecewise least squares linear fit provides an estimate of the slip rate. Our repeating earthquake catalog shows that the 2012 Ometepec and 2014 Tecpan earthquakes significantly increased the rate of repeating earthquake occurrences, a well‐known consequence of the sudden release of stress accumulation after a large event [ Schaff et al , ; Lengliné and Marsan , ; Okada et al , ; Chen et al , ; Taira et al , ]. The slip rate after the 2012 Ometepec earthquake largely exceeded the background convergence rate of 5.9 cm/yr [ DeMets et al , ], which indicates postseismic slip after the main shock.…”

“…Previous studies have identified repeating earthquakes in a large variety of tectonic environments including California [ Vidale et al , ] Japan [ Uchida et al , ; Matsuzawa et al , ; Kimura et al , ], China [ Schaff and Richards , ], Taiwan [ Chen et al , , ], Turkey [ Peng and Ben‐Zion , ], and Tonga‐Vanuatu [ Yu , ]. Here repeating earthquakes have been observed along the creeping segment of the San Andreas Fault [ Nadeau and Johnson , ; Schaff et al , ; Rubin et al , ; Taira et al , ] and along the Calaveras fault [ Vidale et al , ; Marone et al , ; Schaff and Beroza , ; Peng et al , ; Zhao and Peng , ; Templeton et al , ]. Characteristic repeating sequences in these environments have been exploited as a common framework to explore the physical mechanism behind their origin and occurrence [ Sammis and Rice , ; Beeler et al , ].…”