Continuous strain measurements during and preceding episodic creep on the San Andreas Fault

Johnston, M. J. S.; Jones, Alan C.; Daul, W.B.

doi:10.1029/jb082i036p05683

Cited by 19 publications

(7 citation statements)

References 20 publications

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“…Models of dislocations penetrating to 0.4-and 2.0-km depth gave a good fit to their data. But further northwest still, near San Juan Bautista, and in Bear Valley, Johnston et al [1977] were unable to detect significant strain signals (> 10 -8) on strainmeters between 1 and 2 km from the San Andreas fault while creep events were being recorded on the fault. This observation also implies that creep events are relatively shallow.…”

Section: Introductionmentioning

confidence: 96%

Repeated creep events on the San Andreas Fault near Parkfield, California, Recorded by a strainmeter array

Goulty¹,

Gilman²

1978

J. Geophys. Res.

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Following the 1966 Parkfield‐Cholame (California) earthquakes a creepmeter was installed across the fresh surface break of the San Andreas fault at Carr Ranch (now part of the Jack Ranch), 10 km southeast of Parkfield. It has recorded continuing slip which since the end of 1968 has occurred at about 10 mm yr−1, occurring primarily in discrete events at intervals of a few months. In April 1976 an array of four strainmeters was installed near this creepmeter at distances between 0.2 and 2.2 km from the fault to detect the elastic strain fields associated with creep events on the fault. Four similar sets of signals have since been observed on the strainmeter array, separated by intervals of 4 to 5 months. A week after three of these events, creep began at the Carr Ranch creepmeter, but no signals were detected by the strainmeters while the creepmeter was recording slip. Analysis of the strainmeter signals shows that they can be modeled by a slip zone on the fault 640 m long and extending from 30 to 510 m in depth, with right lateral slip of about 3.5 mm. Propagation of a dislocation from the lower northwest corner of the slip zone to the upper southeast corner is indicated. The phenomenon may be due to an asperity or an area of higher friction on the fault at Carr Ranch, which is repeatedly loaded to failure by steady slip on the fault around it. This is the first report of a well‐defined fault creep event which repeats itself with a high degree of similarity and which has been observed at a distance of over 2 km from the fault.

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Section: Introductionmentioning

confidence: 96%

Repeated creep events on the San Andreas Fault near Parkfield, California, Recorded by a strainmeter array

Goulty¹,

Gilman²

1978

J. Geophys. Res.

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“…The creep rate decreases northward toward SJB, where geodetic data constrain an average creep rate of ~1.1 cm/yr and a long‐term rate of ~2.3 cm/yr [ Johanson and Bürgmann , ]. The shallow deformation process of the SJB segment is characterized by episodic creep events that take place over hours to days and involve slip only in the upper ~500 m of the fault [ Johnston et al ., ; Gladwin et al ., ]. Larger slow slip transients in the upper few kilometers of the fault have been recorded by strainmeters with moment release equivalent to M 4–5 earthquakes released over a period of several days in 1992, 1996, 1998, 2003, and 2004 [ Linde et al ., ; Gwyther et al ., ; Pollitz and Johnston , ].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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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.

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“…---•2(•1 = •//2 in simple shear) is 7.5 x 10 -14 s -1. However, the surface movements in these zones might not be truely representative of the deeper crustal levels [Johnston et al, 1977].…”

Section: Introductionmentioning

confidence: 99%

Constraints on geological strain rates: Arguments from finite strain states of naturally deformed rocks

Pfiffner¹,

Ramsay²

1982

J. Geophys. Res.

397

136

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A summary of known finite strain states is presented; longitudinal strains (1 + e) as measured in many rocks often range from 1 to 40 and I to 0.025. The time span available to produce such measurable strains in young orogenic zones seems to be less than 10 m.y., possibly less than 1 m.y., which constrains conventional strain rates into the range of 10 -13 s -! to 10 -15 s -!. For both pure and simple shear (the most efficient way and a much less efficient way to accumulate incremental strains, respectively) the ellipticity of the finite strain ellipse increases in a nonlinear manner. Finite strain variations in adjacent layers, which give rise to features such as cleavage refraction, arise with only slight differences in the strain rates within these layers.

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Continuous strain measurements during and preceding episodic creep on the San Andreas Fault

Cited by 19 publications

References 20 publications

Repeated creep events on the San Andreas Fault near Parkfield, California, Recorded by a strainmeter array

Repeated creep events on the San Andreas Fault near Parkfield, California, Recorded by a strainmeter array

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

Constraints on geological strain rates: Arguments from finite strain states of naturally deformed rocks

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