Aseismic slip and fault‐normal strain along the central creeping section of the San Andreas fault

Abstract

[1] We use GPS data to measure the aseismic slip along the central San Andreas fault (CSAF) and the deformation across adjacent faults. Comparison of EDM and GPS data sets implies that, except for small-scale transients, the fault motion has been steady over the last 40 years. We add 42 new GPS velocities along the CSAF to constrain the regional strain distribution. Shear strain rates are less than 0.083 ± 0.010 mstrain/yr adjacent to the creeping SAF, with 1 -4.5 mm/yr of contraction across the Coast Ranges. Dislocation modeling of the data gives a deep, long-term slip rate of 31-35 mm/yr and a shallow (0 -12 km) creep rate of 28 mm/yr along the central portion of the CSAF, consistent with surface creep measurements. The lower shallow slip rate may be due to the effect of partial locking along the CSAF or reflect reduced creep rates late in the earthquake cycle of the adjoining SAF rupture zones.

Change of apparent segmentation of the San Andreas fault around Parkfield from space geodetic observations across multiple periods

“…As this region did not produce large earthquakes in recorded history, it likely experiences cycles of accelerated and reduced aseismic slip. Overall, the slip rates on the creeping segment are not uniform, compatible with the results of Rolandone et al [] obtained with GPS data alone and those of [ Ryder and Bürgmann , ] obtained from InSAR analysis.…”

“…We use average velocities of surface displacement derived from analysis of continuous GPS times series and interferometric synthetic aperture radar (InSAR). Many analyses of InSAR and GPS have been successful at constraining slow interseismic deformation across faults [ Wright et al , ; Fialko , ; Cavalié et al , ; Jolivet et al , ; Elliott et al , ; Wang et al , ; Fay and Humphreys , ; Lundgren et al , ; Bell et al , ; Lindsey and Fialko , ; Jolivet et al , ], and our work extends studies focused on the northern termination of the central SAF section [ Rolandone et al , ; Ryder and Bürgmann , ; Johanson and Bürgmann , ]. Because the apparent interseismic velocity can change appreciably during the interseismic cycle [e.g., Tse and Rice , ; Lapusta et al , ; Barbot et al , ; Lapusta and Barbot , ], we compare interseismic fault slip rates before and after the 2004 Parkfield earthquake.…”

“…Shallow creep in the creeping section is higher but in some places markedly slower than plate rate at greater depths [ Thatcher , ; Johanson and Bürgmann , ; Rolandone et al , ; Ryder and Bürgmann , ]. The implications of this shallow slip deficit is not fully understood and may be the result of a process of stress buildup released in earthquakes [ Toppozada et al , ], spontaneously nonsteady fault slip due to a particular friction behavior in a manner similar to slow slip events of slow earthquakes [e.g., Rogers and Dragert , ; Liu and Rice , ; Miyazaki et al , ; Ito et al , ] or transient loading from earthquakes on neighboring segments [e.g., Ben‐Zion et al , ].…”

The role of space-based observation in understanding and responding to active tectonics and earthquakes

“…Interseismic and postseismic strain rates for four strike-slip faults where data are available before and after a major earthquake74105108125126127128. Strain rates in units of microstrain per year and are normalized by the long-term slip rate of the fault.…”

Fault-zone controls on the spatial distribution of slow-moving landslides

“…The creeping section of the San Andreas fault extends north-northwest from Parkfi eld, California, to San Juan Bautista, California, and it creeps at a rate of ~3 cm/yr (Savage and Burford, 1973;Burford and Harsh, 1980;Titus et al, 2005;Rolandone et al, 2008;Ryder and Bürgmann, 2008) (Fig. 1).…”