Map of study area
Map of ground velocity south of the San Francisco Bay area, where the San Andreas fault (outlined in black as all faults and noted SAF) splits into several branches, including the Calaveras Fault (CF). It is derived from radar interferometry (InSAR), a geodetic technique using time series of radar satellite images to track changes in satellite-ground distances. Velocities are averaged over a 5-year period (2015-2020). They are measured in the line of sight (LOS) of the satellite but reflect 3D ground movements. They are consistent with velocities derived from GPS (colored circles at GPS stations with same color code as InSAR velocities). Sharp color contrasts across the SAF and CF are the signature of continuous surface motion along them, which subtle spatial and temporal variations are analyzed in the study. Credit: Credit: Li et al. [2023], Figure 2a
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Solid Earth

Monitoring how faults slip is essential to improve seismic hazard assessment. The San Andreas fault and nearby Calaveras fault in the South Bay area in California, USA are both known to slip continuously and aseismically near or at the surface (also known as “creep”).

Using high resolution time series of radar images acquired by the Sentinel-1 satellites over a five-year period (2015-2020), Li et al. [2023] provide fine constraints on the creep velocities, how they vary spatially along the faults, and why (mainly controlled by the fault geometry and the regional tectonic stress field). Subtle temporal fluctuations in creep velocities, likely associated with small loading perturbations, are also captured and are consistent with complementary indirect observations of creep and state of stress on faults by seismology. These new observations are key to understanding what controls fault slip behavior and how aseismic slip may interplay with, and impact, fault seismic activity.

Citation: Li, Y., Bürgmann, R., & Taira, T. (2023). Spatiotemporal variations of surface deformation, shallow creep rate, and slip partitioning between the San Andreas and southern Calaveras Fault. Journal of Geophysical Research: Solid Earth, 128, e2022JB025363.

—Cécile Lasserre, Associate Editor, JGR: Solid Earth

Text © 2023. The authors. CC BY-NC-ND 3.0
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