Interseismic coupling and refined earthquake potential on the Hayward‐Calaveras fault zone

Abstract

Interseismic strain accumulation and fault creep is usually estimated from GPS and alignment arrays data, which provide precise but spatially sparse measurements. Here we use interferometric synthetic aperture radar to resolve the interseismic deformation associated with the Hayward and Calaveras Faults (HF and CF) in the East San Francisco Bay Area. The large 1992–2011 SAR data set permits evaluation of short‐ and long‐wavelength deformation larger than 2 mm/yr without alignment of the velocity field to a GPS‐based model. Our time series approach in which the interferogram selection is based on the spatial coherence enables deformation mapping in vegetated areas and leads to refined estimates of along‐fault surface creep rates. Creep rates vary from 0 ± 2 mm/yr on the northern CF to 14 ± 2 mm/yr on the central CF south of the HF surface junction. We estimate the long‐term slip rates by inverting the long‐wavelength deformation and the distribution of shallow slip due to creep by inverting the remaining velocity field. This distribution of slip reveals the locations of locked and slowly creeping patches with potential for a M6.8 ± 0.3 on the HF near San Leandro, a M6.6 ± 0.2 on the northern CF near Dublin, a M6.5 ± 0.1 on the HF south of Fremont, and a M6.2 ± 0.2 on the central CF near Morgan Hill. With cascading multisegment ruptures the HF rupturing from Berkeley to the CF junction could produce a M6.9 ± 0.1, the northern CF a M6.6 ± 0.1, the central CF a M6.9 ± 0.2 from the junction to Gilroy, and a joint rupture of the HF and central CF could produce a M7.1 ± 0.1.

Fault Creep and Strain Partitioning in Trinidad‐Tobago: Geodetic Measurements, Models, and Origin of Creep

“…Studies of the overlapping strands, for example, the Southern San Andreas and San Jacinto Faults, indicate temporal and spatial variability in the accommodation of plate boundary strain (Bennett et al, ). Furthermore, interseismic behavior along‐strike on individual faults in this continental transform system exhibits highly variable interseismic behavior, from fully coupled to creeping (e.g., Chaussard et al, ). Our new GPS‐derived horizontal velocity field for the CA‐SA plate boundary in Trinidad‐Tobago and our results of elastic modeling of an interseismic period provide a new example of plate boundary strain partitioning and variable interseismic behavior on one additional continental transform system.…”

Remote Sensing of Ground Deformation for Monitoring Groundwater Management Practices: Application to the Santa Clara Valley During the 2012–2015 California Drought

“…Such large load changes are nonnegligible even if local and should therefore be integrated into large‐scale models as they could influence the seismicity on nearby active faults. The SCV confined aquifer is as close as ~10 km east of the San Andreas Fault and ~7 km west of the Hayward‐Calaveras fault zone (Chaussard, Burgmann, Fattahi, Johnson, et al, ; Chaussard, Burgmann, Fattahi, Nadeau, et al, ), but as the aquifer extent is small, it leads to only minimal load changes. However, in the San Joaquin Valley, given the significantly larger spatial extent of the load (~40 times the area of the SCV) and the much larger load fluctuations induced by prolonged groundwater withdrawal (Farr et al, ), aquifer load changes may play a role on the stress fluctuations of the San Andreas Fault system, as close as ~15 km to the west.…”

Creeping faults: Good news, bad news?

“…While it may be relatively good news that some faults release tectonic energy by slow creep that only damages structures built across them (Figures and ), the bad news is that most of these creeping faults are still capable of hosting large earthquakes. Both the Hayward fault [e.g., Chaussard et al ., ] and the Chishang fault [ Thomas et al ., ] were found to have large locked fault sections hidden at several kilometer depth, some of which have already slipped in damaging earthquakes.…”