Creep Variability and Seismicity at the Junction of the Calaveras and San Andreas Faults
Abstract
The junction of the San Andreas and Calaveras faults in the San Juan Bautista region of California is an area of complex faulting; both faults produce earthquakes, creep and slow slip events. While the historic record indicates as many as seven M>6 events in the 19th century, the largest earthquake in the last 100 years was the 1998 M5.1 San Juan Bautista earthquake. This earthquake occurred within an area of heterogeneously distributed creep and triggered a slow slip event equivalent to a M5, which subsequently evolved over a week. In general, creep on these two faults has been highly variable in time, with slip occurring in creep events, slow slip events and as steady, secular creep. Creep rates also changed in response to the 1989 M7.0 Loma Prieta earthquake, with rates accelerating on the San Andreas fault and decreasing on the Calaveras fault. On the Calaveras fault, creep is now back at its pre-Loma Prieta rates, however, the San Andreas has yet to recover. This sensitivity suggests that creep and earthquakes feed back on each other, such that understanding both the creep history and earthquake history is important for evaluating a fault area's potential for either behavior and for constructing a slip budget. In this project we use 20 years of InSAR data over the San Juan Bautista region to investigate the variability of creep within this time span. We use the Small Baseline Subset approach to analyze InSAR data from the ERS and Envisat satellites (Track 299 Frames 2853-2871). This area is challenging for any type of InSAR analysis because it is predominantly agricultural land cover, which is very changeable and quickly leads to temporal decorrelation. For this reason, we choose profiles at strategic locations and measure creep through time where it can be constrained well. Furthermore, vertical motions due to groundwater changes are sometimes bounded by the faults and can mask or mimic tectonic signals. However, data from an ascending orbit path will help separate vertical from horizontal motions. Preliminary results show that creep rates on the Calaveras that are higher than those measured by alinement arrays and have modest time variability.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.G32B..04J
- Keywords:
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- 1207 GEODESY AND GRAVITY Transient deformation;
- 1209 GEODESY AND GRAVITY Tectonic deformation;
- 1240 GEODESY AND GRAVITY Satellite geodesy: results