Fault creep observed on the Maacama and Rodgers Creek faults, northern California using PS-InSAR

Jerlyn L. Swiatlowski, & Gareth J. Funning

Published August 3, 2016, SCEC Contribution #6466, 2016 SCEC Annual Meeting Poster #136

Fault creep north of the San Francisco Bay Area has been observed in a few discrete locations, along the Maacama and Rodgers Creek faults, but the distribution of creep along these faults are not mapped in detail. This is due to a high degree of vegetation and minimal man-made structures surrounding the faults. The Maacama fault is observed to creep at a four alinement arrays along its entire 180 km extent (McFarland et al., 2009). The Rodgers Creek fault has two more alinement arrays than the Maacama fault as well as a previous InSAR study showing fault creep around the city of Santa Rosa (Funning et al., 2007).
Here we present persistent scatterer InSAR (PSI) results that map creep on the Maacama and Rodgers Creek faults. We processed a 39 image ERS descending track dataset, spanning 1992-2000, using the StaMPS PSI code (Hooper et al., 2004; Hooper 2008), significantly increasing the density of surface deformation observations along the southern Maacama fault (track 113, frame 2817) and northern Rodgers Creek fault (track 113, frame 2835).
We identify fault creep along the Maacama fault surrounding the cities of Ukiah and Willits, where creep has been detected at two alinement arrays (McFarland et al., 2009). There is a change in line-of-sight (LOS) velocity localized on the mapped fault trace, consistent with right-lateral sense of fault motion. To compare the LOS velocity on either side of the fault, the LOS velocity points were projected onto profiles perpendicular to the fault, in windows of 2 km long and 6 km wide. A best-fitting linear gradient is subtracted and the change in velocity at the fault estimated by fitting horizontal lines to data from either side of the fault. At Ukiah and Willits, there are LOS velocity rates ranging from 0.1 – 1.6 mm/yr and 1.8 – 1.9 mm/yr, respectively. If projected into the fault parallel direction, and assuming pure right-lateral strike-slip motion, these rates are equivalent to creep rates of 0.3 – 4.1 mm/yr and 4.2 – 4.8 mm/yr, respectively.
Fault creep is identified on the Rodgers Creek fault surrounding the city of Santa Rosa, CA, showing a change in LOS velocity along the mapped fault trace where creep has been detected by three alinement arrays (McFarland et al., 2009). This distribution of creep is consistent with a previous study (Funning et al., 2007) that identified right-lateral fault creep at rates of up to 6 mm/yr between 1992-2001 using an ERS descending track dataset (track 342, frame 2835). Additional LOS velocity estimates will be created using other ERS tracks as well as using the small baseline subset (SBAS) technique of StaMPS and processing datasets from other satellites (e.g. Envisat, ALOS-1, ALOS-2, Sentinel-1A and Sentinel-1B).

Key Words
fault creep, Maacama fault, Rodgers Creek fault

Citation
Swiatlowski, J. L., & Funning, G. J. (2016, 08). Fault creep observed on the Maacama and Rodgers Creek faults, northern California using PS-InSAR. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy