Testing the inference of creep on the northern Rodgers Creek fault, California, using ascending and descending persistent scatterer InSAR data

Abstract

We revisit the question of whether the Rodgers Creek fault in northern California is creeping, a question with implications for seismic hazard. Using imagery acquired by Envisat between 2003 and 2010, we process two persistent scatterer interferometric synthetic aperture radar (InSAR) data sets, one from an ascending track and the other from a descending track, covering the northernmost segment of the Rodgers Creek fault between the cities of Santa Rosa and Healdsburg. The two different viewing geometries provided by the two different tracks allow us to distinguish vertical velocities, which may reflect nontectonic deformation processes, from fault‐parallel velocities, which can be used to identify creep. By measuring offsets in InSAR line‐of‐sight velocity from 12 fault‐perpendicular profiles through both data sets, we identify seven locations where we have a high degree of confidence that creep is occurring (estimated creep rate is more than two standard deviations above zero). The preferred creep rates at these locations are in the range 1.9–6.7 mm/yr, consistent within uncertainty with alignment array measurements. Creep is probable (P≥0.70) at another three locations, defining a creeping zone ∼20 km long in total, extending northwest from Santa Rosa. We also estimate the map patterns of fault‐parallel and vertical velocities in the region covered by both data sets; these suggest that the Rodgers Creek fault immediately southeast of Santa Rosa remains locked.

Interseismic Ground Deformation and Fault Slip Rates in the Greater San Francisco Bay Area From Two Decades of Space Geodetic Data

“…Plotting along‐fault profiles on our InSAR horizontal velocity map (Figure a), we estimate that the average creep rate of the Rodgers Creek fault is about 2 mm/year along much of its trace, consistent with the AA data, although the AA data seem to suggest that the along‐fault creep rates decrease from north to south (Figures a and S5). Our estimated shallow fault slip rate of 2 mm/year is slightly higher than the lower bound (0.4 mm/year) of a recent estimated value by Jin and Funning () and is much lower than the 6 ± 0.6 mm/year rate that was estimated from seven years of ERS‐1/2 data (Funning et al, ). Limited near‐fault coverage southeast of Santa Rosa prohibits identifying evidence of shallow creep, similar to previous studies (Funning et al, ; Jin & Funning, ).…”

“…Positive values reflect right‐lateral creep. The shaded blue bars show the one‐tailed probability of the right‐lateral creep rate greater than zero (Jin & Funning, ).…”

Widespread Fault Creep in the Northern San Francisco Bay Area Revealed by Multistation Cluster Detection of Repeating Earthquakes

“…Shallow creep (up to ∼ 2-km depth) is inferred along this segment from InSAR data (Funning et al, 2007;Jin & Funning, 2017), further confirming the association of REs with creep. Shallow creep (up to ∼ 2-km depth) is inferred along this segment from InSAR data (Funning et al, 2007;Jin & Funning, 2017), further confirming the association of REs with creep.…”

Map of recently active traces of the Rodgers Creek Fault, Sonoma County, California

“…This result substantiates the work of early mappers who cited evidence consistent with geologically young surface rupture to delineate the Healdsburg Fault as active in the Quaternary (for example, Gealey, 1951;Huffman and Armstrong, 1980). Evidence of Holocene activity along essentially the entire length of the Healdsburg Fault section is consistent with the results of interferometric synthetic aperture radar (InSAR) studies (Funning and others, 2007;Jin and Funning, 2017) showing that shallow creep, at preferred rates in the range of 1.9-6.7 mm/yr, is occurring along the fault between Santa Rosa and Healdsburg. We observed field evidence of creep on the Healdsburg section of the fault at a location in Santa Rosa (strand FID 518) and east of Healdsburg (strand FID 614).…”

“…More research is needed to clarify other aspects of the fault's behavior, such as timing of earlier events, lengths of earthquake ruptures, and amounts and distribution of displacement through time. Aseismic shallow fault slip, or creep, a phenomenon documented along many parts of the San Andreas Fault system in northern California, has been recognized along the Rodgers Creek Fault, from Santa Rosa northward, only relatively recently (Funning and others, 2007;Lienkaemper and others, 2014;McFarland and others, 2016;Jin and Funning, 2017).…”