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Creep on the Rodgers Creek fault, northern California, revealed by PS-InSAR

Gareth Funning(1), Roland Burgmann(2), Alessandro Ferretti(3), Fabrizio Novali(3) and Alfio Fumagalli(3)

(1) University of California, Riverside, Geology Building, Riverside, CA 92521, United States
(2) University of California, Berkeley, 215 McCone Hall, Berkeley, CA 94720, United States
(3) Tele-Rilevamento Europa, Via Vittoria Colonna 7, Milan 20149, Italy

Abstract

A number of faults that creep interseismically have been identified in California, Turkey and Afghanistan. Given that some portion of the stress on such a fault is dissipated aseismically, models of the rates and extents of creep on active faults are important inputs into seismic probability estimates. Furthermore, an understanding of creep and the factors that promote it (be they friction, stress, lithology or geometry) may lead to a deeper understanding of fault mechanics.

In order to look for common factors that may allow faults to creep, it is desirable to develop a full inventory of the faults that do so. In the absence of obviously offset cultural features, creep can be difficult to detect, even with dense GPS networks. Permanent Scatterer InSAR (PS-InSAR), on the other hand, has great potential for such a task, given its high precision and spatial density of coverage.

We show here a 30 image PS-InSAR dataset of the northern San Francisco Bay Area spanning the time interval 1992-2001. A good density of points is obtained across the region, despite widespread agriculture and viticulure, which do not favor conventional InSAR. A discontinuity is identified in observed surface velocities across the previously assumed locked Rodgers Creek fault, around the city of Santa Rosa and further north. This is consistent with shallow creep at rates of up to 6 mm/yr. The creeping segments are located in areas of local transtension - a local releasing bend, and a 8 km stepover to the Maacama fault - suggesting that lowered normal stresses may play a role in allowing creep in this area.

 

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry