Geodetic Evidence for a Near-Fault Compliant Zone along the San Andreas Fault in the San Francisco Bay Area

Abstract

Global Positioning System measurements in 1996 and 1997 and Electronic Distance Measuring data from the 1970s and 1980s at sites in five smallaperture geodetic networks along the San Andreas fault in northern California were used to determine the near-fault strain rate. The tensor shear strain rate 12 (referreḋ e to a coordinate system with the 1 axis parallel to the fault and the 2 axis normal to the fault) in the Bodega-Tomales, Lake San Andreas, and Black Mountain-Radio Facility networks (from north to south) are 0.339 ‫ע‬ 0.025, 0.366 ‫ע‬ 0.095, and 0.316 ‫ע‬ 0.060 lstrain/yr, respectively. The shear strain rate near the fault in the Black Mountain-Radio Facility and Lake San Andreas networks can be explained either by a 2D inhomogeneous model in which a low-rigidity compliant zone concentrates strain near the fault or by a very shallow locking depth of 8 km. Other evidence points to a locking depth greater than 10 km, so we prefer the first explanation. The contrast in rigidity between the fault zone and the surrounding rock appears to become stronger to the south, starting at approximately the northern extent of the Salinian block at Bodega Bay, suggesting that both the materials on either side of the fault and the cumulative fault offset play a role in the development of a compliant fault zone. Estimates of fault slip rates from far field geodetic data are only weakly sensitive to the presence of a compliant zone, but estimates of locking depths can be biased by approximately 10% toward shallower values if a compliant zone is present and unmodeled.

Three-dimensional models of elastostatic deformation in heterogeneous media, with applications to the Eastern California Shear Zone

“…Field observations suggest that the thickness of the cataclasite zones correlates with the cumulative fault slip (Scholz 1987). Intense damage gives rise to a reduction in the effective elastic shear modulus of the fault zone material, as predicted by theoretical models (Rybicki 1971;Kachanov 1986;Lyakhovsky et al 2001;Turcotte et al 2003), and evidenced by geodetic (Chen & Freymueller 2002;Fialko et al 2002;Fialko 2004;Hamiel & Fialko 2007) and seismic (Li et al 1994;Ben-Zion et al 2003;Thurber et al 2003;Cochran et al 2009) observations.…”

Block‐like plate movements in eastern Anatolia observed by InSAR

“…In eastern Anatolia, where elevation varies drastically between the plains ( 300 m in Syria) and the highest mountains ( 3000 in central Turkey), this correction is a key step to obtaining a successful measurement of tectonic signals by InSAR. Furthermore, we used Doppler orbitography and radiopositioning integrated by satellite orbital and Shuttle Radar Topography Mission topographic [Farr and Kobrick, 2000] information in the processing and then pixel multilooking and adaptive filtering to improve the coherence of the interferograms before unwrapping them using the SNAPHU (StatisticalCost, Network-Flow Algorithm for Phase Unwrapping) software [Chen and Freymueller, 2002]. Before computing the surface displacement time series, we corrected the interferograms for ramps caused by a drift in the local oscillator onboard the Envisat satellite [Marinkovic and Larsen, 2013].…”

Rheology of the mantle and tectonics of the oceanic lithospheric plates

“…Для того что бы анализировать деформационные процессы, обу словленные асейсмичным скольжением, из результа тов исключались косейсмические смещения, вызван ные землетрясением в Loma Prieta в 1989 г. [Chen, Freymueller, 2002].…”

“…Авторы работы [Chen, Freymueller, 2002] определи ли скорости деформаций сдвига ε 12 -правостороннего сдвига поперек линии с севера на юг. Для этого ис пользовались три линии различной ориентации.…”

“…15. Результаты длительных наблюдений за горизонтальными движениями в геодезической сети Black MountainRadio Facility (Северная Калифорния) [Chen, Freymueller, 2002]. [Chen, Freymueller, 2002].…”