Block models of crustal motion in southern California constrained by GPS measurements

Abstract

We estimate slip rates on major active faults in southern California using a block model constrained by Global Positioning System measurements of interseismic deformation. The block model includes the effects of block rotation and elastic strain accumulation consistent with a simple model of the earthquake cycle. Our estimates of the right‐lateral strike‐slip rate on the San Andreas fault vary by at least a factor of 5, from a high of 35.9 ± 0.5 mm/yr in the Carrizo Plain to a low of 5.1 ± 1.5 mm/yr through the San Bernadino segment. Shortening across the Puente Hills Thrust and left‐lateral slip on the Raymond Hill fault are consistent with both thickening and escape tectonics in the Los Angeles Basin. Discrepancies between geodetic and geologic slip rate estimates along the San Andreas and San Jacinto faults, as well as in the Eastern California Shear Zone, may be explained by a temporal change in fault system behavior. We find no substantial evidence for long‐term postseismic relaxation and infer that the viscosity of the lower crust/upper mantle may be relatively high (η > 1019 Pa s).

Late Quaternary slip rate gradient defined using high‐resolution topography and 10Be dating of offset landforms on the southern San Jacinto Fault zone, California

“…This, in turn, suggests a complex kinematic evolution, which may explain apparent discrepancies between slip rate estimates obtained from geologic and geodetic data. Our results are at odds with combined InSAR and GPS data, which suggest much higher slip rates for the southern SJFZ [Fialko, 2006;Lundgren et al, 2009], but consistent with GPS block models, as well as elastic and viscoelastic models of crustal deformation in this region [Bennett et al, 1996;Meade and Hager, 2005;Becker et al, 2005;Fay and Humphreys, 2005]; the large differences of these geodetically derived slip rates may result from differences in modeling approaches, or temporal and spatial coverage of the geodetic data. Seismic hazard studies commonly rely on long-term Quaternary rates to infer short-term hazard.…”

“…The southern San Andreas and the San Jacinto fault zones are the two principal structures, together accommodating ∼35 mm/yr, that is ∼80%, of the Pacific-North America (PA-NA) relative plate motion in this region [King and Savage, 1983;DeMets and Dixon, 1999;Bennett et al, 1996;Fialko, 2006]. Geodetically derived slip rate estimates are on the order of 10-20 mm/yr for both of these fault zones, but only 2-6 mm/yr for the Elsinore fault zone [Johnson et al, 1994;Bennett et al, 1996;Meade and Hager, 2005;Becker et al, 2005;Fay and Humphreys, 2005].…”

“…Block models of GPS data from the southern SJFZ indicate slip rates of 9-15 mm/yr (Table 1) [Bennett et al, 1996;Becker et al, 2005;Meade and Hager, 2005], which is consistent with a 14-15 mm/yr slip rate estimate inferred from elastic and viscoelastic models of crustal deformation (Table 1) [Fay and Humphreys, 2005]. In contrast, the results of a study by Fialko [2006], combining interferometric satellite synthethic aperture radar (InSAR) data with an elastic deep slipping SJFZ suggest a slip rate of 21 ± 1 mm/yr along the southern part of the fault zone, although this rate probably includes the strain accommodated by folding and NE-striking cross-faults.…”

Geodetic constraints on present‐day motion of the Arabian Plate: Implications for Red Sea and Gulf of Aden rifting

“…For the Dead Sea fault and Owens fracture zone, we decompose the relative motion at the location of the plate boundary faults into fault-parallel and fault-normal components to estimate strike-slip and normal (i.e., extension or shortening) motion on the faults. We have chosen to use this approach, rather than an elastic block model [e.g., Meade and Hager, 2005;Reilinger et al, 2006] because of the concentration of GPS velocities along plate boundary faults (Figure 1). Any errors in defining the boundary fault (location, locking depth, dip) would result in mismodeling the elastic strain and could introduce spurious velocities for estimating plate motion.…”

Acceleration and evolution of faults: An example from the Hunter Mountain–Panamint Valley fault zone, Eastern California

“…However, before this can be realized, we need to better understand the various sources for discrepancies between rates spanning different times. For large offset, mature fault zones such as the Carizzo segment of the San Andreas fault in central California, geodetic rates averaged over decadal time scales, and geologic rates over longer time scales, are usually very similar (Sieh and Jahns, 1984;Lisowski et al, 1991;Dickinson, 1996;Meade and Hager, 2005;Liu-Zeng et al, 2006;Schmalzle et al, 2006).…”