A unified analysis of crustal motion in Southern California, 1970-2004: The SCEC crustal motion map

Abstract

[1] To determine crustal motions in and around southern California, we have processed and combined trilateration data collected from 1970 to 1992, VLBI data from 1979 to 1992, and GPS data from 1986 to 2004: a long temporal coverage required in part by the occurrence of several large earthquakes in this region. From a series of solutions for station positions, we have estimated interseismic velocities, coseismic displacements, and postseismic motions. Within the region from 31°N to 38°N. and east to 114°W, the final product includes estimated horizontal velocities for 1009 GPS, 190 trilateration, and 16 VLBI points, with ties between some of these used to stabilize the solution. All motions are relative to the Stable North American Reference Frame (SNARF) as realized through the velocities of 20 GPS stations. This provides a relatively dense set of horizontal velocity estimates, with well-tested errors, for the past quarter century over the plate boundary from 31°N to 36.5°N. These velocities agree well with those from the Plate Boundary Observatory, which apply to a later time period. We also estimated vertical velocities, 533 of which have errors below 2 mm/yr. Most of these velocities are less than 1 mm/yr, but they show 2-4 mm/yr subsidence in the Ventura and Los Angeles basins and in the Salton Trough. Our analysis also included estimates of coseismic and postseismic motions related to the 1992 Landers, 1994 Northridge, 1999 Hector Mine, and 2003 San Simeon earthquakes. Postseismic motions increase logarithmically over time with a time constant of about 10 days, and generally mimic the direction and relative amplitude of the coseismic offsets.

Pore pressure sensitivities to dynamic strains: Observations in active tectonic regions

“…This type of spatial pattern suggests a dependence on rates of secular shear strain accumulation across the fault, which in the case of the SAF can vary significantly along strike: profiles of strain are expected to be broader in the locked section than in the creeping section, where they are expected to be focused at the fault owing to shallow creep. Gradients in geodetic velocity profiles [Shen et al, 2011;Tong et al, 2013] highlight this expected pattern.…”

Change of apparent segmentation of the San Andreas fault around Parkfield from space geodetic observations across multiple periods

“…Pre‐earthquake GPS velocity field and forward model at the SCEC Crustal Motion Map 4 (CMM4) compilation network [ Shen et al , ]. Baseline velocity, forward model, and residuals are shown in Figure S4.…”

Stress modulation on the San Andreas fault by interseismic fault system interactions

“…2A) (McClusky et al, 2001;Shen et al, 2003;Hammond and Thatcher, 2005;Williams et al, 2006;McCaffrey et al, 2007; Plate Boundary Observatory network velocity fi eld, http://pboweb.unavco.org) and a three-dimensional spherical block model (see the GSA Data Repository 1 ) (Meade and Loveless, 2009) to constrain kinematically consistent slip rates (Weldon and Humphreys, 1986;Minster and Jordan, 1987) on ~60,000 km 2 of fault area throughout the Southern California fault system. Block models describe the interseismic GPS velocity fi eld as the combined effects of two processes, long-term microplate rotations and local elastic strain accumulation effects (Savage and Burford, 1973;Savage, 1983;Matsu'ura et al, 1986).…”