Space geodetic measurement of crustal deformation in central and southern California, 1984–1992

Abstract

We estimate the velocity field in central and southern Calitbrnia using Global Positioning System (GPS) observations from 1986 to 1902 and very long baseline interferometry (VLB!) observations from 1984 to 1991. Our core network includes 12 GPS sites spaced approximately 50 km apart, mostly in the western Transverse Ranges and the coastal Borderlands. The precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 05% confidence ellipse with a semiminor axis of approximately 2 mm/yr oriented roughly north-south, and a semimajor axis of approximately 3 mm/yr oriented east-west. For other stations, occupied fewer than 5 times, or occupied during experiments with poor tracking geometries, the uncertainty is larger. These uncertainties are calibrated by analyzing the scatter in three types of comparisons: (1) multiple measurements of relative position ("repeatability"), (2) independent velocity estimates from separate analyses of the GPS and VLBi data, and (3) rates of change in baseline length estimated t¾om the joint GPS+VLB! solution and from a comparison of GPS with trilateration. The dominant tectonic signature in the velocity field is shear deformation associated with the San Andreas and Garlock faults, which we model as resulting from slip below a given locking depth. Removing the effects of this simple model l¾om the observed velocity field reveals residual deformation that is not attributable to the San Andreas fault. Baselines spanning the eastern Santa Barbara Channel, the Ventura basin, the Los Angeles basin, and the Santa Maria Fold and Thrust Belt are shortening at rates of up to 5 _.+ I, 5 _.+ I, 5 _.+ 1, and 2 _.+ I mm/yr, respectively. North of Ihe Big Bend, some compression normal to the trace of the San Andreas fault can be resolved on both sides of the fault. The rates of rotation about vertical axes in the residual geodetic velocity field differ by up to a factor of 2 from those inferred from paleomagnctic declinations. Our estimates indicate that the "San Andreas discrepancy" can be resolved to within the 3 mm/yr uncertainties by accounting for deformation in California between Vandenberg (near Point Conception) and the westernmost Basin and Range. Strain accumulation of I-2 mm/yr on structures offshore of Vandenberg is also allowed by the uncertainties. South of the Transverse Ranges, the deformation budget must include 5 mm/yr between the ofl•horc islands and the mainland. INTRODU(q'!ONDetermining the velocity field in the vicinity of the Pacific-North America plate boundary in central and southern Calitbrnia (Figure 1) is a long-standing problem in tectonics. While most of the motion between these plates occurs on the San Andreas fault, the deformation extends for a substantial distance on either side of this structure. Such off-fault deformation is evident in geologic structures, seismicity, paleomagnetic declinations, and geodetic networks. Measuring that deformation with space geodesy is the primary objective of this study, w...

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Mantle Heterogeneities and the SCEC Reference Three-Dimensional Seismic Velocity Model Version 3

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Submarine landslides in the Santa Barbara Channel as potential tsunami sources

“…2a) during the Pleistocene and 2 mm/yr today based on repeated precision leveling (Sylvester, 2000). The basin itself is being actively shortened by compression as shortening rates across the basin measured by geodetic observations using very-long-baseline interferometry and global positioning systems range from 5-8 mm/yr east of Ventura to approximately 2 mm/yr in the western part of the basin (Feigl et al, 1993;Larsen et al, 1993). Post-Miocene shortening also decreases from up to 34% near Ventura to 2% in the southern and western part of the basin (Sorlien et al, 2000).…”