GPS Measurements of Regional Deformation in Southern California: Some Constraints on Performance

Geodetic measurements are an important tool for understanding plate boundary zone deformation. They provide data on fault motion rates and indirectly provide constraints on crustal rheology, earthquake processes, and evolution of geologic structures. In southern California the pattern of strain resulting from interaction of the Pacific and North American plates is very complex, and a robust geodetic experiment requires dense spatial sampling. In addition, the signals of interest may have strain rates smaller than 10−7/yr. Taken together, these conditions imply the need for geodetic techniques that are both economical, enabling large numbers of measurements, and highly accurate. Conventional terrestrial surveying techniques can satisfy the requirements for sampling density and accuracy for some applications, but are limited to line-of-sight, or distances less than about 50 km [e.g., Snay et al, 1983; Savage et al., 1986]. The precision a of these techniques may be described by σ = (a2 + b2L2)frac12; (1) where L is baseline length (station separation) and a and b are constants representing, respectively, length-independent and length-dependent sources of error [Savage and Prescott, 1973]. For high-precision Geodolite surveys, a = 3 mm, and b = 2 × 10−7 [Savage et al., 1987]