Multiwavelength EDM measurements in southern California
We installed a precise geodetic network along the San Andreas fault near Pearblossom, California in November, 1980. The network is within the region frequently referred to as the "Palmdale Uplift" and consists of 13 lines radiating from a central benchmark. The lines range in length from 3.2 to 8.1 km are generally measured several times each week. The multiwavelength distance measuring (MWDM) instrument is located at the central benchmark and is housed in a small protective shelter. The MWDM instrument has demonstrated a capability to make measurements to a precision of 1 part in 10 million. Using a coordinate system whose x-axis is parallel to the local trace of the San Andreas fault the following strain rates were observed during the first 10 months of this effort: ɛ xx = -0.180 ± 0.025 μ str / yr ɛ yy = -0.031± 0.029 μ str / yr ɛ xx = +0.077 ± 0.024 μ str / yr △ -0.213 ± 0.039 μ str / yr The observed strain rates do not appear to be constant in time, much of the deformation occurs in fairly well defined episodes. These changes in strain rate are particularly obvious in the ɛ yy component.