Continuous GPS monitoring at Parkfield, CA

Two-color EDM in operation

The sites shown with blue triangles are receivers recently (after 2003) installed in central California. Many of these are operated by the Plate Boundary Observatory (PBO). The sites shown with red inverted triangles form the core GPS network around Parkfield; most of these sites have been operated from 2001. These sites are operated jointly by USGS, PBO, UC Berkeley, and UC San Diego. Also shown with faint lines are the baselines measured by the two color EDM. In addition, one other site is monitored, MUSB, located east of Parkfield by 120 KM.

The data are processed using the GIPSY software with point positioning. Prior to plotting, “bad” measurements of position are identified and removed. These outliers are identified as points that deviate significantly relative to position measurements made within a 3 month window. To improve the precision, an addition step is taken. For each component, (north, east, and vertical), a common mode signal is identified and removed. To extract the common mode signal, the data from each component are high-passed filtered to remove any long-term signals including station velocity, coseismic offsets, postseismic deformation (Parkfield and the San Simeon earthquakes) and annual periodicities. The residual, high-frequency data are then averaged for each day. That is, for each day, the residual position of all of the sites are averaged which is then defined as the common mode signal. The original, unfiltered data are adjusted by the common-mode signal by simple subtraction. The results are plotted in terms of fault parallel (N48W) and fault normal (N42E) displacements. In addition, a translation is appled such that the results are in a “fault coordinate system” That is, for sites located east of the San Andreas fault, they move to the southeast; and those that are west of the San Andreas fault, they move to the northwest.

Plots of the data

Displacement vector map of the data

Follow the links below to look at maps of displacement vectors determined from the continuous GPS network. The vectors show the magnitude and direction of displacement of each continuous GPS site. Those plotted without an error ellipse are not statistically significant. Otherwise, the error ellipse represents the 95% confidence region assuming that the measurement error statistics are known completely. Those displacements that are not significant either have very small displacements or the error in the measurement is high. High measurement error can be due to lack of data.

For plots of raw data and the data themselves:

Parkfield GPS data