Data reduction

While the Parkfield earthquake has been highly anticipated, it is nonetheless a moderate sized event. As Figure 13.9 shows, the earthquake produced ground deformation resulting in  1 fringe (2${\pi}$ radians), corresponding to 28 mm of range change (change in distance between the ground and the satellite). This is comparable to the expected size of atmospheric errors in an interferogram (Zebker et al., 1997). The interferogram also displays ground deformation due to groundwater movement. The signal from the Paso Robles Basin to the southwest (circled in Figure 13.9) is particularly noticeable. We have pared the interferogram down to just the immediate vicinity of the Parkfield earthquake (dashed line in Figure 13.9) and removed areas affected by groundwater induced vertical motion in the Paso Robles and Salinas basins and topography-correlated atmospheric errors to the East and South.

Figure 13.9: Interferogram from 7/3/2003 to 9/30/2004. Star is the epicenter of the 2004 Parkfield earthquake, dashed line borders area used in the inversion and dot is the location of the San Andreas Fault Observatory at Depth (SAFOD). Color scale is from 0 to 2$\pi $ and repeats.
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For the inversion, the geocoded and trimmed interferogram was sub-sampled on a grid with 1 km spacing. We correct our interferogram samples for coseismic and postseismic slip from the San Simeon earthquake and interseismic motion using an unpublished model based on GPS and InSAR and the model of Rolandone et al. (2004), respectively.

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