Residual between postseismic and Inversion

Afterslip versus relaxation

The difference between the observations and model shows the larges residuals to the north and to the west where we have little or no GPS observations. We plan to conduct a joint inversion of both the GPS and SAR data which should improve the model.

The lower plots show the line of sight displacement observed with GPS plotted against that observed with SAR for the 5 sites where we have a phase measurement. The SAR data covers the earthquake and we have removed the Wald and Heaton joint model to analyze the post-seismic displacment. Since the joint inversion used GPS data collected several days or later after the earthquake, the scaling using the time interval from day-3 to 12/6/95 is probably more justified. The SAR displacement is relative and since the reference site RCAG is not in the radar frame, the SAR measurements can be shifted arbitrarily. There is likely an unwrapping problem near site CSUN, which, when solved, may shift it by -2.8 cm or -5.6 cm. If this is the case, all the dots will appear pretty well aligned on the lower right plot (log fit from 3 days). These results imply that afterslip was the dominant mechanism in the first 1-2 years following the earthquake.