Interferometric Synthetic Aperture Radar (InSAR) provides
a practical means of mapping creep along major strike-slip faults.
The small amplitude of the creep signal (< 10 mm/yr), combined with
its short wavelength, makes it difficult to extract from long timespan
interferograms, especially in agricultural or heavily vegetated areas.
We utilize two approaches to extract the fault creep signal from 37 ERS
SAR images along the southern San Andreas Fault. First, amplitude
stacking is utilized to identify permanent scatterers, which are then used
to weight the interferogram prior to spatial filtering. This weighting
improves correlation and also provides a mask for poorly correlated areas.
Second, the unwrapped phase is stacked to reduce tropospheric and other
short-wavelength noise. This combined processing enables us to recover
the near-field (~ 200 m) slip signal across the fault due to shallow creep.
Displacement maps from 60 interferograms reveal a diffuse secular strain
buildup, punctuated by localized interseismic creep of 4-6 mm/yr LOS (12-18
mm/yr horizontal). With the exception of Durmid Hill, this entire
segment of the southern San Andreas experienced right-lateral triggered
slip of up to 10 cm during the 3.5-year period spanning the 1992 Landers
earthquake. The deformation change following the 1999 Hector Mine
earthquake was much smaller (< 1 cm) and broader than for the Landers
event. Profiles across the fault during the interseismic phase show
peak-to-trough amplitude ranging from 15-25 mm/yr (horizontal component)
and the minimum misfit models show a range of creeping/locking depth values
that fit the data.