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Sandwell, DT, Sichoix L, Smith B.  2002.  The 1999 Hector Mine earthquake, southern California: Vector near-field displacements from ERS InSAR. Bulletin of the Seismological Society of America. 92:1341-1354.   10.1785/0120000901   AbstractWebsite

Two components of fault slip are uniquely determined from two line-of-sight (LOS) radar interferograms by assuming that the fault-normal component of displacement is zero. We use this approach with ascending and descending interferograms from the ERS satellites to estimate surface slip along the Hector Mine earthquake rupture. The LOS displacement is determined by visually counting fringes to within I kin of the outboard ruptures. These LOS estimates and uncertainties are then transformed into strike- and dip-slip estimates and uncertainties; the transformation is singular for a N-S oriented fault and optimal for an E-W oriented fault. In contrast to our previous strike-slip estimates, which were based only on a descending interferogram, we now find good agreement with the geological measurements, except at the ends of the rupture. The ascending interferogram reveals significant west-side-down dip-slip (similar to1.0 in) which reduces the strike-slip estimates by I to 2 in, especially along the northern half of the rupture. A spike in the strike-slip displacement of 6 m is observed in central part of the rupture. This large offset is confirmed by subpixel cross correlation of features in the before and after amplitude images. In addition to strike slip and dip slip, we identify uplift and subsidence along the fault, related to the restraining and releasing bends in the fault trace, respectively. Our main conclusion is that at least two look directions are required for accurate estimates of surface slip even along a pure strike-slip fault. Models and results based only on a single look direction could have major errors. Our new estimates of strike slip and dip slip along the rupture provide a boundary condition for dislocation modeling. A simple model, which has uniform slip to a depth of 12 km, shows good agreement with the observed ascending and descending interferograms.

Price, EJ, Sandwell DT.  1998.  Small-scale deformations associated with the 1992 Landers, California, earthquake mapped by synthetic aperture radar interferometry phase gradients. Journal of Geophysical Research-Solid Earth. 103:27001-27016.   10.1029/98jb01821   AbstractWebsite

The Landers earthquake (M-w 7.3) occurred on June 28, 1992, and ruptured nearly 100 km of previously mapped and unmapped faults in the Mojave Desert. We use synthetic aperture radar interferometry (InSAR) to examine the cumulative surface deformation between April 24 and August 7, 1992, in a 100 x 100 km region surrounding the northern portion of the earthquake rupture. Also, we introduce a technique for manipulating SAR interferograms to extract short-wavelength displacement information. This technique involves computation and subsequent combination of interferometric phase gradient maps. The InSAR results show significant deformation signatures associated with faults, fractures, dry lake beds, and mountainous regions within 75-100 km of the main rupture. Using the phase gradient method, we are able to extract small-scale deformation patterns near the main rupture. Many of the preexisting, mapped faults within 50 km of the main rupture experienced triggered slip; these include the Old Woman, Lenwood, Johnson Valley, West Calico, and Calico Faults. The InSAR results also indicate right-lateral offsets along secondary fractures trending N-NE within the left-lateral zone of shear between the main rupture and the Johnson Valley Fault. Additionally, there are interesting interferogram fringe signatures surrounding Troy Dry Lake and Coyote Dry Lake that are related to deformation of dry lake beds.