Shallow Slip Deficit of the 1992 Mw 7.3 Landers Earthquake Using Sub-Pixel Image Correlation
Milliner, Chris W.; Hollingsworth, James; Dolan, James; Leprince, Sebastien; and Ayoub, Francois
Near-field co-seismic deformation can be measured using sub-pixel optical image correlation. We use the program COSI-Corr to co-register, orthorectify and correlate pairs of high-resolution NAPP aerial photos taken before and after the 1992 Landers (Mw 7.3) earthquake. Using this technique, we are able to measure the detailed horizontal displacement field produced by this earthquake. Detailed investigation of both the surface displacement field and geology of the fault zone allow us to better quantify the extent to which geological properties, such as fault zone maturity and lithology, control variability in the location, width and magnitude of distributed deformation at the surface. Horizontal surface displacement of the Landers earthquake is determined by co-registering and correlating 14 image pairs, acquired 2 years before and 3 years after the earthquake. Although the spatial resolution of the aerial photos are ~1 meter, COSI-Corr can detect horizontal surface movements as low as 10 cm (corresponding to 1/10 of the input photo resolutions). We extract along-strike displacement profiles from the COSI-Corr-derived displacement maps, which are then compared to published coseismic displacement data measured by field geologists. COSI-Corr offers the advantage of measuring displacement over a far wider aperture than that available to field geologists who are often restricted to a small number of discrete offset markers. Thus, where field measurements underestimate those determined by optical image correlation, we assume this difference to result from distributed deformation missed by field surveys. Furthermore, using displacements measured by COSI-Corr we can quantify the width of the deformation zone across the fault by measuring the distance between the minimum and maximum displacements either side of the fault. Knowledge of the location, width and magnitude of distributed deformation for the Landers rupture has implications for understanding the mechanics of fault zones, as well as the geological factors which control near-surface co-seismic behavior, such as fault zone maturity and lithology.
AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013