Source model of 18 September 2004 Huntoon Valley earthquake estimated from InSAR

Abstract. On 18 September 2004, an M_w= 5.5 earthquake struck the Huntoon Valley, California, USA. To measure the coseismic deformation field, we applied interferometric synthetic aperture radar (SAR) (InSAR) technique on ascending and descending SAR images from the ENVISAT satellite. Multi-temporal InSAR images were stacked to reduce the atmospheric artifact and other noise. Deformation signals are obvious across the northeast-trending, left-lateral strike-slip fault that produced the earthquake. Ascending and descending deformation maps allowed us to retrieve the east–west and vertical displacement components. Our results show that the displacement in the east–west component is between −3 and 3 cm while the vertical component is between −1 and 1 cm on both sides of the fault. Modeling the averaged deformation images from both descending and ascending tracks with an elastic dislocation source resulted in a best-fit 8 km-long by 3 km-wide fault model that strikes northeast at a depth of about 4.7 km. The magnitude calculated by InSAR data is M_w= 5.6, which is similar to that from the local earthquake catalog and slightly larger than estimates from global earthquake catalogs. Moreover, the InSAR-derived depth is similar to that from the local catalog; both are shallower than those reported in the global catalogs. Our results suggest that the earthquake parameters based on global seismic catalogs can be improved by high-resolution InSAR imagery and modeling.