InSAR AND SUBPIXEL-CORRELATION PIXEL-TRACKING MEASUREMENTS OF THE 2010 EL MAYOR-CUCAPAH EARTHQUAKE

We use interferometric analysis of synthetic aperture radar (SAR) images (InSAR) and pixel tracking by subpixel correlation of SAR and optical images to map the fault ruptures and surface deformation of the 4 April 2010 El Mayor-Cucapah earthquake (Mw 7.2) in Baja California, Mexico. The pixel-tracking measurements from SPOT 2.5 m panchromatic images and from Envisat ASAR and ALOS PALSAR images measure the large ground displacements close to the fault ruptures, with a strong discontinuity where the rupture reached the surface. The optical image subpixel correlation measures horizontal displacements in both the east-west and north-south directions and show the earthquake ruptured the Pescadores fault in the southern Sierra Cucapah and the Borrego fault in the central and northern edge of the mountain range. At the south end of the Sierra Cucapah, the fault ruptures fork into two subparallel strands with substantial slip on both visible until the agricultural area where correlation is lost and where the epicenter was located. The SAR image subpixel correlation measures horizontal deformation in the along-track (azimuth) direction of the satellite (approximately north or south) and in the radar line-of-sight (range) direction that is a combination of east-west and vertical displacements. The SAR along-track offsets, especially on the L-band ALOS images, show that there is a large amount of right-lateral slip (1-3 m) on a previously unmapped system of faults extending about 60 km to the southeast of the epicenter beneath the Colorado River Delta. The InSAR analyses of Envisat, ALOS and UAVSAR images, which use the phase of the SAR interferograms, measure the surface displacements in the same radar line-of-sight as the range pixel tracking, but with much greater precision. The combination of SAR images from different directions allows the separation of the vertical and east components of the deformation, revealing the large normal fault slip in the Sierra Cucapah (down to the east) and blocks with substantial vertical motion in the Delta (both down to the east and down to the west). The InSAR also reveals slip on many minor faults on both sides of the Sierra Cucapah and to the northwest, with displacements of cm to 10’s of cm.

Also co-authored on this abstract is Sinan Akciz, Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139