Crustal Deformation of Luzon Island, Philippines from GPS-based Geodynamic Models and Structural Analyses of Satellite Imagery

We develop a comprehensive model of plate boundary deformation, based on satellite-based structural analyses combined with geodetic and seismic evidence of present-day deformation of Luzon Island, Philippines. The region comprises the northern part of the Philippine Mobile Belt, a plate boundary zone situated between two active, opposing subduction zones. Correlation of geodetic and seismic evidences with the structural map generated from the Shuttle Radar Topography Mission (SRTM) DEM and Landsat images reveal the complexity of recent deformation style of the island. Geologic structures were mapped using co-registered sets of SRTM DEM shaded relief images and Landsat 7 images. The SRTM shaded reliefs were processed at different illumination directions and overlaid with cloud-free Landsat 7 mosaic. We then use the satellite-based identification of active faults to develop a microplate model for active deformation in the Philippine arc. We apply an elastic block model to describe active deformation within the region, utilizing simultaneous inversions of GPS-observed site velocity vectors and earthquake slip vectors to solve for block rotations, elastic fault strain accumulation on block boundaries, and internal block strain. Campaign-based GPS observations acquired from 1996-2002, and focal mechanism data from the Harvard-CMT catalogue from 1972-2003 were primary inputs for deriving the block models. Findings for slip across the major faults show 35-44 mm/y sinistral slip along the Philippine fault system, 19-28 mm/y along the Digdig fault and 21-28 mm/y motion along the northern Cordillera fault. Slower slip rates are detected along the Macolod Corridor System , with 11-13 mm/y left lateral, trans-tensional motion. Strain across the Philippine fault is modeled as a near vertical strike-slip fault, with elastic strain accumulation on a fully locked fault to 15 km. depth.