Application of GPS Measurements of Crustal Deformation in Luzon
Chia-Chu Yang
Abstract
The Philippine archipelago is a deformed orogenic belt resulting from the collage and collision of blocks of oceanic and continental affinities. It is wedged between twoconverging plates: the oceanic northwest-moving Philippine Sea Plate in the east and the newly discovered Sundaland Block in the west.One of the major crustal structures of the archipelago is the Philippine Fault, a 1200-km left-lateral, strike slip fault that transects the Philippine Islands from north to south. Historical and recent seismic data show that the Luzon segment is one of the most seismically-active segments of the Philippine Fault. It’s commonly and repeatedly in the partitioning of slip at oblique subduction zone, and therefore lithospheric blocks being detached from the overriding plate. A method is described to solve simultaneously for both block rotations on a sphere and locking on block-bounding faults using GPS vectors and other geophysical data. Matsu’ura et al. [1986] modeled translating crustal blocks in a Cartesian coordinate system strained at their edges by fault interactions but did not include rotations. Prawirodirdjo et al. [1997], using my computer program DEF-NODE [McCaffrey, 1995], modeled the multi-plate problem of slip partitioning using spherical Euler poles to describe both the kinematics of block motions and the relative slip on block-bounding faults. Backslip was applied to estimate the contribution of fault locking to the total velocity field. So we separated six blocks for explicit interpretation from Luzon region. Major tectonic structures that were found to absorb the plate convergence include the Manila Trench (20–100 mm yr?1) and East Luzon Trough (~ 9–15 mm yr?1)/Philippine Trench (~ 29–34 mm yr?1), which accommodate eastward and westward subduction beneath Luzon respectively. Our analysis suggests that much of the Philippine Fault and associated splays are locked to partly coupled, while the Manila and Philippine trenches appear to be poorly coupled. Luzon is best characterized as a tectonically active plate boundary zone, comprising six mobile elastic tectonic blocks between two active subduction zones. The Philippine Fault and associated intra-arc faults accommodate much of the trench parallel component of relative plate motion.
Rerferences
Galgana, G., M. Hamburger, R. McCaffrey, E. Corpuz, and Q. Chen (2007). Crustal deformation in Luzon Island, Philippines using terrain models, geodetic observations and focal mechanisms, Tectonophysics, 432, 63-87.
McCaffrey, R. (2002), Crustal block rotations and plate coupling, in Plate Boundary Zones, Geodynamics Series 30, S. Stein and J. Freymueller, editors, 101-122, AGU.