Geodetic investigations of active crustal deformation in the Philippine plate boundary zone and the intraplate region of the central United States

This thesis investigates active tectonic and volcanic deformation in two distinct plate tectonic settings: a plate boundary zone (PBZ) accommodating oblique plate convergence, and an intraplate continental seismic zone, using high-precision space geodetic techniques. The Philippine Mobile Belt (PMB), a seismically active, rapidly deforming PBZ situated along the convergent Philippine Sea/Eurasian plate boundary, is examined using geodetic and seismological data. Oblique convergence between the Philippine Sea Plate and the Sundaland/Eurasian Plate is accommodated by nearly orthogonal subduction along the Philippine Trench, East Luzon Trough, and the Manila Trench, as well as by strike-slip faulting along the Philippine Fault system. A kinematic model of active plate boundary deformation in this region is developed, using elastic block models constrained by known fault geometries, published GPS observations and focal mechanism solutions. I present an estimate of block rotations, fault coupling, and intra-block deformation, based on the best-fit model that minimizes the misfit between observed and predicted geodetic vectors and earthquake slip vectors. In the preferred model, the Philippine Mobile Belt can be represented by at least nine independently moving tectonic blocks, separated by active faults and subduction zones.;I also model active deformation patterns associated with magmatic activity at Taal Volcano, an active tholeiitic volcano located within the Taal caldera in southwestern Luzon. Elastic and combined elastic-viscoelastic modeling results are compared with observed deformation, measured by continuous GPS on and near the volcano. Continuous dual- and single-frequency (L1) GPS data (1998--2005) provide evidence for smoothly transitioning periods of inflation and deflation centered under Volcano Island. Elastic modeling of the source region indicates a relatively stable point source, located under Volcano Island's central crater, at ∼5 km depth with time-varying pressure/volume changes. I model finite-element models of volcanic deformation using an axisymmetric geometry, with a small spherical source and annuli of viscoelastic shells, embedded within a multi-layered elastic half-space. Using simply varying pressure histories as input, forward models are fit to the time history of continuously observed GPS deformation for both dual-frequency and L1 stations surrounding Taal Volcano relative to station KAYT, situated on the southwest side of Volcano Island. The use of viscoelastic shell models that incorporate geologically appropriate material properties provide simpler pressure histories that require significantly reduced overall pressure increases, relative to equivalently fitting purely elastic models.;In contrast to the Philippine PBZ, I investigate active intraplate crustal deformation within the southern Illinois Basin, which includes the Wabash Valley seismic zone, a faulted and seismically active area in the U.S. mid-continent, located north-northeast of the New Madrid seismic zone. I analyze GPS-derived velocity solutions for the region based on 11 years (1997--2008) of campaign observations at 67 sites in S. Indiana, S. Illinois and W. Kentucky. Improved estimates of site motions indicate a marginal but resolvable systematic north to NNW-oriented pattern of the GPS velocity vectors in the Stable North American Reference Frame (SNARF). I investigate internal deformation within this continental intraplate region, modeled as an area defined by relatively rigid elastic blocks with deformation concentrated along narrow zones of weaknesses or faults. Models based on a single continuously deforming plate indicate small areas of deformation localized in SE Illinois, SW Indiana and NW Kentucky, with seismicity and recent events possibly reflecting transpressional tectonics in the area.