FOUR-DIMENSIONAL STRUCTURAL EVOLUTION OF THE SUBDUCTING PACIFIC PLATE ALONG THE WESTERN PACIFIC MARGIN

Plate motions and subducting slab morphology are intricately connected. Through the integration of seismicity, tomographic images, and relative plate motions the evolution of mantle structure can be interpreted. Tomographic images of P-wave, shear wave-speed, and bulk sound speed perturbations of the Western Pacific region have been interpreted to define the extent and geometry of the subducting Pacific plate in the upper mantle. The morphology of the subducted Pacific plate along the Kurile-Japan-Izu-Bonin-Mariana arc system was found to vary both in geometry and subduction angle along the entire length of the margin. To understand the differences and evolution of the slab morphology a tectonic reconstruction for the Western Pacific was created, which describes the geologic history of the past 20 million years. The paleogeographic reconstruction illustrates the disparity in Pacific plate velocities along the convergent margin, variation in rates of trench retreat along different segments of the arc system, the collision of the Japan and Kurile arcs, and the change in motion of the Izu-Bonin arc, developing curvature of the Mariana arc due to the impingement of the Marcus-Necker and Caroline Island Ridges. Interpretations of the tectonic reconstruction and the tomographic images illustrate the importance of collision and subsequent subduction of aseismic ridges along the Western Pacific margin. The evolution of the slab morphology can be attributed to the variation in subducting plate velocities and angle of subduction, as well as the effects bathymetric features found on the subducting plate. The new plate motion model and interpretations of the physical properties of the mantle imaged with the P-wave and joint tomography are tools to assess the spatial and temporal evolution of the Pacific plate morphology from the mid-Miocene to the present and provide limitations in plausible plate motions for the region.