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Intraplate stresses and plate-driving forces in the Philippine Sea Plate

Authors

  • Kim M. Pacanovsky,

  • Dan M. Davis,

  • Randall M. Richardson,

  • David D. Coblentz


Abstract

We use a spherical shell elastic finite element analysis to characterize intraplate stresses and plate-driving forces in the Philippine Sea Plate. Our finite element mesh is comprised of 489 nodes and 914 elements, and provide a spatial resolution of about 1°. The Philippine Sea Plate is unusual in that it does not have large numbers of seismic or tectonic stress indicators, and there are no midplate borehole stress data which can be used as constraints in this finite element study. However, it does possess a unique boundary configuration which potentially can lend more insight to plate forces and stresses than can similar studies on plates with more seismically active interiors. Because the plate's boundary consists primarily of subduction zones with roughly equal proportions of boundary on the overlying and downgoing sides of trench, the resultant plate stress field is very sensitive to subduction-related forces. As a result, borehole stress measurements in certain parts of the plate would be useful in further constraining these forces. We find that trench pull forces can explain a large component of the velocity of the Philippine Sea Plate. However, trench pull has somewhat less overall effect on the stresses across the plate than do the lateral density and topographic variations within the plate (i.e., gravitational or potential energy force), and trench suction forces are probably about an order of magnitude smaller than the net trench pull forces. Collisional forces may dominate the stress fields near Taiwan and the Izu Peninsula, but they are of only secondary importance in determining the motion and deformation of the Philippine Sea Plate. The forces that generate stress orientations most closely matching the observed stress indicators produce a lithospheric stress field across the plate that averages about 15 MPa over a 70 km thick lithosphere, scaling inversely with lithosphere thickness. Values up to four times as great are produced locally.

Ancillary