A MODEL FOR THE MOTION OF THE PHILIPPINE SEA PLATE CONSISTENT WITH NUVEL-1 AND GEOLOGICAL DATA

We investigate angular velocity vectors of the Philippine S- (PH) plate relative to the adjacent major plates, Eurasia (EU) and Pacific (PA), and the smaller Caroline (CR) plate. Earthquake slip vector data along the Philippine Sea plate boundary are inverted, subject to the constraint that EU-PA motion equals that predicted by the global relative plate model NUVEL-1. The resulting solution fails to satisfy geological constraints along the Caroline-Pacific boundary: convergence along the Mussau Trench and divergence along the Sorol Trough. We then seek solutions satisfying both the CR-PA boundary conditions and the Philippine Sea slip vector data, by adjusting the PA-PH and EU-PH best fitting poles within their error ellipses. We also consider northern Honshu to be pan of the North American plate and impose the constraint that the Philippine Sea plate subducts beneath northern Honshu along the Sagami Trough in a NNW-NW direction. Of the solutions satisfying these conditions, we select the best EU-PH as 48.2-degrees-N, 157.0-degrees-E, 1.09-degrees/m.y., corresponding to a pole far from Japan and south of Kamchatka, and PA-PH, 1.2-degrees-N, 134.2-degrees-E, 1.00-degrees/m.y. Predicted NA-PH and EU-PH convergence rates in central Honshu are consistent with estimated seismic slip rates. Previous estimates of the EU-PH pole close to central Honshu are inconsistent with extension within the Bonin backarc implied by earthquake slip vectors and NNW-NW convergence of the Bonin forearc at the Sagami Trough.