We investigate the resolving power of ISC/NEIC P travel time data in tomographic inversions for the geometry of the subduction zones in the NW Pacific. From thermal models for the Kurile, Japan, Izu-Bonin, Mariana and Ryukyu slabs, we generate three dimensional synthetic velocity anomalies for subducting slabs which are the projected onto a cell model for the uppermost 1400 km of the mantle. Using these synthetic models we compute synthetic delay times for ray paths corresponding to the source and receiver locations used for the actual data, add Gaussian noise, invert the synthetic data, and compare the resulting velocity structure to the initial synthetic models. This comparison is illustrated for sections through the Kuriles and the Mariana arcs. A variety of resolution artifacts are observed, which in many cases resemble features visible in the tomographic results obtained from inverting the actual ISC/NEIC data. ¿ American Geophysical Union 1989