The Yap Trench composes a unique arc-trench system because there does not exist a deep seismic plane and the Caroline Ridge collides with the trench. We combine the bathymetry obtained by multi-beam sounding and the detailed topography by the submersible ﾒShinkai 6500ﾓ and estimate tectonic stresses on the seaward slope region of the Yap Trench. Grabens with strikes of N20｡E-N508E wee observed from the multi-beam bathymetry and from the submersible. The strike is almost parallel to the trench axis, which suggests tensional field in the central Yap Trench.