Submarine topography of the northern end of Yap trench.

Abstract

Hydrographic department conducted nallow multi beam bathymetric survey in the trench junction between the Yap trench and the Mariana trench. The survey area includes the western end of Caroline ridge, the western end of the Mariana trench, and the northern end of the Yap trench. The Yap trench has no sediment on the trench axis except for its northern end. However, several bench in the water depth of 5000 m to 6800 m are recognized on the lower trench slope of the Yap arc. The Mariana arc also has a bench on its trench slope. The bench of the Mariana arc is composed from NW-SE trending micro ridges and troughs in echelon. This can be explained by the strike slip motion between the Pacific plate and the Mariana arc. Upper trench slope of the Yap and Mariana arc is simple gradient. However, the Caroline ridge is covered with irregular ups and downs. This feature suggests the geological difference between the Caroline ridge and the Yap or Mariana ridge. A small ridge locates on the arc junction. The ridge has 30 km length and 20 km width. The Yap arc and the Marina arc is connected by the ridge. Normal faults are recognized on the back of the ridge. The largest fault has N20'W trend, and displacement is more than 1500 m. These faults are evidence of extension force between the Yap arc and the Mariana arc.