Sunda Trench an underwater ridge, and much of the trench is at least partially filled with sediments. Mappings after the 2004 Indian Ocean earthquake of the plate boundary showed resemblance to suspension bridge cables, with peaks and sags, indicative of asperity and locked faults, instead of the traditional wedge shape expected. Some of the earliest exploration of the Trench occurred in the late 1950s when Robert Fisher, Research Geologist at the Scripps Institution of Oceanography, investigated the trench as part of a worldwide scientific field exploration of the world's ocean floor and sub-oceanic crustal-structure. Bomb-sounding, echo-train analysis and manometer were some of
Ryukyu Trench margin right up to the northeastern Taiwan coastline, also without the existence of a dextral north-south trending fault. Ocean bottom seismography methods combined with earthquake studies of the Benioff zone constrain the dip angle of the Philippine Sea Plate along the Ryukyu trench. In the Northern part of the Ryukyu trench, the dip of the Philippine Sea Plate is shallow at shallow depth, reaching only about 11° in the first 50 km, and steeper at deeper depths, reaching 70° below about 70 km. In contrast, the slab dip in the central and southern parts of the Ryukyu trench is more