Why is the Challenger Deep so deep?

Recent sidescan surveys of the deepest segment of the southern Mariana Trench in the western Pacific Ocean provide the first detailed images of this plate boundary, which includes the world's greatest ocean depth, the Challenger Deep. The surveys reveal details of the southern Mariana plate margin, identify another deep rivaling the Challenger, and document widespread deformation of the overriding plate. Our data show a subduction-generated deep ocean trench, not the transform fault boundary suggested by other work [D.E. Karig, Geol. Soc. Am. Bull. 82 (1971) 323-344; D.E. Karig et al., J. Geophys. Res. 83 (1978) 1213-1226; D.E. Karig, B. Ranken, in: The Tectonic and Geologic Evolution of Southeast Asian Seas and Islands, Part 2, American Geophysical Union, Washington, DC, 1983, pp. 266-280; K. Fujioka et al., Geophys. Res. Lett. 19 (2002) 1-4]. We present the geological characteristics of the region, including seismic evidence for a tear in the subducting plate that has influenced the deformation of the overriding plate. The rollback caused by this tear creates greater depths along the southern part of the trench than elsewhere along its length. (C) 2003 Elsevier Science B.V. All rights reserved.