Marine Geophysical Researches 21: 489–511, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. 489 Bathymetry of the Tonga Trench and Forearc: a map series Dawn J. Wright 1 , Sherman H. Bloomer 1 , Christopher J. MacLeod 2 , Brian Taylor 3 and Andrew M. Goodlife 3 1 Department of Geosciences, Oregon State University, Corvallis, OR 97331-5506 USA; 2 Department of Earth Sciences, University of Wales, Cardiff CF1 3YE, UK; 3 Department of Geology & Geophysics, School of Ocean & Earth Science &Technology, University of Hawai‘i, Honolulu, HI 96822 USA Received 24 September 1998; accepted 16 June 2000 Key words: Convergent margins, map series, multibeam bathymetry, tectonic erosion, Tonga forearc, Tonga Trench Abstract Four new bathymetric maps of the Tonga Trench and forearc between 14 ◦ S and 27 ◦ S display the important morphologic and structural features of this dynamic convergent margin. The maps document a number of important geologic features of the margin. Major normal faults and fault lineaments on the Tonga platform can be traced along and across the upper trench slope. Numerous submarine canyons incised in the landward slope of the trench mark the pathways of sediment transport from the platform to mid- and lower-slope basins. Discontinuities in the trench axis and changes in the morphology of the landward slope can be clearly documented and may be associated with the passage and subduction of the Louisville Ridge and other structures on the subducting Pacific Plate. Changes in the morphology of the forearc as convergence changes from normal in the south to highly-oblique in the north are clearly documented. The bathymetric compilations, gridded at 500- and 200-m resolutions and extending along ∼500 km of the landward trench slope and axis, provide complete coverage of the outer forearc from the latitude of the Louisville Ridge-Tonga Trench collision to the northern terminus of the Tonga Ridge. These maps should serve as a valuable reference for other sea-going programs in the region, particularly the Ocean Drilling Program (ODP) and the National Science Foundation MARGINS initiative. Introduction In recent years, large, regional-scale bathymetric maps published in Marine Geophysical Researches have fo- cused on various portions of the global mid-ocean ridge (Purdy et al., 1990; Macdonald et al., 1992; Cochran et al., 1992; Scheirer et al., 1996; Kee- ton et al., 1997). Here we present a regional-scale map series of a convergent margin, consisting of four foldout maps (Maps 1–4, found at the back of this is- sue) of the Tonga Trench and forearc between 14 ◦ S and 27 ◦ S (Figure 1). These maps provide a num- ber of insights into the geology and structure of an active intraoceanic forearc and trench, and serve as a companion and reference for the more detailed ge- ological studies of this region appearing elsewhere (e.g., Clift et al., 1998; Kelman, 1998; Clift and MacLeod, 1999), as well as a valuable reference for other sea-going efforts, such as ODP drilling and ma- rine geological/geophysical cruises under the auspices of the National Science Foundation’s MARGINS ini- tiative (Taylor et al., 1998). The bathymetric grids used to create these maps are available on the World Wide Web as binary Generic Mapping Tools (GMT; Wessel and Smith, 1995) grid files (see Appendix). Bathymetric studies of the Tonga Trench and fore- arc have been important tools in interpretations of ge- ological processes along this margin for four decade, beginning with Raitt et al. (1955). The morphology of the trench slopes has been used as: (1) part of the inter- pretations of basement and sedimentologic processes (Fisher and Engel, 1969; Bloomer and Fisher, 1987; Tappin, 1994; Clift et al., 1998); (2) inferences about the consequences of the subduction of the large, aseis- mic Louisville Ridge (e.g., Dupont and Herzer, 1985; Lonsdale, 1986; Ballance et al., 1989; Pelletier and Dupont, 1990); and (3) interpretations of the structural consequences of the change in relative plate motion at the northern end of the Tonga Trench (e.g., Hawkins and Natland, 1975; Wright, 1992; Millen and Ham- burger, 1998). The maps presented here build on these types of studies, and provide the most complete bathy- metric data to date for most of the landward slopes of the trench. Most of the bathymetric data presented in this map series were collected during Boomerang Leg 8 aboard