Bending-Related Topographic Structures of the Subducting Plate in the Northwestern Pacific Ocean - Accretionary Prisms and Convergent Margin Tectonics in the Northwest Pacific Basin - page 7

Where multibeam bathymetric data are stored in the original vendor format,
bathymetry data were manually edited using the interactive graphical utility “mbedit”
module of the MB-System to remove bad beams. After identification of bad beams,
sound-velocity correlation was done if necessary. The depth recorded by any echo-
sounder is strongly dependent on the sound-velocity profile through the water column.
We reconstructed bathymetry directly from the travel-time data by full raytracing
through an appropriate water sound-velocity profile. If there are available data of
expendable bathythermograph or Conductivity-Temperature-Depth casts, sound-velocity
profiles in the water column were computed per cruise using the equation of Del Grosso
( 1974 ). If not available, temperature and salinity data from the 1982 Climatological
Atlas of the World Ocean (Levitus 1982 ) were used. Finally, a grid file was made,
whose interval is 300 m, using the “mbgrid” module of MB-system.
The accuracy of the widely used multibeam echo-sounder system in the cruises
for this study, SeaBeam 2112, is approximately 0.5% of water depth. The depth of
oceanward slopes has a range from 6,000 to 9,500 m. Thus, the accuracy of the
multibeam system is about 3-5 m. The horizontal resolution of the multibeam sys-
tem is about 2° × 2°. This indicates that the horizontal resolution in the study area
is about 210-330 m.

2.2 Geomagnetic Data

Geomagnetic data incorporated in this study were derived from several different
sources (Table 2 ). We used the same geomagnetic data as Nakanishi et al. ( 1989 )
in which magnetic anomaly lineations were identified in the northwestern
Pacific Ocean. After 1989, to investigate a pattern of lineations which had been

Table 2 Sources of geomagnetic data used for this study except for data supplied by JHOD that
are not included in the database of NOAA /NGDC

Number of
cruises Institution Cruise identification

ORI, UT 28 KH-67-1, KH-67-5, KH-68-3, KH-68-4A, KH-69-2,

KH-70-2, KH-74-2, KH-74-4, KH-75-3, KH-75-4,
KH-78-2, KH-78-3, KH-80-3, KH-82-4, KH-82-5,
KH-84-1, KH-88-3, KH-89-2, KH-96-3, KH-03-1,
KH-06-1, UM6402-A, UM6503-A, UM6402-C,
UM6503-B, UM66-A, UM67, DELP86KA

JAMSTEC 10 KR98-07, KR99-1, KR03-07, KR04-08, KR05-10,

KR06-03, KR07-06, KR08-10, YK05-06, YK08-09

JHOD 30 HM6703, HM6801, HM6802, HM6804, HM7002,

HM7003, HM7103, HM7104, HM7201, HM7807,
HM970824, HS000822, HS020810, HS7201,
HS7202, HS7502, HS7604, HS7703, HS7802,
HS7803, HS980906, HS981012, HS991013,
HT881203, HT91T253, HT91T260, HT92T261,
HT92T262, HT92T271, HT92T272

(continued)