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 34

Table 3 Orientations of bending-related structures, trench axes, and magnetic anomaly lineations
and types of graben

Mode of strike
of topographic
features

Magnetic
anomaly
lineation Trench Trench axis Types of graben

Kuril N65-70°E N65°E N70°E A or H

Japan N15-20°E N10°E N70°E A, H, or S

39°20¢-41°00¢N
Japan N10-15°E N00°E N70°E A or S

38°00¢-39°20¢N
Japan

N55-60°E N20-35°E N50-65°E A or H

35°40¢-38°00¢N
Izu-Ogasawara

N15-20°E N20°E N70°E A, H, or S

35°11¢-35°40¢N
Izu-Ogasawara N20-25°W N-S N70°E A, H, or S

33°36¢-35°11¢N
Izu-Ogasawara N05-10°W N10°W N70°E A, H, or S

33°05¢-33°36¢N
Izu-Ogasawara N00-05°E N-S N70°E A, H, or S

32°00¢-33°05¢N
A asymmetric graben, H half graben, S symmetric graben

Between 38°N and the Joban Seamounts (Fig. 23d ), N50-65°E trending structures
are predominant. The direction is close to the strike of the magnetic anomaly linea-
tions, which strike is N50-65°E. Ranero et al. ( 2005 ) mapped bending-related
structures roughly parallel to Juan Fernandez Ridge along the Chile Trench off-
shore of Valparaiso, Chile. The trend of Joban Seamounts is N50°E, which is not
parallel to any hotspot tracks on the Pacific plate. Thus, it is reasonable that the
NE-SW trending bending-related topographic structures were form by reactivation
of the abyssal hill fabric and that the Joban Seamounts were formed along a crustal
structure parallel to the abyssal hill fabrics.
Bending-related structures in the northern Izu-Ogasawara Trench have two dis-
tinguishable strikes (Fig. 23e-h ). One has the same direction of the trench axis. The
other strikes N20°W that is perpendicular to abyssal hill fabrics and dominant
between 33°36¢N and 35°11¢N (Fig. 23f ). Seta et al. ( 1991 ) mapped the elongated
escarpments with the similar strike in the southern Izu-Ogasawara Trench and con-
cluded that the escarpments were formed by reactivation of weak zones, for
instance fracture zones, perpendicular to abyssal hill fabrics. This striking also sup-
ports the formation of the bending-related structures with an N20°W strike results
from reactivation of weak zones perpendicular to abyssal hill fabrics.
Elongated topographic structures with an NE-SW strike are also dominant in the
northern Izu-Ogasawara Trench west of Kashima Fracture Zone (Fig. 23e, f ). Some
of the structures were formed by propagation of a spreading ridge and are not
related to plate bending. The abandoned propagating spreading ridge is situated
north of Lineation M8 (Fig. 19 ). No magnetic anomaly lineations younger than