Source mechanisms of subcrustal and upper mantle earthquakes around the northeastern Kyushu region, southwestern Japan, and their tectonic implications.

Imagawa, Kazuhiko; Hirahara, Kazuro; Mikumo, Takeshi

doi:10.4294/jpe1952.33.257

Cited by 10 publications

(1 citation statement)

References 12 publications

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“…The kink under northern Kyushu predicted in the present model is consistent with the observed slab geometry (Savage and Thatcher 1992;Imagawa et al 1985). Future works incorporating gravitational pulling to force the slab subduction instead of implementing the unrealistic boundary conditions used in the current study are under way to investigate how slab geometry responds to the membrane deformation constraints.…”

Section: Discussionsupporting

confidence: 80%

Strain segmentation and lateral membrane deformation rate of the subducted Ryukyu slab

Chiao

1993

Island Arc

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Focal mechanisms of intermediate‐depth earthquakes within the subducted Ryukyu slab indicate a systematic pattern of down‐dip extension in the northern part under Kyushu. These mechanisms switch rapidly around the Tokara channel to down‐dip compression in the southern part toward Taiwan. This intriguing pattern of strain segmentation, together with the differences between the slab geometry of the northern and southern parts, has raised the question of whether stress segmentation, as defined possibly by a tear fault, might exist in the slab. However the Ryukyu trench has a concave oceanward shape in the northern segment while it is convex in the southern oceanward part toward Taiwan. The inflection zone is located around the Tokara channel. The concept of Gaussian curvature of a curved surface suggests that the along‐arc variation of the geometric configuration of a subducted slab is related to the shape of the trench. This is in order to accommodate the lateral membrane deformation of the slab as the oceanic lithosphere subducts from a spherical shell to the geometry delineated by the Wadati‐Benioff zone. The membrane deformation regime of the subducted Ryukyu slab and its relation with the trench geometry was examined by assuming that the subduction be modelled by the flow field of a thin viscous sheet. A projection operator was utilized to compute the membrane strain‐rate tensor of an arbitrary non‐Euclidean surface. Numerical experiments indicated that the northern segment of the slab was dominated by lateral compression and down‐dip extension and the southern part by lateral extension and down‐dip compression. This transition is sharply located near the Tokara channel. These patterns were compatible with what had been observed from studies of focal mechanisms, suggesting that the strain segmentation might be controlled, at least in part, by the lateral membrane deformation within the slab due to the trench shape in this subduction zone. The slab geometry was predicted by minimizing the integrated total dissipation power; this revealed distinct features that were consistent with observations. This implies that the slab geometry may also be affected by the membrane deformation in a systematic fashion.

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Section: Discussionsupporting

confidence: 80%