Shape of the Wadati-Benioff Zone beneath Kyushu, Japan

Nagamune, Tomeo; Tashiro, Hironori

doi:10.4294/zisin1948.42.1_13

Cited by 5 publications

(4 citation statements)

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“…1 (Yamazaki and Ooida, 1985;Nagamune and Tashiro, 1989;Kakuta et al, 1991;Ishihara and Yoshida, 1992). Moreover, the southern Kyushu district is remarkable for other characteristic tectonic features.…”

Section: Introductionmentioning

confidence: 99%

Resistivity structure of high-angle subduction zone in the southern Kyushu district, southwestern Japan

2014

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Magnetotelluric observations were carried out in the southern Kyushu district of southwestern Japan to investigate the characteristics of the electrical resistivity structure of a high-angle subduction zone. We constructed a 2-D resistivity model parallel to the subducting plate motion by using the inversion technique with the Akaike Bayesian Information Criterion (ABIC) smoothness constraint. The general features of the obtained resistivity structure are as follows: (1) a conductive block (below 1 ·m) is found beneath the volcanic zone and is widespread bilaterally below 40 km depth, (2) a resistive block (about 1000 ·m) distributes from 10 to 25 km depth in the forearc region and (3) a conductor (1 ∼ 30 ·m) is embedded beneath the resistive block, which may correspond to the negative Bouguer gravity anomaly observed in this region. We propose the following for the high-angle subduction zone: A serpentinized block is generated in the lower crust of the forearc region and a partial melting and hydrothermal fluid are well developed beneath the volcanic front.

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Section: Introductionmentioning

confidence: 99%

Resistivity structure of high-angle subduction zone in the southern Kyushu district, southwestern Japan

2014

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“…North of the Tokala Strait, the curvature is significant at depths of 70-100 km and the dip angle is about 60-70 • . In the southern part of the Tukala Strait, the dip angle of the subduction zone is about 50 • at depths greater than 100 km [12,17]. The cross-sections of the 10 different segments of the Ryukyu Islands subduction zone created in this study (Figure 3) extend through the Ryukyu Trench and the Ryukyu Island Arc from east to northwest and into the Okinawa Trough back-arc basin.…”

Section: Focal Depth Distributionmentioning

confidence: 76%

“…Several studies have revealed that the maximum depth of seismicity in Kyushu, Japan, is 200 km, while it is about 270 km in the central and southern parts of the island arc [12,[16][17][18]. According to these studies, the subduction zone has a shallow dip angle of about 30 • .…”

Section: Focal Depth Distributionmentioning

confidence: 99%

Seismicity and Stress State in the Ryukyu Islands Subduction Zone

2022

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Based on the newly compiled and mostly complete unified earthquake catalogue for China’s seas and adjacent areas, further information was obtained about the structural shape and dip angle of the Benioff zone in the Ryukyu Islands subduction zone during the different subduction stages. In addition, using the damped regional stress tensor inversion method, we were able to investigate the complex stress field characteristics and the dynamic significance of the shallow and intermediate earthquakes in the Ryukyu Islands subduction zone. The results show that the tectonic stress field of the Ryukyu Islands subduction zone was extensional along the subduction direction in the northern area of the Tokara Strait and was compressional along the subduction direction in the southern area of the Tokara Strait. The R value of the shallow stress field of the Okinawa Trough was low, and the σ3 was stable in the NNW direction with a small dip angle (>30°). The type of stress field in the shallow part of the Okinawa Trough transitioned from strike-slip type to normal fault type from north to south, reflecting the difference in the degree of development of the trough, and the southern segment of the trough began to transform into the expansion stage. The northeastern portion of the study area and southeast Taiwan constituted the high R value (0.68–0.87) region where the σ2 had tensile components. The stress state was biaxial tension–uniaxial compression, and the principal compressive stress was determined to be in the SEE direction with a large dip angle (>30°). The σ1 in northeast Taiwan exhibited a nearly vertical (>60°) plunge, while the σ2 and σ3 were nearly horizontal. The σ2 was thrust in the ENE–WSW direction, and the σ3 was extended in the NNW direction. Through this research, a greater understanding has been gained of the seismicity characteristics and shape of the Ryukyu Islands subduction zone. Supplementary research has also been completed on the focal mechanism solution and stress field of the Ryukyu Islands subduction zone. Finally, this research is important for earthquake hazard analysis and earthquake engineering safety evaluation in this area.

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“…(1) The leading edge of the Wadatibeneath the Hikosan and Nagasaki areas (Nagamune and Tashiro, 1989). (2) The oldest reported K -Ar age of the backarc HMA is 8.3 Ma (Tatsumi et al, 1980).…”

Section: The Relationship Between Hma Magma-tism and Tectonics In Normentioning

confidence: 99%

K-Ar ages of high-magnesian andesite lavas from northern Kyushu, Japan

Miyoshi¹,

Nasu²,

Tajima³

et al. 2008

Journal of Mineralogical and Petrological Sciences

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We determined the K -Ar ages for the high -magnesian andesites from Miocene -Pliocene period from Hikosan and Nagasaki areas in northern Kyushu, Japan. The obtained K -Ar ages of Hikosan and Nagasaki samples are 4.0 -3.6 Ma and 5.8 -3.7 Ma, respectively. These K -Ar ages suggest that the magmatisms of the high -magnesian andesites coincided with the development of the Okinawa Trough. The upwelling of the hot asthenospheric mantle associated with the backarc rifting probably has a close relationship with the origin of the northern -Kyushu high -magnesian andesite magma.

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Shape of the Wadati-Benioff Zone beneath Kyushu, Japan

Cited by 5 publications

References 0 publications

Resistivity structure of high-angle subduction zone in the southern Kyushu district, southwestern Japan

Resistivity structure of high-angle subduction zone in the southern Kyushu district, southwestern Japan

Seismicity and Stress State in the Ryukyu Islands Subduction Zone

K-Ar ages of high-magnesian andesite lavas from northern Kyushu, Japan

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