日本九州俯冲带b值成像及其构造意义 *

doi:10.11978/2020031

Abstract

Abstract:

The Kyushu subduction zone is a unique region on the convergent boundary between the Philippine Sea Plate and Eurasian Plate. The zone is an ideal place to study plate interaction within the subduction zone. To understand the stress state and interaction characteristics between plates in the subduction zone in this region, we use 97251 earthquake events beneath 20-km depth in the region to delineate the upper surface of the subduction plate and the section of the vertical trench direction by detailing b-value. We found that the b-value in this area has significant spatial variation, which gradually increases from the northeast to the southwest along the Nankai Trough and Ryukyu Trench. There is also a significant low b-value zone on the subducted Kyushu-Palau Ridge. It is inferred from the negative correlation between the b-value and stress that the ridge has entered the subduction zone, and that the Shikoku Basin ocean crust on the northeast side of the ridge is strongly coupled with the overlying slab of the subduction zone, while the coupling effect of the convergent plates in the subduction zone on the southwest side of the ridge is relatively weak. We believe that the formation times and convergence rates of subduction ocean crusts on both sides of the Kyushu-Palau Ridge played important roles. For the Kyushu-Palau Ridge, the low b-value zone in the shallow part of the subduction zone is mainly due to enhanced coupling between the towering ridge and overlying plate. With the increase of the subduction depth and the steepening of the inclination of the subducting plate, a plate tear along the ridge may occur, thereby releasing the compression-shear stress between the ridge and overlying plate, and causing the degree of coupling to be greatly weakened.

Key words: Kyushu subduction zone, b-value, plate interaction, ridge subduction

CLC Number:

P736.14

LI Yunjie, ZHOU Pengxiang, XIA Shaohong, WAN Kuiyuan, SUN Jinlong. The b-value mapping in the Kyushu subduction zone and its tectonic significance[J].Journal of Tropical Oceanography, 2021, 40(1): 122-132.

Figures/Tables 9

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	海脊东北侧	海脊西南侧
地震b值	0.71	0.76
板块年龄	≤26Ma	115~37Ma
板块俯冲倾角	较缓	较陡
板块俯冲速度	3.8~5.5cm·a^-1	约2cm·a^-1
板块俯冲方向	北西向	西向
板块滑差率	5~6cm·a^-1	<5cm·a^-1
海底热流值	120~200mW·m^-2	40~80mW·m^-2
俯冲板间联结程度	较强	较弱

The b-value mapping in the Kyushu subduction zone and its tectonic significance

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