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Study on the Mantle-Upwelling Structure of Non Island-Arc Type West off Kyushu

九州西部非岛弧型地幔上涌构造研究

基本信息

批准号：
10304034
负责人：
SUZUKI Sadaomi
金额：
$ 19.33万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A).
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10304034/
关键词：
West off Kyushu Back-arc of Kyushu Crustal Strucuture Mantle-Upwelling Seismic Tomography Okinawa Trough Seismic Travel Time 地震トモグラフィー九州西方自身トモグラフィー

项目摘要

The Okinawa trough which is considered to be in an early stage of backarc spreading locates in the backarc region of Ryukyu-Kyushu arc. Understanding mechanism of backarc spreading and backarc volcanism of Kyushu, we conducted an explosion seismology in the northeastern Okinawa trough west off Kyushu by using ocean bottom seismographs (OBSs) in fall of 1999. Twenty OBSs were deployed at intervals of 15 km in the NNE-SSW seismic profile of 300 km in length along the trough center. We used airguns and 76 explosives as controlled sources. During shooting of the airguns, reflection waves were recorded by 24-ch hydrophone streamer towed from the shooting ship. An obtained seismic reflection profile shows large lateral heterogeneity in the upper crust in spite of smooth seafloor topography of the surveyed area. On the distance-time sections of OBSs, apparent velocities of first arrivals vary due to the heterogeneity. The sedimentary section consists of two layers. The upper sedimentary layer … More has a thickness of 200-500m with P-wave velocity (Vp) of 1.7 - 1.9 km/s. A vertical velocity gradient of the upper layer is small. The lower sedimentary layer has Vp of 2.0 - 3.5 km/s with relatively large vertical velocity gradient. The thickness of the lower layer has large variety from 800 m to 3500m. The upper crust has large lateral heterogeneity and is also divided into two layers. Vp at the top of the uper crust vary in 3.0 - 4.9 km/s. The lower layer of the upper crust has Vp of 5.6 - 6.0 km/s. The thickness of the upper crust changes from 3 km to 9 km. The boundary between the upper and lower crust is about 10 km in depth below the sea surface. The lower crust has Vp of 6.5 - 6.7 km/s. Compared with the upper crust, the lower crust is relatively homogeneous. A thickness of the lower crust is about 15 km. The crust has a thickness of about 25 km in total and the Pn velocity is estimated to be 7.7 -7.8 km/s. The distribution of Vp and the thickness of the crust indicated that the crust of the northeastern Okinawa trough is similar to that of island arc than to that of ocean. It is suggested from the obtained seismic structure that the northeastern Okinawa trough is in the incipient stage of the back-arc rifting. Less

冲绳海槽位于琉球-九州弧弧的弧后区域，被认为是弧后扩张的早期阶段。为了了解九州弧后扩张和弧后火山活动的机制，我们于1999年秋季利用海底地震仪(OBSS)在九州以西的冲绳海槽进行了爆炸地震。在沿海槽中心长300公里的NNE-SSW地震剖面上，以15公里的间隔布设了20个OBS。我们使用气枪和76枚炸药作为受控制的来源。在拍摄气枪的过程中，从拍摄船上拖来的24通道水听器流光记录下了反射波。获得的地震反射剖面显示，尽管调查区海底地形平坦，但上地壳的横向非均质性很大。在OBSS的距离-时间截面上，由于不均匀，初至波的视速度也不同。沉积段由两层组成。上沉积层…MORE厚度200-500m，P波速度(Vp)为1.70-1.9公里/S，上层垂直速度梯度小。下部沉积层Vp为2.0~3.5 km/S，垂向速度梯度较大。下层厚度变化较大，从800米到3500米不等。上地壳具有很大的横向非均质性，也分为两层。上地壳顶部Vp为3.0~4.9公里/S，下层Vp为5.6~6.0公里/S，上地壳厚度为3~9公里。上地壳和下地壳之间的边界在海平面以下约10公里深。下地壳的Vp为6.5-6.7公里/S，与上地壳相比，下地壳相对均匀。下地壳的厚度约为15公里。地壳总厚度约25公里，Pn速度估计为7.7-7.8公里/S。VP分布和地壳厚度表明，冲绳海槽东北部的地壳类似于岛弧地壳，而不是洋壳。从所获得的地震构造来看，冲绳海槽东北部处于弧后裂谷的初始阶段。较少