Marine geophysical study of the Solomon Arc convergent zone

所罗门弧汇聚带的海洋地球物理研究

基本信息

批准号：
05044041
负责人：
SUYEHIRO Kiyoshi
金额：
$ 5.76万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for international Scientific Research
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1994
项目状态：
已结题

项目摘要

The Solomon island arc area is a complex plate convergence zone. On the northern side is the North Solomon Trench at which the Pacific plate is being consumed. Another trench on the southern side is the San Cristobal Trench, where the Indo-Australian plate and the Solomon Sea plate seem to be subducting beneath the Solomon arc. The San Cristobal Trench becomes less conspicuous west of Guadalcanal.A plate subduction zone is usually best described by the seismic data, that is by the determination of hypocenters that define the geometry of the subducting slab. However, in a complex region like the Solomon area, the worldwide seismic network dataset is unable to resolve the complexity unless one assumes the tectonics operating in the region. Only less than 10 events are determined each year west of Guadalcanal.The only way to obtain high spatial resolution in hypocenter determination is to conduct an on-site seismic observation with very high sensitivity. We have improved our digital ocean bottom seismograph (OBS) in 1993 and made a temporary microseismicity observation west of Guadalcanal using 5 OBS's for the period of Aug.28 through Sep.7 in 1994.Our preliminary results indicate (1) about 200 times higher seismic detectability compared to the International Seismological Center determinations, (2) subduction of the Indo-Australian plate to about 50 km with a surprisingly large dip angle of about 50 degrees, (3) almost no seismicity in the small basin between the double arc, (4) 60 to 90 km deep events probably associated with the Pacific plate subduction.We are planning an arc transect to obtain the whole crustal structure of the arc system, which will help to link the above findings with the structure and tectonics.

所罗门岛弧区是一个复杂的板块汇聚带。北侧是北所罗门海沟，太平洋板块在此被吞噬。南侧的另一个海沟是圣克里斯托瓦尔海沟，印度-澳大利亚板块和所罗门海板块似乎正在此处俯冲到所罗门弧之下。圣克里斯托瓦尔海沟在瓜达尔卡纳尔岛以西变得不那么明显。板块俯冲带通常最好通过地震数据来描述，即通过确定定义俯冲板片几何形状的震源来描述。然而，在所罗门地区这样的复杂地区，除非假设该地区的构造运动，否则全球地震台网数据集无法解决其复杂性。瓜达尔卡纳尔岛以西每年仅确定不到 10 起事件。在震源确定中获得高空间分辨率的唯一方法是进行具有非常高灵敏度的现场地震观测。我们于1993年改进了我们的数字海底地震仪（OBS），并于1994年8月28日至9月7日期间使用5个OBS对瓜达尔卡纳尔岛以西进行了临时微震观测。我们的初步结果表明（1）约高出200倍与国际地震中心测定结果相比的地震可探测性，(2) 印度-澳大利亚板块俯冲至约 50 公里，倾角大得惊人角度约为50度，（3）双弧之间的小盆地几乎没有地震活动，（4）60至90公里深的事件可能与太平洋板块俯冲有关。我们正在规划弧横断面以获得整个地壳结构弧系统的研究，这将有助于将上述发现与结构和构造联系起来。