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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.

所罗门岛弧地区是一个复杂的板块辐合带。北侧是北所罗门海沟，太平洋板块在那里被吞噬。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在所罗门弧下俯冲。圣克里斯托瓦尔海沟在瓜达尔卡纳尔岛以西变得不那么显眼。板块俯冲带通常最好由地震资料来描述，即通过确定震源来确定俯冲板块的几何形状。然而，在像所罗门地区这样的复杂地区，除非假设该地区的构造活动，否则世界地震台网数据无法解决复杂性问题。每年在瓜达尔卡纳尔岛以西只确定不到10个项目。在震源确定中，获得高空间分辨率的唯一途径是进行高灵敏度的现场地震观测。我们在1993年改进了我们的数字海底地震仪（OBS），并在1994年8月28日至9月7日期间使用5台OBS对瓜达康纳尔西部进行了临时微地震活动观测。我们的初步结果表明：(1)地震可探测性比国际地震中心确定的高约200倍；(2)印度-澳大利亚板块俯冲约50公里，倾角惊人地大，约50度；(3)在双弧之间的小盆地中几乎没有地震活动；(4)60至90公里深的事件可能与太平洋板块俯冲有关。我们正在规划一个弧样带，以获得弧系的整个地壳结构，这将有助于将上述发现与构造和构造联系起来。