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台湾岛是以欧亚大陆架为代表的大陆与以律菲海宾板块上吕宋弧的北延部分为代表的岛屿间几次活跃碰撞之一的产物。为了更好地了解这次碰撞的演变和现代构造,我们从由台湾遥测地震台网测定的一套50000个原始地震中选取了1260个记录完好的地震,来测定岛下一维和三维 P 波和 S 波速度结构。无论是速度结构还是地震位置重定的结果都表明,台湾岛在构造上分成三个不同的带。在东部,菲律宾海板块正在下冲于南北界线(它由地震活动和一个高波速区很好地限定)以东的欧亚板块下。在南部,欧亚大陆板块正在下冲于约23°N 的东西边界(它由壳下地震活动和一个低波速区清楚地限定)以南的菲律宾海板块下。俯冲大陆的倾角直到主岛以东50千米的吕宋岛弧为止,一直是较缓的。在23°N 以北的主岛主体部分下的波速结构揭示,在西部25千米深度之上的一条平缓倾斜的低速带在中央山脉之下至少50千米以下深度变窄和变陡。这低速带的倾角由一狭地震活动带显示出来,它伸到100千米深度。此地震带位于速度“鞍部”内,并标志24°N 处的中夹低速区内有一明显错断。因此,关于欧亚大陆俯冲于台湾之下的证据在岛各处都存在。地幔内的低速区证实(但不一定是必要的),约6—16千米的下部陆壳俯冲到了至少50千米的深度。23°N 处的速度结构和地震活动的明显变化及24°N 处的低速区的错断表明,跨这两个纬度的俯冲的性质有很大的变化。这种变化可能由吕宋弧同俯冲大陆架相互作用造成的,在地表它以一种明显的较小的相互关系呈现出来。最后,俯冲的菲律宾海板块的速度结构证实,70千米深度以下的地震没有出现于板块的高波速区,而可能位于板块上缘附近。还存在由地震位置和速度结构证实的俯冲板块分段内的证据,及俯冲作用明显存在于远至南面22°N 的证据。
The island of Taiwan is a product of one of several active clashes between the mainland represented by the Eurasian continental shelf and the islands represented by the northern extension of the Luzon arc on the Rubi Hai Bin plate. In order to better understand the evolution of the collision and the modern structure, we selected 1260 well-recorded earthquakes from a set of 50,000 original earthquakes measured by the Taiwan telemetric seismic network to measure the 1D and 3D P wave and S-wave velocity structure. Both the velocity structure and the repositioning of the earthquake show that the island of Taiwan is structurally divided into three distinct zones. In the east, the Philippine Sea Plate is subducting beneath the Eurasian plate east of the north-south boundary (well defined by seismic activity and a high-velocity zone). In the south, the Eurasian plate is subducting below the Philippine Sea plate south of the east-west boundary of about 23 ° N, which is clearly defined by the sub-seismogenic activity and a low velocity region. The subduction of the mainland until the arc of Luzon Island 50 kilometers east of the main island has been slow. The wave velocity structure below the main part of the main island north of 23 ° N reveals that a gently sloping low velocity zone 25 km above the west narrows and steeps below the Central Mountain Range at a depth of at least 50 km. The dip of this low velocity belt is shown by a narrow seismic belt that extends to a depth of 100 km. This seismic zone is located within the speed “saddle” and marks a clear fault in the mid-clamp low speed zone at 24 ° N. Therefore, evidence that the Eurasian continent has subdued under Taiwan exists everywhere on the island. The low-velocity zone within the mantle confirms (but is not necessarily required) that the lower continental crust of about 6-16 km has been subducted to a depth of at least 50 km. The pronounced change in velocity structure and seismicity at 23 ° N and the failure of the low velocity region at 24 ° N indicate that there is a large variation in the nature of subduction across these two latitudes. This change may be caused by the interaction of the Luzon arc with the subducted continental shelf, where it appears in a clearly smaller, interdependent relationship. Finally, the velocity structure of the subducted Philippine Sea plate confirms that earthquakes below the depth of 70 km do not appear in the plate’s high-velocity zone but may be located near the upper edge of the plate. There is evidence of subduction plate segments as evidenced by the location and velocity structures of the earthquakes and the evidence that subduction is evident at as much as 22 ° N to the south.