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台湾岛是欧亚大陆架和属菲律宾海板块的吕宋岛弧向北延伸形成的弧形列岛间少有的活动碰撞产物。为了更好地认识这个碰撞的演化和近代构造,我们从台湾遥测地震台网记录的50000个原始记录中挑选了1260个好的地震记录,用于决定该岛下的一维和三维P与S波速度结构。速度结构和地震再定位的结果指出,该岛在构造上分为三个不同的地带。在东部,菲律宾海板块正俯冲于欧亚板块的东部,其北西向边界由地震活动和高速度区圈定。在南部,欧亚大陆板块正俯冲于菲律宾海板块,在大约23°N的东西向边界的南端,它可由壳下地震活动性和相当低的速度区很好地圈定。消减大陆的倾角很小,在吕宋岛弧东边,距主要岛屿50 km内都是这样。在该岛23°N以北的主要部分的结构指出,中央山脉的西部25 km的深度以上有一低速度缓倾带,而在那个深度以下,至少到50 km,呈现窄而陡的倾斜。由窄地震活动带勾画出该低速区的倾向,并延伸到100 km。这个地震带处于速度的鞍部,在24°N的中部低速区呈现明显的断错。因而,欧亚大陆消减带在台湾的证据在该岛下处处存在,地幔低速区证实,但未必需要,在大陆下地壳约6—16 km的消减带至少已达50 km的深度。在23°N速度结构和地震活动性的明显变化及在24°N低速范围的水平断错表明,在通过这些纬度时,消减带特性有突然变化。这些变化可以是吕宋岛弧和消减大陆架相互作用引起,它类似于表面的相互影响。最后,消减的菲律宾海板块的速度结构指出,在70 km深度以下,地震不在板块的高速区内发生,但有可能处于板块的上缘附近。地震位置和速度结构也指出,消减板块是分段的,而且消减作用当今正在22°N的南部发生。
Taiwan Island is a rare collision event between the Eurasian continental shelf and the arc-shaped archipelago extending northward from the Luzon arc of the Philippine Sea plate. To better understand the evolution of this collision and its modern structure, we selected 1260 good seismograms from the 50,000 records recorded by Taiwan’s Telemetered Seismostation to determine the one-dimensional and three-dimensional P and S waves of the island Speed structure. The results of velocity structure and seismic relocation indicate that the island is structurally divided into three distinct zones. In the east, the Philippine Sea Plate is subducting east of the Eurasian Plate and its north-western boundary is delineated by seismic activity and high-velocity zones. In the south, the Eurasian plate is subducting over the Philippine Sea plate at the southernmost east-west boundary of about 23 ° N, which can be well delineated by the sub-seismogenic and rather low velocity zones. The subduction of the continent is very small and to the east of the Luzon arc, within 50 km of the main island. The structure of the main part of the island north of 23 ° N indicates that there is a slow slow dip above the depth of 25 km west of the central mountain range and below that depth at least 50 km with a narrow and steep slope. The narrow seismic zone delineates the low-velocity zone and extends to 100 km. This seismic zone lies at the speed of the saddle and presents a clear fault at the central 24 ° N low velocity zone. As a result, evidence of the Eurasia depletion belt in Taiwan is present everywhere under the island, as evidenced by the low mantle velocity zone but not necessarily required that the abatement zone of about 6-16 km below the continental crust has reached at least 50 km depth. Significant changes in velocity structure and seismicity at 23 ° N and horizontal faults at a low range of 24 ° N indicate a sudden change in the attenuation band characteristics across these latitudes. These changes can be caused by the interaction of the Luzon arc with the descending continental shelf, which is similar to the surface interaction. Finally, the reduced velocity structure of the Philippine Sea Plate indicates that below 70 km depth, earthquakes do not occur in the plate’s high velocity zone, but are likely to be near the upper edge of the plate. The earthquake location and velocity structure also pointed out that the abatement plate is segmented and the abatement is occurring in the south at 22 ° N today.