Seismological features of island arc crust as inferred from recent seismic expeditions in Japan
Seismological features of island arc crust as inferred from recent seismic expeditions in Japan
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DOI：
10.1016/s0040-1951(02)00134-8
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发表时间：
2002-09
期刊：
影响因子：
2.9
通讯作者：
T. Iwasaki;T. Yoshii;T. Ito;Hiroshi P. Sato;N. Hirata
中科院分区：
文献类型：
--
作者：
T. Iwasaki;T. Yoshii;T. Ito;Hiroshi P. Sato;N. Hirata
日本列岛的地壳研究对岛弧地壳的物理性质和变形方式提供了重要的制约。日本列岛的上地壳具有明显的不均匀性，其特点是速度变化大（5.5-6.1 km/s）和地震衰减高（5-15 Hz的Qp=100-400）。在主要构造线上有时会出现横向速度变化。在最近的折射/广角反射剖面图的许多情况下，在5-15公里的深度范围内发现速度为6.2-6.5公里/秒的“中地壳”。浅源微地震多集中在中上地壳。下地壳的速度估计为6.6-7.0 km/s。下地壳通常包含一个地震活动较少的高反射带，表明其具有韧性流变性。上地幔Pn速度较低，为7.5- 7.9km/s。PmP相位的几个观测结果表明，莫霍面不是一个具有明显速度对比的尖锐边界，而是形成了上地幔到下地壳的过渡带。最近的地震反射实验显示，日本岛屿内的地壳正在变形。在北海道中部的一个弧-弧碰撞带中获得了一幅清晰的地壳拆沉图象，为岛弧向长英质陆壳演化过程提供了重要的线索。在本州北方，中新世弧后扩张形成的铲状断层系统被成功地测绘到12-15 km。
Crustal studies within the Japanese islands have provided important constraints on the physical properties and deformation styles of the island arc crust. The upper crust in the Japanese islands has a significant heterogeneity characterized by large velocity variation (5.5–6.1 km/s) and high seismic attenuation (Qp=100–400 for 5–15 Hz). The lateral velocity change sometimes occurs at major tectonic lines. In many cases of recent refraction/wide-angle reflection profiles, a “middle crust” with a velocity of 6.2–6.5 km/s is found in a depth range of 5–15 km. Most shallow microearthquakes are concentrated in the upper/middle crust. The velocity in the lower crust is estimated to be 6.6–7.0 km/s. The lower crust often involves a highly reflective zone with less seismicity, indicating its ductile rheology. The uppermost mantle is characterized by a low Pn velocity of 7.5–7.9 km/s. Several observations on PmP phase indicate that the Moho is not a sharp boundary with a distinct velocity contrast, but forms a transition zone from the upper mantle to the lower crust. Recent seismic reflection experiments revealed ongoing crustal deformations within the Japanese islands. A clear image of crustal delamination obtained for an arc–arc collision zone in central Hokkaido provides an important key for the evolution process from island arc to more felsic continental crust. In northern Honshu, a major fault system with listric geometry, which was formed by Miocene back arc spreading, was successfully mapped down to 12–15 km.