Gently north-dipping Median Tectonic Line (MTL) revealed by recent seismic reflection studies, southwest Japan
Gently north-dipping Median Tectonic Line (MTL) revealed by recent seismic reflection studies, southwest Japan
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最近的地震反射研究揭示了日本西南部的中位构造线（MTL）轻轻向北倾斜
DOI：
10.1016/s0040-1951(96)00117-5
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发表时间：
1996
期刊：
影响因子：
2.9
通讯作者：
T. Maeda
中科院分区：
文献类型：
--
作者：
T. Ito;T. Ikawa;S. Yamakita;T. Maeda
中央构造线（MTL），长度超过1000公里，是日本最重要的断层。它将高P/T的Sambagawa变质岩与Ryoke带的低P/T变质岩并列。MTL可能形成于白垩纪，随后多次活化。MTL的西段仍然活跃，几乎是纯右侧运动感。虽然已积累了大量的MTL的地质信息，但关于MTL的地下，特别是深部结构的信息仍然不足。一般认为，MTL是垂直的或在深度上急剧倾斜，因为它的直表面轨迹和最近的横向运动。最近，新的地球物理数据表明，MTL在深度上向北倾斜。我们已经获得了一套补充的地球物理剖面（地震反射和折射，重力和MT）在东四国MTL。我们的研究结果证实，MTL向北倾斜约30至40度，从表面到约5公里的深度，在那里它成为铲形。这种断层几何形状更合理地解释了MTL的再活化历史：运动发生在所谓的斜向或侧向斜坡方式的Listric型断层上。
The Median Tectonic Line (MTL), with a length of more 1000 km, is the most significant fault in Japan. It juxtaposes the high-P/T Sambagawa metamorphic rocks against the low-P/T metamorphic rocks of the Ryoke belt. The MTL was probably formed in the Cretaceous with many subsequent reactivations. The western segment of the MTL is still active with an almost pure right-lateral sense of motion. Although a great amount of geological information on the MTL has been accumulated, information about the subsurface, especially the deep-seated structure of the MTL, is still insufficient. It has been generally assumed that the MTL is vertical or steeply dipping at depth because of its straight surface trace and its recent lateral motion. Recently, new geophysical data have suggested that the MTL dips gently northward at depth. We have acquired a complementary set of geophysical profiles (seismic reflection and refraction, gravity and MT) across the MTL in east Shikoku. Our results confirm that the MTL dips northward at about 30 to 40 degrees from the surface to about 5 km depth, where it becomes listric. This fault geometry more reasonably explains the reactivation history of the MTL: the motion has occurred on a listric-type fault in so-called oblique or lateral ramp manner.