Subsurface structure and faulting of the Median Tectonic Line, southwest Japan

日本西南部中部构造线的地下结构和断层活动

• 批准号: 10440129
• 负责人: TABEI Takao
• 金额: $ 6.02万
• 依托单位: Kochi University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B).
• 财政年份: 1998
• 资助国家: 日本
• 起止时间: 1998 至 2000
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-10440129/
• 关键词: Median Tectonic Line; GPS measurement; Crustal deformation; Fault lock and slip; Fault deep structure; 固着・すべり分布; 地殻変動モデリング

Main purpose of this study is to clarify deep structure and slip distribution of the Median Tectonic Line (MTL) in southwest Japan from dense GPS traverse measurements at the surface. We constructed 22 stations along a 220km-long line and conducted three campaign measurements in 1998-2000. We determined horizontal crustal velocities at 64 sites in total including adjacent continuous stations of the nationwide network. Campaign velocities obtained are so accurate as to show very good accordance to the velocities from continuous measurements.We quantitatively discriminated deformation field into two categories : elastic deformation caused by the subduction of the Philippine Sea plate and block-like movements across the MTL.We made both forward and inversion modelings. In the former we extracted block motion across the MTL, fault locking in the uppermost part and steady slip at depth by calculating elastic deformation from a plate subduction model and subtracting it from the observed velocity field In the latter we simultaneously estimated plate subduction, block motion across the MTL and slip deficit in the uppermost part of MTL.Two modelings gave the nearly same results :1. Southern block of the MTL moves westward at a rate of about 5mm/yr relative to the northern one, consistent to the geological right-lateral slip rate of 5-10mm/yr.2. The block boundary does not agree with the stuface trace of the MTL, clearly displaced 20-30km to the north.3. The above results are interpreted that the fault plane of MTL dips into the north at an angle of 30-40 degrees, and the uppermost part of MTL is locked to the depth of 15-20km and steady right-lateral slip occurs below. These results have been presented at several meetings in Japan and USA.The manuscript for the publication in the international journal is being prepared.

本研究的主要目的是通过地面密集的 GPS 导线测量来阐明日本西南部中位构造线 (MTL) 的深层结构和滑移分布。我们在 220 公里长的线路上修建了 22 个测站，并在 1998 年至 2000 年期间进行了 3 次测量活动。我们总共测定了 64 个站点的水平地壳速度，其中包括全国网络的相邻连续站。获得的运动速度非常准确，与连续测量的速度非常吻合。我们将变形场定量区分为两类：菲律宾海板块俯冲引起的弹性变形和穿过 MTL 的块状运动。正演和反演模型。在前者中，我们通过计算板块俯冲模型的弹性变形并将其从观测到的速度场中减去，提取了跨 MTL 的块体运动、最上部的断层锁定和深度的稳定滑动。在后者中，我们同时估计了板块俯冲、块体运动跨越 MTL 和 MTL 最上部的滑动赤字。两个模型给出了几乎相同的结果：1。 MTL 南部地块相对于北部地块以约 5 毫米/年的速度向西移动，与 5-10 毫米/年的地质右滑速率一致2。块体边界与MTL的断面轨迹不一致，明显向北偏移20-30km。3．上述结果解释为MTL断层面向北倾斜30~40°，MTL最上部锁定在15~20km深度，下方发生稳定的右旋滑移。这些结果已在日本和美国的多次会议上发表。在国际期刊上发表的手稿正在准备中。