Quaternary Crustal Movements along Nagamachi-Rifu Dislocation Line in the Vicinity of Sendai, Northeast Japan
Quaternary Crustal Movements along Nagamachi-Rifu Dislocation Line in the Vicinity of Sendai, Northeast Japan
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日本东北部仙台附近的长町利府位错线第四纪地壳运动
DOI：
10.5190/tga1948.28.111
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发表时间：
1976
期刊：
影响因子：
--
通讯作者：
T. Imaizumi
中科院分区：
文献类型：
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作者：
T. Nakata;K. Otsuki;T. Imaizumi
长町利府错位线沿东北-西南方向延伸，标志着东南部仙台沿海平原和西北丘陵地带的边界。沿着这条错位线，广濑川和名取川的阶地变形已被许多学者注意到。为了明确第四纪沿位错线的地壳运动特征，本文作者对上新世仙台群阶地的变形方式和结构进行了深入的研究。主要结果如下： 1）错位阶地，即。 e.青叶山梯田、大野原梯田、上町梯田、长町梯田、下町梯田按顺序排列，形成平行于错位线延伸10公里、宽1公里的高地带。在该区域的西北边缘，大年寺山断层（逆冲断层）位于形成猩红色或缓坡的位置，阶地沉积物经常在断层上移位。在东南边缘，与地下 Nagamachi-Rifu 断层相关的挠曲构造（被认为是逆冲断层）形成了明显的猩红色或陡坡，伴随着淹没在冲积层之下的翘曲阶地沉积物。 2）这些阶地在相同模式下以较老阶地更大的速度变形，并且该模式也与上新世仙台群一致。自青叶山台地III形成以来，大念寺山断层和长町利府线的平均垂直位移率分别为每年0.1+毫米和0.5毫米。该阶地相对于上新统大念寺地层最上部的变形率约为2～3.3）沿位错线的小断层多为逆冲断层，以倾滑成分为主，走向呈NE-SW向，与西侧1km的大念寺山断层和狮子内断层的特征相吻合。4）从仙台群脆性剪切断裂变形和地层厚度不变的变形情况来看。组中，沿着长町-利府线的地壳运动开始的时间可能是在第四纪，继上新世最上面的大年寺地层出现之后。5）由沿位错线的主要和次要断层的特征所阐明的最大压缩主应力轴位于NW-SE方向，并且与根据周边地区最近的大地震和微地震分析的震源机制推导出来的方向一致。6）这个最大应力方向模式也符合根据附近显着活动断层特征推断的应力场。历史上一些大地震沿这些断层发生，表明这些断层在同一应力场下仍然活动。因此可以说，第四纪时期，在西北-东南压应力场下，沿着长町-利府错位线发生了连续的、累积的地壳运动。
Nagamachi-Rifu Dislocation Line runs in the NE-SW direction marking the boundary between Sendai Coastal Plain in the southeast and hilly land in the northwest. Along this dislocation line, deformation of terraces of the Hirose and Natori rivers have been noticed by many scholars. The present writers have investigated intensively the mode of deformation of the terraces and structure of Pliocene Sendai group, in order to clarify characteristics of Quaternary crustal movements along the dislocation line.Main results are as follows:1) The dislcoated terraces, i. e. Aobayama, Dainohara, Uwamachi, Nagamachi and Shimomachi Terraces in descending order, form an elevated zone stretching parallel to the dislocation line for 10km with width of 1km. On the northwestern margin of the zone, Dainenjiyama Faults (thrusts) are located shaping scarplets or gentle slopes and terrace deposits are often displaced on the faults. On the southeastern margin, a flexure structure associated with subsurface Nagamachi-Rifu Fault, which is presumed to be a thrust, forms conspicuous scarplets or steep slopes accompanying warped terrace deposits which submerge below alluvium.2) These terraces are deformed with the greater rate on the older terrace in a same mode and the mode is also in harmony with that of Pliocene Sendai group. Average rates of vertical displacements on Dainenjiyama Faults and Nagamachi-Rifu Line are calculated to be 0.1+mm per year and 0.5mm per year respectively since formation of Aobayama Terrace III. Deformation rate of this terrace to that of uppermost Pliocene Dainenji bed is about 2 to 3.3) Most of minor faults along the dislocation line are thrusts chiefly with dip-slip components and their strikes appear in the NE-SW direction, which coincide with characteristics of Dainenjiyama Faults and Shishiochi Fault located 1km to the west.4) Judging from the deformation of Sendai Group with brittle shear fracture and unchangeable thickness of the group, commencement of crustal movements along Nagamachi-Rifu Line may be dated in Quaternary succeeding to the emergence of uppermost Pliocene Dainenji bed.5) Maximum compressive principal stress axis, which is elucidated by the characteristics of major and minor faults along the dislocation line, lies in the NW-SE direction and coincides with the direction deduced from focal mechanisms of recent major earthquakes and microearthquakes analysis in the surrounding area.6) This maximum stress direction pattern also concides with stress field inferred from characteristics of notable active faults in the vicinity. Some of historical great earthquakes have occurred along these faults indicating that these faults are still active under the same stress field.Therefore it can be said that during Quaternary period continuous and accumulative crustal movements have been taking place along Nagamachi-Rifu Dislcoation Line under the NW-SE compressive stress field.