ACTIVE FAULTS IN WESTERN AND SOUTHERN MARGINS OF THE KRFU BASIN, CENTRAL JAPAN
ACTIVE FAULTS IN WESTERN AND SOUTHERN MARGINS OF THE KRFU BASIN, CENTRAL JAPAN
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日本中部 KRFU 盆地西缘和南缘的活动断层
DOI：
10.4157/grj.54.473
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发表时间：
1981
期刊：
影响因子：
--
通讯作者：
H. Sawa
中科院分区：
文献类型：
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作者：
H. Sawa
作者调查了甲府盆地西部和南部边缘的地形和地质，以便根据变形地貌考虑这些地区晚第四纪活动断层的特征。横径约20公里的甲府盆地是日本中部的构造盆地之一，由高度不到500米的一系列解剖扇组成（图1）。在盆地的西部（一之濑高地）和南部（骨山）边缘，解剖扇非常发育，并分为几个台阶。作为阶地划分的时间标志，Pm-Ⅰ是一个广泛分布的浮岩层（约100 μ m）。8万美元。B。P.，町田和铃木，1971年），这是爆发的Ontake火山，和Nirasaki泥流沉积物（约。三十万。B。第页）使用了从八岳火山喷发的火山灰（表1）。在一之濑高地，地貌表面分为五个级别，从高到低依次为高级阶地、Ia、Ib、II和III表面（图3）。在Sone Hill中，它们被分为六个级别（Ia、Ib、II、IIIa、IIIb和IV表面，按降序排列），如图5所示。表1显示了这两个地区梯田的相关性。在甲府盆地，特别是在一之濑高地和曾根山两个地区，观察到许多活动断层使这些地貌面发生位移（图1A和1B）。1、3和5）。甲府盆地的活动断层为倾滑断层，不含走滑分量。它们大多分布在高地和丘陵的边缘。变形表面和阶地沉积物的详细特征在地图和横截面中说明（图1和图2）。6 - 13）。所有活动断层均表现为断层崖、陡坎和挠曲崖，其中大部分估计为逆断层或逆冲断层。翘曲阶地面和向山区的反向倾斜是这些地区变形地貌的典型类型。表2列出了这些地区活断层的断裂速率。由于较老的阶地通常比较年轻的阶地变形更大，因此表明在第四纪晚期存在渐进断层作用。经计算，平均垂直位移率为0.3一之濑高地为1.4m/1000年，曾根山为0.6m/1000年以下。值得注意的是，主要的活动断层位于远离皮埃蒙特线的阶地外缘，无论是在一之濑高地还是曾根山，尽管在一之濑高地的皮埃蒙特沿线可以观察到一些断层崖。由于活动断层的这种排列，最古老的反倾阶地位于现代冲积扇附近，其顶点区域通常被较年轻的阶地覆盖。断层地形的上述特征可以用“断层面弯曲模型”（池田和米仓，1979年）来解释（图14）。在Sone Hill中，可以应用该模型（图15-C）。但是，在一之濑高地，设计了另一种模型，因为皮埃蒙特地区的活动断层并不是不活动的（图2）。15-A、B）。
The author investigated topography and geology in western and southern margins of the Kofu Basin, in order to consider a characteristic of active faults through late Quaternary in these areas, on the basis of deformed landforms. The Kofu Basin, about 20km accross, is one of the tectonic basins in Central Japan, and consists of a flight of dissected fans in the area less than 500 m high (Fig. 1). In the western (Ichinose Upland) and the southern (Bone Hill) margins of the basin, dissected fans are well developed and classified into several steps. As a time marker tephra for the classification of terraces, Pm-I, one of widely distributed pumice layer (ca. 80, 000 y. B. P., Machida and Suzuki, 1971) which was erupted from Ontake Volcano, and Nirasaki mud flow deposits (ca. 300, 000y. B. P.) which were erupted from Yatsugatake Volcano, were used (Table 1). In the Ichinose Upland, geomorphic surfaces are classified into five levels, Higher terraces, Ia, Ib, II and III surfaces in descending order (Fig. 3). In the Sone Hill, they are classified into six levels (Ia, Ib, II, IIIa, IIIb and IV surfaces in descending order) as shown in Fig. 5. Table 1 shows correlation of terraces in both areas. Many active faults which displace these geomorphic surfaces are observed in the Kofu Basin, especially in the both areas of the Ichinose Upland and Sone Hill (Figs. 1, 3 and 5). Active faults of the Kofu Basin are dip slip faults without strike slip component. Most of them are distributed in margins of the Upland and the Hill. Detailed features of deformed surfaces and terrace deposits are illustrated in the maps and cross sections (Figs. 6-13). All the active faults are expressed as fault scarps, scarplets and flexure scarps, and most of them are estimated to be reverse faults or thrust faults. Warped terrace surfaces and reverse tilting towards mountain area are the typical types of deformed landforms in these areas. Rate of faulting of active faults in these areas are listed in Table 2. Since older terraces are usually much more deformed than the younger ones, progressive faulting in the late Quaternary is indicated. Average rate of vertical displacement is calculated to be 0.3_??_1.4m/1, 000 yrs. for the Ichinose Upland and less than 0.6m/1, 000 yrs. for the Sone Hill. It is interesting to note that major active faults are located at the outer margins of terraces far away from the piedmont lines themselves, both in the Ichinose Upland and Sone Hill, although some fault scarplets can be observed along the piedmont in the Ichinose Upland. Due to such arrangement of the active faults, the oldest terraces with reverse tilting are located immediately adjacent to the modern alluvial fans, and their apex area are often covered with the younger terraces. Above-mentioned characteristics of fault topographies may be explained by “a bending model of fault plane” (Ikeda and Yonekura, 1979) (Fig. 14). In the Sone Hill, this model can be applied (Fig. 15-C). But, in the Ichinose Upland, another models are devised because active faults in piedmont area were not inactive (Figs. 15-A, B).