Resistivity mapping using the VLF‐MT method around surface fault ruptures of the 1995 Hyogo‐ken Nanbu earthquake, Japan
Resistivity mapping using the VLF‐MT method around surface fault ruptures of the 1995 Hyogo‐ken Nanbu earthquake, Japan
复制标题
使用 VLF-MT 方法绘制 1995 年日本兵库县南部地震地表断层破裂周围的电阻率测绘
DOI：
10.1111/j.1440-1738.2001.00328.x
复制
发表时间：
2001
期刊：
影响因子：
1.5
通讯作者：
H. Inokuchi
中科院分区：
文献类型：
--
作者：
S. Yamaguchi;T. Murakami;H. Inokuchi
摘要 1995年兵库县南部地震（神户地震）时，淡路岛西北海岸出现了野岛断层和小仓断层等独特的断层破裂。为了描绘断层刚形成后周围的浅层电阻率结构，在野岛断层沿线的 5 个地点和小仓断层沿线的 1 个地点进行了甚低频大地电磁 (VLF-MT) 勘测。在小仓断层的一个地点制作了十四条横断面，另一条横断面覆盖了两个断层之间的区域。当穿过其中一个断层的表面位置时，视电阻率或相位或两者都会发生变化，但小仓断层 OGR-0 处的北部横断面除外。第三纪和第四纪沉积物的视电阻率值小于 100 Ωm，花岗岩的视电阻率值大于 200 Ωm。电阻率结构与断层破裂的形态特征有关。发现了显着的导电带（视电阻率小于 10 Ωm，宽度为 30-40 m），其中沿单个断层面的地表位移明显且突出。如果在 1995 年兵库县南部地震时形成了显着的导电区，则结果对一次地震造成的地表附近导电区的尺寸提供了良好的约束。或者，如果地震前存在特征电阻率结构，则导电区可能是由相对现代的数十次地震形成的。在这种情况下，这种现象被推断为狭窄区域中的集中压裂，并且与粘土矿物的形成有关，粘土矿物增强了岩石的导电性。
Abstract Distinctive fault ruptures, the Nojima Fault and Ogura Fault, appeared along the northwestern coast of Awaji Island at the time of the 1995 Hyogo‐ken Nanbu earthquake (Kobe earthquake). In order to delineate the shallow resistivity structures around the faults just after they formed, Very Low Frequency Magnetotelluric (VLF‐MT) surveys were made at five sites along the Nojima Fault and at one site along the Ogura Fault. Fourteen transects were made at the one site on the Ogura Fault, and another transect covers the area between the two faults. Changes in apparent resistivity or phase, or both, commonly occur when crossing the surface location of one of the faults, except for the northern transects at OGR‐0 on the Ogura Fault. Apparent resistivity values of less than 100 Ωm were observed for Tertiary and Quaternary sediments and values larger than 200 Ωm for granitic rocks. The resistivity structures are related to the morphological characteristics of the fault ruptures. Remarkably conductive zones (less than 10 Ωm in apparent resistivity and 30–40 m in width) were found where the surface displacement is distinct and prominent along a single fault plane. If remarkably conductive zones were formed at the time of the 1995 Hyogo‐ken Nanbu earthquake, the results provide a good constraint on the dimensions of a conductive zone near the surface that was made by one earthquake. Alternatively, if characteristic resistivity structures existed prior to the earthquake, the conductive zone was probably formed by some tens of earthquakes in relatively modern times. In this case, this phenomenon is inferred to be a concentration of fracturing in a narrow zone and is associated with the formation of clay minerals, which enhance rock conductivity.