ESR & OSL analyses of seismic frictional heating events recorded in fault gouge and their application to deep drill core samples

血沉

基本信息

批准号：
13640462
负责人：
FUKUCHI Tatsuro
金额：
$ 0.32万
依托单位：
Yamaguchi University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640462/
关键词：
FSR OSL fault frictional heat fault gouge pseudotachylyte ferrimagnetism FMR 活断層強磁性共鳴

项目摘要

We examine the Nojima pseudotachylyte found along the Nojima fault, which caused the 1995 Kobe Earthquake (M=7.2) in Japan, using the electron spin resonance technique. The Nojima pseudotachylyte has a strong FMR (ferrimagnetic resonance) signal derived from bulky trivalent iron ions in ferrimagnetic iron oxides (a^^~-Fe_2O_3: maghemite). This FMR signal appears by heating the surrounding fault gouge that is the source material of the Nojima pseudotachylyte. Furthermore, the magnetic susceptibilities of the Nojima pseudotachylyte are 10^2〜10^3 times larger than those of the surrounding fault gouge and are proportional to the FMR signal intensities. We reconstructed the magnetization process of fault gouge during ancient seismic fault slip using the FMR signal. As a result, the maximum instantaneous magnetization of the Nojima fault gouge may have reached about 10-20nT and may have further induced a maximum geoelectric potential change of about 120mV/km^2 by electromagnetic induction. F … More urthermore, we carried out high-speed shearing tests using the dry fault gouge. As a result, we have found that the frictional heat temperature in a dry fault gouge zone remains a high temperature such as 600℃ even though the frictional coefficient suddenly decreases due to thermal pressurization with the release of absorptive and interlayer waters by frictional heating. The dry fault gouge changes into a black ferrimagnetic material (a^^~-Fe_2O_3: maghemite) by high-speed shearing. The coercive force obtained from the black ferrimagnetic material after high-speed shearing is much smaller than that after heating in an electric furnace. This indicates that we can determine whether it is pulsated heating or long-term heating by estimating the magnitude of coercive force. On the other hand, we studied physical basis of optically stimulated luminescence (OSL) emitted from feldspars. The blue peak detected from feldspars in the Nojima fault gouge by UV-stimulations completely decays by heating at 600℃ and at the same time another broad yellow peak appears. This yellow peak also completely decays by heating until 870℃. These results indicate that these OSL peaks are applicable to the detection of seismic frictional heat. In case of feldspars in the Nojima pseudotachylyte, the blue and red peaks have been much more decreased. This suggests that the feldspars have been subjected to high temperature by ancient seismic frictional heating. Less

我们使用电子自旋共振技术检查了沿着野岛断层发现的野岛假速电石，该断层引发了 1995 年日本神户地震（M=7.2）。野岛假速电石具有源自大体积三价铁离子的强 FMR（亚铁磁共振）信号。在亚铁磁性氧化铁（a^^~-Fe_2O_3：磁赤铁矿）中，该 FMR 信号通过加热而出现。周围断层泥是野岛拟速电岩的源物质，而且野岛拟速电岩的磁化率比周围断层泥大10^2〜10^3倍，并且与FMR信号强度成正比。利用FMR信号重建了古地震断层滑移过程中断层泥的磁化过程，由此得出野岛断层泥的最大瞬时磁化强度。达到约10-20nT，并可能进一步通过电磁感应感应出约120mV/km^2的最大地电势变化。此外，我们利用干断层泥进行了高速剪切试验。研究发现，干断层泥带的摩擦热温度即使由于热加压导致摩擦系数突然降低，但仍保持在 600℃ 的高温。干燥的断层泥通过高速剪切而转变为黑色亚铁磁性材料（a^^~-Fe_2O_3：磁赤铁矿），高速剪切后的黑色亚铁磁性材料所获得的矫顽力很大。比电炉加热后的小，这说明我们可以通过估计其大小来判断是脉动加热还是长时间加热。另一方面，我们研究了长石发出的光受激发光（OSL）的物理基础，通过紫外线刺激从野岛断层泥中的长石中检测到的蓝色峰值在600℃的加热下完全衰减。另一个宽的黄色峰出现，该黄色峰在加热到870℃时也完全衰减。这些结果表明这些OSL峰适用于地震摩擦的检测。就野岛假速晶石中的长石而言，蓝色和红色峰值明显减少，这表明长石受到古代地震摩擦加热的影响较小。