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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

利用电子自旋共振技术研究了1995年日本神户地震（M=7.2）发生的野岛断裂带附近发现的野岛伪水杨酸。野岛伪羧酸盐具有较强的FMR（铁磁共振）信号，源自铁磁氧化铁（a^^~-Fe_2O_3：磁铁矿）中大块的三价铁离子。这个FMR信号是通过加热周围的断层泥而出现的，而断层泥是野岛假羟基酸盐的来源。此外，野岛假木屑的磁化率比周围断层泥的磁化率大10^2 ~ 10^3倍，并与FMR信号强度成正比。利用FMR信号重建了古地震断层滑动过程中断层泥的磁化过程。因此，野岛断层泥的最大瞬时磁化强度可能达到约10-20nT，并可能进一步通过电磁感应引起约120mV/km^2的最大地电势变化。此外，我们还利用干断层泥进行了高速剪切试验。结果表明，在干断层泥带中，由于热增压作用，吸收水和层间水释放，摩擦系数突然降低，但摩擦热温度仍保持在600℃左右的高温。干断层泥经高速剪切作用转化为黑色铁磁性物质（a^^~-Fe_2O_3：磁铁矿）。黑色铁磁材料经高速剪切得到的矫顽力比电炉加热得到的矫顽力小得多。这表明我们可以通过估计矫顽力的大小来确定是脉动加热还是长期加热。另一方面，研究了长石光激发发光的物理基础。紫外激发法在野岛断层泥长石中探测到的蓝色峰在600℃加热后完全衰减，同时出现另一个宽黄色峰。加热至870℃，黄色峰也完全衰减。结果表明，这些声发射峰可用于地震摩擦热的探测。野岛伪长石中长石的蓝色峰和红色峰的下降幅度更大。这表明长石受到了古代地震摩擦加热的高温作用。少