ESR detection of seismic frictional heating events in the Nojima fault drill core samples, Japan
ESR detection of seismic frictional heating events in the Nojima fault drill core samples, Japan
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DOI：
10.1016/j.tecto.2007.01.020
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发表时间：
2007-10
期刊：
影响因子：
2.9
通讯作者：
T. Fukuchi;J. Yurugi;N. Imai
中科院分区：
文献类型：
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作者：
T. Fukuchi;J. Yurugi;N. Imai
为了探测地震摩擦加热事件，特别是1995年神户地震期间的摩擦加热事件，我们用ESR(电子自旋共振)技术分析了野岛断裂NIED 1800米钻芯样品。距断裂面10 cm的深灰色断层泥具有铁磁共振(FMR)信号，其深度约为1140米，由古断裂运动产生。加热实验表明，该铁磁共振信号来源于结晶度不完全的亚铁磁性三价离子氧化物(γ-Fe_2O_3：磁铁矿)，它是由γ-FeO_2O_3(锂镁铁矿)或Fe(OH)_3(褐铁矿)热脱水而产生的。FMR信号的存在意味着曾经发生过摩擦加热等干加热，在古地震断层滑动期间，沿深灰色断层泥的摩擦热温度可能已上升到350℃以上。为了探测断裂带的摩擦加热事件，铁磁共振信号的增加和断层泥颜色向深灰色或黑色的变化是重要的指标。另一方面，仅在约1140米和1300米深的两个断裂面上的断层泥中没有检测到FMR信号，这两个断裂面被认为是1995年神户地震的可能主断裂面。这两个断裂面在地震中可能没有起到重要的断层滑动作用。
We have analyzed the Nojima fault NIED 1800 m drill core samples by ESR (Electron Spin Resonance) to detect seismic frictional heating events, especially during the 1995 Kobe Earthquake. Dark gray fault gouge with foliation >10 cm away from the fault plane at about 1140 m in depth, which was produced by ancient fault movements, has a FMR (ferrimagnetic resonance) signal. Heating experiments show that this FMR signal is derived from ferrimagnetic trivalent ion oxides (γ-Fe2O3: maghemite) with imperfect crystallinity, which is produced by thermal dehydration of γ-FeOOH (lepidocrocite) or Fe(OH)3(limonite). The existence of the FMR signal means that dry heating such as frictional heating once occurred, and that the frictional heat temperature along the dark gray fault gouge may have risen to over 350 °C during ancient seismic fault slip. In order to detect frictional heating events in fault zones, the increase of the FMR signal and the color change of fault gouge into dark gray or black are important indexes. On the other hand, no FMR signal is detected from the fault gouges just on two fault planes at about 1140 m and 1300 m in depth, which are considered to be possible main fault planes in the 1995 Kobe Earthquake. These two fault planes may not have played an important role of fault slip in the Earthquake.