Ferrimagnetic resonance signal produced by frictional heating: A new indicator of paleoseismicity
Ferrimagnetic resonance signal produced by frictional heating: A new indicator of paleoseismicity
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DOI：
10.1029/2004jb003485
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发表时间：
2005-12
影响因子：
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通讯作者：
T. Fukuchi;K. Mizoguchi;T. Shimamoto
中科院分区：
文献类型：
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作者：
T. Fukuchi;K. Mizoguchi;T. Shimamoto
地震期间高速断层滑动可能产生足够的摩擦热，从而产生熔融断层岩，如伪岩。我们利用天然断层泥进行了高速滑动试验，以判断地震断层滑动中是否普遍发生摩擦加热。在我们的剪切试验中，将天然断层泥置于两个圆柱形硅玻璃之间，在0.61 MPa的固定轴向应力下剪切。尽管地球表面附近的应力如此之低，但当以1500转/分的高速剪切时（边缘的最大滑移率达到1.96米/秒），沿圆形剪切面边缘的断层泥会形成一种类似伪achylyte的深色粘性物质。电子自旋共振测量结果表明，暗化黏合材料具有较强的铁磁共振（FMR）信号，该信号来源于铁磁性氧化铁（γ-Fe2O3）中体积较大的三价铁离子。FMR信号是由断层泥中反铁磁性氧化铁（γ-FeOOH）的热脱水产生的。这可能适用于地震断层滑动时的过去加热探测。因此，我们试图利用FMR信号反演1995年神户地震（M = 7.3）中野岛断层面上产生的摩擦热温度。计算机模拟表明，1995年神户地震期间，野岛断裂面在~ 390 m深度处产生的摩擦热可能达到~ 390°C。断层面的温度可能在1年后恢复到初始状态。这一结果表明，由断层引起的热流异常可能难以探测到。
[1] High-speed fault slips during earthquakes may generate sufficient frictional heat to produce fused fault rocks such as pseudotachylyte. We have carried out high-speed slip tests using natural fault gouge to judge whether or not frictional heating universally occurs during seismic fault slips. In our shearing tests, natural fault gouge is put between two cylindrical silica glasses and sheared under a fixed axial stress of 0.61 MPa. Despite such a low stress near the Earth's surface, a darkened cohesive material resembling pseudotachylyte is made from the fault gouge along the edge of a circular shear plane when shearing at a high speed of 1500 rpm (the maximum slip rate reaches ∼1.96 m/s at the edge). Electron spin resonance measurements reveal that the darkened cohesive material has a strong ferrimagnetic resonance (FMR) signal, which is derived from bulky trivalent iron ions in ferrimagnetic iron oxides (γ-Fe2O3). The FMR signal is produced by the thermal dehydration of antiferromagnetic iron oxides (γ-FeOOH) in the fault gouge. This may be applicable to the detection of past heating during seismic fault slip. We thus attempt to reconstruct the temperature of frictional heat generated on the Nojima fault plane in the 1995 Kobe earthquake (M = 7.3) by inversion using the FMR signal. The computer simulation indicates that the frictional heat generated on the Nojima fault plane at ∼390 m depth may have attained ∼390°C during the 1995 Kobe earthquake. The temperature in the fault plane may have returned to its initial state after ∼1 year. This result suggests that a heat flow anomaly generated by faulting may be difficult to detect.