Collaborative Research: Origin of High Magnetic Remanence in Fault Pseudotachylites

如果滑动是重要的，同震变形期间的对流加热可导致断层岩熔融和假玄武玻璃岩的形成。越来越多的关于地震闪电存在的报道表明，大强度的瞬态同震电流与大震级地震（M 6.0）。这种电流很可能是沿着假玄武玻璃岩脉，因为它们的导电性，是熔体，是远远大于未熔融的岩石。所有以前和初步的结果表明，与断层有关的假玄武玻璃具有异常高的剩磁。它们的剩余磁性与被闪电击中的岩石相似，这表明磁化过程中涉及大的电脉冲。 本项目旨在证明假玄武玻璃岩中普遍存在剩磁异常，并证明同震电流是造成这种异常的原因。研究人员建议通过收集定向样品进行古地磁研究，对来自地震活动断裂带（加州、日本和西阿尔卑斯山）的三种年轻假玄武玻璃岩进行检验。在主断层面不同点采集的样本将使我们能够检验同震电流假说。的几何形状和磁化场的特点将与地球的磁场在假玄武玻璃形成的时候。这将为同震电流假设提供独立的第二次检验。通过一系列的实验，利用摩擦焊接的方法制备出人造的假玄武玻璃。将比较人造和天然的假玄武玻璃，以评估天然样品中异常磁化的可能原因。同震电流的瞬变特性使得直接研究同震电流变得困难。利用受电现象影响的岩石的反射磁记录，可以解决这一问题。 这项研究将开辟断层岩同震电流研究的新方向，并应有助于更好地了解同震电现象--

GeissmanEAR-0228849Frictional heating during coseismic deformation can lead to the melting of the fault rocks and formation of pseudotachylite if slip is important. The increasingly reported existence of earthquake lightning shows that transient coseismic electric currents of large intensity are associated with large magnitude earthquakes (M 6.0). Such currents are likely to follow pseudotachylite veins because their electric conductivity, being melts, is considerably larger than that of the unmolten rocks. All previous and preliminary results on fault-related pseudotachylites show that they have an anomalously high remanent magnetization. Their remanent magnetic properties are similar to those of lightning struck rocks, which suggests that large electric pulses were involved in the magnetization. This project aims at demonstrating that remanence anomalies in pseudotachylites are generally observed and that coseismic electric currents are responsible for it. The investigators propose to test the hypothesis on three young pseudotachylites from seismically active fault zones (California, Japan and Western Alps) by collecting oriented samples for paleomagnetic studies. Samples collected at various points with respect to the main fault plane will enable us to test the coseismic current hypothesis. The geometry and the characteristics of the magnetizing field will be compared with the Earth's magnetic field at the time of pseudotachylite formation. This will provide an independent second test for the coseismic current hypothesis. A series of experiments will generate artificial pseudotachylites using the friction welding method. The artificial and natural pseudotachylites will be compared to assess the possible causes of anomalous magnetization in natural specimens. The direct study of coseismic currents is made difficult by their transient nature. This problem can be circumvented by using the remanent magnetic record of rocks affected by the electrical phenomenon. This research will open new directions of investigation on coseismic electric currents in fault rocks and should contribute to a better understanding of coseismic electric phenomena--