Collaborative Research: Origin of High Magnetic Remanence in Fault Pseudotachylites

同震形变过程中的摩擦加热可导致断层岩石的熔融和假玄武岩的形成(如果滑动是重要的)。越来越多地报道地震闪电的存在表明，大强度的瞬时同震电流与大震级地震(M6.0)有关。这种电流很可能沿着假玄武岩矿脉流动，因为它们熔化时的导电性比未熔融岩石的导电性大得多。所有与断层有关的假黄长岩的前人和初步结果表明，它们具有异常高的剩余磁化强度。它们的剩余磁性类似于被闪电击中的岩石，这表明磁化过程中涉及到巨大的电脉冲。这个项目的目的是证明在伪快长岩中普遍观察到剩磁异常，并证明同震电流是造成这种异常的原因。研究人员建议对来自地震活动断裂带(加利福尼亚州、日本和阿尔卑斯山西部)的三个年轻的假黄长岩进行测试，收集定向样品进行古地磁研究。在相对于主断层面的不同点上采集的样本将使我们能够检验同震流假说。磁化场的几何形状和特征将与假钙钛矿形成时的地球磁场进行比较。这将为同震流假说提供一个独立的第二个检验。一系列实验将使用摩擦焊接方法产生人造假黄铁矿。将比较人造和天然假黄长石，以评估天然样品中异常磁化的可能原因。同震电流的瞬变性质使直接研究变得困难。利用受电性现象影响的岩石的剩磁记录可以绕过这个问题。这项研究将为断层岩同震电流的研究开辟新的方向，并将有助于更好地理解同震电现象--

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--