Collaborative Research: Origin of High Magnetic Remanence in Fault Pseudotachylites

同震变形过程中的摩擦加热可以导致断层岩石的熔化和伪水晶石的形成，如果滑动是重要的。地震闪电的存在越来越多的报道表明，大强度的瞬态同震电流与大震级地震（6.0级）有关。这样的电流很可能沿着伪水晶石脉流动，因为它们的电导率在熔化时比未熔化的岩石要大得多。所有与断层相关的假铜绿石的先前和初步结果表明，它们具有异常高的剩余磁化强度。它们的残余磁性与被闪电击中的岩石相似，这表明大的电脉冲参与了磁化过程。本项目旨在证明在伪石中普遍观察到残余异常，并且同震电流是造成这种异常的原因。研究人员建议通过收集古地磁研究的定向样本，对来自地震活跃断裂带（加利福尼亚、日本和西阿尔卑斯山）的三颗年轻的伪水晶石进行假设测试。在主断层面的不同地点收集的样本将使我们能够检验同震电流假说。将磁场的几何形状和特征与伪水蛭形成时的地球磁场进行比较。这将为同震电流假说提供独立的第二次检验。一系列的实验将使用摩擦焊接的方法产生人造假石英石。将比较人造和天然的假铜石，以评估自然标本中异常磁化的可能原因。同震电流的瞬态特性使直接研究同震电流变得困难。这个问题可以通过利用受电现象影响的岩石的剩磁记录来解决。该研究将为断层岩同震电流的研究开辟新的方向，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--