Remote Triggering of Deep Earthquakes

深层地震是神秘的，因为在非常高的压力下，摩擦应该会阻止岩石破裂。所以我们发现，在地球的大部分地幔中没有地震，岩石也会发生塑性变形。然而，在俯冲的板块区域，有相当数量的真正非常大的地震发生在近700公里深的地方——这些是深地震。为了研究这种深度的地震活动性，我们需要一种机制，使应力达到临界水平，然后产生非常快的应变，足以在地球表面产生和记录地震波。室内实验表明，从上地幔主要矿物橄榄石到其高压多晶岩的相变可以提供这种应力临界过程，称为抗裂断裂。但是在700千米深的地方并不会一直发生断裂，事实上，最大的深层地震也不会发生在亚稳橄榄石持续存在的地区。一种可能性是，在变形区内产生的断层导致变形外区域的应力增加，破裂可以从裂缝断裂区缓慢地传播到周围的板块。这种模型被称为远程触发，在研究深层地震的地震学家中很受欢迎，但它尚未在断层过程的实验模拟中得到证实。本研究将探讨裂缝充填如何在远离变形区域的地方引起更大的地震。在研究这一远程触发过程时，我们将开发新的断层机制测试，这些测试既适用于地球深部，也适用于监测资源开采和碳封存期间可能发生的人为地震活动。

Deep earthquakes are enigmatic because at very high pressures friction should stop rocks from rupturing. So we find in most of the Earth's mantle there are no earthquakes and rocks deform plastically. However in subducting slab regions there are significant numbers of really quite large earthquakes occurring down to almost 700 km depth - these are deep earthquakes. In order for seismicity at this depth we need a mechanism which will allow stresses to build up to a critical level and then produce very rapid strains, sufficiently fast for seismic waves to be produced and recorded at the Earth's surface. Laboratory experiments have shown that phase transformation from the main upper mantle mineral olivine to its high-pressure polymorphs can provide this kind of stress critical process, known as anticrack faulting. But anticrack faulting does not occur all the way down to 700 km depth and indeed the largest deep earthquakes do not occur in a region where metastable olivine persists.One possibility is that faults produced in the transforming region then cause stresses to increase in regions outside transformation and the rupture can slowly propagate from the anticrack faulting region into the surrounding slab. This model is known as remote triggering, and is popular among seismologists who study deep earthquakes, but it has yet to be proven demonstrated in experimental simulations of faulting processes. This study will investigate ways in which anticrack fulting can cause larger earthquakes away from the region of transformation. In studying this remote triggering process we will develop new tests for faulting mechanisms which will be applicable to both the deep Earth and also to monitoring man-made seismicity such as might occur during resource abstruction and carbon sequestration.