Criticality in Regional Seismicity: How Do We Test It and What Does It Mean?

提案EAR0105405 （PH # 43x）摘要标题：区域地震活动的临界性：我们如何测试它以及它意味着什么？越来越多的观测证据表明，大地震之后是几十年的中等规模的区域性平静期，而在此之前是一段可比较的加速地震释放期。这种加速（主要是由于中等规模事件的增加）可以符合失效时间方程的幂律，这提供了在中期（也许是几年）预测大地震的可能性。最佳加速区域的半径R的大小为对数R ~ 1/2 M，相当于R与断层长度l成正比。这种现象被解释为表明一个区域接近临界状态，并从临界状态撤退。当接近临界点时，应力场的幂律缩放和相关长度的增长将导致越来越大的事件。我们计划设计和实施区域地震活动性和临界现象之间的这种类比的定量观测试验。这并不需要详细了解为什么地震应该是临界现象。临界性，就像自组织临界性一样，导致了普遍的特征，如幂定律和缩放关系，这些特征与所涉及的机制无关。为了进行测试，我们将探索由临界点模型预测的地震活动性的空间、时间和震级分布的演变。我们将对较小的事件的行为特别感兴趣，它们还没有被用来帮助监测接近临界的情况。

Abstract for proposal EAR0105405 (PH # 43x)Title: Criticality in Regional Seismicity: How Do We Test For It and What Does It Mean?PI's: C. Sammis and H. Saleur, University of Southern CaliforniaThere is mounting observational evidence that large earthquakes are followed by tens of years of regional quiescence of intermediate-size events, and preceded by a comparable time period of accelerating seismic release. This acceleration (due mostly to an increase in intermediate-size events) can be fit to a power law of the time-to-failure equation, which offers the possibility of predicting large earthquakes on an intermediate-term basis, of perhaps a few years. The radius R of the optimally accelerating region scales with magnitude as log R ~ 1/2 M, which is equivalent to R being proportional to fault length L. This phenomenology has been interpreted as signifying the approach of a region to, and retreat from, a critical state. Power law scaling and growth of the correlation length of the stress field leading to increasingly larger events are expected behavior when approaching a critical point. We plan to devise and implement quantitative observational tests of this analogy between regional seismicity and critical phenomena. This does not require having a detailed understanding of why earthquakes should be critical phenomena. Criticality, like self-organized criticality, leads to universal features like power laws and scaling relations, that are independent of the mechanisms involved. To develop the tests, we will explore the evolution of the spatial, temporal, and magnitude distributions of seismicity that are predicted by critical point models. We shall be especially interested in the behavior of the smaller events, which have not, as yet, been used to help monitor the approach to criticality.