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

提案EAR 0105405（PH #43 x）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？PI's：C. Sammis和H.越来越多的观测证据表明，大地震之后是数十年的中等规模事件的区域平静，之前是一个相当长的时间段的加速地震释放。这种加速（主要是由于中等规模地震的增加）可以符合失效时间方程的幂律，这提供了在中期基础上预测大地震的可能性，也许是几年。最佳加速区的半径R与震级成log R ~ 1/2 M的比例，相当于R与断层长度L成正比。这种现象学被解释为一个地区接近和退出临界状态的标志。当接近临界点时，应力场的幂律缩放和相关长度的增长导致越来越大的事件是预期的行为。我们计划设计和实施定量的观测测试，区域地震活动和关键现象之间的这种类比。这并不需要详细了解为什么地震应该是关键现象。临界性，像自组织临界性一样，导致了普遍的特征，如幂律和标度关系，它们独立于所涉及的机制。为了开发测试，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。我们将对较小事件的行为特别感兴趣，这些事件还没有被用来帮助监控临界状态的方法。

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.