Earthquake hazard from 36-Cl exposure dating of elapsed time and Coulomb stress transfer

概述：我们请求提供资金，利用36-Cl宇宙成因测年法测量意大利中部活动断层发生大地震以来的时间，并计算历史/古地震的应力转移。这将允许（1）将知识转移到该地区的风险社区，以便他们能够为未来的地震做好准备，如果一个长时间的地震过去的断层已经通过邻近的地震转移了应力，以及（2）将这一过程传达给其他具有类似地震危险的地区。技术总结：只有当断层接近其破坏应力时，活动断层才会由于邻近地震的应力转移而发生地震破裂。我们缺乏关于哪些断层接近它们的破坏应力的知识，因此不能根据地震发生的概率来解释应力转移的计算。我们建议，在意大利中部的一个活跃的正断层系统，测量过去的时间，因为最后一次地震归一化断层滑动率使用原位36-Cl宇宙成因同位素测年，因为这是一个代理断层是如何接近其破坏应力。我们将联合收割机与历史和古地震的应力转移计算相结合，以计算哪些断层破裂的概率最高。背景：当地震使活动断层破裂时，应力转移到邻近的活动断层上。这种应力的转移可能会导致邻近的活动断层在随后的地震中破裂。例如，2004年苏门答腊附近俯冲板块边界的节礼日地震在当天造成了严重的生命损失，但随后在2005年、2007年、2009年和2010年也引发了地震，每一次都造成了重大的生命损失。这样的触发地震也发生在板块内的活动断层上，例如公元1349年9月9日在意大利中部发生的三次> Mw 6的地震，它们发生在同一天，但发生在不同的活动断层上;这增加了人们对继2009年拉奎拉地震之后未来发生主震的可能性的担忧（Mw 6.3），其持续的余震已转移到邻近的断层上（图1）。一个关键点是，尽管有上述例子，地震并不总是引发后续地震。只有当邻近的断层由于地壳运动或板块之间的长期负荷而已经接近破裂时，后续的地震才会发生。这些断层的识别可以在未来发生地震之前通知当地居民和民防机构，从而允许位置优先的减灾工作。然而，不幸的是，我们不能直接测量12-15公里深处的断层上的应力，而板内主震正是在那里形成的，因此我们无法识别这样的断层。然而，我们可以用宇宙成因同位素（36-Cl）来测量应力随时间的变化，即自上次地震以来所经历的时间。在次表面，36-Cl浓度随着时间的推移而积累，主要是由于宇宙粒子撞击钙原子。在每次地震中，活动正断层滑动1-2米，并了解36-Cl在深度的生产率，在1-2米深度测量的36-Cl浓度量化了自上次地震以来的时间。我们可以挖沟暴露断层面到1-2米深，并测量断层面上的36-Cl浓度。如果邻近的地震对36-Cl浓度高的地点施加了负荷/压力，因此经过了很长时间，我们将能够通知负责规划减灾的民防机构;目前没有这样的数据。我们可以进行此类测量，并与政府民防项目合作伙伴保持联系，这些合作伙伴为意大利中部绘制地震危险图，并参与向全球传达地震危险。

Overview: We request funds to make measurements of the elapsed time since major earthquakes on active faults in central Italy using 36-Cl cosmogenic dating, and calculate stress transfer from historical/palaeoseismic earthquakes. This will allow (1) knowledge transfer to at-risk communities in the region so they can prepare for future earthquakes if a fault with a long earthquake elapsed time has had stress transferred onto it by a neighboring earthquake(s), and (2) communication of this process to other regions with similar earthquake hazard. Technical Summary: Active faults experience earthquake rupture due to stress transfer from neighboring earthquakes only if the fault in question is close to its failure stress. We lack knowledge of which faults are close to their failure stress and thus cannot interpret calculations of stress transfer in terms of the probability of impending earthquakes. We propose, for an active normal fault system in central Italy, to measure the elapsed time since the last earthquake normalised to fault slip-rates using in situ 36-Cl cosmogenic isotope dating, because this is a proxy for how close a fault is to its failure stress. We will combine this with calculations of stress transfer from historical and palaeoseismic earthquakes in order to calculate which faults have the highest probability of rupture.Background: When an earthquake ruptures an active fault, stress is transferred onto neighboring active faults. This transfer of stress may cause a neighboring active fault to rupture in a subsequent earthquake. For example, the 2004 Boxing day earthquake on the subduction plate boundary near Sumatra caused severe loss of life on that day, but also triggered subsequent earthquakes in 2005, 2007, 2009 and 2010, each of which caused major loss of life. Such triggered earthquakes also occur on active faults within plates, such as the three 9th September > Mw 6 earthquakes in 1349 A.D. in central Italy, which occurred on the same day, but on different active faults; this has increased concern for the possibility of a future mainshock to follow the 2009 L'Aquila earthquake (Mw 6.3) whose ongoing aftershocks have transferred onto a neighboring fault (Fig. 1). A key point is that, despite the above examples, earthquakes do not always trigger subsequent earthquakes. Subsequent earthquakes only occur if the neighboring fault(s) are already close to failure due to long-term loading from motions in the crust or between plates. Identification of such faults could inform local populations and civil protection agencies in advance of a future earthquake allowing location-prioritised mitigation efforts. However, unfortunately, we cannot directly measure stress on a fault at 12-15 km depth where intra-plate mainshocks nucleate and so cannot identify such faults. However, we can measure a proxy for stress-through-time, that is elapsed time since the last earthquake, using cosmogenic isotopes (36-Cl). In the sub-surface, 36-Cl concentrations accumulate through time mainly due to hits on calcium atoms by cosmic particles. With 1-2 m slip in each earthquake on active normal faults, and with knowledge of 36-Cl production rates at depth, 36-Cl concentrations measured at 1-2 metres depth quantify elapsed time since the last earthquake. We can dig trenches to expose the fault plane to 1-2 metres depth and measure 36-Cl concentrations on the fault planes. If a neighboring earthquake has loaded/stressed a location with a high 36-Cl concentration, and hence a long elapsed time, we will be able to inform civil protection agencies responsible for planning mitigation; no such data are available at present. We can make such measurements, and have ongoing links with government civil protection project partners who make the seismic hazard maps for central Italy, and who are involved in communicating seismic hazard worldwide.