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

概述：我们申请资金，使用36-Cl宇宙测年法测量意大利中部活动断层大地震发生后的时间，并计算历史/古地震的应力传递。这将允许(1)将知识传递给该地区的风险社区，以便他们能够在地震发生时间较长的断层被相邻地震转移到其上时为未来的地震做好准备；(2)将这一过程传达给具有类似地震危险的其他地区。技术总结：活动断层只有在接近其破坏应力时，才会由于邻近地震的应力传递而发生地震破裂。我们不知道哪些断层接近其破裂应力，因此不能根据即将发生地震的概率来解释应力传递的计算。我们建议，对于意大利中部的一个活跃的正断层系统，使用原位36-Cl宇宙成因同位素定年法测量自上次地震标准化到断层滑动率的经过时间，因为这是断层离其破裂应力有多近的一个代理。我们将把它与历史地震和古地震的应力传递计算结合起来，以便计算出哪些断层破裂的可能性最大。背景：当地震使一个活动断层破裂时，应力被转移到邻近的活动断层上。这种应力的转移可能导致相邻的活动断层在随后的地震中破裂。例如，2004年节礼日发生在苏门答腊岛附近俯冲板块边界的地震在当天造成了严重的生命损失，但也引发了随后发生在2005年、2007年、2009年和2010年的地震，每一次地震都造成了重大的生命损失。这种触发的地震也发生在板块内的活动断层上，例如公元1349年9月9日意大利中部发生的三次地震，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2009年拉奎拉地震（里氏6.3级）之后发生主震的可能性的担忧，该地震的余震已经转移到邻近的断层上（图1）。关键的一点是，尽管有上述例子，地震并不总是引发后续的地震。只有当邻近的断层由于地壳或板块间运动的长期负荷已经接近破裂时，才会发生后续地震。对这些断层的识别可以在未来地震发生之前通知当地居民和民防机构，从而使减灾工作按地点优先进行。然而，不幸的是，我们不能直接测量12-15公里深度断层上的应力，在那里板块内主震成核，因此无法识别这样的断层。然而，我们可以使用宇宙成因同位素（36-Cl）来测量时间应力，即自上次地震以来经过的时间。在地下，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。每次地震在活动的正断层上滑动1-2米，并了解深度的36-Cl产量，在1-2米深度测量36-Cl浓度，量化自上次地震以来经过的时间。我们可以挖沟将断裂面暴露到1-2米深，测量断裂面上36-Cl的浓度。如果邻近的地震对36-Cl浓度高的地点造成了负荷/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；目前还没有这样的数据。我们可以进行这样的测量，并与政府的民防项目合作伙伴保持持续的联系，这些合作伙伴为意大利中部绘制地震危险地图，并参与在全球范围内传播地震危险。

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.