Collaborative Research: Improving the Chronology of Deformation and Earthquakes at La Rinconada, Argentina: Testing Segmentation and Recurrence Patterns of Blind Thrust Regimes

了解隐伏逆冲断层(不到达地球表面的断层)的地震潜力对美国洛杉矶和西雅图等人口稠密地区以及世界各地地震活跃地区的其他人口中心具有重大地震危险意义。有关破坏性地震断层的长期行为的关键问题包括地震的规模和频率，以及这些地震在时间和空间上的变化。更好地了解过去地震的时间和规模是用于预测未来事件、确定当地和区域地震危险的特征以及向公众和应急规划者提供信息的基本信息。然而，人口稠密的地区很难研究，因为混凝土、建筑和发展掩盖了活动断层的表现。在这项研究中，阿根廷圣胡安附近的一个活动断裂系统正在进行调查，以更好地了解几个活动的盲冲断层的地表表现和地震历史。该系统在结构上与美国大都市区内的盲断层相似，但具有该地区基本上不受干扰的优势。该项目的重点是对从河流阶地和被地震断层变形和断层的冲积层中收集的大量样品进行测年。根据这些新的数据，将建立过去五次大地震对盲断层系统的计时。新的年龄数据将使人们能够与早期工作中记录的附近断层系统的地震历史进行比较，这些断层是1944年和1977年该地区破坏性地震的罪魁祸首。该项目将测试单个断层上的地震频率是否具有准周期性(因此是可预测的)，这些断层系统是否产生在时间上聚集的地震，并测试过去的地震是否可能破裂了更大的震源区，或者是否被限制在与历史事件相同的震源尺寸内。像这个项目早期阶段的结果一样，阿根廷的合作者和其他人将利用这个项目的新结果来限制地震危险，告知地震工程师，并教育公众有关地震危险的知识。

Understanding the earthquake potential of blind thrust faults (faults that do not reach the Earth?s surface) has major seismic hazard implications for heavily populated areas such as Los Angeles and Seattle in the United States as well as other population centers within seismically active regions around the World. Key questions regarding the long-term behavior of destructive earthquake faults include what are the size and frequency of earthquakes and how do those vary in time and space. Better knowledge of the timing and sizes of past earthquakes is essential information used to forecast future events, to characterize local and regional seismic hazards, and to inform the public and emergency planners. Heavily populated areas, however, are difficult to study because concrete, buildings, and development obscure the expression of active faults. In this study, an active fault system near San Juan Argentina, which bears structural similarities to blind faults within metropolitan regions in the United States, but has the advantage that the area is largely undisturbed, is being investigated to better understand the surficial expression and earthquake history of several active blind thrust faults. This project is focused on dating of a large suite of samples collected from river terraces and alluvium deformed and faulted by the earthquake faults. From these new data, the timing of the past five large earthquakes on the blind fault system will be established. The new age data will allow comparison with the earthquake history of nearby fault systems documented in earlier work, faults that were responsible for damaging earthquakes in 1944 and 1977 in the region. This project will test whether earthquake frequency on individual faults is quasi-periodic (and therefore predictable), whether these fault systems produce earthquakes that cluster in time, and test whether some past earthquake may have ruptured a larger source region or have been confined to the same source dimensions as the historical events. Like the results from an earlier phase of this project, the Argentinean collaborators and others will use the new results from this project to constrain seismic hazard, inform earthquake engineers, and educate the public about earthquake hazards.