Collaborative Research: Towards an Understanding of the Collective Behavior of Regional Fault Networks: The Marlborough Fault System, New Zealand

该项目的主要目标是确定区域断层网络中的不同断层如何相互作用，以适应从一次地震到几十次地震的时间尺度上构造板块的相对运动。研究小组将专注于新西兰南岛北部一个特别有希望的研究区域，在那里，太平洋和澳大利亚板块之间的相对运动被一组被称为马尔伯勒断层系统的四条平行走滑断层分割开来。马尔伯勒断裂系统的历史和古地震数据提供了世界其他地方(例如加利福尼亚州北部和南部、土耳其西北部、伊斯帕尼奥拉、中亚和东南亚部分地区、伊朗-巴基斯坦)类似断层系统的有用模拟数据，揭示了复杂地震发生的诱人迹象，可能存在不同周期的地震时空聚集。但目前仅有太少的断层滑动速率和古地震年龄和位移数据，无法全面评估马尔伯勒断裂系统的集体时空行为。为了详细记录四个马尔伯勒断层如何分享板块构造运动，研究小组将确定这些断层在不同时间尺度上的滑动速率，范围从几次到几十次地震，以及过去地震的年龄和位移。这项工作的关键将是从马尔伯勒四个主要断层系统获得约300平方公里的高分辨率激光雷达数字地形数据。这些数据使得能够以前所未有的细节有效地绘制和测量最近地震中发生的从大约100米到最小的断层偏移量。在这方面，马尔伯勒断裂系统是一个特别富含目标的环境，因为马尔伯勒地区许多大型跨断层河流展示了一套河流阶地边缘，这些河流阶地边缘被不同数量的偏移量所抵消。将这些偏移量特征与来自不同地质计时器(放射性碳和光激发发光)的年龄数据相结合，将在几十次地震后的各个破裂的时间范围内获得异常详细的断层滑移率。研究人员还将在四条断层上挖掘战壕，以确定古地震的年龄和位移，从而与最年轻的滑移率进行相互关联。由此产生的数据，连同现有的数据和其他研究小组正在进行的研究结果，将允许记录马尔伯勒断层在广泛的时间和空间尺度上的行为，为系统地与世界其他地方类似系统的地震行为进行比较提供必要的信息。该项目的主要目的是增进对区域大断层网络存储和释放地震能量的方式的理解，特别侧重于确定所谓的紧急现象的相对重要性，例如大震级地震群和地震能量储存瞬间升高的时期，这些现象在目前对地震物理学的理解中可能是没有预料到的，在目前的地震评估战略中也没有考虑到。这些结果将有助于地震危险界了解区域断层网络如何在时间和空间上分布形变--这是制定更准确的下一代地震危险性评估战略的关键，也是今后旨在了解此类现象原因的建模工作的基础。这一国际努力将扩大美国研究人员与他们的新西兰合作者之间已经很强大的科学合作，通过促进两个小组之间的互动而使两个小组受益，这两个小组在各自的国家都面临着类似的地震危险。具体地说，除了与美国地质调查局的地震危险规划者密切合作以确保他们的结果及时实施外，私人投资者还积极与负责在新西兰实施地震危险评估的GNS Science的同事合作，确保该项目的结果也将被纳入新西兰下一阶段的地震危险评估。

The primary goal of this project is to determine how different faults in regional fault networks interact with one another to accommodate the relative motion of tectonic plates over time scales ranging from one to a few dozen earthquakes. The research team will focus on a particularly promising study area in northern South Island, New Zealand, where relative motions between the Pacific and Australian plates are partitioned amongst a set of four, parallel strike-slip faults known as the Marlborough fault system. Historical and paleo-earthquake data from the Marlborough fault system, which provides a useful analog for similar fault system elsewhere in the world (e.g., northern and southern California, Northwest Turkey, Hispaniola, parts of central and Southeast Asia, Iran-Pakistan), reveal tantalizing hints of complex earthquake occurrence, with possible temporal and spatial clustering of earthquakes that varies from cycle to cycle. But currently there are too few fault slip rate and paleo-earthquake age and displacement data to fully assess the collective spatial-temporal behavior of the Marlborough fault system. In order to document in detail how the four Marlborough faults share the tectonic plate motions, the research team will determine the rates of slip along each of these faults at a variety of time scales, ranging from a few to a few dozen earthquakes, as well as the ages and displacements of past earthquakes. Key to this effort will be the acquisition of about 300 square kilometers of high-resolution lidar digital topographic data from the four main Marlborough fault system faults. These data allow the efficiently mapping and measurement in unprecedented detail of fault offsets ranging from about 100 meters down to the smallest offsets that occurred in the most recent earthquakes. The Marlborough fault system is a particularly target-rich environment in this regard because many of the large fault-crossing rivers in the Marlborough region exhibit suites of river terrace edges that have been offset by variable amounts. Combining these offset features with age data from different geochronometers (radiocarbon and optically stimulated luminescence) will yield exceptionally detailed fault slip rates at a range of time scales from individual ruptures back though several dozen earthquakes. The researchers will also excavate trenches across the four faults to determine paleo-earthquake ages and displacements, allowing cross-correlation with the youngest slip rates. The resulting data, together with existing data and the results of ongoing studies by other groups, will allow documentation of the behavior of the Marlborough faults over a wide range of temporal and spatial scales, providing the information necessary for systematic comparison with the earthquake behavior of similar systems elsewhere in the world.The primary aim of this project is to advance understanding of the way regional networks of large faults store and release seismic energy, with a particular focus on determining the relative importance of so-called emergent phenomena such as clusters of large-magnitude earthquakes and periods of transiently elevated storage of seismic energy that may not be expected in the current understanding of earthquake physics and that are not accounted for in current seismic assessment strategies. The results will help the seismic hazard community to understand how regional fault networks distribute deformation in time and space - the keys to developing more accurate, next-generation seismic hazard assessment strategies, as well as the basis for future modeling efforts aimed at understanding the causes of such phenomena. This international effort will expand already strong scientific collaboration between the US researchers and their New Zealand collaborators, benefitting both groups by fostering increased interaction between the groups, both of which face similar seismic hazards in their respective countries. Specifically, in addition to working closely with seismic hazard planners at the US Geological Survey to ensure timely implementation of their results, the PIs are actively collaborating with colleagues at GNS Science, which is responsible for implementation of seismic hazard assessment in New Zealand, ensuring that the results of this project will be also incorporated into New Zealand's next-phase seismic hazard assessments.