Collaborative Research: New Zealand as a Natural Laboratory to Investigate Earthquake Stress Variation

对震源参数的全球研究表明，高应力降事件更有可能发生在板内区域，沿走滑断层和更深的深度。这些研究结合了从各种方法确定的压力下降，这些方法的不确定性鲜为人知。pi将使用单一分析技术（经验格林函数法）对新西兰现代宽带网络记录的中等规模（4.0 - 6.0）地震进行有效性调查，该网络已经运行了7年以上。计划中的研究有三个目的：1)确定控制新西兰四种不同构造状态下地震破裂过程的因素；2)检查使用格林函数（EGF）技术估计应力降的不确定性；3)初步检查新西兰北岛Hikurangi边缘地震参数的空间变化。最初的重点将是研究四种不同的构造体系，在这些体系中，具有丰富余震序列或群序列的大地震为我们提供了许多中等震级（4′Ü ML′Ü 6）的事件。这些区域包括强耦合俯冲（Dusky Sound 2009）、弱耦合/地震俯冲（Gisborne 2007）、走滑地壳（Darfield 2010和Christchurch 2011）和弧后扩张（Matata 2005-2010）。很少有研究关注中等震级地震的震源过程，尽管这些知识对于建立标度关系和检查地震自相似性至关重要。通过对单个网络记录的数据使用单一分析技术来确定这些不同环境下地震的应力降，研究人员最大限度地提高了发现应力降显著差异的机会，并可靠地确定了分析技术中的不确定性。这些结果将对研究俯冲带过程或地震破裂过程动力学的科学家有用。研究人员将把重点放在对新西兰北岛边缘地震的初步研究上，在那里太平洋板块被推到岛下。这个边缘在地质和构造上有很大的沿走向的变化，这些变化会影响太平洋板块在板块下降时部分板块如何粘住或蠕动。研究结果也将与其他俯冲带（如Cascadia和Alaska）的SSE和地震危害研究相关。由于世界上许多城市地区（如日本、卡斯卡迪亚、印度尼西亚、智利）都位于这些类型的板块边缘，研究结果将有助于科学家研究这些边缘的地质和构造过程，以及改进这些高度城市化地区的地震危险模型和建筑规范。不确定性分析的结果将有助于研究地震之间的相似程度，或者利用小地震的观测结果来预测大地震可能发生的情况的有效性。

Global studies of earthquake source parameters have suggested that high stress drop events are more likely to occur in intraplate regions, along strike-slip faults, and at deeper depths. These studies combine stress drops determined from a variety of methods whose uncertainties are poorly known. The PIs will investigate the validity of these general observations by using a single analysis technique (empirical Green¡¯s function method) on moderate-sized (4.0ML6.0) earthquakes recorded by the modern broadband New Zealand network that has been operating for over 7 years. The planned research has three aims: 1) determine factors controlling the earthquake rupture process in four distinct tectonic regimes of New Zealand, 2) examine uncertainties in estimating stress drops obtained using the empirical Green¡¯s function (EGF) technique, and 3) a preliminary examination of spatial variations in earthquake parameters along the Hikurangi Margin, North Island, New Zealand. The initial focus will be to investigate four distinct tectonic regimes where large earthquakes with prolific aftershock sequences or swarm sequences provide us with numerous moderate magnitude (4 ¡Ü ML¡Ü 6) events. These regions include strongly coupled subduction (Dusky Sound 2009), weakly coupled/aseismic subduction (Gisborne 2007), strike-slip crustal (Darfield 2010 and Christchurch 2011), and back-arc spreading (Matata 2005-2010). Few studies have focused on the source processes of moderate magnitude earthquakes, although this knowledge is critical in developing scaling relationships and examining earthquake self-similarity. By using a single analysis technique for data recorded by a single network to determine stress drops for earthquakes in these diverse settings the researchers maximize their chances of finding significant differences in stress drops and of reliably determining the uncertainties in the analysis technique. The results will be useful to scientists who study subduction zone processes or the dynamics of the earthquake rupture process. The researchers will focus on a preliminary study of earthquakes along the margin of the North Island of New Zealand where the Pacific plate is being subducted (pushed) beneath the island. This margin has large, along-strike variations in geology and structure that affect how parts of the Pacific plate stick or creep as the plate descends. The results will also be relevant to studies of SSE and seismic hazards in other subduction zones such as Cascadia and Alaska. Since many urban regions of the world (e.g. Japan, Cascadia, Indonesia, Chile) are located along these types of plate margins, the results will be useful to scientists who study geologic and tectonic processes at these margins, as well as to improving earthquake hazards models and building codes for these highly urbanized areas. The results of the uncertainty analysis will be useful to researchers studying how similar earthquakes are to one another or how valid it is to use observations from small earthquakes to predict what may happen in larger earthquakes.