Collaborative Research: Revealing the Environment of Shallow Slow Slip

俯冲带，即一个构造板块在另一个构造板块之下弯曲的地方，在地球表面的演变中很重要，同时也是对社会造成重大地震和海啸危害的地方。近15年来，密集的全球定位系统（GPS）和在俯冲带进行的地震观测揭示了一种新的断层滑动类型。除了连续滑动和突然地震运动外，许多断层还经历缓慢滑动。在某些情况下，已观察到缓慢滑动与破坏性大地震之间的关系。大多数慢滑观测发生在海底以下20-40公里深度。在新西兰近海的Hikurangi边缘，缓慢滑动也发生在浅层深处，但由于缺乏合适的海底观测，对浅层缓慢滑动的详细调查受到了阻碍。了解浅层慢滑事件的程度、分布和物理条件的范围是很重要的，特别是因为浅层断层界面是地震产生海啸的地方。本项目使用最近从Hikurangi边缘收集的海底地震和绝对压力计数据来研究地震与慢滑之间的关系以及有利于它们的物理条件。这项研究的结果将被纳入加州大学圣克鲁斯分校高中学生的加州州立数学与科学暑期学校的地震科学课程。该项目涉及指导和培训三名研究生和两至四名本科生实习生，其中至少一名来自地球科学领域代表性不足的群体。所有学生都将受益于来自不同机构的研究人员的培训。2014年10月，在Hikurangi海底地震和慢滑仪器阵列的正下方发生了一次大的浅层慢滑事件，这是美国领导的一项与日本和新西兰研究人员进行的主要国际实验。该实验旨在研究Hikurangi俯冲逆冲上浅层缓慢滑动的物理环境及其与破坏性地震滑动的关系。本项目将以该实验的初步数据分析为基础，以实现四个主要目标：1)利用PageRank技术和匹配滤波互相关技术改进初始地震和地震探测定位；2)研究2014年慢滑事件中大逆冲断层的库仑破坏应力变化，并将其与地震和地震位置进行比较，以检验静应力变化是否可以解释其位置；3)确定震源参数，并探讨其与慢滑的时空关系。4)利用体波速度与衰减层析成像和环境噪声面波层析成像改善地震速度与衰减结构图像。该项目将补充Cascadia和日本的类似工作，允许比较浅层和深层慢滑的性质和环境，并建立地震和地震滑动之间的关系及其对速度和衰减结构的依赖的详细图片。

Subduction zones, where one tectonic plate bends down beneath another tectonic plate, are important in the evolution of Earth's surface as well as being a major earthquake and tsunami hazard for society. In the last 15 years, dense Global Positioning System (GPS) and earthquake observations made at subduction zones have revealed a new style of fault slip. In addition to continuous slip and sudden earthquake motion, many faults experience slow slip. In some instances, a relationship between slow slip and damaging large earthquakes has been observed. Most observations of slow slip occur at 20-40 km depth below the seafloor. At the Hikurangi margin offshore of New Zealand, slow slip also occurs at shallow depths, but detailed investigation of shallow slow slip has been hampered by the lack of suitable seafloor observations. Understanding the extent, distribution, and range of physical conditions for shallow slow slip events is important, especially since the shallow fault interface is where tsunamis are generated by earthquakes. This project uses recently collected ocean bottom seismic and absolute pressure gauge data from the Hikurangi margin to investigate the relationship between earthquake and slow slip and the physical conditions that favor them. Results of this research will be incorporated into an earthquake science course for the California State Summer School for Mathematics and Science program for high school students at the University of California-Santa Cruz. This project involves the mentoring and training of three graduate students and two to four undergraduate interns, including at least one from an underrepresented group in the Earth Sciences. All students will benefit by receiving training from researchers at different institutions.A large shallow slow slip event occurred in October 2014, directly beneath the Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip instrument array, a major U.S. led international experiment with Japanese and New Zealand researchers. The experiment was designed to investigate the physical environment that hosts shallow slow slip and its relationship to destructive, seismic slip on the Hikurangi subduction thrust. This project will build on the initial data analysis from this experiment to tackle four main objectives: 1) to improve initial tremor and earthquake detection and location using the PageRank technique and matched filtering cross correlation, 2) to investigate changes in coulomb failure stress imparted on the megathrust from the 2014 slow slip event and compare it to earthquake and tremor locations to test whether static stress changes can explain their location, 3) to determine earthquake source parameters and explore their spatial and temporal relationships with slow slip, geodetic coupling and physical properties of the plate interface and 4) to improve images of seismic velocity and attenuation structure using body wave velocity and attenuation tomography and ambient noise surface wave tomography. This project will complement similar efforts in Cascadia and Japan, allowing comparison of the properties and environment of shallow and deep slow slip and build a detailed picture of the relationship between seismic and aseismic slip and its dependence on the velocity and attenuation structure.