Collaborative Research: Revealing the Environment of Shallow Slow Slip

俯冲带，即一个构造板块弯曲到另一个构造板块之下的地方，在地球表面的演化中很重要，也是社会的主要地震和海啸危险。在过去的15年里，密集的全球定位系统(GPS)和俯冲带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，许多断层还经历了缓慢滑动。在某些情况下，观察到了缓慢滑动和破坏性大地震之间的关系。大多数缓慢滑动的观测都发生在海底以下20-40公里处。在新西兰近海的Hikurangi边缘，浅层也会发生慢滑，但由于缺乏适当的海底观测，对浅层慢滑的详细调查一直受到阻碍。了解浅层慢滑事件的范围、分布和物理条件是很重要的，特别是因为浅层断层界面是地震产生海啸的地方。该项目使用最近从Hikurangi边缘收集的海底地震和绝对压力计数据来研究地震和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生加州州立大学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到四名本科生实习生，其中至少一人来自地球科学中代表性不足的群体。所有学生都将受益于不同机构的研究人员的培训。2014年10月发生了一次大型浅层缓滑事件，就在Hikurangi洋底调查地震和慢滑仪器阵列的正下方，这是美国牵头的与日本和新西兰研究人员进行的一项重大国际实验。该实验旨在研究Hikurangi俯冲推覆上存在浅层慢滑的物理环境及其与破坏性地震滑移的关系。该项目将以本次实验的初步数据分析为基础，以解决四个主要目标：1)利用PageRank技术和匹配滤波互相关来改进初始震动和地震的检测和定位；2)调查2014年慢滑事件后施加在巨型逆冲带上的库仑破裂应力的变化，并将其与地震和地震位置进行比较，以测试静应力变化是否可以解释其位置；3)确定震源参数，并探索其与板块界面慢滑、大地耦合和物理性质的时空关系；4)利用体波速度和衰减层析成像以及环境噪声面波层析成像，改善地震速度和衰减结构的图像。该项目将补充卡斯卡迪亚和日本的类似工作，能够比较浅层和深层慢滑的性质和环境，并建立地震和无震滑移之间的关系及其对速度和衰减结构的依赖的详细图景。

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.