Seismic study of subduction zones, rifted margins and mid-ocean ridges

拟议的研究计划集中在地球的三个主要边界：俯冲带、裂谷边缘和大洋中脊，所有这些都是地球板块构造旋回的一部分。俯冲带是大洋板块和大陆板块交汇的地方，在那里，较薄但密度较大的海洋板块在大陆板块下“潜伏”，最终被回收到地球地幔中。大陆边缘因大陆岩石圈的伸展和破裂而形成，这一过程打开了新的海洋盆地。大洋中脊是一个发散的板块构造边界，在那里不断产生新的洋壳。它们构成了地球上最大的山系和最长的火山链。拟议的研究计划依赖于将最先进的数据分析方法的创新组合应用于新的多通道地震和海底地震仪数据。目标是以前所未有的分辨率成像目标地下结构，以测试领先的科学假设和问题，这些假设和问题有可能改变该计划关注的研究领域。所选择的研究区域是：阿拉斯加俯冲带、胡安德富卡板块和卡斯卡迪亚俯冲带、加拿大东部裂谷边缘和西南印度洋海脊。该计划要解决的研究领域和问题是根据它们对实现我的短期和长期科学目标的适宜性、重大发现的潜力以及广大地球科学家和公众的兴趣来选择的。卡斯卡迪亚和阿拉斯加俯冲带的火山喷发和地震对美国西北部和加拿大西南部人口稠密的地区构成了重大风险。从基础科学(例如地球固体内部和海洋之间的能量和物质交换)和社会影响(俯冲地震灾害)的角度来看，洋壳如何从山脊演化到海沟都是重要的。这一计划的预期结果是改善对俯冲地震期间最大同震滑动向下极限的约束，换句话说，更好地理解这些大型近海地震可以发生在离沿海城市多近的地方。这项研究计划的另一个成果是关于俯冲推覆(巨型逆冲)耦合的横向变化的更详细的信息，或者，简单地说，俯冲带的哪些区段受到强烈的干扰，因此可能在俯冲地震期间释放大部分破坏性地震能量。这一知识将导致巨型断裂事件概率地震危险图的准确性提高，并改进建筑规范，这是我们用来减轻这些破坏性地震的主要手段。更好地了解活动岩浆系统的内部工作机制，将有助于更好地预测未来的海底喷发，并从总体上提高对火山的了解。对裂谷边缘深层结构的新限制，将有助于引导未来的石油勘探走向新的发现。裂谷边缘也是主要沉积盆地的所在地，这些盆地拥有最近钻探的最大碳氢化合物矿藏。所有组成拟议研究计划的项目都是备受瞩目的国际合作项目，因为对海底深处的结构进行调查需要大量的人力和物力。海底是地球最后的边界之一。

The proposed research program is focused on three of the Earth's major boundaries: subduction zones, rifted margins and mid-ocean ridges, all of which form as part of the Earth's plate tectonic cycle. Subduction zones are places where oceanic and continental plates converge, and where the thinner but denser oceanic plate "ducks" under the continental plate to eventually become recycled into the Earth's mantle. Rifted continental margins form by extension and breakup of the continental lithosphere, a process that opens up new ocean basins. Mid-ocean ridges are a divergent plate tectonic boundary where new oceanic crust is being continuously generated. They make up the most extensive mountain system and the longest chain of volcanoes on planet Earth. The proposed research program relies on applying an innovative combination of state-of-the-art data analysis methods to new multichannel seismic and ocean bottom seismometer data. The goal is to image the targeted subsurface structures at unprecedented resolution in order to test leading scientific hypothesis and questions that have the potential to transform the fields of study this program focuses on. The selected study areas are: Alaska subduction zone, Juan de Fuca plate and Cascadia subduction zone, rifted margins of eastern Canada, and Southwest Indian ridge. The study areas and problems to be addressed by this program are chosen based on their suitability for achieving my short- and long-term science goals, the potential for high-impact discoveries, and interest to a broad group of earth scientists and general public. Volcanic eruptions and earthquakes at the Cascadia and Alaska subduction zones pose significant risk in the heavily populated areas of northwestern United States and southwestern Canada. How oceanic crust evolves from ridge to trench is important from the perspectives of both basic science (e.g., energy and mass exchange between the Earth's solid interior and the oceans) and societal impacts (subduction earthquake hazards). An expected outcome of this program are improved constraints on the downdip limit of maximum coseismic slip during subduction earthquakes or, in other words, better understanding of how close to the coastal cities can these large offshore earthquakes occur. Another outcome of this research program is more detailed information on lateral variations in subduction thrust (megathrust) coupling or, in simpler terms, which sections of subduction zones are strongly jammed and therefore likely to release most of the destructive seismic energy during subduction earthquakes. This knowledge will lead to advances in accuracy of probabilistic seismic hazards maps for megathrust events and improved building codes, our primary means used to mitigate against these damaging earthquakes. Better understanding of the inner workings of active magmatic systems, which are the least challenging to investigate at mid-ocean ridges because of the thin crust and relatively simple tectonic setting, will lead to better prediction of future undersea eruptions and to improved understanding of volcanoes in general. New constraints on the deep structures at rifted margins, that are also the site of major sedimentary basins that host the largest recently drilled hydrocarbon deposits, will help guide future petroleum exploration to new discoveries. All of the projects that comprise the proposed research program are high-profile international collaborations because investigations of structures deep below the seabed, which is one of the Earth's last frontiers, require major resources, both human and material.