NSF East Asia and Pacific Summer Institute (EAPSI) for FY 2013 in Japan

这项行动资助俄勒冈大学的Joseph Byrnes于2013年夏天在东京文京区东京大学地震研究所开展地球科学研究项目。这个项目的题目是“利用遥远地震的记录来测量构造板块的厚度”。主持人是川胜仁教授。最近的研究表明，在海洋构造板块的底部存在着地震速度的明显不连续。假定这种不连续性是为了区分刚性板块（岩石圈）和底层对流地幔（软流圈）。不连续性存在的原因尚不清楚。该项目旨在利用位于太平洋西北海岸附近的胡安·德富卡板块的海底地震仪，测量与板块年龄有关的不连续深度。由于不连续性很明显，来自遥远事件的P波和S波在穿过板块时相互转换。由于横波的速度较低，直接相和转换相之间到达时间的差异决定了不连续的深度。利用这种技术，可以确定这个神秘边界的演变。人们提出了几种相互竞争的理论来解释这种不连续性的存在。最简单的假设是，板的厚度随着其年龄的平方根而增长，正如通过导电冷却板生长的模型所预测的那样。最可能的选择是，不连续层具有恒定的深度，与年龄无关，这可能代表一个板块，该板块形成时，地幔中的水被除去，形成一个刚体，定义了构造板块。EAPSI奖学金的广泛影响包括为研究员提供美国以外的第一手研究经验；介绍该地区的科学、科学政策和科学基础设施；以及对社会、文化和语言的了解。这些活动符合美国国家科学基金会的目标，即在其科学家、工程师和教育工作者的职业生涯早期培养国际合作，从而确保美国科学劳动力具有全球意识。此外，该研究员希望建立能够在夏季之后产生科学成果的关系。在资助期间进行的研究将为美国和日本研究人员之间的未来合作奠定基础。

This action funds Joseph Byrnes of the University of Oregon to conduct a research project in Geoscience during the summer of 2013 at the Earthquake Research Institute, University of Tokyo in Bunkyo-ku, Tokyo. The project title is "Using Recordings of Distant Earthquakes to Measure the Thickness of Tectonic Plates." The host scientist is Professor Hitoshi Kawakatsu.It has recently been shown that a sharp discontinuity in seismic velocity exists at the bottom of tectonic plates in the ocean. This discontinuity is postulated to distinguish the rigid plate (the 'Lithosphere') from the underlying convective mantle (the 'Asthenosphere'). The reason the discontinuity exists is poorly understood. This project aims to measure the depth of the discontinuity with plate age using ocean bottom seismometers located on the Juan De Fuca Plate, just off the coast of the Pacific Northwest. Since the discontinuity is sharp, P and S waves from distant events convert into one another when passing through the plate. The difference in arrival time, due to the lower velocity of S waves, between the direct and converted phases gives the depth to the discontinuity. Using this technique, the evolution of this enigmatic boundary can be established. Several competing theories have been put forward to explain why this discontinuity exists. The simplest hypothesis is that the plate thickness grows as the square root of its age, as predicted by models of a plate growing by conductive cooling. The most likely alternative is that the discontinuity has constant depth and is independent of age, which would likely represented a plate defined by the removal of water from the mantle when the plate is created, forming a rigid body that defines the tectonic plate.Broader impacts of an EAPSI fellowship include providing the Fellow a first-hand research experience outside the U.S.; an introduction to the science, science policy, and scientific infrastructure of the respective location; and an orientation to the society, culture and language. These activities meet the NSF goal to educate for international collaborations early in the career of its scientists, engineers, and educators, thus ensuring a globally aware U.S. scientific workforce. Furthermore, the Fellow hopes to establish relationships that produce scientific results beyond the summer. The research done during the funding period will lay the groundwork for future collaboration between researchers in the U.S. and Japan.