Collaborative Research: Seismic Investigation of Slab Structure and Back Arc Volcanism in the Sea of Japan Region

我们计划以前所未有的分辨率拍摄中国东北、朝鲜和日本的地壳和地幔的地震图像。该地区在构造上是活跃的，其中包括日本地下的俯冲带，该俯冲带曾发生大的破坏性地震(例如2011年东北地震)，日本和中国东北部的活火山，以及中国东北部的伸展历史，导致了一个丰富的自然资源，如煤炭和石油的沉积盆地。该地区目前的地震图像将通过最近扩大该地区的数据复盖率以及使用一种新的数字反演技术加以改善，该技术将与地震波形和旅行时间相匹配。开发新的地震模型的最终目的是更好地了解这一复杂地区地球深部的物理过程，以及它们与地表构造活动的关系。反演将利用3D谱元素方法来模拟波的传播。伴随震源将与线性最优化方法相结合，用来反演地震速度的观测波形。通过波形反演，我们将模拟三重波形以及多路径地震波到达。这种类型的信息在该区域以前的断层成像中没有使用过，因此将产生比以前可获得的分辨率高得多的图像。我们将使用数据和合成之间的互相关作为目标函数，而不是时间延迟。这对于由短时间窗口内的多个到达干扰但同时对数据的绝对幅度不敏感的数据进行建模是理想的。尽管这个项目本质上是地震性质的，但由此产生的高分辨率图像将对一些重要的构造过程和问题施加限制，例如：1.过去50 Ma期间在日本地下俯冲的所有板块都可以被解释为地震快速异常吗？2.上地幔深部是否存在从目前俯冲的太平洋板块剥离的停滞板块？如果我们在东亚下方发现板块分割，它们是否与日本海的开放以及东北中国地区的新生代岩浆活动有关？3.是否有来自停滞板块下方的暖上升流，为长白山火山提供补给？东北中国是否有从板块上方升起的羽流为火山活动提供动力？4.日本海下方是否存在与深地震活动空区有关的板块空隙？如果是这样的话，这个缺口会不会和这个洞有关呢？在北东向中国之下的停滞板块中观察到了？5.俯冲板块内能看到亚稳相吗？可能与水进入地幔有关的低速结构能被成像吗？

We propose to develop a seismic image of the crust and mantle beneath Northeast China, Korea, and Japan with unprecedented resolution. This region is tectonically active and includes a subduction zone beneath Japan that has produced large devastating earthquakes (for example the 2011 Tohoku event), active volcanoes both in Japan as well as in Northeast China, and a history of extension in Northeast China that has resulted in a sedimentary basin rich in natural resources such as coal and oil. Current seismic images of the region will be improved through recent increased data coverage in the region as well as using a new numerical inversion technique that will fit seismic waveforms as well as travel times. The ultimate goal of developing the new seismic models is to better understand the physical processes in the deep Earth in this complicated region and how they relate to the surface tectonic activity.The inversion will utilize 3D spectral element methods to model wave propagation. Adjoint sources will be used in combination with linear optimization methods to invert observed waveforms for seismic velocity. Through waveform inversion we will model triplicated waveforms as well as multipathed seismic arrivals. This type of information has not been used in previous tomographic imaging of the region and thus will result in far higher resolution images than was previously attainable. We will use the crosscorrelation between data and synthetics as an objective function rather than time delays. This is ideal for modeling data that consist of multiple arrivals interfering within short time windows but at the same time it is insensitive to the absolute amplitude of the data. Although this project is essentially seismic in nature, the resulting high resolution images will place constraints on a number of important tectonic processes and questions such as:1. Can all slab subducted beneath Japan for the past 50 Ma be accounted for as seismically fast anomalies?2. Are there stagnant slabs in the deep upper mantle that are detached from the current subducting Pacific plate? If we find segmentation in slabs beneath eastern Asia, can they be associated with the opening of the Japan Sea, as well as Cenozoic magmatism in NE China?3. Is there a warm upwelling coming from beneath stagnant slabs feeding Changbaishan volcano? Are there plumes rising from above the slab feeding volcanic activity in NE China?4. Is there a slab gap associated with the deep seismicity gap beneath the Japan Sea? If so, can this gap be related to the ?hole? observed in the stagnant slabs beneath NE China?5. Can metastable phases be imaged within subducting slab? Can low velocity structures likely associated with water transport into the mantle be imaged?