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

我们建议以前所未有的分辨率开发中国东北、韩国和日本地壳和地幔的地震图像。该地区构造活跃，包括日本下方的俯冲带，该俯冲带曾发生过大型破坏性地震（例如2011年的东北地震），日本和中国东北地区都有活火山，中国东北地区的延伸历史导致了一个富含煤炭和石油等自然资源的沉积盆地。目前该地区的地震图像将通过最近增加该地区的数据覆盖范围以及使用新的数值反演技术来改进，该技术将适合地震波形和旅行时间。开发新的地震模型的最终目的是为了更好地了解这个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。反演将利用三维谱元方法模拟波的传播。伴随震源将与线性优化方法相结合，用于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到达。这种类型的信息在以前的区域层析成像中没有被使用，因此将产生比以前更高分辨率的图像。我们将使用数据和合成物之间的相互关系作为目标函数，而不是时间延迟。这对于在短时间窗口内由多个到达干扰组成的数据建模是理想的，但同时它对数据的绝对幅度不敏感。虽然该项目本质上是地震性质的，但由此产生的高分辨率图像将限制许多重要的构造过程和问题，例如：在过去的50 Ma中，所有在日本地下俯冲的板块都可以被解释为地震快速异常吗？上地幔深处是否存在从当前俯冲的太平洋板块分离出来的停滞板块？如果在东亚板块中发现分段，是否与日本海的开闭以及中国东北部的新生代岩浆活动有关？是不是有一股温暖的上升流从停滞的板块下面涌来，滋养着长白山火山？中国东北部是否有从板块上方升起的羽流为火山活动提供补给？日本海下是否存在与深地震活动间隙相关的板块间隙？如果是这样，这个间隙是否与孔有关？在中国东北部的停滞板块中观察到的。亚稳相能否在俯冲板块内成像？可能与水进入地幔有关的低速结构能否成像？

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?