基于密集台阵地震背景噪声和近震波形的沉积层S波速度与衰减结构研究

沉积层S波速度低、衰减强，是地震学重要的模型参数之一。准确的沉积层S波速度和衰减结构对于地震灾害评估、强地面运动模拟、地震震级和位置测定、壳幔结构成像等研究具有重要意义。然而，对于数千米较厚沉积层，目前尚缺乏一种低成本、大深度、高分辨、不依赖地震事件的S波速度和衰减结构被动源研究方法。本申请拟利用密集台阵地震背景噪声方法，提取面波频散和衰减曲线，实现对小区域、大厚度沉积层结构的有效探测。拟选择沉积厚度大、地震活动性高的首都圈两个井下摆开展多期次密集台阵观测（100台地震仪），基于理论数值模拟和实际观测，研究布设方式、台阵尺度、台站间距、观测周期等因素的影响；布设地表地震仪与井下摆共同记录近震波形，基于反射波、转换波等方法开展沉积层结构探测，并与密集台阵方法对比验证。优化密集台阵地震背景噪声方法的观测、数据处理和反演方法，改善数千米厚度沉积层S波速度和衰减结构的探测效果。

Sediment is characterized as extremely low S wave velocity and strong attenuation, which also is one the most important part of the velocity model for seismology. Accurate S wave velocity and attenuation structures of sediment are essentially important for earthquake disaster assessment, strong ground motion simulation, determination of earthquake magnitude and location, tomography of crust and upper mantle, et al. However, for current methods, it’s still very difficult to obtain reliable S wave velocity and attenuation structures of sediment with several kilometer thickness. An effective method with low-cost, deeper-depth, high-resolution as well as independent of earthquakes is needed. The proposal will implemented the investigation of the S wave velocity and attenuation structures of thick sediments in a relative small area by surface wave dispersion and attenuation information derived from ambient noise recorded by dense seismic array. Dense seismic array with 100 short-period seismographs will be deployed in the two borehole seismic stations located in the capital region (Beijing) with thick sediment and strong seismicity. By synthetic simulations and field observations, we will study the effects of array scale, insterstation distance, array geometry, observation period et al, on the obtained sedimentary structures. With the reflected and converted waves recorded by seismic stations in the borehole and on the surface, S wave velocity and attenuation structures of sediments will be studied independently and compared with the results from dense seismic array. The observation, data processing and inversion method with dense seismic array and ambient noise method will be optimized and improved for investigating the S wave velocity and attenuation structures of thick sediments.