全球非均匀模型中的远震走时层析成像

Teleseismic traveltime tomography based on global heterogeneous model

远震走时层析成像是研究地球内部结构的重要工具.通常,远震走时层析成像使用一维地球参考模型计算研究区域外地震射线.由于地球存在广泛非均匀结构,传统远震走时层析成像在计算射线时忽略了研究区域外非均匀结构对射线的影响,最终导致对研究区域内的成像结果产生影响.为了减小模型外地球非均匀结构对远震走时层析成像的影响,本文利用迎风差分格式数值求解程函方程,得到全球非均匀模型中的远震射线,以此为基础发展了基于全球非均匀模型的远震走时成像方法.为了检验本文成像方法提升成像精度的有效性,选取青藏高原东北缘为研究对象.合成测试和实际数据成像结果显示,在考虑地球非均匀结构以后,成像结果更精确,结果展现更多成像细节.

Teleseismic traveltime tomography is an important tool to study the structure of the Earth's interior. In teleseismic traveltime tomography, a one-dimensional reference model is usually employed to compute seismic rays outside the study domain. Owing to the existence of widely spread heterogeneities inside the Earth, the impacts from global heterogeneities are not taken into count in conventional teleseismic tomography. Therefore, tomographic images inside the study area are affected by heterogeneities outside. In order to reduce the impacts, we use upwind schemes to numerically solve the eikonal equation and obtain seismic rays in a heterogeneous global model. Based on the solved seismic rays in the heterogeneous global model, we conduct teleseismic traveltime tomographic study. To demonstrate the effectiveness of the tomography method in improving imaging accuracy, we select the northeastern Tibetan Plateau for synthetic and practical tomographic studies. Tomographic results show that the imaging accuracy is increased and more imaging details are presented when conducting teleseismic traveltime tomography based on a heterogeneous global model.