Seismic Imaging of Southern Californian Crust Using Deformable-Layer Tomography and Prestack Depth Migration

为了加深我们对南加州地壳结构和地球动力学的了解，开展了一个新的地壳地震成像项目，以显著改进区域三维地壳速度结构和跨圣安德烈斯断裂系统的主要反射事件的绘制。这些数据包括南加州地震中心(SCEC)汇编的地震读数和洛杉矶区域地震实验(LARSE)的地震反射记录。该项目的一项创新是使用了一种新的可变形层析成像技术，直接绘制了地壳和上地幔中的P波和S波速度不连续的几何图形，并受来自接收函数和其他分析的已知地壳厚度变化的约束。此外，还应用了一种改进的波动方程叠前深度偏移方法，为大剖面提供了新的反射图像。该项目的初步结果表明，新的层析成像方法具有更高的垂直分辨率和更逼真的透镜状地质特征表示，如盆地边缘和岩性尖灭，这是对传统层析成像方法的重大改进，传统的层析成像方法在固定空间网格上反演速度值。到目前为止获得的大反射图像表明，叠前深度偏移可以更好地处理近地表横向速度变化，并提高分辨率和反射层连续性。有趣的是，该项目的结果表明，高噪声水平、强烈的横向速度不均匀和弯曲的测量几何结构的存在支持而不是反对使用叠前深度成像而不是简单的共中心点叠加技术。这个为期两年的项目预计将大大改进加利福尼亚州南部的三维P波和S波地壳速度模型，以及圣安德烈斯断裂系统两次陆上大地震调查下的叠前深度偏移图像。该项目的更广泛影响包括为今后的地壳和地幔研究实地展示创新的地震成像技术，例如为EarthScope/USArray设想的那些技术，以及促进固体地球物理和勘探地球物理之间在思想和培训方面的杂交，这将导致地震成像本科生和研究生教育的根本改变。

To advance our understanding of the crustal structure and geodynamics of southern California, a new crustal seismic imaging project is carried out to significantly improve the mapping of the regional 3D crustal velocity structure and major reflection events across the San Andres fault system. The data include the earthquake readings compiled by the Southern California Earthquake Center (SCEC) and seismic reflection records from the Los Angeles Regional Seismic Experiment (LARSE). An innovation of the project is the use of a new deformable-layer tomography to directly map the geometry of P-wave and S-wave velocity discontinuities in the crust and uppermost mantle, and constrained by known crustal thickness variations from receiver functions and other analyses. In addition, an advanced wave equation prestack depth migration is applied to provide new reflection images for the LARSE profiles. The preliminary results from this project indicate that the new tomography method produces sharper vertical resolution and more realistic representations of lens-shaped geologic features like the edges of basins and lithologic pinchouts, which is a significant improvement over traditional tomography that inverts for velocity values on fixed-in-space mesh grids. The LARSE reflection images obtained so far indicate that prestack depth migration can better handle near surface lateral velocity variations and improve the resolution and reflector continuity over previous images of the LARSE datasets. Interestingly, the results from this project suggest that the presence of high noise level, strong lateral velocity heterogeneity and crooked survey geometry argue for, rather than against, the use of prestack depth imaging over the simple CMP stack techniques. This two-year project is expected to provide significantly improved 3D P-wave and S-wave crustal velocity models for southern California and prestack depth migrated images beneath two onshore LARSE surveys across the San Andres fault system. The broader impacts of the project include field demonstration of innovative seismic imaging techniques for future crustal and mantle studies, such as those envisioned for EarthScope/USArray, as well as promotion of crossbreeding in ideas and training between solid Earth geophysics and exploration geophysics that will lead to a fundamental modification of undergraduate and graduate education in seismic imaging.