Seismic Full-Waveform Inversion of the Crust-Mantle Structure Beneath China and

Adjacent Regions: Model Construction and Comparison, and Dynamics Interpretations

马锦程 博士

开云app体育 地球与空间科学学院

2024.12.06（星期五）15:00，理科二号楼2821

摘要：

    We present the first-generation full-waveform tomographic model (SinoScope 1.0) for the crust-mantle structure beneath China and adjacent regions. The three-component seismograms from 410 earthquakes recorded at 2,427 stations are employed in iterative gradient-based inversions for three successively broadened period bands of 70–120 s, 50–120 s, and 30–120 s. Synthetic seismograms were computed using GPU-accelerated spectral-element simulations of seismic wave propagation in 3-D anelastic models, and Fréchet derivatives were calculated based on an adjoint-state method facilitated by a checkpointing algorithm. The inversion involved 352 iterations, which required 18,600 wavefield simulations. SinoScope 1.0 is described in terms of isotropic P-wave (VP), horizontally and vertically polarized S-wave velocities (VSH and VSV), and mass density (ρ), which are independently constrained with the same data set coupled with a stochastic L-BFGS quasi-Newton optimization scheme. It systematically reduced differences between observed and synthetic full-length seismograms. We performed a detailed resolution analysis by repairing input random parametric perturbations, indicating that resolution lengths can approach the half propagated wavelength within the well-covered areas. SinoScope 1.0 reveals strong lateral heterogeneities in the lithosphere, and features correlate well with geological observations, such as sedimentary basins, Holocene volcanoes, Tibetan Plateau, Philippine Sea Plate, and various tectonic units. The asthenosphere lies below the lithosphere beneath East and Southeast Asia, bounded by subduction trenches and cratonic blocks. Furthermore, we observe an enhanced image of well-known slabs along strongly curved subduction zones, which do not exist in the initial model. In this talk, we also strive to address two long-standing questions: (1) the morphology and physical state of the subducting Indian slab under Tibet, along with its impact on the growth dynamics of the plateau, and (2) the driving forces behind the ongoing northward motion of the Indian Plate during its post-collision with Asia. We present evidence that the Indian slab subducts beneath almost the entire plateau, with a subhorizontal geometry at ~300 km depth. The mechanism by which the plateau maintains its high-elevation, low-relief topography is potentially attributed to buoyancy of the low-velocity zone above the flat slab. Mantle drag, exerted on the base of the Indian Plate by plume-associated northward mantle convective flows, likely serves as the primary force driving the India-Asia collision.

报告人简介：

  马锦程，开云app体育 地球与空间科学学院博雅博士后研究员（入选教育部首届海外高层次人才引进专项）。2015年于吉林大学获得地球物理学学士学位(李四光理科试验班)，2018年于吉林大学获得地球物理学硕士学位，2023年于德国慕尼黑大学 (Ludwig-Maximilians-Universität München)获得自然科学博士学位。主要研究领域为地震学、观测和理论地球动力学以及高性能计算，旨在以多学科视角和技术来探讨亚洲地区与滨太平洋构造域以及全球尺度岩石圈和地幔深部结构、构造演化、深部物质的循环及时空变化特征。致力于在满足基本物理、化学规律的地球动力学模型中，通过地震学和地球动力学之间的数据联系，以定量的方式弥合地球物理假设与地震学观测之间的差距，进而建立起四维时空下的地球深时演化模型。