CRUSTAL AND MANTLE STRUCTURE BENEATH EASTERN EURASIA FROM FINITE FREQUENCY SEISMIC TOMOGRAPHY (FFST)

An accurate, high-resolution 3-D earth model is crucial to the seismic calibration for nuclear monitoring. We use the newly developed Finite Frequency Seismic Tomography (FFST) approach to construct the crustal and mantle structure beneath eastern Eurasia. Traditionally, travel times of seismic waves are calculated based on the ray theory, which is valid strictly for infinite-frequency waves. Observed seismic waves, however, are finite frequency signals. As a result of scattering and diffractive effects, travel times of realistic finite frequency waves are sensitive to 3-D structure around the geometrical rays, and the travel time shifts caused by heterogeneities diminish gradually from the heterogeneities to receivers- a phenomena named the wave front healing. The ray theory ignores this ubiquitous effect of the propagation of realistic seismic waves. Tomographic inversions based on it, therefore, tend to underestimate the magnitudes of heterogeneities. The newly developed FFST utilizes the 3-D Born-Fréchet sensitivity kernels of the travel times of finite-frequency seismic waves. The new method accounts for the wave front healing, off-ray scattering and other non-geometrical diffraction phenomena, and significantly improves the resolution of the velocity heterogeneity. In addition to the new methodology, we will use a more comprehensive data set than in previous studies to construct the new earth model beneath eastern Eurasia. We will collect data from the publicly accessible sources e.g.