Studies On Topography Of Free Surface And Core Mantle Boundary With Representation Theorem

Geomorphological and seismological studies have illustrated all scale topography of free surface and core mantle boundary, which are Earth’s two most significant discountinities. The topography mechanisms are closely related to landscape evolution and mantle convections processes leading an extremely strong constrains on dynamic modelings.We report an observation of unexpected surface waves on LVC station from deep earthquakes occurred in Chile. The surface waves are identified as Rayleigh wave by arrival time, slowness and particle motion analysis. The location results suggest the S->Rayleigh conversion mechanism due to surface topography, and Spectral Element Method(SEM) numerical simulation confirms it. For a better understanding of the effect of relief on converted Rayleigh waves, we derive analytical solutions of homogeneous half-space model with free surface topography.On the other hand, it’s usually effective to resolve core mantle boundary features with short period(1Hz) core reflected phases. We develop an algorithm based on ray theory and representation theorem to calculate short period ScP synthetics. Forward modeling tests prove that a dip and bump case would cause focusing and defoucing effects on ScP amplitude. Moreover, a bump CMB model with H= 1.2km beneath northeastern Japan overall matches the observed pattern of 2D PcP/ScP amplitude ratios. However, we still can not rule out other facts, such as 3D tomography and D", that may effect PcP/ScP because of the limitation of ray-based algorithms. Thus, a hybrid method combining ray theory and numerical method is very promising for studying complicated 3D structures in the future.