A New Method to Minimize the Influence of Lateral Heterogeneity on Inversion Applying Triplicated Phases

Abstract:

Triplicated phases have already been successfully used to constrain seismic structure of the mantle, especially the discontinuities surrounding the transition zone. However, triplicated phase inversion greatly suffers from laterally heterogeneous mantle structure, which is also a common issue of geophysical inversion problems.

To solve this, we propose an I-cubed (isolation, inversion, integration) method to minimize the influence of lateral heterogeneity both in and out of the target region. The first step of this method is to isolate the effect of the lateral inhomogeneity. We deduct the influence of lateral inhomogeneity given by former tomography on the arrivals of the triplicated phases, which leaves a nearly 1-D question for further inversion. The second step is to do the traditional triplicated phase inversion to obtain a 1-D solution. At the final step, we add the deducted deviation from the 1-D earth model in the first step to the 1-D solution in the second step, and obtain a final velocity profile along an inclined line delineated by turning points of triplicated phases.This method is good at both stability and reliability because 1-D requirement of traditional inversion applying triplicated phases is assured, and the contamination of lateral heterogeneity is annihilated to great extent while useful information is kept. To test the robustness of I-cubed method, we apply it to synthetic records. It shows that the I-cubed method can derive better result than the traditional one.