The inversion of reflected waves for Moho discontinuity along the Hayward Fault, California

Abstract

This paper is to achieve an in-depth understanding of the crustal structure of the Hayward Fault. Based on past experiments, investigating PmP phases could significantly improve the obtained resolution images and particle motions of the ray path under the crustal structure. To achieve the purpose of optimal reliability, 428 hand-labeled PmP phases were picked from the Northern California earthquake catalog for the Hayward Fault area throughout the past 19 years. The two inversion methods have been incorporated with selected PmP observations to determine the depth of the Moho discontinuity. One of the inversion methods discussed how the deviation of the earthquake source location affect the deviation of the PmP traveltime and interpreted in mathematical functions. The other method suggests the average Moho depth could be achieved through the seismic velocity model, these picked data archives were trained to construct the velocity model according to their focal depth, epicentral distance and arrival time. By varying these characteristics of Moho-reflected PmP phases, the crustal thicknesses and upper mantle velocities in the targeted area are constrained. Besides, an efficient algorithm searching method has been used to find the average crustal thicknesses with minimum mismatches using the velocity model. With the base of the single-layered initial model, a general seismic velocity structure can be extended by adding the complex seismic velocity discontinuities gradually. The resulting model contributes to the distribution of source-receiver ray paths, this may provide strong evidence to obtain Moho-reflected phases during future earthquakes.