Exploring source regions of single- and double-frequency microseisms recorded in eastern North American margin (ENAM) by cross-correlation

Abstract

Summary Strongly asymmetric cross-correlation functions (CCF) of ambient noise indicate an inhomogeneous distribution of the noise sources, and can be used to locate these sources. With this premise, a grid-search procedure is applied to explore the frequency dependent source locations of the single- (SF) and double-frequency (DF) microseisms recorded in eastern North American margin (ENAM). The frequency dependent Rayleigh wave group velocities are determined based on CRUST1.0 model and the Preliminary Reference Earth model and then the theoretical travel time differences from each hypothetical source to all station pairs are calculated by the fast marching method. Then a misfit function at each hypothetical source is defined to take the difference between the calculated travel time differences and the time lags observed from CCFs. A factor of reliability is defined considering the Rayleigh wave attenuation, the correlation coefficients between the microseisms and the Wavewatch III hindcasts of ocean wave spectra, and the efficiency of conversion from DF energy in water to seismic Rayleigh waves as a function of water depth and frequency. Together with the correlation analyses of the power spectra densities of the microseisms among stations, the primary source regions of SF and DF microseisms recorded in ENAM are estimated: 1) the sources of SF microseisms are likely distributed in the continental shelf dominantly as well as adjacent deep ocean area in western North Atlantic Ocean, and 2) the long-period and short-period DF microseisms appear generated in deep ocean near the continental slope and in the continental shelf and slope of ENAM, respectively.