Directionality of ambient noise in the Mississippi embayment

Abstract

SUMMARY Cross-correlations of ambient seismic noise from 277 broad-band stations within the Mississippi embayment (ME) with at least 1 month of recording time between 1990 and 2018 are used to estimate source locations of primary and secondary microseisms. We investigate source locations by analysing the azimuthal distribution of the signal-to-noise ratios (SNRs) and positive/negative amplitude differences. We use 84 stations with 1 yr of continuous recordings to explore seasonal variations of SNRs and amplitude differences. We also investigate the seasonal ambient noise ground motions using 2-D frequency–wavenumber (FK) analysis of a 50-station array. We observe that: (1) two major azimuths can be identified in the azimuthal distribution of SNRs and amplitude differences. We also observe two minor azimuths in the seasonal variation of SNRs, amplitude differences and 2-D FK power spectra. Monthly 2-D FK power spectra reveal that two energy sources are active in the Northern Hemisphere winter and two relatively weak sources are active in summer. (2) Backprojection suggests that primary microseisms originate along the coasts of Australia or New Zealand, Canada and Alaska, Newfoundland or Greenland and South America. (3) Secondary microseisms are generated in the deep water of the northern and southern Pacific Ocean, along the coasts of Canada and Alaska associated with near-shore reflections and in the deep water of south of Greenland. (4) Weak energy is observed in the third quadrant of the azimuthal distribution of amplitude differences of sedimentary Rayleigh and Love waves in the period band of 1–5 s and correlates with the direction of widening of the basin.