Nature of “transparency windows” in the broadband spectrum of seafloor microseisms

Abstract

The peculiarities of the microseisms spectra shape when recording on the ocean floor in the frequency band of 0.003–20 Hz are examined. The origin of the stable minima in the microseisms spectrum (“transparency windows”) at frequencies of about 0.02–0.1 Hz and 5–15 Hz is analyzed. In these frequency bands, weak earthquake signals are recorded by bottom instruments. The origin of the low-frequency “transparency windows” can be explained by the conditions of the microseisms propagation in the oceanic waveguide (between the bottom and the water’s surface) in the abyssal plain zones. The results of the full-waveform numerical simulation of the seismoacoustic waves propagation in the oceanic environment and on the ocean-continent border are presented, and the experimental data as well. The peculiarities of the microseisms spectra in the band of high-frequency “transparency windows” can be caused by the constructive resonance in the water-saturated layer of bottom sediments. The theoretical foundation and experimental results are given.