Impact of the tsunami excited by the 2011 M_W9.0 Japan earthquake on seismic ambient noises

The M_W9.0 earthquake on March 11, 2011 occurred in the northeastern sea of Japan triggered a catastrophic tsunami, which had significant influences on the seismic ambient noises with ocean-lithosphere coupling. This study uses the continuous data recorded by seismic stations along the coast and inland of North America, combined with the seafloor pressure data recorded by the DART system nearby, as well as the predicted tidal data to analyze the impact of this tsunami on the seismic ambient noises by using time-frequency analysis and polarization analysis methods. The results show that this tsunami had little impact on the high-frequency noise （1.3−1.5 Hz） and short-period double-frequency microseisms （0.18−0.4 Hz）, while it significantly enhanced the amplitudes of long-period double-frequency microseisms （0.1−0.15 Hz）, single-frequency microseisms （0.05−0.08 Hz）, as well as the Earth’s background free oscillations （0.004−0.007 Hz）. Moreover, as the frequency of the ambient noise decreases, the amplitude enhancement becomes more pronounced and lasts longer. When the tsunami reaches the shore, it has an impact on the ambient noise of coastal stations nearby for all three frequency-bands of Earth’s background free oscillations, microseisms, and high-frequency noise and becomes the main energy source of seismic ambient noises at all three frequency bands. And the position of the dominant tsunami sources changes with time. All above-mentioned suggests that the influence of tsunami on seismic ambient noise is related to the propagation characteristics of tsunami, that is, due to the influence of water depth, reflections and diffractions of seafloor and inshore topography, the energy accumulation area changes with time, and the energy does not propagate uniformly to the coast, resulting in the changes of dominant polarization direction of seismic ambient noise in different frequency bands with time. By cross-disciplines of seismology and oceanography, this study is of significance for advancing studies on the coupling mechanism of ocean-lithosphere, identifying the characteristics of tsunami waves from the perspective of seismology, as well as exploring new tsunami warning mechanisms.