Increasing near-coastal ocean wave energy observed in Earth’s seismic wavefield since the late 1980

Abstract

Earth’s seismic wavefield is continuously excited by forces on the seafloor arising from ocean gravity waves. The resulting microseism signal is detected worldwide by seismographic networks, even in the deep interiors of the continents, and its spatially and temporally variations reflect global ocean wave conditions. The primary microseism signal between 20 – 14 s period is principally composed of seismic Rayleigh waves that represent the spatiotemporal integrated seismic radiation excited across near coastal bathymetry. We analyze primary microseism vertical-component amplitudes, which are insensitive to Rayleigh wave propagation direction, through late 2022 using continuous seismic data recorded by globally distributed seismographs with operational intervals exceeding 20 years and beginning with the advent of modern continuous digital broadband recording in the late 1980s. Widespread increasing median amplitudes are apparent at the majority of global stations even prior to removing non-seismic instrumental and large earthquake signals and subtraction of the stationary component of the annual signal. Increasing primary microseism amplitudes and energies at 3σ significance occur for 41 of 52 stations. Significant decreasing trends for stations are geographically restricted to the northern and western Pacific region and to two sites in the southern United States. Amplitude and energy changes show broad proportionality, with the greatest absolute increases occurring at stations with historically high microseism levels. The most rapidly proportionately intensifying energy occurs at eastern North American and European sites that are principally sensitive to wave energy in the North Atlantic, and which show median average seismic energy increases over the past three decades of 0.7 – 0.8% per year relative to long-term median values. median values. The most rapidly intensifying primary microseism levels on an absolute basis are observed for the Antarctic Peninsula with an annualized vertical seismic acceleration, velocity, and energy trends (3σ uncertainties) of 0.037 ± 0.008 nm/s2/yr (0.36 ± 0.08 %/yr), 0.093 ± 0.02 nm/s/yr (0.35 ± 0.08 %/yr), and 4.16 ± 1.07 (nm/s)2 (0.58 ± 0.15 %/yr), respectively. Average inferred wave energy increase from seismic energy metrics across analyzed stations is 0.27±0.03 %/yr for the entire data period and 0.35±0.04 %/yr for the era beginning on January 1 2000.