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Global Frequency-dependent Primary and Secondary Band Microseism Change Since the Late 20th Century

Description: 

Extensive digital seismic data archives enable the analysis of the global microseism wavefield across nearly four decades. We examine multi-decade variability in vertical-component (Rayleigh wave-dominated) primary and secondary microseism signals between 1988 and 2024. 73 stations from 82.5^o N to 89.9^o S latitude from the Global Seismographic, New China Digital, and GEOSCOPE networks are used; all with >20 years of data and >80% data completeness. Acceleration power spectral densities are estimated using 50%-overlapping, 1-hr moving windows integrated in 2-s wide period bands to produce band-passed amplitude time series. We remove nonphysical outliers, earthquake signals, and harmonic seasonal variations (using a fundamental period of T₀ = 365.2422 d). We smooth with a T₀/6 moving-median window to emphasize seasonal-scale and secular variability and estimate primary (14–20 s) and secondary (4–10 s) band trends using L1 residual norm-minimizing functions. Increasing microseism amplitude is observed for most of the Earth in both the primary and secondary bands (averages of 0.16 and 0.09 %/yr, respectively). The two microseism secular change rates correlate at R=0.65 and have a regression slope 1.04. However, secondary trends are systematically lower by about 0.05 %/yr, consistent with variable excitation of the secondary source relative to the primary due to its dependence on interfering ocean waves. Primary microseism signal station histories regionally cluster to station separations of 1000’s of km and multiyear signal variations reflect the effects of interannual variability (e.g., El Niño–Southern Oscillation) on large-scale storm and ocean wave energy. Microseism intensity histories in 2-s period bands exhibit global to regional correlations that reflect teleconnected ocean swell, Rayleigh wave propagation and attenuation, and the large-scale reach of climate variation. Secular trends as a function of period suggest greater intensification of microseism energy at long periods, consistent with more frequent large-scale storm systems that produce longer-period ocean swell.

Session: Geophysics in a Changing World: Monitoring Applications from Seismology and Beyond - I

Type: Oral

Date: 4/15/2025

Presentation Time: 05:00 PM (local time)

Presenting Author: Richard

Student Presenter: No

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