Seasonal Variability of Short-Period Ocean Wave Interactions from Ambient Seismic Noise Cross-Correlations in the Southern Pacific of Costa Rica

Using the cross-correlation of ambient seismic noise, recorded by the permanent broad-band seismological stations operated by the Volcanological and Seismological Observatory of Costa Rica (OVSICORI), along the Osa and Burica Peninsulas in the southern Pacific, we analyze the temporal stability of daily Green’s functions (GFs) between 2019 and 2023. Green’s functions, composed mainly by surface waves, are used for monitoring and studying the internal composition of the Earth and its possible changes with time, in a technique known as waveform interferometry. We analyzed the period band of 1-10 s, which seismic energy radiation is modulated by the so-called second microseism, a complex ocean wave interaction with the Earth crust and between similar frequency waves traveling in opposite directions. Our study demonstrates seasonal variations in the sources of ambient seismic noise as a function of time, retrieved as periodic changes in the correlation coefficient (CC) between the daily GFs and the reference GF. For each station pair analyzed, the seasonality is strongest in the period band of 1-3 s, where sources are influenced by shorter-period wave interactions. The largest reduction in CC (~ 90%) is measured along the Golfo Dulce, during the months of January and April every year. These variations are likely associated with the dry season and the cease of the coastal storms, hurricanes and oceanic swells. The periodicity observed in the correlation of GFs is in concert with precipitation tables and water heights measured from buoys in the region. Thus, seismic interferometry has enormous potential for investigating complex interactions in Ocean dynamics, especially along those micro economic regions depending on the ecological, biological and marine diversity that could be more affected by climate change in the coming future.