Abstract
In this work, we investigated the microseism recorded by a network of broadband seismic stations along the coastline of eastern Sicily. Microseism is the most continuous and ubiquitous seismic signal on Earth, and is mostly generated by the ocean - solid earth interaction. On the basis of spectral content, it is possible to distinguish three types of microseism: primary, secondary and short period secondary microseism. We showed how most of the microseism energy recorded in eastern Sicily is contained in the secondary and short period secondary microseism bands. This energy exhibits strong seasonal patterns with maxima during the winters. By applying array techniques, we observed how the short period secondary microseism sources are located in areas of extended shallow water depth: the Catania Gulf and a part of the Northern Sicily coastlines. Finally, by using the significant wave height data recorded by two buoys installed in the Ionian and Tyrrhenian Seas, we developed an innovative method, selected among up-to-date machine learning techniques, able to reconstruct the time series of sea wave parameters from microseism recorded in the three microseism period bands by distinct seismic stations. In particular, the developed model, based on random forest regression, allowed estimating the significant wave height with a low average error (~0.14 - 0.18 m). The regression analysis suggests that the closer the seismic station to the sea, the more information concerning the sea state are contained in the recorded microseism. This is particularly important for a future development of an experimental monitoring system of the sea state conditions based on microseism recordings.
Highlights
Microseism is the most continuous and ubiquitous seismic signal on Earth and is mostly generated by the ocean–solid earth interaction (Tanimoto et al, 2015)
Concerning the median error in the back azimuth estimations obtained by the jackknife technique, it was equal to 21◦ and 12◦ for back azimuths oriented toward the Tyrrhenian and Ionian Seas, respectively
We investigated the microseism recorded close to the Eastern Sicily coasts and its relationship with the significant wave height recorded by two buoys installed in the Ionian and Tyrrhenian Seas
Summary
Microseism is the most continuous and ubiquitous seismic signal on Earth and is mostly generated by the ocean–solid earth interaction (Tanimoto et al, 2015). Concerning PM, it shares the same spectral content as the ocean waves (period band 13–20 s) and its source is associated with the energy transfer of ocean waves breaking/shoaling against the shoreline (Hasselmann, 1963; Ardhuin et al, 2015). As for SM, it is likely to be generated by Insights Into Microseism Sources by Array and MLTs interactions between waves of the same frequency traveling in opposite directions, has roughly twice the frequency of ocean waves (period band 5–10 s), and generally shows a higher amplitude than does PM (Longuet-Higgins, 1950; Oliver and Page, 1963; Ardhuin et al, 2012, 2015). Grevemeyer et al (2000) analyzed a 40-year-long record of wintertime microseism and observed an increase in the number of monthly days with strong microseism activity, inferring an increase over time in surface air temperatures and storminess of the northeast Atlantic Ocean
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