Seafloor seismic noise at Central Eastern Mediterranean sites

Abstract

This work focuses on long-term broadband seismic signals acquired in shallow and deep seafloor sites of the Central-Eastern Mediterranean. We generated a reference model of background seismic noise based on seafloor observatories data. The observatories have been deployed at sites in the Ionian Sea, Tyrrhenian Sea, Marmara Sea and Gulf of Corinth. We concentrate on interesting and peculiar features of the noise signal in the frequency band 0.003-50 Hz. The main contribution in the short period band >5Hz (<2s) comes from anthropic noise. In this band we find a peak around 0.8Hz (1.25s) which appears to be a persistent characteristic of the Mediterranean basins. Seasonal variations (summer-winter) are visible in the microseismic band 0.05-0.5Hz (2-20s). In the Ionian and Tyrrhenian deep seafloor sites we can distinguish the splitting of the DF in the long period (LPDF) and the short period (SPDF) peaks. The seasonal variations of the ratio between the LPDF and the SPDF amplitudes suggests that the SPDF depends on sea wave regime generated by local winds, while the LPDF can be considered a feature of deep seafloor sites not far from the coastlines. The shallow enclosed Mediterranean sites are characterized by an energetic bump between 0.3-0.4 Hz, which could be explained by a combination of effects which depend on bathymetry, water depth and local seastate.