Seismic noise characterization in NE Iberia

Microseisms are predominantly generated through two mechanisms: the interaction between ocean waves and the shore (primary microseisms, PM) and the interaction of ocean swells traveling in opposite directions with similar frequencies (secondary microseisms, SM). In some regions, the SM spectrum exhibits a splitting into long-period and short-period components (LPSM and SPSM, respectively), typically associated with local wave-wave interactions.

As part of the EPYSIM project and with the aim to perform an ambient noise imaging study, we deployed an array of 19 broad-band stations in two different profiles in Catalonia (NE of the Iberian peninsula). The profiles are surrounded by coastline at different azimuths and the distance to the coast along each profile increases progressively. This particular setting provides an ideal environment to investigate the characteristics of SPSM. Using the EPYSIM stations and other nearby permament stations, we conduct a detailed analysis of microseisms, including spectral time evolution, polarization analysis, and attenuation patterns.

Our findings are consistent across all analyzed years and reveal distinct back-azimuths for the microseisms: PM and LPSM predominantly originate from the North Atlantic, while SPSM exhibits markedly different back-azimuths, pointing towards the Mediterranean. Additionally, the spectral intensity of SPSM differs significantly from that of PM and LPSM, suggesting a local source for SPSM, consistent with observations in other regions.

This work has benefited from support of the EPYSIM Project, funded by the Spanish Ministry of Science and Innovation (Ref.: PID2022-136981NB-I00).