Characterization of Microseismic Noise in Cape Verde

The interaction of ocean waves with either the seafloor or other ocean waves generates primary (PM) and secondary microseisms (SM) that propagate through the crust and mantle, predominantly as Rayleigh waves. The horseshoe geometry and surrounding bathymetry of the Cape Verde archipelago play a significant role in the ambient‐noise generation in this region. We analyze the microseisms recorded in the region using two different temporary seismic networks, and we determine the number of signals polarized as Rayleigh waves and their back azimuth (BAZ) as a function of time and frequency. The relative number of polarized signals between PM and SM varies between the stations. At most of the stations, the SM can be divided into two frequency bands. At lower frequencies (0.1–0.2 Hz), the number of SM signals is stable throughout the year, whereas at higher frequencies (0.2–0.3 Hz) this number varies with the season, with more polarized signals during the northern hemisphere spring and summer. In both frequency ranges and at most stations, the BAZ does not vary significantly over the year and points toward sources within the archipelago and outside. We compute the source site effect and show that the local bathymetry around the Cape Verde Islands strongly amplifies local SM sources. Finally, we compare the measured BAZ with source areas derived from an ocean‐wave model, which confirms that Cape Verde stations mostly record local sources.The authors thank projects CVPLUME (Ref. PTDC/CTE-GIN/64330/2006) and Cape Verde Mantle Structure (YW network) for providing the broadband seismic data they used in this research. This study was partially supported by projects Atmosphere-Ocean-Solid Earth Coupling: Seismic Tools to Explore and Monitor the Oceans (STORM) (Ref. UTAP-EXPL/EAC/0056/2017) and Transnational cooperation-Pessoa Program (PHC-PESSOA) (Ref. 4318/40851YL). This is a contribution to project Fogo Island volcano: multi disciplinary Research on 2014 Eruption (FIRE) (Ref. PTDC/GEO-GEO/1123/2014). Fundacao para a Ciencia e Tecnologia (FCT) Ph.D. Grant Ref. PD/BD/114480/2016 supported Joana Carvalho. Publication supported by FCT-project UID/GEO/50019/2019-Instituto Dom Luiz. The authors are grateful to the European COST action TIDES (ES1401) for all the discussions and for supporting Short-term scientific mission (STSM) of the authors.Peer reviewe