Persistent Narrowband Seismic Signal from the Eastern Mediterranean

Abstract The analysis of continuous seismic records provides valuable information on the origin of seismic noise and other long-lasting processes acting within or at the surface of our planet. Unlike impulsive earthquake signals, these emergent wavefields often reflect physical mechanisms linked to fluids, ocean–solid Earth interactions, and broader geodynamic activity. Identifying such unconventional signals is therefore essential for revealing previously unrecognized components of the Earth system. In this work, we present results from a continuous analysis based on seismic wavefield coherence. This approach allowed us to identify a previously unknown persistent signal at a frequency of 0.03 Hz. The signal is observed over a 15 yr period and originates from the Nile Fan, a region characterized by deep fluid reservoirs and active fluid seepage at the seafloor. Consistent with these geological observations, we model the signal as the resonance of a kilometer-scale, fluid-filled crack. Additionally, we document a significant seasonal modulation of the signal strength, revealing an important interaction between processes in the solid Earth and oceanic activity.