Shallow seismic velocity structure beneath San Miguel volcano, El Salvador, estimated using seismic ambient noise (0.2–1.3 Hz)

San Miguel volcano is one of the most active volcanoes in El Salvador, yet its structural characteristics remain underexplored. We developed a one-dimensional seismic velocity structure model by analyzing seismic ambient noise recorded around the volcano and inverting the Rayleigh wave dispersion curves. The data were obtained from a temporary seismograph network deployed in 2014. We applied the spatial autocorrelation (SPAC) method and ambient noise seismic interferometry (ANSI), assuming the temporal and spatial uniformity of ambient noise characteristics. The SPAC method enabled the derivation of phase velocities for surface waves within the frequency range of 0.2 to 1.0 Hz. Additionaly, we estimated Rayleigh wave group velocities using ANSI, which employs Green's function derived from cross-correlating ambient noise. The resulting dispersion curve was acquired in the 1.0–1.3 Hz frequency band. The velocity model revealed four sedimentary layers, with S-wave velocities ranging from 1.0 to 2.5 km/s overlying a half-space layer. Using the obtained velocity model, we located volcano-tectonic earthquakes, resulting in more accurate hypocenter determinations. The seismicity was found to align with a deformation zone known as the San Miguel Fracture Zone, situated on the volcano's northern flank.