Shallow seismic velocity structure beneath San Miguel Volcano, El Salvador, estimated using seismic ambient noise (0.2–3.0 Hz)

We investigated the shallow seismic velocity structure of San Miguel Volcano, El Salvador, using seismic ambient noise data recorded by a temporary broadband seismic network. Phase velocities were estimated using the spatial autocorrelation (SPAC) method, and group velocities were obtained through ambient noise interferometry. Although the array geometry was irregular, the extended observation period allowed reliable velocity estimation across a broad frequency range (0.2–3.0 Hz). A joint inversion of phase and group velocity dispersion curves yielded a one-dimensional shear-wave velocity (Vs) model, comprising four layers overlying a high-velocity half-space to a depth of approximately 3 km. To evaluate the applicability of the velocity model, we relocated volcano-tectonic earthquakes using P-wave arrival times. The resulting hypocenters showed tighter clustering along the San Miguel Fracture Zone than those estimated using a conventional regional model. These results highlight the influence of shallow structure on earthquake location and demonstrate the importance of site-specific velocity models in volcanic regions. This study presents the first Vs model for San Miguel Volcano and provides a geophysical basis for future high-resolution tomography and volcanic hazard assessment.

Graphical Abstract