Seismic Tomography in the Târgu Jiu Region (Romania): Relationships with Seismic Velocity Anomalies and Fault Activity

This study presents a seismic tomography analysis of the Târgu Jiu region in southwestern Romania, an area that experienced an unusual earthquake sequence in 2023. Using P- and S-wave arrival times local earthquakes, we applied the LOTOS algorithm to produce high-resolution 3D crustal seismic velocities models. High Vp and Vs values in the northern and northeastern areas suggest the presence of dense, rigid geological formations, likely associated with consolidated magmatic or metamorphic units. In contrast, the central region exhibits low Vs values, coinciding with an active seismic zone and intersecting major fault structures. This suggests the presence of highly fractured and weakly consolidated rocks, potentially saturated with fluids. The Vp/Vs ratio in the central region reached values of ≥1.8–1.9, indicating fluid-filled fractures that may influence fault dynamics and earthquake occurrence. In the southern region, velocity anomalies suggest weakly consolidated sedimentary units with a high degree of fracturing. These findings contribute to a better understanding of the geodynamic behavior of the Târgu Jiu area and its seismic hazard potential.