Investigation of the Upper Crustal Structure in the NW Dinarides Using Local Earthquake Tomography

The area of the NW Dinarides lies in the northeastern corner of the Adriatic microplate – a promontory of the African plate – which plays a major role in the collision processes occurring in the peri-Adriatic region. Taking advantage of the greatly increased amount of data due to the modernization of the Slovenian seismological network, improved cross-border data exchange, and the tempoprary deployments within the large pan-european AlpArray project, we performed 3-D simultaneous hypocenter–velocity inversions with routinely picked arrival times of P- and S-waves from 502 local earthquakes. The resolution analysis showed that the resulting 3-D P-velocity and vP/vS model could be successfully recovered at least up to a depth of 15 km. Our results are consistent with previous studies, but provide better resolution in the upper crust and, for the first time, a uniform and simultaneously computed vP/vS model for the entire study area. The final 3-D models show two distinct velocity anomalies with a narrow transition zone in between. The velocity anomaly in the west of our study area reflects the thrust structure that formed due to the underthrusting of the Adriatic microplate, while the anomaly in the east marks the transition to the Pannonian basin. The recovered velocity distribution also appears to correlate spatially with seismicity, which is tied to the Moho topography at depth. The seismicity relocated with the computed models is on average shallower and has better determined locations than the seismicity located with the 1-D velocity model used in the daily earthquake analysis.