The studied area of the NW Dinarides lies in the NE corner of the Adriatic microplate. We investigated the velocity structure of the Earth’s crust using the concept of the minimum 1-D velocity model and the method of local earthquake tomography (LET), taking advantage of the greatly increased amount of data available after the modernisation of the Slovenian seismological network. We performed 1-D and 3-D simultaneous hypocentre–velocity tomographic inversions with routinely picked P- and S-wave arrival times. Most of the models computed in the combined 1-D P- and S-velocity inversion converged to a stable solution up to a depth of 26 km. The results of the 1-D inversion were evaluated using stability tests and relocations of earthquakes and quarry blasts to select the best performing regional 1-D P- and S-velocity model. In the next step, the study area was divided into three subregions and the combined 1-D inversion was rerun for each to gain better insight into the crustal structure. The regional 1-D model served as the starting point for the LET inversion for the 3-D P-wave velocity and vP/vS model. We then evaluated the resulting 3-D models with extensive analyses of various resolution parameters, synthetic tests, and relocation of earthquakes and blasts, showing that the velocities were successfully recovered at least to a depth of 15 km. Our results agree well 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 distribution of velocities in the final 3-D model shows two distinct velocity anomalies and indicated to the thrust structure in the west formed in response to the underthrusting of the Adriatic microplate. The recovered velocities can also be associated with seismicity patterns. The seismicity relocated with the computed models is shallower and has better determined locations compared to the routinely located seismicity.
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