Abstract
Abstract. The studied area of the northwestern (NW) Dinarides is located in the northeastern (NE) corner of the Adriatic microplate and is bordered by the Adriatic foreland, the Southern Alps, and the Pannonian basin. Its complex crustal structure is the result of interactions among different tectonic units, the most important of which are the Eurasian plate and the Adriatic microplate. Despite numerous seismic studies in this tectonically complex area, there is still a need for a detailed, small-scale study focusing mainly on the upper, brittle part of the crust. In this work, we investigated the velocity structure of the crust with one-dimensional (1-D) simultaneous hypocenter–velocity inversion using routinely picked P- and S-wave arrival times. Most of the models computed in the combined P and S inversion converged to a stable solution in the depth range between 0 and 26 km. We further evaluated the inversion results with hypocenter shift tests, high- and low-velocity tests, and relocations. This helped us to select the best performing velocity model for the entire study area. Based on these results and the seismicity distribution, we divided the study area into three subregions, reselected earthquakes and stations, and performed the combined P and S inversion for each subregion separately to gain better insight into the crustal structure. In the eastern subregion, the P velocities in the upper 8 km of the crust are lower compared to the regional velocities and the velocities of the other two subregions. The P velocities between 8 and 23 km depth are otherwise very similar for all three models. Conversely, the S velocities between 2 and 23 km depth are highest in the eastern subregion. The NW and southwestern (SW) subregions are very similar in terms of the crustal structure between 0 and 23 km depth, with slightly higher P velocities and lower S velocities in the SW subregion. High vP/vS values were obtained for the layers between 0 and 4 km depth. Below that, no major deviations of vP/vS in the regional model from the value of 1.73 are observed, but in each subregion we can clearly distinguish two zones separated by a decrease in vP/vS at 16 km depth. Compared to the model currently used by the Slovenian Environment Agency to locate earthquakes, the obtained velocity models show higher velocities and agree very well with some of the previous studies. In addition to the general structural implications and the potential to improve the results of seismic tomography, the new 1-D P and S velocity models can also be used for reliable routine earthquake location and for detecting systematic travel time errors in seismological bulletins.
Highlights
The study area of the northwestern (NW) Dinarides lies at the northeastern (NE) corner of the Adriatic microplate and is bounded by the Southern Alps to the north, the Pannonian basin to the east, and the Adriatic foreland to the west, representing an important junction between these units (Fig. 1)
The first 3-D compressional (P) wave velocity model in this area was obtained with local earthquake tomography (LET) study done by Michelini et al (1998)
The authors proposed a relocation study using the 3-D velocity model to map active faults and trends in seismicity. This was partly realized by a study that focused on the Idrija fault system in western Slovenia (Vicicet al., 2019)
Summary
The study area of the northwestern (NW) Dinarides lies at the northeastern (NE) corner of the Adriatic microplate and is bounded by the Southern Alps to the north, the Pannonian basin to the east, and the Adriatic foreland to the west, representing an important junction between these units (Fig. 1). The first 3-D compressional (P) wave velocity model in this area was obtained with local earthquake tomography (LET) study done by Michelini et al (1998) It revealed two areas of distinct high and low velocities in western and eastern Slovenia, which were interpreted as the upper-crustal expression of the ongoing convergence between the Adria and the Eurasia. The model of Guidarelli et al (2017) was obtained with ambient seismic noise tomography and shows distinct lateral change in the crustal structure under western Slovenia This was interpreted as a transformation from a uniform to a more variable crustal structure across the bounding strike-slip Idrija fault, indicating the transition between the Dinarides and Pannonian basin units. The latest receiver functions study applied to the Dinarides and the surrounding area (Stipcevicet al., 2020) showed the transition from the thick Dinaric crust to the thinner Pannonian crust and indicated that the earthquake depths generally follow the crustal thickness
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
