## 5 Conclusions  
We applied the LOTOS algorithm to investigate as in detail as possible the seismic velocity variations in the area located in the proximity of Targu Jiu city, where a large earthquake sequence was recorded in 2023. The distribution of Vp and Vs anomalies reveals significant variations in the crustal structure, highlighting compact rock zones and areas affected by a complex system of faults and fractures. A well-defined NE-SW alignment is emphasized, separating a zone of high velocity toward the northwestern side from a zone of low velocity toward the southeastern side. It reflects the structural contrast between the orogen and the depression areas. It also coincides with the epicentral distribution of the sequence of 2023 and could be considered the active fault that generated this sequence. The alternation between high-velocity and low-velocity anomalies is visible in the area where the hypocenters are located. On the one side, the hypocenters appear to be located mostly in a high-velocity body, but on the other side in the immediate vicinity of low-velocity anomalies, which makes us believe that fluids played an important role at least in the migration process of the hypocenters and could explain the unusually long duration of the aftershocks. Thus, evidence of an anomaly with high \(\mathrm{Vp/Vs}\) in the epicentral area, at a depth of around 10-15 km, may be an important argument in favor of the hypothesis of the presence of fluids in the tectonic process studied. The outcome of our analysis provides new elements for a better understanding of the crustal structure and tectonics in the Targu Jiu area and can help improve seismic hazard and risk modeling at a regional scale. While seismic tomography codes such as LOTOS present certain technical limitations--particularly related to model initialization, sensitivity to input parameters, and manual data configuration--these challenges can be partially mitigated through the integration of AI-driven methods in the data pre-processing phase. Future studies should explore the development of hybrid workflows that combine physics-based inversion with automated, intelligent data handling to improve model stability, scalability, and resolution quality. [PERSON] performed the tomographic model calculation and prepared a substantial part of the manuscript, [PERSON] supplied the geotectonic of the area, [PERSON] provided the 1D velocity model input for the study, [PERSON] developed the scripts for data conversion to LOTOS format, [PERSON] and [PERSON] supplied the information about the seismic station network, [PERSON] provided important feedback during the writing of the paper. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] participated in discussions of the results and contributed to writing the manuscript and preparing figures. All authors have read and agreed to the published version of the manuscript. The APC was funded by grant no. PN23360301/2023 from NUCLEU Progam \"Cerecetari avansate pentru modelarea fenomenelor naturale si antropice din sistemul cuplat Pamant-Atmosfera in scopul reducerii riscuplat.\" SOL4 RISC\" supported by the Ministry of Education and Research. Not applicable. The data presented in the study are available in the repository: Zenodo: \"[[https://zenodo.org/records/15099788](https://zenodo.org/records/15099788)]([https://zenodo.org/records/15099788](https://zenodo.org/records/15099788)) (accessed on 21 May 2025)\". The files are currently embargoed. The record is publicly accessible. On 15 August 2025, the files will automatically be made publicly accessible. Until then, the files can only be accessed by users specified in the permissions. The embargo can be lifted after the article is accepted for publication. This work was carried out in the framework of grant no.