Studying the stress field variations in the Vrancea-zone using clustering-based stress inversions

The SE-Carpathians indicate significant geodynamic activity, especially in the external part due to the current subduction processes. This part is the so-called Vrancea-zone where the distribution of the seismic events is quite dense considering the relatively small area (around 30*70 km).

The authors have carried out cluster analyses of the focal mechanism solutions and their inversions to support the recent and previously published studies in this region. They have applied different pre-existing clustering methods – e.g. HDBSCAN (hierarchical density-based clustering for applications with noise) and agglomerative hierarchical analysis – considering the geographical coordinates, focal depths and parameters of the focal mechanism solutions of the used seismic events, as well. Moreover, they have attempted to improve a fully-automated algorithm for the clustering of the earthquakes for the estimations. This algorithm has only one optional hyper-parameter which is eligible to detect the outliers from the input dataset. Due to this, it is possible to reduce the running time and subjectivity. In all cases, the calculated stress tensors are in close agreement with the previously published results.