Croatian catalogue and database of focal mechanism solutions, characteristic mechanisms, and stress field properties in the Dinarides and the surrounding regions

Abstract

This report presents the CroFMS catalogue and database of focal mechanism solutions (FMS). It is based on the first-motion polarity data for earthquakes in Croatia and the neighbouring regions, collected over last four decades. The current catalogue version contains FMS for 410 earthquakes that were computed consistently, using the same programs, velocity models, and sets of parameters. Its content is described in terms of distributions of the time and origin of polarity picks, magnitudes, epicentral distances of stations, the quality marks, the phases used, azimuthal gap and distance to the closest station. It was also shown that solutions from the CroFMS catalogue and those independently obtained from the moment tensor inversions are generally consistent.

Comparison of observed FMS with the latest European model of active fault sources (EFSM20) revealed several inconsistencies, most notably in the Zagreb and Petrinja epicentral areas, the greater Rijeka region, the Central Adriatic archipelago, and in the zone of surface traces of the thrust fronts of the East-Bosnian–Durmitor and Drina–Ivanjica nappes in Bosnia and Herzegovina.

Spatial averaging of FMS over the whole study area produced maps of characteristic focal mechanisms, which may be found useful in the seismic hazard assessment in the areas where active faults are not identified or characterised.

A formal stress inversion of the focal mechanism solutions produced a map of maximum horizontal stress orientations across the study area, revealing localized lateral variations that had not been identified in previous studies.

Electronic supplement:

Three FMS catalogues in the form of Excel-files are available for free download:

1. The CroFMS catalogue ­– file: CroFMS_2024.xlsx
2. The catalogue of characteristic focal mechanisms based on first-motion polarity solutions only – file: Characteristic_FMP_2024.xlsx
3. The catalogue of characteristic focal mechanisms based on the first-motion polarity solutions and the best double-couple solutions by the moment inversion – file: Characteristic_FMP_MTI_2024.xlsx

The first row is the header: N – Serial number of FMS; Year; Month; Day; Hour; Minute; Second; Lat. – latitude °N; Lon. – longitude °E: Depth – in km; M­ – magnitude M_L; NP1str – strike of nodal plane 1; NP1dip – dip of nodal plane 1; NP1rake – rake of nodal plane 1; NP2str – strike of nodal plane 2; NP2dip – dip of nodal plane 2; NP2rake – rake of nodal plane 2; Pst – strike of the P-axes; Pdip – dip (plunge) of the P-axes; Tst – strike of the T-axes; Tdip – dip (plunge) of the T-axes; Qual – Quality of solution (1–5).

 None of the two nodal planes is the preferred one. The catalogues are up to date until 30 June 2024.