Present state of tectonic stress of the Friuli area (eastern Southern Alps)

Abstract

Stress orientations are determined for the Friuli area from focal mechanisms using the inversion technique of Gephart and Forsyth (1984). The data consist of 244 fault plane solutions selected for the period 1988–1995. Where the data coverage was poor, this period was extended to 1978–1996. Local magnitude ranges from 2.0 to 4.3 and the depths extend from 4 to 16 km. The Friuli area is subdivided into five seismotectonic zones on the basis of tectonic characteristics, seismic activity and focal mechanisms, and for each zone a stress tensor is determined. The results show that the active tectonic stress in the Friuli area is heterogeneous and conditioned by the complex structural pattern, which is characterized by two indented tectonic wedges. The western and central parts of the area are mainly affected by a compressional state of stress, while in the eastern part a strike-slip state of stress prevails. The orientation of the principal stresses varies from the western to the eastern part of the area, and differences are also noticeable with depth. In the central part of the Friuli area the maximum compressional stress is N–S trending at shallow depths (<10 km), changing to NW–SE at deeper levels. The maximum compressional stress is NW–SE oriented in the western part, while in the eastern part it is N–S oriented.