Seismicity, seismogenic structures, and crustal stress fields in the greater Rome area (central Italy)

Abstract

Instrumental seismicity of the greater Rome area is analyzed using the most recent seismological database. The aim of this study is to identify potential seismogenic structures responsible for the moderate seismicity that characterizes this sector, where no surface faulting is expected on the basis of the absence of strong local earthquakes, as evidenced by the 2000‐year‐long historical record. Nevertheless, in light of the great value and the high vulnerability of the architectural and monumental patrimony of Rome, even the occurrence of moderate events imposes a careful assessment of the hazard, linked to the presence of active faults that are undetectable by means of classic geological field investigation. Seismic data here analyzed belong to the period 1997–2008 and show local magnitude (ML) ranging from 1.5 to 4.7. To better constrain the hypocentral depths, we computed the Vp/Vs ratio using a modified Wadati method and the minimum 1‐D velocity model that approximates the seismic structure of the study area. Moreover, we applied a double‐difference hypocentral determination technique to improve earthquake locations. Most of the located seismicity appears to be concentrated within seven main clusters. Spatial distribution of the seismicity allowed us to identify several seismogenic structures, corresponding to previously undetected or only supposed active faults. The stress tensor obtained by inverting the focal mechanisms computed in this study is in agreement with the NE–SW extensional tectonic stress active in the inner chain of the Apennines, although there is evidence of some local stress field heterogeneities.