The present-day stress field orientation in Italy: new release

Abstract:

When contemporary stress field in a region is well-known and faults are identified, it is possible to determine which faults are favorably oriented and are more likely to slip in the future. Stress data are also an important input in integrated crustal modeling to get more reliable evaluations in many applicative researches. Then, the knowledge of the active stress field contributes to the seismotectonic zoning of a region.

In Italy, although at large scale a first order stress field due to plate boundary forces controls the contemporary tectonics, some areas show changes in stress regime over small distances and/or with depth clearly linked to localized stress perturbations. Where information is lacking each prediction of stress patterns could significantly differ from the reality and any further evaluation would be weakly supported by data.

Therefore we continuously collect the available stress indicators and here present an update of present-day stress orientations in Italy with the last 5 years data, relative to crustal earthquake focal mechanisms (0-40 km depth), borehole breakouts from deep wells and fault data. About 100 new quality-ranked entries complete the definition of the horizontal stress orientation and tectonic regime in some areas, and bring new information mainly in Po Plain and Calabria area, recently affected by important earthquake sequences. Now the global Italian dataset consists of ~800 data points, including ~580 of A-C quality, with an increase of 17% compared to the previous compilation (Montone et al., 2012). We use A-, B- and C-quality stress indicators for analyzing first-order stress patterns while we also consider D-quality data to define second-or third-order stress field, as observed in other studies in the world. In particular we discuss the simultaneous occurrence of different stress regimes and the complex interaction between first order stress field and local effects, and the influence of the inherited tectonic structures.