Stress field of Italy — Mean stress orientation at different depths and wave-length of the stress pattern

Abstract

We have studied the stress pattern of Italy using a dataset with 590 data records from the World Stress Map database release 2008 and 106 new data records to test the hypothesis the mean orientation of maximum horizontal stress is different at different depth sections. For this, we split the dataset into a shallow (0-6 km) and a deep (6-40 km) depth section. For the data analysis we used a new statistical tool that calculates the mean orientation on a 0.2° grid. The tool takes into account the distance to each grid point, number and quality of the data records within the search radius, and the radial distribution. The result is a smoothed Italian stress map that displays both; the mean orientation and the wave-length of the stress pattern. The stress pattern does not vary in depth except for two areas (Sardinia and southern Apulia). Therefore stress data from different depths can be used to estimate the mean orientation and the wave-length of the stress pattern in Italy. Furthermore, the smoothed Italian stress map reveals that most of Italy has short wave-length stress patterns (<150 km). This indicates that the stress field is not controlled by first-order stress sources of plate tectonics, i.e. the convergence of Africa with respect to Eurasia, but that second-order stress sources such as topography, density, strength contrasts, and major faults systems are of great importance. In four regions (western part of the Alps, northern Tuscany, northern Adriatic Sea, Calabria and eastern part of Sicily) the wave-length is <100 km. High values of the circular variance of the mean orientation observed here are driven by third-order local stress sources, such as basins or local neotectonic structures.

Active tectonics of the outer northern Apennines: Adriatic vs. Po Plain seismicity and stress fields

“…(d) Focal mechanism computed by INGV (http://cnt.rm.ingv.it/data id//4004047121/map dmt review.pdf) for the MW = 3.4, August 9, 2014 event. Seismic stations (triangles) are listed in Table 1. the other hand, the 2013 Marche offshore earthquakes (Mazzoli et al, 2014) confirmed a more complex tectonic behaviour of the Adriatic sector of the outer northern Apennines already suggested by Macchiavelli et al (2012) and Pierdominici and Heidbach (2012). There, focal mechanisms for events preceding the 2013 earthquakes were characterized by a wide range of orientation of P and T axes, and included thrust, strike-slip and extensional fault plane solutions (e.g.…”

“…On the other hand, the occurrence of NE-SW horizontal compression is clearly recorded by the 2013 Marche offshore earthquakes), suggesting that the complex, inherited fault structure characterizing the investigated area (Coward et al, 1999) may trigger significant local variations of the stress field resolved by seismological analysis (see also Macchiavelli et al, 2012;Pierdominici and Heidbach, 2012). This is consistent with the results obtained by Petricca et al (2013), who showed that a large variability of the stress field in this area results from a combination of first-order controls, due to plate tectonics (involving NNW-SSE convergence between the African and the Euroasian plates, occurring at a rate of 10 mm/year; Argus et al, 1989;Mazzoli and Helman, 1994) and mantle interaction, with second-and third-order sources including crustal structure, inherited Mesozoic features and present-day topography.…”

“…Catalano et al, 2004;Ferranti et al, 2009), it is widely accepted that extension became dominant since ca. 0.7 Ma and is still acting over the whole chain including the outer zones, as shown by breakout data and seismicity (Montone et al, 2004(Montone et al, , 2012Frepoli et al, 2011;Pierdominici and Heidbach, 2012), as well as by geological and tectonic geomorphology analyses (e.g. Cello et al, 1982;Cinque et al, 1993;Hippolyte et al, 1994;D'Agostino et al, 2001;Villani and Pierdominici, 2010).…”

A multi-stage 3-D stress field modelling approach exemplified in the Bavarian Molasse Basin

“…This results in an average data density of 0.21 data records per 100 km 2 , which is the typical claim size for exploration. In general, the orientation of the stress field does not change with depth in the upper crust Pierdominici and Heidbach, 2012;. Laterally the stress field in the Alpine Molasse rotates only gently anticlockwise from east to west .…”

A soft linkage between major seismogenic fault systems in the central-southern Apennines (Italy): Evidence from low-magnitude seismicity

“…Active normal faults along the crest of the Apennines are sub-parallel to the NW-SE striking mountain range and are controlled by the current large-scale, NE-SW trending extensional regime (for a summary: Basili et al, 2008;Devoti et al, 2008Devoti et al, , 2011DISS Working Group, 2010;Petricca et al, 2013;Pierdominici and Heidbach, 2012). The area among the southern Abruzzi, northern Campania, southeastern Lazio and southwestern Molise regions is the border between the central and southern Apennines and encompasses a large section of the OrtonaRoccamonfina Line, a regional structure striking NNE-SSW discussed by numerous authors (Fig.…”