Seismotectonic investigations in the inner Cottian Alps (Italian Western Alps): An integrated approach

Abstract

This work integrates the results of recent geological-structural studies with new seismological data for the inner Cottian Alps to investigate the connection between faults and seismicity. The major post-metamorphic tectonic feature of this sector is represented by a N-S structure, named LisTrana Deformation Zone (LTZ). Since the Late Oligocene this structure accommodated right-lateral (Late Oligocene-Early Miocene) and subsequently normal (post-Early Miocene) displacements. In the Pleistocene, the activity of the LTZ seems to have caused the development of lacustrine basins inside the valleys that drain this sector of Western Alps. The present-day seismicity joins the northern part of the LTZ and, southwards, other minor sub-parallel structures. In transversal crosssection hypocentres highlight steep surfaces. Focal mechanisms calculated along this structure show both extensional and strike-slip solutions, mostly with one roughly N-S striking nodal plane. 3Both sub-horizontal (with NE-SW to ENE-WSW trend) and steeply dipping P axes with N-S to NW-SE sub-horizontal T axes are observed.Even if clear evidence of Quaternary tectonic activity in the area is missing, on the basis of the available seismological and geological data we propose that in the inner Northern Cottian Alps the present-day seismic activity may be connected to the LTZ, interpreted as minor sub-parallel fault strand of the Canavese Line. The kinematics of this structure is consistent with the focal mechanisms calculated in this area. Structural and seismological data indicate that LTZ is active under a bulk dextral-transtensive regime since the late Oligocene in the inner Cottian Alps, in agreement with the data published for the adjacent domain of the chain.

Post-collisional tectonics in the Northern Cottian Alps (Italian Western Alps)

“…In the analysed area, this extension direction corresponds well with that observed for the second faulting stage and may be related to the present-day activity of N-S normal and/or oblique-normal faults, as proposed by Eva et al (1997) and by Perrone et al (2009b).…”

Current tectonic activity and differential uplift along the Cottian Alps/Po Plain boundary (NW Italy) as derived by PS-InSAR data

“…The Alps-Apennines junction zone, which is subjected to moderate differential uplift, as observed by GPS data (Devoti et al, 2011), is affected by low magnitude instrumental seismicity (M L < 5) despite the fact that historically, earthquakes that have struck this area have reached up to a moderate magnitude (seismic event of the April 2 nd IKM have been compared with the available geological, structural, geomorphological, seismological and GPS data to study the relationship between differential uplift, crustal mobility and the current tectonic activity of this sector. This study contributes to improving the knowledge of the current tectonic activity in the Western Po Plain and provides some new constraints for the recently outlined seismotectonic model (Perrone et al, 2010(Perrone et al, , 2011b …”

“…Seismotectonic studies (Perrone et al, 2010(Perrone et al, , 2011a recently showed that the seismic activity of this area could be partly related to the current activity of the N-S regional faults (Col del Lis-Trana Deformation Zone) affecting the inner border of the Cottian Alps, as seismological and structural data show consistent geometry (map view and cross-section) and kinematics (Fig. 4).…”

“…By contrast, in the Stura di Lanzo, Sangone, Chisone and Pellice valleys, glaciers did not ever reach the Western Po Plain. The development of Pleistocene intra-mountain lacustrine basins in the lower Pellice and Chisone valleys may be, therefore, related to the activity of the N-S faults bordering the inner part of the Alpine chain (Perrone et al, 2010(Perrone et al, , 2011b and references therein).…”

Geological map of the Mount Ciantiplagna rock avalanche (Chisone Valley, Italian Western Alps)

“…Lastly, seismic activity that affects the central sector of the Western Alps, with few strong historical earthquakes with a maximum MCS intensity I 0 ¼ VII -VIII (e.g. the 2 April 1808, seismic sequence; Perrone et al, 2010) can be regarded as a probable triggering factor for the rock avalanche.…”