Abstract I present the results of a crustal rheological analysis of the Potenza 1990 and Molise 2002 (southern Italy) deep foci (10–25 km) strike–slip earthquake sequences ( M max =5.7) located in the upper half of the middle crust. The analysis consists of geotherms and two-mechanism (brittle frictional v. ductile plastic flow) strength envelopes. Strength envelopes are calculated along a sub-vertical E–W-striking inherited crustal-scale fault zone reactivated under a strike–slip tectonic regime. The effects of high pore-fluid pressure ( Pf ) and strain rate increase due to afterslip processes during the co-seismic and early post-seismic phases are evaluated. The results are compared with the depth-distribution of seismicity. Under long-term strain rates, the rheology predicts a brittle layer in the upper part of the middle crust embedded by two plastic horizons: the base of the carbonates and the Verrucano layer (above) and the lower part of middle crust (below). The best rheological model for the observed seismicity is that considering high Pf in the middle crust (λ≥0.65). Brittle faulting aided by high Pf in the middle crust is in agreement with the focal depths and magnitudes of the main shocks. The upward and downward widening of the brittle layer in the middle crust, due to the increased strain rate in the co-seismic and early post-seismic phases (afterslip), agrees with the width of the aftershock zones. The weak ductile layer at the base of the carbonates (and possibly within the Verrucano) appears to have an important role in delimiting the seismogenic faulting upwards and probably played a role in defining a seal to fluid up-flow along the fault zone.

Abstract This study focused on a set of shallow subvolcanic bodies, mainly laccoliths and sills, that intruded the Upper Permian-Lower Triassic sedimentary sequence of the central Southern Alps, in the area of Montecampione (Val Camonica, Italy). These intrusions represented a shallow magmatic reservoir probably associated with Triassic volcanism. Based on a detailed stratigraphic reconstruction, this paper presents results dealing with the evaluation of the emplacement depth, the estimated volume of the subvolcanic bodies, a description of their geometries, and their relation to the host rock and response of the sedimentary units to the intrusions. The emplacement depth was estimated using the thickness of the sedimentary overburden at the time of emplacement, and by applying simple equations involving laccolith dimensions. The results are comparable, and support an average emplacement depth of about 1300 m. The minimum volume of the intrusions was obtained using a GIS, and is about 1 km 3 . Concerning the relationship between the intrusive bodies and the host rock, we observed that sills are mainly emplaced into the Servino Formation, while the laccoliths are emplaced near the contact between the Verrucano Lombardo and the Servino Formation. The two sedimentary units show a different response to the intrusion: the Verrucano Lombardo always appearing fractured and tilted, while the Servino Formation shows a range of deformation patterns, from light ductilization at the contact, to folding, brecciation and foliation. These different responses reflect the mechanics of emplacement and geometry of the intrusions, and local heterogeneities in the host rock. Both units show a local thermal effect close to the contact.