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Climate change and the energy crisis forced industrialized countries to contain CO2 emissions and use indigenous renewable energy sources. Geothermal energy undoubtedly has great potential, particularly thermal energy, given that 48% of the final energy consumption in the EU20 countries in 2021 was related to heating and cooling systems. The present study verifies and compares the feasibility of realizing district heating systems in two different contexts: (i) depleted hydrocarbon fields with the repurposing of existing hydrocarbon wells into geothermal wells and (ii) areas with documented geothermal resources. The two selected case studies are located, respectively, near Romentino (Northern Italy, province of Novara) and Tuscania (Central Italy, province of Viterbo). Following an assessment of the geothermal resources in the two selected case studies, specific methodological tools have been developed to evaluate the energy demand in the municipalities and determine the projects' economics. Both case studies show positive economic indices assuming heat tariffs aligned with the values recorded in the 2020–2021 period. However, our results show how reusing hydrocarbon wells in geothermal wells constitutes an excellent opportunity to access geothermal resources, significantly reducing the necessary investment and the mining risk and strongly improving the economics of the projects. [ABSTRACT FROM AUTHOR]

The kinematics of subduction zones shows a variety of settings that can provide clues for dynamic understandings. Two reference frames are used here to describe the simple 2D kinematics of subduction zones. In the first, the upper plate is assumed fixed, whereas in the second frame upper and lower plates move relative to the mantle. Relative to a fixed point in the upper plate U, the transient subduction hinge H can converge, diverge, or be stationary. Similarly, the lower plate L can converge, diverge or be stationary. The subduction rate Vs is given by the velocity of the hinge H minus the velocity of the lower plate L ([V.sub.s]= [V.sub.H] - [V.sub.L]). The subduction rate 1) increases when H diverges, and 2) decreases when H converges. Combining the different movements, at least 14 kinematic settings can be distinguished along the subduction zones. Variable settings can coexist even along a single subduction zone, as shown for the 5 different cases occurring along the Apennines subduction zone. Apart from few exceptions, the subduction hinge converges toward the upper plate more frequently along E- or NE-directed subduction zone, whereas it mainly diverges from the upper plate along W-directed subduction zones accompanying backarc extension. Before collision, orogen growth occurs mostly at the expenses of the upper plate shortening along E-NE-directed subduction zones, whereas the accretionary prism of W-directed subduction zones increases at the expenses of the shallow layers of the lower plate. The convergence/shortening ratio is > 1 along E- or NE-directed subduction zones, whereas it is < 1 along accretionary prisms of W-directed subduction zones. Backarc spreading forms in two settings: along the W-directed subduction zones it is determined by the hinge divergence relative to the upper plate, minus the volume of the accretionary prism, or, in case of scarce or no accretion, minus the volume of the asthenospheric intrusion at the subduction hinge. Since the volume of the accretionary prism is proportional to the depth of the decollement plane, the backarc rifting is inversely proportional to the depth of the decollement. On the other hand, along E- or NE-directed subduction zones, few backarc basins form (e.g., Aegean, Andaman) and can be explained by the velocity gradient within the hangingwall lithosphere, separated into two plates. When referring to the mantle, the kinematics of subduction zones can be computed either in the deep or in the shallow hotspot reference frames. The subduction hinge is mostly stationary being the slab anchored to the mantle along W-directed subduction zones, whereas it moves W- or SW-ward along E- or NE-directed subduction zones. Surprisingly, along E- or NE-directed subduction zones, the slab moves 'out' of the mantle, i.e., the slab slips relative to the mantle opposite to the subduction direction. Kinematically, this subduction occurs because the upper plate overrides the lower plate, pushing it down into the mantle. As an example, the Hellenic slab moves out relative to the mantle, i.e., SW-ward, opposite to its subduction direction, both in the deep and shallow hotspot reference flames. In the shallow hotspot reference frame, upper and lower plates move 'westward' relative to the mantle along all subduction zones. This kinematic observation casts serious doubts on the slab negative buoyancy as the primary driving mechanism of subduction and plate motions. W-directed subduction zones rather provide about 2-3 times larger volumes of lithosphere re-entering into the mantle, and the slab is pushed down. This opposite behavior is consistent with the down-dip extension seismicity along E-NE-directed subduction zones, and the frequent down-dip compression along the W-directed subduction zones. Subduction kinematics shows that plate velocity is not dictated by the rate of subduction. Along the W-directed subduction zones, the rate of subduction is rather controlled i) by the hinge migration due to the slab interaction with the 'easterly' trending horizontal mantle wind along the global tectonic mainstream, ii) by the far field plate velocities, and, iii) by the value of negative buoyancy of the slab relative to the country mantle. Alternatively, E-NE-NNE-directed subduction zones have rates of sinking chiefly determined i) by the far field velocity of plates, and ii) by the value of negative buoyancy of the slab relative to the country mantle. Along this type of subduction, the subduction hinge generally advances E-NE-ward toward the upper plate decreasing the subduction rate, but it moves W-SW-ward relative to the mantle. All this indicates that subduction zones have different origin as a function of their geographic polarity, and the subduction process is more a passive feature rather than being the driving mechanism of plate motions. A rotational component combined with mantle density and viscosity anisotropies seems more plausible for generating the global tuning in the asymmetry of subduction zones. Keywords: subduction; kinematics; hinge migration; remounting slab; westward drift

[1] The deep structure of the southern Apennines (SA) accretionary wedge is still debated since industrial seismic reflection and well data provide reliable constraints only to a depth of about 10 km. As a consequence, two directly linked questions regard (1) the shortening in the accretionary prism (particularly within the buried Apulian thrust units) and (2) the degree of involvement of the lower plate basement (i.e., the Apulian crystalline basement). To address these issues, we have constructed a regional section along a recently released deep seismic reflection profile (CROP-04) which intersects the entire SA. The resulting cross section, adequately constrained to a depth of about 15 km, has been framed in a geodynamic scenario characterized by the eastward roll-back of the westward subducting Apulo-Adriatic lithosphere. On the basis of this section we speculate on the deep structure, building both thin- and thick-skinned thrust models. A cross-check of these end-members models against documented tectonic, geophysical, and geochemical features shows that the thin-skinned model is generally more consistent with the available data. The development of basement slices with thicknesses of tens of kilometers is unlikely, while it remains possible that the Apulian basement could have been involved with its upper few kilometers. In the thin-skinned model, the total shortening of the allochthonous units (i.e., Apennine and Apulian carbonate platforms and Lagonegro basin) is estimated to be greater than 280-300 km. Some 90 km of shortening can be attributed to the Apulian thrust units. Citation: Scrocca, D., E. Carminati, and C. Doglioni (2005), Deep structure of the southern Apennines, Italy: Thin-skinned or thick-skinned?, Tectonics, 24, TC3005, doi:10.1029/2004TC001634.

The maximum possible earthquake magnitude is one of the fundamental parameters to assess possible threats and effects on populations and infrastructures. Empirical scaling laws between fault/slip dimensions and earthquake magnitude can be used to assess this fundamental parameter. Upon the assumption of the reactivability of any fault, these seismic scaling laws are used at the national scale in Italy, considering all known faults regardless of their age, stress field orientation, or strain rate. Italy is a suitable case for comparing the fault-size-derived seismic magnitudes with the existing accurate catalogues of historical-instrumental earthquakes. To do so, (1) a comprehensive catalogue of all known faults is compiled by merging the most complete databases available, (2) the potential expected maximum magnitude of earthquakes (PEMM) is simply derived from fault dimensions, and (3) the resulting PEMMs are compared (i.e., the mathematical difference) with catalogued earthquake magnitudes. Results show that the largest PEMMs as well as the largest differences between PEMMs and catalogued magnitudes are observed for poorly constrained faults (inferred from subsurface data). Where, in contrast, the knowledge of faults is geologically well constrained, the calculated PEMM is often consistent with the catalogued seismicity, with the 2σ value of the distribution of differences being 1.47 and reducing to 0.53 when considering only the M ≥ 6.5 earthquakes. This overall consistency gives credibility to the used empirical scaling laws; however, some large differences between the two datasets suggest the validation of this experiment elsewhere. The largest differences are probably connected with the partial activation of presumed long continuous faults. The main advantages of this method are its rapidity, once the faults are mapped, and its independence from temporal and (paleo)seismological information. The novelty is not the method, but its use at the national scale also for faults considered inactive. This method cannot, however, be a substitute for time-dependent (paleo)seismological methods for seismic hazard assessments. Rather, it can rapidly provide a perspective time-independent seismic potential of faults. [ABSTRACT FROM AUTHOR]