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West-directed subduction zones show east-verging arcs of 1500–3000 km. They are usually younger than 50 Ma and are characterized by a frontal accretionary wedge and a back-arc basin propagating together toward the east. The accretionary wedge scrapes off superficial layers of the downgoing plate (thin-skinned tectonics) whereas the back-arc extension cross-cuts the entire subduction hanging wall (thick-skinned tectonics). The slab of this type of subduction is steep to vertical and the hanging wall of the subduction has a mean elevation of 1000 m below sea level. Trenches and foredeeps are the deepest basins of the Earth and the mean depth is of 5000 m below sea level. West-directed subduction occurs both in case of the highest E-W convergence rates among plates (e.g. W Pacific examples) and no or very low convergence (e.g. Carpathians). Following Atlantic W-directed subduction examples, the W-directed subductions seem to develop along the back-thrust belt of former E-directed subduction zones, where oceanic lithosphere occur in the foreland to the east with the narrowing of the American continents. This could be applied to the onset of the Apennines subduction along the back-thrust belt of the Alpine-Betic orogen where Tethys oceanic crust was present. The Alpine orogen was stretched and scattered in the Apennines back-arc basin. The back-arc extension is internally punctuated by necks (sub-basins) and boudins (horsts of continental lithosphere). Asymmetric extension in the back-arc basin appears controlled by differential drag between the eastward mantle flow and the overlying passively transported crustal remnants. Compression in the accretionary prism may be interpreted as the superficial expression of the shear occurring between the downgoing lithosphere and the horizontally moving mantle which compensates the slab roll-back. The area of the Apennines appears lower than the area of the sedimentary cover before subduction: this favours the idea that not significant crustal slices have been involved in the Apenninic accretionary prism, and the basement thrust sheets included in the western part of the belt are mainly relicts of the Alpine-Betic orogen.

The Apennines comprise a Neogen—Quaternary accretionary prism that shows several anomalies with respect to classic alpine‐type mountain belts, namely (i) low elevation, (ii) a shallow new Moho below the core of the belt, (iii) high heat flow in the internal parts, (iv) mainly sedimentary cover involved in the prism, (v) a deep foredeep and (vi) a fully developed back‐arc basin. The suction exerted by a relatively eastward migrating mantle can determine the eastward retreat of the subduction zone and an asthenospheric wedging at the retreating subduction hinge. Heat flow, geochemical and seismological data support the presence of a hot mantle wedge underlying the western side of the Apenninic accretionary prism. A thermal model of the belt with foreland dipping isotherms fits with deepening of the seismicity toward the east. Mantle volatiles signatures are also widespread in springs along the Apennines.

During the 2002 seismic sequence in Molise (Italy), the town of Bonefro suffered moderate damage (I MCS ‫ס‬ VII) except for two reinforced concrete (RC) buildings. These buildings are located on soft sediments, close to each other and very similar in design and construction. The main difference is the height: the most damaged one (European Macroseismic Scale damage 4) has four stories, whereas the less damaged (EMS damage 2) has three stories. The M 5.4 shock on 31 October damaged both of them. The second shock on 1 November (M 5.3) increased the damage on the four-story building substantially, just while a 5-min. seismic recording was taken. We analyzed the recorded data by four different techniques: short-time fourier transform (STFT), wavelet transform (WT), horizontal-to vertical spectral ratio (HVSR), and horizontal-to-vertical moving window ratio (HVMWR). All the results agree upon the estimate of the main building frequency before the second shock and upon the shift of frequency due to damage. All the fundamental frequencies (pre-, during, and postdamage) are in the range 2.5-1.25 Hz. The fundamental frequency of the less damaged building was estimated at about 4 Hz.To test if the soil-building resonance effect could have increased the damage, we also evaluated the soil fundamental frequency by three different techniques: noise HVSR, strong motion HVSR of seven aftershocks, and 1D modeling based on a velocity profile derived from noise analysis of surface waves (NASW) measurements. The results are again in good agreement, showing that resonance frequencies of the soil and of the more damaged building are very close.

Large earthquakes occurring worldwide have long been recognized to be non Poisson distributed, so involving some large scale correlation mechanism, which could be internal or external to the Earth. Till now, no statistically significant correlation of the global seismicity with one of the possible mechanisms has been demonstrated yet. In this paper, we analyze 20 years of proton density and velocity data, as recorded by the SOHO satellite, and the worldwide seismicity in the corresponding period, as reported by the ISC-GEM catalogue. We found clear correlation between proton density and the occurrence of large earthquakes (M > 5.6), with a time shift of one day. The significance of such correlation is very high, with probability to be wrong lower than 10-5. the correlation increases with the magnitude threshold of the seismic catalogue. A tentative model explaining such a correlation is also proposed, in terms of the reverse piezoelectric effect induced by the applied electric field related to the proton density. This result opens new perspectives in seismological interpretations, as well as in earthquake forecast. Worldwide seismicity does not follow a Poisson distribution 1 , not even locally 2. Many authors have proposed specific statistical distributions to describe such a non-poissonian behavior 3-7 but none of these is really satisfactory, probably because the underlying physical process has not been really understood. Many authors have hypothesized that a tidal component may show up in earthquake activity (e.g. 8,9) but generalized evidence has never been proven. Quite recently, some authors 10 suggested that earthquake occurrence might be linked to earth rotation speed variations. There is also a smaller number of researchers that studied possible links among solar activity, electromagnetic storms and earthquakes (e.g. 11-16). The first idea that sunspots could influence the earthquake occurrence dates back 1853, and is due to the great solar astronomer Wolf 17. Since then, a number of scientists has reported some kind of relationship between solar activity and earthquake occurrence 16,18,19 ; or among global seismicity and geomagnetic variation 15,20 or magnetic storms 21,22. Also, some mechanisms have been proposed to justify such correlations: small changes induced by Sun-Earth coupling in the Earth's rotation speed 23 ; eddy electric currents induced in faults, heating them and reducing shear strength 24 ; or piezoelectric increase in fault stress caused by induced currents 25. However, none of these studies allowed achieving a statistically significant conclusion about the likelihood of such mechanisms. On the contrary, 26 argued that there is no convincing argument, statistically grounded, demonstrating solar-terrestrial interaction favoring earthquake occurrence. However, the large interest nowadays for possible interactions between earthquake occurrence and extra-terrestrial (mainly solar) activity, is testified for instance by the Project CSES-LIMADOU, a Chinese-Italian cooperation aimed to launc...