**1. Introduction**

It is well known that seismic activity in the periAdriatic zones (**Figure 1**) is related to the interaction of the Adriatic plate (Adria hereafter) with the surrounding belts (**Figure 2**).

Stressed by the convergence of the confining structures, Adria tries to move roughly northward [10–12, 14–16].

This gradual displacement is allowed by the activation of the decoupling fault systems located along the lateral boundaries of Adria (Dinarides and Apennines) and in the northern front of that plate, in the Eastern Southern Alps. The central and southern Dinarides and the Eastern Southern Alps are characterised by thrust faults while a dextral transpressional regime prevails in the northern

**Figure 1.**

*Major earthquakes (red circles, M* ≥ *5) since 1000 A. D in the periAdriatic zones [1–9].*

#### **Figure 2.**

*Tectonic sketch of the Adriatic region (e.g., [10–12]). The main wedges in the eastern sector of the Apennine belt are evidenced by colours (inset). See text for explanations. The proposed kinematic pattern with respect to Eurasia [13, 14] is indicated by red empty arrows. 1) Compressional, 2) extensional 3) transcurrent features, 4) Outer fronts of Neogenic belts. Am = Amatrice fault system, Aq = L'Aquila fault system, AVT = Alta Valtiberina trough, CSD = Central-Southern Dinarides; ESA = Eastern Southern Alps; ET = Enza-Taro thrust, FBF = Ferrara buried folds, Fu = Fucino fault system; Ga = Garfagnana, Lu = Lunigiana, LuA = Lucanian Apennines, Ma, Be, Ir = Matese, Benevento and Irpinia fault systems, ND = Northern Dinarides, No-Cf-Gu = Norcia-Colfiorito-Gubbio fault system; OV = Olevano-Antrodoco-Sibillini transversal thrust, RA = Rimini-Ancona thrust front, Re = Reno thrust, Rom = Romagna fault system, Se = Secchia thrust, Si = Sillaro thrust, SV = Sangro-Volturno oblique thrust, UV = Umbra valley.*

**19**

Adria plate.

*Tectonics and Seismicity in the periAdriatic Zones: Implications for Seismic Hazard in Italy*

Dinarides e.g., [17–21]. The decoupling mechanisms along the western Adria boundary (Apennines) are more complex [10–12, 16], due to the presence of a shallow crustal structure (eastern sector of the chain, coloured in **Figure 2**), that is moving independently from Adria and the western (Tyrrhenian) sector of the belt. This tectonic/kinematic context has been determined by the fact that in the most recent evolution (Quaternary) the outer chain, stressed by Adria, has undergone longitudinal shortening, accommodated by major deformations:

• Strong uplift, recognised in various sectors of the chain [22–25].

• Formation of arcs, as the Campania-Lucania and the Matese-Benevento in the Southern Apennines (see [12] and references therein), the Gran Sasso in the Central Apennines [26, 27] and the Emilian and Ferrara buried folds in the Northern Apennines [28]. This deformation is also suggested by the transition from a cylindrical to a non-cylindrical (arcs) geometry of the

• The zones of interaction between the main belt sectors are characterised by transversal/oblique thrusts, as the Olevano-Antrodoco-Sibillini Mts. and the

• Roughly NE ward extrusion of major wedges, with particular regard to the Molise-Sannio (MS) and the Romagna-Marche-Umbria (RMU). This process is compatible with a large amount of geological evidence reported by Viti et al.

The divergence between the MS and RMU escaping wedges with respect to the inner less deformed belt has caused the formation of extensional and transtensional fault systems along the axial part of the chain, where a number of troughs has developed. Roughly NW-SE sinistral transtensional and transpressional faults developed in the Lucania Apennines e.g. [31–34]. Extensional faults are recognised in the Irpinia, Benevento and Matese zones, along the inner side of the MS wedge e.g., [35, 36]. The L'Aquila and Fucino transtensional fault systems allow the relative motion between the Lazio-Abruzzi (LA) wedge and the inner belt [26, 37–40]. The decoupling of the RMU wedge from the inner belt is accommodated by the Norcia-Colfiorito-Gubbio-Alta Valtiberina extensional and transtensional fault system and the parallel Umbra Valley trough (e.g., [41–43] and references therein). The simultaneous development of uplift and extensional features in the belt cannot easily be explained without assuming belt-parallel

The occurrence of several major earthquakes in the Romagna Apennines reveals the presence of an important roughly S-N fault system (Rom in **Figure 2**, [44] and references therein, [42, 45]). This discontinuity allows the RMU wedge to decouple from the Tuscany-Emilia Apennines sector that is not parallel to the

Another evidence consistent with the longitudinal compressional regime in the northernmost Apennines is the presence of transverse thrust faults, as the Sillaro,

The kinematic field that is suggested by the Quaternary deformation pattern in the Apennine belt [11, 48, 49] is compatible with the present displacement field, inferred from geodetic GPS data e.g., [11, 50, 51], which indicates that the outer Adriatic sector of the Apennine chain is moving faster (4–5 mm/y) and more

*DOI: http://dx.doi.org/10.5772/intechopen.94924*

orogenic accretion e.g., [28].

Sangro-Volturno [26, 29, 30].

[12] and references therein).

compression as driving force.

Reno, Secchia and Enza-Taro faults [23, 46, 47].

northward with respect to the inner belt (about 1 mm/y).

## *Tectonics and Seismicity in the periAdriatic Zones: Implications for Seismic Hazard in Italy DOI: http://dx.doi.org/10.5772/intechopen.94924*

Dinarides e.g., [17–21]. The decoupling mechanisms along the western Adria boundary (Apennines) are more complex [10–12, 16], due to the presence of a shallow crustal structure (eastern sector of the chain, coloured in **Figure 2**), that is moving independently from Adria and the western (Tyrrhenian) sector of the belt. This tectonic/kinematic context has been determined by the fact that in the most recent evolution (Quaternary) the outer chain, stressed by Adria, has undergone longitudinal shortening, accommodated by major deformations:


The divergence between the MS and RMU escaping wedges with respect to the inner less deformed belt has caused the formation of extensional and transtensional fault systems along the axial part of the chain, where a number of troughs has developed. Roughly NW-SE sinistral transtensional and transpressional faults developed in the Lucania Apennines e.g. [31–34]. Extensional faults are recognised in the Irpinia, Benevento and Matese zones, along the inner side of the MS wedge e.g., [35, 36]. The L'Aquila and Fucino transtensional fault systems allow the relative motion between the Lazio-Abruzzi (LA) wedge and the inner belt [26, 37–40]. The decoupling of the RMU wedge from the inner belt is accommodated by the Norcia-Colfiorito-Gubbio-Alta Valtiberina extensional and transtensional fault system and the parallel Umbra Valley trough (e.g., [41–43] and references therein). The simultaneous development of uplift and extensional features in the belt cannot easily be explained without assuming belt-parallel compression as driving force.

The occurrence of several major earthquakes in the Romagna Apennines reveals the presence of an important roughly S-N fault system (Rom in **Figure 2**, [44] and references therein, [42, 45]). This discontinuity allows the RMU wedge to decouple from the Tuscany-Emilia Apennines sector that is not parallel to the Adria plate.

Another evidence consistent with the longitudinal compressional regime in the northernmost Apennines is the presence of transverse thrust faults, as the Sillaro, Reno, Secchia and Enza-Taro faults [23, 46, 47].

The kinematic field that is suggested by the Quaternary deformation pattern in the Apennine belt [11, 48, 49] is compatible with the present displacement field, inferred from geodetic GPS data e.g., [11, 50, 51], which indicates that the outer Adriatic sector of the Apennine chain is moving faster (4–5 mm/y) and more northward with respect to the inner belt (about 1 mm/y).

*Earthquakes - From Tectonics to Buildings*

**18**

**Figure 2.**

**Figure 1.**

*Tectonic sketch of the Adriatic region (e.g., [10–12]). The main wedges in the eastern sector of the Apennine belt are evidenced by colours (inset). See text for explanations. The proposed kinematic pattern with respect to Eurasia [13, 14] is indicated by red empty arrows. 1) Compressional, 2) extensional 3) transcurrent features, 4) Outer fronts of Neogenic belts. Am = Amatrice fault system, Aq = L'Aquila fault system, AVT = Alta Valtiberina trough, CSD = Central-Southern Dinarides; ESA = Eastern Southern Alps; ET = Enza-Taro thrust, FBF = Ferrara buried folds, Fu = Fucino fault system; Ga = Garfagnana, Lu = Lunigiana, LuA = Lucanian Apennines, Ma, Be, Ir = Matese, Benevento and Irpinia fault systems, ND = Northern Dinarides, No-Cf-Gu = Norcia-Colfiorito-Gubbio fault system; OV = Olevano-Antrodoco-Sibillini transversal thrust, RA = Rimini-Ancona thrust front, Re = Reno thrust, Rom = Romagna fault system, Se = Secchia thrust,* 

*Si = Sillaro thrust, SV = Sangro-Volturno oblique thrust, UV = Umbra valley.*

*Major earthquakes (red circles, M* ≥ *5) since 1000 A. D in the periAdriatic zones [1–9].*
