**1. Introduction**

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This chapter describes a methodology for constraining the structural lineaments in active tectonic areas by integrating morphological and morphometrical data derived by DEMs (Digital Elevation Models) processing, with different geophysical data, as local seismicity and ground deformation data. Furthermore, validation of the lineaments extracted from DEM is carried out by looking over geological and geomorphological maps of literature, available aerial photo and field surveys reports (Fig.1).

Fig. 1. Flow chart describing the methodology applied for investigating active tectonic areas.

The morphometric parameters of the terrain slope, terrain aspect, profile curvature, tangential curvature and topographic residual surface are chosen for identifying the linear continuity of the morphostructural features observed on the DEM. The criteria of lineament extraction is based on the identification of linear topographic surface features, such as valleys, ridges, breaks in slope, boundaries of elevated areas aligned in a rectilinear or slightly curvilinear shape and that distinctly differ from the patterns of adjacent features.

The geophysical data considered in this analysis include spatial distribution of local earthquakes, accurate locations of seismic sequences and relative focal mechanisms, which could confirm activity of local tectonic structures.

The areas selected for testing our methodology, located in Southern Italy, are the Agri Valley (Campania-Lucania regions), hit by the strong historical earthquake of December 26, 1857 (Imax=XI, Me=7.0) and also by recent micro-seismicity; the Sannio area (Campania-Molise regions), affected in historical time by the strong earthquake of June 5, 1688 (Imax=XI, Me=6.7) and in recent time by seismic sequences of moderate energy; the Campi Flegrei volcanic district (Campania region, Thyrrenian coast), characterized in the past decades by major bradyseismic crises with remarkable ground uplift and intense seismic activity, and recently by minor crises with lower deformation (Fig. 2).

Fig. 2. Historical and recent earthquakes in the Southern Apennines of Italy (red squares) from CPTI04 catalogue; the epicenters of the 1688 Sannio earthquake (Imax=XI, Me=6.7) and the 1857 Agri Valley earthquake (Imax=XI, Me=7.0, CPTI, 1999) are pointed out; the Campi Flegrei volcanic area location is indicated by the orange circle.

Particulary, the Agri Valley and the Sannio area are active tectonic areas of the Southern Apennines chain and are characterized by a complex inherited tectonic setting, low-tectonic deformation rates that hide the seismogenic sources geometry, and youthfulness of the sources. Whereas the morphotectonic features of the Campi Flegrei caldera resulted from the combined action of both volcanism and regional tectonics, mainly correlated with a circular geometry of deformation (volcanism), and NW-SE, NE-SW normal faults (regional tectonics).

As regards all the above studied areas, due to the difficulty or not straightforward recognition of the induced surface deformation, besides the lack of recent surveyed structural data, the operation of the GIS system has enabled us to process and generate original informative layers, through image analysis, such as new structural lineaments.

The synthesis of our main findings has consisted in structural thematic maps of the new lineaments, which are the final results of our application, representing a contribution to understanding the potential active faults of the investigated areas, for the assessment of local geological-environmental hazard parameters.
