This paper presents a brief summary of the main geological data and geologically based criteria that can be
considered in the first two steps of every seismic hazard analysis (SHA): Definition and Characterization of
Seismogenic Sources. Two main seismogenic sources are discussed: zones and main faults. Seismogenic
zones are defined on the basis of the relationships between crustal rheological parameters and seismicity,
as well as on the characteristics of the internal fault systems. Main faults are characterized by their size,
age of last deformation, and slip rate. Both types of sources can be implemented in a SHA adopting a
hybrid model. Seismicity occurrence inside zones is assumed Poissonian and magnitudes distribute
exponentially, while in main faults is assumed to follow a characteristic ear thquake model