GNGTS 2013 - Atti del 32° Convegno Nazionale

has focused on the rivers azimuthal distribution, in order to understand the relationships between faults and drainage system arrangement. The data show that the overall faults and active faults segments have the same NW-SE preferential orientation, at about N140-150° (Fig. 2c). This means that the fresh bedrock scarps are the result of the reactivation of previous faults, in accordance with the collected kinematics data measured along the fault planes. The azimuthal distribution of the subsequent IV-VII orders streams, show a clear main direction of about N130-150° (Fig. 2c), coincident with the azimuthal orientation of the overall faults. In contrast, this analysis indicates that the I-III order streams are widely distributed, with a slightly marked main direction focused between 30° and 50° (Fig. 2c), perpendicularly to the main faults. This group of streams would include both relicts of the heads of basins of the ancient drainage system and the new tributary channels flanking the NW-pointed subsequent streams. In order to thoroughly understand the relationships between the faults activity, the behav- iour of the drainage system and the fluvial network arrangement, a more detailed analysis has regarded the evaluation of the streams flow-directions (rose diagrams in Fig. 2d). The results, obtained for several streams of different hierarchical orders, show that the IV-VII order sub- sequent streams flow towards the north-west. In contrast, the flow-direction orientations of the I-III order channels show anomalous differences between the streams flowing towards the northern sector and those flowing towards the southern one. The first group covers a 180° wide range of directions, without a clear main value, while the channels flowing to the opposite sense are mostly confined in a narrow azimuthal range, focusing between 200° and 270° (Fig. 2d). These anomalous distributions has been explained considering that the streams point- ing towards the northern sector are represented by both sub-sequent and re-sequent chan- nels belonging to an inherited drainage system. In addition, they result from fluvial captures of previous smaller basins that complied in time the NE-ward tilting of the faulted blocks. Fig. 2 – a) AF map of the main drainage basins in the SW sector of the PMB. The map also shows the results of the T index. b) NE-SW oriented swath profile across the faulted belt; the trace of the profile is showed in Panel a. c) Azimuthal distribution of fluvial streams distinguished by hierarchical order (green bars), azimuthal distribution of faults (violet bars) and active faults recognized in the studied area (red bars). d) Flow directions of streams calculated for different hierarchical orders. 179 GNGTS 2013 S essione 1.2