GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 1.1 55 The field-collected data consist of a series of photographs taken at different heights and positions using a tripod. Photos are acquired using a reflex camera set with low ISOs, high f/ stops (small apertures and long acquisition time) that help to sharpen the background increasing the depth of field. Photo alignment and three-dimensional model creation was achieved using the software Agisoft Photo Scan Pro (http://www.agisoft.com ). For each fault surface, around 200 photos were used as input data to create the digital point cloud model. Before Power Spectral Density (PSD) analysis, trimmed patches of the point clouds were processed using an in-house MATLAB script for (i) re-orienting the surface, (ii) interpolation, and (iii) resampling in a regular grid. For the analysis of the resampled surface topography, the PSD was used both along and perpendicular to slip direction. This provides an objective description of the roughness based on the distribution of the asperities in the Fourier domain (see Ogilvie et al. , 2006; Corradetti et al. , 2017; Zambrano et al. , 2019). The PSD is a function of (wave number) k in a bi-logarithmic scale graph of a self-affine function which exhibits an apparent linear slope, defined by the Fig. 1 - Location of the study areas: a) Geological map of the Monte Vettore area (after Pierantoni et al. , 2013), exposed fault surfaces at b) Forca di Presta, and c) Colli Alti e Bassi.