AFATA (Active FAult Tectonic Analysis): a semi-automatic tool on ArcGIS.for estimating fault offset on superficial ruptures

The automation of data acquisition and calculation is advancing in many sectors. At the same time, the use of software and the difficulty, in certain cases, in programming languages could lead to various problems. In relation to the automation of fault offset estimation, many authors have given their contribution (Stewart et al., 2018; Wolfe et al., 2020) combining steps in GIS environment with external programming languages. AFATA is a new toolbox proposal for ArcGIS® based on Model Builder and on ArcPy language for the evaluation of the three components of rupture offset (vertical, horizontal and along plane offsets) of a normal fault. This tool, that only needs the use of GIS environment, is intuitive and does not require many steps from the user. The semi-automatic process allows the operator to modify and improve the shapefiles on which the analysis is carried out. The AFATA main inputs are (i) line shapefiles, drawn by the operator, defining the two limits of the fault offset, and (ii) a slope raster obtained through a Digital Elevation Model (DEM) with a resolution comparable with the fault geometry. The result is a line shapefile containing the sampling transects whose frequency is chosen by the user along the fault plane. The measurements (maximum, minimum and average) of the three offset components and the value of the slope angle for each transect are shown in the attribute table. The application and validation of the proposed toolbox are located in the Central Apennines of Italy on the surface ruptures related to the 2016 earthquakes. The study area was surveyed with a digital geological field survey and with low-altitude aerial photos, using an Unmanned Aerial Vehicle (UAV). A 3D Virtual Outcrops Model (VOM) was generated by the Structure from Motion – MultiView Stereo (SfM-MVS) photogrammetry (Westoby et al., 2012; Tavani et al., 2016); from this, a 0.009 m resolution ortophoto and a 0.02 m resolution DEM were derived for spatial analysis in ArcGIS 10.8.1. The AFATA application may contribute to obtain a higher number of measurements by regularly scanning the three components of the slip fault, in particular on ruptures difficult to access. The extent of the error for this tool primarily depends on the accuracy with which the user draws the limits; the estimated error obtained on the study area is about 10% of the total slip.