GNGTS 2016 - Atti del 35° Convegno Nazionale

336 GNGTS 2016 S essione 2.2 Advantages of integrating photo-geology and field-based geological mapping. An example from post-seismic activities in Amatrice (Central Italy) M. Cardinali 1 , M. Santangelo 1 , M. Mancini 2 , M. Moscatelli 2 , G. Vignaroli 2 , Working group CNR IRPI and IGAG 1 CNR IRPI, Perugia, Italy 2 CNR IGAG, Area della Ricerca di Roma 1- Montelibretti, (RM), Italy Introduction. On 24 August 2016, central Italy was struck by a M W 6.0 earthquake, which damaged many villages in the Lazio, Marche, Abruzzo, and Umbria regions. Immediately following the early rescue activities, it was necessary to develop a seismic microzonation within the area showing the higher level of damage. In this paper, we show an integrated approach, at wide area scale, of photogeological mapping and field-based geological survey, which was developed and adopted for the 140 km 2 wide Amatrice depression, a relatively homogeneous physiographic area situated along the Central Apennines ridge (between the Gorzano Mt ridge to the east, and the Sibillini Mts thrust front, to the west). The aim of this approach is to detect and detail those morphological, stratigraphic and structural features (terraces edges, alluvial fans, flat surfaces, escarpments, landslides, fault lines, bedding) critical for defining subsoil models for seismic microzonation. Method. Photo-geological information was obtained by the visual interpretation of one set of black and white stereoscopic aerial photographs flown in 1954, at 1:33,000 scale. Aerial photographs were interpreted by two researchers, using a Galileo SFG 3/B discussion stereoscope, with 1.25× and 4× zoom capability. Interpretation was then validated using an improved Galileo Siscam Falcon ZII discussion stereoscope, with a 1.5× to 13.5× continuous zoom, which allows for more detailed analyses. The main benefits of using 1954 black and white aerial photographs consists in the less extent and density of the forest coverage, and in a less developed urbanization and human modification of the landscape compared to the present day. These characteristics facilitate the identification and recognition of features related to bedding, fault lines and landslides. The photo-geological information was originally drawn on a transparent plastic sheet placed over the aerial photographs, and then transferred on a 1:10,000 scale topographic base map using a semi-automatic rigorous orthorectification procedure (GRASS development team, 2016) designed to reduce mapping errors and make the overall mapping procedure more efficient (Santangelo et al ., 2015a); a photo-geological map was thus produced (Fig. 1). Since the activity of microzonation is a work still in progress, the map presented in this paper is in a draft version. Interpretation of the aerial photographs was also aided by field-based geological surveys and the review of bibliographical data including geological maps (Koopman, 1983; Cacciuni et al. , 1991; Festa, 2005). Field data were collected at 1:5,000 scale and were used to validate and integrate the photo-geological map. Aerial photographs interpretation. The photo-geological map of the study area (Fig. 1) incorporates five thematic layers including: i) ������� ����������� �� ��� ������� ��� ����������� ��������� bedding information of the bedrock and continental deposits; ii) ���������� �������� ����� ����� ������ ��� ���������� ���������� �������� structural features (e.g. fault traces and associated triangular facets); iii) ������������ �������� ������ ���������� ��� ���������� ����������� ���������� lithological features (e.g., substratum and Quaternary continental deposits); The overall time needed for completing the interpretation of four stereograms at 1:33,000 scale (140 km 2 ) and the orthorectification of the aerial photographs was of 12 working days of two researchers, which means a ratio of 1.5 km 2 per hour by two researchers. Bedding information. ABedding trace (BT) is the linear intersection between a rock layer and the topographic surface (Santangelo et al. , 2015b). Visual evidence of a BT on remote imagery depends on multiple factors, including: (i) the type, mechanical and hydrological characteristics