GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 2.2 395 “Fontevena site” and the two others in the “Marcite” area. The noise data have a duration of at least one hour and were recorded through Reftek130 digitizer with Lennartz-5 sec equipment, and in few sites though a SARA Geobox 4.5 Hz. The data were processed and analyzed using Geopsy (http://geopsy.org/ ), by first removing the transients, then obtaining the HVSR ratios and fundamental resonance (F0) peaks for each station. Results and conclusions. The results of the HVSR analysis display a really heterogeneous pattern of “fundamental frequency” (F0) in the different parts of the basin, even if a clear difference is visible between the North and South sector. The first sector is characterized by F0 values ranging between 0.6-0.8 Hz, whilst in the second sector between 0.9-1.3 Hz for the majority of the stations. A preliminary integration of all the datasets available, provide a first image of the deep structure of the basin, in particular about a variable interface between the infilling Quaternary units and the rigid bedrock, that was dissected by the normal faults activity. Clear changes in the thickness of the deposits, and therefore in the depth of the top bedrock interface, are visible mainly in the SW-NE direction in the Northern part of the basin (high amplitude and narrow HVSR peaks), but also a clear variability in visible in the NW- SE direction along the basin, with a progressive reduction southward. Integrating the velocity information from the literature and the microzonation 3 th lev. (http://www.regione.umbria.it/ paesaggio-urbanistica/area-terremoto-2016/2017), and the new ones coming from the arrays analyses, we have defined the velocity models in order to obtain the depth values from the HVRS peaks. Therefore, we extrapolated the average thickness of the deposits, that look considerably higher in the Northern sectors in the “Marcite” area (250-300 m), whilst the thickness appears lower in the southern sector. We currently provide as results: 1) a new digital geological map (scale 1:10.000) created in a GIS environment (QGIS, https://www.qgis.org/en/site/ ); 2) a new “Frequency-Amplitude” map obtained after the HVSR analysis for the entire basin (Fig. 2); 3) four new deep velocity models, particularly in areas like the “Marcite” previously uncovered by Fig. 1 - Location Map of the study area; dots represent the location of the noise measurements.