GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 3.1 77 water (and sediment) inputs are localized mainly in the W sector of the Valli di Comacchio, and that the peninsula could act as a sill for sediment supply. Moreover, the W part of the lagoon, close to the Adriatic shoreline, is probably supplied probably by aeolian deposits from the coast, which are sheltered by the presence of the peninsula. If this hypothesis is correct, while in the E side the limited circulation could cause anoxia or hypoxia due to the limited water circulation, the W part is more prone to overfeeding of sediment, that could eventually alter the hydrological and ecological equilibrium the lagoon. We note how relatively basic geophysical surveys could give interesting insights for understanding the complex geological processes regulating the equilibrium of such sensitive environments. The Lake Trasimeno . Lake Trasimeno is located in the Umbria Region of Central Italy is the broadest lake of Central Italy. The extremely low depths, the flat bottom morphology, and the absence of natural outflows and dams along its shorelines caused wide lake-level oscillations and periodical floods since ancient times, only partially attenuated by creation of an artificial outflows. Lake Trasimeno is an interesting geological site for the its peculiar formation (Cattuto and Gregori, 1993), and for the sedimentary succession found below its floor, which records the deformation history of this portion of the Central Apennine since the late Pliocene (Bortoluzzi et al. , 2005; Gasperini et al. , 2010). Due to its location, the lake area has been a natural crossroad since proto-historical times. Several Neolithic settlements were found along the lake shores (Moroni Lanfredini, 2003) and important historical events took place in the vicinity of the lake, such as the famous Trasimeno battle (217 B.C.), when the Romans were defeated by the Hannibal’s army during the Second Punic War (Brizzi and Gambini, 2007). For this reason, the Lake Trasimeno area is an important archeological/historical site, and was surveyed using different geophysical techniques including a close spaced grid of high resolution seismic reflection lines (Gasperini et al. , 2009). However, some sectors of the lake, close to the N shore, too shallow to be accessible using conventional vehicles, were surveyed using SWAP. Prior the survey, to test the quality of the data collected by the chirp-sonar mounted onboard of the USV, we performed a comparison with an industry standard chirp-sonar system, the Teledyne Benthos Chirp-III. Result of this benchmark is reported in Fig. 2, where the shallowest part (first 15-20 msec TWT) of the Trasimeno sedimentary sequence is imaged with similar vertical resolutions and penetration by both seismic reflection systems. The Cavo Napoleonico artificial channel. The Cavo Napoleonico an artificial channel connecting the Po and the Reno rivers in the Po plain. The channel is oriented perpendicularly to the thrust-and-fold belt, named Pieghe Ferraresi , falling in the area undergoing the maximum superficial deformation after the earthquake. For this reason, it is the site of geophysical data acquisition, to image the surface and the subsurface in search for coseismic deformation of the 2012 Emilia earthquakes and seismogenic structures at depth (Priore et al. , 2013). Among other data acquisition, we carried out a side-scan sonar survey of the channel using a Strarfish SSS system in search of possible earthquake-related structures, such as fractures, fissures or sediment fluidization. First analysis of side-scan sonar mosaics, combined with results of high- resolution seismic reflection survey indicate a correlation between channel-floor disturbances maximum co-seismic deformation. In particular, we observe the presence of such features in correspondence of paleo-channel incisions imaged by chirp-sonar seismic sections, in agreement with observations carried out on land. The Reno River. Reno is the river that forms a wide alluvial fan on which the western edge of the town of Bologna (Central Italy), lays. In such part of its course, the river is particularly prone to periodical flows, close to the connection between the alluvial plain (the southern Po plain) and the Apennines. For this reason, the regime of the river has been artificially regulated since the Roman times and the Middle Age (Barbieri, 2003). We investigated a segment of the river stream close to a major bridge, the Pontelungo bridge, whose piers are affected by base erosion. A bathymetric and a reflectivity map (Fig. 3) were compiled using data collected by a 200 kHz echosounder onboard of SWAP. These maps highlight the presence of a deep