GNGTS 2019 - Atti del 38° Convegno Nazionale

548 GNGTS 2019 S essione 3.1 (June 2017 – February 2018). Additionally, two seismic refraction profiles were shot to provide the velocity distribution within the Ligurian Basin lithosphere (Fig. 1) with the aim to image the offshore ocean-continent boundary. Data and processing. Profile P01 extends from the Central Corsican margin across the Ligurian Basin to the Ligurian Provencal margins. A total of 35 stations were deployed along the 147 nm long E-W profile, which was extended on Corsica with 3 land stations recording the 2418 air gun signals. The NE-SW trending profile P02 covers the central Ligurian Basin with a length of 73.5 nm. A total of 15 stations recorded 1033 shots. The data quality of both refraction seismic profiles is good and instruments show clear mantle phases. At the long-term network, the data quality of the seismometer components is good and the instruments recorded local as well as teleseismic events. The instruments are working autonomously at the seafloor. Therefore the clock is not permanently synchronised via GPS as would be the case for land stations. Clocks are synchronised before and after the deployment. Over the period of eight month, a mean drift of 2.5 s and a maximum drift of 4.5 s was observed and the data were corrected for the time difference assuming a linear drift. The correct timing was verified by the active shots recorded at the end of the deployment. All recorded data were corrected for timing errors. Once the instruments are deployed from the vessel they fall independently through the water column down to the seafloor. During the free fall they can drift in the water column and turn Fig. 1 - Station and profile distribution in the Ligurian Sea. Two refraction/reflection profiles (P01 and P02) were acquired with 35 and 15 stations, respectively. In addition, shooting along profile P01 was extended to the SE in order for the long-termAlpArray OBS to record the shots. The yellow shades display the angle of the horizontal component H1 of the seismometer at each instrument.