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We show a sub-set of data acquired by MEDUSA, the Multiparametric Elastic-beacon Devices and Underwater Sensors Acquisition system, a marine research infrastructure for monitoring shallow water environment, with a focus on the low-rate ground subsidence and uplift processes (bradyseism) occurring in the last tree-years in the volcanic caldera of the Campi Flegrei (Gulf of Pozzuoli-Naples, Italy).MEDUSA infrastructure consists of four instrumented geodetic buoys with cabled seafloor multi-parameter modules and 152+ channels with sampling rate in the range from 60 seconds to 200 Hz. The conspicuous dataset available from the MEDUSA is visualised by means of a dedicated data-portal allowing downloading in various formats.We show the augmented possibility offered by these innovative multi-parametric observatories, designed mainly to monitor the local seismicity and the seafloor movements in shallow-waters of a volcanic area.Seismic recordings of local and regional earthquakes obtained by the hydrophones, show high quality signal highlighting a improved signal to noise ratio than the co-located seismometer.The long time-series of the geodetic GPS data acquired on the MEDUSA buoys processed with a standard software (RTK-lib), show an accurate and stable agreement of the vertical seafloor displacement measured with the land GPS stations. The GPS measurements of MEDUSA have been also used to confirm that data recorded by the bottom pressure recorders (BPRs), located in the same site on board the seafloor modules, provide an independent measure of the seafloor vertical uplift in shallow water. Finally, the data recorded by BPRs are compared with the tide-gauge reference station located outside the deformation area, used as reference baseline to correct the data.The use of GPS, BPR and tide gauge data provided by MEDUSA, have allowed assessing for the first time the seafloor deformation field in the Gulf of Pozzuoli: we estimated a seafloor vertical displacement of about 10 ± 1 cm over a period of twenty months embracing 2016 to 2018.A network of permanent GPS buoys represents a powerful tool to measure the seafloor vertical deformation field in shallow water. In fact, the performance of this system is comparable to on-land high-precision GPS networks, marking a significant achievement and advance in seafloor geodesy and extending volcano monitoring capabilities to shallow offshore areas (up to 100 meters depth). [ABSTRACT FROM AUTHOR]

In recent years, seafloor observatories were deployed in two sites of the mediterranean area where important geophysical processes that have geohazard impact take place: offshore Eastern Sicily (Italy) in the Ionian Sea at 2100 m water depth and at the base of Marsili Seamount in the Tyrrhenian Sea at 3320 m water depth. The Ionian site, near Etna volcano, where the SN1 seafloor Observatory is deployed is a key point of the EMSO (European Multidisciplinary Seafloor and water-column Observatory Research Infrastructure, www.emsoeu.org). The second site, where the GEOSTAR seafloor Observatory was deployed during the ORION experiment, is the location of Europe's largest submarine volcano. In the present work we focus on seismically generated acoustic waves, called T-phases, that propagate within the ocean's low-velocity waveguide known as the SOund Fixing And Ranging or SOFAR channel. T-phases can propagate over great distances (thousands of kilometers) with little loss in signal strength. The study of T-phases are interesting to scientist for a number of reasons, one of them is that they might give information on the structure of subduction zones. T-phases were first studied on signals recorded at coastal seismic stations but thanks to the increased deployments of Ocean Bottom Seismometers worldwide, they also have been observed at the seafloor at depths greater than the SOFAR channel. The two seafloor observatories recorded high quality 3-component time series of acoustic signals that we identify with T-phases generated at nearby subduction zones. Thanks to accurate time reference of the data and knowledge of component direction for the seismometers on-board seafloor observatories it is possible to extract significant features on the T-phase signal. In particular, we show the efficient T-phase generation from earthquakes along the Hellenic and Calabrian subduction zones by computing of the maximum amplitude of the envelope of the T-phase emax(t) and the T-phase energy flux (TPEF) as function of the local Magnitude. Following, we performed a prelimary polarization analysis, on the three seismic components, at different frequencies, to investigate the conversion process that take place when body waves convert to acoustic waves at the seafloor-water interface. [ABSTRACT FROM AUTHOR]

MEDUSA stands for Multiparametric Elastic-beacon Devices and Underwater Sensors Acquisition system. It is a marine monitoring research infrastructure based on instrumented geodetic-buoys with cabled seafloor multi-parametric modules operating in the Gulf of Pozzuoli (Naples, Italy) within the Campi Flegrei caldera. It mainly monitors the local seismicity and the seafloor movements (bradyseisms).MEDUSA infrastructure is the result of the close collaboration between different groups inside INGV (Istituto Nazionale di Geofisica e Vulcanologia, Italy) and is part of a marine system of infrastructures developed in the EMSO-MedIT national project aimed at structuring the Italian contribution to EMSO, one of ESFRI Research Infrastructure.The infrastructure consists of four buoys and as many submarine cabled modules, at water depth ranging from 38 to 96 meters, equipped with geophysical and oceanographic sensors. The infrastructure has been operating since 2016 and allows the acquisition and real time transmission of the data to the INGV monitoring center in Naples, where they are integrated with those acquired by the land networks.The implementation of this new infrastructure, which significantly enhances the previous monitoring capabilities, is based on a previous experience gained during the construction of CUMAS (Cabled Underwater Multidisciplinary Acquisition System), the first prototype of instrumented buoy operating in the Gulf of Pozzuoli since 2008. CUMAS has allowed the acquisition of new skill in the design and management of fixed marine monitoring systems in shallow waters, making possible to reach precious milestones in the field of geophysical monitoring technologies.Each MEDUSA buoy is equipped with a standard geodetic GNSS receiver (Leica GR10 and AR10 radome antenna), a heading (±1°), pitch and roll (±0.1°) monitoring system, the power-supply monitoring device of the overall system (current, voltage and photo-voltaic panel's power), and, only for one of the buoy, a meteorological station (air pressure and temperature, wind velocity and direction), an IP web-enabled camera, and a pulsed K-band radar tide-gauge.Each seafloor module is equipped with a Bottom Pressure Recorder (Paroscientific, 8CDP-130I), low-frequency and broad-band hydrophones, a tri-axial broad-band (120s ÷ 25Hz) Ocean Bottom Seismometer with auto-leveling system, a tri-axial Micro Electro-Mechanical Systems accelerometer (DC ÷ 100Hz), clock synchronization (1PPS and NMEA) with absolute GPS time reference on RS-422 interface, a compass sensor, the power-supply monitoring system (current, voltage, water detector and on-off power control), and, for only-one of this, a 3-D current-meter with water temperature sensor. Recently, a seafloor borehole precision tiltmeter (LILY, Jewell Instruments) has been installed to extend the land tiltmeter network to the Gulf of Pozzuoli.The overall marine monitoring research infrastructure therefore acquires more than 150 channels with sampling rate varying from 60 seconds to 200 Hz. The data are stored in a relational database and the complete time series can be visualised on a data portal, where all data can be downloaded from in various formats. [ABSTRACT FROM AUTHOR]