Abstract
We present 4 years of continuous seafloor deformation measurements carried out in the Campi Flegrei caldera (Southern Italy), one of the most hazardous and populated volcanic areas in the world. The seafloor sector of the caldera has been monitored since early 2016 by the MEDUSA marine research infrastructure, consisting of four instrumented buoys installed where sea depth is less than 100 m. Each MEDUSA buoy is equipped with a cabled, seafloor module with geophysical and oceanographic sensors and a subaerial GPS station providing seafloor deformation and other environmental measures. Since April 2016, the GPS vertical displacements at the four buoys show a continuous uplift of the seafloor with cumulative measured uplift ranging between 8 and 20 cm. Despite the data being affected by environmental noise associated with sea and meteorological conditions, the horizontal GPS displacements on the buoys show a trend coherent with a radial deformation pattern. We use jointly the GPS horizontal and vertical velocities of seafloor and on-land deformations for modeling the volcanic source, finding that a spherical source fits best the GPS data. The geodetic data produced by MEDUSA has now been integrated with the data flow of other monitoring networks deployed on land at Campi Flegrei.
Highlights
Seafloor geodesy is an established branch of geodesy for precise underwater measurements of position and displacements and is used for monitoring submerged volcanic areas, tectonic deformation and subsidence related to offshore oil extraction
This vertical correction is negligible for CFBA, CFBB and CFBC stations, due to the mechanical system adopted in the deployment of the three new buoys (Iannaccone et al, 2018)
Iannaccone et al (2018) demonstrated that a single Mogi model point source can explain both the onshore and seafloor deformation from Continuous Global Positioning System (cGPS) data. They compared the expected vertical displacement in the marine sector to that predicted by a Mogi model computed using only horizontal and vertical, on-land, cGPS measurements in the period between April 2016 and July 2017
Summary
Seafloor geodesy is an established branch of geodesy for precise underwater measurements of position and displacements and is used for monitoring submerged volcanic areas, tectonic deformation and subsidence related to offshore oil extraction. The main limitation of the acoustic techniques arises from the variation over time of properties of the marine environment, with the consequent difficulty estimating the path length starting from the measurement of the propagation time Another common technique in marine geodesy that is suitable for monitoring vertical ground displacement is based on the variation of hydrostatic pressure at the sea bottom measured by a bottom pressure recorder (BPR). Geodetic measurements on the seafloor are more frequently performed at large depths, typically greater than 1,000 m, than in shallow water This is because the large variability over time of the sound speed strongly degrades the quality of acoustic measures. We present the data acquired in continuous mode by the GPS stations of the MEDUSA infrastructure for 4 years after April 2016 and examine their contribution to the interpretation of the ground deformation pattern of the Campi Flegrei caldera
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