Summary Ultra-slow seafloor deformations are frequent in several marine environments like volcanic calderas, offshore oil and gas extraction fields subject to subsidence, and river delta regions; they can exhibit unpredictable behaviors, particularly in caldera systems situated along coastlines. However, offshore monitoring of seafloor uplift and subsidence is still very challenging. Here we present a new method to recover vertical seafloor deformation at Campi Flegrei caldera (CFc), Southern Italy, using Bottom Pressure Recorder (BPR) sensors, tide gauges and a barometer. Using data from two BPRs installed on the seabed within the MEDUSA marine infrastructure of the INGV ‘Osservatorio Vesuviano’, we transform pressure measurements into equivalent water level changes to derive the vertical seafloor displacements. We obtain high accuracy, vertical deformation records from the BPRs measurements by taking into account the high-resolution mean seawater density variation over time, estimated by applying an innovative procedure to the BPRs data and using additional barometric and sea level data. We obtained for the two BPRs an uplift of 22.8 cm over about two years, and 7 cm over about 18 months, respectively. We compare the results with data acquired by GPSs installed on the top of MEDUSA buoys, deployed at the same sites as the BPRs, which recorded the vertical seafloor deformation values of 22 cm and 6.9 cm, respectively, over the same periods. These independent datasets show a strong correlation, with correlation coefficient values of 0.98 and 0.87, and very good agreement in both the trend and amplitude of vertical motion, proving the reliability of BPRs in accurately measuring vertical seafloor deformation. The methodology we developed allows a cost-effective implementation of high accuracy seafloor vertical deformation monitoring networks.
Read full abstract