Monitoring Shallow Water Vertical Seafloor Displacement: a Challenge for Seafloor Geodesy

Vertical displacement measurement in shallow seafloor poses a unique challenge for geodesy, as neither traditional land geodesy nor classical deep water marine geodesy provide valid techniques for accurate evaluations. Vertical displacement monitoring is of paramount importance in submarine volcanic areas, in marine oil extraction fields, in the study of coseismic ground movements in seismogenic areas. Sea bottom measurement of hydrostatic pressure variations could be the base to measure the vertical ground displacements. Although bottom Pressure Recorders (BPR) are affected by intrinsic limitations such as the signal drift, and shallow water are particularly affected by tides and other oceanographic effects, or rapid and sharp variations of physical properties of the sea water (e.g. temperature and salinity), BPR can be effective tools to evaluate sea bottom vertical deformation. We present unprecedented vertical displacement assessment of the marine sector of Campi Flegrei volcanic area (Southern Italy). These new results come from the integration of new GPS buoy, BPR and tide gauges measurements provided by the integrated monitoring system of Campi Flegrei. The multiparametric marine systems are operational since spring 2016 and consist of three geodetic buoys equipped with seafloor multisensor modules. The new data show on-going seafloor uplift of the submerged part of the Campi Flegrei caldera and provide new contributions to the regional deformation assessment. The methodology adopted for the data processing can significantly improve our ability to understand the volcanic process extending our monitoring capabilities offshore.