Analysis of Seismo-Gravity Signals Associated with Volcanic Explosions Recorded at Stromboli, Italy in May 2018

In May 2018, we temporarily deployed 7 seismometers, 7 infrasonic microphones, an FTIR, FLIR, and MultiGAS station at Stromboli Volcano, Italy. Simultaneously, we conducted a continuous gravity experiment with the goal of characterizing the source of inflation-deflation-inflation cycles observed in tilt time series for stations located within 1 km of Stromboli's summit vents. A Scintrex CG-6 gravimeter recorded gravity continuously at a sampling rate of 10 Hz at three different locations around the summit crater. For each gravity site we use the nearest broadband seismometer to estimate the inertial acceleration component of the gravity signal due to ground motion. In addition, ambient temperature, barometric pressure, and wind speed were recorded locally to identify any correlation with the gravity changes. After correcting for the long term drift and Earth tides, the residual gravity variations are analyzed in the frequency domain using the Fourier and Continuous Wavelet Transforms. We interpret the residual gravity variations in terms of volumetric changes associated with mass transport in the upper conduit. Data from the seismo-acoustic network provide the timing and duration of each explosive event. By isolating the gravity signature of the Strombolian explosions, we are able to study mass transport in the upper volcanic conduit on the timescale of 500 seconds. Finally, the gravity-estimated volumes of gas input to the system can be compared to the volatile budget estimated from gas measurements and from the seismically-derived tilt source. This gravity experiment represents an important step towards the identification of precursory gravity changes prior to volcanic explosive events and a test of the utility of continuous gravity in real-time volcano monitoring.