Changes In CO2 Gas Flux And Soil Temperatures Induced By A Vibratory Seismic Source At Solfatara (Phlegrean Fields, Italy).

Abstract:

Solfatara, the most active crater of Phlegrean Fields (Italy) is characterized by a fumarolic activity and an intense diffuse degassing, with 1500 tons of CO2 and > 3000 tons of water vapor released per day. A major part of the emitted water vapor is condensed at the near surface producing a thermal power flux around 100 MW, and contributing substantially to the total water input into the hydrothermal system. On May 2014, during a seismic experiment (RICEN) in the frame of the MED-SUV European project, a Minivib vibratory seismic source was used to generate a frequency modulated seismic signal at different points of Solfatara. We performed CO₂ flux measurements at a few meters from the seismic source during the vibrations. In certain points, the vibrations induced a remarkable increase in the CO₂ diffuse degassing, with a flux that doubled during the low-frequency seismic vibrations and returned to previous values afterwards. The observed CO₂ flux increase could be due to permeability enhancement in the sub-surface soil layers during the seismic vibrations.

Close to Fangaia mud pool, we also monitored the soil temperature at different levels above the condensation depth and observed transient temperature changes during the vibrations but also outside the vibration periods. Seismic vibrations likely favor the triggering of thermal instabilities of gravitational or convective origin in the liquid-saturated condensate layer.