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Periodic behavior of soil CO 2 emissions in diffuse degassing areas of the Azores archipelago: Application to seismovolcanic monitoring
Author(s) -
Viveiros Fátima,
Vandemeulebrouck Jean,
Rinaldi Antonio P.,
Ferreira Teresa,
Silva Catarina,
Cruz José V.
Publication year - 2014
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2014jb011118
Subject(s) - volcano , hydrothermal circulation , environmental science , geothermal gradient , atmospheric sciences , geology , soil gas , flux (metallurgy) , induced seismicity , soil science , hydrology (agriculture) , soil water , chemistry , geochemistry , seismology , geophysics , geotechnical engineering , organic chemistry
Time series of soil CO 2 efflux recorded in the Azores archipelago volcanic‐hydrothermal areas feature daily and seasonal variations. The recorded CO 2 efflux values were lower during summer than in the winter season. The diurnal CO 2 efflux values were higher at dawn and lower in the early afternoon, contrary to that observed in biogenic environments. CO 2 efflux cycles correlated well with the environmental variables, such as air temperature, wind speed, and barometric pressure, which also showed low‐ and high‐frequency periodicities. Several simulations were performed here using the Transport of Unsaturated Groundwater and Heat 2 (TOUGH2) geothermal simulator to complement the study of Rinaldi et al. (2012). The effects of the water table depth, air temperature perturbation amplitude, and soil thermal gradient contributed to an explanation of the contrasts observed in the diurnal ( S 1 ) and semidiurnal ( S 2 ) soil CO 2 efflux peaks for the different monitoring sites and seasons. Filtering techniques (multivariate regression analysis and fast Fourier transform filters) were also applied to the recorded time series to remove effects of external variables on the soil CO 2 efflux. The resulting time series (the residuals) correspond to the best approach to the deep‐seated (volcanic/hydrothermal) CO 2 emissions and thus should be used in seismovolcanic monitoring programs. Even if no evident correlation can be established yet between the soil CO 2 residuals and seismicity over the monitored time, a seismic swarm that occurred around the end of 2008 might have triggered some deviations from the observed daily cycles.