Very slightly anomalous leakage of CO_2, CH_4 and radon along the main activated faults of the strong L'Aquila earthquake (Magnitude 6.3, Italy) Implications for risk assessment monitoring tools public acceptance of CO_2 and CH_4 underground storage

摘要

The 2009-2010 L'Aquila seismic sequence is still slightly occurring along the central Apenninic Belt (August 2010), spanning more than one year period. The main-shock (Mw 6.3) occurred on April 6th at 1:32 (UTC). The earthquake was destructive and caused among 300 casualties. The hypocenter has been located at 42.35°N, 13.38° at a depth of around 10 km. The main shock was preceded by a long seismic sequence starting several months before (i.e., March, 30, 2009 with Mw 4.1; April, 5 with Mw 3.9 and Mw 3.5, a few hours before the main shock). A lot of evidences stress the role of deep fluids porepressure evolution - possibly CO_2 or brines - as occurred in the past, along seismically activated segments in Apennines. Our geochemical group started to survey the seismically activated area soon after the main-shock, by sampling around 1000 soil gas points and around 80 groundwater points (springs and wells, sampled on monthly basis still ongoing), to help in understanding the activated fault segments geometry and behaviour, as well as leakage patterns at surface (CO_2, CH_4, Radon and other geogas as He, H_2, N_2, H_2S, O_2, etc...), in the main sector of the activated seismic sequence, not far from a deep natural CO_2 reservoir underground (termomethamorphic CO_2 from carbonate diagenesis), degassing at surface only over the Cotilia-Canetra area, 20 km NW from the seismically activated area. The work highlighted that geochemical measurements on soils are very powerful to discriminate the activated seismogenic segments at surface, their jointing belt, as well as co-seismic depocenter of deformation. Mostly where the measured "threshold" magnitude of earthquakes (around 6), involve that the superficial effects could be absent or masked, our geochemical method demonstrated to be strategic, and we wish to use these methods in CO_2 analogues/CO_2 reservoir studies abroad, after done in Weyburn. The highlighted geochemical -slight but clear- anomalies are, in any case, not dangerous for the human health and keep away the fear around the CO_2-CH_4 bursts or explosions during strong earthquakes, as the L'Aquila one, when these gases are stored naturally/industrially underground in the vicinity (1-2 km deep). These findings are not new for these kind of Italian seismically activated faults and are very useful for the CO_2-CH_4 geological storage public acceptance: not necessarily (rarely or never) these geogas escape abruptly from underground along strongly activated faults.