Activité du gaz radon dans l'air du sol et sismicité locale : exemple du bassin de l'Arax (Arménie)

Abstract

Radon soil-gas concentrations and local seismicity: case of the Arax basin (Armenia). A survey of soil gas radon concentrations has been carried out at three sites, in the seismic area of Armenia, from 1996 to 1999. The seismicity generates opposed behaviours at the different sites. This heterogeneity is related to the sites locations in the tectonic frame. An increase of radon concentration occurs inside the tectonic micro-blocks during local seismic activity. On the contrary, an abrupt co-seismic decrease is recorded close to the fault area. These variations can be due to 'pore-collapse' phenomena which expulse the pore-gas and increases Rn concentration in soil at intra-blocs sites, but also to pore-elastic deformations and microfracturing modifications in the fault area. To cite this article: K. Kharatian et al., C. R. Geoscience 334 (2002) 179-185.  2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS soil gas radon / precursor gas / earthquake / Caucasus / Armenia Résumé -L'activité du gaz radon du sol a été examinée sur trois sites du bassin de l'Arax, zone sismique d'Arménie, pour la période 1996-1999. La crise sismique de fin 1998-début 1999 engendre des comportements opposés sur ces différents sites. Cette hétérogénéité semble être conditionnée par leurs positions par rapport au cadre tectonique et par les caractéristiques propres des séismes. Une augmentation du radon a été enregistrée dans des micro-blocs tectoniques. Dans la zone de faille, on observe au contraire une baisse pré et co-sismique saccadée de l'activité du radon. Ces variations pourraient s'expliquer par un mécanisme de type pore-collapse qui, en expulsant les gaz des pores, augmente leur concentration dans le sol sur les sites intra-blocs, mais aussi par des déformations poro-élastiques et des modifications de la microfracturation dans la zone de faille. Pour citer cet article : K. Kharatian et al., C. R. Geoscience 334 (2002) 179-185.  2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS radon du sol / gaz précurseur / séisme / Caucase / Arménie

Evidence of Multiple Sources of Soil Gas in the Tangshan Fault Zone, North China

“…Soil gas geochemical surveys in seismically active areas have been carried out across the world [5,6,18,19], and some anomalies appearing before earthquakes have been identified [11,20]. In the Arax Basin (Armenia), radon volume activities have been observed to vary before and after earthquakes [21]. Similarly, anomalously high radon volume activity fluctuations were observed several hours to a few days before an earthquake (M L > 3) that occurred in northern Taiwan [7].…”

In-soil radon anomalies as precursors of earthquakes: a case study in the SE slope of Mt. Etna in a period of quite stable weather conditions

“…So, soil-gas radon activity increases in the range of 2e3 are possible. These increases are not simultaneous, due to their location relative to epicentres (Kharatian et al, 2002).…”

Geochemical Characteristics of Soil Gas and Strong Seismic Hazard Potential in the Liupanshan Fault Zone (LPSFZ)

“…Anomalously high Rn volume activity fluctuations were observed several hours to a few days before an earthquake (M L > 3) that occurred in northern Taiwan [8]. Similarly, Rn volume activities in the Arax basin (Armenia) were observed to vary before and after earthquakes [25]. A large amount of observed Rn data in ground water and soil has been collected in China [26,27].…”

“…CO 2 is the second most abundant magmatic gas after H 2 O and is the main gas investigated during diffuse degassing studies as well as at many permanent stations using the accumulation chamber method (ACM) [34,35]. Soil gas anomalies are usually complex because they are subject to multiple influences (atmospheric, biogenic, organic, and from the deep crust and mantle [23,25,36,37]) and occasionally, their relationships with seismic events can be ambiguous [4,7,38,39]. Accordingly, if soil gas observations in fault zones become a useful method of fault activity assessment and seismic forecasting, further analysis of their relationships is required and the source identification of soil gas in the seismically active areas is a prerequisite.…”