BERNARD DUCARME, V. Y. TIMOFEEV
(RESUMÉ)
The Institute of Geophysics (UIGGM, SB-RAS) in Novosibirsk developed a geodynamics station in a mine gallery at Talaya (51.68°N, 103.65°E) in the lake Baïkal rift, 3 km south of the main fault of Sayan. Tilt (1985), extensometric (1989) and absolute gravimetric (1992) measurements are performed in this station. The different types of measurement are affected by local and regional seismic activity up to 400 km distance. This activity comprised several episodes between 1985 and 1999. Between 1985 and 1989, it was first concentrated in an area of approximately 40 km around the station and was associated to a tilt following a NS axis. This behaviour ceased in 1989, after an earthquake localized in the SSE of the station. The relaxation time corresponding to this phenomenon allows us to evaluate the viscosity of the crust. In 1991, a major earthquake 400 km west strongly modified the orientation of the principal constraints. We could use this phenomenon to evaluate the viscosity of the astenosphere. A gravity variation noticed between 1995 and 1998 seems to be associated to the preparation of the earthquake of February 1999, 80 km west of the station. We can explain this phenomenon by a porosity variation at the level of the Sayan fault.
Mots-clé: clinométrie, extensométrie, gravimétrie
absolue, activité sismique, temps de relaxation, viscosité de
la croûte, viscosité de l'asténosphère.