Liquefaction and ground failure induced by the 1988 Saguenay, Quebec, earthquake

Abstract

Ongoing geological and geotechnical investigations are under way for two sites in Ferland, Quebec, where sand boil deposits, ground fissures, and liquefaction-related damage to homes were documented immediately following the M = 5.9 Saguenay earthquake of November 25, 1988. Both sites are about 26 km from the epicentre. To date, the geological investigation of the sites suggests that (i) liquefaction and ground failure have occurred in this area in the past, (ii) lateral spreading was the principal mode of ground failure in 1988 and in the past, (iii) 1988 and earlier displacements due to lateral spreading were on the order of centimetres, and (iv) topography played an important role in the localization and characterization of ground failure. The geotechnical investigation suggests that (i) liquefaction at these sites is predictable using Seed's method, and (ii) the material that liquefied during the Saguenay earthquake is a gray, siltysand or sandy silt that is about 0.3 m thick and occurs at a depth ranging from 2.5 to 4.5 m below the surface. These preliminary results suggest that the potential for liquefaction and related damage may be higher than previously recognized in the Ferland–Boilleau valley in particular and in the Saguenay area in general. Key words: liquefaction, ground failure, earthquake, geological investigation, geotechnique, silty sand, damage.