Clastic dykes in east Belgium: Evidence for upper Pleistocene strong earthquakes west of the Lower Rhine rift segment

Fissures of seismic origin are described from terrace deposits of the Meuse river in the Liege-Maastricht area, west of the Lower Rhine-Roer rift segment. Though associated with hydroplastic deformation of the sediments, they are not injection structures. They are interpreted as tension cracks resulting from local deformation of susceptible layers inferred to be due to cyclic loading by seismic waves: the fissures have been filled afterwards from above by vertically laminated sands and silts. The distribution of the fissured areas and the special features of some ground cracks suggest that they could be linked to more than one earthquake between 650 and 100 ka sp. By comparison with liquefaction phenomena described in relation to actual earthquakes. the failure of the Meuse terrace deposits could have been produced by seismic events of M(L) greater than or equal to 6.5.