EARTHQUAKE-TRIGGERED LANDSLIDES AT THE BRUNSSUMMERHEIDE, LIMBURG, THENETHERLANDS - PRELIMINARY STUDIES FOLLOWING THE 1992 ROERMOND EARTHQUAKE

Two landslides occurred at the Brunssummerheide during, or shortly aft er the main shock of the 1992 Roermond earthquake. The Brunssummerheid e is located 25 km south of the epicentre. An earthquake can reduce th e stability of a hillslope in three ways: firstly, the ground accelera tion from seismic waves forms an additional destabilizing force; secon dly, the shear strength may be reduced by an increase of the pore pres sure, and thirdly, an earthquake may cause the breaking of small cohes ive bonds between soil particles, thus reducing the overall cohesion. Slope stability back-analyses were carried out to reconstruct the forc es and processes during the event. Peak ground accelerations as predic ted by empirical attenuation relationships are insufficient to cause i nstability of the slopes. It is concluded that an increase of at least 100% in the pore pressures was required to destabilize the two hillsl opes.