Micromorphological studies relating the soil formation history (processes and timing) to activity events of the Peel Boundary Fault (PBF) showed rotation features (circular distribution pattern of sand grains) in mechanically displaced rounded fragments of Bt bands. These features are interpreted as being caused by ‘mudflow’ during active faulting event (PBF event F2). The micromorphological interpretation of Late Weichselian soil formation (clay illuviation, degradation features and offsetting of Bt bands) agrees with the hypothesized 3 PBF periods of fault activity events (Fl, F2 and F3).

To provide quantitative information on the ground acceleration necessary to break speleothems, laboratory measurements on samples of stalagmite have been performed to study their failure in bending. Due to their high natural frequencies, speleothems can be considered as rigid bodies to seismic strong ground motion. Using this simple hypothesis and the determined mechanical properties (a minimum value of 0.4 MPa for the tensile failure stress has been considered), modelling indicates that horizontal acceleration ranging from 0.3 m/s2 to 100 m/s2 (0.03 to 10g) are necessary to break 35 broken speleothems of the Hotton cave for which the geometrical parameters have been determined. Thus, at the present time, a strong discrepancy exists between the peak accelerations observed during earthquakes and most of the calculated values necessary to break speleothems. One of the future research efforts will be to understand the reasons of the defined behaviour. It appears fundamental to perform measurements on in situ speleothems.