The berill fault and its relation to a deep seated gravitational slope deformation (dsgsd)

Abstract

Within the Innfjorddalen valley (Møre og Romsdal, Norway) a 1.5 km long linear NNE-SSW striking feature, forming a 3-4 m high step in the topography, occurs on the SE facing slope of the Middagstinden mountain and was previously discussed as a Holocene reverse fault, called the "Berill fault". Our intense structural field mapping and a high resolution digital elevation model based on LiDAR data derived from airborne and terrestrial laser scanning indicate that the "Berill fault" is a normal fault that has the orientation of the collapse of the Caledonian orogen, that is today reactivated as a limiting structure of a Deep Seated Gravitational Slope Deformation (DSGSD). Differential Global Navigation Satellite System (dGNSS) surveys over the instability indicate velocities of the DSGSD of ca. 0.6 cm/yr. Three electric resistivity profiles on the valley floor attest that the fault is a structure with regional extend. Three trenches with a total length of 100 m parallel to the electric resistivity profiles although down to glacial deposits or the underlying bedrock do not indicate any Holocene activity of the fault. Hence reactivation of the fault by the DSGSD produces the linear feature oblique to the slope.