Critical taper analysis reveals lithological control of variations in detachment strength: An analysis of the Alpine basal detachment (Swiss Alps)

Abstract

[1] Although evidence for weak detachments underlying foreland thrust belts exists, very little is known about the lateral variations in effective strength, as well as the geological nature of such variations. Using critical taper analysis, we show that a detailed and systematic measurement of surface slope of the Central European Alps reveals variations in strength parameter F along the detachment, based on the argument that the Alps are close to the critical state. We show that the basal detachment is very weak near the deformation front but strengthens toward the hinterland. Very low F (effective coefficient of friction plus normalized cohesion) values of <0.1 and even 0.05 occur within evaporites and within shales in Triassic (west) or Upper Cretaceous/Lower Tertiary sequences (east) used by the Alpine sole detachment. These very low values in shales-comparably low values are reported from other orogens-are caused partly by slightly elevated pore pressures (k > 0.54) but may also require additional mechanisms of dynamic weakening.

Tectonic evolution around the Mont Terri rock laboratory, northwestern Swiss Jura: constraints from kinematic forward modelling

“…The values determined here should not be considered as absolute values, because of the many simplifications done in these models, but they have relative significance. We note, however, that the low friction values obtained here for the Triassic décollement are in accordance with those obtained by von Hagke et al (2014) for the Triassic evaporites and shales.…”

“…Both depend on basal friction and material of the wedge, its density, and shear strength (Chapple 1978;Davis et al 1983;Dahlen 1990). As a consequence, tectonic evolution and kinematics of thinskinned fold-and-thrust belts are strongly controlled by the thickness of the sedimentary cover overlying the basal décollement, eventually modified by syn-tectonic erosion or sedimentation as well as aspects influencing the basal friction of the décollement, such as fluid pressure and fracture strength (Sommaruga and Burkhard 1997;Hindle 2008;von Hagke et al 2014). In addition to these principal controlling mechanisms, localisation and development of contractional structures in thin-skinned foreland fold-andthrust belts is known to be commonly influenced by preexisting structures (i.e.…”

Multi-scale imaging of a slow active fault zone: contribution for improved seismic hazard assessment in the Swiss Alpine foreland

“…In addition, but also in general, excess water loads may act as a trigger on a critically stressed fault system and thus induce earthquake swarms. Although, the present data record for our study area, is too sparse and incomplete to make a plausible correlation, this has been postulated elsewhere in the Alps (von Hagke et al 2014 and references therein). Similar situations of induced seismicity can also be linked to excess rainfall and flooding, as known in other regions in Switzerland and southeastern Germany (e.g.…”

The importance of missing strain in Deep Water Fold and Thrust Belts

“…the critical taper angle between surface and the basal surface and its evolution in response to plate convergence rates, sedimentation rates, exhumation and climate (Willet et al, 2003;Roe et al, 2006;Stolar et al, 2006;Simpson, 2010;Fillon et al, 2013;von Hagke et al, 2014) In addition, a number of studies consider the internal geometry of the wedge, and the individual structures that interact through the fold and thrust belt. Our results imply that an additional, and unrecognized 5%, should be accounted for in such studies.…”