Modelling of stresses in the Fennoscandian lithosphere induced by Pleistocene glaciations

Abstract

The seismicity observed in Fennoscandia is usually explained by tectonic stresses. The question of the contribution of stresses induced by glacial-isostatic adjustment to the seismicity has not nally been settled yet. In order to quantify the isostatic stress eld generated by the Fennoscandian glacial load, we consider layered Maxwell-viscoelastic half-spaces loaded by axisymmetric discs. In particular, we calculate the maximum shear-stress distribution induced by the load model and the associated stress regimes in the lithosphere. Emphasis is placed on a discussion of the sensitivity of the calculated isostatic stresses to variations in load cross-section, lithosphere thickness and asthenosphere viscosity. We also examine the e ects produced by the viscous relaxation of the lithosphere, whose viscosity is parameterized according to the strati cation expected for temperature-activated di usion creep.Our results show that the isostatic shear stresses typically reach 2 MPa near the surface at the present time but that their distribution may be modi ed strongly by the details of the earth and load models investigated. The viscous relaxation of the lithosphere becomes particularly important, if more than one glaciation is considered. Since the last ice age in Fennoscandia consisted of several glaciations, the model of a perfectly elastic lithosphere conventionally employed in models of glacialisostatic adjustment therefore may not be justi ed when calculating the isostatic stresses.

Ocean loading effects on stress at near shore plate boundary fault systems

“…The maximum shear stress (s 1 − s 3 )/2, where s 1 and s 3 are the maximum and minimum principal stresses, reflects the patterns of the other stress components with high magnitudes near the surface offshore and onshore and high magnitudes at depth at the coastline. When computed for an elliptical discshaped load of the same dimensions, these stress components match those published in studies by Ivins et al [2003], Klemann and Wolf [1998], and Johnston et al [1998], though we note the vertical normal stress t zz of those models corresponds to the vertical normal stress of our bending model with an additional stress due to the buoyancy of the deflected mantle, t zz + r m gW.…”

Extensional neotectonics around the bend of the Western/Central Alps: an overview

“…A sensitivity study by Gudmundsson (1994) shows that post-glacial elastic rebound might well be a significant component of the present-day vertical tilt rate of 1.5 mm/year observed between the inner Alpine valleys (Valais) and the Alpine foreland. The disappearance of the large Alpine glaciers should have provoked generalized uplift as observed in Scandinavia (e.g., Klemann and Wolf 1998;Wu et al 1999). Such a rebound, if still active, should induce uplift mainly in the areas of maximum ice thickness (e.g., Kelly et al 2004) and may actually be integrated in a more general isostatic uplift of other origin.…”

The early Quaternary North Sea Basin

“…Ice sheets are known to have an impact on isostasy both through the loading of the ice sheet itself (James & Bent 1994;Klemann & Wolf 1998;Davis et al 1999;James et al 2000;Stewart et al 2000) and the changes to groundwater conditions affecting compaction of sediment (Boulton & Dobbie 1993;Saettem et al 1996;Piotrowski & Kraus 1997;O'Regan et al 2010O'Regan et al , 2016. The effects of changes to groundwater drainage under a significant ice load can result in strongly differential compaction.…”

“…Although modern postglacial rebound models, constrained by field-based investigations, have improved greatly over the years they are reliant on knowing the extent and thickness of the ice sheet in question (James & Bent 1994;Klemann & Wolf 1998;Davis et al 1999;James et al 2000;Stewart et al 2000), for which the data are truly available only in the North Sea for the last glacial maximum (Huuse & Lykke-Andersen 2000;Graham et al 2011). Additionally, modern rebound models may not fully account for the cumulative effect of repeated glaciations, which the North Sea is known to be subject to (Klemann & Wolf 1998;Stewart et al 2000). With a limited understanding of ice extents prior to the last glacial maximum and lacking any direct measurements of potential over-or under-consolidation the impact of glacial loading on the Quaternary stratigraphy remains uncertain.…”