Dependence of horizontal stress magnitude on load dimension in glacial rebound models

Abstract

Summary It has been proposed that the deglaciation of the Northern Hemisphere triggered large earthquakes within intraplate environments and in this paper we examine this hypothesis by evaluating quantitatively the stress state in the lithosphere produced by time‐dependent surface loads. A series of models demonstrate the dependence of horizontal incremental stress in an elastic plate overlying an inviscid or viscoelastic mantle on the lateral extent of a load applied at the surface. The horizontal stress is largest when the dominant wavelength (that is twice the diameter) of the load is close to eight times the elastic thickness of the plate when the mantle is inviscid and, for the particular viscosity model employed in this paper, close to 12 times the elastic thickness for a viscoelastic mantle. At wavelengths close to the critical wavelength, the horizontal incremental stress may be up to six times as large as the vertical incremental stress. For appropriate earth‐model parameters amplification of horizontal stress is close to maximum for ice loads with a radius of 280 km, comparable to the dimensions of the former ice sheet over Great Britain. This amplification may be sufficiently large that loading by small ice sheets can lead to failure on marginally stable faults, in contrast to the behaviour for large ice sheets. The models also predict greater fault instability for Fennoscandia than for the larger Laurentide ice sheet, consistent with the observation of large postglacial faults in northern Sweden. The model is used to predict the stability of faults and style of faulting due to rebound stresses in the absence of a background tectonic stress field since the last glacial maximum (∼ 18 000 years ago) in Northern Europe. Within the formerly glaciated region thrust faulting is predicted to occur at the end of deglaciation and normal faulting is predicted to occur in peripheral regions for the entire period since the last glacial maximum.

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.…”

Composite faults in the Swiss Alps formed by the interplay of tectonics, gravitation and postglacial rebound: an integrated field and modelling study

“…As numerical models without faults showed, the stress changes induced by postglacial unloading and rebound are sufficient to induce faulting (e.g. Johnston et al, 1998). Recent models that explicitly included a fault quantify the variations in the fault slip rate caused by glacialinterglacial changes in surface loads (Hetzel & Hampel 2005;Hampel & Hetzel 2006).…”

Postglacial Faults in Fennoscandia: Targets for scientific drilling

“…These data are then applied in numerical analyses of how the stress field is influenced by different ice load weights and configurations. Theoretical modeling of the bedrock stress field under a glacial load has been carried out by several authors (e.g., Johnston 1989; Wu & Hasegawa 1996a, 1996bJohnston et al 1998;Klemann & Wolf 1998;Wu et al 1999;Lund 2005;Turpeinen et al 2008;Lund et al 2009). These studies have indicated that earthquake activity is diminished under an ice sheet but greatly enhanced at the end of deglaciation.…”