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

• Published in: Geophysical Journal International
• Main Authors: Johnston, Paul, Wu, Patrick, Lambeck, Kurt
• Format: Text
• Language: English
• Published: Oxford University Press 1998
• Subjects: Articles; Fennoscandia; Ice Sheet; Northern Sweden
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/132/1/41; https://doi.org/10.1046/j.1365-246x.1998.00387.x

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.