Surface Deformation in Iceland and Crustal Stress over a Mantle Plume

Abstract

The horizontal radial flow of plastic material near the top of a mantle plume excerts stresses on the lower lithosphere. The velocity of this flow is a function of the distance from the center of the plume. The radial stress in the lithosphere will be tensional over the plume but compressional outside of the plume, while the tangential stress is tensional throughout the whole region of the radial flow. The difference between radial and tangential stress represents a shear stress. This has a maximum a short distance outside of the plume. If both radial and tangential stress is tensional, as above the plume, the surface deformation will be related to normal faults. High volcanic activity is expected but seismic activity will be low and only small earthquakes will occur because of the low tensile strength of crustal rocks. Where the radial stress is compressional and the tangential stress is tensional, as in areas outside of the plume, the ground de-formation will be largely associated with strike-slip faults. Volcanic activity is expected to be low, but seismic activity may be high with occasional large earthquakes because of the relatively great shear strength of crustal rocks.