Elastic buckling of fractured basalt on the Columbia Plateau, Washington State

The continental flood basalts of the Columbia Plateau, Washington State, have been deformed into a series of anticlines termed the Yakima Fold Belt. These periodically spaced folds may be associated with buckling instability of a basaltic layer overlying a sedimentary substrate. Previous calculations of critical stress and dominant wavelength of buckling for these rocks assumed the strength properties of intact basalt. Those calculations suggested that buckling required very large modulus contrasts. Here we investigate the effect of using a rock-mass strength criterion and a deformation modulus on simple elastic models for buckling of basalts at the Earth’s surface. We find that buckling can be predicted for smaller, more plausible values of modulus contrast. Using revised parameters, the buckling model provides a reasonable explanation for periodic folding in these fractured basalts.