Aseismic Multifissure Modeling in Unfaulted Heavily Pumped Basins: Mechanisms and Applications

摘要

Aseismic earth fissures are among the most dangerous by-products of excessive groundwater exploitation in many subsiding sedimentary basins. Improving our understanding of the mechanisms of earth fissuring is important for land planning and risk management. We employ an advanced finite-element interface-element modeling approach to understand the generation and propagation of multiple fissures in unfaulted basins. Almost parallel earth fissures at a relative short distance (on the order of tens of meters) generally develop above impermeable and/or incompressible ridges buried by the compacting sedimentary units. Initially, we investigate the effect of the ridge slope on a simplified geological setting sketched from the Luke salt dome, Arizona. Then, we apply the model to the hydrogeologic setting at Guangming village, Wuxi, China. In both analyses, the model simulates the formation of multifissures above the ridge, as observed at the sites. The earth fissures initiate at land surface and propagate downward. They are caused by the combination of tensile stress (bending condition) and shear stress (shearing conditions) accumulation around and above the tip and the slopes of the ridge, respectively. The steeper the ridge, the more concentrated stress zone develops above the ridge tip, favoring the formation of fissures with significant opening and small or null offset. The opposite facilitates a widening of the stress accumulation area, with less-deep fissures characterized by larger sliding and smaller opening. At Guangming, the model suggests that fissures propagate down to 20-50-m depth, with maximum opening and sliding of similar to 50 cm.