CONTINENTAL-SLOPE INSTABILITY TRIGGERED BY SEEPAGE: AN EXPERIMENTAL APPROACH

摘要

Mass-transport complexes (MTCs), mass-transport deposits (MTDs), and associated facies and features are widely recognized in continental slopes around the world. In most current stratigraphic models of MTCs and MTDs, these submarine sediment failures are related to aquifer outflow (sapping, seepage) along continental slope fronts that originated during relative sea-level fall. We test a hypothetical scenario that is favored during early forced regression using reduced-scale physical simulation. A major underground subaerial hydraulic gradient is assumed to flow towards the basin depocenter as a function of relative sea-level fall. We developed an experimental apparatus with slope angles varying between 15 and 30 degrees to test this concept. Hydraulic gradients, aquifer outflow velocities, and triggered collapses induced by the seepage effect were recorded at various positions of the slope. Analysis shows that steeper slope gradients require lower seepage velocities (and shear stresses) to trigger collapse, but gentler slopes remain unchanged. Experimental data are compatible with a seepage effect that could potentially trigger mass failure and the formation of MTCs during relative sea-level fall. The features produced in the experiment have geometries comparable to natural environments, and the experimental seepage velocities are of an order of magnitude similar to those monitored in submarine aquifers. The experimental results advance understanding of mass transport in continental slopes by introducing and testing new methods, and also provide new insights into potential submarine geohazard risks where tectonic uplift operates along some coastal regions.