Quasi-static versus dynamic fault rupture: centrifuge modeling and instrumentation

The transmission of seismic tectonic plate movements to near-surface soils can cause large, rapid, and damaging faults. These deformations can cause catastrophic failure of foundations and buildings at the surface, as well as buried utilities that are near or spanning a fault. Correctly predicting the fault propagation to assess risk to existing structures or for safe zoning is crucial yet challenging due to soil non-linearity, large soil deformations, and dynamic effects. Geotechnical centrifuge modelling enables this complex and large-scale phenomenon to be captured with reduced-scale models. The current study presents the development of a compact fault rupture simulator compatible with the medium-sized 15 g-ton centrifuge at CU Boulder. The setup allows comparison of the rupture propagation in soils subjected to quasi-static and dynamic normal fault rupture. The contrasting uses of multiple instrumentation techniques are highlighted, for example, tracking the soil displacements directly versus inferred from accelerometers detecting the radial g-field in the quasi-static tests versus obtaining static and dynamic acceleration changes during the dynamic faulting. Overall, differences in the observed rupture propagation due to the vertical accelerations are demonstrated in two identically prepared dry sand models, highlighting an often-ignored rate effect in this complex process.