CENTRIFUGE MODELING OF NORMAL FAULT RUPTURE THROUGH COMPOSITED OVERBURDEN STRATA

Permanent ground deformation due to fault rupture accompanied by an earthquake can be dangerous and result in considerable economic losses and human fatalities, as experienced during the 1959 Hebgen Lake earthquake in Montana and 1983 Borah Peak earthquake in Idaho, USA. Reducing the damage to the structure within the fault zone requires an understanding of fault-soil interactions through composite overburden strata. Here, a series of centrifuge modeling tests simulating normal fault rupture through different thickness ratios of composite overburden strata were conducted. The soft rock layer was simulated by cemented sand with a uniaxial compressive strength of 0.975 MPa. In all centrifuge modeling tests, a constant total model thickness of 100 mm was used. The normal fault simulation was started once the model was spun at 80 g, which correlates to 8 m of total soil thickness, and subjected to 4 m vertical offset along a normal fault dipping 60°. The results show that thickness ratio of the composite overburden strata affects the fault-affected zone properties and lengthens this zone up to a thickness ratio between soft rock and sandy soil of 70:30.