The influence of near-fault motions on liquefaction triggering during the Canterbury Earthquake Sequence

摘要

The objective of this study is to examine the influence of near-fault motions on liquefaction triggering in Christchurch and neighboring towns during the 2010-2011 Canterbury Earthquake Sequence (CES). The CES began with the 4 September 2010,M_w7.1 Darfield earthquake and included up to ten events that triggered liquefaction. However, most notably, widespread liquefaction was induced by the Darfield earthquake and the M_w6.2, 22 February 2011 Christchurch earthquake. Of particular relevance to this study is the forward directivity effects that were prevalent in the motions recorded during the Darfield earthquake, and to a much lesser extent, during the Christchurch earthquake. A 2D variant of the Richart-Newmark fatigue theory was used to compute the equivalent number of cycles (neq) for the ground motions, where volumetric strain was used as the damage metric. This study is unique because it considers the contribution and phasing of both the fault-normal and fault-parallel components of motion on n_(eq) and the Magnitude Scaling Factor (MSF). It was found that when the fault-normal and fault-parallel motions were treated individually, the former yielded a lower n_(eq) than the latter. Additionally, when the combined effects of fault-normal and fault-parallel components were considered, it was found that the MSFwere higher than those commonly used. This implies that motions containing near-fault effects are less demanding on the soil than motions that do not. This may be one of several factors that resulted in less severe liquefaction occurring during the Darfield earthquake than the Christchurch earthquake.