Seismically induced boulder displacement in the Port Hills, New Zealand during the 2010 Darfield (Canterbury) earthquake

Abstract

An analysis of boulders displaced during the September 2010 M w 7.1 Darfield (Canterbury) earthquake provides noninstrumental constraints on the variability, distribution and origin of strong ground motion during major earthquakes. Boulders ranging in mass from 10 to 5000 kg were displaced 8-970 cm laterally from hosting soil sockets of < 1 cm to 50 cm depth at several sites in the Port Hills, roughly 35 km southeast of the earthquake epicentre. Boulder displacement was observed on N-striking (000-015°) ridges above c. 400 m elevation but not on NE-, NW- and SE-striking ridges. The prevailing boulder horizontal displacement azimuth of 250 ± 20° is subparallel with the direction of instrument..