Abstract

The 1929 M 7.7 Murchison earthquake in northwestern South Island, New Zealand, triggered at least 1850 landslides larger than 0.25 ha within a 1200-km2 (45 × 25 km) area close to the epicenter. The area surveyed in detail totals 25% of the area in which the earthquake initiated landslides. About 2.5 × 108 m3 of debris was transported by landslides in the area surveyed, equivalent to an average debris yield of 210 000 m3/km2. Landsliding was most common on well-bedded and jointed, calcareous, Tertiary mudstones and fine sandstones and was particularly concentrated on scarp slopes in areas of both gentle and moderate to steep dip. On moderately to steeply dipping mudstones, scarp slopes facing away from the origin of the seismic waves were particularly prone to landsliding. Large dip-slope landslides were common on thick-bedded Tertiary sandstones. Landslides on granitic rocks were generally smaller, shallower, and composed of finer grained debris than those of sedimentary rocks.

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