Landslides caused by the 1929 M=7.8 Murchison earthquake in New Zealand

Whilst there is a strong focus in New Zealand at the moment on the multiple landslides triggered by the Kaikoura earthquake last month, GNS Science have released a new report about the landslides triggered by the 1929 M=7.9 Murchison earthquake on the other side of South island.  This was a major event that probably triggered even more landslides than the most recent earthquake.  The report details the collation and analysis of a full inventory of the landslides triggered by the earthquake, based upon mapping from aerial photographs, supplemented with other sources of data. Because the primary source of information is a set of images collected in 1968, the inventory is only for larger landslides (those with a surface area grater than 2500 square metres).  Nonetheless there are 5356 landslides in the inventory extending over an area of about 16,000 square kilometres.

Some of the statistics are impressive – the earthquake triggered two landslides with a volume of more than 100 million cubic metres, and there are 42 valley blocking landslides (landslide dams) in the dataset.  Several of these landslide dams breached catastrophically over the weeks following the earthquake.  As a result there was extensive flooding and damage in the towns of Seddonville, Little Wanganui and Karamea.  In total 14 people were killed by landslides, and two miners died in mine collapse events triggered by the shaking.

To give an idea of the extent of the landsliding triggered by the Murchison Earthquake, the report includes this twin oblique and vertical pair of images of an area of landslides in the Karamea Valley:

Landslide triggered by the 1929 Murchison Earthquake. From the new GNS Science Report

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Some of the large landslides are truly impressive.  This is the 18 million cubic metre Lake Stanley rock avalanche, some 85 km from the epicentre for example:

The Lake Stanley rock avalanche triggered by the 1929 Murchison Earthquake in New Zealand, from the new GNS Science report.

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At the first AGU landslides session tomorrow (which will be streamed live), one of the authors, Brenda Rosser, will be describing the New Zealand landslide dataset compiled by GNS Science.

Reference

Hancox, G.T., Ries, W.F., Parker, R.N., Rosser, B., 2015. Landslides caused by the MS 7.8 Murchison earthquake of 17 June 1929 in northwest South Island, New Zealand. GNS Science Report 2015/42. pp127 (2 Volumes)