Additional words by NZ History

It’s been 13 years since the start of the deadly Darfield earthquake sequence.

The magnitude 7.1 earthquake occurred at 4:35 am on 4 September, the epicentre was 40 km west of Christchurch City, and the depth of the quake was at 10 km.

The epicentre was close to the town of Darfield.

The Darfield earthquake sequence initiated three other significant earthquakes close to the city of Christchurch including the fatal 6.2 Christchurch on Tuesday Feburary 22 2011.

The September earthquake inflicted a wide range of damage on buildings – everything from minor spills and breakages to structural damage to foundations, walls and roofs.

The earthquake’s shaking turned water-saturated layers of soft sand and silt into liquid mush, a process known as liquefaction.

The most badly affected areas were close to the coast, especially the town of Kaiapoi and the Christchurch suburb of Bexley, where a number of modern houses were damaged.

The ground above the liquidised layers subsided unevenly, cracking footpaths, roads and houses.

Water and sewer pipes broke, leading to local flooding. Silty sludge squirted up through cracks to produce small sand volcanoes.

Cracks opened up close to rivers and streams where the ground moved down towards the water, causing damage to man-made structures – a process known as lateral spreading.

The earthquake shook apart some older unreinforced brick and masonry buildings, and many more lost chimneys, either during the earthquake or through subsequent removal because of the risk they posed.