What are Earthquakes?

Earthquakes are caused by a sudden release of violent ground energy caused either by the shifting of the earth’s crust or volcanic/magmatic activity. Most earthquakes occur when two sides of a fault slide past each other. The crust may either be being compressed, pulled apart, moving sideways or a combination of these. The resulting seismic waves are felt as earthquakes. ³⁸⁰³

Earthquakes occur frequently in New Zealand due to its position upon the boundary of two plates of the earth’s crust, the Pacific and Australian plates. New Zealand sits on the Pacific “Ring of Fire”; a zone of intensified earthquake and volcanic activity that straddles the margins of land around the Pacific plate. Over 15,000 earthquakes are recorded every year in New Zealand, although only 100 - 150 of these are actually felt. ⁴⁷¹¹ The majority of New Zealand’s earthquakes occur along the main fault line which stretches in a wide band from Fiordland to the East Cape. New Zealand’s mountain ranges have been formed by the tremendous power of these fault movements. ³⁸⁰⁴

Major earthquakes can cause widespread destruction when they occur near towns and cities. In 1848 an estimated 7.5 magnitude earthquake centred in Marlborough destroyed many of Wellington’s building’s which were mainly built of masonry and brick. In response Wellington was rebuilt with mostly timber buildings. Napier was devastated in 1931 by the 7.8 magnitude Hawkes Bay earthquake and the fires that followed. In February 2011, a 6.3 magnitude earthquake struck Canterbury, very close to the city of Christchurch. The earthquake's shallow epicentre was at a depth of only 5 km and lay just 6 km south-east of the city's centre. The proximity of the earthquake to the city caused extremely strong shaking, and other earthquake-related hazards, resulting in severe damage and the loss of 185 lives. ⁴⁷¹² New Zealand's latest major earthquake occured in Hurunui/Kaikoura on 14 November 2016 and was 7.8 in magnitude. It caused severe damage in the local area, and to buildings in the city of Wellington. It also caused parts of the South Island to move 5m closer to the North Island, and be uplifted by as much as 8m. The earthquake was so complex and unusual it has led to changes in the way scientists think about earthquake hazards in plate boundaries worldwide. ⁴⁷⁰⁸

As a result of this experience with destructive earthquakes, building codes in New Zealand are more stringent than in most countries and are credited with the relatively low level of fatalities during recent major earthquakes.

Last updated at 1:10PM on February 8, 2018