Earthquake Preparedness in Christchurch, New Zealand

Patricia Stapleton, Social Science & Policy Studies, Worcester Polytechnic Institute

Summary

On February 22, 2011, residents of the then-second-largest city in New Zealand – Christchurch, located on the South Island's Canterbury Plains – were hit hard by a magnitude 6.3 earthquake. Outside of New Zealand, the earthquake became known as the "Christchurch Earthquake", and it resulted in the deaths of 185 people and injuries of several thousand. The epicenter of the quake was approximately 3 miles from the city center of Christchurch. The earthquake occurred more than five months after the September 4, 2010 earthquake of a 7.1 magnitude (in which no one died), and is considered to be an aftershock. Within New Zealand, the September 2010 earthquake and its aftershocks are thus also known as the Canterbury earthquakes.

Every year, thousands of earthquakes occur in New Zealand that are too small to be felt, although more serious quakes have occurred. For example, between 1992 and 2007, New Zealand experienced over 30 earthquakes of magnitude 6 or more. However, prior to the two seismic events in September 2010 and February 2011, Canterbury Plains likely had not experienced a major earthquake in thousands of years. In fact, scientists did not even know there was a geologic fault there until the September 2010 earthquake. Christchurch was understandably unprepared for activity on a fault that was previously unidentified.

Additional factors exacerbated the damage of the February 2011 earthquake. For one, the proximity of the epicenter to the downtown area limited the amount of energy the quake dissipated before reaching Christchurch. Two, the quake was comparatively shallow (the aftershock struck only about 2.5 miles in depth below the city, whereas the September 2010 temblor originated about 25 miles outside of the city and was approximately 6.2 miles deep). As a result, the rock on either side of the fault accelerated almost three times as fast as in a typical quake, producing extra violent shaking. This shaking was significantly greater than the levels Christchurch's structures had been designed to withstand. And, the February 2011 quake brought down many structures that had been damaged the preceding September. Third, liquefaction was much more extensive than in the September 2010 earthquake, with the shaking turning water-saturated layers of sand and silt beneath the surface into sludge, burying properties and streets in thick layers of silt, and wrecking the foundations of homes. Finally, the timing of the earthquake contributed to the damage and the number of casualties: the February 2011 quake happened at 12:51pm, in the middle of a busy weekday, with correspondingly more lethal consequences.

Earthquake hazards include: ground shaking, tsunamis, landslides and rockfalls, subsidence and lateral spreading, liquefaction, and edifice destruction. Governments can regulate zoning and development to address potential hazards that result from natural disaster risk. Additionally, governments can create emergency response teams and regulations for preparedness. Citizens can also make efforts to be prepared in the case of earthquakes.

Individuals with expertise/responsibilities in the following areas have helped create the case study:
National Crisis Management Centre; Canterbury Earthquake Recovery Authority (CERA); Minister for Canterbury Earthquake Recovery; Christchurch City Council; residents (current & former) of Christchurch and Canterbury Plains; ANZ seismologists.

Key teaching points:
Risk assessment, risk management, risk regulation, hazard.

How this example is used in the classroom:
I haven't yet used this example in class. But I would like to develop it to illustrate the use of scientific data and expertise in risk regulation and how there are limits to understanding and regulating risks.

References

GNS Science: Earthquakes (http://www.gns.cri.nz/Home/Our-Science/Natural-Hazards/Earthquakes);
Australian Geographic (http://www.australiangeographic.com.au/news/2011/02/new-zealand-earthquakes-linked,-say-experts/);
The Encyclopedia of New Zealand: The 2011 Christchurch Earthquake (http://www.teara.govt.nz/en/historic-earthquakes/page-13);
The Brisbane Times: Pictures of Christchurch after Earthquake