6.0 Earthquake Strikes New Zealand City of Christchurch

June 15, 2011

Still recovering from two previous earthquakes that struck the region in September 2010 and February 2011, Christchurch, New Zealand was shaken by a series of strong tremors on June 13, according to catastrophe modeling firm AIR Worldwide.

The United States Geological Survey (USGS) reported that the largest earthquake had a moment magnitude of 6.0 and occurred at a depth of just 9 kilometers.

The USGS estimated that the quake’s epicenter was located 13 kilometers southeast of Christchurch at Lyttelton, the city’s port. The quakes collapsed dozens of buildings and knocked out power to thousands.

The city of Christchurch bore the brunt of the damage. Local authorities report that more than 75 buildings were tagged for demolition.

There has been significant new damage to already weakened buildings and according to a statement from New Zealand’s Prime Minister, it is now expected that as many as 900 buildings in the city’s central business district (CBD) will need to be demolished for safety reasons as a result of the last two events.

The ground shaking in the CBD caused by this latest earthquake is similar to that of last September’s quake, according to AIR. The areas likely to experience the most severe damage are east and southeast of Christchurch.

Given the good performance of New Zealand’s residential wood construction, further significant shake damage to these structures should be limited. However, AIR believes the severity of liquefaction damage in the city’s east and southeast will likely exceed that from the previous earthquakes, while in other areas, such as those near the city center and further north, liquefaction damage is likely to be less than that from the previous events.

There have been reports of several sink holes opening up and several rock falls, mainly in eastern hills of Sumner, Taylors Mistake, Redcliffs, Morgan Valley.

Although the recent events were on a different fault from the event that struck Christchurch on February 22, they are part of the same aftershock sequence that was initiated by the Darfield earthquake, according to AIR. Aftershocks occur as a natural readjustment to the changes in stress caused by a quake and can last for many months or even years, depending on the size of the initial shock.

New Zealand’s South Island, on which Christchurch is situated, has an active fault zone in the north, which includes a region known as “Porters Pass-Amberley Fault Zone” and two others, the Alpine fault zone and the Hope fault zone. According to AIR, most known historic earthquakes on South Island have occurred in this 200-mile wide collision plate boundary zone. The entire earthquake sequence is broadly associated with the regional plate boundary deformation as the Pacific and Australia plates interact in the central South Island.

Source: AIR Worldwide

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