Lessons from the Destructive Mw 6.3 Christchurch, New Zealand, Earthquake

At 12:51 local time on 22 February 2011 New Zealand's second largest city was struck by a close, shallow Mw 6.3 earthquake. The event caused widespread damage in the city and resulted in about 180 deaths. At the time of this writing parts of the central business district are still cordoned off because of damage to structures (particularly unreinforced masonry). It is estimated that 800 buildings in the central business district will have to be demolished, and that 10,000 of the 140,000 domestic dwellings in the city will suffer the same fate. There has been extensive liquefaction and lateral spreading in the eastern half of the city, and 200,000 tons of ejected silt have already been removed. Costs of the damage are in the NZ$15–20 billion (US$11–15 billion) range. Given that Christchurch contributes 15% of New Zealand's GDP, this earthquake will have a significant effect on the nation's economy. The problem is that the extreme ground motions recorded for both the mw 7.1 mainshock and mw 6.3 aftershock were greater than this model predicted (even at 10,000-year return periods for the case of the mw 6.3 aftershock). The 22 February event was an aftershock of the Mw 7.1 earthquake of 04 September 2010 at 04:35 local time (see Figure 1). This complex event caused surface rupture of up to 5 m on the …