The M 7.1 Darfield earthquake of 4 Sept. 2010 produced ground shaking levels in the Christchurch CBD that were generally at or below building code levels, and were viewed as being consistent with expected shaking level and thus the "Old Normal." In contrast, the M 6.2 Christchurch earthquake of 22 Feb. 2011, which occurred directly beneath Christchurch, generated ground motions in central Christchurch that were generally well above the median levels expected from such an earthquake. This gave rise to concern that there were flaws in our understanding of earthquake hazards in Christchurch, and perhaps further afield in New Zealand, which might require us to accept a "New Normal." Ongoing research is identifying explanations for why the ground motions recorded in central Christchurch were so much larger than expected; these relate to the geometry of the fault and the effects of the deep and shallow geology beneath central Christchurch. If such local explanations of the unexpectedly large ground motions are borne out, then it may not be necessary to view the Christchurch earthquake as having established a "New Normal" in other locations in New Zealand unless similar conditions are found to exist in those locations.
About Paul Somerville
Professor Paul Somerville has been Chief Geoscientist at Risk Frontiers at Macquarie University in Sydney for the past ten years, where he works on the development of earthquake loss and tsunami hazard models for Australia, New Zealand, Japan, and other Asian countries, and has provided perspective on earthquake hazards in New Zealand and Japan following the 2010-11 Canterbury earthquakes and the 2011 Tohoku earthquake. He has worked at AECOM and its predecessor organizations for the past 38 years on the development of seismic design ground motions for major bridges, buildings, dams and power generation facilities in many countries, including Australia, New Zealand, the United States and Japan.
Note: Papers, presentation slides and any other material provided by the Guest Lecturer will be made available some time after the lecture at Publications > Media & Speeches > Guest Lectures by Visiting Academics.