Report on the Darfield, New Zealand Earthquake of September 3, 2010
Failure of pedestrian bridge in Christchurch.
On September 3, 2010 a 7.1 magnitude earthquake struck the South Island of New Zealand. The epicenter was located at a depth of 10 kilometers and approximately 30 miles west of the city of Christchurch, close to the town of Darfield. The earthquake did not result from the rupture of the Alpine or Hope Faults, which form at the Australia-Pacific plate boundary zone, but of a formerly unknown fault, the Greendale Fault. Numerous aftershocks have occurred following the mainshock including 116 aftershocks between magnitude 4.0-4.9 and nine aftershocks of magnitude 5.0 and above during the first month after the event.
Damage in piers of the tallest unreinforced masonry building in Christchurch’s central
The Darfield earthquake caused widespread damage in the city of Christchurch, especially in the city’s central business district, as well as in the towns of Lyttelton, Kaiapoi and Rolleston. No fatalities and few injuries were reported, which was attributed to the fact that the earthquake happened in the early hours of a Saturday morning (4:35 a.m. local time), when most people were asleep. The New Zealand Treasury has estimated that the recovery and repair activity that will take place over the next few years will reach NZ$4 billion, whereas the New Zealand Earthquake Commission (EQC) has estimated the cost related to insured private dwellings and their contents to be in the range of NZ$1-2 billion.
On September 11, 2010, Michel Bruneau, Professor, and Myrto Anagnostopoulou, Structural and Test Engineer, Structural Engineering and Earthquake Simulation Laboratory, both in the Department of Civil, Structural and Environmental Engineering, University at Buffalo, visited Christchurch on behalf of MCEER and the Earthquake Engineering Research Institute (EERI). Other members of the EERI team included Mary Comerio, UC Berkeley; Ian Aiken, Seismic Isolation Engineering Inc; Lucy Arendt, University of Wisconsin; Peter Dusicka, Portland State University; William Holmes, Rutherford & Chekene; Charles Roeder, University of Washington; and Fred Turner, California Seismic Safety Commission.
Damaged reinforced concrete column of parking garage in Christchurch.
The MCEER team focused their investigation on the performance of bridges, unreinforced masonry and Heritage buildings, schools, hospitals, churches and residential houses located in the city of Christchurch as well as in the general Canterbury area. The main conclusions are summarized as follows:
- Bridges suffered little damage, and this damage was mostly limited to the Christchurch and Kaiapoi areas. The bridges were small to moderate spans and shared a number of common design features that gave them high seismic resistance.
- Unreinforced masonry buildings (URM) suffered extensive damage, especially in the area of Christchurch’s central business district. Toppled chimneys and parapets, failure of gables and poorly secured face-loaded walls, and in-plane damage to masonry frames were observed. However, URM that had been seismically retrofitted appeared to perform well.
- Modern engineered buildings of various construction materials located in Christchurch’s central business district performed well and minor damage was observed.
- Residential houses that were predominately light timber structures suffered significant damage in Christchurch and Kaiapoi. Minor structural damage occurred due to ground shaking, whereas the most significant structural damage to houses resulted from differential settlement of foundations, induced by soil liquefaction and/or lateral spreading.
- Extensive liquefaction and ground deformations were observed in the Canterbury area, which significantly affected the structural behavior of buildings, bridges and lifelines.
Significant ground deformations and
liquefaction in the area of Kaiapoi.
A more detailed report by the MCEER team is available online.
Submitted by Myrto Anagnostopoulou, University at Buffalo