4 September 2010 and 22 February 2011 Christchurch earthquakes from a transmission infrastructure perspective: asset structural performance and lessons learned

摘要

A magnitude 7.1 earthquake struck the Canterbury region of the South Island at 4:36am on Saturday 4 September 2010 causing significant damage to buildings and infrastructure throughout the region. A further magnitude 6.3 earthquake struck the city of Christchurch at 12:51pm on Tuesday 22 February 2011. That earthquake caused a large number of fatalities and widespread damage with the collapse of many buildings -in the CBD and significant disruption of lifelines. These two events challenged the resilience of the transmission infrastructures in the Canterbury and northern South Island region. Some of the most important assets of the South Island grid backbone are located in the Christchurch region with Islington substation, a major node, supplying a high percentage of the load to Christchurch, Nelson, Marlborough and the West Coast. These earthquakes also tested the structural resilience of the transmission grid exit points serving high population areas (nine in the Christchurch region) and Transpower's ability to have them back up and running promptly after these events. From a seismic perspective substations are the most critical and potentially the most vulnerable infrastructures of our transmission network. Substations are designed to remain operational after rare and severe earthquakes as required by Transpower seismic policy, complying with the latest codes and the Civil Defence Emergency Management Act. The main purpose of this paper is to discuss the structural performance of the transmission assets during these two events, outlining the damage suffered, and a comparison of the actual performance against the design and expected performance requirements. The two events will be put in perspective with their features (magnitude, spectral accelerations and location) compared. Finally the paper will outline the key lessons learned from these events from a transmission assets perspective.