Friday was our last day in Christchurch. The government declared it a national holiday and held a memorial service in the CBD.
We took a few hours to look at evidence of the Greendale Fault Rupture from the Darfield September 2010 Mw7.1 Earthquake. While the trace was still visible in many places and kinks in roads and fences where still prominent its expression was slowly fading. The cleared fields that had once clearly shown the trace were now overgrown with vegetation and the fault scarp was slowing slumping to a diffuse hump.
This brought to my attention the importance of understanding the earth’s past when assessing hazards and risk today.
– Parts Christchurch are built on an old alluvial system comprised of meandering channels that controls the distribution of liquefiable sediments. Liquefaction hazard was recognized in ChCh, but the magnitude and spatial distribution of liquefiable sediments was not known in enough detail to lesson the hazard.
– Most of the slopes and cliff in the hilly east of ChCh have evidence of historic rockfall. The large boulders help create a beautiful landscape. These are areas where rockfall hazard has always been recognized, but the extent of the hazard when triggered by an earthquake was overlooked.
– The fault rupture in the Canterbury Plain is a stark reminder of the earthquake and it potential to cause damage, but within a few seasons it will subtly blend back into the landscape to be only represented by a line on a map.
