Christchurch NZ
AEES Earthquake Reconnaissance Mission

Kevin McCue and Gary Gibson
Monday 14th to Friday 18th March 2011

The 22nd February magnitude 6.3 aftershock caused more damage than the 4th September 2010 mainshock magnitude 7.1 because it was so close to the city generating very strong ground motion between the city and Lyttelton.

After visits by AEES structural engineers Professor Hong Hao, Dr Helen Goldsworthy and Lisa Moon, seismologists Kevin McCue and Gary Gibson arrived Monday and Tuesday. On the flight to Christchurch from Sydney, AEES member Bill Jordan, consultant structural engineer from Newcastle, managed to organise adjacent seats for he and Kevin. Bill was planning to look especially at restoration of Heritage buildings. After arrival, we were joined by another visiting AEES member and seismologist Dr Andre Phillips, a Christchurch native. Andre had hired a car for the week to ferry Gary and me around so we were quite independent. Later in the week we met up with geotechnical engineer Dr Tim Mote from Arup, Sydney yet another AEES member.

At the Arts Centre where the earthquake response was being coordinated, we contacted NZ colleague Dr Kelvin Berryman and discussed our programs for the week. Monday night we all attended the team meeting for overseas visitors.

Synopsis

• The team installed an ES&S EchoPro accelerograph and EPSO seismograph in suburban Christchurch and these recorded several aftershocks including one within about 1.5 km of the instrument site ie right under the site below the thick gravel sequences. A PGA of 0.22g was recorded on the accelerograph vertical component, the aftershock magnitude M3.1.
• We drove around the city documenting landslides, liquefaction features and damage to infrastructure (bridges), domestic houses and large buildings.
• We met with the science coordinating unit in the Christchurch Arts Centre and gave an AEES team briefing at an evening meeting of overseas delegates at the Chateau on the Park, convened by Dr Bruce Deam. Others included EERI, EEFIT, Japan, NZ Universities and others.
• Wednesday we had lunch with the NZSEE President Peter Wood and Pacific workshop coordinator Dr Clark Hyland. We decided to postpone the workshop to June/July at IUGG, Melbourne, conditional on funding being made available for national delegates. There was not sufficient time for SW Pacific delegates to organise both their trip and their oral contribution to the workshop, and NZ engineers were fully committed to the recovery effort in Christchurch.
• We visited one of the critical GeoNet strong motion sites near the Lyttelton Tunnel with Dr John Zhou GNS, Dr John Berrill Canterbury Uni and US and Japanese engineers and found both the cause of the two 2+g spikes - a non earthquake source, and the reason for the pre-cast concrete panel failure at the school swimming pool.
• The epicentre of the earthquake was at Lyttelton so we walked around looking at the landslides, ground deformation, retaining walls and structural failures, the ground motion was undoubtedly very strong. We met and talked with residents, some of them planning to move away from Christchurch because of the loss of their jobs due to the earthquake.
• Dr Mark Quigley, earthquake geologist at University of Canterbury, invited us to a meeting at his house in Avonside (the University was closed) and took us for a walk to inspect the lateral spreading along the river banks and consequent bridge damage and liquefaction everywhere. The pattern of liquefaction was similar in both earthquakes except at Kaiapoi during the aftershock when the liquefaction was minimal.
• Friday was a public holiday to commemorate the earthquake. We met up with the Arup team at breakfast and later called in on Dr Berryman to give him a brief report and a sample of the EchoPro strong motion data before departing.

More photos from Andre Phillips available here.

Some data from the EPSO seismograph available here and here.