First Impressions from New Zealand

by William Holmes, EERI Reconnaissance Team Member

The themes of the M7.1 Canterbury earthquake are URMs and liquefaction, with the following qualifications:

  1. Christchurch is only in a moderate zone and an M7 at 30 k was not expected. However, the ground motions, for whatever reasons, were in general less than the zoned spectra.
  2. While not zero, there was very little structural damage in engineered buildings. There is a lot of nonstructural damage, but most has been hard to document.
  3. There are 800+ URMs in Christchurch, most very similar to California style. Information on those that are retrofitted and to what retrofit level is not available at this time (but probably will be studied by the New Zealand Society for Earthquake Engineering). A tremendous amount of typical damage occurred in URMs: parapets, gables (hundreds), out-of-plane failures (either complete or partial), many side walls falling through shorter adjacent buildings. There were few complete collapses, but the event in daytime would have killed hundreds.
  4. All the normal issues are present: owners wanting to demolish and preservationists wanting them to stop; the downtown’s character is based completely on the URMs. However, many isolated very small URMs in the outer business strips have been demolished. Repair/retrofit standards for damage are unclear. Some surprising tagging has occurred (green or yellow when the damage level appears to be red, and vice versa).
  5. Liquefaction has devastated pockets of certain neighborhoods. Estimates are that 5,000 homes may be unsalvageable (not so much from direct damage but due to out-of-level settlement, the settlement of surrounding area, and questions about site suitability to repair/rebuild. Everyone has EQC insurance ($67 per year premium for $100,000) and 100,000 claims are expected on 150,000 houses estimated. Many owners will need more than the $100,000 for their $300,000 to $1,000,000 houses. Water service is probably permanently repairable, but sewer service is problematic because of grade changes. Ditto storm run off.
  6. Questions abound concerning repair on existing (inadequate) foundations in these areas and in some cases, whether a new house should even be built on the lots.
    • Will folks walk away?
    • Will the government step in and improve soil or provide funding for a new house?
    • Whose fault is it?
    • Did owners sign waivers for potential liquefaction, which was not surprising in most areas?
    • Did the government allow inappropriate developments? (See the team leader standing next to the street sign 2 feet above the street.)
  7. Response from the city with temporary solutions was remarkable. Many people are at least back in their homes with water and a jury-rigged sewer. There never was an emergency housing problem – at most, the number of people in shelters was about 300. Others are apparently staying with family and friends. For those who can’t return until decisions are made, the hard truth will start to sink in soon.
  8. The University of Canterbury suffered typical nonstructural damage in labs, libraries and offices. One very heavy ceiling came down (but no one was there).
  9. The port had some settlement damage, probably costly, but not very disruptive to operations.
  10. An unusual amount of glass breakage occurred downtown and at the university. It is not easily explainable except to assume poor perimeter detailing (to accommodate drift).
  11. It is rumored that some big storage pallet racks came down, but no one yet has found them.
  12. Schools and hospitals are mostly okay.

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