How much shaking did you feel?

PAUL GORMAN
Last updated 11:04 08/02/2013

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Christchurch Earthquake 2011

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Scientists are knocking on Christchurch doors to find out how much shaking residents experienced in the February 2011 earthquake.

The responses will help engineers and planners develop safer suburbs and infrastructure around the country.

Half a dozen researchers from GNS Science and the University of Canterbury will visit homes across the city for two weeks from tomorrow.

Residents and tenants will be asked whether the research team can inspect the outside of their properties for shaking damage. They will also be asked to fill in a two-page questionnaire about their experiences of the deadly quake.

Questions will include:

❏ How strong was the earthquake shaking that you felt?

❏ What was your first reaction?

❏ Did you evacuate for any reason after the quake?

GNS Science earthquake hazard modeller and project leader Mark Stirling said the information would help develop mathematical equations converting felt-shaking intensity to ground-acceleration values.

Those calculations could then be used to draw quake-hazard maps.

Stirling told The Press that measurements of strong earthquake shaking in New Zealand went back only about 30 years.

"Christchurch has provided a huge amount of strong-motion data in terms of accelerations,'' he said.

''What we are wanting to do is use that information to improve these relationships we have developed that allow you to convert between acceleration and intensity, and intensity and acceleration.

"Once you have an equation that can do that, and do it well, you can estimate instrumental measures of acceleration from the older felt-intensity information."

About four properties would be visited within a series of 500 by 500-metre grids correlated with about 26 strong-motion stations across the city.

However, properties in areas badly affected by liquefaction would not be included as it would be difficult to detect what was purely shaking damage, Stirling said.

The research team hoped the survey would allow it to better determine felt intensities above intensity 8, labelled "heavily damaging", on the 12-level Modified Mercalli scale.

"GeoNet have felt reports, but for strong, above 8, they don't discriminate, so I guess what we're doing is to find out and distinguish between those of 8, 9 [destructive], 10 [very destructive] and 11 [ devastating]," he said.

They were prepared for personal accounts of the quake to have faded or changed over two years, Stirling said.

"We will know how that is going to be affecting the study once we start into the survey,'' he said.

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''We also expect we'll get a lot of misses, people saying, 'We don't want to talk about it', 'We don't remember', 'We weren't living here at the time'."

The project is funded by the Earthquake Commission.

- The Press

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