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Friday, April 15, 2011

Seismic secrets slowly revealed

Seismic secrets slowly revealed

Last updated 05:00 15/04/2011
Christchurch's deepest secrets are slowly revealing themselves to teams of researchers.

Scientists and technicians from Canterbury University and Canada's Calgary University completed the first stage of their seismic surveying work yesterday.

Project leader Jarg Pettinga, the head of Canterbury's geological sciences department, said the researchers had finished their north-south survey line along Barbadoes St and planned to resume work southwest of the city early next month.

He said the research team last weekend carried out a survey along the beach from Southshore to North Beach.

Preliminary results on what the signals had shown on breaks in rocks and possible faults underneath Christchurch would probably be available next week, he said.

The team wanted to move out of the city next month to see what was between the eastern end of the Greendale Fault near Rolleston and the western end of the Port Hills Fault around Cashmere.

It was hoped the survey would help confirm the location of the Port Hills Fault, responsible for the February 22 earthquake, and show if there was another fault further north that generated the Boxing Day quake and other significant aftershocks.

GNS Science researcher Vaughan Stagpoole said a two-week investigation of subtle changes in gravity around the city and Can-terbury had made a good start.

The work uses a briefcase-sized meter that can detect small changes in gravity caused by different rock densities, such as those found around faults.

Gravity measurements were yesterday taken at Godley Head, Mt Pleasant, Redcliffs, Cashmere and around Lyttelton.

Researchers would return next week to take readings between Christchurch and Darfield and north to the Waimakariri River, he said.

Several hundred gravity measurements already exist for Canterbury but they are unevenly spaced, meaning there are gaps in the record of the subsurface geology.

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