When a devastating earthquake struck Christchurch, New Zealand, in 2011, the University of Calgary responded with geophysical assistance.
This past August, the university was preparing to meet a geophysical challenge closer to home.
Even before the 2011 earthquake, researchers at the University of Calgary had planned to conduct a seismic study in New Zealand, said Don Lawton, professor of geophysics in the school’s department of geoscience.
“I’m a New Zealander by origin so I have a lot of contacts there,” he said. “We’d been looking at taking our equipment down there because they have no high-capacity survey equipment in the country at all.”
New Zealand is highly active seismically, and Christchurch, the country’s second-largest city, already had seen a 7.1 magnitude quake in September 2010. That event caused serious damage but no loss of life.
The magnitude 6.3 earthquake in February 2011 resulted in 182 deaths and severe damage to buildings and other infrastructure already damaged by the 2010 quake.
Because of its history of earthquakes, New Zealand has an extensive system of seismic monitoring equipment, Lawton said. But it has no geophysical equipment to conduct large, industry-type seismic surveys for mapping subsurface faults.
Lawton explained that oil and gas seismic work in New Zealand has been conducted by out-of-country geophysical companies, usually from Australia.
By contrast, the University of Calgary is one of a handful of North American universities that have their own industry-standard seismic survey equipment. Located in a hydrocarbon-producing province and having close ties to the industry, the school wants its students to gain experience with state-of-the-art geophysical gear, Lawton said.
So Lawton and his colleagues already had prepared and sent a proposal for a seismic survey to identify faults in New Zealand, using the university’s equipment.
The proposal “just sat there,” Lawton recalled, until the February 2011 earthquake struck.
“A week later,” he said, “we got a call saying they wanted the stuff down there.”
Fault Finding
The New Zealand government arranged air freighting for the equipment, which included a 600-channel Aries recording system and an Envirovibe seismic source.
Some of the seismic-survey work was conducted within the urban area of Christchurch itself, leading to both logistical and practical problems. Lawton recalled working in heavy truck traffic bringing debris out of the city.
“Working in a city is not trivial at any time. And at this time, the downtown part of Christchurch had been severely damaged and the public was not let in, which was a good thing and a bad thing,” he said.
One limitation was the care needed in conducting seismic operations near unstable heritage buildings in downtown Christchurch, Lawton said.
Fortunately, the program had the advantage of advance strategic planning.
“We had looked at it in a fair amount of detail,” he said. “We’d actually planned out where we thought we could put the lines through the city.”
A goal of the seismic program was to map previously unknown faults for hazard assessment. Data came from six 2-D lines – two within Christchurch and four in rural areas west of the metropolitan center. In total, about 42 line-kilometers of seismic data were recorded.
Despite the challenges, all of the seismic lines resulted in good images, Lawton said. Events were interpretable to a depth of about 1.5 kilometers, and numerous faults were imaged and interpreted in two groups.
The first was older faults that showed clear offset in reflections deeper than one kilometer. The second was younger faults showing displacement in shallow reflections; some of those were interpreted as associated with hypocenters of the earthquake aftershocks.
“The surprises were somewhat pleasant in data quality – the data quality was better than we expected. We would have liked to get a bit deeper,” Lawton said.
“The shallowest focal depths are around two kilometers, so there’s a slight gap,” he said. “But we were able to identify where we could see faults coming from depth.”
Lawton praised the government agencies in New Zealand for facilitating the seismic program. At one point, a seismic line crossed a major, six-lane highway. Authorities closed the highway at night and trenched in the cables.
“That level of support,” Lawton said, “was really good.”
The Social Network
This year, Calgary had a natural disaster of its own. Heavy rainfall in the province of Alberta in June led to catastrophic flooding along a number of rivers, and more than 100,000 people in the region were displaced.
Parts of Calgary flooded and 26 neighborhoods were put under a mandatory evacuation order. Most of the city was without electricity for a period of time.
Afterward, the university decided to use its equipment to profile the flood-plain area in Calgary to assess mitigation strategies, Lawton said. He was preparing to get students involved in the project.
Lawton also is putting together a proposal to do another seismic project in New Zealand, this time a 3-D survey near Christchurch.
Funding for the initial project came from the New Zealand Crisis Management Centre, the Institute of Geological and Nuclear Sciences and the University of Canterbury.
Industry also contributed support for the first survey, including software for quality control and initial processing, and full processing of data from the initial phase of the project.
“The response we got from industry was very positive,” Lawton said. “Seeing industry-specific equipment used for societal purposes got a very strong positive response.”