ROCKY MOUNTAIN HOUSE — Keith and Betty Graham have felt the floor rumble and heard the dishes rattle in their cupboards.
“I didn’t really think much of it,” says the Strachan-area landowner whose family homestead, established in the 1930s, sits on one of the busiest earthquake zones in Alberta.
The rumbles the Grahams have experienced from time to time would have been a magnitude 3 earthquake, about the strongest earthquake recorded in Alberta since 1918.
Since the first recording stations were set up in 1918, the Geological Survey of Canada and the Alberta Geological Survey have recorded 918 earthquakes ranging from magnitude 1 to magnitude 3, says geophysics professor Dave Eaton, head of the geophysics department at the University of Calgary.
A magnitude 3 quake would have about the same effect as a heavy truck rumbling past the house, says Eaton.
“This is actually a hot spot of earthquake activity in Alberta. So, if you look over the last few decades where earthquakes have been recorded, there’s a cluster of activity just around this area.”
One of his students is now using seismic monitors to map earthquake activity in the area and, hopefully, determine what influence, if any, the nearby Strachan Gas Plant is having on that activity.
Eaton visited the Graham place on Wednesday to help geophysics students Andrew Iverson and Mai Swasdichira set up a seismic testing station for Iverson’s Bachelor of Science thesis.
A seismic monitor that is far more sensitive than anything previously available has been dug into the old hay field, hidden between Prairie Creek and a thick wall of trees. Solar powered, it works from one of five sites chosen to monitor seismic activity at the Strachan Gas Plant. One monitor is placed at the centre of the plant with the rest positioned in a 10-km radius.
Studies suggest a link between gas production and swarms of small earthquakes, says Eaton. The small earthquakes would happen anyway, but seem to be encouraged when gas extraction causes pressure changes deep in the formation, he says.
“(The area) is active enough that we’re confident that by operating this station for about four months we’ll be able to detect a significant number of very tiny earthquakes of magnitude 1 or 2 at the most,” says Eaton.
He suspects that any earthquake activity related to gas production would occur at about two kilometres below the surface.
By collating data from the five monitors, Iverson will be able to draw a three-dimensional picture of seismic activity in the area to help determine the locations from which the earthquakes occur and infer from those data the impact of gas production on earthquake activities.
“The depth is going to be one of the more important parts of this,” says Iverson.
“We’ll get a much better idea of the actual fault structure and several other components of the actual earthquake.”
Because the locations of gas field activities are already known, mapping the earthquakes should help identify which of them have occurred naturally and how many, if any, are been induced by pressure changes related to the gas production, says Iverson.
The monitors can also collect data from aftershocks of bigger quakes, such as the deadly magnitude 7 quake that struck in Haiti in January and the magnitude 5 quake that hit Ottawa on June 23.
The data will assist in developing a better understanding of earthquakes in general, says Eaton.
Iverson will start working on data from the five monitors in November, with plans to present his completed thesis on May 21, 2011.
bkossowan@www.reddeeradvocate.com