Seismic Monitoring on Turtle Mountain

What is Passive Microseismic Monitoring?

Passive microseismic monitoring uses a network of sensors called geophones or accelerometers to 'listen' to the mountain to detect small tremors. By 'listening' to the mountain, sensitive seismic monitoring stations can detect extremely small earth tremors anywhere within the mountain. These tremors may be strain accumulation or the release of stress built up in the rock from movement. These movements may be from regional seismic activity or from within the mountain due to adjustments within the rocks, possibly caused by the gradual collapsing of abandoned mines or other small internal movements, such as landslides.

Seismic Monitoring at Turtle Mountain

Although a microseismic monitoring system was installed in the 1980s, the University of Calgary installed a modern passive microseismic system in 2003. It has an array six surface and one borehole seismic stations. The surface stations are over a wide area ranging from the Crowsnest River (at the bottom of the mountain) to South and Third Peaks. The borehole station is near South Peak and has instruments at 24 and 38 metre depths. The seismic data are radioed continuously to the Frank Slide Interpretive Centre.

Not only can the seismic system detect tiny earthquakes in the mountain, it is so sensitive it can detect mine blasting in the Elk Valley in B.C. and larger earthquakes anywhere in the world.

Results

The microseismic network was to help locate the movements within the mountain. Unfortunately, this has not been successful due to a number of factors, including the highly fractured bedrock.

Most of the seismicity seen on Turtle Mountain is minor; however, we have seen a clear connection between increased seismicity and rock temperatures passing through the 0°C point.

On February 16, 2006, the South Peak seismic station detected a significant, localized seismic event. It was very sharp, but not large enough to register at any other station. Based on the arrivals, we believe it came from the northeast quadrant relative to South Peak, most likely within a few hundred metres.

The plot below shows the channels recorded at the northeast (red), southwest (green) and northwest (blue) geophones, relative to the mast at South Peak. We believe this event was rock fracturing when temperatures plummeted from -12°C to -32°C in less than a day.

As of winter 2008, the passive microseismic system was no longer functional, but AGS archived and documented all triggered event data from 2003 to 2007 for future review and interpretation.

Amplitude traces for a seismic event occurring near South Peak station. Click on graph to enlarge.

Installing seismic monitors on Turtle Mountain. Click on images to enlarge.