Analysis of microseismicity at a mountain site

Zuolin Chen, Robert R. Stewart, Henry C. Bland

Data from a six-station seismic network provide the first detailed information on microseismicity in the vicinity of Turtle Mountain, Southern Alberta. A network of seismometers on Turtle Mountain collected data between 1986 and 1996. During this time, 121 local seismic events were located. We analyse these events, making note of their location, magnitude and the direction of first motion at each seismometer station. Results of the analysis show magnitudes varying from MF-P -1.3 to about 1.0. We analyse the direction of first motion for each arrival, and classify these arrivals into a set of direction patterns depending on whether the microseism was upgoing or downgoing at each of the monitoring sites. When pattern symbols are placed on a map at the seismic events' hypocenter, we find there is some correlation to the underlying geology. These pattern-maps suggest possible focal mechanisms responsible for the seismicity. If we consider the distribution of the microseismic events, topography, the post-mining weaknesses and local geology we conclude that the seismicity is likely associated with a tectonic process operating on the geological weaknesses.