Long-term safety for people and the environment is the NWMO's top priority in selecting a site for Canada's deep geological repository for used nuclear fuel. A key aspect of assessing safety is understanding the long-term stability of the geologic setting, including resilience to future earthquakes. Understanding ancient earthquakes in a given region is one of the methods that are used to assess the likelihood and magnitude of future earthquakes.In Canada, written records of earthquakes go back to the mid-17th century, though it was not until the late 19th century that they were first measured with instruments. A national seismographic network for detecting and routinely reporting earthquake activity was established in the 1960s.
To go back farther in time, the NWMO is working with the Geological Survey of Canada (GSC) to examine whether layers of lake bed sediments may preserve evidence of moderate to strong earthquake activity that occurred many thousands of years ago. The goal is to establish a more complete picture of a region's long-term seismic history. This specialized area of work is known as paleoseismicity.
"The preliminary results are very encouraging," says Mark Jensen, the NWMO's Director of Deep Geological Repository Geoscience and Research. "They indicate that such paleoseimic techniques may be effective in providing evidence of earthquake activity going back many thousands of years. While the research is continuing, this type of information is helpful in evaluating regional seismic activity and may be able to further establish the scientific basis to evaluate the long-term safety of a deep geological repository."The research is led by Dr. Greg Brooks, a research scientist at the GSC, and focuses on identifying distinct levels of lake-bottom deposits where numerous landslide deposits are present. The research methods were pioneered in Switzerland.
Dr. Brooks and his team have been conducting their fieldwork in a moderately sized Canadian Shield lake. Their work started with conducting extensive sonar surveys across the lake. These were used to create a dense network of two-dimensional images from which a three-dimensional picture of the lake-bottom deposits was established. This picture was used to identify key locations in the lake bed from which core samples were extracted and landslide deposits dated.
The next step will be to corroborate the results with evidence from other lakes in the region.