Last year’s massive landslide at Kennecott Bingham Canyon Mine near Salt Lake City was not only the biggest non-volcanic landslide in North America’s modern history, but it also triggered 16 small earthquakes, says a study by University of Utah scientists.
In a paper published in the January 2014 issue of the Geological Society of America’s magazine, GSA Today, scientists from the College of Mines and Earth Sciences at the University of Utah in Salt Lake City said the April 10, 2013, landslide moved at an average of almost 70 miles per hour and reached estimated speeds of at least 100 mph in order to have triggered the quakes.
Bingham Canyon mines 25% of the copper used in the United States and has produced more copper than any mine in history. It is considered one of the largest—if not the largest—man-made excavation in the world at more than 970 meters deep.
Landslides are among the most destructive geologic forces in nature, causing billions of dollars in damages annually, according to the U.S. Geological Survey. From 2004 to 2011 more than 32,000 landslide-related deaths have been documented, not including landslides caused by earthquakes.
While the two rock avalanches that happened 90 minutes apart in the Bingham Canyon pit were measured at seismic magnitudes up to 5.1 and 4.9, respectively, the subsequent real earthquakes they triggered were smaller. “We don’t know of any case until now where landslides have been shown to trigger earthquakes,” said Jeff Moore, assistant professor of geology and geophysics at the university. “It’s quite commonly the reverse.”
“Here we describe a recent massive landslide in Utah that was successfully forecast and thus resulted in no fatalities or injuries,” said paper authors' Kristine Pankow, Mark Hale, Keith Koper, Tex Kubacki, Katherine Whidden, Michael McCarter and Moore. “Furthermore, it occurred within a dense regional network of seismic and acoustic sensors, generating a valuable and unique data set for studying landslide physics.”
Right after the second rock slide, a real earthquake of magnitude 2.5 on the Richter scale was measured. Six small earthquakes occurred in the 90 minutes between the two avalanches, while the other 10 earthquakes occurred afterwards, data showed. Each avalanche lasted about 90 seconds.
The landslide traveled almost two miles in the 107-year old copper-gold mining pit, which was monitored by a “dense regional network of seismometers and infrasound sensors, making the 10 April landslide one of the best recorded in history,” according to the UOU paper. While both avalanches moved bedrock, the second contained more mining waste rock.
The study estimated that the bedrock landslide left a deposit so large it would “cover New York’s Central Park with about 66 feet of debris” and was equivalent to the amount of material contained in 21 of Egypt’s Great Pyramids of Giza. The landslide deposit had a volume of 65 million cubic meters (2.3 billion cubic feet).
The authors suggested several important research questions that have yet to be answered. How is the geometry of the rock avalanches reflected in the geophysical data? How are the 16 small seismic events that occurred in the mine area in the 10 days following the landslide related to the two rock avalanches?
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