Chinese Records Shed Light on Earthquake Mechanisms
The Chinese have been recording and describing the earthquakes that rumble underneath their country for the past two-thousand years. Using this data, University of Missouri researcher Mian Liu, professor of geological sciences in the College of Arts and Science, has theorized that mid-continent earthquakes tend to move among fault systems, rather than along the same fault line.
“In North China, where large earthquakes occur relatively frequently, not a single one repeated on the same fault segment in the past two thousand years,” Liu said. “So we need to look at the ‘big picture’ of interacting faults, rather than focusing only on the faults where large earthquakes occurred in the recent past.”
This research comes before December of this year marks the bicentennial of the New Madrid earthquakes of 1811-12, which are the largest recorded quakes to have occurred in the central US.
These mid-continent quakes occur on a complicated system of interacting faults which are spread throughout a larger region. A large earthquake on one fault can increase the stress on surrounding faults, increasing their likelihood of seismic activity.
“The New Madrid faults in the central U.S., for example, had three to four large events during 1811-12, and perhaps a few more in the past thousand years. This led scientists to believe that more were on the way,” said co-author Seth Stein, a professor of earth and planetary sciences at Northwestern University. “However, high-precision Global Positioning System (GPS) measurements in the past two decades have found no significant strain in the New Madrid area. The China results imply that the major earthquakes at New Madrid may be ending, as the pressure will eventually shift to another fault.”
And though this study goes a long way to showing how random mid-continent earthquakes can be, the researchers believe there is help buried within the data.
“The rates of earthquake energy released on the major fault zones in North China are complementary,” said Hui Wang, a Chinese Earthquake Administration researcher. “Increasing seismic energy release on one fault zone was accompanied by decreasing energy on the others. This means that the fault zones are coupled mechanically.”
“What we’ve discovered about mid-continent earthquakes won’t make forecasting them any easier, but it should help,” Liu added.