Today’s earthquakes could represent the echo of past earthquakes. Thus, North America remains haunted by the echoes of seismic events that occurred more than a century ago, according to recent research that analyzes the complex dynamics of aftershocks on the continent.
The study, by geologist Yuxuan Chen of Wuhan University in China and geologist Mian Liu of the University of Missouri, challenges conventional wisdom about the nature of seismic activity in relatively stable regions such as North America.
The research suggests that a significant portion of contemporary North American seismic shocks, particularly in the New Madrid Seismic Zone, may be aftershocks dating back to the early 19th century. The authors estimate that about 23% to 30% of the seismic shocks experienced in the region between 1980 and 2016 were triggered by four large earthquakes in 1811 and 1812, each with magnitudes between 7.2 and 8.
Furthermore, the study highlights another seismic event of historical importance – the 1886 earthquake in Charleston, South Carolina. With a magnitude between 6.7 and 7.3, this earthquake is believed to account for up to 72% of the seismic shocks experienced in the region since then. These findings raise interesting questions about the longevity of aftershocks in geologically stable areas and challenge the hypothesis that earthquake aftershocks are short-lived phenomena.
The research used a new statistical method, the “nearest neighbor” method, to analyze seismic events. This method assumes that if earthquakes are close together in space, time, and magnitude, they are likely related, challenging previous interpretations of seismic data in the region. The results indicate that on stable continents, where tectonic activity is minimal, aftershocks can persist for decades or even centuries.
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The current earthquakes could be replicas of those of a few centuries ago
Chen and Liu focused their analysis on three major historical earthquakes in North America: the 1663 event in southeastern Quebec, Canada, the 1811 earthquake on the Missouri-Kentucky border, and the 1886 earthquake in South Carolina. Despite being located far from tectonic plate boundaries, these areas continue to experience contemporary earthquakes, prompting researchers to investigate potential aftershock sequences.
The study suggests that the debate over whether contemporary North American earthquakes are aftershocks or background seismicity is oversimplified. Chen points out that it is likely a mixture of both, challenging scientists to reconsider existing frameworks for understanding seismic activity on stable continents.
However, not all experts are convinced. Susan Hough, a geophysicist at the United States Geological Survey, notes that the spatial distribution of earthquakes could be misleading. While some may appear to be aftershocks, other factors, such as the creep process, could contribute to tightly clustered seismic events. Therefore, the study leaves room for ongoing discussion and further research to fully understand the complex nature of seismic activity in North America, Science Alert reports.