by Earthquakes that struck North America’s continental interior in the 1800s may still be causing aftershocks in the central and eastern United States, according to a new study published in the Journal of Geophysical Research: Solid Earth.
Aftershocks, smaller quakes that occur after the main shock of an earthquake, can continue to shake an area for days to years. While they are smaller in magnitude, these aftershocks can still cause damage to infrastructure and hinder recovery efforts from the original earthquake.
“Contemporary seismicity in parts of stable North America could be aftershocks, or they could be background seismicity,” said Yuxuan Chen, the lead author of the study. “We wanted to take a different approach using a statistical method.”
The study focused on three major earthquake events that occurred between the 1660s and 1886: an earthquake near southeastern Quebec, Canada, in 1663; a trio of quakes near the Missouri-Kentucky border from 1811 to 1812; and an earthquake in Charleston, South Carolina, in 1886. These historic earthquakes are the largest recorded in stable North America, and larger earthquakes tend to trigger more aftershocks.
The central and eastern regions of the United States, located far from plate boundaries, have less tectonic activity compared to the west coast. As a result, earthquakes in these areas are less common, making it even more intriguing to study their origins.
To determine if modern earthquakes are aftershocks, the researchers analyzed earthquakes within a 250-kilometer radius of the historic epicenters. They focused on earthquakes with a magnitude of 2.5 or higher, as smaller earthquakes are difficult to reliably record.
Using the nearest neighbor method, a statistical approach, the team analyzed the data to determine if recent earthquakes were likely aftershocks or unrelated background seismic activity. Aftershocks occur close to the original earthquake’s epicenter and before the level of background seismicity has resumed.
The study found that the aftershock sequence near southeastern Quebec in 1663 has ended, and modern seismic activity in the area is unrelated to the historic quake. However, in the Missouri-Kentucky border region, approximately 30% of all earthquakes from 1980 to 2016 were likely aftershocks of the earthquakes that occurred in 1811 and 1812. In Charleston, South Carolina, around 16% of modern-day quakes were likely aftershocks from the earthquake in 1886.
The researchers also found that background seismicity, the normal level of seismic activity in a region, is the dominant cause of earthquakes in all three study regions. This suggests that strain may still be accumulating in these areas, potentially leading to larger earthquakes in the future. However, some faults can creep along without building up strain.
Understanding the causes of modern seismicity and assessing the future risk of earthquakes in these regions is crucial for disaster preparedness. By studying the aftershocks and background seismic activity, scientists can develop hazard assessments and monitor strain accumulation to better predict and mitigate the impact of future earthquakes.
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1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it
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