Earthquakes have been a major hazard in the United States throughout its history, particularly in the West. Now, scientists believe that some of the earthquakes in the 21st century could actually be aftershocks from quakes that happened two centuries ago.
Using modern seismic maps and data, researchers from the University of Utah have concluded that some of the quakes that have occurred in the western states in the past century may in fact be “re-activated” aftershocks from major event earthquakes that struck some two hundred years ago.
The researchers analyzed the seismic activity of historic earthquakes in California, Nevada, and Utah according to the official records of the Sensitive Earthquake Detector Network. They found that most of the earthquake clusters had a near-regular activity pattern, which suggested that the clusters could have been the result of aftershocks from the historic quakes.
These data suggest that the level of activity may not just be random, but that there is a direct link to historic earthquakes. This means that the timing and locations of some recent earthquakes are related to much older events.
It is estimated that at least 25% of the earthquakes that have occurred in this region in the last century could have been aftershocks from historic quakes. This implies that the area has been gradually losing energy that has accumulated from previous seismic events, and that this energy is being released slowly over time.
The most likely candidate for a historic event that could have caused these aftershocks is a “great earthquake” that struck in 1811-1812 in the New Madrid Fault region of the Midwest, which affected an estimated 1 million people.
The findings offer new insight into the risks that people living in earthquake-prone areas are facing. The researchers argue that in order to better prepare for possible future events, it is essential to understand the seismic history of the region, and how it is linked to the present-day activity.
Ultimately, understanding how earthquakes are related to the past can help us to better prepare for and predict the future activity. As the researchers point out, “Knowing the seismic histories of the regions affected by seismic activity is essential for properly forecasting them in the future.”