Final answer:
In the early 1980s, four magnitude 6 earthquakes happened in the United States near Yellowstone National Park, Mount St. Helens, Long Valley Caldera, and the San Andreas Fault.
Step-by-step explanation:
In the early 1980s, the United States experienced a series of earthquakes, four of which were of magnitude 6 and caused significant damage. These earthquakes occurred near: Yellowstone National Park in Wyoming, Mount St. Helens in Washington, Long Valley Caldera in California, and the San Andreas Fault in California.
For example, the San Andreas Fault near the town of Parkfield, California, slipped every 25 years on average during the past century, moving about 1 meter each time, while the Los Angeles region experienced major earthquakes every 150 years, with an average slippage of 7 meters. This meant that since the last major slip, the tension in the region has been building, resulting in a distortion and contraction of the Los Angeles basin as captured by sensitive instruments.
The US Geological Survey provides a global view of earthquake occurrences including areas of tectonic plate boundaries. Untamed activities in the subduction zones lead to destructive earthquakes and volcanic activities as has happened in places like Yokohama in 1923 and Sumatra in 2004.
Learn more about Earthquakes