Question: The most destructive earthquake in the United States was the 1906 San Francisco earthquake that measured 7.8 on the Richter scale. This quake was the seventeenth most violent in the United States. Among the 40 most severe U.S. quakes, the only one that occurred east of the Mississippi River shook Charleston, South Carolina in 1886 and measured 7.3. How many times more intense was the San Francisco quake?