Use the formula R = log (I/I₀) in Problems.

The most destructive earthquake in the United States was the 1906 San Francisco quake that measured 7.8 on the Richter scale. The quake and subsequent fires that burned for several days destroyed 80% of the city. This 1906 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?