Final answer:
The Richter scale is used to quantify the energy produced by an earthquake. The numbers on the Richter scale are a logarithmic scale, meaning each whole number increase represents a tenfold increase in energy release. The 1906 San Francisco earthquake had an intensity approximately 1.8 times greater than the 1989 Loma Prieta earthquake.
Step-by-step explanation:
The Richter scale is used to quantify the energy produced by an earthquake. The numbers on the Richter scale represent the amplitude of seismic waves recorded by seismographs. These numbers are a logarithmic scale, meaning that each whole number increase on the scale represents a tenfold increase in energy release. For example, a magnitude 7.0 earthquake releases 10 times more energy than a magnitude 6.0 earthquake.
In the given question, the 1906 San Francisco earthquake had a magnitude of 7.8 on the Richter scale, while the 1989 Loma Prieta earthquake had a magnitude of 6.9. To compare the intensities of the two earthquakes, we can subtract the magnitudes and round the result to the nearest whole number. In this case, the difference is 0.9, so the intensity of the 1906 earthquake was approximately 1.8 times greater than the intensity of the 1989 earthquake.