The magnitude of an earthquake, measured on the Richter scale, is [tex]\log _{10} \frac{I}{I_0}[/tex], where [tex]I[/tex] is the amplitude registered on a seismograph [tex]100 \, \text{km}[/tex] from the epicenter of the earthquake, and [tex]I_0[/tex] is the amplitude of a certain (small) size. Find the Richter scale rating for an amplitude of [tex]100,000,000 I_0[/tex].

The magnitude, [tex]R[/tex] (measured on the Richter scale), is [tex]\square[/tex].



Answer :

To find the Richter scale rating [tex]\( R \)[/tex] for an amplitude of [tex]\( 100,000,000 I_0 \)[/tex], we will use the formula for the magnitude on the Richter scale:

[tex]\[ R = \log_{10} \left( \frac{I}{I_0} \right) \][/tex]

Given that:
[tex]\[ I = 100,000,000 I_0 \][/tex]

we substitute [tex]\( I \)[/tex] into the formula for [tex]\( R \)[/tex]:

[tex]\[ R = \log_{10} \left( \frac{100,000,000 I_0}{I_0} \right) \][/tex]

Since [tex]\( I_0 \)[/tex] appears in both the numerator and the denominator, it cancels out:

[tex]\[ R = \log_{10} \left( 100,000,000 \right) \][/tex]

Next, we recognize that [tex]\( 100,000,000 \)[/tex] can be written as [tex]\( 10^8 \)[/tex]:

[tex]\[ R = \log_{10} \left( 10^8 \right) \][/tex]

The logarithmic property [tex]\( \log_{10}(10^a) = a \)[/tex] tells us that:

[tex]\[ R = 8 \][/tex]

Therefore, the magnitude [tex]\( R \)[/tex] on the Richter scale for an amplitude of [tex]\( 100,000,000 I_0 \)[/tex] is:

[tex]\[ R = 8 \][/tex]