Questão de Matemática e suas Tecnologias #01a0e94a

In a region with a high incidence of earthquakes, it was observed that two earthquakes had magnitudes $M_1$ and $M_2$, measured on the Richter scale, and released energies equal to $E_1$ and $E_2$, respectively. Among experts in the field, an algebraic expression relating these values is well known and given by:
$M_2-M_1=\frac{2}{3}\log \left(\frac{E_2}{E_1}\right)$
More comprehensive studies observed that the first earthquake had a magnitude $M_1=6.9$ and the energy released was one-tenth of that observed in the second earthquake.
The approximate value of the magnitude $M_2$ of the second earthquake, expressed to one decimal place, is equal to