The latest eruption, in 1707 (the 4th year of the Hōei era), was known as the great Hōei eruption. It followed several weeks after the Great Hōei earthquake, an 8.7 on the Richter scale. The earthquake severely damaged the city of Osaka, but more than that, it created enough seismic activity to compress the magma chamber 20 km deep in the inactive Mt. Fuji. Due to the compression of the magma chamber, basaltic lava rose from the bottom to the higher dacitic magma chamber at 8 km deep. The mixing of the two different types of magma caused a Plinian eruption to occur. Previous to the Hoei, another earthquake named Genroku had struck Japan in 1703. The earthquake affected both Kanagawa and Shizuoka prefectures, and was measured as an 8.2 on the Richter Scale. The Genroku earthquake had a similar effect on Mt. Fuji as Hoei but with less severity. It clamped the dike of the mountain at 8 km to the surface (where the dacitic magma resides), as well as the basaltic chamber at 20 km deep. Many articles found a correlation between the two earthquakes, arriving at the conclusion that without either earthquake the Hoei eruption would not have happened.