From one of his earliest papers describing the eruption of Mount Azuma in 1893 to his death, Omori studied Japanese volcanos. He described several types of volcanic earthquakes from data obtained at regular eruptions of Mount Asama in central Japan, the 1910 Mount Usu eruption and the 12 January 1914 eruption of Sakurajima. At the latter two eruptions, his warnings to the population prevented greater loss of life.