According to the census in 2005, there were 2,628,811 residents in Osaka, an increase of 30,037 or 1.2% from 2000. There were 1,280,325 households with approximately 2.1 persons per household. The population density was 11,836 persons per km². The 1923 Great Kantō earthquake caused a mass migration to Osaka between 1920 and 1930, and the city became Japans largest city in 1930 with 2,453,573 people, outnumbering even Tokyo, which had a population of 2,070,913. The population peaked at 3,252,340 in 1940, and had a post-war peak of 3,156,222 in 1965, but continued to decrease since, as the residents moved out to the suburbs.
Question: How many years passed between 1920 to 1930  during the mass migration of the 1923 Great Kanto earthquake?
Answer: 10