The Nikkei dropped 6.18% today on the first full day of trading after a weekend of damage assessment.
The first chart below shows the Nikkei 225 daily closes since 1985 with a callout for the 1995 Kobe earthquake (also known as the Great Hanshin earthquake).
The next chart shows the market behaviour following the 1995 earthquake. The Nikkei fell 24.7% over about 5 1/2 months. It then rallied 52.2% over the next 10 months.