A very large, highly destructive earthquake disaster that causes widespread damage (often with collapses, tsunamis, etc.).
昭和の大震災は多くの人命と家屋を失わせた。
The great earthquake in the Showa era cost many lives and homes.
大震災に備えて非常袋を用意しておこう。
Prepare an emergency kit in case of a major earthquake disaster.
その地域では過去に大震災が起きており、地盤が不安定だ。
A major earthquake disaster occurred in that area in the past, and the ground is unstable.