Nankai Trough and Japan’s great earthquakes

歴史に学ぶ

1,400 years of great earthquakes

Every great Nankai Trough earthquake since the first written record, set against Japan’s other major earthquakes. Select a marker for details.

800100012001400160018002000Nankai TroughOther majorquakesNow203 yrs209 yrs265 yrs137 yrs107 yrs102 yrs147 yrs90 yrs82 yrs49 days684Hakuhō887Ninna1096Eichō–Kōwa1361Shōhei1498Meiō1605Keichō1707Hōei1854Ansei1944Shōwa8648691586161117031707184718551923193319952004
RupturedUncertain in the recordDid not ruptureOcean-trench earthquake (tsunami)Inland or shallow crustal earthquakeMt. Fuji eruption
Hōei earthquake
Nankai Trough earthquakeSegments, west → east
Hōei earthquake · Oct 28, 1707 · M8.6

Which segments broke

West to east along the trough. Sometimes the whole trough broke at once; sometimes in two halves, hours or years apart.

NankaiTōnankaiTōkai
684 Hakuhō
887 Ninna
1096 Eichō–KōwaSecond half: 2 years later
1361 Shōhei
1498 Meiō
1605 Keichō
1707 Hōei
1854 AnseiSecond half: 32 hours later
1944 ShōwaSecond half: 2 years later

Intervals between episodes

684 → 887203 yrs
887 → 1096209 yrs
1096 → 1361265 yrs
1361 → 1498137 yrs
1498 → 1605107 yrs
1605 → 1707102 yrs
1707 → 1854147 yrs
1854 → 194490 yrs
1944 → Now82 yrs
Grey: before 1361, when the written record is probably incomplete
All 8 intervals
Mean
157.5 yrs
Median
142 yrs
Std. deviation
62.1 yrs
Coeff. of variation
0.39
Range
90–265 yrs
5 intervals since 1361
Mean
116.6 yrs
Median
107 yrs
Std. deviation
24.3 yrs
Coeff. of variation
0.21
Range
90–147 yrs

What the numbers say

  1. Roughly periodic, not regular. Since 1361 the coefficient of variation is 0.21. Completely random timing would give about 1, a perfect clock 0. Great Nankai earthquakes do recur, but the gap has ranged from 90 to 147 years.
  2. Often in two halves. In 1096–99, 1854 and 1944–46 the eastern and western halves broke separately, 32 hours to about 2 years apart. In 1707 the whole trough broke at once (M8.6), the largest known earthquake in Japan before 2011.
  3. The early gaps are longer, probably because events went unrecorded. Before 1361 every interval exceeds 200 years. Researchers think some earthquakes are missing from the written record, so the recent intervals are the more reliable sample.
  4. Mt. Fuji’s last eruption began 49 days after the 1707 Hōei earthquake. Scientists still debate how closely the two were linked. Fuji has not erupted since.
  5. Disasters also come from elsewhere. Between Nankai episodes, other trenches and inland faults caused some of Japan’s worst disasters, including 1923 Kantō, 1995 Kobe and 2011 Tōhoku. Preparing for one is preparing for all.
This is history, not a forecast. With this few events, statistics cannot tell when the next one will happen. The government’s official evaluation (Earthquake Research Committee, revised September 2025) puts the chance of an M8–9 Nankai Trough earthquake within 30 years at 60–90% or more, or 20–50%, depending on the model, and advises planning with the higher figure.
Read the official evaluation · jishin.go.jp

Sources: Headquarters for Earthquake Research Promotion; JMA. Dates before 1582 are given as years; magnitudes of historical earthquakes are estimates.