1096 Eichō earthquake
  | |
| Local date | 17 December 1096 |
|---|---|
| Magnitude | Mw 8.0–8.5 |
| Epicenter | 39°30′N 140°24′E / 39.50°N 140.40°E |
| Areas affected | Japan |
| Tsunami | 7 m (23 ft)[1] |
The 1096 Eicho earthquake affected the coast of Japan on 17 December during the Heian period. It is postulated by geologists to be a large megathrust earthquake along the Nankai subduction zone off southern Honshu with a magnitude between 8.0 and 8.5. The earthquake also generated a destructive tsunami with a maximum height of 7 m (23 ft).
Tectonic setting
[edit]
The Nankai Trough delineates a subduction zone along the southwestern coast of Honshu where the Philippine Sea plate subducts northwestward beneath the Amurian plate. This fault zone has been the source of several large megathrust earthquakes in historic times with moment magnitudes of 8.0 or greater. The Nankai megathrust can be divided into three segments from east to west; Nankai, Tonankai and Tokai. These are further segmented into regions A and B for the Nankai segment; C and D for the Nankai segment; and E for the Tokai segment. Another segment west of the Nankai segment is known as Hyuganada (region Z). Scientists have identified patterns in the historic ruptures on the Nankai Trough; the Nankai segment may rupture with the Tokai or Tonankai segments or these segments may rupture in one earthquake. Another pattern involves the Nankai segment rupture separated by up to three years before the Tokai or Tonankai segments ruptures. The return period for Mw 8.5 earthquakes on the Nankai Trough is estimated at 400 to 600 years with the last example in 1707. The 1707 earthquake is the only event to have ruptured all segments of the Nankai Trough though there is uncertainty over whether the Tokai segment ruptured.[2]
Earthquake
[edit]Seismologist Hiroshi Kawasum provided the first estimate of the earthquake's magnitude at 7.0 on the energy class magnitude scale M(K) .[3] Tatsuo Usami placed the moment magnitude at 8.0 to 8.5 while Tokuji Utsu and others placed the magnitude at 8.3.[4][5] Based on the observation of strong ground motion in the Kinai, Lake Biwa, and Ibi River areas, and a destructive tsunami in Tsu and Suruga, regions C and D of the Nankai subduction zone (in the Enshū and Kumano seas) were likely the location of the rupture. Additionally, the rupture may have extended beneath Suruga Bay involving region E.[6][7]
Impact
[edit]Japanese court noble Munetada Fujiwara documented the earthquake's damage to several temples in his journal titled Chūyūki. Fujiwara wrote of a large bell at the Tōdai-ji which fell while a corridor of the Yakushi-ji collapsed. At the Hōjō-ji, a sōrin toppled, and two pagodas of the Hosshō-ji were damaged.[8] The document also recorded serious damage in Kyoto including a collapse of the Seta Bridge. At present-day Tsu in Mie Prefecture, many homes were destroyed by a tsunami.[9] Fujiwara no Moromichi said that more than 400 shrines, temples, and houses were swept away by the tsunami in Suruga Province.[9]
See also
[edit]References
[edit]- ^ National Geophysical Data Center. "Tsunami Event Information". National Geophysical Data Center / World Data Service: NCEI/WDS Global Historical Tsunami Database. NOAA National Centers for Environmental Information. doi:10.7289/V5PN93H7. Retrieved 20 June 2025.
- ^ Hirose, Fuyuki; Maeda, Kenji; Fujita, Kenichi; Kobayashi, Akio (2022). "Simulation of great earthquakes along the Nankai Trough: reproduction of event history, slip areas of the Showa Tonankai and Nankai earthquakes, heterogeneous slip-deficit rates, and long-term slow slip events". Earth, Planets and Space. 74 (13): 131. Bibcode:2022EP&S...74..131H. doi:10.1186/s40623-022-01689-0.
- ^ Kawazumi, Hiroshi (1951). "Measures of Earthquake Danger and Expectancy of Maximum Intensity Throughout Japan as Inferred from the Seismic Activity in Historical Times". Bulletin of the Earthquake Research Institute. 29 (3): 469–482. doi:10.15083/0000034145.
- ^ Usami, Tatsuo (2003). 最新版 日本被害地震総覧 [Latest Edition: Comprehensive List of Damaging Earthquakes in Japan] (in Japanese). University of Tokyo Press. p. 41-42. ISBN 978-4-13-060742-1.
- ^ Utsu, Tokuji; Shima, Etsuzo; Yoshii, Toshiaki; Yamashina, Kenichiro (2001). 地震の事典 [Encyclopedia of Earthquakes] (in Japanese). Asakura Publishing.
- ^ Ishibashi, Katsuhiko (1999). "文献史料からみた東海・南海巨大地震" [The Tokai and Nankai Great Earthquakes as seen from historical documents]. Chigaku Zasshi. 104 (4). doi:10.5026/jgeography.108.4_399.
- ^ 石橋克彦, 2002, フィリピン海スラブ沈み込みの境界条件としての東海・南海巨大地震-史料地震学による概要-, 京都大学防災研究所研究集会13K-7 報告書, 1-9.
- ^ Ishibashi, Katsuhiko (1999). "Historical Seismology of Next Generation. Great Tokai and Nankai, Japan, Earthquakes as Revealed by Historical Seismology. 1. Review of the Events until the mid-14th Century". Journal of Geography (Chigaku Zasshi). 108 (4): 399–423. doi:10.5026/jgeography.108.4_399.
- ^ a b Yada, Toshifumi (2009). 中世の巨大地震 [Great earthquakes in the Middle Ages] (in Japanese). Yoshikawa Kōbunkan. ISBN 9784642056649.