# 2001 Geiyo earthquake

The 2001 Geiyo earthquake (2001年芸予地震 Nisen-ichi-nen Gēyo Jishin) occurred with a magnitude of M$_{JMA}$ 6.7 on March 24 at 15:27:53 JST, and an epicenter located near the Geiyo Islands of Hiroshima, Japan.

## Tectonic setting

Near the Geiyo region, a M$_s$ 7.8 earthquake occurred in June 1905, which was an intraslab event within the subducting Philippine Sea plate.

## Earthquake

The United States Geological Survey (USGS) gave the earthquake a magnitude of M$_w$ 6.8, while the Japan Meteorological Agency (JMA) reported the magnitude at M$_{JMA}$ 6.7, with its epicenter located near the island of Kurahashi-jima in Kure, Hiroshima Prefecture. The released seismic moment of the earthquake was 1.3×10$^{19}$ Nm. This earthquake is a normal faulting intraslab event within the subducting Philippine Sea plate. The slip of the earthquake was estimated to be about 1.5–2.4 meters (4 ft 11 in – 7 ft 10 in). The locations of aftershocks were distributed roughly in N–S direction. It has been suggested that this earthquake was related to the dehydration of the Philippine Sea plate slab.

### Intensity

Locations with a seismic intensity of Shindo 5− and higher :
| Intensity | Prefecture | Locations |
| 6− | Hiroshima | Higashihiroshima, Ōsakikamijima, Kumano |
| 5+ | Hiroshima | Kure, Etajima, Hiroshima, Hatsukaichi, Mihara, Onomichi, Kitahiroshima |
| 5+ | Ehime | Kamijima, Imabari, Saijō, Kumakōgen, Matsuyama, Masaki, Seiyo, Uwajima, Tobe |
| 5+ | Yamaguchi | Suō-Ōshima, Yanai, Tabuse, Hirao, Waki, Iwakuni, Yamaguchi |
| 5− | Hiroshima | Fukuyama, Sera, Miyoshi |
| 5− | Ehime | Ikata, Yawatahama, Ōzu, Uchiko, Iyo, Tōon, Niihama |
| 5− | Yamaguchi | Kaminoseki, Hikari, Kudamatsu, Shūnan |
| 5− | Shimane | Gōtsu, Hamada, Ōnan |
| 5− | Kōchi | Kōchi |
| 5− | Ōita | Saiki |
The JMA reported it recorded a maximum seismic intensity of Shindo 6- on its seismic intensity scale; the maxinum intensity was reported in Higashihiroshima, Ōsakikamijima and Kumano, Hiroshima Prefecture. Shindo 5+ was recorded in parts of Ehime and Yamaguchi Prefectures, while Shindo 5-was observed in multiple areas of Shimane, Kōchi and Ōita Prefectures; Shindo 1-4 was also reported in Kyushu, Kansai and Chūbu regions, with shaking recorded as far away as Shizuoka, Noto, Ishikawa, Iizuna and Kōzushima, Tokyo. A maximum peak ground acceleration of 832 gal (0.85 g) was recorded at Saeki-ku, Hiroshima; strong ground motions from the earthquake were amplified and spread to areas far from the epicenter, due to the ground beneath the region comprising soft sediments. On the Modified Mercalli intensity scale, the earthquake registered a maximum intensity of IX (Violent). Tremors were also felt along the eastern and southern coasts of South Korea.

## Impact

Two people were killed; one in Kure, Hiroshima due to a wall collapse and other in Matsuyama, Ehime after being hit by falling roof tiles. Additionally, 288 others were injured, 43 of them seriously, including 183 in Hiroshima, 75 in Ehime, 12 in Yamaguchi, 4 in Kochi, 3 in Shimane and 1 in Okayama. The earthquake completely destroyed 76 homes, severely damaged 865 and partially damaged 53,243 others, with all structural collapses occurring in Hiroshima, Ehime and Yamaguchi; landslides destroyed 39 homes, mostly in Hiroshima. Additionally, 40,739 waterways, 1,209 cultural and educational facilities, 787 roads, 149 harbors, 97 hospitals, 9 bridges, 8 public buildings and 71 other structures were also affected.
In Hiroshima, over 3,700 buildings were damaged, train lines were suspended, Hiroshima Airport was temporarily closed for inspection, telecommunications were disrupted and soil liquefaction was reported. Most of the damaged residential buildings in the city were built on steep slopes. Liquefaction also occurred at Tōyo, Ehime. Power outages occurred in the prefectures of Hiroshima, Ehime, Okayama, Yamaguchi, and Kōchi.