| UTC time | 2003-05-26 09:24:33 |
|---|---|
| 2003-07-25 22:13:29 | |
| ISC event | 6849185 |
| 7006322 | |
| USGS-ANSS | ComCat |
| ComCat | |
| Local date | May 26, 2003 |
| July 26, 2003 | |
| Local time | 18:24:33JST (UTC+9) |
| 07:13:29JST (UTC+9) | |
| Magnitude | Mw 7.0,MJMA 7.1 |
| Mw 6.0,MJMA 6.4 | |
| Depth | 68.0 km (42.3 mi) |
| 6 km (3.7 mi) | |
| Fault | Asahiyama flexure(July 26) |
| Type | Oblique-reverse |
| Total damage | ¥92.9 billion(US$644 million, equivalent to $1.12 billion in 2025) |
| Max. intensity | JMA 6+ (MMI IX) |
| Peak acceleration | 1.134g(May 26) 2.08g(July 26) |
| Peak velocity | 60.13 cm/s(May 26)[1] |
| Landslides | Yes |
| Aftershocks | 27 ≥Mw 4.0(May 26) |
| Casualties | 851 injuries |
Two majorearthquakes struckMiyagi Prefecture inJapan in 2003. The first event measuredMJMA 7.1, had a near-intermediate depth of 68 km (42 mi) and struck the town ofKesennuma, near the border withIwate Prefecture, injuring 174 people in fiveprefectures, while the second event, despite having a lower magnitude ofMJMA 6.4, was much more destructive and intense due to occurring much closer to the surface at 6 km (3.7 mi), injuring nearly 680 people across multiple towns nearSendai andIshinomaki in Miyagi. Both events caused moderate damage to infrastructure, triggered landslides,soil liquefaction and other ground effects, and damaged or destroyed 18,488 homes, 5,108 of them severely.
The Pacific plate, made of oceaniclithosphere, subducts beneath the Okhotsk Sea plate along a convergent boundary located off the east coast of the northern half of Japan.[2] It runs from theBoso triple junction and ends nearHokkaido, where it joins theKuril–Kamchatka Trench. At this location, the Pacific plate moves approximately westward relative to the North American plate at a velocity of 70 mm (2.8 in)/yr, subducting beneath Japan at theJapan Trench. This subduction zone is capable of producing megathrust earthquakes with magnitudes greater than 8.5, evident in the historical records. It was on the subduction interface where the2011 Tōhoku earthquake nucleated. That event involved a 220 km (140 mi) x 400 km (250 mi)rupture area on the subduction zone.[3]
With an epicenter inKesennuma,Miyagi Prefecture, the earthquake occurred as the result ofoblique-reverse faulting at a depth of 68 km (42 mi).[4] TheUnited States Geological Survey (USGS) reported a magnitude of Mwb 7.0,[4] while theJapan Meteorological Agency (JMA) measured the earthquake at MJMA 7.1.[5] According to GPS observations, horizontal crustal deformation of up to approximately 1.5 cm (0.59 in) was observed west of the epicenter, consistent with the earthquake'sfocal mechanism.[6] The earthquake was followed by 27aftershocks that struck throughout the remainder of 2003, most of which occurred in Kesennuma, Miyagi andRikuzentakata, Iwate; the largest aftershock measured mb 4.8.[7]
The earthquake had a maximum intensity ofShindo 6- onJapan Meteorological Agency seismic intensity scale, which was observed in both Miyagi and Iwate Prefectures.[5] A USGS seismic installation atHanamaki, Iwate recorded 0.297g in ground acceleration (pga) and 53.31 cm/s (20.99 in/s) in ground velocity (pgv); the station data corresponded to a Modified Mercalli intensity (MMI) of IX (Violent); another station inIshinomaki recorded a pga of 1.134g.[1] MMI IX shaking was also estimated inKesennuma, based on damage to a road near the epicenter in the town.[8] Additionally, a map created by theNational Research Institute for Earth Science and Disaster Resilience estimated that shaking exceeding 1,000gal (1.02g) had likely been observed in much of northeastern Miyagi and southeastern Iwate.[9]
| Intensity | Prefecture | Locations |
|---|---|---|
| 6− | Miyagi | Ishinomaki,Wakuya,Kurihara |
| Iwate | Ichinoseki,Ōfunato,Hiraizumi,Ōshū | |
| 5+ | Miyagi | Kesennuma,Minamisanriku,Tome,Higashimatsushima,Misato,Ōsaki,Shikama,Kami |
| Iwate | Rikuzentakata,Morioka,Kanegasaki,Sumita,Kamaishi,Tōno,Hanamaki,Yahaba,Hirono,Ninohe | |
| Akita | Daisen | |
| Aomori | Hashikami | |
| Yamagata | Yamgata | |
| 5− | Miyagi | Ōhira,Ōsato,Taiwa,Sendai,Natori,Kawasaki,Zaō,Ōgawara,Watari |
| Iwate | Kitakami,Nishiwaga,Shiwa,Takizawa,Ōtsuchi,Yamada,Miyako,Iwaizumi,Fudai,Fudai,Kuji,Hachimantai | |
| Akita | Yuzawa,Ugo,Yokote,Daisen,Akita | |
| Aomori | Hachinohe,Nanbu,Gonohe | |
| Yamagata | Murayama | |
| Fukushima | Sōma,Minamisōma,Tamura,Tomioka |
At 07:13:29JST (UTC+9) on 26 July (22:13UTC on 25 July), a Mw 6.0[10] or MJMA 6.4[11] event struckŌsato, Miyagi, at a depth of 6 km (3.7 mi) and occurring as a result ofreverse faulting.[12] It was preceded by a Mw 5.5 or MJMA 5.6 foreshock at 00:13:07JST,[13][11] which had a maximumintensity ofShindo 6- atHigashimatsushima.[14] The mainshock had a maximumintensity ofShindo 6+ inHigashimatsushima andMisato, Miyagi.[15] It also had aModified Mercalli intensity of VIII (Severe),[12] and a pga of 2,037gal (2.08g) was recorded in Naruse (now merged into Higashimatsushima), the highest ever recorded at the time.[16] The mainshock occurred on the previously-unknown Asahiyama flexure, an 8 km (5.0 mi) north-south trending fault in Higashimatsushima.[17] Aftershocks from the event were distributed in a 15 km x 15 km area, occurring 2–13 km (1.2–8.1 mi) beneath the surface.[11]
| Intensity | Prefecture | Locations |
|---|---|---|
| 6+ | Miyagi | Higashimatsushima,Misato |
| 6− | Miyagi | Ishinomaki,Wakuya,Ōsaki |
| 5+ | Miyagi | Tome |
| 5− | Miyagi | Kurihara,Ōsato,Sendai |
| 4 | Miyagi | Kawasaki,Ōgawara,Watari,Natori,Tagajō,Shichigahama,Rifu,Matsushima,Ōhira,Shikama,Minamisanriku,Kesennuma |
| Iwate | Rikuzentakata,Ichinoseki,Hiraizumi,Ōshū,Hanamaki,Ōtsuchi,Yahaba,Morioka,Fudai,Fudai,Ninohe | |
| Akita | Daisen | |
| Yamagata | Murayama,Mogami,Shinjō,Nakayama | |
| Fukushima | Shinchi,Iwaki |
At least 174 people were injured, 25 of them seriously, including 91 in Iwate, 64 in Miyagi, 10 in Yamagata, 8 in Akita and 1 in Aomori. At least 23 homes partially or completely collapsed, including 12 in Iwate and 11 in Miyagi. At least 2,404 other households suffered partial damage, including 1,183 in Iwate, 1,085 in Miyagi, 132 in Fukushima and 2 each in Akita and Yamagata.[18] Damage also occurred to 15 libraries in both prefectures, 10 of which suffered broken glass.[16] Twenty-threepiers supporting theTōhoku Shinkansen were damaged in Iwate, mainly inŌshū andMorioka.[19] Five building fires and 63 landslides occurred and some power and water lines broke in Iwate and Miyagi. Possiblesoil liquefaction with groundsubsidence of at least 10 cm (3.9 in) occurred atŌfunato,[4] where a 190 m (620 ft) longground crack was observed.[16] Overall, damage from the May 26 event was estimated at ¥33.62 billion (US$233 million).[20]
The Mw 5.5 foreshock and Mw 6.0 mainshock injured 677 people, including 675 in Miyagi and 2 in Yamagata; 51 of the injuries in Miyagi were classified as serious. At least 1,276 homes were completely destroyed, 3,809 were partially destroyed and 10,976 more were partially damaged; one home was damaged in Iwate Prefecture while the rest were in Miyagi.[21] Over 47,000 people and 13,000 households were affected by water outages in eight cities and towns in Miyagi.[22] The towns of Nango, Yamoto,Naruse and Kawanami received the worst damage, with 50 homes collapsing or suffering severe damage in Nango alone. Landslides were also reported.[23] AtZuigan-ji Temple, many walls were affected by cracks or peelingplaster.[24] The shaking also caused a train to derail on theIshinomaki Line.[13] Overall damage costs from the July 26 events were estimated at ¥59.3 billion (US$411 million).[20]
