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|mapsize = |caption = |date = 11 April 2011 (+09:00) |origintime = 17:16:13 |duration = |magnitude = 6.6 Mw |depth = |location = |type = Dip-slip |countries affected = Japan |damage = |intensity = VIII (''Severe'') |PGA = |tsunami = No |landslide = Yes |foreshocks = |aftershocks = |casualties = 4 dead, 10 injured }} The was a potent magnitude 6.6 Mw intraplate aftershock that occurred at 17:16 JST (08:16 UTC) on Monday, 11 April 2011, in the Hamadōri region of Fukushima, Japan. With a shallow focus of , the earthquake was centred inland about west of Iwaki, causing widespread strong to locally severe shaking. It was one of many aftershocks to follow the 11 March Tōhoku earthquake, and the strongest to have its epicentre located inland. The earthquake occurred as a result of normal faulting to the west of Iwaki and triggered numerous landslides across adjacent mountainous areas. A few fires broke out, and 220,000 households lost electricity. Officials issued localised tsunami alerts, though no significant waves were generated. The earthquake caused little structural damage, but killed four people and injured ten others. The strong ground movements triggered the reactivation of a nearby geological fault, prompting researchers to conduct extensive surveys in the region. ==Geology== The magnitude 6.6 Mw Fukushima Hamadōri earthquake occurred inland on 11 April 2011 at 08:16 UTC at a focal depth of , about west of Iwaki, Fukushima, or north-northeast of Tokyo.〔 To the east of the epicentre, the oceanic Pacific Plate is subducted beneath the continental Okhotsk Plate, on which much of Honshu's Tōhoku region is situated. Building stress near the resultant plate boundary has led to the development of shallow inland faults through crustal deformation and folding along the east coast of Tōhoku. This intraplate earthquake occurred in the vicinity of the Idosawa Fault – a shallow crustal fault in the Hamadōri region near Tabito town, Iwaki city, that had previously been inactive. Surveys near the epicentre revealed a surface rupture of about and numerous fault scarps, with general vertical displacements of ; a maximum displacement of occurred at the small village of Shionohira. Localised right-lateral slip of was observed at the subsiding west side of the rupture. The segments of the Idosawa Fault associated with this surface feature were classified as the "Shionohira Fault" in 2011. The proximate Yunodake Fault, a normal dip-slip fault northeast of the Shionohira Fault that had been dormant for 120,000–130,000 years, also ruptured during the quake. These observations indicated that the earthquake occurred as a result of normal dip-slip faulting with some strike-slip component.〔 Although it was centred near a different fault zone, the earthquake was classified as an aftershock of the 11 March Tōhoku earthquake, which occurred offshore about to its northeast.〔 The magnitude 9.0 Mw earthquake triggered widespread seismic activity, and its aftershock sequence includes well-over 67 earthquakes of magnitude 6.0 Mw or greater. Apart from the Fukushima Hamadōri earthquake, four of the aftershocks measured magnitude 7.0 Mw or higher. The Fukushima Hamadōri earthquake, however, was the strongest of the aftershocks to have its epicentre located inland.〔〔 Early estimates placed the strength of the earthquake at a magnitude of 7.0–7.1, but the United States Geological Survey (USGS) lowered the magnitude to 6.6. The Japan Meteorological Agency (JMA) assessed a magnitude of 7.0 Mj and a depth of . The Fukushima Hamadōri earthquake was succeeded by a number of smaller tremors; that same day, at least 11 earthquakes of magnitude 3.5 Mj or higher were recorded near its epicentre. Of the series, the strongest registered at a magnitude of 5.5 Mj and occurred within 3.5 hours after the initial quake. A shallow magnitude 6.0 Mw (6.4 Mj) earthquake and several smaller tremors struck the region on 12 April. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「April 2011 Fukushima earthquake」の詳細全文を読む スポンサード リンク
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