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|magnitude = 5.1 Mfa 〔 |depth = |location = 〔 |countries affected = Kansas United States |intensity = VII (''Very Strong'') 〔 |casualties = }} On April 24, the 1867 Manhattan earthquake struck Riley County, Kansas. It measured 5.1 on a seismic scale that is based on an isoseismal map or the event's felt area. The earthquake's epicenter was by the town of Manhattan and is the strongest earthquake to originate in the state. The earthquake had an intensity of VII (''Very Strong'') on the Mercalli intensity scale, and was felt over an area of roughly . It caused largely minor damage, reports of which were confined to Kansas, Iowa, and Missouri, according to the United States Geological Survey. Manhattan is near the Nemaha Ridge, a long structure that is bounded by several faults. The nearby Humboldt Fault Zone in particular poses a threat to the city; though Kansas is not known for earthquake activity, an earthquake could occur at any time. == Background and geography == The earthquake's epicenter lay near Manhattan, Kansas, a town just off the connection of the Kansas River and the Big Blue River.〔 Nearby is the anticline Nemaha Ridge, which has been associated with at least a few earthquakes of Kansas. A 300‑million-year-old Precambrian granite range bounded by faults, it hosts the Humboldt Fault Zone, which, in addition to serving as the range's easternmost boundary, has produced a large portion of the state's earthquakes. Each year, it is responsible for at least several small tremors less than magnitude 2.7.〔 It cuts through Permian rock, and according to the Geological Society of America, may actually be a complex fault. Previously, it was believed to be a simple, Precambrian structure. The Nemaha Range lies roughly east of the Midcontinent rift, which forms a layer of basaltic rock around 1.1 billion years old. This rift extends northward to Lake Superior and the surrounding area and southward to Kansas, then stops abruptly. Also present in the state is the Central Kansas Uplift, the faults of which produced several small earthquakes during the late 1980s. According to United States Geological Survey geophysicist Don Steeples, earthquakes at the Humboldt Zone have decreased and activity at the Uplift has increased. Felt over an area of , the earthquake followed the Midcontinent seismic trend:〔 unlike earthquakes on the Western Coast of the US, events in the central and east-central sectors of the country are spread out over extensive areas; for example, the 1968 Illinois earthquake also followed this trend. The 1867 Manhattan earthquake remains the only notable earthquake to originate in the state, though 25 in total have taken place since. According to the ''Bulletin of the Seismological Society of America'', the frequency between earthquakes is between 40 and 45 years. 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「1867 Manhattan, Kansas earthquake」の詳細全文を読む スポンサード リンク
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