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The 2007–2008 Nazko earthquakes were a series of small volcanic earthquakes measuring less than 4.0 on the Richter magnitude scale. They took place in the sparsely populated Nazko area of the Central Interior of British Columbia, Canada starting on October 9, 2007 and ending on June 12, 2008. They occurred just west of Nazko Cone, a small tree-covered cinder cone that last erupted about 7,200 years ago. No damage or casualties resulted from the Nazko earthquakes, which were too small to be felt by people, but local seismographs recorded them. The earthquake swarm occurred at the eastern end of a known volcanic zone called the Anahim Volcanic Belt. This is an east-west trending line of volcanic formations extending from the Central Coast to the Central Interior of British Columbia. == Geology == The 2007–2008 Nazko earthquake swarm is interpreted to have originated below the surface. The character of the seismic waves indicated that the swarm originated from a magmatic source. It could have formed as a result of rock fracturing at the tip of a dike and/or by movement along fault planes due to changes in the local stress field by the expansion and movement of magma.〔 This magmatic activity is potentially linked to the hypothesized Anahim hotspot, a mantle plume that is probably responsible for older volcanism throughout the Anahim Volcanic Belt. This volcanic belt includes the Rainbow, Ilgachuz and Itcha range shield volcanoes west of the Nazko swarm.〔 Individual Anahim volcanoes generally become older to the west of the Nazko swarm, indicating that the North American Plate is moving in a westerly direction with respect to the hotspot, carrying the volcanoes along with it at a rate of to per year. Because the area where the 2007–2008 Nazko earthquake swarm originated is at the eastern end of the volcanic belt, it probably represents the youngest portion of the hotspot track. This suggests any future volcanic earthquakes will occur in the Nazko region or further to the east. Before the Nazko earthquake swarm began in 2007, the Anahim hotspot was not known to be an earthquake zone. On October 10 of the following year, a swarm of earthquakes occurred. These earthquakes were normally no more than magnitude 1.0 on the Richter magnitude scale, but at least one earthquake was as strong as magnitude 3.9. Since the appearance of the Nazko swarm, Natural Resources Canada has expressed interest in the adjacent 7,200‑year‑old Nazko Cone. Even though earthquake swarms can be dangerous, scientists are able to model such events to analyze their structure.〔 During the earthquake swarm in 2007, a group of scientists investigated the possibility that a volcanic eruption would occur. Five additional seismographs were placed in the earthquake zone, and scientists closely monitored the seismic activity. After additional data were gathered, scientists with the United States Geological Survey, the University of Washington, and other organizations, agreed that the Nazko earthquakes probably originated from movement of magma beneath the surface near Nazko Cone. However, because of the number and small size of the Nazko earthquakes, no volcanic eruption is likely. Other recent earthquakes in North America that have been attributed to magma but did not result in a volcanic eruption include the 2003 earthquakes under Lake Tahoe in the U.S. state of California and a 2004 earthquake swarm at Jordan Craters in the U.S. state of Oregon.〔 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「2007–2008 Nazko earthquakes」の詳細全文を読む スポンサード リンク
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