User:Qbulakema114/sandbox

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Geology[edit]

Mechanism of 2011 Tohoku earthquake

This megathrust earthquake was a recurrence of the mechanism of the earlier 869 Sanriku earthquake, which has been estimated as having a magnitude of at least 8.4 Mw, which also created a large tsunami that inundated the Sendai plain.[1][2][3] Three tsunami deposits have been identified within the Holocene sequence of the plain, all formed within the last 3,000 years, suggesting an 800 to 1,100 year recurrence interval for large tsunamigenic earthquakes. In 2001 it was reckoned that there was a high likelihood of a large tsunami hitting the Sendai plain as more than 1,100 years had then elapsed.[4] In 2007, the probability of an earthquake with a magnitude of Mw 8.1–8.3 was estimated as 99% within the following 30 years.[5]

This earthquake occurred where the Pacific Plate is subducting under the plate beneath northern Honshu.[6][7] The Pacific plate, which moves at a rate of 8 to 9 cm (3.1 to 3.5 in) per year, dips under Honshu's underlying plate, building large amounts of elastic energy. This motion pushes the upper plate down until the accumulated stress causes a seismic slip-rupture event. The break caused the sea floor to rise by several metres.[7] A quake of this magnitude usually has a rupture length of at least 500 km (310 mi) and generally requires a long, relatively straight fault surface. Because the plate boundary and subduction zone in the area of the Honshu rupture is not very straight, it is unusual for the magnitude of its earthquake to exceed 8.5 Mw; the magnitude of this earthquake was a surprise to some seismologists.[8] The hypocentral region of this earthquake extended from offshore Iwate Prefecture to offshore Ibaraki Prefecture.[9] The Japanese Meteorological Agency said that the earthquake may have ruptured the fault zone from Iwate to Ibaraki with a length of 500 km (310 mi) and a width of 200 km (120 mi).[10][11] Analysis showed that this earthquake consisted of a set of three events.[12] Other major earthquakes with tsunamis struck the Sanriku Coast region in 1896 and in 1933.

The source area of this earthquake has a relatively high coupling coefficient surrounded by areas of relatively low coupling coefficients in the west, north, and south. From the averaged coupling coefficient of 0.5–0.8 in the source area and the seismic moment, it was estimated that the slip deficit of this earthquake was accumulated over a period of 260–880 years, which is consistent with the recurrence interval of such great earthquakes estimated from the tsunami deposit data. The seismic moment of this earthquake accounts for about 93% of the estimated cumulative moment from 1926 to March 2011. Hence, earthquakes in this area with magnitudes of about 7 since 1926 had only released part of the accumulated energy. In the area near the trench, the coupling coefficient is high, which could act as the source of the large tsunami.[13]

Most of the foreshocks are interplate earthquakes with thrust-type focal mechanisms. Both interplate and intraplate earthquakes appeared in the aftershocks offshore Sanriku coast with considerable proportions.[14]

  1. ^ Cite error: The named reference w was invoked but never defined (see the help page).
  2. ^ Sawai, Yuki; Namegaya, Yuichi (9 November 2012). "Challenges of anticipating the 2011 Tohoku earthquake and tsunami using coastal geology". Geophysical Research Letters. 39 (21): L21309. Bibcode:2012GeoRL..3921309S. doi:10.1029/2012GL053692.
  3. ^ Goto, Kazuhisa; Chagué-Goff, Catherine (29 August 2012). "The future of tsunami research following the 2011 Tōhoku-oki event" (PDF). Sedimentary Geology. 282: 1–13. Bibcode:2012SedG..282....1G. doi:10.1016/j.sedgeo.2012.08.003. Archived from the original (PDF) on 28 May 2015.
  4. ^ Minoura, K.; Imamura F.; Sugawara D.; Kono Y.; Iwashita T. (2001). "The 869 Jōgan tsunami deposit and recurrence interval of large-scale tsunami on the Pacific coast of northeast Japan" (PDF). Journal of Natural Disaster Science. 23 (2): 83–88.
  5. ^ Satake, K.; Sawai, Y.; Shishikura, M.; Okamura, Y.; Namegaya, Y.; Yamaki, S. (2007). "Tsunami source of the unusual AD 869 earthquake off Miyagi, Japan, inferred from tsunami deposits and numerical simulation of inundation". American Geophysical Union, Fall Meeting 2007, Abstract #T31G-03. 31: T31G–03. Bibcode:2007AGUFM.T31G..03S.
  6. ^ Chang, Kenneth (13 March 2011). "Quake Moves Japan Closer to U.S. and Alters Earth's Spin". The New York Times. Archived from the original on 16 March 2011. Retrieved 14 March 2011.
  7. ^ a b Ian Sample (11 March 2011). "newspaper: Japan earthquake and tsunami: what happened and why". The Guardian. London. Archived from the original on 14 March 2011. Retrieved 14 March 2011.
  8. ^ Maugh, Thomas H (11 March 2011). "Size of Japan's quake surprises seismologists". Los Angeles Times. Archived from the original on 7 April 2011. Retrieved 11 March 2011.
  9. ^ "地震調査委 想定外の連動地震 NHKニュース". .nhk.or.jp. Archived from the original on 14 March 2011. Retrieved 12 March 2011.
  10. ^ "時事ドットコム：M8．8、死者300人超＝行方不明540人以上−大津波10m・宮城で震度7". Jiji.com. Archived from the original on 13 December 2013. Retrieved 12 March 2011.
  11. ^ "気象庁"マグニチュードは9．0" NHKニュース". .nhk.or.jp. Archived from the original on 14 March 2011. Retrieved 13 March 2011.
  12. ^ "asahi.com（朝日新聞社）：地殻破壊3連鎖、計6分 専門家、余震拡大に警鐘 – 東日本大震災". Asahi Shimbun. Japan. Archived from the original on 7 April 2011. Retrieved 13 March 2011.
  13. ^ [1] Archived 7 December 2011 at the Wayback Machine
  14. ^ "Spatial distribution and focal mechanisms of aftershocks of the 2011 off the Pacific coast of Tōhoku Earthquake" by Y. Asano, T. Saito, Y. Ito, K. Shiomi, H. Hirose, T. Matsumoto, S. Aoi, S. Hori, and S. Sekiguchi.
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