Sedimentary deposits of the 26 December 2004 tsunami on the northwest coast of Aceh, Indonesia

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概要

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• The 2004 Sumatra-Andaman tsunami flooded coastal northern Sumatra to a depth of over 20 m, deposited a discontinuous sheet of sand up to 80 cm thick, and left mud up to 5 km inland. In most places the sand sheet is normally graded, and in some it contains complex internal stratigraphy. Structures within the sand sheet may record the passage of up to 3 individual waves. We studied the 2004 tsunami deposits in detail along a flowparallel transect about 400 m long, 16 km southwest of Banda Aceh. Near the shore along this transect, the deposit is thin or absent. Between 50 and 400 m inland it ranges in thickness from 5 to 20 cm. The main trend in thickness is a tendency to thicken by filling low spots, most dramatically at pre-existing stream channels. Deposition generally attended inundation-along the transect, the tsunami deposited sand to within about 40 m of the inundation limit. Although the tsunami deposit contains primarily material indistinguishable from material found on the beach one month after the event, it also contains grain sizes and compositions unavailable on the current beach. Along the transect we studied, these grains become increasingly dominant both landward and upward in the deposit; possibly some landward source of sediment was exposed and exploited by the passage of the waves. The deposit also contains the unabraded shells of subtidal marine organisms, suggesting that at least part of the deposit came from offshore. Grain sizes within the deposit tend to fine upward and landward, although individual units within the deposit appear massive, or show reverse grading. Sorting becomes better landward, although the most landward sites generally become poorly sorted from the inclusion of soil clasts. These sites commonly show interlayering of sandy units and soil clast units. Deposits from the 2004 tsunami in Sumatra demonstrate the complex nature of the deposits of large tsunamis. Unlike the deposits of smaller tsunamis, internal stratigraphy is complex, and will require some effort to understand. The Sumatra deposits also show the contribution of multiple sediment sources, each of which has its own composition and grain size. Such complexity may allow more accurate modeling of flow depth and flow velocity for paleotsunamis, if an understanding of how tsunami hydraulics affect sedimentation can be established.

• 公益社団法人 日本地震学会、地球電磁気・地球惑星圏学会 、特定非営利活動法人 日本火山学会、日本測地学会、日本惑星科学会の論文

著者

• Moore Andrew

  Department Of Geology Kent State University

• KAMATAKI Takanobu

  Active Fault Research Center, Geological Survey of Japan, AIST

• TRIYONO Rahmat

  Badan Meteorologi and Geofisika

• Gelfenbaum Guy

  U.s. Geological Survey Coastal And Marine Geology Program

• Nishimura Yuichi

  Institute Of Seismology And Volcanology Hokkaido University

関連論文

• スマトラ島沖地震(2004年12月)に伴う津波と津波堆積物 (総特集 スマトラ島沖地震とインド洋津波/2004) -- (2部 インド洋大津波)
• スマトラ沖地震津波によって形成された津波堆積物 : インドネシアスマトラ島アチェ州西海岸の例((2)断層と地震:地質学はどう貢献するか)
• 2004年スマトラ・アンダマン地震津波調査報告:スマトラ島北西端における津波波高と堆積物の分布
• Sedimentary deposits of the 26 December 2004 tsunami on the northwest coast of Aceh, Indonesia
• Tsunami run-up heights of the 2003 Tokachi-oki earthquake
• Tsunami run-up heights of the 2004 off the Kii peninsula earthquakes
• Rupture process of the 2004 great Sumatra-Andaman earthquake estimated from tsunami waveforms
• Nature and origin of volcanic ash in the 2000 eruption of Usu volcano, southwestern Hokkaido, Japan
• Sedimentary deposits of the 26 December 2004 tsunami on the northwest coast of Aceh, Indonesia
• Tsunami run-up heights of the 2003 Tokachi-oki earthquake

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