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南 裕介*; 大場 司*; 林 信太郎*; 國分 陽子; 片岡 香子*
Journal of Volcanology and Geothermal Research, 387, p.106661_1 - 106661_17, 2019/12
被引用回数：8 パーセンタイル：32.44(Geosciences, Multidisciplinary)鳥海火山北麓に分布するラハール堆積物について堆積層解析、放射性炭素同位体年代測定、古記録解析を行った。以上の結果から、過去2500年間において少なくとも紀元前2
5世紀、紀元前24世紀、紀元57世紀、紀元871年、紀元1801年に大規模なラハールが発生していることが明らかになった。これらのラハールはその原因となった火山現象から以下の3つのタイプに区分でき、それぞれ(1)岩屑なだれ堆積物の再堆積、(2)マグマ噴火、(3)水蒸気噴火である。これら3種類のラハールは遠方において、以下の異なる特徴を示すことが明らかになった、(1)遠方においても大規模な粘着性土石流として流動する、(2)流動中の分化・希釈により遠方では河川流として流動する、(3)小規模な粘着性ラハールとなる。
南 裕介*; 大場 司*; 林 信太郎*; 國分 陽子; 片岡 香子*
no journal, ,
鳥海火山北麓に分布するラハール堆積物について堆積層解析、放射性炭素同位体年代測定、古記録解析を行った。以上の結果から、過去2500年間において少なくとも紀元前2-5世紀、紀元前2-4世紀、紀元5-7世紀、紀元871年、紀元1801年に大規模なラハールが発生していることが明らかになった。これらのラハールは(1)岩屑なだれ堆積物の再堆積、(2)マグマ噴火、(3)水蒸気噴火の主に3通りの発生原因を持ち、それぞれ以下の異なる特徴を示すことが明らかになった、(1)遠方においても大規模な粘着性土石流として流動する、(2)流動中の分化・希釈により遠方では河川流として流動する、(3)小規模な粘着性ラハールとなる。
Malatesta, L.*; Weiss, N.-M.*; 塚本 すみ子*; 末岡 茂; 石村 大輔*; Gailleton, B.*; 西村 卓也*; 高橋 直也*; 片岡 香子*; 小松 哲也; et al.
no journal, ,
On January 1st, 2024, the Mw 7.5 Noto Peninsula earthquake ruptured on a series of coastal offshore reverse faults in the back arc of central Japan. Recent Holocene terraces mapped along the northern coast, where coseismic uplift was greatest on January 1st 2024, suggest that they may be attributable to similar past ruptures. The Peninsula itself is remarkable for its 4767 unique terraces ranging in age from Holocene to 1.02 Ma. We digitized all terraces and recorded the elevation of their landward edge, and derived a rock uplift rate for each based on their age and the corresponding original sea level. The southeast-tilting crustal deformation recorded by the terraces associated with the last two interglacial high stands strongly resembles that caused by the Mw 7.5 earthquake. Older terraces, on the contrary all record a spatially uniform rate of uplift across the Peninsula. We conclude that the faults that caused the most recent earthquake became the dominant structures on the Peninsula over a quarter million year ago. This onset of seismogenic activity informs us about the regional plate tectonics of the area. The boundary separating Eurasia from the North American Plate currently runs south of the Noto Peninsula, linking the cities of Niigata and Kobe along a northeast-striking Tectonic Zone (NKTZ). Immediately east of the Peninsula lies another north-striking Tectonic Line, from Itoigawa to Shizuoka (ISTL). East of the ISTL and north of the NKTZ is the Island of Sado, which terraces also suggest a change in deformation with strong southeast tilting synchronous and similar to Noto. Together, Noto and Sado act as a railroad switch, indicating which of the ISTL or the NKTZ is the active plate boundary. When the ISTL is active, the sites are on different tectonic plates and evolve differently. When the NKTZ takes over, Sado Island becomes part of Eurasia and is more likely to evolve similarly to the Noto Peninsula.
Malatesta, L.*; Weiss, N.-M.*; 塚本 すみ子*; 末岡 茂; 石村 大輔*; Gailleton, B.*; 西村 卓也*; 高橋 直也*; 片岡 香子*; 小松 哲也; et al.
no journal, ,
On January 1st, 2024, the Mw 7.5 Noto Peninsula earthquake ruptured on a series of coastal offshore reverse faults in the back arc of central Japan. The coastal rocks uplifted as much as 4.4 m. The coastline accordingly moved seaward by up to 200 m creating new wide bedrock platforms. Holocene terraces mapped along the northern coast suggest similar past ruptures. Many of the ruptured faults follow the coast at a depth of ca. 60 m below modern sea level, which strongly suggests that these faults define the extent of the continental domain. The Peninsula itself hosts 4767 unique mapped terraces ranging in age from Holocene to 1.02 Ma. The terraces associated with the last two interglacial high stands record a tectonic SE-tilting similar to that of the Mw 7.5 earthquake. Older terraces all record a spatially uniform rate of uplift across the Peninsula. We conclude that the faults that caused the most recent earthquake became the dominant structures on the Peninsula around 250 ka and that the Peninsula is in a state of transient equilibration. 80 km to the northeast of the Noto Peninsula lies the Island of Sado. The Island is made of two mountain ranges oriented SW-NE along the main tectonic lineation of the back arc, roughly parallel to the northern coast of Noto Peninsula. The marine terraces of the northern range, Oosado, record a strong southeast tilting synchronous and similar to that observed on the Noto Peninsula. The landscape morphology is not equilibrated to this pattern of deformation either. Earlier work suggested a hypothesis that the tilt is driven by a fault lying just offshore of the Oosado coast. Closer inspection of the bathymetry reveals a ramp at around -60 m reflecting a geometry similar to the Noto Peninsula. The lessons from the Noto Peninsula earthquake can be applied to Sado Island where information about the seismic cycle is lacking. It confirms the hypothesis and highlights a potential seismogenic source close to the shore.
Malatesta, L.*; 末岡 茂; 片岡 香子*; 小松 哲也; 塚本 すみ子*; Bruhat, L.*; Olive, J.-A.*
no journal, ,
On January 1st 2024, a Mw 7.6 earthquake shook the Noto Peninsula on the Sea of Japan coast of Central Japan. A large number of landslides and rockfalls dissected the road network. Liquefaction damaged infrastructure up to 150 km away from the epicenter. Meter-scale coseismic uplift modified the northern shoreline with displacement of the coastline by up to 200 m seaward discernible on SAR and aerial image data. At the time of abstract submission, we only have limited preliminary observations. It appears that the Noto Earthquake ruptured the same or adjacent fault to the May 5 2023 Mw 6.5 earthquake and was in the vicinity of the March 25 2007 Mw 6.9 Noto earthquake. Coseismic displacement measured geodetically shows uplift of up to +3-4 m (SAR) in the northwest of the peninsula, and +1.06 m (GPS) in the main town of Wajima-shi. The uplift magnitude decreases gradually to the SE. The uplift is near zero (SAR) or -0.3 m (GPS) on Noto Island 30 km to the south of the town of Wajima. Surface deformation goes back to near zero (GPS) a further 20 km to the south. The coseismic deformation pattern broadly reflects the deformation recorded in the Noto landscape. Long-term moderate rock uplift in the north gives way to a complex history of long-term slow uplift around Noto Island that likely includes sustained episodes of subsidence, highlighted by its sinuous "drowned" coastline. Along the western shore, marine terraces presumed to be 120 ka (last Interglacial) show a gradient in elevation also decreasing to the south. In the north, the newly emerged platform does not have a higher marine terrace counterpart. This may reflect the relationship between high wave power and moderate rock uplift resulting in the long-term retreat of the coastline and erosion of any terrace. The Noto Peninsula also holds widespread evidence of drainage reorganization that would reflect varying boundary conditions, in particular rock uplift, in deeper time beyond 100s ka.
