Sedimentary features of the seismo-turbidites, Lake Biwa, Japan

Fujiwara

et al. 2016

Earth-Science Reviews

Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACTThe Nankai-Suruga Trough, the subduction zone that lies immediately south of Japan's densely populated southern coastline, generates devastating great earthquakes (magnitude > 8) characterised by intense shaking, crustal deformation and tsunami generation. Forecasting the hazards associated with future earthquakes along this >700 km long fault requires a comprehensive understanding of past fault behaviour. While the region benefits from a long and detailed historical record, palaeoseismology has the potential to provide a longer-term perspective and additional crucial insights. In this paper, we summarise the current state of knowledge regarding geological evidence for past earthquakes and tsunamis along the Nankai-Suruga Trough. Incorporating literature originally published in both Japanese and English and enhancing available results with new age modelling approaches, we summarise and critically evaluate evidence from a wide variety of sources. Palaeoseismic evidence includes uplifted marine terraces and biota, marine and lacustrine turbidites, liquefaction features, subsided marshes and tsunami deposits in coastal lakes and lowlands. While 75 publications describe proposed evidence from more than 70 sites, only a limited number provide compelling, well-dated evidence. The best available records enable us to map the most likely rupture zones of twelve earthquakes that occurred during the historical period. This spatiotemporal compilation suggests that the AD 1707 earthquake ruptured almost the full length of the subduction zone and that earthquakes in AD 1361 and 684 may have been predecessors of similar magnitude. Intervening earthquakes were of lesser magnitude, highlighting the variability in rupture mode that characterises the Nankai-Suruga Trough. Intervals between ruptures of the same seismic segment range from less than 100 to more than 450 years during the historical period. Over longer timescales, palaeoseismic evidence suggests intervals between earthquakes ranging from 100 to 700 years, however these figures reflect a range of thresholds controlling the creation and preservation of evidence at any given site as well as the genuine intervals between earthquakes. At present, there is no geological data that suggest the occurrence of a larger magnitude earthquake than that experienced in AD 1707, however few studies have sought to establish the relative magnitudes of different earthquake and tsunami events along the Nankai-Suruga Trough. Alongside the lack of...

Section: The Western Tōnankai (C) Segmentmentioning

confidence: 99%

Section: The Western Tōnankai (C) Segmentmentioning

confidence: 99%

A systematic review of geological evidence for Holocene earthquakes and tsunamis along the Nankai-Suruga Trough, Japan

Fujiwara

et al. 2016

Earth-Science Reviews

Nat. Hazards Earth Syst. Sci.

“…GBs are associated with turbidity currents triggered by either flood events or mass movements (e.g. Sturm and Matter, 1978;Shiki et al, 2000;Arnaud et al, 2002;Mulder and Chapron, 2011;Wilhelm et al, 2012b). In the latter case, they are formed by the sediment that is transported in suspension during the mass movement and then deposited over the mass-wasting deposits and/or further in the lake basin (e.g.…”

Section: Trigger Of Msb Hb Gb-iii and The Deformed Layermentioning

confidence: 99%

“…In the latter case, they are formed by the sediment that is transported in suspension during the mass movement and then deposited over the mass-wasting deposits and/or further in the lake basin (e.g. Shiki et al, 2000;Schnellmann et al, 2005). These mass-movement-induced GBs are also known to be generally thicker than those induced by flood events because mass movements may mobilize much larger quantities of sediments than floods (e.g.…”

Section: Trigger Of Msb Hb Gb-iii and The Deformed Layermentioning

confidence: 99%

“…These mass-movement-induced GBs are also known to be generally thicker than those induced by flood events because mass movements may mobilize much larger quantities of sediments than floods (e.g. Shiki et al, 2000;Schnellmann et al, 2005;Fanetti et al, 2008;Wilhelm et al, 2013). Accordingly, the rare GB-III characterized by large thicknesses may be associated with mass movements.…”

Section: Trigger Of Msb Hb Gb-iii and The Deformed Layermentioning

confidence: 99%

See 1 more Smart Citation

A multi-centennial record of past floods and earthquakes in Valle d'Aosta, Mediterranean Italian Alps

Wilhelm

Vogel

Anselmetti

2017

Abstract. Mediterranean Alpine populations are particularly exposed to natural hazards like floods and earthquakes because of both the close Mediterranean humidity source and the seismically active Alpine region. Knowledge of longterm variability in flood and earthquake occurrences is of high value since it can be useful to improve risk assessment and mitigation. In this context, we explore the potential of a lake-sediment sequence from Lago Inferiore de Laures in Valle d'Aosta (Northern Italy) as a long-term record of past floods and earthquakes. The high-resolution sedimentological study revealed 76 event layers over the last ca. 270 years; 8 are interpreted as most probably induced by earthquakes and 68 by flood events. Comparison to historical seismic data suggests that the recorded earthquakes are strong (epicentral Medvedev-Sponheuer-Kárník (MSK) intensity of VI-IX) and/or close to the lake (distance of 25-120 km). Compared to other lake-sediment sequences, Lago Inferiore de Laures sediments appear to be regionally the most sensitive to earthquake shaking, offering a great potential to reconstruct the past regional seismicity further back in time. Comparison to historical and palaeoflood records suggests that the flood signal reconstructed from Lago Inferiore de Laures sediments represents the regional and (multi-)decadal variability of summer-autumn floods well, in connection to Mediterranean mesoscale precipitation events. Overall, our results reveal the high potential of Lago Inferiore de Laures sediments to extend the regional earthquake and flood catalogues far back in time.

Quantified sensitivity of small lake sediments to record historic earthquakes: Implications for paleoseismology

et al. 2016

Seismic hazard assessment is a critical but challenging issue for modern societies. A key parameter to be estimated is the recurrence interval of damaging earthquakes. This requires the establishment of earthquake records long enough to be relevant, i.e., far longer than historical observations. We study how lake sediments can be used for this purpose and explore conditions that enable lake sediments to record earthquakes. This was achieved (i) through the compilation of eight lake-sediment sequences from the European Alps to reconstruct chronicles of mass movement deposits and (ii) through the comparison of these chronicles with the well-documented earthquake history. This allowed 24 occurrences of mass movements to be identified, of which 21 were most probably triggered by an earthquake. However, the number of earthquake-induced deposits varies between lakes of a same region, suggesting variable thresholds of the lake sequences to record earthquake shaking. These thresholds have been quantified by linking the mass movement occurrences in a single lake to both intensity and distance of the triggering earthquakes. This method offers a quantitative approach to estimate locations and intensities of past earthquake epicenters. Finally, we explored which lake characteristics could explain the various sensitivities. Our results suggest that sedimentation rate should be larger than 0.5 mm yr À1 so that a given lake records earthquakes in moderately active seismotectonic regions. We also postulate that an increasing sedimentation rate may imply an increasing sensitivity to earthquake shaking. Hence, further paleoseismological studies should control carefully that no significant change in sedimentation rates occurs within a record, which could falsify the assessment of earthquake recurrence intervals.