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Localities of Holocene tsunami deposits. Subduction zone earthquakes which occured along the Nankai-Suruga Troughs are classified according to rupture areas; Nankai, Tonankai and Tokai Earthquakes, shown by the Headquarters for Earthquake Research Promotion, Japan. Those along the Sagami Trough are called Kanto earthquakes. See Table 1 for references.

Localities of Holocene tsunami deposits. Subduction zone earthquakes which occured along the Nankai-Suruga Troughs are classified according to rupture areas; Nankai, Tonankai and Tokai Earthquakes, shown by the Headquarters for Earthquake Research Promotion, Japan. Those along the Sagami Trough are called Kanto earthquakes. See Table 1 for references.

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Tsunami deposits provide a basis for reconstructing Holocene histories of great earthquakes and tsunamis on the Pacific Coast of southwest Japan. The deposits have been found in the past 15 years at lakes, lagoons, outcrops, and archaeological excavations. The inferred tsunami histories span 3000 years for the Nankai and Suruga Troughs and nearly 1...

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... first discovery of tsunami deposits along the Nankai and Suruga Troughs was reported from an archeological site near Lake Hamanako ( Fig. 1) and sand bar deposits at the lake inlet (NISHINAKA et al., 1996). They reported sand layers which were transported by the AD 1707 Hoei earthquake tsunami. Subsequently, tsunami deposits correlated with historical tsunami events have been mainly discovered in cored samples from lake deposits in these areas (e.g., OKAMURA et al., ...
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... deposits from the coast of the Sagami Trough were firstly reported by FUJIWARA et al. (1997FUJIWARA et al. ( , 1999a. They discovered the tsunami sands from the Holocene buried valley sequences in the Boso and Miura Peninsulas (Fig. 1). These tsunami deposits were correlated to the emergence of Holocene marine terraces distributed along the southern Kanto District. Historical tsunami deposits also have been discovered on coastal plains along the Sagami Trough. Tsunami deposits attributed to the AD 1498 Meio earthquake, AD 1703 and 1923 Kanto earthquakes were ...
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... deposits attributed to the AD 1498 Meio earthquake, AD 1703 and 1923 Kanto earthquakes were reported from this area (FUJIWARA et al., 2005a,b). Figure 1 shows localities where Holocene tsunami deposits have been discovered. Most of the tsunami deposits were reported from muddy and organic sediments in coastal lakes, lagoons, swamps and lowlands which were enclosed by barriers such as beach ridges during the Holocene (A, B, C, D, E, G, I in Fig. 1). ...
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... from this area (FUJIWARA et al., 2005a,b). Figure 1 shows localities where Holocene tsunami deposits have been discovered. Most of the tsunami deposits were reported from muddy and organic sediments in coastal lakes, lagoons, swamps and lowlands which were enclosed by barriers such as beach ridges during the Holocene (A, B, C, D, E, G, I in Fig. 1). Low-energy lake and lagoon environments have high preservation potential of tsunami deposits. Washover sand into the lakes and lagoons recorded as an abrupt facies change in stratigraphic record. Such event deposits are rapidly covered by a high sediment flax in the lakes and lagoons, and protected from subsequent ...
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... deposits are sometimes found in archeological excavation sites (F, H, K in Fig. 1). They are mainly represented as an unusual layer composed of clean, well-sorted marine sand, overspreading a ruin (e.g., KUMAGAI, ...
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... to the coastal erosion. Tsunami deposits, in contrast, have relative high preservation potential under the coastal lowland including the shallow bay. On the other hand, tsunamis from the outer side of the Age distribution of tsunami deposits for each locality, showing recent 10,000 years. A -O are localities of discovered tsunami deposits (see Fig. 1). See text for classification of tsunami deposits. KgP: Kawagodaira Pumice, K-Ah: Kikai-Akahoya Tephra. A magnified diagram of recent 15,000 years (rectangle) is shown in Figure ...

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Citations

... Garrett et al., 2015;Meltzner et al., 2010;Natawidjaja et al., 2004;Nelson et al., 1996;Shennan et al., 2016), tsunami inundation (e.g. Kempf et al., 2017;Komatsubara & Fujiwara, 2007;Pinegina et al., 2017), and the identification of coseismic deposits and/or sedimentary structures in subaquatic settings (e.g. Avşar et al., 2016;Goldfinger et al., 2017;Howarth et al., 2014;Moernaut et al., 2014;Praet et al., 2017;St-Onge et al., 2012). ...
... Goldfinger et al., 2003;Kuehl et al., 2017) and the search for tsunami deposits (e.g. Kempf et al., 2017;Komatsubara & Fujiwara, 2007) or biological and sedimentological indicators for co-seismic elevation changes (e.g. Garrett et al., 2015;Philibosian et al., 2017) in coastal areas. ...
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About 90% of the world’s earthquakes occur along the ‘Ring of Fire’, a horseshoe-shaped belt surrounding the Pacific Ocean. This seismically highly active zone consists of a quasi-continuous series of subduction trenches, formed at convergent plate boundaries. The process of subduction, where one lithospheric plate subducts below the other due to a density contrast, is associated with the largest and most destructive earthquakes on Earth. These are capable of reaching moment magnitudes (Mw) of 9.0 or higher, nucleating at the interface between the two convergent lithospheric plates (megathrust earthquake). Recent examples include the 2004 Sumatra-Andaman earthquake (Mw 9.1) and the 2011 Tohoku earthquake in Japan (Mw 9.0). These earthquakes are respectively the deadliest and costliest earthquakes of the 21st century, which includes the losses caused by the tsunami wave that is typically generated during these megathrust earthquakes. As a result, subduction zones are an important target for natural hazard studies, aiming at estimating and mitigating the impact of future earthquakes and potentially associated tsunamis on communities at risk. A key aspect in seismic hazard assessment is understanding the earthquake recurrence mode and rate. For this purpose, numerous paleoseismic studies have explored the seismic history of subduction zones around the world by studying, for example, coastal marshes, coral microatolls as well as lakes, fjords and offshore environments. The sedimentary record of lakes and fjords in particular has proven exceptionally suitable for reconstructing the paleoseismological history of a specific region through the identification of multiple synchronous seismically-generated landslides and/or turbidites within the same basin. Most paleoseismic studies of subduction zones tend to focus on tsunamigenic, high-magnitude earthquakes in particular. Nevertheless, additional destructive earthquakes can occur in subduction-zone settings, i.e. within the subducting slab (intraslab earthquake) or overriding plate (crustal earthquake) rather than at the plate boundary. This is demonstrated by, for example, the 2017 Chiapas intraslab earthquake in Mexico (MW 8.2), with just under 100 casualties and an estimated economic cost that amounts to US$ 2 billion, or the 2006 Yogyakarta crustal earthquake in Indonesia (MW 6.4), resulting in over 5,700 casualties and US$ 3 billion of financial losses as a result of the high population density and poor construction practices in the affected area. This underscores the significant contribution of intraplate earthquakes to the imminent seismic hazard in subduction zones, which is often neglected in current paleoseismic research. This highlights the urgent need for more inclusive studies of the shaking history in these areas. To meet the underrepresentation of intraplate earthquakes in paleoseismic research, this dissertation is focused on two particular areas along the ‘Ring of Fire’ (southern Chile and Sumatra), where inter- as well as intraplate earthquakes are known to occur. More specifically, these are located in a context of oblique subduction, resulting in clustering of crustal earthquakes along extensive strike-slip fault systems that accommodate the trench-parallel component of plate convergence. To disentangle the contribution of each of the different types of earthquake sources that results in coseismic movement (i.e. deformation and/or shaking) of the considered area, we combine a series of seismotectonic and sedimentological approaches. In this way, we aim to advance our current knowledge on the interplay between megathrust, crustal and intraslab earthquakes and improve future seismic hazard assessments.
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... Tsunamis following two M9-class earthquakes that occurred in close succession in the 21st century, the 2004 CE Indian Ocean tsunami and 2011 CE Tōhoku tsunami, have provided a clear incentive to study the record of past tsunamis and incorporate paleotsunami data into forecasts of future events. Results of paleotsunami studies along the Nankai and Sagami Troughs up to 2006 CE are summarized in Komatsubara and Fujiwara (2007). Garrett et al. (2016) provides a comprehensive review of the recurrence history of great Nankai Trough earthquakes in the Middle to Late Holocene, including not only tsunami deposits and liquefaction features on land, but also marine and lacustrine turbidites. ...
... The two older deposits formed between 4000 and 3000 cal BP; storm surges and tidal channel migration also remain possible explanations for them. The three youngest deposits are linked with tsunami inundation in 1707, 1605 and 1498 CE by Tsuji et al. (1998) and Komatsubara and Fujiwara et al. (2007); however, more recent recalibration of radiocarbon data highlights difficulties with ascribing particular historical tsunamis to these deposits (Garrett et al., 2016). Sato et al. (2016b) identified a marine incursion event around 4790-4420 cal. ...
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... For example, overwash deposits from high-energy flood events that are preserved within the sedimentary sequences of coastal environments, such as those from back-barrier lakes and marshes, can be used to reconstruct pre-instrumental tsunami and typhoon frequency and intensity (e.g. Komatsubara and Fujiwara 2007;Komatsubara et al. 2008;Chagué-Goff et al. 2012;Wallace et al. 2014;Brandon et al. 2015; Baranes et al. 2016Baranes et al. , 2018Chaumillon et al. 2017). The sandy overwash deposits left by tsunamis and typhoons can often have very similar characteristics including being composed of coarse-grained beach material, exhibiting a lateral thinning landward, and containing elemental signatures consistent with marine-derived sediments. ...
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... Paleoseismic evidence along the Nankai-Suruga Trough were summarized in Komatsubara and Fujiwara (2007) and Garrett et al. (2016). Geological evidence of tsunamis has been studied at coastal ponds in Kochi Prefecture. ...
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This study investigates the Holocene sedimentary history of a small coastal lowland in Nankoku, Kochi Prefecture, on the coast of southern Japan facing the Nankai Trough. The sedimentary fill of the lowland area consists mainly of marine-brackish clay overlain by beds of freshwater clay and peat. We found four laterally extensive sand sheets, one directly underlying the freshwater deposits and the other three interbedded with them. Radiocarbon dates show that these sand sheets were deposited between 5970 and 2440 cal. BP. Although the sand sheets contained few marine-brackish diatoms, they were concentrated in the seaward part of the study site, suggesting that they were deposited by marine inundations. These sand sheets were formed as a result of tsunamis or unusually large storm surges. The apparent frequency of marine inundations during 5970–2440 cal. BP was much lower than that of megathrust earthquakes along the Nankai Trough recorded during the last 1300 years. Event deposits were absent between 2440 and 960 cal. BP, a gap that we attribute to the development of beach ridges. The new marine inundation records reported here will aid efforts to reconstruct the timing and recurrence intervals of megathrust earthquakes in the western Nankai Trough.
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Japanese historical documents reveal that Mw 8 class earthquakes have occurred every 100–150 years along the Suruga and Nankai troughs since the 684 Hakuho earthquake. These earthquakes have commonly caused large tsunamis with wave heights of up to 10 m in the Japanese coastal area along the Suruga and Nankai troughs. From the perspective of tsunami disaster management, these tsunamis are designated as Level 1 tsunamis and are the basis for the design of coastal protection facilities. A Mw 9.0 earthquake (the 2011 Tohoku-oki earthquake) and a mega-tsunami with wave heights of 10–40 m struck the Pacific coast of the northeastern Japanese mainland on 11 March 2011, and far exceeded pre-disaster predictions of wave height. Based on the lessons learned from the 2011 Tohoku-oki earthquake, the Japanese Government predicted the tsunami heights of the largest-possible tsunami (termed a Level 2 tsunami) that could be generated in the Suruga and Nankai troughs. The difference in wave heights between Level 1 and Level 2 tsunamis exceeds 20 m in some areas, including the southern Izu Peninsula. This study reviews the distribution of prehistorical tsunami deposits and tsunami boulders during the past 4000 years, based on previous studies in the coastal area of Shizuoka Prefecture, Japan. The results show that a tsunami deposit dated at 3400–3300 cal BP can be traced between the Shimizu, Shizuoka and Rokken-gawa lowlands, whereas no geologic evidence related to the corresponding tsunami (the Rokken-gawa–Oya tsunami) was found on the southern Izu Peninsula. Thus, the Rokken-gawa–Oya tsunami is not classified as a Level 2 tsunami.
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... Atwater et al., 2005;Cisternas et al., 2005;Jankaew et al., 2008;Sawai et al., 2012;Shennan et al., 2014a). Previous reviews by Komatsubara et al. (2006a) and Komatsubara and Fujiwara (2007) summarise the spatial and temporal distribution of proposed palaeoseismic evidence along the Nankai-Suruga Trough. While these studies conclude that geological evidence is generally consistent with historical data, they note the difficulties in accurately dating evidence and in reconstructing past earthquake or tsunami characteristics from individual sites. ...
... Geological evidence suggests that the earthquakes of 1361 CE and 684 may have been of similar rupture length. There is no published geological evidence that currently suggests that earthquakes with longer rupture lengths have occurred along the Nankai-Suruga Trough; however, few attempts have been made to use geological evidence to compare the absolute or relative magnitudes of different historical or prehistoric earthquakes in this region (Komatsubara and Fujiwara, 2007;Komatsubara et al., 2006a). ...
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