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See detailA 3800 yr paleoseismic record (Lake Hazar sediments, eastern Turkey): Implications for the East Anatolian Fault seismic cycle
Hubert, Aurelia ULiege; Lamair, Laura ULiege; Hage, Sophie et al

in Earth and Planetary Science Letters (2020), 538

The East Anatolian Fault (EAF) in Turkey is a major active left-lateral strike-slip fault that was seismically active during the 19th century but mostly quiet during the 20th century. Geodetic data ... [more ▼]

The East Anatolian Fault (EAF) in Turkey is a major active left-lateral strike-slip fault that was seismically active during the 19th century but mostly quiet during the 20th century. Geodetic data suggests that the fault is creeping along its central part. Here we focus on its seismic history as recorded in the sediments of Lake Hazar in the central part of the EAF. Sediment cores were studied using X-ray imagery, magnetic susceptibility, grain-size, loss-on-ignition and X-ray fluorescence measurements. Recurring thin, coarse-grained sediment units identified as turbidites in all cores were deposited synchronously at two deep study sites. The turbidite ages are inferred combining radiocarbon and radionuclide (137Cs and 210Pb) dating in an Oxcal model. A mean recurrence interval of ~190 years is obtained over 3800 yrs. Ages of the recent turbidites correspond to historical earthquakes reported to have occurred along the EAF Zone or to paleoruptures documented in trenches just northeast of Lake Hazar. The turbidites are inferred to be earthquake-triggered. Our record demonstrates that Lake Hazar has been repeatedly subjected to significant seismic shaking over the past 3800 years. The seismic sources are variable: ~65% of all turbidites are associated with an EAF source. The seismic cycle of central EAF is thus only partly impacted by creep. [less ▲]

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See detailQuestion about the seismic cycle of the East Anatolian Fault and its seismic versus aseismic behavior
Hubert, Aurelia ULiege; Lamair, Laura ULiege; Hage, Sophie et al

Conference (2019, January 29)

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See detailUse of high-resolution seismic reflection data in the paleogeographical reconstruction of shallow Lake Yamanaka (Fuji Five Lakes, Japan)
Lamair, Laura ULiege; Hubert, Aurelia ULiege; Yamamoto, S. et al

in Palaeogeography, Palaeoclimatology, Palaeoecology (2019), 514

High-resolution seismic profiles, combined with the integration of published drilling data, provide a detailed paleoenvironmental history of Lake Yamanaka (Fuji Five Lakes, Japan). This study presents a ... [more ▼]

High-resolution seismic profiles, combined with the integration of published drilling data, provide a detailed paleoenvironmental history of Lake Yamanaka (Fuji Five Lakes, Japan). This study presents a detailed analysis of the different depositional stages of the area currently occupied by Lake Yamanaka (floodplain wetland, river and lake). From ca. 5500 cal yr BP to ca. 5050 cal yr BP, the Yamanaka basin was occupied by floodplain wetlands. During that period, the landscape was very stable and erosion on northeastern flank of Mt. Fuji was relatively limited. From ca. 5050 cal yr BP to ca. 3050 cal yr BP, the water level increased and the floodplain wetlands became a lake. From ca. 3050 cal yr BP to ca. 2050 cal yr BP, the water level progressively decreased, leading to a reduction in lake extent. During this lowering of the lake's water level, a 1 km2 mass-transport deposit modified the physiography of the lake floor. From ca. 2050 cal yr BP to ca. 1050 cal yr BP, the lake disappeared and a river flowing towards the northwest occupied the depression. Ponds occupied morphological lows formed by mass transport deposits. From ca. 1050 cal yr BP to the present day, the lake water level rose again, connecting the ponds with the main lake. Since then, the lake water level has continued to rise to the current level. Lake water level fluctuations are the results of several factors that could be interconnected: (i) changes in precipitation rates; (ii) margin destabilization (the Yamanaka mass-transport deposit), (iii) changes in river inlets and therefore variation in water supplies, (iv) volcanic eruptions (scoria fall-out and lava flows) and (v) changes in vegetation cover. This study highlights the importance of coupling sediment cores and high-resolution seismic reflection profiling to identify lateral variation and modification of sedimentary inputs through time. [less ▲]

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See detailPaleoearthquakes recorded in the Fuji Five Lakes during the last ca. 6000 years (Fuji Five Lakes, Japan
Lamair, Laura ULiege; Hubert, Aurelia ULiege; Yamamoto, Shinya et al

Conference (2018, May)

In Japan, one pioneering lacustrine paleoseismological study was conducted in Lake Biwa in the 1990s. However, despite the high seismicity of Japan, the field of lacustrine paleoseismology did not expand ... [more ▼]

In Japan, one pioneering lacustrine paleoseismological study was conducted in Lake Biwa in the 1990s. However, despite the high seismicity of Japan, the field of lacustrine paleoseismology did not expand. Paleoseismological studies were more focused on inland trenches and coastal records. The paleoseismological data obtained by that way covers the last ~6000 years but contains hiatuses. Using lacustrine sediment allows us to span the same time period and to have a continuous record. Here, we present the second lacustrine paleoseismological study conducted in Japan. The Fuji Five Lakes are situated close to the triple junction, where the North American Plate, the Eurasian plate and the Philippine Sea Plate meet. Therefore, the region can be impacted by megathrust earthquakes generated along the Nankai-Suruga and the Sagami subduction zones. In addition, intraplate earthquake may affect the Fuji Five Lakes region. In the framework of the QuakeRecNankai project, we investigated two of the Fuji Five Lakes, Lake Motosu and Lake Sai. Here, we present the paleoseismological record of Lake Motosu and Lake Sai over the last 6000 and 2000 years, respectively. The turbidites were identified based on geophysical (magnetic susceptibility, grainsize) and geochemical properties (XRD, XRF) as well as SEM analysis. The turbidites were dated by 210Pb/137Cs, 14C dating and correlated with historical earthquakes. For prehistorical earthquakes (i.e., before the 6th century), they were correlated with geological evidences recorded along the Eastern Honshu coastline (i.e., tsunami deposits, coastal uplift, emerged ridge beaches). Over the last 6000 years, seismo-turbidites occurred with a mean recurrence time of 184±8 years. The near absence of large mass-transport deposits in the last 6000 years suggest that earthquake shaking mostly induced the remobilization of thin veneers of sediments in Lake Motosu. In Lake Sai, the earthquake fingerprint differs from Lake Motosu. Over the last 1200 years, past earthquake shaking induced turbidites, delta collapse and liquefaction (sediment volcanoes). [less ▲]

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See detailNatural hazards recorded in the Fuji Five Lakes: earthquake shaking, typhoon induced flooding and volcanic eruptions ral hazards recorded in the Fuji Five Lakes: earthquake shaking, typhoon induced flooding and volcanic eruptions
Hubert, Aurelia ULiege; Lamair, Laura ULiege; Yamamoto, Shinya et al

Conference (2018, May)

The 2014-2018 QuakeRecNankai project (acronym for "Paleo-tsunami and earthquake records of ruptures along the Nankai Trough, offshore South-Central Japan") funded by the Belgium Sciences Policy Office ... [more ▼]

The 2014-2018 QuakeRecNankai project (acronym for "Paleo-tsunami and earthquake records of ruptures along the Nankai Trough, offshore South-Central Japan") funded by the Belgium Sciences Policy Office focuses on the Fuji Five Lake area (central Japan) with the aim of a better understanding of the spatial and temporal recurrence of natural disasters. The region is susceptible to be impacted by natural hazards such as earthquake shaking, typhoon-induced floods and volcanic eruptions. The study location for natural hazard disaster is highly relevant since Mt. Fuji and the Fuji Five Lakes were recognized as a world heritage site in 2013 with about 300 000 tourists visiting the area every year. Within the framework of the project, the lacustrine sediments from Lake Motosu, Lake Sai and Lake Yamanaka were investigated and used to reconstruct the natural hazard history of the region. In the sedimentary infill of Lake Motosu, mass-transport deposits and turbidites triggered by earthquakes were recorded. Over the last ca. 6000 years, the mean recurrence time of seismic event triggering turbidites in Lake Motosu is 184±8 years. A comparison between the age of the turbidites and historical and paleoseismological records suggest that earthquake shaking impacting the Fuji Five Lakes area can be attributed mostly to large magnitude earthquakes occurring along the Sagami trench or along the Nankai-Suruga Subduction Zone. The two most recent earthquakes occurring along these subduction zones (i.e., the 1944 Showa Tonankai and the 1923 Kanto earthquakes) were recorded. By contrast with the sedimentary record of Lake Motosu, the lacustrine sediments collected in Lake Sai are a good archive for flood events. Detrital layers associated with the debris flow triggered by the 1966 Typhoon Ida (189 killed people, 3.9 millions yens damages) were identified, as well as other flood events associated with extreme precipitation events. Regarding volcanic eruptions, Lake Yamanaka and its catchment were repeatedly impacted by scoria fall-out due to their proximity to the Mt. Fuji volcano and the westerly wind direction . The last eruption (Hoei, A.D. 1707) strongly affected the lacustrine sedimentation and has a long-term effect on the catchment and on the lake, due to the sealing of the underlying sediments by the thick scoria layer. The geolimnology study of the Fuji Five Lakes gave us a better comprehension of the long-term recurrence of natural hazards affecting the region as well as their effects on the environment. [less ▲]

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See detailNumerical investigation on the seismic performance of aqueduct bridge structures: application to the Antioch on the Orontes Aqueduct (Antakya, Turkey)
Lamair, Laura ULiege; Hubert, Aurelia ULiege; Degée, Hervé et al

E-print/Working paper (2018)

Seismic shaking can damage building, especially historical structures which were not designed with building codes. Here we focus on Roman aqueduct bridge structures, which remains can be found all over ... [more ▼]

Seismic shaking can damage building, especially historical structures which were not designed with building codes. Here we focus on Roman aqueduct bridge structures, which remains can be found all over the Mediterranean area, a highly seismic region. We developed simple models using a finite element software to realize static and dynamic linear analyses of these structures when they are subject to imposed ground motion. The effects of basic variations in the pier-arch architectural design and in the type of material used were investigated. We identified two main weak zones: the arch extremities and the bottom part of the piers. The damage occurrence in these two areas could be attributed to earthquake shaking. Our first-order vulnerability analysis also points to different ways to enhance the structure stability: building narrow arches, adding buttress zones and using bricks which are light materials. Finally, we also investigated the vulnerability to seismic shaking of a real case example, the Antioch on the Orontes Aqueduct in Harbiye (Turkey). The aqueduct shows different stages of constructions, damage areas and repairs. The modeling suggests that the observed damages were the results of earthquake shaking. The repairs reinforced the structure and stabilized it pointing to the adaptive technology and skills of the roman engineers. [less ▲]

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See detailLate Holocene changes on erosion pattern on a lacustrine environment: landscape stabilization by volcanic activity versus human activity
Lamair, Laura ULiege; Hubert, Aurelia ULiege; El Ouahabi, Meriam ULiege et al

in Geochemistry, Geophysics, Geosystems (G3) (2018)

The most recent eruption of Mt. Fuji (Japan), the VEI 5 Hōei plinian eruption (CE 1707) heavily impacted Lake Yamanaka, a shallow lake located at the foot of Mt. Fuji. Here, we discuss the influence of ... [more ▼]

The most recent eruption of Mt. Fuji (Japan), the VEI 5 Hōei plinian eruption (CE 1707) heavily impacted Lake Yamanaka, a shallow lake located at the foot of Mt. Fuji. Here, we discuss the influence of the Hōei eruption on the lacustrine sedimentation of Lake Yamanaka using high resolution geophysical and geochemical measurements on gravity cores. Hōei scoria fall-out had two major impacts on Lake Yamanaka: (i) reduction of the sedimentation rate (from ~0.16 cm/yr to ~0.09 cm/yr); and (ii) the increase of in-situ lake productivity. Sedimentation rates after the eruption were relatively low due to the thick scoria layer, trapping underlying sediments in the catchment. The lacustrine system took over more than ~170 years to begin to recover from the Hōei eruption: sedimentation recovery have been accelerated by changes in land use. Since the beginning of the 20th Century, vegetated strips delimited cultivated parcels, trapping sediment and minimizing the anthropogenic impacts on the sedimentation rate. Over the last decade, the decline of agriculture and the increase of other human activities led to an increase in the sedimentation rate (~1 cm/yr). This study highlights the effect of the grainsize of the volcanic ejecta on the sedimentation rate following a volcanic eruption. Coarse-grained tephra are difficult to erode. Therefore, their erosion and remobilization is largely limited to intense typhoons when porous scoria deposits are saturated by heavy rains. Moreover, this study suggests that recent anthropogenic modifications of the catchment had a greater impact on the sedimentation rate than the Hōei eruption. [less ▲]

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See detailHistorical Nankai-Suruga megathrust earthquakes recorded by tsunami and terrestrial mass movement deposits on the Shirasuka coastal lowlands, Shizuoka Prefecture, Japan
Garrett, Ed; Fujiwara, Osamu; Riedesel, Svenja et al

in Holocene (2018)

Geological investigations of coastal sediment sequences play a key role in verifying earthquake and tsunami characteristics inferred from historical records. In this paper, we present a multi-proxy ... [more ▼]

Geological investigations of coastal sediment sequences play a key role in verifying earthquake and tsunami characteristics inferred from historical records. In this paper, we present a multi-proxy investigation of a coastal lowland site facing the Nankai-Suruga megathrust and appraise evidence for tsunamis and earthquake-triggered terrestrial mass movements occurring over the last 800 years. Combining a high-resolution chronology with X-ray computed tomography and analyses of particle size, diatoms, pollen, non-pollen palynomorphs and aerial photographs, we present the most compelling geological evidence of the 1361 CE Kōan (also known as Shōhei) tsunami reported to date from any site along the megathrust. This finding is consistent with either of two recent hypotheses: a single larger rupture of both the Nankai and Tōnankai regions or two smaller ruptures separated by a few days. Enhancing the site chronology using Bayesian age modelling, we verify evidence for inundation during the 1498 CE Meiō tsunami. While previous investigations identified evidence for historically recorded tsunamis in 1605, 1707 and 1854 CE and a storm surge in 1680 or 1699 CE, we encountered a thick sand layer rather than discrete extreme wave deposits in this interval. The overprinting of evidence highlights the potential for geological records to underestimate the frequency of these events. A terrestrial mass movement also deposited a sand layer at the site; radionuclide dating and aerial photographs provide independent confirmation that this may have been triggered by intense shaking in 1944 CE during the most recent great Nankai-Suruga megathrust earthquake. [less ▲]

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See detailMt. Fuji Holocene eruption history reconstructed from proximal lake sediments and high-density radiocarbon dating
Obrochta, S. P.; Yokoyama, Y.; Yoshimoto, M. et al

in Quaternary Science Reviews (2018), 200

An 8000-year lacustrine sediment record from Lake Motosu (Fuji Five Lakes) records several eruptions, including potentially unreported events, of the active Mt. Fuji volcano, which receives approximately ... [more ▼]

An 8000-year lacustrine sediment record from Lake Motosu (Fuji Five Lakes) records several eruptions, including potentially unreported events, of the active Mt. Fuji volcano, which receives approximately 47 million annual visitors. A high-fidelity age model is constructed from tephra ages and high-density radiocarbon dating of terrestrial macrofossil and bulk organic matter. Variability in lake reservoir age is constrained by modern lake water radiocarbon measurement and reverse calibration of tephra calendar ages. We present more accurate ages for known eruptions, detect a wider distribution of ejecta for several eruptions, including the most recent summit eruption, and potentially identify previously undetected flank eruptions. There are closely spaced scoria-fall layers that may be difficult to differentiate as separate events in land-based surveys. These results demonstrate the utility of lacustrine sediments as powerful tools for understanding characteristics of volcanic eruptions. © 2018 Elsevier Ltd [less ▲]

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See detailVolcanic influence of Mt. Fuji on the watershed of Lake Motosu and its impact on the lacustrine sedimentary record
Lamair, Laura ULiege; Hubert, Aurelia ULiege; Yamamoto, Shinya et al

in Sedimentary Geology (2018), 363

Lacustrine sediments are particularly sensitive to modifications within the lake catchment. In a volcanic area, sedimentation rates are directly affected by the history of the volcano and its eruptions ... [more ▼]

Lacustrine sediments are particularly sensitive to modifications within the lake catchment. In a volcanic area, sedimentation rates are directly affected by the history of the volcano and its eruptions. Here, we investigate the impact of Mt. Fuji Volcano (Japan) on Lake Motosu and its watershed. The lacustrine infill is studied by combining seismic reflection profiles and sediment cores. We show evidence of changes in sedimentation patterns during the depositional history of Lake Motosu. The frequency of large mass-transport deposits recorded within the lake decreases over the Holocene. Before ~8000 cal yr BP, large sublacustrine landslides and turbidites were filling the lacustrine depression. After 8000 cal yr BP, only one large sublacustrine landslide was recorded. The change in sedimentation pattern coincides with a change in sediment accumulation rate. Over the last 8000 cal yr BP, the sediment accumulation rate was not sufficient enough to produce large sublacustrine slope failures. Consequently, the frequency of large masstransport deposits decreased and only turbidites resulting from surficial slope reworking occurred. These constitute the main sedimentary infill of the deep basin. We link the change in sediment accumulation rate with (i) climate and vegetation changes; and (ii) theMt. Fuji eruptions which affected the LakeMotosu watershed by reducing its size and strongly modified its topography. Moreover, this study highlights that the deposition of turbidites in the deep basin of Lake Motosu is mainly controlled by the paleobathymetry of the lakefloor. Two large mass-transport deposits, occurring around ~8000 cal yr BP and ~2000 cal yr BP respectively, modified the paleobathymetry of the lakefloor and therefore changed the turbidite depositional pattern of Lake Motosu. [less ▲]

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See detailSingle-grain feldspar luminescence chronology of historical extreme wave event deposits recorded in a coastal lowland, Pacific coast of central Japan
Riedesel, Svenja; Brill, Dominik; Roberts, Helen et al

in Quaternary Geochronology (2018), 45

The Shirasuka lowlands, located on the Enshu-nada coast of central Japan, record evidence for numerous ex- treme wave events. Here we test the applicability of using the luminescence signal from feldspars ... [more ▼]

The Shirasuka lowlands, located on the Enshu-nada coast of central Japan, record evidence for numerous ex- treme wave events. Here we test the applicability of using the luminescence signal from feldspars to date these young (< 1000 a) extreme wave event deposits. The signal used for dating is the IRSL signal (measured at 50 °C) as part of a post-IR IRSL130 procedure. We demonstrate that this IRSL50 (pre-IR130) signal results in reliable ages when corrected for fading, and the post-IR IRSL130 stimulation functions as an optical wash for both the natural/ regenerated luminescence signal (Lx) and the test dose signal (Tx), lowering the recuperation and removing any remaining charge from previous steps in the protocol. The single grain IRSL50 (pre-IR130) ages generated cover the historical record of the past 800 years and correlate well with past earthquakes and tsunamis in 1361 CE, 1498 CE and 1605 CE. Another identified tsunami deposit may correlate with the 1707 CE earthquake and tsunami. A slope failure deposit, probably caused by the earthquake in 1944 CE, is also identified. This study demonstrates that accurate ages can be determined for the young, extreme wave events at this site using the luminescence signal from feldspars. [less ▲]

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See detailMt. Fuji Holocene eruption history reconstructed from proximal lake sediments and high-density radiocarbon dating
Obrochta, Steve; Yokoyama, Yusuke; Yoshimoto, Mitsuhiro et al

in American Geophysical Union, Fall Meeting 2017 abstract (2017, December)

Understanding the eruption history of volcanos located near large population centers is of direct societal relevance. Here we present a 8,000-year lacustrine record that includes previously unreported ... [more ▼]

Understanding the eruption history of volcanos located near large population centers is of direct societal relevance. Here we present a 8,000-year lacustrine record that includes previously unreported eruptions of the active Mt. Fuji volcano, which receives approximately 47 million annual visitors with another 40 million living in the adjacent Kanto Plain. A high-fidelity age model is constructed from a number of terrestrial macrofossil and bulk organic radiocarbon measurements and is extremely consistent with the independently determined age of diagnostic tephra layers. In addition to reporting new eruptions, we also present more accurate ages for known eruptions and detect a wider distribution of ejecta for the most recent summit eruption, that latter of which will alter modeled prevailing wind vector during eruption. Furthermore, closely spaced fall-scoria layers, unlikely to be differentiated as separate events in land-based surveys, will lower the estimated mass of ejecta erupted and in turn reduce calculated magnitude. These results, the first of their kind from a highly populated region, demonstrate the utility of lacustrine sediments as powerful tools for understanding characteristics of volcanic eruptions and will improve disaster mitigation plans for the region. [less ▲]

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See detailUsing lacustrine sediments to record past natural hazards: The case of Fuji Five Lakes (Japan)
Lamair, Laura ULiege; Hubert, Aurelia ULiege; Yamamoto, Shinya et al

Scientific conference (2017, November 17)

In this presentation, we will focus on the Fuji Five Lakes region. Since 2013, Mt. Fuji and the Fuji Five Lakes area (Lake Motosu, Lake Shoji, Lake Sai, Lake Kawaguchi and Lake Yamanaka) are added on the ... [more ▼]

In this presentation, we will focus on the Fuji Five Lakes region. Since 2013, Mt. Fuji and the Fuji Five Lakes area (Lake Motosu, Lake Shoji, Lake Sai, Lake Kawaguchi and Lake Yamanaka) are added on the world heritage list of UNESCO. Mt. Fuji is a main touristic attraction in Japan bringing each year 300 000 tourists. The Fuji Five Lakes are located at the foot of Mt. Fuji Volcano close to the triple junction where the North American Plate, the Eurasian plate and the Philippine Sea Plate meet. Therefore, the region can be impacted by Mt. Fuji volcanic eruption as well as by large magnitude earthquakes. Additionally, nearly every year, Japan is hit by strong winds, heavy rains with flood, landslides and high waves. These natural hazards may affect the Japanese economy by causing casualties and infrastructure damage. In the regions frequently affected by natural disasters like Japan, it is crucial to have a better knowledge of the recurrence times of such disasters in order to refine the probabilistic models. For that purpose, lacustrine sediments are often used. Lacustrine sediments retrieving by coring offer several advantages compared to onland drilling: the method is cheaper, the cores are easier to take and they have longer temporal span. Lacustrine sediments are generally good archives to record past natural hazards. However, each lake has its own particular setting and a different sensitivity to record paleohazards. Coupling geophysical data, sedimentological analysis and historical records is often required to identify natural paleohazards in the sedimentary records and to define the threshold sensitivity of the lake. Here, we will used Fuji Five Lakes as natural laboratory for the recording of paleohazards (typhoons, earthquakes and volcanic eruptions) and will discuss the sedimentary record of Lake Motosu, Lake Sai, Lake Yamanaka and Lake Kawaguchi over the last ca. 6000 years regarding their geomorphological characteristics. [less ▲]

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See detailA 3000 yr paleoseismological history of the central East Anatolian Fault (Turkey) based on sedimentary record of Hazar Lake
Lamair, Laura ULiege; Hubert, Aurelia ULiege; Hage, Sophie et al

Poster (2017, October 10)

The East Anatolian Fault (EAF) is a major left-lateral strike-slip fault accommodating with the conjugate North Anatolian Fault the westward extrusion of the Anatolian Plate away from the Arabia-Eurasia ... [more ▼]

The East Anatolian Fault (EAF) is a major left-lateral strike-slip fault accommodating with the conjugate North Anatolian Fault the westward extrusion of the Anatolian Plate away from the Arabia-Eurasia collision zone. During the 20th century, the EAF activity was mostly quiestcent with only two events of magnitude greater than 6 recorded (1905 Malatya and the 1971 Bingol earthquakes). Historical seismicity suggests that the EAF is capable of generating earthquakes of magnitude greater than 7. In order to retrace the seismic history of the EAF in its central part, we study Hazar Lake. Hazar Lake is a 20 km long pull-apart basin with a maximum depth of 216 m. Short cores and long sediment cores were collected at four different sites to retrieve a paleoseismological record. Detailed analysis of the sediment cores (e.g. magnetic susceptibility, XRF, XRD, thin sections) were performed to identify sedimentary events. The ages of the sedimentary events were inferred based on a detailed age-depth model combining radiocarbon dating and 137Cs/210Pb. In total, 65 radiocarbon dating were done on bulk sediment and on terrestrial organic matter. The results show that Hazar Lake region was impacted by two fault zones: The East Anatolian Fault (EAF) and the North Anatolian Fault. Based on historical documents, the seismic intensity of each seismic event recorded in Hazar Lake was calculated. Here, we discuss the seismic threshold for earthquake records as well as the seismic recurrence pattern for the EAF over the last 3000 years. [less ▲]

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See detailSedimentation influx and volcanic interactions in the Fuji Five Lakes: implications for paleoseismological records
Lamair, Laura ULiege; Hubert, Aurelia ULiege; Yamamoto, Shinya et al

Conference (2017, April 27)

The Fuji Fives Lakes are located at the foot of Mount Fuji volcano close to the triple junction, where the North American Plate, the Eurasian plate and the Philippine Sea Plate meet. These lakes are ... [more ▼]

The Fuji Fives Lakes are located at the foot of Mount Fuji volcano close to the triple junction, where the North American Plate, the Eurasian plate and the Philippine Sea Plate meet. These lakes are ideally situated to study Mount Fuji volcanism and the interaction between volcanism, changes in lake sedimentation rates and the ability of lakes to record paleoearthquakes. Here, we present newly acquired geological data of Lake Yamanaka and Lake Motosu, including seismic reflection profiles, gravity and piston cores. These two lakes and their respective watersheds were affected by several eruptions of Mount Fuji. Lake Yamanaka, a very shallow lake (max. depth 14 m), was heavily impacted by the scoria fall-out of the A.D. 1707 Hoei eruption of Mount Fuji. A detailed investigation of the effect of the Hoei eruption was conducted on short gravity cores, using high resolution XRD, C/N and 210Pb/137Cs analyses. The preliminary results suggest that the sedimentation rate of Lake Yamanaka drastically reduced after the Hoei eruption, followed by an increase until the present day. Similarly, lacustrine sedimentation in Lake Motosu (max. depth 122 m) was disturbed by Mount Fuji volcanism at a larger scale. The watershed of Lake Motosu was impacted by several lava flows and scoria cones. For example, the Omuro scoria cone reduced the catchment size of Lake Motosu and modified its physiography. The related scoria fall out covered an extensive part of the lake catchment and reduced terrigenous sedimentary influx to Lake Motosu. Within the deep basin of Lake Motosu, seismic reflection data shows two different periods that are distinguished by a major change in the dominant sedimentary processes. During the first period, sublacustrine landslides and turbidity currents were the dominant sedimentation processes. During the second one, the seismic stratigraphy evidences only deposition of numerous turbidites interrupting the hemipelagic sedimentation. Changes in sedimentary processes can be linked to the modification of the lake watershed by Mount Fuji volcanism, leading to a decrease in the sediment volume that can be remobilized, and therefore disappearance of large sublacustrine landslides. Turbidites are deposited due to surficial remobilization of lake slope sediments most probably as a result of earthquake shaking. When studying sedimentological records of lakes to define the paleoearthquake record, eruptions of nearby volcanoes should be taken into account. This study suggests that a large magnitude earthquake occurring few decades after a volcanic eruption (with large scale scoria fall-out), might not be recorded in a lake, or would only be fingerprinted in the sedimentary record by small turbiditic flows. References: Miyaji N., Kan'no A., Kanamaru T., Mannen K. 2011. High-resolution reconstruction of the Hoei eruption (AD 1707) of Fuji volcano, Japan. Journal of Volcanology and Geothermal Research 207, 113–129. [less ▲]

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See detailClay minerals behaviour in thin sandy clay-rich lacustrine turbidites (Lake Hazar, Turkey)
El Ouahabi, Meriam ULiege; Hubert, Aurelia ULiege; Lamair, Laura ULiege et al

Poster (2017, April 23)

Turbidites have been extensively studied in many different areas using cores or outcrop, which represent only an integrated snapshot of a dynamic evolving flow. Laboratory experiments provide the missing ... [more ▼]

Turbidites have been extensively studied in many different areas using cores or outcrop, which represent only an integrated snapshot of a dynamic evolving flow. Laboratory experiments provide the missing relationships between the flow characteristics and their deposits. In particular, flume experiments emphasize that the presence of clay plays a key role in turbidity current dynamics. Clay fraction, in small amount, provides cohesive strength to sediment mixtures and can damp turbulence. However, the degree of flocculation is dependent on factors such as the amount and size of clay particles, the surface of clay particles, chemistry and pH conditions in which the clay particles are dispersed. The present study focuses on thin clayey sand turbidites found in Lake Hazar (Turkey) occurring in stacked thin beds. Depositional processes and sources have been previously studied and three types were deciphered, including laminar flows dominated by cohesion, transitional, and turbulence flow regimes (Hage et al., in revision). For the purpose of determine the clay behavior in the three flow regimes, clay mineralogical, geochemical measurements on the cores allow characterising the turbidites. SEM observations provide further information regarding the morphology of clay minerals and other clasts. The study is particularly relevant given the highly alkaline and saline water of the Hazar Lake. Clay minerals in Hazar Lake sediments include kaolinite (1:1-type), illite and chlorite (2:1-type). Hazar lake water is alkaline having pH around 9.3, in such alkaline environment, a cation-exchange reaction takes place. Furthermore, in saline water (16‰), salts can act as a shield and decrease the repulsive forces between clay particle surfaces. So, pH and salt content jointly impact the behaviour of clays differently. Since the Al-faces of clay structures have a negative charge in basic solutions. At high pH, all kaolinite surfaces become negative-charged, and then kaolinite particles are dispersed, and the suspension is stabilized supported by our SEM observations. In alkaline water, kaolinite reveals a lower degree of consolidation. While, alkaline water has no measurable effect on illite and chlorite surface properties due to the absence of modifications in charge. Illite and chlorite form with other clasts clusters or aggregate structures in suspension when the particle interactions are dominated by attractive energies were formed. The aggregate structure plays a major part in the flow behavior of clay suspensions. Flocs will immobilize the suspending medium, and give rise to increasing viscosity and yield strength of the suspension. [less ▲]

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See detailThe role of natural hazards and human activities on change of sedimentation patterns: The case of Lake Yamanaka (Fuji Five Lakes, Japan)
Lamair, Laura ULiege; Hubert, Aurelia ULiege; El Ouahabi, Meriam ULiege et al

Conference (2017, April 10)

The last eruption of Mt Fuji (Japan) occurred in A.D. 1707. The eruption lasted 16 days from 16 December 1707 to 1 January 1708 (Tsuya, 1955) and 1.8 km3 of volcanic materials were ejected in total ... [more ▼]

The last eruption of Mt Fuji (Japan) occurred in A.D. 1707. The eruption lasted 16 days from 16 December 1707 to 1 January 1708 (Tsuya, 1955) and 1.8 km3 of volcanic materials were ejected in total (Miyaji et al., 2011). Lake Yamanaka, a very shallow lake (max. 14. 3 m depth) located at the foot of the east-north-eastern flank of Mt Fuji, was heavily impacted by the eruption. A thick scoria layer entirely covered the catchment of Lake Yamanaka. The thickness of the deposit varies from 5 to 37 cm around Lake Yamanaka and reaches up to 149 cm at the south-west extremity of the catchment (Miyaji et al., 2011). In order to study the influence of Hoei eruption on Lake Yamanaka, 5 gravity cores were taken during the 2014 QuakeRecNankai campaign. The Hoei scoria was present at the bottom of the one core and in the core catcher of the four other cores. High resolution magnetic susceptibility, XRD, XRF, LOI, C/N and 210Pb/137Cs analyses were performed on the gravity cores. The results shows three distinct periods of sedimentation: (1) From Hoei eruption to A.D. 1900; (2) From A.D. 1900 to A.D. 1990; (3) From A.D. 1990 to A.D. 2014. The first period is characterized by a very low sedimentation rate (~0.07 cm/yr). During this period, the sediments of the catchment were trapped below the thick Hoei scoria layer. However, peaks of terrigenous input are recorded. We link such detrical signals with violent typhoons that hit the Fuji Five Lakes region. The water from the heavy rains percolated through the porous thick scoria layer and saturated it. As a result, surface runoffs carried the sediments from the catchment into Lake Yamanaka. The second period (from A.D. 1900 to A.D. 1990) is defined by an increase of the sedimentation rate (~0.16 cm/yr). The development of soil and the agriculture (e.g. pastureland, rice field, mulberry plantations) reduced the impact of Hoei scoria. The terrigenous inputs are higher than previously but remained more or less constant during this period of time. As the thickness of the scoria layer is partially reduced or covered by new soil, rains triggered by smaller typhoons could drain the sediments from watershed and transport them into the lake. The most recent period representing the last 27 years is characterized by a very high sedimentation rate (~1.036 cm/yr). The transition between period 2 and period 3 corresponds to the development of mass tourism and the urbanization around Lake Yamanaka. It is marked by an increasing of atmospheric pollution (Pb, Zn). In the upper part of the cores, a peak of 137Cs is observed. Such peak is related to cesium fall-out after Fukushima incident in 2011. In addition to the fingerprint of human impact, the lake also record a terrigenous signal related to the 2007 Fitow typhoon which provoked damage in the area. This study highlights the influence of eruptions and typhoons on the sedimentation of Lake Yamanaka. In the present day, the sedimentation recovery after a major eruption is accelerated by human activity. References: Miyaji N., Kan'no A., Kanamaru T., Mannen K. 2011. High-resolution reconstruction of the Hoei eruption (AD 1707) of Fuji volcano, Japan. Journal of Volcanology and Geothermal Research 207, 113–129. Tsuya, H. 1955. Geological and petrological studies of volcano, Fuji, V.: 5. on the 1707 eruption of Volcano Fuji. Bulletin of the Earthquake Research Institute 33, 341–383. [less ▲]

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