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Vinh V.D.,Institute of Marine Environment and Resources | Ouillon S.,French National Center for Space Studies | Ouillon S.,Hanoi University of Science and Technology | Thao N.V.,Institute of Marine Environment and Resources | Tien N.N.,Institute of Marine Geology and Geophysics
Water (Switzerland) | Year: 2016

The Mekong River is ranked as the 8th in terms of water discharge and as the 10th in terms of sediment load in the world. During the last 4500 years, its delta prograded more than 250 km to the south due to a tremendous amount of sediments deposited, and turned from a "tide-dominated" delta into a "wave-and-tide dominated" delta. This study aims at completing our knowledge on the fate of sediments that may be stored in estuarine or coastal systems, or dispersed over the continental shelf and slope. Sediment transport in the Mekong River Delta (MRD) coastal area was studied by numerical simulations using the Delft3D model. The model configuration was calibrated and validated from data collected in situ during 4 periods from 2012 to 2014. Then, 50 scenarios corresponding to different wave conditions (derived from the wave climate) and river discharge values typical of low flow and flood seasons enabled us to quantify the dispersal patterns of fluvial sediments close to the mouths and along the coast. Sediments mostly settled in the estuary and close to the mouths under calm conditions, and suspended sediment with higher concentrations extend further offshore with higher waves. Waves from the Southeast enhanced the concentration all along the MRD coastal zone. Waves from the South and Southwest induced coastal erosion, higher suspended sediment concentrations in front of the southern delta, and a net transport towards the Northeast of the delta. Because of episodes of Southern and Southwestern waves during the low flow season, the net alongshore suspended sediment transport is oriented Northeastward and decreases from the Southwestern part of the coastal zone (~960 × 103 t yr-1) to the Northeastern part (~650 × 103 t yr-1).


Matoza R.S.,CEA DAM Ile-de-France | Le Pichon A.,CEA DAM Ile-de-France | Vergoz J.,CEA DAM Ile-de-France | Herry P.,CEA DAM Ile-de-France | And 4 more authors.
Journal of Volcanology and Geothermal Research | Year: 2011

Sarychev Peak (SP), located on Ostrov Matua, Kurils, erupted explosively during 11-16 June 2009. Whereas remote seismic stations did not record the eruption, we report atmospheric infrasound (acoustic wave ~. 0.01-20. Hz) observations of the eruption at seven infrasound arrays located at ranges of ~. 640-6400. km from SP. The infrasound arrays consist of stations of the International Monitoring System global infrasound network and additional stations operated by the Korea Institute of Geoscience and Mineral Resources. Signals at the three closest recording stations IS44 (643. km, Petropavlovsk-Kamchatskiy, Kamchatka Krai, Russia), IS45 (1690. km, Ussuriysk, Russia), and IS30 (1774. km, Isumi, Japan) represent a detailed record of the explosion chronology that correlates well with an eruption chronology based on satellite data (TERRA, NOAA, MTSAT). The eruption chronology inferred from infrasound data has a higher temporal resolution than that obtained with satellite data. Atmosphere-corrected infrasonic source locations determined from backazimuth cross-bearings of first-arrivals have a mean centroid ~. 15. km from the true location of SP. Scatter in source locations of up to ~. 100. km result from currently unresolved details of atmospheric propagation and source complexity. We observe systematic time-variations in trace-velocity, backazimuth deviation, and signal frequency content at IS44. Preliminary investigation of atmospheric propagation from SP to IS44 indicates that these variations can be attributed to solar tide variability in the thermosphere. It is well known that additional information about active volcanic processes can be learned by deploying infrasonic sensors with seismometers at erupting volcanoes. This study further highlights the significant potential of infrasound arrays for monitoring volcanic regions such as the Kurils that have only sparse seismic network coverage. © 2010 Elsevier B.V.


Rozhnoi A.,Russian Academy of Sciences | Shalimov S.,Russian Academy of Sciences | Solovieva M.,Russian Academy of Sciences | Levin B.,Institute of Marine Geology and Geophysics | And 2 more authors.
Journal of Geophysical Research: Space Physics | Year: 2012

A network of VLF receivers, sited in the Far East, has been used to observe the response of the lower ionosphere to tsunamis resulting from the November 15, 2006 (Kuril region) and the March 11, 2011 (Tohoku region) earthquakes. Specific perturbations in the phase and amplitude of VLF signals have been found for both cases. A qualitative interpretation of the observed effects is suggested in terms of the interaction of internal gravity waves with lower ionosphere. © 2012. American Geophysical Union.


Golozubov V.V.,Russian Academy of Sciences | Kasatkin S.A.,Far Eastern Federal University | Malinovskii A.I.,Russian Academy of Sciences | Nechayuk A.E.,Russian Academy of Sciences | Grannik V.M.,Institute of Marine Geology and Geophysics
Geotectonics | Year: 2016

The contemporary structure of the West Sakhalin Terrane started to form in the Pleistocene and the process of its formation continues up to now in a setting of ENE (60°–90°) shortening. Evidence of the preceding NE (30°–45°) compression was revealed during the study. This compression prevailed in the Eocene–Pliocene. Under the settings of NE (30°–45°) compression, dextral displacements occurred along the West Sakhalin and Tym’–Poronai fault systems, bounding the West Sakhalin Terrane. © 2016, Pleiades Publishing, Inc.


Borisov A.,Institute of Marine Geology and Geophysics | Borisov S.,Institute of Marine Geology and Geophysics | Levin B.,Institute of Marine Geology and Geophysics | Sasorova E.,Institute of Marine Geology and Geophysics
Proceedings of Meetings on Acoustics | Year: 2012

The results of hydroacoustic observations of signals from the weak (M<4) earthquakes in natural conditions within the area of South Kuril Islands are presented. A part of the observed earthquakes was registered by seismograph stations as well and another part was registered by the hydrophone station only. The peculiarity of observations was that the record of seismic signals performed in shallow water area that is in conditions of high noise level. Analysis of hydroacoustic records captured from the hydrophone station showed that there was no any evident foregoing response of geological medium on weak distant events. So geoacoustic emission was not detected neither before period of earthquake preparation nor during period of preparation. It is shown that in spite of unfavourable noise conditions even distant weak earthquakes can be confidently registered by hydrophone stations and application of proper signal processing techniques makes it possible to determine the moments of arrival of seismic waves and to measure their parameters. It is also established that frequency spectrum of acoustic signals from weak earthquakes perceived by hydrophone stations has continuous noise-type character in the range up to 90-100 Hz. Low frequency signals fore-running some weak earthquakes and microearthquakes are discovered. © 2012 Acoustical Society of America.


Stattegger K.,University of Kiel | Tjallingii R.,Netherlands Institute for Sea Research | Saito Y.,Geological Survey of Japan | Michelli M.,University of Kiel | And 2 more authors.
Global and Planetary Change | Year: 2013

Beachrocks, beach ridge, washover and backshore deposits along the tectonically stable south-eastern Vietnamese coast document Holocene sea level changes. In combination with data from the final marine flooding phase of the incised Mekong River valley, the sea-level history of South Vietnam could be reconstructed for the last 8000. years. Connecting saltmarsh, mangrove and beachrock deposits the record covers the last phase of deglacial sea-level rise from 5 to + 1.4 m between 8.1 to 6.4 ka. The rates of sea-level rise decreased sharply after the rapid early Holocene rise and stabilized at a rate of 4.5. mm/year between 8.0 and 6.9. ka. Southeast Vietnam beachrocks reveal that the mid-Holocene sea-level highstand slightly above +. 1.4. m was reached between 6.7 and 5.0. ka, with a peak value close to +. 1.5. m around 6.0. ka. This highstand is further limited by a backshore and beachridge deposit that marks the maximum springtide sea-level just below the base of the overlying beach ridge. After 5.0. ka sea level dropped below +. 1.4. m and fell almost linearly at a rate of 0.24. mm/year until 0.63. ka and +. 0.2. m as evidenced by the youngest beachrocks.The Holocene sea-level fluctuations observed in Southeast Vietnam resulted from eustatic and isostatic processes. The sea-level rise up to the mid-Holocene highstand was provoked by the last melting phase of glacial polar ice-sheets. The sea-level drop after the mid-Holocene highstand was induced by the isostatic processes of continental levering with an uplift of continents in low latitudes and depression of adjacent flooded continental shelf areas and Equatorial Ocean Siphoning transferring oceanic waters from low latitudes to the increasing volume of oceanic basins in higher latitudes. The regional expression in terms of magnitude and timing of relative sea-level change might contribute to validation of geophysical model simulations. © 2013 Elsevier B.V.


Rybin A.,Institute of Marine Geology and Geophysics | Chibisova M.,Institute of Marine Geology and Geophysics | Webley P.,University of Alaska Fairbanks | Steensen T.,University of Alaska Fairbanks | And 3 more authors.
Bulletin of Volcanology | Year: 2011

After 33 years of repose, one of the most active volcanoes of the Kurile island arc-Sarychev Peak on Matua Island in the Central Kuriles-erupted violently on June 11, 2009. The eruption lasted 9 days and stands among the largest of recent historical eruptions in the Kurile Island chain. Satellite monitoring of the eruption, using Moderate Resolution Imaging Spectroradiometer, Meteorological Agency Multifunctional Transport Satellite, and Advanced Very High Resolution Radiometer data, indicated at least 23 separate explosions between 11 and 16 June 2009. Eruptive clouds reached altitudes of generally 8-16 km above sea level (ASL) and in some cases up to 21 km asl. Clouds of volcanic ash and gas stretched to the north and northwest up to 1,500 km and to the southeast for more than 3,000 km. For the first time in recorded history, ash fall occurred on Sakhalin Island and in the northeast sector of the Khabarovsky Region, Russia. Based on satellite image analysis and reconnaissance field studies in the summer of 2009, the eruption produced explosive tephra deposits with an estimated bulk volume of 0. 4 km 3. The eruption is considered to have a Volcanic Explosivity Index of 4. Because the volcano is remote, there was minimal risk to people or infrastructure on the ground. Aviation transport, however, was significantly disrupted because of the proximity of air routes to the volcano. © 2011 Springer-Verlag.


Dung B.V.,Institute of Marine Geology and Geophysics | Stattegger K.,University of Kiel | Unverricht D.,University of Kiel | Phach P.V.,Institute of Marine Geology and Geophysics | Thanh N.T.,Institute of Marine Geology and Geophysics
Global and Planetary Change | Year: 2013

The Late Pleistocene-Holocene sedimentary architecture of the Southeast (SE) Vietnam Shelf was investigated using high-resolution seismic profiles and core samples. Three systems tracts and a prominent seismic reflection surface at the base of the sequence were revealed. This surface (SB1) is interpreted as a sequence boundary formed by subaerial processes during the Late Pleistocene sea-level fall and subsequent marine reworking during transgression. A surface map of the lowstand surface, compiled from seismic profiles and sediment cores, revealed the W-E to N-S oriented incised-valley system of the paleo-Mekong River. The incised valleys show a clear change in morphology from the north to the south in the study area. The northern incised-valley system off Vung Tau appears as a narrow and deep V-shape in cross-section (<. 5. km wide and tens of meters deep) likely as a result of the high-gradient morphology of the paleo-shelf. In contrast, the wide and low-gradient paleo-shelf off the modern Mekong Delta and Ca Mau Peninsula created shallow incised-valleys (5-15. km wide and <. 15. m deep) on the exposed shelf. The lowstand systems tract (LST) consists of a prograding outer shelf delta-wedge formed during the Last Glacial Maximum (LGM) sea-level lowstand period. The transgressive systems tract (TST) was well preserved in the incised-valleys, where its thickness reaches 15-25. m. Sediment core analysis results and seismic facies reveal that the TST deposits within the incised-channels were marked by a transition from fluvial deposits at the base to marine deposits in the upper part of the channels. On the exposed shelf and the interfluvial area of the incised-channels, the TST is a sandy layer overlying the sequence boundary SB1. Thickness of the TST on the shelf varies from 0 to 15. m. The highstand systems tract (HST) consists of thick mud clinoforms of the modern Mekong subaqueous delta. The HST wedge prograded onto the shelf primarily after the mid-Holocene sea-level highstand was at approximately 6.5-5.5. kyr BP ago. The HST wedge extends along the southwestern shore, and its maximum thickness (30. m) was recorded in the Cape Ca Mau area. The HST wedge pinches out at modern water depths of 20-30. m, resulting in a thin HST layer on the middle and outer shelf. The proposed post-Pleistocene sequence-stratigraphic model for the SE Vietnam Shelf is a variation on the theoretical model of Vail (1987). The thick highstand wedge on the SE Vietnam Shelf is confined to the inner shelf due to the broad and low-gradient shelf morphology and the strong local hydrodynamic conditions driven by the monsoon system. Except for the one deposited within the incised-valley system, the TST deposits on the SE Vietnam Shelf tend to disperse over the shelf instead of forming a thick backstepping unit. The accommodation space was probably created faster than the sediment supply during the rapid transgression. © 2013 Elsevier B.V.


Choi B.H.,Sungkyunkwan University | Kaistrenko V.,Institute of Marine Geology and Geophysics | Kim K.O.,Korea Ocean Research and Development Institute | Min B.I.,Sungkyunkwan University | Pelinovsky E.,RAS Institute of Applied Physics
Natural Hazards and Earth System Science | Year: 2011

We propose a method to compute tsunami runup heights that is based on an integration of numerical, 2-D shallow-water modelling and an analytical, 1-D long-wave runup theory. This approach provides a faster forecast of tsunami runup heights than a complicated coastal inundation model. Through simulations of potential tsunami scenarios, this approach can also be applied to long-term tsunami prediction. We tested the model by simulating the historical event in the East (Japan) Sea and found that the estimates of runup heights agreed well with the available observations. © Author(s) 2011.


Fyhn M.B.W.,Geological Survey of Denmark | Phach P.V.,Institute of Marine Geology and Geophysics
Tectonics | Year: 2015

Continental extrusion may take up much of the deformation involved in continental collisions. Major strike-slip zones accommodate the relative extrusion displacement and transfer deformation away from the collision front. The Red River fault zone (RRFZ) accommodated left- and right-lateral displacements when Indochina and South China were extruded during the Indian-Eurasian collision. The northern Song Hong basin onshore and offshore in the Gulf of Tonkin delineates the direct extension of the RRFZ and thus records detailed information on the collision-induced continental extrusion. We assess the rapidly evolving kinematics of the fault zone buried within the basin based on seismic analysis. Contrary to previous studies, we do not identify indications for latest Miocene left-lateral motion across the RRFZ. We tentatively consider the shift from left- to right-lateral motion to have occurred already during the middle Late Miocene as indicated by inversion of NE-SW-striking faults in the Bach Long Vi area. Right-lateral displacement terminated around the end of the Miocene in the Song Hong basin. However, continued inversion in the Bach Long Vi area and NNW-SSE-striking normal faulting suggests a stress regime compatible with right-lateral motion across the onshore part of the RRFZ continuing to the present. Inversion around the Bach Long Vi Island may have accommodated up to a few kilometers of right-lateral displacement between the Indochina and South China blocks. Comparable NE-SW-striking fault zones onshore may have accommodated a larger fraction of the right-lateral slip across the RRFZ, thus accounting for the restricted transfer of lateral displacement to the offshore basins. © 2015. American Geophysical Union. All Rights Reserved.

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