source parameters and scaling relations for small earthquakes in the matsushiro region southwest honshu japan abstract using near field broadband data from a suite of crustal earthquakes which occurred in a small homogeneous source region we examine the scaling relationships among source parameters for earthquakes in the critical 1 5 to 4 5 magnitude range we take special precautions to insure that our conclusions are not biased by local structure seismic moment fault radius and stress drop relations were determined for 32 small shallow strike slip earthquakes 1 6 m l 4 3 in the matsushiro region of southwest honshu japan spectral and cepstral analyses of short period arrivals exhibit structure interpreted as resulting from reverberations within thin low velocity surface layers below the recording site furthermore calculated crustal transfer functions for sh predict a peak over the range of 2 to 4 hz this type of site response can bias estimates of spectral parameters particularly corner or characteristic frequencies for simple sources such a bias can be reduced by filtering in the cepstral domain the effect of cepstral filtering on corner frequency determinations is generally less than 20 per cent and tends to decrease them particularly for larger events where the structurally induced spectral enhancement is at frequencies above the source related corner frequencies estimates of the seismic moment brune stress drop and fault radius for each event were calculated from sh displacement amplitude spectra the seismic moments range from 10 18 to 10 22 dyne cm the stress drops range from 0 008 to 16 bars the relationship between log stress drop and log moment is approximately linear with a slope of 1 up to a moment of 2 10 21 dyne cm but for higher moments the slope is not significantly different from zero fault radii range from 0 3 to 1 2 km there is a physical scatter in radius for any given moment up to a factor of 1 5 for moments less than 2 10 21 dyne cm there is no significant trend in the radius as a function of moment but for higher moments the radius increases with moment the main conclusion is that the stress drop is the dominant scaling factor for moments less than 10 21 dyne cm for higher moment the source dimension becomes the controlling factor

source mechanisms of usu volcano japan earthquakes and their tectonic implications abstract an intensive earthquake swarm and remarkable surface deformation due to dacitic doming have taken place at the usu volcano in southwestern hokkaido japan since august 1977 a major u shaped fault has formed in the summit crater and the amount of upheaval reached 180 m for 5 years in order to reveal the quantitative relation between this doming deformation and the associated earthquakes the mechanisms of the latter have been studied for this purpose broadband and wide dynamic range seismic observations were performed in a near field region of the usu volcano for the period from june 1979 to july 1980 long period seismometers and a digitally recording accelerometer system were used for relatively large earthquakes the data from the digital recording system permit very accurate calculations of ground displacements by employing the recursive filter method source parameters such as seismic moment average dislocation stress drop and fault dimensions for five earthquake families have been determined from a comparison of the observed ground displacements with synthetic ones synthetic displacements were computed using haskell s formulation for relatively deep earthquakes the discrete wavenumber dw method was used for relatively shallow earthquakes the stress drop varies widely among earthquakes in the same earthquake family the cumulative seismic deformation caused by the large earthquakes is almost consistent with the observed surface deformation it is suggested that the large earthquakes are caused by stick slip motions at the two sides of the u shaped fault

depositional history of quaternary sediments on the continental shelf off the southeastern coast of korea korea strait abstract the depositional history of quaternary sediments on the continental shelf off the southeastern coast of korea korea strait was investigated by means of analysing high resolution seismic profiles and sediment samples quaternary sediments up to 50 m thick overlie the irregular surface of the acoustic basement in the inner shelf the sedimentary column is comprised of two main sequences separated by a mid reflector which is interpreted as the pre holocene surface the holocene sequence reaching up to 30 m in thickness with a depocenter near the present river mouth is characterized by deposition in a prodelta environment while the upper pleistocene sequence represents deposition in deltaic or shallow water environments during the late glacial period most of the shelf was subaerially eroded and deposition took place only in the trough region the present location of marine built terraces indicates that the lowest position of sea level was about 130 m below its present level the subsequent postglacial transgression reworked pleistocene sediments to form a thin veneer of transgressive facies sea level rose rapidly in the early stages of the postglacial transgression and approached the present level at approximately 7000 5000 yrs b p recent sedimentation the holocene sequence probably began at that time

sedimentary facies and evolution in the qiantang river incised valley eastern china abstract this paper deals with the sedimentary facies and evolution of the qiantang river qr estuary and the characteristics and formation of the incised valley sequences and the related shallow biogenic gas reservoir on the basis of analysis of over 500 cores the result shows that since the last glaciation the late quaternary formation of the qr estuary area underwent three stages 1 deep cutting stage 2 rapid filling stage and 3 burial stage the fall of global sea level during the last glacial maximum enhanced the fluvial gradient and river cutting resulting in the formation of the large scale qr and taihu incised valleys with the interfluve being exposed to air on both flanks of the incised valley fluvial terraces at the elevations are present near the present qr estuarine mouth corresponding to 60 70 90 100 and 115 125 m burial depths the valleys were filled rapidly with fluvial sediments during the post glacial period with the rise of sea level the river mouth migrated to landward and backwater and retrogressive aggradation was enhanced the qr and taihu incised valleys are associated with an early filling and transgressive channel infilling sequence formation and a late filling and transgressive floodplain estuary formation subsequently the qr valley was buried under estuarine marine and estuarine sand bar sediments from bottom to top the incised valley successions can be grouped into four sedimentary facies river channel floodplain estuary estuary shallow marine and estuary sand bar the thickness of the river channel infilling deposits is controlled mainly by base level rising backwater retrogressive aggradation and neotectonism further localized thickening took place where deeper scour pools were present in the incised valley or fluvial terraces were formed during the fall of elative sea level during the deposition of the floodplain estuary facies the conditions of sea level rise tidal regime sediment supply and accommodation space were suitable for the development of a tidal ridge system the sand lenses associated with this facies may represent a tidal ridge system in the incised valley at the later stage when the estuarine sand bars were formed the sedimentary conditions were no longer favourable resulting in absence of sand ridge deposits biogenic gas is stored in the floodplain estuary sand lenses of the incised valleys the changjiang river provides the major sediment supply for the qr estuary sand bar and the qr carried sediments constitute only a small portion of the deposits

coherence between solar activity and the east asian winter monsoon variability in the past 8000 years from yangtze river derived mud in the east china sea ams 14 c dating and grain size analysis for core pc 6 located in the middle of a mud area on the inner shelf of the east china sea ecs were used to rebuild the holocene history of the east asian winter monsoon eawm the 7 5 m core recorded the history of environmental changes during the postglacial transgression the core s mud section the upper 450 cm has been formed mainly by suspended sediment delivered from the yangtze river mouth by the ecs winter coastal current ecswcc since 7 6 kyr bp using a mathematical method called grain size vs standard deviatiow we can divide the core pc 6 s grain size distribution into two populations at about 28 mu m the fine population 28 mu m is considered to be transported by the ecswcc as suspended loads content of the fine population changes little and represents a stable sedimentary environment in accord with the present situation thus variation of mean grain size from the fine population would reflect the strength of ecswcc which is mainly controlled by the east asian winter monsoon abrupt increasing mean grain size in the mud section is inferred to be transported by sudden strengthened ecswcc which was caused by the strengthened eawm thus the high resolution mean grain size variation might serve as a proxy for reconstruction of the eawm a good correlation between sunspot change and the mean grain size of suspended fine population suggests that one of the primary controls on centennial to decadal scale changes of the eawm in the past 8 ka is the variations of sun irradiance i e the eawm will increase in intensity when the number of sunspots decreases spectral analyses of the mean grain size time series of core pc 6 show statistically significant periodicities centering on 2463 1368 128 106 100 88 91 7678 and 70 72 years the eawm and the east asian summer monsoon easm agree with each other well on these cycles and the east asian monsoon eam and the indian monsoon also share in concurrent cycles in holocene which are in accord with the changes of the sun irradiance c 2005 elsevier b v all rights reserved

a numerical study of transport dynamics and seasonal variability of the yellow river sediment in the bohai and yellow seas abstract a sediment numerical model was embedded into a wave tide circulation coupled model to simulate the transport processes of the yellow river derived sediment considering the wave induced vertical mixing bv and the wave current coupled bottom shear stress bss numerical results show that the main stream of the yellow river derived sediment moves first eastward off the northern shandong peninsula and then southward into the south yellow sea all year round in spring the sediment moves northeastward in the bohai sea in summer there is a northeastward branch of sediment in the bohai sea off the west coast of the liaodong peninsula while the main part goes eastward to the yellow sea the yellow river derived sediment transport from the bohai sea to the north yellow sea across the bohai strait is mainly limited to the top 10 m and with a maximum centered at 37 9 n in summer the transport from the north yellow sea to the south yellow sea across the transect of 37 n is mainly in the 0 30 m layer with a maximum around 123 7 e in autumn the simulated yellow river discharged sediment deposits along the shandong peninsula and between 20 and 30 m isobaths in the yellow sea which is consistent with observation if surface waves are not considered in the model the sediment deposits westward to the nearshore area in the south yellow sea the sediment would deposit further southward in the numerical experiment results without wind influence in the numerical experiment of no tide there is hardly any sediment deposited on the yellow sea floor while in the bohai sea most of the sediment is transported southward and northwestward around the river mouth instead of eastward as in the control run indicating the tides play a key role in forming the deposition pattern

influence of the yangtze river and grain size on the spatial variations of heavy metals and organic carbon in the east china sea continental shelf sediments abstract bulk heavy metal fe mn zn cu pb cd al organic carbon and carbonate concentrations grain sizes and c13 of the organic carbon distributions were studied in sediments collected throughout the east china sea continental shelf and the yangtze river delta the results demonstrated that terrigenous sediments from the yangtze river is a dominating factor controlling the spatial variations of heavy metals and organic carbon concentrations on the east china sea continental shelf in addition grain size and recent anthropogenic influences are also major factors modifying the spatial and vertical variations of heavy metals large spatial variations with a band type distribution of heavy metals grain size organic carbon and carbonate were observed higher concentrations of heavy metal and light c13 of the organic carbon were found primarily in the deltaic and inner shelf sediments the band type distribution generally followed the coastline with little variations in the north south direction away from the delta and inner shelf west east direction most heavy metal concentrations decreased rapidly with the exception of cd where high concentrations of cd were also found in the carbonate rich shelf break sediments coarse grained relict sediments and biogenic carbonate are two primary diluting agents for the fine grained aluminosilicate sediments from the yangtze river with high concentrations of heavy metals unusually high concentrations of cu pb and cd showed both spatially and vertically that more pollution prevention measures are needed in the yangtze river drainage basin in order to prevent further heavy metal pollution of the east china sea inner continental shelf

recent sediment accumulation and origin of shelf mud deposits in the yellow and east china seas abstract modern last 100 yr accumulation rates of shelf mud deposits in the yellow and east china seas were investigated using the distribution of excess 210pb 210pbex in sediment core samples compilation and merger of new and previously published data helped clarify sediment accumulation in these seas the estimated accumulation rates together with data of suspended sediment concentrations provided findings on the sediment budget origin and transport pathway of the mud deposits the overall accumulation distribution in the yellow and east china sea shelf revealed a general cross shelf decreasing trend along the sediment dispersal system away from the rivers except for the south sea ssm and southeastern yellow sea seysm mud patches found along the korean coast notably 210pbex activity profiles within the ssm and the seysm yielded a relatively high accumulation rate of 2 5 mm yr implying a sedimentation rate of 4 15 107 tons per year in this coastal zone such an annual accumulation rate is about one order of magnitude greater than the total sediment discharge 6 20 106 tons yr from korean rivers suggesting an additional offshore source the distribution pattern of the well defined suspended plume clearly showed the possible transport and exchange of fine grained sediments between the ecs shelf and the coastal area of korea especially during winter such a high accumulation in korean coastal areas is attributable to the sediments supplied from the mud deposit of the ecs i e swcim with origins in chinese rivers therefore the korean coastal area may be an important sink for some of chinese river sediments being transported from the south by the yellow sea warm current

sedimentary record of environmental evolution off the yangtze river estuary east china sea during the last 13 000 years with special reference to the influence of the yellow river on the yangtze river delta during the last 600 years abstract a 35 60 m long core ecs 0702 recovered from a water depth of 22 m in the muddy area off the yangtze river estuary was analyzed for sedimentary characteristics clay and detrital mineral components and element geochemistry as well as by ams 14 c dating to document sediment provenance changes and environmental evolution during the postglacial period in the study area on the basis of the lithology the benthic foraminiferal and ostracod assemblages and the ams 14 c ages we divided the core into four depositional units du1 du4 in descending order representing the postglacial sedimentary sequence during the last 13 000 years du 4 was deposited in a littoral to tidal flat environment during 13 000 11 500 cal yr bp du 3 in a nearshore subtidal environment upwards to the nearshore shelf with tidal influence in response to the postglacial sea level rise during 11 500 7400 cal yr bp du 2 in a tide affected nearshore shallow sea environment during 7400 540 cal yr bp on the delta front of the yangtze river when the delta was actively prograding and du 1 in a nearshore shallow sea environment during the last 540 years on the delta front under modern marine conditions in du 1 the depositional rate was much higher than in the underlying units and the sediment composition reflects more influence from the yellow river this unit can therefore be logically linked to the period when the yellow river last discharged into the south yellow sea from ad 1128 to 1855 according to historical records this period can be divided into an early stage ad 1128 1494 when the shoreline near the yellow river mouth was advancing slowly eastward and a late stage 1495 1855 when the shoreline was advancing rapidly the initiation of du 1 deposition corresponds to the latter part of the early stage suggesting that since that time a relatively large amount of sediment from the old yellow river mouth area has been transported to the offshore area of the yangtze river mouth our study has identified a high resolution sedimentary signature associated with the last course shift of the yellow river in the yangtze river delta front thus highlighting the intricate relationship between sediment sources and sinks in coastal areas a significant contribution of the old yellow river sediments to the yangtze subaqueous delta during the last 600 years must be considered when the evolutional history of the yangtze delta is examined and especially when the influence of the three gorge dam construction on the future changes of the yangtze estuary and ecological environments in the east china sea is estimated

active moribund and buried tidal sand ridges in the east china sea and the southern yellow sea shallow seismic profiles and borehole data revealed active moribund and buried tidal sand ridges in the east china sea and the southern yellow sea the ridges consist of relatively clean well sorted sands with fairly uniform sequences the microfossil assemblage exhibits a high diversity including both euryhaline and stenohaline species the ridges are huge elongated sand bodies several kilometres wide 10 60 km long and up to 20 m thick and occur in groups with a spacing of several to 10 km normally they are parallel with each other extending in the direction of the tidal currents the field of tidal sand ridges on the east china sea shelf covers an area of 57 000 km2 tidal sand ridges in the east china sea and the southern yellow sea were formed in estuarine and shallow shelf environments where strong tidal currents reworked transported and redeposited large amounts of relict sands from older deltaic and fluvial sediments the development of tidal sand ridges in estuary mouth areas is accompanied by a net sand transport from the shelf into the estuary the evolution of tidal sand ridges is closely related to transgressions active tidal sand ridges are formed during sea level rises they show distinct morphology and active migrations in a lateral as well as in a landward direction they are generally in equilibrium with present day tidal processes and their distribution patterns are related to the flow field of the tidal currents as the sea level rises further these tidal sand ridges become moribund sand bodies with less distinct morphologies their upper surfaces are covered by a thin calcareous rich layer with very high contents of foraminifera tests reflecting a submarine hiatus condition on the shelf during the highstand period during the subsequent steady fall in sea level tidal sand ridges are often buried by fine grained shelf and prodelta sediments they have therefore a good chance of being preserved in stratigraphic records the sequential buildup during a sea level rise tr tract and a subsequent sea level fall hs and ls tract would consist of estuarine channel and tidal flat facies tidal sand ridge facies shelf mud facies delta facies and fluvial facies in an ascending order tidally dominated estuary conditions may also occur when a major distributary is abandoned such as at the northern branch of the modern changjiang river mouth where the accumulation of sand from an abandoned delta lobe and the development of tidal sand ridges have been observed the observed features have important implications for the subsurface recognition of fossil tidal sand ridges for the reconstruction of the regional palaeogeography and transgressional history and for the prediction of potential reservoir sandstones

observations of long period earthquakes accompanying hydraulic fracturing waveforms of most seismic events accompanying hydraulic fracturing have been reported to contain clear p and s waves and have fault plane solutions consistent with shear displacement across a fault this observation is surprising since classical hydraulic fracturing theory predicts the creation of a tensile opening of a cavity in response to fluid pressure very small long period events similar to long period earthquakes observed at volcanoes were found to occur during four hydraulic fracturing experiments carried out at fenton hill new mexico since the long period earthquakes occur in the same region as the shear type events it is concluded that the unusual character of the long period earthquake waveforms is due to a source effect and not a path effect the occurrence of long period earthquakes during hydraulic fracturing could indicate tensile fracturing many waveforms of these events are identical which implies that these events represent repeated activation of a given source a proposed source for these long period events is the sudden opening of a channel that connects two cracks filled with fluid at different pressures the sizes of the two cracks differ which causes two or more peaks to appear in the spectra each peak beingmore associated with one physical dimension of each crack from the frequencies at which spectral peaks occur crack lengths are estimated to be between 3 and 20m less

sediment budget of the yellow river delta china the importance of dry bulk density and implications to understanding of sediment dispersal abstract this study constructs sediment budgets for the delta of the yellow river one of the world s largest muddy rivers and based on these budgets discusses the characteristics and related mechanisms of sediment dispersal at the river mouth the sediment budgets are derived from quantifying deposits in the deltaic lobe formed at the diaokouhe mouth of the river a detailed investigation of the dry bulk density of deposits in the delta which yields models of dry bulk density of deposits in the main depositional settings of the delta guarantees the reliability of the sediment budgets results show that deposits behind the delta front of the diaokouhe lobe over the period of 1965 to 1974 account for 73 5 of the incoming sediment the constructed sediment budgets reveal that the proportions of the deposits accumulated behind the delta front vary considerably over time the main factor responsible for the variations is the change in sediment discharge of the river there is no evidence for the anticipated positive relationships between the proportion of sediment escaping from the delta and water discharge clay content of incoming sediment or mouth channel efficiency the characteristics of sediment dispersal on the delta are related to the rapid extinction of sediment charged hyperpycnal underflows which are dominant in the plumes off the yellow river mouth and sediment deposition in the overbank flow on the delta plain because both of these processes trap a higher proportion of sediment at a higher sediment discharge

sedimentary evolution of the holocene subaqueous clinoform off the shandong peninsula in the yellow sea abstract a subaqueous clinoform wraps around the end of the shandong peninsula in the yellow sea the clinoform previously called the shandong mud wedge is up to 40 m thick nearshore and thins seaward its origin has been controversial since it was first noted in the 1980s for our recent investigation offshore of the northeastern shandong peninsula high resolution shallow seismic profiles covering about 1700 km were obtained and two drilling cores penetrating the clinoform were recovered we described the lithofacies characteristics identified benthic foraminifera and ostracoda measured grain size analyzed the mineral components of the cores and obtained ams 14 c dates on 28 samples to decipher the sedimentary evolution of the clinoform in response to postglacial sea level changes the shallow seismic profiles show that the clinoform comprises three units a lowermost seismic unit su 3 less than 2 3 m thick showing a retrogradational aggradational stacking pattern with subhorizontal internal reflectors a middle seismic unit su 2 up to 35 m thick showing a prograding reflection pattern with mostly seaward stepping reflectors separated by several erosive surfaces and an uppermost seismic unit su 1 maximum thickness 18 m exhibiting an aggradational reflection pattern with subparallel reflectors the three seismic units are bounded on the bottom by distinct erosion surfaces analyses of the two cores indicate that the clinoform comprises three depositional units du 1 du 2 and du 3 in descending order corresponding respectively to su 1 su 2 and su 3 the depositional units are distinguished by lithofacies characteristics and the downcore distributions of benthic foraminiferal and ostracod assemblages mineral components of the cores suggest that the clinoform s provenance is predominantly yellow river derived sediments ams 14 c dates suggest that du 3 was formed from about 11 6 to 9 6 cal kyr bp du 2 from 9 6 to 6 5 cal kyr bp and du 1 after ca 6 5 cal kyr bp some major meltwater pulse mwp events during the deglacial transgression were registered in the clinoform stratigraphy with the basal surfaces sediments of du 3 and du 2 corresponding respectively to mwp 1b ca 11 6 11 3 cal kyr bp and mwp 1c ca 9 6 9 2 cal kyr bp events and with du 2 being largely formed after the 8 4 8 2 cal kyr meltwater event rapid centennial to multidecadal scale flooding events were presumably responsible for the erosive surfaces separating the downlapping internal reflectors in su 2 the change of depositional pattern from progradational in su 2 to aggradational in su 1 is attributed to a change from strong dominantly to and fro tidal currents to the modern circulation in the bohai sea as well as to the weakening of the tidal current field during the highstand after about 6500 cal yr bp as a product of complex interactions among sediment supply sea level changes and hydrodynamic regimes the clinoform can be regarded as the distal part of the tidal depositional system in the eastern bohai sea which was largely derived from the yellow river

sediment transport over an accretional intertidal flat with influences of reclamation jiangsu coast china this paper focuses on the hydrodynamic and suspended sediment transport processes in response to sequential reclamations over the intertidal flat jiangsu coast which used to be one of the widest intertidal flats in china investigations into the sediment transport patterns reveal that net suspended sediment fluxes increased from 102 kg m 1 on the upper intertidal flat to 103 4 kg m 1 on the lower intertidal flat per tidal cycle this variation was caused mainly by the phases of the current velocity suspended sediment concentration ssc local bed geomorphology inundation patterns and extreme weather conditions the longshore component of tidal currents intensifies seaward over the intertidal flat extreme weather conditions e g storms and strong winds were important factors affecting the current velocity structures the intensity of residual currents and the sscs the sscs were characterized by several peaks throughout the tidal cycle these peaks were associated with strong currents combined wave current interactions and intense turbulences due to the initial flood surge furthermore the suspended sediment was finer and contained more clay materials during the flood phase of the tidal cycle than during the ebb fine particles were transported within the upper water column by landward residual currents but coarse particles were transported within the lower water column by seaward residual currents overall residual currents were apt to transport fine grained sediment landward and coarse grained sediment seaward this pattern indicates that the suspended sediment fluxes are highly variable in the water column even for very shallow tidal environments the cross shore component accounted only for a small percentage of the total sediment flux however this part of sediment supply dominated accretion over the intertidal flat the intertidal flat has become narrower and steeper following sequential reclamations a negative feedback process existed to maintain the convex profile shape although the human activities i e reclamation could have modified the natural process the surficial sediment tended to become finer on the mid upper intertidal flat but coarser on the lower intertidal flat following reclamations in response to a reduction in the tidal currents over the intertidal zone and enhancement of wave action over the lower intertidal flat accretion with high rates was maintained by landward transport of sediment in such an accretional system with influences of reclamation the width or slope of the intertidal flat is adjusted continuously before the cease of reclamation the intertidal flat is unable to achieve an equilibrium shape

sedimentary facies of the tide dominated paleo changjiang yangtze estuary during the last transgression abstract a large estuary was formed by marine inundation of the paleo changjiang yangtze incised valley during the transgression after the last glacial maximum this paper presents the sedimentary facies and architecture of the estuary fill based on the analysis of three sediment cores cm97 js98 and hq98 obtained from the present changjiang delta plain estuary fill deposits showing an upward fining succession were grouped into five depositional facies tidal river distributary channel muddy intertidal to subtidal flats transgressive lag and estuary front based on sedimentary textures lithology and physical sedimentary structures sand mud couplets are common in these deposits indicating that tides played a significant role in producing these sedimentary structures and that the estuary type was tide dominated some of the successive sand mud couplets probably recorded neap spring cycles as well as semidiurnal tidal cycles the nature of the estuary was very different from other representative tide dominated estuaries in sediment facies its distribution and sediment source for estuarine fill unlike the other estuaries that receive sediments mainly from the sea the paleo changjiang estuarine fill deposits were supplied largely from the river this difference would also have a great influence on the sedimentological and morphological component in the estuary the sediment distribution of the estuary showed fining seaward and estuary mouth sand bodies fed by marine source sand were absent the architecture model of tide dominated estuaries should be divided into two types by the degree of fluvial sediment supply the paleo changjiang estuary shows a good example for an estuary of large rivers

delta progradation and chenier formation in the huanghe yellow river delta china abstract to clarify holocene development of the huanghe yellow river delta and the relationship between delta progradation and chenier formation detailed sediment analyses and high resolution radiocarbon dating were done on borehole samples taken from two sites on the present huanghe h9601 latitude 37 40 5 n and longitude 118 28 7 e with an altitude of 5 5 m and h9602 lat 37 47 8 n and long 118 54 3 e 4 8 m downcore changes of sediment facies and accumulation rate show that delta progradation occurred at least twice during ca 2 6 1 2 c 14 yrbp and 1855 present at the two borehole sites these phases of progradation correlate with superlobes 6 and 7 and superlobe 10 respectively of ten superlobes composing the holocene huanghe delta shown by c xue historical changes in the yellow river delta china marine geology 113 321 329 1993 the boundary of these sediments at h9602 is sharp and erosional and correlates with cheniers located between borehole sites on the delta plain the diastem period between these phases of progradation almost coincides with the periods when the river mouth of the huanghe was located in the northwestern part of the bohai sea during 1048 1128 ad superlobe 8 and the jiangsu region facing the yellow sea during 1128 1855 superlobe 9 this suggests that chenier formation and delta progradation are linked and controlled by sediment supply and river course shifts of the lower reaches of the huanghe

man s influence on the erosion and transport of sediment by asian rivers the yellow river huanghe example during the holocene sediment input from the yellow river to the yellow sea and adjacent areas has amounted to about 3000 km 3 detailed records from river gauging stations over the past 70 yrs together with estimates based on earlier historic records suggest that the river has contributed 2300 km 3 of sediment during the last 2300 yrs an average discharge of 1 km 3 yr 1 x 10 9 t yr prior to extensive agricultural use of the loess plateau in northern china beginning about 200 bc therefore the river s load must have been about 0 1 km 3 yr an order of magnitude lower than that at present a broad delta 20 m below sea level suggests that early holocene rates were higher than the pre agricultural average and therefore that middle holocene loads were low

neogene planktonic foraminifera and events in japan abstract the warm water constituents of successive neogene planktonic foraminiferal assemblages in japan are identified and expressed as percentages of the total planktonic fauna by this means five major events have been recognized 1 a marine temperature optimum in the earliest middle miocene zone n8b 2 an abrupt cooling since early middel miocene time 3 a rise in temperature culminating in latest miocene to earliest pliocene time zones n17b and n18 4 an accelerated evolutionary event during the early pliocene zone n19b n21a 5 a short warm episode in the early pliocene zone n21a

stratigraphy and paleoenvironmental changes in the yangtze delta during the late quaternary the yangtze delta area may be subdivided into paleo valley and paleointerfluves of the last glaciation the postglacial transgressive sedimentary cycle ptsc on the front zones of the paleointerfluves is composed of marsh nearshore and barrier lagoon shallow marine and nearshore tidal flat units with a basement in stiff clay the ptsc in back zones of the paleointerfluves consists of lacustrine marsh deposits the ptsc in the incised valley contains river channel floodplain estuary estuarine shallow marine and deltaic units with an erosional surface at its bottom the stiff clay and the erosional surface constitute the ptsc lower boundary the stiff clay consisting of a paleosol experienced deposition alternating with pedogenesis during the falling of sea level during 18o stage 3 ongoing pedogenesis in the sea level lowstand of 18o stage 2 and early diagenesis after paleointerfluve inundation by the sea level rise of 18o stage 1 the climate during the paleosol formation was temperate with more than 500 mm a 1 rainfall and frequently fluctuating groundwater the yangtze river incised its course during falling sea level of stage 3 and a huge incised valley was formed during the sea level lowstand stage 2 the filling of the incised valley took place during the postglacial sea level rise and delta formation occurred at a late stage of ptsc development

partitioning of transgressive deposits in the southeastern yellow sea a sequence stratigraphic interpretation abstract the last glacio eustatic sea level fluctuation in the southeastern part of the yellow sea formed a number of unconformity bounded sedimentary sequences these sequences comprise 1 regressive to transgressive incision fills unit c 2 transgressive sand ridges and swales unit b and 3 transgressive to highstand muds lower mud unit a2 upper mud unit a1 the sequence boundary between unit c and the lower unit comprises erosional surface which can be traced for the entire study area the even and sharp boundary between the incision fills unit c and the sand ridges unit b represents a transgressive surface of erosion the depositional boundary between the lower mud unit a2 and the upper mud unit a1 suggests a change in oceanographic conditions the boundary is confined landward and correlated offshore with the top of units b and c that is exposed on the seafloor these transgressive deposits show partitioning controlled by currents tides and sediment supply as well as physiography of the seafloor

yangtze shoal a modern tidal sand sheet in the northwestern part of the east china sea abstract from an analysis of other s data on tidal currents bedforms and sediment grain sizes it is concluded that the yangtze shoal in the northwestern east china sea is a typical modern tidal sand sheet rather than a paleo changjiang submarine delta or a relict sedimentary accumulation on the continental shelf formed during a stillstand of the postglacial transgressive sea the yangtze shoal and the jiangsu offshore tidal ridges of the subei shoal to the northwest jointly comprise the active tidal geomorphic system off the changjiang estuary

sediment dynamic processes of the yuehu inlet system shandong peninsula china in order to investigate the sediment dynamic behavior of the yuehu a small inlet system characterized by abundant sediment supply and rapid sediment infilling measurements and sampling were undertaken to obtain data sets of tidal water levels current velocities suspended sediment concentrations grain size parameters deposition rates and organic carbon contents sediment budget and the time velocity asymmetry patterns of the inlet system were analyzed the results show that the deposition rates are relatively high within the tidal basin the total sediment flux cannot be balanced by the input from the open sea the aerosol and biological production rather the material from land which has been intensified by agricultural activities over the past several decades represents a major component for the balance thus the denudation rate must be reduced to protect the yuehu as a natural reserve furthermore it is found from the present study that the yuehu inlet system exhibits all of the four time velocity asymmetry patterns with varied frequencies of occurrence compared with the two asymmetry patterns identified for larger inlet systems such phenomena are partly due to the adjustment of entrance channel geometry this behavior may be representative of the small tidal inlets at their late stage of morphological evolution and therefore may be utilized to prolong the lifespan of small inlet systems c 2003 elsevier ltd all rights reserved

stratigraphy and sedimentary environments during the late quaternary in the eastern bohai sea north china platform abstract the bohai sea is a shallow sea at the east coast of china it communicates with the yellow sea through a narrow strait during and since the late pleistocene the bohai sea has been a filled subsiding basin submitted to successive regressive transgressive cycles in the east bohai sea a number of finger shaped ridges are present near the strait where tidal currents are dominant very high resolution seismic reflection data have been interpreted relative to sedimentological data provided by a formerly drilled borehole seven seismic units are identified and correlated with the following events units u7 u6 with the bohai relative sea level rise 65 000 53 000 yr b p and a relative sea level fall 53 000 39 000 yr b p unit u5 with the xianxian relative sea level rise 39 000 22 000 yr b p unit u4 with the period of the late wurm glaciation 22 000 15 000 yr b p units u3 u2 with the transitional period from the end of the pleistocene to the beginning of the holocene 15 000 9000 yr b p and unit u1 with the holocene huanghua marine intrusion in the bohai sea since 9000 yr b p in the bohai sea formation of the tidal ridges is probably due to a substantial increase in tidal current velocities during the late holocene rise of sea level constriction due to the strait amplifies the tidal process so that the sediments of the late holocene transgressive sequence have been remodeled as tidal ridge

effects of ambient currents and waves on gravity driven sediment transport on continental shelves abstract observations from several shelf environments show that down slope gravity driven transport may constitute an important mode of suspended sediment dispersal across shelves and highlight the influence of ambient waves and currents on gravity induced sediment flux the phenomena discussed here involve high concentrations of suspended sediment mixed with seawater and thus differ in genesis from hyperpycnal plumes released directly from sediment laden rivers the field sites examined are the gulf of bohai off the mouth of the yellow river huanghe the northern california shelf off the mouth of the eel river and the louisiana shelf west of the mouths of the mississippi river off the yellow river rapid down slope transport over distances of a few km occurred when frictional resistance induced by strong along shelf currents was temporarily relaxed more prolonged down slope motion over longer distances occurred following floods of the eel river when wave and current agitation provided turbulence to sustain gravity driven transport of fluid mud on the louisiana inner shelf the down slope gravity force was much weaker but observations suggest that thin gravity flows may still have occurred in the presence of waves a simple analytical theory is developed that incorporates the influence of ambient shelf currents on gravity driven transport of suspended sediment this theory is quantitatively consistent with the observations from the three sites if the supply of easily suspended sediment is less than the capacity of ambient currents including waves to carry sediment then intense turbulence limits gravity induced sediment transport by increasing the drag at the base of the flow when ambient currents abruptly cease rapid down slope transport can then occur over short distances until the sediment settles such flows do not remain intensely turbulent because the slope of the continental shelf is too gentle to induce shear instability within the gravity flow the maximum sustained rate of gravity induced sediment transport occurs when ambient currents are strong but the supply of easily suspended sediment exceeds the resuspension capacity of the ambient currents feedback then leads to values of the gradient richardson number ri within the flow that are near the critical value of 1 4 this partially damps bottom drag but still allows the generation of sufficient turbulence to maintain sediment in suspension observations also indicate systematic relationships among ri the supply of easily suspended sediment and the bottom drag coefficient acting on the gravity flow

tidal hydrodynamics and fine grained sediment transport on the radial sand ridge system in the southern yellow sea abstract the large radial sand ridge rsr system located in the southern yellow sea off the jiangsu coast is characterized by a radial current field and high suspended sediment concentrations sscs significant rectilinear currents are present over the northern sand ridge area whereas rotary currents prevail over the southern area the transition between the two being dominated by a locally generated trapped wave observations undertaken in 2006 and 2007 indicate a seasonal pattern in the ssc and associated dynamic characteristics the results of a calibrated hydrodynamic model show that the m2 tide dominates the rsr area the maximum tidal amplitude in the core region close to land being approximately 2 m an amphidromic point is located some distance north of the rsr off the abandoned yellow river mouth 121 686 e 34 6 n specifically the eulerian and lagrangian residual currents flow southward in both summer and winter whereas the stokes drift is directed southward in the north and northward in the south moreover in deep water the lagrangian residual current is mainly determined by the eulerian residual current whereas it is strongly influenced by the stokes drift in shallow water the seasonal variation in the residual current in the southern yellow sea is a good indicator for the location of the yellow sea warm current yswc in both summer and winter measurements show that a ssc peak appears off the abandoned yellow river delta in response to the strong currents and plentiful supply of fine grained sediment from coastal erosion another ssc peak lying close to the north branch of the changjiang river mouth is related to the abundant suspended sediment supplied by the river seasonal variations in ssc are observed in the study area maximum average values and widest diffusion from land occurring in winter this being contrasted by minimum mean values in summer sensitivity experiments demonstrate that the main factor influencing the distribution of ssc is the tide while river discharge wind and wave effects are small and very localized to explain the seasonal variation in ssc the role of hydrodynamics initial conditions and temperature are tested in the model the results show that the hydrodynamics play a significant role whereas the initial conditions only have a minor regional influence temperature on the other hand is also shown to greatly influence the seasonal variation in ssc because of substantial changes in the viscosity of the water and the erosion shear stress the modeled results are used to calculate sediment fluxes which are shown to be consistent with the lagrangian residual current pattern while wind waves can significantly change the fluxes in winter bed elevations change substantially on a monthly time scale in general the deep channels are undergoing erosion while the shallow ridges and coastal tidal flats are accreting the net sediment transport being directed towards the coastal tidal flat and the changjiang yangtze river subaqueous delta

holocene evolution of bottom sediment distribution on the continental shelves of the bohai sea yellow sea and east china sea abstract coastline shifts due to transgression and regression can remodel tidal fields of continental shelves and this can control transport of sediments and modulate sediment distribution accordingly tidal currents have become the dominant hydrodynamic processes on the continental shelves of the bohai sea yellow sea and east china sea byecs since the transgression after the last glacial maximum lgm to examine the evolution of the bottom sediment distributions on the continental shelves of the byecs we simulated patterns of tides and tidal currents sediment transport and bottom sediment types sand mud and mixed sediments for five periods corresponding to sea level lowstands of 80 m 52 m and 30 m below present the holocene transgression maximum htm and the present the simulation shows that both sediment transport and shelf sediment distribution patterns were controlled by the strength type and asymmetry of tidal currents in the byecs since the lgm evolution of shelf sediment distribution patterns occurred in two stages 1 sediment emplacement and formation stage before the htm and 2 local adjustment after the htm the marked changes in coastline configuration since the lgm are the dominant factor controlling tide and tidal current evolution distribution of shelf sediment types in the byecs is closely related to tidal current fields during transgression after the lgm

quaternary seismic stratigraphy and paleoenvironments on the continental shelf of the east china sea abstract paleoenvironments and stratigraphy have been interpreted from 4380 km of seismic profiling collected during a geological and geophysical cruise on the continental shelf of the east china sea ecs undertaken in 1996 the geophysical data are correlated with a borehole situated on the outer shelf obtained by shanghai marine geology bureau indicating that six seismic units have been preserved since oxygen isotope stage 6 including four regressive transgressive cycles seismic units u2 u3 u4 u5 u6 and u7 are interpreted to correspond respectively to oxygen isotope stages 1 3 5 and 6 implying that sediment partitioning and sequence architecture in the ecs have been controlled by glacio eustasy and global climate changes alternating continental and marine strata corresponding to glaciation and interglaciation are well preserved on the outer shelf of the ecs most of the cold environment strata which formed on the outer shelf during oxygen isotope stages 2 and 4 are too thin to be recognized on sig 600j because of resolution but corresponding erosion surfaces exist seismic unit u7 is widespread over the shelf extending to the continental edge and showing little variation in thickness as the regression was pronounced and lasted a long time thus u7 can be used as a marker layer for correlation of quaternary strata on the shelf of the ecs post glacial transgression is obvious in the ecs marine strata with varied thickness were developed in the shallow sea of the inner shelf thinning toward the outer shelf the continental shelf of the ecs has been influenced by pacific tide wave systems for a long time forming tidal sand ridge sequences developed during transgressions corresponding to oxygen isotope stages 7 or 9 5 3 and 1

inter eruptive volcanism at usu volcano micro earthquakes and dome subsidence abstract post eruptive crustal activity after the 2000 eruption of usu volcano was investigated by seismic and geodetic field observations remarkable features of the magmatic eruptions that occur almost every 30 years include lava dome formation and strong precursory earthquakes on the other hand rapid dome subsidence was observed by electronic distance meter edm measurement after the 1977 1982 summit eruption since the 2000 eruption seismic activity at a shallow part under the summit crater has remained at a high level relative to that after the 1977 1982 eruption although eruption occurred at the western foot of the volcano during the 2000 eruption to reveal the shallow crustal activity in the inter eruptive period around the summit area seismicity and crustal deformation have been investigated since 2006 dense temporary seismic observations and hypocenter relocation analysis using a three dimensional velocity structure model revealed that the focal area is localized along the u shaped fault that developed in the dome forming stage of the 1977 1982 eruption three major focal clusters are distributed on the southwestern side of usu shinzan cryptodome which was built up during the 1977 1982 eruption for the seven major events with magnitudes larger than 1 the focal mechanism was a large dip slip component which suggests the subsidence of usu shinzan cryptodome interferomatetric satellite aperture radar insar image analysis and repeated gps measurements revealed subsidence of the summit dome which is almost centered at the usu shinzan cryptodome the area of rapid deformation is restricted to a small area around the summit crater the estimated rate of dome subsidence relative to the crater floor is about 3 cm year these results strongly suggest that subsidence of usu shinzan is associated with the small earthquakes along the u shaped fault that surrounds the cryptodome according to prior seismic and geodetic studies it is thought that most of the magma rising under the summit crater during the 2000 eruption stopped around a depth of 2 km below sea level which is sufficiently deep relative to the focal area of the present seismicity a part of the magma intruded under the western foot and contributed to the 2000 eruption we conclude that the 2000 eruption scarcely affected the shallow crustal activity under the summit crater and that usu shinzan cryptodome is continuing to subside just as it was before the 2000 eruption the shallow volcanic earthquakes that began increasing from 1995 are closely related to the successive subsidence of the summit domes temporal change in fumarole temperature suggests a relationship between the shallow earthquakes and cooling of the magma that intruded under usu shinzan during the 1977 1982 eruption

a tensile shear crack model for the mechanism of volcanic earthquakes abstract temporary seismic observations were carried out for about 1 month at miyakejima island on the izu bonin arc after an eruption on october 3 1983 more than 3000 seismic events were observed and they are classified into 4 different categories short period earthquakes long period earthquakes isolated tremors and continuous tremors two active source regions of the short period earthquakes were located along the old caldera rim of the miyakejima volcano one region was very close to the eruptive fissures another was about 1 2 km northwest of the fissures almost all the earthquakes in the former region showed dilatant first motions of p waves at all the stations in the island on the other hand almost all events in the latter region showed compressive first motions of p waves at all the stations the first motions of p waves for these earthquakes cannot be explained by the quadrant type pattern due to a double couple force system nucleation of a tensile crack coupled with a shear crack a tensile shear crack model is proposed as a source mechanism of the short period earthquakes moment tensor elements of tensile and shear cracks have been determined by the least squares method using observed p and s wave data results suggest that tensile cracking opening or closing is dominant for generating those earthquakes in comparison with shear cracking the strikes of the tensile cracks for the earthquakes are shown to be nearly parallel to the strike of the fissures the earthquakes that occurred in the northwestern region of the fissures are considered to be generated by a sudden opening of tensile shear cracks due to the excess pressure of intrusive magma in contrast the earthquakes occurring beneath the fissures are probably generated by a sudden closing of tensile shear cracks and this suggests that the magmatic pressure under the fissures rapidly decreased after the eruption moment tensor analysis of the tensile shear crack model in this study demonstrates the non double couple source mechanism for volcanic earthquakes related to magmatic activity

cheniers on the east coastal plain of china abstract three to four cheniers are found in the coastal areas of the bohai sea and west yellow sea they are formed in the sheltered low tidal flat coast with low to medium wave energy large quantity of fine sediment supply and shells and a coastal slope of 0 9 3 0 the huanghe river played a major role in controlling the chenier development by either providing sediment supply or cutting off the supply through shifting of its course cheniers may be used to determine the coastal development and dynamic processes

holocene regression and the tidal radial sand ridge system formation in the jiangsu coastal zone east china abstract a radial tidal sand ridge system rtsrs spans more than 20 000 km 2 in the southwest yellow sea is fan shaped and stretches from qianggang toward the sea the marine rtsrs is located in a convergent divergent tidal current field cdtcf numerous drilling holes reveal an area of 3000 km 2 containing tidal sand strata in the jiangsu coastal plain on land adjacent to the marine rtsrs which stretches eastward from chengdong and is also a fan shaped with a central angle of 130 the tidal sand unit lies on a transgressive coastal barrier lagoon unit with an erosional surface between them and the latter unit is in turn lying on late pleistocene stiff mud the tidal sand unit is overlain by the littoral tidal flat unit and together they constitute the holocene regressive succession paleo current study reveals that a paleo current pattern similar to the modern marine cdtcf was present in the holocene sub aerial tidal sand strata therefore the sub aerial tidal sand bodies are deduced to be an ancient rtsrs that was formed during the holocene regression and gradually exposed and changed into land as the changjiang and huanghe deltas prograded both sub aerial and marine rtsrs should be formed in the same tidal depositional environment but in different development stages thus the radial tidal sand ridges in southwestern yellow sea should have formed not during the holocene transgression as most previous studies have inferred but in the process of holocene regression mineralogical analyses demonstrate that the sediment source of the sub aerial rtsrs initially came from the changjiang and later predominantly from the huanghe sea floor erosion by tidal currents may also provide sandy material to form the rtsrs drilling cores and ground penetrating profiles show that the paleo valleys in the study area are much smaller than the present distributaries of the changjiang river thus the presumption of direct sand supply by a large river to form the rtsrs through its apical area is cannot be supported after the sea level reached the present high stand the jiangsu coastline has been prograding seaward as the changjiang delta expanded and this progradation was accelerated when the huanghe debouched in the study area the nearshore part of rtsrs has been gradually changing into land while the entire rtsrs extends seawards in the process of the development the rtsrs apex changed from chengdong to qianggang at present the coastline is still moving seaward while the outer part of the rtsrs suffers from some erosion owing to reduction of sediment supply from both the changjiang delta and the abandoned huanghe delta

sedimentary facies and holocene progradation rates of the changjiang yangtze delta china abstract the changjiang yangtze river one of the largest rivers in the world has formed a broad tide dominated delta at its mouth during the holocene sea level highstand three boreholes cm97 js98 and hq98 were obtained from the changjiang delta plain in 1997 1998 to clarify the characteristics of tide dominated delta sediments and architecture based on sediment composition and texture and faunal content core sediments were divided into six depositional units in ascending order they were interpreted as tidal sand ridge prodelta delta front subtidal to lower intertidal flat upper intertidal flat and surface soil deposits the deltaic sequence from the prodelta deposits to the delta front deposits showed an upward coarsening succession overlain by an upward fining succession from the uppermost part of the delta front deposits to the surface soil thinly interlaminated to thinly interbedded sand and mud sand mud couplets and bidirectional cross laminations in these deposits show that tide is the key factor affecting the formation of changjiang deltaic facies sediment facies and their succession combined with ams 14c dating revealed that isochron lines cross unit boundaries clearly and delta progradation has occurred since about 6000 to 7000 years bp when the rising sea level neared or reached its present position the average progradation rate of the delta front was approximately 50 km kyear over the last 5000 years the progradation rate however increased abruptly ca 2000 years bp going from 38 to 80 km kyear the possible causes for this active progradation could have been an increase in sediment production in the drainage basin due to widespread human interference and or decrease in deposition in the middle reaches related to the channel stability caused by human activity and climatic cooling after the mid holocene

pleistocene forced regressions and tidal sand ridges in the east china sea abstract tidal sand ridges are common features on modern shelves but only few examples of such preserved sand bodies are described in pleistocene deposits in the stratigraphic record some sand bodies encased in shales previously interpreted as sand ridges have been reinterpreted as shoreface deposits more than 5000 km of high resolution seismic data from the east china sea correlated to geotechnical boreholes and shallow cores demonstrate the potential of sand ridge preservation and allow reconstruction of the depositional history of pleistocene fourth order 100 kyr depositional sequences a high subsidence rate of about 300 m myr allows the preservation of three elementary sedimentary facies constitutive of a motif which was repeated during glacio eustatic cycles they consist of 1 regressive marine prodeltaic prograding wedges 2 estuarine and continental deltaic facies and 3 transgressive sand ridges similar in shape and orientation to modern sand ridges major discontinuities traceable over the entire outer continental shelf along distances of hundreds of kilometers are transgressive and regressive surfaces of marine erosion whereas sequence boundaries formed by fluvial erosion are difficult to identify on this low gradient shelf because of the asymmetry of the pleistocene glacio eustatic cycles most of the preserved sedimentary record with the exception of sand ridges corresponds to forced regressive deposits deposits that formed during a seaward shift of the shoreline due to relative sea level lowering

transgressive sand ridges on the mid shelf of the southern sea of korea korea strait formation and development in high energy environments abstract the mid shelf of the southern sea of korea korea strait is covered by a series of shore parallel sand ridges up to 63 km long 3 9 km wide and 22 m thick the ridges are a moribund type but show well organized dipping strata indicating appreciable progradation the submerged paleo channel system the paleo seomjin river associated with the sand ridge field suggests that the ridges primarily originated from river mouth sandy shoals which subsequently developed into shore parallel linear sand bodies in high energy environments the combined effect of coastal tidal and longshore and offshore ocean currents was possibly responsible for shore parallel sediment transport and growth of the ridges 14c dates core lithology and sea level data suggest that the sand ridges mainly formed and developed during the middle period of the postglacial transgression they are postulated to have developed sequentially from offshore to onshore in response to sea level rise during that time very slow sea level rise and high sediment supply through the paleo channel system probably provided favorable conditions for forming the sand ridges the ridges became inactive during the late transgression period as a result of a substantial reduction of wave and current strength and remained on the mid shelf

provenance structure and formation of the mud wedge along inner continental shelf of the east china sea a synthesis of the yangtze dispersal system surficial grain size and down core clay mineralogical data show that sediment along the inner most part of the continental shelf in east china sea is mainly derived from the yangtze river changjiang spanning from the yangtze mouth 33 degrees n similar to 1000 km southward to the southwestern corner of the taiwan strait 24 degrees n high resolution chirp seismic profiles reveal an elongated mud wedge extending along the inner shelf with a northern depocenter on the modern yangtze delta and a southern depocenter at 27 5 degrees n four distinct acoustic units are delineated within the mud wedge from bottom up unit i late pleistocene mainly valley fills unit ii formed by transgressions thin strata unit iii 11 2 kyr bp downlapping strata and unit iv 2 0 kyr bp flat and opaque strata incised valleys up to 15 m deep are filled by flat lying or inclined strata in unit i the thin 3 m and acoustically transparent unit ii is only seen between 30 and 26 degrees n in water depths between 40 and 90 m separated by acoustically opaque strata or unconformities units iii and iv are widely distributed during the past 11 kyr yangtze sediment accumulation has been unsteady showing two high and one low accumulation rate periods the high accumulation period at 5 8 kyr bp may be related to maximum east asian summer monsoon precipitation in the yangtze basin the other high accumulation period 0 2 kyr bp probably reflects intensive human activities in the river s watershed the low accumulation rate period at 2 5 kyr bp which is seen in both northern and southern yangtze depocenters is probably related to low river discharge and or intensified taiwan warm current and china coastal current c 2011 elsevier b v all rights reserved

an early holocene sea level jump and delta initiation 1 early holocene sea level change controlled the evolution of clastic coastal depositional systems radiocarbon dated borehole cores obtained from three incised valley fill systems in asia changjiang song hong and kiso river record very similar depositional histories especially between about 9000 and 8500 cal bp sedimentary facies changes from estuarine sand and mud to shelf or prodelta mud suggest that the marine influence in the incised valleys increased during this period in addition large decreases in sediment accumulation rates occurred a sea level jump causes an estuarine system and its depocenter to move rapidly landward it is possible that the final collapse of the laurentide ice sheet accompanied by catastrophic drainage of glacial lakes at approximately 8500 cal bp caused such a jump the jump was followed immediately by a period of decelerated sea level rise that promoted delta initiation

early neogene biochemostratigraphy of pohang basin a paleoceanographic response to the early opening of the sea of japan east sea abstract the location of the pohang basin near the korea strait in the southwest of the sea of japan east sea makes this area appropriate for providing a record of paleoenvironmental biotic changes associated with the early neogene 16 5 ma opening of this gateway to the pacific ocean stable isotopic and planktonic foraminiferal records are presented that assist with the understanding of paleoenvironmental changes in the sea of japan resulting from the opening of the korea strait the oldest sediments of early neogene age of the pohang basin overlie cretaceous basement and are early miocene 16 5 ma shallow estuarine facies containing a benthic foraminiferal assemblage dominated by ammonia beccarii l the oldest early neogene planktonic foraminiferal assemblages in the basin are 16 5 ma in age latest early miocene foraminiferal zone n8 the migration of these planktonic assemblages to the sea of japan at that time appears to have resulted from the initial opening of the korea strait the overlying early neogene marine sequence of the pohang basin extends from 16 5 ma zone n8 through 14 ma zone n10 change in the oxygen isotopic record of the pohang basin sequence suggests strong local paleoenvironmental control related to the early opening of the korea strait early middle miocene isotopic temperatures of planktonic foraminifera are relatively cool at 15 ma at a time when global temperatures were high in the middle low latitude regions it was not until 14 8 ma that isotopic temperatures of planktonic foraminifera increased markedly this distinct warming is inferred to reflect the major intrusion of the kuroshio current into the sea of japan probably as a result of further critical opening and deepening of the korea strait at this time planktonic foraminifera increased in abundance reflecting expanding oceanic influence a cooling that followed at 14 5 ma when the strait was well open is unlikely to reflect local tectonic control on the paleoceanography but global cooling during the early middle miocene associated with the expansion of the east antarctic ice sheet

late quaternary transgressive and highstand systems tracts in the northern east china sea mid shelf abstract analysis of very high resolution 3 5 khz seismic profiles and sediment data from the northern east china sea mid shelf region reveals that the sedimentary sequence above the acoustic basement consists of five late quaternary sedimentary units comprising transgressive and highstand systems tracts formed after the last glacial maximum the transgressive systems tract includes four units 1 incised valley fill unit i 2 transgressive estuarine deltaic complex unit ii 3 transgressive sand sheet unit iii and 4 tidal sand ridge unit iv the lower two units units i and ii representing a paralic environment consist of sediment preserved from shoreface erosion the upper units units iii and iv corresponding to a marine environment consist of sediments produced through shoreface erosion during the holocene transgression a ravinement surface separates the lower and the upper units the highstand systems tract is composed of a distal mud patch unit v derived from the huanghe and changjiang rivers in china dispersal and deposition of this modern mud are largely controlled by the regional circulation pattern and sediment supply

modeling the growth limit of the changjiang delta river deltas grow in response to sediment discharge from the land it is not clear however whether or not there is a limit for such growth conceptual geometric models are used in this paper in association with the principle of mass conservation in an attempt to answer this question preliminary analyses of the changjiang delta indicate that delta growth is constrained by a number of factors the original topography bathymetry sediment supply sediment retention in the estuary sea level rise ground subsidence the quantity of sediment supply per unit area and the sediment retention index for the subaqueous delta decrease as the delta progrades towards deeper water resulting in a decreasing rate of growth the limit of growth is reached when the index approaches zero i e the shoreline reaches the shelf edge if the combined effect of sea level rise and ground subsidence is considered together with decrease in the sediment discharge from land the limit is reached at an earlier stage for the changjiang delta the model output using hypothesized sediment retention index estimates implies that the delta growth will reach its limit in the near future this will occur sooner if the sediment output of the river is reduced to 60 of its original level in response to the upstream basin changes further knowledge however is required of the retention index together with the information on future changes in river input and the character of the sediments in order to improve the accuracy of the simulations

marine climatic responses to neogene tectonics of the pacific ocean seaways abstract based upon surface marine climatic evolution on both sides of the pacific ocean recently revealed by biochronostratigraphy in japan and south america the tectonics of pacific ocean seaways and associated responses of adjacent seas and ocean currents are discussed the rapid opening of the sea of japan at about 15 ma in early middle miocene time mainly by the rotation of the southwest japan arc can be correlated with the abrupt appearance of a cold water fauna on the pacific coast of northeast japan beginning ca 15 ma and an extensive hiatus along the pacific coast of southwestern japan spanning 15 ma to 12 ma the abrupt and extensive development of biosiliceous lithofacies along the pacific coast of peru beginning about 14 ma might also represent a response to the tectonic anticlockwise rotation of the peruvian block of the andean mountain range estimated to have occurred sometime during the miocene as the tectonic closing of the indonesian seaway would have strongly intensified the warm kuroshio current in the northwest pacific it is most probable that this seaway was effectively closed just prior to 15 5 ma in the earliest middle miocene when tropical marine faunas were developed in most of the japanese islands the closing of the central american seaway is estimated to have been completed at 3 5 3 ma in pliocene time the closure of this seaway would likely have intensified the warm kuroshio current affecting the marine fauna along the pacific coast of southwestern japan it is also possible that a decrease in surface temperatures at about 3 ma along the pacific coast of ecuador was due to this pliocene tectonic event

quantitative models of sedimentary basin filling summary quantitative modelling of the filling of sedimentary basins was begun in earnest in the 1960s dozens of themes and variations have been proposed since then and have yielded an abundance of idealized stratigraphic patterns as functions of both imposed changes and basin properties post plate tectonic modelling began with rigid lid models which show the stratigraphic signature of subsidence variation this work introduced the connection between stratigraphy and the rheology of the lithosphere rigid lid models are the simplest type of geometric model in which the sediment surface is assigned prescribed geometries usually corresponding to different depositional environments these can reproduce many aspects of overall stratal geometry but are formally restricted to relatively long timescales for which quasi steady surface topography can be assumed so called dynamic models attempt to represent the morphodynamics of the sediment surface by abstracting and averaging short term transport processes most of the dynamic models proposed to date can be seen as special cases of a single general morpho dynamic equation the most important result of the first wave of quantitative basin filling models is that even relatively simple models can produce reasonable stratal patterns we now have a wide array of tools for exploring scenarios searching for general behaviours and effects and making initial quantitative predictions we have also learned that basin response to external forcing as recorded in stratigraphy can be as sensitive to the characteristics of the basin as to the forcing the main brake on the development of basin modelling is not computing power but lack of methods and data for testing the models we have already developed physical experiments which are only just beginning are one means of doing this experimental stratigraphy is a bridge to quantitative field tests which will require collaboration among academic researchers from a wide range of areas and between academia and industry on projects of greater scale and degree of integration than we have seen so far the advancement of quantitative sedimentary geology will also require significant changes in the way the subject is taught at all levels

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

the 1980 pressure response and flank failure of mount st helens usa inferred from seismic scaling exponents the cataclysmic 18 may 1980 eruption at mount st helens was preceded by intense seismic activity marking the mechanical response of the volcanic edifice to interior pressurisation this seismicity is analysed to yield the temporal change in the seismic scaling exponent d inferred from the seismic b value that in turn is related to the seismic moment of an earthquake time evolution of d preceding the eruption onset reveals 1 a major decrease in d occurring over only a few days at the end of march 2 a steady but stepped decrease in d steps 5 10 days occurring from the end of march to early may 3 a sharp decrease in d in early may and 4 steady low values of d occurring 2 3 days before the eruption onset this response is interpreted as major ruptures formed at the end of march arresting and participating in but not triggering the ultimate failure of the flank rather the rate of interior fracturing slowed in the 2 months preceding the 18 may 1980 major blast and the triggering of failure is consistent with interior gas overpressurisation the occurrence of two swarms of low frequency seismic events and the high values of the harmonic tremor indicate the action of interior pressurisation on a cycle of 20 25 days solutions are applied to represent the harmonic interior pressurisation of the edifice by gas exsolving from the volcano core the transient radial migration of overpressured gas may reduce the apparent strength of the edifice and ultimately trigger failure of the flank importantly this mechanism is capable of triggering flank failure both after multiple core pressurisation cycles have been sustained and as core pressures are low and diminishing and may be a minimum these twin attributes are both apparent in the seismic record for mount st helens used as a proxy for the unrecorded timing and magnitude of gas pressurisation at the volcano core d 2004 elsevier b v all rights reserved

ree geochemistry of fine grained sediments from major rivers around the yellow sea abstract to investigate the distribution pattern and controlling factors of rare earth elements rees in riverine sediments river mouth sediments were collected at five geographically different rivers around the yellow sea two 1 m hcl leached and residual fractions and five step sequential extraction schemes the sedex method were applied to size separated sediments

the sand ridge field of the south yellow sea origin by river sea interaction abstract the origin of a large field of sand ridges offshore from the north jiangsu coast in the south yellow sea has been investigated on the basis of bathymetry seabed samples high resolution seismic profiles and 31 to 71 m deep boreholes sediment composition including heavy minerals and clay minerals sampled from surface sediments shows that most of the sand was derived from the changjiang yangtze river but in the northern part of the field particularly the clay came from the huanghe yellow river seismic profiles show late pleistocene distributary channels of the ancient changjiang river underlying much of the southern part of the sand ridge field the holocene transgression cut a widespread ravinement surface reworking abundant late pleistocene sandy sediment the available sand was reworked by tidal currents into large ridges the location of the ridges is strongly influenced by relict channels in the southern part of the field and by tidal currents in the northern and especially the northeastern part of the field resulting in a radiating ridge pattern these ridges provide an example of the evolution of a large scale geomorphic feature resulting from river sea interaction in which climatic and sea level changes played an important role

high resolution acoustic characteristics of epicontinental sea deposits central eastern yellow sea abstract large amounts 45390 line km of closely spaced 2 2 4 4 km high resolution subbottom profiles chirp 2 7 khz made it possible to identify detailed echo types and their distribution in an epicontinental shelf environment on the basis of seafloor morphology surface bedforms and subbottom acoustic characters 10 echo types were identified in the uppermost sedimentary sequence of the central eastern yellow sea flat seafloor with sharp bottom echoes echo types 1 1 1 2 and 1 3a transgressive sediment sheets or relict sands is widespread in the offshore area and underlain to the west by an acoustically transparent wedge echo type 1 3b highstand muds mounded seafloor with either smooth surface or superposed bedforms echo types 2 1 2 2 and 2 3 tidal ridges and flat seafloor with regularly spaced wavy bedforms echo type 1 4 large scale dunes are dominant in the eastern nearshore area large scale mounds with continuous inclined internal reflectors echo type 2 4 giant mud bank occur in the southeastern nearshore area various scale eroded seafloor echo types 3 1 and 3 2 channels and flat seafloor with regularly spaced wavy bedforms echo type 1 4 large scale dunes are present in the northern part of the sea the distribution pattern of echo types in the central eastern yellow sea reflects depositional processes and sediment dispersal systems during the holocene transgression and highstand period 1 development of tidal ridges and large scale dunes in response to strong tidal currents and waves in the eastern nearshore area 2 construction of transgressive to highstand mud bank huksan mud belt by deposition of muds derived from the keum river in the southeastern nearshore area 3 active erosion due to intensified currents in the northern part and 4 highstand mud deposition derived from the huanghe river on the transgressive sediment sheets in the offshore area

forward modelling of the sequence stratigraphic architecture of shelf cyclothems application to late pliocene sequences wanganui basin new zealand we demonstrate a procedure for forward modelling of the sequence stratigraphic architecture i e positions of systems tract boundaries of shelf cyclothems as observed at outcrop sites or in well logs the 1 d model is based on the fact that the deposition of facies within shelf sequences and those defining the key stratigraphic surfaces between systems tracts respond directly to changes in depth between the sea surface and seafloor this accommodation bathymetry model incorporates three reference surfaces sea surface seafloor and lower sequence boundary each of which varies independently as a result of changes in the rates of eustatic sea level sedimentation and subsidence the model input and boundary conditions are an eustatic sea level curve i e late cenozoic deep sea 18o record an independent chronology for the outcrop or well section and a subsidence curve the model outputs are changes in accommodation and palaeobathymetry throughout the sequence and the time missing at erosional sequence boundaries the main variable in the model i e sedimentation rate is established by comparison of a model output bathymetry with the model target palaeobathymetry established from the faunal and facies content of the sequence being modelled when the model output and target are compatible the model sedimentation rate curve is adopted and the theoretical positions of the systems tract boundaries can be read off the model in relation to the lower sequence boundary and compared with independent field based interpretations of their stratigraphic position the model is designed to predict the architecture of sequences as they appear at particular outcrop sites or in well sections its usefulness lies in establishing the timing of accumulation of systems tracts in relation to stages in a eustatic sea level cycle in particular distinguishing between units deposited during highstand versus regressive systems tracts the model is applied to 6th order 41 ka plio pleistocene cyclothems in wanganui basin new zealand where it distinguishes the boundary between highstand systems tracts hst and regressive systems tracts rst the modelling has implications for the definition of systems tracts especially in late cenozoic successions for which the record of eustatic sea level changes is known independently

transgressive and highstand systems tracts and post glacial transgression the east china sea abstract the late pleistocene holocene depositional sequence on the shelf in the east china sea ecs is interpreted on the basis of the analyses of four sediment cores and high resolution seismic reflection sub bottom profiler records along a ne sw across shelf transect sedimentary strata deposited above a lowermost planar erosional surface that was formed during sea level fall of the last glacial are divided into two units along a ne sw across shelf transect changjiang okinawa the lower unit is characterized by seaward dipping tangential clinoforms with a thickness of 30 40 m at mid shelf depths and less than 30 m beneath the outer shelf prograding clinoforms are more obvious in mid shelf environments the upper unit is characterized by an upper transparent layer that is formed into ridge and swale topography the boundary between the upper and lower units is sharp and erosional surficial sediments taken by cores from the central ecs shelf are also divided into two facies a sandy facies consisting of sand or sandy gravel with moderately abundant molluscan shell fragments and a muddy facies comprising mud intercalated with thin sand layers the sandy facies is widely distributed on the middle to outer shelf seafloor and has a measured thickness of 30 cm up to several metres radiocarbon ages of molluscan shells in this sediment are less than approximately 10 ka bp except for ages from basal shell lag deposits which are 10 40 ka bp the muddy facies underlies the sandy facies and has radiocarbon ages of 2 7 2 9 ka bp previous work and 20 38 ka bp this study and tl ages of 27 50 ka bp previous work the boundary between these lithologic units is an erosional sharp contact the sandy and muddy facies are correlated with the upper and lower seismic units respectively the lower unit is characterized by prograding clinoforms and is interpreted to represent deltaic or nearshore tidal ridge sediments of the paleo changjiang river that were deposited during the last glacial lowstand of sea level as a lowstand systems tract the underlying erosional surface is interpreted to be a sequence boundary formed as a regressive marine erosional surface during the fall of sea level the erosional boundary between the lower and upper units is interpreted as a transgressive surface of erosion formed during the subsequent rise of sea level the upper unit has a modern sand ridge topography and is interpreted to represent offshore shelf sand ridges of the transgressive to highstand systems tract

sediment dynamics in a submarine canyon a case of river sea interaction this paper presents findings from a 1 month field experiment conducted during the flood season of 2000 on the southern coast of taiwan to examine the delivery of lithogenic siliciclastic sediment to kao ping submarine canyon from the nearby kao ping river and shelf sources and the transport of suspended lithogenic and nonlithogenic particles near the canyon floor collected time series data included simultaneous measurements of coastal winds salinity temperature flow field suspended sediment concentration ssc and size composition of suspended particles at the river mouth and inside the submarine canyon as well as results from seawater and sediment trap data other collected data included river discharge and sediment load and hydrographic measurements along and across the axis of the canyon during the experiment two significant episodic river sediment discharge events occurred relating to a typhoon and extreme precipitation conditions the findings show that theoretically the time difference between sand and clay siliciclastic grains to settle from the sea surface to the canyon floor is on the order of hours to months analogous to a sorting process river plume dynamics and the coastal wind field largely control the delivery of terrigenous fine grained sediment to the canyon inside the canyon the behavior of suspended lithogenic and nonlithogenic particles of different sizes can be differentiated into a coarse grained group sand which forms the drop in population and a fine grained group mud which forms the standing population each group has distinct spectral characteristics the coarse grained group is delivered directly to the canyon by the river effluent and by wave resuspension of the shelf substrate during the study period the net transport of suspended particles near the canyon floor was landward mostly by tidal currents whose direction was also modulated by spring neap tide both lithogenic and nonlithogenic particles contribute to high mass fluxes exceeding 700 g m 2 day 1 in the lower part of the canyon this river sea system represents a type of systems that consist of three geographically separated dynamic entities the river plume the shelf and the canyon under fair weather conditions the river plume and shelf processes are coupled through the tide and wind field the river and canyon form a direct source to sink link via coarse grained siliciclastic sediment during the flood season in both continuous and pulsed fashion in the typhoon season the shelf becomes a pulsed source region for coarse grained sediment

seismological significance of the 1977 1978 eruptions and the magma intrusion process of usu volcano hokkaido abstract an earthquake swarm and the major pumice eruptions in august 1977 which followed marked the start of the dacitic doming activity of usu volcano in southwestern hokkaido japan the sequence of magma intrusion processes was investigated in detail by means of seismological and other geophysical data the distribution of the abundant hypocenters shows clearly an earthquake free zone beneath the summit crater the hypocenters migrated in a manner consistent with the development of the observed asymmetrical surface deformations considered due to magma intrusion into this earthquake free zone the earthquake mechanism solutions are mostly of dip slip type and are interpreted in terms of the doming deformations the existence of earthquake families earthquakes with similar waveforms is the main cause of the peculiar occurrence of earthquakes in space time and magnitude the concept of scattered barriers of different sizes and strengths can explain well the distinct characteristics of the occurrence of the swarm and the observed episodic deformations

oceanography chemical twins separated how the chemical composition of sea water changes on its journey through the world s oceans is poorly understood systematic measurements of dissolved trace metals across the pacific ocean suggest that these metals may help track sources and mixing of water masses

on the formation of sand banks of finite extent we consider a model where the fluid depth depends on both horizontal coordinates quasi steady depth uniform non divergent fluid flow is governed by inertial pressure and bottom frictional forces sand transport is proportional to the cube of the instantaneous current but augmented by a down slope component and by wind wave action and sand is conserved it is found that low parallel banks grow fastest so that in an extensive spatially uniform sea previous calculations for linear banks are appropriate the inclination of banks to the tidal currents can be interpreted in terms of similarly inclined deposition bands resulting from vorticity generation and advection in flow over a small isolated hump a small bump can evolve to an equilibrium bank typically after an initial rapid extension across the tidal currents provided that sand is sufficiently restricted and particularly if some wind wave action prevents growth up to the sea surface sand banks are likely to be in a late stage of evolution when the main change is a slow lengthening as the net current and transport along the bank side slows and turns around the bank end with net deposition the equilibrium is apparently stable except when there is an overall bed slope in the direction of the tidal currents or when sand is abundant

sediment retention at the changjiang sub aqueous delta over a 57 year period in response to catchment changes the growth of a river delta system is controlled mainly by fluvial sediment discharge and sediment retention in the deltaic areas in the present study we attempt to define a sediment retention index r and its relation to the deposition rate of the delta based upon two assumptions that the amount of the sediment that escapes from the deltaic areas qe is stationary with minor fluctuations and that there is a linear relationship between the deposition rate averaged over the sub aqueous delta dav and the deposition rate at accretion sites within the delta dr the changes in the accretion erosion patterns of the changjiang sub aqueous delta during the period of 1951 2007 in response to river sediment discharge changes are analyzed the results show that the sediment retention index can be related to the deposition rate of the sub aqueous delta the spatial temporal distribution pattern of the deposition rate reveals the behaviour of sediment retention of a delta system for the changjiang sub aqueous delta fluvial sediment discharge data together with pb 210 based deposition rates provide useful information on sediment retention changes in the sediment retention index and the accretion erosion patterns of the sub aqueous delta have taken place in response to river input changes in order to improve our understanding of the processes associated with estuarine sediment retention sediment cores with sufficient spatial coverage may be collected and analyzed to establish accurate qe r and dav dr relationships in combination with numerical modeling of sediment transport these relationships form a basis for the analysis of sediment retention mechanisms

sedimentology and stratigraphy of a tidal sand bank in the southern north sea abstract a set of 125 vibrocores collected on the basis of a dense grid of high and very high resolution seismic coverage over a tidal sand bank the middelkerke bank provides a unique opportunity to reconstruct the stratigraphy and sedimentary facies succession of such a large tidal sand body five sedimentary facies are distinguished they range from clay to pebble and display various types of bedding and lithologies corresponding to different depositional environments a succession of four late quaternary units are defined on the basis of the stratigraphic framework given by the seismic grid the first unit represents the infill of a palaeovalley system by tidally influenced sedimentary facies it is followed by extensive and thick lagoonal or sub tidal deposits the third unit reveals the development of a landward prograding storm dominated sand bar this unit is dominated by clean fine sand the last unit corresponds to the present day tidal sand bank it shows the typical offshore tidal sand bank facies cross bedded sand prograding in an offshore direction like other banks located in a more offshore position the middelkerke bank is a composite bank incorporating facies which do not occur in classic tidal sand banks

source parameters and scaling relationships of small earthquakes in the northeastern caribbean abstract the seismic moments and stress drops of 23 earthquakes 1 1 m 2 4 that occurred during an earthquake swarm in the virgin islands were determined from the analysis of their p waveforms the data consist of digitally recorded seismograms collected by a short period seismic network operating in the northeastern caribbean the events of the swarm are particularly useful for comparing the relative stress drops of small earthquakes because their source to receiver paths and focal mechanisms are very similar the static stress drops calculated for these earthquakes varied from about 0 2 to 2 bars the data clearly illustrate that the static and dynamic stress drops of these earthquakes generally increased with the size moment of the events the fault radii for these shocks increased with seismic moment but only by a factor of 2 for a 100 fold increase in seismic moment the velocity waveforms of the larger events were systematically more impulsive than those of the smaller earthquakes these observations imply that for this set of earthquakes the final fault radius is a function of the stress drop that occurs during the rupture process

magnetic and geochemical evidence of yellow and yangtze river influence on tidal flat deposits in northern jiangsu plain china abstract the formation of a broad tidal flat along the coast of the northern jiangsu province of china depends largely on the sediment supply from the yellow and yangtze rivers although the relative contributions from each of these two large rivers remain uncertain knowledge of sediment sources to the tidal flat is critical for understanding the evolution of this muddy coast impacted by the large rivers the present study focuses on tracking the sediment source of the tidal flat deposits based on sediment magnetic properties and geochemical analyses as well as statistical analysis the study shows that sediments to the north of yangkougang site 9 have lower values of saturation isothermal remanence magnetization sirm magnetic susceptibility demagnetization parameter s 100 ratios lower fe al values and higher ca concentrations while the opposite is true for samples south to haozhigang site 18 in addition sirm values of the 63 m fractions generally display increasing trend from north to south these results suggest that sediment sources rather than particle size variation are the dominant factors influencing the bulk magnetic properties in light of the sediment composition comparison between the yellow river and yangtze river factor analysis is used to identify sediment source of the tidal flat sediments it is indicated that the yellow river in its former course is the dominant supplier for sites to the north of yangkougang site 9 while the yangtze river is the dominant supplier for sites to the south of haozhigang site 18 the coast between yangkougang site 9 and haozhigang site 18 is a transition zone influenced by both rivers the inferred provenance contrasts are consistent with the pattern of coastal geomorphological evolution our data also suggest that sediments eroded from the former yellow river delta have contributed to the evolution of the yangtze estuary in historical time this study demonstrates that a combined magnetic and geochemical fingerprinting techniques in couple with statistical analysis is valuable for identifying sediment sources of tidal flats and deltas influenced by large rivers in the world

source parameters of seismic events at heinrich robert mine ruhr basin federal republic of germany evidence for nondouble couple events abstract a three component digital seismic station is in operation at heinrich robert coal mine in the ruhr basin at a depth of 890 m a cluster of seismic events occurred at the beginning of 1987 at a distance of about 5 km from the station and continued in 1988 source parameters of 46 tremors selected from the cluster with local magnitude from 1 2 to 2 3 are studied the ratio of p wave to s wave corner frequency is variable implying its dependence on the angle of observation and in turn the variability of focal mechanism with time the scaling relations indicate that characteristic tremors with a fault length of about 200 m are possibly generated in the area but the evidence is not conclusive the seismic energy for a given seismic moment can vary by a factor of 20 and the ratio of s wave to p wave energy ranges from 1 5 to 30 stress release estimates show low values not exceeding a few bars typical for tremors induced by mining a comparison of the apparent stress with the static stress drop divides the selected tremors into high and low apparent stress events the latter events are characterized by high p wave energy and almost constant and large ratio of p wave to s wave corner frequency which differs from the lower ratios of other events implying similar focal mechanism these high p wave energy tremors are the most likely candidates for nondouble couple events

evolution of late quaternary mud deposits and recent sediment budget in the southeastern yellow sea abstract analysis of high resolution seismic reflection profiles and sediment samples has revealed the evolution and sediment budget of the southeastern yellow sea mud belt seysm along the southwestern korean peninsula the seysm up to 50 m thick over 250 km long and 20 55 km wide can be divided into three stratigraphic units a1 a2 and b from oldest to youngest unit a1 overlying the acoustic basement comprises the northern part of the seysm unit a2 comprises the southern part of the seysm much of unit a2 is exposed at the seafloor unit b completely covers unit a1 and pinches out southward 14c data suggest that evolution of each unit is closely related to the postglacial sea level changes unit a1 consists of estuarine deltaic or shallow water muds deposited during the early to middle stage of postglacial sea level rise ca 14 000 7000 yr b p unit a2 corresponds to relict muds deposited during the last deceleration stage of sea level rise ca 7000 3 500 yr b p unit b consists of shelf muds deposited during the recent sea level highstand ca very low background activities of 210pb of the surface sediment of unit a2 suggest that the present day sediment accumulation is negligible in the southern seysm on the other hand 210pb excess activity profiles in unit b yield an average sediment accumulation rate of 3 9 mm yr indicating active sediment accumulation in the northern seysm the annual sink 3 0 10 7 tons yr of fine grained sediment in unit b is about an order of magnitude greater than can be explained by the sediment input from the korean rivers alone we propose that reworking of unit a2 has provided large volumes of muds to unit b resulting in excessive sediment accumulation in the northern seysm much of unit a2 in turn is likely to have originated from erosion of unit a1 in the north this rather unique erosional depositional regime of the seysm is probably owing to the tidal and regional currents characteristic in the southeastern yellow sea

changing pattern of accretion erosion of the modern yellow river huanghe subaerial delta china based on remote sensing images abstract the yellow river shifted from the diaokou course to the qingshuigou course in 1976 and shifted again at the north bank of the qingshuigou course in 1996 as a result the entire modern yellow river delta has experienced complicated patterns of erosion and accretion multitemporal remote sensing data of landsat mss and tm from 1976 to 2000 totaling twenty scenes were used to examine the changing pattern of accretion and erosion of the modern yellow river subaerial delta with gis tools during the period 1976 to 2000 the maximum erosion occurred at the head of the last two abandoned promontories diaokou and shenxiangou promontories where the coastline retreated landward over 7 and 4 5 km respectively with mean net erosion rates of 0 29 and 0 19 km a respectively in contrast the maximum accretion occurred at the head of the qingshuigou promontory where the coastline advanced seaward over 20 km with a mean net accretion rate of 0 83 km a the coastline at the head of the q 8 promontory also advanced seaward 7 km with a mean net accretion rate of 0 29 km a during the period 1996 to 2000 total area of the diaokou and shenxiangou promontories was reduced by 141 3 km 2 with a mean net erosion rate of 6 03 km 2 a total area of the qingshuigou and q 8 promontories increased by 384 16 and 11 88 km 2 respectively with mean net accretion rates of 16 4 and 3 03 km 2 a respectively relative to the diaokou shenxiangou and qingshuigou promontories the west area of the diaokou promontory and south area of the qingshuigou promontory were relatively stable although minor erosion occurred the general pattern of accretion and erosion of the modern yellow river subaerial delta was divided into three stages rapid accretion stage 1976 1984 accretion erosion adjustment stage 1985 1995 and slow erosion stage 1996 present the factors affecting the pattern of erosion and accretion over the yellow river delta such as structural geology the yellow river sediment discharge coastal processes meteorological conditions human activity sea level rise and land subsidence were summarized the cumulative area of increase over the entire subaerial delta is closely correlated with the cumulative yellow river sediment discharge wave induced longshore current is the major driving force to transport sediment from eroded areas along the last two abandoned promontories diaokou and shenxiangou promontories mostly westerly and partially easterly together with these coastal processes is the geographical shift of the yellow river course associated with its discharge regime after 1976 leading to the accretion along the present qingshuigou promontory and then the q 8 promontory

subaqueous deltaic formation of the old yellow river ad 1128 1855 on the western south yellow sea abstract the yellow river presently flows into the bohai sea but during the period ad 1128 1855 the river called the old yellow river oyr flowed into the western south yellow sea sys where the dispersal of its sediment load was controlled by the interactions among alongshore currents waves and tides and shelf morphology in this study high resolution shallow seismic profiles vibrocores boreholes and water depth data which were obtained during geological surveys in the western sys in recent years are used to examine the depositional pattern and stratigraphic record related to the oyr entering the sea our data reveal compound clinoform morphologies double clinoforms a subaerial subaqueous delta couplet sourced by the oyr in the western sys the subaerial delta comprises the currently onshore delta plain and deltafront extending to 17 m in water depth while the subaqueous delta is composed of a wide gently inclined topset and a relatively narrow steeply sloping foreset stretching seaward about 160 km away from the shoreline and showing a morphological asymmetry with a generally southward deflection relative to the oyr mouth the topset is 25 100 km wide in a shore normal direction at water depths of 10 25 m but is generally less than 4 m thick the foreset is much narrower and thicker than the topset is generally 5 30 km wide at 10 45 m water depth and is mostly 4 16 m thick with a maximum thickness of 20 m it shows seaward dipping internal reflectors generally 0 3 0 5 the rollover points topset foreset transition of the subaqueous clinoform range mostly between 10 and 25 m water depth results of 210pb and 137cs geochronology indicate that maximum sediment accumulation rates 1 06 to 2 16 cm yr correspond to the foreset region with much lower rates in the topset and surrounding shallow sea regions 97 in ad 1128 1855 has accumulated on the subaerial delta and that about 10 16 of the total load on the subaqueous delta our data also reveal that the subaqueous delta related to the oyr is underlain by a large scale clinoform broadly confined to 2 5 9 8 cal kyr bp in age as thick as 4 13 m with seaward dipping lower angled

precursory swarms of long period events at redoubt volcano 1989 1990 alaska their origin and use as a forecasting tool abstract during the eruption of redoubt volcano from december 1989 through april 1990 the alaska volcano observatory issued advance warnings of several tephra eruptions based on changes in seismic activity related to the occurrence of precursory swarms of long period lp seismic events dominant period of about 0 5 s the initial eruption on december 14 occurred after 23 years of quiescence and was heralded by a 23 hour swarm of lp events that ended abruptly with the eruption after a series of vent clearing explosions over the next few days dome growth began on december 21 another swarm with lp events similar to those of the first began on the 26th and ended in a major tephra eruption on january 2 eruptions continued over the next two weeks and then ceased until february 15 when a large eruption initiated a long phase of repetitive dome building and dome destroying episodes that continued into april warnings were issued before the major events on december 14 and january 2 but as the eruptive sequence continued after january 2 the energy of the swarms decreased and forecasting became more difficult a significant but less intense swarm preceded the february 15 eruption which was not forecast this eruption destroyed the only seismograph on the volcanic edifice and stymied forecasting until march 4 when the first of three new stations was installed within 3 km of the active vent from march 4 to the end of the sequence on april 21 there were eight eruptions six of which were preceded by detectable swarms of lp events although weak these swarms provided the basis for warnings issued before the eruptions on march 23 and april 6 the initial swarm on december 13 had the following features 1 short duration 23 hours 2 a rapidly accelerating rate of seismic energy release over the first 18 hours of the swarm followed by a decline of activity during the 5 hours preceding the eruption 3 a magnitude range from 0 4 to 1 6 4 nearly identical lp signatures with a dominant period near 0 5 s 5 dilatational first motions everywhere and 6 a stationary source location at a depth of 1 4 km beneath the crater this occurrence of long period events suggests a model involving the interaction of magma with groundwater in which magmatic gases steam and water drive a fixed conduit at a stationary point throughout the swarm the initiation of that sequence of events is analogous to the failure of a pressure relief valve connecting a lower supercharged magma dominated reservoir to a shallow hydrothermal system a three dimensional model of a vibrating fluid filled crack recently developed by chouet is found to be compatible with the seismic data and yields the following parameters for the lp source crack length 280 380 m crack width 140 190 m crack thickness 0 05 0 20 m crack stiffness 100 200 sound speed of fluid 0 8 1 3 km s compressional wave speed of rock 5 1 km s density ratio of fluid to rock 0 4 and ratio of bulk modulus of fluid to rigidity of rock 0 03 0 07 the fluid filled crack is excited intermittently by an impulsive pressure drop that varies in magnitude within the range of 0 4 to 40 bar such disturbance appears to be consistent with a triggering mechanism associated with choked flow conditions in the crack

depositional patterns of sand ridges in tide dominated shallow water environments yellow sea coast and south sea of korea abstract the continental shelf of the yellow sea and the korean south sea is a tide dominated shelf a number of sand ridges occur in this area which form bathymetric highs surveyed were one large sand ridge jangan satoe along the western yellow sea coast and a group of mid shelf sand ridges in the south sea to delineate their depositional pattern and probable origin in tide dominated shallow water environments analyses of sediment samples side scan sonographs and seismic profiles reveal that these ridges show regionally different characteristics in morphology bedforms and sediment the sand ridge in the yellow sea shows a composite form of various bedforms including sand waves and megaripples this ridge is interpreted to be in an accretional active stage maintained by strong tidal currents in contrast the sand ridges on the mid shelf of the south sea show rounded single forms without bedforms on them they are interpreted to represent moribund type sand ridges in the shelf environment which were formed near the shoreline during the holocene sea level transgression these ridges developed off the paleo seomjin river during a period of a stillstand or slow sea level rise approximately between 10 000 and 7000 yrs b p

geophysical characteristics of dacite volcanism the 1977 1978 eruption of usu volcano abstract the 1977 1978 eruption of usu volcano is discussed from the geophysical standpoint as a classic example of dacite volcanism the activities of dacitic volcanoes are characterized by persistent earthquake swarms and remarkable crustal deformations due to the high viscosity of the magmas the former include shocks felt near the volcanoes and the latter accompany formation of lava domes or cryptodomes the hypocenters of the earthquakes occurring beneath usu volcano have been located precisely their distribution defines an earthquake free zone which underlies the area of doming within the summit crater this zone is regarded as occupied by viscous magma the domings within the summit crater forming the cryptodomes have amounted to about 160 m in addition to uplift they showed thrusting towards the northeast as a result the northeastern foot of the volcano has contracted by about 150 m the relation between crustal deformation and earthquake occurrence is examined and it is found that the abrupt domings are accompanied by the larger earthquakes m 3 4 3 both the seismic activity and the ground deformation are shown to have a unique and common energy source the energy of activities of usu volcano consists of the explosive type the deformation type and the seismic type the second and the third are in parallel with each other in discharges and both energies are complementary to the explosive energy the explosive energy and the seismic energy have been calculated for an explosion sequence and it is concluded that the deformation energy is about 10 times greater than the seismic energy the discharge rate of the seismic energy and the upheaval rates of the cryptodomes have continued to decrease since the outburst of the eruption except for a small increase at the end of january 1978 eruptions are governed not only by the supply of the energies but also by the depth of the magma which has gradually approached the surface the last eruption occurred in october 1978 however the crustal deformations and the earthquake swarms are still proceeding as of january 1980 albeit at a lower rate of activity

sediment transport off the huanghe yellow river delta and in the adjacent bohai sea in winter and seasonal comparison abstract based on the data on the current velocity water temperature salinity turbidity and concentration of suspended sediment collected in november 2006 along three survey transects at three time series ship based stations off the huanghe yellow river delta and at twenty four grid survey stations in the adjacent bohai sea sediment transport off the huanghe delta and in the adjacent bohai sea under winter regime were studied and compared with those from the summer season the homogeneous distribution of salinity temperature and sediment in the water column indicated a well mixed body of water a zone of high suspended sediment concentrations ssc 100 mg l 1 with a width of 35 km was identified along the delta coast two highest ssc centers were found in the surface and middle water layers around the abandoned diaokou huanghe river mouth and the present huanghe river mouth and the third one in the bottom layer around the abandoned qingshuigou huanghe river mouth these three highest ssc centers become major sediment source areas in winter based on the location of the high bottom shear stress zone the prevailing wave directions and the protuberant topography of the river mouths we identified the resuspension origin of the three highest ssc centers caused mostly by the winter storm waves partially by tidal currents suspended sediment flux ssf along the three coastal transects indicated that the sediment in the northwest part of the delta was transported northeastward and southeastward along the coast of the recent delta lobe the ssc and ssf were higher in winter than summer by 1 7 27 1 and 2 122 5 times respectively except around the present river mouth this indicates that the intensity of sediment transport in winter is much stronger than in summer due to the powerful effect of winter storms although the river water and sediment discharges to the sea were much greater in summer the massive huanghe sediment to the sea was accumulated in a narrow coastal area due to weak hydrodynamics in summer and then strongly resuspended mostly by storm waves in winter and transported to the offshore area the coastal area off the huanghe delta acts as a sediment sink in summer and converted to be a sediment source in winter in response to the seasonal variation of the east asian monsoon in this region the erosion accumulation pattern of the huanghe subaqueous delta from 1976 to 2003 illustrates that river laden sediment is deposited mainly in the southern part off the coastal area and it is also the result of intensive southward sediment transport in winter

preliminary study of the dynamic origin of the distribution pattern of bottom sediments on the continental shelves of the bohai sea yellow sea and east china sea the bottom sediment types in the bohai sea yellow sea and east china sea byecs are diversified and their distribution pattern is very complicated however the bottom sediment types can be simplified to be sandy sediment clayey sediment and mixed sediment which comprise the complicated distribution pattern of bottom sediment in the byecs the continental shelves of the byecs are broad with shallow water depths and tidal currents which are permanent and dominate the marine dynamics in the byecs based on numerical simulation of tidal elevations and currents in the byecs the rates of suspended load transport and bed load transport during a single tidal cycle for sediments of eight different grain size ranges are calculated the results show that any sediment whose threshold velocity is less than that of tidal current has the same transport trend suspended load transport rare bed load transport rate and the ratio of the former to the latter decrease with grain size becoming coarser and coarser the erosion accretion patterns of sediments with different grain sizes are determined by the sediment transport rate divergences and the results show that the patterns are the same for sediments with different grain sizes three main bottom sediment types i e sandy sediment mainly composed of fine sand clayey sediment mainly composed of silty clay and mixed sediment mainly composed of fine sand silt and clay are obtained by computation the three bottom sediment types and their distribution pattern are consistent not only with sediment transport field and the sea bed erosion accretion pattern obtained by simulation but also with field data of bottom sediment types and divisions in the byecs sand ridges form mainly in the areas with strong rectilinear tidal currents sand sheets form mainly in the areas dominated by strong rotatory tidal currents and clayey sediments i e mud patches form mainly in the areas with weak tidal currents hence not only the sandy sediments but also the clayey sediments in the byecs are formed under the control of the whole tidal current field of the byecs the three main bottom sediment types are not isolated respectively in fact they constitute a whole tidal depositional system under the condition with no cyclonic cold eddy the clayey sediments in the byecs can form in weak tidal current environments therefore a cold eddy is not necessary for the deposition of clayey sediments in the byecs c 2000 academic press

variation of turbidity and particle transport in the bottom layer of the east china sea abstract field surveys of the bottom turbid layer were undertaken from the changjiang estuary to the mid continental slope area in the east china sea to study the bottom turbid layer formation process and ascertain the role of material transport a dramatic development of bottom turbid layers in the continental shelf area of the east china sea was observed from summer to fall this seasonal variation is relatively consistent with seasonal changes in the discharge of suspended particles ss from the changjiang the ss forming the bottom turbid layer in the east china sea are often fine grained particles transported from the continental coastal area which undergo continuous settling and resuspension during transport through the convectively mixed seawater season the average current velocities at the bottom b 10 m layer at the edge of the continental shelf were approximately 5 2 cm s in an east northeast direction but 2 9 cm s almost true north during the stratified season with the 200 m depth contour as the benchmark the bottom current at the continental shelf edge flowed from inside the continental shelf outward during the mixing season and from outside the continental shelf inward during the stratified seawater season the average horizontal flux of the ss is 60 mg m 2 s during the mixing season and 24 mg m 2 s during the stratified season with almost the same direction as that of the bottom current the direction of the ss horizontal flux in the bottom layers is dominated by the bottom current which is driven by the strong south north monsoon in the east china sea

late quaternary evolution of the yellow east china sea tidal regime and its impacts on sediments dispersal and seafloor morphology the evolution of a tidal current field in the yellow sea and east china sea yecs in response to the sea level rise since the last glacial maximum lgm was investigated using a two dimensional tidal model with special attention to changes in the sedimentary environment of the continental shelf region it was found that tidal currents on the yecs shelf have generally been semi diurnal throughout the post glacial stages with f ratio index of diurnal inequality and s2 m2 ratio index of spring neap cycle remaining similar to present on the other hand the spatial distribution of the tidal bottom stress associated with m2 and m4 tidal currents changed greatly during the transgression as the sea level rose two core regions showing high bottom stress values migrated shoreward from cheju island toward the west coast of korea and along the retreat path of the paleo changjiang estuary distribution of extremely intense tidal bottom stress suggested that intense tidal reworking may have occurred at sea levels from 90 to 45 m in the southeast yellow sea and at 75 to 60 m off the paleo changjiang estuary the latter of which agreed with the timing of a large terrigenous organic c flux observed on the shelf slope distribution of slightly weaker bottom stress indicated that the sand ridges off the changjiang estuary and in the southeast yellow sea also might have formed at during those periods on the other hand when the sea level was between 45 and 15 m the tidal bottom stress was generally not strong enough to invoke significant reworking even though the stress intensity may be stronger than present correlation with modern and relict sedimentary features suggested that the tidal process have played a significant role on the reworking and deposition of sediments on the yecs shelf

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

architecture and long term evolution of a tidal sandbank the middelkerke bank southern north sea abstract the internal structure of the middelkerke bank one of the flemish banks located in the southern north sea off the coast of oostende belgium has been studied in the framework of the marine science and technology mast program co funded by the european community a dense grid of high and very high resolution seismic profiles has been used as well as several vibrocorings seven major seismic units can be identified in the quaternary sediments bounded by major discontinuities correlated across the whole study area the lower units clearly appear as being deposited during periods of relative low sea level channel infillings shoreface estuarine and or ebb tidal delta deposits the present shape of the bank results partly from recent erosional processes reworking the underlying deposits thus the lower part of the bank as a morphological feature does not consist of offshore tidal sands the master bedding of the upper part of the bank consists of inclined reflectors dipping at an angle of about 5 in the same direction as the bank s steep face these reflectors very similar to those described by houbolt 1968 are interpreted as being the result of alternating periods of deposition and erosion related to the episodic combination of tidal currents and storms

storm generated surface waves and sediment resuspension in the east china and yellow seas abstract surface winds derived from atmospheric pressure fields are used as input to a finite depth wind wave model to predict the sea state during a cold air frontal passage over the yellow and east china seas which occurred 15 18 november 1983 the predicted maximum wave stress field near the bottom is used to examine the concept of turbulent wave intensities causing sediment resuspension the temporal variability of the wave field at three sites is used to illustrate the dependence of the bottom response on depth within the yellow sea maps of the temporal and spatial distribution of index for initiation of sediment movement are computed for different noncohesive sediment materials during this storm period and compared to sedimentological results for this region this study demonstrates that wave action is a mechanism which can significantly influence the sediment transport pattern induced by the regional circulation existing in this marginal sea the results also identify regions where winter storm g

historical changes in the yellow river delta china abstract the lower yellow river delta has experienced numerous avulsions during the last 2000 years and the floodplain can be divided into four provinces alluvial fan western plain middle plain and eastern plain coastal deltas the yellow river delta complex is composed of several delta superlobes resulting from shifts in the lower river channel and each delta superlobe consists of several smaller lobes formed by shifts in the distributary channels these two kinds of channel shifts have resulted in a complicated imbrication pattern in the delta complex two imbricated delta superlobes are divided by a reworked bed and buried shelf deposits shelly ridges form the surface boundaries between the various delta superlobes the delta superlobes passed through an active stage a reworking stage and were then finally overlain by later superlobes

seasonality and composition of downward particulate fluxes at the continental shelf and okinawa trough in the east china sea abstract as part of the marginal sea flux experiment in the west pacific masflex program conventional sediment traps were deployed at three mooring sites on the east china sea shelf for 1 2 days during 4 seasonal cruises time series sediment traps also were deployed in the east china sea one at the northern part of the okinawa trough stn sst 1 and the other to the north west of the okinawa island sst 2 for 1 year from march 1993 to february 1994 the settling particles were analyzed for total mass flux and the abundance of major biogenic constituents organic carbon nitrogen inorganic carbon and opal on the inner shelf particulate fluxes were large and rapidly increased near the bottom throughout the year probably due to resuspended bottom sediment and suspended particles from the changjiang forming a bottom turbid layer btl on the central shelf particulate fluxes in the btl were extremely high in summer when changjiang discharge peaks possibly indicating a seasonal supply of the changjiang particles to the central shelf at the shelf edge the fluxes in the btl were significantly higher in autumn and winter than in spring and summer at the okinawa trough stations ca 1100 m particulate fluxes at 600 m depth were extremely low but increased noticeably with depth 800 and 50 m above the bottom the flux generally peaked from late autumn to early spring and was lowest during summer with an unusually large peak in september at sst1 considering that there is no strong seasonality of the primary productivity and phytoplankton biomass in the surface layers at the okinawa trough we hypothesize that the seasonality of particle fluxes at the deep waters of the trough is linked to seasonal events in shelf waters downwelling and seaward bottom flow induced by the northeast monsoon in winter favor the offshore transport of particles in the btl while in summer a transverse circulation pattern may inhibit it hu 1994 yanagi et al 1996 near bottom transport may be a key process for shelf to deep sea export of biogenic lithogenic particles as a result the continental slope and the okinawa trough may play an important role as a carbon sink for the east china sea

the huanghe yellow river and changjiang yangtze river deltas a review on their characteristics evolution and sediment discharge during the holocene abstract today asian rivers play an important role in delivering sediment from the land to the oceans however past sediment discharge before human activities modified the landscape is not well known and is estimated to have been roughly one third to one half of the present level chinese rivers have been strongly influenced by human activities and their sediment discharge has changed over the last 6000 years for the study of the long term human impact on rivers and catchment basins chinese rivers provide excellent examples because continuous historical records are available here the characteristics evolution and sediment discharge during the holocene of the deltas of two large chinese rivers huanghe yellow river and changjiang yangtze river are summarized the huanghe and changjiang deltas are different with respect to coastal environments water and sediment discharge the pattern of development of the delta lobe thickness of holocene sediments and basal topography of the incised valleys formed during the last glacial period the huanghe delta is characterized by a high concentration of sediment huge sediment discharge thin holocene deltaic sediments a lateral delta lobe shift and a steep longitudinal profile in its lower reaches the changjiang delta is characterized by a large water discharge a large interseasonal water level change a tide dominated coastal environment continuous seaward progradation with isolated river mouth sand bodies thick holocene sediments and a deep incised valley formed during the last glacial period based on the sediment volume of prograding deltaic sediments over the last 6000 years the sediment discharge of huanghe 1000 years ago is estimated to have been 1 10 8 tons year 1 10 of the present level an abrupt increase occurred at ca 1000 years ago as a consequence of human activities on the loess plateau especially involving cultivation and deforestation moreover the estimated sediment load of huanghe at sanmenxia station prior to 1000 years was 2 7 4 0 10 8 tons year or about 20 15 25 of the present level our recent study estimated that the sediment discharge of changjiang before 2000 years bp was ca 2 4 10 8 tons year total sediment discharge of both rivers before 2000 years bp is estimated to have been 3 4 10 8 tons year or only about 20 of the present level moreover the total sediment load to the lower reaches is estimated to have been 5 6 10 8 tons year or one fourth the present level

variabilities of particulate flux and 210pb in the southern east china sea and western south okinawa trough abstract variabilities of the particulate mass flux and associated 210 pb activity were examined on samples collected from time series sediment traps deployed in the continental slope area of the east china sea off northeast taiwan and in the western south okinawa trough sot as a part of the keep program the particulate flux decreases laterally from the continental slope toward the trough increases vertically toward the bottom at most of the mooring sites and shows fairly synchronous temporal variations among the traps in each mooring for most of the deployments the temporal variation of 210 pb is generally smaller than that of the particulate flux in terms of relative change as expressed in standard deviation of the mean of each trap in the lower slope area the mean particulate flux varies between 9 5 and 79 g m 2 d and the mean 210 pb varies between about 44 and 81 dpm g in the trough the mean particulate flux has the smallest values from 0 06 to 5 7 g m 2 d while the mean 210 pb has the highest from 82 to 192 dpm g the particulate flux decreases while the 210 pb activity increases from the slope toward the trough in the trough 210 pb increases with depth while the particulate flux may show a mid depth maximum of a nepheloid layer although the 210 pb activity increases from the slope toward the trough the 210 pb flux decreases toward the trough because of much greater particulate flux in the slope area within the trough the 210 pb flux as determined from the traps is comparable to that determined from the underlying sediments but on the lower slope the 210 pb flux determined from the traps is much higher than that obtained from the underlying sediments thus a large portion of the particulates and the associated 210 pb may have been transported laterally from elsewhere to the slope area in transit without depositing onto the underlying sediments plots of the mean 210 pb flux versus the mean mass flux for each of the traps show positive linear correlation with four distinctive slopes each representing a mean 210 pb activity of a particular area or a group of traps in the mien hua canyon the mean activity is about 40 dpm g in the sot the mean value is about 130 dpm g on the lower slope the mean values fall in between those of the canyon and the trough in the middle traps where the mass flux is higher in a nepheloid layer the mean activity is about 47 dpm g while the remaining traps yield a mean of about 65 dpm g taking the mean activity of the canyon and that of the trough as the two end member values the slope with a nepheloid layer is a mixture of about 90 canyon and 10 trough materials indicating the canyon as the major particulate provider for the nepheloid layer the slope without a nepheloid layer is a mixture of about 70 canyon and 30 trough materials

water and sediment movement in the vicinity of linear sandbanks the norfolk banks southern north sea geophysical surveys current meter measurements and fluorescent sand tracer experiments were undertaken in the vicinity of the broken bank the data are used to establish localised and regional patterns of water and sediment movement the results obtained confirm mechanisms proposed previously for sandbank growth with particular reference to the north sea these include the clockwise circulation of water and sand with convergence at the crestline secondary helical water circulations do not appear to be a dominant process influencing sandbank maintenance however such circulation may still be important in the initial formation of linear sandbanks and or at some stages in the bank development on a regional basis residual currents bedform asymmetries and tracer dispersion indicate an offshore sediment transport component this observation supports the hypothesis of other investigators formed on the basis of geomorphological observations and numerical model predictions concerning the movement of sand under extreme conditions moreover these transport pathways may persist under low wave and tidally dominated conditions as opposed to being restricted to storm activity

the dispersal of sedimentary terrestrial organic matter in the east china sea ecs as revealed by biomarkers and hydro chemical characteristics terrestrial organic matter tom in surface sediments from the lower yangtze river and adjacent east china sea ecs shelf was characterized using elemental stable carbon isotope and molecular analysis the results show that it is heterogeneous and derives from various sources in the lower river transect rc transect and inner shelf transect zj transect but is more homogeneous and presumably derives from a single source in the cross shelf transect pn transect the trends in sedimentary tom abundance indicated by high molecular weight n alkane abundances and distributions lignin derived products 13c values of total organic carbon 13ctoc and ratio of toc to total nitrogen c n suggest a southward off estuary transport mode of tom along the inner shelf transect while counter intuitively the opposite or no trend in tom off estuary transport occur along the cross shelf transect we therefore suggest that yangtze discharged om is transported southwards along the zhejiang fujian coast zj transect and enters the southern okinawa trough via near bottom currents from where it is ultimately delivered back upslope to the middle shelf by the kuroshio invading water consistent with the hydro chemical characteristics of the ecs