the application of geochemical methods in earthquake prediction in china several geochemical anomalies were observed before the haichen longling tangshan and songpan earthquakes and their strong aftershocks they included changes in groundwater radon levels chemical composition of the groundwater concentration of ca mg cl so4 and hco3 ions conductivity and dissolved gases such as h2 co2 etc in addition anomalous changes in water color and quality were observed before these large earthquakes before some events gases escaped from the surface and there were reports of ground odors being smelled by local residents the large amount of radon data can be grouped into long term and short term anomalies the long term anomalies have a radon emission build up time of from a few months to more than a year the short term anomalies have durations from a few hours or less to a few months

acoustic facies on the inner kara sea shelf implications for late weichselian to holocene sediment dynamics abstract we studied the impact of the last glacial late weichselian sea level cycle on sediment architecture in the inner kara sea using high resolution acoustic sub bottom profiling the acoustic lines were ground truthed with dated sediment cores furthermore we refined the location of the eastern lgm ice margin by new sub bottom profiles new model results of post last glacial maximum lgm isostatic rebound for this area allow a well constrained interpretation of acoustic units in terms of sequence stratigraphy the lowstand or regressive system tract sediments are absent but are represented by an unconformity atop of pleistocene sediments on the shelf and by a major incised dendritic paleo river network the subsequent transgressive and highstand system tracts are best preserved in the incised channels and the recent estuaries while only minor sediment accumulation on the adjacent shelf areas is documented the kara sea can be subdivided into three areas estuaries a the shelf b and c deeper lying areas that accumulated a total of 114 1010 t of holocene sediments

deposition and modification of a flood layer on the northern california shelf lessons from and about the fate of terrestrial particulate organic carbon the 1995 flood of the eel river in northern california provided an opportunity to follow the short term history of riverine particulate matter on a continental shelf particulate organic carbon including both vascular plant debris and soil carbon was utilized as a tracer of the distribution and modification of the shelf flood deposit these components were sorted during initial emplacement of the deposit both in the river plume and in the benthic boundary layer during the 8 months following the flood lateral transport shallow burial and bioturbation contributed to spatial changes in the amount and character of carbon in the flood deposit study of the deposit suggests that this and previous flood layers may be preserved in the shelf and upper slope stratigraphic record as clay rich beds with relatively high carbon to nitrogen ratios and more negative 13c values than background non flood sediment concentrations of vascular plant debris are locally characteristic of such layers and may serve as distinctive stratigraphic markers investigation of organic carbon in the 1995 flood layer on the eel river shelf provides insight into the fate of terrestrial particulate carbon on continental margins in general flooding of the eel river and of similar river systems draining mountainous terrains introduces large quantities of terrestrial carbon to the marine environment and may favor the preservation of both terrestrial and marine carbon the abundant woody vascular plant debris discharged during floods is especially likely to survive oxidation and sulfate reduction in the shallower zones of the seabed this study reveals the dominant role that physical and biological processes may play in attenuating the terrestrial organic carbon signal on shelves over monthly to yearly time scales

tracking the last sea level cycle seafloor morphology and shallow stratigraphy of the latest quaternary new jersey middle continental shelf seafloor geomorphology and surficial stratigraphy of the new jersey middle continental shelf provide a detailed record of sea level change during the last advance and retreat of the laurentide ice sheet 120 kyr b p to present a nw se oriented corridor on the middle shelf between water depths of 40 m the mid shelf paleo shore and 100 m the franklin paleo shore encompasses 500 line km of 2d huntec boomer profiles 500 3500 hz an embedded 4 6 km2 3d volume and a 490 km2 swath bathymetry map we use these data to develop a relative stratigraphy core samples from published studies also provide some chronological and sedimentological constraints on the upper 5 m of the stratigraphic succession the following stratigraphic units and surfaces occur from bottom to top 1 r a high amplitude reflection that separates sediment 46 5 kyr old by ams 14c dating from overlying sediment wedges 2 the outer shelf wedge a marine unit up to 50 m thick that onlaps r 3 channels a reflection sub parallel to the seafloor that incises r and appears as a dendritic system of channels in map view 4 channels fill the upper portion of which is sampled and known to represent deepening upward marine sediments 12 3 kyr in age 5 the t horizon a seismically discontinuous surface that caps channels fill 6 oblique ridge deposits coarse grained shelly units comprised of km scale shallow shelf bedforms and 7 ribbon floored swales bathymetric depressions parallel to modern shelf currents that truncate the oblique ridges and cut into surficial deposits we interpret this succession of features in light of a global eustatic sea level curve and the consequent migration of the coastline across the middle shelf during the last 120 kyr the morphology of the new jersey middle shelf shows a discrete sequence of stratigraphic elements and reflects the pulsed episodicity of the last sea level cycle r is a complicated marine non marine erosional surface formed during the last regression while the outer shelf wedge represents a shelf wedge emplaced during a minor glacial retreat before maximum wisconsin lowstand i e marine oxygen isotope stage 3 1 channels is a widespread fluvial subarial erosion surface formed at the late wisconsin glacial maximum 22 kyr b p the shoreline migrated back across the mid shelf corridor non uniformly during the period represented by channels fill oblique ridges are relict features on the new jersey middle shelf while the ribbon floored swales represent modern shelf erosion there is no systematic relationship between modern seafloor morphology and the very shallowly buried stratigraphic succession

helium content in thermal waters in the caucasus from 1985 to 1991 and correlations with the seismic activity abstract a wide data set of groundwater helium content collected in the caucasus from 1985 to 1991 has been analyzed the strongest earthquakes that occurred in this area during the helium measurement period were the paravani may 13th 1986 m 5 6 spitak december 7th 1988 m 6 9 and georgian april 29th 1991 m 6 9 earthquakes the analysis of the helium content data revealed statistically significant increases in this parameter on the occasion of the paravani and spitak earthquakes and no increase on the occasion of the georgian earthquake these results corroborate those obtained by the analysis of scanty helium content data presented in previous papers with the exception of the anomalous increases the helium content data were subjected to randomness tests and spectral analysis and cross correlation with meteorological parameters and areal seismicity were also attempted the main result obtained is that the destructive spitak earthquake produced some statistical changes in the groundwater helium content fluctuations some years before and after its occurrence

factors controlling late cenozoic continental margin growth from the ebro delta to the western mediterranean deep sea abstract the ebro continental margin sedimentation system originated with a messinian fluvial system this system eroded both a major subaerial canyon cutting the margin southeastward from the present ebro delta and an axial valley that drained northeastward down valencia trough post messinian submergence of this topography and the pliocene regime of high sea levels resulted in a marine hemipelagic drape over the margin late pliocene to pleistocene glacial climatic cycles drainagebasin deforestation and sea level lowstands combined to increase sediment supply cause the margin to prograde and create a regime of lowstand sediment gravity flows in the deeper margin the depositional patterns of regressive transgressive and highstand sea level regimes suggest that location of the sediment source near the present ebro delta throughout the late cenozoic southward current advection of sediment and greater subsidence in the southern margin combined to cause generally asymmetric progradation of the margin to the southeast thicker less stable deposits filling the messinian subaerial canyon underwent multiple retrograde failures eroded wide gullied canyons and formed unchanneled base of slope sediment aprons in the central margin area other margin areas to the north and south developed a series of channel levee complexes on the basin floor the formation of valencia valley over the messinian subaerial valley and earlier faults led to draining of about 20 of the ebro pleistocene sediment from channel levee complexes through the valley to prograde valencia fan as much as 500 km northeast of the margin thus the ebro margin has two growth directions mainly southeastward during higher sea levels and eastward to northeastward during lower sea levels the northeastward draining of turbidity currents has produced unusually thin and widely dispersed turbidite systems compared to those on ponded basin floors during the past few centuries man s impact has exceeded natural controls on ebro margin growth deforestation of the drainage basin more than doubled the normal holocene sediment supply and construction of dams then reduced the supply by 95 this reduction of the past 50 years has caused erosion of the delta and contamination of bottom sediment because normal holocene sediment discharge is not available to prograde the delta or help dilute pollutants

effects of triple junction migration and glacioeustatic cyclicity on evolution of upper slope morphologies offshore eel river basin northern california abstract the upper continental slope of the eel river basin is affected both by uplift and seismicity associated with the northward migrating mendocino triple junction mtj and by glacioeustatic fluctuations as a result seismically imaged slope sequences vary dramatically along strike the southern slope is dominated by the humboldt slide a stack of nine deformed sequences older undeformed sequences thicken landward while slide sequences maintain a constant travel time thickness onset of deformation was abrupt within the slide reflector amplitudes alternate high amplitude reflectors are wavy to shingled and suggest increasing deformation with depth low amplitude reflectors are sub parallel to wavy throughout high and low amplitude sequence couplets suggest repetitive deposition of contrasting lithologies a response we ascribe to late pleistocene glacioeustatic cyclicity if each couplet represents a 100 kyr late pleistocene sea level cycle then humboldt slide deformation began 450 ka this is approximately coeval with onset of deformation on the adjacent shelf 500 ka previously attributed to uplift and seismicity associated with northward encroachment of the mtj we believe migration of the mtj triggered the slide and is the cause for continuing deformation today by sediment creep along internal glide planes north of the humboldt slide we interpret an upper slope anticline as a seaward extension of the little salmon fault zone lsfz previously identified landward both faulting and folding extend to the seafloor indicating that deformation continues an adjacent buried anticline suggests that deformation has also jumped northward within the lsfz on some parts of the upper slope north of the lsfz the slope is dominated by downslope trending channels and gullies these features are v shaped vertically stacked and increase in depth downslope they are mostly infilled their physiographic expression is generally subdued by sediment draping channel fills generally consist of basal high amplitude reflectors overlain by reflectors of lower amplitudes several large channels on older surfaces are concentrated near the northern end of the seismic coverage smaller channels are more evenly distributed along the margin on younger surfaces channels also extend increasingly landward on progressively younger surfaces indicating migration in that direction with time these incisions are clearly inactive during highstands as at present slope deposition today is dominated by draping of hemipelagic sediments channels form and migrate landward through headward erosion during base level changes when both shoreface and fluvial sediment sources are more proximal to the upper slope the increasing lateral distribution of channels through time supports an increase in shoreface erosion north of the lsfz a possible explanation is a known decrease in fluvial sediment input from the north combined with mtj related uplift in the south along strike contrasts in upper slope sequence morphology in the southern eel river basin are clearly a function of both regional tectonism and proximity to sediment sources influenced by base level changes humboldt slide sequences while deformed are continuously influenced by systematic lithological variations occurring as a result of glacioeustatic cycles effects of base level changes similarly control the distribution and fill of incisions on the northern slope all of these observations reinforce previous seismic investigations of the offshore eel river basin shelf and confirm that the competing effects of tectonism and glacioeustacy on the preservation of continental margin stratigraphy can be differentiated

identification of anomalous radon concentrations due to geodynamic processes by elimination of rn variations caused by other factors summary it has been suggested that temporal variations of radon rn concentrations in various media may be used as a possible predictive indicator of seismic activity however observed rn measurements are a function of a number of diierent physical processes including seismic activity this paper describes a generalized approach to removing noise components from the observed data to leave a residual component of radon concentration that re ects geodynamic processes at depth the approach is demonstrated using data gathered in israel at the time of the 1992 october 12 giza earthquake in egypt

uplifted neogene margin southernmost cascadia mendocino triple junction region california along a 10 km length of coast north of the mendocino triple junction a neogene accretionary complex has been uplifted 2 km and tilted northward in response to the interaction of the southern juan de fuca gorda plate with the older north american and pacific plates these plate interactions were accompanied by tectonic intercalation of miocene to pliocene deposits of the southern cascadia forearc wildcat group with penetratively deformed oligocene to miocene accretionary prism deposits of the false cape terrane new name and the cretaceous to eocene coastal terrane of the franciscan complex north of cape mendocino more than 2 km of stratigraphic section of the accretionary false cape terrane crops out at beach level in an east west trending anticline and recumbent syncline the folded false cape rocks are juxtaposed with forearc deposits to the north along the subvertical russ shear zone to the south a second subvertical shear zone truncates the false cape terrane near the mouth of the bear river this north bear river shear zone interleaves rocks of the false cape and coastal terranes with additional neogene forearc deposits the bear river beds south of the north bear river shear zone the bear river beds crop out for about 5 km in a continuous folded and imbricated section that is again truncated to the south by a third subvertical shear zone this south bear river shear zone interleaves rocks of the coastal terrane the bear river beds and pliocene to pleistocene shelf deposits folding tilting and shear zone development reflect ongoing north south crustal shortening that has occurred in response to interplate coupling and wedge thickening in the deforming miocene and younger accretionary complex the strain recorded in the accreted terranes and in the forearc overlap assemblage reflects a stress regime unlike that in the cascadia fold and thrust belt north of the eel river syncline thus the deformation pattern may be unique to the triple junction area the false cape terrane is one of only two localities along the cascadia margin where the oligocene to miocene accretionary complex is exposed on land the other locality is that of the hoh melange on the southwest olympic peninsula on land exposure of accretionary rocks in these two areas is a consequence of high uplift rates focused compression and triple junction tectonism framework grain composition data for sandstones in the hoh melange and coeval continental deposits in northernmost california the oligocene to miocene weaverville formation suggest a provenance link while sandstone of the false cape terrane presently situated directly west of the weaverville formation is dissimilar given the northward component of farallon juan de fuca plate translation with respect to north america for the past 20 m y provenance links of hoh and weaverville sandstones might reflect a substantial component of northward translation between the farallon and north american plates that was accommodated within the accretionary prism

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

strataform overview of its design and synthesis of its results abstract the strata formed on continental margins record the history of both marine and terrestrial events occurring on earth the strataform program was created to develop a better understanding of relationships between these events and margin stratigraphy in order to obtain the maximum information from strata they are being examined simultaneously on various temporal and spatial scales and their formation is being studied where events and accumulation are known to be active the general objectives of strataform are to add geological perspective to studies of sedimentary processes to constrain stratigraphic interpretations better and to develop numerical models relating processes and stratigraphy this research is being undertaken on margins off northern california and new jersey which provide unique opportunities for investigation of short term and long term stratigraphy respectively this volume and paper focus upon studies undertaken off northern california north of cape mendocino this area is tectonically active with a coastal mountain range narrow shelf and input of sediment primarily from the eel river recent estimates indicate that 1 to 3 10 7 t yr of mud silt and clay are supplied to the continental shelf sand accumulates on the inner shelf 70 reaches the continental slope or deeper during the previous lowstand of sea level sediment discharge was 25 greater and probably led to hyperpycnal debris and other flows transporting sediment down the slope on the eel shelf flood and storm events combine to create normally stratified fine grained layers with basal sand and much terrestrial organic debris these layers are modified through time but some can be buried and preserved subsurface flood layers seem to impact observations of acoustic backscatter on the middle shelf and subsurface fluids gas freshwater affect electromagnetic measurements on the inner shelf budgets of eel river mud accumulation for the past century indicate 20 trapped on the adjacent shelf and 20 on the upper slope 150 600 m the remaining 60 is dispersed to more distal locations over holocene time scales eel river sediment has built a small sandy subaqueous delta and a subtle bulge of muddy sediment on the middle shelf north of the river gullies have been eroded on the open slope during lowstands of sea level and have accreted upward during highstands a massive failure has formed the humboldt slide due to earthquake activity and unstable substrates possibly from excess pore pressures and gas the tectonic setting has impacted margin stratigraphy from small scales fluid expulsion pockmarks to large scales spatial variation of late cenozoic sedimentation the broad dispersal of eel sediment demonstrates the three dimensional character of the resulting stratigraphy including the large scale clinoform structure developed on the shelf upper slope the rollover point topset foreset boundary for this feature is the shelf break i e below sea level which is important information for stratigraphic interpretations of sea level change

radon variations at arrowhead and murrieta springs continuous and discrete measurements two continuous radon monitors crms have been deployed at arrowhead hot springs along the san andreas fault near san bernardino and at murrieta hot springs along the elsinore fault the recorded hourly and daily radon variations during 1983 are within 5 of the mean values the radon levels increased however by about 10 20 above their normal baseline levels in midyear several small magnitude earthquakes m 3 0 3 5 occurred within 20 km of the arrowhead site near the end of the period of the radon increase

buried fluvial channels off new jersey did sea level lowstands expose the entire shelf during the miocene high resolution multichannel seismic profiles from the new jersey continental margin reveal that some middle to late miocene sea level falls exposed the entire continental shelf at several sequence boundaries fluvial channels occur landward of the clinoform breakpoints that mark paleo shelf edges the seismically observed progradation therefore resulted from sediment delivery to the shelf edge by rivers during lowstands suspended sediment crossing the relatively shallow water 30 40 m shelf also fostered progradation during highstands river systems reaching the outermost shelf were small and closely spaced they approximated a line source of sediment this finding helps to explain the observed linearity of miocene shelf edges although these systems discharged near clinoform tops they did not form canyons incising the clinoforms such canyons were rare in this active depositional setting in contrast to their prevalence on the modern continental slope

strain on the san andreas fault near palmdale california rapid aseismic change frequently repeated strain measurements near palmdale california during the period from 1971 through 1980 indicate that in addition to a uniform accumulation of right lateral shear strain engineering shear 0 35 microradian per year across the san andreas fault a 1 microstrain contraction perpendicular to the fault that accumulated gradually during the interval 1974 through 1978 was aseismically released between february and november 1979 subsequently november 1979 to march 1980 about half of the contraction was recovered this sequence of strain changes can be explained in terms of south southwestward migration of a slip event consisting of the south southwestward movement of the upper crust on a horizontal detachment surface at a depth of 10 to 30 kilometers the large strain change in 1979 corresponds to the passage of the slip event beneath the san andreas fault

temporal and spatial variability of the sediment grain size distribution on the eel shelf the flood layer of 1995 abstract sediment grain size characteristics observed on the eel shelf have been analyzed using a wet sieving technique that minimizes breakage of aggregates at several sites on the 70 m isobath north of the river where a 1995 flood layer attained a maximum thickness of about 9 cm replicate box cores were collected on seven cruises during february 1995 to january 1997 these samples provide a unique opportunity to follow the evolution of a flood layer over a two year period as it was modified and gradually buried one month after the flood a layer of tan colored high porosity sediment with up to 96 of its particles in the size range of 0 20 m had accumulated on the central part of the shelf 7 30 km north of the river and principally between the 50 m and 90 m isobaths substantial coarsening of this layer occurred between february 1995 and may 1995 particularly along the southern and the landward edge of the deposit in water depths of

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

geology of the gahcho kue kimberlite pipes nwt canada root to diatreme magmatic transition zones abstract the cambrian gahcho kue kimberlite cluster includes four main pipes that have been emplaced into the archaean basement granitoids of the slave craton each of the steep sided pipes were formed by the intrusion of several distinct phases of kimberlite in which the textures vary from hypabyssal kimberlite hk to diatreme facies tuffisitic kimberlite breccia tkb the tkb displays many diagnostic features including abundant unaltered country rock xenoliths pelletal lapilli serpentinised olivines and a matrix composed of microlitic phlogopite and serpentine without carbonate the hk contains common fresh olivine set in a groundmass composed of monticellite phlogopite perovskite serpentine and carbonate a number of separate phases of kimberlite display a magmatic textural gradation from tkb to hk which is characterised by a decrease in the proportion of pelletal lapilli and country rock xenoliths and an increase in groundmass crystallinity proportion of fresh olivine and the degree of xenolith digestion the pipe shapes and infills of the gahcho kue kimberlites are similar to those of the classic south african pipes particularly those of the kimberley area similar intrusive magmatic emplacement processes are proposed in which the diatreme zone results from the degassing after breakthrough of the intruding magma column the transition zones represent frozen degassing fronts the style of emplacement of the gahcho kue kimberlites is very different from that of many other pipes in canada such as at lac de gras fort a la corne or attawapiskat

competence and lithostratigraphy of host rocks govern kimberlite pipe morphology we use analogue experimentation to test the hypothesis that host rock competence primarily determines the morphology of kimberlite pipes which are subdivided into three classes class 1 pipes are steep sided diatremes emplaced into crystalline rock class 2 pipes have a wide shallow crater emplaced into sedimentary rock overlain by unconsolidated sediments class 3 pipes comprise a steep sided diatreme with a shallow angled crater emplaced into competent crystalline rock overlain by unconsolidated sediments we use different configurations of three analogue materials with varying cohesions to model the contrasting geological settings proposed to explain kimberlite pipe morphology pulses of compressed air representing the energy of the gas rich head of a kimberlitic magma are used to disrupt the experimental substrate in the case of an eruption of a gas containing no particles or fluids the organization of the analogue materials controls the excavation processes as well as the final shape of the ana

river plume sedimentation modeling for sequence stratigraphy application to the eel margin northern california abstract sediment deposition in the coastal zone from riverine input is of key importance in understanding the construction of sediment sequences through time a turbulent jet model is used to simulate sediment input to the continental margin from a riverine source turbulent jet models track the momentum which is the first order force carrying most of the sediment flowing into the ocean the froude number at the river mouth remains supercritical during floods of the eel river justifying the use of a jet model for the initial dispersion of the sediment laden plume sediment is deposited from the plume prior to the centerline froude number decreasing to its critical value empirically derived first order removal rate constants are used for each grain size in an advection diffusion equation to predict the areal extent of sediment deposition one strength of using a jet model is its ability to simulate deposits on a daily time step over intermediate time scales thousands of years using a limited number of input parameters a number of simulations of the eel river plume are shown for conditions of the present day and 18 000 yr bp during the last glacial maximum the model results for modern conditions show that a majority of the deposition occurs within 20 km north of the river mouth and is typically confined to within 10 km of the coastline corresponding well with the shelf sands on the eel margin however the initial mud deposit from a 1995 flood was farther offshore and northward additional advection of the mud fraction must occur after it leaves the surficial plume and prior to its initial deposition the model runs of 18 000 yr bp with 100 m lower sea level wetter and colder climate and the river mouth assumed to be at the canyon show that the plume is able to transport sand silt and clay out of the canyon and onto the continental slope

research on groundwater radon as a fluid phase precursor to earthquakes groundwater radon monitoring work carried out in southern california by the university of southern california since 1974 is summarized here this effort began with a sampling network over a locked segment of the san andreas fault from tejon to cajon and was later expanded to cover part of the southern transverse mountain ranges groundwater samples were brought back weekly to the laboratory for high precision scintillation counting needs for more frequent sampling and less labor prompted the development of an economical and field worthy instrument known as the continuous radon monitor about 10 have been installed in the network since early 1980 the groundwater radon content was found to show anomalous increases mostly at a single station before a number of moderate and nearby earthquakes our work is hampered by a lack of large earthquakes that may have a regional impact on radon anomalies and by the complexity of the underground hydrological regime to circumvent this difficulty we have chosen to monitor only deep artesian wells or hot spring wells

modern accumulation rates and a sediment budget for the eel shelf a flood dominated depositional environment the northern california continental margin is periodically impacted by geologically significant storms which have a marked influence on terrigenous sediment supply flood deposition and long term accumulation of fine grained sediment on the eel shelf accumulation of eel river muds on the adjacent shelf was investigated using 210pb and 137cs geochronologies in order to understand the fate of sediment discharged by the eel river and to relate patterns of net sediment accumulation 100 yr time scale to sediment dynamics 210pb data demonstrate that modern accumulation of river mud occurs from the 50 m isobath seaward across shelf accumulation rates decrease from maximum mid shelf values of 0 6 1 7 g cm 2 yr 1 to values of 0 2 0 4 g cm 2 yr 1 at the shelf break with a spatially weighted mean of 0 5 g cm 2 yr 1 0 4 cm yr for the entire shelf 210pbxs sediment depth profiles from the region of highest accumulation rate are characterized by subsurface intervals of low and uniform activity which are produced by flood deposition in some cores particular 210pbxs activity intervals may be associated with major eel river floods of 1955 1964 and 1974 it is postulated that because of the coincidence of high river flow events and southerly winds during cyclonic winter storms net northward transport allows for preferential deposition of fine grained sediment north of the river mouth over the past 100 years fluvial sediment input combined with marine dispersal processes have produced a mid shelf depocenter evident by both the spatial distribution of 210pb accumulation rates and by clay rich flood layers partially preserved in shelf deposits a fine grained sediment budget for the dispersal system based on hydrological data and 210pb geochronologies demonstrates that a maximum of 20 3 109 kg yr of the mean annual supply of fluvial mud 14 109 kg yr is trapped on the shelf the results of this study demonstrate that 1 short term sedimentation processes associated with floods can influence sediment accumulation on longer time scales and 2 a major fraction of fine grained sediment supplied to tectonically active margins by flood prone mountainous rivers bypasses narrow continental shelves

a theoretical model for change of shape of spring water radon anomalies with epicentral distance a model for radon anomalies before earthquakes with a relatively fast increase in radon concentration at the beginning of the anomaly is postulated a calculation based on this model shows that a parameter can be deduced from the form of the radon anomalies which depends on the epicentral distance of the measurement point after adjustment of some parameters the model calculation is in good agreement with observed earthquake precursor anomalies

late quaternary fluvial terraces of the romagna and marche apennines italy climatic lithologic and tectonic controls on terrace genesis in an active orogen abstract we synthesize a new fluvial terrace chronostratigraphy of the bidente and musone rivers cast within a broader european framework which forms the basis of a terrace genesis and river incision model for the northern apennines italy our model supported by terrace long profiles correlation to po foreland sediments 15 new radiocarbon dates and published numeric and relative stratigraphic ages highlights how drainage basin substrate drives concurrent formation of strath terraces in the bidente basin and fill terraces in the musone basin quaternary climate change paces the formative geomorphic processes through unsteady discharges of water and sediment in the weathering limited setting represented by the bidente basin siliciclastic detritus carves broad strath surfaces during glacial climates that are preserved as terraces as the river incises during the transition to an interglacial climate in contrast the transport limited and carbonate detritus dominated musone basin sees valleys deeply buried by aggradation during glacial climates followed by river incision during the transition to an interglacial climate incision of these rivers over the past 1 million years has been both unsteady and non uniform these and all po adriatic draining rivers are proximal to a base level defined by mean sea level and have little room for increasing their longitudinal profile concavities through incision particularly in their lower reaches despite periodic glacio eustatic drawdowns as a result the observed incision is best explained by rock uplift associated with active local fault or fold growth embedded in the actively thickening and uplifting apennine foreland

late pleistocene channel incisions in the southern eel river basin northern california implications for tectonic vs eustatic influences on shelf sedimentation patterns abstract high resolution multichannel seismic mcs profiles from the southern offshore eel river basin off northern california show multiple superimposed buried channels beneath the continental shelf these channels display consistent southwest orientations their dendritic map pattern and low but consistent cross shelf gradients suggest that they formed by fluvial erosion during periods of shelf exposure associated with relative sea level lowstands all of the channels were incised after 500 ka the age of the onshore offshore hookton datum their frequency of incision exceeds that of known glacioeustatic lowstands since 500 ka confirming that some of the surfaces must have formed during relative lowstands initiated by local tectonic uplift sedimentation patterns in the eel river basin shift dramatically in response to relative sea level fluctuations today sediments from the eel river move north and west on the shelf in response mainly to large winter storm events in contrast fluvial incision on the exposed shelf during relative lowstands directed sediments to the southwest most likely into the head of the eel canyon shelf channels were probably fed not only by ancestral rivers but also by local uplifts like the table bluff anticline increases in gradient and channel depths at the southern end of the mcs coverage indicate that canyon forming processes modified fluvial channels as they converge towards embayments near the head of the eel canyon cyclic recurrence and consistent orientation of these channels demonstrate that the eel canyon has been extant through numerous relative sea level cycles and is perhaps as old as 500 ka

kimberlite emplacement models the implications for mining projects abstract the significance of the emplacement model for kimberlite pipes or sheets is commonly recognized in resource geology however its importance is not always appreciated in the mine design process the fact is that knowledge of the orebody geometry character of the contact zones internal structures rock mass competency and distribution of inclusions could directly influence the selection of the underground mining method pit wall stability dilution treatability and the dewatering strategy the problems are exacerbated in smaller pipes and narrower sheets and in more irregular shapes they are more apparent in underground mining as opposed to open cast various kimberlite emplacement processes have a major impact on the nature of the kimberlite orebody and host rocks that will influence the mine design and mining strategy failure to understand these processes can adversely affect the economic outcome for developing a mine it is therefore important to investigate those processes in order to better characterize the mining constraints and risks and more accurately predict the mine s economic viability

durable terrestrial bedrock predicts submarine canyon formation though submarine canyons are first order topographic features of earth the processes responsible for their occurrence remains poorly understood potentially analogous studies of terrestrial rivers show that the flux and caliber of transported bedload are significant controls on bedrock incision here we hypothesize that coarse sediment load could exert a similar role in the formation of submarine canyons we conducted a comprehensive empirical analysis of canyon occurrence along the west coast of the contiguous united states which indicates that submarine canyon occurrence is best predicted by the occurrence of durable crystalline bedrock in adjacent terrestrial catchments canyon occurrence is also predicted by the flux of bed sediment to shore from terrestrial streams surprisingly no significant correlation was observed between canyon occurrence and the slope or width of the continental shelf these findings suggest that canyon incision is promoted by a greater yields of durable terrestrial clasts to the shore

a strategy for short term prediction of earthquakes abstract physical processes leading to laboratory rupture have a nonlinear character which justifies optimism that earthquakes are predictable however nonlinear effects at the source of a smaller earthquake may be an insufficient basis for the prediction of an earthquake with rupture lengths tens to hundreds of kilometers thus a strategy for predicting such major or great events must depend on knowing the state of readiness of the entire length of the suspect fault the two most promising avenues are 1 to search for variations in shear and dilatational strains within the fault zone and in the bordering regions that signify the onset of a stuart instability and 2 to follow in detail the seismicity in response to the temporal variations of shear and normal strains as a measure of what parts of a long fault are at the point of failure an observational strategy based on these physical models requires detailed and frequent to continuous observation of strain within the fault and border zones focal mechanisms and accurate locations of earthquakes m 2 are needed to relate seismicity to a given configuration of the strain field with the exception of observations such as levels in water wells which carry information on the strain field a purely empirical search for earthquake precursors needs to be deemphasized

upper plate contraction north of the migrating mendocino triple junction northern california implications for partitioning of strain geologic measurement of permanent contraction across the cascadia subduction margin constrains one component of the tectonic deformation along the convergent plate boundary the component critical for the seismic hazard assessment of crustal faults a comprehensive survey of active faults in onshore subduction margin rocks at the southern end of the cascadia subduction zone indicates that these thrust faults accommodate 10 mm yr of convergence oriented 020 045 seismotectonic models of subduction zones typically assign this upper plate strain to the estimate of aseismic slip on the megathrust geodetic models include this permanent crustal strain within estimates of elastic strain accumulation on the megathrust both types of models underestimate the seismic hazard associated with crustal faults subtracting the observed contraction from the plate convergence rate 40 50 mm yr directed 040 055 leaves 30 40 mm yr of convergence to be partitioned between slip on the megathrust contraction within the southern juan de fuca plate and crustal contraction outside the subduction complex rocks this simple estimate of slip partitioning neglects the discrepancy between the plate convergence and contraction directions in the vicinity of the mendocino triple junction the san andreas and cascadia limbs of the mendocino triple junction are not collinear the eastern edge of the broad san andreas boundary is 85 km east of the cascadia subduction boundary and across this zone the pacific plate converges directly with the north america plate the skewed orientation of crustal structures just north of the leading edge of the pacific plate suggests that they are deforming in a hybrid stress field resulting from both juan de fuca north america motion and pacific north america motion the composite convergence direction 50 mm yr directed 023 is consistent with the compressive stress axis 020 inferred from focal mechanisms of crustal earthquakes in the humboldt region deformation in such a hybrid stress field implies that the crustal faults are being loaded from two major tectonic sources the slip on crustal faults north of the mendocino triple junction may consume 4 5 mm yr of pacific humboldt convergence the remaining 17 18 mm yr of convergence may be consumed as distributed shortening expressed in the high rates of uplift in the cape mendocino region or as northward translation of the continental margin north of the triple junction

depositional and erosional bedforms in late pleistocene holocene pro delta deposits of the gulf of patti southern tyrrhenian margin italy abstract multibeam bathymetry high resolution seismic profiles and seafloor samples have been analyzed to characterize depositional and erosional dynamics recorded pro deltaic deposits and outer shelf sediments along of a sector of the ne sicilian margin southern tyrrhenian sea the deltaic deposits cover an area of ca 15 km 2 in front of the mazzarra river and are morphologically characterized by waveforms trending overall along strike and incised cross strike gullies of variable length the gullies are shallow and characterized by small coaxial erosive scours in the inner middle shelf whereas they become larger and deeper in the outer shelf upper slope in relation to the marked increase of slope gradients at the shelf break here the wider gullies are characterized by a frame of crescent shaped bedforms interpreted as cyclic steps indicating the occurrence of sedimentary gravity flows in supercritical regime prodelta waveforms are widespread between 50 and 120 m with wave lengths of 34 110 m and wave heights of 0 5 3 m morphometric characterization and spatial distribution of the waveforms suggests a main role in their genesis played by hyperpycnal flows although we cannot discard the possible effect of internal waves or slow deformation processes i e creep depositional and erosional features similar to those observed on the seafloor are evident in the subsurface stratigraphy revealing the onset and growth of the mazzarra delta since the last glacial maximum the post glacial sea level rise caused lateral shifts of the mazzarra river mouth controlling migration of depositional lobes and intensity of seafloor incision and sediment reworking ultimately resulting in the observed wavy bedforms extending from the inner shelf to the upper slope

radon and hydrologic anomalies on the rough creek fault possible precursors to the m5 1 eastern kentucky earthquake 1980 soil radon emanation increased sharply on the rough creek fault near the illinois kentucky border in april 1980 3 1 2 months before a m5 1 earthquake in eastern kentucky july 27 1980 the spikelike anomaly was similar to a radon anomaly in the new madrid seismic zone in 1979 that preceded by 2 months a m3 9 tremor at the site of that anomaly weekly radon monitoring was initiated on the rough creek fault after abrupt cessation of spring flow on the fault occurred at a site that had experienced similar flow cessation 1 month prior to a m5 3 earthquake in southeastern illinois in 1968 although the recent kentucky epicenter was 380 km east of the site of the detected radon anomaly factors relating to regional structures recent seismicity additional radon data and the stress regime suggest that the hydrologic and radon anomalies may have been precursors to an eastward progression of strain that culminated in the eastern kentucky tremor

prediction of central california earthquakes from soil gas helium fluctuations the observations of short term decreases in helium soil gas concentrations along the san andreas fault in central california have been correlated with subsequent earthquake activity the area of study is elliptical in shape with radii approximately 160 80 km centered near san benito and with the major axis parallel to the fault for 83 percent of them 4 earthquakes in this area a helium decrease preceded seismic activity by 1 5 to 6 5 weeks there were several earthquakes without a decrease and several decreases without a corresponding earthquake owing to complex and unresolved interaction of many geophysical and geochemical parameters no suitable model is yet developed to explain the observations

radon content of groundwater as an earthquake precursor evaluation of worldwide data and physical basis the properties of a worldwide data set of 91 radon 222 rn anomalies the frequency of occurrence the precursor time interval and the distribution of peak amplitudes are correlated with earthquake data such as the respective magnitude and epicentral distance these anomalies were reported as precursors to earthquakes in the united states ussr china japan and iceland although the data set is incomplete and limited by experimental deficiencies several consistent patterns emerge radon anomalies from different tectonic regions show similar patterns the radon anomalies occur at greater epicentral distances for earthquakes of the larger magnitude anomalies preceding large earthquakes m 6 are frequently observed at a distance of 100 to 500 km these distances are larger than several times the rupture dimensions of the future earthquakes the time from the onset of an anomaly to the time of the earthquake the precursor time increases with magnitude but decreases with distance between epicenter and radon station in addition radon anomalies are observed more frequently prior to large earthquakes than prior to small ones indicating that the preparation zone increases in size as magnitude increases the peak amplitude does not scale with magnitude but forms a consistent pattern with epicentral distance in that the larger the earthquake magnitude the farther away the largest amplitudes tend to occur the preparation zone of the earthquake where the anomalies occur forms an almost continuous annulus that expands with time away from the future rupture zone the outer radius of this annulus scales with the earthquake magnitude model calculations indicate that strain fields of at most 10 6 to 10 8 strain caused the radon anomalies if these strains are divided by the appropriate precursor time minimum strain rates from 10 7 day 1 to 10 10 day 1 are obtained such small strains and strain rates suggest that in most cases neither mechanical crack growth induced by dilatancy nor mechanical coupling between pore pressure and the rock matrix caused the anomalies large changes in the orientation of the local strain field however could occur and affect the local stress intensity factor since changes in the stress intensity factor can result in stress corrosion the occurrence of radon anomalies is attributed to slow crack growth controlled by stress corrosion in a rock matrix saturated by groundwater

holocene sediment deposition on the poverty slope margin by the muddy waipaoa river east coast new zealand the margin off the raukumara peninsula east coast north island of new zealand is characterised by high terrigenous sediment flux the dramatic effects of historic land use change the rapid uplift of mesozoic and soft tertiary sediments and by complex sediment tectonic interactions on a steep and unstable continental slope the poverty bay shelf and slope indentation are adjacent to the waipaoa river which delivers 15 mt year 1 of mud this study presents new data from the poverty slope the seaward extension of the waipaoa dispersal system a 3 km3 lobe of postglacial sediment emerges from the poverty gap and feathers down onto the upper slope downslope the poverty indentation has received a significant holocene flux of terrigenous sediment accumulating in two mid slope basins the paritu trough and a smaller lower slope basin below the south paritu ridge hemipelagic sediment has accumulated on the mid slope at around 0 05 g cm 2 year 1 0 06 cm year 1 since the mid late holocene seismic reflection echo type and backscatter imagery indicate mud deposits on the mid slope debris at the base of regularly spaced upper slope gullies and a large avalanche deposit in the upper paritu trough the consistency of the tephrostratigraphy indicates that despite slope instability hemipelagic sedimentation is the dominant background process operating at millennial time scales at least since the mid holocene the poverty slope should be included in any budget calculation of post colonisation increased sediment yield for the margin the poverty canyon has probably been largely inactive during the holocene highstand

acoustic backscatter of the 1995 flood deposit on the eel shelf abstract acoustic swath mapping and sediment box coring conducted on the continental shelf near the mouth of the eel river revealed regional variations in acoustic backscatter that can be related to the shelf sedimentology the acoustic backscatter variations observed on the shelf were unusually narrow compared to the response of similar sediment types documented in other areas however the acoustic data revealed four principal bottom types on the shelf that can be related to sedimentologic differences observed in cores the four areas are 1 low acoustic backscatter associated with the nearshore sand facies and the prodelta terraces of the eel and mad rivers composed of fine sands and coarse silts with low porosity 2 high acoustic backscatter associated with fine silts characterized by high porosity and deposited by the 1995 flood of the eel river 3 intermediate acoustic backscatter in the outer shelf muds where clayey silts are accumulating and the 1995 flood apparently had limited direct effect and 4 intermediate acoustic backscatter near the fringes of the 1995 flood deposits and in areas where the flood sediments were more disrupted by post depositional processes the highest acoustic backscatter was identified in areas where the 1995 flood sediments remained relatively intact and near the shelf surface into the summer of 1995 cores collected from these areas contained wavy or lenticular bedding the rapid deposition of the high porosity muddy layers results in better preservation of incorporated ripple forms than in areas less directly impacted by the flood deposit the high porosity muddy layers allow acoustic penetration into the sediments and result in greater acoustic backscatter from incorporated roughness elements

late quaternary sedimentation off new jersey new results using 3 d seismic profiles and cores abstract regional seismic reflection surveys have delineated a wedge of late quaternary sediment extending 150 km south from the hudson apron along the edge of the continental shelf off new jersey the bottom of the sediment wedge is defined by a prominent reflector r assumed to represent an erosional surface carved during a low stand of sea level probably corresponding to the wisconsinan maximum glaciation a 3 d reflection survey of a 5 0 5 km area of the southern part of the wedge was carried out in october 1989 line spacing was 10 m and shot spacing 2 5 m navigation achieved position accuracies to the survey shows that the outer shelf sediment wedge has a complex internal structure unrelated to the present seafloor morphology the sedimentary sequence appears to have been formed by a series of depositional events related to glacial melting and interrupted by at least one erosional episode marked by a seismic surface that defines a system of meandering channels faunal studies of samples from cores indicate that the sediments were deposited at shallower depths than at present but there is no evidence for deposition in shallower water or closer proximity to land than the modern mid shelf it appears that the history of periglacial marine sedimentation which accompanied the post wisconsinan deglaciation is no less complex than its continental counterpart

effect of the northward migrating mendocino triple junction on the eel river forearc basin california structural evolution offshore northern california the gorda plate is subducting obliquely beneath north america the resulting complicated tectonic setting forms the southern end of the cascadia subduction zone the southern cascadia subduction zone and overlying eel river forearc basin lie just north of the unstable mendocino triple junction the neogene strata of the eel river basin record structural deformation caused by the underthrusting of the gorda plate as well as deformation generated by northward migration and encroachment of the mendocino triple junction three distinct deformation regimes are present in the eel river forearc basin 1 along the western margin of the forearc basin and within the foreslope of the accretionary prism thrust faults and anticlines record pliocene pleistocene shortening caused by subduction of the gorda plate 2 the southern part of the basin rotated counterclockwise in the late pleistocene resulting in modern transpressional deformation offshore humboldt bay the rotation and deformation are caused by north south convergence across the boundary between the pacific plate and the southernmost part of the forearc basin at the triple junction 3 the northeastern margin of the eel river basin is deformed by high angle faults with a component of strike slip motion that may represent the incipient northward propagation of the pacific north american transform system north of the triple junction

tectonics sedimentation and erosion in northern california submarine geomorphology and sediment preservation potential as a result of three competing processes abstract on the continental margin of northern california north of the mendocino triple junction the geomorphic grain varies dramatically between the coast and the toe of the accretionary wedge this grain represents the composite signature of three competing processes tectonics sedimentation and erosion all three are active across the region but their rates and orientations vary spatially and temporally affecting the resultant grain and preservation potential in this rapid sedimentation environment at the toe of the accretionary wedge the relative rate of tectonic deformation exceeds the rate of sediment accumulation and erosion is largely limited to areally restricted but at times large mass wasting features in this region isobaths representing the geomorphic grain are parallel to structural highs and lows as in most forearcs and sediment accumulation is restricted to small basins located between anticlinal ridges the slope between the shelf break and the accretionary complex shows the competing effects of sediment accumulation erosion and tectonism slope perpendicular gullies are the prominent erosional features in this area especially in the region surrounding the trinity submarine canyon anticlinal ridges crop out on the seafloor although the ridge crests decrease in bathymetric expression both up and down slope on the shelf the rate of sediment accumulation 6 12 mm yr exceeds the relative rate of tectonic deformation with 1 3 mm yr of active uplift on land in this region the geomorphic grain is controlled by sediment accumulation with compressed but continuous stratigraphic sections above anticlinal highs and expanded sections in actively subsiding regions

effect of the northward migrating mendocino triple junction on the eel river forearc basin california stratigraphic development the eel river forearc basin northern california lies at the southern end of the cascadia subduction zone and at the leading edge of the migrating mendocino triple junction stratigraphic relationships within the eel river forearc basin suggest that the current outer arc high formed between ca 3 and 2 ma when the margin switched from a nonaccretionary to an accretionary phase and then uplifted to attain critical taper between ca 2 and 1 ma an influx of sedimentation from the ancestral klamath and eel river systems increased the width of the northern california margin and caused continued uplift followed by widespread erosion of the western margin of the basin at ca 1 ma in the northeastern part of the forearc basin localized erosion of the shelf occurred at ca 500 ka the arrival of the northward migrating mendocino triple junction at ca 500 ka is documented by uplift northward tilting erosion of the margin as much as 20 km north of cape mendocino and reduced deposition within the forearc basin as much as 80 km north of the current position of the triple junction terrestrial sediments delivered to the continental margin and eroded sediments near the triple junction largely bypassed the southern part of the basin and were likely deposited in northern areas of the basin or flowed down the eel canyon to be deposited within the gorda fan

sub decadal turbidite frequency during the early holocene eel fan offshore northern california remotely operated and autonomous underwater vehicle technologies were used to image and sample exceptional deep sea outcrops where an 100 m thick section of turbidite beds is exposed on the headwalls of two giant submarine scours on eel submarine fan offshore northern california usa these outcrops provide a rare opportunity to connect young deep sea turbidites with their feeder system 14 c measurements reveal that from 12 8 ka to 7 9 ka one turbidite was being emplaced on average every 7 yr this emplacement rate is two to three orders of magnitude higher than observed for turbidites elsewhere along the pacific margin of north america the turbidites contain abundant wood and shallow dwelling foraminifera demonstrating an efficient connection between the eel river source and the eel fan sink tur bidite recurrence intervals diminish fivefold to 36 yr from 7 9 ka onward reflecting sea level rise and re routing of eel river sediments

sand bodies and incised valleys within the late quaternary sanaga nyong delta complex on the middle continental shelf of cameroon abstract seismic data and sediment cores collected offshore from the sanaga river and nyong river mouths were used to analyse a loose mantle of yellow to reddish sandy gravel with a range of fluvial and deltaic characteristics cropping out in the middle part 25 65 m water depth of the continental shelf of cameroon contrary to most of the atlantic shelves where the lowstand systems tract was destroyed by erosion we found 80 120 ms 60 90 m of sediment mainly in the middle part of the shelf which correspond credibly to mis 2 4 fluvial paleodrainage systems are preserved beneath the shelf and individual filled channels with planar infillings were mapped that cross the shelf along two surfaces of erosion these incisions suggested westerly and northwesterly drainage shifts during presumed lowered base level the presence of closely spaced channel fills suggests repeated avulsion of a single stream during a long lasting sub aerial erosion period the seismic facies of these pleistocene deposits distinguish themselves clearly from well stratified older strata showing deformation pliocene or intense folding miocene the orientation of the paleovalleys appears strongly controlled by the n60 e trending cross faults within mesozoic cenozoic strata on the basis of approximately 80 000 years of accumulation an estimate of the yearly mass of sediment transported was calculated for the sanaga and nyong rivers and compared to the present sediment load of the two rivers it is estimated that as much as 50 of the sediment discharge must have bypassed the upper slope we show that deposition took place near the terrestrial break in slope even though the coastline had already regressed across the shelf in contrast the gradient of the lower course of the nearby niger river remains below 0 05 through several hundreds of kilometres and no lowstand deposits have been preserved we conclude that the break in slope even terrestrial is the determining factor regarding preservation of shelf deposits during relative sea level rise

preliminary spectral analysis of near real time radon data fast fourier analysis of the near real time radon data collected since 1977 by the caltech automated radon thoron monitoring system has been carried out in order to determine if any characteristic frequency components are present that can be associated either with precursors to seismicity or with environmental factors preliminary results indicate that during quiet periods with low seismicity and no rainfall the spectral power is distributed as 1 f before four local earthquakes a departure from this 1 f behavior was observed at low frequency during periods of heavy rainfall an increase in both low and high frequency power was observed the spectral power of the large radon anomaly observed prior to the october 15 1979 imperial valley earthquake was found to have a 1 f distribution but with power at all frequencies about four times greater than that of data from quiet periods

anomalous radon emanation at local and regional distances preceding earthquakes in the new madrid seismic zone and adjacent areas of the central mid continent of north america 1981 84 anomalous soil radon activity including several spike like surges over periods of 5 2 and 2 1 2 months and a year long declining trend preceded the most significant earthquakes of the central mid continental region of north america during 1981 and early 1984 the 5 month period of erratic weekly radon activity february june 1981 was followed by a tremor of magnitudem 4 0 40 km from the monitoring site in the new madrid seismic zone an unusual earthquake swarm in central arkansas 160 km from the new madrid seismic zone and 230 km from the monitoring site in the seismic zone began in january 1982 shortly after a year long declining trend in anomalous radon emanation earthquakes of magnitudes 4 5 4 1 and 4 0 occurred at the swarm s outset in early 1982 fitting a pattern anticipated for the new madrid seismic zone on the basis of the radon activity two periods of coincident peak radon emanation have since been observed in the arkansas and new madrid seismic regions as have synchronous seismic pulses for the two separate areas

continuous measurement of nontidal variations of gravity records from seven superconducting gravimeters operated at five different locations in california and one in boulder colorado are examined after removal of tides and the gravitational attraction of the atmosphere fluctuations over periods between a few days and several months were observed at all sites with peak amplitudes of order 10 gal by contrast a 640 day record obtained with one of the instruments in germany showed peak fluctuations of only 2 gal in most of the records the causes of these aperiodic variations were not determined so that they serve to set limits on the vertical motion or displacement of mass at the respective locations however at the geysers geothermal field much of the gravity variation is correlated with seismic activity reinjection rate and rainfall measurements of this type were not possible prior to the development of the superconducting device consequently these results provide the first evidence for the existence of gravity variations on the time scale and of the magnitude described here vertical crustal motion motion related to seismic events and hydrological phenomena can lead to variations on this scale unambiguous identification of causal relationships will require either special circumstances such as found at the geysers or operation of the instruments in pairs

detailed investigation of continental shelf morphology using a high resolution swath sonar survey the eel margin northern california abstract the eel shelf northern california lies within an active compressional tectonic margin subject to abundant terrigenous sediment input from the eel river a recent high resolution swath sonar survey provides us with the opportunity to investigate seafloor morphology and acoustic backscatter patterns within this dynamic region our analysis of the statistical character of bathymetry demonstrates a clear separation into large and small scale morphologies at a 3 10 km scale with smaller scale morphology heavily damped relative to large scale morphology the eel shelf bathymetry is subtle but several structures can be readily discerned in a residual bathymetry formed by removal of the downslope gradient some shelf structures are evidently related to depositional processes as evidenced by correlation with 100 yr sediment accumulation rates whereas others appear related to tectonic processes as evidenced by correlation with subsurface synclines and anticlines the sidescan structure of the shelf is dominated by the low backscatter over the eel and mad river subaqueous deltas evidently associated with the sand to mud transition however contrary to usual correlations between backscatter and grain size in this situation higher backscatter is associated with the muddy sediments in addition we observe a series of shore perpendicular striations or ribbons spaced 0 2 1 0 km apart which extend northward from the eel river subaqueous delta and lie at or near the sand to mud transition some aspects of ribbon morphology suggest that they may be associated with down slope flows

delta development and channel incision during marine isotope stages 3 and 2 in the western south yellow sea abstract approximately 4100 km of high resolution seismic profiles recently obtained from the western south yellow sea were subdivided into seven seismic units by six major seismic surfaces three sediment cores between 60 and 71 m in length obtained from localities on the seismic profile lines were analyzed for sedimentary characteristics clay mineral components and benthic foraminiferal and ostracod assemblages and were also dated by ams 14 c and optically stimulated luminescence to document the environmental history of the region stratigraphic units in the cores were confidently correlated with seismic units in the profiles stratigraphic correlation among these three cores and the previous well studied core qc 2 was facilitated by the cold water deposits in marine isotope stage mis 5 the three cores document the sedimentary sequence during the period from mis 6 up to mis 1 strata formation and sedimentary environment changes since mis 5 are strongly controlled by sea level fluctuations most of the successions were formed in mis 5 mis 3 and mis 1 with major erosions in mis 4 and mis 2 particularly our data revealed the presence of a large delta active during mis 3 likely from the early stage of mis 3 to about 40 cal kyr bp that was subsequently affected by channel incision the delta succession and incised channel fills have a high concentration of smectite in their clay mineral components suggesting that the paleo yellow river was the main contributor to the delta development and channel incision the delta sequence has a coarsening upward trend and consists of two seismic facies the upper facies shows lateral alternations of chaotic and oblique or very low angle reflectors which correspond to sandy proximal delta front and delta plain facies and the lower facies is characterized by seaward dipping clinoforms which correspond to muddy distal delta front and prodelta facies the top surface of the delta inclines very gently seaward consistent with a deltaic development associated with the sea level fall in mis 3 the incised channel system consists of two main channels with multiple tributaries in a dendritic pattern the incised channel fills begin with fluvial and then estuarine sediments which are truncated by a transgressive ravinement surface and capped by transgressive deposits the main incision channels have a terraced cross sectional morphology which is interpreted to reflect multiple episodes of sea level fall during incision presumably from the late mis 3 to the last glacial maximum

late cenozoic basins of northern california the late cenozoic basins of northern california developed in response to both convergent tectonics associated with subduction of the farallon plate and its modern representatives the juan de fuca and gorda plates and transform tectonics associated with northward migration of the mendocino triple junction and formation of the san andreas fault system the modern eel river basin north of the mendocino triple junction is an active forearc basin located between the cascade magmatic arc to the east and the trench at the foot of the continental slope of northern california and oregon to the west five different types of late cenozoic basins or fragments of basins are preserved in onshore northern california south of the mendocino triple junction 1 remnants of a formerly more extensive neogene forearc basin preserved locally in downdropped blocks within the san andreas fault system 2 remnants of slightly older trench slope basins that generally developed west of but which may locally structurally underlie the younger forearc basin 3 younger strike slip related structural basins that have developed along active right lateral faults of the san andreas fault system 4 broad shallow embayments perhaps similar to the modern san francisco bay that were connected to the deeper pacific ocean to the west and 5 structurally emplaced remnants of oceanic crust and its overlying sedimentary cover the king range terrane our preliminary stratigraphic and sedimentologic studies suggest that much of northern california was covered during the neogene by a forearc basin that may have extended as far south as the san francisco bay region and into the southern san joaquin valley as the mendocino triple junction migrated northward during the late cenozoic the southern margin of the forearc basin was uplifted basin deposits were stripped off by erosion and the locus of forearc sedimentation shifted progressively northward through time preserved but isolated fragments of the forearc basin provide a partial record of the original paleogeography and tectonic framework of northern california during the late cenozoic

active venting at the isis mud volcano offshore egypt origin and migration of hydrocarbons abstract the isis mud volcano is an active camembert like mud expulsion structure in the eastern nile deep sea fan area it has been investigated during the nautinil 2003 and mimes 2004 cruises carried out within the mediflux project active gas rich fluid venting occurs at the isis mud volcano as indicated by enhanced gas content in the sediments having a measured 7 5 mmol of methane per liter of wet sediment in the central area of the mud volcano in addition gas bubble expulsions have resulted in the formation of multiple hydrocarbon plumes in the water column with methane concentrations as high as 1550 nmol l compared to 1 nmol l for background levels in deep water in view of the stable carbon and hydrogen isotopic composition of methane 13 c 55 1 vpdb d 203 vsmow and of higher hydrocarbons 13 c of 30 3 26 1 28 4 and 25 0 vpdb for ethane propane i butane and n butane respectively their origin is mainly thermogenic these isotopic data also show that the wet compounds are co generated with oil and we suggest they predominantly originate from type ii kerogen source rocks of potentially variable maturity levels at the centre of the mud volcano the distinct kink observed in the pore water isotopic and dissolved species composition and its depth level change between subsequent cruises indicates a high frequency of fluid gas expulsion the seawater signature of the pore fluid in the upper part of the sediment column suggests that each expulsion is followed by a downward migration of overlying seawater such downward advection of bottom seawater may not only be related to the replacement of the ejected gas but also to the replacement of lower density pore fluid by bottom seawater this mechanism is thought to be a common feature at mud volcanoes and gas seepage sites in the peripheral zone pore fluid is at seawater concentration and isotopic composition down to a coring depth of 430 cmbsf we suggest that the deeper downward advection of bottom seawater is related to the less frequent fluid gas expulsion occurring at these sites compared to the centre sites in this paper we show that a combination of geochemical tools used for hydrocarbons and pore water geochemistry is a powerful approach to detect sources of ascending fluid and to reveal post eruptional fluidodynamic processes within mud volcanoes

architecture and sequence stratigraphy of a late neogene incised valley at the shelf margin southern celtic sea abstract valleys on the outer celtic sea shelf were cut and filled during the late pliocene early pleistocene the kaiser valley is one of several valleys forming an anastomosed network the main valley directed 20 azimuth true n is 50 m deep and 10 km wide it is connected to the parallel dompaire and parsons valleys by several 120 140 directed incisions of lesser width and depth analyzed by mean of very high resolution seismic data the kaiser valley is interpreted as containing a compound fill consisting of eight erosionally based depositional sequences a typical sequence comprises two facies 1 fluvial channels at the base which represent lowstand to early transgressive deposits and 2 onlapping transgressive bay fill deposits that are locally interbedded at the top with isolated small channels attributed to flood tidal deltas the erosional bases of the fluvial facies correspond to sequence boundaries these are interpreted to result from relative sea level falls successive fluvial and bay fill facies are separated by flat erosional surfaces of high acoustic amplitude which extend laterally across the entire composite valley locally beveling sequence boundaries and creating terraces on the valley walls these flat facies contacts are interpreted as bay ravinement surfaces produced by waves in an estuarine setting the larger scale stacking pattern of the depositional sequences defines a progradational retrogradational trend in which the lowest sequence is mainly constituted by fluvial channel deposits whereas upper sequences display mostly bay fill facies the sequences are related to fifth order glacioeustatic fluctuations whereas their progradational retrogradational trend reflects fourth order eustatic variations and or rapid tectonic tilting of the area as indicated by the presence of two incision orientations the preservation of the system took place during a third order sea level rise and was favored by subsidence of the margin leading to its present occurrence down to 240 m below present sea level

gas geochemistry applied to earthquake prediction an overview terrestrial gases in groundwater and soil air have been extensively studied in recent years in seismically active areas especially in ussr china japan and united states in search of premonitory changes that might be useful for earthquake prediction concentrations of radon helium hydrogen mercury carbon dioxide and several other volatiles have been found generally to be anomalously high along active faults suggesting that the faults may be paths of least resistance for the terrestrial gases generated or stored in the earth to escape to the atmosphere temporal gas concentration changes with durations of a few hours to many months have been observed before many large earthquakes at a relatively small number of favorably situated stations at epicentral distances of up to several hundreds of kilometers these sensitive stations are generally located along active faults especially at intersections or bends of faults or some other structurally weak zones possibly because of tectonic strain concentration at such places however gas concentrations especially those measured at or near the ground surface may also be significantly affected by meteorological hydrological and other nontectonic changes in the environment the nontectonically induced variations must be carefully eliminated or recognized in the search of true earthquake related anomalies

radon and rilt anomalies detected before the irpinia south italy earthquake of november 23 1980 at great distances from the epicenter some investigators of istitute of physics and istitute of geology of the university of rome are carrying out measurements of tilt and groundwater radon content in sites located in central italy beginning from june to november 1980 anomalous variations in the radon content have been detected in rome and rieti sites water samples for discrete measurements of radon content were drawn periodically from underground strata the amplitude of the anomalies were 25 and 170 compared with the background level from about march 15 a bubble type tiltmeter installed at l aquila site showed a first anomalous tilting with a time scale of about two mounths and an amplitude of 15 rad a second anomalous tilting about 20 rad in amplitude was observed from the middle of may to november the seismicity m 4 0 4 7 within about 100 km of the sites seems to justify only the first anomalous tilting on november 23 1980 a strong m 6 5 earthquake took place in irpinia southern italy at about 250 km from rome rieti and l aquila sites we suggest to assume both the radon content anomalies and the second anomalous tilting as precursors of the irpinia earthquake

geology of the eel river basin and adjacent region implications for late cenozoic tectonics of the southern cascadia subduction zone and mendocino triple junction two upper cenozoic depositional sequences of principally marine strata about 4000 m thick overlie accreted basement terranes of the central and coastal belts of the franciscan complex in the onshore offshore eel river basin of northwestern california the older depositional sequence is early to middle miocene in age and represents slope basin and slope blanket deposition whereas the younger sequence late miocene to middle pleistocene in age consists largely of forearc basin deposits youthful tectonic activity related to gorda north american plate convergence indicates an active cascadia subduction zone and strong partial coupling between these plates structures of the northeastern margin of the eel river basin are principally north northwest trending east northeast dipping thrust and reverse faults that form imbricate thrust fans many faults merge downward into sole thrusts that extend to or near the gorda north american plate interface in the southern part of the region these structures have been modified by northward encroachment of the pacific plate the coastal belt fault the early tertiary accretionary suture between the franciscan central and coastal belts can be traced from arcata bay northward offshore to the southern oregon border it is tentatively extended farther northward based on aeromagnetic data to an offshore position west of cape blanco thereafter it may coincide with the offshore fulmar fault if so the franciscan coastal belt in california is correlative with the offshore fulmar terrane in oregon the cascadia subduction zone csz does not join the mendocino transform fault at the commonly depicted offshore location of the mendocino triple junction mtj instead the csz extends southeastward around the southern eel river basin and shoreward along mendocino canyon to join the petrolia shear zone similarly the mendocino fault may extend shoreward via mattole canyon and join the cooskie shear zone these two shear zones intersect onshore north of the king range and the area of their intersection is the probable location of the mtj

relationship of the 1979 southern california radon anomaly to a possible regional strain event during the second half of 1979 anomalously high emanation of radon was recorded at two stations of the automated radon thoron monitoring network operated by the w k kellogg radiation laboratory of the california institute of technology the two stations exhibiting major anomalies kresge and dalton canyon are located approximately 30 km apart on the frontal fault system of the transverse ranges of southern california at kresge the anomaly began on june 21 1979 and continued through december 1979 at dalton canyon the anomaly started about 3 weeks later and also continued through december 1979 at both sites the anomalous levels of radon decreased but did not return entirely to normal values shortly before october 15 1979 during the week of october 15 1979 a 6 6 m earthquake occurred about 290 km to the southeast of the two stations and later in that week earthquakes of magnitude 4 2 and 4 1 occurred at malibu and lytle creek the latter two events were within 60 km of the monitors a radon thoron monitor at lytle creek recorded no long term anomaly but did record a sharp spikelike decrease in the radon level on october 13 1979 coincident with our observations of anomalous radon levels other investigators have reported anomalies or suspected anomalies in several other geodetic geophysical and geochemical signals from the same general region the rapid temporal development of several of the anomalies together with the large area over which they were observed suggests that a large scale strain event took place which may have been responsible both for the widespread anomalies and for the seismicity that occurred in the region subsequent to the onset of the anomalies

ancestral head of wilmington canyon a 12 channel seismic reflection survey over parts of the head of wilmington canyon and the surrounding shelf revealed four major buried valleys and many small channels the data indicate that the ancestral delaware river valley was the most recent of a series of valleys to enter the canyon from the west the head of wilmington canyon probably was eroded and then filled at various times from late miocene to late pleistocene time thick sedimentary sequences indicate a sediment supply from both the north and west a large buried valley entering the canyon from the north was not mapped with the data presented here but it is possible that such a valley exists this is one of the first documentations of the long history of erosion of the united states east coast canyons

lower pleistocene to present structural deformation and sequence stratigraphy of the continental shelf offshore eel river basin northern california seismic stratigraphic sequences and deformational features are mapped beneath the continental shelf of the offshore eel river basin of northern california using a closely spaced high resolution multichannel seismic grid geometries of sequences and morphologies of bounding unconformities reflect competing tectonic and glacioeustatic influences producing shifting sedimentation patterns in the offshore basin during the last v1 myr estimated timing of unconformity formation correlates generally with a deep ocean global n 18 o curve both before and after a v500kyr transition from 41 kyr to 100 kyr dominated cycles we suggest that glacioeustatic fluctuations are the dominant control on unconformity formation basinwide however regional tectonic influences on sequence development are also observed folding associated with gorda north america plate convergence ended progressively from south to north between v1 0 ma and v500 ka in response to northward migration of the mendocino triple junction mtj since v500 ka continued encroachment of the mtj produces rotation of preexisting structures uplift of the table bluff anticline tba related periods of channel incision south of the tba and generally reduced sediment preservation across the shelf mtj related uplift may also have induced formation of eel canyon over the past v1 0 myr a dominant northern sediment source becomes progressively less important a southern source probably the paleo eel river has become dominant since v750 ka seismic unconformities fall into two categories 1 irregular surfaces of limited mappable extent interpreted as incision exposure surfaces forming during relative sea level lowstands and 2 smooth laterally extensive regional unconformities interpreted as ravinement surfaces that erode lowstand surfaces in all but deeply incised areas during sea level transgressions a sequence stratigraphic model for sediment deposition and preservation on the eel river shelf predicts that preserved sediment on the eel margin is dominated by fluvially derived highstand silts and muds deposited by longshore directed currents and waves lowstand sediments are preserved only in fluvial channels infilled during late lowstand early transgression preserved transgressive sediments are likely limited to a thin veneer of well sorted coarse sediment or shell debris deposited above the transgressive ravinement future deep coring will be required to confirm these predictions 2002 elsevier science b v all rights reserved

correlated radon and co2 variations near the san andreas fault correlations have been observed between groundwater radon and thoron concentrations and carbon dioxide discharges at the lake hughes station of the caltech radon monitoring network the lake hughes site is one of three radon monitoring stations located near the big bend segment of the san andreas fault which began to record anomalous radon levels in august 1981 two stations lake hughes and lytle creek recorded anomalous increases in radon while the third sky forest recorded an anomalous decrease several weeks after the onset of the anomaly strongly correlated radon fluctuations began at lake hughes and lytle creek these radon spikes also were found to be phase anti correlated with barometric pressure fluctuations analyses of gas grab samples showed relatively high levels of co 2 and ethylene in borehole air at lake hughes and lytle creek while analyses of water samples showed relatively large increases in hco 3 at both sites isotopic analysis of one gas sample from lake hughes yielded a 13 c value of 22 which suggests that the co 2 originates from the oxidation of organic material the correlation in radon fluctuations at lake hughes and lytle creek and their common dependence on barometric pressure changes began shortly after the onset of the radon anomaly in august and probably resulted from the simultaneous saturation of the water in these boreholes with carbon dioxide

controls of tectonics and sediment source locations on along strike variations in transgressive deposits on the northern california margin abstract we identify two surfaces in the shallow subsurface on the eel river margin offshore northern california a lowstand erosion surface likely formed during the last glacial maximum and an overlying surface likely formed during the most recent transgression of the shoreline the lowstand erosion surface which extends from the inner shelf to near the shelfbreak and from the eel river to trinidad head 80 km truncates underlying strata on the shelf above the surface inferred transgressive coastal and estuarine sedimentary units separate it from the transgressive surface on the shelf early in the transgression eel river sediment was likely both transported down the eel canyon and dispersed on the slope allowing transgressive coastal sediment from the smaller mad river to accumulate in a recognizable deposit on the shelf the location of coastal mad river sediment accumulation was controlled by the location of the paleo mad river throughout the remainder of the transgression dispersed sediment from the eel river accumulated an average of 20 m of onlapping shelf deposits the distribution and thickness of these transgressive marine units was strongly modified by northwest southeast trending folds thick sediment packages accumulated over structural lows in the lowstand surface the thinnest sediment accumulations 0 10 m were deposited over structural highs along faults and uplifting anticlines the eel margin an active margin with steep high sediment load streams has developed a thick transgressive systems tract on this margin sediment accumulates as rapidly as the processes of uplift and downwarp locally create and destroy accommodation space sequence stratigraphic models of tectonically active margins should account for variations in accommodation space along margins as well as across them

sediment transport events on the northern california continental shelf abstract a long term monitoring tripod has been maintained in 60 m water depth at the northern end of the strataform study site on the northern california continental shelf as part of this ongoing study tripod data for 1 year beginning 24 september 1995 are used to provide a sediment transport analysis on an event by event basis the objective of this paper is to highlight the energetic nature of this shelf region in terms of the frequency duration and magnitude of sediment suspension events and the associated particle flux analyses are based on measurements from two current meters and two optical backscatterance sensors located at 30 and 100 cm above the bed data from these instruments and a pressure sensor were averaged over 7 5 min every hour during the year of record 41 distinct sediment suspension events occurred i e sustained suspended sediment concentrations greater than 20 mg l above background level at 100 cm above bed suspended sediment events were associated with significant wave activity tidal currents and river discharge the average duration of a sediment suspension event was 3 1 days and varied from 0 7 to 8 days during events mean suspended sediment concentrations of 110 mg l were observed with peak hourly observations exceeding 1000 mg l concentrations between events averaged 35 mg l the overall sediment flux for the period of record was directed seaward and southward the distribution and magnitude of sediment suspension events and particle flux showed a strong seasonality for example of the sediment transport during events 98 of the net along shelf and 73 of the net across shelf sediment transport occurred in the winter three major winter storms could account for 72 of the total along shelf transport but only 10 of the across shelf transport the across shelf flux was more evenly distributed over the year and occurred as a result of mean currents and very low frequency seaward flows associated with mesoscale circulation patterns

estimates of suspended sediment flux and bedform activity on the inner portion of the eel continental shelf energetic waves strong bottom currents and relatively high rates of sediment discharge from the eel river combined to produce large amounts of suspended sediment transport on the inner continental shelf near the eel river during the winter of 1995 1996 bottom boundary layer bbl measurements at a depth of 50 m using the geoprobe tripod showed that the strongest near bottom flows combined wave and current speeds of over 1 m s and highest sediment concentrations exceeding 2 g l at 1 2 m above the bed occurred during two storms one in december 1995 and the other in february 1996 discharge from the eel river during these storms was estimated at between 2 and 4 103 m3 s suspended sediment flux ssf was measured 1 2 m above the bed and calculated throughout the bbl by applying the tripod data to a shelf sediment transport model these results showed initially northward along shelf ssf during the storms followed by abrupt and persistent southward reversals along shelf flux was more pronounced during and after the december storm than in february across shelf ssf over the entire measurement period was decidedly seaward this seaward transport could be responsible for surficial deposits of recent sediment on the outer shelf and upper continental slope in this region sediment ripples and larger bedforms were observed in the very fine to fine sand at 50 m depth using a sector scanning sonar mounted on the tripod ripple wavelengths estimated from the sonar images were about 9 cm which compared favorably with photographs of the bottom taken with a camera mounted on the tripod the ripple patterns were stable during periods of low combined wave current bottom stresses but changed significantly during high stress events such as the february storm two different sonic altimeters recorded changes in bed elevation of 10 to 20 cm during the periods of measurement these changes are thought to have been caused principally by the migration of low amplitude long wavelength sand waves into the measurement area

estimating river sediment discharge to the ocean application to the eel margin northern california abstract hydrotrend a synthetic river discharge numerical model can simulate the natural variability daily annually and longer in the flux of water and sediment delivered to the coastal ocean the numerical model is designed to make discharge predictions based on climate even though field measurements of river flow are not available provided that appropriate assumptions are made regarding past climate the model can predict how a river may have behaved in the geological past sediment load is determined from a river s rating coefficients when applied to the flood dominated eel river northern california hydrotrend captures the intermonthly and interannual variability of discharge and loads over a century or more hydrotrend is applied to the ice age paleo eel river when sea level was lower and climate much cooler and wetter the paleo eel river at 18 000 year bp would see its hinterland runoff increase but not the magnitude of the peak discharges the post dicted sediment load of the paleo eel river was 25 greater than today s although basin precipitation was 45 greater and the hinterland area 4 greater through sea level lowering a method is provided to obtain sediment discharge rating coefficients for unmonitored modern rivers and paleo rivers the relationship q s g 1 2 h 3 2 a 1 2 provides for an estimate of a river s sediment load q s to within a factor of 3 over 7 orders of magnitude from knowledge of basin relief h and basin area a rating coefficients are determined from this estimate of q s and the power law rating curve q s aq b 1 where q is discharge

evolution of a trench slope basin within the cascadia subduction margin the neogene humboldt basin california the neogene humboldt eel river basin is located along the north eastern margin of the pacific ocean within the cascadia subduction zone this sedimentary basin originated near the base of the accretionary prism in post eocene time subduction processes since that time have elevated strata in the south eastern portion of the basin above sea level high resolution chronostratigraphic data from the onshore portion of the humboldt basin enable correlation of time equivalent lithofacies across the palaeomargin reconstruction of slope basin evolution and preliminary delineation of climatic and tectonic influence on lithological variation emergent basin fill is divided into five lithofacies which clearly document shoaling of the inner trench slope from deep water environments in early miocene time to paralic environments in pleistocene time the oldest strata consist of hemipelagic mudstones and minor debris flow breccias deposited in a deep water setting during elevated sea level these strata are overlain by glauconite rich fine grained turbidites which heralded an increasing influx of terrigenous detritus water depths shoaled earlier in the eastern basin area as the palaeoshoreline prograded seaward turbidite deposition ceased in the eastern basin area at about 2 2 ma whereas 22 km to the west turbidite deposition continued until about 1 8 ma lithofacies at the western study site change abruptly across a middle pleistocene unconformity from outer shelf to paralic deposits in the east a more complete pleistocene section records transition from outer to inner shelf beach and fluvial environments the humboldt basin lithofacies sequence is overprinted by eustatic control of sediment source comparison of sediment character with palaeoceanographic conditions indicates dominance of hemipelagic facies during periods of elevated sea level in the middle miocene and early pliocene when depocentres were isolated from terrigenous sediment glauconite rich facies were mobilized from an upper slope setting following these periods of elevated sea level and redeposited in a deep marine environment pleistocene shoreline lithofacies display glacio esutatic control of depositional environment by recording several cycles of nearshore to fluvial progressions general models of accretionary prism behaviour and trench slope basin evolution are compatible with the overall coarsening upward lithofacies sequence filling the humboldt basin early structural barriers precluded deposition of terrigenous material except from locally derived debris flows subsequent shoaling and burial of deactivated thrust folds enabled turbidity flows to reach the basin floor however late stage tectonism apparently controlled the onset of coarse grained deposition in this sequence significant sand rich turbidite deposition began in the middle pliocene synchronous with tectonic uplift of the southern basin margin conversely cessation of turbidite deposition in the eastern basin area in latest pliocene time was synchronous with growth of anticlinal structures which again blocked widespread dispersal of turbidity flows this middle pliocene to holocene period of crustal shortening is synchronous with continued reduction in spreading rate along the southern juan de fuca ridge and probably reflects partial coupling between the subducting lithosphere and the overlying accretionary prism