quantification of rock mass damage in underground excavations from microseismic event monitoring abstract rock mass damage assessment is required for many applications in rock engineering practice including support design contamination transport control stope design amongst others while various methods such as displacement measurement seismic refraction and direct observation using borehole camera have been used relatively few efforts have been made to use microseismic monitoring to quantify the rock mass damage from laboratory tests it is well known that microseismic events are indicators of fracturing or rock damage as the rock mass is brought to failure at high stress by capturing the microseismic events underground excavation induced rock mass degradation or damage can be located but can the amount of damage in terms of changes to strength or deformation properties be measured in the present study a method of characterizing rock mass damage near excavations based on microseismic event monitoring is developed and a damage driven numerical model is presented that takes the microseismic data as input to determine the damage state described by fracture density the approach is built on the discovery that a realistic crack size corresponding to a seismic event can be established by applying a tensile cracking model instead of the traditional shear model commonly used in earthquake analysis the rock mass is softened by the introduction of cracks and this is simulated by a micro mechanics based constitutive model the material property input for the model are young s modulus poisson s ratio of the intact rock and information obtained from the monitoring of microseismic events such as the location and the source size of each event calculated from source parameters using data from the atomic energy of canada limited mine by experiment this model has been verified by investigating the linkage between microseismicity rock mass damage and ground deformation it is found that when damage related softening based on microseismic data is considered predicted rock mass displacements are in good agreement with extensometer measurements

temporal changes of groundwater pressure in a natural slope of nonfissured clay this paper presents results from a field investigation in which groundwater pressures were measured in a natural slope of soft clay over a 10 year period measurements of piezometric levels are reported together with calculated annual changes of safety factor of the slope using consolidation theory predictions were made of changes of piezometric levels for the condition of zero infiltration based on the postulate that these changes were the direct result of changes of hydraulic conditions at the ground surface the predictions were in agreement with the field measurements a method is suggested for estimating the most severe groundwater pressures that a clay slope can be expected to experience using this method estimates were made of the minimum expected value of safety factor of the slope at the test site keywords natural slope clay pore pressures field measurements stability long term

the shallow porosity structure of the eel shelf northern california results of a towed electromagnetic survey a towed electromagnetic survey mapping the electrical resistivity of the seafloor was conducted over an area of the eel shelf off humboldt bay california continuous resistivity profiles to 20 m below the seafloor were measured along 120 km of track line from water depths of 100 m to around 30 m the shallow structure along the shelf is highly variable and we identify three distinct environments based on the recorded resistivities and the porosities inferred from them the first region is a mid shelf depocenter characterized by a thin 2 m moderately high porosity 45 60 surface layer which overlies a less porous 35 45 and homogeneous substrate uniform both laterally and vertically this region is found to the northwest of the humboldt bay entrance from water depths of about 65 m to at least 100 m and is roughly coincident with recent flood deposits the second region is located closer to shore and contains extremely high resistivities for a shallow sedimentary environment it reveals a high degree of spatial variability on length scales of several hundred meters several possibilities exist to explain such high resistivities and these include upwelling fresh water channeled to the seafloor through local fault and anticline systems a significant volume of natural gas within the sediments or a continuous process of carbonate precipitation through oxidation of methane near the seafloor which over time builds a substantial thickness of lithified material none of the above explanations are mutually exclusive and all could act in concert to increase resistivities the third region roughly coincides with the eel river delta and features a buried layer of moderately low porosity 30 35 at a depth of about 5 m and with a thickness of between 5 and 10 m this layer extends from near the entrance to humboldt bay in a southwesterly direction across the shelf 1999 elsevier science b v all rights reserved

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

statistical characterization of high frequency shallow water seafloor backscatter knowledge of the background reverberation environment is a prerequisite for the design of any target detection scheme while the problem of understanding and predicting high frequency background seafloor reverberation level or mean energy scattered per unit area of the seabed has received considerable attention studies of high frequency reverberation amplitude statistics are relatively scarce of these studies many have dealt with scattering from more or less homogeneous seafloors in terms of bottom type whereas most shallow water areas will not be homogeneous but will have patchiness in space and time which will have a strong influence on scattered amplitude statistics in this work a comparison is presented between 80 khz seafloor backscatter statistics obtained at shallow water sites around sardinia and sicily the data include measurements from several distinct bottom provinces including sites with posidonia oceanica sea grass and sites covered with live shellfish results of the analysis are cast both in terms of mean power level or backscattering coefficient as well as of the amplitude statistics the reverberation statistics did not always exhibit a rayleigh probability distribution function pdf but exhibited statistical distributions with heavier tails several more appropriate models of reverberation pdf were examined in order to better describe the measured amplitude distributions the rayleigh mixture and the k models were found to be the most robust in describing the observed data

beach nourishment effects on sand porosity variability abstract a standard assumption in coastal engineering is that the porosity of natural beach sand non cohesive is 40 however is this assumption correct for all beach sand this paper proposes an accurate and simplified method to assess changes in sand porosity after beach nourishment by means of in situ density surveys through a nuclear densimeter this novel application has been applied to different beaches in the southwest of spain according to the tidal range grain size and beach morphology in several terms general results show that sand porosities range from 25 6 to 43 4 after beach nourishment works this research can be considered a support tool in coastal engineering to find shifting sand volumes as a result of sand porosity variability after beach nourishment and later marine influence

regional scale landslide susceptibility mapping using the weights of evidence method an example applied to linear infrastructure large landslides are common in the gently sloping clay plains of the saint lawrence lowlands of eastern canada these tend to occur along rivers carved into the marine soils deposited in the former champlain sea which occupied the area roughly 10 000 years ago this paper presents a landslide susceptibility model developed at the regional scale using a bivariate statistical method the weights of evidence method the analysis considers the association of existing large landslides in a portion of the study area with key terrain features such as ground elevation flow accumulation in adjacent streams soil type soil thickness and land use the resulting model identifies three different levels of susceptibility low low to moderate and moderate to high these descriptors are related statistically to the probability of encountering existing large landslides within 500 m 1 or 2 km respectively the model is tested along primary railway corridors and isolates 8 of the total length for further consider

marine controlled source electromagnetic method used for the gas hydrate investigation in the offshore area of sw taiwan abstract bottom simulating reflectors bsrs high methane flux shallow sulfide methane interfaces fluids venting from the seafloor authigenic carbonates within sediments methane reefs and self biomes are common seafloor features in the area off southwest taiwan the geophysical and geochemical signatures of these features suggest a high potential for gas hydrate gh reservoirs in the region the bsrs are typically interpreted as the boundary between free gases and solid hydrate whereas the upper reaches of the hydrate stability zone and the distribution of gas hydrate in shallow sediments are not well understood this study shows the first results of a marine controlled source electromagnetic survey conducted in the offshore area of sw taiwan in 2010 the survey aimed to provide electrical resistivity information of the shallow sediments three target areas were surveyed 1 an area to the southeast of the xiaoliuchiu island gas seep g96 2 an area in the west of the yung an ridge yar and 3 an area in the northwest of the good weather ridge gwr in total fourteen survey lines with a total length of 72 km were completed our preliminary results show that relatively high resistivity anomalies occur within pockmarks and at gas seepage sites the apparent resistivity is estimated to be about 1 ohm m higher than background in g96 and yar sites while an anomaly up to 2 ohm m is found in the gwr at gas seep site g96 the high resistivity anomaly may be due to the existence of authigenic carbonates whereas the high resistivity anomaly in the nw of the gwr site may also be due to the existence of gas hydrate in the shallow seabed based on the resistivity anomaly the gas hydrate saturation is about 16 in the shallow sediments below the pockmark area in the northwest side of the gwr site

geophysical evidence for karst formation associated with offshore groundwater transport an example from north carolina 1 marine geophysical data from long bay north carolina involving a novel combination of electromagnetic and high resolution chirp seismics show evidence of submarine karst formation associated with what has been inferred to be a site of high flux submarine groundwater discharge sgd a substantial distance offshore recently observed temperature and chemical signals from wells in this area provide the basis for the interpretation of the high flux sgd here and they also suggest a terrestrial source for the groundwater and thus a potentially important route for nutrient transport to the oceans our data indicate that karstification is localized to the high flux zone and we suggest that mixing of the chemically distinct but saline groundwater with seawater has resulted in the karstification as karstification increases permeability and flux a positive feedback would tend to progressively enhance submarine groundwater discharge our data reveal a significant local anomaly in apparent porosity a dense block that may have initiated the local focusing of groundwater flow conditions favorable to the formation of similar locally punctuated sites of high flux sgd are likely to exist along the mid to inner shelf of the southeastern united states where carbonate aquifers are prevalent

a tensile model for the interpretation of microseismic events near underground openings for small scale microseismic events the source sizes provided by shear models are unrealistically large when compared to visual observations of rock fractures near underground openings a detailed analysis of the energy components in data from a mine by experiment and from some mines showed that there is a depletion of s wave energy for events close to the excavations indicating that tensile cracking is the dominant mechanism in these microseismic events

using csem techniques to map the shallow section of seafloor from the coastline to the edges of the continental slope many important processes occur within the shallow section of the seafloor on the continental shelf and slope yet conventional geophysical constraints on the physical properties within this critical boundary layer are limited some of the key constraints involve quantification of fluids within the seafloor which can be provided by electrical methods this paper reviews the application of a towed em system to map the uppermost 20 m of seafloor in a variety of settings ranging from nearshore regions in water depths of approximately 10 m on the continental shelf out to water depths of 1300 m the system is a mapping tool that provides areal maps of seafloor resistivity and has been used for a variety of purposes including sedimentary characterization and facies mapping evaluation of groundwater discharge and mapping seafloor mounds in the gulf of mexico thought to contain massive deposits of gas hydrate

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

high resolution 3d seismic reflection and coring techniques applied to late quaternary deposits on the new jersey shelf studies of variable small scale features typical of quaternary glacimarine environments require an interdisciplinary approach precisely navigated high resolution 3d seismic surveys nested within a regional 2d seismic framework and integrated with a precisely navigated coring program designed to sample specific shallow acoustic facies we illustrate this approach with examples from continuing studies of sediments on the new jersey continental shelf surficial stratigraphy associated with the latest pleistocene holocene deglaciation has been imaged twice in true 3d using the huntec dts system a deep towed high frequency 500 3500 hz boomer source in both cases nominal profile spacing was 10 m 2 5 m shot points penetration of 40 ms 30 m was achieved seismic facies in the upper 5 m have been interpreted using differential gps navigated vibra cores accuracy of position of both seismic profiles and core locations approaches 5 m much smaller than the wavelengths of the geologic features being imaged sampled survey results show multiple sediment filled channels buried beneath the modern outer shelf meandering south and southeast in the general direction of the shelf edge channels are typically a few meters deep and 100 200 m across lateral continuity between the channeled surfaces within the outer shelf wedge and the mid shelf cannot be demonstrated because of later erosion but both sets of channels incise reflector r believed to be a pre late wisconsinan exposure surface ams14c dates on benthic foraminifers from cores show that channels on the midshelf are cut into sediment 45 000 yrs old and filled with muddy sediment as young as 12 500 yrs whereas channels on the outer shelf are filled with coarser and perhaps older sediment both sets of filled channels are buried beneath a surficial sand layer the integrated approach described here can remove some uncertainties and considerably sharpen the quaternary stratigraphic picture without the perspective obtained from 3d seismic surveys and equally precise sampling interpretations based on broader regional seismic surveys and spot coring are inevitably constrained by the potential for mismatching shallow acoustic and sedimentary facies

rapid and widespread dispersal of flood sediment on the northern california margin the dispersal of flood sediment from small river systems is a poorly studied yet potentially important aspect of active continental margin sedimentation in january 1995 during a flood with a 30 yr return period the eel river northern california delivered an estimated 25 3 106 t metric tons of fine grained 62 m sediment to the ocean the flood formed a distinct layer on the sea bed that was centered on the 70 m isobath extended for 30 km along shelf and 8 km across shelf and was as thick as 8 5 cm but contained only 6 106 t of sediment thus 75 of the flood derived sediment did not form a recognizable deposit but was instead rapidly and widely dispersed over the continental margin stratigraphic models of and compilations of sediment flux to active continental margins need to take the dispersive nature of small river systems into account

structural characteristics of columnar jointed basalt in drainage tunnel of baihetan hydropower station and its influence on the behavior of p wave anisotropy abstract researches about the structural characteristics of rock mass are the basis for understanding their failure modes mechanism properties as well as evaluation of structural stability during the process of excavation natural columnar jointed basalt has complex structures and exhibits remarkable anisotropy and size effect in this study the observation window method was firstly applied to describe the natural columnar joints and pillar shapes at engineering scale and then the structural characteristics of columnar joints were analyzed the roughness of columnar joints scanned from large size rock core obtained at drainage tunnel 1 1 was secondly investigated based on the 3d scanning method some techniques such as field statistical analysis and ct scanning were used to analyse the characteristics of internal implicit joints in columnar jointed basalt thirdly the large scale columnar jointed basalt cores were tested by p wave which assisted to investigating the anisotropy of columnar jointed basalt the experimental and analytical results indicate that at the engineering scale natural columnar jointed basalt is heterogeneous exhibiting the features of mosaic structure and mainly quadrilateral in shape at the large size rock core scale the roughness of columnar joints is low with the value of 5 558 at the basalt column scale the internal implicit joints are not randomly distributed instead showing obvious tendency the internal implicit joints and columnar joints are important factors contributing to the special failure mode of columnar jointed basalt at the rock core scale with increasing angle between the p wave propagation direction and column the anisotropy of columnar jointed basalt core gradually increases and the degree of anisotropy is proportional to the number of columnar joints the internal implicit joints could also affect the p wave anisotropy of basalt column and the results in this study can provide some references for projects related to columnar jointed rock mass

high resolution swath sonar investigation of sand ridge dune and ribbon morphology in the offshore environment of the new jersey margin abstract sand ridges on the northeast us atlantic shelf form in the near shore environment most likely in response to storm driven flows as the holocene transgression has continued the ridges have been transferred to an offshore hydrodynamic regime where currents are not constrained by the coast and storms do not influence bottom currents as frequently or as strongly here we qualitatively and quantitatively investigate the morphology of offshore sand ridges and smaller scale features in an effort to place constraints on bedform development in these deeper waters a recent high resolution swath sonar survey mapped a portion of the new jersey shelf from 20 m water depth to the shelf break 120 m imaging both sand ridges and smaller scaled dunes and ribbons in far greater detail than has been previously possible using a robust statistical analysis we find that the gross morphology of ridges height width length does not change with depth beyond 20 m water depth and changes in ridge orientation generally mirror changes in regional contour orientation hence ridges have not continued to grow since transgression has brought them into the offshore hydrodynamic regime however on the inner shelf 20 m water depth to the mid shelf shore we do find evidence in the ridge shape which has an asymmetry opposite to that seen near shore and in the complex backscatter response that some important modifications to ridges are taking place at these water depths in contrast on the mid shelf from the mid shelf shore to the franklin shore ridges tend to have higher backscatter at the crests implying that these are largely winnowed relict features lineated smaller scale 100 500 m wavelength

electromagnetic surveying of seafloor mounds in the northern gulf of mexico seafloor controlled source electromagnetic data probing the uppermost 30 m of seafloor sediments have been collected with a towed magnetic dipole dipole system across two seafloor mounds at approximately 1300 m water depth in the northern gulf of mexico one of these mounds was the focus of a recent gas hydrate research drilling program rather than the highly resistive response expected of massive gas hydrate within the confines of the mounds the em data are dominated by the effects of raised temperatures and pore fluid salinities that result in an electrically conductive seafloor this structure suggests that fluid advection towards the seafloor is taking place beneath both mounds similar responses are seen at discrete locations away from the mounds in areas that might be associated with faults further suggesting substantial shallow fluid circulation raised temperatures and salinities may inhibit gas hydrate formation at depth as has been suggested at other similar locations in the gulf of mexico

origine de la preconsolidation des argiles du saguenay quebec the clays of eastern canada and in particular the saint jean vianney clay in the saguenay region have often been described as clays with a preconsolidation due partly to cementation in order to check this assumption the geological history and the geomorphology of the saguenay region have been analyzed further to the evidence of significant erosion available geotechnical data in the form of variations of water content undrained shear strength and preconsolidation pressure have been analyzed to determine the elevation of the original ground surface in the hypothesis of a preconsolidation resulting from deposition and erosion the results of this analysis are in good agreement with the geological and geomorphological data and they suggest that cementation has had a negligible effect on the preconsolidation of the saguenay clays a regional map of preconsolidation pressures is also presented keywords clay preconsolidation geomorphology erosion shear strength journal translation

influence of the groundwater on the stability of a clay bank in baie james quebec the riviere broadback in northern quebec flows westward almost parallel to latitude 51 n to discharge into baie james at its southern end near the estuary the river banks are in clay surveys of the landsliding activity showed that many of the slides are superficial with depths seldom greater than about 2 m and are usually in the clay crust instrumentation revealed regional groundwater pattern close to the river banks that showed areas varying from those with significant underdrainage to those with hydrostatic pressure conditions the stability of 26 m high river slopes inclined at 27 in an area of underdrainage was investigated triaxial testing on undisturbed tube samples was used to obtain the postpeak parameters stability analyses gave a factor of safety close to one for shallow failure surfaces with underdrainage the factor of safety for deep failure surfaces is appreciably higher when hydrostatic pore pressure conditions are assumed analysis gave a factor of safety for deep failure that was

paleoenvironmental evidence for latest pleistocene sea level fluctuations on the new jersey outer continental shelf combining high resolution sequence stratigraphy and foraminiferal analysis foraminiferal assemblages in vibracored sediments within 5 m of the seafloor document high resolution sea level fluctuations and confirm the complex quaternary depositional history of the new jersey margin biostratigraphic data have been integrated with ongoing 2 d 3 d high resolution seismic analyses to interpret paleoenvironments of surficial stratigraphy beneath the modern middle to outer shelf cluster analysis of foraminiferal assemblages sampled every 20 cm average define four sample groups a d dominated by benthic species group a characterized by cibicides lobatulus is a middle to outer shelf assemblage 60 100 m water depths group b is composed of middle shelf species 30 60 m water depths and is characterized by low abundances and a fairly uniform distribution of foraminifera which suggests reworking and or a high rate of sediment accumulation group c dominated by elphidium excavatum is an inner to middle shelf assemblage 10 40 m water depths group d present in only one core and dominated by ammonia beccarii represents marginal marine environments 0 10 m water depths with fluctuations in salinity in general the modern sedimentary veneer i e the upper 20 cm is characterized by the deeper water fauna of group a sediments below these modern deposits are characterized by groups b and c reflecting shallower water depths and variable sediment accumulation rates on the inner and middle shelf taken together the group succession in the cores suggests an overall se to nw landward transgression in these latest pleistocene holocene deposits seismic analysis indicates that one core 27 penetrates the flank of a buried channel including its fill and the pre channel section within the channel three alternations of groups c and d suggest fluctuations between marginal marine and middle shelf paleoenvironments high frequency perhaps very small 10 m changes in base level are indicated using previously published ams 14c dates these fluctuations can be constrained as having occurred between 45 000 yr b p channel incision and 12 500 yr b p channel filling suggesting the non uniform nature of the last wisconsinan deglaciation

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

slope instability and valley formation in canadian soft clay deposits the purposes of the paper are to examine the deepening of valleys in clay deposits of eastern canada and in particular to look at the changes in the groundwater regime and slope stability conditions during valley formation field observations and laboratory testing indicate that the rate of valley deepening in champlain clay deposits is of the order of only a few millimetres a year owing to the low erodibility of the intact clay the clay banks are however more erodible owing to alteration and fissuration the stratigraphy of eastern canadian clay deposits can be simplified by considering it to be a stratum of low permeabilityconfined between two boundary layers of relatively high permeability which are the till layer at the base and a weathered crust or coarse grained layer at the top as the valley bottom get closer to the bottom till layer the groundwater regime and consequently the stability conditions are modified during the process of valley formation the groundwater regime passes through a

fourth canadian geotechnical colloquium strength and slope stability in canadian soft clay deposits it is generally admitted that the long term stability of clay slopes should be analysed in terms of effective stresses which necessitates the knowledge of the pore pressure conditions and of the relationship between the shear strength and the effective stresses this paper deals with the determination of shear strength for stability analysis of clay slopes in eastern canada first the various concepts pertinent to slope stability in soft clay are examined and a certain justification of the use of the post peak or large strain strength is demonstrated in a second part 14 case records of natural slopes or permanent excavation slopes are presented and analysed in terms of the post peak strength finally values of post peak strength determined in the laboratory for more than 30 sites are presented and it is attempted to derive correlations by which the shear strength parameters could be readily approximated from other properties such as the apparent preconsolidation pressure or the vane strength

erosivity of natural intact structured clay evaluation previous studies on erodibility of cohesive soil are briefly reviewed and it is concluded that experimental observations have been mainly concerned with remolded and reconsolidated or weathered cla

moment tensor inversion of induced microseisnmic events evidence of non shear failures in the 4 m 2 moment magnitude range to assess objectively the source mechanism of mining induced seismic events we developed an algorithm to invert for the moment tensor components from this inversion the ratio of isotropic deviatoric component in the source is obtained we are applying this method to microseismic events 4 m 2 recorded at the underground research laboratory url in pinawa manitoba where a tunnel is being excavated at 420 m depth to monitor the seismic activity induced by this opening an array of 16 triaxial accelerometers was installed around the planned tunnel results from the moment tensor inversion on a fist data set provide evidence of non shear failure mechanisms furthermore the location of events displaying a tensile component corresponds to a breakout observed underground in the roof of the tunnel

controlled electromagnetic sources for measuring electrical conductivity beneath the oceans 1 forward problem and model study exact closed form expressions for the electromagnetic induction fields produced by vertical and horizontal current sources in the conducting ocean overlying a one dimensional earth are derived from the maxwell equations numerical methods for the evaluation of the solutions are given including correction for the finite size of real sources simple models of the electrical conductivity structure of the ocean crust and lithosphere are deduced from geologic petrologic and laboratory data and their electromagnetic response is modeled horizontal electric dipole sources produce much larger field amplitudes than their vertical counterparts for a given frequency and range and the horizontal electric field offers superior received signal performance reflections of electromagnetic waves from the sea surface and thermocline must be considered for low enough frequencies or long ranges estimates of the ambient noise level from natural electromagnetic sources in the frequency range 0 01 10 hz are presented the ability of controlled sources to determine features of the conductivity of the ocean crust and upper mantle especially low conductivity zones is demonstrated if the mantle conductivity is low enough horizontal ranges of 50 km and conductivity estimates to over 20 km depth can be achieved

late quaternary sedimentation on the outer and middle new jersey continental shelf result of two local deglaciations high resolution seismic profiles show two prominent late quaternary sediment wedges on the outer and middle new jersey continental shelf an extensive wedge along the outermost shelf and upper slope up to 50 m thick appears to have been deposited on the hudson apron during an early melting of the late wisconsin laurentide ice sheet subsequent southward transport of this sediment occurred during sea level regression still stand and transgression a mid shelf sediment wedge which forms the fortune shore probably was deposited during a second melt event 11 to 12 ka as sea level was transgressing over the shelf

measuring the shallow porosity structure of sediments on the continental shelf a comparison of an electromagnetic approach with cores and acoustic backscatter we validate estimates of shallow sedimentary porosities made on the continental shelf by electromagnetic methods through a comparison with those measured directly in cores specifically we show that an electromagnetic surveying system we have used to measure sediment resistivity in a number of seafloor locations returns porosity depth profiles that are related to those measured in cores and that our data have good sensitivity to the structure within the uppermost few tens of centimeters of seafloor we then consider inferences of sediment type made by observations of acoustic backscatter in the light of our porosity measurements our results suggest that electromagnetic methods provide complementary information that can be used to improve grain type estimates at and just below the seafloor especially when combined with acoustic backscatter data because the system is pulled along the seafloor data can be quickly collected from a large area of seafloor and can be used to interpolate facies conditions between core locations

a large rapid landslide in sensitive glaciomarine sediments at mink creek northwestern british columbia canada abstract a landslide of 2 5 million m 3 of sensitive glaciomarine sediments predominantly silty clays occurred at mink creek near terrace british columbia 54 27 n 128 37 w some time between 1 december 1993 and 9 january 1994 we divide the landslide deposit into seven zones distinguished on the basis of morphological characteristics we interpret processes of flowing spreading and sliding often in succession as the landslide retrogressed the landslide is similar to other movements involving sensitive marine sediments but is unique in that both flowing and spreading occurred involving multiple rupture surfaces thus the landslide may be classified as a composite earth flow spread a decade of warm and wet climate preceded the landslide event since most global circulation models predict a warmer and wetter future for terrace more of these landslides may be expected

inversion of marine multifrequency electromagnetic profiling data a new approach to resolve surficial sediment stratification s u m m a r y electromagnetic induction emi methods are widely used on land tomap electric conductivity and or magnetic susceptibility distributions of surficial sediments in contrast the application of these methods in marine environments is relatively novel based on the recently developed electromagnetic benthic profiler marum neridis iii we investigate the potential of concentric loop emi methods to recover conductivity and susceptibility of layered marine sediments sensitivity analyses based on a data and model normalized jacobian matrix were performed to compare the influence of conductivity and susceptibility to in phase and quadrature components at different frequencies both parameters substantially affect the em response however the influence of susceptibility decreases more with depth and offers lower depth resolution than that of conductivity a 1 d inversion algorithm to reconstruct vertical conductivity distributions was developed from existing non linear inversion methods using apparent conductivity and apparent susceptibility recovered from simultaneous half space inversion as a priori information this algorithmwas tested on synthetic and real marine emdata from a commercial multifrequency concentric loop emi system gem 3 the results indicate that our inversion algorithm yields meaningful results down to approximately 3 m depth under typical shallowmarine conditions the comparison of inversion results recovered with 1 d and 2 d constraints showed that combining lateral with vertical constraints substantially improves the resolution of the inversion outputs field data from the nw iberian shelf was calibrated according to a processing flow specifically designed for underwater conditions and analysed inversion outputs are in good agreement with ground truthing stratigraphic investigations and deliver relevant clues on past and present sediment dynamics

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

buried paleo channels on the new jersey continental margin channel porosity structures from electromagnetic surveying abstract we report on a marine electromagnetic em survey across two portions of the new jersey continental margin that have been previously shown to contain buried paleo channels the em method used provides bulk porosity estimates to depths of around 20 m below the seafloor and is thus able to place porosity constraints on the nature of the channel infill and the contrast in physical properties across the channel boundaries our data show that a key condition for the channels to have an electrical signature is that they incise an underlying regional unconformity r thought to represent a subaerially eroded surface exposed during the late wisconsinan glaciation channels that cut r are seen through increases in apparent porosity another seismically imaged channel sequence which lies within the outer shelf sediment wedge sequence above r does not have an electrical signature indicating that the sediments above and below the channel boundaries have similar physical properties

source transport and evolution of saline groundwater in a shallow holocene aquifer on the tidal deltaplain of southwest bangladesh deltaic groundwater resources are often vulnerable to degradation from seawater intrusion or through interaction with saline paleowaters the ganges brahmaputra meghna river delta in bangladesh and west bengal india is a particularly vulnerable area with an estimated 20 million coastal inhabitants directly affected by saline drinking water the shallow groundwater of the coastal regions is primarily brackish with pockets of fresher water a small scale hydrologic investigation of groundwater salinity beneath an embanked tidal channel island was undertaken to explore possible hydrogeological explanations of the distribution of water salinities in the shallow aquifer this study employs a combination of 3h and 14c dating electromagnetic subsurface mapping and a 2 d solute transport model the authors conclude that the shallow groundwater salinity can best be explained by the slow infiltration of meteoric water into paleo brackish estuarine water that was deposited during the early mid holocene

quantification and interpretation of seismicity abstract methods based on acoustic emission and microseismicity ae ms have proven to be valuable for monitoring microcracking at the underground research laboratory url in canada the source locations of the seismic events induced by the excavation have helped to map out the extent of the excavation damage disturbed zone edz around tunnels this paper describes methods for advanced processing and interpretation of ae ms data and the quantification of changes in material properties using velocity interferometry examples of methods that are generally not used routinely in the analysis of ae ms data are given these include 1 long term spatial and temporal source parameter trends and magnitude frequency studies 2 source mechanism analysis and 3 source location refinement by the use of relative location and clustering techniques results from these studies are shown to aid in the understanding of the effect of confining pressure on ae ms activity around tunnels and the mechanics of rock failure in the edz also the reduction of source location error is shown to be critical for delineating structures that may exist in clusters of ae ms data finally examples of the use of seismic sources to produce repeat measurements of seismic velocity along raypaths in 3d orientations through a rock mass are given this is found to be a highly sensitive method for quantifying changes in rock properties such as young s modulus as well as for modelling the change in crack density and saturation occurring in a rock mass with time

use of terrestrial laser scanning for the characterization of retrogressive landslides in sensitive clay and rotational landslides in river banks for more than 10 years digital elevation models dem produced by light detection and ranging lidar technology have provided new tools for geomorphologic studies and especially for landslide stu

stress estimated using microseismic clusters and its relationship to the fracture system of the hijiori hot dry rock reservoir a method for estimating the in situ stress state by analyzing microseismic clusters induced by hydraulic injections is proposed the method is based on focal mechanism analysis supplemented with microseismic doublet analysis the latter is used to discriminate between the fault plane and the auxiliary planes of the focal mechanism solution the method was applied to estimate the stress field within the hijiori hot dry rock geothermal reservoir and yielded results which were consistent with other estimates the mechanics of permeability creation within the reservoir during major hydraulic injections was then examined by evaluating the interaction of the inferred stress field with the natural fracture system the characteristics of the latter were determined by integrating information obtained from core samples acoustic borehole televiewer images and pressure temperature and spinner logs the results indicated that the observed microseismicity and orientation dependent permeability characteristics of the fracture population are well explained by shear failure inferred from coulomb s friction theory it is also shown that the growth direction of the reservoir is strongly controlled by the distribution of favorably oriented pre existing fractures and their interaction with the stress field

studies on temporal and spatial variation of microseismic activities in a deep metal mine abstract aiming at forecasting techniques of ground pressure hazards in deep metal mines a microseismic monitoring system was established at a deep stope in hongtoushan copper mine in china based on theories of geophysics and rock mechanics a forecasting approach was introduced using microseismic multi parameters including cumulative apparent volume energy index spatial correlation length fractal dimension and b value the approach was used to predict large scale fractures and ground pressure hazards in rock masses the results showed that microseismic activities were very weak before mining commenced however activities became significant when mining started when mining finished microseismic activities remained at a higher level for about one week then became weakened before large scale fractures occurred all microseismic multi parameters behaved differently the apparent volume and spatial correlation length were continually increasing while energy index fractal dimension and b value were gradually dropping to their minimum values therefore these parameters could be used as precursory indicators for great ground pressure hazards comprehensive analysis on microseismic multi parameters changes could improve reliability of forecasting which is of great significance to deep metal mines in managing ground pressure failure risks

temporal imaging of mine induced stress change using seismic tomography abstract in an effort aimed at monitoring mining induced stress changes that may influence ground failure the us bureau of mines conducted a series of active 3 d seismic tomographic surveys at the homestake lead south dakota and lucky friday mullan idaho mines existing rock bolts were used to mount geophones and as strike points for introducing seismic energy using a 3 6 kg sledge hammer travel time measurements were recorded spanning up to 160 m between drifts at several levels the tomographic uncertainty was minimized by computing iso velocity surfaces of constant probability based on statistics from multiple reconstructions and a threshold criteria periodic imaging using tomographic velocity surfaces demonstrated that temporal and spatial changes in the local stress field occurred in response to ground failure and stope advancement at a gold and silver mine respectively

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

the lachenaie clay deposit some geochemical and geotechnical properties in relation to the salt leaching process this paper summarizes a detailed geotechnical and geochemical characterization program for the champlain clay deposit in lachenaie quebec presently the clay pore water is saline the main objective of the testing program was to study the leaching of the clay saline pore water since its deposition four issues are discussed in this paper first the deposit is shown to comprise two distinct clay layers with contrasting geotechnical properties the liquid limit and grain size distribution are the properties that best distinguish the two materials the upper layer is more plastic while the lower one is relatively silty the occurrence of these two layers is shown to be in agreement with some recent findings in quaternary geology second the relatively high pre consolidation pressures of the clay in the lachenaie area are shown to be coherent with an erosion scenario and the elevation of a neighbouring bluff previously interpreted as an erosion terrace third the relatively constant hydraulic conductivit

magnetic mineral and sediment porosity distribution on a storm dominated shelf investigated by benthic electromagnetic profiling bay of plenty new zealand abstract magnetic susceptibility and electric conductivity within the uppermost meter of the seafloor were measured with high resolution along 33 coast normal profiles in the bay of plenty new zealand using the recently developed electromagnetic benthic profiler marum neridis iii these parameters are used to determine magnetic mineral concentration and porosity of mostly volcanoclastic sediments between 2 and 35 m water depth to investigate distribution and formation of magnetic mineral enrichments on a storm dominated shelf in general magnetic mineral concentration susceptibility is inversely correlated to porosity conductivity along profiles susceptibility maxima and conductivity minima were commonly found on bathymetrical elevations such as dune and ripple crests cores and grab samples show the highest degree of enrichment in the uppermost 20 cm of the seafloor complementing petromagnetic analysis indicates a spectrum of feti oxides in the sediment ranging from magnetite and hematite over titanomagnetite tm40 and tm60 to titanohematite likely th80 and th95 three distinct zones of magnetic mineral enrichment could be identified a coast parallel structure with low porosity in recent fine sand between 5 and 20 m water depth a widespread structure with low porosity in older transgressionally reworked coarse sand in up to 30 m water depth and third structure coarse sand with high porosity located mostly below 30 m while the fine sand structure is interpreted as the result of an active process the other two appear to be relics sorting by grain size selective entrainment appears to be the major formation mechanism this study demonstrates how electromagnetic benthic profiling in combination with environmental magnetic laboratory analysis provides reliable highly interpretable data that allow insight into sorting processes within the boundaries of established lithofacies that are difficult to detect using a classical sedimentological approach

the role of paleochannels in groundwater seawater exchange relict fluvial channels that are infilled with high permeability sediments act as preferred pathways for groundwater flow and solute transport in coastal regions such paleochannels can provide a hydraulic connection between freshwater aquifers and the sea facilitating saltwater intrusion landward or freshwater discharge offshore although paleochannels have been implicated in several instances of saltwater intrusion there has been little direct study of these channels to confirm their role in this work simulation modeling of a general multi layered coastal plain aquifer setting indicates that when a paleochannel breaches a confining unit offshore submarine groundwater discharge of intermediate salinity occurs this discharge is largely concentrated along the margins of the channel conversely seawater inflow occurs along the channel axis resulting in higher salinity in the middle of the channel relative to the flanks chirp seismic and electromagnetic data collected offshore wrightsville beach nc usa confirm these simulation results and indicate fresher porewater along channel flanks and slightly higher porewater salinity along the channel axis hence paleochannels contribute to the spatial variability in submarine groundwater discharge by serving as conduits of focused fluid exchange simulations also reveal that the freshwater saltwater transition zone is closer to land below paleochannels than in locations with a continuous confining unit this indicates that such channels are likely to be significant modes of saltwater intrusion into confined aquifers when excess freshwater extraction occurs on land

mapping the magnetic susceptibility and electric conductivity of marine surficial sediments by benthic em profiling distribution accumulation and diagenesis of surficial sediments in coastal and continental shelf systems follow complex chains of localized processes and form deposits of great spatial variability given the environmental and economic relevance of ocean margins there is growing need for innovative geophysical exploration methods to characterize seafloor sediments by more than acoustic properties a newly conceptualized benthic profiling and data processing approach based on controlled source electromagnetic csem imaging permits to coevally quantify the magnetic susceptibility and the electric conductivity of shallow marine deposits the two physical properties differ fundamentally insofar as magnetic susceptibility mostly assesses solid particle characteristics such as terrigenous or iron mineral content redox state and contamination level while electric conductivity primarily relates to the fluid filled pore space and detects salinity porosity and grain size variations we develop and validate a layered half space inversion algorithm for submarine multifrequency csem with concentric sensor configuration guided by results of modeling we modified a commercial land csem sensor for submarine application which was mounted into a nonconductive and nonmagnetic bottom towed sled this benthic em profiler neridis ii achieves 25 soundings second at 3 4 knots over continuous profiles of up to a hundred kilometers magnetic susceptibility is determined from the 75 hz in phase response 90 signal originates from the top 50 cm while electric conductivity is derived from the 5 khz out of phase quadrature component 90 signal from the top 92 cm exemplary survey data from the north west iberian margin underline the excellent sensitivity functionality and robustness of the system in littoral 0 50 m and neritic 50 300 m environments susceptibility versus porosity crossplots successfully identify known lithofacies units and their transitions all presently available data indicate an eminent potential of csem profiling for assessing the complex distribution of shallow marine surficial sediments and for revealing climatic hydrodynamic diagenetic and anthropogenic factors governing their formation

estimating in situ rock stress from spalling veins a case study stress induced failures have typically been considered as engineering disasters in deep underground excavations this paper highlights the importance of stress driven rock failures as a means to estimate the in situ rock stress at the depth the method which is based on the observation and documentation of a failure mode referred to here as spalling in deep tunnels or caverns is put forward and presented to estimate the macro scale rock stress using the proposed method the orientation of the principal stresses in situ can be deduced by the spalling intensity and associated stress induced spalling veins in the rock mass surrounding the opening and the magnitude of the principal stresses can be estimated by the assumed crack initiation stress required to generate spalling in the given rock by careful documentation of spalling failure characteristic in the field a real case study at baihetan powerhouse site has been carried out and indicates that the proposed method is an available way to enriching recognition of in situ rock stress and a helpful supplement to traditional methods of stress measurements after strictly numerical verification analysis of the regional tectonic setting as well as measurements of in situ stress supports the results by the suggested approach

the permeability of natural soft clays part ii permeability characteristics reply the permeability characteristics of a number of intact natural soft clays from quebec the usa and sweden have been investigated in the laboratory the variation of permeability with void ratio is best represented in terms of a linear e vs lg k relation which is generally valid in the range of volumetric strains encountered in engineering practice the permeability at the in situ void ratio is shown to be a complex function of such parameters as the void ratio the clay fraction the plasticity index and the fabric of the clay permeability anisotropy is negligible in marine clays the e vs lg k relationships of the various clays tested are well ordered in terms of an empirical parameter ip clay fraction irrespective of the geological origin of the clay the slope of the e vs lg k relationship referred to as permeability change index ck is simply related to the initial void ratio by ck 0 5eo keywords permeability clays laboratory tests permeability anisotropy permeability void ratio re

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

deformation forecasting and stability analysis of large scale underground powerhouse caverns from microseismic monitoring abstract to assess the stability of the underground powerhouse caverns and analyse the failure mechanism of the surrounding rock mass at the baihetan hydropower station in southwest china a high resolution microseismic ms monitoring system was implemented in the left bank underground powerhouse caverns based on the temporal and spatial distribution of ms events the correlation between ms activities and construction was established and three damage regions for the surrounding rock mass during excavation were identified ms clusters were found to occur most often in stress concentration regions of the underground powerhouse caverns and to result from various factors including excavation induced unloading and geological structure activation the seismic source parameters i e moment magnitudes and s wave to p wave energy ratios e s e p of the three ms clusters demonstrate the different failure modes and risks of the surrounding rock mass the temporospatial evolution of the ms activities apparent stress and cumulative apparent volume in localized rock mass during the period of a typical large deformation were used to develop a comprehensive analytical method for forecasting the deformation of the surrounding rock mass thus this comprehensive analytical method which incorporates ms monitoring conventional monitoring geological survey and construction is promising for identifying the damage zones and forecasting the macro deformation of the surrounding rock mass in underground powerhouse caverns subjected to excavation

a porosity mapping survey in hecate strait using a seafloor electro magnetic profiling system abstract a newly developed marine electromagnetic e m system was used to create apparent porosity maps of the uppermost 20 m of sediments on the seafloor measurements of electrical conductivity were interpreted to give the porosity of the bottom sediments and underlying units the data were collected continuously in a surveying mode using two receivers at different spacings to improve the resolution of porosity as a function of depth the variations in apparent porosity over the area correlate well with information obtained from cores and acoustic profiles acoustic profiles indicated the presence of biogenic gas in the central region of the survey area the absence of distinct changes in apparent porosity over regions of gas allows us to conclude that the concentration of gas trapped within the queen charlotte muds does not exceed about 4 of the sediment by volume if we assume that the gas displaces fluid in the sediment a buried lower porosity layer was detected its position reflecting changes in the depth to the glaciomarine layer mapped variations in apparent porosity are well correlated with features on the acoustic record this illustrates the system s ability to obtain continuous profiles of apparent porosity over seafloor features the marine e m survey provided rapid areal coverage and combined with the acoustic profiles information on the porosity of deeper units

mechanical anisotropy of columnar jointed basalts an example from the baihetan hydropower station china abstract columnar jointed basalts are characterized by a self organized joint network of discontinuities and pose a difficult challenge for geotechnical engineering design due to their inherent anisotropic nature we explore here the anisotropic characteristics of the columnar basalt formation in the chinese baihetan hydropower station including aspects of the geometrical rock structure deformation and strength anisotropy site investigations reveal that a typical cross section of the columnar basalt blocks is mainly quadrangular and pentagonal with an average edge length of 0 152 m three types of joints with different macro and micro characteristics form the columnar jointed rock mass and are identified by scanning electron microscopy in situ ultrasonic tests further confirm that the columnar basalt prisms exhibit transverse isotropy with the plane of isotropy perpendicular to the column axis as can also be observed in the field strength anisotropy is confirmed by point load and uniaxial compression tests the mechanical and anisotropic characteristics of baihetan s jointed basalt mass can be explained by its multi scale joints pattern by means of goodman s stiffness equation we find that the anisotropic coefficients obtained for its deformability and strength are similar for all testing methods employed including in situ p wave velocity point load tests and uniaxial compression tests this result confirms the strong anisotropic effect in these rock masses and facilitates an issue that must be considered when assigning input parameters for various classification and numerical analyses schemes

assessing in situ microcrack damage using ultrasonic velocity tomography abstract to characterize the damage induced during excavation of a test tunnel in granite ultrasonic wave velocity and amplitude measurements were made in situ around one quadrant of the tunnel sixteen 1 m deep boreholes were drilled into the tunnel wall these boreholes spanned the region from tensile stress induced damage in the sidewall to compressive stress induced damage in the well developed notch measurements were made by pulsing a source transducer at numerous points within a given borehole and on the tunnel surface and then capturing the transmitted ultrasonic waves at transducers located in the adjacent borehole the travel times of the waves between sources and receivers were used to compute the average velocities and to construct two dimensional 2d tomographic images wave velocities and amplitudes in the tensile stress region are low and show significant anisotropy indicating the presence of oriented microcracks even as deep as 1 m from the tunnel wall velocities and amplitudes are higher in the compressive stress region and show lower anisotropy indicating the rock is relatively undamaged away from the tunnel wall the velocity anisotropy indicates that the dominant orientation of microcrack planes is everywhere tangential to the tunnel wall even though the minimum principal stress is tangential and tensile in the sidewall the distribution of microcracks inferred from these results is consistent with the extensive microseismicity detected during and after excavation and suggests that both the stress history and current stress state have impacted the current state of damage around the tunnel

the saint jude landslide of 10 may 2010 quebec canada investigation and characterization of the landslide and its failure mechanism a landslide occurred on 10 may 2010 along the salvail river in the municipality of saint jude quebec debris of the landslide was formed of clay having horst and graben shapes typical of spread

on the theory of sea floor conductivity mapping using transient electromagnetic systems the electrical conductivity of the sea floor is usually much less than that of the seawater above it a theoretical study of the transient step on responses of some common controlled source electromagnetic systems to adjoining conductive half spaces shows that two systems the horizontal in line electric dipole dipole and horizontal coaxial magnetic dipole dipole are capable of accurately measuring the relatively low conductivity of the sea floor in the presence of seawater for these systems the position in time of the initial transient is indicative of the conductivity of the sea floor while at distinctly later times a second characteristic of the transient is a measure of the seawater conductivity the diagnostic separation in time between the two parts of the transient response does not occur for many other systems including several systems commonly used for exploration on land a change in the conductivity of the sea floor produces a minor perturbation in what is essentially a seawater response some transient responses which could be observed with a practical deep towed coaxial magnetic dipole dipole system located near the sea floor are those for the half space the layer over a conductive or resistive basement and the half space with an intermediate resistive zone the system response to two adjoining half spaces representing seawater and sea floor respectively is derived analytically the solution is valid for all time provided the conductivity ratio is greater than about ten or less than about one tenth the analytic theory confirms the validity of numerical evaluations of closed form solutions to these layered earth models a lateral conductor such as a vertical infinite conductive dike outcropping at the sea floor delays the arrival of the initial crustal transient response the delay varies linearly with the conductance of the dike this suggests that time delay could be inverted directly to give a measure of the anomalous integrated conductance of the sea floor both between and in the vicinity of the transmitter and the receiver dipoles

microseismicity monitoring and failure mechanism analysis of rock masses with weak interlayer zone in underground intersecting chambers a case study from the baihetan hydropower station china abstract a weak interlayer zone wiz is a rock mass system with poor mechanical properties large scale random distribution water softening causing an adverse effect on the safety of the construction and project progress to investigate the fracture process and the mechanism of rock masses with wizs in the intersecting chambers during the excavation process in situ microseismic ms monitoring was carried out in the underground powerhouse on the right bank of the baihetan hydropower station china during the monitoring the spatio temporal evolution process of the microseismicity of the rock masses around the intersecting chambers was obtained during the excavation unloading of multiple working faces the spatial evolution of ms events illustrates the dynamic progressive characteristics of ms activities as they propagate and accumulate along the wiz and finally form a cluster zone the fracture mechanism of moment tensor inversion reveals the distribution and evolution of ms events with respect to different fracture types tensile fracture events are distributed near the free surface while non tensile fracture events are far from the free surface finally the study proposes support measures restraining fracture development in surrounding rock masses with wiz the effectiveness of reinforced support measures is verified by ms events and the deformation of surrounding rocks the results of the study are particularly valuable for the stability analysis excavation and support optimization of similar engineering studies

hydrogeology of a complex champlain sea deposit quebec canada implications for slope stability the thick sequences of marine clayey deposits which blanket the st lawrence lowlands in south eastern canada are highly susceptible to landslides with 89 of the population of the province of que