impact of poroelastic response of sandstones on geothermal power production during geothermal power production using a borehole doublet consisting of a production and injection well the reservoir conditions such as permeability k porosity and skempton coefficient b at the geothermal research site gross schoenebeck germany will change besides a temperature decrease at the injection well and a change of the chemical equilibrium also the pore pressure pp will vary in a range of approximately 44 mpa 10 mpa in our reservoir at 3850 to 4258 m depth this leads to a poroelastic response of the reservoir rocks depending on effective pressure p eff difference between mean stress and pore pressure resulting in a change in permeability k porosity and the poroelastic parameter skempton coefficient b hence we investigated the effective pressure dependency of flechtinger sandstone an outcropping equivalent of the reservoir rock via laboratory experiments the permeability decreased by 21 at an effective pressure range from 3 to 30 mpa the porosity decreased by 11 p eff 6 to 65 mpa and the skempton coefficient decreased by 24 p eff 4 to 25 mpa we will show which mechanisms lead to the change of the mentioned hydraulic and poroelastic parameters and the influence of these changes on the productivity of the reservoir the most significant changes occur at low effective pressures until 15 to 20 mpa for our in situ reservoir conditions p eff 43 mpa a change of 10 mpa effective pressure will result in a change in matrix permeability of less than 4 and in matrix porosity of less than 2 besides natural fracture systems fault zones and induced hydraulic fractures the rock matrix its only one part of geothermal systems all components can be influenced by pressure temperature and chemical reactions therefore the determined small poroelastic response of rock matrix does not significantly influence the sustainability of the geothermal reservoir

pressure dependent production efficiency of an enhanced geothermal system egs stimulation results and implications for hydraulic fracture treatments a series of stimulation experiments were carried out at the geothermal research well in gros schonebeck egrsk 3 90 located in the northeastern part of germany the intended purpose of these experiments was to develop concepts for a productivity increase of the geothermal well to create an enhanced geothermal system egs two different kinds of stimulation types were performed hydraulic gel proppant stimulations were conducted in sandstone sections with high initial permeability then a different fracturing concept was applied injecting high amounts of water this waterfrac stimulation was realized in the entire open section including sandstones and volcanic rocks evidence of the creation and properties of a very long vertical fracture was retrieved from pressure response analyses demonstrating a bilinear flow regime the production efficiency of the produced artificial fractures shows a strong dependence on reservoir pressure at increased reservoir pressure the artificial fractures of all stimulated intervals are highly conductive and subsequently become less conductive during pressure decline hence the range of a suitable reservoir pressure is constrained by this fracture efficiency and limits the usage of this well as an injection well for geothermal power production

site investigations to evaluate flow liquefaction slides at sand heads fraser river delta l ecoulement par liquefaction spontanee est un processus recurrent dans la progradation du delta du fleuve fraser une portion du delta a ete etudiee au moyen d essais de penetration au cone sismique et de resistivite et au moyen de l analyse spectrale de la methode des ondes de surface et de l echantiollonage de sol et de vapeur dans un effort pour determiner la stratigraphie du site l etat in situ et le degre de saturation afin explorer l enigme de l ecoulement par liquefaction spontanee un ensemble de capteur de pression interstitielle et d inclinaison a ete installe comme partie de l etude pour mesurer les effets de la vidange resultant du reflux de la maree les resultats ont indique que le lit de la mer a faible profondeur etait partiellement sature contenant un volume significatif de gaz methane qui affectait la reponse dynamique de la pression interstitielle durant le jusant une reduction de la contrainte effective atteignant 16 5 kpa a ete mesuree de meme qu un delai de 50 min entre le reflux de la maree et la reaction de la pression interstitielle ceci suggere que les effets de tampon sont un facteur significatif dans le declenchement de la liquefaction spontanee des sables l ches non viellis la ou ils reposent sur des pentes sous marines les resultats des essais in situ montrent que les sables nouvellement deposes du fleuve fraser ont une forte susceptibilite a l ecoulement par liquefaction

tectonic constraints on a deep seated rock slide in weathered crystalline rocks abstract deep seated rock slides dsrss recognised as one of the most important mass wasting processes worldwide involve large areas and cause several consequences in terms of environmental and economic damage they result from a complex of controlling features and processes dsrss are common in calabria southern italy where the complex geo structural setting plays a key role in controlling the geometry of the failure surface and its development this paper describes an integrated multi disciplinary approach to investigate a dsrs in palaeozoic high grade metamorphic rocks of the sila massif it focuses on the definition of the internal structure and the predisposing factors of the serra di buda landslide near the town of acri which is a paradigm for numerous landslides in this area an integrated interdisciplinary study based on geological structural and geomorphological investigations including field observations of weathering grade of rocks minero petrographic characterisations geotechnical investigations and in particular fifteen years of displacement monitoring is presented stereoscopic analysis of aerial photographs and field observations indicate that the serra di buda landslide consists of two distinct compounded bodies i an older and dormant body 7 ha and ii a more recent and active body 13 ha that overlies the previous one the active landslide shows movement linked to a deep seated translational rock slide block slide the velocity scale ranges from slow 1 6 m year during paroxysmal stages to extremely slow

investigation of multiple reflections and wave conversion by means of a vertical wave test vertical seismic profiling in southern mississippi a vertical wave test employing the vertical seismic profiling vsp technique in southern mississippi confirmed suspicions that apparent multiple reflections might include converted waves as well as multiply reflected compressional waves both compressional p and shear s waves generated near the source were observed to travel to great depths and p to s conversions were apparent in deep zones as well as shallow p wave reflections were observed in agreement with predictions from synthetic records based on the sonic log up traveling p waves were reflected a short distance below the surface at the base of the low velocity layer and were followed as down traveling p waves to 200 ft depth by means of a vertical spread below 2000 ft and following the first p wave train the predominate energy appeared to be down traveling p waves which could not be traced back to the reflection of up traveling p waves the continuity of wavelets indicated instead that the strong down traveling s waves generated near th

large scale seismically induced mass movements in a former glacial lake basin lake temiscouata northeastern appalachians eastern canada abstract disturbed lacustrine deposits of eastern canada have been associated with past seismic events in the intraplate western quebec seismic zone wqz and the charlevoix kamouraska seismic zone cksz with five major earthquakes that occurred during historical times and hundreds of minor earthquakes the cksz is the most active seismic zone in eastern canada here we present new high resolution multibeam bathymetric subbottom profiler and sediment core data collected in lake temiscouata southeastern quebec the largest lake located within the influence of the cksz the occurrence of mass movements in the highly cohesive glaciolacustrine deposits of the lake produced a peculiar lacustrine landscape consisting of steep slide scars and residual mounds and very narrow residual crests our data indicate that postglacial times were marked by recurrent seismically induced mass movement events that cannot be individually identified in the sedimentary record due to the highly disturbed stratigraphy of the lake and to the absence of significant postglacial background sediments between events the most recent recorded mass movement is a distinct debris flow sediment layer on the lake floor that was deposited at 1300 cal bp very shortly after a distinct large scale mass movement event observed across the entire lake basin the presence of silt layers in gyttja overlying these disturbed units suggests that the region was affected by other seismic events following this event although no mmds could be directly related to these layers

submarine canyons and channels in the lower st lawrence estuary eastern canada morphology classification and recent sediment dynamics abstract series of submarine canyons and channels observed in the lower st lawrence estuary lsle provide an opportunity to analyze in great detail the morphology spatial distribution and modern activity of such systems in a relatively shallow 300 m semi enclosed basin based on their geomorphology and physical settings the canyons and channels were classified into four categories according to their feeding sources ancient or recent glacially fed river fed longshore drift fed and sediment starved systems their activity was interpreted based on geomorphological characteristics such as the presence of bedforms related to gravity flows backscatter intensity axial incision and the presence of rapidly deposited layers in surficial sediments river fed deltas were interpreted as inactive mainly because suspended sediment concentrations at river mouths are low preventing the generation of hyperpycnal currents or delta lip failures related to high sediment supply longshore drift fed canyons present where the coastal shelf narrows were found to be episodically active probably due to earthquakes or extreme storm events unlike other longshore drift fed canyons observed elsewhere in the world they are active infrequently because of the modern low rates of sediment supply to their heads the most active canyons are the sediment starved type and were observed near pointe des monts their activity is probably due to slope failures and to the presence of strong hydrodynamic processes therefore sediment supply is not the main mechanism responsible for modern canyon and channel activity in the lsle however sediment supply has been an important factor during the formation of the submarine channels and canyons their quasi exclusive occurrence on the quebec north shore is attributed to its larger watershed and important sedimentary delivery during deglaciation the quebec north shore watershed is 20 times greater than the quebec south shore watershed which favored the transport of greater volumes of sediment during the early holocene moreover the slope proximity to the shore led to the formation of longshore drift fed systems on the north shore when sediment supplied to rivers were transferred on a narrow shelf

elastic finite difference modeling of volcanic hosted massive sulfide deposits a case study from half mile lake new brunswick canada abstractwe present elastic finite difference modeling results over a geologically realistic 2d representation of the half mile lake volcanic hosted massive sulfide deposit new brunswick canada the model is constrained by geologic information from surface mapping and boreholes whereas petrophysical properties are provided by wireline logging data acquired in two boreholes intersecting different parts of the deposit we analyzed the p p p s s p and s s responses of the lower and deep mineralized zones and assessed some compositional effects by substituting massive sulfides with gabbro properties in the model finite difference modeling results predict complex scattering signature associated with the lower and deep sulfide zones both zones scattered back p p p s s p and s s waves generally having strongest amplitudes in the stratigraphy down dip direction the p s s p and s s scattered waves if properly recorded on multicomponent data represent useful signal that could help the targeting of de

late quaternary morpho sedimentology and submarine mass movements of the betsiamites area lower st lawrence estuary quebec canada abstract a complex submarine geomorphology was revealed from multibeam bathymetry and seismic reflection surveys conducted between 2001 and 2007 in the lower st lawrence estuary offshore betsiamites river quebec canada in this paper we describe the submarine morpho sedimentology of an area of 500 km 2 with focus on the consequences of four mass movement events the general morpho sedimentology of the area and submarine features resulting from mass movement processes channel erosion and gas seepage are described a spatio temporal sequence for the occurrence of the mass movements and a chronology for the failures are established we propose dates for four of the observed mass movement deposits a buried paraglacial debris flow deposit is dated as older than 9280 cal bp whereas a major landslide scar characterized by two topographic depressions on the shelf and a sediment lobe in the laurentian channel were dated around 7250 cal bp morphological observations and sediment core analyses allow us to identify a least two different recent i e less than 500 yr old debris flow accumulations associated with two recent earthquakes 1 the ad 1663 m 7 and 2 ad 1860 m 6 or ad 1870 m 6 5 earthquakes in addition to a complex geomorphology influenced by mass movements we have identified several regions on the shelf and on the laurentian channel with evidence of pockmarks which could potentially influence submarine slope stability in the estuary

forced regressions and lowstand deltas holocene canadian examples abstract some canadian holocene deltas that formed during and after relative sea level falls of over 100 m are modern examples of forced regressions and lowstand deltas the principal controls on deltaic morphology and stratigraphy are rate of sea level change sediment supply timing type basin physiography and sediment dispersal processes in the receiving basin our observations indicate important alongstrike variability in deposition and erosion that affect facies architecture and stratal geometry during rapid relative sea level fall fluvial channels incise rapidly and do not migrate lateral channel migration which would produce a widespread fluvial unconformity begins once relative sea level fall has slowed and continues through the early part of relative sea level rise parts of he emerging shoreline cut off from the fluvial sediment supply become sites of shoreface incision into prodelta deposits regressive marine erosion and wave cut terraces are developed where sandy sediment is then supplied to the shoreface by rivers or updrift sources sharp based littoral sandbodies directly overlie the shoreface erosion surface other parts of the deltas below wave base that become abandoned through lobe switching can also be eroded by tidal currents deltas that have prograded into deep water show evidence of submarine slope instability such as submarine channel development base of slope turbidites and thick and thin skinned failures that disrupt clinoforms isopach trends reflect the existence of underlying structure with holocene sediments locally either thi ning or pinching over bedrock highs

liquefaction and flow failure during earthquakes two aspects of seismically induced liquefaction are discussed which are of vital engineering significance the triggering condition and the consequences of liquefaction the triggering condition is examined with respect to liquefaction analysis note being taken of the onset condition which is governed by cyclic strength consequences of liquefaction are discussed with respect to post seismic stability analysis in which the residual strength plays a major role procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced and the applicability of this method for estimating associated ground settlements is discussed the evaluation of residual strength requires a better understanding of undrained sand behaviour results of extensive laboratory rests on japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better the results of laboratory tests on silty sands are examined in the same way ah the results are

results and implications of seismic performance studies for duncan dam screening level studies indicated large zones of the foundation soil beneath duncan dam could be triggered to liquefy under the design earthquake resulting in flow slides that could lead to breaching of the dam in these studies estimates of the key soil parameters were obtained from an indirect procedure using penetration tests and seed s chart which is based on field experience during past earthquakes together with empirical correction factors for high confining stress and static bias this is state of the practice procedure in north america and is used because of the difficulty in retrieving and testing undisturbed samples of sand with the high confining stresses present at the site the indirect approach gave very low values of the key liquefaction properties of the soil and the use of such low values in analyses indicated that major and costly remedial measures were required thus a more direct approach was undertaken this involved both direct and semidirect determination of the key soil parame

undrained shear strength of clean sands to trigger flow liquefaction this paper attempts to evaluate the undrained shear strength of sand during flow failures based on both laboratory testing and field observations in the laboratory the minimum shear resistance d

sub decadal submarine landslides are important drivers of deltaic sediment flux insights from the mississippi river delta front submarine mass failures triggered by energetic forcing events such as hurricanes and earthquakes are relatively well studied due to the potential for infrastructure damage and tsunami generation such failures are common on heavily sedimented margins where underconsolidated deposits are preconditioned to fail however studies of seafloor sediment movement between large events remain scarce using repeat bathymetric surveys of the mississippi river delta front mrdf we document substantial seafloor movement in absence of major hurricanes about 1 m yr of deepening was observed within preexisting failures with downslope sediment transport on the order of 10 5 m 3 yr outside failure features seafloor depths remained stable or showed minor 20 cm yr accretion mrdf volumetric sediment flux during hurricane driven mass failures is an order of magnitude greater than the annual flux during a quiescent interval when normalized by time however sediment flux during the quiescent interval 5 5 10 5 m 3 yr was half that of hurricane driven mass failures 1 1 10 6 m 3 yr these observations corroborate our wave modeling results which infer that even waves of 1 yr recurrence interval can generate differential seafloor pressures sufficient to trigger submarine landslides this does not exclude the possibility of river floods also being agents of failure these findings indicate that sub decadal submarine landslides are important to mrdf dynamics comparable to the role of major hurricanes and observation during seemingly quiescent periods is necessary to holistically assess sediment flux the periodicity and prevalence of moderate scale mass transport documented here corroborates similar recent studies offshore other deltas globally indicating that highstand mass and time budgets of shelf to deep sea sediment flux in addition to organic carbon and bioreactive particles may need to be revised

evaluation of the in situ state of fraser river sand les glissements de type coulee par liquefaction sont des phenomenes qui arrivent souvent dans le delta de la riviere fraser du cote de sand heads ces ruptures n ont pas trouve d explication et leurs causes restent du domaine de la speculation l etude d un tel glissement ayant eu lieu en 1985 dans la riviere fraser a proximite de sand heads a ete entreprise en utilisant les concepts d etats stationnaires pour qu un glissement par coulee impliquant la liquefaction de depots de sables puisse prendre place le sable doit presenter un ramollissement lors du cisaillement non draine et les contraintes de cisaillement en place doivent etre superieures a la resistance non drainee mobilisable on a effectue des essais de laboratoire sur des echantillons reconstitues de sable de la riviere fraser de facon a etablir les parametres d etat stationnaire les specimens de sol ont ete prepares par compaction humide et pluviation dans l eau des mesures de vitesse de propagation des ondes de cisaillement ont ete utilisees pour evaluer l etat en place des depots de sable recents et non cimentes on a trouve que l etat en place des depots recents au voisinage de sand heads se situait du cote l che de l etat stationnaire ce qui correspond aux instabilites observees sur le site

evaluation of static liquefaction potential of silty sand slopes the mechanism of instability in granular soils is explained and its requirement as a forerunner to the liquefaction of level or sloping ground is described case histories support the observation t

a delta plain sheet sand in the fraser river delta british columbia canada abstract borehole data in the fraser river delta demonstrate that a nearly continuous sand unit generally 8 to 20 m thick underlies the surficial silts and sands of most of the delta plain the sand unit consists of one or more sharp based fining upward sequences and is interpreted to be a complex of distributary channel deposits distributary channel migration and the resulting accumulation of channel sands has occurred primarily in a tidal flat environment due to the interaction of tidal and fluvial processes and the high proportion of sand in the sediment load this sand unit thus provides a model for sand rich river and tide dominated delta plains jetties now maintain the position of the main channel of the fraser river where it crosses the tidal flats and prevent channel migration and further storage of sand in the lower delta plain as a result more of the available sand is being transported directly to the river mouth where failures transport the sand downslope consequently these structures contribute to instability at the river mouth

control of hazard due to seismicity induced by a hot fractured rock geothermal project in 2003 hydraulic stimulations were carried out in a geothermal field in eastern el salvador central america as part of a project to explore the feasibility of commercial hot fractured rock energy generation a key requisite for this environmentally friendly energy source is that the fracturing of the hot rocks at depths of 1 2 km must not produce levels of ground shaking at the surface that would present a serious disturbance or threat to the local population thresholds of tolerable ground motion were inferred from guidelines and regulations on tolerable levels of vibration and from correlations between instrumental strong motion parameters and intensity considering the vulnerability of the exposed housing stock the thresholds were defined in terms of peak ground velocity pgv and incorporated into a traffic light system that also took account of the frequency of occurrence of the induced earthquakes the system was implemented through a dedicated seismograph array and locally derived predictive equations for pgv the traffic light was used as a decision making tool regarding the duration and intensity of pumping levels during the hydraulic stimulations the system was supplemented by a small number of accelerographs and re calibrated using records obtained during the rock fracturing

permeability creation and damage due to massive fluid injections into granite at 3 5 km at soultz 2 critical stress and fracture strength 1 the stress acting on fractures in a 3 5 km deep borehole in granite is examined to place constraints on fracture strength and to evaluate whether permeable fractures tended to be critically stressed two data sets consisting of some 500 fractures are analyzed the first considers the permeable impermeable fracture populations in their natural state the second considers the populations after the hole had been subject to a prolonged 9 mpa overpressure in two major injections which increased the number of permeable fractures from 18 to more than 95 for both data sets it is found that permeable fractures are critically stressed inasmuch as they support levels of shear stress that would be verging on failure if their strength were governed by a coulomb friction law with a coefficient of 0 6 1 0 however the vast majority of impermeable fractures are also critically stressed implying that critical stressing is a necessary but not a sufficient condition for permeability to develop most permeable fractures showed evidence of shear failure after the injections and tended to occur in hydrothermally altered cataclastic shear zones suggesting that they may have been relatively weak because of the presence of illite to prevent failure of the impermeable fractures during the injections requires a cohesion of at least 6 5 mpa to augment a maximum allowable friction coefficient of 1 0 these are probably early mode 1 fractures that are sealed primarily with calcite the strength of the shear zones appears to be significantly greater than the illite rich fractures from which they are composed this imposes constraints on their internal architecture

hydraulic fracturing in a sedimentary geothermal reservoir results and implications field experiments in a geothermal research well were conducted to enhance the inflow performance of a clastic sedimentary reservoir section due to depths exceeding 4050 m bottom hole temperatures exceeding 140 c and open hole section dual zone technically demanding and somewhat unprecedented conditions had to be managed the fracturing operations were successful fractures were created in two isolated borehole intervals and the inflow behaviour of the reservoir was decisively enhanced the effective pressures applied for fracture initiation and propagation were only slightly above in situ pore pressures nevertheless the stimulation ratio predicted by fracture performance modelling could not be achieved multiple reasons could be identified that account for the mismatch an insufficient fracture tie back as well as chemical and mechanical processes during closure led to reduced fracture conductivities and therefore diminished productivity the insights gained are the basis for further fracture design concepts at the given and geologic comparable sites

the foreslope hills large scale fine grained sediment waves in the strait of georgia british columbia abstract the foreslope hills are a set of 20 m high 5 km long ridges at 230 350 m water depth in the south central strait of georgia occupying a 60 km 2 area at the base of the fraser river delta foreslope they are composed of clay silt and fine sand previous authors have interpreted them as 1 a single mass slide deposit 2 mud diapirs 3 in situ rotational failures and 4 creep deformation features but collaborative evidence for these interpretations is lacking seafloor surface morphological renders derived from recent multibeam sonar bathymetry data show linear evenly spaced symmetrical ridges with ridge bifurcation resembling wave ripples but on a much larger scale detailed multichannel and single channel seismic reflection data show sinusoidal internal reflections suggesting upslope migration the ridges occur within the uppermost portion of the holocene section in a very high sedimentation rate environment consequently they are probably less than 3000 years old moored current meter records for the region show reversing currents largely oriented normal to the ridge crests averaging 10 cm s with a maximum of 50 cm s this evidence combined with increasing documentation of large scale sedimentary bedforms in slope and rise environments suggests that the foreslope hills should be re interpreted as sediment waves upslope migration is typical of many large scale fine grained sediment waves the preferred physical interpretation for the creation and maintenance of the foreslope hills as sediment waves is the lee wave model requiring a phase shift in density stratified flow as it passes over the wavy topography maximum measured bottom currents are easily strong enough to entrain silt and clay delivered to the site by turbidity currents or by sediment plume fallout from fraser river outflow either strong flood tides or severe biannual density intrusions due to their intense stratification may be susceptible to lee wave formation and the creation of sediment waves leading to the observed pattern of upslope migration

late glacial stratigraphy and history of the gulf of st lawrence reply the three dimensional configuration of the quaternary sediments in the gulf of st lawrence is described based on analysis of 8000 km of high resolution seismic reflection data complemented by anal

morphodynamics in sediment starved inner shelf submarine canyons lower st lawrence estuary eastern canada abstract the contemporaneous activity and sedimentary processes in a series of inner shelf submarine canyons located in the lower st lawrence estuary were examined using high resolution multibeam bathymetry and backscatter data the presence of crescent shaped bedforms csbs displaced upslope at the bottom of the canyons between 2007 and 2012 indicates that they are currently active through the remobilization of sediment by gravity flows however the shelf and shores of the region are characterized by the absence of sediment our results indicate that gravity flows currently eroding the canyon floors do not transport new material downslope coming from the shelf but rather remobilize in situ deglacial sediments within the canyon thalweg we suggest that slope failures and internal tides waves are responsible for sediment remobilization in these canyons although their role in the upslope migrating csbs is unclear this paper provides evidence that sediment supply is not a prerequisite for the modern activity of inner shelf submarine canyons when processes such as slope failures and internal tides waves are frequent enough to remobilize in situ sediments

large scale subaerial and submarine holocene and recent mass movements in the betsiamites area quebec canada abstract at least three major landslide events formed the submarine and subaerial betsiamites quebec canada landslide complex and mobilized an estimated total volume of 2000 million m3 2 km3 linkage between offshore and onshore geophysical investigations with borehole data and in situ testing allows reconstruction of the architecture of the betsiamites river delta area and leads to the identification of the main failure events the submarine scar of the betsiamites landslide complex may have resulted from a first failure dated at about 9250 cal bp which mobilized a minimum volume of 200 million m3 a second landslide dated at 7250 cal bp mobilized a volume of 1300 million m3 over an area of 54 km2 the betsiamites submarine landslide event dated at 7250 cal bp left the largest scar yet identified on the st lawrence estuary seafloor furthermore this paper demonstrates that the subaerial scar of the betsiamites landslide complex is a result of the colombier landslide event which was initiated by the 1663 earthquake and involved four successive failure phases one submarine and three subaerial the february 5th 1663 earthquake triggered a submarine landslide event which reached the shoreline and led in a short period of time successively to two subaerial flowslides in sensitive clayey material and a subaerial lateral spread the four failure phases mobilized a possible total volume of about 530 million m3 over an area of 20 km2 the colombier landslide event is among the largest documented historic landslides in canada the presence of submarine scars left by the early holocene events acted as predisposition factors for the development of the failure while the earthquake of 1663 was the main triggering factor of the first submarine failure

evaluation of preconsolidation pressure and the overconsolidation ratio from piezocone tests of clay deposits in quebec the preconsolidation pressure and overconsolidation ratio profiles are the most important factors related to the mechanical behaviour of clay deposits they are interpreted on the basis of a limited number of laboratory tests but the near continuous information provided by the piezocone can allow local data to be extrapolated to an entire site numerous methods have been proposed for relating piezocone data to preconsolidation pressure and the overconsolidation ratio but their validity is still uncertain in this paper nine methods are compared on the basis of data collected on 31 sensitive clay sites in quebec whose preconsolidation pressure profiles are well known each method is briefly presented and the most promising are identified the simplest method which directly relates preconsolidation pressure to net tip resistance also appears to be the most effective key words clay preconsolidation pressure overconsolidation ratio piezocone correlations

postglacial deltaic sediments southern fraser river delta british columbia the fraser river delta the largest delta on the west coast of canada has been built into the strait of georgia during the holocene drill hole and seismic reflection records reveal a succession of sedimentary units deposited during early holocene progradation of the delta these overlie an irregular surface developed on pleistocene drift mud and silt similar to sediments presently accumulating off the mouth of fraser river in the southern strait of georgia are conformably overlain by a thick unit of sandy foreset beds dipping gently to the south southwest into boundary bay and deposited in a foreslope environment the foreset unit is sharply overlain by a much thinner topset sequence comprising silt and sand deposited in intertidal fluvial channel and overbank environments and peat deposited in swamps and bogs fifteen accelerator mass spectrometry radiocarbon dates on shell and wood indicate that most of the deltaic sediments south of the main channel of fraser river were deposited between ca 7

geomorphology and potential slope instability on the fraser river delta foreslope vancouver british columbia le delta du fleuve fraser est localise dans une des regions ayant les plus hauts risques sismiques au canada et comprend pour une bonne part des sables fluviaux meubles tres connus comme possedant un potentiel eleve de liquefaction sismique des etudes recentes de la rive ouest du delta du fraser indiquent que la liquefaction cyclique durant un fort tremblement de terre est possible engendrant potentiellement des deformations incluant des extensions laterales un ramollissement cyclique et possiblement une coulee l on presente une evaluation preliminaire de la stabilite statique des pentes apres secousse dans laquelle les analyses ont ete limitees aux valeurs estimees des resistances au cisaillement ultimes ou a l etat d equilibre deduites de correlations avec les donnnees du terrain et aux contraintes de cisaillement calculees en partant de la bathymetrie du lit de mer existant l on a trouve que le coefficient postliquefaction de securite contre le glissement etait inferieur a l unite pour la pente de la terrasse superieure roberts en supposant une limite inferieure de resistance au cisaillement ultime equivalente a 0 06 p 0 les donnees pour evaluer la validite de cette hypothese sont insuffisantes cependant il y a abondance de depots de rupture le long de la base de la pente du delta

large scale mass wasting events on the fraser river delta front near sand heads british columbia although the fraser river delta front supports coastal structures including ports a lighthouse jetties submarine power cables and sewage pipelines the stability of the delta front is little understood five large scale mass wasting events at the mouth of the main channel near sand heads have been detected by comparing successive bathymetric surveys conducted by public works canada between 1970 and 1986 these events can involve the downslope movement of more than 1 106 m3 of silty sand and the landward retrogression of the delta front crest of up to 350 m or more morphologic and sedimentologic evidence suggests that these events are slope failures which result from the liquefaction of silty sand rapid deposition at the river mouth is likely a prerequisite for failure although interstitial gas tidal currents waves and earthquakes also may contribute to failure these results have important implications for the foundation stability of the sand heads lighthouse and future coastal structures in t

seabed instability due to flow liquefaction in the fraser river delta les ruptures par liquefaction de depots de sables l ches peuvent representer une menace importante pour les structures cotieres on a evalue a partir des concepts d etats stationnaires les contributions possibles de divers mecanismes de declenchement lors d une rupture par liquefaction qui a eu lieu en 1985 a l embouchure du chenal principal de la riviere fraser parmi les mecanismes qui ont pu declencher le glissement par liquefaction en 1985 on a etudie la sedimentation les vagues de surface et les marees basses l analyse montre qu une sedimentation rapide genere des contraintes de cisaillement dans la pente mais ne pourrait pas faire demarrer des ruptures par liquefaction lorsqu on evalue l effet des vagues de surface et leur capacite a causer des glissements de type coulee profonde on trouve qu il ne s accumule pas de pressions interstitielles significatives dues aux vagues de surface pouvant exister dans la region les marees basses ne peuvent pas non plus declencher de rupture dans des sables submerges et completement satures l apparition de gaz provoque cependant la desaturation des sediments ce qui peut induire des pressions interstitielles residuelles pendant les marees basses on emet donc l hypothese que c est la combinaison de sediments l ches de faibles quantites de gaz et de marees basses qui favorise les ruptures par coulees liquefiees dans le delta ces ruptures conduisent a des glissements regressifs

liquefaction flow of submarine slopes under partially undrained conditions an effective stress approach the stability of submarine slopes is commonly assessed based on undrained soil response liquefaction flow may occur when pore pressure rise in soil elements under constant shear stress causes a reduction in effective stresses recent experimental studies have shown that a small net flow of water into an element results in additional pore pressure generation and further reduces its strength as a result soil elements can liquefy due to expansive volumetric strains that cannot be predicted by undrained analysis submarine deposits of the fraser river delta are known to contain high concentrations of methane gas tidal variations can cause unequal pore pressure generation with depth and time in these soils such changes reduce the effective stresses during low tides and may induce liquefaction flow of slopes due to partial drainage conditions an effective stress approach based on an elastic plastic stress strain relationship is presented to model liquefaction flow of sand a fully coupled analysis is carr

an in hole shotgun source for engineering seismic surveys we have conducted several source comparisons involving 12 gauge and 8 gauge buffalo guns a 7 3 kg sledgehammer and a 75 kg weight drop the results are strongly site dependent we found that when the near surface consisted of fine grained water saturated sediments the 12 gauge buffalo gun produced up to two orders of magnitude more energy than the conventional hammer across a broad frequency range under such conditions the gun produced the greatest improvement in energy between 200 and 400 hz where it yielded up to ten times more energy than the 75 kg weight drop this indicates that the buffalo gun may be particularly useful as a shallow reflection seismic source however at sites where the near surface materials were coarse grained and the water table was well below the ground surface the advantages of using an in hole shotgun source as opposed to a hammer or weight drop were minimal nevertheless in many areas we believe that the buffalo gun is an excellent source for engineering seismic surv

the present state of seismic data acquisition one view seismic data acquisition in the mid 1980s is briefly reviewed in terms of hardware the trend has been toward an increased number of data channels in both land and marine applications this has led to the development of digital telemetry systems positioning systems particularly for marine work have made use of artificial satellites the perceived need for s wave information has led to development of s wave sources such as the horizontal vibrator s waves in a few cases have been used to validate hydrocarbon indicators on seismic records there has been a distinct trend toward three dimensional 3 d seismic recording both on land and at sea and for both exploration and production applications

an assessment of the megathrust earthquake potential of the cascadia subduction zone the active tectonic setting of the southwest coast of canada and the pacific northwest coast of the united states is dominated by the cascadia subduction zone the zone can be divided into four segments where oceanic lithosphere is converging independently with the north american plate the winona and the explorer segments in the north the larger juan de fuca segment that extends into both canada and the united states and the gorda segment in the south the oceanic lithosphere entering the cascadia subduction zone in all segments is extremely young less than 10 ma of the other six zones around the pacific where young 20 ma lithosphere is being subducted five have had major thrust earthquakes megathrust events on the subduction interface in historic time an estimation based on potential area of rupture gives maximum possible earthquake magnitudes along the cascadia subducting margin of 8 2 for the winona segment 8 5 for the explorer segment 9 1 for the juan de fuca segment and 8 3 for the so

infaunal holothurian distributions and their traces in the fraser river delta front and prodelta british columbia canada abstract holothurians sea cucumbers constitute one of the largest and most abundant infaunal groups inhabiting the fraser river delta front 0 to 150 m water depth and prodelta greater than 150 m water depth the spatial distribution and density of animals reveal their preferred substrate grain sizes and their tolerance or sensitivity to various stress factors including salinity fluctuations available food resources sedimentation rate and pollution in the delta front below 25 m water depth below storm wave base holothurians are asymmetrically distributed with respect to the main distributary channel population densities primarily reflect asymmetry in grain size distributions across the delta front holothurians are absent or occur in low density in the sand dominated southern delta front sdf whereas the mud dominated northern delta front ndf is more heavily colonized sedimentation rate and nutrient content are equally important in holothurian distribution population densities of certain holothurians show significant increase where there are moderate sedimentation rates 2 4 cm yr 1 and river derived nutrient supply several subsurface traces and their surface expressions are attributed to holothurians subsurface traces include diminutive and robust artichnus thalassinoides and u shaped bio deformation structures on the sediment surface bio topographic structures such as mounds and funnel shaped depressions are produced by the activity of sea cucumbers of the holothurian generated traces only artichnus can conclusively be attributed to sea cucumbers based on the distributions of the trace makers of artichnus we hypothesize that in the rock record this trace fossil can be used as evidence of stable euhaline salinity conditions and sediment deposition and colonization below storm wave base artichnus occurs mainly in mud dominated 55 mud substrates

chronologie th u des concretions calcaires des varves du lac glaciaire de deschaillons wisconsinien inferieur late pleistocene lake deschaillons varves from the central st lawrence lowlands represent a lithostratigraphic unit whose upper limit is defined by the overlying gentilly till which was laid down

proprietes caracteristiques des argiles de l est du canada the compilation of numerous geotechnical data has allowed the definition of the main physical mechanical and hydraulic properties of marine and lacustrine clays of eastern canada as well as the establishment of correlations between some of these properties the possible uses of these correlations are described this study shows that the clays of eastern canada exhibit a behaviour similar to that of other clays but that they are characterized by a higher degree of structuration keywords physical properties mechanical properties hydraulic properties clays canada correlations journal translation

a massive sensitive clay landslide quyon valley southwestern quebec canada and evidence for a paleoearthquake triggering mechanism abstract a landslide debris field covering 31 km2 the presence of large sediment blocks up to hundreds of meters long and the exposure of deposits of a single landslide along the incised course of the quyon river are evidence of a massive failure of sensitive champlain sea glaciomarine sediments along the lower quyon valley southwestern quebec canada seventeen radiocarbon ages indicate that the failure occurred between 980 and 1060 cal yr bp twenty four additional radiocarbon ages reveal that nine landslides within a 65 km belt in the quyon ottawa area also occurred at approximately this time in combination the contemporaneous occurrence of ten landslides between 980 and 1060 cal yr bp the setting or morphology of five of the other failures and the close proximity of two of the failures to the quyon valley landslide provide circumstantial evidence of a paleoearthquake triggering mechanism the paleoearthquake is estimated to be mw 6 1 or larger with the epicenter within the west quebec seismic zone a common earthquake triggering mechanism for the three largest landslides in eastern canada suggests a close link between massive failures of sensitive glaciomarine sediments and the regional seismicity

effects of mass wasting on the stratigraphic architecture of a fjord valley fill correlation of onshore shear wave seismic and marine seismic data at trondheim norway abstract a combined record of onshore high resolution shear wave seismic and marine p wave seismic data shows the near shore stratigraphic organisation of a fjord valley fill at trondheim central norway the overall stratigraphy shows a typical fjord valley fill of up to 160 m in thickness that is composed of glaciomarine and fjord marine sediments overlain by deltaic deposits which in the onshore section are draped by an anthropogenic fill an interval characterised by low shear wave velocities below the onshore anthropogenic fills is shown by sampled drillings to comprise part clay and part organic deposits the seismic record reveals evidence of recurrent mass wasting events that include landslide debris turbidite deposits and channel features a chronological framework for the stratigraphy is provided by existing radiocarbon dates for local deglaciation and mass wasting events the combined onshore offshore datasets document the lateglacial to holocene development of an emerging fjord and delta system affected by major mass wasting events the architectural development of the younger part of the stratigraphy is interpreted as particularly affected by two known mass wasting events each involving several million m 3 of debris a thick layer of debris from a 3500 cal yr event probably resulted in a blockage of the subaqueous channels diversion of turbidity currents and deposition of lateral accretion packages whereby local fjord sedimentation temporarily increased a 2200 cal yr event resulted in a sudden reorganisation of the distributary system whereby distal delta sedimentation abruptly shifted north to northeastwards to an area temporarily subjected to marine erosion during fall of relative sea level the study adds to the understanding of landslides and low stiffness zones in the area of importance for near shore geohazard assessment the study also provides insight into the stratigraphic variability of fjord valley fills and highlights the interplay between fjord marine sedimentation marine abrasion delta progradation and mass wasting during late stages of fjord filling

a high resolution holocene paleomagnetic secular variation and relative paleointensity stack from eastern canada abstract a high resolution holocene paleomagnetic secular variation psv and relative paleointensity rpi stack was constructed using u channel paleomagnetic data from six radiocarbon constrained marine sedimentary sequences raised along the main axis of the laurentian channel eastern canada from its head to its mouth centennial to millennial scale declination and inclination features of the eastern canadian stack can be correlated within the dating uncertainties with other holocene north american icelandic and european psv records suggesting a common possibly hemispheric in character geomagnetic origin both magnetic inclination and declination of the eastern canadian stack are generally consistent with the time varying spherical harmonic model of the geomagnetic field cals7k 2 notably during the last 4000 cal bp in addition the eastern canadian holocene rpi stack reveals similar millennial and even centennial time scale variations consistent with some virtual axial dipole moment vadm reconstructions derived from absolute paleointensity data as well as with north american lacustrine rpi records accordingly these results suggest that the holocene paleomagnetic secular variation in north america is significantly driven by large scale 5000 km geomagnetic field changes at these timescales

slip tendency analysis fault reactivation potential and induced seismicity in a deep geothermal reservoir abstract a slip tendency analysis is used to assess the reactivation potential of shear and dilational fractures in a deep geothermal reservoir in the northeast german basin based on the notion that slip on faults is controlled by the ratio of shear to normal stress acting on the plane of weakness in the in situ stress field the reservoir rocks composed of lower permian sandstones and volcanics were stimulated by hydraulic fracturing a surprisingly low microseismic activity was recorded with moment magnitudes mw ranging from 1 0 to 1 8 the slip tendency analysis suggests a critically stressed reservoir exists in the sandstones whereas the volcanic rocks are less stressed rock failure first occurs with an additional pore pressure of 20 mpa presumed failure planes form a conjugate set and strike nw and ne slip failure is more likely than tensional failure in the volcanic rocks because high normal stresses prevent tensional failure these results from slip tendency analysis are supported by the spatial distribution of recorded microseismicity source characteristics indicate slip rather than extension along presumed ne striking failure planes this suggests that slip tendency analysis is an appropriate method that can be used to understand reservoir behavior under modified stress conditions

small and large scale soft sediment deformations in a triassic lacustrine delta caused by overloading and seismicity in the ordos basin central china abstract the instability of an upper triassic lacustrine deltaic system in the southwestern ordos basin central china is examined based mainly on detailed measurements and descriptions of core data nine lithofacies associations are identified including undeformed and deformed channel deposits sandy and muddy slumps sandy debrites sandy dykes undeformed and deformed fringe silty deposits and muddy deposits quantification of the vertical and horizontal spatial distribution of these sediments reveals the deformed sediments can comprise more than one third of the entire cored interval in more than half of the wells indicating the significance of soft sediment deformation structures as essential components of this deltaic system a depositional model is constructed which highlights the location of deformed and remobilized sediments and their relationships with undeformed sediments in the proximal part of the delta the undeformed and deformed channel deposits and sandy slumps dominate the sandy sediments which are interbedded to form thick amalgamated sandstones in areas distant from these massive sandstones undeformed and deformed fringe fine grained deposits are well developed which could generate muddy slumps in the distal part of the delta besides undeformed and deformed fringe fine grained deposits sandy debrites are present as isolated sandbodies large scale sandy dykes formed between thick sandstones and adjacent mudstones two possible trigger mechanisms for initial deformation development are identified sediment overloading induced by sudden deposition of remobilized sediments and seismicity which caused large scale remobilization in the study area the high percentage of soft sediment deformation structures in this delta influences the reservoir heterogeneity of the three types of sandstones undeformed channel deposits sandy slumps and sandy debrites porosity permeability analysis reveals that reservoir quality of these three types varies significantly and thus distinguishing deformed sediments from undeformed deltaic sediments is essential for hydrocarbon development in this area

far field poroelastic response of geothermal reservoirs to hydraulic stimulation treatment theory and application at the gros schonebeck geothermal research facility abstract enhanced geothermal systems egs are engineered reservoirs developed to extract heat from low permeability and low porosity geological formations cyclic hydraulic stimulation treatments can be used in some cases to create hydraulic fractures and gain access to the target formation fluids drain the geothermal fluid and increase the overall productivity of the reservoir during these operations successive cycles of injection at high flow rates are conducted to decrease the effective minimum principal stress to the tensile strength of the material developing a mode i fracture opening of the newly developed fractures induces additional deformation of the reservoir rocks whose impact on the far field reservoir hydraulics has not been addressed so far for real case applications these rates of compressive deformation can be significantly high in the context of cyclic stimulation treatments and can lead to a poroelastic pore pressure increase which spans quasi instantaneously at greater distances than diffusive processes in this study such a poroelastic response resulting from cyclic deformation during hydraulic stimulation treatment of a well is investigated using hydromechanical coupling between pore pressure variations and rock deformation the effects of this poroelastic response on the hydromechanical state of a reservoir is illustrated with field measurements of a cyclic hydraulic stimulation treatment conducted at the gros schonebeck geothermal research site in august 2007 this study demonstrates that the pore pressure increase monitored in a neighbor well located approximately 475 m away from the stimulated well at reservoir depth is controlled by diffusive processes responsible for the long term increase of pore pressure but also by poroelastic effects responsible for the quasi instantaneous local peaks in pore pressure the results from this applied study helped to quantify the relevance of the poroelastic behavior of stimulated reservoir rocks in a way than can improve current understanding of such hydraulic stimulation settings

characterisation of a fractured reservoir using microearthquakes induced by hydraulic injections abstract microseismic activity is induced by a number of engineering activities which involve fluid injection or extraction in naturally fractured rock masses evidence collected during the last 15 years of hot dry rock hdr geothermal energy research has clearly indicated the very strong positive correlation between induced microearthquake locations and fluid flow paths within the fractured rock mass microseismic monitoring is now used regularly in hdr research as the only effective means of mapping hydraulic stimulations and monitoring hydromechanical processes during operation of the fractured reservoir many of the techniques that have been developed through hdr research are directly applicable to the hydrocarbon industry for the monitoring of hydraulic fracturing treatments waterflood operations and reservoir depletion this paper provides a brief introduction to the hydromechanical interactions that result in induced microseismicity and presents case studies from three european hdr sites where the monitoring of microseismic activity has proved vital in targeting production wells mapping the progress of stimulation and waterfloods and understanding the hydromechanical behaviour of the fractured system

numerical modelling of tsunamis generated by hypothetical landslides in the strait of georgia british columbia a modified and corrected version of the viscous slide model of jiang and leblond 1994 is used to assess the tsunami risk associated with hypothetical underwater slope failures in two coastal areas of british columbia having potentially unstable sediment deposits a malaspina strait separating the mainland coast and texada island in the central strait of georgia and b roberts bank on the foreslope of the fraser river delta in the southern strait of georgia the intent of this study is to demonstrate the capability of the model for tsunami risk assessment and to improve upon previous studies of tsunami risk in the region based on reasonable submarine landslide scenarios the potential risk from tsunamis associated with slide failures has been examined but the likelihood of failure events themselves was not considered for the malaspina strait scenarios simulated tsunamis are generated by failure of a lobe of perched sediment situ ated on the slope of eastern texada island failure as a flow slide of the estimated 1 250 000 m3 of sediment generates wave troughs reaching 4 9 m and trough to crest heights of 6 to 8 m along the coast of texada island at cape cockburn on the opposite side of the strait wave heights of 1 5 to 2 0 m are produced for roberts bank simulated waves are examined for two separate failure scenarios the larger slide case 1 involves the failure of a sediment lobe with lateral dimensions of 7 3 km2 and volume of 0 75 km3 while the smaller slide case 2 fails a sediment lobe with dimensions of 4 2 6 km2 and volume of 0 23 km3 computations were made both for high 3 m and low 3 m tide conditions for both failure volumes maximum wave amplitudes up to 18 m for case 1 and 8 m for case 2 occur on the coasts of mayne and galiano islands opposite the source area wave amplitudes are much smaller 1 to 4 m on the mainl and coast because of the reflection of the initial waves from roberts bank additional numerical experiments were conducted for both regions to estimate the sensitivity of the computed tsunami wave heights to input parameters such as slide viscosity bulk density and slide position

identification and dating of a key late pleistocene stratigraphic unit in the st lawrence estuary and gulf eastern canada abstract a recently acquired 8 m long sediment core along with high resolution seismic reflection and subbottom profiler sections allowed the identification characterization and dating of a widespread seismic unit extending from the head of the laurentian channel lower st lawrence estuary to honguedo strait gulf of st lawrence eastern canada this seismic unit labelled unit 2 is characterized by a series of parallel high amplitude reflections with thicknesses ranging from 68 m near the head of the laurentian channel to 250 m in the st lawrence estuary leaving it very difficult to be reached by conventional coring operations here we reveal how we were able to trace and core this seismic unit in an area where it lays closer to the seafloor near the southern wall of the laurentian channel in the lower st lawrence estuary this seismic unit consists of two sedimentary facies sandy mud including ice rafted debris ird underlying faintly laminated to homogenous and plastic silty clays based on the sedimentary facies we interpret the upper clays as ice distal glaciomarine sediments and the lower sandier sediments as ice proximal glaciomarine sediments this interpretation is further supported by the fact that no seismic nor sediment facies present above seismic unit 2 throughout the estuary and gulf of st lawrence can be linked to glacial i e ice contact sediments such as till moraines esker etc sediments seismic unit 2 is highly disturbed by iceberg scouring in the gulf of st lawrence where it is found at shallower depths indicating that it was deposited during deglaciation the available ams 14c dates obtained in the ice proximal glaciomarine sediments indicate that the lower part of seismic unit 2 was deposited during local re advances or stillstands of the laurentide ice sheet margins in the goldthwait sea that began at or before the younger dryas cold event 11 100 10 000 yr bp and that seismic unit 2 can be used as a chronostratigraphic marker throughout the st lawrence estuary and northwestern gulf of st lawrence

evidence for a large earthquake and tsunami 100 400 years ago on western vancouver island british columbia abstract a peaty marsh soil is sharply overlain by a sand sheet and intertidal mud at tidal marshes near tofino and ucluelet vancouver island british columbia foraminifera and vascular plant fossils show that the buried soil was submerged suddenly and was covered quickly by sand radiocarbon ages place this event between 100 and 400 yr ago the coastal subsidence suggested by the submergence occurred in an area of net late holocene emergence perhaps during the most recent great earthquake on the northern part of the cascadia subduction zone the sand sheet overlying the peaty soil records the tsunami triggered by this earthquake similar stratigraphic sequences of about the same age have been reported from estuaries along the outer coasts of washington and northern oregon suggesting that hundreds of kilometers of the cascadia subduction zone may have ruptured during one or a series of plate boundary earthquakes less than 400 yr ago

powerful unconfined turbidity current captured by cabled observatory on the fraser river delta slope british columbia canada turbidity currents are one of the main sediment transport processes on earth yet are notoriously difficult to monitor directly this article presents the first direct and high bandwidth observation of a turbidity current using a cabled sea floor observatory on 5 june 2012 a platform on ocean networks canada located in 107 m of water on the fraser river delta slope was displaced downslope and severed from its data cable the platform weighed ca 1000 kg in water the event took place during high river discharge high tides and rapid sediment accumulation on adjacent upslope areas of the sea floor data recorded as it tumbled downslope allow a reconstruction of the flow which is inferred to have been an unconfined turbidity current lines of evidence indicate that the flow came in as a bed hugging wedge and built up to between 1 m and 4 m in height as the head passed through comparison with laboratory data suggest that the flow was initially supercritical while the adjacent slope offset to the north clearly exhibits change over an annual resurvey period the bathymetry directly at the event location show no resolvable change over a period from seven months before the event to one month after sediment cores collected after the event were pervasively biototurbated and they contain no obvious deposit connected with this event the remarkable aspects of this research follow the flow was powerful enough to carry a 1 tonne platform and sever a heavily armoured cable the current occurred on the unchannelized open slope this powerful event failed to cause discernible seabed elevation change the flow was triggered by tidal conditions the event was detected by a purpose designed cabled observatory thus providing high bandwidth data and also alerting researchers in real time to mount follow on investigations

fracture mapping in the soultz sous forets geothermal field using microearthquake locations 1 in 2003 a massive hydraulic fracturing experiment was carried out at the european geothermal hot dry rock site at soultz sous forets france the 2 week injection of water generated a high level of microseismic activity triggering about 90 000 microearthquakes during and after the fluid injection of these 21 000 events detected at all stations were located individually with a grid search algorithm to characterize the extent of the seismic zones and ultimately of the fracture network the accuracy of these initial locations was around 70 m not sufficient to map detailed fracture patterns a precise relocation effort was undertaken to reduce the location uncertainties using three different techniques joint hypocenter determination jhd collapsing and multiplet analysis the collapsing method was added to the jhd results to further consolidate the hypocenters on the other hand a multiplet analysis was performed on the initial data set for identifying microearthquakes with similar waveforms and hence relocating relatively the correlated events the delays in traveltime were computed by wavelet analysis and the events were relocated using a grid search algorithm we found 7463 events whose seismograms correlated with a correlation coefficient of 0 8 or higher most of which were doublets multiplets are horizontal tube like structures with lengths from a hundred to several hundred meters striking along the direction of the maximum compressive horizontal stress we interpret these structures as the preferential paths where fluid flow is largely confined this hypothesis is reinforced by the good correlation in depth between the events and the fluid outflows observed in the well therefore we believe that these relocated events highlight the zones where the permeability of the reservoir is increased

sediment transport by tidal currents and implications for slope stability fraser river delta british columbia tidal currents on the sandy southern slope of fraser river delta have generated dunes with heights of 0 5 3 5 m and lengths of 11 108 m dune geometry and migration measurements indicate net sediment transport to the northwest in the direction of flood tidal currents two current meters moored in the dune field showed greater frequencies of occurrence and higher mean current speeds in the flood direction compared with the ebb predictions from two bed material load models indicate sediment transport is overwhelmingly dominated by flood currents there is no obvious source of sand to replace sediment transported in the dune field suggesting net erosion of the surface a previous analysis of bathymetric data also shows recent erosion of the lower slope and overall slope steepening these patterns of erosion could lead to slope failure and damage to coastal structures

a river mouth submarine channel and failure complex fraser delta canada abstract high resolution seismic and side scan sonar surveying combined with coring of the fraser delta slope seaward of the main fluvial distributary has revealed a complex suite of morphologic units which include undisturbed delta slope sediments shallow rotational slides relict and active slope channels debris accumulations and ponded turbidites sediment transport through the main submarine channel is thought to be primarily by debris flows rather than by turbidity currents although this is a seismically active region the instability related features described here are probably due primarily to rapid sediment deposition on the upper delta slope at the river mouth

post liquefaction stability and deformation analysis of duncan dam duncan dam is a 39 m high zoned embankment and is founded on a deep deposit of unconsolidated sediments consisting of sands silts and gravels that are susceptible to liquefaction during earthquake loading a comprehensive program of field laboratory and analytical investigations was conducted to evaluate the liquefaction potential of the foundation soils and performance of the dam during an earthquake this paper describes the evaluation procedures and analyses and presents results of the post liquefaction stability and deformation analysis of the dam analyses were carried out based on the total stress approach using two methods namely the lab method and seed s method the lab method is a site specific direct laboratory based approach utilizing soil parameters from laboratory tests on undisturbed soil samples obtained in situ after freezing the ground seed s method is indirect and is based on field penetration data and past experience from earthquakes the lab method indicates that the residual

downhole seismic imaging of a massive sulfide orebody with mode converted waves halfmile lake new brunswick canada multioffset multiazimuth downhole seismic data were acquired at halfmile lake new brunswick to image known massive sulfide lenses and to investigate the potential existence of a steeply dipping mineralized zone connecting them the massive sulfide lenses which have significantly higher elastic impedances than host rocks produce strong scattering the downhole seismic data show prominent scattered p p and s s and modeconverted p s and s p waves originating from the deposit such complex scattering from massive sulfide ore was not observed previously in vertical seismic profiling data migration of the scattered and mode converted waves from several shot points imaged different parts of the deepest lens the scattered s waves and modeconverted waves provide additional imaging capabilities that should be considered when selecting downhole seismic methods for mining exploration

influence of placement method on the in situ density of hydraulic sand fills the range of densities achievable by hydraulic placement of sand straddles the boundary between values giving acceptable potential performance and those giving unacceptable potential performance this has led to concerns over the safety of structures using hydraulic fills such as the artificial drilling islands in the canadian beaufort sea liquefaction failures of hydraulically placed sand have occurred at four or more of these islands until recently the factors affecting in situ density were little understood data obtained from several artificial islands are presented and these are used to demonstrate the overwhelming influence of method of placement on in situ density the possible reasons for this influence and the implications for design are discussed recommendations are made for research that together with conclusions drawn in the paper should allow hydraulic fills to be used with more confidence in the future key words sand hydraulic fill liquefaction cone penetration test

stability of the fraser river delta front the distributary front deposits of the delta consist mainly of interlayered sand and silt and lie in one of the most seismically active zones in canada subsurface deposits at the north tend to be siltier than those at the south sediments on the surface of the delta slope range from clayey silts at the north to pure sands at the south slope angles vary from 23 at the head of the slope to 1 2 within 2 km beyond the tidal flats hydraulic bedforms observed on the sandy slopes southeast of the main channel gradually increase in size from small ripples to large asymmetric sand waves 2 3 m high and approximately 30 m long they are generated primarily by flood tidal currents which scour the seabed to a water depth in excess of 100 m formation of gullies which crease the delta slope probably is initiated principally by failure of oversteepened deposits at a channel mouth previous studies have suggested that the large hummocks or ridges at the base of the slope off the main channel have been formed by the co

time and size of a giant earthquake in cascadia inferred from japanese tsunami records of january 1700 geological evidence shows that great earthquakes have occurred in the recent prehistoric past in the cascadia subduction zone off the pacific coast of north america the most recent event or series of events is dated at about 300 years ago1 4 but the precise date and magnitude have not been determined geological investigations have not been able to distinguish a single giant earthquake from a series of great earthquakes occurring over a timespan of a decade or two4 although this information is important for the assessment of future hazard5 we have found several tsunami records in japan from ad 1700 with no indication of a local cause historical earthquake records and palaeoseismic evidence indicate the absence of a large earthquake in 1700 in south america alaska or kamchatka leaving cascadia as the most likely source of this tsunami the estimated time of the earthquake is the evening about 21 00 local time of 26 january 1700 the magnitude is estimated as 9 from the tsunami heights in which case the earthquake ruptured the entire length of the cascadia subduction zone2 these estimates are consistent with native american legends that an earthquake occurred on a winter night6

unexpected fast rate of morphological evolution of geologically active continental margins during quaternary examples from selected areas in the italian seas abstract in the last few decades seafloor imagery systems have drastically changed our vision of a mostly regular and depositional marine landscape evidencing how erosive and mass wasting processes are widespread in the marine environments with particular reference to geologically active areas most of the previous studies have focused on the characterization of these features whereas a very few ones have tried to estimate what is the extent and order of magnitude of erosion rates in these areas in this paper we show several examples from some of the most geologically active margins off southern italy aimed to a quantify the spatial extent of such processes b better understand the role of submarine erosion in the morphogenesis of the coastal sector and c try to roughly estimate the order of magnitude of erosion rates in these areas the results are impressive with mass wasting features widespread from coast down to 2600 affecting from the 52 up to 97 of the whole continental slope because of the narrow or totally lacking shelves in these areas mass wasting processes often occur close to the coast and match embayment of the coast so indicating a key role in the morphogenesis of coastal sector with significant implication on the related geohazard finally based on a morphological approach integrated by available stratigraphic constraints we have roughly estimated average erosion rates in these areas ranging from at least some mm year to a few cm year i e some hundreds of meters up to kilometers eroded in each eustatic cycle despite the large uncertainties of these estimates as well as their spatial and temporal variability in response to regional and local factors the obtained values are very high and they should be considered for future model of margin evolution source to sink computation and marine coastal geohazard assessment

holocene paleomagnetic records from the st lawrence estuary eastern canada centennial to millennial scale geomagnetic modulation of cosmogenic isotopes two long holocene piston cores md99 2220 and md99 2221 were raised from the st lawrence estuary eastern canada because of the expanded holocene sediment sequence this location provides a u channel based paleomagnetic study supported by an accelerator mass spectrometry ams 14c chronology rock magnetic and sedimentological data indicates that these sediments provide a paleomagnetic directional secular variation psv and relative paleointensity rpi proxy records for the last 8500 cal bp sedimentation rates vary from 1 2 to 4 2 m kyr comparison of inclination and declination features with other north american holocene psv records are generally consistent and temporal offsets are within chronological uncertainties the normalized natural remanent magnetization intensity record a rpi proxy from the postglacial sediments of core 2220 compares favorably with north american and european holocene rpi records at millennial and even some centennial timescales comparisons between core 2220 rpi proxy and the 10be flux record from the greenland summit gisp2 ice core finkel and nishiizumi j geophys res 102 1997 26699 26706 and a 14c production rate record bond et al science 294 2001 2130 2136 suggest that geomagnetic modulation may control the millennial and even some centennial scale variability within cosmogenic isotope records this implies that the core 2220 rpi record reflects changes in global scale geomagnetic field at these timescales

seismotectonic characteristics of the lower st lawrence seismic zone quebec insights from geology magnetics gravity and seismics the estuary of the st lawrence river between baie comeau and sept iles is an area where 50 to 100 earthquakes are detected yearly this study defines the major lineaments of the precambrian basement and compares them with mapped faults where possible and examines their possible correlation with the local earthquakes onshore aerial photographs remote sensing images and field mapping are used to identify the geological structures of the precambrian basement while offshore they are interpreted from potential field magnetic gravity and a published synthesis of seismic reflection profiles the precambrian basement dips towards the southeast under the appalachian nappes with normal faults with kilometre scale throw and east west or ene wsw strikes onshore a system of normal brittle faults with a complex history of movements crosscuts both the precambrian basement and the overlying ordovician sedimentary cover most earthquakes occur beneath the st lawrence river at focal depths between about 7 and

can thin coals be resolved in seismic data an example of the challenges for carboniferous visean to westphalian source rock definition across the elbow spit platform netherlands and the mid north sea high uk through well synthetic modelling

the stress regime in a rotliegend reservoir of the northeast german basin in situ stresses have significant impact either positive or negative on the short and long term behaviour of fractured reservoirs the knowledge of the stress conditions are therefore important for planning and utilization of man made geothermal reservoirs the geothermal field gros schonebeck 40 km north of berlin germany belongs to the key sites in the northeastern german basin we present a stress state determination for this lower permian rotliegend reservoir by an integrated approach of 3d structural modelling 3d fault mapping stress ratio definition based on frictional constraints and slip tendency analysis the results indicate stress ratios of the minimum horizontal stress s hmin being equal or increasing 0 55 times the amount of the vertical stress s v s hmin 0 55s v and of the maximum horizontal stress s hmax 0 78 1 00s v in stress regimes from normal to strike slip faulting thus acting stresses in the 4 100 m deep reservoir are s v 100 mpa s hmin 55 mpa and s hmax 78 100 mpa values from hydraulic fracturing support these results various fault sets of the reservoir are characterized in terms of their potential to conduct geothermal fluids based on their slip and dilatation tendency this combined approach can be adopted to any other geothermal site investigation

rock specific hydraulic fracturing and matrix acidizing to enhance a geothermal system concepts and field results abstract enhanced geothermal systems egs are engineered reservoirs developed to extract economic amounts of heat from low permeability and or porosity geothermal resources to enhance the productivity of reservoirs a site specific concept is necessary to actively make reservoir conditions profitable using specially adjusted stimulation treatments such as multi fracture concepts and site specific well path design the results of previously performed stimulation treatments in the geothermal research well gtgrsk4 05 at gros schonebeck germany are presented the reservoir is located at a 4100 4300 m depth within the lower permian of the ne german basin with a bottom hole temperature of 150 c the reservoir rock is classified by two lithological units from bottom to top volcanic rocks andesitic rocks and siliciclastics ranging from conglomerates to fine grained sandstones fluvial sediments the stimulation treatments included multiple hydraulic stimulations and an acid treatment in order to initiate a cross flow from the sandstone layer the hydraulic stimulations were performed in different depth sections two in the sandstone section and one in the underlying volcanic section in low permeability volcanic rocks a cyclic hydraulic fracturing treatment was performed over 6 days in conjunction with adding quartz in low concentrations to maintain a sustainable fracture performance flow rates of up to 150 l s were realized and a total of 13 170 m3 of water was injected a hydraulic connection to the sandstone layer was successfully achieved in this way however monitoring of the water level in the offsetting well egrsk3 90 which is 475 m apart at the final depth showed a very rapid water level increase due to the stimulation treatment this can be explained by a connected fault zone within the volcanic rocks two gel proppant treatments were performed in the slightly higher permeability sandstones to obtain long term access to the reservoir rocks during each treatment a total of 100 ton of high strength proppants was injected with 500 m3 of cross linked gel the subsequent production test in conjunction with flowmeter logging showed an improvement of productivity by a factor of more than 4 due to assumed residual drilling mud constituents calcite dolomite and aragonite in the near wellbore vicinity an acid matrix stimulation was performed thereafter using a coil tubing unit the following nitrogen lift test demonstrated another increase of productivity by 30 50 to an overall increase by a factor of 5 5 6 2