stress strain paradox plate coupling and forearc seismicity at the cascadia and nankai subduction zones abstract in the continental forearcs of the cascadia and nankai subduction zones geodetic strain measurements indicate crustal contraction in the direction of plate convergence nearly margin normal but earthquake focal mechanisms and other stress indicators show maximum compression along strike margin parallel it is evident that the geodetic strain signals reflect the temporal fluctuations of elastic stress associated with subduction earthquake cycles not the absolute stresses the absolute margin normal stress is not only much less than the margin parallel stress but also no greater than the lithostatic value indicating a very weak subduction thrust fault weak subduction faults are also consistent with geothermal data which require very low frictional heating along the faults great subduction earthquakes occur at very low shear stresses and cause small perturbations to the forearc stress regime because these small elastic stress perturbations are relatively fast they give large strain rates that are detected by geodetic measurements the present nearly margin normal contraction in both places is due to the locking of the subduction fault and the consequent increase in elastic stress in the direction of plate convergence with the margin parallel compression being dominant the small increase in margin normal stress may change the forearc seismicity in cascadia from a mixture of thrust and strike slip types into mainly thrust before the next great subduction earthquake in nankai the change should be from strike slip to quiescence as observed in the nankai forearc prior to the 1944 1946 great subduction earthquakes

mechanics of low stress forearcs nankai and cascadia the nankai and cascadia subduction zones have low stress forearcs where the margin normal horizontal compressive stress is similar to or less than the vertical stress except in the accretionary prisms in the absence of active back arc spreading the forearc margin normal stress is controlled mainly by the total shear force along the subduction fault or the plate coupling force and the gravitational force the plate coupling force creates compression and the gravitational force in the presence of margin topography creates lateral tension we give a simple expression that relates the forearc stress to topography and average fault strength with the latter represented by an effective coefficient of friction we also use a finite element model of two converging plates in frictional contact to model the forearc stresses the analyses indicate that a low stress forearc requires not only the subduction fault to be very weak but also the mechanically coupled fault area to be narrow in the downdip direction and shallow in depth for nankai and cascadia where the coupled fault areas are narrow and shallow because of the young and hot subducting plates is about 0 05 or less and in any case less than 0 09 the low fault strength is probably not a unique property of low stress forearcs since the same low values combined with wider and deeper coupled areas can be shown to create large margin normal compression in addition there does not seem to be any relation between subduction earthquake magnitudes and plate coupling forces great earthquakes occur at subduction zones having low stress forearcs such as nankai and cascadia

interpretation of porosity and lwd resistivity from the nankai accretionary wedge in light of clay physicochemical properties evidence for erosion and local overpressuring in this study we used porosity to assess the compaction state of the nankai accretionary wedge sediments and any implications for stress and pore pressure however hydrous minerals affect porosity measurements and accounting for them is essential toward defining the interstitial porosity truly representative of the compaction state the water content of sediments was measured in core samples and estimated from logging data using a resistivity model for shale we used the cation exchange capacity to correct the porosity data for the amount of water bound to clay minerals and to correct the porosity estimates for the surface conductivity of hydrous minerals the results indicate that several apparent porosity anomalies are significantly reduced by this correction implying that they are in part artifacts from hydrous minerals the correction also improves the fit of porosity estimated from logging while drilling lwd resistivity data to porosity measured on cores low overall porosities at the toe of the accretionary wedge and in the splay fault area are best explained by erosion and we estimated the quantity of sediments eroded within the splay fault area by comparing porosity effective stress relationships of the sediments to a reference curve additionally a comparison of lwd data with core data resistivity and p wave velocity obtained at site c0001 landward of the mega splay fault area suggested a contribution from the fracture porosity to in situ properties on the formation

interseismic stress accumulation at the locked zone of nankai trough seismogenic fault off kii peninsula abstract a primary source of stress variation prior to great subduction zone earthquakes is the tectonic loading due to plate convergence we have calculated the elastic stress around the locked zone accumulated during an interseismic period numerically using a 2d plane strain finite element model in the nankai trough off kii peninsula and examined its dependence on elastic properties and some boundary conditions for the modeling we used the geometry of subducting plate interface determined previously through seismic surveys and the physical properties that were obtained through iodp scientific drilling offshore kii peninsula to construct a physically realistic model a dislocation along the plate interface is calculated from a 5 m displacement imposed on one side of the subducting plate with the locked zone defined at a depth of 10 to 25 km along the plate interface calculated shear stress is maximized at the downdip edge of the locked zone decreases exponentially seaward and is almost zero near the updip edge maximum shear stress is primarily proportional to the young s modulus of the overlying section comparing the maximum shear stress with the average stress drop for subduction earthquakes 3 4 mpa the most appropriate young s modulus and poisson s ratio ranges are 50 70 gpa and 0 3 respectively which are in good agreement with previous estimations from observed vp vs the stress accumulated during one seismic cycle can be reasonably explained by a linear elastic model with an appropriately sized locked region we found that the envelope of simulated horizontal displacement on the surface agrees well with gps velocity data which also supports this inference disturbance near the updip edge is no larger than 0 1 mpa of stress or 0 1 radian of tilt which are difficult to detect with current borehole measurement techniques and likely complex borehole conditions

effect of anisotropic borehole wall failures when estimating in situ stresses a case study in the nankai accretionary wedge abstract breakouts observed in a vertical borehole c0002a drilled through two major tectonic sedimentary formations consisting of forearc basin upper and accretionary prism lower sediments in the nankai accretionary wedge japan exhibit distinctive geometric features in respective formations breakouts in the lower accretionary prism sediments are markedly wider than those in the forearc basin sediments and breakout azimuths in the two units are horizontally rotated relative to one another breakout azimuths are widely used as a proxy for the determination of principal stress directions however strength anisotropies related to the presence of bedding planes may affect both breakout azimuths and widths which can result in misleading in situ stress interpretations while thinly bedded mudstones are the dominant lithology in both the forearc basin and accretionary prism sediments bedding planes in the accretionary prism sediments are relatively steeper than those in the forearc basin sediments with possible implications for breakout geometry and interpretations of principal stress directions to investigate the effects of bedding planes on breakout geometry azimuth and width we conducted borehole wall failure analyses using a weak plane failure model that incorporates material strength anisotropies the model results show that breakout widths and orientations are strongly affected by steeply dipping 40 bedding planes in cases where dip directions are unaligned with the principal stress orientation our theoretical results suggest that variations in breakout azimuths in the c0002a site may be associated with bedding plane related strength anisotropy and not associated with the rotation of stress field that is stress orientation is consistent throughout the borehole down to the bottom hole depth of 1495 m below sea floor in addition disregarding the effects of bedding planes tends to yield an overestimation of in situ stress magnitude

elevated pore pressure and anomalously low stress in regions of low frequency earthquakes along the nankai trough subduction megathrust 1 recent seismic reflection and ocean bottom seismometer obs studies reveal broad regions of low seismic velocity along the nankai subduction plate boundary megathrust offshore sw japan these low velocity zones lvz s extend 55 km landward from the trench corresponding to depths of 10 km below sea floor here we estimate the in situ pore pressure and stress state within these lvz s by combining p wave velocities obtained from the geophysical surveys with new well constrained empirical relations between p wave velocity porosity and effective mean stress defined by laboratory deformation tests on drill core samples of the incoming oceanic sediment we document excess pore pressures of 17 87 mpa that extend 55 km into the subduction zone indicating that trapped pore fluids support 45 91 of the overburden stress along the base of the upper plate and surrounding major fault zones the resulting effective stresses in the lvz are limited to 1 3 of the values expected for non overpressured conditions these low effective stresses should lead to a mechanically weak and predominantly aseismic plate boundary the region of lowest effective stress coincides with precisely located very low frequency earthquakes providing the first quantitative evidence linking these anomalous slip events to low stress and high pore pressure

wave beach and dune interactions in southeastern australia abstract a morphodynamic classification of surfzones beaches and dunes of the microtidal low to high energy southeast australian coast is presented the first section a waves and beaches briefly deals with the transformation of deep water wave energy as it crosses the shelf nearshore and surfzone depending on the deep water wave characteristics and shelf and inshore morphology resultant breaker wave energy may be high moderate or low and the accompanying beach surfzone morphodynamic state in fine to medium sand beaches either dissipative intermediate or reflective dissipative beaches have wide surfzones with shore parallel bar s and channel s and predominantly shore normal circulation intermediate beaches are characterised by rip circulation crescentic transverse bars and megacusps and reflective beaches by a barless surfzone and steep cusped or bermed beach each beach form has a characteristic level of beach stability zone of sediment storage and mode of beach and dune erosion landward aeolian sediment transport of swash deposited sand section b is dependent on the subaerial beach topography and the aerodynamic flow regime across that topography characteristic profile shapes are ascribed to each beach type dissipative intermediate and reflective aeolian sand transport rates are potentially highest on dissipative beaches moderate on intermediate beaches and lowest on reflective beaches these rates determine the potential size of foredunes which are correspondingly largest on dissipative beaches and smallest on reflective beaches the combination of mode and frequency of beach dune erosion rates of aeolian sand transport and foredune volume and morphology provide an explanation of the nature and morphology of landward occurring large scale dune systems dissipative beaches are frequently characterised by large scale transgressive dune sheets intermediate by a trend from large scale parabolic dune systems high wave energy to small scale blowouts low wave energy and reflective beaches by minimal dune development

current stress state and principal stress rotations in the vicinity of the chelungpu fault induced by the 1999 chi chi taiwan earthquake 1 we carried out various stress measurements in boreholes penetrating the northern segment of the chelungpu fault drilled about 5 years after the 1999 chi chi taiwan earthquake in the possible depth range of the chelungpu fault three major fault zones were encountered clearly recognizable principal stress rotations in the vicinity of the shallowest major fault zone at 1133 m depth in hole b suggest that this fault zone ruptured during the 1999 earthquake moreover the fault s rupturing altered the stress state in the area surrounding this fault zone in this paper we constrain the possible magnitudes of the current principal horizontal stresses around the fault zone and show that the current stress state belongs to a normal or strike slip fault regime therefore the stress state was changed from that of a reverse fault regime by the rupturing

determination of stress state in deep subsea formation by combination of hydraulic fracturing in situ test and core analysis a case study in the iodp expedition 319 1 in situ test of hydraulic fracturing hf provides the only way to observe in situ stress magnitudes directly the maximum and minimum horizontal stresses shmax and shmin are determined from critical borehole pressures i e the reopening pressure pr and the shut in pressure ps etc observed during the test however there is inevitably a discrepancy between actual and measured values of the critical pressures and this discrepancy is very significant for pr for effective measurement of pr it is necessary for the fracturing system to have a sufficiently small compliance a diagnostic procedure to evaluate whether the compliance of the employed fracturing system is appropriate for shmax determination from pr was developed furthermore a new method for stress measurement not restricted by the system compliance and pr is herein proposed in this method the magnitudes and orientations of shmax and shmin are determined from i the cross sectional shape of a core sample and ii ps obtained by the hf test performed near the core depth these ideas were applied for stress measurement in a central region of the kumano fore arc basin at a water depth of 2054 m using a 1 6 km riser hole drilled in the integrated ocean drilling program iodp expedition 319 as a result the stress decoupling through a boundary at 1285 m below seafloor was detected the boundary separates new upper layers and old lower ones with an age gap of 1 8 ma which is possibly the accretionary prism the stress state in the lower layers is consistent with that observed in the outer edge of accretionary prism

runaway slip to the trench due to rupture of highly pressurized megathrust beneath the middle trench slope the tsunamigenesis of the 2011 tohoku earthquake off the east coast of northern japan abstract the gigantic 2011 march 11 mw 9 tohoku earthquake is examined from the viewpoint of the pre seismic forearc structure the seismic reflection properties of a megathrust around the usual up dip limit of the seismogenic zone the thermal state of a shallow subduction zone and the dehydration of underthrust sediments at the japan trench the pacific plate is subducting westward beneath northeast japan at a dip angle of 4 6 the middle and lower slopes of the landward side dip eastward at angles of 2 5 and 8 0 respectively the forearc prism beneath the middle and lower slopes is inferred to be in extensionally and compressively critical states respectively based on the presence of clear internal deformation features and on the occurrence of aftershock earthquakes the rapid uplift of the forearc that caused the 2011 tohoku tsunami may have been associated with this internal deformation of the prism the critical state of the prism indicates that the effective basal friction b of the plate boundary megathrust is 0 08 for the lower prism the megathrust especially under the middle slope is characterized by a prominent reflector with negative polarity one of multiple possible explanations is that the megathrust hosts highly pressurized fluids underthrust sediments in this part of the japan trench are dominated by pelagic and siliceous vitric diatomaceous silt with clay the dehydration kinetics of opal a to quartz the clay transformation of smectite illite and the thermal structure of the japan trench suggest that maximum dehydration of the sediments would take place at 50 60 km horizontally from the deformation front where the temperature along the megathrust is 100 120 c the zone of maximum dehydration coincides with the prominent seismic reflector that has negative polarity we hypothesize a possible free slip along this portion of the megathrust during the 2011 tohoku earthquake caused by anomalously high fluid pressure resulting from fluid accumulation over centuries

mapping crustal stress and strain in southwest british columbia 1 this paper investigates the orientation and sources of stress in the forearc of the cascadia subduction zone in southwest british columbia using bayesian inversion results from focal mechanism data and comparing results with gps derived short term strain rates the subduction margin in this region includes a change in orientation from n s in washington state to nw se in british columbia over 1000 focal mechanisms from north american crustal earthquakes have been calculated to identify the dominant style of faulting and 600 were inverted to estimate the principal stress orientations and the stress ratio our results indicate the maximum horizontal compressive stress orientation changes with distance to the trench from approximately margin normal along the coast to approximately margin parallel 100 150 km inland from the coast comparing stress orientations with gps data we relate the margin normal stress direction to subduction related strain rates due to the locked interface between the north american and juan de fuca plates just west of vancouver island further from the margin the plates are coupled less strongly and the margin parallel maximum horizontal compressive stress in the north american plate relates to the northward push of the oregon block which is also observed in the horizontal shortening direction of the residual strain rates after the subduction component is removed

tectonic sediment thickening fluid expulsion and the thermal regime of subduction zone accretionary prisms the cascadia margin off vancouver island tectonic sediment thickening fluid expulsion and the resulting thermal regime of the northern cascadia subduction zone accretionary prism have been described by numerical models both the sediment thickening and the fluid expulsion are found to have important thermal effects constraints on the models are provided by 1 detailed heat flow profiles across the continental slope accretion zone from variations in the thermally controlled depth to a gas hydrate bottom simulating reflector bsr and 2 porosity changes across the accretion zone inferred from the landward variation in the p wave velocity depth profiles the heat flow in the region of rapid prism thickening centered 15 km landward of the deformation front is 20 below that predicted by a larger scale thermal model that ignores the thermal effects of the sediment accretion processes the porosity also is substantially higher in this region compared to at the same depths in the adjacent deep sea cascadia basin the model results are in agreement with both the thermal and velocity data if the incoming sediment section is initially simply tectonically shortened horizontally and thickened vertically generating a high porosity underconsolidated section reconsolidation and fluid expulsion in response to the tectonic thickening is slow occurring mainly 20 30 km landward of the deformation front the maximum predicted fluid expulsion rate is about 4 10 11 m s 1 1 3 mm a 1 the pore pressure distribution across the deformation front region has been estimated from the velocity data using the simplifying assumption that velocity is only a function of effective pressure pore pressures are high reaching 80 of lithostatic 15 to 20 km landward of the deformation front an estimate of the bulk permeability in the seaward tens of kilometers of the prism ranging from 10 16 m2 near the top to about 10 18 m2 near the base has been obtained through matching the pore pressure distribution in the numerical model to that obtained from the velocity data the prism sediments are inferred to be substantially underconsolidated and pore pressures to be high for at least the seaward 30 km of the accretionary prism

water filtration through reflective microtidal beaches and shallow sublittoral sands and its implications for an inshore ecosystem in western australia abstract volumes of seawater filtered through the intertidal zone were measured on three modally reflective microtidal beaches in western australia the filtered volumes were large 19 m 3 m 1 day 1 and 73 m 3 m 1 day 1 on two clean beaches but only 0 4 m 3 m 1 per tidal cycle on a beach covered in kelp and seagrass wrack the mean residence times of this water in the interstitial system and its percolation paths were both short 1 7 h and 2 5 m respectively water input was greater across a beach cusp horn than across a cusp embayment most input occurred in the upper swash zone where the water table was less than 20 cm deep tidal variations in input volumes were evident even with tide ranges of only 20 cm the inshore zone off these beaches filters on average 0 07 m 3 m 2 day 1 at an average depth of 5 5 m under 0 4 m waves of 6 5 s duration the importance of these procedures in the mineralization of organic materials and the regeneration of nutrients for an inshore lagoon ecosystem is estimated and discused

distribution of resistive and conductive structures in nankai accretionary wedge reveals contrasting stress paths in this article we study the characteristics and spatial distribution of the deformation structures along the kumano transect of the nankai accretionary wedge and use this information to interpret the stress path followed by the sediments deformation structures are identified from logging while drilling lwd resistivity images of the materials surrounding the drill hole and from 3 dimensional x ray ct images of cores acquired during the iodp nantroseize project the relative resistivity of the structures identified on logs and the strike dip and density of structures identified on ct scan images are measured the analysis of dip and strike of structures indicates that most of the resistive structures identified on logging data correspond to compactive shear bands results also indicate that conductive structures predominate at the toe of the prism and above the main out of sequence thrust in locations where past and recent erosion occurred we propose several mechanisms that could explain the relation between erosion and the absence of compactive shear bands we conclude that sediments followed different stress paths depending on their location within the wedge and that those differences explain the distribution of deformation structures within the wedge we also show the coexistence of dilatant and compactant structures in fault zones including the frontal thrust and mega splay fault and we interpret the coexistence of these structures as a possible consequence of a transient fluid pressure

spatial variation of intertidal macrofauna on a sandy ocean beach in australia abstract spatial variation of macrofauna on a sandy beach was examined simultaneously over two scales across shore among and within zones and three nested scales along shore over the entire length of the beach prior to the main study pilot studies were performed to determine 1 the relative efficiency accuracy and precision of combinations of core size depth of sampling and sieve mesh size and 2 the likely distribution of macrofauna across shore so that stratification of sampling in the main study would be meaningful from this three zones were defined across shore namely 1 the high shore zone which extended 10 m downshore of the drift line and was dominated by two species of isopod 2 the mid shore zone which extended across the beach from the bottom of the high shore zone to the top of the swash zone and was dominated by the glycerid polychaete hemipodus sp and 3 the swash zone which contained more species than the other two zones and was dominated by amphipods hemipodus sp the bivalve donax deltoides and a species of cumacean in the main study multivariate analyses confirmed that assemblages of macrofauna varied significantly among zones despite smaller scale variation within zones and along shore variation significant along shore variation was detected in assemblages of macrofauna from each zone and occurred at different scales for different zones only assemblages in the swash zone showed a pattern of along shore variation that was consistent with a gradient in wave exposure along the beach univariate analyses showed that significant variation in populations of individual taxa occurred at both large and small scales significant variation was detected across shore within zones for nearly all variates and this demonstrated the importance of formally assessing variation within zones when making comparisons among zones significant variation was also detected along shore in analyses of particular taxa and interactions of across and along shore variation also occurred these results illustrate the necessity of considering both across and along shore variation for describing spatial patterns in assemblages or individual species of macrofauna unfortunately sampling a single transect across a beach which is common in many published descriptions of spatial patterns will not provide an adequate nor representative description of the macrofauna of that beach because this approach fails to consider all important sources of variation and confounds large and small scale variation the authors conclude that a better understanding of small scale variation both along and across shore within beaches is required in order to provide better descriptions of patterns provide a basis for larger scale studies allow unconfounded comparisons among beaches and ultimately to improve our understanding of the ecology of sandy beaches

horizontal compressive stress regime on the northern cascadia margin inferred from borehole breakouts during integrated ocean drilling program expedition 311 five boreholes were drilled across the accretionary prism of the northern cascadia subduction zone logging while drilling borehole images are utilized to determine breakout orientations to define maximum horizontal compressive stress orientations additionally wireline logging data at two of these sites and from site 889 of ocean drilling program leg 146 are used to define breakouts from differences in the aperture of caliper arms at most sites the maximum horizontal compressive stress shmax is margin normal consistent with plate convergence deviations from this trend reflect local structural perturbations our results do not constrain stress magnitudes if the margin normal compressional stress is greater than the vertical stress the margin normal shmax direction we observe may reflect current locking of a velocity weakening shallow megathrust and thus potential for trench breaching tsunamigenic rupture in a future megathrust earthquake

a low velocity zone with weak reflectivity along the nankai subduction zone three dimensional seismic reflection data reveal the presence of a low seismic velocity zone lvz with weak reflectivity character along the nankai accretionary prism this lvz is intercalated between an upper offscraped layer and a lower underthrusting layer in the outer accretionary wedge wide angle ocean bottom seismograph data also support the presence of the lvz which is estimated to be a maximum of 2 km thick 15 km wide and 120 km long the lvz could be an underthrust package underplated in response to the lateral growth of the nankai accretionary prism underplating of the underthrusting layer beneath the overlying offscraped layer would maintain a critical taper of the accretionary prism so that the offscraped layer can continue to grow seaward the lvz could have elevated fluid pressure leading to rigidity reduction of the entire outer accretionary wedge the rigidity lowered outer wedge containing the lvz may be more easily uplifted and thus eventually foster tsunami generation during a nankai megathrust earthquake if the fluid rich lvz supplies a significant amount of the fluid to the megasplay fault zone at depth it may affect stick slip behavior of the fault

co seismic ruptures of the 12 may 2008 ms 8 0 wenchuan earthquake sichuan east west crustal shortening on oblique parallel thrusts along the eastern edge of tibet abstract the m s 8 0 wenchuan earthquake which devastated the mountainous western rim of the sichuan basin in central china produced a surface rupture over 200 km long with oblique thrust dextral slip and maximum scarp heights of 10 m it thus ranks as one of the world s largest continental mega thrust events in the last 150 yrs field investigation shows clear surface breaks along two of the main branches of the ne trending longmen shan thrust fault system the principal rupture on the nw dipping beichuan fault displays nearly equal amounts of thrust and right lateral slip basin ward of this rupture another continuous surface break is observed for over 70 km on the parallel more shallowly nw dipping pengguan fault slip on this latter fault was pure thrusting with a maximum scarp height of 3 5 m this is one of the very few reported instances of crustal scale co seismic slip partitioning on parallel thrusts this out of sequence event with distributed surface breaks on crustal mega thrusts highlights regional ew directed present day crustal shortening oblique to the longmen shan margin of tibet the long rupture and large offsets with strong horizontal shortening that characterize the wenchuan earthquake herald a re evaluation of tectonic models anticipating little or no active shortening of the upper crust along this edge of the plateau and require a re assessment of seismic hazard along potentially under rated active faults across the densely populated western sichuan basin and mountains

earthquakes as beacons of stress change aftershocks occurring on faults in the far field of a large earthquake rupture can generally be accounted for by changes in static stress on these faults caused by the rupture1 2 this implies that faults interact and that the timing of an earthquake can be affected by previous nearby ruptures3 4 5 6 here we explore the potential of small earthquakes to act as beacons for the mechanical state of the crust we investigate the static stress changes resulting from the 1992 landers earthquake in southern california which occurred in an area of high seismic activity stemming from many faults we first gauge the response of the regional seismicity to the landers event with a new technique and then apply the same method to the inverse problem of determining the slip distribution on the main rupture from the seismicity assuming justifiable parameters we derive credible matches to slip profiles obtained directly from the landers mainshock7 8 our results provide a way to monitor mechanical conditions in the upper crust and to investigate processes leading to fault failure

shallow dynamic overshoot and energetic deep rupture in the 2011 mw 9 0 tohoku oki earthquake strong spatial variation of rupture characteristics in the moment magnitude mw 9 0 tohoku oki megathrust earthquake controlled both the strength of shaking and the size of the tsunami that followed finite source imaging reveals that the rupture consisted of a small initial phase deep rupture for up to 40 seconds extensive shallow rupture at 60 to 70 seconds and continuing deep rupture lasting more than 100 seconds a combination of a shallow dipping fault and a compliant hanging wall may have enabled large shallow slip near the trench normal faulting aftershocks in the area of high slip suggest dynamic overshoot on the fault despite prodigious total slip shallower parts of the rupture weakly radiated at high frequencies whereas deeper parts of the rupture radiated strongly at high frequencies

landslides triggered by earthquakes and their relations with faults and mountain slope geometry an example from ecuador abstract a large number of landslides occurred during two seismic events respectively 6 9 and 6 1 msw on 5 march 1987 in the ecuadorian andes these landslides have been mapped digitized and coregistered with topography at 1 50 000 scale geometry of coseismic and holocene faulting has been assessed integrating field and geophysical data landslide distribution and holocene tectonic features have been compared with earthquake foci geological deposits slope area inclination and orientation and vegetation cover the macro seismic field deduced by landslide distribution is ellipse shaped with the major axis striking nne and coinciding with the trend of the coseismic and holocene faults landslide distribution also shows a correlation with respect to the dip direction of these faults and the orientation of mountain slopes slopes parallel to the coseismic fault planes sloping towards wnw are almost unaffected by landsliding while this increases on the slopes at high angle to the fault plane and lying along its strike if these results could be confirmed in other areas a method of reconstruction of geometry of seismogenetic faults from topographic effects appears feasible

deformation and in situ stress in the nankai accretionary prism from resistivity at bit images odp leg 196 1 borehole resistivity images from odp leg 196 allow rapid and complete qualitative assessment of deformation within the toe of the nankai prism japan borehole breakouts were common within the prism but prominent in the trench wedge unit around the frontal thrust suggesting reduced sediment strength breakouts indicate consistent 2 orientations 050 compatible with northwesterly convergence deformation is dominated by discrete zones including the frontal thrust and decollement zone prism fractures trend ne sw consistent with convergence the decollement shows minimal deformation and the dominant structural trend is n s prism deformation zones are characterized by high resistivity compaction whereas the decollement is apparently dilated both with conductive fractures distribution of fracture orientations varies between log units confirming lithologic and rheologic influence pore pressure is elevated within the decollement and the misalignment of conductive fractures may reduce permeability

seismic hazard in western canada from gps strain rates versus earthquake catalog 1 probabilistic seismic hazard analyses psha are commonly based on frequency magnitude statistics from 50 100 yearlong earthquake catalogs assuming that these statistics are representative of the longer term frequency of large earthquakes we test an alternative psha approach in continental western canada including adjacent areas of northwestern u s a using regional strain rates derived from 179 global positioning system gps horizontal velocities gps strain rates are converted to earthquake statistics seismic moment rates and ground shaking probabilities in seismic source zones using a logic tree method for uncertainty propagation median gps based moment rates and shaking estimates agree well with those derived from earthquake catalogs in only two zones puget sound and mid vancouver island in most other zones median gps based moment rates are 6 150 times larger than those derived from earthquake catalogs shaking estimates 2 5 times larger although the gps based and catalog estimates commonly agree within their 67 uncertainties this discrepancy may represent an under sampling of long term moment rates and shaking by earthquake catalogs in some zones however a systematic under sampling is unlikely over our entire study area although not demonstrated with a high confidence level long term regional aseismic deformation may account for a significant part of the gps catalog discrepancy and in some areas represent as much as 90 of the total deformation budget in order to integrate gps strain rates in psha models seismic versus aseismic partitioning of long term deformation needs to be quantified and understood in terms of the underlying mechanical processes

landslides triggered by the 8 october 2005 kashmir earthquake abstract the 8 october 2005 kashmir earthquake triggered several thousand landslides these were mainly rock falls and debris falls although translational rock and debris slides also occurred in addition a sturzstrom debris avalanche comprising 80 million m3 buried four villages and blocked streams to create two lakes although landsliding occurred throughout the region covering an area of 7500 km2 the failures were highly concentrated associated with six geomorphic geologic anthropogenic settings including natural failures in 1 highly fractured carbonate rocks comprising the lowest beds in the hanging wall of the likely earthquake fault 2 tertiary siliciclastic rocks along antecedent drainages that traverse the hazara kashmir syntaxis 3 steep 50 slopes comprising precambrian and lower paleozoic rocks 4 very steep 50 lower slopes of fluvially undercut quaternary valley fills and 5 ridges and spur crests the sixth setting was associated with road construction extensive fissuring in many of the valley slopes together with the freshly mobilized landslide debris constitutes a potential hazard in the coming snowmelt and monsoon seasons this study supports the view that earthquake triggered landslides are highly concentrated in specific zones associated with the lithology structure geomorphology topography and human presence

seismic velocity studies of a gas hydrate bottom simulating reflector on the northern cascadia continental margin amplitude modeling and full waveform inversion on the northern cascadia subduction margin the multichannel seismic amplitude versus offset avo behavior of a bottom simulating reflector bsr suggests a p wave velocity change from high velocity hydrate bearing sediment to lower velocity sediment containing a small amount of free gas the observed nonlinear avo behavior constant or slightly decreasing amplitudes at near to mid offsets and a large amplitude increase at far offsets can be reproduced in the models if an s wave velocity enhancement is assumed as expected from hydrate cementation the avo behavior of the hydrate bsr is found not to be as useful as was earlier thought for determining the amount of free gas below the bsr this is because poisson s ratio change below the bsr due to gas is likely very small in high porosity unconsolidated sediments the uncertainty in the models is large as there is no reliable s wave velocity information for the sediments containing hydrate or gas avo modeling alone is not sufficient to distinguish different velocity models across the bsr our interpretation of the bsr amplitude behavior is that a p wave velocity increase above the bsr is the main cause of the bsr reflection amplitude increase at large incidence angles caution must be taken in applying avo analysis as little is known about s wave velocities however subtle differences in bsr amplitude behavior and reflection waveform can provide constraints through very careful full waveform inversion a well defined reference velocity depth profile is also required to represent water saturated sediment unaffected by either hydrate or free gas using full waveform velocity inversion a high resolution velocity model for the hydrate bsr has been derived the best fit model for the seismic data near the ocean drilling program odp sites 889 890 consists of a high velocity zone above the bsr and a thin low velocity layer below in agreement with the odp downhole velocity data

growth of borehole breakouts with time after drilling implications for state of stress nantroseize transect sw japan resistivity at the bit tools typically provide images of wellbore breakouts only a few minutes after the hole is drilled in certain cases images are taken tens of minutes to days after drilling of the borehole the sonic caliper can also image borehole geometry we present four examples comparing imaging a few minutes after drilling to imaging from about 30 min to 3 days after drilling in all cases the borehole breakouts widen with time the tendency to widen with time is most pronounced within a few hundred meters below the seafloor mbsf but may occur at depths greater than 600 mbsf in one example the widening may be due to reduced borehole fluid pressure that would enhance borehole failure in the three other cases significant decreases in fluid pressure during temporal evolution of breakouts are unlikely the latter examples may be explained by time dependent failure of porous sediments that are in an overconsolidated state due to drilling of the borehole this time dependent failure could be a consequence of dilational deformation decrease of pore fluid pressure and maintenance of sediment strength until migrating pore fluids weaken shear surfaces and allow spallation into the borehole breakout orientations and thus estimates of stress orientations remain consistent during widening in all four cases in vertical boreholes breakouts wider than those initially estimated by resistivity imaging would result in higher estimates of horizontal stress magnitudes because the vertical overburden stress is fixed higher estimated horizontal stresses would favor strike slip or thrust faulting over normal faulting

changes in paleostress state along a subduction zone preserved in an on land accretionary complex the yokonami melange in the cretaceous shimanto belt kochi southwest japan a change in paleostress along a subduction zone plate interface in the shallow portion of a seismogenic zone was detected in an on land accretionary complex the yokonami melange in southwest japan using the microfault inversion method microfaults were classified into two groups based on location those occurring throughout the yokonami melange and those occurring in the goshikinohama fault zone which is considered to be a fossil seismogenic fault and is located at the northern end of the yokonami melange stresses obtained for these classified microfaults indicate that two different stress states exist for each deformation feature one is subhorizontal 1 and subvertical 3 with a smaller stress ratio and the other is subvertical 1 and subhorizontal 3 with a larger stress ratio the difference between these stress states could be related to the horizontal stress change by stress drop after large earthquakes that were recently observed after the tohoku oki great earthquake

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

intraslab stresses in the cascadia subduction zone from inversion of earthquake focal mechanisms at the cascadia subduction zone intraslab earthquakes occur mostly in the northern part of the margin and its southern end the mendocino triple junction mtj we determine intraslab stress orientations by inverting earthquake focal me chanisms and develop working hypotheses to explain the inferred intraslab stresses and observed seismicity our inversion results show that the subducting juan de fuca jdf slab in northern cascadia is primarily under compression normal to the slab surface and tension in the downdip direction most likely controlled by the net slab pull an exception is a northernmost shallow region near the nootka fault zone where the state of stress is dominated by nearly east west tension we hypothesize that the shear force on the nootka fault zone and margin parallel mantle resistance to slab motion induce the east west tension in this region near the mtj stresses in the jdf plate are dominated by north south compression down to about 20 km depth consistent with a strong push by the pacific plate from south of the mendocino trans form fault but the deeper part of the slab shows downdip tension similar to northern cascadia deviatoric stresses in the jdf slab appear to be very low resulting in very low intraslab seismicity in comparison with northern cascadia the stresses in most of southern cascadia are even lower resulting in nearly no intraslab seismicity

in situ stress magnitudes at the toe of the nankai trough accretionary prism offshore shikoku island japan quantifying the orientation and magnitude of tectonic stresses is essential toward understanding deformation and faulting in subduction zones however constraints on in situ horizontal stress magnitudes shmin and shmax are rare we estimate shmin and shmax at ocean drilling program site 808 at the toe of the nankai accretionary prism offshore japan using coupled constraints from 1 the width of wellbore breakouts together with estimates of rock strength and a model describing stress redistribution at the borehole wall and 2 limits on regional differential stress defined by failure on preexisting faults our analysis extends from 175 to 915 m below seafloor mbsf and spans the active frontal thrust for an upper bound on rock unconfined compressive strength ucs and assuming hydrostatic formation pore pressure shmin and shmax referenced to the seafloor increase from 6 5 mpa at 175 mbsf to 17 4 mpa at 915 mbsf with the stress state gradually transitioning from a thrust or strike slip faulting regime above 800 mbsf to a normal faulting regime below for cases with higher formation pore pressure horizontal stresses are slightly lower but follow a similar pattern we show that estimated shmin and shmax are strongly dependent on ucs breakout width and friction coefficient all of which are characterized by uncertainty our results suggest that the prism is near thrust failure in the upper 300 mbsf but far from failure below this may be reconciled with active thrusting if thrust faults are locally weaker than the surrounding rock or if shmax fluctuates during the seismic cycle

evaluation of factors controlling earthquake induced landslides caused by chi chi earthquake and comparison with the northridge and loma prieta events over 10 000 landslides were triggered by the september 21 1999 chi chi earthquake a large number of these landslides have been mapped from spot images and a smaller number were described in a detailed field investigation geographic information systems gis was used to conduct a spatial characterization of the slope failures including distribution of type size slope angle bedrock geology ground motion and distance from earthquake source the most abundant landslides were shallow disaggregated rock and soil slides landslides occurred primarily in tertiary sedimentary rocks which are well known for their susceptibility to landsliding in many parts of the world landslide concentration values diminish beyond epicentral distances of 40 and 70 km from the epicenter and the surface projection of the fault plane respectively ground motion was found to be the most significant factor in triggering the shallow landslides in the chi chi earthquake overall 74 of all slope failures occurred in regions with vertical ground motions greater than 0 2g and 81 of all slope failures occurred in the region with mean horizontal peak ground accelerations pga greater than 0 15g these factors were used to compare landslides generated by the chi chi earthquake to the landslides triggered by the 1989 loma prieta earthquake and the 1994 northridge earthquake the major difference in distribution of landslides between the chi chi earthquake and the two california earthquakes was the distribution of slope angles in the chi chi earthquake 90 of the failures occurred on slopes steeper than 45 while more than 80 of failures occurred on slopes less than 50 in california apparently reflecting much steeper and tectonically more active geologic setting in taiwan

experimental and numerical investigations of the seismic response of a rock soil mixture deposit slope inertial instability induced slope failure is one of the most destructive seismic hazards encountered in china depositional slopes are widely distributed across the south western part of china to study the seismic performance of rock soil mixture deposit rsmd slopes in detail physical and mechanical tests of air dried rsmd and a 1 50 geometric scale generalised rsmd slope centrifugal shaking table modelling tests were conducted the acceleration response slope deformation and instability mode of the air dried rsmd slope under the continuous action of four earthquakes with different intensities are analysed besides the dynamic finite difference numerical simulations were performed with flac to simulate the centrifuge model test the numerical simulation results were compared with the test results in terms of the horizontal acceleration response time history of crest settlements and the slope failure characteristics the results show that the horizontal peak ground acceleration pga amplification factors of the rsmd slope reflect typical elevation and surface amplification effects in addition the spectral distribution of the seismic wave has changed significantly with propagation along the slope elevation the energy of input seismic wave in a frequency range close to the natural frequency of an rsmd slope is significantly amplified during the test it was observed that the failure of an air dried rsmd slope occurred when the pga reached 0 216 g and the settlement at the crest of the slope was obvious the failure mode was dominated by shallow collapse

principal horizontal stress orientations prior to the 2011 mw 9 0 tohoku oki japan earthquake in its source area 1 we determined principal horizontal stress orientations as of 1999 at sites in the source area of the 2011 mw 9 0 tohoku oki earthquake on the deep sea terrace of the japan trench the maximum principal horizontal stress orientation at site 1151 of ocean drilling program leg 186 located in an aseismic zone was east southeast parallel with the plate convergence direction and the stress orientation at site 1150 of leg 186 in a seismically active zone was south southeast suggestive of a local stress feature due to the influence of seismic activity aftershocks with normal faulting mechanisms observed in the hanging wall of the plate interface that ruptured during the tohoku oki earthquake indicate a normal faulting postseismic stress regime which clearly differs from the stress state prior to the earthquake consequently the stress state may have changed from a reverse to a normal faulting stress regime during the tohoku oki earthquake sequence

frontal ridge slope failure at the northern cascadia margin margin normal fault and gas hydrate control on the northern cascadia accretionary margin off vancouver island canada there are numerous sedimentary slide features near the base of the slope and significant amounts of gas hydrate found beneath the ridge suggest a possible connection a 2 km wide collapse structure with a 300 m high headwall has been studied by multibeam bathymetry and a single channel seismic reflection grid migrated seismic reflection lines on the frontal ridge image multiple 15 75 m high seafloor scarps perpendicular to the margin that are the seafloor expressions of normal faults that cut deeply into the sediment section two of the largest faults are aligned with the sidewalls of the slide indicating that the lateral extent of the collapse is fault controlled the presence of marine gas hydrate beneath the ridge is based on a widespread hydrate bottom simulating reflector bsr high velocities determined by ocean bottom seismograph data and sediment core samples and downhole logs collected by the integrated ocean drilling program at site u1326 the depth of the bsr at 255 15 m coincides closely with the estimated depth of the glide plane beneath the slide this suggests that the base of the slope failure is related to the contrast between strong hydrate cemented sediments above the bsr and underlying weak sediments containing free gas strong earthquake shaking on this convergent margin likely provides the trigger for the slide

the great sumatra andaman earthquake of 26 december 2004 the two largest earthquakes of the past 40 years ruptured a 1600 kilometer long portion of the fault boundary between the indo australian and southeastern eurasian plates on 26 december 2004 seismic moment magnitude mw 9 1 to 9 3 and 28 march 2005 mw 8 6 the first event generated a tsunami that caused more than 283 000 deaths fault slip of up to 15 meters occurred near banda aceh sumatra but to the north along the nicobar and andaman islands rapid slip was much smaller tsunami and geodetic observations indicate that additional slow slip occurred in the north over a time scale of 50 minutes or longer

accretionary prisms in subduction earthquake cycles the theory of dynamic coulomb wedge 1 we expand the theory of critically tapered coulomb wedge for accretionary prisms by considering stress changes in subduction earthquake cycles building on the coulomb plasticity of the classical theory we assume an elastic perfectly coulomb plastic rheology and derive exact stress solutions for stable and critical wedges the new theory postulates that the actively deforming most seaward part of an accretionary prism the outer wedge overlies the updip velocity strengthening part of the subduction fault and the less deformed inner wedge overlies the velocity weakening part the seismogenic zone during great earthquakes the outer wedge is pushed into a compressively critical state with an increase in basal and internal stresses and pore fluid pressure after the earthquake the outer wedge returns to a stable state the outer wedge geometry is controlled by the peak stress of the updip velocity strengthening part of the subduction fault achieved in largest earthquakes the inner wedge generally stays in the stable regime throughout earthquake cycles acting as an apparent backstop and providing a stable environment for the formation of forearc basins the new theory has important implications for the studies of the updip limit of the seismogenic zone the evolution of accretionary prisms and forearc basins activation of splay faults and tsunami generation evolution of the fluid regime and mechanics of frontal prisms at margins dominated by tectonic erosion

geological and geomorphological characteristics of landslides triggered by the 2004 mid niigta prefecture earthquake in japan abstract the 2004 mid niigta prefecture earthquake mjma 6 8 triggered more than one thousand landslides in the miocene to quaternary sedimentary rocks in japan the most common landslides were shallow disrupted landslides on steep slopes which has been common in many previous disastrous earthquakes in the world the mid niigta prefecture earthquake also triggered more than one hundred deep landslides providing valuable information on the conditions for their occurrence a field investigation and the interpretation of aerial photographs taken before and after the earthquake suggest that reactivation of existing landslides and undercutting of slopes are the most important factors for deep landslides to be triggered by earthquakes in addition planar sliding surfaces seem to be essential for the generation of catastrophic landslides triggered by this earthquake planar bedding parallel sliding surfaces were formed at the boundary between the overlying permeable sandstone and underlying siltstone or along the bedding planes of alternating beds of sandstone and siltstone sliding surfaces along the slope parallel oxidation front were formed in the area of black mudstone new landslides rockslide avalanches occurred with the sliding surfaces in a several cm thick tuff interbedded in siltstone one rockslide avalanche occurred on a slope where buckling deformation preceded the earthquake gentle valley bottom sediments were mobilized in many locations probably because they were saturated and partial liquefaction had occurred due to the earthquake shaking

accretion and recent deformation of sediments along the northern cascadia subduction zone new multichannel seismic reflection profiles acoustic imagery and swath bathymetric data from the vancouver island continental margin reveal the surface morphology cross sectional geometry and deformation style of this part of the cascadia accretionary prism the incoming 3 to 5 km thick sediment section fails most commonly along landward dipping thrusts that penetrate to or very close to the top of the underlying oceanic crust the faults are listric with approximately circular cross sections and hanging wall sediments are back tilted in a planar manner high near lithostatic pore pressures in the deeper part of the section are inferred from the flattening of the faults near the decollement and from the long distances over which the decollement has propagated seaward the faults dip more steeply at 40 45 near the surface where pleistocene turbidites are displaced similar folds have developed where the turbidites are particularly thick 4 km and near hydrostatic pore pressures are inferred to occur in the turbidite part of the section an increase in pore pressure with depth is expected as a consequence of sedimentation and tectonic loading particularly because the deeper hemipelagic sediments are probably far less permeable than are the overlying turbidites the top of the downgoing juan de fuca plate which defines the base of the accreted sedimentary wedge beneath the margin is well imaged in the new seismic reflection profiles and is further defined by land reflection data seismic refraction and earthquake hypocenters the landward dipping continental backstop to the prism is also well located if these constraints are used for the geometry of the accretionary prism a general balance is found between the present prism volume and the estimated total sediment supply over the approximately 42 m y accretion history this result along with the observation that deformation front faults penetrate most or all of the sediment section suggests that little or no sediment has been subducted since initiation of the present phase of subduction in the eocene application of the critically tapered wedge model of davis and others to the observed prism geometry suggests that high average pore pressures occur in the prism particularly the seawardmost part beneath the lower slope beneath the continental shelf the dip of the subducting slab increases to greater than 11 a dip that according to the critically tapered wedge model is too steep to allow upward growth of an accretionary prism this provides a simple explanation for ongoing subsidence of the tofino sedimentary basin over the older part of the accretionary complex to the southeast the juan de fuca plate dips much more gently beneath the olympic peninsula of northern washington allowing the accretionary prism to grow upward well above sea level to form the olympic mountains

effects of frictional behavior and geometry of subduction fault on coseismic seafloor deformation abstract the seismogenic zone of subduction faults appears to have an updip limit seaward of which the fault exhibits velocity strengthening behavior we use a two dimensional finite element model including a frictional subduction fault to explore how coseismic strengthening of the updip segment affects seafloor deformation for a stress drop of a few mpa along the seismogenic zone strengthening of the updip segment by a comparable amount can prevent the rupture from breaking the trench the resultant seafloor uplift is much larger than that predicted by a model of equal seismic moment or maximum fault slip in which the seismogenic zone extends to the trench with a curved fault geometry although a lower degree of coseismic strengthening of the updip segment leads to greater slip in the shallowest part of the fault it produces smaller seafloor uplift contrary to a popular belief given the paucity of direct observations of the coseismic behavior of the updip segment the models yield important information for understanding rupture mechanics of subduction faults and tsunami generation we also illustrate how the results may be used to guide fault slip parameterization in analytical dislocation models

independent active microplate tectonics of northeast asia from gps velocities and block modeling 1 independent okhotsk and amurian microplate motions are tested using velocities from 123 gps sites 80 from within the proposed okh and amu plate boundaries used to constrain the plate kinematics of northeast asia a block modeling approach is used to incorporate both rigid block rotation and near boundary elastic strain accumulation effects in a formal inversion of the gps velocities models include scenarios with and without independent okh and amu plate motion our modeling favors scenarios with independent okh and amu motion based on the application of f test statistics the independent okh plate rotates 0 231 deg myr clockwise with respect to north america about a pole located north of sakhalin the modeled amu plate rotates 0 298 deg myr counterclockwise with respect to nam about a pole located west of the magadan region the plate motion parameters of the independent plates are consistent with the kinematics inferred from earthquake focal mechanism solutions along their boundaries

slipstream an early holocene slump and turbidite record from the frontal ridge of the cascadia accretionary wedge off western canada and paleoseismic implications slipstream slump a well preserved 3 km wide sedimentary failure from the frontal ridge of the cascadia accretionary wedge 85 km off vancouver island canada was sampled during canadian coast guar

case for very low coupling stress on the cascadia ssubduction fault a fundamental problem in plate tectonics is the shear strength of major plate boundary faults this translates to the question whether the generally observed small earthquake stress drops of 3 10 mpa on major faults release most of the accumulated stress or only a small fraction of it there is strong evidence that the san andreas fault a major transform plate boundary is weak 20 mpa shear resistance it is not yet clear whether subduction thrust faults are also weak we present two types of evidence from the northern cascadia subduction zone that indicate very low coupling shear stress on that plate interface and hence very low strength of the subduction thrust fault comparable to that estimated for the san andreas fault first the well defined surface heat flow and heat generation allow negligible frictional heating on the plate interface the average shear stress on the fault must thus be very low over a time scale of a few million years second focal mechanism solutions for small crustal earthquakes in the southern vancouver island area indicate that the horizontal stress in the direction of plate convergence has a similar magnitude to the vertical stress this inferred stress state requires the present tectonic stress coupled across the subduction thrust fault to be very low one explanation for the weakness of the fault is the presence of near lithostatic pore fluid pressure in the region of the fault zone for which there is independent evidence the conclusion of a weak subduction thrust fault does not conflict with geodetic observations of contemporary surface deformation which indicate that the fault is currently locked accumulating strain energy toward a future great earthquake the surface deformation responds to the small 20 mpa temporal changes of the stress field associated with the subduction earthquake cycle this transient stress is superimposed on the larger background regional stress field in which the maximum compression is parallel to the margin the weakness of the cascadia subduction thrust fault and the unusual stress state of the forearc region have important implications for earthquake hazards for example a subduction earthquake may induce large strike slip earthquakes in the forearc that affect a large area

effects of beach raking and sand fences on dune dimensions and morphology abstract raking beaches to remove wrack natural and human litter to enhance recreational use and using sand fences to build and stabilize dunes are common practices on developed shores but their effects on the landscape are not well understood managers in avalon nj ceased using sand fences and raking in a portion of beach in 1991 providing the opportunity to evaluate evolution of natural and managed dune systems over a 19 year period topographic and vegetation characteristics were evaluated on 15 transects within 5 sites in a managed area where raking and sand fences are still used and at 15 transects within 5 sites in a naturally evolving unmanaged area raking and deploying fences in the managed area restricted the size of the cross shore zone in which aeolian accretion occurred but resulted in greater dune crest heights than in the unmanaged area crest heights of the foredune in the managed area ranged from 4 45 m to 5 27 m crest heights in the unmanaged area ranged from 3 02 m to 4 27 m dune volume and beach volume were greater on average in the unmanaged area and the dune was wider mean of 72 m versus 40 m and had an additional ridge the unmanaged area had 35 more species and contained a greater percentage of all species encountered in the study area than the managed area 88 compared to 65 more species occurred in the swales than any other of the cross shore habitats and most of these species were observed in the deeper wider swales in the unmanaged area removing wrack from the beach prevents incipient dunes from forming thus reducing the number of dune crests and size of swales that create topographic variability and increase the number and types of habitats for flora and fauna suspension of raking can allow the dunes to build seaward while producing a greater variety and number of habitats but seaward growth does not mean that the height of the dune will increase substantially and fences may be needed to build an initial dune ridge for flood protection thereafter a policy of not raking in specially designated zones would be a good compromise between the need to accommodate nature and beach recreation

horizontal principal stress orientation in the costa rica seismogenesis project crisp transect from borehole breakouts the costa rica seismogenesis project crisp drilled the pacific margin of the middle america trench just north of where the cocos ridge enters the subduction zone resulting in basal erosion of the upper plate here we report the orientations of the maximum horizontal principal stress shmax from borehole breakouts detected by logging while drilling and wireline downhole measurements all shmax directions were estimated in the sediment cover of the margin above the deeper rocks of the deformed margin wedge we observe three overall shmax orientations nne ssw 25 azimuth in the deepest interval drilled at the upper slope site u1379 ene wsw 82 in the rest of site u1379 and in site u1413 also drilled in the upper slope and nnw sse 157 in the mid slope site u1378 our preferred interpretation is that the deepest interval of site u1379 records the stress conditions in the underlying margin wedge as shmax is parallel to the direction of the cocos caribbean plate convergence and of the compressional axes of plate boundary fault earthquakes the variable shmax directions observed elsewhere are likely due to the effect of a network of normal faults that subdivide the sediment cover into a number of independently deforming blocks in addition the observed shmax directions may be influenced by the subducting cocos ridge which acts as an indenter causing oblique deformation and by the transition to seismogenic subduction along the plate boundary fault

remediation and analysis of kinematic behaviour of a roadway landslide in the upper minjiang river southwest china because of terrain geological structure river down incising and human activities the upriver minjiang valley in sichuan province southwest china constitutes a disaster area prone to frequent landslides during the roadway rebuilding periods the xiaozongqu landslide reactivated on the g213 roadway in maoxian district of sichuan province from the september to november in 2002 the landslide sped up reaching a maximum movement rate of 32 mm d the rapid slide seriously threatened the road to stabilize the landslide and eliminate the damage of landslide to the road remedying its damage and monitoring further developments are crucial based on its kinematic behaviour remediation was implemented in two phases from november 2002 to october 2003 systematic monitoring has been carried out since 18 june 2003 to determine kinematic variations of the landslide during the post remediation period and to assess the effects of remediation and the potential of the landslide for further destructive influences on the roadway

in situ stress state in the nankai accretionary wedge estimated from borehole wall failures we constrain the orientations and magnitudes of in situ stress tensors using borehole wall failures borehole breakouts and drilling induced tensile fractures detected in four vertical boreholes c0002 c0001 c0004 and c0006 from nw to se drilled in the nankai accretionary wedge the directions of the maximum horizontal principal stress shmax indicated by the azimuths of borehole wall failures are consistent in individual holes but those in c0002 margin parallel shmax are nearly perpendicular to those in all other holes margin normal shmax constrained stress magnitudes in c0001 and c0002 using logged breakout widths combined with empirical rock strength derived from sonic velocity as well as the presence of the drilling induced tensile fractures suggest that the stress state in the shallow portion of the wedge fore arc basin and slope sediment formations is predominantly in favor of normal faulting and that the stress state in the deeper accretionary prism is in favor of probable strike slip faulting or possible reverse faulting thus the stress regime appears to be divided with depth by the major geological boundaries such as unconformities or thrust faults the margin perpendicular tectonic stress components in the two adjacent sites c0001 and c0002 are different suggesting that tectonic force driven by the plate pushing of the philippine sea plate does not uniformly propagate rather the stress field is inferred to be influenced by additional factors such as local deformation caused by gravitation driven extension in the fore arc and thrusting and bending within individual geologic domains

characteristics and remediation of a landslide complex triggered by the 2008 wenchuan china earthquake case from yingxiu near the earthquake epicenter during the 2008 wenchuan earthquake the river valley from yingxiu to wenchuan experienced numerous landslides and became a prominent area of landslide complexes the present large landslide complex near the earthquake epicenter consisted of laohuzui slide 1 laohuzui slide 2 and douyaping slide the scale geology morphology sliding process and failure mechanism of the landslide complex are analyzed by means of field investigation aerial photograph and stereographic projection technique characteristics of these three slides including seismic response of slope landslide debris damage and potential failure are discussed the convex slope and the upslope of fractured granitic rock at high altitude are highly prone to landsliding under earthquake the high source altitude and long travel path determine grain sizes and the deposit angle of the slide debris the landslide complex completely buries the g213 roadway and dams up the minjiang river in these sections after the earthquake rainfall aftershocks and river erosion may retrigger new failures such as retrogressive slide of weathered fractured rock colluvial landslide debris flow embankment failure and rockfall the following are presented as suggested remedial measures to protect the roadway and stabilize the slope the removing and trenching protective concrete rock blocks against erosion retaining structure rockfall stopping wall rockfall restraining net rock bolt and the planting of vegetation

extension during active collision in thin skinned wedges insights from laboratory experiments the occurrence of strike normal extension in mountain belts undergoing active contraction is not predicted by analytical solutions for the mechanics of purely frictional orogens to test the idea that ductile rocks at depth might allow extensional deformation to occur in otherwise frictional and contractional orogens we have conducted a series of analog experiments with purely frictional and layered frictional ductile rheologies by precisely measuring the horizontal deformation field we have quantitatively confirmed the qualitative observation that analog frictional wedges do not extend this is consistent with published numerical models and is in contrast to purely viscous models that commonly display coeval extension with contraction our modeling also demonstrates that layered frictional ductile models can during active convergence result in discrete extensional normal faulting even when only a relatively thin ductile layer is present the resulting extension though relatively small in magnitude compared to the active contraction can greatly modify the final profile of a convergent orogen and can lead to the formation of a broad plateau between the pro wedge and the retro wedge

analysis of normal fault populations in the kumano forearc basin nankai trough japan 1 multiple orientations and generations of faults from 3 d coherency mapping 1 analyses of normal faults in the kumano forearc basin of the nankai trough reveal multiple normal fault populations in a region generally thought to be under compression most faults have offsets of less than 20 m and dips of 60 70 and show no growth structures indicating that the faults were active for short periods of time the oldest generation of faults is older than 0 9 ma and strikes 50 60 the next oldest faults strike 160 170 are older than 0 44 ma and are related to local uplift along the western edge of the region the youngest faults cut the seafloor shallow faults near the se margin of the basin curve from 100 in the middle of the survey area to 145 at the se corner of the area the pattern of the two youngest fault populations is consistent with the regional stress pattern maximum horizontal stress subparallel to the trench orientations of older fault populations are caused by uplift of the underlying accretionary prism implying that the forearc basin region is not as stable as previously thought reconstruction of displacements on the youngest faults shows that the overall horizontal extension is less than 2 concentrated near the seaward edge of the basin the active normal faults distributed throughout the basin support the idea that the horizontal stress parallel to the plate convergence direction does not reach the critical stress to activate or form thrust faults and produce horizontal shortening within the shallow portion of the inner wedge

impacts of the chi chi earthquake on subsequent rainfall induced landslides in central taiwan abstract the influence of the chi chi earthquake on subsequent rainfall induced landslides was evaluated by comparing the occurrence of landslides in the choushui river watershed through eight spot images that covered the period from 1996 to 2001 the chi chi earthquake not only triggered serious coseismic landslides itself but also extensively disturbed surface strata around the epicentral area after surface strata have been highly disturbed heavy rainfalls in 2000 and 2001 have triggered more landslides than the earthquake itself compared with the data obtained from images before the earthquake it is obvious that the density of rainfall induced landslides increased significantly after the earthquake and the places where landslides occurred changed as well although typhoon herb in 1996 brought more precipitation than typhoon toraji in 2001 only 9 77 km 2 landslides were induced by herb while 48 8 km 2 landslides almost five times larger than those caused by herb were triggered by toraji besides landslides induced by herb were mainly distributed in mid slope areas with slopes of 20 30 after the chi chi earthquake the rainfall induced landslides occurred mainly in places with slopes between 40 and 50

in situ stress state from walkaround vsp anisotropy in the kumano basin southeast of the kii peninsula japan to reveal the stress state within the kumano basin which overlies the nankai accretionary prism we estimated seismic anisotropy from walkaround vertical seismic profiling vsp data recorded at site c0009 during integrated ocean drilling program iodp expedition 319 we obtained the following anisotropic parameters 1 p wave velocity anisotropy derived from azimuthal normal moveout nmo velocity analysis 2 p wave amplitude variation with azimuth and 3 axes of symmetry of s wave splitting azimuthal variations of p wave velocity by ellipsoidal fitting analysis showed that p wave velocity anisotropy within sediments of the kumano basin was 5 both the directions of fast p wave velocity and strong amplitude are aligned with the convergence vector of the philippine sea plate furthermore s wave splitting analysis indicated that s wave polarization axes were parallel to and normal to the direction of plate subduction these results indicate that the maximum horizontal stress at site c0009 in the kumano basin is in the direction of plate subduction the horizontal differential stress estimated from the p wave velocity anisotropy 2 7 5 5 mpa indicates that the maximum horizontal stress is similar in magnitude to or a little higher than the vertical stress

aeolian transport rates across raked and unraked beaches on a developed coast wind characteristics and aeolian transport were measured on a naturally evolving beach and dune and a nearby site where the beach is raked and sand trapping fences are deployed the beaches were composed of moderately well sorted to very well sorted fine to medium sand the backshore at the raked site was wider and the foredune was more densely vegetated and about 1 m higher than at the unraked site wind speeds were monitored using anemometers placed at 1 m elevation and sand transport was monitored using vertical traps during oblique onshore alongshore and offshore winds occurring in march and april 2009 inundation of the low backshore through isolated swash channels prevented formation of a continuously decreasing cross shore moisture gradient the surface of the berm crest was dryer than the backshore making the berm crest the greatest source of offshore losses during offshore winds the lack of storm wrack on the raked beach reduced the potential for sediment accumulation seaward of the dune crest during onshore winds and the higher dune crest reduced wind speeds and sediment transport from the dune to the backshore during offshore winds accretion at wrack seaward of the dune toe on the unraked beach resulted in a wider dune field and higher narrower backshore although fresh wrack is an effective local trap for aeolian transport wrack that becomes buried appears to have little effect as a barrier and can supply dry sand for subsequent transport aeolian transport rates were greater on the narrower but dryer backshore of the unraked site vegetation growth may be necessary to trap sand within zones of buried wrack in order to allow new incipient foredunes to evolve copyright 2010 john wiley sons ltd

analysis of normal fault populations in the kumano forearc basin nankai trough japan 2 principal axes of stress and strain from inversion of fault orientations 1 we use a high resolution 3 d seismic survey to map a population of recent normal faults within the kumano basin of the nankai subduction zone in order to quantify patterns of strain and stress state over the last 0 44 myr we identify distinct fault populations that define three phases of extension phases 1 and 2 comprise nw se striking faults located along the western basin edge and in the northwestern portion of the study area respectively the ne sw striking faults of phase 3 comprise the largest population and extend 20 km landward from the basin s seaward edge phase 2 faults typically terminate within a few reflectors of the seafloor whereas most phase 3 faults form seafloor scarps inversion of the fault populations documents ne sw extension during phases 1 and 2 and nw se extension during phase 3 consistent with both core scale structures and horizontal stress orientations observed at integrated ocean drilling program iodp boreholes slip on phase 3 faults accommodates strain of up to 1 2 concentrated near the basin s seaward edge inversion for a best fit stress tensor yields a subvertical 1 and subhorizontal 2 and 3 for all faulting phases we find that during phase 3 in most portions of the basin 2 3 shmax shmin reflecting widely varying fault strikes this contrasts with distinct shmax and shmin magnitudes inferred from iodp borehole data these observations may be reconciled if the orientation of maximum horizontal stress fluctuates due to variation of subduction parallel compression through the seismic cycle

a seismic landslide susceptibility rating of geologic units based on analysis of characteristics of landslides triggered by the 17 january 1994 northridge california earthquake abstract one of the most significant effects of the 17 january 1994 northridge california earthquake m 6 7 was the triggering of thousands of landslides over a broad area some of these landslides damaged and destroyed homes and other structures blocked roads disrupted pipelines and caused other serious damage analysis of the distribution and characteristics of these landslides is important in understanding what areas may be susceptible to landsliding in future earthquakes we analyzed the frequency distribution and geometries of triggered landslides in the santa susana 7 5 quadrangle an area of intense seismic landslide activity near the earthquake epicenter landslides occurred primarily in young late miocene through pleistocene uncemented or very weakly cemented sediment that has been repeatedly folded faulted and uplifted in the past 1 5 million years the most common types of landslide triggered by the earthquake were highly disrupted shallow falls and slides of rock and debris far less numerous were deeper more coherent slumps and block slides primarily occurring in more cohesive or competent materials the landslides in the santa susana quadrangle were divided into two samples single landslides 1502 and landslide complexes 60 which involved multiple coalescing failures of surficial material we described landslide morphologies by computing simple morphometric parameters area length width aspect ratio slope angle to quantify and rank the relative susceptibility of each geologic unit to seismic landsliding we calculated two indices 1 the susceptibility index which is the ratio given as a percentage of the area covered by landslide sources within a geologic unit to the total outcrop area of that unit and 2 the frequency index given in landslides per square kilometer ls km2 which is the total number of landslides within each geologic unit divided by the outcrop area of that unit susceptibility categories include very high 2 5 landslide area or 30 ls km2 high 1 0 2 5 landslide area or 10 30 ls km2 moderate 0 5 1 0 landslide area or 3 10 ls km2 and low

landslides triggered by the 1949 khait earthquake tajikistan and associated loss of life abstract earthquake triggered landslides are a major geological hazard in central asia in july 1949 the m7 4 khait earthquake triggered many hundreds of landslides in a mountainous region near the southern limit of the tien shan mountains central tajikistan these landslides involved widespread rock slope failure as well as large numbers of flowslides in loess that mantles the steep slopes of the region in the yasman valley hundreds of loess landslides coalesced to form a massive loess flow est vol 245 mm 3 that travelled up to 20 km on a slope of only 2 in an adjacent valley the khait landslide involved transformation of an earthquake triggered rockslide into a very rapid flow by the entrainment of saturated loess into its movement it travelled 7 41 km over a vertical distance of 1421 m with an estimated average velocity of 30 m s we estimate its volume as 75 mm 3 an order of magnitude less that previously published estimates the khait landslide was simulated using dan the number of casualties due to earthquake triggered landslides in the epicentral region was considerable approximately 4000 people were killed in the yasman valley loess flow as 20 villages kishlaks were overwhelmed in the khait landslide alone we estimate ca 800 people lost their lives when the villages of khait and khisorak were overrun by rapidly moving debris our data indicates that a total of approximately 7200 people were killed by earthquake triggered landslides in the epicentral region of the khait earthquake and that in terms of loss of life the 1949 yasman valley loess flow was one of the most destructive landslides in recent history

landslides induced by the 2008 wenchuan earthquake sichuan china the 2008 wenchuan earthquake with a magnitude of mw 7 9 induced numerous slope movements on the hanging walls of fault surface ruptures and on steep inner valleys along the minjiang river landslide moving directions showed preferred orientations normal to the fault ruptures indicating the effect of the directivity of the seismic wave the most common landslides were of carbonate rocks which are easily dissolved and decrease the contact surfaces the largest non volcanic landslide in history was induced in bedded dolomite by the earthquake and was preceded by gravitational deformation with ridge top depressions valley fill materials were mobilized at 36 locations probably by pore water pressure build up

distribution of stress state in the nankai subduction zone southwest japan and a comparison with japan trench to better understand the distribution of three dimensional stress states in the nankai subduction zone southwest japan we review various stress related investigations carried out in the first and second stage expeditions of the nankai trough seismogenic zone experiment nantroseize by the integrated ocean drilling program iodp and compile the stress data overall the maximum principal stress 1 in the shallower levels 1 km below seafloor or in underlying accretionary prism with 1 becoming horizontal is also suggested at all deeper drilling sites we also make a comparison of the stress state in the hanging wall of the frontal plate interface between site c0006 in the nankai and site c0019 in the japan trench subduction zone drilled after the 2011 mw 9 0 tohoku oki earthquake in the japan trench a comparison between stress state before and after the 2011 mega earthquake shows that the stress changed from compression before the earthquake to extension after the earthquake as a result of the comparison between the nankai trough and japan trench a similar current stress state with trench parallel extension was recognized at both c0006 and c0019 sites hypothetically this may indicate that in nankai trough it is still in an early stage of the interseismic cycle of a great earthquake which occurs on the decollement and propagates to the toe around site c0006

present day principal horizontal stress orientations in the kumano forearc basin of the southwest japan subduction zone determined from iodp nantroseize drilling site c0009 a 1 6 km riser borehole was drilled at site c0009 of the nantroseize in the center of the kumano forearc basin as a landward extension of previous drilling in the southwest japan nankai subduction zone we determined principal horizontal stress orientations from analyses of borehole breakouts and drilling induced tensile fractures by using wireline logging formation microresistivity images and caliper data the maximum horizontal stress orientation at c0009 is approximately parallel to the convergence vector between the philippine sea plate and japan showing a slight difference with the stress orientation which is perpendicular to the plate boundary at previous nantroseize sites c0001 c0004 and c0006 but orthogonal to the stress orientation at site c0002 which is also in the kumano forearc basin these data show that horizontal stress orientations are not uniform in the forearc basin within the surveyed depth range and suggest that oblique plate motion is being partitioned into strike slip and thrusting in addition the stress orientations at site c0009 rotate clockwise from basin sediments into the underlying accretionary prism

possible strain partitioning structure between the kumano fore arc basin and the slope of the nankai trough accretionary prism 1 a 12 km wide 56 km long three dimensional 3 d seismic volume acquired over the nankai trough offshore the kii peninsula japan images the accretionary prism fore arc basin and subducting philippine sea plate we have analyzed an unusual trench parallel depression a notch along the seaward edge of the fore arc kumano basin just landward of the megasplay fault system this bathymetric feature varies along strike from a single steep walled 3 5 km wide notch in the northeast to a broader 5 km wide zone with several shallower linear depressions in the southwest below the notch we found both vertical faults and faults which dip toward the central axis of the depression dipping faults appear to have normal offset consistent with the extension required to form a bathymetric low some of these dipping faults may join the central vertical fault s at depth creating apparent flower structures offset on the vertical faults is difficult to determine but the along strike geometry of these faults makes predominantly normal or thrust motion unlikely we conclude therefore that the notch feature is the bathymetric expression of a transtensional fault system by considering only the along strike variability of the megasplay fault we could not explain a transform feature at the scale of the notch strike slip faulting at the seaward edge of fore arc basins is also observed in sumatra and is there attributed to strain partitioning due to oblique convergence the wedge and decollement strength variations which control the location of the fore arc basins may therefore play a role in the position where an along strike component of strain is localized while the obliquity of convergence in the nankai trough is comparatively small 15 we believe it generated the kumano basin edge fault zone which has implications for interpreting local measured stress orientations and suggests potential locations for strain partitioning related deformation in other subduction zones

the 26 december 2004 sumatra tsunami analysis of tide gauge data from the world ocean part 1 indian ocean and south africa the m w 9 3 megathrust earthquake of december 26 2004 off the northwest coast of sumatra in the indian ocean generated a catastrophic tsunami that was recorded by a large number of tide gauges throughout the world ocean part 1 of our study of this event examines tide gauge measurements from the indian ocean region at sites located from a few hundred to several thousand kilometers from the source area statistical characteristics of the tsunami waves including wave height duration and arrival time are determined along with spectral properties of the tsunami records

stress state in the largest displacement area of the 2011 tohoku oki earthquake the 2011 moment magnitude 9 0 tohoku oki earthquake produced a maximum coseismic slip of more than 50 meters near the japan trench which could result in a completely reduced stress state in the region we tested this hypothesis by determining the in situ stress state of the frontal prism from boreholes drilled by the integrated ocean drilling program approximately 1 year after the earthquake and by inferring the pre earthquake stress state on the basis of the horizontal stress orientations and magnitudes estimated from borehole breakouts and the increase in coseismic displacement during propagation of the rupture to the trench axis in situ horizontal stress decreased during the earthquake the stress change suggests an active slip of the frontal plate interface which is consistent with coseismic fault weakening and a nearly total stress drop

seismic investigations of a vent field associated with gas hydrates offshore vancouver island 1 a three dimensional seismic reflection survey was carried out over a gas hydrate field offshore vancouver island in the area of ocean drilling program leg 146 site 889 890 the area of investigation is located on the accretionary prism of the cascadia margin in water depths of 1200 1500 m several seismic blank zones were observed in the seismic data over a frequency range from 30 hz to 3 5 khz where the degree of blanking increases with seismic frequency time slices and selected horizon slices were used to define the spatial distribution of the blank zones the zones range from 80 m to several hundred meters in width one blank zone almost circular with a diameter of 400 m has a distinct seafloor expression it shows the characteristics of a mud carbonate mound and is probably associated with free gas expulsion hydrate was found at four sites with a piston corer within this blank zone at depths of 3 8 m below the seafloor we present a tectonic model that explains the blank zones to be a result of differential uplift along thrust faults the blank zones represent conduits for fluids and gas migrating upward blanking of the seismic energy is believed to be mainly the result of increased hydrate formation in lenses within the faults the blanking effect is enhanced locally because of scattering at carbonates formed at the seafloor

stress state estimation by geophysical logs in nantroseize expedition 319 site c0009 kumano basin southwest japan 1 to understand the stress regime in the shallow portion of the nankai trough seismogenic zone we carefully investigated the resistivity image logs at iodp site c0009 that penetrated to 1600 meters below the sea floor mbsf in the central kumano forearc basin during the riser drilling several downhole measurements were run including image logs caliper and comprehensive geophysical logs sets borehole resistivity images obtained by a wireline logging tool were reprocessed in order to eliminate image artifacts generated by sticky tool movements etc the constraints on the possible magnitude and orientation of horizontal principal stresses are provided from the borehole images rock strength and logging data the absence of borehole breakouts above 1285 mbsf represents a small difference shmin

emplacement of the longmen shan thrust nappe belt along the eastern margin of the tibetan plateau abstract the topographic descent from the eastern margin of the tibetan plateau to the sichuan basin passes through the longmen shan thrust nappe belt which is sub divided by six nw dipping major listric thrusts with accompanying duplexes and imbricate fans into five large scale nappes each nappe has its own stratigraphic and deformational features in the inner longmen shan longmen mountains allochthonous nappe units have incorporated both mesoproterozoic basement and sinian neoproterozoic to triassic cover sequences as thick skinned horses whereas in the frontal longmen shan sinian cretaceous cover sediments have been stripped from the basement as thin skinned fold and thrust sheets including the extensively distributed klippen structures pre thrusting extension during devonian to middle late triassic times resulted in syn depositional normal faults structural inversion of these faults initiated the peng xian guan xian basement complex jiuding shan and tangwangzhai nappes during the early episode of the indosinian orogeny norian to rhaetian this was followed by episodic thrusting during latest triassic to early cretaceous times to develop the guan xian an xian and southeastern marginal nappes that have incorporated sediments from the neighbouring foreland basin into the frontal part of the thrust nappe belt during a late miocene reactivation of the pre existing thrusts differential thrusting occurred across the thrust nappe belt

statistical analysis of an earthquake induced landslide distribution the 1989 loma prieta california event the 1989 loma prieta california earthquake moment magnitude m 6 9 generated landslides throughout an area of about 15 000 km2 in central california most of these landslides occurred in an area of about 2000 km2 in the mountainous terrain around the epicenter where they were mapped during field investigations immediately following the earthquake the distribution of these landslides is investigated statistically using regression and one way analysis of variance anova techniques to determine how the occurrence of landslides correlates with distance from the earthquake source slope steepness and rock type the landslide concentration defined as the number of landslide sources per unit area has a strong inverse correlation with distance from the earthquake source and a strong positive correlation with slope steepness the landslide concentration differs substantially among the various geologic units in the area the differences correlate to some degree with differences in lithology and degree of induration but this correlation is less clear suggesting a more complex relationship between landslide occurrence and rock properties

a mechanism for the formation of methane hydrate and seafloor bottom simulating reflectors by vertical fluid expulsion bottom simulating reflectors bsr are observed commonly at a depth of several hundred meters below the seafloor in continental margin sedimentary sections that have undergone recent tectonic consolidation or rapid accumulation they are believed to correspond to the deepest level at which methane hydrate clathrate is stable we present a model in which bsr hydrate layers are formed through the removal of methane from upward moving pore fluids as they pass into the hydrate stability field in this model most of the methane is generated below the level of hydrate stability but not at depths sufficient for significant thermogenic production the methane is primarily biogenic in origin the model requires either a mechanism to remove dissolved methane from the pore fluids or disseminated free gas carried upward with the pore fluid the model accounts for the evidence that the hydrate is concentrated in a layer at the base of the stability field for the source of the large amount of methane contained in the hydrate and for bsrs being common only in special environments strong upward fluid expulsion into the hydrate stability field does not occur in normal sediment depositional regimes so bsrs are uncommon upward fluid expulsion does occur as a result of tectonic thickening and loading in subduction zone accretionary wedges and in areas where rapid deposition results in initial undercconsolidation in these areas hydrate bsrs are common the most poorly quantified aspect of the model is the efficiency with which methane is removed and hydrate is formed as pore fluids pass into the hydrate stability field the critical boundary in the phase diagram between the fluid plus hydrate and fluid only fields is not well constrained however the amount of methane required to form the hydrate and limited data on methane concentrations in pore fluids from deep sea boreholes suggest very efficient removal of methane from rising fluid that may contain less than the amount required for free gas production in most fluid expulsion regimes the quantity of fluid moved upward to the seafloor is great enough to continually remove the excess chloride and the residue of isotope fractionation resulting from hydrate formation thus as observed in borehole data there are no large chloride or isotope anomalies remaining in the local pore fluids the differences in the concentration of methane and probably of co2 in the pore fluid above and below the base of the stability field may have a significant influence on early sediment diagenetic reactions

splay fault slip in a subduction margin a new model of evolution in subduction zones major thrusts called splay faults are thought to slip coseismically during large earthquakes affecting the main plate interface we propose an analytical condition for the activation of a splay fault based on force balance calculations and suggest thrusting along the splay fault is generally conditioned by the growth of the accretionary wedge or by the erosion of the hanging wall in theory normal slip on the splay fault may occur when the decollement has a very low friction coefficient seaward such a low friction also implies an unstable extensional state within the outer wedge finite element elasto plastic calculations with a geometry based on the nankai kumano section were performed and confirm that this analytical condition is a valid approximation furthermore localized extension at a shallow level in the splay hanging wall is observed in models for a wide range of friction coefficients from 0 to the value of internal friction coefficient of the rock here equals to 0 4 the timing of slip established for the splay fault branch drilled on nankai kumano transect suggests a phase of concurrent splay and accretionary wedge growth 2 ma to 1 5 ma followed by a locking of the splay 1 3 ma active extension is observed in the hanging wall this evolution can be explained by the activation of a deeper and weaker decollement followed by an interruption of accretion activation of a splay as a normal fault as hypothesized in the case of the tohoku 2011 earthquake can be achieved only if the friction coefficient on the decollement drops to near zero we conclude that the tectonic stress state largely determines long term variations of tightly related splay fault and outer decollement activity and thus influences where and how coseismic rupture ends but that occurrence of normal slip on a splay fault requires coseismic friction reduction

crustal velocity field of southwest japan subduction and arc arc collision we investigate crustal deformation in southwest japan over a 3 year period revealed by a permanent dense global positioning system gps array southwest japan is a part of the amurian plate a microplate moving about 10 mm yr toward the east with respect to the eurasian plate it overrides the philippine sea plate at the nankai trough and collides with the northeast japan arc in the central part of japan in this paper we first derive gps site velocities relative to the stable part of the amurian plate in order to isolate signals of crustal deformation caused by the subduction and or the collision the velocity field has a conspicuous feature indicating the interseismic elastic loading by the philippine sea plate slab at the nankai trough characterized by the northwestward movements of points throughout the studied area their amplitudes are the largest at the pacific coast and decay toward the japan sea coast with a subtle systematic shift of azimuths a model assuming an elastic half space the convergence rate at the nankai trough based on a refined euler vector and the strength of the coupling inferred from a thermal model could explain the velocity field in the western part of the studied area to a large extent those in the eastern part systematically deviate from them and the residual components there show east west shortening and north south extension this may represent crustal thickening and trenchward extrusion of crustal blocks caused by the collision between southwest and northeast japan this suggests that the collision between southwest and northeast japan gives rise to not only crustal thickening but also trenchward extrusion of crustal block a velocity contrast was found across the median tectonic line the largest inland active fault in japan but the current permanent gps network is not dense enough for us to discuss its coupling depth

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

physical properties of hydrate bearing sediments 1 methane gas hydrates crystalline inclusion compounds formed from methane and water are found in marine continental margin and permafrost sediments worldwide this article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate bearing sediments formation phenomena include pore scale habit solubility spatial variability and host sediment aggregate properties physical properties include thermal properties permeability electrical conductivity and permittivity small strain elastic p and s wave velocities shear strength and volume changes resulting from hydrate dissociation the magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate bearing sediments to changes in mechanical thermal or chemical boundary conditions these predictions are vital for mitigating borehole local and regional slope stability hazards optimizing recovery techniques for extracting methane from hydrate bearing sediments or sequestering carbon dioxide in gas hydrate and evaluating the role of gas hydrate in the global carbon cycle

transform push oblique subduction resistance and intraplate stress of the juan de fuca plate the juan de fuca plate is a small oceanic plate between the pacific and north america plates in the southernmost region referred to as the gorda deformation zone the maximum compressive stress 1 constrained by earthquake focal mechanisms is n s off oregon and possibly off washington nw trending left lateral faults cutting the juan de fuca plate indicate a 1 in a ne sw to e w direction the magnitude of differential stress increases from north to south this is inferred from the plastic yielding and distribution of earthquakes throughout the gorda deformation zone to understand how tectonic forces determine the stress field of the juan de fuca plate we have modeled the intraplate stress using both elastic and elastic perfectly plastic plane stress finite element models we conclude that the right lateral shear motion of the pacific and north america plates is primarily responsible for the stress pattern of the juan de fuca plate the most important roles are played by a compressional force normal to the mendocino transform fault a result of the northward push by the pacific plate and a horizontal resistance operating against the northward or margin parallel component of oblique subduction margin parallel subduction resistance results in large n s compression in the gorda deformation zone because the force is integrated over the full length of the cascadia subduction zone the mendocino transform fault serves as a strong buttress that is very weak in shear but capable of transmitting large strike normal compressive stresses internal failure of the gorda deformation zone potentially places limits on the magnitude of the fault normal stresses being transmitted and correspondingly on the magnitude of strike parallel subduction resistance transform faults and oblique subduction zones in other parts of the world can be expected to transmit and create stresses in the same manner

the biomass of macro and interstitial fauna on clean and wrack covered beaches in western australia the benthic faunal spectrum including bacteria protozoans meiofauna wrack epifauna and macrofauna was quantitatively surveyed on two modally reflective moderate energy western australian beaches the more exposed beach had coarser sand no intertidal macrofauna and a poor interstitial fauna the less exposed beach had a large deposit of wrack totalling 161 kg m 1 dry mass concentrated on the lower shore the amphipod allorchestes compressa was abundant in the fresh wrack comprising most of the macrofauna there were also fairly abundant small epifauna on the wrack dry biomass of macrofauna epifauna meiofauna protozoans and bacteria was 0 0 15 4 and 180 g m 1 on the more exposed beach and 160 3 112 9 and 901 g m 1 on the less exposed beach with wrack on the latter beach there was an inverse correlation between meiofaunal densities and the densities of protozoans and bacteria suggesting grazing by the former on the latter on both beaches meiofauna was concentrated in the mid to upper beach protozoans near the surface and bacteria in the mid to lower beach it is estimated that bacteria are responsible for most of the secondary production on both beaches

mechanical characterization of slope sediments constraints on in situ stress and pore pressure near the tip of the megasplay fault in the nankai accretionary complex we performed mechanical tests on mudstone samples cored in the hanging wall of a major out of sequence thrust fault in the nankai accretionary complex prism sw japan 1 to understand the consolidation and shear behaviors of slope sediments that form the fault zone and wall rock of this important structural feature in the upper several kilometers and 2 to constrain in situ stresses and pore pressure two fundamental parameters governing deformation processes in subduction zones which are notoriously difficult to measure we conducted deformation experiments on a suite of samples taken from depths of 20 150 mbsf including six uniaxial consolidation tests and one isotropic consolidation test for three of these tests we conducted undrained triaxial compression testing following consolidation our results suggest that in situ pore pressure is hydrostatic and that during sedimentation and burial the effective horizontal stress is 41 of the effective vertical stress in combination with analysis of wellbore failures documented during drilling of the borehole our experimental data allow us to define the complete stress tensor including the magnitude of in situ minimum and maximum horizontal stresses in the hanging wall of this major fault zone the maximum horizontal stress magnitude is comparable to that expected for sedimentation and uniaxial burial whereas the minimum horizontal stress lies below this value this suggests 1 that the shallow sedimentary section was subjected to extension subparallel to the trench during or following burial and 2 that stresses associated with plate convergence are not effectively transmitted within these shallow sediments

study of a rockfall in a limy conglomerate canyon covarrubias burgos n spain in this paper a rockfall of some tenths of cubic metres of rock occurred in a conglomerate canyon in the northern castilian plateau n central spain is described in detail this includes the basic data geology mapping meteorological data and rock involved the mechanical mechanism of the instability the propagation and reach of the fallen rock boulders and the final location of the pieces the study is based on detailed geological aerial photography and geotechnical studies and advance topographical measurements geological engineering techniques are used to analyze the instability initiation and rockfall propagation this study contributes to a better understanding of the geological processes leading to the occurrence of calcareous canyons and cliffs in the drainage network of the upper castilian plateau it is also helpful to improve our knowledge on natural rockfall phenomena for risk engineering purposes aiming to quantify control and mitigate associated hazards

plate convergence and long term crustal deformation in central japan surveys by continuous global positioning system in and around japan revealed that the amurian plate collides with the north american plate in central japan by 2 cm yr long term crustal deformation seems to be influenced mainly by this collision although subduction of oceanic plates governs short term elastic deformation over the arc here we study the long term deformation field by carefully removing the short term signals inferred from a priori plate convergence vectors and coupling strengths predicted by a thermal model the obtained field shows that the change in velocities occurs along the longitude 135 137 and there exist a relatively rigid block and zones accommodating strains characteristic compressional deformation is found northwest of izu due possibly to the collision of the izu bonin arc with honshu plate convergence rate along the nankai suruga trough is considerably smaller in eastern parts due partly to the transition from the amurian to the north american plate of the landward side and partly to the motion of the izu microplate relative to the philippine sea plate this accounts for longer recurrence intervals of interplate earthquakes in the suruga trough where the tokai earthquake is anticipated to occur

elongate fluid flow structures stress control on gas migration at opouawe bank new zealand highlights elongated fault structures are conduits for focused fluid flow gas migration occurs only along a sub set of faults across opouawe bank stress state deduced from 3d fault structures appears partially stratigraphically controlled abstract high resolution 2d and 3d seismic data from opouawe bank an accretionary ridge on the hikurangi subduction margin off new zealand show evidence for exceptional gas migration pathways linked to the stress regime of the ridge although the ridge has formed by thrusting and folding in response to a sub horizontal principal compressive stress 1 it is clear that local stress conditions related to uplift and extension around the apex of folding i e sub vertical 1 are controlling shallow fluid flow the most conspicuous structural features are parallel and horizontally elongated extensional fractures that are perpendicular to the ridge axis at shallower depth near the seafloor extensional fractures evolve into more concentric structures which ultimately reach the seafloor where they terminate at gas seeps in addition to the ridge perpendicular extensional fractures we also observe both ridge perpendicular and ridge parallel normal faults this indicates that both longitudinal and ridge perpendicular extension have occurred in the past the deepest stratigraphic unit that we image has undergone significant folding and is affected by both sets of normal faults shallower stratigraphic units are less deformed and only host the ridge parallel normal faults indicating that longitudinal extension was limited to an older phase of ridge evolution present day gas migration has exploited the fabric from longitudinal extension at depth as the gas ascends to shallower units it self generates its flow pathways through the more concentric structures near the seafloor this shows that gas migration can evolve from being dependent on inherited tectonic structures at depth to becoming self propagating closer to the seafloor