comparison of smectite and illite rich gouge frictional properties application to the updip limit of the seismogenic zone along subduction megathrusts along plate boundary subduction thrusts the transformation of smectite to illite within fault gouge at temperatures of 150 c is one of the key mineralogical changes thought to control the updip limit of seismicity if correct this hypothesis requires illite rich gouges to exhibit frictionally unstable velocity weakening behavior here we report on laboratory experiments designed to investigate the frictional behavior of natural and synthetic clay rich gouges we sheared 5 mm thick layers of commercially obtained pure ca smectite a suite of smectite quartz mixtures and natural illite shale grain size ranging from 2 to 500 m in the double direct shear geometry to shear strains of 7 30 at room humidity and temperature xrd analyses show that the illite shale contains dominantly clay minerals and quartz within the clay sized fraction 40 mpa our data specifically the velocity strengthening behavior of illite shale under a wide range of conditions do not support the hypothesis that the smectite illite transition is responsible for the seismic aseismic transition in subduction zones we suggest that other depth and temperature dependent processes such as cementation consolidation and slip localization with increased shearing may play an important role in changing the frictional properties of subduction zone faults and that these processes in addition to clay mineralogy should be the focus of future investigation

new insights into deformation and fluid flow processes in the nankai trough accretionary prism results of ocean drilling program leg 190 moore g f taira a klaus a becker l boeckel b cragg b a dean a fergusson c l henry p hirano s hisamitsu t et al 2001 new insights into deformation and fluid flow processes in the nankai trough accretionary prism results of ocean drilling program leg 190 geochemistry geophysics geosystems 2 article no 2001gc000166

scaling of the critical slip distance for seismic faulting with shear strain in fault zones theoretical and experimentally based laws for seismic faulting contain a critical slip distance1 5 dc which is the slip over which strength breaks down during earthquake nucleation on an earthquake generating fault this distance plays a key role in determining the rupture nucleation dimension6 the amount of premonitory and post seismic slip7 10 and the maximum seismic ground acceleration1 11 in laboratory friction experiments d c has been related to the size of surface contact junctions2 5 12 thus the discrepancy between laboratory measurements of dc 10 5m and values obtained from modelling earthquakes 10 2m has been attributed to differences in roughness between laboratory surfaces and natural faults5 this interpretation predicts a dependence of dc on the particle size of fault gouge2 breccia and wear material but not on shear strain here we present experimental results showing that dc scales with shear strain in simulated fault gouge our data suggest a new physical interpretation for the critical slip distance in which dc is controlled by the thickness of the zone of localized shear strain as gouge zones of mature faults are commonly 102 103 m thick12 17 whereas laboratory gouge layers are 1 10 mm thick our data offer an alternative interpretation of the discrepancy between laboratory and field based estimates of dc

impact of the 2008 wenchuan earthquake in china on subsequent long term debris flow activities in the epicentral area abstract the 2008 wenchuan earthquake triggered the largest number of landslides among the recent strong earthquake events around the world the loose landslide materials were retained on steep terrains and deep gullies in the period from 2008 to 2015 numerous debris flows occurred during rainstorms along the provincial road 303 pr303 near the epicentre of the earthquake causing serious damage to the reconstructed highway approximately 5 24 10 6 m 3 of debris flow sediment was deposited shortly after the earthquake this paper evaluates the evolution of the debris flows that occurred after the wenchuan earthquake which helps understand long term landscape evolution and cascading effects in regions impacted by mega earthquakes with the aid of a gis platform combined with field investigations we continuously tracked movements of the loose deposit materials in all the debris flow gullies along an 18 km reach of pr303 and the characteristics of the regional debris flows during several storms in the past seven years this paper presents five important aspects of the evolution of debris flows 1 supply of debris flow materials 2 triggering rainfall 3 initiation mechanisms and types of debris flows 4 runout characteristics and 5 elevated riverbed due to the deposited materials from the debris flows the hillslope soil deposits gradually evolved into channel deposits and the solid materials in the channels moved towards the ravine mouth accordingly channelized debris flows became dominant gradually due to the decreasing source material volume and changes in debris flow characteristics the triggering rainfall tends to increase from 30 mm h 1 in 2008 to 64 mm h 1 in 2013 and the runout distance tends to decrease over time the runout materials blocked the river and elevated the riverbed by at least 30 m in parts of the study area the changes in the post seismic debris flow activity can be categorized into three stages i e active unstable and recession

quantitative analysis of debris flow flexible barrier capacity from momentum and energy perspectives abstract in depth understanding of debris structure interaction is hindered by a lack of physical data of debris flow impacting structures this study reports a set of centrifuge experiments investigating the impact load exerted by debris flow on rigid and flexible barriers a combination of high speed imagery and load displacement sensors enabled a comprehensive grasp of the impact details including flow depth velocity impact pressure bending moment and cable force elongation of flexible barrier test results reveal that the debris structure interaction plays a major role in the energy dissipation and impact load reconstruction the built up of static load behind the barrier occurs simultaneously with the grow up of impact force as a result the momentum flux of incoming flow is not merely a surrogate of the impact force a quantitative analysis from the energy perspective has been conducted under the experimental conditions of this study debris flow impact results in over 90 of debris energy dissipated through the internal and boundary shearing leaving

a new mechanism of slip weakening and strength recovery of friction associated with the mechanical consolidation of gouge i present results of a series of slide hold slide tests on granite surfaces separated by a layer of simulated granite gouge the shear stress during the hold period hold was controlled and used as a major control parameter of the experiments in addition to the time of hold time dependent fault healing which has been observed in many previous similar experiments was observed only at very high hold above 90 of the sliding friction a time independent strengthening termed consolidation strengthening occurred at all hold with a magnitude proportional to the reduction of hold the magnitude of this strengthening was as large as 25 of the residual friction the consolidation strengthening was found to be erased by subsequent slip in quite a different manner than is time dependent healing the friction decreased linearly with slip displacement at a rate independent of the magnitude of the strengthening and hence larger slip displacement is required to erase larger consolidation strengthening on the basis of these results together with earlier authors results of the measurements of porosity change under similar conditions i conclude that the time independent strengthening is due to the occurrence of gouge particle rearrangement to tighter packing enabled by decreased shear stress under a constant normal stress and that the subsequent slip weakening is due to unconsolidation of gouge enabled by particle rearrangement dilatancy during shearing the rate and state dependent friction rsf law was extended to incorporate the present findings

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

a novel dynamic impact pressure model of debris flows and its application on reliability analysis of the rock mass surrounding tunnels abstract assessing the influence of the impact pressure exerted on surrounding rock mass by potential debris flows is one of the challenges in a mountain tunnel construction project this paper proposes an effective mathematical model for the assessment of impact pressure exerted by debris flows on obstacles the characteristics of the new model are analyzed and the parameters determination method for the new model are deduced also a new method for dynamic reliability analysis of the rock mass surrounding tunnels is proposed and is constituted into three key steps first by inputting impact pressure of debris flows generated by the aforementioned new model the flac3d is used as the dynamic analysis engine to obtain the time varying stress distribution of surrounding rock mass during the impact of debris flow second the factor of safety fos contours of surrounding rock mass are generated based on element states using the maximum tensile stress criterion and the mohr coulomb yield criterion third by using the time varying contours of the fos a failure probability and a reliability index are obtained from a reliability perspective a case study shows the complete analysis process and confirms the effectiveness of the above methodology in sum this paper provides new ideas new methods and a reference example for evaluating the influence of dynamic impact exerted by debris flows on the rock mass surrounding tunnels

frictional strength rate dependence and healing in dfdp 1 borehole samples from the alpine fault new zealand abstract the alpine fault in southern new zealand is a major plate boundary fault zone that according to various lines of evidence may be nearing the end of its seismic cycle and approaching earthquake failure in order to better characterize this fault and obtain a better understanding of its seismic potential two pilot boreholes have been completed as part of a larger drilling project samples representative of the major lithologic subdivisions of the fault zone at shallow 100 m depths were recovered and investigated in laboratory friction experiments we show here that materials from within and very near the principal slip zone psz tend to exhibit velocity strengthening frictional behavior and restrengthen heal rapidly compared to samples of the wall rock recovered near the psz fluid saturation causes the psz to be noticeably weaker than the surrounding cataclasites 0 45 and eliminates the velocity weakening behavior in these cataclasites that is observed in dry tests our results indicate that the psz has the ability to regain its strength in a manner required for repeated rupture but its ability to nucleate a seismic event is limited by its velocity strengthening nature we suggest that seismogenic behavior at depth would require alteration of the psz material to become velocity weakening or that earthquake nucleation occurs either within the wall rock or at the interface between the wall rock and the psz coseismic ruptures which propagate to the surface have been inferred for previous earthquakes on the alpine fault and may be facilitated by the slightly weaker psz material and or high rates of healing in the psz which support fault locking and eventual stress drops

frictional properties of sedimentary rocks and natural fault gouge from the longmen shan fault zone sichuan china in this paper we report friction experiments performed on samples collected from the region hit by the 2008 wenchuan earthquake in the longmen shan fault zone lfz of sichuan southwestern china the materials tested consisted of simulated gouges prepared from intact clay rich mudstone and sandstone a calcite limestone plus a natural fault gouge from a trenched surface rupture cutting the mudstone and sandstone the clay rich samples including the natural gouge were dominated by illite and quartz in our experiments we sheared 1 mm thick gouge layers between saw cut driver blocks using a triaxial testing machine at conditions corresponding to 2 km depth in the lfz temperature was varied from 25 c to 150 c and to investigate the velocity dependence of friction we stepped the shear displacement rate between 1 22 and 0 122 m s our results show that the natural gouge was more illite rich and much weaker than the protolith mudstone and sandstone and showed a steady state friction coefficient of 0 4 compared with 0 6 for the latter the limestone gouge displayed values of 0 6 0 7 all samples except the limestone showed stable velocity strengthening slip the limestone showed velocity strengthening at 25 c 50 c but quasi static oscillations at 100 c 150 c along with velocity weakening behavior at 150 c we apply our results to discuss the role of the sedimentary rocks studied during events such as the wenchuan earthquake and argue that the clay rich sediments of the region may have a damping effect upon ruptures propagating from depth whereas the limestone may accelerate propagation producing significant stress drops

elementary theory of bed sediment entrainment by debris flows and avalanches 1 analyses of mass and momentum exchange between a debris flow or avalanche and an underlying sediment layer aid interpretations and predictions of bed sediment entrainment rates a preliminary analysis assesses the behavior of a coulomb slide block that entrains bed material as it descends a uniform slope the analysis demonstrates that the block s momentum can grow unstably even in the presence of limited entrainment efficiency a more detailed depth integrated continuum analysis of interacting deformable bodies identifies mechanical controls on entrainment efficiency and shows that entrainment rates satisfy a jump condition that involves shear traction and velocity discontinuities at the flow bed boundary explicit predictions of the entrainment rateeresult from making reasonable assumptions about flow velocity profiles and boundary shear tractions for coulomb friction tractions predicted entrainment rates are sensitive to pore fluid pressures that develop in bed sediment as it is overridden in the simplest scenario the bed sediment liquefies completely and the entrainment rate equation reduces toe 2 1gh1 cos 1 1 v 1 where is the slope angle 1 is the flow s coulomb friction coefficient h1 is its thickness 1 is its degree of liquefaction and v 1is its depth averaged velocity for values of 1ranging from 0 5 to 0 8 this equation predicts entrainment rates consistent with rates of 0 05 to 0 1 m s measured in large scale debris flow experiments in which wet sediment beds liquefied almost completely the propensity for bed liquefaction depends on several factors including sediment porosity permeability and thickness and rates of compression and shear deformation that occur when beds are overridden

friction on subduction megathrust faults beyond the illite muscovite transition abstract previous experimental studies addressing subduction megathrust friction have focused on shallow fault gouges dominated by smectite illite and quartz here we aim to determine the effect of the transition to muscovite rich fault rock at depths beyond the illite dominated region of the seismogenic zone to achieve this rotary friction experiments were performed on simulated muscovite quartz 65 35 gouge at 100 600 c an effective normal stress of 170 mpa pore pressures of 100 and 200 mpa and sliding velocities of 1 100 m s we isolated the effects of muscovite by shearing pure muscovite gouge at 200 600 c under otherwise identical conditions at low shear strains 1 muscovite quartz gouge showed a friction coefficient of 0 4 0 5 while pure muscovite gouge exhibited 0 3 both gouges showed an increase in with and temperature the muscovite quartz gouge was characterised by velocity strengthening or neutral behaviour at 100 350 c velocity weakening at 350 500 c and velocity strengthening at 500 600 c in contrast pure muscovite gouge showed predominantly velocity strengthening or neutral behaviour demonstrating a key role of quartz in producing velocity weakening the velocity weakening regime in the mixed gouge extends that of 250 400 c recently reported for illite quartz gouge up to 500 c taking into account the observed effect of sliding velocity on a b the data for illite quartz and muscovite quartz together help explain the depth extent of seismogenesis on subduction megathrusts interestingly comparison with previous microphysical models suggests that the mechanism causing velocity weakening in phyllosilicate quartz gouges is one of granular flow involving competition between shear induced dilation and compaction through thermally activated quartz deformation

on the mechanical role of smectite in subduction zones smectites a group of hydrated phyllosilicate minerals are often a main component of sediments entering a subduction zone they are common in hemipelagic sediments and consist of an authigenetic component that arises from the alteration of volcanic ash intercalated in the sediment and a detrital component smectite rich strata are structurally weak retain water and are highly porous a review of sediment lithology in subduction zones around the world suggests that decollement zones may preferentially form in smectite rich horizons one consequence of this observation is that the assignment of high frictional resistance to materials in a decollement may be unwarranted at deeper structural levels smectite is transformed to illite a mechanically stronger mineral estimates of the depth of this transition coincide with the depth at which earthquakes are first detected along plate interfaces i speculate that the smectite illite transition in subduction zones may be an important component of sediment consolidation processes that trigger interplate seismicity

sliding behavior and deformation textures of heated illite gouge abstract the run products of a series of triaxial friction experiments on an illite rich gouge have been examined petrographically to study the relationship between textural development and sliding mode the samples show a complete range of textures from ones in which the entire gouge layer is deformed to ones in which the deformation is concentrated along narrow subsidiary shears and the rest of the gouge layer is massive the samples with a pervasively developed deformation fabric slide stably whereas the samples containing shear bands show stick slip motion if the intersection angles between boundary parallel and cross cutting riedel shears are also relatively high these textural differences suggest that localization of shear combined with higher angle riedel shears are somehow involved in stick slip motion the orientation of riedel type shears in natural fault zones may also have potential as a paleoseismological tool

numerical analysis of dynamics of debris flow over erodible beds in wenchuan earthquake induced area the basal entrainment of debris flows play a significant role in its amplification and the final volume of deposition could be several to hundred times of its initial volume in this paper the shallow water equations coupled with basal material entrainment applied in debris flows have been given to demonstrate the amplification a new basal entrainment model taking advantage of both coulomb and voellmy frictional laws are proposed providing a unified formula to simulate the stop and go process of debris flows both time and space second order maccormack tvd finite difference method is suggested to solve the coupled equations numerical comparisons with usgs flume experiment and hongchun gully debris flow in wenchuan earthquake induced area are carried out to prove its effectiveness it is established that the momentum exchange term between the flows and the basal materials has a significant influence on the dynamic characteristics and the entrainment effects are essential to model the dynamic process of debris flows in an earthquake induced area c 2014 elsevier b v all rights reserved

instability and surge development in debris flows 1 debris flows are often described as a succession of surges which are characterized by enhanced peak depth and velocity and therefore by a tremendous increase of their destructive power for given characteristics of the base flow if the channel is sufficiently long to allow an appreciable wave development the linear stability analysis in shallow streams is shown to provide a reasonable prediction of the critical flow condition and of the instability growth rate the one dimensional 1 d theory however does not allow the determination of the wave period of the fastest growing perturbations debris waves most frequently develop following a mechanism similar to water roll waves instabilities grow up becoming clearly distinguishable waves and then waves overtake one another with increasing wave period and amplitude the typical hydrograph of a multiple peak event is shown to be composed of a first surge which is usually characterized by the highest depth the longest duration the greatest erosive power and the most symmetrical shape and of secondary waves that burst on the flow tail in the recession phase the characteristics of the first surge can be explained by two different mechanisms all waves that rise up near the flood crest run faster than this first surge and coalesce into it causing its high depth and great volume moreover segregation during the flow induces the concentration of boulders at the fronts contributing to its depth enhancement erosive power and symmetrical shape when a debris surge impacts a structure the force pattern can be interpreted as the superposition of the reflection of the bouldery front and the formation of a vertical muddy jet due to the impact of the front wedge wave reflection can be described by a 1 d mass and momentum balance across the front whereas the pressure impulse due to the incompressibility of the interstitial fluid can be analyzed through inviscid formulations validated for the representation of tsunami forces

evaluation of landslide mechanisms characterized by high speed mass ejection and long run out based on events following the wenchuan earthquake abstract in the 2008 wenchuan earthquake the mass ejection type of high speed and long run out landslide was an unusual hazard characterized by its dramatic phenomenon of a huge slope mass launching into the air and becoming airborne for a long distance quantitative and qualitative combined techniques were applied to reveal the formation mechanism of this type of landslide four prerequisites critical to form mass ejection are identified high position of the toe of the surface of rupture critical height and critical inclination of slope sufficient open space in the movement direction and adequate take off speed of ski jump like mass ejection these four area specific prerequisites provide a promising approach for screening and targeting the potential landslides subsequently a dynamic reliability analysis method that considers the feature of energy time distribution is proposed this site specific method provides a more credible evaluation by emphasizing the most significant period within the whole earthquake duration finally an aerodynamic inverse method combined with an energy conservation based method is applied in the quantitative evaluation to calculate take off speed of mass ejection this paper provides a viable solution for regional screening and site assessment for new potential targets of this type of landslide

influence of kinetics on the smectite to illite transition in the barbados accretionary prism low chloride pore fluids observed along faults in clay rich accretionary complexes are commonly attributed to the release of interlayer water during the smectite to illite transformation however to date there has been no thorough analysis of the location and quantity of fluids that may be generated by this mechanism to address this problem a temperature and time dependent rate expression describing the dehydration reaction was coupled to a kinematic model of the northern barbados accretionary complex temperatures in the complex were estimated by modeling heat flow through the prism sediments as they thicken arcward the sediments temperature time histories were computed using a model for the velocities of sediment motion through the complex in this model the prism sediments follow uniformly diverging paths from the toe while the underthrust sediments undergo uniaxial strain the model predictions are validated against clay mineralogy data from barbados island mudstones our results show that the location of the peak dehydration rate is 20 km farther arcward in the underthrust sediments than in the prism complex the fresh water produced by the reaction results in pore waters that are 10 30 fresher at a distance of 50 70 km from the prism toe this constraint indicates a probable fluid migration path of more than 50 km from the reaction zone to the sites where freshened pore fluids have been observed the peak rate of fluid production when expressed as the volume of fluid per volume of sediment per second is 2 l0 15

earthquake rupture propagation inferred from the spatial distribution of fault rock frictional properties abstract the frictional properties of fault rocks that rupture during earthquakes are expected to affect the nucleation and propagation of seismic slip but these properties and their variation under in situ earthquake conditions are typically unknown here we present experimental results on the variation of frictional properties of fault rocks from the alhama de murcia fault amf in se spain which ruptured in the 2011 lorca earthquake in the epicentral area the fault zone is characterized by the presence of abundant phyllosilicate rich gouges that surround more competent fractured lenses of the phyllitic basement measurements of lineaments and orientations of r shears in the gouges are consistent with cmt solutions of the 2011 lorca earthquake suggesting that the bulk of displacement on the amf was accommodated within similar gouges at depth in order to evaluate the frictional properties of the fault rocks of the amf we performed rotary shear experiments under hydrothermal conditions of samples obtained from surface outcrops of the amf zone progressively simulating deeper levels in the crust by stepping temperature effective normal stress and fluid pressure a negative velocity dependence of friction expressed as a negative value of the rate and state friction rsf parameter a b and which is a prerequisite for the nucleation of an instability was observed only for samples derived from competent lenses under hydrothermal conditions gouge derived samples exhibited only velocity strengthening properties i e positive values of a b which increase with deeper conditions in particular with increasing effective normal stress combined with our outcrop observation of the anastomosing nature of gouges surrounding more competent lenses of fractured protolith our results suggest that the 2011 lorca earthquake nucleated in the competent lenses followed by propagation of slip into the frictionally weaker gouges the inferred upward propagation direction of the 2011 lorca earthquake is consistent with propagation of the rupture into the velocity strengthening gouges which at shallower levels provide a smaller barrier to seismic slip due to lower values of effective normal stress and a b our results suggest that the spatial variation of the frictional properties along the amf was an important factor controlling the nucleation and propagation of seismic slip which together with the shallow hypocenter close to the city of lorca led to serious damage we infer that understanding of such variations in frictional properties may significantly improve seismic hazard evaluations in tectonically active regions

assessment of the dynamic stability of the portals of the dorukhan tunnel using numerical analysis abstract instability problems may arise during the construction and operation of tunnels depending on the quality of the rock mass in particular determining instability problems at the portals of a tunnel is of utmost importance during excavation and operation of the tunnel slope instability and rockfalls are the most frequent instability problems that may be encountered at tunnel portals such instability problems can be triggered by dynamic effects such as earthquakes blasting etc this study investigates the stability of the portals of the dorukhan tunnel connecting the provinces of zonguldak and bolu in the close vicinity of the north anatolian fault zone nafz which is a well known strike slip 1500 km long fault the effect of an earthquake that may occur in the nafz on the extent of failure has also been studied by numerical analyses in the analyses a three dimensional dynamic analysis computer code based on the finite difference method has been used according to results of the dynamic numerical analyses the devrek portal was found to be more stable than the mengen portal moreover it was found that for acceleration values of dynamic wave higher than 0 5 g tunnel portal slopes and the areas as far as 20 50 m from the tunnel entrance may suffer serious damage wave propagation perpendicular to the tunnel axis was established to cause more damage around the openings and in the portal slopes as wave compared to propagation parallel to the tunnel axis

positive feedback and momentum growth during debris flow entrainment of wet bed sediment debris flows typically occur when intense rainfall or snowmelt triggers landslides or extensive erosion on steep debris mantled slopes the flows can then grow dramatically in size and speed as they entrain material from their beds and banks but the mechanism of this growth is unclear indeed momentum conservation implies that entrainment of static material should retard the motion of the flows if friction remains unchanged here we use data from large scale experiments to assess the entrainment of bed material by debris flows we find that entrainment is accompanied by increased flow momentum and speed only if large positive pore pressures develop in wet bed sediments as the sediments are overridden by debris flows the increased pore pressure facilitates progressive scour of the bed reduces basal friction and instigates positive feedback that causes flow speed mass and momentum to increase if dryer bed sediment is entrained however the feedback becomes negative and flow momentum declines we infer that analogous feedbacks could operate in other types of gravity driven mass flow that interact with erodible beds the mechanisms by which debris flows acquire mass and momentum as they entrain material are unclear large scale experiments suggest that the pore pressure of wet bed sediment increases as the flow moves over the bed leading to reduced friction and progressive scouring of the base

experimental tests for the application of an analytical model for flexible debris flow barrier design abstract the design of flexible barriers against debris flows is a complex procedure because of the large number of parameters involved in order to face this difficult task the authors have developed a simplified approach the proposed simplified model involves the determination of parameters related to both the mobilized material and the various mechanical portions of the structure a calibration phase is required to appropriately model the deformation of the net and the load transfer that occurs between the net and the horizontal structural cables the determination of the parameters required to set up the analytical model is discussed in the first part of the paper tests carried out to calibrate the transfer function that allows the deformation behavior of the barrier to be reproduced using the analytical model are then reported

depth of seismic coupling along subduction zones underthrusting at subduction zones can cause large earthquakes at shallow depths but it is always accommodated by aseismic deformation below a certain depth the maximum depth of the seismically coupled zone or seismogenic zone is a transition from unstable to stable sliding along the plate interface we have determined the depth of this stability transition for the circurn pacific subduction zones of honshu kuriles kamchatka aleutians alaska mexico and chile these subduction zones have experienced great interplate earthquakes and the aftershock regions are well located depth estimates of interplate events that are located at the downdip edge of the aftershock regions are used to determine the maximum depth of seismic coupling for an average p wave velocity of 6 7 km s 1 above the plate interface we find that for most subduction zones the stability transition occurs at 40 5 km depth there are however several exceptions at the hokkaido trench junction where the japan trench and the kurile trench intersect seismic coupling is deep and extends down to 52 55 km deep coupling was also found in the coquimbo region in central chile the mexico subduction zone has shallow coupling the transition occurs at 20 30 km depth previous studies of micro earthquakes in honshu hokkaido the aleutians and alaska show that earthquakes within the upper plate extend no deeper than the downdip edge of the coupled zone that we find given our measurements of seismic coupling depth we then explore the mechanism that may determine coupling depth the concept of critical temperature has been used to explain the depth of seismic coupling in other tectonic environments thus we first test whether a critical temperature can explain our results temperatures at the plate interface are dependent on many variables but two that are poorly determined are shear stress and radiogenic heat generation shear stress has been constrained by inversion of heat flow data assuming a crustal radiogenic heat production rate of 3 1 exp z 8 5 wm 3 and a constant coefficient of friction we find two critical temperatures of about 400 c and 550 c the lower critical temperature may be characteristic of regions with a relatively thick continental crust and the higher temperature of regions with a relatively thin continental crust on the other hand one single critical temperature of about 250 c can explain the coupling depths if shear stresses are constant with depth

anatomy of a megathrust the 2010 m8 8 maule chile earthquake rupture zone imaged using seismic tomography abstract knowledge of seismic velocities in the seismogenic part of subduction zones can reveal how material properties may influence large ruptures observations of aftershocks that followed the 2010 m w 8 8 maule chile earthquake provide an exceptional dataset to examine the physical properties of a megathrust rupture zone we manually analysed aftershocks from onshore seismic stations and ocean bottom seismometers to derive a 3 d velocity model of the rupture zone using local earthquake tomography from the trench to the magmatic arc our velocity model illuminates the main features within the subduction zone we interpret an east dipping high p wave velocity anomaly 6 9 km s as the subducting oceanic crust and a low p wave velocity we assess the role played by physical heterogeneity in governing megathrust behaviour greatest slip during the maule earthquake occurred in areas of moderate p wave velocity 6 5 7 5 km s where the interface is structurally more uniform at shallow depths high fluid pressure likely influenced the up dip limit of seismic activity the high velocity bodies lie above portions of the plate interface where there was reduced coseismic slip and minimal postseismic activity the northern velocity anomaly may have acted as a structural discontinuity within the forearc influencing the pronounced crustal seismicity in the pichilemu region our work provides evidence for how the ancient geological structure of the forearc may influence the seismic behaviour of subduction megathrusts

the instantaneous rate dependence in low temperature laboratory rock friction and rock deformation experiments 1 earthquake occurrence probabilities that account for stress transfer and time dependent failure depend on the product of the effective normal stress and a lab derived dimensionless coefficient a this coefficient describes the instantaneous dependence of fault strength on deformation rate and determines the duration of precursory slip although an instantaneous rate dependence is observed for fracture friction crack growth and low temperature plasticity in laboratory experiments the physical origin of this effect during earthquake faulting is obscure we examine this rate dependence in laboratory experiments on different rock types using a normalization scheme modified from one proposed by tullis and weeks 1987 we compare the instantaneous rate dependence in rock friction with rate dependence measurements from higher temperature dislocation glide experiments the same normalization scheme is used to compare rate dependence in friction to rock fracture and to low temperature crack growth tests for particular weak phyllosilicate minerals the instantaneous friction rate dependence is consistent with dislocation glide in intact rock failure tests for each rock type considered the instantaneous rate dependence is the same size as for friction suggesting a common physical origin during subcritical crack growth in strong quartzofeldspathic and carbonate rock where glide is not possible the instantaneous rate dependence measured during failure or creep tests at high stress has long been thought to be due to crack growth however direct comparison between crack growth and friction tests shows poor agreement the crack growth rate dependence appears to be higher than the rate dependence of friction and fracture by a factor of two to three for all rock types considered

experimental analysis on the impact force of viscous debris flow a miniaturized flume experiment was carried out to measure impact forces of viscous debris flow the flow depth 7 2 11 2 cm velocity 2 4 5 2 m s and impact force were recorded during the experiment the impact process of debris flow can be divided into three phases by analyzing the variation of impact signals and flow regime the three phases are the sudden strong impact of the debris flow head continuous dynamic pressure of the body and slight static pressure of the tail the variation of impact process is consistent with the change in the flow regime the head has strong rapid impact pressure which is shown as a turbulent type flow the body approximates to steady laminar flow accordingly the process of debris flows hitting structures was simplified to a triangle shape ignoring the pressure of the tail in order to study the distribution of the debris flow impact force at different depths and variation of the impact process over time the impact signals of slurry and coarse particles were separated from the original signals using wavelet analysis the slurry s dynamic pressure signal appears to be a smooth curve and the peak pressure is 12 34 kpa when the debris flow head hits the sensors which is about 1 54 0 36 times the continuous dynamic pressure of the debris flow body the limit of application of the empirical parameter a in the hydraulic formula was also noted we introduced the power function relationship of a and the froude number of debris flows and proposed a universal model for calculating dynamic pressure the impact pressure of large particles has the characteristic of randomness the mean frequency of large particles impacting the sensor is 210 50 287 29 times per second and it is 336 114 490 69 times per second for the debris flow head which is greater than that in the debris flow body peak impact pressure of particles at different flow depths is 40 160 kpa which is 3 2 1 5 times the impact pressure of the slurry at the bottom of the flow 3 1 0 9 times the flow in the middle and 3 3 0 9 times the flow at the surface the differences in impact frequency indicate that most of the large particles concentrate in the debris flow head and the number of particles in the debris flow head increases with height this research supports the study of solid liquid two phase flow mechanisms and helps engineering design and risk assessment in debris flow prone areas c 2015 the authors earth surface proccesses and landforms published by john wiley sons ltd

experimental study on the triggering mechanisms and kinematic properties of large debris flows in wenjia gully debris flows are typically caused by natural terrain landslides triggered by intense rainfalls if an incoming mountain torrent flows along sloping channels at high velocity huge amounts of sediment from landslide dams and eroded channel beds will be entrained into the flows to form debris flows it is likely that large debris flows are due to the failure of many landslide dams of different scales due to bank slides or collapses bed erosion and solid transport the catastrophic debris flows that occurred in wenjia gully wenchuan earthquake area china on august 13 2010 two years after the mega earthquake were caused by intense rainfall and the serious erosion of sloping channels in the wake of the incident experimental tests were conducted to better understand the process of sediment erosion and entrainment on the channel bed and the formation of debris flows the results show that the bed erosion bank collapses and channel widening caused by erosion accounted for the triggering and scale amplification of downstream debris flows in the wenjia gully event this study illustrates how the hazardous process of natural debris flows can begin several kilometers upstream and how such a complex cascade of geomorphic events failure of landslide dams and erosion of the sloping bed can lead to catastrophic discharges neglecting recognition of these hazardous geomorphic and hydrodynamic processes may result in high cost c 2014 elsevier b v all rights reserved

real time measurement and preliminary analysis of debris flow impact force at jiangjia ravine china impact forces associated with major debris flows jiangjia ravine china august 25 2004 were recorded in real time by a system consisting of three strain sensors installed at different flow depths this provides the first real time and long duration record of impact forces associated with debris flows a comprehensive approach including low pass filtering and moving average methods were used to preprocess the recorded signals the upper limit of impact frequency in the debris flows was estimated at 188 66 hz under the assumption that only coarse grains cause effective impact loadings thus a low pass filter with a 200 hz cut off frequency was needed to denoise the original data in order to extract the impact force then the moving average method was applied to separate long term and random components of the filtered data these were interpreted as respectively the fluid pressure and grain impact loading it was found that the peak grain impacts at different depths were non synchronous within the debris flows the impact loadings were far greater than and not proportional to the fluid pressures analysis of the impact force of 38 debris flow surges gives an empirical value for the ratio of the hydrodynamic pressure to the momentum flow density i e the product of debrisflow density and mean velocity square which provides a very valuable basis for understanding debris flow dynamics and designing debris flow management systems copyright c 2011 john wiley sons ltd

coulomb constitutive laws for friction contrasts in frictional behavior for distributed and localized shear we describe slip rate dependent friction laws based on the coulomb failure criteria frictional rate dependence is attributed to a rate dependence of cohesionc and friction angle we show that differences in the stress states developed during sliding result in different coulomb friction laws for distributed shear within a thick gouge layer versus localized shear within a narrow shear band or between bare rock surfaces for shear within gouge shear strength is given by c cos n sin whereas for shear between bare rock surfaces the shear strength is c cos n tan where and n are shear and normal stress respectively in the context of rate dependent coulomb friction laws these differences mean that for a given material and rate dependence of the coulomb parameters pervasive shear may exhibit velocity strengthening frictional behavior while localized shear exhibits velocity weakening behavior we derive from experimental data the slip rate dependence and evolution ofc and for distributed and localized shear the data show a positive rate dependence for distributed shear and a negative rate dependence for localized shear indicating that the rate dependence ofc and are not the same for distributed and localized shear even after accounting for differences in stress state our analysis is consistent with the well known association of instability with shear localization in simulated fault gouge and the observation that bare rock surfaces exhibit predominantly velocity weakening frictional behavior whereas simulated fault gouge exhibits velocity strengthening followed by a transition to velocity weakening with increasing displacement natural faults also exhibit displacement dependent frictional behavior and thus the results may prove useful in understanding the seismic evolution of faulting

laboratory micro seismic signature of shear faulting and fault slip in shale this article reports the results of a triaxial deformation experiment conducted on a transversely isotropic shale specimen this specimen was instrumented with ultrasonic transducers to monitor the evolution of the micro seismic activity induced by shear faulting triaxial failure and subsequent fault slip at two different rates the strain data demonstrate the anisotropy of the mechanical quasi static compliance of the shale the p wave velocity data demonstrate the anisotropy of the elastic dynamic compliance of the shale the spatio temporal evolution of the micro seismic activity suggests the development of two distinct but overlapping shear faults a feature similar to relay ramps observed in large scale structural geology the shear faulting of the shale specimen appears quasi aseismic at least in the 0 5 mhz range of sensitivity of the ultrasonic transducers used in the experiment concomitantly the rate of micro seismic activity is strongly correlated with the imposed slip rate and the evolution of the axial stress the moment tensor inversion of the focal mechanism of the high quality micro seismic events recorded suggests a transition from a non shear dominated to a shear dominated micro seismic activity when the rock evolves from initial failure to larger and faster slip along the fault the frictional behaviour of the shear faults highlights the possible interactions between small asperities and slow slip of a velocity strengthening fault which could be considered as a realistic experimental analogue of natural observations of non volcanic tremors and very low frequency earthquakes triggered by slow slip events

the effect of sub seismic fault slip processes on the isotopic signature of clay minerals implications for k ar dating of fault zones abstract clay minerals are abundant in fault gouges and isotope dating of the radiogenic noble gases that they contain may be used to constrain timing of fault initiation reactivation and to estimate recurrence intervals of earthquakes the potential influence of fault slip and ambient temperature on the isotope signature of authigenic clay minerals however remains unknown this study reports measurements of the k ar isotope signature of samples that have been sheared experimentally at sub seismic slip rates within a range of ambient temperatures as well as of samples undergoing standardised clay heating degas experiments in the investigation and comparison of the influence of sub seismic frictional slip and external heating on clay gouge the age data confirm that the sub seismic frictional slip of clay gouge affects the clay microstructures and releases radiogenic 40ar the experimental data indicate that radiogenic 40ar release due to external heating can be disregarded until 350 c which is supported by ar diffusion modelling frictional slip at sub seismic slip rates and at room temperature results in a significant radiogenic 40ar loss of 56 and the remaining clay will inherit 44 of radiogenic 40ar sub seismic frictional slip experiments at imposed elevated temperatures from 150 to 450 c increase the amount of radiogenic 40ar loss and decrease the amount of inherited radiogenic 40ar at a relatively high temperature of 450 c about 16 of radiogenic 40ar will be present in the remaining sample portion reinforcing the importance of rigorous clay grain size separation processes required prior to fault gouge dating

seismic damage mechanism and dynamic deformation characteristic analysis of mountain tunnel after wenchuan earthquake abstract after the 2008 wenchuan earthquake mw 8 3 many mountain highway tunnels in the affected area were severely damaged in order to improve the current knowledge about the seismic performance of mountain tunnels under strong earthquakes a forensic investigation was conducted on 52 tunnels after the earthquake based on the seismic damage data the damage level of the inspected tunnels was classified using a new damage evaluation criterion subsequently typical seismic damage characteristics and mechanisms of mountain tunnels were analyzed based on three different damage patterns damage to shallow tunnel damage to deep buried tunnel structure and damage to pavement finally based on the relative displacement rd method a three dimensional numerical model was developed to investigate the deformation characteristics of the portal structure under a strong earthquake the numerical results showed that the tunnel lining cross section exhibited an alternate tension compression deformation at the diagonal directions and the relative displacement value of the upper structure above the sidewall was generally more than that of the lower structure under the sidewall three stress states of the lining were deduced from the numerical model which provided a good interpretation for the seismic tunnel damages observed after the wenchuan earthquake

application of the critical coulomb wedge theory to hyper extended magma poor rifted margins the critical coulomb wedge theory ccwt has been extensively used in compressional tectonics to resolve the shape of orogenic or accretionary prisms while it is less applied to extensional and gravitational wedges despite the fact that it can be described by the same equation in particular the hyper extended domain at magma poor rifted margins forming the oceanward termination of extended continental crust satisfies the three main requirements of the ccwt 1 it presents a wedge shape 2 the rocks forming the wedge are completely brittle frictional and 3 the base of the wedge corresponds to a low friction decollement however hyper extended margins present a fully frictional behaviour only for a very thin crust therefore this study is limited to the termination of hyper extended continental crust which deforms in the latest stage of continental rifting in this paper we define a method to measure the surface slope and the basal deep of this wedge that we apply to 17 hyper extended magma poor rifted margins in order to compare the results to the values predicted by the ccwt because conjugate pairs of hyper extended magma poor rifted margins are commonly asymmetric due to detachment faulting the wedges in the upper and lower plate margins corresponding respectively to the hanging wall and footwall of the detachment system are different while the stress field in the upper plate wedge corresponds to a tectonic extensional wedge the one in the lower plate matches that of a gravity extensional wedge using typical frictional properties of phyllosilicates e g clays and serpentine the shape of the hyper extended wedges can be resolved by the ccwt using consistent fluid overpressures our results show that all lower plate margins are gravitationally stable and therefore have a close to critical shape whereas the tectonic extensional wedges at upper plate margins are critical sub or sup critical due to the detachment initial angle and the duration of the tectonic activity in this paper we discuss the geometry and structural evolution of the most distal parts of hyper extended continental margins and the formation of extensional allochthons during hyper extension using the ccwt theory

pressure solution seams in carbonatic fault rocks mineralogy micro nanostructures and deformation mechanism we have investigated mineralogy and micro nanostructures of pressure solution seams in four different carbonatic faults with kilometric displacement cropping out in the northern apennines italy disregarding the different protoliths and deformation conditions the stylolite filling material has almost constant mineralogical characteristics being invariably formed by an ultrafine matrix that encloses relic insoluble grains among which quartz feldspars and detritic micas the ultrafine matrix also hosts syn and post dynamic phases e g foliation parallel goethite flakes and apatite euhedral nanocrystals in random orientation the ultrafine matrix is formed by smectitic clays in nanosized 001 lamellae showing pervasive interlayer fissuring layer bending and preferred orientation parallel to the slipping surface stylolite mineralogy and micro nanostructures may affect deformation mechanisms and permeability properties of the fault rock in particular we propose that the extremely low friction coefficient of smectite would favour frictional sliding along the faults and that the fissured and oriented nanostructure of the smectite dominated seams would enhance the sealing attitude of the structures in the fault perpendicular direction

laboratory results indicating complex and potentially unstable frictional behavior of smectite clay a central problem in explaining the apparent weakness of the san andreas and other plate boundary faults has been identifying candidate fault zone materials that are both weak and capable of hosting earthquake like unstable rupture our results demonstrate that smectite clay can be both weak and velocity weakening at low normal stress 30 mpa our data are consistent with previous work which has focused on higher normal stress conditions 50 mpa and greater and found only velocity strengthening if natural fault zones contain significant smectite one key implication of our results is that localized zones of high pore pressure which reduce effective normal stress could be important in controlling potential sites of earthquake nucleation our experiments indicate that friction of smectite is complex and depends upon both sliding velocity and normal stress this complexity highlights the need for detailed experiments that reflect in situ conditions for fault gouges

updip limit of the seismogenic zone beneath the accretionary prism of southwest japan an effect of diagenetic to low grade metamorphic processes and increasing effective stress off southwest japan the seaward limit of coseismic displacement or updip limit of the seismogenic zone of the 1946 mw 8 3 thrust earthquake reaches to 4 km depth and 40 km landward of the trench this limit coincides with the estimated location of the 150 c isotherm and has been linked to changes in physical properties associated with the smectite to illite clay mineral transition here we show that this limit correlates with a suite of diagenetic to low grade metamorphic processes characterized by 1 declining fluid production and decreasing fluid pressure ratio and 2 active clay carbonate and zeolite cementation and the transition to pressure solution and quartz cementation these diagenetic to low grade metamorphic changes cause the onset of velocity weakening during thrust faulting an increase in effective stress and strengthening of the hanging wall which together combine to produce recordable earthquakes

thermal regime from bottom simulating reflectors along the north ecuador south colombia margin relation to margin segmentation and great subduction earthquakes 1 the north ecuador south colombia nesc margin has three transverse morphotectonic segments the manglares tumaco and patia segments each with different tectonic and structural patterns following the 1906 subduction earthquake the nesc margin has been the site of three megathrust events in 1942 1958 and 1979 for which the rupture zones abut one another we first investigated variations in heat flow derived from bottom simulating reflectors bsr observed along multichannel seismic lines sampling the three morphotectonic segments strong along strike variations of the bsr derived heat flow just landward of the deformation front suggest that each morphotectonic segment has a specific thermal regime finite element thermal models show that these variations are mainly produced by changes in the age and the dip of the oceanic plate and local hydrothermal cooling we then examined the relationship between seismogenesis and thermal structure along the plate boundary the updip limits of the 1942 and 1979 seismogenic zones estimated from the aftershock area and rupture zone reach the trench where the temperature at the top of the subducting plate appears to be 50 60 c between these events the seismogenic zone of the 1958 earthquake is restricted to a region landward of a prominent outer basement high where the temperature appears to be 100 120 c we propose that on the nesc margin the updip limit of the seismogenic zone is primarily controlled by low temperature processes except for the 1958 event for which the seismogenic updip limit appears to be related to a structural feature in the upper plate

abundance of smectite and the location of a plate boundary fault barbados accretionary prism isolating the respective roles of factors responsible for the initiation and localization of fault zones remains one of the more important goals of research in neotectonics the frontal decollement zone of the northern barbados accretionary prism provides several important clues as to how the interwoven variables of clay mineralogy fluid flow chemical interactions and sediment physical properties affect strain localization this plate boundary fault is centered at a lithologic contact between miocene claystone and fine grained oligocene turbidites the fault zone is nearly 40 m thick at ocean drilling program site 948 and its upper part passes through smectite rich deposits a sharp minimum in percent smectite and a maximum in percent illite mark the base of the decollement there is a consistent increase in percent smectite with distance above the base of the decollement but the top of the decollement is poorly defined by clay mineralogy the intrinsic mechanical weakness of strata with abundant smectite group clays probably influences where the fault tip propagates into the undeformed stratigraphy of the atlantic abyssal plain a second inherited parameter is the local abundance of radiolarians which contribute to higher than normal porosities sediment shear strength also decreases because pore pressure within the fault zone is significantly greater than hydrostatic the principal cause of excess pore pressure seems to be updip fluid advection in theory however decreases in pore fluid salinity and porosity collapse should increase the amount of physicochemical stress generated by expandable clay minerals the imported fluid is unusually low in salinity because it has migrated from zones of deeper seated dehydration reactions if fresher pore water migrates to the propagating tip of the decollement its arrival should increase smectite swelling and reduce the shear strength of the mudstone even more the location and evolution of the decollement therefore are controlled by a complicated interplay of static factors inherited from the abyssal atlantic stratigraphy and dynamic factors associated with episodic fluid flow and changing fluid chemistry

high position debris flow a long term active geohazard after the wenchuan earthquake after the 12 may 2008 wenchuan earthquake in sichuan a special type of long term active compounded geohazard namely high position debris flow frequently occurred in the seismic area 136 high position debris flow gullies were recognized from the 796 active debris flow gullies to investigate distinctive characteristics of such debris flows in terms of their geomorphological conditions spatial distribution and causal factors they usually initiate at high steep slopes and have high mobility and long runout high position debris flows have significantly larger magnitude and destructive force than those of common debris flows observed in the regions not affected by recent large earthquake the high position debris flows have been recognized as the most threatening geohazards among post earthquake geological disasters in the wenchuan earthquake region detailed investigation on 45 debris flows suggests three quantitative indices for recognizing the high position debris flows i the height difference between the material source and the debris flow exit or gully mouth should be larger than 350 m ii the volume of source debris accumulation should be bigger than 1 0 x 10 6 m 3 and iii the gradient ratio of a debris flow channel should be steeper than 270 parts per thousand the spatial distribution of high position debris flows was highly controlled by the seismogenic fault due to the abundant loose materials caused by earthquake the rainfall threshold triggering high position debris flows was found to have decreased at least 36 4 63 7 when compared to the pre earthquake one three disaster forming models have been identified for the high position debris flows in the wenchuan earthquake region the long term post earthquake effect of high position debris flow is becoming more concerned in the area of high intensity the characteristics of long term activity of high position debris flows using a case study indicate a 15 years of extremely active period after a strong earthquake such as the wenchuan one a number of issues regarding the classification investigation runout prediction and controlling measures for high position debris flow are discussed to provide insight into the foundation for high position debris flow mitigation and its risk assessment c 2014 elsevier b v all rights reserved

assessment of dynamic impact force of debris flow in mountain torrent based on characteristics of debris flow landslides and debris flows that occur around residential areas are considered globally as significant disasters that cause damage to human life and property with terrain slope defining the flow characteristics of debris flows flow depth flow velocity and impact force vary by time and distance in particular when a structure is located in the flow path of debris flows the flow characteristics of debris flows vary by terrain slope and direction angle to simulate the flow characteristics of these debris flows the simulation results obtained by flo 2d were analyzed with six stage conditions for the research area in the analysis the flow depth flow velocity and impact force were estimated on the basis of the outlet of the research area in the presence and absence of structure s at certain distances with this the variation of the impact force in accordance with the variation of the flow depth of the debris flows was highly similar to the simulation results obtained by flo 2d when the correction index of the suggested dynamic impact force equation was 0 3 0 4 there were sections where the estimated value of the impact force was overestimated near the outlet and it was judged that the fixed values of the terrain factors width roughness coefficient slope etc caused the impact force to be overestimated however the correlation analysis showed that the correlation index was above the normal ranges in the suggested dynamic impact force equation for debris flows with the application of the terrain factors

importance of thermochemical pressurization in the dynamic weakening of the longmenshan fault during the 2008 wenchuan earthquake inferences from experiments and modeling 1 we determined the internal structure and mineral composition of the yingxiu beichuan fault zone at the zhaojiagou exposure and measured frictional and transport properties of the fault rocks collected to gain a better understanding of dynamic weakening mechanisms during seismic fault motion this fault is a major fault in the longmenshan fault system that caused the 2008 wenchuan earthquake the exposure studied is located midway along the surface rupture close to where the largest coseismic displacement occurred high velocity friction experiments reveal exponential slip weakening from a peak friction toward a steady state value slip weakening is more pronounced for water dampened gouge than dry gouge suggesting thermal pressurization the fault gouge has a very low permeability 10 21 m2 at 165 mpa effective pressure and is surrounded by fault breccia with a permeability of 10 19 to 10 17 m2 grading into less permeable fractured country rocks the fault zone thus exhibits a conduit barrier structure allowing fluid flow only in the breccia zone we numerically modeled coseismic slip weakening including thermal pressurization and mineral dehydration decarbonation basing our calculation on measured frictional and transport properties and on the slip history inferred for the wenchuan earthquake the results indicate that 1 thermochemical pressurization played an important role in causing dynamic slip weakening 2 the slip weakening distance is similar to the seismologically determined values and 3 pore pressures might have exceeded the normal stress thus maintaining temperatures below 600 c interestingly enough heat was generated to fully remove and thermally pressurize the interlayer water from smectite contributing an excess pore pressure of 6 mpa in addition we found that the incorporation of state dependent fluid properties predicts much more efficient fluid pressurization than using constant properties the dramatic weakening predicted probably offers a compelling explanation for the large coseismic displacement and slip acceleration observed near beichuan city

shocks in a box an analogue model of subduction earthquake cycles with application to seismotectonic forearc evolution 1 we introduce and test an experimental approach to simulate elastoplastic megathrust earthquake cycles using an analogue model and apply it to study the seismotectonic evolution of subduction zones the quasi two dimensional analogue model features rate and state dependent elastic frictional plastic and viscoelastic material properties and is scaled for gravity inertia elasticity friction and viscosity the experiments are monitored with a high resolution strain analysis tool based on digital image correlation particle imaging velocimetry piv providing deformation time series comparable to seismologic geodetic and geologic observations in order to separate elastic and nonelastic effects inherent the experimental deformation patterns we integrate elastic dislocation modeling edm into a hybrid approach we use the analogue earthquake slip and interseismic locking distribution as edm dislocation input and forward model the coseismic and interseismic elastic response the residual which remains when the edm prediction is subtracted from the experimental deformation pattern highlights the accumulation of permanent deformation in the model the setup generates analogue earthquake sequences with realistic source mechanisms and elastic forearc response and recurrence patterns and reproduces principal earthquake scaling relations by applying the model to an accretionary type plate margin we demonstrate how strain localization at the rupture peripheries may lead to a seismotectonically segmented forearc including a tectonically stable shelf and coastal high 20 plate convergence accommodated by internal shortening overlying the area of large megathrust earthquake slip fifty to 75 of plate convergence is accommodated by internal shortening in the slope region where earthquake slip tapers out toward the trench the inner forearc region remains undeformed and represents a basin

on the evolution of elastic properties during laboratory stick slip experiments spanning the transition from slow slip to dynamic rupture the physical mechanisms governing slow earthquakes remain unknown as does the relationship between slow and regular earthquakes to investigate the mechanism s of slow earthquakes and related quasi dynamic modes of fault slip we performed laboratory experiments on simulated fault gouge in the double direct shear configuration we reproduced the full spectrum of slip behavior from slow to fast stick slip by altering the elastic stiffness of the loading apparatus k to match the critical rheologic stiffness of fault gouge kc our experiments show an evolution from stable sliding when k kc to quasi dynamic transients when k kc to dynamic instabilities when k kc to evaluate the microphysical processes of fault weakening we monitored variations of elastic properties we find systematic changes in p wave velocity vp for laboratory seismic cycles during the coseismic stress drop seismic velocity drops abruptly consistent with observations on natural faults in the preparatory phase preceding failure we find that accelerated fault creep causes a vp reduction for the complete spectrum of slip behaviors our results suggest that the mechanics of slow and fast ruptures share key features and that they can occur on same faults depending on frictional properties in agreement with seismic surveys on tectonic faults our data show that their state of stress can be monitored by vp changes during the seismic cycle the observed reduction in vp during the earthquake preparatory phase suggests that if similar mechanisms are confirmed in nature high resolution monitoring of fault zone properties may be a promising avenue for reliable detection of earthquake precursors

nucleation of frictional instability caused by fluid pressurization in subducted blueschist pore pressure is an important factor in controlling the slip instability of faults and thus the generation of earthquakes particularly slow earthquakes are widespread in subduction zones and usually linked to the occurrence of high pore pressure yet the influence of fluid pressure and effective stress on the mechanics of earthquakes is poorly understood therefore we performed shear experiments on blueschist fault rocks which likely exist at depth in cold and old subduction zones to investigate the influence of effective stress on frictional behavior our results show potentially unstable behavior at temperatures characterizing the seismogenic zone as well as a transition from stable to unstable behavior with decreasing effective normal stress which is mechanically equivalent to increasing fluid pressure this transition is a prerequisite for generating slow earthquakes our results imply that high pore pressures are a key factor for nucleating slip leading to both megathrust and slow earthquakes

evolution of debris flow activities in gaojiagou ravine during 2008 2016 after the wenchuan earthquake abstract the 2008 wenchuan earthquake in sichuan china triggered numerous landslides in the stricken area the loose landslide materials retained on mountain slopes and in gullies are prone to reactivation and may transform into debris flows in the rainy season nine years after the wenchuan earthquake debris flows are still active in gaojiagou ravine 16 5 km north of the epicentre on 14 august 2010 3 july 2011 13 july 2013 and 6 july 2016 four large scale debris flows were triggered by heavy storms in gaojiagou ravine the four debris flows blocked the minjiang river twice and caused severe damage to nearby villages and reconstruction sites several questions arise from these repeated debris flows did the level of triggering rainfall change in the four debris flow events how did the initiation mechanism evolve over time what are the differences in the runout characteristics in the four events how did the check dams constructed in 2012 function in the subsequent debris flows in this paper we evaluated the loose deposit volumes in gaojiagou ravine before and after each of the four debris flows and the runout volumes and analysed the triggering rainfall intensities initiation mechanisms and runout characteristics of the four debris flows the rainfall threshold for the debris flows in gaojiagou ravine increased over time and the initiation mechanisms evolved from landslides to channel bed failure and subsequently to channel bank erosion the mobility of the debris flows decreased from 2010 to 2016 as the initiation positions moved lower and the particle size of the runout materials became coarser

the brittle ductile transition in porous sedimentary rocks geological implications for accretionary wedge aseismicity abstract thrusting earthquakes in subduction zones generally occur along only part of the plate boundary with motion along the shallowest part of the plate boundary occurring ascismically the maximum size of subduction boundary thrust earthquakes depends strongly upon the down dip width of the seismogenic zone the single most uncertain factor in determining that width is the location of the up dip limit of the zone the seismic front which depends upon the mechanical state of the sedimentary rocks in the plate boundary zone in order to come to a better understanding of the seismic potential of sediments in a subduction zone we carried out a series of triaxial experiments on berea and kayenta sandstones based on our experimental data a brittle ductile transition map was constructed showing that both porosity and effective pressure are important factors controlling the transition from brittle to macroscopically ductile behavior in porous rocks in the brittle field a sample fails by shear localization on one slip plane accompanied by strain softening and dilatancy whereas in the ductile field a sample deforms homogeneously with a constant yield stress or slight hardening by comparing such a map with the estimated porosity profile of an accretionary wedge the likely nature and rough location of the boundary between brittle and ductile behavior can be inferred if the sediments along a plate boundary are too young and undercompacted to be capable of brittle shear localization then their deformation is likely to be aseismic in this way it may be possible for even a very broad fore arcs to produce no great earthquakes however great earthquakes are to be expected at margins that have large zones of plate contact along which many sediments are compacted and well lithified such rocks are expected to be capable of shear localization and brittle failure with the potential for stick slip behavior

quantitative analysis of debris torrent hazards for design of remedial measures debris torrents which are rapid flows of soil and organic debris down steep mountain channels are a major natural hazard in many parts of british columbia a series of recent occurrences along the

intense pp reflection beneath the aseismic forearc slope of the japan trench subduction zone and its implication of aseismic slip subduction 1 strong anticorrelation between intensity of plate boundary pp reflection and seismicity had been revealed by a seismic reflection refraction survey conducted in 1996 in a seismic aseismic boundary region on the forearc slope of the japan trench amplitude of the strong reflection was explained by the presence of a thin layer 200 m of low p wave velocity 3 4 km s at the top of the plate boundary we conducted another seismic survey in 2001 in the same region as that of 1996 and verified the strong anticorrelation with planer extension along the plate boundary therefore existence of the thin layer of low p wave velocity along the plate boundary is expected within the aseismic regions extremely low p wave velocities along the plate interface at depths of around 10 20 km suggest that the layer may include fluid clay minerals and or serpentine chlorite because these materials have low mechanical strength or cause low friction between the overriding and subducting plates large strain may not be accumulated and aseismic slip may be dominant as a result of the above speculation the intense reflection observed within the aseismic regions may imply aseismic slip between the plates amplitude of the plate boundary pp reflection phase was found maximum about reflections from deeper plate interface although the reflected waves propagate for longer distances one possible explanation to this phenomenon is the presence of serpentinized wedge mantle material that is buoyancy driven to move along the top of the slab

the relationship between seismic and aseismic slip on the philippine fault on leyte island bayesian modeling of fault slip and geothermal subsidence delineating seismic and aseismic slip on faults allows the exploration of the complex relationship between these different modes of slip further quantifying them helps in the assessment of seismogenic potential we present a distributed slip model of the rate of aseismic slip along the leyte island section of the philippine fault and make comparisons with the extent of seismic slip from the latest significant earthquakes in july 2017 we derived both coseismic and aseismic slip distributions from kinematic inversions of synthetic aperture radar interferometric insar observations using a probabilistic bayesian framework velocity maps from stacking and time series analysis of alos interferograms spanning 4 years 2007 2011 show a step change in ground deformation right on the fault inverting for slip at depth reveals along strike variations of aseismic slip rate over 100 km aseismic slip on the surface reaches rates of more than 3 cm yr equivalent to the long term slip rate 3 3 0 2 cm yr over the same period a 20 km segment in tongonan appears to be locked this segment ruptured in mw 6 5 and mw 5 8 earthquakes on 6 and 10 july 2017 respectively as constrained by sentinel 1 and alos 2 insar data seismic slip appears to be restricted within the tongonan segment with up to 152 21 cm of left lateral displacement the slip budget and complementarity between the extents of interseismic and coseismic slip suggest that a seismogenic asperity exists in tongonan the presence of active hydrothermal systems and rate strengthening materials provide physical conditions that can promote aseismic slip

low to high velocity frictional properties of the clay rich gouges from the slipping zone of the 1963 vaiont slide northern italy the final slip of about 450 m at about 30 m s of the 1963 vaiont landslide italy was preceded by 3 year long creeping phase which was localized in centimeter thick clay rich layers 60 70 smectites 20 30 calcite and quartz here we investigate the frictional properties of the clay rich layers under similar deformation conditions as during the landslide 1 5 mpa normal stress 2 10 7 to 1 31 m s slip rate and displacements up to 34 m experiments were performed at room humidity and wet conditions with biaxial torsion and rotary shear apparatus the clay rich gouge was velocity independent to velocity weakening in both room humidity and wet conditions in room humidity experiments the coefficient of friction decreased from 0 47 at v 0 70 m s full lubrication results from the formation of a continuous water film in the gouge the vaiont landslide occurred under wet to saturated conditions the unstable behavior of the landslide is explained by the velocity weakening behavior of the vaiont clay rich gouges the formation of a continuous film of liquid water in the slipping zone reduced the coefficient of friction to almost zero even without invoking the activation of thermal pressurization this explains the extraordinary high velocity achieved by the slide during the final collapse

prediction of impact force of debris flows based on distribution and size of particles a debris flow is a solid liquid two phase flow the composition and gradation of the particles within have a significant influence on its impact force this paper proposes a new method for studying the impact force according to the composition of a debris flow based on analysis of existing calculation methods the impact force is divided into three parts 1 the dynamic pressure provided by the debris flow slurry which is composed of fine particles and water 2 the impact force of coarse particles and 3 the impact force of boulders this paper analyzes the established formulations used to calculate the impact force by using hydrodynamic theory and contact mechanics to propose a debris flow impact model according to the debris flow type the results show that the impact force is closely related to the solid volume fraction composition of particle materials motion velocity and depth of a debris flow among all the components of the impact force the boulder impact force is the largest followed by the impact force of coarse particles the dynamic pressure is minimal

influence of particle shape on the frictional strength of sediments a numerical case study abstract numerous direct and ring shear tests supply that composition and texture of sediments are crucial for shear and frictional strength we simulate particle interactions on a micro scale level during shearing with a numerical shear box using the discrete element method dem based on the granular model approach detailed information about slip localisation and rates forces at particle contacts as well as particle rotation can be quantified as function of particle shape stress conditions and shear rate our numerical experiments show that the deformation behaviour of clay is largely controlled by their particle shape two key factors sphericity and roughness could be identified as relevant for frictional strength shear zone development and particle rotation with sphericity dominating over roughness decreasing sphericity leads to complex initial microfabrics whose breakdown with increasing strain is caused by particle rotation preferred particle orientation favours low friction decreasing volume strain and the evolution of particle domains of similar orientation decreasing roughness results in particle interlocking of different degrees which obstructs slip and rotation to preferred orientations so that friction is high and volume strain positive spatial and temporal shear zone development depends on the roughness of particles increasing roughness precludes shear zone development and particle domain evolution shear zone localisation depends on particle sphericity increasing sphericity leads to more localised but vertically dilated deformation

the updip and downdip limits to great subduction earthquakes thermal and structural models of cascadia south alaska sw japan and chile this study examines thermal and structural controls of the updip and downdip rupture limits of great subduction thrust earthquakes data on past great earthquake seismic limits have been compiled for four continental subduction zones cascadia sw japan south alaska and chile these limits have then been compared to the predictions of several models for what constrains great earthquake rupture temperatures on the subduction thrusts have been estimated by finite element numerical models the landward limits of the observed updip aseismic zones correspond to the position where the thrust temperature reaches about 100 c that is depths of about 2 to 10 km for the subduction zones studied this temperature agrees with the dehydration of stable sliding smectite clays to illite chlorite the temperatures in this region are controlled mainly by the thickness of sediment on the incoming crust and by the crustal age and thus heat flow the downdip limits correspond to the depth on the thrust where either 1 the temperature reaches about 350 c which corresponds to thermally activated stable sliding behavior for crustal rocks with a transition to 450 c or 2 about 40 km depth if 350 c is reached at greater depth depths of about 40 km approximately correspond to the intersection of the thrust with the continental forearc moho and this downdip limit may be a consequence of stable sliding serpentinite or talc and other hydrated forearc mantle rocks the primary temperature controls on the downdip region are the age of the subducting oceanic plate and the thrust dip profile secondary control comes from the thickness of incoming sediment the convergence rate and the radioactive heat generation in the overlying forearc the 100 c updip limit occurs near the trench for young subducting plates with a thick sediment section such as cascadia 6 8 ma and up to 80 km landward for older oceanic crust such as south alaska 50 ma the 350 c downdip thermal limit is applicable for young oceanic plates e g cascadia and nankai whereas the forearc mantle limit applies for older plates e g south alaska and chile except near the chile rise for the margins studied that have experienced great earthquakes there is generally good agreement between the postulated thermal and moho limits and the rupture or seismogenic zone as defined by the distribution of aftershocks and by waveform tsunami and dislocation modeling the downdip limit of the interseismic locked zone from dislocation modeling is also in agreement with these limits

dynamic characteristics and safety criterion of deep rock mine opening under blast loading abstract the blasting vibration in deep mining affects the safety of the adjacent roadways to estimate the stability of a deep rock mass opening during blasting excavation the dynamic responses of the deep rock mass subjected to blast loading are investigated in this study the relationships between the blasting vibration velocity and the frequency over time horizontal distance and depth are analyzed and the stress distribution of the surrounding rock mass is depicted through field tests and numerical simulation the failure mechanism of deep rock mass is thus revealed and a new safety criterion regarding the blasting vibration of the deep rock mass is put forward the results indicate that the vertical vibration velocity is higher than the horizontal vibration velocity and that the vertical tension of the seismic wave of the blast is larger than that of the shearing action in the near blasting field which contrasts that of the far field both the vibration velocity and frequency decrease with an increase in time distance and depth and the range of influence of the blasting vibration in terms of depth is larger than that for the horizontal direction therefore the deep rock mass is more vulnerable to damage than the shallow rock mass under blast loading in addition the surrounding rock stress tends to transfer from the arc foot on the blasting side to the straight wall on the rear side and the shear stress is ahead of the tensile stress it was verified through a case calculation that the new criterion has practical value and can be used as a guide for evaluating the blasting vibration effects of the deep rock mass

experimental constraints on the relationship between clay abundance clay fabric and frictional behavior for the central deforming zone of the san andreas fault the presence of smectite saponite in fault gouge from the central deforming zone of the san andreas fault at parkfield ca has been linked to low mechanical strength and aseismic slip however the precise relationship between clay mineral structure fabric development fault strength and the stability of frictional sliding is not well understood we address these questions through the integration of laboratory friction tests and fib sem analysis of fault rock recovered from the san andreas fault observatory at depth safod borehole intact fault rock was compared with experimentally sheared fault gouge and different proportions of either quartz clasts or safod clasts extracted from the sample nano textural measurements show the development of localized clay particle alignment along shear folia developed within synthetic gouges such slip planes have multiples of random distribution mrd values of 3 0 4 9 the mrd values measured are higher than previous estimates mrd 1 5 that show lower degrees of shear localization and clay alignment averaged over larger volumes the intact fault rock exhibits less well developed nano clay fabrics than the experimentally sheared materials and mrd values decrease with smectite content we show that the abundance strength and shape of clasts all influence fabric evolution via strain localization quartz clasts yield more strongly developed clay fabrics than serpentine dominated safod clasts our results suggest that 1 both clay abundance and the development of nano scale fabrics play a role in fault zone weakening and 2 aseismic creep is promoted by slip along clay shears with 20 wt smectite content and mrd values 2 7

lithification facilitates frictional instability in argillaceous subduction zone sediments abstract previous work suggests that in subduction zones the onset of large earthquake nucleation at depths 5 10 km is likely driven by a combination of factors associated with the process of lithification at these depths lithification processes affect the entire fault system by modifying the mechanical properties of both the plate boundary fault zone and the wall rock to test the hypothesis that lithification of subduction zone sediments produces rocks capable of earthquake nucleation via diagenesis and low grade metamorphism we conducted friction experiments on fossil subduction zone sediments recovered from exposures in the shimanto belt in sw japan these meta sediments represent accreted and subducted material which has experienced maximum temperatures of 125 to 225 c which are representative of seismogenic depths along the active nankai subduction megathrust in the foreland of the shimanto belt we find that intact shimanto rock samples which preserve the influence of diagenetic and metamorphic processes exhibit the potential for unstable slip under in situ pressure conditions powdered versions of the same samples tested under the same conditions exhibit only velocity strengthening friction thus demonstrating that destroying the lithification state also removes the potential for unstable slip using advanced porosity loss to quantify the lithification process we demonstrate that increased velocity weakening correlates with increasingly advanced lithification in combination with documented frictionally stable behavior of subduction zone sediments from shallower depths our results provide evidence that the sediment lithification hypothesis can explain the depth dependent onset of large earthquake nucleation along subduction zone megathrusts

characteristics and hazard prediction of large scale debris flow of xiaojia gully in yingxiu town sichuan province china the wenchuan earthquake of may 12 2008 produced large amounts of loose solid material that can lead to the development of devastating debris flows in 5 years since the earthquake large numbers of large scale debris flows occurred and caused great damage to the resettled population and the reconstruction efforts the reconstructed yingxiu town suffered debris flow and its secondary disaster in the past 5 years and will be in the risk range of debris flow hazard in the future it is very important to predict debris flow and its secondary hazard especially the dam breaking flood near the town the debris flow of the xiaojia gully was described and analyzed as a typical large scale case in the yingxiu area the study aimed to describe the debris flow event investigate the sediment supply conditions analyze the characteristics of the debris flow deposition calculate the river blocking parameters and predict the damage of dam breaking flood to yingxiu town under different debris flow frequencies debris flows in xiaojia gully were well developed and occurred several times resulting in frequent interruption of traffic on the s303 road the interpretation of satellite images showed that landslide deposition channel deposition and soil erosion sediment were three kinds of sediment supply types for debris flow formation 188 sediment supply sites in total were identified in the catchment the total area for the supply of sediment for debris flows is about 0 99 km 2 giving a total volume of 532 09 x 10 4 m 3 if the yuzi river is blocked by debris flow material the dam breaking flood can cause potential damage to the newly constructed yingxiu town the calculation results reveal that debris flows with a frequency of 5 and 10 are impossible to cause river blockage and consequently the yingxiu town is safe in these situations however debris flows with a frequency of 1 and 2 may cause river blockage and the dam breaking flood can cause damage to the yingxiu town c 2014 elsevier b v all rights reserved

heavy rainfall triggered loess mudstone landslide and subsequent debris flow in tianshui china abstract continuous and heavy precipitation triggered a large loess landslide at the southern dagou village of mapaoquan town tianshui city gansu province of china on july 21 2013 the landslide debris rapidly turned into a debris flow that was deposited in the ravine mouth with the volume of 1 9 105 m3 detailed field mapping three dimensional laser scanning aerial photograph interpretation and laboratory tests were carried out to study the formation and moving characteristics of the landslide and subsequent debris flow the results showed that 1 the peak flow velocity and peak discharge of the debris flow were estimated to be approximately 7 2 m s and 730 m3 s respectively the velocity had a tendency to first increase and then decrease from the head to entrance in the dagou gully 2 the analysis of rainfall conditions showed that the effective antecedent rainfall within 7 days and hourly rainfall intensity which triggered the slide debris flows was 239 mm and 20 mm h respectively compared with the critical rainfall in this area the effective antecedent rainfall was found to be more significant in triggering this event 3 the mean and effective particle sizes were approximately 0 73 1 3 mm and 0 036 0 087 mm respectively and had the same distribution along the gully as the velocity which confirmed the process of the variation in the flow velocity 4 the scale amplification was very obvious in the formation and moving process of the slide debris flows

patterns and processes of sediment dispersal on the continental slope off nice se france the distribution of surficial sediments and sediment dispersion patterns on the steep continental slope off nice se france have been studied using side scan sonar 3 5 khz profiles short piston cores and bottom photographs the input of terrigenous material to the baie des anges a submarine embayment bounded by two prominent ridges is dominated by fluvial input from the var river the paillon river being only a minor source the var river provides very coarse bedload material gravel and cobble directly to the head of the var canyon gravel and cobble deposits are found all along the var canyon and the upper fan valley of the var submarine fan and have been shaped into gravel waves the fine particles suspension load are separated from the coarse bedload upon entering the sea and form up to 60 m thick deposits on the uppermost continental slope of the baie des anges these deposits are formed by settling out of sediment plumes the presence of silt and fine sand laminae that decrease in thickness and frequency away from the var river mouth indicate the influence of meso and hyperpycnal flows on these plume deposits areas outside the baie des anges are not connected to major fluvial input and receive only hemipelagic sediments these primary deposits are highly unstable and sediment failure due to seismic loading sedimentary loading or undercutting is frequent sediment failure produces secondary sediment gravity flows that export most of the material to the basin but also produce turbidity current over spill deposits on ridges bounding the slope canyons and on terraces within the var canyon slump and debris flow deposits are also observed at least some of these secondary flows erode the continental slope as cross cutting chutes on the upper continental slope and erosional scours in the upper fan valley demonstrate modern sediment dispersal patterns on the continental slope off nice are proposed as a modern analogue to lowstand conditions on continental margins in fact the absence of a continental shelf together with a steep slope strongly reduces the influence of sealevel on the physiography of the margin