numerical simulation of 2 d seismic wave propagation in the presence of a topographic fluid solid interface at the sea bottom by the curvilinear grid finite difference method

three dimensional dynamic simulation of the 1992 landers earthquake the 1992 landers california earthquake magnitude 7 3 was modeled as the propagation of a spontaneous rupture controlled by a realistic prestress distribution with the use of a three dimensional finite difference method the dynamic rupture reproduces the general slip pattern used to compute the initial stress distribution and generates near fault ground motions at the surface similar to observations the simulated rupture propagates on the fault along a complex path with highly variable speed and rise time changing the magnitude and pattern of the stress significantly the method provides the framework to estimate earthquake rupture parameters from recorded seismic and geodetic data

effect of normal stress during rupture propagation along nonplanar faults 1 we study a symmetrical three forked shear fault under simple triaxial stress rupture initiates in the central primary plane and propagates toward the branching point one of the two branches is in the compressional quadrant while the other is in the tensional domain we study the following question does rupture always prefer propagating along the tensional branch because of the effect of normal stress when the primary plane is located in the most favorable direction as determined by mohr coulomb criterion one finds that the compressional branch is almost always preferred for various dynamic coefficients and confining pressures simultaneous rupture propagation on both branches appears only under a very special condition found by aochi et al 2000b these results indicate that shear stress changes produced by the rupture front dominate during dynamic rupture propagation compared to normal stress changes this result depends completely on the orientation of the whole fault system in all cases we can explain the branch selection by analyzing the applied initial shear stress and the fault properties change of normal stress may play a role similar to shear stress change for disjoint faults since the effect of normal stress change sometimes dominates

electromagnetic induction studies recent developments in electromagnetic induction studies of the lithosphere and the asthenosphere are reviewed attention is given to geoelectrical studies of active tectonic areas in terms of the major zones of crustal extension the basin and range province along western regions of north america and the rio grande rift studies have also been performed of tectonic activity around iceland the salton trough and cerro prieto and the subduction zones of the cascade mountains volcanic belt where magnetotelluric and geomagnetic variation studies have been done geomagnetic variations experiments have been reported in the central appalachians and submarine electromagnetic studies along the juan de fuca ridge controlled source electromagnetic and dc resistivity investigations have been carried out in nevada hawaii and in the adirondacks mountains laboratory examinations on the conductivity of representative materials over a broad range of temperature pressure and chemistry are described

dynamic simulation of a dipping fault using a three dimensional finite difference method with nonuniform grid spacing 1 we propose a method to analyze dynamic rupture processes of earthquakes with a dipping fault using a three dimensional finite difference fd method with nonuniform grid spacing this approach does not require aligning the fault plane to the fd grid for implementation of the fd method it can be used to deal with a realistically complex fault geometry model we validate our method by studying two dynamic source problems that have been analyzed by madariaga et al one is the instantaneous rupture of a circular fault embedded in a homogeneous elastic medium the other is the spontaneous rupture of a rectangular fault which starts from a local circular asperity on the fault plane our numerical results for different dipping faults are similar with those obtained by madariaga et al using a horizontal fault plane model in full space thus validating our method for dipping fault models

dynamic faulting studied by a finite difference method we have developed a finite difference method that is especially adapted to the study of dynamic shear cracks we studied a number of simple earthquake source models in two and three dimensions with special emphasis on the modeling of the stress field we compared our numerical results for semi infinite and self similar shear cracks with the few exact solutions that are available in the literature we then studied spontaneous rupture propagation with the help of a maximum stress criterion from dimensional arguments and a few simple examples we showed that the maximum stress criterion depended on the physical dimensions of the fault for a given maximum stress intensity the finer the numerical mesh the higher the maximum stress that had to be adopted a study of in plane cracks showed that at high rupture velocities the numerical results did not resolve the stress concentration due to the rupture front from the stress peak associated with the shear wave propagating in front of the crack we suggest that this is the reason why transonic rupture velocities are found in the numerical solutions of in plane faulting when the rupture resistance is rather low finally we studied the spontaneous propagation of an initially circular rupture two distinct modes of nucleation of the rupture were studied in the first a plane circular shear crack was formed instantaneously in a uniformly prestressed medium after a while once stress concentrations had developed around the crack edge the rupture started to grow in the second type of nucleation a preexisting circular crack became unstable at time t 0 and started to grow the latter model appeared to us as a more realistic simulation of earthquake triggering in this case the initial stress was nonuniform and was the static field of the preexisting fault

three dimensional nonplanar simulation of the 1992 landers earthquake 1 we have simulated the rupture process of the 1992 landers california earthquake using a realistic nonplanar fault geometry including fault bends and branches through a three dimensional boundary integral equation method considering an external loading system due to local tectonics as well as a nonplanar fault structure we could reproduce the characteristic features of this earthquake such as spontaneous rupture transfer between faults pattern of slip distribution and propagation of rupture front without assuming any laterally heterogeneous distribution of parameters we could also reproduce seismic waveforms near the faults especially in the forward direction of rupture propagation where rupture directivity controlled by rupture transfer between faults significantly affects ground motion

alluvial fans on volcanic islands a morphometric perspective sao vicente cape verde abstract the distribution morphology and development of volcanic island alluvial fans are investigated using sao vicente from the cape verde volcanic chain east central atlantic ocean this is a tectonically and volcanically inactive dryland setting comprising an eroded plio pleistocene composite volcano overlying a submarine shield volcano we mapped 228 alluvial fans quantifying fan f and catchment c morphological properties area a gradient g relief r length l fans and catchments of varying size and gradient are distributed around the island coastal margins 6 and along interior valley sides 94 regression results i e ve ve slopes of best fit lines conformed to broader fan research but with weak correlations and coefficient exponent values outside or at the lower end of values reported from non volcanic settings analysis of fan area and gradient vs catchment area regression residuals revealed fans were dominated by small steep gradient 28 and large low gradient forms 39 fan building space is a fundamental control specifically linked to volcano structure but with interplay between rock strength base level and climate fans around the volcanic edifice flanks are uncommon due to steep flank slopes where flank margin fans occur they are typically small and steep forms due to marine erosion fans along flank incised valleys are common large low gradient fans are associated with a major volcanic rift aligned valley structure with extensive erosion into altered and weathered edifice core lithologies small steep gradient fans are associated with edifice flank valleys steeper and narrower valley forms reflect incision into stronger lithologies of the composite volcano flanks restricting fan building space fans located within the volcano central depression are amongst the largest and lowest gradient types building into the eroded and unconfined edifice core space coalescence apex toe incision toe erosion and catchment stream channel backfilling displayed by most fans suggest landscape erosion dominates during more arid periods e g interglacials with the dryland setting generating limited sediment and insufficient flood runoff for transport and fan deposition fan building likely occurs during wetter periods linked to quaternary climate variability quaternary eustatic variations are relevant for the volcano edifice margins where sea level changes control fan building space and erosion

geometry of the kapuskasing structure from a lithoprobe pilot reflection survey a short 10 km pilot seismic reflection profile recorded in the kapuskasing structural zone near foleyet ontario reveals reflections with travel times of at least 5 0 s about 16 km depth an event dipping west from about 1 7 to 3 4 s probably corresponds to the ivanhoe lake cataclastic zone the true geologic dip on this boundary is calculated to be about 35 38 west northwest and is consistent with interpretations of this zone as a west dipping crustal scale thrust fault east dipping reflections are observed with longer travel times than the fault zone arrival and are likely from within the greenstone terrane of the abitibi subprovince

a grid doubling finite element technique for calculating dynamic three dimensional spontaneous rupture on an earthquake fault summary we present a new finite element technique for calculating dynamic 3 d spontaneous rupture on an earthquake fault which can reduce the required computational resources by a factor of six or more without loss of accuracy the grid doubling technique employs small cells in a thin layer surrounding the fault the remainder of the modelling volume is filled with larger cells typically two or four times as large as the small cells in the resulting non conforming mesh an interpolation method is used to join the thin layer of smaller cells to the volume of larger cells grid doubling is effective because spontaneous rupture calculations typically require higher spatial resolution on and near the fault than elsewhere in the model volume the technique can be applied to non planar faults by morphing or smoothly distorting the entire mesh to produce the desired 3 d fault geometry using our faultmod finite element software we have tested grid doubling with both slip weakening and rate and state friction laws by running the scec usgs 3 d dynamic rupture benchmark problems we have also applied it to a model of the hayward fault northern california which uses realistic fault geometry and rock properties faultmod implements fault slip using common nodes which represent motion common to both sides of the fault and differential nodes which represent motion of one side of the fault relative to the other side we describe how to modify the traction at split nodes method to work with common and differential nodes using an implicit time stepping algorithm

dynamic earthquake ruptures in the presence of lithostatic normal stresses implications for friction models and heat production we simulate dynamic ruptures on a strike slip fault in homogeneous and layered half spaces and on a thrust fault in a layered half space with traditional friction models sliding friction exceeds 50 of the fault normal compressive stress and unless the pore pressures approach the lithostatic stress the rupture characteristics depend strongly on the depth and sliding generates large amounts of heat under application of reasonable stress distributions with depth variation of the effective coefficient of friction with the square root of the shear modulus and the inverse of the depth creates distributions of stress drop and fracture energy that produce realistic rupture behavior this ad hoc friction model results in 1 low sliding friction at all depths and 2 fracture energy that is relatively independent of depth additionally friction models with rate weakening behavior which form pulselike ruptures appear to generate heterogeneity in the distributions of final slip and shear stress more effectively than those without such behavior which form cracklike ruptures for surface rupture on a thrust fault the simple slip weakening friction model which lacks rate weakening behavior accentuates the dynamic interactions between the seismic waves and the rupture and leads to excessively large ground motions on the hanging wall waveforms below the center of the fault which are associated with waves radiated to teleseismic distances indicate that source inversions of thrust events may slightly underestimate the slip at shallow depths

spontaneous rupture processes on a bending fault 1 we simulated spontaneous rupture processes on a vertical bending strike slip fault in a three dimensional half space using a finite difference method rupture area and overall slip distribution on the fault vary with the initial stress field which depends on strike change at the bend rupture velocity and detailed slip distribution around the bend on the other hand are affected by time dependent normal stress change caused by rupture this dynamic stress change plays an important role in the rupture process ahead of the bend as well as in the resulting ground motion the numerical simulation method demonstrated here in a simplified geometry is equally applicable to modeling strong ground motion from geometrically complex ruptures in realistic earth models

heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults 1 we combine a viscoelastic model for the interseismic process and an elastodynamic model for the coseismic process to explore the dynamics over multiple earthquake cycles of two parallel strike slip faults embedded in a two dimensional full space the step over fault geometry results in a buildup of heterogeneous fault stress near the step over this heterogeneous stress accumulates at the early stage of the evolution of the fault system and finally stabilizes after a number of earthquake cycles the heterogeneity in fault stress varies with the geometrical parameters e g width and along strike overlap gap of the step over as well as the rupture history of the fault system this heterogeneous fault stress from previous earthquakes has significant effects on earthquake rupture initiation propagation and termination the locations with a low normal stress level near a step over are favorable points for earthquake initiation rupture can jump a 4 km wide compressional step over and a 8 km or wider dilational step over if the fault system has historically experienced many earthquakes a young step over with less induced heterogeneity allows rupture to jump only smaller step over widths these results may have important implications for seismic hazard analysis in areas where segmented strikeslip faults predominate particularly for estimating maximum earthquake potential citation duan b and d d oglesby 2006 heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults j geophys res 111 b05309 doi 10 1029 2005jb004138

construction of equivalent single planar fault model for strike slip stepovers abstract non planarity is a common and natural characteristic of seismic faults that strongly affects the rupture dynamics and the associated seismic waves geometrically uniform planar fault model is widely used in studies of kinematic source inversion seismic hazard estimation and rupture dynamic simulation because of the simplicity and computational efficiency of this method the influence of the geometric heterogeneity of faults on rupture dynamics and associated seismic waves may under some circumstances be reasonably approximated by an appropriate heterogeneous distribution of shear strength of planar faults particularly for the case with uniform initial stress distribution an outstanding issue is how to approximate the dynamic behavior of a non planar fault by means of heterogeneous properties on a planar fault thus we propose the construction of an equivalent planar fault model for a given stepover fault through the introduction of a heterogeneous distribution of static friction coefficient our study shows that the distribution of static friction coefficient on the equivalent planar fault model is mainly controlled by the geometric irregularities of the stepovers regardless of the initial shear stress thereby providing a way to quantify the effect of fault geometry particularly the step width effect in seismic hazard estimation moreover our results indicate that the influence of geometric discontinuity of stepovers on rupture dynamics is equivalent to a barrier of the planar fault model

dynamic rupture simulations with heterogeneous initial stresses inversed from a given slip distribution a case study of the 2017 mw 6 5 jiuzhaigou earthquake abstract heterogeneous initial stresses are extremely important in understanding the physics of earthquake rupture processes we propose a method to estimate heterogeneous initial stresses by comparing the slip from dynamic rupture simulations and the input joint inversion result and apply it to the 2017 mw 6 5 jiuzhaigou earthquake which occurred in the intersection area of the minjiang tazang and huya faults in sichuan province china with the slip distributed on two distinct left lateral strike slip faults as shown in previous geodetic and seismic joint inversion we use the seismic efficiency empirical relation to infer the average stress and the average stress drop is estimated using the static stress drop with the angle of the maximum principal stress and the nucleation fault determined from the relocated aftershocks different principal stresses are calculated with different combinations of average stress and average stress drop the initial normal and residual stresses can be determined using the projection of the principal stresses the initial shear stresses are generated by adding the residual stress and the heterogeneous stress drop which is generated by a set of gaussian random numbers with a given mean and the variance and mapped one by one with the given slip on the fault so that the area with a large slip has a large stress drop by comparing the slip from dynamic rupture simulations and the input joint inversion result we show that the case with a 36 mpa average stress and 2 1 mpa average stress drop provides the best fitting slip snapshots the dynamic coulomb stress change shows that the 2017 mw 6 5 jiuzhaigou earthquake could bring the southeast of the tazang fault and the middle of the minjiang fault closer to failure this work provides a new insight to understand the initial stresses of nature earthquakes

the origin of certain wide valleys in the canary islands abstract the present work addresses a long term controversy concerning the origin of orotava valley one of the most peculiar valleys in the island of tenerife the canary islands spain this valley is characterized by its great width its flat floors gently inclined towards the sea its parallel and almost vertical lateral slopes and its equally steep but irregular valley head where there are recent volcanic cones the source of the lava flows that have covered the valley floor several different theories were formulated since the last century for the formation of orotava valley examination of other wide volcanic valleys and gorges in tenerife whose origin may be similar to orotava valley indicate an alternation of erosion volcanism analysis of the key features of orotava valley itself leads to formulation of an hypothesis which could be applicable to numerous volcanic areas such valleys are developed as volcanic valleys undergo lateral expansion due to repeated alternations of processes initial erosion of the gorges by streams the burial of the gorges by lava flows and the inversion of the relief by erosion at the base of valley walls the continued occurrence of this mechanism causes the side walls of the valley to retreat progressively giving a configuration similar to that of orotava valley

seismic reflections and electrical conductivity a case of holmes s curious dog is there any other point to which you wish to draw my attention to the curious incident of the dog in the night time the dog did nothing in the night time that was the curious incident remarked sherlock holmes arthur conan doyle in the purcell anticlinorium of the canadian cordillera prominent upper crustal seismic reflectors and areas of high electrical conductivity coincide over a wide area reflective layers traceable to outcrop and to a drill hole are caused mostly by impedance contrasts between proterozoic gabbroic sills and metasedimentary rocks layers with high electrical conductivity are zones enriched in magnetic sulfide probably pyrrhotite within the sedimentary rocks attempts to interpret reflectivity and high conductivity in terms of a single geologic process although tempting and certainly satisfying by appealing to occam9s razor must be done with care we speculate that some explanations for crustal reflectors and conductors may be unrealistic and propose an alternative paradigm of interlayered sills and meta sedimentary rocks rich in high conductivity minerals to explain both

dynamic rupture process of the 1999 chi chi taiwan earthquake 1 the dynamic rupture process of the chi chi earthquake has been investigated based on a 3 d spontaneous shear crack model using a thick fault zone model and a slip weakening friction law our results show that the dynamic rupture process of this event is very complex the distribution of the rupture starting time is much more inhomogeneous than that of the kinematic model we find that the zones with a large strength excess on the fault surface delay the rupture propagation the rupture front jumps from the zones with high strength excess to the near zones with low strength excess when encounters the zones with high strength excess leaving the unbroken zones behind which subsequently rupture we also found that the motion on the hanging wall side is larger than that on the foot wall side

effects of realistic surface topography on seismic ground motion in the yangminshan region of taiwan based upon the spectral element method and lidar dtm we combine light detection and ranging lidar digital terrain model dtm data and an improved mesh implementation to investigate the effects of high resolution surface topography on seismic ground motion based upon the spectral element method in general topography increases the amplitude of shaking at mountain tops and ridges whereas valleys usually have reduced ground motion as has been observed in both records from past earthquakes and numerical simulations however the effects of realistic topography on ground motion have not often been clearly characterized in numerical simulations especially the seismic response of the true ground surface here we use lidar dtm data which provide two meter reso lution at the free surface and a spectral element method to simulate three dimensional 3d seismic wave propagation in the yangminshan region in taiwan incorporating the effects of realistic topography a smoothed topographic map is employed beneath the model surface in order to decrease mesh distortions due to steep ground surfaces numerical simulations show that seismic shaking in mountainous areas is strongly affected by topography and source frequency content the amplification of ground motion mainly occurs at the tops of hills and ridges whilst the valleys and flat topped hills experience lower levels of ground shaking interaction between small scale to pographic features and high frequency surface waves can produce unusually strong shaking we demonstrate that topographic variations can change peak ground accel eration pga values by 50 in mountainous areas and the relative change in pga between a valley and a ridge can be as high as a factor of 2 compared to a flat surface response this suggests that high resolution realistic topographic features should be taken into account in seismic hazard analysis especially for densely populated moun tainous areas

archean crust as revealed in the kapuskasing uplift superior province canada in the central superior province of the canadian shield a 120 km wide transition from the low grade michipicoten greenstone belt to the high grade kapuskasing structural zone represents an oblique section through some 20 km of archean crust uplifted along a northwest dipping thrust fault the restored vertical section through the upper and middle crust consists of three megalayers with undulating boundaries 1 0 to 25 km a high grade heterogeneous gneissic assemblage in part older than the upper supracrustal succession

finite element simulations of dynamic shear rupture experiments and dynamic path selection along kinked and branched faults we analyze the nucleation and propagation of shear cracks along nonplanar kinked and branched fault paths corresponding to the configurations used in recent laboratory fracture studies by rousseau and rosakis 2003 2009 the aim is to reproduce numerically those shear rupture experiments and from that provide an insight into processes which are active when a crack initially propagating in mode ii along a straight path interacts with a bend in the fault or a branching junction the experiments involved impact loading of thin homalite 100 a photoelastic polymer plates which had been cut along bent or branched paths and weakly glued back together everywhere except along a starter notch near the impact site strain gage recordings and high speed photography of isochromatic lines provided characterization of the transient deformation fields associated with the impact and fracture propagation we found that dynamic explicit 2 d plane stress finite element analyses with a simple linear slip weakening description of cohesive and frictional strength of the bonded interfaces can reproduce the qualitative rupture behavior past the bend and branch junctions in most cases and reproduce the principal features revealed by the photographs of dynamic isochromatic line patterns the presence of a kink or branch can cause an abrupt change in rupture propagation velocity additionally the finite element results allow comparison between total slip accumulated along the main and inclined fault segments we found that slip along inclined faults can be substantially less than slip along the main fault and the amount depends on the branch angle and kink or branch configuration

the conductivity of the crust and mantle beneath the kapuskasing uplift electrical anisotropy in the upper mantle summary kapuskasing uplift has been interpreted as an oblique cross section of up to 25km of crust and thus provides the opportunity to examine the properties of exposed mid to lower crustal material a magnetotelluric mt survey mapped a remarkably uniform upper crust and provided no evidence for upper crustal conductive zones that could be related to the often observed increase in mid and lower crustal conductivity the only shallow conductive anomaly is related to the ivanhoe lake cataclastic zone but its electrical signature does not appear to extend more than one kilometer in depth a regional apparent resistivity curve was determined from mt data and confirmed by subsequent controlled source electromagnetic surveys regional curves are essential for proper structural interpretation but are often difficult to determine because of electric field distortions the data show a decrease in resistivity at depths below 15 km which is typical of continental crust in many areas of the world there is a clear difference in orthogonal apparent resistivity and phase curves at periods greater than 10s which is most pronounced in a n65 e and n25 w coordinate frame two different models are proposed to explain the data the first consists of a conducting 2 d slab of approximately 50 km width in the lower crust and striking n65 e the strike direction is consistent with a number of regional structural trends but there is no other direct supporting evidence for it the second model invokes either micro or macro electrical anisotropy in the upper mantle there is considerable evidence for seismic anisotropy in the region the electrical anisotropy could be the result of preferential conduction along the c axis of olivine crystals hydrogen dissolved in the olivine lattice with preferential conduction along the a axis or possible alignment of dykes joints and faults in the upper mantle if the anisotropy is related to strain induced orientations of crystals or fabric it will provide evidence for the motions of the mantle associated with plate tectonics

3d finite difference dynamic rupture modeling along nonplanar faults properunderstandingofseismicemissionsassociatedwiththe growth of complexly shaped microearthquake networks and larger scale nonplanar fault ruptures both in arbitrarily heterogeneousmedia requiresaccuratemodelingoftheunderlyingdynamic processes we present a new 3d dynamic rupture finitedifference model called the finite difference fault element fdfe method it simulates the dynamic rupture of nonplanar faults subjected to regional loads in complex media fdfe is based on a 3d methodology for applying dynamic rupture boundary conditions along the fault surface the fault is discretizedbyasetofparallelepipedfaultelementsinwhichspecific boundary conditions are applied these conditions are applied to the stress tensor once transformed into a local fault reference frame numerically determined weight functions multiplying particle velocities around each element allow accurate estimates offaultkinematicparametersi e slipandsliprateindependent of faulting mechanism assuming a coulomb like slip weakeningfrictionlaw aparametricstudysuggeststhatthefdfemethod converges toward a unique solution provided that the cohesive zone behind the rupture front is well resolved i e four or more elements inside this zone solutions are free of relevant numerical artifacts for grid sizes smaller than approximately 70 m results yielded by the fdfe approach are in good quantitative agreement with those obtained by a semianalytical boundaryintegralmethodalongplanarandnonplanarparabola shaped faults thefdfemethodthusprovidesquantitative accurateresults for spontaneous rupture simulations on intricate fault geometries

slip maxima at fault junctions and rupturing of barriers during the 2008 wenchuan earthquake the devastating wenchuan earthquake in 2008 struck along a fault zone that showed low rates of deformation analysis of gps and insar data suggests that as structural barriers failed during a single earthquake the rupture cascaded across multiple fault segments which may explain the high magnitude of the event

investigation on the dynamic rupture of the 1970 ms 7 7 tonghai yunnan china earthquake on the qujiang faultinvestigation on the dynamic rupture of the 1970 ms 7 7 tonghai yunnan china earthquake on the qujiang fault

environmental and sea level changes on banks peninsula canterbury new zealand through three glaciation interglaciation cycles abstract a greater than 200 ka record of marine transgressions and regressions is recorded from a 75 m core from banks peninsula canterbury new zealand this record comprises thick suites of muddy sediments attributed to back barrier lake and lagoonal environments alternating with thin soil and loess complexes these deposits have been dated using radiocarbon and thermoluminescence tl techniques supported by proxy data diatoms phytoliths pollen and sedimentology the aqueous deposits are attributed to three interglacials and an interstadial marine isotope stages 1 5a 5c 6 and 7 the loesses and paleosols date to the intervening stadials isotope stages 2 5d or 6 and probably 8 on the basis of transgressive beach facies back barrier swamps and barrier blocked lake deposits a partial sea level curve including data from isotope stage 5 is presented our data indicate that banks peninsula has been tectonically stable over that period and we provide sea level points that support the existing isotope curve during stages 5 and 6 detailed diatom records are limited to isotope stage 1 and the latter part of stage 5 diatom histories recorded from these stages are remarkably consistent both indicate a progressive floral change from marine types through freshwater colonising species to freshwater planktonic assemblages these reflect parallel histories of coastal evolution during the two interglacials in both cases marine transgression in the early part of the isotope phase was followed by lagoon development implying that a gravel spit extended across the embayment from the west this was succeeded by lake development when the lagoon was cut off by the juncture of the spit with banks peninsula this lake deepened as the coast rotated into swash alignment and the spit was converted into a gravel barrier the vegetation history of the site indicates that mixed podocarp broadleaf forests similar to the pre european flora of banks peninsula occupied the region during isotope stages 1 and 7 this contrasts with the palynological interpretation of a marine record dsdp site 594 from off the canterbury coast which suggested that isotope stage 7 was markedly cooler than the holocene during glacial periods forest was eliminated and replaced by a tall shrubland of mixed montane and coastal affinities

modeling dynamic rupture in a 3d earthquake fault model we propose a fourth order staggered grid finite difference method to study dynamic faulting in three dimensions the method uses an implementation of the boundary conditions on the fault that allows the use of general friction models including slip weakening and rate dependence because the staggered grid method defines stresses and particle velocities at different grid points we preserve symmetry by implementing a two grid row thick fault zone slip is computed between points located at the borders of the fault zone while the two components of shear traction on the fault are forced to be symmetric inside the fault zone we study the properties of the numerical method comparing our simulations with well known properties of seismic ruptures in 3d among the properties that are well modeled by our method are full elastic wave interactions frictional instability rupture initiation from a finite initial patch spontaneous rupture growth at subsonic and supersonic speeds as well as healing by either stopping phases or rate dependent friction we use this method for simulating spontaneous rupture propagation along an arbitrarily loaded planar fault starting from a localized asperity on circular and rectangular faults the shape of the rupture front is close to elliptical and is systematically elongated in the in plane direction of traction drop this elongation is due to the presence of a strong shear stress peak that moves ahead of the rupture in the in plane direction at high initial stresses the rupture front becomes unstable and jumps to super shear speeds in the direction of in plane shear another interesting effect is the development of relatively narrow rupture fronts due to the presence of rate weakening friction the solutions for the thick fault boundary conditions scale with the slip weakening distance do and are stable and reproducible for do greater than about 4 in terms of 2t t ax finally a comparison of scalar and vector boundary conditions for the friction shows that slip is dominant along the direction of the prestress with the largest deviations in slip rate direction occurring near the rupture front and the edges of the fault

a unified view of craton evolution motivated by recent deep seismic reflection and refraction results summary an attempt is made to integrate recent continental seismic reflection refraction and geologic observations into a unified scheme of craton evolution 1 nascent continental crust of basaltic bulk composition is produced in island arcs as with oceanic crust moho in this setting lies within the magmatic edifice and corresponds to a downward transition from dominantly mafic cumulate rocks above to dominantly ultramafic cumulates below the petrologic crust mantle boundary lying 25 per cent deeper in the lithosphere has no seismic expression and corresponds to a depositional magmatic contact between cumulate ultramafic rocks above and residual mantle ultramafic tectonite below both contacts are presumably extensively disrupted by magmatic injection 2 island arcs are amalgamated into continents at collision zones delamination of the lower mafic ultramafic portion of the crust along with the mantle lithosphere during hard collisions acts as a mechanical refining process that pushes the bulk crust toward intermediate composition 3 subsequent extensional collapse of the overthickened crust together with thermal re equilibration of the lithosphere results in youthful stable continental crust which is 30 km thick with its top surface awash at sea level and has the bulk composition of andesite this crust characteristically exhibits extensional features half grabens in the upper portion and is prominently laminated in the lower portion due to the injection of modest amounts of basaltic magma in the form of sills during delamination the moho and petrologic base of the crust coincide in this setting and can correspond to either a ductile high strain zone or intrusive contact separating mafic intermediate composition material above from fertile mantle lherzolite below 4 subsequent cratonization is the cumulative effect of episodic injection of the crust by mafic magma at intervals of hundreds of myr as manifest by the ubiquitous overlapping dike swarms of the precambrian shields this results in net long term thickening of the crust by underplating shifts the bulk crust back toward mafic composition periodically produces a new deeper moho and petrologic crust mantle boundary that do not coincide and through repeated dike injection disrupts pre existing laminated reflectors the first magmatic injection event sweats out the light melting fraction in the pre existing andesitic crust producing voluminous granitic magmatism typified by the great proterozoic anorogenic granite rhyolite provinces subsequent injection events into refractory crust produce uplift with attendant erosional denudation of supracrustal sequences the cumulative result is shield type crust in which intermediate crustal levels are exposed over wide areas crustal thickness commonly exceeds 40 km average crustal velocity is somewhat higher than in younger stable crust and the crust is commonly complexly reflective diffractive throughout

dynamic rupture models for the southern san andreas fault abstract dynamic rupture and resultant ground motions up to 0 25 hz are simulated for an m w 7 6 earthquake on the southern san andreas fault spontaneous rupture is modeled with slip weakening friction and 3d viscoelastic wave solutions are computed with a support operator numerical method the initial traction model is derived from inversions of the m w 7 3 1992 landers strong ground motion records and borrows heavily from that used for the terashake2 simulations by olsen et al 2008 heterogeneity in the traction model leads to focusing of the rupture front and the focusing produces cases of supershear rupture velocity in asperities areas of high initial traction as well as cases of high peak slip rate and cohesive zone contraction in antiasperities separate solutions are computed for version 3 0 and 4 0 respectively of the southern california earthquake center community velocity model scec cvm we also compare the case of a flat ground surface a common simplification made for finite difference simulations to the case of the ground surface conformed to regional topography the overall distribution of simulated ground motion intensity is consistent with that derived from the empirical model of campbell and bozorgnia 2008 in the sense that the bulk of simulated pseudospectral velocity psv values are within the 68 confidence intervals of the empirical model simulated psvs corresponding to low probability in the empirical model are principally associated with basin wave guide and directivity effects an important example first identified by the terashake1 simulations olsen et al 2006 is the stronger than expected ground motions at the site of montebello due to a basin wave guide effect we find that this effect is lessened for version 4 0 of the scec cvm relative to version 3 0 due to a shallower model for the chino basin

high grade metamorphism in the chapleau foleyet area ontario archean rocks superior province kapuskasing structural zone in migmatitic mafic gneiss paragneiss dioritic and tonalitic rocks a lower grade garnet clinopyroxene plagioclase gt cpx pl zone and patchy higher grade orthopyroxene zones are distinguished based on mineral melt equilibria minimum conditions for the gt cpx pl zone are 750 degrees c 6 kbar a h 2 o 0 5 0 7 and for the orthopyroxene zone 770 degrees c 6 kbar a h 2 o 800 degrees c pressure values are 5 4 8 4 kbar and define a nne trending area of relatively high p in the kapuskasing zone supporting the interpretation of a tilted crustal section modified journal abstract

a summary of electromagnetic studies on the abitibi grenville transect electromagnetic surveys on the abitibi grenville lithoprobe transect have elucidated a number of conductivity signatures that can be genetically linked to precambrian tectonic processes some major fault zones are moderately conductive possibly signalling graphite deposition from a mantle co2 flux along crust penetrating fault systems however conductive graphitic metasedimentary rocks characteristic of foreland basins are apparently absent from the transect area a weak inverse correlation between metamorphic grade and electrical conductivity was observed by following rock units across the grenville front into high grade equivalents within the parautochthonous belt a uniformly conductive mid crustal layer extends across the grenville front apparently without change in character the existence of this ubiquitous mid crustal conductor has been interpreted to mean that electrical conductivity is controlled by the present day pressure temperature and fluid saturation of the lower crust independent o

a controlled source time domain electromagnetic survey over an upthrust section of archean crust in the kapuskasing structural zone summary a pilot controlled source electromagnetic survey was conducted in the kapuskasing structural zone to test the application of the utem technique for determining the electrical conductivity structure of the earth s crust to depths of up to 10 km in general the data are consistent with the results of an earlier broadband magnetotelluric mt survey and indicate a quasi layered earth below a variable overburden zone with conductances between 0 1 and 0 5 s at some depth below 10 km conductivity appears to increase in agreement with the mt interpretation and provides confidence that the static shift of the mt data was corrected a weakly conductive layer located at depths greater than 2 km is possibly associated with a feature of the ivanhoe lake cataclastic zone ilcz a major fault zone along which up to 30 km of the earth s crust has been thrust to the surface there was no clear evidence in the utem data for a conductive zone extending to the proposed surface strike location of the ilcz a conductive anomaly at depths of 1 2 km may extend east of the present survey area and suggested that a subsequent utem survey must expand the coverage to the east

dynamic rupture simulations of the 1920 ms 8 5 haiyuan earthquake in chinadynamic rupture simulations of the 1920 ms 8 5 haiyuan earthquake in china

scale model and numerical simulations of near fault seismic directivity foam rubber experiments simulating unilaterally propagating strike slip earthquakes provide a means to explore the sensitivity of near fault ground motions to rupture geometry subsurface accelerometers on the model fault plane show rupture propagation that approaches a limiting velocity close to the rayleigh velocity the slip velocity waveform at depth is cracklike slip duration of the order of narrower fault dimension w divided by s wave speed surface accelerometers record near fault ground motion enhanced along strike by rupture induced directivity most experimental features initiation time shape duration and absolute amplitude of acceleration pulses are successfully reproduced by a 3d spontaneous rupture numerical model of the experiments numerical and experimental model acceleration pulses show similar decay with distance away from the fault and fault normal components in both models show similar large amplitude growth with distance along fault strike this forward directivity effect is also evident in response spectra the fault normal spectral response peak at period w 3 increases approximately sixfold along strike on average in the experiments with similar increase about fivefold in the corresponding numerical simulation the experimental and numerical model response spectra agree with an empirical directivity model for natural earthquakes at long periods near w and both overpredict shorter period empirical directivity effects with the amount of overprediction increasing systematically with diminishing period we attribute this difference to rupture and wavefront incoherence in natural earthquakes due to fault zone heterogeneities in stress frictional resistance and elastic properties present in the earth but absent or minimal in the experimental and numerical models rupture front incoherence is an important component of source models for ground motion prediction but finding an effective kinematic parameterization may be challenging

a new biem for rupture dynamics in half space and its application to the 2008 iwate miyagi nairiku earthquake summary we developed a code for dynamic rupture propagation on arbitrarily shaped faults embedded in half space using boundary integral equation method biem it is based on an existing code for the full space case in which virtual free surface elements were introduced computations in half space are definitely necessary for the modelling of shallow dipping fault ruptures first we describe the implementation and conduct some validation tests that demonstrate the accuracy of the code the validation tests are carried out by comparing the biem results both with the analytical static solution and with the seismic wavefield obtained by a discrete wavenumber method then we apply the code to the study of the 2008 iwate miyagi japan earthquake mw 6 9 rupture dynamics the average stress drop was estimated to be rather large 16 mpa in the asperity area while the average strength excess was 5 mpa the average fracture energy inside the asperity was found to be 36 mjm 2 finally the free surface effect examination showed that the stress drop and the fracture energy were overestimated at shallow depth in the full space computation

a support operator method for 3 d rupture dynamics summary we present a numerical method to simulate spontaneous shear crack propagation within a heterogeneous 3 d viscoelastic medium wave motions are computed on a logically rectangular hexahedral mesh using the generalized finite difference method of support operators som this approach enables modelling of non planar surfaces and non planar fault ruptures our implementation the support operator rupture dynamics sord code is highly scalable enabling large scale multiprocessors calculations the fault surface is modelled by coupled double nodes where rupture occurs as dictated by the local stress conditions and a frictional failure law the method successfully performs test problems developed for the southern california earthquake center scec u s geological survey usgs dynamic earthquake rupture code validation exercise showing good agreement with semi analytical boundary integral method results we undertake further dynamic rupture tests to quantify numerical errors introduced by shear deformations to the hexahedral mesh we generate a family of meshes distorted by simple shearing in the along strike direction up to a maximum of 73 for scec usgs validation problem number 3 grid induced errors increase with mesh shear angle with the logarithm of error approximately proportional to angle over the range tested at 73 rms misfits are about 10 per cent for peak slip rate and 0 5 per cent for both rupture time and total slip indicating that the method which up to now we have applied mainly to near vertical strike slip faulting is also capable of handling geometries appropriate to low angle surface rupturing thrust earthquakes additionally we demonstrate non planar rupture effects by modifying the test geometry to include respectively cylindrical curvature and sharp kinks

constraints on crust mantle transition zone with pn waveforms a case study of eastern china and southern korean peninsula abstract the seismic velocity structure of the crust mantle transition zone cmtz provides key constraints on crustal dynamics and can be studied with pn wave which propagates horizontally along the moho discontinuity in this study we first explore an effect of velocity gradient structures in the cmtz through synthetic pn waveforms and demonstrate that the shape of pn changes from step like to pulse like when the cmtz becomes from sharp to a gradient velocity structure respectively we then use pn waveforms of the regional earthquakes the july 2012 mw 4 8 earthquake in east china and the september 2016 mw 5 1 earthquake in south korea to examine the cmtz structures to the west and east of the yellow sea and thus to constrain tectonic affinity between the eastern china and southern korean peninsula the pn waveforms from the mw 4 8 event in east china show that the moho in southern yangtze craton is sharp whereas there may be a gradient structure in cmtz with a 6 10 km thickness in northern yangtze craton the pn waveforms from the mw 5 1 event in south korea show that the cmtz in south korea is also sharp similar to the southern yangtze craton observed difference in cmtz structures suggest that sulu orogenic belt may extend along the north of the gyeonggi massif in korea

three dimensional finite difference simulation of fault dynamics rectangular faults with fixed rupture velocity we analyze three dimensional finite difference solutions for a simple shear crack model of faulting to determine the effects of fault length and width on the earthquake slip function the fault model is dynamic with only rupture velocity fault dimensions and dynamic stress drop prescribed the numerical solutions are accurate for frequencies up to 5 hz and are combined with asymptotic results for shear cracks in order to characterize the slip function at higher frequencies near the hypocenter the slip velocity exhibits a square root singularity whose intensity increases with hypocentral distance at distances greater than the fault width w growth of the velocity intensity ceases and the slip function becomes nearly invariant with distance along the fault length closed form expressions are developed for the dependence of static slip s slip rise time tr and slip velocity intensity v on fault geometry along the center line of a long narrow fault at hypocentral distances exceeding w these expressions reduce to s w tr 0 5 w vr and v w 2 vr where is the dynamic stress drop the shear modulus and vr the rupture velocity the numerical results imply that uniform dislocation kinematic earthquake models in which slip is represented by a ramp time function will underpredict high frequency ground motion relative to low frequency ground motion a further implication of the numerical solutions is that the nature of inelastic processes at the advancing edge of a long fault will depend on fault width but will be independent of rupture length

earthquake rupture extents and coseismic slips promoted by damaged fault zones here we investigate the effects of damage fault zones on rupture propagation by conducting a series of 3 d dynamic rupture simulations on a planar vertical strike slip fault we find that damage fault zones can promote rupture extent and increase earthquake potency the waves reflected from the bottom of shallow damage fault zones can increase shear stress on the fault and thus promote rupture propagation in addition the promotional effects increase with the width and depth extent of damage fault zones the overall effects of the waves reflected from the fault parallel side boundaries of damage fault zones are unfavorable for rupture propagation therefore rupture propagation is promoted with the increased width of fault zones due to geometrical spreading effects moreover nonground breaking ruptures may reach the ground surface with the effects of damage fault zones furthermore along strike segmented fault zones as suggested by observations could also promote ruptures and may lead to preferred rupture directions if epicenters are close to fault zones the effects of damage fault zones on rupture propagation hold important implications on assessing earthquake risk

carbonaceous films in midcrustal rocks from the ktb borehole germany as characterized by time of flight secondary ion mass spectrometry 1 amphibolites from 4 6 and 9 1 km depth in the kontinentales tiefbohrprogramm der bundesrepublik deutschland ktb borehole have developed extensive interconnected networks of carbonaceous films on cracks and grain boundaries as determined by electron probe and time of flight secondary ion mass spectrometry in the sample from 9 1 km depth the carbon is dominantly to completely elemental in contrast the carbonaceous matter in the samples from 4 6 km depth comprises a mixture of elemental carbon and simple hydrocarbons such as alkanes and possibly c o h compounds the microcracks within the 4 6 km sample also contain a retrograde micro assemblage consisting of ferri oxy hydroxide calcite and possibly clay minerals suggesting that the carbonaceous matter and retrograde minerals formed together at relatively high crustal levels and at a time much later than the peak metamorphism because the carbon films likely influence the electrical conductivity of the rocks in situ it is proposed that production of hydrocarbons during retrograde metamorphism of grain boundary and microcrack carbon tends to increase the resistivity of the rocks this chemical destruction of the interconnectivity of electrical pathways may contribute to the observed diminished conductivity of the shallow crust relative in relation to thto the deep crust

supershear transition due to a free surface in 3 d simulations of spontaneous dynamic rupture on vertical strike slip faults supershear rupture propagation has been inferred from seismic observations for natural faults and observed in laboratory experiments we study the effect of the free surface on the transition of earthquake rupture from subshear to supershear speeds using simulations of spontaneous dynamic rupture on vertical strike slip faults we find that locally supershear rupture near the free surface can occur due to i the generalized burridge andrews mechanism that is a supershear loading field between p and sv wave arrivals generated by the main rupture front at depths and ii the phase conversion of sv to p diffracted waves at the free surface weaker supershear slip due to the generalized burridge andrews mechanism is caused by the low strength at shallow portions of the fault relative to deeper ones dominant supershear rupture is supported by the additional supershear loading field produced by phase conversion locally supershear propagation at the free surface occurs regardless of the level of prestress and can cause transition to supershear propagation over the entire seismogenic depth such global supershear transition which depends on prestress can occur under prestress levels lower than the theoretical estimates for models with no free surface although the effectiveness of supershear transition due to the free surface can be diminished by several potentially important factors it may play an important role on natural faults at least in those strike slip earthquakes that accumulate significant surface slip

reconnaissance electromagnetic induction study of the kapuskasing structural zone implications for lower crustal conductivity abstract a large scale electromagnetic induction study has been carried out over the kapuskasing structural zone ksz an upthrust section of lower crustal rocks in north central ontario the absence of an overall anomalous response from the ksz even though the lower crust in this region of the canadian shield is known to be anomalously conductive implies that enhanced lower crustal conductivity is related to intrinsic conditions at lower crustal depths and not to mineralogical composition

heterogeneous distribution of the dynamic source parameters of the 1999 chi chi taiwan earthquake 1 the spatial and temporal distribution of the stress on the fault plane of the 1999 chi chi taiwan earthquake is calculated from kinematic inversion results using a three dimensional finite difference method for solving the elastodynamic equations we analyze the relations between stress and slip for all grid positions on the fault and use these relations to infer the friction law for the rupture the dynamic source parameters were also determined our results show that for most of the points on the fault the relation between stress and slip was consistent with the slip weakening law during the rupture process especially for those points with large slip however consistency with the velocity weakening law is not clear from the observed relation between stress and slip velocity the distributions of the dynamic parameters on the fault are very heterogeneous the peak value of the static stress drop is 35 mpa in general high stress drop occurred in the areas with large slip the estimated strength excesses are generally small suggesting that the tectonic shear stress had reached the level of the fault strength before the main shock the slip weakening distance dc and the fracture energy gc are proportional to the final slip the aftershock activity correlates with the spatial distribution of dynamic source parameters usually the aftershocks near the fault plane are concentrated in regions with small or negative static stress drop and there were few aftershocks in regions which had large values of critical slip weakening distance dc

grain boundary graphite in kapuskasing gneisses and implications for lower crustal conductivity surface electromagnetic measurements commonly reveal that the intermediate and lower continental crust has an appreciable electrical conductivity much higher than that found for laboratory analogues of deep crustal rocks or for upper crustal rocks either formed at shallow depths or uplifted from deeper levels conducting films at grain boundaries are thought to play an important part in enhancing deep crustal conductivity with brines and graphite being the main candidates1 at present however there is a lack of direct evidence for such films frost et al 2 have reported an enhancement in conductivity of igneous lower crustal rocks from the la ramie complex apparently owing to the presence of graphite films but the possible role of brines was not clear from this work here we present a study of the grain surface composition of metamorphic and one igneous rocks exhumed from 20 km depth by the kapuskasing uplift of the canadian shield3 we expect these samples to be representative of metamorphic and igneous rocks of the deep archaean crust auger spectroscopy provides evidence for graphite films at grain boundaries which can account for the present electrical signature of the kapuskasing crust4 6 we also detect traces of chlorine sulphur and iron which suggest that brines and solid conductors other than graphite may have helped to enhance the conductivity but their abundance suggests at best a minor role relative to graphite

3 d finite difference elastic wave modeling including surface topography three dimensional finite difference fd modeling of seismic scattering from free surface topography has been pursued we have developed exact 3 d free surface topography boundary conditions for the particle velocities a velocity stress formulation of the full elastic wave equations together with the boundary conditions has been numerically modeled by an eighth order fd method on a staggered grid we give a numerical stability criterion for combining the boundary conditions with curved grid wave equations where a curved grid represents the physical medium with topography implementation of this stability criterion stops instabilities from arising in areas of steep and rough topographies we have simulated scattering from teleseismic p waves using a plane vertically incident wavefront and real topography from a 40 40 km area centered at the noress array of seismic receiver stations in southeastern norway synthetic snapshots and seismograms of the wavefield show clear conversion from p waves to rg sh

spectral element modeling of spontaneous earthquake rupture on rate and state faults effect of velocity strengthening friction at shallow depths we develop a spectral element methodology sem for simulating dynamic rupture on rate and state faults and use it to study how the rupture is affected by a shallow fault region of steady state velocity strengthening friction our comparison of the developed sem and a spectral boundary integral method bim for an anti plane two dimensional test problem shows that the two methods produce virtually identical solutions for the finest resolution we use and that the convergence with grid reduction of the developed sem methodology is comparable to that of bim we also use the test problem to compare numerical resolution required for different state evolution laws and for linear slip weakening friction using our three dimensional implementation of the methodology we find that a shallow velocity strengthening fault region can significantly alter dynamic rupture and ground motion the velocity strengthening region suppresses supershear propagation at the free surface occurring in the absence of such region which could explain the lack of universally observed supershear rupture near the free surface in addition the velocity strengthening region promotes faster fall off of slip velocity behind the rupture front and decreases final slip throughout the entire fault causing a smaller average stress drop the slip decrease is largest in the shallow parts of the fault resulting in the depth profile of slip qualitatively consistent with observations of shallow co seismic slip deficit the shallow velocity strengthening region also reduces the amplification of strong ground motion due to a low velocity bulk structure

anteconsequent drainage an unusual example formed during constructive volcanism abstract drainage on the north and west flanks of the miocene lyttelton volcano does not have the expected radial and consequent pattern instead it has a paleoradial pattern antecedent to the obvious edifice but consequent to an earlier now buried volcanic cone the centre of which is 3 km from the centre of the present eroded cone there seems to be no completely appropriate term for such a sequence of development it is proposed that the term anteconsequent previously used in the context of orogenesis and erosion should be extended to cover the situation described on the lyttelton volcano

near field radiated wave field may help to understand the style of the supershear transition of dynamic ruptures abstract supershear earthquakes are known to leave special signatures in the signals on the fault fault slip velocity dynamic traction evolution energy flux etc and in the ground motions moreover two different styles of supershear transition have been identified in the direct transition dt mechanism the rupture speed continuously increases from the sub rayleigh to the terminal speed of p waves while in the mother daughter md mechanism a forbidden zone of rupture speed exists and a secondary pseudo rupture is generated ahead of the primary rupture front here we found that the off fault signals wavefields generated by these two mechanisms are rather different in that the md case contains an enhanced trailing rayleigh field which has very low amplitudes or it is even practically absent in the dt case and possess higher frequency content therefore we show that it is possible to distinguish the style of the supershear transition from the records of real earthquakes in particular basing on the results of our numerical simulations we can conclude that the denali alaska earthquake was basically controlled by a classical md mechanism

imaging of deep fluids in archaean crust despite the importance of aqueous fluids in tectonic metamorphic and magmatic activity in the earth s crust few techniques are available for directly observing their distribution at depth even in stable continental crust such observations as have been made electromagnetic deep sounding which by inference1 2 images saline fluids and super deep drilling3 suggest that fluids are present in varying amounts throughout the crust in direct conflict4 with the normal petrological inference of a very dry deep crust here we report the results of an unusually high resolution electromagnetic sounding method to image the deep electrical conductivity structure below a 30 km profile in ontario which crosses archaean lower crustal material of high metamorphic grade exposed by a proterozoic thrust fault the ivanhoe lake cataclastic zone the electrical resistivity image obtained shows embedded in very resistive crystalline crust two nearly continuous sub horizontal zones of enhanced electrical conductivity at depths of 2 3 and 5 6 km below this the commonly observed2 5 7 mid crustal rise in conductivity is seen at depths of 15 20 km the image does not correlate well with the structure inferred from surface geology suggesting that the transport and distribution of fluids was not strongly controlled by lithological boundaries or the thrust fault itself

estimating rupture scenario likelihood based on dynamic rupture simulations the example of the segmented middle durance fault southeastern france summary the middle durance fault system southeastern france is a slow active fault that produced moderate size historical seismic events and shows evidence of at least one m w 6 5 event in the last 29 000 yr based on dynamic rupture simulation we propose earthquake scenarios that are constrained by knowledge of both the tectonic stress field and of the 3 d geometry of the durance fault system we simulate dynamic rupture interaction among several fault segmentations of different strikes dips and rakes using a 3 d boundary integral equation method 50 combinations of reasonable stress field orientations stress field amplitudes and hypocentre locations are tested the probability of different rupture evolutions is then computed each segment ruptures mainly as a single event 44 per cent of the 50 simulations test in this paper however the probability that an event triggers simultaneously along three segments is high 26 per cent leading to a potential rupture length of 45 km finally 2 per cent of the simulations occur along four adjacent segments producing the greatest total rupture length of 55 km the simulation results show that the southernmost segment is most easily ruptured 40 per cent because of its favourable orientation with respect to the tectonic stress and of its favourable location for interaction with the other segments south bound unilateral propagation is slightly preferable 41 per cent compared to north bound unilateral and bilateral propagation modes although these rupture scenarios cannot be directly translated into probabilities of occurrence they do provide a better insight as to which rupture scenarios are more likely an important element to better estimate near field strong ground motion and seismic hazard

2d finite difference elastic wave modelling including surface topography1 a 2d numerical finite difference algorithm accounting for surface topography is presented higher order dispersion bounded cost optimized finite difference operators are used in the interior of the numerical grid while non reflecting absorbing boundary conditions are used along the edges transformation from a curved to a rectangular grid achieves the modelling of the surface topography we use free surface boundary conditions along the surface in order to obtain complete modelling of the effects of wave propagation it is important to account for the surface topography otherwise near surface effects such as scattering are not modelled adequately even if other properties of the medium for instance randomization can improve numerical simulations inclusion of the surface topography makes them more realistic

significant lateral dip changes may have limited the scale of the 2015 mw 7 8 gorkha earthquake the 2015 mw 7 8 gorkha earthquake has drawn interest due to its complex fault geometry both geodetic and geologic studies have focused on the dip variations in this study we invert the coseismic geodetic data for the 2 d dip variations of the earthquake the best fit model confirms that the dip varies with depth and suggests that there is a significant lateral dip anomaly along strike the depth dependent dip variation suggests that the earthquake ruptured a ramp flat fault the shallow ramp may have prevented the rupture breaking through the surface in addition a lateral large dip anomaly is found in the northeastern corner of the slip area which supports the previous findings of inferred interseismic fault coupling coseismic high frequency radiations and the aftershock mechanisms this lateral dip anomaly is likely associated with local tearing within the indian slab it may have blocked the east southeastward rupture propagations of the gorkha earthquake implying important controls on the earthquake scale and the spatial limits of ruptures

ground motion signatures of supershear ruptures in the burridge andrews and free surface induced mechanisms abstract we analyze the ground motions of supershear ruptures in the burridge andrews bam and free surface induced fsi mechanisms bam supershear ruptures require higher initial shear stress than fsi supershear ruptures thus cause faster rupture speed the supershear slip pulse initiates at the free surface or upper boundary of a fault for fsi and at the hypocenter depth in the in plane direction for bam in homogeneous models both bam and fsi supershear ruptures can generate mach waves and the rayleigh wave field the bam and the faster fsi supershear ruptures can make stronger shear mach waves the shear mach waves show a larger amplitude of negative component for a faster fsi supershear rupture the fsi supershear ruptures make the strongest dilatational wave next to the fault while it is at a distance away from the fault for the bam supershear ruptures the different shapes of supershear rupture front locations of supershear triggered and the rupture speeds contribute to these contrasts and we find that the bam and the faster fsi supershear ruptures can trigger more high frequency radiation due to the sharper and stronger shear mach waves finally the comparisons between the simulated seismograms and the records of ps10 indicate that the 2002 denali earthquake may represent a supershear one with the fsi mechanism and a slow supershear rupture speed

rupture dynamics and ground motion from 3 d rough fault simulations 1 we perform three dimensional 3 d numerical calculations of dynamic rupture along non planar faults to study the effects of fault roughness on rupture propagation and resultant ground motion the fault roughness model follows a self similar fractal distribution over length scales spanning three orders of magnitude from 102 to 105 m the fault is governed by a strongly rate weakening friction and the bulk material is subject to drucker prager viscoplasticity fault roughness promotes the development of self healing rupture pulses and a heterogeneous distribution of fault slip at the free surface and at depth the inelastic deformation generated by the large dynamic stress near rupture fronts occurs in a narrow volume around the fault with heterogeneous thickness correlated to local roughness slopes inelastic deformation near the free surface however is induced by the stress waves originated from dynamic rupture at depth and spreads to large distances 10 km away from the fault the present simulations model seismic wave excitation up to 10 hz with rupture lengths of 100 km permitting comparisons with empirical studies of ground motion intensity measures of engineering interest characteristics of site averaged synthetic response spectra including the distance and period dependence of the median values absolute level and intra event standard deviation are comparable to appropriate empirical estimates throughout the period range 0 1 3 0 s this class of model may provide a viable representation of the ground motion excitation process over a wide frequency range in a large spatial domain with potential applications to the numerical prediction of source and path specific effects on earthquake ground motion

magnetotelluric interpretation of crustal and mantle structure in the grenville province summary accurate determinations of depths and conductivities of electrical structures in shield regions are often difficult because of the inhomogeneity of the uppermost crust a magnetotelluric mt station bat in the grenville province of the precambrian shield in eastern canada has been in operation since 1975 for time dependency studies of electrical resistivity changes related to earthquakes the mt response of the station displays low skew with small to moderate anisotropy one dimensional inversion of the apparent resistivity and phase reveals two well defined conductors in the crust one at 10 km and the second at the base of the crust the latter has a resistivity less than 50 m these results are substantiated by three additional mt stations located up to 40 km distant data from other new mt stations and from stations previously published in the literature are compared with two dimensional computer model results and with the three dimensional analogue scale model results of dosso et al while additional data for periods less than 100 s would be desirable the results from a number of the mt stations are not inconsistent with a widespread occurrence of a conducting zone at the base of the crust in the grenville the inversion analysis also indicates the existence of a conductor at some depth greater than 100 km with a resistivity less than 30 m this may coincide with a seismic low velocity zone observed in the mantle under the canadian shield

a review of electromagnetic investigations in the kapuskasing uplift and surrounding regions electrical properties of key rocks electromagnetic investigations of the kapuskasing uplift show that the gross electrical conductivity structure of the present crust is subhorizontal contrary to the lithology as defined by seismic experiments with increasing conductivity with depth a feature common to most continental crusts the current upper crust of the chapleau block includes zones of reduced resistivity the near surface expression of the ivanhoe lake cataclastic zone 40 k m these include a subhorizontal layer at 5 km and a subhorizontal to dipping layer at 2 km the deeper layer is interpreted as imaging deep fluids porosities 0 5 postdating the uplift the shallower feature possibly related to the seismically detected detachment zone dipping at 15 could be imaging conductors s

the simulation of rupture dynamics from potential earthquakes around xiluodu reservoir dam china abstract the xiluodu reservoir dam located on the jinsha river is one of the largest dams in the world nearby faults are very active and two m 7 strong earthquakes have occurred around the dam simulating the rupture dynamics of potential earthquakes on the surrounding faults is very important to estimate the seismic hazard for the dam in this research we use the curved grid finite difference method cg fdm to simulate spontaneous ruptures on the major faults around the dam the main results are that the leibo middle and south faults lbmf and lbsf are more likely to have large destructive earthquakes than the mabian yanjin east fault mb yjef asperities on faults that have an impact on strong ground motion are formed under the combined influence of the regional background stress field and fault geometry spontaneous ruptures on the lbmf and lbsf are mainly strike slip with minor thrust components while those on the mb yjef are strike slip and thrust these results are consistent with the focal mechanisms of recorded small and moderate earthquakes in this area

petrophysical model of deep electrical conductors graphite lining as a source and its disconnection due to uplift petrophysical information including stress release data recently made available for low porosity 0 1 0 4 crystalline rocks has been used to develop a broken conductor model that may explain the origin of enhanced electrical conductivity of the intermediate to lower continental crusts of shields and its disappearance when the rocks are uplifted average pore size and pore density of their fluid flow paths are 0 1 0 4 m and 1 400 m respectively the model assumes that these paths are filled or lined with interconnected electrical conducting minerals such as graphite resulting in the rocks having resistivities as low as 40 to 800 m in situ graphite film thicknesses required to produce these resistivities are 5 20 nm 50 200 a the model also assumes that electrical conducting paths break up during uplift due to stress release resulting in a poorly conducting rock petrophysical data of granites and observations from deep drill holes suggest a porosity increase of the order of 3 from an uplift of 10 km or more however the newly formed pore space would fill with deposits or intruded material so that surface rock porosities would not be much larger than at depth electrical resistivities of rock samples containing disconnected grain boundary graphite presently exposed by the kapuskasing uplift of the canadian shield are in the range of 3000 12000 m for the direction of foliation these values are 10 100 times larger than the estimates for similar rocks containing interconnected graphite but are 10 100 times smaller than usually observed in the canadian shield for similar rocks absent of grain boundary graphite these observations are in good agreement with the results predicted by the broken conductor model for an uplift of 10 km or more if a gross linear relationship is assumed between crack porosity and uplift for the upper 10 km of the crust

seismic characteristics of supershear and sub rayleigh earthquakes implication from simple cases numerous investigations of supershear earthquakes make a conclusion that a supershear earthquake produces a seismic shock wave on the ground that may increase the resulting destruction we investigate a supershear rupture promoted by the free surface and find out that although the seismic energy of a supershear earthquake can be transmitted further with large amplitudes the peak slip velocity on a fault near the free surface is smaller than that caused by a subshear rupture earthquake our results show that the free surface induced supershear rupture mitigates the amplitudes of ground motions near the fault plane compared with the subshear rupture the coulomb failure change derived from dynamic modeling further suggests that this free surface induced supershear reduces aftershock potential compared to a subshear rupture both ground motion at near fault and aftershock possibility show low risk for the free surface induced supershear rupture earthquake than subshear earthquake contrary to the traditional concept

direct current resistivity and lotem model for the deep structure of the northern edge of the kaapvaal craton south africa abstract the transition from the high grade metamorphic southern marginal zone smz of the limpopo belt to the low grade kaapvaal craton was studied by means of geoelectrical techniques the d c data showed conclusively that the high grade rocks were thrust over the low grade rocks this contradicts earlier geological ideas but agrees with recent seismic reflection data the area where high grade rocks occur above low grade strata was mapped out and the southern boundary of the smz was established the conductor that occurs at lower crustal depths in the kaapvaal craton was traced into the smz using the lotem method the conductor shallows from 30 to 22 km over 12 km on the surface but does not reflect the difference in metamorphic depth of 30 km seen at the surface this indicates that the conductor is a transient feature of the crust the conductor is not associated with a seismically reflective crust the cause of the conductor remains enigmatic