stress slip and earthquakes in models of complex single fault systems incorporating brittle and creep deformations numerical simulations of slip evolution along a cellular vertical strike slip fault in an elastic half space are performed for several models representing discrete fault systems embedded in three dimensional elastic continua the geometry and imposed boundary conditions correspond approximately to the central san andreas fault the simulations incorporate brittle and creep deformations in series the net fault zone deformation rate is the sum of creep rate and frictional slip rate brittle fault properties are given by various distributions of earthquake stress drops on failing segments numerical cells the assumed distributions represent two idealized situations corresponding to different extreme states along an evolutionary path of a fault 1 a strongly disordered state characterized by a wide range of size scales representing immature fault zones and extended spatial domains and 2 a relatively regular state having a narrow range of size scales representing mature highly slipped faults the assumed creep properties are identical in all cases these are prescribed in terms of coefficients characterizing a power law dependency of creep slip rate on stress the combined brittle creep process and employed parameters lead to an overall pine tree stress depth profile with a brittle ductile transition depth of about 12 5 km and variable stress along strike profiles with brittle creep transition around 65 km nw of the 1857 rupture the spatial patterns of simulated hypocenters are statistically similar to observed data the results indicate that the range of size scales characterizing strong fault zone heterogeneities has important manifestations on the seismic response of a fault system a narrow range of size scales leads to frequency size statistics of earthquakes resembling the characteristic earthquake distribution and quasi periodic temporal distribution of large events as in the seismic gap hypothesis on the other hand a wide range of size scales leads to gutenberg richter power law frequency size statistics and random or clustered temporal distribution of large events the simulations demonstrate that treatment of the various observed forms of frequency size and temporal statistics of earthquakes can be unified through the concept of range of size scales characterizing fault zone heterogeneities this has a clear physical interpretation in terms of structural properties of a given fault zone or broad lithospheric domain and is supported by observed earthquake and fault data in some simulated cases the frequency size statistics of small earthquakes fall sharply below the self similar gutenberg richter line the results indicate that small earthquakes prepare the fault for the occurrence of a large event by smoothing during gradual tectonic loading the long wavelength components of stress on the fault this is done through short wavelength stress roughening associated with the numerous ruptures of the small events the above pattern of smoothing roughening of long short wavelengths of stress on the fault is reversed during large scale ruptures of the big events

two dimensional probabilistic cell automaton model for broadband slow earthquakes slow tectonic events such as deep tectonic tremor low frequency earthquakes very low frequency earthquakes and slow slip events are regarded as broadband slow earthquakes various observational properties of these events have previously been explained using a one dimensional 1d stochastic model that mimics brownian motion in the time domain here we present a simple two dimensional 2d slow earthquake model using a probabilistic cell automaton pca where each cell possesses one of two states slip or hold at a given time step the status of each cell is updated as a markov process dependent on its own status and that of neighboring cells the seismic moment rate of the event in the 2d pca model is assumed to be proportional to the number of slipping cells which is approximated using a stochastic differential equation equivalent to the previous 1d brownian model approach this 2d pca model is therefore able to explain the various observational properties of slow earthquakes moreover it includes an additional degree of freedom to separate the effects of loading and dissipation which enables us to explain the variations in episodic slow slip activity the size of the slow earthquake is limited by either the system size or the characteristic size which is controlled by the degree of dissipation such a simple representation of slow earthquakes is useful for characterizing the broad spectrum of slow earthquake behavior in different environments

modelling fluid induced seismicity on a nearby active fault summary we present a numerical investigation of the effect that static stress perturbations due to fluid injection have on a nearby active fault where the fluid does not come in physical contact with the fault our modelling employs a lattice boltzmann pore diffusion model coupled with a quasi dynamic earthquake rupture model as diffusivities and frictional parameters can be defined independently at individual nodes cells this allows us to replicate complex 3 d geological media in our simulations we demonstrate the effect an injection can have on an active nearby fault compared with our control catalogue identical to the original simulation but without the injection the injection not only altered the timing of the next earthquake sequence it also changed its size producing a mw 6 7 event the largest observed earthquake on the fault this large event pushes the fault into a subcritical state from which it took roughly 200yr of continuous tectonic loading for the fault to return to a critical state

observations and modeling of coseismic and postseismic deformation due to the 2015 mw 7 8 gorkha nepal earthquake we use space geodetic data to investigate coseismic and postseismic deformation due to the 2015 mw 7 8 gorkha earthquake that occurred along the central himalayan arc because the earthquake area is characterized by strong variations in surface relief and material properties we developed finite element models that explicitly account for topography and 3 d elastic structure we computed the line of sight displacement histories from three tracks of the sentinel 1a b interferometric synthetic aperture radar insar satellites using persistent scatter method insar observations reveal an uplift of up to 70 mm over 20 months after the main shock concentrated primarily at the downdip edge of the ruptured asperity gps observations also show uplift as well as southward movement in the epicentral area qualitatively similar to the coseismic deformation pattern kinematic inversions of gps and insar data and forward models of stress driven creep suggest that the observed postseismic transient is dominated by afterslip on a downdip extension of the seismic rupture a poroelastic rebound may have contributed to the observed uplift and southward motion but the predicted surface displacements are small we also tested a wide range of viscoelastic relaxation models including 1 d and 3 d variations in the viscosity structure models of a low viscosity channel previously invoked to explain the long term uplift and variations in topography at the plateau margins predict opposite signs of horizontal and vertical displacements compared to those observed our results do not preclude a possibility of deep seated viscoelastic response beneath southern tibet with a characteristic relaxation time greater than the observation period 2 years

an isotopic model for basal freeze on associated with subglacial upward flow of pore water 1 subglacial freezing in polar glaciers can have a significant dynamical effect recent studies have shown that freezing of pore water flowing upward through subglacial fine grained sediments at the freezing interface and progression of this freezing front downward are responsible for fast ice flow stoppage in ice streams the upward pore water flow leads to the formation of debris bearing basal ice layers a model for stable isotope composition both in d and 18o is developed for predicting the isotopic composition of the ice segregated by such a mechanism the development of this isotopic model for water films present along the grains of the subglacial sediment predicts the absence of apparent fractionation for the ice formed this prediction is tested against two east antarctic outlet glaciers by studying the d 18o relationships in the basal ice layers of these glaciers

interseismic deformation and creep along the central section of the north anatolian fault turkey insar observations and implications for rate and state friction properties 1 we present high resolution measurements of interseismic deformation along the central section of the north anatolian fault naf in turkey using interferometric synthetic aperture radar data from the advanced land observing satellite and envisat missions we generated maps of satellite line of sight velocity using five ascending advanced land observing satellite tracks and one descending envisat track covering the naf between 31 2 e and 34 3 e the line of sight velocity reveals discontinuities of up to 5 mm yr across the ismetpasa segment of the naf implying surface creep at a rate of 9 mm yr this is a large fraction of the inferred slip rate of the naf 21 25 mm yr the lateral extent of significant surface creep is about 75 km we model the inferred surface velocity and shallow fault creep using numerical simulations of spontaneous earthquake sequences that incorporate laboratory derived rate and state friction our results indicate that frictional behavior in the ismetpasa segment is velocity strengthening at shallow depths and transitions to velocity weakening at a depth of 3 6 km the inferred depth extent of shallow fault creep is 5 5 7 km suggesting that the deeper locked portion of the partially creeping segment is characterized by a higher stressing rate smaller events and shorter recurrence interval we also reproduce surface velocity in a locked segment of the naf by fault models with velocity weakening conditions at shallow depth our results imply that frictional behavior in a shallow portion of major active faults with little or no shallow creep is mostly velocity weakening

shallow slip deficit due to large strike slip earthquakes in dynamic rupture simulations with elasto plastic off fault response summary slip inversions of geodetic data from several large magnitude 7 strike slip earthquakes point to coseismic slip deficit at shallow depths 3 4 km that is coseismic slip appears to decrease towards the earth surface while the inferred slip distribution may be consistent with laboratory derived rate and state friction laws suggesting that the uppermost brittle crust may be velocity strengthening there remains a question of how the coseismic slip deficit is accommodated throughout the earthquake cycle the consequence of velocity strengthening fault friction at shallow depths is that the deficit of coseismic slip is relieved by post seismic afterslip and interseismic creep however many seismic events with inferred shallow slip deficit were not associated with either resolvable shallow interseismic creep or robust shallow afterslip hence the origin of shallow slip deficit remains uncertain in this study we investigate whether inelastic failure in the shallow crust due to dynamic earthquake rupture can explain the inferred deficit of shallow slip evidence for such failure is emerging from geologic seismic and geodetic observations we find that the amount of shallow slip deficit is proportional to the amount of inelastic deformation near the earth surface such deformation occurs under a wide range of parameters that characterize rock strength in the upper crust however the largest magnitude of slip deficit in models accounting for off fault yielding is 2 4 times smaller than that inferred from kinematic inversions of geodetic data to explain this discrepancy we further explore to what extent assumptions in the kinematic inversions may bias the inferred slip distributions inelastic deformation in the shallow crust reduces coseismic strain near the fault introducing an additional artificial deficit of up to 10 per cent of the maximum slip in inversions of geodetic data that are based on purely elastic models the largest magnitude of slip deficit in our models combined with the bias in inversions accounts for up to 25 per cent of shallow slip deficit which is comparable but still smaller than 30 60 per cent deficit inferred from kinematic inversions we discuss potential mechanisms that may account for the remaining discrepancy between slip deficit predicted by elasto plastic rupture models and that inferred from inversions of space geodetic data

rate and state friction properties of the longitudinal valley fault from kinematic and dynamic modeling of seismic and aseismic slip the longitudinal valley fault lvf taiwan is a fast slipping fault 5 cm yr which exhibits both seismic and aseismic slip geodetic and seismological observations 1992 2010 were used to infer the temporal evolution of fault slip thomas et al 2014a this kinematic model is used here to estimate spatial variations of steady state velocity dependence of fault friction and to develop a simplified fully dynamic rate and state model of the lvf based on the postseismic slip we estimate that the rate and state parameter a b over bar decreases from 1 2 mpa near the surface to near velocity neutral at 19 km depth the inferred a b values are consistent with the laboratory measurements on clay rich fault gouges comparable to the lichi melange which borders the lvf the dynamic model that incorporates the obtained a b over bar estimates as well as a vw patch with tuned rate and state properties produces a sequence of earthquakes with some realistic diversity and a spatio temporal pattern of seismic and aseismic slip similar to that inferred from the kinematic modeling the larger events have moment magnitude m w 6 7 similar to the 2003 chenkung earthquake with a range of smaller events the model parameterization allows reproducing partial overlap of seismic and aseismic slip before the earthquake but cannot reproduce the significant postseismic slip observed in the previously locked patch we discuss factors that can improve the dynamic model in that regard including the possibility of temporal variations in a b due to shear heating such calibrated dynamic models can be used to reconcile field observations kinematic analysis and laboratory experiments and assess fault behavior

a constitutive law for the shear failure of rock under lithospheric conditions abstract this paper first reviews recent studies on constitutive formulations for shear failure which leads to the conclusion that revealing the constitutive property for not only frictional slip failure but also shear failure of intact rock in the brittle to brittle plastic transition regimes is critical to establish the constitutive law which governs earthquake shear failure that proceeds in the lithosphere to this end a unique high stiffness testing apparatus capable of applying polyaxial stress fields to rectangular rock specimens has been constructed for which a brief description is given the paper then presents new results of laboratory experiments on constitutive properties of shear fracture of intact granite at lithospheric conditions in view of the physical principles and constraints to be imposed on the constitutive law for shear failure the slip dependency is a more fundamental property than the time or rate dependency and hence the constitutive law for shear failure should primarily be slip dependent this slip dependent constitutive law which itself is self consistent can unifyingly and quantitatively treat the entire phases from stable quasistatic ruture growth to unstable dynamic fast speed rupture propagation for shear failure of any type whether it is frictional slip failure along a preexisting fault or shear fracture of intact materials the slip dependent constitutive law includes a scaling parameter dc critical slip displacement explicitly which in turn is scaled by a characteristic length c representing geometrical irregularities of the fault surfaces incorporation of dc or c enables this constitutive law to provide a common interpretation for shear failure of any size scale as an earthquake source from small scale in the laboratory to large scale in the earth the present experiments corroborate the slip dependent constitutive relation and other constitutive properties over the entire process from slip strengthening to slip weakening of intact granite under the conditions that confining pressure is in the range 440 to 500 mpa pore pressure is in the range 30 to 300 mpa temperature is in the range from room temperature to 456 c and strain rate is in the range 10 4 to 10 7 s it is found that some constitutive law parameters are not independent but mutually related the constitutive relation for shear failure and the parameters such as p breakdown stress drop and dc prescribing its relation are affected by ambient conditions such as temperature and strain rate

post seismic and interseismic fault creep i model description we present a model of localized aseismic fault creep during the full interseismic period including both transient and steady fault creep in response to a sequence of imposed coseismic slip events and tectonic loading we consider the behaviour of models with linear viscous non linear viscous rate dependent friction and rate and state dependent friction fault rheologies both the transient post seismic creep and the pattern of steady interseismic creep rates surrounding asperities depend on recent coseismic slip and fault rheologies in these models post seismic fault creep is manifest as pulses of elevated creep rates that propagate from the coseismic slip these pulses feature sharper fronts and are longer lived in models with rate state friction compared to other models with small characteristic slip distances in rate state friction models interseismic creep is similar to that in models with rate dependent friction faults except for the earliest periods of post seismic creep our model can be used to constrain fault rheologies from geodetic observations in cases where the coseismic slip history is relatively well known when only considering surface deformation over a short period of time there are strong trade offs between fault rheology and the details of the imposed coseismic slip geodetic observations over longer times following an earthquake will reduce these trade offs while simultaneous modelling of interseismic and post seismic observations provide the strongest constraints on fault rheologies

statistical properties of seismicity of fault zones at different evolutionary stages summary we perform a systematic parameter space study of the seismic response of a large fault with different levels of heterogeneity using a 3 d elastic framework within the continuum limit the fault is governed by rate and state friction and simulations are performed for model realizations with frictional and large scale properties characterized by different ranges of size scales we use a number of seismicity and stress functions to characterize different types of seismic responses and test the correlation between hypocenter locations and the employed distributions of model parameters the simulated hypocenters are found to correlate significantly with small l values of the rate and state friction the final sizes of earthquakes are correlated with physical properties at their nucleation sites the obtained stacked scaling relations are overall self similar and have good correspondence with properties of natural earthquakes

kinematic inversion of physically plausible earthquake source models obtained from dynamic rupture simulations one approach to investigate earthquake source processes is to produce kinematic source models from inversion of seismic records and geodetic data the setup of the inversion requires a variety of assumptions and constraints to restrict the range of possible models here we evaluate to what extent physically plausible earth quake scenarios are reliably restituted in spite of these restrictions we study which characteristics of ruptures such as rupture velocity slip distribution stress drop rise time and slip function can be reliably determined from the inversion of near field seismic and geodetic data using spontaneous dynamic rupture simulations we gen erate five earthquake scenarios each of which has different characteristics of the source process then we conduct a blind test by modeling the synthetic near source data using a standard inversion scheme that optimizes the fit to the observations while searching for solutions with minimum roughness the inversion procedure assumes a rupture front propagating away from the hypocenter with variable rupture velocity and a simple cosine slip time function our results show that overall slip distribution and stress drop are reasonably well determined even for input models with relatively complex histories such as a subshear rupture transitioning to supershear speeds depth averaged rupture velocities are also reasonably well resolved although their estimate progressively deteriorates away from the hypocenter the local rise time and slip function are not well resolved but there is some sensitivity to the rupture pulse width which can be used to differentiate between pulse like and crack like ruptures our test for understanding the inaccuracies in green s functions shows that random 3d perturbations of 5 standard deviation do not lead to significant degradation of the estimation of earthquake source parameters as remedies to the current limitations we propose smoothing slip function parameters and using more complicated inversion schemes only if data necessitates them online material figures showing snapshots of forward and inverse modeling of rupture l curves slip models and waveform fits

critical behaviour and the evolution of fault strength during earthquake cycles the problem of how fault rheology and heterogeneity interact to produce the observed scaling of earthquakes such as the power law moment frequency relationship remains largely unsolved rock friction experiments have elucidated the properties of smooth faults1 2 3 but seem insufficient to explain the observed complexity of real fault dynamics4 5 the recognition of a connection between fault related processes and critical phenomena in other physical systems together with numerical models of repeated earthquakes have resulted in significant progress in the theoretical interpretation of earthquake scaling4 5 6 7 8 9 10 11 12 13 14 but fault rheology and heterogeneity have so far been treated separately here i attempt to unify the requirements of fault rheology and heterogeneity using numerical calculations of quantized slip in an elastic continuum i show that cyclical fault strength evolves naturally by means of a statistical selection for high strength fault patches asperities resulting in the accumulation and eventual failure of those asperities the applicability of these results to real fault systems is supported by a recent analysis of time dependent earthquake statistics15 these results imply that self similarity and criticality on a fault emerge during an earthquake cycle and suggest that the character of local seismicity can be useful in earthquake forecasting by revealing how advanced a fault is within its cycle

a composite rate and state dependent law for rock friction existing constitutive laws of rock friction cannot describe both observed strengthening in the absence of slip and frictional behavior around steady state sliding combining existing rate and state dependent friction laws we propose a new friction law which expresses logarithmically time dependent healing at sliding velocities smaller than a cut off velocity v c and approaches the so called slip law at velocities larger than v c numerical simulations show that the new friction law adequately explains experimental results of velocity stepping tests and slide hold slide tests which have widely been used to examine velocity time and displacement dependent property of rock friction because the new friction law has a simple form and appears appropriate for a wide range of conditions it is useful for application to numerical modeling of seismic cycles

incremental growth of normal faults insights from a laser equipped analog experiment we conducted a laser equipped analog experiment aimed at quasi continuously monitoring the growth of a dense population of normal faults in homogeneous conditions to further understand the way geological faults progressively gain in slip and length as they accumulate more strain we measured with great precision the incremental slip and length changes that the analog faults sustain as they grow these measurements show that the analog faults share common features with the natural ones in particular during their growth the faults develop and maintain cumulative slip profiles that are generally triangular and asymmetric the growth takes place through two distinct phases an initial short period of rapid lateral lengthening followed by a longer phase of slip accumulation with little or no lengthening the incremental slip is found to be highly variable in both space along the faults and time resulting in variable slip rates in particular short and long term slip rates are markedly different we also find that slip measurements at local points on fault traces do not contain clear information on the slip increment repeat mode finally while the fault growth process is highly heterogeneous when considered at the scale of a few slip events it appears homogeneous and self similar at longer time scales which integrate many slip increments this is likely to be the result of a feedback between stress heterogeneities and slip development the long term scale homogeneity also implies that the long term faulting process is primarily insensitive to the short term heterogeneities that are rapidly smoothed or redistributed we propose a new conceptual scenario of fault growth that integrates the above observations and we suggest that faults grow in a bimodal way as a result of a self driven and self sustaining process

fault heterogeneity and the connection between aftershocks and afterslip whether aftershocks originate directly from the mainshock and surrounding stress environment or from afterslip dynamics is crucial to the understanding of the nature of aftershocks we build on a classical description of the fault and creeping regions as two blocks connected elastically subject to different friction laws we show analytically that upon introduction of variability in the fault plane s static friction threshold a non trivial stick slip dynamics ensues in particular we support the hypothesis that the aftershock occurrence rate is proportional to the afterslip rate up to a corrective factor that is also computed thus the omori law originates from the afterslip s logarithmic evolution in the velocity strengthening region we confirm these analytical results with numerical simulations generating synthetic catalogs with statistical features in good agreement with instrumental catalogs in particular we recover the gutenberg richter law with a realistic b value b 1 when coulomb stress thresholds obey a power law distribution

direct simulations of the stress redistribution in the scaling organization of fracture tectonics soft model summary a time dependent stochastic process with three states solid broken and moving is considered in a hierarchical system made of embedded cells of increasing levels an earthquake of a given scale k is associated with the moving state of a cell of level k and results from the coherent self organization of fractures of lower scales a direct cascade of stress redistribution generates small scale stress heterogeneities in the neighbourhood of the active fracture an interesting feature of the model is that the size of the domain where stress redistribution takes place grows proportional to the length of the fracture in the framework of the general model inspired by the progress in the use of the renormalization techniques in approaching critical point phenomena we independently study a fracturing submodel and a friction submodel these submodels are two state models that act on diierent timescales in the friction submodel which comprises broken and moving states the transitions between these two states are associated with stick slip behaviour in a completely fractured fault zone in the fracturing submodel which comprises solid and broken states we model the brittle behaviour of rock material in both models we obtain a spatio temporal clustering of earthquakes realistic aftershock sequences whose frequency decreases respect the modi ed omori law and a frequency magnitude relationship that respects the gutenberg richter law we show that the model behaviour is controlled by the stress heterogeneity in the fault zone we nd evidence for a relationship between the periodicity of the largest earthquakes and the b value and we indicate how the diierent physical ingredients underlying each submodel can be gathered together in a more general model

spectral element simulations of long term fault slip effect of low rigidity layers on earthquake cycle dynamics we develop a spectral element method for the simulation of long term histories of spontaneous seismic and aseismic slip on faults subjected to tectonic loading our approach reproduces all stages of earthquake cycles nucleation and propagation of earthquake rupture postseismic slip and interseismic creep we apply the developed methodology to study the effects of low rigidity layers on the dynamics of the earthquake cycle in 2 d we consider two cases small m 1 earthquakes on a fault surrounded by a damaged fault zone and large m 7 earthquakes on a vertical strike slip fault that cuts through shallow low rigidity layers our results indicate how the source properties of repeating earthquakes are affected by the presence of a damaged fault zone with low rigidity compared to faults in homogeneous media we find 1 reduction in the earthquake nucleation size 2 amplification of slip rates during dynamic rupture propagation 3 larger recurrence interval and 4 smaller amount of aseismic slip based on linear stability analysis we derive a theoretical estimate of the nucleation size as a function of the width and rigidity reduction of the fault zone layer which is in good agreement with simulated nucleation sizes we further examine the effects of vertically stratified layers e g sedimentary basins on the nature of shallow coseismic slip deficit our results suggest that low rigidity shallow layers alone do not lead to coseismic slip deficit while the low rigidity layers result in lower interseismic stress accumulation they also cause dynamic amplification of slip rates with the net effect on slip being nearly zero

complexity of seismicity due to highly rate dependent friction we study a simple antiplane fault of finite length embedded in a homogeneous isotropic elastic solid in order to understand the origin of seismic source heterogeneity in the presence of nonlinear rate dependent friction all the mechanical properties of the medium and friction are assumed to be homogeneous starting from a heterogeneous initial stress distribution we apply a slowly increasing uniform stress load far from the fault and we simulate the seismicity for more than 20 000 events in some cases the style of seismicity produced by this model is determined by a control parameter which measures the degree of rate dependence of friction for classical friction models with rate independent friction no complexity appears and seismicity is perfectly periodic for weakly rate dependent friction seismicity becomes slightly nonperiodic but most events are still characteristic earthquakes when friction is highly rate dependent seismicity is completely irregular and ruptures of all sizes occur inside the fault highly rate dependent friction destabilizes the healing process producing premature healing of slip and partial stress drop premature healing causes rupture to take the form of narrow propagating slip episodes the so called heaton s 1990 pulses partial stress drop produces large variations in the state of stress which in turn produce earthquakes of different sizes we make the conjecture that all models in which static stress drop is only a fraction of the dynamic stress drop produce stress heterogeneity

slow slip predictions based on granite and gabbro friction data compared to gps measurements in northern cascadia received 7 october 2008 revised 17 april 2009 accepted 12 june 2009 published 29 september 2009 1 for episodic slow slip transients in subduction zones a large uncertainty in comparing surface deformations predicted by forward modeling based on rate and state friction to gps measurements lies in our limited knowledge of the frictional properties and fluid pore pressure along shallow subduction faults in this study we apply the laboratory rate and state friction data of granite and gabbro gouges under hydrothermal conditions to a cascadia like 2 d model to produce spontaneous aseismic transients and we compare the resulting intertransient and transient surface deformations to gps observations along the northern cascadia margin an inferred region along dip of elevated fluid pressure is constrained by seismological observations where available and by thermal and petrological models for the cascadia and sw japan subduction zones for the assumed

quantitative modeling of the lithosphere dynamics earthquakes and seismic hazard abstract understanding of lithosphere dynamics tectonic stress localization earthquake occurrences and seismic hazards has significantly advanced during the last decades meanwhile despite the major advancements in geophysical sciences yet we do not see a decline in earthquake disaster impacts and losses although earthquake disasters are mainly associated with significant vulnerability of society comprehensive seismic hazards assessments and earthquake forecasting could contribute to preventive measures aimed to reduce impacts of earthquakes modeling of lithosphere dynamics and earthquake simulations coupled with a seismic hazard analysis can provide a better assessment of potential ground shaking due to earthquakes here we present a block and fault dynamics bafd model which simulates earthquakes due to lithosphere dynamics and allows for studying the influence of fault network properties and regional movements on seismic patterns the model s performance is analyzed in terms of reproduction of basic features of the observed seismicity such as the frequency magnitude relationship clustering of earthquakes occurrences of large events fault slip rates and earthquake mechanisms several studies related to the application of the bafd model to the following earthquake prone regions are reviewed the southeastern carpathians caucasus the western india tibet himalaya and the sunda arc we examine then a new approach to seismic hazard analysis which is based on instrumentally recorded historical and bafd simulated earthquakes and analyze how earthquake modeling can assist in hazard assessment finally we discuss perspectives in modeling of earthquake occurrences and improvements in hazard assessment

nitrogen release from rock and soil under simulated field conditions abstract a laboratory study was performed to simulate field weathering and nitrogen release from bedrock in a setting where geologic nitrogen has been suspected to be a large local source of nitrate two rock types containing nitrogen slate 1370 mg n kg 1 and greenstone 480 mg n kg 1 were used along with saprolite and bc horizon sand from soils derived from these rock types the fresh rock and weathered material were used in batch reactors that were leached every 30 days over 6 months to simulate a single wet season nitrogen was released from rock and soil materials at rates between 10 20 and 10 19 mol n cm 2 s 1 results from the laboratory dissolution experiments were compared to in situ soil solutions and available mineral nitrogen pools from the bc horizon of both soils concentrations of mineral nitrogen no 3 nh 4 in soil solutions reached the highest levels at the beginning of the rainy season and progressively decreased with increased leaching this seasonal pattern was repeated for the available mineral nitrogen pool that was extracted using a kcl solution estimates based on these laboratory release rates bracket stream water no 3 n fluxes and changes in the available mineral nitrogen pool over the active leaching period these results confirm that geologic nitrogen when present may be a large and reactive pool that may contribute as a non point source of nitrate contamination to surface and ground waters

earthquake scaling the effect of a viscoelastic asthenosphere summary viscous creep in the crust and mantle can have important consequences for earthquake patterns in time and space here numerical models of repeating earthquake rupture are used to investigate how viscoelasticity can affect size distributions of repeated earthquakes on vertical planar fault segments the earthquake model is based on exact solutions of static 3 d elasticity theory viscous flow beneath the seismogenic crust is modelled as a maxwell relaxation process two different fault strength models are used a smooth rate and state dependent friction model and a strongly heterogeneous asperity model in a previous paper it was shown that the characteristic scale of fault segmentation is proportional to the vertical width of a seismogenic fault for both the heterogeneous and smooth friction models viscous relaxation of the substrate modifies the spatio temporal distribution of cumulative slip and slip events for the heterogeneous models the resulting quake size distributions are independent of the viscous relaxation time in contrast for the smooth models it is shown that the characteristic event size is inversely proportional to the relaxation time of the substrate these results imply a connection between the spatial complexity of fault zones and the maximum earthquake size a fault can sustain whereas earthquake sizes on complex fault zones depend only weakly on the viscous rheology beneath the seismogenic crust the sizes of large events on relatively simple faults can be substantially increased due to viscous relaxation and partial decoupling of the seismogenic crust from the deeper crust and mantle

multifractal omori law for earthquake triggering new tests on the california japan and worldwide catalogues summary the multifractal stress activated model is a statistical model of triggered seismicity based on mechanical and thermodynamic principles it predicts that above a triggering magnitude cut off m 0 the exponent p of the omori law for the time decay of the rate of aftershocks is a linear increasing function p m a 0 m b0 of the main shock magnitude m we previously reported empirical support for this prediction using the southern california earthquake center scec catalogue here we confirm this observation using an updated longer version of the same catalogue as well as new methods to estimate p one of this methods is the newly defined scaling function analysis sfa adapted from the wavelet transform this method is able to measure a mathematical singularity hence a p value erasing the possible regular part of a time series the sfa also proves particularly efficient to reveal the coexistence and superposition of several types of relaxation laws typical omori sequences and short lived swarms sequences which can be mixed within the same catalogue another new method consists in monitoring the largest aftershock magnitude observed in successive time intervals and thus shortcuts the problem of missing events with small magnitudes in aftershock catalogues the same methods are used on data from the worldwide harvard centroid moment tensor cmt catalogue and show results compatible with those of southern california for the japan meteorological agency jma catalogue we still observe a linear dependence of p on m b ut with a smaller slope the sfa shows however that results for this catalogue may be biased by numerous swarm sequences despite our efforts to remove them before the analysis

quasi dynamic versus fully dynamic simulations of earthquakes and aseismic slip with and without enhanced coseismic weakening physics based numerical simulations of earthquakes and slow slip coupled with field observations and laboratory experiments can in principle be used to determine fault properties and potential fault behaviors because of the computational cost of simulating inertial wave mediated effects their representation is often simplified the quasi dynamic qd approach approximately accounts for inertial effects through a radiation damping term we compare qd and fully dynamic fd simulations by exploring the long term behavior of rate and state fault models with and without additional weakening during seismic slip the models incorporate a velocity strengthening vs patch in a velocity weakening vw zone to consider rupture interaction with a slip inhibiting heterogeneity without additional weakening the qd and fd approaches generate qualitatively similar slip patterns with quantitative differences such as slower slip velocities and rupture speeds during earthquakes and more propensity for rupture arrest at the vs patch in the qd cases simulations with additional coseismic weakening produce qualitatively different patterns of earthquakes with near periodic pulse like events in the fd simulations and much larger crack like events accompanied by smaller events in the qd simulations this is because the fd simulations with additional weakening allow earthquake rupture to propagate at a much lower level of prestress than the qd simulations the resulting much larger ruptures in the qd simulations are more likely to propagate through the vs patch unlike for the cases with no additional weakening overall the qd approach should be used with caution as the qd simulation results could drastically differ from the true response of the physical model considered

slip complexity in earthquake fault models we summarize studies of earthquake fault models that give rise to slip complexities like those in natural earthquakes for models of smooth faults between elastically deformable continua it is critical that the friction laws involve a characteristic distance for slip weakening or evolution of surface state that results in a finite nucleation size or coherent slip patch size h models of smooth faults using numerical cell size properly small compared to h show periodic response or complex and apparently chaotic histories of large events but have not been found to show small event complexity like the self similar power law gutenberg richter frequency size statistics this conclusion is supported in the present paper by fully inertial elastodynamic modeling of earthquake sequences in contrast some models of locally heterogeneous faults with quasi independent fault segments represented approximately by simulations with cell size larger than h so that the model becomes inherently discrete do show small event complexity of the gutenberg richter type models based on classical friction laws without a weakening length scale or for which the numerical procedure imposes an abrupt strength drop at the onset of slip have h 0 and hence always fall into the inherently discrete class we suggest that the small event complexity that some such models show will not survive regularization of the constitutive description by inclusion of an appropriate length scale leading to a finite h and a corresponding reduction of numerical grid size

inferring fault mechanical conditions from the source parameters of a complex microseismic multiplet in the corinth rift greece we develop a mechanical model of tight clusters of coplanar seismic asperities to investigate a particular microearthquake swarm located at 8 km depth in the corinth rift in greece which was active between 2001 and 2007 although it is classified as a multiplet based on waveform similarity this seismic sequence is much more complex than a repeating earthquake sequence and cannot be interpreted as the regular failure of a single asperity forced by surrounding aseismic creep here we suggest that such complex sequences could be generated by the failure of a set of coplanar asperities interacting in a small region of a fault segment we show that in order to reproduce the dynamics of the observed sequence and the characteristics of the events the cluster of asperities has to be located very close to an aseismically slipping fault segment which could be an updip extension of the deep detachment zone in the rift creeping at 1 5 cm yr for more general cases of coplanar clustered asperities we show that the shape of the cumulative coseismic displacement pattern associated with the repeated failures of the asperities is strongly controlled by the behavior of the fault area surrounding the asperity cluster in particular if the cluster is part of a locked fault area the resulting long term cumulative displacement is maximum at the center of the cluster in contrast an asperity cluster surrounded by aseismic creep leads to a uniform cumulative coseismic slip pattern the ratio between cumulative slip at the center of the seismogenic patch and cumulative slip at its periphery could therefore be an indicator of the mechanical conditions prevailing on the fault a systematic study of the source parameters of complex microseismic sequences could therefore provide insights into the mechanical state of active faults continuously generating microseismicity

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

slow slip slow earthquakes period two cycles full and partial ruptures and deterministic chaos in a single asperity fault abstract the assimilation of geological geophysical and laboratory data in physics based models of fault dynamics promises increasingly realistic simulations of the seismic cycle to assist this effort i explore the dynamics of a single velocity weakening asperity to delineate the relationship between a fault physical properties and the style of faulting during the seismic cycle based on a micro physical model of rate and state friction from a dimensional analysis four non dimensional parameters control the characteristics of slip events and the behavior during the interseismic period including the dieterich ruina rice number ru which is proportional to the ratio of asperity to critical nucleation size w h and rb b a b where a and b control the direct and local evolutionary effects respectively for sufficiently large rb the ru number controls the spectrum of fault slip from periodic slow slip events to aperiodic fast ruptures in finite faults but not in semi infinite faults the transition between these end members includes a bifurcation that involves period two period four period six cycles and deterministic chaos with increasing ru macroscopic fault slip is stabilized as rb vanishes even as ru 1 for finite faults but not for semi infinite faults the transition between slow and fast ruptures for increasing rb includes another type of bifurcation with period two and period four cycles of slow and fast ruptures for 0

aseismic slip transients emerge spontaneously in three dimensional rate and state modeling of subduction earthquake sequences 1 to investigate the possible physical mechanisms of recently observed aseismic slip events in the cascadia japan and mexico subduction zones we apply a dieterich ruina rate and state friction law to a three dimensional model of a shallow subduction fault that is loaded by imposed steady plate slip rate far downdip along the thrust interface friction properties are temperature and hence depth dependent such that sliding is stable at depths below about 30 km the system is perturbed into a significantly nonuniform slip mode along strike by introducing small along strike variations in the constitutive parameters a and a b in addition to large heterogeneous earthquake slip at seismogenic depths and associated postseismic transients we found that slip events which have clearly aseismic slip rates emerge spontaneously around the downdip end of the seismogenic zone both transients which start well after a seismic event and those which are triggered by other transients are observed from the simulations the slip velocity depth range and sometimes along strike migration speed of simulated transients are similar to the observations from natural subduction zones unstable stable transitional friction properties near the downdip end of the seismogenic zone are suggested to be an ingredient allowing such transients simulated transients can weaken the locking intensity of the updip seismogenic zone while enhancing that of the transition zone spatial temporal correlation of aseismic transients and nearby seismicity in the guerrero mexico area suggests that transients may signal a period of increased probability for nucleating their high frequency counterparts as damaging subduction thrust events

the predictability of large earthquakes evidence from an analogue model of earthquake rupture the recurrence behaviour of large earthquakes in several tectonic settings has been explained by simple models of stress accumulation and release which assume that the fault stress state is solely a function of the far field tectonic strain rate however the limited dataset of large event recurrence intervals has been a major obstacle to the verification of these and other models we present the results from a simple analogue model of earthquake rupture and stick slip which displays power law frequency size statistics and involves many cycles of large events we show that despite the macroscopic homogeneity of the model large events do not conform to simple deterministic time or slip predictable patterns however when the recurrence intervals for large events are divided by the median recurrence interval the normalized data are composed of two distinct lognormally distributed populations one population is characterized by events which are strongly clustered in time with relatively short recurrence intervals and low moment release the other by events which are weakly clustered in time with median sized recurrence intervals it is suggested that the long term recurrence behaviour of large earthquakes whilst being non deterministic may be modelled by a well defined statistical distribution of recurrence intervals

3 d simulation of earthquake generation cycles and evolution of fault constitutitve properties the earthquake generation cycle consists of tectonic loading quasi static rupture nucleation dynamic rupture propagation and stop and subsequent stress redistribution and fault restrengthening from a macroscopic point of view the entire process of earthquake generation cycles should be consistently described by a coupled nonlinear system of a slip response function a fault constitutive law and a driving force on the basis of such a general idea we constructed a realistic 3 d simulation model for earthquake generation cycles at a transcurrent plate boundary by combining the viscoelastic slip response function derived for a two layered elastic viscoelastic structure model the slip and time dependent fault constitutive law that has an inherent mechanism of fault restrengthening and the steady relative plate motion as a driving force into a single closed system with this model we numerically simulated the earthquake generation cycles repeated in a seismogenic region on a plate interface and examined space time changes in shear stress slip deficits and fault constitutive properties during one complete cycle in detail the occurrence of unstable dynamic slip brings about decrease both in fault strength and shear stress to a constant residual level after the arrest of dynamic slip the breakdown strength drop p of fault is restored rapidly and the process of stress accumulation resumes in the seismogenic region on the other hand the restoration of the critical weakening displacement d c proceeds gradually with time through the interseismic period the restoration of d c can be regarded as the macroscopic manifestation of the microscopic recovery process of fractal fault surface structure through numerical simulation with a multi segmented fault model we examined the effects of viscoelastic faultto fault interaction the effect of transient viscoelastic stress transfer through the asthenosphere is significant as well as the direct effect of elastic stress transfer and it possibly explains the time lag of the sequential occurrence of large events along a plate boundary

california foreshock sequences suggest aseismic triggering process 1 foreshocks are one of the few well documented precursors to large earthquakes therefore understanding their nature is very important for earthquake prediction and hazard mitigation however the triggering role of foreshocks is not yet clear it is possible that foreshocks are a self triggering cascade of events that simply happen to trigger an unusually large aftershock alternatively foreshocks might originate from an external aseismic process that ultimately triggers the mainshock in the former case the foreshocks will have limited utility for forecasting the latter case has been observed for several individual large earthquakes however it remains unclear how common it is and how to distinguish foreshock sequences from other seismicity clusters that do not lead to large earthquakes here we analyze foreshocks of three m 7 mainshocks in southern california these foreshock sequences appear similar to earthquake swarms in that they do not start with their largest events and they exhibit spatial migration of seismicity analysis of source spectra shows that all three foreshock sequences feature lower average stress drops and depletion of high frequency energy compared with the aftershocks of their corresponding mainshocks using a longer term stress drop catalog we find that the average stress drop of the landers and hector mine foreshock sequences is comparable to nearby swarms our observations suggest that these foreshock sequences are manifestations of aseismic transients occurring close to the mainshock hypocenters possibly related to localized fault zone complexity which have promoted the occurrence of both the foreshocks and the eventual mainshock

properties of the seismic nucleation phase abstract near source observations show that earthquakes begin abruptly at the p wave arrival but that this beginning is weak with a low moment rate relative to the rest of the main shock we term this initial phase of low moment rate the seismic nucleation phase we have observed the seismic nucleation phase for a set of 48 earthquakes ranging in magnitude from 1 1 8 1 the size and duration of the seismic nucleation phase scale with the total seismic moment of the earthquake suggesting that the process responsible for the seismic nucleation phase carries information about the eventual size of the earthquake the seismic nucleation phase is characteristically followed by quadratic growth in the moment rate consistent with self similar rupture at constant stress drop in this paper we quantify the properties of the seismic nucleation phase and offer several possible explanations for it

postseismic deformation following the april 25 2015 gorkha earthquake nepal afterslip versus viscous relaxation abstract the postseismic deformation consecutive to the april 25 2015 gorkha earthquake mw 7 9 is estimated in this paper based on a cgnss network installed prior to the earthquake and supplemented by 6 cgnss stations installed after the main shock postseismic displacement are obtained from daily time series corrected for interseismic deformation and seasonal variations the maximum postseismic displacement is found north of the rupture area where locally it reached 100 mm between the date of the earthquake and late 2016 the postseismic deformation affects the northern part of the rupture area but not the southern part along the southern part of the main himalayan thrust mht three hypotheses for the mechanisms controlling postseismic deformation are tested through numerical simulations of the postseismic time series i viscous relaxation ii afterslip or iii a combination of these two mechanisms we can exclude postseismic deformation controlled by viscous relaxation of a thick deformation zone along the northern and lower flat of the mht however it is impossible to discriminate between postseismic deformation controlled by either afterslip along the mht northern part of the rupture zone crustal ramp and lower flat of the mht or a combination of afterslip along the mht northern part of the rupture zone crustal ramp and viscous relaxation controlled by a thin 3 4 km thick low viscosity body centered on the lower flat of the mht the occurrence of afterslip along the northern part of the upper flat of the mht and its longitudinal variations have been established thanks to the densification of gnss network by our team presented in this paper

seismicity on a fault controlled by rate and state dependent friction with spatial variations of the critical slip distance 1 we perform systematic simulations of slip using a quasi dynamic continuum model of a two dimensional 2 d strike slip fault governed by rate and state dependent friction the depth dependence of the a b and l frictional parameters are treated in an innovative way that is consistent with available laboratory data and multidisciplinary field observations various realizations of heterogeneous l distributions are used to study effects of structural variations of fault zones on spatiotemporal evolution of slip we demonstrate that such realizations can produce within the continuum class of models realistic features of seismicity and slip distributions on a fault we explore effects of three types of variable l distributions 1 a depth dependent l profile accounting for the variable width of fault zones with depth 2 uncorrelated 2 d random distributions of l with different degrees of heterogeneity and 3 a hybrid distribution combining the depth dependent l profile with the 2 d random l distributions the first type of l distribution with relatively small l over the depth range corresponding to the seismogenic zone and larger l elsewhere generates stick slip events in the seismogenic zone and ongoing creep above and below that region the 2 d heterogeneous parameterizations generate frequency size statistics with event sizes spanning 4 orders of magnitude our results indicate that different degrees of heterogeneity of l distributions control 1 the number of simulated events and 2 the overall stress level and fluctuations other observable trends are 3 the dependency of hypocenter location on l and 4 different nucleation phases for small and large events in heterogeneous distributions

modulation of fault strength during the seismic cycle by grain size evolution around contact junctions abstract earthquake prediction is fundamentally hampered by insufficient knowledge of the constitutive behavior of faults laboratory and theoretical work by dieterich 1978 and ruina 1983 formed the basis of rate and state friction a constitutive framework that captures the healing and weakening of frictional contacts the rate and state law successfully explains the frictional behavior of a wide range of rocks and many phenomena associated with fault slip the physics underlying the rate and state friction law is not fully understood but it is generally accepted that several micro mechanisms operate depending on the texture maturity fluid content and other physical and kinematic conditions of the fault here i formulate a constitutive framework that unifies a number of laboratory experiments on silicate rocks and the gouges derived from these rocks that describe the effect of grain size temperature real area of contact gouge thickness and fault roughness fundamental to the model is that fault strength is controlled by the area of the interfacial contact junctions that support the shear and normal loads the curvature of asperities weakly controls the area of their contact junction and the resulting fault strength as a result the dynamics of grain size evolution around micro asperities enables the seismic cycle the model quantitatively explains the correlation between the characteristic weakening distance and the gouge thickness marone and kilgore 1993 the correlation of the static friction coefficient with the rate dependence parameters ikari et al 2011 the dependence of frictional resistance to sub solidus temperatures chester 1994 and predicts a range of grain sizes that is compatible with observations at exposed fault zones however the dynamics of grain size evolution is still challenging to verify experimentally the model features a regularization at vanishing slip speeds that implies distinct dynamics at low strength for friction coefficients lower than 0 1 seismic cycle simulations predict the emergence of frictional instabilities with complex source time functions this is a significant departure from the predictions of rate and state friction that is most relevant to the dynamics of decollements serpentinized shear zones and other low strength faults

seismic hazard from instrumentally recorded historical and simulated earthquakes application to the tibet himalayan region abstract we present a new approach to assessment of regional seismic hazard which accounts for observed instrumentally recorded and historic earthquakes as well as for seismic events simulated for a significantly longer period of time than that of observations we apply this approach to probabilistic seismic hazard analysis psha for the tibet himalayan region the large magnitude synthetic events which are consistent with the geophysical and geodetic data together with the observed earthquakes are employed for the monte carlo psha earthquake scenarios for hazard assessment are generated stochastically to sample the magnitude and spatial distribution of seismicity as well as the distribution of ground motion for each seismic event the peak ground acceleration values which are estimated for the return period of 475 yr show that the hazard level associated with large events in the tibet himalayan region significantly increases if the long record of simulated seismicity is considered in the psha the magnitude and the source location of the 2008 wenchuan m 7 9 earthquake are among the range of those described by the seismic source model accepted in our analysis we analyze the relationship between the ground motion data obtained in the earthquake s epicentral area and the obtained psha estimations using a deaggregation technique the proposed approach provides a better understanding of ground shaking due to possible large magnitude events and could be useful for risk assessment earthquake engineering purposes and emergency planning

frictional behavior of oceanic transform faults and its influence on earthquake characteristics 1 we use a three dimensional strike slip fault model in the framework of rate and state dependent friction to investigate earthquake behavior and scaling relations on oceanic transform faults otfs gabbro friction data under hydrothermal conditions are mapped onto otfs using temperatures from 1 a half space cooling model and 2 a thermal model that incorporates a visco plastic rheology non newtonian viscous flow and the effects of shear heating and hydrothermal circulation without introducing small scale frictional heterogeneities on the fault our model predicts that an otf segment can transition between seismic and aseismic slip over many earthquake cycles consistent with the multimode hypothesis for otf ruptures the average seismic coupling coefficient c is strongly dependent on the ratio of seismogenic zone width w to earthquake nucleation size h c increases by four orders of magnitude as w h increases from 1 to 2 specifically the average c 0 15 0 05 derived from global otf earthquake catalogs can be reached at w h 1 2 1 7 further in all simulations the area of the largest earthquake rupture is less than the total seismogenic area and we predict a deficiency of large earthquakes on long transforms which is also consistent with observations to match these observations over this narrow range of w h requires an increase in the characteristic slip distance dc as the seismogenic zone becomes wider and normal stress is higher on long transforms earthquake magnitude and distribution on the gofar and romanche transforms are better predicted by simulations using the visco plastic model than the half space cooling model

the parkfield tremors reveal slow and fast ruptures on the same asperity a tremor source on the san andreas fault produced an unusual sequence of low frequency earthquakes until it was disrupted by the 2004 parkfield earthquake the peculiar recurrence pattern has now been modelled showing that such slip behaviour occurs when the tremor asperity size is close to the critical nucleation size of earthquakes an isolated tremor source on the san andreas fault near parkfield california produces an unusual sequence of low frequency earthquakes which regularly oscillated between recurrence intervals of three and six days until it was disrupted by the 2004 magnitude 6 0 parkfield earthquake after that event the source ruptured every three days only gradually returning to its initial alternating recurrence pattern after two years deepa mele veedu and sylvain barbot have now modelled the mechanism driving the tremor source to form this peculiar recurrence pattern they demonstrate that such slip behaviour can occur when the tremor asperity size is close to the critical nucleation size of earthquakes they also show that changes in pore pressure following the 2004 parkfield earthquake can explain the sudden change and gradual recovery of the recurrence intervals the deep extension of the san andreas fault is believed to be creeping but the recent observations of tectonic tremors from these depths indicate a complex deformation style1 in particular an isolated tremor source near parkfield has been producing a sequence of low frequency earthquakes2 that indicates an uncommon mechanism of stress accumulation and release the tremor pattern regularly oscillated between three and six days from mid 2003 until it was disrupted by the 2004 magnitude 6 0 parkfield earthquake after that event the tremor source ruptured only about every three days but over the next two years it gradually returned to its initial alternating recurrence pattern the mechanism that drives this recurrence pattern is unknown here we use physics based models to show that the same tremor asperity the region from which the low frequency earthquakes radiate can regularly slip in slow and fast ruptures naturally resulting in recurrence intervals alternating between three and six days this unusual slip behaviour occurs when the tremor asperity size is close to the critical nucleation size of earthquakes we also show that changes in pore pressure following the parkfield earthquake can explain the sudden change and gradual recovery of the recurrence intervals our findings suggest a framework for fault deformation in which the same asperity can release tectonic stress through both slow and fast ruptures

the scale dependent slip pattern for a uniform fault model obeying the rate and state dependent friction law a uniform antiplane fault model obeying the rate and state dependent friction law and surrounded by a steady slipping region with a constant loading rate is studied through quasi dynamic numerical method findings indicate that the model exhibits scale dependent slip characteristics previous studies have demonstrated that the fault slip pattern changes from aseismic creep or slow earthquakes to seismic instabilities as the fault length w increases from around the nucleation size hc to well above hc in the latter instabilities typically nucleate periodically from the center of the fault and develop into characteristic events after the whole fault reaches a background stress level for a fault with larger w hc characteristic events nucleate near the boundary or alternatively from both sides before the entire fault returns to background level as w hc increases further additional events with rupture size between hc and w appear the number of small events is expected to increase with w hc the reason these small events do not rupture the whole fault is that the locked region forming on the fault when nucleation occurs acts as a large and low stress barrier these small events continually create stress concentrations that serve as preparations for the next larger earthquake until the final characteristic event occurs meanwhile the fault in this process gradually evolves into extreme sensitivity that any slight perturbation could change the original slip pattern although the current result is far from explaining the observed slip complexity on natural faults it suggests a trend of increasing slip complexity with w hc therefore our understanding of the fault behavior may differ from previous knowledge that a relatively uniform and isolated fault model obeying the rate and state dependent friction law only exhibits periodic or aperiodic system size events

a mechanism for preseismic steady rupture fronts observed in laboratory experiments it has been shown that the onset of frictional instability is characterized by a transition from stable quasi static rupture growth to unstable inertially controlled high speed rupture in particular slow rupture fronts propagating at a steady speed v slow of the order of 5 of the s wave speed have been observed prior to the onset of dynamic rupture in recent fault friction laboratory experiments however the precise mechanism governing this v slow stage is unknown here we reproduce this phenomenon in numerical simulations of earthquake sequences that incorporate laboratory derived rate and state friction laws our simulations show that the v slow stage originates from a stress concentration inherited from the coalescence of interseismic slow creep fronts its occurrence is limited to a narrow range of the parameter space but is found in simulations with two commonly used state variable evolution laws in the rate and state formulation the sensitivity of the speed v slow to the model parameters suggests that the propagation speed v slow reported in laboratory experiments may also be sensitive to parameters of friction and stress conditions our results imply that time and space dimensions associated with the propagation of v slow on natural faults can be as much as a few seconds and several hundred meters respectively hence the detection of such preseismic signals may be possible with near field high resolution observations

quasi dynamic modeling of seismicity on a fault with depth variable rate and state dependent friction 1 neither the omori type of clustering prior to and following large earthquakes nor the gutenberg richter distribution are reproducible by present continuous models discrete models on the other hand give rise to more complex and closer to realistic earthquake clustering the objective of this study is twofold to explore the consequences of spatial discreteness on the distribution in time and space of earthquake activity on a fault governed by rate and state friction and to examine the effect of interaction between seismic slip and aseismic creep on aftershock sequences to that end we model a long vertical two dimensional strike slip fault that is governed by rate and state dependent friction and is embedded in a three dimensional elastic half space quasi dynamic motion on the fault is driven by steady displacement applied below the fault and at distance w 2 on either side of the fault plane the model is said to be spatially discrete in that the computational cells are oversized with respect to the critical length scale that is implied by the friction law the model reproduces some of the characteristics of natural seismicity including the nonperiodic recurrence times and the omori type of clustering prior to and following large earthquakes it also produces a wide range of earthquake magnitudes but with a ratio of small to large earthquakes that is in excess with respect to what is inferred form natural catalogs we examined the effect of a stress step applied on the creeping portions of the model and confirmed that aftershock sequences resulting from stress relaxation on creeping segments decay asymptotically to 1 time finally we discuss fundamental differences between seismicity models employing rate and state friction and those employing static kinetic friction

dynamic rupture in a 3 d particle based simulation of a rough planar fault an appreciation of the physical mechanisms which cause observed seismicity complexity is fundamental to the understanding of the temporal behaviour of faults and single slip events numerical simulation of fault slip can provide insights into fault processes by allowing exploration of parameter spaces which influence microscopic and macroscopic physics of processes which may lead towards an answer to those questions particle based models such as the lattice solid model have been used previously for the simulation of stick slip dynamics of faults although mainly in two dimensions recent increases in the power of computers and the ability to use the power of parallel computer systems have made it possible to extend particle based fault simulations to three dimensions in this paper a particle based numerical model of a rough planar fault embedded between two elastic blocks in three dimensions is presented a very simple friction law without any rate dependency and no spatial heterogeneity in the intrinsic coefficient of friction is used in the model to simulate earthquake dynamics the model is sheared in a direction parallel to the fault plane with a constant velocity at the driving edges spontaneous slip occurs on the fault when the shear stress is large enough to overcome the frictional forces on the fault slip events with a wide range of event sizes are observed investigation of the temporal evolution and spatial distribution of slip during each event shows a high degree of variability between the events in some of the larger events highly complex slip patterns are observed

modeling seismic cycles of great megathrust earthquakes across the scales with focus at postseismic phase subduction is substantially multi scale process where the stresses are built by long term tectonic motions modified by sudden jerky deformations during earthquakes and then restored by following multiple relaxation processes here we develop a cross scale thermomechanical model aimed to simulate the subduction process from 1 minute to million years time scale the model employs elasticity nonlinear transient viscous rheology and rate and state friction it generates spontaneous earthquake sequences and by using an adaptive time step algorithm recreates the deformation process as observed naturally during the seismic cycle and multiple seismic cycles the model predicts that viscosity in the mantle wedge drops by more than three orders of magnitude during the great earthquake with a magnitude above 9 as a result the surface velocities just an hour or day after the earthquake are controlled by viscoelastic relaxation in the several hundred km of mantle landward of the trench and not by the afterslip localized at the fault as is currently believed our model replicates centuries long seismic cycles exhibited by the greatest earthquakes and is consistent with the postseismic surface displacements recorded after the great tohoku earthquake we demonstrate that there is no contradiction between extremely low mechanical coupling at the subduction megathrust in south chile inferred from long term geodynamic models and appearance of the largest earthquakes like the great chile 1960 earthquake

universality of the seismic moment frequency relation we analyze the seismic moment frequency relation in various depth ranges and for different seismic regions using flinn engdahl s regionalization of global seismicity three earthquake lists of centroid moment tensor data have been used the harvard catalog the usgs catalog and the huang et al 1997 catalog of deep earthquakes the results confirm the universality of the values and the maximum moment for shallow earthquakes in continental regions as well as at and near continental boundaries moreover we show that although fluctuations in earthquake size distribution increase with depth the values for earthquakes in the depth range of 0 500 km exhibit no statistically significant regional variations the regional variations are significant only for deep events near the 660 km boundary for declustered shallow earthquake catalogs and deeper events we show that the worldwide values have the same value of 0 60 0 02 this finding suggests that the value is a universal constant we investigate the statistical correlations between the numbers of seismic events in different depth ranges and the correlation of the tectonic deformation rate and seismic activity the number of earthquakes above a certain threshold level per year the high level of these correlations suggests that seismic activity indicates tectonic deformation rate in subduction zones combined with the universality of the value this finding implies little if any variation in maximum earthquake seismic moment among various subduction zones if we assume that earthquakes of maximum size are similar in different depth ranges and the seismic efficiency coefficient is close to 100 for shallow seismicity then we can estimate for deeper earthquakes for intermediate earthquakes 5 and 1 for deep events these results may lead to new theoretical understanding of the earthquake process and better estimates of seismic hazard

variability of earthquake nucleation in continuum models of rate and state faults and implications for aftershock rates using two continuum models of rate and state faults one with a weaker patch and the other with rheological transition from steady state velocity weakening to velocity strengthening friction we simulate several scenarios of spontaneous earthquake nucleation plausible for natural faults investigate their response to static shear stress steps and infer the corresponding aftershock rates overall nucleation processes at weaker patches behave similarly to theories based on spring slider models with some notable deviations in particular nucleation and aftershock rates are affected by normal stress heterogeneity in the nucleation zone nucleation processes at rheological transitions behave differently producing complex slip velocity histories nonmonotonic responses to static stress changes and aftershock rates with pronounced peaks and seismic quiescence for such processes positive stress steps sometimes delay nucleation of seismic events by inducing aseismic transients that relieve stress and postpone seismic slip superposition of the complex aftershock response for spatially variable stress changes results in omori s law for a period of time followed by seismic quiescence such behavior was observed at the base of the seismogenic zone near the 1984 morgan hill earthquake we show that the computed aftershock rates are linked to unperturbed slip velocity evolution in the nucleation zone and construct simplified analytical scenarios that explain some features of the response the qualitative differences that we find between the two nucleation models indicate that aftershock response of rate and state faults to static stress changes would depend on the conditions under which nucleation occurs on natural faults and may be different from predictions based on spring slider models

implications of rate and state friction for properties of aftershock sequence quasi static inherently discrete simulations 1 dieterich 1994 modeled the response to a stress step of a population of faults governed by rate and state dependent friction this model assumes that aftershocks nucleate over areas on the fault that at the time of the main shock are already accelerating toward failure and disregards the effect of interactions among aftershocks the main objective of this study is to examine consequences of relaxing these underlying assumptions aftershock activity is simulated using an inherently discrete earthquake fault model with a fault surface governed by an approximate constitutive friction law similar to the one used by dieterich we find that the governing equations in nondimensional form are a function of three main parameters and explore the effect of these parameters on the simulated catalogs we derive a simple expression for the time dependent seismicity response to a stress step that approximates the effect of multiple interactions among aftershocks as a time dependent stressing rate close match is found between the simulated seismicity response to a stress step and that predicted analytically however the numerical simulations show that the effect of the main shock is not only to raise the local seismicity rate but also to systematically modify the earthquake size distribution as a result the actual seismicity rate change early during the aftershock sequence may be higher than that predicted whereas seismicity rate late in the sequence may be lower than that predicted such a modification of the earthquake size distribution can explain observations of lower b values immediately following a stress step

elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate and state dependent friction we present an efficient and rigorous numerical procedure for calculating the elastodynamic response of a fault subjected to slow tectonic loading processes of long duration within which there are episodes of rapid earthquake failure this is done for a general class of rate and state dependent friction laws with positive direct velocity effect the algorithm allows us to treat accurately within a single computational procedure loading intervals of thousands of years and to calculate for each earthquake episode initially aseismic accelerating slip prior to dynamic rupture the rupture propagation itself rapid post seismic deformation which follows and also ongoing creep slippage throughout the loading period in velocity strengthening fault regions the methodology is presented using the two dimensional 2 d antiplane spectral formulation and can be readily extended to the 2 d in plane and 3 d spectral formulations and with certain modifications to the space time boundary integral formulations as well as to their discretized development using finite difference or finite element methods the methodology can be used to address a number of important issues such as fault operation under low overall stress interaction of dynamic rupture propagation with pore pressure development patterns of rupture propagation in events nucleated naturally as a part of a sequence the earthquake nucleation process earthquake sequences on faults with heterogeneous frictional properties and or normal stress and others the procedure is illustrated for a 2 d crustal strike slip fault model with depth variable properties for lower values of the state evolution distance of the friction law small events appear the nucleation phases of the small and large events are very similar suggesting that the size of an event is determined by the conditions on the fault segments the event is propagating into rather than by the nucleation process itself we demonstrate the importance of incorporating slow tectonic loading with elastodynamics by evaluating two simplified approaches one with the slow tectonic loading but no wave effects and the other with all dynamic effects included but much higher loading rate

scaling of the shear rupture process from nucleation to dynamic propagation implications of geometric irregularity of the rupturing surfaces a series of systematic high resolution laboratory experiments have been performed on the nucleation of propagating slip failure on preexisting faults having different surface roughnesses to demonstrate how the size scale and duration of shear rupture nucleation are affected by geometric irregularity of the rupturing surfaces on the basis of the experimental results it has been discussed theoretically how consistently scale dependent physical quantities inherent in shear rupture are scaled the experiments led to conclusive results that the nucleation process consists of two phases phase i an initial quasi static phase and phase ii a subsequent accelerating phase and that the nucleation process is greatly affected by geometric irregularities on the rupturing surfaces in phase i the rupture grows at a slow steady speed which is independent of the rupture growth length l in contrast during phase ii the rupture develops at accelerating speeds v which increase with an increase in l obeying a power law v vs l c n where vs is the shear wave velocity c is the characteristic length representing the geometric irregularity of the fault surfaces and and n are constants 8 87 10 29 and n 7 31 scale dependency of scale dependent physical quantities including the nucleation zone size and its duration is commonly ascribed to scale dependency of the slip dependent constitutive law parameter dc which is in turn governed by c it has been discussed that a unified comprehension can be provided for shear rupture of any size scale if the constitutive law for shear rupture is formulated as a slip dependent law

can observations of earthquake scaling constrain slip weakening summary we use observations of earthquake source parameters over a wide magnitude range m w 0 7 to place constraints on constitutive fault weakening the data suggest a scale dependence of apparent stress and stress drop both may increase slightly with earthquake size we show that this scale dependence need not imply any difference in fault zone properties for different sized earthquakes we select 30 earthquakes well recorded at 2 5 km depth at cajon pass california we use individual and empirical green s function spectral analysis to improve the resolution of source parameters including static stress drop and total slip s we also measure radiated energy e s w ecompare the cajon pass results with those from larger california earthquakes including aftershocks of the 1994 northridge earthquake and confirm the results of abercrombie 1995 e s m 0 where rigidity and both e s m 0 and increase as m 0 and s increases uncertainties remain large due to model assumptions and variations between possible models and earthquake scale independence is possible within the resolution assuming that the average trends are real we define a quantity g 2 es m 0 s 2w hich is the total energy dissipation in friction and fracture minus 1 s w here 1 is the final static stress if 1 d the dynamic shear strength during the last increments of seismic slip then g g the fracture energy in a slip weakening interpretation of dissipation

nucleation and early seismic propagation of small and large events in a crustal earthquake model 1 earthquake nucleation and early seismic propagation are studied in a two dimensional strike slip fault model with depth variable properties the fault is governed by the dieterich ruina rate and state friction law we use an efficient and rigorous numerical procedure for elastodynamic analysis of earthquake sequences on slowly loaded faults developed by lapusta et al 2000 we find that for decreasing values of the characteristic slip distance of the friction law small events appear at the transition from the locked to creeping behavior toward the bottom of the seismogenic zone small and large events have very similar nucleation phases in our simulations here by nucleation phase we mean gradually accelerating aseismic slip in a small slowly expanding zone before the breakout of the dynamic seismically detectable event moment acceleration to which velocity seismograms are proportional in early stages of seismic propagation exhibits irregular fluctuations in the form of speedups and slowdowns in the moment release rate consistently with observations as reported by ellsworth and beroza 1995 our simulations show that such irregular moment acceleration can at least in part be due to the heterogeneous stress distribution imprinted on the fault by the arrest of previous small events and by stress concentrations at the borders of creeping regions and to partial arrest of the rupture in velocity strengthening fault regions which inhibit seismic slip index terms 7209 seismology earthquake dynamics and mechanics 7260 seismology theory and modeling 3220 mathematical geophysics nonlinear dynamics 7230 seismology seismicity and seismotectonics 3230 mathematical geophysics numerical solutions 8164 tectonophysics stresses crust and lithosphere keywords earthquake nucleation phase event clustering irregular moment release stress concentrations rate and state friction earthquake sequences

simulation of the transition of earthquake rupture from quasi static growth to dynamic propagation we have simulated a rupture transition from quasi static growth to dynamic propagation using the boundary integral equation method in order to make a physically reasonable model of earthquake cycle we have to evaluate the dynamic rupture propagation in the context of quasi static simulation we used a snapshot of the stress distribution just before the earthquake in the quasi static simulation the resultant stress will be fed back to the quasi static simulation since the quasi static simulation used the slip and time dependent constitutive relation the friction law itself evolves with time thus we used the slip weakening constitutive relation for dynamic rupture propagation consistent with that used for the quasi static simulation we modeled a san andreas type strike slip fault in which two different size asperities existed

dilatancy controlled spatiotemporal slip evolution of a sealed fault with spatial variations of the pore pressure summary a range of observations suggest the formation and maintenance of sealed and hence overpressured compartments in fluid infiltrated fault zones it is assumed that hydromechanical properties of regions with variable pore pressure states control the fault s stability and thus its characteristic response that is seismic or aseismic slip accumulation we investigate in a systematic parameter space study the effects of spatial variations in pore pressure on spatiotemporal slip evolution along a hydraulically isolated fault plane the 3 d continuum model is governed by rate and state friction and constitutive laws for porosity reduction we show that the model response is sensitive to the degree of overpressurization and the efficiency of dilatant hardening mechanisms low pore pressures and small dilatancy effects result in unstable response types whereas high pore pressures and large dilatant effects lead to stable and aseismic creep regions with an unstable response are shown to support most of the stresses accumulated during interseismic periods accelerated slip nucleates preferably in regions of low pore pressure statistical properties of model seismicity produce a wide range of event sizes for moderate and large earthquakes in the case where dilatant mechanisms are inefficient in case of efficient slip rate controlled porosity increase less instabilities grow into large earthquakes final slip maps demonstrate the applicability of the chosen method to model seismicity controlled by frictional and hydraulic processes on a planar fault plane the evolution of governing variables that depend on the pore pressure environment provide a conceptual basis for the interpretation of observed response characteristics

coseismic and postseismic deformation of the 2016 mw 6 2 lampa earthquake southern peru constrained by interferometric synthetic aperture radar

fluids migration and dynamics of a blocks and faults system abstract we explore the impact of fluids migrating through a fault network on the dynamics of lithosphere both on slow movements and seismicity for that purpose fluids in the fault zones are incorporated into modelling of blocks and faults systems which takes into account driving forces and the system s geometry simulations have been performed for two dimensional models an idealised brick wall structure and a coarse image of sinai subplate migrating fluids originating in different locations are considered as well as fluids trapped in closed pockets basic features of the modelled and observed seismicity are in good accord as shown by comparison with the earthquake catalog compiled by geophysical institute of israel

the effect of shear load on frictional healing in simulated fault gouge we report on frictional strengthening healing in granular quartz gouge as a function of time of true stationary contact to distinguish between the slip dependent ruina 1983 and time dependent dieterich 1979 friction constitutive laws we designed tests similar to conventional slide hold slide shs tests except that shear load was completely removed prior to holds we find large healing values 0 033 0 054 for holds of 101 102 s compared with quasi static shs experiments and our data indicate time dependent weakening in contrast with strengthening observed from shs tests gouge layer compaction increases with increasing hold time comparable to observations from conventional shs tests our data indicate that purely time dependent processes have a minor influence on healing under the conditions studied and or that such effects are efficiently erased by particle rearrangement during removal reapplication of shear load the data are not adequately described by either the time dieterich or slip ruina dependent state evolution laws

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

slip sequences in laboratory experiments resulting from inhomogeneous shear as analogs of earthquakes associated with a fault edge faults are intrinsically heterogeneous with common occurrences of jogs edges and steps we therefore explore experimentally and theoretically how fault edges may affect earthquake and slip dynamics in the presented experiments and accompanying theoretical model shear loads are applied to the edge of one of two flat blocks in frictional contact that form a fault analog we show that slip occurs via a sequence of rapid rupture events that initiate from the loading edge and are arrested after propagating a finite distance each successive event extends the slip size transfers the applied shear across the block and causes progressively larger changes of the contact area along the contact surface resulting from this sequence of events a hard asperity is dynamically formed near the loaded edge the contact area beyond this asperity is largely reduced these sequences of rapid events culminate in slow slip events that precede a major unarrested slip event along the entire contact surface we suggest that the 1998 m5 0 sendai and 1995 off etorofu earthquake sequences may correspond to this scenario our work demonstrates qualitatively how the simplest deviation from uniform shear loading may significantly affect both earthquake nucleation processes and how fault complexity develops