dynamic earthquake rupture modelled with an unstructured 3 d spectral element method applied to the 2011 m9 tohoku earthquake an important goal of computational seismology is to simulate dynamic earthquake rupture and strong ground motion in realistic models that include crustal heterogeneities and complex fault geometries to accomplish this we incorporate dynamic rupture modelling capabilities in a spectral element solver on unstructured meshes the 3 d open source code specfem3d and employ state of the art software for the generation of unstructured meshes of hexahedral elements these tools provide high flexibility in representing fault systems with complex geometries including faults with branches and non planar faults the domain size is extended with progressive mesh coarsening to maintain an accurate resolution of the static field our implementation of dynamic rupture does not affect the parallel scalability of the code we verify our implementation by comparing our results to those of two finite element codes on benchmark problems including branched faults finally we present a preliminary dynamic rupture model of the 2011 m w 9 0 tohoku earthquake including a non planar plate interface with heterogeneous frictional properties and initial stresses our simulation reproduces qualitatively the depth dependent frequency content of the source and the large slip close to the trench observed for this earthquake

inelastic off fault response and three dimensional dynamics of earthquake rupture on a strike slip fault 1 large dynamic stress off the fault incurs an inelastic response and energy loss which contributes to the fracture energy limiting the rupture and slip velocity using an explicit finite element method we model three dimensional dynamic ruptures on a vertical strike slip fault in a homogeneous half space the material is subjected to a pressure dependent drucker prager yield criterion initial stresses in the medium increase linearly with depth our simulations show that the inelastic response is confined narrowly to the fault at depth there the inelastic strain is induced by large dynamic stresses associated with the rupture front that overcome the effect of the high confining pressure the inelastic zone increases in size as it nears the surface for material with low cohesion 5 mpa the inelastic zone broadens dramatically near the surface forming a flowerlike structure the near surface inelastic strain occurs in both the extensional and the compressional regimes of the fault induced by seismic waves ahead of the rupture front under a low confining pressure when cohesion is large 10 mpa the inelastic strain is significantly reduced near the surface and confined mostly to depth cohesion however affects the inelastic zone at depth less significantly the induced shear microcracks show diverse orientations near the surface owing to the low confining pressure but exhibit mostly horizontal slip at depth the inferred rupture induced anisotropy at depth has the fast wave direction along the direction of the maximum compressive stress

constitutive relationships and physical basis of fault strength due to flash heating 1 we develop a model of fault strength loss resulting from phase change at asperity contacts due to flash heating that considers a distribution of contact sizes and nonsteady state evolution of fault strength with displacement laboratory faulting experiments conducted at high sliding velocities which show dramatic strength reduction below the threshold for bulk melting are well fit by the model the predicted slip speed for the onset of weakening is in the range of 0 05 to 2 m s qualitatively consistent with the limited published observations for this model earthquake stress drops and effective shear fracture energy should be linearly pressure dependent whereas the onset speed may be pressure independent or weakly pressure dependent on the basis of the theory flash weakening is expected to produce large dynamic stress drops small effective shear fracture energy and undershoot estimates of the threshold slip speed stress drop and fracture energy are uncertain due to poor knowledge of the average contact dimension shear zone thickness and gouge particle size at seismogenic depths

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

variability of near field ground motion from dynamic earthquake rupture simulations this study investigates near field ground motion variability due to dynamic rupture models with heterogeneity in the initial shear stress ground velocity seismograms are synthesized by convolving the time histories of slip velocity obtained from spontaneous dynamic rupture models with green s functions of the medium calculated with a discrete wavenumber finite element method peak ground velocity pgv estimated on the synthetics generally matches well with an empirically derived attenuation relation whereas spectral acceleration sa shows only an acceptable match at periods longer than 1 sec using the geometric mean to average the two orthogonal components leads to a systematic bias for the synthetics in particular at the stations closest to the fault this bias is avoided by using measures of ground motion that are independent of the sensor orientation the contribution from stress heterogeneity to the overall ground motion variability is found to be strongest close to the fault and in the backward directivity region of unilaterally propagating ruptures in general the intraevent variability originating from the radiation pattern and the effect of directivity is on the same order or larger than the interevent variability the interevent ground motion variability itself is dominated by the hypocenter station configuration and is influenced only to a lesser extent by the differences in the dynamic rupture process due to the stress heterogeneity in our modeling approach the hypocenter location is not picked arbitrarily but is determined to be mechanically consistent with the stress heterogeneity through a procedure emulating tectonic stress loading of the fault and nucleation compared to the peak ground motion recorded during the 2004 parkfield california earthquake our simulated seismograms show enhanced spatial correlation that may be attributed to the simplicity of the assumed crustal model or to an incomplete representation of the spatial heterogeneity of dynamic rupture parameters nevertheless the intraevent pgv variability in the near fault region determined for the parkfield dataset is of the same order of magnitude as for our simulations

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

contribution of radar interferometry to a two step inversion of the kinematic process of the 1992 landers earthquake we study the rupture process of the 1992 landers earthquake to limit the trade off between slip amplitude and rupture time that affects solutions using only seismological data we adopt a two step approach we first constrain the slip distribution and its uncertainty by independent geodetic data to recover in the second step the temporal details of the rupture propagation the first step consists of an inversion of interferometric data and global positioning system measurements both independently and together to constrain slip distribution on a three segment fault model along both strike and dip direction we use a genetic algorithm to test the uniqueness of the solution and a least squares formulation to find the model which best fits the data we conclude from the results of these geodetic inversions that interferometric data are rich enough to access the slip distribution in the case of the landers earthquake since the surface deformations are more sensitive to shallow slip in our configuration the slip amplitude is better resolved near the surface than at depth the resulting slip distribution is in agreement with geological observations at the surface and confirms the heterogeneous nature of the landers earthquake most of the slip occurs at shallow depths on the homestead valley fault second segment with a maximum value of around 7 m another high slip zone is observed on the johnson valley fault first segment at 8 km depth in the second step we invert strong motion data with the a priori final slip amplitude and its uncertainty deduced from geodetic data to constrain the time history of the rupture process this second step emphasizes a strong variation of the temporal development of the earthquake fast rupture front velocities appear within high slip zones and the rupture slows when it encounters a resistance along the fault on average the rupture front propagates with velocities close to the s wave velocity and terminates about 20 s after initiation the large variations in both slip amplitude and rupture velocity suggest that the rupture process is better described by successively breaking asperities than by a pulse propagating with constant velocity

surface rupturing and buried dynamic rupture models calibrated with statistical observations of past earthquakes in the context of the slip weakening friction model and simplified asper ity models for stress state we calibrate dynamic rupture models for buried and surface rupturing earthquakes constrained with statistical observations of past earth quakes these observations are the kinematic source models derived from source in versions of ground motion and empirical source models of seismic moment and rupture area the calibrated parameters are the stress drop distribution on the fault and average stress drop we develop a set of dynamic rupture models that consist of asperities and surrounding background areas the distribution of dynamic stress drop outside the asperity is characterized by a fraction of the stress drop on the as perity from this set of models we identify dynamic fault models with defined stress drop characteristics that satisfy the observations the selected dynamic fault models show that surface rupturing earthquakes are characterized by a large area of negative stress drop surrounding the asperities while buried earthquakes present positive or zero stress drop in addition the calibrated fault models that match the observations show that the average stress drop is independent of earthquake size for buried earth quakes but scale dependent for surface rupturing earthquakes this suggests that in the context of our parameterization buried earthquakes follow self similarity scaling and surface rupturing earthquakes break this self similarity we apply the calibrated dynamic models to simulate near source ground motion consistent with observations that suggest that buried earthquakes generate stronger ground motion than surface rupturing earthquakes at high frequency we propose possible mechanisms that satisfy this observation as follows buried rupture has a hypocenter location below the as perity this can produce strong directivity of the slip velocity function toward the free surface that effect in addition to a reduced fault area and low fracture energy during rupture may be significant in enhancing high frequency ground motion on the other hand surface rupturing earthquakes have a shallow hypocenter large fracture energy on the asperities and enhanced energy absorption due to large areas of negative stress drop in the background area these characteristics of large earthquakes inhibit severe directivity effects on the slip velocity function directly toward the free surface redu cing the high frequency ground motion

structural trends and back arc extension in the havre trough the havre trough is an active back arc ocean btsin located to the west of the kermadec trench arc system in the southwest pacific two recent cruises have provided reconnaissance swaths of sea beam bathymetry and gloria side scan sonar data through much of the havre trough as well as a detailed survey at 33 5 s allowing the overall structural character of the trough and the nature of crustal extension within the detailed survey area to be assessed the orientation of the tectonic fabric within the havre trough is consistently oblique to the basin as a whole trending 045 to 060 while the bounding kermadec and colville ridges trend 015 to 025 the oblique internal structure indicates that the havre trough has not opened perpendicular to its own trend within the detailed survey area a series of short 15 35 km long en echelon basins are interpreted as an active spreading center a lack of sediment cover and the dredging of fresh basalt from one of the 3500 4000 m deep basins confirms the youth of these features no recent extensional features are observed in a gloria crossing of the trough at 31 5 s suggesting that this part of the havre trough may currently be inactive

fault roughness at seismogenic depths from lidar and photogrammetric analysis fault surface roughness is a principal factor influencing earthquake mechanics and particularly rupture initiation propagation and arrest however little data currently exist on fault surfaces at seismogenic depths here we investigate the roughness of slip surfaces from the seismogenic strike slip gole larghe fault zone exhumed from ca 10 km depth the fault zone exploited pre existing joints and is hosted in granitoid rocks of the adamello batholith italian alps individual seismogenic slip surfaces generally show a first phase of cataclasite production and a second phase with beautifully preserved pseudotachylytes of variable thickness we determined the geometry of fault traces over almost five orders of magnitude using terrestrial laser scanning lidar ca 500 to 1 10 m is not anisotropic and less evolved than at smaller scales these observations are consistent with an evolution of roughness due to fault surface processes that takes place only at scales smaller or comparable to the observed net slip differences in roughness evolution between shallow and deeper faults the latter showing evidences of seismic activity are interpreted as the result of different weakening versus induration processes which also result in localization versus delocalization of deformation in the fault zone from a methodological point of view the technique used here is advantageous over direct measurements of exposed fault surfaces in that it preserves in cross section all of the structures which contribute to fault roughness and removes any subjectivity introduced by the need to distinguish roughness of original slip surfaces from roughness induced by secondary weathering processes moreover offsets can be measured by means of suitable markers and fault rocks are preserved hence their thickness composition and structural features can be characterised providing an integrated dataset which sheds new light on mechanisms of roughness evolution with slip and concomitant fault rock production

rupture reactivation during the 2011 mw 9 0 tohoku earthquake dynamic rupture and ground motion simulations near source ground motion observations and kinematic source inversions suggest that the rupture process of the 2011 m w 9 0 tohoku earthquake involved rupture reactivation that is repeated rupture nucleation in the same hypocentral area this unusual phenomenon may have provided a second breath to the rupture that enhanced its final size here we propose that rupture reactivation may have been governed by a slip weakening friction model with two sequential strength drops the second one being activated at large slip such frictional behavior has been previously observed in laboratory experiments and attributed to pressurization of fault zone fluids by mineral decomposition reactions activated by shear heating such as dehydration and decarbonation further evidence of this double slip weakening friction model is obtained here from the dynamic stress changes in the hypocentral region derived from a finite source inversion model we incorporate this friction model in a dynamic rupture simulation comprising two main asperities constrained by source inversion models and several deep small asperities constrained by backprojection source imaging studies our simulation produces ground motion patterns along the japanese coast consistent with observations and rupture patterns consistent with a kinematic source model featuring rupture reactivation the deep small asperities serve as a bridge to connect the two main asperities and the rupture reactivation mechanism is needed to reproduce the observed ground motion pattern therefore we argue that rupture reactivation during the 2011 tohoku earthquake is consistent with a second strength drop possibly caused by activation of thermochemical weakening processes at large slip online material movie of simulated rupture and wave propagation and ground velocities recorded at the kik net and k net seismic networks

shakeout d ground motion estimates using an ensemble of large earthquakes on the southern san andreas fault with spontaneous rupture propagation 1 we simulate ground motion in southern california from an ensemble of 7 spontaneous rupture models of large mw7 8 northwest propagating earthquakes on the southern san andreas fault shakeout d compared to long period spectral accelerations from the next generation attenuation nga empirical relations shakeout d predicts similar average rock site values i e within roughly their epistemic uncertainty but significantly larger values in los angeles and ventura basins due to wave guide focusing effects the shakeout d ground motion predictions differ from those of a kinematically parameterized geometrically similar scenario rupture 1 the kinematic rock site predictions depart significantly from the common distance attenuation trend of the nga and shakeout d results and 2 shakeout d predictions of long period spectral acceleration within the basins of the greater los angeles area are lower by factors of 2 3 than the corresponding kinematic predictions we attribute these differences to a less coherent wavefield excited by the complex rupture paths of the shakeout d sources

earthquake ruptures with strongly rate weakening friction and off fault plasticity part 1 planar faults abstract observations demonstrate that faults are fractal surfaces with deviations from planarity at all scales we study dynamic rupture propagation on self similar faults having root mean square rms height fluctuations of order 10 3 to 10 2 times the profile length our 2d plane strain models feature strongly rate weakening fault friction and off fault drucker prager viscoplasticity the latter bounds otherwise unreasonably large stress concentrations in the vicinity of bends our choice of a cohesionless yield function prevents tensile stress states and thus fault opening a consequence of strongly rate weakening friction is the existence of a critical background stress level above which self sustaining rupture propagation in the form of self healing slip pulses first becomes possible around this level at which natural faults are expected to operate ruptures become extremely sensitive to fault roughness and exhibit substantial fluctuations in rupture velocity except for shallow inclinations of the maximum compressive stress to the fault less than about 20 the fluctuations are anticorrelated with the local fault slope these accelerations and decelerations of the rupture together with naturally emerging slip heterogeneity excite waves of all wavelengths and result in ground acceleration spectra that are flat at high frequency consistent with observed strong motion records

simulation of active tectonic processes for a convecting mantle with moving continents summary numerical models are presented that simulate several active tectonic processes these models include a continent that is thermally and mechanically coupled with viscous mantle flow the assumption of rigid continents allows use of solid body equations to describe the continents motion and to calculate their velocities the starting point is a quasi steady state model of mantle convection with temperature pressure dependent viscosity after placing a continent on top of the mantle the convection pattern changes the mantle flow subsequently passes through several stages eventually resembling the mantle structure under present day continents a extension tectonics and marginal basins form on boundary of a continent approaching to subduction zone roll back of subduction takes place in front of moving continent b the continent reaches the subduction zone the extension regime at the continental edge is replaced by strong compression the roll back of the subduction zone still continues after closure of the marginal basin and the continent moves towards the upwelling as a result the ocean becomes non symmetric and c the continent overrides the upwelling and subduction in its classical form stops the third stage appears only in the upper mantle model with localized upwellings

roughness of fault surfaces over nine decades of length scales 1 we report on the topographic roughness measurements of five exhumed faults and thirteen surface earthquake ruptures over a large range of scales from 50 m to 50 km we used three scanner devices lidar laser profilometer white light interferometer spanning complementary scale ranges from 50 m to 10 m to measure the 3 d topography of the same objects i e five exhumed slip surfaces vuache sillingy bolu corona heights dixie valley magnola a consistent geometrical property i e self affinity emerges as the morphology of the slip surfaces shows at first order a linear behavior on a log log plot where axes are fault roughness and spatial length scale covering five decades of length scales the observed fault roughness is scale dependent with an anisotropic self affine behavior described by four parameters two power law exponents h constant among all the faults studied but slightly anisotropic h 0 58 0 07 in the slip direction and h 0 81 0 04 perpendicular to it and two pre factors showing variability over the faults studied for larger scales between 200 m and 50 km we have analyzed the 2 d roughness of the surface rupture of thirteen major continental earthquakes these ruptures show geometrical properties consistent with the slip perpendicular behavior of the smaller scale measurements our analysis suggests that the inherent non alignment between the exposed traces and the along or normal slip direction results in sampling the slip perpendicular geometry although a data gap exists between the scanned fault scarps and rupture traces the measurements are consistent within the error bars with a single geometrical description i e consistent dimensionality over nine decades of length scales

surface rupture effects on earthquake moment area scaling relations empirical earthquake scaling relations play a central role in fundamental studies of earthquake physics and in current practice of earthquake hazard assessment and are being refined by advances in earthquake source analysis a scaling relation between seismic moment m0 and rupture area a currently in use for ground motion prediction in japan features a transition regime of the form m0 a2 between the well recognized small self similar and very large w model earthquake regimes which has counterintuitive attributes and uncertain theoretical underpinnings here we investigate the mechanical origin of this transition regime via earthquake cycle simulations analytical dislocation models and numerical crack models on strike slip faults we find that even if stress drop is assumed constant the properties of the transition regime are controlled by surface rupture effects comprising an effective rupture elongation along dip due to a mirror effect and systematic changes of the shape factor relating slip to stress drop based on this physical insight we propose a simplified formula to account for these effects in m0 a scaling relations for strike slip earthquakes

geomorphic processes influence human settlement on two islands in the islands of four mountains alaska the islands of four mountains island group of the aleutian island arc is remote and difficult to access consequently little fieldwork has focused on geomorphic processes and their relationship to island morphology climatic change and human settlement we investigated glacial fluvial and slope processes on the morphologically different carlisle cleveland and tana volcanoes the islands were extensively glaciated at the last glacial maximum lgm and there is evidence for a neoglacial advance on the highly dissected tana volcano a large basin is likely the result of a pre lgm sector collapse and subsequent glacial erosion into weak hydrothermally altered rock valley and moraine morphology is also influenced by hydrothermal alteration on both tana and carlisle there are sediment fans composed dominantly of thick debris flow deposits mantled by 3 m of layered tephras fine grained alluvium and anthropogenic deposits debris flow deposition was favored during the unstable paraglacial landscape of the early holocene latest pleistocene the earliest direct archaeological evidence for settlement is 3 8 cal ka bp but soil geochemical evidence suggests that the islands were inhabited by 7 3 cal ka bp this discrepancy in the archaeological record may be explained by geomorphic processes including coastal erosion and unstable geomorphic surfaces

evaluating the compatibility of dynamic rupture based synthetic ground motion with empirical ground motion prediction equation we performed an assessment of a database of synthetic ground motion generated by a suite of dynamic rupture simulations to verify compatibility of the peak ground amplitudes with respect to empirical ground motion prediction equations gmpes the dynamic rupture model database developed by dalguer and mai 2011 is composed of 360 earthquake scenarios with moment magnitudes in the range of 5 5 7 for three mechanisms of faulting reverse normal and strike slip and for both buried faults and surface rupturing faults having depth and non depth dependent normal stresses initial shear stress distribution follows a von karman stochastic distribution overall we show quantitatively that the upper frequency limit of the suite of simulations is 1 0 hz up to this frequency the synthetic data are compatible with the empirical model which means that the residuals defined as the differences between observed and predicted ground motions fall in the range of of the empirical gmpe characteristics of the mean values along distance 10 45 km and period t 1 0 s including standard deviation of the synthetic response spectra and peak ground velocity are comparable to their counterpart empirical gmpe at very near source 1 2 km synthetics show supersaturation of the mean peak values which is different from the saturation features predicted by the gmpes the effect of source parameters such as stress drop peak slip velocity and rupture speed and of surface and buried rupture as well as hanging wall and footwall are highly sensitive to ground motion suggesting that these effects contribute to the variability of ground motion near the source and that inclusion of them in the source terms may contribute to reducing uncertainties in gmpes

a combined study of radar facies lithofacies and three dimensional architecture of an alpine alluvial fan illgraben fan switzerland alluvial fans serve as useful archives that record the history of depositional and erosional processes in mountainous regions and thus can reveal the environmental controls that influenced their development economically they play an important role as groundwater reservoirs as well as host rocks for hydrocarbons in deeply buried systems the interpretation of these archives and the evaluation of their reservoir architecture however are problematic because marked heterogeneity in the distribution of sedimentary facies makes correlation difficult this problem is compounded because the accumulated sedimentary deposits of modern unconsolidated fan systems tend to be poorly exposed and few such systems have been the focus of investigation using high resolution subsurface analytical techniques to overcome this limitation of standard outcrop analogue studies a geophysical survey of an alpine alluvial fan was performed using ground penetrating radar to devise a scaled three dimensional subsurface model radar facies were classified and calibrated to lithofacies within a fan system that provided outcropping walls and these were used to derive a three dimensional model of the sedimentary architecture and identify evolutionary fan stages the illgraben fan in the swiss alps was selected as a case study and a network of ca 60 km sections of ground penetrating radar was surveyed seven radar facies types could be distinguished which were grouped into debris flow deposits and stream flow deposits assemblages of these radar facies types show three depositional units which are separated by continuous fan wide reflectors they were interpreted as palaeo surfaces corresponding to episodes of sediment starvation that affected the entire fan an overall upward decline in the proportion of debris flow deposits from ca 50 to 15 and a corresponding increase in stream flow deposits were identified the uppermost depositional unit is bounded at its base by a significant incision surface up to 700 m wide which was subsequently filled up mostly by stream flow deposits the pronounced palaeo surfaces and depositional trends suggest that allocyclic controls governed the evolution of the illgraben fan making this fan a valuable archive from which to reconstruct past sediment fluxes and environmental change in the alps the results of the integrated outcrop geophysical approach encourage similar future studies on fans to retrieve their depositional history as well as their potential reservoir properties

an equivalent viscoelastic model for rock mass with parallel joints an equivalent viscoelastic medium model is proposed for rock mass with parallel joints a concept of virtual wave source vws is proposed to take into account the wave reflections between the joints the equivalent model can be effectively applied to analyze longitudinal wave propagation through discontinuous media with parallel joints parameters in the equivalent viscoelastic model are derived analytically based on longitudinal wave propagation across a single rock joint the proposed model is then verified by applying identical incident waves to the discontinuous and equivalent viscoelastic media at one end to compare the output waves at the other end when the wavelength of the incident wave is sufficiently long compared to the joint spacing the effect of the vws on wave propagation in rock mass is prominent the results from the equivalent viscoelastic medium model are very similar to those determined from the displacement discontinuity method frequency dependence and joint spacing effect on the equivalent viscoelastic model and the vws method are discussed

recipe for predicting strong ground motion from crustal earthquake scenarios we developed a recipe for predicting strong ground motions based on a characterization of the source model for future crustal earthquakes from recent developments of waveform inversion of strong motion data used to estimate the rupture process we have inferred that strong ground motion is primarily related to the slip heterogeneity inside the source rather than average slip in the entire rupture area asperities are characterized as regions that have large slip relative to the average slip on the rupture area the asperity areas as well as the total rupture area scale with seismic moment we determined that the areas of strong motion generation approximately coincide with the asperity areas based on the scaling relationships the deductive source model for the prediction of strong ground motions is characterized by three kinds of parameters outer inner and extra fault parameters the outer fault parameters are defined as entire rupture area and total seismic moment the inner fault parameters are defined as slip heterogeneity inside the source area of asperities and stress drop on each asperity based on the multiple asperity model the pattern of rupture nucleation and termination are the extra fault parameters that are related to geomorphology of active faults we have examined the validity of the earthquake sources constructed by our recipe by comparing simulated and observed ground motions from recent inland crustal earthquakes such as the 1995 kobe and 2005 fukuoka earthquakes

on the causes of back arc spreading addition of the spreading rates in the back arc basins of the lau basin havre trough and the mariana trough to the absolute motions of the indian and philippine plates respectively provides an estimate of the absolute motion of the tonga kermadec and mariana trenches the trenches are moving toward the pacific basin for all absolute motion models back arc spreading is considered an unlikely cause for the trench motion given the seismic evidence for poor coupling at the trenches thus the cause of spreading at these arcs must rest at least partly with motion of the lower plate rollback due to negative buoyancy is rejected as a cause for this motion because it fails to explain the recent onset of the spreading no net torque reference frames for 5 and 10 ma indicate that the rate of subduction of the pacific plate at each of these arcs may have increased by 2 3 cm yr between 5 and 10 ma providing support for the model of furlong et al in which back arc spreading is initiated by adjustment of the slab profile to a change in subduction rate

neoglacial history of robson glacier british columbia as glaciers in the canadian rockies recede glacier forefields continue to yield subfossil wood from sites overridden by these glaciers during the holocene robson glacier in british columbia forme

terashake2 spontaneous rupture simulations of mw 7 7 earthquakes on the southern san andreas fault abstract previous numerical simulations terashake1 of large m w 7 7 southern san andreas fault earthquakes predicted localized areas of strong amplification in the los angeles area associated with directivity and wave guide effects from northwestward propagating rupture scenarios the terashake1 source was derived from inversions of the 2002 m w 7 9 denali alaska earthquake that source was relatively smooth in its slip distribution and rupture characteristics owing both to resolution limits of the inversions and simplifications imposed by the kinematic parameterization new simulations terashake2 with a more complex source derived from spontaneous rupture modeling with small scale stress drop heterogeneity predict a similar spatial pattern of peak ground velocity pgv but with the pgv extremes decreased by factors of 2 3 relative to terashake1 the terashake2 source excites a less coherent wave field with reduced along strike directivity accompanied by streaks of elevated ground motion extending away from the fault trace the source complexity entails abrupt changes in the direction and speed of rupture correlated to changes in slip velocity amplitude and waveform features that might prove challenging to capture in a purely kinematic parameterization despite the reduced pgv extremes northwest rupturing terashake2 simulations still predict entrainment by basin structure of a strong directivity pulse with pgvs in los angeles and san gabriel basins that are much higher than predicted by empirical methods significant areas of those basins have predicted pgv above the 2 probability of exceedance poe level relative to current attenuation relationships even when the latter includes a site term to account for local sediment depth and wave guide focusing produces localized areas with pgv at roughly 0 1 0 2 poe about a factor of 4 5 above the median in contrast at rock sites in the 0 100 km distance range the median terashake2 pgvs are in very close agreement with the median empirical prediction and extremes nowhere reach the 2 poe level the rock site agreement lends credibility to some of our source modeling assumptions including overall stress drop level and the manner in which we assigned dynamic parameters to represent the mechanical weakness of near surface material future efforts should focus on validating and refining these findings assessing their probabilities of occurrence relative to alternative rupture scenarios for the southern san andreas fault and incorporating them into seismic hazard estimation for southern california

dynamic rupture on a material interface with spontaneous generation of plastic strain in the bulk abstract we discuss 2d simulations of in plane ruptures on a fault between different solids in a model that includes dynamic generation of plastic strain off the fault the fault is governed by a regularized friction with a gradual response to abrupt changes of normal stress while plastic strain in the bulk is governed by a coulomb yielding criterion the occurrence of off fault damage stabilizes the slip velocity on the fault stable self sustaining ruptures propagate on the material interface as narrow unidirectional pulses in the direction of slip on the more compliant side of the fault plastic strain is generated only on the stiffer side of the fault the tensional quadrant in the direction of rupture propagation in a strip of approximately constant width that is correlated with the slip velocity on the fault simulations for various values of confining normal stress material contrast and cohesion in the bulk suggest that significant generation of off fault damage is limited to conditions that correspond to the top few kilometers of the crust the results are compatible with field observations of shallow asymmetric damage patterns in the structure of several large faults

correlation of earthquake source parameters inferred from dynamic rupture simulations 1 we analyzed 315 dynamic strike slip rupture models computed up to 5 0 hz to get a quantitative understanding of the correlation and amplitude distributions of parameters describing the earthquake source such as slip and rupture velocity to account for the epistemic uncertainty of the problem we constructed a database of dynamic ruptures computed by ourselves and other authors this database contains ruptures computed using different models of initial stress peak stress and critical slip weakening distance using the set of computed ruptures we constructed probability density functions pdfs for the amplitude distributions of the source parameters and for the correlation between the source parameters we tried to extract parameter pairs that showed a small variability in the spatial correlation given the large epistemic uncertainty in the input we only analyzed the areas on the fault with subshear propagation speed the principal findings are as follows 1 final slip amplitude does not show correlation with the local rupture velocity 2 final slip amplitude correlates well with risetime 3 rupture velocity correlates well with peak slip rate and the duration of the impulsive part of the slip rate function 4 the pdf of rupture velocity risetime and peak slip rate depends on the distance from the nucleation zone 5 fracture energy is not the single controlling factor for the rupture velocity the slope of the linear slip weakening curve has a significant effect on the rupture velocity 6 the crack length length that is slipping at a given time decreases with the distance from the nucleation zone

strong velocity weakening and powder lubrication of simulated carbonate faults at seismic slip rates 1 high velocity friction tests were conducted on solid and hollow cylinders of carrara calcite marble dolomite marble silicate bearing calcite marble and calcite gouge to investigate the strength of carbonate faults during seismic slip the experiments performed at normal stresses of 0 6 14 7 mpa slip rates of 0 03 1 60 m s and room temperature in a rotary shear friction testing machine yielded an extraordinarily low steady state friction coefficient 0 1 at slip rates of 1 1 1 2 m s the slip weakening distance of 4 28 m became shorter at higher normal stress or frictional work rate strong velocity weakening was observed not only in steady state but also in nonsteady state friction while the slip rate was changing thus slip deceleration was accompanied by fault strength recovery large rapid temperature rises in narrow shear localization zones less than a few micrometers induced carbonate decomposition such as the breakdown of calcite into aggregates of cao nanograins and co2 in carrara marble scanning electron microscope observation revealed that the shear localization zone in the highly porous decomposition product was a layer of scattered small grains mostly 1 m in diameter these microstructures and the measured high permeability 10 14 m2 of the decomposed marble indicate that the dominant weakening mechanism in our experiments was possibly powder lubrication powder rheology at high slip rates is not yet well understood but the frictional behavior of nanograins appears to be strongly velocity dependent if decarbonation occurs during seismic slip in natural carbonate faults powder lubrication may make the faults slippery even under fluid drained conditions

fault geometry rupture dynamics and ground motion from potential earthquakes on the north anatolian fault under the sea of marmara summary using the 3 d finite element method we develop dynamic spontaneous rupture models of earthquakes on the north anatolian fault system in the sea of marmara turkey considering the geometrical complexity of the fault system in this region we find that the earthquake size rupture propagation pattern and ground motion all strongly depend on the interplay between the initial static regional pre stress field and the dynamic stress field radiated by the propagating rupture by testing several nucleation locations we observe that those far from an oblique normal fault stepover segment near istanbul lead to large through going rupture on the entire fault system whereas nucleation locations closer to the stepover segment tend to produce ruptures that die out in the stepover however this pattern can change drastically with only a 10 rotation of the regional stress field our simulations also reveal that while dynamic unclamping near fault bends can produce a new mode of supershear rupture propagation this unclamping has a much smaller effect on the speed of the peak in slip velocity along the fault finally we find that the complex fault geometry leads to a very complex and asymmetric pattern of near fault ground motion including greatly amplified ground motion on the insides of fault bends the ground motion pattern can change significantly with different hypocentres even beyond the typical effects of directivity the results of this study may have implications for seismic hazard in this region for the dynamics and ground motion of geometrically complex faults and for the interpretation of kinematic inverse rupture models

stability of faults with heterogeneous friction properties and effective normal stress abundant geological seismological and experimental evidence of the heterogeneous structure of natural faults motivates the theoretical and computational study of the mechanical behavior of heterogeneous frictional fault interfaces fault zones are composed of a mixture of materials with contrasting strength which may affect the spatial variability of seismic coupling the location of high frequency radiation and the diversity of slip behavior observed in natural faults to develop a quantitative understanding of the effect of strength heterogeneity on the mechanical behavior of faults here we investigate a fault model with spatially variable frictional properties and pore pressure conceptually this model may correspond to two rough surfaces in contact along discrete asperities the space in between being filled by compressed gouge the asperities have different permeability than the gouge matrix and may be hydraulically sealed resulting in different pore pressure we consider faults governed by rate and state friction with mixtures of velocity weakening and velocity strengthening materials and contrasts of effective normal stress we systematically study the diversity of slip behaviors generated by this model through multi cycle simulations and linear stability analysis the fault can be either stable without spontaneous slip transients or unstable with spontaneous rupture when the fault is unstable slip can rupture either part or the entire fault in some cases the fault alternates between these behaviors throughout multiple cycles we determine how the fault behavior is controlled by the proportion of velocity weakening and velocity strengthening materials their relative strength and other frictional properties we also develop through heuristic approximations closed form equations to predict the stability of slip on heterogeneous faults our study shows that a fault model with heterogeneous materials and pore pressure contrasts is a viable framework to reproduce the full spectrum of fault behaviors observed in natural faults from fast earthquakes to slow transients to stable sliding in particular this model constitutes a building block for models of episodic tremor and slow slip events

glacier dynamics during a phase of late quaternary warming in patagonia reconstructed from sediment landform associations abstract the geomorphological record in glaciated landscapes can provide important information for the study of the response of glaciers to rapid climate change this study presents a new reconstruction of the glacial history of the northern monte san lorenzo ice cap southern south america during a period of accelerated warming and deglaciation following the antarctic cold reversal 14 5 12 8 ka we present a detailed geomorphological map of the valleys to the north of monte san lorenzo sediment landform assemblages identified include lateral and terminal moraine ridges flutes deltas ice contact fans palaeoshorelines kame terraces and outwash plains we map 14 primary ice limits 7 of which are newly identified and 7 of which are from previous studies mapped here in greater detail we devise landsystem models to formalise and document spatial and temporal changes in glacial processes and environments our new geomorphological mapping and landsystem reconstructions provide an important insight into the response of temperate patagonian glaciers to rapidly warming climate

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

source properties of dynamic rupture pulses with off fault plasticity large dynamic stresses near earthquake rupture fronts may induce an inelastic response of the surrounding materials leading to increased energy absorption that may affect dynamic rupture we systematically investigate the effects of off fault plastic energy dissipation in 2 d in plane dynamic rupture simulations under velocity and state dependent friction with severe weakening at high slip velocity we find that plasticity does not alter the nature of the transitions between different rupture styles decaying versus growing pulse like versus crack like and subshear versus supershear ruptures but increases their required background stress and nucleation size we systematically quantify the effect of amplitude and orientation of background shear stresses on the asymptotic properties of self similar pulse like ruptures peak slip rate rupture speed healing front speed slip gradient and the relative contribution of plastic strain to seismic moment peak slip velocity and rupture speed remain bounded from fracture mechanics arguments we derive a nonlinear relation between their limiting values appropriate also for crack like and supershear ruptures at low background stress plasticity turns self similar pulses into steady state pulses for which plastic strain contributes significantly to the seismic moment we find that the closeness to failure of the background stress state is an adequate predictor of rupture speed for relatively slow events our proposed relations between state of stress and earthquake source properties in the presence of off fault plasticity may contribute to the improved interpretation of earthquake observations and to pseudodynamic source modeling for ground motion prediction

magmatic evolution of late cenozoic volcanic rocks of the lau ridge fiji three main groups of lavas are exposed on islands of the lau ridge the lau volcanic group lvg 14 0 5 4 ma are predominantly andesite korobasaga volcanic group kvg 4 4 2 4 ma are predominantly basalt and mago volcanic group mvg 2 0 0 3 ma are basalt hawaiite lvg and kvg lavas are mostly medium k tholeiitic rocks with high lile hfse ratios characteristic of islands ares while mvg lavas are ne normative alkalic rocks with high lile and hfse characteristic of ocean island basalts lvg lavas have high nd 8 0 8 4 and low 87sr 86sr 0 70273 0 70349 similar to n morb whereas kvg lavas have slightly more radiogenic values nd 7 5 8 4 87sr 86sr 0 70323 0 70397 mvg lavas form an isotopically distinct group having lower nd 4 6 4 9 and 87sr 86sr ranging from 0 70347 0 70375 lvg lavas were erupted in a primary oceanic island arc vitiaz arc during the miocene basaltic lavas were derived by approximately 19 partial melting of mantle wedge peridotite with only minor subduction component andesites and dacites were produced by low pressure plagioclase pyroxene titanomagnetite dominated crystal fractionation kvg lavas were erupted during the period immediately prior to or during the initial stages of rifting in the lau basin and like lvg lavas show significant chemical differences at the northern and southern ends of the lau ridge lavas at the northern end type ii appear to be derived from a more depleted source than lvg but with a greater amount of subduction component those at the southern end type i probably came from a slightly more enriched source with less subduction component mvg basalts and hawaiites were derived from an enriched mantle with little or no subduction input the hawaiites type i could not have been derived from the basalts type ii and the two magma types must have come from different sources indicating mantle heterogeneity the lack of subduction influence indicates the mvg lavas are tectonically unrelated to the present day tonga arc and the lack of depletion indicators suggests they have tapped a different new part of the mantle wedge this may reflect introduction of sub pacific mantle through the present tonga lau subduction system

evidence for an earthquake barrier model from mw 7 8 kokoxili tibet earthquake slip distribution abstract the slip distribution of the mw 7 8 kokoxili tibet 2001 earthquake has been measured at high resolution using optical correlation of satellite images and provides both the parallel and perpendicular components of the horizontal co seismic slip this reveals a variation of the horizontal slip at a scale of 20 km along strike anti correlation of slip parallel and perpendicular to the fault indicates transfer of slip from the horizontal to the vertical component at the ends of segments these features suggest a rupture model with segments separated by strong persistent geometric barriers the unexpected ending of the rupture south of the main fault can be explain by such a structure but bears important implications for the initiation and rupture directivity of the next earthquake

off fault plasticity favors the arrest of dynamic ruptures on strength heterogeneity two dimensional cases we study the effects of a plastic behavior of the volume around the fault on in plane and anti plane 2d rupture dynamics both rupture modes exhibit similar answer to off fault yielding in terms of modification of the kinematics of the rupture front and in terms of energy lost outside the fault plane we then compare the ability of the rupture to propagate through a barrier on the interface the plastic behavior responsible for a linear increase of the global fracture energy during dynamic crack growth enhances the rupture front sensitivity to a static resistance increase on the fault consequently the rupture arrest is more easily provoked in heterogeneous models that include a plastic yielding even with relatively small variations of frictional resistance along the fault plane

pre spread rifting and heterogeneous volcanism in the southern havre trough back arc basin abstract the havre trough is an active back arc basin associated with pacific australian plate convergence two segments within the southern havre trough sht surveyed with gloria sea beam and sys09 swath data now provide the first detailed data to reliably document the structure and morphology of this complex back arc region at the southern segment 35 40 37 s along a strike length of some 120 km the sht structure comprises a series of segmented en echelon generally flat floored sediment filled axial rift grabens flanked by ridge and basin rift block topography prominent fault escarpments with relief of 500 1000 m and a marked zig zag arrangement mark the outer margins of the rift system within the rift grabens extensional tectonism is pervasive extensive shallow seismicity within the sht can only partly be associated with the rift graben system at present youthful constructional volcanic terrains within the rift grabens are not common and invariably have a restricted areal extent and a relief an identical rift morphology has been identified at the northern 33 34 s site data from both sites show individual rifts are 15 35 km in length 6 10 km wide and have axial depths of 3100 4000 m apart from at least one 15 20 km wide cross trough ridge available data indicate the rift graben system is contiguous between 33 s and 37 s this rift graben morphology by analogy with other known rifting back arc basins is considered here not to be consistent with true oceanic back arc spreading rather it is argued that the sht possibly indeed all of the havre trough is undergoing back arc rifting prior to true spreading further the rifting tectonic fabric within the sht and in the onshore taupo to the south extension is consistently dextrally oblique relative to the bounding colville and kermadec ridges the degree of obliquity increases from south to north if accepted that the sht is rifting rather than spreading magnetic anomaly data within the trough do not record the accretion of new oceanic crust and consequently can no longer be used to establish the spreading history of the sht the sht magnetic anomalies are here interpreted as pseudo linear magnetic anomalies resulting from the generally irregular spatial and temporal emplacement of magnetic sheeted lava and dike intrusives between older low magnetisation arc basement rift blocks flanking the axial rift proxy data from onshore north island new zealand and offshore sht suggest that the rate of extension and age of initiation of back arc rifting are between 35 and 37 s respectively 15 20 mm yr 1 and 5 ma

back arc spreading in the proterozoic a theoretical approach abstract the early proterozoic earth probably had a hotter mantle and a lower residence time for oceanic plates at the surface than the modern one the hotter mantle may have led to thinner oceanic plates young ocean floor has low negative buoyancy and therefore exerts low slab pull forces in subduction zones this effect would have been greater if the plates were thinner since they would have warmed up more quickly as they descended into the mantle thus the negative buoyancy of slabs and the slab pull forces were probably substantially lower in the early proterozoic calculations show that this applies even if subduction rates were higher and the crust was thicker lower slab pull leads to lower rates of rollback in subduction zones and lower rates of retreat of upper plates from trenches the limited age range of oceanic crust and the more rapid heating of descending slabs in subduction zones probably leads to a smaller range of slab profiles since this range is controlled by thermal properties of the slab and therefore to more stability in subduction zones thus many of the proposed mechanisms for back arc spreading may have been less effective and backarc spreading may have been less common in early proterozoic subduction zones this may explain the apparent absence of ophiolite complexes of that age

southern australian rainfall and the subtropical ridge variations interrelationships and trends 1 monthly values of the latitude and intensity mean maximum pressure of the subtropical ridge str averaged across australian longitudes 105 155 e have been related to variations and trends in rainfall over southern australia south of 30 s for 1958 2005 there is an abrupt shift of latitude of the subtropical ridge over australia at the onset of winter in the cooler part of the year the intensity of the str is more closely related to rainfall variations and correlations between latitude and rainfall are a by product of the relationship of intensity with both latitude and rainfall whereas in summer the latitude of the str is more closely related to rainfall the decline in southern australian rainfall in recent decades which has occurred principally in autumn appears related to a trend towards a more intense str rather than a trend in the latitude of the str

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

holocene palaeoenvironmental record preserved in a paraglacial alluvial fan sunwapta pass jasper national park alberta canada abstract the soil stratigraphy of a 1 5 m section in the distal portion of a paraglacial alluvial fan in sunwapta pass jasper national park has been examined as part of a long term investigation into holocene palaeoenvironments of the area the section is complex and its characteristics are a result of both episodic sediment inputs and pedogenesis a series of sediments comprising debris flows and aeolian material including three discrete tephra layers mazama st helens yn bridge river underlie the present day soil multiple criteria including stratigraphy radiocarbon dates glass shard morphology and electron microprobe analysis of glass and titanomagnetite composition confirmed the identity of the tephras most fan development occurred before deposition of mazama tephra pedogenesis has been active on the fan throughout the holocene soils have formed between phases of sediment deposition during periods of greater relative site stability soil horizonation is best developed where tephric material has influenced soil chemistry and clay mineralogy leading to the formation of brunisols the sequence of events inferred from the icefield fan s stratigraphy accord well with the holocene palaeoenvironmental history inferred from other sites in the canadian rockies

age and nature of paraglacial debris cones along the margins of the san rafael glacier chilean patagonia this study employs sedimentological indices and lichenometric dating on the lichen species plac opsis patagonica to investigate the nature and age of debris cones which have accumulated at the margins of the downwasting san rafael glacier in chilean patagonia these cones appear to have accumulated by the resedimentation of glacigenic deposits by debris flows with debris movement starting in the early 1980s cone activity follows a pattern of intense initial activity and sediment mobilisation followed by increased stability and colonization by vegetation three of the four cones had stabilized within 15 years of sediment movement initiation these features may be seen as being conditioned by glacial activity with second order controls provided by the local climate and sediment supply the cones have accumulated in a paraglacial environment

euclidean and fractal models for the description of rock surface roughness accurate description of the topography of rock surfaces is essential because surface roughness affects frictional strength the flow of fluids in joints and fractures the seismic behavior of faults and the formation of gouge and breccia in fault zones real rock surfaces can be described using self similar and self affine fractal models of surface roughness if a surface is self similar a small portion of the surface when magnified isotropically will appear statistically identical to the entire surface if a surface is self affine a magnified portion of the surface will only appear statistically identical to the entire surface if different magnifications are used for the directions parallel and perpendicular to the surface at least two parameters are required to describe a fractal model one parameter typically describes how roughness changes with scale while the other specifies the variance or surface slope at a reference scale the divider method and the spectral method are in common use to determine the best fit fractal model from surface profile data power spectra from self similar surfaces have slopes of 3 on log log plots of power spectral density versus spatial frequency while spectra from self affine surfaces have slopes other than 3 power spectra can be interpreted with greater facility if dimensionless amplitude to wavelength ratios are contoured on plots of power spectral density versus frequency the topography of many natural rock surfaces including both fractures and faults is approximately self similar within the 6 5 order of magnitude wide wavelength band of 10 m to 40 m within smaller wavelength bands natural rock surfaces may exhibit self affine behavior

plates and their motions the last reviews which covered research in plate motions were those of herron and pitman 1975 on marine magnetic anomalies and dewey 1975 on plate tectonics both reporting on research for the period 1971 1974 in the last 12 years there has been considerable refinement of relative motion models as well as further development of global models also major effort has gone into defining reference frames for the study of plate motions and discriminating between them more recently the role of errors in individual plate rotations and the associated uncertainties in reconstructions have received attention in this report i concentrate on work published in the last 4 years 1983 1986 citing a minimum of publications from previous years however some papers in press for early 1987 have been included this report first reviews work on relative plate motions for the present and past and reconstructions and then models for these motions global ones for driving forces and local ones determining subduction history and back arc spreading the problem of reference frames both hotspot and paleomagnetic is discussed next i end with a review of work on the errors in plate motions

using discriminant function analysis to identify holocene tephras based on magnetite composition a case study from the sunwapta pass area jasper national park the magnetite composition from three sets of samples of mazama st helens set y and bridge river tephras from jasper and banff national parks are used to test whether discriminant function analysis can unambiguously distinguish these tephras the multivariate method is found to be very sensitive to the change in reference samples st helens set y tephra is clearly distinguished however discrimination between mazama and bridge river tephras is less distinct a set of unknown tephras from the sunwapta pass area was used to test the classification schemes unknown tephras are assigned to different tephra types depending on which reference tephra set is used in the discriminant function analysis

earthquake cycle modelling of multi segmented faults dynamic rupture and ground motion simulation of the 1992 m w 7 3 landers earthquake we perform earthquake cycle simulations with the goal of studying the characteristics of source scaling relations and strong ground motions in multi segmented fault ruptures the 1992 mw 7 3 landers earthquake is chosen as a target earthquake to validate our methodology the model includes the fault geometry for the three segmented landers rupture from the scec community fault model extended at both ends to a total length of 200 km and limited to a depth to 15 km we assume the faults are governed by rate and state rs friction with a heterogeneous correlated spatial distribution of characteristic weakening distance dc multiple earthquake cycles on this non planar fault system are modeled with a quasi dynamic solver based on the boundary element method substantially accelerated by implementing a hierarchical matrix method the resulting seismic ruptures are recomputed using a fully dynamic solver based on the spectral element method with the same rs friction law the simulated earthquakes nucleate on different sections of the fault and include events similar to the mw 7 3 landers earthquake we obtain slip velocity functions rupture times and magnitudes that can be compared to seismological observations the simulated ground motions are validated by comparison of simulated and recorded response spectra

high velocity frictional properties of gabbro high velocity friction experiments have been performed on a pair of hollow cylindrical specimens of gabbro initially at room temperature at slip rates from 7 5 mm s to 1 8 m s with total circumferential displacements of 125 to 174 m and at normal stresses to 5 mpa using a rotary shear high speed friction testing machine steady state friction increases slightly with increasing slip rate at slip rates to about 100 mm s velocity strengthening and it decreases markedly with increasing slip rate at higher velocities velocity weakening steady state friction in the velocity weakening regime is lower for the non melting case than the frictional melting case due perhaps to severe thermal fracturing a very large peak friction is always recognized upon the initiation of visible frictional melting presumably owing to the welding of fault surfaces upon the solidification of melt patches frictional properties thus change dramatically with increasing displacement at high velocities and such a non linear effect must be incorporated into the analysis of earthquake initiation processes

characterization of fault roughness at various scales implications of three dimensional high resolution topography measurements accurate description of the topography of active fault surfaces represents an important geophysical issue because this topography is strongly related to the stress distribution along fault planes and therefore to processes implicated in earthquake nucleation propagation and arrest to date due to technical limitations studies of natural fault roughness either performed using laboratory of field profilometers were obtained mainly from 1 d profiles with the recent development of light detection and ranging lidar apparatus it is now possible to measure accurately the 3 d topography of rough surfaces with a comparable resolution in all directions both at field and laboratory scales in the present study we have investigated the scaling properties including possible anisotropy properties of several outcrops of two natural fault surfaces vuache strike slip fault france and magnola normal fault italy in limestones at the field scale digital elevation models of the fault roughness were obtained over surfaces of 0 25 m2 to 600 m2 with a height resolution ranging from 0 5 mm to 20 mm at the laboratory scale the 3 d geometry was measured on two slip planes using a laser profilometer with a spatial resolution of 20 m and a height resolution less than 1 m

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

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

crustal genesis on the oregon plateau the areal and temporal distribution and the chemical and isotopic characteristics of cenozoic volcanic rocks from the oregon plateau reflect the changing tectonic conditions affecting this area over the last 20 m y following subduction zone related calc alkaline volcanism flood basalt eruptions occurred in the time interval 18 14 ma this primarily basaltic volcanism is interpreted to be the result of a major shift in spreading orientation of the juan de fuca ridge that resulted in changes in the geometry of subduction against the pacific northwest the compositions of the mid miocene flood basalts show signs of extensive crystal fractionation in some cases accompanied by crustal contamination roughly 11 m y ago basalt eruptions showed an increasing tendency toward smaller volumes and less evolved compositions this implies that as extension in the oregon plateau proceeded the crust became less of an impediment to the passage of relatively unfractionated mantle melts initial sr nd and pb isotopic compositions of all the basalts show more correlation with the geographic position of eruption than with the composition of the lava primary control over the isotope systematics appears to be due to changes in the age and chemical characteristics of the crust and mantle throughout this area these observations suggest that an area of some 130 000 km2 of crust and basalt depleted subcontinental mantle has been added to northwestern north america over the last 20 m y the intensity of basalt volcanism as manifest in the columbia river group and in the oregon plateau does not appear to reflect the presence of a hot spot beneath the area both the areal and temporal distribution of the lavas and their geochemical characteristics are more easily reconciled with the suggestion that this crustal section grew by back arc spreading in a manner analogous to the formation of the marginal basins of the western pacific this spreading initiated along the western border of the archean wyoming craton with the location of mantle ascent melt production and extraction controlled by the changing geometry of subduction the existence of a zone of lithospheric weakness and the presence of a thick low density subcontinental mantle keel existing beneath the archean craton in this area

plate motion controls on back arc spreading the motions of the subducting and the overriding plates influence the spatial and temporal distribution of back arc spreading cenozoic plate motions in hot spot fixed and no net rotation reference frames were studied with attention to correlations between changes in motion and episodes of back arc spreading in the western pacific the results suggest that major back arc opening occurs when both the overriding plate retreats from the trench in an absolute sense and the subducting plate undergoes a significant speed up neither phenomenon alone is sufficient to initiate spreading three major plate velocity increases can be identified in the cenozoic 1 the pacific plate 5 9 ma 2 the indian plate at 27 ma and 3 the pacific plate at 43 ma due to its shift from northerly to more westerly motion at the present time the indian and philippine are the only overriding plates that are retreating from their pacific trenches and back arc spreading occurs only on these two retreating plates although the indian plate has been retreating for at least 25 ma back arc spreading began only following the pacific plate speed up 5 9 ma earlier during the indian plate speed up no overriding plates were retreating strongly and no back arc spreading episodes are preserved from this time for the earliest pacific plate shift at 43 ma the eurasian plate was not advancing thus creating the only favorable plate kinematic conditions in the cenozoic for back arc basin formation in this region it is unclear whether extension in the japan sea is a result of these conditions

a re examination of the three most prominent holocene tephra deposits in western canada bridge river mount st helens yn and mazama abstract volcanic ash deposits tephra in western canada are instrumental in providing independent chronologic control for many archaeological and paleoenvironmental sites in alberta tephra are a key chronologic tool in a region where radiocarbon dates are often unreliable because of the prevalence of carbonate rich bedrock and other old carbon sources such as coal however many studies using tephra for age control particularly archaeological projects identify tephra simply through field characteristics or light microscopy in both alberta and british columbia many radiocarbon dates that were used to date key tephra deposits were bulk conventional ages on peat and lake sediments which are not always reliable these factors have led to uncertainty in the age and number of bridge river and mount st helens msh set y tephra present in the region and incomplete distribution maps new major element geochemical analyses from archaeological and sedimentary sites across south central alberta complemented by new analyses of tephra from british columbia and saskatchewan refine the distribution of the bridge river msh yn and mazama tephra new geochemical data radiocarbon dates and a detailed overview of proximal msh set y stratigraphy and geochemistry show that only one msh layer yn is present in this region rather than two msh set y tephra as previously suggested additionally re assessment of age data combined with new geochemical analyses confirm that there is also only one bridge river tephra a bayesian modelled age estimate is determined for msh yn based on new ams dates on the tephra and vetted existing conventional ages providing a revised age estimate for msh yn of 3805 3535 cal bp mean of 3660 cal bp

slip distribution of the 1992 landers earthquake and its implications for earthquake source mechanics we use near source 10 to 164 km displacement seismograms to image the slip distribution and rupture history of the 28 june 1992 mw 7 3 landers california earthquake aftershock seismograms from similar distances are modeled to find the velocity model and frequency range 0 05 to 0 25 hz over which theoretical green s functions are most accurate and the measure of fit is used as an upper bound on theoretical error in the mainshock inversion we represent the rupture surface with three planar segments divided into 3 by 3 km elements extending from the surface to 18 km depth and solve for the slip distribution and the rupture time model that minimizes misfit to both recorded seismograms and mapped surface displacement in a least squares sense we investigate two faulting models one with a uniformly short 3 sec rise time everywhere on the fault surface and the other with a variable rise time 2 to 6 sec we perform sensitivity tests using synthetic data from a hypothetical earthquake to evaluate model resolution and solution stability in the sensitivity tests both fault models recover similar slip and rupture features but neither is capable of imaging details of the rise time for the landers earthquake we find an average rupture velocity of 2 5 km sec and use this average for a starting model in a linearized inversion for rupture time in our solutions of slip amplitude distribution the southernmost johnson valley fault segment has 20 of the total seismic moment 6 to 8 1019 n m with small displacements near the hypocenter the homestead valley segment contributes half of the moment with the largest slip amplitudes 25 to 35 km northwest of the hypocenter at 4 to 12 km depth and the camp rock emerson segment contributes the remaining moment with the largest slip amplitude 35 to 50 km northwest of the hypocenter in the shallow crust 9 km there is some evidence that the rupture front is delayed as it encounters high slip regions suggesting that prior to the mainshock these areas were further from failure owing either to greater strength or lower prestress

stress and deformation along wavy frictional faults locally inhomogeneous stress states are expected along faults owing to slip on geometrically irregular fault surfaces we use an analytical model of elastic deformation along a wavy frictional fault to evaluate the variation in local stress state as a function of surface roughness elastic modulus slip coefficient of friction and far field stress the total stress state along the fault may be described by the sum of a basic stress component resulting from frictional slip on a planar fault surface and a perturbed stress component resulting from the presence of roughness roughness produces a variation in normal stress across the fault surface and assuming roughness and modulus appropriate to crustal faults the normal stress should be reduced to a near zero magnitude locally such that separation of fault walls is likely the large variation in normal stress along the fault surface resulting from fault roughness may be responsible in part for complexity in moment release during large earthquakes and for lateral variation in seismic coupling along faults the variation in principal stress orientations and magnitudes along a fault increases with a decrease in the coefficient of friction of the fault the location and size of regions with a high likelihood for brittle failure depend on the orientation of the far field principal stress and fault friction the average orientation of the principal stresses in the region of likely failure is not the same as the far field principal stress orientation although inversion of earthquake and fabric data for stress orientation along a fault may be possible the model results suggest that inversion results are insufficient to determine far field stress states and fault friction without additional independent data

a numerical approach toward the classification of magnetites from tephra in southern alberta high titanium glass encased magnetites associated with intermixed tephras in upper subalpine soils in banff national park are shown to be characteristic of mazama tephra and of regional significance similar magnetites occur in a mazama layer above a paleosol at fish creek alberta and within a sample of mazama ash ua 396 from windy point alberta detailed sampling and analysis of the fish creek tephra indicate that the magnetites do not represent a separate eruptive event or an older ashfall cluster analysis of glass encased magnetites from reference samples of mazama st helens y and bridge river ashes revealed composite grouping of mazama and bridge river magnetites and separate and strong groupings of high tio2 magnetites discriminant analysis identifies mgo tio2 and al2o3 as the most significant chemical discriminants between the various ashes discriminant function analysis identifies the high titanium magnetites as mazama in type and successfully classifies 96 of the tephra derived magnet

frequency domain inversion of strong motions application to the 1992 landers earthquake we present a frequency domain inversion in which the observed earthquake strong ground motions are used to constrain the space time dependence of slip on a fault green s functions are numerically evaluated and the parameters describing the rupture are the local slip rupture time and rise time these parameters are simultaneously evaluated without additional constraints this procedure allows for large variations in the local rupture velocity the june 28 1992 landers earthquake mw 7 3 offers an exceptional opportunity to apply this technique to a major strike slip event we model the rupture evolution including local differences in slip durations and variations in rupture velocity our final results are in good agreement with other inversion studies geodetic and surface observations the main discrepancies occurred at depth and at the end of the johnson valley fault we show that a relatively low resolution could be an explanation for these differences rupture velocity and slip are extremely heterogeneous both along strike and with depth a moment of 0 90 1020 n m was found the slip distribution shows that this event consists of a series of regions of high slip subevents separated by regions of relative low slip approximately 50 of the moment was released on the homestead valley fault in this region of large slip the rupture velocity inferred by our inversion is well constrained and is equal to 3 0 km s at depth and 2 5 km s near the surface our inversion favors the hypothesis that the duration of the slip at each point of the fault is of the order of the duration of rupture of each subevent

late quaternary vegetation history of wilcox pass jasper national park alberta five pollen zones are recognized in a radiocarbon and tephra dated core from an alpine site at an elevation of ca 2355 masl in wilcox pass jasper national park and record late quaternary vegetation history the two lower zones underlie material dated at 9600 305 yr b p gx 8785 and record early postglacial vegetation the basal zone wp1 containing an artemisia dominated assemblage represents tundra vegetation after deglaciation in zone wp2 arboreal pollen mainly diploxylon pine becomes dominant and represents a lodgepole pine forest the pollen assemblage of zone wp3 which initially contains large amounts of haploxylon pine as well as picea and abies pollen shows a transition from a forest with large amounts of whitebarkpine to vegetation resembling present day subalpine forest during this phase temperatures were probably warmer than present zone wp4 beginning after the influx of mazama tephra 6800 yr b p to the site records an expansion of the subalpine forest to higher elevations with a warmer climate in zone wp5 beginning about 2800 yr b p values of the main arboreal components fluctuate indicating cooler temperatures and less favourable environmental conditions probably associated with neoglacial ice advances the environmental trends observed from this record accord with those from other vegetation records in the canadian rockies

revised 14c age for st helens y tephra at tonquin pass british columbia the age of a mount st helens set y tephra at tonquin pass british columbia previously assumed to be 4300 years bp is revised to ca 3400 years bp based on bracketing 14c dates of 3140 70 beta 13558 and 3680 80 years bp beta 13559 the implications of this revision for tephrostratigraphy of this area are discussed

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

rough faults distributed weakening and off fault deformation 1 we report systematic spatial variations in fault rocks along nonplanar strike slip faults cross cutting the lake edison granodiorite sierra nevada california sierran wavy fault and lobbia outcrops of the adamello batholith in the italian alps lobbia wavy fault in the case of the sierran fault pseudotachylyte formed at contractional fault bends where it is found as thin 1 2 mm fault parallel veins epidote and chlorite developed in the same seismic context as the pseudotachylyte and are especially abundant in extensional fault bends we argue that the presence of fluids as illustrated by this example does not necessarily preclude the development of frictional melt in the case of the lobbia fault pseudotachylyte thickness varies along the length of the fault but the pseudotachylyte veins thicken and pool in extensional bends we conduct a quantitative analysis of fault roughness microcrack distribution stress and friction along the lobbia fault numerical modeling results show that opening in extensional bends and localized thermal weakening in contractional bends counteract resistance encountered by fault waviness resulting in an overall weaker fault than suggested by the corresponding static friction coefficient the models also predict static stress redistribution around bends in the faults which is consistent with distribution of microcracks indicating significant elastic and inelastic strain energy is dissipated into the wall rocks due to nonplanar fault geometry together these observations suggest that damage and energy dissipation occurs along the entire nonplanar fault during slip rather than being confined to the region close to the dynamically propagating crack tip

nonplanar faults mechanics of slip and off fault damage stress interactions and sliding characteristics of faults with random fractal waviness in a purely elastic medium differ both qualitatively and quantitatively from those of faults with planar surfaces with nonplanar fault models solutions for slip diverge as resolution of the fractal features increases and the scaling of fault slip with fault rupture dimension becomes nonlinear we show that the nonlinear scaling of slip and divergence of solutions arise because stresses from geometric interactions at irregularities along nonplanar faults grow with increasing slip and produce backstresses that progressively impede slip however in real materials with finite strength yielding will halt the growth of the interaction stresses which will profoundly affect slip of nonplanar faults we infer that in the brittle seismogenic portion of the earth s crust off fault yielding occurs on pervasive secondary faults predicted rates of stress relaxation with distance from major faults with random fractal roughness follow a power law relationship that is consistent with reported clustering of background seismicity up to 15 kilometers from faults

earthquake source characteristics from dynamic rupture with constrained stochastic fault stress one of the challenging tasks in predicting near source ground motion for future earthquakes is to anticipate the spatiotemporal evolution of the rupture process the final size of an event but also its temporal properties propagation velocity slip velocity depend on the distribution of shear stress on the fault plane though these incipient stresses are not known for future earthquakes they might be sufficiently well characterized in a stochastic sense we examine the evolution of dynamic rupture in numerical models of a fault subjected to heterogeneous stress fields with varying statistical properties by exploring the parameter space of the stochastic stress characterization for a large number of random realizations we relate generalized properties of the resulting events to the stochastic stress parameters the nucleation zone of the simulated earthquake ruptures in general has a complex shape but its average size is found to be independent of the stress field parameterization and is determined only by the material parameters and the friction law furthermore we observe a sharp transition in event size from small to system wide events governed mainly by the standard deviation of the stress field a simplified model based on fracture mechanics is able to explain this transition finally we find that the macroscopic rupture parameters e g moment moment rate seismic energy of our catalog of model quakes are generally consistent with observational data