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

the evolution of tungsten sources in crustal mineralization from archean to tertiary inferred from lead isotopes lead isotope compositions of 31 tungsten bearing mineral occurrences worldwide with ages ranging be tween archean and tertiary have been determined to assess the evolution of tungsten sources in crustal min eralization through time the data indicate that tungsten of crustal mineralization was mainly supplied by the mantle between 3 0 and 2 4 ga the possibility of increasing contributions from the newly formed crust to tungsten mineralization throughout the archean is suggested by the available data although this suggestion needs to be tested by additional measurements the tungsten occurrences of proterozoic age contain mature crustal lead reflecting their association with crustal reworking through metamorphism and magmatism in the proterozoic mobile belts from 0 5 ga onward tungsten mineralization displays a renewed mantle lead con tribution owing to the direct or indirect association of post 0 5 ga tungsten occurrences with subduction re lated magmatic rocks of the phanerozoic orogenic cycles the data presented also suggest that several tungsten mineralization pulses may have recycled tungsten from older reservoirs

u pb dating of zircon and 40ar 39ar dating of biotite at bingham utah uranium lead dating of zircon and 40ar 39ar dating of biotite provide a new estimate of the age of the bingham hydrothermal system the u pb age of zircon from the last chance monzonite establishes the age of crystallization of this intrusion at 38 55 0 19 ma 2 mswd 2 08 the oldest hydrothermal event in the monzonite is dated at 38 40 0 16 ma and is based on a 40ar 39ar determination plateau age of primary igneous biotite this age is indistinguishable from the u pb zircon age of emplacement of the monzonite petrographic and fluid inclusion data show that the biotite bearing sample was propylitically altered at 400 c which would reset the 40ar 39ar age within 115 ka thus the concordance of the biotite age with the intrusion age of the monzonite suggests that propylitic alteration was essentially contemporaneous with monzonite emplacement the 40ar 39ar ages from three hydrothermal biotites sampled within the 0 35 percent cu isopleth in the monzonite overlap within uncertainty and indicate that potassic alteration in monzonite occurred at 37 57 0 11 ma the youngest hydrothermal activity is identified from a biotite sample 37 07 0 21 ma correlation age in potassically altered quartz monzonite porphyry within the central mos2 zone hydrothermal biotite within the bingham deposit was produced over a time period of approximately 0 50 0 32 ma

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

free surface effects on the propagation of dynamic rupture dynamic rupture of reverse and normal fault intersecting the surface are investigated in the case of a normal fault nucleating at depth and propagating upwards coupling of rupture radiated stress and free boundary conditions at the surface may induce a shallow secondary nucleation anticipating up to a few seconds the arrival of the main rupture front indeed the free surface induces normal stress fluctuations modifying the fault frictional strength no significant effect on rupture velocity is observed in the case of reverse faulting these incidences are explained by a stress analysis and illustrated by some numerical simulations in the case of dynamic normal faulting in a homogeneous half space the described effects could explain some observations of high frequency radiation close to the surface in documented shallow earthquakes like in kalamata 1986 bouin 1994

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

analysis of the reliability and resolution of the earthquake source history inferred from waveforms taking the chi chi earthquake as an example summary in the inversion of observed waveforms to obtain the earthquake source faulting process some uncertain factors may influence the reliability of the results several numerical tests have been analysed in this paper in order to understand the effect of some of these uncertain parameters such as the number and width of multiple time windows that define the source time function the assumed strike and dip of the fault the velocity structure and noise also the influence of the sampling rate the time window of the data and the distribution of observational stations is studied our research indicates the near source waveform data can adequately recover the source rupture process of the shallow part of the fault however they poorly constrain the slip distribution on the deep part of the fault using near source and teleseismic waveform data jointly can provide a more complete view of the rupture process of the whole fault the result using near fault data is very sensitive to the assumed strike and dip parameters of the fault model a 2 deviation of the presumed strike and a 5 deviation of the presumed dip from that of the true fault will lead to a distorted inversion result the influence of the uncertainty of the seismic velocity structure for the chi chi earthquake might be ignored if we can take the difference between ma et al s model and wu et al s model as the measure of the media uncertainty

mineral chemical and isotopic studies of namaqualand granulites south africa a grenville analogue the northwestern part of south africa and southern south west africa namibia is amongst the most extensive granulite terranes in africa this work reports the results of electron microprobe studies of minerals from two pyroxene cordieriteorthopyroxene gedrite sapphirine and garnet and or cordierite parageneses from namaqualand in the n w cape province of south africa determined pt conditions of prograde metamorphism based on thermodynamic calculations are 800 900 c and ca 6 7 kb and it is argued that rocks of unusual composition notably cordierite orthopyroxene rocks are restites after the extraction of granitic liquid from former argillites this interpretation is consistent with previously published data on similar rocks and with mccarthy s 1976 suggestion of extensive partial melting in the quartzofeldspathic rocks in the area

distribution of dynamic and static stress changes during 2000 tottori japan earthquake brief interpretation of the earthquake sequences foreshocks mainshock and aftershocks 1 the dynamic and static stress changes during the 2000 tottori earthquake have been recovered from the results of waveform inversion we use the dem to solve the elastodynamic equation specifying the slip along the fault obtained by a kinematic fault model the resulting shear stress distribution suggests an explanation of the foreshock and aftershock distributions we conclude that the fault zone heterogeneity is strong and most of the foreshocks and aftershocks were located in the zone of negative stress drop and mainly in the area surrounding the asperity this suggests that the asperity behaved as a barrier during the foreshocks and after the main shock the stress in the area surrounding the asperity increased and triggered most of the aftershocks the foreshock distribution was confined to a finite localized zone in the central part of the fault suggesting that this zone was bordered by barriers

nickeliferous sulfides in xenoliths olivine megacrysts and basaltic glass the composition of olivine and nickeliferous sulfide inclusions from a selection of mafic and ultramafre rocks xenoliths and megacrysts including picritic basalts from kilauea volcano hawaii kimberlite from fayette county pennsylvania and megacrysts from mount shasta california are compared with the mean experimental value of the distribution coefficient for ni fe exchange kd3 32 only nine of the forty five olivipe bulk sulfide pairs investigated have compositions consistent with equilibration at high temperature yielding calculated kd3 values in the range 22 to 41 the remaining pairs have calculated kd3 values which range from 0 to 19 bulk sulfides in disequilibrated assem blages are consistently depleted in nickel and within both indivudual associations and individual petrographic sections they exhibit a wide variation in nis content the bulk copper contents of olivine and groundmass hosted sulfides from kilauea volcano range from 0 5 to 43 at and samples from the kilauea iki lava lake are more fe and cu rich and generally have lower kd3 values than those from the eruption itself as with magmatic ni cu sulfide deposits most nickeliferous sulfide inclusions in mantle related rocks and xenoliths and in volcanic rocks do not have pristine early magmatic bulk compositions and it would seem to be premature to attribute these sulfides solely to either a mantle or an early magnatic origin

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

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

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

earthquake source nucleation a physical model for short term precursors abstract ohnaka m 1992 earthquake source nucleation a physical model for short term precursors in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 149 178 this paper deals with a quasistatic leading to a quasidynamic at a later time nucleation process that precedes the earthquake dynamic rupture and models of the earthquake source nucleation are put forward based on physical principles a quasistatic to quasidynamic rupture nucleation process is an intrinsic part of the ensuing earthquake dynamic rupture in other words the nucleation process itself is an short term or immediate precursor that occurs in a localized zone during the earthquake nucleation premonitory slip proceeds in the localized nucleation zone and shear stress also decreases gradually in the zone since slip weakening occurs during the nucleation immediate foreshock activity is a part of the nucleation process leading to the mainshock dynamic rupture therefore hypocentral locations of foreshocks are necessarily restricted to lie near the mainshock hypocentre onset of the mainshock rupture whether or not foreshocks occur during the mainshock nucleation depends on how the rupture growth resistance varies on a local to small scale since patches of greater rupture growth resistance are considered to prevail on a local to small scale in the fault zone carrying immediate foreshocks would be one of the major characteristics of earthquakes that nucleate within the brittle seismogenic layer when a mainshock earthquake nucleates within the brittle seismogenic layer and its hypocentre is located near the base of the seismogenic layer immediate foreshocks for this mainshock are necessarily restricted to lie within a localized region shallower than hypocentral depth of the mainshock by contrast the nucleation process below the base of the seismogenic layer is aseismic in nature so that carrying no conspicuous foreshocks would be a common characteristic of interplate earthquakes that nucleate below the base of the brittle seismogenic layer the breakdown strength p the breakdown stress drop b and the critical slip displacement dc are indicative of the rupture growth resistance to estimate depth variations of these parameters the effects of the normal stress n and temperature t on those parameters are examined using available data so far published the combined effects of n and t on p in the brittle to semibrittle regime are found to be represented empirically by p n t po n 1 cosh 50 t 40 sinh 50 t exp 2000 t where po n 135 7 0 750 n and t is measured in k and n in mpa it is found that dc increases sharply with t but is insensitive to n above 300 c while dc depends on n but is insensitive to t below 300 c on the basis of these results variations in p dc and b at mid crustal depths are estimated for quartzo feldspathic rocks for a given geothermal gradient

contributions from mafic alkaline magmas to the bingham porphyry cu au mo deposit utah usa the bingham porphyry cu au mo deposit utah may only be world class because of substantial contributions of sulfur and metals from mafic alkaline magma to an otherwise unremarkable calc alkaline system volcanic mafic alkaline rocks in the district are enriched in cr ni and ba as well as cu au platinum group elements pge and s the bulk of the volcanic section that is co magmatic with ore related porphyries is dacitic to trachytic in composition but has inherited the geochemical signature of high cr ni and ba from magma mixing with the mafic alkaline rocks the volcanic section that most closely correlates in time with ore related porphyries is very heterogeneous containing clasts of scoriaceous latite latitic and minette and flows of melanephelinite shoshonite and olivine latite in addition to volumetrically dominant dacite trachyte bingham ore related porphyries show ample evidence of prior mixing with mafic alkaline magmas intrusive porphyries that have not been previously well studied have several chemical and mineralogical indications of magma mixing these mixed lithologies include the hybrid quartz monzonite porphyry biotite porphyry and minette dikes even some of the more silicic latite and monzonite porphyries retain high cr and ba contents indicative of mixing and contain trace amounts of sapphire 1 mm the heterogeneous block and ash flow deposits also contain sapphire and are permissively correlated with the intrusions based on chemical mineralogical and isotopic data magma mixing calculations suggest about 10 of the monzonitic latitic ore related magma may have been derived from mafic alkaline magma similar to the melanephelinite if the original s content of the mafic magma was about 2 000 4 000 ppm comparable with similar magmas then the mafic magma may have been responsible for contributing more than half of the s and a significant portion of the cu au and pge in the bingham deposit

the three dimensional dynamics of dipping faults recent two dimensional dynamic simulations of dip slip faulting niel sen 1998 oglesby et al 1998 2000 shi et al 1998 have shown that the asym metric geometry of dip slip faults that intersect the free surface can have large effects on the dynamics of earthquake rupture the nonvertical dip angle of such faults leads to larger motion on the footwall than the hanging wall as well as much larger motion from thrust reverse faults than from normal faults with the same geometry and stress magnitudes in the present work we perform full three dimensional simulations of thrust reverse normal and strike slip faults and show that the same effects exist in three dimensions strike slip fault motion is either in between or lower than the motion of both dip slip faults additional three dimensional effects include strong rake rotation at the free surface the results confirm the findings of the previous studies and further elucidate the dynamic effects of the free surface on fault rupture slip and ground motion they are also borne out by early analyses of the 1999 chi chi taiwan thrust earthquake which displayed higher motion on the hanging wall than on the footwall and a strong oblique component of motion at the surface

3d simulation of near field strong ground motion based on dynamic modeling abstract we simulate the strong ground motion generated from the earthquake rupture process on a shallow strike slip fault using a 3d finite difference method the faulting process is modeled using a crack model with fixed rupture velocity the variability of peak ground velocity patterns correlated with fault location and source parameters such as stress drop or rupture velocity is investigated our findings suggest that these patterns are strongly affected by rupture directivity and the uppermost depth of the fault or that of the asperity when a fault breaks the ground surface the peak ground velocity and the peak ground acceleration show a narrow region of strong motion when a fault is buried under the ground the high peak ground velocity zone of the fault parallel component is apart from the fault trace by a distance comparable to the fault depth on the other hand the fault normal peak ground velocity is a maximum along the fault trace the fault length or asperity length is not so effective for peak ground velocities the effect of heterogeneity in stress drop and rupture velocity on strong ground motion is also investigated when stress drop is not uniform but increases linearly with depth from zero at the uppermost depth the peak ground velocity is reduced these results help better predict the strong ground motion generated from a potential fault

unusually cu rich magmas associated with giant porphyry copper deposits evidence from bingham utah mass balance constraints indicate that formation of giant porphyry copper deposits pcds requires either highly efficient collection of cu from large volumes of magma or unusually cu rich parent magmas support for the second of these possibilities has been discovered in the form of mafic enclaves with abundant bornite and chalcopyrite in the last chance stock one of the parent intrusions of the giant bingham pcd utah united states mineral assemblages and compositions indicate that the last chance enclaves are autoliths consisting of phases that crystallized from the intrusion and that the intrusion was unusually enriched in cu one possible mechanism for generating cu rich magmas is fractional crystallization during pyrrhotite undersaturated conditions the high fo 2 conditions observed for the last chance stock may have allowed such an evolution alternatively if the magma has not undergone significant fractionation early crystallization of chalcopyrite and bornite from the magma would indicate that the lower crustal source region for the magma probably contained cu fe sulfides possible cu rich source regions are a subcrustal mafic intrusion with sulfide cumulates or a deeply buried metamorphic terrane containing cu deposits such as those in the curaca valley brazil or okiep south africa heterogeneous distribution of cu fe sulfides in an okiep type source terrane would produce local pcds such as bingham or large accumulations of cu fe sulfides possibly in the form of cumulates in subcrustal intrusions at convergent margins could produce giant pcd provinces such as those in indonesia papua new guinea and central chile

constitutive relations between dynamic physical parameters near a tip of the propagating slip zone during stick slip shear failure abstract constitutive relations between physical parameters in the cohesive zone during stick slip shear failure are experimentally investigated stick slip was generated along a 40 cm long precut fault in tsukuba granite samples using a servocontrolled biaxial loading apparatus dynamic behavior during local breakdown processes near a tip of the slipping zone is revealed the slip velocity and acceleration are given as a function of the slip displacement and the cohesive or breakdown shear stress as a function of the slip velocity a cycle of the breakdown and restrengthening process of stick slip is composed of five phases characterized in terms of the cohesive strength and the slip velocity the cohesive strength can degrade regardless of the slip velocity during slip instabilities the maximum slip acceleration u max and the maximum slip velocity u max are obtained experimentally as u max 2 u c u max 2 and u max b g v where u c is the critical displacement b the breakdown stress drop g the rigidity and v the rupture velocity these relations are consistent with ida s theoretical estimation based on the cohesive zone model the above formula gives good estimates for the maximum slip acceleration of actual earthquakes the cutoff frequency max of the power spectral density of the slip acceleration increases with increasing normal stress in particular max is found to be directly proportional to the normal stress n within the normal stress range less than 17 mpa as max khz 4 0 n mpa n max increase with an increase in u max or u max all these results lead to the conclusion that u max u max and max increase with increasing normal stress this is consistent with a previous observation that b increases with increasing normal stress the above empirical linear relation between max and n can be explained by a linear dependence of b on n the size scale dependence of physical parameters is discussed and such size scale dependent parameters as u max and apparent fracture energy are scaled to the breakdown zone size regarded as a characteristic length to extend the results obtained in the laboratory to an earthquake failure in the earth

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

linearized elastic parameter sections contrasts in elastic parameters can be estimated directly from seismic data using offset dependent information in the pp reflection coefficient a linear approximation to the pp reflection coefficient including three coefficients is fitted to the data and relative contrasts in various elastic parameters are obtained from linear combinations of the estimated coefficients linearized elastic parameter sections for the contrasts in p wave impedance p wave velocity density plane wave modulus and the change in bulk modulus and shear modulus normalized with the plane wave modulus are estimated if the average p to s wave velocity ratio is known linearized parameter sections including the contrast in the average p to s wave velocity ratio and a fluid factor section can be computed applied to synthetic data visual comparison of the estimated and true elastic parameter sections agree qualitatively and the results are confirmed by an analysis of the standard deviation of the estimated parameters the parameter sections obtained by inversion of a shallow seismic anomaly in the barents sea are promising but the reliability is uncertain because neither well data nor regional trends are available

combined seismic inversion and gravity modeling of a shallow anomaly in the southern barents sea a combination of prestack elastic inversion with gravity modeling has been applied to a shallow seismic anomaly in the southern barents sea the anomaly is crosscutting dipping layers of late paleocene age earlier seismic interpretations indicate a possible origin in gas hydrated sediments trapping underlying free gas our interpretation includes seismic inversion of a seismic model which consists of a stack of isotropic homogeneous and anelastic layers the unknown parameters are the p and s wave velocities density and thickness for each layer as densities are poorly determined by this method we included gravity modeling which improved the density estimates the resulting parameters have been integrated by rock physics calculations and the knowledge of typical attributes of gas hydrate occurrences the top of the seismic anomaly is interpreted as a reflection from the base of a gas hydrated sediment trapping underlying free gas the base of the anomaly is the gas water contact which deviates from a flat spot due to capillary pressure differences related to lithology and the generation process of gas hydrate the estimated density has been interpreted together with well results and indicates a significant amount of gas filling the pore volume

the importance of the dynamic source effects on strong ground motion during the 1999 chi chi taiwan earthquake brief interpretation of the damage distribution on buildings the 1999 chi chi taiwan earthquake that originated on a low angle reverse fault showed complexity and uncommon characteristics the records show that the hanging wall side is characterized by larger particle motions than the foot wall and the ground motion is stronger in the northern part than in the southern part of the causative fault although the strongest ground motion occurred near the north ern part of the trace structural damage was heavier in the southern part in order to get a better understanding of the complex damage distribution caused by this earth quake the dynamic rupture process was numerically simulated because of the dif ferences between the observed features of the rupture process in the northern and southern parts of the fault each part was modeled independently by using a 2d discrete element model dem the principal results of the simulation show that the velocity ground motions in the northern part in the frequency range of 0 5 2 hz natural frequency range of standard structures are small near the surface break thus light structural damage might be predicted near the surface rupture moreover in the northern part the fault rupture propagation reaches the surface with a very slow velocity about 1 2 km sec however in the southern part the rupture propa gation reaches the surface with higher velocity about 3 0 km sec these differences between the models could explain why the ground motion near the surface rupture in the northern part caused less damage in structures than the ground motion in the southern part

temperature estimates of coseismic heating in clay rich fault gouges the chelungpu fault zones taiwan abstract to investigate the coseismic frictional temperature in seismogenic fault zones we examine the characteristics of clays in the chelungpu fault zones with isothermal heating experiments scanning electron microscope coupled to an energy dispersive spectrometer sem edx and thermogravimetry analysis tga in the tcdp case taiwan chelungpu fault drilling project three fault zones of the chelungpu fault system were identified at the depth of 1111 m 1153 m and 1222 m described as fz1111 fz1153 and fz1222 hereafter respectively the clay mineral assemblages of fz1111 show evidence of melting and the temperature in a 2 cm band within the black gouge zone is estimated to be from 900 c to 1100 c by comparing the sem images of in situ natural samples with those of heated materials and the finding of no recrystallization of kaolinite amorphous aluminosilicates spinel in the fault samples the clay mineral assemblages of fz1153 suggested that kaolinite has been broken down by the thermal decomposition dehydroxylation but chlorite has not the clay characteristics and results of sem edx and tga constrain the faulting temperature from 500 c to 900 c with a spatial distribution up to 1 3 m the clay characteristics of fz1222 indicated that clays were changed by experiencing high temperature acid fluids instead of thermal decomposition dehydroxylation processes and that the temperature is localized in 2 cm and ranges from 350 c to 500 c the lowest temperature among three fault zones the estimates of temperature ranges and thermal anomaly intervals among three fault zones provide important information and constraints on the physical and chemical processes coseismic dynamic weakening mechanism and earthquake energy budget in the future

dynamic rupture processes on a dipping fault and estimates of stress drop and strength excess from the results of waveform inversion summary the dynamic rupture processes on a dipping fault in a horizontally layered medium are investigated on 3 d spontaneous shear crack models the wave equations for the 3 d space are solved numerically by a finite difference method under appropriate boundary conditions the displacement components right above and right below the dipping fault plane have been obtained by solving the boundary conditions across the fault it was found that the final fault slip on the hanging wall side is appreciably larger than that on the foot wall side and that their amount is quite sensitive to the fault depth and the elastic heterogeneities of the medium particularly of the existence of low velocity surface layers on the basis of the above model the dynamic rupture process of the 1961 kita mino earthquake in central japan has been investigated with constraints of the fault parameters derived from the results of waveform inversion analysis for this purpose a locking fracture criterion was introduced for rupture propagation from which a lower bound of the maximum shear stress before the rupture and hence of the strength excess has been estimated the dynamic stress drop has also been evaluated by repeated iterations to minimize the difference between the dynamic and kinematic fault slips the results revealed quite heterogeneous distribution of strength excess indicating large values near the sw section of the fault at shallow depths and in the central bottom section in contrast to small values at mid depths in the ne section around the rupture nucleus zone the distribution of stress drop was also found to be heterogeneous with the existence of high stress drop zones in the ne shallow and bottom sections and a low stress drop zone at most of mid depths except in the sw section these results suggest that the dynamic rupture of this earthquake initiates at a small nucleus zone with low strength excess and small stress drop then broke the shallower and deeper fault sections with moderate strength excess and high stress drop and finally ruptured barrier zones with high strength excess these zones may be interpreted as weak and strong asperities and barriers respectively

dynamic faulting under rate dependent friction we discuss the effects of rate dependent friction on the propagation of seismic rupture on active faults several physicists using burridge and knopoff s box and spring model of faulting have proposed that fault complexity may arise from the spontaneous development of a self similar stress distribution on the fault plane if this model proves to be correct it has important consequences for the origin of the complexity of seismic sources in order to test these ideas on a more realistic earthquake model we developed a new boundary integral equation method for studying rupture propagation along an antiplane fault in the presence of nonlinear rate dependent friction we study rupture dynamics of models with single and twin asperities in our models asperities are places on the fault with a higher value of prestress othewise all fault parameters are homogeneous we show that for models with such asperities a slip velocity weakening friction leads to the propagation of supersonic healing phases and to the spontaneous arrest of fracture if the prestress outside the asperities is low enough for models with asperities we can also observe narrow slip velocity pulses qualitatively similar to the so called heaton pulses observed in some earthquake accelerograms we also observe a complex distribution of stress after the rupture that depends on details of the initial distribution of asperities and on the details of the friction law

tungsten deposits in the wolfram schist namaqualand south africa strata bound versus granite related genetic concepts several tungsten deposits from which ca 1 800 metric tons t of concentrate at 65 3 percent w03 was produced occur in the okiep copper district south africa which is part of a high temperature low pressure granulite terrane m 2 750 degrees 850 degrees 5 7 kbars the 1 2 to 1 0 ga high grade metamorphism of proterozoic supracrustal and older intrusive rocks is polymetamorphic and was accompanied by crustal melting resulting in formation of several early to postorogenic granitoid suites the w mo deposits are spatially and genetically associated with the 1 1 ga concordia granite a silica rich 70 76 wt peraluminous leucogranite with subalkaline monzonitic magma characteristics more fractionated cogenetic intrusions are interpreted as separated residual granitic liquids they are enriched in large ion lithophile k 2 o rb and some high field strength w nb etc elements mineralized pegmatites replacement orebodies strongly silicified granitic rocks and exo and endogranitic veins are distinguished ferberite and minor scheelite are associated with mo cu and bi sulfides and u th nb ree silicates oxides and phosphates metapelites wolfram schist hosting s 2 subparallel exogranitic veins are characterized by m 2 upper amphibolite lower granulite facies assemblages biotite sillimanite or garnet or cordierite plus quartz alkali feldspar and plagioclase schistose host rocks were derived from normal clastic sedimentary material slightly peraluminous lithologies probably from more pelitic kaolinite rich precursors the facts that late to postorogenic granites and the w mo deposits are deformed metamorphic ore textures e g garnet coronas around ore minerals are preserved and ore deposit specific hydrothermal low temperature alteration is absent suggest that the second m 3 late kibaran metamorphic overprint postdated mineralization oxygen isotope temperatures of ca 600 degrees to 660 degrees c for coexisting garnet and quartz from mineralized veins and host rocks indicate that high grade conditions were again reached during this late kibaran overprint retrograde greenschist facies metamorphism is of pan african age ca 560 590 ma and is unrelated to mineralizing processes the w mo deposits are interpreted as metamorphosed deep seated granitic ore deposits occurring in a polymetamorphic high grade terrane two high grade events of kibaran age m 2 and m 3 and a low grade event of pan african age m 4 are distinguished

frequency wavenumber elastic inversion of marine seismic data we present an inversion method for determining the velocities densities and layer thicknesses of a horizontally stratified medium with an acoustic layer at the top and a stack of elastic layers below the multioffset reflection response of the medium generated by a compressional point source is transformed from the time space domain into the frequency wavenumber domain where the inversion is performed by minimizing the difference between the reference data and the modeled data using a least squares technique the forward modeling is based on the reflectivity method where the solution for each frequency wavenumber component is found by computing the generalized reflection and transmission matrices recursively the gradient of the objective function is computed from analytical expressions of the jacobian matrix derived directly from the recursive modeling equations the partial derivatives of the reflection response of the stratified medium are then computed simultaneously with the reflection response by

the role of hydrothermal alteration in tungsten mineralization at the dahutang tungsten deposit south china abstract the giant dahutang tungsten deposit has total reserves of more than 1 31 mt of wo3 with a scheelite wolframite ratio of 1 and is mainly hosted by the neoproterozoic jiuling granodiorite batholith 820 ma the deposit is characterized by four types of alteration including biotite alteration phyllic alteration greisenization and silicification whole rock geochemical analyses showed that the elements ti ni v sc and lu exhibited immobility during the four alteration processes the mobile element geochemistry effectively differentiated among four distinct hydrothermal alteration styles during the biotite mineralization there were mass gains in al2o3 fe2o3 mno mgo k2o p2o5 and w and depletions in sio2 cao and na2o the phyllic alteration exhibited mass gains in sio2 fe2o3 mgo and w and depletions in cao na2o and k2o but al2o3 mno and p2o5 were immobile the weak greisenization exhibited mass gains in sio2 fe2o3 k2o p2o5 and w and depletions in na2o mgo and cao whereas al2o3 and mno remained immobile the silicification exhibited mass gains in sio2 and w and depletions in al2o3 fe2o3 mgo cao na2o and k2o but mno exhibited immobility these alterations were related to at least three major hydrothermal fluid systems firstly a hydrothermal fluid caused biotitization zones and fe mn w mineralization mostly biotite at temperatures ranging from 560 to 450 c and the magmatic hydrothermal fluids were derived from the jurassic porphyritic biotite granite 150 ma and characterized by alkaline oxidized moderate pressure and low salinity features secondly a hydrothermal fluid was formed by the mixing of magmatic fluid with meteoric water and was responsible for the phyllic weak greisenization alteration zones at temperatures ranging from 440 to 450 c and characterized by alkaline weakly oxidized moderate pressure and low salinity features thirdly a hydrothermal fluid caused greisenization and silicification zones at temperatures ranging from 440 to 160 c which were characterized by acidic reduced high pressure and moderate to low salinity features derived from the cretaceous fine grained biotite granite 144 ma and associated with the main w mineralization at dahutang the characteristics of fe enriched biotite in the biotitized and greisenized rock decreasing temperature high pressure and high log fh2o fhcl could facilitate the formation of scheelite deposits but the high f suppressed it the decreasing temperature and f o2 and the fe mn released from biotite contributed to the formation and precipitation of wolframite during alkaline alteration biotite and apatite acted as storage places for fe mn and ca which were subsequently released by acidic alteration to form scheelite and wolframite there was no enough ca was released from biotitized rock for the acidic alteration to provide the wo42 to form scheelite meanwhile fe was added and mn was released to form the scheelite wolframite deposit based on all the results we have developed a genetic model for tungsten mineralization including superimposed alteration processes alkaline overprinted by acidic alteration which led to the gain and loss of elements and corresponding to two magmatic events the jurassic porphyritic biotite granite and the cretaceous fine grained biotite granite the superposition of alterations played an important role in the mineralization of the dahutang giant tungsten deposit

development of dynamic asperity models to predict surface fault displacement caused by earthquakes asperity models for ground motion prediction is widely used in japan here we expand the application of these asperity models to predict fault displacement caused by surface rupture the proposed approach is rather simple and practical for the use in fault displacement hazard analysis in nuclear installations and other critical infrastructures as it is the emphasis of the current topical issue the proposed method mainly consists of two steps the first step consists in the characterization of asperities at the seismogenic zone based on the kinematic asperity source model following irikura s recipe irikura and miyake in pure applied geophysics 168 85 104 2011 for strong ground motion prediction since the kinematic model does not take into account surface rupture mechanism this first step assumes that the fault is buried and then by trial and error procedure the stress drop on the asperities are estimated so that the average slip at each asperity be consistent with the ones from the kinematic model at this stage the dynamic model predicts strong ground motion consistent with those from the kinematic model in the second step the surface rupture is included by calibrating the shallow layer sl with stress drop strength excess and critical slip distance so that the final fault displacement along the fault be consistent with observations the 2010 mw 7 0 darfield new zealand earthquake is used to test the proposed method surface rupturing was observed in several sites along the main fault reaching values of fault displacement larger than 5 m the main fault of this earthquake is strike slip almost vertical therefore a simplified planar fault asperity model to capture the main features of the fault displacement is assumed the fault dimensions are assumed to have a length of 60 km and a width of 24 km with three asperities the preferred model of the first step predicts average slip for each asperity of 2 7 2 7 and 2 m corresponding respectively to stress drops of 6 0 mpa 8 5 mpa and 7 0 mpa in the second step the surface rupture is calibrated assuming a sl zone of 3 km depth we found that negative stress drop is not necessary in the sl because this strongly inhibits surface rupturing our preferred model produces fault displacement distribution closer to the observed ones but average slip at each asperity increases to 3 4 m 3 2 and 2 8 m this increase in average slip is due to the contribution of surface rupturing ground motion differences between fault surface rupturing and buried models are negligible except at the very near source these differences are attributed to the sl rupture that mainly affect the ground motion at the very near source overall our simple asperity model captures the main features of the observed fault displacement and near source ground motion proving that the proposed simple and practical two step procedure provides meaningful estimate of fault displacement and near source ground motion consistent with observations as such this method has the potential to be used in practical fault displacement hazard analysis

simulation of tensile crack generation by three dimensional dynamic shear rupture propagation during an earthquake 1 as there is no evidence that cracks are created directly in modes ii and iii shear cracks probably occur only along a weakness plane as in a preexisting fault mode i fracture therefore may be an important factor in crack formation during shallow earthquakes a three dimensional shear dynamic rupture process was simulated on the assumption that shear slip occurs only in a preexisting fault and the possibility of introducing new internal cracks that propagate under tensile stress as a consequence of the dynamic process of shear slip propagation the discrete element method dem was used to solve this problem because it can introduce internal tensile cracks the simple slip weakening model was used as the friction law on the preexisting fault for shear rupture propagation for new tensile cracks fracture follows classical griffith theory when the critical value for tensile fracture surface energy is reached the proposed model was used to simulate the rupture process of a strike slip shallow fault results show that the generation of new cracks is affected by rupture directivity in terms of the hypocenter and asperity location as well as by fault geometry with respect to the free surface cracks develop a flower like structure that surrounds the preexisting fault when the asperity is located at less than a certain depth the flower like structure that originates from the top of the fault reaches the free surface we consider that this is the mechanism for forming the flower structure near surface during a strike slip shallow earthquake

analyses of pseudotachylyte from hole b of taiwan chelungpu fault drilling project tcdp their implications for seismic slip behaviors during the 1999 chi chi earthquake abstract the seismic slip behavior during the 1999 chi chi taiwan earthquake m w 7 6 was contrastive between the northern and southern segments of the activated chelungpu fault large fast and smooth slips with large stress drop in the north while smaller slower and irregular slips with smaller stress drop in the south we analyzed the pseudotachylyte samples recovered from 1194 m 1243 m and 1314 m depths of hole b of taiwan chelungpu fault drilling project tcdp to reveal the spatial difference in friction mechanism all pseudotachylyte layers are thin 0 7 2 8 cm the volume fraction of protoliths is very large more than 63 and the estimated temperature distribution is very heterogeneous from ca 750 1750 c these observations suggest that these pseudotachylyte melts were in the partial melting regime of montgomery montgomery r s 1976 friction and wear at high sliding speeds wear 36 275 298 where friction coefficient is abnormally large similar pseudotachylyte was found already in the core sample from 175 m depth of the nanto borehole penetrating the southern fault since both pseudotachylyte samples from the two boreholes are older than the 1999 chi chi event and have been uplifted from depths farther down dip of their current locations it is likely that recent seismic ruptures also would have encountered these mechanical barriers of viscous melt patches at deeper parts in the north than in the south elastohydrodynamic lubrication of clayey gouge worked effectively at the shallower parts of the northern segment however there is no evidence that it played an important role in the south these differences are the plausible causes of the contrastive local slip behaviors during the chi chi earthquake

dynamic 3d simulations of earthquakes on en echelon faults one of the mysteries of earthquake mechanics is why earthquakes stop this process determines the difference between small and devastating ruptures one possibility is that fault geometry controls earthquake size we test this hypothesis using a numerical algorithm that simulates spontaneous rupture propagation in a three dimensional medium and apply our knowledge to two california fault zones we find that the size difference between the 1934 and 1966 parkfield california earthquakes may be the product of a stepover at the southern end of the 1934 earthquake and show how the 1992 landers california earthquake followed physically reasonable expectations when it jumped across en echelon faults to become a large event if there are no linking structures such as transfer faults then strike slip earthquakes are unlikely to propagate through stepover s 5 km wide

the role of strain localization in the segregation and ascent of anatectic melts namaqualand south africa granulite facies gneisses of the late proterozoic okiep copper district of the namaqua province in south africa preserve evidence of a range of anatectic melt features that reflect the initial stages of segregation and ascent of crustally derived magmas during high grade metamorphism these melt bodies include both in situ and sharply transgressive subvertical pipe like bodies that show vertical dimensions of several hundreds of metres and horizontal dimensions of tens to hundreds of metres migmatite bodies are spatially closely linked with narrow upright zones characterized by intense high strain fabrics locally referred to as steep structures they display a progressive textural development from diktyonitic textures in in situ bodies via schollen and raft textures to largely homogeneous intrusive granites that have migrated vertically for distances of several hundreds of metres or more the intimate association of the migmatite bodies with the steep structures reflects strain induced melt segregation facilitated by increased permeabilities in these ductile deformation zones and migration of melts into sites of strain incompatibility at the intersections between the regional subhorizontal gneissosity and the superimposed high strain zones subsequent melt migration was focused along the network of subvertical structural anisotropies provided by the steep structures melt migration was controlled by a combination of buoyancy shear enhanced melt compaction during ongoing deformation melt compaction due to the settling of wall rock fragments from higher stratigraphiclevels and subordinate brittle fracturing the unusual geometry of the steep structures and the intensely heterogeneous nature of the strain and the absence of similar strain features and voluminous melt bodies elsewhere in the granulite facies terrane suggest a positive feed back mechanism between melt generation and strain localization in steep structures the structural development of the migmatite bodies illustrates that the efficiency of melt segregation and migration in a mid crustal segment is dependent not only on the fertility of its lithologies but also on its deformational style

a review of least squares inversion and its application to geophysical problems geophysical inversion involves the estimation of the parameters of a postulated earth model from a set of observations since the associated model responses can be nonlinear functions of the model parameters nonlinear least squares techniques prove to be useful for performing the inversion a common type of inversion applies iterative damped linear least squares through use of the marquardt levenberg method traditionally this method has been implemented by solving the associated normal equations in conventional ways however singular value decomposition svd produces significant improvements in computational precision when applied to the same system of normal equations iterative least squares modeling finds application in a wide variety of geophysical problems two examples illustrate the approach 1 seismic wavelet deconvolution and 2 the location of a buried wedge from surface gravity data more generally nonlinear least squares inversion can be used to estimate earth models for any set of geophysical observations for which an appropriate mathematical description is available

tungsten isotope composition of the acasta gneiss complex high precision tungsten 182w 184w isotope measurements on well characterised mafic and felsic samples of the ca 3960 ma acasta gneiss complex agc northwest territories canada show radiogenic e182w values between 0 06 to 0 15 two ca 3600 ma felsic samples from this terrane have e182w 0 and are the oldest samples so far documented to have a w isotopic composition indistinguishable from that of the modern mantle the e182w data are correlated with e142nd roth et al 2014 and we attribute this variability to incomplete metamorphic homogenisation of the 3960 ma protolith with more recent material in a 3370 ma tectono thermal event notably the value of the positive e182w anomalies seen in the 3960 ma agc samples that are least affected by metamorphic homogenisation is comparable to that observed in other early archean rocks isua supracrustal belt greenland nuvvuagittuq supracrustal belt canada and the late archean kostomuksha komatiites karelia this demonstrates a globally constant signature we infer that the presence of a pre late veneer mantle represents the most straightforward interpretation of a uniform distribution of ew182 0 15 value in archean rocks of different ages we show that such a notion is compatible with independent constraints from highly siderophile element abundances in mafic and ultra mafic archean mantle derived rocks the absence of anomalous e182w and e142nd so far measured in samples younger than ca 2800 ma suggests progressive convective homogenisation of silicate reservoirs the downward mixing of an upper mantle rich in late delivered meteoritic material might account for these combined observations

fault structure control on fault slip and ground motion during the 1999 rupture of the chelungpu fault taiwan the chelungpu fault taiwan ruptured in a mw 7 6 earthquake on 21 september 1999 producing a 90 km long surface rupture analysis of core from two holes drilled through the fault zone combined with geologic mapping and detailed investigation from three outcrops define the fault geometry and physical properties of the chelungpu fault in its northern and southern regions in the northern region the fault dips 45 60 east parallel to bedding in both the hanging wall and footwall and consists of a narrow 1 20 cm core of dark gray sheared clay gouge the gouge is located at the base of a 30 to 50 m zone of increased fracture density confined asymmetrically to the hanging wall microstructural analysis of the fault gouge in dicates the presence of extremely narrow clay zones 50 300 lm thick that are interpreted as the fault rupture surfaces few shear indicators are observed outside of the fault gouge implying that slip was localized within the gouge zone slip localization along a bed parallel surface resulted in a narrow gouge zone that pro duced less high frequency ground motion and larger displacements average 8 m during the earthquake than in the southern region displacement in the southern region averaged only 2 m but ground shaking consisted of large amounts of high frequency ground motion the fault in the southern region dips 20 30 at the surface and consists of a wide 20 70 m thick zone of sheared foliated shale with numerous gouge zones these data demonstrate a potential correlation between fault structure i e gouge width geometry and earthquake characteristics such as displacement and ground motion i e acceleration

platinum group elements in cu sulphide ores at carolusberg and east okiep namaqualand south africa cu sulphide ores at carolusberg and east okiep have cu ni ratios of up to 80 an order of magnitude higher than most magmatic sulphide ores elsewhere in contrast se s ratios 500 1700 10 6 and pge tenors up to 5 ppm of the sulphides are in the range of more typical magmatic sulphide ores the observed metal patterns may be explained by a process of monosulphide solid solution mss fractionation of a magmatic sulphide melt at depth but this model is currently considered unlikely due to the paucity of refractory ores in the district assimilation of cu rich country rocks during ascent of the koperberg magmas proved difficult to test with the available data but this provides no explanation for the common high grade metamorphic setting of similar ores elsewhere a restitic origin of the pyroxenites appears to explain many of the observed ore features and is presently favoured here desulphidization of a primary magmatic sulphide ore could not have yielded the observed metal patterns and is therefore considered to be of relatively minor importance in ore genesis

evidence for fault lubrication during the 1999 chi chi taiwan earthquake mw7 6 the ground motion data of the 1999 chi chi taiwan earthquake exhibit a striking difference in frequency content between the north and south portions of the rupture zone in the north the ground motion is dominated by large low frequency displacements with relatively small high frequency accelerations the pattern is opposite in the south with smaller displacements and larger accelerations we analyze the fault dynamics in light of a fault lubrication mechanism using near field seismograms and a detailed rupture model the fault zone contains viscous material e g gouge in which pressure increases following the reynolds lubrication equation when the displacement exceeds a threshold lubrication pressure becomes high enough to widen the gap thereby reducing the area of asperity contact with less asperity contact the fault slips more smoothly suppressing high frequency radiation

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

estimation of the high frequency radiation of the 2000 tottori japan earthquake based on a dynamic model of fault rupture application to the strong ground motion simulation abstract in the present study we investigate the high frequency hf radiation mechanism of the 2000 tottori earthquake in japan based on a 3d spontaneous fault rupture dynamic model we generalize the model of hf radiation of a suddenly stopping circular crack madariaga 1977 boatwright 1982 to the radiation from a general 3d rupture in a planar fault where hf is radiated during gradual changes of rupture velocity at the rupture front local rupture velocity changes are expressed as the divergence of local rupture velocity vectors that are derived from gradients of rupture times from the dynamic model our numerical model of the tottori earthquake indicates that rupture velocity changes are largely induced by barriers locally stronger fault sections across the fault plane and that hf radiation mainly originates within asperities large stress drop regions in areas where the product of dynamic stress drop and rupture velocity changes is maximum we develop a strong ground motion simulation methodology that incorporates hf radiation inferred from a dynamic fault rupture model using this methodology we investigate the hf radiation of the tottori earthquake by inverting observed near source acceleration envelopes of the earthquake our inversion results corroborate that hf radiation originates within asperities and show that significant hf radiation represents no more than a 20 of the total asperity area our results show that the incorporation of a directivity factor on the basis of a well defined physical rupture model to the radiation pattern leads to a significant improvement in fitting of observed ground motions our simulated near source strong ground motions of the tottori earthquake are also able to reproduce the 2 radiation theoretically predicted in 2d dynamic fault rupture models

thermal and pore fluid pressure history on the chelungpu fault at a depth of 1111 m during the 1999 chi chi taiwan earthquake 1 on 20 september 1999 the ms7 6 chi chi earthquake ruptured the chelungpu fault in central taiwan in 2005 the taiwan chelungpu fault drilling project was launched to drill two deep holes holes a and b cutting across the fault plane the heat strength 7 0 c m within a heated layer of 5 mm on the fault at hole a due to frictional faulting is evaluated from the values of shear stress and thermal and mechanical parameters measured from the core samples based on a 1 d heat conduction equation and 2 d faulting model with the values of thermal diffusivity evaluated within a representative temperature range the thermal and pore fluid pressure history at depths 1110 37 1111 34 m in hole a is constructed results show that the peak temperature at the center of the heated layer could have been higher than 1100 c during faulting and temperature rise decreased with increasing distance and time the possible relationships between the temperatures and chemical reactions of clay minerals are discussed in detail in the heated layer pseudotachylites have been formed and quartz plasticity might also have been operative during faulting outside this slip zone the temperature rise was low and thus clay minerals were stable during faulting the evaluated pore fluid pressure is 22 5 mpa this suggests the existence of a suprahydrostatic state in the fault zone during the earthquake indirect evidence of the existence of fluids in the fault zone during faulting is described additionally rock physics is applied to interpret the observations

bayesian inversion of microtremor array dispersion data in southwestern british columbia summary this paper applies bayesian inversion with evaluation of data errors and model parametrization to produce the most probable shear wave velocity profile together with quantitative uncertainty estimates from microtremor array dispersion data generally the most important property for characterizing earthquake site response is the shear wave velocity vs profile the microtremor array method determines phase velocity dispersion of rayleigh surface waves from multi instrument recordings of urban noise inversion of dispersion curves for vs structure is a non unique and non linear problem such that meaningful evaluation of confidence intervals is required quantitative uncertainty estimation requires not only a non linear inversion approach that samples models proportional to their probability but also rigorous estimation of the data error statistics and an appropriate model parametrization this paper applies a bayesian formulation that represents the solution of the inverse problem in terms of the posterior probability density ppd of the geophysical model parameters markov chain monte carlo methods are used with an efficient implementation of metropolis hastings sampling to provide an unbiased sample from the ppd to compute parameter uncertainties and inter relationships nonparametric estimation of a data error covariance matrix from residual analysis is applied with rigorous a posteriori statistical tests to validate the covariance estimate and the assumption of a gaussian error distribution the most appropriate model parametrization is determined using the bayesian information criterion which provides the simplest model consistent with the resolving power of the data parametrizations considered vary in the number of layers and include layers with uniform linear and power law gradients parameter uncertainties are found to be underestimated when data error correlations are neglected and when compressional wave velocity and or density nuisance parameters are fixed in the inversion bayesian inversion of microtremor array data is applied at two sites in british columbia the area of highest seismic risk in canada to study the ability to recover an accurate vs profile in relatively deep and shallow geological settings on the fraser river delta in greater vancouver and in victoria respectively a well resolved vs profile to at least 110 m depth is determined at the fraser river delta site for a power law gradient parametrization at the victoria site a layer with low vs and a weak linear gradient is indicated to 15 18 m depth above much higher velocity material invasive vs measurements from seismic cone penetration testing and or surface to downhole methods are used to assess the reliability of the bayesian microtremor inversion results with excellent agreement obtained at both sites

low p high t metamorphism in the okiep copper district western namaqualand south africa the okiep copper district part of the 1 2 1 0 ga high grade terrane in western namaqualand is composed of a mid proterozoic supracrustal sequence and several pre to post orogenic intrusive suites affected by two high grade events m2a m2b m3 of kibaran and one low grade event m4 of pan african age peak assemblages in quartz bearing pelites are characterized either by garnet cordierite coexisting with sillimanite biotite or by biotite sillimanite garnet a difference controlled by bulk composition and variation in water activities 0 1 0 7 during dehydration melting maximum p t conditions were reached during m2a coevally with the major deformational event d2a and are estimated at 750 820 c and 5 6 kbar a counterclockwise p t path is indicated by regionally occurring pseudomorphs of sillimanite after andalusite and by prograde reaction textures preserved as relics in m2a porphyroblasts two stages of retrograde metamorphism are distinguished m2a garnet cordierite bearing assemblages were retrogressed to biotite sillimanite quartz m2b along discontinuous foliation planes and shear zones d2b retrograde m3 corona assemblages formed at similar p t conditions 580 660 c and 5 8 0 5 kbar to the m2b assemblages but m3 crystallization postdates penetrative d2 deformation intrusion of 1 06 ga granitoids and formation of associated w mo deposits it is concluded that a kibaran high grade metamorphism in the okiep copper district is thermally punctuated and b reaction textures documenting apparent isobaric cooling of this low p high t terrane must be interpreted with caution

magmatic sulfides and au cu ratios in porphyry deposits an experimental study of copper and gold partitioning at 850 c 100 mpa in a haplogranitic melt pyrrhotite intermediate solid solution gold metal assemblage at gas saturation abstract the behavior of copper and gold in the phase assemblage pyrrhotite po intermediate solid solution iss haplogranitic melt gold metal capsule at 850 c 100 mpa and gas saturation ah2o 0 9 has been investigated the results are presented as nernst partition coefficients the partition coefficient dcupo melt 2 6 0 3 103 1 was determined for po and melt in equilibrium with an iss of composition cu 19 1 fe 30 1 s 51 1 2 for gold the partition coefficients are dauiss melt 5 7 2 2 103 1 between iss and melt and daupo melt 140 40 1 between po and melt these imply dauiss po 42 9 1 between iss and po the oxygen fugacity for the experiments log f o 2 13 2 0 3 1 was determined by using the hydrogen sensor technique the sulfur fugacity log f s 2 1 0 0 7 1 was calculated from the composition of po in our experiments melts at iss saturation have cu fe by weight of ca 1 100 the results indicate that crystallization of iss may deplete a melt in gold and crystallization of po may deplete a melt in copper however a melt saturated with iss at a given bulk composition temperature pressure oxygen and sulfur fugacity and feo concentration will have a fixed concentration of cu preventing strong depletion of the melt in cu until iss is fractionated from the melt or changes in environmental conditions destabilize iss a thermodynamic model for the partitioning of cu and au between po and melt in terms of oxygen and sulfur fugacity indicates that dcupo melt and daupo melt may increase greatly with increasing sulfur fugacity and decreasing oxygen fugacity within the po stability field the model also suggests that destabilization of both iss and po relative to magnetite due to changes in oxygen and sulfur fugacities can result in the release of cu and au from the sulfides to the melt

the influence of sediment cover variability on long term river incision rates an example from the peikang river central taiwan 1 this study explores the hypothesis that the relative frequency of rock exposure in the bed of an incising channel can have a first order impact on the long term average erosion rate the 1999 chi chi earthquake in central taiwan generated thousands of landslides along the middle reach of the peikang river sediment from these landslides produced widespread aggradation such that much of the river s bed remains shielded from active bedrock incision we present data that constrain the spatial and temporal variability of sediment cover for the peikang river because the river is undergoing spatially variable holocene bedrock incision 1 10 mm yr it offers a unique natural experiment to test the influence of intermittent sedimentation on long term incision rates published electrical resistivity surveys at seven locations along the river reveal median sediment depth values ranging from 1 9 to 11 5 m the sediment depth correlates inversely with long term incision rate and sediment transport capacity we interpret this as an indication that the frequency of bedrock exposure exerts a major influence on incision along the peikang river

the o okiep copper district namaqualand south africa a review of the geology with emphasis on the petrogenesis of the cupriferous koperberg suite the o okiep copper district is the oldest formal mining area in south africa between 1852 and 2002 the 2 500 km2 area yielded two million tons of copper from 32 mines ranging in ore tonnages from 140 000 to 37 million tons this paper summarizes the calendar of events from the formation of the first primitive crust 1 700 2 000 ma ago to early cambrian times 500 ma ago with particular emphasis on the namaquan grenville orogeny notably the o okiepian episode 1 180 1 210 ma ago of alpine type folding regional granite plutonism and granulite facies metamorphism and the klondikean episode 1 020 1 040 ma ago of open and tight folding and the intrusion of the rietberg granite and the koperberg suite almost all of the copper in the o okiep district occurs in the koperberg suite of which there are 1 700 small bodies that constitute 0 7 of the outcrop area the suite comprises jotunite anorthosite biotite diorite and hypersthenic rocks ranging from leuconorite to hypersthenite and it is one of only two world examples of economic copper mineralization in rocks of the anorthosite charnockite kindred the second example is caraiba brazil high isr and low end for a 1 030 ma intrusion age and high 2 of 10 1 for koperberg rock types indicate a crustal progenitor for the suite and the presence of jotunite suggests a subducted crustal source at ca 40 50 km depth the magmatic sulphide paragenesis in the koperberg suite is chalcopyrite pyrrhotite narrap type ore that in a number of ore bodies has been inverted under upper amphibolite facies conditions to bornite ti free magnetite carolusberg type ore meteoric fluids resulted in supergene cu enrichment in koperberg bodies to 500 m below the pre nama peneplane and lower greenschist facies metamorphism 500 570 ma ago is reflected by inter alia hoits type ore bearing second generation bornite chalcopyrite covellite chalcocite

simulation of the frictional stick slip instability a lattice solid model capable of simulating rock friction fracture and the associated seismic wave radiation is developed in order to study the origin of the stick slip instability that is responsible for earthquakes the model consists of a lattice of interacting particles in order to study the effect of surface roughness on the frictional behavior of elastic blocks being rubbed past one another the simplest possible particle interactions were specified corresponding to radially dependent elastic brittle bonds the model material can therefore be considered as round elastic grains with negligible friction between their surfaces although breaking of the bonds can occur fracturing energy is not considered stick slip behavior is observed in a numerical experiment involving 2d blocks with rough surfaces being rubbed past one another at a constant rate slip is initiated when two interlocking asperities push past one another exciting a slip pulse the pulse fronts propagate with speeds ranging from the rayleigh wave speed up to a value between the shear and compressional wave speeds in agreement with field observations and theoretical analyses of mode ii rupture slip rates are comparable to seismic rates in the initial part of one slip pulse whose front propagates at the rayleigh wave speed however the slip rate is an order of magnitude higher in the main part of pulses possibly because of the simplified model description that neglected intrinsic friction and the high rates at which the blocks were driven or alternatively uncertainty in slip rates obtained through the inversion of seismograms particle trajectories during slip have motions normal to the fault indicating that the fault surfaces jump apart during the passage of the slip pulse normal motion is expected as the asperities on the two surfaces ride over one another the form of the particle trajectories is similar to those observed in stick slip experiments involving foam rubber blocks bruneet al 1993 additional work is required to determine whether the slip pulses relate to the interface waves proposed by brune and co workers to explain the heat flow paradox and whether they are capable of inducing a significant local reduction in the normal stress it is hoped that the progressive development of the lattice solid model will lead to realistic simulations of earthquake dynamics and ultimately provide clues as to whether or not earthquakes are predictable

generation of new cracks accompanied by the dynamic shear rupture propagation of the 2000 tottori japan earthquake the 2000 tottori japan earthquake caused fracture zones of surface rupture at some places away from the trace of the main causative fault in order to explain this observation the 3d dynamic rupture process of the 2000 tottori japan earthquake was simulated the attractive feature of the problem under consideration is the possibility of introducing internal new cracks that propagate under tensile stress as a consequence of the dynamic process of shear slip propagation the discrete element method was used to solve this problem because it can introduce internal tensile cracks for the shear rupture propagation the simple slip weakening model was used as a friction law on the fault the new tensile cracks occur following the classical griffith theory when the critical value of tensile fracture surface energy has been reached the first step to solve the problem was the estimation of the dynamic parameters such as stress drop strength excess and critical slip which were recov ered from the results of waveform inversion in the second step a shear dynamic rupture process was simulated assuming that shear slip occurs only on the pre existing fault and the tensile stress concentration resulting from shear slip causes the new cracks that propagate away from the pre existing fault the results which are consistent with the observations show a free surface rupture caused by the new cracks and the development of a flowerlike structure springing from the borders of the pre existing fault and main asperity

dynamic rupture modelling of the 1999 duzce turkey earthquake the dynamic rupture process and near source ground motion of the 1999 mw 7 1 duzce earthquake are simulated the fault rupture is governed by the slip weakening friction model coupled to a three dimensional viscoelastic wave equation the problem is solved numerically by a 3 d dynamic rupture code that uses a generalized finite difference method initial parameterization of stress drop delta tau and strength excess s text e for dynamic rupture calculations is obtained from the slip velocity distribution of a kinematic waveform inversion ki model by solving the elastodynamic equation with the kinematic slip as a boundary condition using the kinematic slip distribution and observed ground motion as constraints a trial and error procedure was followed to define the stress parameterization preferred model describes the source in terms of stress with three asperities located respectively at the deep middle and shallow and strong barriers between asperities s text e is as high as 19 mpa at barriers between the three asperities and delta tau is maximum about 40 mpa at the deepest asperity this heterogeneity in stress distribution produces abrupt jumps in rupture velocity exhibiting locally apparent rupture speed exceeding the p wave velocity at the borders between barriers and asperities due to sharp changes of fault strength and stress drop at those areas overall consistent with other studies the rupture propagation is dominated by supershear speed toward the eastern asperities and at shallow surface simulated surface rupture at the eastern fault is consistent with other studies nevertheless the western shallower parts did not rupture during the simulation suggesting that those regions may have already broken during the 1999 kocaeli event which occurred three months earlier ground motion simulation catches the major characteristics of the observed waveforms distribution of simulated peak ground velocity pgv in low frequency 0 1 0 5 hz inside the study area reveals the propagation pattern on the field with pgv reaching to 1 2 and 2 2 m s in the ns and ew components respectively

accounting for limited spatial aperture in the waveform inversion of rho tau seismograms the finite length of seismic arrays results in smeared estimates of the plane wave decomposition of the recorded wave field the smearing is a fundamental property of plane wave decomposition it can be reduced but not eliminated if not accounted for this smearing can have a significant effect upon the waveform inversion of plane wave seismograms this paper illustrates the effects of limited spatial aperture on the plane wave decomposition and demonstrates that these truncation artifacts can be described by a linear ray parameter dependent filter experiments with synthetic data indicate that including the effects of limited aperture in the forward model of an iterative inversion produces a stable inversion result without significantly reducing the information content of the data the method is illustrated with synthetic data derived for an earth consisting of elastic isotropic flat layers

earthquakes on dipping faults the effects of broken symmetry dynamic simulations of earthquakes on dipping faults show asymmetric near source ground motion caused by the asymmetric geometry of such faults the ground motion from a thrust or reverse fault is larger than that of a normal fault by a factor of 2 or more given identical initial stress magnitudes the motion of the hanging wall is larger than that of the footwall in both thrust reverse and normal earthquakes the asymmetry between normal and thrust reverse faults results from time dependent normal stress caused by the interaction of the earthquake generated stress field with earth s free surface the asymmetry between hanging wall and footwall results from the asymmetric mass and geometry on the two sides of the fault

rupture dynamics on a bimaterial interface for dipping faults dip slip faulting may juxtapose different geologic materials with differ ent properties such that a strong material contrast will naturally tend to form both the material contrast across a fault and dip slip motion on a nonvertical fault lead to normal stress variations during earthquake rupture this normal stress variation will significantly affect dynamic rupture propagation to demonstrate this we model dynamic rupture propagation on two dimensional 2d reverse and normal faults 30 45 and 60 dipping with 20 material contrasts for predominantly up dip rupture propagation we find that normal stress variations due to the free surface and material contrast can either reinforce or counteract each other depending on the configuration for reverse faults we find a larger strength drop for a more com pliant hanging wall and a lower strength drop for a more compliant footwall for normal faults we find a larger strength drop for a more compliant footwall and a lower strength drop for a more compliant hanging wall for both reverse and normal faults ground motion will be more symmetric between the hanging wall and footwall with compliant material on the footwall and more asymmetric if more compliant materials are on the hanging wall our results have important implications for the dynamics of crustal and perhaps subduction zone earthquake faulting where strong bimaterial contrasts across dipping faults are possible in continental settings reverse faulting will tend to advect rigid materials from greater depth onto the hanging wall such that the effects of fault dip and material contrast will counteract one another in subduction zones the hanging wall is likely to be more compliant and hence the material and geometric effects may reinforce one another

large rock avalanches triggered by the m 7 9 denali fault alaska earthquake of 3 november 2002 the moment magnitude m 7 9 denali fault alaska earthquake of 3 november 2002 triggered thousands of landslides primarily rock falls and rock slides that ranged in volume from rock falls of a few cubic meters to rock avalanches having volumes as great as 20 10 6 m 3 the pattern of landsliding was unusual the number and concentration of triggered slides was much less than expected for an earthquake of this magnitude and the landslides were concentrated in a narrow zone about 30 km wide that straddled the fault rupture zone over its entire 300 km length despite the overall sparse landslide concentration the earthquake triggered several large rock avalanches that clustered along the western third of the rupture zone where acceleration levels and ground shaking frequencies are thought to have been the highest inferences about near field strong shaking characteristics drawn from interpretation of the landslide distribution are strikingly consistent with results of recent inversion modeling that indicate that high frequency energy generation was greatest in the western part of the fault rupture zone and decreased markedly to the east d 2005 elsevier b v all rights reserved

determination of constitutive relations of fault slip based on seismic wave analysis constitutive laws define the boundary conditions on fault plane and govern many aspects of earthquake failure although several constitutive laws have been formulated based on laboratory rock experiments and applied to theoretical studies in various fields no actual relation during a natural earthquake has been determined the 1995 kobe earthquake is suitable for detailed kinematic analysis and this enables the first evaluation of constitutive relations for a natural earthquake in this study we determine spatiotemporal slip distribution on an assumed fault plane of the 1995 kobe earthquake by waveform inversion and then solve elastodynamic equations using a finite difference method to determine the stress distribution and constitutive relations on the fault plane an inversion method based on bayes theorem is employed to obtain a spatiotemporal slip distribution and enables us to ensure the objective uniqueness of the solution with numerous parameters and smoothing constraints this slip distribution is then used as part of the boundary condition in the finite difference calculation the time histories of slip and shear stress obtained then provide a constitutive relation at each point on the fault plane they show slip weakening relations almost everywhere on the fault plane while slip rate dependency is not clear the slip weakening behavior has a clear depth dependency indicating that the slip weakening rate d du is smaller in the shallow crust than that in the deep crust this may be associated with the paucity of shallow seismicity observed in the source region of this earthquake as reported for many mature fault systems

dynamics of thrust faulting 2d lattice model particle motions in a foam rubber model of shallow angle thrust faulting show many features different from those commonly assumed in dislocation models of subduction thrusts brune 1996 as a complement to a physical foam rubber experiment we have carried out dynamic simulation using a 2d lattice numerical model the model is constructed as a triangular block sliding over a rectangular elastic block it consists of a 2d set of particles interacting with each other by nonlinear hooke s forces and obeying newton s equations of motion rough surfaces are introduced on the contact plane of the two blocks to simulate realistic friction the numerical simulations demonstrate several key features of thrust faulting including stick slip fault opening and strong breakout and shaking at the hanging wall toe the wedge shaped tip of the outcropping hanging wall block of the thrust fault all consistent with the foam rubber experiments the stick slip motion shows an approximate time and slip repeatable behavior each slip event is characterized by a self healing pulse associated with fault opening and frictional locking the rupture pulse propagates steadily along the fault when rupture reaches the toe of the fault outcrop the hanging wall breaks away from the foot wall and creates a large opening vibration of the hanging wall the peak acceleration observed at the hanging wall toe of the fault outcrop is about 3 to 4 times the peak acceleration in the center part of the fault and about 2 to 3 times the motion of the foot wall such a large increase in peak acceleration at the toe is caused mainly by multiply reflecting stress waves trapped in the wedge shaped hanging wall of the fault the strong asymmetry of the particle velocity between the hanging wall and foot wall is an important feature of the results consistent with the foam rubber model but different from standard dislocation models this dynamic result illustrates the important effects of thrust faulting geometry on fault slip and ground motion

three dimensional dense strong motion waveform inversion for the rupture process of the 1999 chi chi taiwan earthquake 1 we inverted the high resolution spatiotemporal slip distribution of the 21 september 1999 chi chi taiwan earthquake utilizing data from densely distributed island wide strong motion stations for a three dimensional 3 d fault geometry and 3 d green s functions calculations based upon parallel nonnegative least squares inversion the 3 d fault geometry consistent with high resolution reflection profile is determined from gps inversion and aftershocks distribution this 3 d fault model presents the dip angle gradually becoming shallower from south to north along the fault and near flat at the deeper portion of the fault the 3 d green s functions are calculated through numerical wavefield simulation from three dimensional heterogeneous velocity structure derived from tomography studies the green s functions show significant azimuthal variations and suggest the necessity of lateral heterogeneity in velocity structure considering complex fault geometry and green s functions in full 3 d scale we invert the spatial temporal slip distribution of the 1999 chi chi earthquake using the best available and most densely populated strong motion waveform data we perform the inversion under a parallel environment utilizing multiple time window to manage the large data volume and source parameters results indicate that most slip occurred at the shallower portion of the fault above the decollement two major asperities are found one in the middle of the fault and another one at the northern portion of the fault near the bend in the fault trace the slip in the southern portion of the fault shows a relatively low slip rate with longer time duration while the slip in the northern portion of the fault shows a large slip rate with shorter time duration the synthetics explain the observations well for the island wide distributed strong motion stations this comprehensive study emphasizes the importance of realistic fault geometry 3 d green s functions and parallel inversion technique in correctly accounting for both the detailed source rupture process and its relationship with the strong ground motion of this intense earthquake

fault dynamic rupture simulation of the hypocenter area of the thrust fault of the 1999 chi chi taiwan earthquake a 2d discrete element model was employed to simulate the rupture propagation and near source ground motion in the epicentral area of the 1999 chi chi taiwan earthquake the observations show that the hanging wall side is characterized by larger particle motions than the footwall side the simulation results reproduce the main features of the recorded ground motion and show that the particle velocity on the hanging wall side and on the footwall side are symmetric in the deeper fault region however as the crack approaches the free surface the hanging wall side is characterized by larger particle motions than the footwall side these results suggest that the difference in the particle motion on the hanging wall and on the footwall is due mainly to the asymmetric geometry of hanging wall and footwall thus the model used leads to good approximations in the vicinity of the epicenter

a rupture model for the 1999 chi chi earthquake from inversion of teleseismic data using the hybrid homomorphic deconvolution method this study investigates the kinematics of the rupture process of the ml 7 3 chi chi taiwan earthquake on september 21 1999 by applying the proposed hybrid homomorphic deconvolution method to deconvolve teleseismic broadband p wave displacement recordings of the earthquake this study derives the apparent source time functions astfs at ten stations located around the epicenter to further characterize the fault the kinematic history of the rupture was inverted from astfs using a genetic algorithm coupled with nonlinear iterative technique the calculated asfts reveal that the total rupture event lasted for approximately 27 s static slip distribution images indicate that most slip occurred at shallower portions of the fault plane especially 20 55 km north of the epicenter the maximum slip reached 20 m at 45 km north of the epicenter and the average slip throughout the observed rupture area was approximately 2 m large asperities on the fault appeared at 25 35 km and 40 50 km north of the hypocenter and coincided with relatively high rupture velocity this suggests that the earthquake s energy may have been released quickly the rupture velocity decreased upon encountering an asperity and increased again after passing the asperity this implies that the rupture required more time to overcome the resistances of the asperities the maximum rupture velocity was 3 8 km s while the average rupture velocity was approximately 2 2 km s the rise time distribution suggests that larger slip amplitudes generally correspond to shorter rise times on the subfaults

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

numerical study of ground motion differences between buried rupturing and surface rupturing earthquakes recent ground motion observations suggest that surface rupturing earth quakes generate weaker near fault ground motion than buried earthquakes this dif ference is significant in the period range of 0 3 3 sec contributing factors to this phenomenon may include the effect of fault zone weakness at shallow depth on rup ture dynamics and rupture directivity during earthquakes we present results from numerical experiments of spontaneous dynamic rupture and near source ground motion simulations of surface rupturing and buried earth quakes and discuss mechanisms for the observed ground motion differences the surface rupturing earthquake is modeled with a shallow zone of 5 km thickness con taining areas of negative stress drop within the framework of the slip weakening fric tion model and lower rigidity surface rupturing models with this weak zone generate lower amplitude ground velocity than do models without this modification observed ground motion differences between surface and buried events are qual itatively reproduced by imposing higher stress drop in the buried earthquakes than in the surface earthquakes combined with introducing a deeper rupture initiation for buried rupture enhancing upward rupture directivity effects for the latter events in the context of our simplified model parameterization then the observed differences in ground motion could arise from combined effects of relative weakness of the shal low layer of faults the relatively larger stress drops of buried ruptures and a tendency of near fault sites to record strong upward directivity from buried ruptures

can economic porphyry copper mineralization be generated by a typical calc alkaline melt numerical simulation of chlorine and copper partitioning between a crystallizing melt and exsolving aqueous fluids indicates that typical calc alkaline magmas contain sufficient copper chlorine and water to produce economic porphyry copper mineralization neither an elevated copper content in the magma nor an additional large volume of magma are required to provide metals or volatiles the most important variables that determine the volume of melt necessary to produce sufficient copper are the degree of compatible behavior displayed by copper the ratio of initial water in the melt to the water saturation level and the initial chlorine water ratio of the melt the absolute values for initial water in the melt and water content at saturation are relatively unimportant in determining the required melt volume the bulk salinity of the exsolved fluid may vary from 2 0 wt nacl to saturation levels 84 wt nacl at 700 c indicating that boiling is not necessary to produce high salinity brines at appropriate p t xnacl conditions the magmatic aqueous fluid separates into a saline liquid which transports most of the copper and a low salinity vapor the salinities of the two immiscible phases are governed by the p t conditions while the bulk fluid salinity determines the mass fractions of liquid and vapor formed pressure quenching causes rapid crystallization of the aplitic groundmass in porphyritic rocks associated with copper mineralization and significantly reduces the amount of chlorine and copper partitioning to the aqueous fluid this results in abrupt and possibly large reductions in fluid salinity and causes copper to become concentrated in the melt as copper is transported from the melt by the earliest exsolving fluids in deep 2 0 kbar systems and by late exsolving fluids in shallow 0 5 kbar systems the relative timing of pressure quenching aplite formation and fluid transport of copper from the melt can vary significantly in systems produced under different confining pressures model results incorporating petrologic constraints determined for yerington nevada are in good agreement with observed mineralization