ion microprobe analysis of oxygen isotopes in garnets of complex chemistry abstract accurate ion microprobe analysis of oxygen isotope ratios in garnet is possible if appropriate standards are employed to correct for instrumental bias a component of which depends on the cation chemistry of the analyzed mineral in this study 26 garnet standards including 14 new standards that span the compositional range of pyrope almandine grossular spessartine and andradite were analyzed repeatedly by ion microprobe to develop a new method of correcting for instrumental bias in garnets all analyses were normalized to a single master garnet standard uwg 2 before bias from cation composition was considered bias due to cation composition in garnet was found to correlate with grossular content in pyralspite garnets and with andradite in ugrandite garnets bias is correlated with molar volume in garnets of all compositions in this study although this correlation is suitable as a correction scheme for bias a more accurate correction scheme based on the grossular and andradite compositions of garnet is proposed this method reproduces the bias of all but one standard to within a range of 0 4 an accuracy that is on the same order as the reproducibility 0 3 2 s d of the master garnet standard uwg 2 but that remains an independent source of error the new correction scheme is used to successfully reproduce laser fluorination analyses along a traverse of a polymetamorphic zoned skarn garnet from the adirondack mountains while previous analyses were at the mm scale the new data resolve a gradient of 18 o of 2 1 over 16 m if experimentally derived diffusion coefficients are correct these new results show that granulite facies metamorphism was significantly faster than previously assumed and the thermal peak was less than 5 myr

evidence for widespread nonlinear strong ground motion in the mw 6 9 loma prieta earthquake we exploit 55 repeating microearthquake sequences on the san andreas fault just south of the rupture zone of the 1989 m w 6 9 loma prieta earthquake to search for time dependent properties of the earth s crust using moving window waveform cross correlation we identify clear and systematic delays as large as 20 msec for the direct s wave and exceeding 50 msec in the early s wave coda following the loma prieta mainshock others have also identified phase delays velocity reductions associated with damaging earthquakes and they have suggested a myriad of possible causal mechanisms here we present new evidence for a mechanism to produce velocity reductions correlated in time and space with an earthquake a strong correlation between the spatial patterns of s delays and the intensity of strong ground motion in the loma prieta earthquake suggests that physical damage the formation or growth of cracks during strong ground motion to the earth s shallow crust is responsible for the observed velocity reductions the strong spatial variability in s delays over short distances and the strong correlation of the magnitude of delays with surface geology indicate that the phase delays accumulate primarily near the receiver the effect is stronger at stations on young soft rocks than at stations on old hard rock disproportionately larger s coda delays than p coda delays suggest that the cracks formed by the strong shaking are fluid filled in the 10 years after loma prieta the initial increase in travel times reduces logarithmically with respect to time often back to the premainshock levels we attribute this behavior to the same slow dynamic healing observed in laboratory studies of the recovery of materials from transient nonlinear strain manuscript received 14 january 2004

temporal changes of shallow seismic velocity around the karadere duzce branch of the north anatolian fault and strong ground motion we analyze temporal variations of seismic velocity along the karadere duzce branch of the north anatolian fault using seismograms generated by repeating earthquake clusters in the aftershock zones of the 1999 mw7 4 izmit and mw7 1 duzce earthquakes the analysis employs 36 sets of highly repeating earthquakes each containing 4 18 events the events in each cluster are relocated by detailed multi step analysis and are likely to rupture approximately the same fault patch at different times the decay rates of the repeating events in individual clusters are compatible with the omori s law for the decay rate of regional aftershocks a sliding window waveform cross correlation technique is used to measure travel time differences and evolving decorrelation in waveforms generated by each set of the repeating events we find clear step like delays in the direct s and early s coda waves sharp seismic velocity reduction immediately after the duzce main shock followed by gradual logarithmic type recoveries a gradual increase of seismic velocities is also observed before the duzce main shock probably reflecting post seismic recovery from the earlier izmit main shock the temporal behavior is similar at each station for clusters at various source locations indicating that the temporal changes of material properties occur in the top most portion of the crust the effects are most prominent at stations situated in the immediate vicinity of the recently ruptured fault zones and generally decrease with normal distance from the fault a strong correlation between the co seismic delays and intensities of the strong ground motion generated by the duzce main shock implies that the radiated seismic waves produced the velocity reductions in the shallow material

spurious velocity changes caused by temporal variations in ambient noise frequency content ambient seismic noise cross correlations are now being used to detect temporal variations of seismic velocity which are typically on the order of 0 1 per cent at this small level temporal variations in the properties of noise sources can cause apparent velocity changes for example the spatial distribution and frequency content of ambient noise have seasonal variations due to the seasonal hemispherical shift of storms here we show that if the stretching method is used to measure time shifts then the temporal variability of noise frequency content causes apparent velocity changes due to the changes in both amplitude and phase spectra caused by waveform stretching with realistic seasonal variations of frequency content in the los angeles basin our numerical tests produce about 0 05 per cent apparent velocity change comparable to what meier et al observed in the los angeles basin we find that the apparent velocity change from waveform stretching depends on time windows and station pair distances and hence it is important to test a range of these parameters to diagnose the stretching bias better understanding of spatiotemporal noise source properties is critical for more accurate and reliable passive monitoring

chemical composition genesis and exploration implication of garnet from the hongshan cu mo skarn deposit sw china abstract in this study we present new mineral chemical data on the garnet from the hongshan cu mo deposit one of the largest skarn deposits in the sanjiang tethyan tectonic domain in sw china the aims are to unravel the formation mechanism of the oscillatory zoned garnet at hongshan and to explore possible applications using garnet trace element to distinguish different types of skarn deposits two generations of garnets i e poorly zoned garnet i grt i and the well zoned garnet ii grt ii are identified from the endoskarn and exoskarn at hongshan based on field and petrographic observations epma and la icp ms analyses show that grt i contains a narrow compositional range adr40 07 61 25 grs36 65 57 08 and chondrite normalized hree enriched and lree depleted patterns with minor positive eu anomalies in contrast grt ii shows a wide compositional range adr27 78 67 53 grs30 67 70 92 to almost pure andradite adr94 41 99 99 grs0 00 4 21 with interlayered al rich and fe rich zones in grt ii its al rich zone is chemically similar to grt i whereas its fe rich zone exhibits chondrite normalized lree enriched and hree depleted patterns with distinct positive eu anomalies the positive ree3 vs mg correlations and the poor ree3 vs y and ca correlations altogether indicate that the ree3 incorporated into garnet was co influenced by the menzerite type substitution mechanism c a 2 1 v i i i r e e 3 1 v i i i a l 3 1 v i m g 2 1 v i fluid chemistry and the physicochemical conditions of precipitation the higher u contents and hree enriched patterns of grt i suggest that it was formed under a relatively reducing and near neutral ph condition varying u contents and ree patterns across different oscillatory zones indicate that grt ii was probably formed under alternating physicochemical fluctuations led by repeating crack seal cycles in the hydrothermal system besides chemical data compilation suggests that the garnet from different types of skarn deposits has different compositions and can be used as mineral prospecting tools we suggested that discrimination plots such as eu vs v and ce vs u can distinguish cu skarn deposit from other skarn deposit types whilst the u vs w plot can discriminate between cu w w sn and w mo skarn deposits

stress based aftershock forecasts made within 24 h postmain shock expected north san francisco bay area seismicity changes after the 2014 m 6 0 west napa earthquake we calculate stress changes resulting from the m 6 0 west napa earthquake on north san francisco bay area faults the earthquake ruptured within a series of long faults that pose significant hazard to the bay area and we are thus concerned with potential increases in the probability of a large earthquake through stress transfer we conduct this exercise as a prospective test because the skill of stress based aftershock forecasting methodology is inconclusive we apply three methods 1 generalized mapping of regional coulomb stress change 2 stress changes resolved on uniform california earthquake rupture forecast faults and 3 a mapped rate state aftershock forecast all calculations were completed within 24 h after the main shock and were made without benefit of known aftershocks which will be used to evaluative the prospective forecast all methods suggest that we should expect heightened seismicity on parts of the southern rodgers creek northern hayward and green valley faults

implications of fault constitutive properties for earthquake prediction the rate and state dependent constitutive formulation for fault slip characterizes an exceptional variety of materials over a wide range of sliding conditions this formulation provides a unified representation of diverse sliding phenomena including slip weakening over a characteristic sliding distance dc apparent fracture energy at a rupture front time dependent healing after rapid slip and various other transient and slip rate effects laboratory observations and theoretical models both indicate that earthquake nucleation is accompanied by long intervals of accelerating slip strains from the nucleation process on buried faults generally could not be detected if laboratory values of dc apply to faults in nature however scaling of dc is presently an open question and the possibility exists that measurable premonitory creep may precede some earthquakes earthquake activity is modeled as a sequence of earthquake nucleation events in this model earthquake clustering arises from sensitivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and assigns physical interpretation to aftershock parameters the seismicity formulation predicts large changes of earthquake probabilities result from stress changes two mechanisms for foreshocks are proposed that describe observed frequency of occurrence of foreshock mainshock pairs by time and magnitude with the first mechanism foreshocks represent a manifestation of earthquake clustering in which the stress change at the time of the foreshock increases the probability of earthquakes at all magnitudes including the eventual mainshock with the second model accelerating fault slip on the mainshock nucleation zone triggers foreshocks

passive monitoring of anisotropy change associated with the parkfield 2004 earthquake 1 we investigate temporal variations in the polarization of surface waves determined using ambient seismic noise cross correlations between station pairs at the time of the mw 6 0 parkfield earthquake of september 28 2004 we use data recorded by the high resolution seismic network s 3 component seismometers located along the san andreas fault our results show strong variations in azimuthal surface wave polarizations for the paths containing station varb one of the closest stations to the san andreas fault synchronous with the parkfield earthquake concerning the other station pair only smooth temporal variations of are observed two principal contributions to these changes in are identified and separated they are 1 slow and weak variations due to seasonal changes in the incident direction of seismic noise and 2 strong and rapid rotations synchronous with the parkfield earthquake for paths containing station varb strong shifts in are interpreted in terms of changes in crack induced anisotropy due to the co seismic rotation of the stress field because these changes are only observed on paths containing station varb the anisotropic layer responsible for the changes is most likely localized around varb in the shallow crust these results suggest that the polarization of surface waves may be very sensitive to changes in the orientations of distributed cracks and that implementation of our technique on a routine basis may prove useful for monitoring stress changes deep within seismogenic zones

effects of cation substitutions in garnet and pyroxene on equilibrium oxygen isotope fractionations high grade metamorphic rocks were used to explore oxygen isotope fractionations between pyroxene and garnet and to investigate the effects on fractionation factors of the cation substitutions fe3 al 1 and ca fe mg 1 recrystallized granulite facies 725 c wollastonite ores from the northern adirondack highlands contain essentially only the minerals clinopyroxene a di hd solid solution garnet a grs adr solid solution wollastonite and exhibit a systematic dependence of measured fractionations on the fe3 content of calcic garnet cpx cagrt 0 14 0 12 0 78 0 20 xadr and wo cagrt 0 15 0 22 0 57 0 33 xadr in eclogites formed at t 650 c measured compositions of ca poor garnet and omphacite combined with experimental data indicate that ca poor fe rich garnet is enriched in 18o compared to both diopside and grossular extrapolating to 1000 k alm di c 0 2 and alm grs c 0 5 orthopyroxene and clinopyroxene from gore mountain new york show a constant fractionation that is independent of rock type as expected if they have the same closure temperature these data imply opx cpx c 0 7 at 1000 k measured fractionations among ca poor garnet orthopyroxene clinopyroxene and hornblende in the gore mountain rocks further indicate an 18o enrichment in ca poor garnet over grs c 0 5 at 1000 k the new measurements are indistinguishable from expected equilibrium values based on experiments for the minerals enstatite diopside grossular wollastonite and feldspar but consistently indicate a significant isotope effect for the simple octahedral cation substitutions fe3 al 1 grs vs adr and ca fe mg 1 ca poor garnet vs grs opx vs cpx neither cation substitution has been directly investigated for its effect on 18o 16o fractionation with experiments in silicates chemical characterization of minerals is required prior to petrological interpretation of oxygen isotope trends

postseismic deformation induced by brittle rock damage of aftershocks 1 large earthquakes are commonly followed by abundant aftershocks that are densely located around the coseismic rupture zone laboratory experiments indicate that microscopic brittle rock failures acoustic emission are associated collectively with a macroscopic damage related inelastic relaxation utilizing basic relations between local brittle failures and gradual inelastic strain in a viscoelastic damage rheology model we develop connections between aftershock decay rates and the aftershocks induced component of geodetic deformation the discussed mechanism is relevant for postseismic relaxation produced by sources located within the seismogenic zone and especially in regions that overlap locations of high aftershocks activity assuming the omori utsu decay rate for aftershocks we find that the temporal decay of the damage related postseismic relaxation follows a generalized power law relation with the standard omori utsu law as a limit case the results provide a way for estimating the separate contributions to observed postseismic displacements that stem from brittle failures in the seismogenic zone aftershocks and other aseismic processes using the obtained theoretical expectations we analyze postseismic displacements measured by gps stations around the north anatolian fault 3 months following the 1999 m7 4 izmit earthquake we find that the observed postseismic displacements decay slower than the aftershock seismicity based on our theoretical results we conclude that up to 50 of the measured surface displacements at near fault sites can be attributed to aftershock induced inelastic deformation in the seismogenic zone the remainder postseismic deformation can generally be explained by relaxation in the deeper ductile substrate

topographic slope as a proxy for seismic site conditions and amplification we describe a technique to derive first order site condition maps directly from topographic data for calibration we use global 30 arc sec topographic data and v s 30 measurements here v s 30 refers to the average shear velocity down to 30 m aggregated from several studies in the u s as well as in taiwan italy and australia v s 30 values are correlated against topographic slope to develop two sets of parameters for deriving v s 30 one for active tectonic regions where topographic relief is high and one for stable shields where topography is more subdued by taking the gradient of the topography and choosing ranges of slope that maximize the correlation with shallow shear velocity observations we can recover to first order many of the spatially varying features of sitecondition maps developed for california our site condition map for the low relief mississippi embayment also predicts the bulk of the v s 30 observations in that region despite rather low slope ranges we find that maps derived from the slope of the topography is often well correlated with other independently derived regional scale site condition maps but the latter maps vary in quality and continuity and subsequently also in their ability to match observed v s 30 measurements contained therein alternatively the slope based method provides a simple approach to uniform site condition mapping

physical modelling of deformation in the tasman orogenic zone abstract structural vergence within the western subprovince of the lachlan fold belt is towards the hinterland rather than the foreland in contrast to many well known orogenic belts high angle reverse faults and upright folds verge eastwards away from the australian craton towards the inferred centre of orogenic and magmatic activity we designed a series of analogue models to test the anomalous vergence in the western lachlan fold belt particularly the interaction of a stable australian craton with tasman line geometry interacting with weaker oceanic or transitional lithospheric material we found consistently that vergence direction in the models was towards the hinterland not the foreland as in the western lachlan fold belt irrespective of the way the model was deformed strength gradients between the oceanic and cratonic lithosphere control the deformation patterns an important result of the models is that they demonstrate that fold belts with different vergences can be generated without the requirement of subducting oceanic lithosphere

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

in situ la icp ms trace element analyses of scheelite and wolframite constraints on the genesis of veinlet disseminated and vein type tungsten deposits south china abstract veinlet disseminated and vein type tungsten deposits are important tungsten resources in south china and show remarkable diversity in dominant tungsten minerals to better understand their genesis scheelite from the shimensi veinlet disseminated deposit and wolframite from the xihuashan and piaotang vein type deposits were selected to conduct in situ laser ablation inductively coupled plasma mass spectrometry trace element analyses the shimensi tungsten mineralization occurs in intensively altered granitic rocks and is characterized by scheelite two generations of scheelite in a single grain can be identified by cathodoluminescence cl imaging the early scheelite dark domains in cl images is characterized by nearly flat chondrite normalized ree ree n patterns with significantly negative eu anomalies whereas the late one bright domains in cl images shows light rare earth element lree enriched ree n patterns and obviously positive eu anomalies the former has higher ree na nb and ta and lower sr contents than the latter the xihuashan and piaotang wolframite quartz veins are developed in greisenized granite type i and metasedimentary rocks type ii both types of wolframite show lree depleted patterns but type i exhibits strongly negative eu anomalies and type ii positive eu anomalies type i contains higher ree nb and ta concentrations and lower feo mno ratios than type ii variations of eu anomalies and trace element compositions in both scheelite and wolframite can be used to decipher the origin and processes of tungsten mineralization both the early scheelite and wolframite type i display significantly negative eu anomalies and have high ree nb and ta contents suggesting that the initial ore forming fluids were of magmatic origin precipitation of tungsten minerals and alteration would effectively modify the composition of ore forming fluids deposition of the early tungsten minerals would lower ree nb and ta in the mineralizing fluids leading to depletion of these elements in the late ones although both the type i and ii wolframite have different ree contents and eu anomalies they show similar left dipped ree n patterns implying that compositional variation of fluids is likely driven by crystallization of wolframite during the processes of fluid evolution in contrast the elevated lree hree heavy rare earth element ratios eu eu n eu n values and sr abundances in the late scheelite are possibly caused by the decomposition of plagioclase and k feldspar alteration plays an important role in the formation of veinlet disseminated scheelite deposits it can be concluded that vein type wolframite mineralization is mainly formed by filling and that veinlet disseminated scheelite mineralization is associated with metasomatism

the geochemistry of zoning in skarn minerals at the king island dolphin mine trends of chemical zoning in crystals of garnet pyroxene scheelite and amphibole in 34 samples collected from the pluton9s contact updip to 500 m from the contact in the main ore horizon at the king islnd scheelite dolphin mine show systematic variations garnet cores up to 400 m from the contact are the most andradite rich reaching values of 98 mole percent nearest the contact andradite values decrease systematically both for a particular part of the garnet crystals away from the contact and across individual grains to the outer edges the mole percent andradite in core and outer core zones decreases to the 500 m mark while in the midsection and edge zones the values decrease to 400 m and then increase a similar relationship occurs in pyroxenes which nearest the contact contain hedenbergite values of 98 mole percent scheelite occurring as inclusions in garnet reach values of scheelite 65 powellites 34 for core zones nearest the pluton while scheelite interstitial to garnet have maximum values of scheelite 72 powellite 27 powellite contents decrease both toward the edges of individual grains and along the traverse to the 400 m mark where a reversal of trend occurs continuing to 500 m from the contact amphibole compositions show a linear decrease of the ratio fe super 2 fe super 2 mg mn from 98 nearest the contact to 88 at 390 and then decreasing abruptly to 65 at 500 m fluid inclusion filling temperatures vary systematically in time and distance from the pluton with a maximum near 800 degrees c for garnet midsections nearest the pluton to temperatures as low as 180 degrees c for interstitial calcite and quartz the salinities decrease from near 65 weight percent total dissolved salts in the early formed minerals i e garnet nearest the pluton to less than 3 weight percent for later formed minerals farthest from the contact i e calcite these decreases occur out from the contact and progressively toward the end of the paragenetic sequence scheelite initially crystallized at higher temperatures but interstitial scheelite precipitation occurred from a concentrated na k ca cl solution approximately 10 molal total dissolved salts at temperatures of approximately 500 degrees c at the pluton9s contact to 300 degrees c at a distance of 500 m from the contact chemical variations of fluid compositions for all but garnet core zones beyond 400 m from the contact occurred due to mixing of solutions derived from the northern boundary fault the interface between solutions which have permeated through and reacted with the developing skarn unit and those derived from the fault marks the maximum outward edge from the pluton of boiling of the solutions the highest concentrations of w ore reversals or inflection points in mineral composition profiles and changes in the elemental ratios of constituents in the brine solutions hot saline solutions initially cooled to approximately 380 degrees c on entering the colder marble horizon flow along this horizon caused the loss of heat dilution and chemical change of the solution this latter in response to both reactions with the marble and hornfelsic units as well as the precipitation of the skarn permeability was produced by the dissolution of caco 3 to produce cacl sub 2 aq and faulting with time thermal equilibrium was reached between the evolving fluid and the contact rocks until boiling of the solution occurred with the loss of a co sub 2 rich vapor during this event the northern boundary fault was tectonically active so that primary fluid now entered the forming skarn both from the fault and the contact of the pluton mo rich scheelite began to precipitate at the time of boiling subsequent to garnet pyroxene crystallization after the boiling event and contemporaneous with the crystallization of amphibole some quartz mo rich scheelite not armored in garnet was dissolved redistributed and redeposited as mo poor scheelite and molybdenite this type of scheelite forms most of the ore being mined

sequential trace element analysis of zoned skarn garnet implications for multi stage fluxing and flow of magmatic fluid into a skarn system abstract a high resolution fluid flux flow model for a shallow crustal system related to skarn formation was established using oscillatory zoning in garnet in situ analytical methods were used to determine major and trace element contents of andradite rich and lower andradite content garnet zones continuous analysis of pure andradite and87 98 shows these garnets record first and second order fluid fluxes the first order fluid flux exhibits a stepwise increase in sn contents and a decrease in the contents of other elements ti v w as mo y and rare earth elements indicating that pure andradite records a large range changes in fluid flux from the magma the second order flux is evident from oscillatory variations in the contents of sn and other elements reflecting small scale and pulsed changes in the fluid flux from a degassing magma reservoir based on the garnet major and trace element variations and mineral textures these fluid fluxes in the skarn system were controlled by pulsed degassing of a cooling magma continuous analysis of oscillatory zoning in garnet with a lower andradite content and72 81 showed that sn concentrations increase gradually and other element concentrations decrease gradually this garnet crystallized from a fluid that was locally equilibrated with a small scale stagnant fluid thick and low andradite garnet bands and62 76 are observed to have grown between the first order fluid fluxing events these bands are al rich and have retrograde textures indicating prolonged magma residence after the first order fluid flux suggesting that circulating fluids persisted for a relatively long time

real time discrimination of earthquake foreshocks and aftershocks immediately after a large earthquake the main question asked by the public and decision makers is whether it was the mainshock or a foreshock to an even stronger event yet to come so far scientists can only offer empirical evidence from statistical compilations of past sequences arguing that normally the aftershock sequence will decay gradually whereas the occurrence of a forthcoming larger event has a probability of a few per cent here we analyse the average size distribution of aftershocks of the recent amatrice norcia and kumamoto earthquake sequences and we suggest that in many cases it may be possible to discriminate whether an ongoing sequence represents a decaying aftershock sequence or foreshocks to an upcoming large event we propose a simple traffic light classification to assess in real time the level of concern about a subsequent larger event and test it against 58 sequences achieving a classification accuracy of 95 per cent

reflectivity and seismic properties of the deep continental crust the recovery of drill core from a section of upper amphibolite facies terrane located in the inner piedmont of south carolina provides a rare opportunity to study in detail the seismic character of rocks which were once part of the deep continental crust seismic reflection profiles over the inner piedmont in the vicinity of the drill hole reveal subhorizontal high amplitude reflections the origin of these reflections has been investigated by measuring compressional wave velocities as a function of confining pressure and densities in 150 samples obtained from 305 m of drill core synthetic seismograms generated from the velocity and density measurements demonstrate that reflections originate from subhorizontal metamotphic layering probably originating from lower crustal ductile flow fine tuning of the metamotphic layering which is temperature and pressure related can produce bright spots in the deep crust anisotropy resulting from preferred mineral orientation is another important propeny of this sectim velocities are low for vertical wave propagatim whereas horizontal velocities are relatively high horizontal velocities show mly a slight variatim with azimuth which is unlikely to be detected using standard refractim techniques reflectivity decreases with increasing anisotropy critical to this study has been the continuous coring of a major section of high grade metamotphic terrane which has provided the necessary stratigraphic and lithologic cmtrol for the generation of accurate synthetic seismograms

zonation patterns of skarn garnets records of hydrothermal system evolution chemically zoned skarn garnets provide a continuous record of hydrothermal processes in lower paleozoic sedimentary rocks within the contact aureole around the drammen granite in the oslo rift southern norway major and trace element zonation profiles the latter obtained using a scanning high resolution proton microprobe reveal early infiltration controlled growth of relatively grossular rich garnets the major and trace elements compositions being buffered by local mineral dissolution subsequent rapid epitaxial growth of andradite rich garnet on grossular rich cores marks the onset of vigorous and focused fluid flow along high permeability zones during this later stage the hydrothermal fluid composition was to a large extent externally controlled and the andradite precipitating from these fluids was characterized by high as and w contents the zonation patterns of the andradite rich garnets record at least five intermittent growth periods with rapid andradite precipitation from fluid batches with high f o 2 and progressively decreasing as and w contents thin layers poor in fe as and w but relatively high in al and mn represent periods of slow growth rates between the major pulses of hydrothermal fluids the marked rimward decrease in the as and w contents of the garnets may reflect influx of meteoric waters or exhaustion of these elements in the hydrothermal fluid reservoir caused by boiling controlled distillation processes at depth

oxygen isotope geothermometers for metamorphic rocks the chicago mineral carbonate oxygen isotope fractionation curves have been combined with mineral water fractionation data for jadeite zoisite and rutile and new data for grossular water to provide a set of self consistent mineral pair calibrations the a coefficients in the equation 1000 in a 106t 2 of the new mineral pair fractionations are jadeite zoisite grossular rutile quartz 1 69 2 00 3 03 5 02 jadeite 0 31 1 34 3 33 zoisite 1 03 3 02 grossular 1 99 the isotopic fractionation properties of natural pyralspite garnet ca fe mg mn 3al2si3o12 can be approximated by those of the grossular end member appropriate substitutions also yield coefficients for the solid solution minerals sodic pyroxene and epidote e g aquartz sodic pyroxene 2 75 1 06xjd aquartz epidote 2 00 0 75xps where xjd and xps are the mole fractions of the jadeite and pistacite components respectively the new data set is particularly suitable for the geothermometry of metamorphic rocks 18o data from minerals of the high pressure metamorphic rocks of the sesia zone of italy and cyclades complex of greece yield well constrained mean temperatures of 572 and 478d c respectively type iii blueschist metabasalts of the franciscan formation of california give mean quartz garnet temperatures of 354d c

seismic velocity changes associated with aseismic deformations of a fault stimulated by fluid injection fluid pressure plays an important role in the stability of tectonic faults however the in situ mechanical response of faults to fluid pressure variations is still poorly known to address this question we performed a fluid injection experiment in a fault zone in shales while monitoring fault movements at the injection source and seismic velocity variations from a near distance 10 meters monitoring network we measured and located the p and s wave velocity perturbations in and around the fault using repetitive active sources we observed that seismic velocity perturbations dramatically increase above 1 5 mpa of injection pressure this is consistent with an increase of fluid flow associated with an aseismic dilatant shearing of the fault as shown by numerical modelling we find that seismic velocity changes are sensitive both to fault opening by fluid invasion and effective stress variations and can be an efficient measurement for monitoring fluid driven aseismic deformations of faults

andradite skarn garnet records of exceptionally low δ 18 o values within an early cretaceous hydrothermal system sierra nevada ca skarn garnets in the mineral king roof pendant of the south central sierra nevada within sequoia national park california usa reveal variable fluid chemistry with a significant component of meteoric water during metasomatism in the early cretaceous sierra nevada batholith we focus on andradite garnet associated with pb zn mineralization in the white chief mine laser fluorination oxygen isotope analyses of 18o of garnet 18o grt from sites along the skarn show a large range of values 8 8 to 4 6 vsmow ion microprobe sims analyses elucidate that individual andradite crystals are strongly zoned in 18o grt up to 7 of variation total rare earth element concentrations ree across individual garnets show progressive depletion of skarn forming fluids in these elements during garnet growth these findings support a skarn model of earliest red high 18o grandite garnet consistent with a magmatic dominated equilibrium fluid 18o h2o as high as 8 later green andradite crystallized in equilibrium with a low 18o fluid indicating a significant influx of meteoric fluid 18o h2o 6 to 5 following a hiatus in garnet growth associated with late stage pb zn mineralization latest orange overprint rims have higher 18o values 18o h2o 0 2 and depleted total rees suggesting influx of high 18o trace element depleted fluid derived from regional metamorphism of the carbonate host remarkably low 18o grt values in the white chief canyon skarn require a significant proportion of meteoric fluid available during 400 c andradite forming metasomatism fluid flow was channelized at the pluton wallrock contact evidenced by the narrow extent of skarn

seismic velocity changes in the epicentral region of the 2008 wenchuan earthquake measured from three component ambient noise correlation techniques 1 we investigate temporal changes of seismic velocity in the epicentral region of the 12 may 2008 mw 7 9 wenchuan earthquake using three component continuous waveforms recorded by a seven station small aperture array we use an ambient noise cross correlation technique to compute the empirical green s function between station pairs from august 2004 to september 2011 our results show no obvious precursory change immediately before the main shock clear coseismic reduction of seismic velocity of up to 0 2 and initial postseismic recovery followed by a long lived velocity reduction the coseismic and postseismic velocity changes are most prominent in the period band of 2 4 s approximate depth of 1 4 km and the velocity changes are smaller in other period bands the seismic velocity in the period band of 1 2 s i e top 2 km correlates well with the water level change of the zipingpu reservoir the observed temporal changes likely reflect damage and healing processes with possible permanent deformation in the upper crust associated with the wenchuan main shock

seismogeodesy of the 2014 mw6 1 napa earthquake california rapid response and modeling of fast rupture on a dipping strike slip fault real time high rate geodetic data have been shown to be useful for rapid earthquake response systems during medium to large events the 2014 mw6 1 napa california earthquake is important because it provides an opportunity to study an event at the lower threshold of what can be detected with gps we show the results of gps only earthquake source products such as peak ground displacement magnitude scaling centroid moment tensor cmt solution and static slip inversion we also highlight the retrospective real time combination of gps and strong motion data to produce seismogeodetic waveforms that have higher precision and longer period information than gps only or seismic only measurements of ground motion we show their utility for rapid kinematic slip inversion and conclude that it would have been possible with current real time infrastructure to determine the basic features of the earthquake source we supplement the analysis with strong motion data collected close to the source to obtain an improved postevent image of the source process the model reveals unilateral fast propagation of slip to the north of the hypocenter with a delayed onset of shallow slip the source model suggests that the multiple strands of observed surface rupture are controlled by the shallow soft sediments of napa valley and do not necessarily represent the intersection of the main faulting surface and the free surface we conclude that the main dislocation plane is westward dipping and should intersect the surface to the east either where the easternmost strand of surface rupture is observed or at the location where the west napa fault has been mapped in the past

static stress change from the 8 october 2005 m 7 6 kashmir earthquake 1 we calculated static stress changes from the devastating m 7 6 earthquake that shook kashmir on 8 october 2005 we mapped coulomb stress change on target fault planes oriented by assuming a regional compressional stress regime with greatest principal stress directed orthogonally to the mainshock strike we tested calculation sensitivity by varying assumed stress orientations target fault friction and depth our results showed no impact on the active salt range thrust southwest of the rupture active faults north of the main boundary thrust near peshawar fall in a calculated stress decreased zone as does the raikot fault zone to the northeast we calculated increased stress near the rupture where most aftershocks occurred the greatest increase to seismic hazard is in the indus kohistan seismic zone near the indus river northwest of the rupture termination and southeast of the rupture termination near the kashmir basin

high resolution long term and short term earthquake forecasts for california we present two models for estimating the probabilities of future earth quakes in california to be tested in the collaboratory for the study of earthquake predictability csep the first is a time independent model of adaptively smoothed seismicity that we modified from helmstetter et al 2007 the model provides five year forecasts for earthquakes with magnitudes m 4 95 we show that large earthquakes tend to occur near the locations of small m 2 events so that a high resolution estimate of the spatial distribution of future large quakes is obtained from the locations of the numerous small events we further assume a universal gutenberg richter magnitude distribution in retrospective tests we show that a poisson distri bution does not fit the observed rate variability in contrast to assumptions in current earthquake predictability experiments we therefore issued forecasts using a better fitting negative binomial distribution for the number of events the second model is a time dependent epidemic type aftershock sequence etas model that we modified from helmstetter et al 2006 and that provides next day forecasts for m 3 95 in this model the forecasted rate is the sum of a background rate propor tional to the time independent model rate and of the expected rate of triggered events due to all prior earthquakes each earthquake triggers events with a rate that increases exponentially with its magnitude and decays in time according to the omori utsu law an isotropic kernel models the spatial density of aftershocks for small m 5 5 events while for larger quakes we smooth early aftershocks to forecast later events we estimate parameter values by optimizing retrospective forecasts and find that the short term model realizes a probability gain of about 6 0 per earthquake over the time independent model online material identification of explosions and etas parameters

seismic evidence of nonlinear crustal deformation during a large slow slip event in mexico repeated cross correlations of ambient seismic noise indicate a long term seismic velocity change associated with the 2006 m7 5 slow slip event sse in the guerrero region mexico because the sse does not radiate seismic waves the measured velocity change cannot be associated with the response of superficial soil layers to strong shaking as observed for regular earthquakes the perturbation observed maximized at periods between 7 s and 17 s which correspond to surface waves with sensitivity to the upper and middle crust the amplitude of the relative velocity change 10 3 was much larger than the volumetric deformation 10 6 at the depths probed 5 20 km moreover the time dependence of the velocity perturbation indicated that it was related to the strain rate rather than the strain itself this suggests that during strong slow slip events the deformation of the overlying crust shows significant nonlinear elastic behavior

oscillatory zoning in skarn garnet implications for tungsten ore exploration abstract the sangdong and weondong deposits taebaeksan mineral district south korea are tungsten skarn ore deposits andradite fe rich garnet is a characteristic mineral in these skarn deposits and is characterized by notable trace element contents w mo sn and u compared to grossular al rich garnet we report characteristics of the trace elements including w in the garnet structure from the vein skarn system outermost exoskarn and identify a relationship of exploration significance between the trace element composition and w ore the chemical characteristics of the garnets were determined using back scattered electron bse imagery electron probe micro analyzer epma point analyses and x ray dot mapping and laser ablation inductively coupled plasma mass spectrometry la icpms point analyses and mapping garnets in the study area are mainly composed of grandite grossular andradite garnets and exhibit compositional variation as oscillatory zoning the chondrite normalized ree patterns of al rich garnets are hree enriched in contrast fe rich garnets are lree enriched tungsten is strongly fractionated into the fe rich garnets average concentration 618 ppm compared to the al rich rims average concentration 19 ppm in addition other trace elements mo sn and u are also closely correlated with w and ree signatures the fe rich garnets are attributed to rapid growth by infiltration metasomatism during disequilibrium which caused the incorporation of these trace elements into the garnet structure that reflect the composition of the ore forming fluid consequently these results indicate that andradite is a useful indicator mineral in the exploration of tungsten ore deposits

two generations of garnets and their relevance for the hydrothermal fluid evolution of the hongyuntan deposit nw china abstract the hongyuntan deposit which is one of the typical volcanic hosted fe deposits in the aqishan yamansu metallogenic belt of the eastern tianshan orogenic belt primarily consists of fe and skarn minerals especially garnet two generations three types of garnets were identified in the hongyuntan deposit based on field and optical characteristics hongyuntan garnets are fe rich and belong to the grossular andradite solid solution series and 50 99 100 00 average 79 06 garnets of the first generation grt1 are massive aggregates and are fine grained with well developed oscillatory zonings they have type i two phase liquid and vapor and type ii multi phase daughter mineral bearing fluid inclusions and experienced high temperature 540 560 c and salinity 9 2 63 2 wt nacl eqv conditions the grt1 have high ree lfree hree eu u y and high field strength element hfse sum of nb ta zr and hf contents garnets of the second generation grt2 are vefin types and are characterized by irregular shapes with irregular zonings type a garnets of the second generation grt2 a usually coexist with mafgnetite and have type i and type ii fluid inclusions with relatively high temperature 480 500 c and salinity 9 5 36 6 wt nacl eqv values compared to grt1 grt2 a have low and u and lree hree together with medium ree eu hfse and y contents type b garnets of the second generation grt2 b usually coexist with epidote and quartz they merely have type i fluid inclusions with medium low temperature 260 280 c and salinity 6 6 12 7 wt nacl eqv values grt2 b have high and eu and lree hree contents but very low ree hfse and y contents the fluid inclusions and geochemical properties of the garnets indicate that the temperature salinity oxygen fugacity fo2 and ph of the ore forming fluid fluctuated indicating hongyuntan deposit likely experienced superimposed mineralization grt1 originated in a magmatic hydrothermal fluid and formed through diffusive metasomatism under relatively high fo2 neutral ph and low water rock w r ratio conditions the reduced fe and other siderophile elements in the ore forming fluid which formed grt1 are believed to be the material basis for iron ores in the later main metallogenic stage grt2 a demonstrate the characteristics associated with transitional fluid which most likely originated from the episodic hydrothermal supplies however the ore forming fluid system gradually opened up during the crystallization of grt2 b and the decreasing temperatures and depletion of ore forming materials were ultimately unfavorable for the deposition of magnetite

distribution of seismic wave speed changes associated with the 12 may 2008 mw 7 9 wenchuan earthquake 1 we used continuous recordings in sichuan china to track the temporal change of the seismic wave speed at a regional scale for 2 years including the wenchuan mw 7 9 earthquake the data are recorded by a temporary network of 156 broad band seismographs in a region that covers the southern 2 3 of the fault activated during the earthquake a doublet analysis applied on the codas of seismic noise cross correlation functions is used to detect temporal velocity changes we found clear evidence that the seismic velocity drops by up to 0 08 in the fault region just after the earthquake with fluctuations within 0 02 before the earthquake we compared the measurements in different sub arrays to get a spatial distribution of the velocity changes this distribution is consistent with the volumetric strain change during the wenchuan earthquake and shows that the co seismic velocity change is not controlled by the response of sediments

chronology and tectonic framework of turbidite hosted gold deposits in the western lachlan fold belt victoria results abstract 40 ar 39 ar data constrain the history of metamorphism deformation and mineralization in the western subprovince of the lachlan fold belt rocks in the mount stavely volcanic complex and the bushy creek pluton give 40 ar 39 ar ages of about 500 ma for hornblende and biotite the dates from the mount stavely volcanic complex limit the age of mineralization in the metavolcanic rocks of the stavely belt whereas the date for the bushy creek pluton extends the area of cambrian ordovician plutons of the delamerian orogeny to east of the grampians mountains and helps define the surface expression of the western border of the paleozoic lachlan fold belt 40 ar 39 ar dating of metamorphic mica growth phengite in cleaved slates and phyllites within the landsborough fault avoca fault zone heathcote fault zone and mount wellington fault zone gives ages of 453 2 440 2 426 4 and 410 390 ma respectively these data indicate a progression of deformation from west to east starting in late ordovician early silurian time in the stawell and bendigo ballarat structural zones the major phase of deformation in the western subprovince of the lachlan fold belt is therefore silurian and not devonian sericites from major gold deposits in the stawell zone and bendigo ballarat zone give 40 ar 39 ar dates of about 440 ma that are coincident with folding and thrusting a second episode of mineralization and fault reactivation at about 420 to 410 ma is found in some deposits in these zones based on data from a previous study in the melbourne zone including the woods point dike swarm and locally in the bendigo ballarat zone some gold deposits give sericite dates of about 380 360 ma these ages are consistent with the close association of many melbourne zone gold deposits with devonian dikes and plutons the results indicate that gold mineralization in the stawell zone bendigo ballarat zone and melbourne zone was episodic and both temporally and spatially associated with crustal heating linked to regional metamorphism and plutonism initial stages of mineralization in the province comprising many of the large deposits in western and central victoria e g bendigo ballarat stawell wattle gully tarnagulla accompanied metamorphism folding and thrusting subsequent mineralization is widespread but produced mainly smaller deposits

monitoring the stability of tailings dam walls with ambient seismic noise tailings dams are massive structures designed to contain the waste slurry remaining after processing ore at open pit and underground mines these structures fail far more regularly than normal water storage dams in recent years catastrophic tailings dam failures have occurred causing significant damage to the environment and even loss of life to mitigate these catastrophic events in the future there is an urgent need to develop cost effective methods to monitor the structural stability of these constructions over time the lack of current cost effective monitoring methods prompted us to investigate whether ambient seismic noise can be used to detect internal changes in a tailings dam wall during a period of heavy rainfall we recorded three weeks of continuous seismic data with 10 short period geophones at a tailings dam in tasmania australia seismic interferometry was used on ambient noise to create virtual seismic sources with these virtual source signals small changes in seismic velocity were

formation of metamorphic and metamorphosed garnets in the low t uhp metagranite during continental collision in the dabie orogen abstract a combined study of major and trace elements in garnet was carried out for low t uhp metagranite in the dabie orogen the results show different fashions of element zoning in the garnet suggesting occurrence of both metamorphic and metamorphosed garnets three generations of garnet growth are distinguished on the basis of the assumption that ca contents mn contents and fe mg ratios of garnet in metagranites are a function of pressure and temperature the first generation of garnet grt i occurs in the core of a skeletal garnet showing homogeneously low x grs values and fe mg ratios but high x sps values this implies that the core garnet grew at the highest temperature but the lowest pressure representing a metamorphosed residue of magmatic garnet in protolith granite the second generation of garnet grt ii occurs in the mantles and cores of many garnet grains exhibiting increased x grs values but decreased fe mg ratios this is ascribed to a continuous increase in temperature and pressure till the peak pressure corresponding to metamorphic growth or overgrowth during the prograde subduction the third generation of garnet grt iii occurs in the rims of all garnet grains displaying decreased x grs values and fe mg ratios in response to a pressure decrease but a temperature increase till the peak temperature these rims overgrew subsequent to the peak pressure with continuous heating during the initial exhumation grt i shows steep mree hree patterns and profoundly negative eu anoalies consistent with growth from granitic melt this kind of metamorphosed garnet from protolith granite has still preserved very high contents of many trace elements such as ree rb ba sr pb th u nb and ta despite the low t uhp metamorphism grt ii and grt iii in one sample exhibit steep mree hree patterns with a continuous decrease in ree contents this suggests their growth from the almost same matrix of mineral assemblages plagioclase k feldspar muscovite during metamorphism however grt ii in the other sample displays flat to steep mree hree patterns with an increase of ree contents from core to mantle this implies that the matrix of mineral assemblages for grt ii changes from common rock forming minerals e g feldspar muscovite and biotite to ree rich minerals e g epidote allanite zircon amphibole apatite and titanite grt iii in the two samples all displays significantly lowered ree contents compared to those of grt i and grt ii this may be due to a decrease in pressure and an increase in temperature during the initial exhumation therefore the two stage growth of metamorphic garnet is evident in the low t uhp metagranite during the continental subduction zone metamorphism in addition the highest pressure occurs in the cores or mantles whereas the highest temperature occurs in the rims this suggests that the peak pressure p max did not occur contemporarily at the peak temperature t max corresponding to the hot exhumation

seismic velocity variations associated with the 2018 lower east rift zone eruption of kīlauea hawaiʻi the 2018 lower east rift zone eruption of k lauea hawai i marked a dramatic change in the volcano s 35 year long rift zone eruption the collapse of the middle east rift zone vent pu u was followed by one of the volcano s most voluminous eruptions in 500 years over the course of this 3 month eruption the draining of summit stored magma led to near daily collapses of a portion of the caldera and ultimately up to 500 m of summit subsidence while deformation data indicated that the summit and middle east rift zone were inflating for the previous several years why pu u collapsed and what initiated down rift dike propagation remains unclear using ambient noise seismic interferometry we show that a ml5 3 decollement earthquake beneath k lauea s south flank in june 2017 induced a coseismic decrease of up to 0 30 in seismic velocity throughout the volcano this velocity decrease may have been caused by dynamic stress induced shallow crustal fracture i e weakening to dilatant crack growth and was greatest near pu u additionally we verify a pre eruptive increase in seismic velocity consistent with increasing pressurization in the volcano s shallow summit magma reservoir this velocity increase occurred coincident with the first in a series of lower crustal earthquake swarms 6 days before a 2 month period of rapid summit and middle east rift zone inflation the increase in up rift magma static pressure combined with the pre existing weakness from the june 2017 earthquake may have facilitated down rift dike propagation and the devastating 2018 eruption

seismic noise correlations to image structural and mechanical changes associated with the mw 7 9 2008 wenchuan earthquake we locate temporal changes of seismic wave speed and scattering properties of the crust associated with the 2008 mw7 9 wenchuan earthquake to that end we analyze ambient seismic noise records from 2007 until the end of 2008 in the 1 3 s period band and in the 12 20 s period band measured in a region that covers the southern two thirds of the fault activated during the earthquake to locate the changes we use a refined imaging procedure based on the sensitivity of scattered waves to weak perturbations this inverse method uses the radiative transfer approximation to describe the intensity of the noise correlation coda our results show that the largest structural changes are observed northeast of the wenchuan epicenter around the fault zone where aftershocks are distributed the spatial and temporal characteristics of the behavior of the crust at depth around the wenchuan earthquake suggest a postseismic and geology dependent signature of the middle crust we also observe a clear seasonal signature within the sichuan basin at depth that we relate to the heavy rainfalls during the monsoon season this seasonality can also be observed at the surface in form of a waveform decoherence our study highlights that seismic velocity changes and waveform decoherence are independent measurements that are sensitive to different parameters and can thus give complementary information in our study we also point out the value of studying the evolution of the changes at different times in the coda

coseismic velocity change in and around the focal region of the 2008 iwate miyagi nairiku earthquake 1 the 2008 m7 2 iwate miyagi nairiku earthquake occurred in ne japan where dense seismic networks exist using the data from these networks we determined the coseismic seismic velocity change associated with this earthquake by two different methods ambient noise interferometry and vertical array interferometry of coda wave the purpose of this article is to reveal the spatial distribution and the cause of the velocity change by integrating these two approaches ambient noise interferometry revealed a coseismic velocity decrease of rayleigh wave by 0 1 0 5 at 0 25 0 5 hz we also estimated the spatial distribution of the velocity change by a tomographic inversion the velocity decrease was distributed in and around the focal area in the second method we applied cross correlation analysis to coda waves observed by the kik net vertical array we detected a shear velocity decrease of approximately 5 in shallow layers up to a few hundred meters depth quantitative comparison of the two results reveals that the 5 shear velocity decrease in shallow layers can explain the 0 1 0 5 decrease of rayleigh wave velocity the distribution of the velocity decrease is similar to that of the strong ground motion and the static stress change however a significant velocity increase is not observed in the compression area where a velocity increase is expected based on the observations we consider that the primary factor affecting the velocity change is damage in shallow layers due to strong motion the effect of the static stress change might be masked by the larger effect of the strong motion

la icp ms trace element geochemistry of garnets constraints on hydrothermal fluid evolution and genesis of the xinqiao cu s fe au deposit eastern china abstract the xinqiao cu s fe au deposit in the tongling ore district an important part of the middle lower yangtze river valley metallogenic belt in eastern china is located along the northern margin of the yangtze block the deposit consists of two major mineralization types stratiform and skarn the genesis of the former is disputed the more important stratiform orebody 90 of the total cu s and fe reserves has abundant garnet as the main gangue mineral similar to the skarn orebody hosted in the intrusive contact garnets from the xinqiao stratiform orebody range from pure andradite and 100 to and 50 gro 46 and can be divided into the early grt1 and late grt2 generation both generations contain low mno 0 19 0 89 wide range of y ho 39 0 40 7 for grt1 29 8 67 9 for grt2 and do not contain melt or fluid melt inclusions indicative of a magmatic hydrothermal replacement origin grt1 and the grt2 cores are grandite whilst the grt2 rims are mainly andradite with some grandite zones grandite is enriched in heavy rare earth elements hrees and displays low lree hree la n yb n and u concentrations with negative eu anomalies whereas andradite is hree depleted and displays high lree hree la n yb n ratios and u concentrations with positive eu anomalies the distinct trace element features suggest that the hydrothermal fluids for grt1 and the grt2 cores were of nearly neutral ph relatively oxidized and hree enriched whereas those for the grt2 rims had experienced episodic inflections between a mildly acidic relatively reduced and hree depleted fluid and a nearly neutral relatively oxidized and hree enriched fluid meanwhile they also reveal that grt1 and the grt2 cores may have formed by diffusive metasomatism in a closed system whereas the grt2 rims may have formed by infiltration metasomatism in an open fracture system possibly related to the unconformity that hosts the xinqiao stratiform orebody we propose that the xinqiao stratiform orebody may have formed from early cretaceous magmatic hydrothermal fluids associated with the jitou stock similar to the skarn type orebodies in the district

deep crustal reflection results from the central eromanga basin australia abstract from 1980 to 1982 deep seismic reflection profiles were recorded across the central eromanga basin in eastern australia to study the regional structure stratigraphy and geological history of the eromanga basin and infra basins the reflection data were recorded to 20 s to obtain additional information on the nature and structure of the crust below the sediments and their relationship to the development of the basins the seismic sections show good quality reflections from the deep crust as well as from the sedimentary layers based on the character strength coherence continuity and spatial distribution of the reflections the sections can be divided into four zones the tope zone between 0 and 2 5 s shows fairly uniform coherent and continuous events which correlate with the mesozoic and late palaeozoic sediments the zone from 2 5 to 8 s 4 to 22 km does not show any primary reflections and is interpreted as the highly deformed metasedimentary and metavolcanic rocks of the early palaeozoic thomson orogen underlying the sediments without any recognisable reflection or diffraction patterns in this zone it is difficult to say whether the faulting and folding observed in the sediments extend into the upper crustal basement the deeper zone of numerous reflection segments between 8 and 12 5 s 22 to 36 km is interpreted as thin laminae of alternating low and high velocity intermediate and basic rocks and correlates with the lower crust bounded by refraction velocity discontinuities the lowest zone of no reflections below 12 5 s corresponds with the upper mantle the reflection character and thickness as well as the refraction velocity structure of the crust under the central eromanga basin area are significantly different from those of the precambrian crust under the georgina basin to the northwest it is proposed that the crust under the eromanga basin is extensionally attenuated crust which had been intruded by sills of basaltic melt from the underlying asthenosphere

the molybdenite re os isotope chronology in situ scheelite and wolframite trace elements and sr isotope characteristics of the chuankou tungsten ore field south china abstract the chuankou tungsten ore field situated in the central area of the qing hang ancient suture zone in south china is characterized by predominantly quartz vein type tungsten mineralization that formed near the contact between the chuankou granite and slightly metamorphosed silt bearing sericite slate based on field work cathodoluminescence molybdenite re os dating and in situ laser ablation inductively coupled plasma mass spectrometry la icp ms analysis the chuankou tungsten ore was formed at 230 6 2 9 ma to 229 4 2 6 ma in a typical indosinian metallogenic event in addition three distinct generations of scheelite and two types of wolframite can be clearly distinguished type 1 wolframite has a semiautomorphic grain or brecciated vein structure with a high heavy rare earth element hree content and an obvious negative eu anomaly type 2 wolframite grains are strongly altered as residual pseudomorphic structures by ore forming fluids and have relatively low ree contents sch 1 scheelite is present in the interior of the type 2 wolframite grains the sch 1 scheelite grains have an elevated ree content and low 87sr 86sr ratios with a strongly negative eu anomaly which suggests an inheritance signal of the host rocks comparatively sch 2 and the altered sch 1 scheelite have characteristic extremely low ree contents and remarkably strong positive eu anomalies these scheelites also have increased 87sr 86sr ratios and low 88sr signals sch 3 is idiomorphic with perfect oscillating zoning the ree content of sch 3 which typically has the lowest 87sr 86sr ratios is higher than those in sch 1 and sch 2 and the extremely high 88sr signals indicate a distinct thermal fluid event that was directly derived from the host rock the correlations between the ree and nb of scheelite imply a type b substitution of sch 1 and sch 2 but a type c substitution for sch 3 the correlation of eun and eun shows an eu3 substitution process for stages sch 1 and sch 2 and an eu2 substitution process for stage sch 3 thus we confirm that ore bearing hydrothermal rocks must undergo early stage metasomatism and filling middle stage fluid mixing between wall rocks and magmatic hydrothermal activity and refilling of late stage magmatic hydrothermal activity during the metallogenic process during the indosinian period the mineralization stages of polymetallic deposits in the indosinian were composed of stage 1 240 to 220 ma and stage 2 220 to 200 ma the chuankou tungsten ore field can be considered as the typical representation of the stage 1 metallogenic event in south china this ore field is derived from remelting of the ancient basement and was reduced by regional extension under the dominant compression regime in the south china block

empirical synthesis of time asymmetrical green functions from the correlation of coda waves we demonstrate the existence of long range field correlations in the seismic coda of regional records in alaska the cross correlations between the different components of coda records at two points are measured for a set of distant earthquakes remarkably while individual correlations have a random character the correlations averaged over source and time exhibit deterministic arrivals that obey the same symmetry rules as the green tensor between the two points in addition the arrival times of these waves coincide with propagating surface waves between the two stations thus we propose to identify the averaged correlation signals with the surface wave part of the green tensor we observe the causal and anticausal parts of the green function however we find experimentally that amplitudes at positive and negative times are not equal we explain this observation by the long lasting anisotropy of the diffuse field we show that the flux of energy coming from the source can still dominate the late coda and result in nonsymmetric cross correlations when the distribution of earthquakes is not isotropic around the stations the extraction of green functions from coda waves allows new types of measurements with seismic waves along paths between stations that could not be obtained with the waves produced by earthquakes

mid crustal detachments controlling basin deformation ramp synforms in southwestern queensland abstract deep seismic data from the adavale basin region of southwestern queensland suggest that westward carboniferous movement of the upper crust over mid crustal ramps was responsible for the present day geometry of two synforms containing devonian sediments we interpret the troughs as hanging wall synforms formed by sub vertical simple shear within the upper crust during down dip movement over the ramp one of these structures the quilpie trough in the southern adavale basin is an asymmetric trough interpreted to be an extensional ramp syncline it overlies a west dipping ramp in the boundary between the seismically non reflective upper crust and the seismically reflective lower crust formation of this basin by the relative movement of the upper crustal thomson fold belt over the mid crustal ramp is postulated the significant asymmetry of the trough suggests that lower crustal extension by pure shear may have occurred during upper crustal translation the other structure the westgate trough contains two palaeozoic sequences we propose that the devonian lower sequence is in a ramp syncline formed by folding of the sediments in a conveyor belt style mechanism during a translation of the upper crust the upper sequence is interpreted as a ramp basin in which sediments were deposited in the synform as it developed deep seismic reflection data from the central eromanga basin region indicate that relative horizontal translation can occur between the upper and lower crust on mid crustal detachments the geometry of the synforms suggests that above these detachments crustal deformation has a sub vertical simple shear style whereas the lower crust below the detachments seems to deform in a pure shear style recognition of relative movement of tens of kilometres on mid crustal detachments is important for our understanding of basin geometry and development in the central eromanga basin

the stratigraphy and deformation history of the tumut region implications for the development of the lachlan fold belt abstract the tumut region forms the southern part of the tumut synclinorial zone in the southeastern part of the lachlan fold belt lfb the area contains two major stratigraphie packages ordovician to early silurian quartz rich to quartz intermediate flysch and volcanics package a and overlying fossiliferous early late silurian volcanics and flysch package b rhyolite within the older package a yields a u pb zircon age of 428 6 ma both packages were meridionally folded during the siluro devonian bowning orogeny following intrusion of the gocup granite at 411 5 ma an earlier deformation characterised by thrust faulting e w recumbent folding and later local coaxial upright folding is present only in the older flysch and volcanics package a this earlier deformation is part of the benambran orogeny that affects the ordovician metamorphics of the wagga metamorphic belt and other parts of the lfb and is constrained to about 425 ma fold characteristics of this deformation are indicative of thin skinned intraplate transpressional deformation rather than classical collisional tectonics as envisaged by some workers for the benambran orogeny here and elsewhere in the lfb the composition and deformational history of the older flysch indicates that it is part of the ordovician to early silurian molong volcanic belt consequently the older concept of an early silurian tumut trough incorporating both packages of rocks is rejected instead it is proposed that up to 2500 m of early late silurian rocks formed in a pull apart basin the tumut basin thus the silurian depositional history of the tumut region previously considered unique in the lfb is little different from other basins of similar age throughout the lfb

oxygen isotope and trace element zoning in hydrothermal garnets windows into large scale fluid flow behavior single garnet crystals from a large multicyclic hydrothermal system in far east russia are strongly growth zoned microscale ion microprobe analysis reveals consistent intracrystalline patterns in oxygen isotope composition and boron and iron contents reflecting evolution of the hydrothermal system from magmatic to meteoric dominated conditions and repetitive influx of magmatic fluids large intracrystalline variations in oxygen isotope composition 12 18 o delimit temporal evolution of magmatic and meteoric fluid input within different portions of the hydrothermal system and suggest that fluid flow regimes differed between central and distal portions of the system these results provide compelling evidence that microanalytical data can be extrapolated from intracrystalline scales to study macroscale processes in complex large scale fluid rock systems

geochronology and geochemistry of eclogites from the marianske lazně complex czech republic implications for variscan orogenesis the marianske lazn complex mlc is located in the bohemian massif along the north western margin of the tepla barrandian microplate and consists of metagabbro amphibolite and eclogite with subordinate amounts of serpentinite felsic gneiss and calcsilicate rocks the mlc is interpreted as a metaophiolite complex that marks the suture zone between the saxothuringian rocks to the north west and the tepla barrandian microplate to the south east sm nd geochronology of garnet omphacite pairs from two eclogite samples yields ages of 377 7 and 367 4 ma samples of eclogite and amphibolite do not define a whole rock sm nd isochron even though there is a large range in sm nd ratio implying that the suite of samples may not be cogenetic eclogites do not have correlated nd values and initial 87sr 86sr ratios five of the eight eclogite samples have high nd values 10 2 to 7 1 consistent with derivation from a morb like source but variable 87sr 86sr ratios 0 7033 to 0 7059 which probably reflect hydrothermal seawater alteration three other eclogite samples have lower nd values 5 4 to 0 8 and widely variable 87sr 86sr ratios 0 7033 to 0 7096 such low nd values are inconsistent with derivation from a morb source and may reflect a subduction or oceanic island basalt component in their source the mlc is an important petrotectonic element in the bohemian massif providing evidence for cambro ordovician formation of oceanic crust and interaction with seawater late devonian frasnian famennian high and medium pressure metamorphism related to closure of a saxothuringian ocean basin early carboniferous visean thrusting of the tepla terrane over saxothuringian rocks and late visean extension

u pb geochronology of grossular andradite garnet abstract this study presents a new laser ablation inductively coupled plasma mass spectrometry la icpms based u pb geochronometric method for dating grossular andradite grandite garnet grandite is a primary skarn mineral therefore dating its growth directly dates hydrothermal activity as zircon u pb geochronometry provides a high resolution record of magmatic processes grandite u pb dating has the potential to provide a complementary record for hydrothermal systems this study characterizes four garnets of variable grossular andradite content and age as potential reference materials for la icpms u pb geochronology willsboro andradite 1020 ma adirondacks usa red and yellow mali grandite 200 ma southern mali and lake jaco grossular 35 ma coahuila mexico isotope dilution thermal ionization mass spectrometry id tims u pb analyses of willsboro andradite yield a mean 206pb 238u date of 1022 16 ma we use willsboro andradite as a primary reference material for la icpms u pb characterization of the two other garnets the non radiogenic pb pbc concentration in grandite is variable between specimens willsboro andradite and mali grandites contain almost purely radiogenic pb pb however lake jaco grossular has a higher pbc concentration comparatively and yields discordant u pb ratios for specimens with highly variable pb pbc linear regression is employed to derive a lower intercept age la icpms u pb dates for yellow mali grandite 202 2 ma 206pb 238u weighted mean and lake jaco grossular 35 2 ma lower intercept agree with independent id tims u pb 202 0 1 2 ma and u th he dates 35 5 ma derived for each specimen the precision of la icpms u pb dates varies between 1 10 2 for the analyzed garnets considering the short estimated lifespans of pluton related hydrothermal systems tens of thousands to a few million years neogene skarns present the best opportunity to test for and resolve separate episodes of garnet growth at these precision levels as a performance test for the method we present new u pb andradite data from a late miocene skarn system on serifos island greece this garnet yields a lower intercept age of 9 15 0 36 ma in agreement with biotite rb sr and zircon u pb dates from the causative pluton

improving temporal resolution in ambient noise monitoring of seismic wave speed 1 the use of ambient seismic noise has been intensively investigated to perform passive tomography at various scales besides passive tomography passive monitoring is another application of seismic noise correlation as was shown by the recent observation of postseismic velocity changes around the san andreas fault in parkfield california one of the drawbacks of using ambient noise correlation for passive monitoring is the need to average the correlations over a long time period in order to obtain a sufficient signal to noise ratio snr for the phase fluctuations to be measured accurately for the application to passive monitoring one wants the possibility of following short term velocity variations 1 day or less using noise correlation functions calculated on short time windows another difficulty may then appear when the spatial distribution of noise sources also evolves with time the aim of this paper is to introduce an adaptive filter to the parkfield data set in order to improve the snr output of the ambient noise correlation functions when applied to passive monitoring the temporal resolution can be increased from 30 days up to 1 day with this improved temporal resolution the velocity drop observed at parkfield is shown to be cosesimic with the 24 september 2004 mw 6 0 event the relationship between the measured velocity fluctuations and the time evolution of the spatial distribution of the noise wavefield is also investigated finally the error bar in the amplitudes of the velocity variations is compared with a theoretical expectation

a detailed record of shallow hydrothermal fluid flow in the sierra nevada magmatic arc from low δ18o skarn garnets garnet from skarns exposed at empire mountain sierra nevada california united states batholith have variable 18o values including the lowest known 18o values of skarn garnet 4 0 in north america such values indicate that surface derived meteoric water was a significant component of the fluid budget of the skarn forming hydrothermal system which developed in response to shallow emplacement 3 3 km of the 109 ma quartz diorite of empire mountain values of 18o measured in situ across single garnet crystals by secondary ion mass spectrometry vary considerably up to 7 and sometimes abruptly indicating variable mixing of meteoric magmatic and metamorphic water brecciation in the skarns and alteration of the empire mountain pluton suggests that fracture enhanced permeability was a critical control on the depth to which surface waters penetrated to form skarns and later alter the pluton compared to other sierran systems much greater volumes of skarn rock suggest an exceptionally vigorous hydrothermal system that saw unusually high levels of decarbonation reaction progress likely a consequence of the magma intruding relatively cold wallrocks inboard of the main locus of magmatism in the sierran arc at that time

ambient noise based monitoring of seismic velocity changes associated with the 2014 mw 6 0 south napa earthquake we perform an ambient noise based monitoring to explore temporal variations of crustal seismic velocities before during and after the 24 august 2014 mw 6 0 south napa earthquake a velocity drop of about 0 08 is observed immediately after the south napa earthquake spatial variability of the velocity reduction is most correlated with the pattern of the peak ground velocity of the south napa mainshock which suggests that fracture damage in rocks induced by the dynamic strain is likely responsible for the coseismic velocity change about 50 of the velocity reduction is recovered at the first 50 days following the south napa mainshock this postseismic velocity recovery may suggest a healing process of damaged rocks

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

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

mapping pressurized volcanic fluids from induced crustal seismic velocity drops volcanic eruptions are caused by the release of pressure that has accumulated due to hot volcanic fluids at depth here we show that the extent of the regions affected by pressurized fluids can be imaged through the measurement of their response to transient stress perturbations we used records of seismic noise from the japanese hi net seismic network to measure the crustal seismic velocity changes below volcanic regions caused by the 2011 moment magnitude m w 9 0 tohoku oki earthquake we interpret coseismic crustal seismic velocity reductions as related to the mechanical weakening of the pressurized crust by the dynamic stress associated with the seismic waves we suggest therefore that mapping seismic velocity susceptibility to dynamic stress perturbations can be used for the imaging and characterization of volcanic systems

sudden drop of seismic velocity after the 2004 mw 6 6 mid niigata earthquake japan observed with passive image interferometry 1 passive image interferometry pii is a seismological method employing ambient seismic noise to monitor the temporal evolution of mean shear wave velocity within the earth first the elastic green s tensor between two seismometers is computed from the cross correlation of seismic noise recorded during a certain period second the constructed seismograms of different time periods are treated as earthquake multiplets and small time shifts in their coda are used to invert a relative change in mean shear wave velocity when applied to the source region of the 2004 mw 6 6 mid niigata earthquake japan centroid depth 5 km we used noise recorded at six seismometers located at a distance of less than 25 km from the epicenter daily inversions during the 2 months before and after the earthquake show a sudden drop of mean shear wave velocity of some tenths of a percent at the time of the mid niigata earthquake using noise in two frequency bands 0 1 0 5 hz and 2 8 hz we find similar amplitudes for the velocity drop which indicates that changes are not restricted to the shallow subsurface possible interpretations of this velocity decrease are a decrease of crustal stress after the earthquake a nonlinear site response in the shallow subsurface layer due to strong ground motion or structural weakening due to the creation of new fractures in the source area of the earthquake

assessment of resolution and accuracy of the moving window cross spectral technique for monitoring crustal temporal variations using ambient seismic noise summary temporal variations in the elastic behaviour of the earth s crust can be monitored through the analysis of the earth s seismic response and its evolution with time this kind of analysis is particularly interesting when combined with the reconstruction of seismic green s functions from the cross correlation of ambient seismic noise which circumvents the limitations imposed by a dependence on the occurrence of seismic events in fact because seismic noise is recorded continuously and does not depend on earthquake sources these cross correlation functions can be considered analogously to records from continuously repeating doublet sources placed at each station and can be used to extract observations of variations in seismic velocities these variations however are typically very small of the order of 0 1 per cent such accuracy can be only achieved through the analysis of the full reconstructed waveforms including later scattered arrivals we focus on the method known as moving window cross spectral analysis that has the advantage of operating in the frequency domain where the bandwidth of coherent signal in the correlation function can be clearly defined we investigate the sensitivity of this method by applying it to microseismic noise cross correlations which have been perturbed by small synthetic velocity variations and which have been randomly contaminated we propose threshold signal to noise ratios above which these perturbations can be reliably observed such values are a proxy for cross correlation convergence and so can be used as a guideline when determining the length of microseismic noise records that are required before they can be used for monitoring with the moving window cross spectral technique

oxygen isotope heterogeneities and diffusion profile in composite metamorphic magmatic garnets from the pyrenees unusually large 1 8 o heterogeneities 4 within single crystals are reported in garnets from dioritic migmatites in the pyrenees these heterogeneities together with contrasting ca and p zoning allow the identification of different growth zones garnet cores with high 1 8 o values 12 14 are relatively poor in ca 7 9 mol grs and rich in p 400 900 ppm p 2 o 5 in contrast garnet rims with lower 1 8 o values 7 12 o are richer in ca 12 14 grs and poorer in p 100 200 ppm these growth zones can be ascribed to a metamorphic event followed by crustal partial melting and contamination by magmas from the mantle high 1 8 o intra crystalline contrasts result from mineral growth in an open magmatic system involving the interaction of partial melts with distinct 1 8 o signatures at the garnet core rim interface compositional profiles in major divalent cations are consistent with the relaxation of an initial sharp step in ca fe and mg by ca fe mg interdiffusion at the same interface an o isotope profile is documented the analogy of ca and o isotope profiles suggests that the 1 8 o distribution may also result from a diffusion process in this particular case temperature garnet composition oxygen fugacity o diffusion appears to be of the same order of magnitude as ca fe mg interdiffusion considering a duration of 10 ma for the plutono metamorphic event in the pyrenees ca and o diffusivities in the range 10 2 2 m 2 s at 850 c are retrieved from the measured profiles like ca o diffusion in garnet at magmatic temperatures 850 900 c is both slow enough to preserve large 1 8 o heterogeneities and fast enough to generate relaxation profiles

extracting earth s elastic wave response from noise measurements recent research has shown that noise can be turned from a nuisance into a useful seismic source in seismology and other fields in science and engineering the estimation of the system response from noise measurements has proven to be a powerful technique to convey the essence of the method we first treat the simplest case of a homogeneous medium to show how noise measurements can be used to estimate waves that propagate between sensors we provide an overview of physics research dating back more than 100 years showing that random field fluctuations contain information about the system response this principle has found extensive use in surface wave seismology but can also be applied to the estimation of body waves because noise provides continuous illumination of the subsurface the extracted response is ideally suited for time lapse monitoring we present examples of time lapse monitoring as applied to the softening of soil after the 2011 tohoku oki earthquake the detection of a precursor to a landslide and temporal changes in the lunar soil

temporal change in site response caused by earthquake strong motion as revealed from coda spectral ratio measurement 1 the spectral ratios of coda waves of local earthquakes have been often used as measures of relative amplification factors of different sites applying this method to coda waves registered by seismometers installed on the surface and at the bottom of a borehole we succeeded in stably measuring the temporal change in site response associated with the occurrence of a large earthquake strong motion a remarkable drop of coda spectral ratio and a shift of the peak frequency were observed during strong shake at two sites by the 2000 western tottori earthquake and at a site by the 2003 tokachi oki earthquake in japan the reduction of the peak frequency reached 30 70 at all the sites after that the peak frequency logarithmically recovered to the value before the strong motions for a few years at two sites whereas the other one quickly recovered in a few tens of minutes

seismic velocity changes in the backarc continental crust after the 2011 mw 9 0 tohoku oki megathrust earthquake the 2011 mw 9 0 tohoku oki megathrust earthquake accompanied coseismic and postseismic displacements around the eastern eurasian continental plate noise cross correlations produced transient seismic waveforms along interstation paths in the korean peninsula we measured the traveltime changes of the fundamental mode rayleigh waves over the range of 0 03 0 08 hz after the megathrust earthquake the temporal seismic velocity changes in the lower crust were assessed from the traveltime changes the traveltimes increased instantly after the megathrust earthquake and were gradually recovered over several hundreds to thousands of days the instant shear wave velocity decreases ranged between 0 731 0 057 and 4 068 0 173 the temporal medium perturbation might be caused by the transient uniaxial tensional stress due to the coseismic and postseismic displacements the medium properties may be recovered by progressive stress field reconstruction

rupture history of 2014 mw 6 0 south napa earthquake inferred from near fault strong motion data and its impact to the practice of ground strong motion prediction the spatiotemporal rupture history of the 2014 south napa earthquake is constrained using near fault strong motion records an aggressive source parameterization with 1372 subfaults is adopted to match the signals in the transverse components up to 4 hz the result reveals that the rupture of the napa earthquake initiated at a depth of 9 84 km and propagated mainly to north northwest nnw and updip on a 13 km long fault patch a gradual increase in average rise time when the rupture propagates to shallower depth is observed however it is the rupture of a small mw 4 9 isolated and high stress drop fault patch that excited the largest ground acceleration at stations south of the epicenter such fine scale rupture heterogeneity shall be considered during seismic hazard analysis

azimuthal seismic anisotropy in the upper crust of the japanese islands induced by the 2011 tohoku oki megathrust earthquake

investigating triggering of the aftershocks of the 2014 napa earthquake abstract the occurrence of the m w 6 0 south napa california earthquake on 24 august 2014 at 03 20 a m local time triggered discussion in the seismological community about the level of damage associated with such a moderate magnitude event and about the geometry and orientation of the causative fault in addition coulomb static stress change mapping does not seem to be able to fully explain near source aftershock distribution here we find clear evidence of a north northwest source directivity from the analysis of the spatial distribution of peak ground motion the area of the highest values of the estimated peak dynamic strain field computed accounting for fault extent and source directivity agrees with the near source aftershock distribution this might suggest that in addition to coulomb static stress change dynamic strain also contributed to the triggering of near source napa earthquake aftershocks the approach used here might be useful to identify areas likely prone to aftershock occurrence

contact metamorphism of layered shale carbonate sequences in the oslo rift iii the nature of skarn forming fluids intrusions of granitic to monzonitic batholiths caused extensive contact metamorphism of lower paleozoic sediments in the permian oslo rift the release of aqueous fluids during crystallization of the silicic intrusions resulted in widespread hydrothermal activity leading to skarn formation and locally to ore deposition in the contact aureoles stable isotope and fluid inclusion data have been used to constrain the composition and evolution of skarn forming fluids at a roof pendant situated on the eastern margin of the large nordmarkite syenite batholith at the eastern margin of the oslo rift three different stages of skarn formation stages i iii one of them stage ii associated with sphalerite mineralization and subsequent quartz calcite vein formation have been recognized in the area oxygen and hydrogen isotope data from biotite and quartz from the intrusive rocks and oxygen isotope zonation profiles across relict carbonate layers in areas characterized by pervasive stage i skarn formation indicate early infiltration of magmatic fluids with delta d 30 to 60 per mil and delta 18 o 5 to 8 5 per mil followed by infiltration of fluids with a significant meteoric component delta 18 o 0 2ppm a similar evolution is inferred from an oxygen isotope zonation profile of a carbonate layer from the fault controlled stage ii skarn zone oxygen and hydrogen isotope data from secondary fluid inclusions extracted from vein stage quartz demonstrate the influx of meteoric dominated fluids with delta d asymp 85ppm and delta 18 o asymp 12ppm stage i skarn forming fluids are characterized by moderate salinity 5 10 wt nacl equiv and significant co 2 contents the fluid composition led to vapor liquid separation at metamorphic conditions fluid inclusion data indicate trapping temperatures in the range 350 degrees to 400 degrees c stage ii fluids were heterogeneous including hydrosaline liquids 30 50 wt nacl equiv low salinity liquids and co 2 rich vapors trapped at temperatures in the range 300 degrees to 400 degrees c stage iii and vein stage fluids were comprised of low salinity liquids 5 wt nacl equiv trapped at temperatures ranging down to 200 degrees c a model for the hydrothermal fluid evolution is presented that includes the coexistence of a vapor of low salinity and a hydrosalin liquid at magmatic temperatures the vapor or its condensed equivalents was responsible for pervasive stage i formation and was a potential transport agent for hydroxy complexes of w and mo on the other hand the dense base metal rich hydrosaline liquid escaping from the fluid saturated melt through a fault zone caused stage ii skarn formation and sphalerite pyrite mineralization meteoric fluids affected both stage i and ii rocks to a large extent controlled stage iii skarn formation and dominated later vein formation the present model is consistent with the isotope and fluid inclusion data the mineralogical characteristics of the skarns the metallogeny of skarn deposits in the oslo rift in general and recent physical models for vapor release from cooling silicic intrusions

rates and mechanisms of isotopic exchange background the proliferation of stable isotope laboratories in recent years has led to a marked increase in the routine use of stable isotope analyses in geochemical studies this trend is likely to continue because of the development of micro analytical techniques e g laser ablation ion microprobe femtomole carrier gas methods etc for stable isotope analysis and the potential of these techniques to reveal the detailed sequence of thermal and fluid histories preserved in the rock record see mckibben et al 1998 equilibrium isotope fractionation factors and rates of isotopic exchange form the cornerstones for the interpretation of stable isotope data from natural systems indeed determination of the distribution of the stable isotopes of c o h s in gases fluids and minerals has become a standard and extremely powerful approach in elucidating the temperatures material fluxes rock and fluid origins and time scales associated with ancient and active fluid rock interaction processes in the earth s crust see valley et al 1986 although the thermodynamic principles underlying isotopic fractionation behavior were developed more than fifty years ago by urey 1947 the calibration of fractionation factors has proven to be difficult during the last four decades a great deal of progress has been made in determining the equilibrium fractionations of 18o 16o d h 13c 12c and 34s 32s among fluid and mineral components at high temperatures 400 c both from experimental exchange studies theoretical calculations using vibrational spectra semi empirical calculations using bond type considerations and empirical calibrations based on natural assemblages see references in o neil 1986 kyser 1987 criss 1991 1999 chacko et al this volume of these the experimental method is the most direct because it involves the least number of a priori assumptions despite the utility of the equilibrium approach in quantifying the isotopic behavior in select water rock

a geophysical transect across the tumut synclinorial zone n s w abstract this integrated geophysical study across the tumut synclinorial zone n s w used seismic magnetic and gravity techniques to determine the structure underlying the zone and the faults which bound it the mooney mooney fault zone to the east and the gilmore fault zone to the west although reflections in the seismic section generally show poor lateral continuity we have recognised domains which display similar reflection character or seismic facies in the seismic data the resulting structural model has been used as the basis for both gravity and magnetic modelling seismic and the gravity interpretations suggest that the mooney mooney fault zone has steep dips to a depth of around 10 km magnetic data suggests that the coolac serpentinite is sub vertical above 7 km depth but declines to the east below this depth below 12 km depth the seismic reflections suggest that structures within the middle crust dip gently to the west the gravity profile is dominated by a positive anomaly west of the mooney mooney fault zone which is associated with the dense bullawyarra schist in the jindalee block the coolac serpentinite dominates the magnetic profiles but has almost no gravity expression a negative bouguer anomaly is associated with the gocup granite and to a lesser extent with the ordovician to early silurian sediments in the tumut block within the tumut synclinorial zone two domains of higher reflectivity are present beneath the jindalee block the top of the first domain is relatively shallow whereas in the tumut block farther to the west the second domain commences beneath the gocup granite at a depth greater than 7 km the tops of these domains are interpreted to be the base of the ordovician to early silurian strata the reflection seismic data indicate no major structural differences between the crust underlying the tumut synclinorial zone and that beneath the goobarragandra block to the east the seismic character of the middle and lower crust of the lachlan fold belt beneath the tumut region is relatively non reflective

mineralogy fluid inclusion and stable isotope studies of the chengchao deposit hubei province eastern china implications for the formation of high grade fe skarn deposits

coseismic and postseismic elastic wave velocity variations caused by the 2008 iwate miyagi nairiku earthquake japan 1 we analyze coseismic and postseismic velocity variations caused by the june 13 2008 iwate miyagi nairiku earthquake mw 6 9 using passive image interferometry pii seismic noise is correlated in order to reconstruct the green s function between two sensors shear wave velocity changes are determined by relating the coda parts of the daily green s functions to a long term reference green s function our study extends from january 2008 to august 2010 and includes the correlations for 190 station pairs in three different frequency ranges from 0 125 to 1 0 hz we show that combining the 9 different component cross correlation functions stabilizes the velocity change estimation and increases analysis resolution the observed velocity change curves can be fitted by model time series consisting of a coseismic velocity drop followed by logarithmic postseismic recovery and seasonal velocity variations the coseismic velocity drops are stronger at higher frequencies and are concentrated in the southern part of the fault zone a tomography algorithm was developed to reproject the observed velocity variations of the different sensor pairs onto the single sensors the depth distribution of coseismic changes was modeled for the three stations with the largest velocity drops at two stations the coseismic velocity changes are located in the upper several hundred meters the third station shows indications for deeper changes in the order of kilometers postseismic recovery takes significantly longer than the analyzed two year period seasonal velocity variations with periods of one year are observed at all analyzed frequencies for most station pairs

co seismic stress transfer and magnitude frequency distribution due to the 2012 varzaqan ahar earthquake doublets m w 6 5 and 6 4 nw iran abstract the coulomb stress changes imparted by the 2012 varzaqan ahar earthquake doublets to the surrounding area have been examined and correlated with the spatial distribution of the aftershocks the stress changes due to the first main shock show that the western half of the south ahar fault the southeastern half of the magnetic lineament ml1 the northeastern end of the ml2 the entire length of the ml3 a large part of the ml4 and the northeastern half of the ml5 were brought closer to failure whereas the entire length of the khajeh fault a part of the north tabriz fault the western half of the ml1 a large part of the ml2 the northwestern end of the ml4 and the southwestern half of the ml5 were moved away from failure along the length of the ml1 some aftershocks were clustered in the southeastern and central sections while around the western section there is no earthquake clustering the epicentral distributions of the aftershocks exhibit that most of the events were concentrated in the increased coulomb stress zones the b value distributions in the map view and in the cross sectional view have been investigated the map view shows that the low b value regions e g the north northwest east northeast and southeast of the main shock are in good agreement with the positive coulomb stress change zones the cross sectional view indicates that the high b value regions correlate with the areas of high co seismic slip release therefore surrounding the hypocenter and the western end of the first main shock fault have high b values more slip and positive stress drop while the central sections of the fault have low b values less slip and negative stress drop

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

stress transferred by the 1995 mw 6 9 kobe japan shock effect on aftershocks and future earthquake probabilities the kobe earthquake struck at the edge of the densely populated osaka kyoto corridor in southwest japan we investigate how the earthquake transferred stress to nearby faults altering their proximity to failure and thus changing earthquake probabilities we find that relative to the pre kobe seismicity kobe aftershocks were concentrated in regions of calculated coulomb stress increase and less common in regions of stress decrease we quantify this relationship by forming the spatial correlation between the seismicity rate change and the coulomb stress change the correlation is significant for stress changes greater than 0 2 1 0 bars 0 02 0 1 mpa and the nonlinear dependence of seismicity rate change on stress change is compatible with a state and rate dependent formulation for earthquake occurrence we extend this analysis to future mainshocks by resolving the stress changes on major faults within 100 km of kobe and calculating the change in probability caused by these stress changes transient effects of the stress changes are incorporated by the state dependent constitutive relation which amplifies the permanent stress changes during the aftershock period earthquake probability framed in this manner is highly time dependent much more so than is assumed in current practice because the probabilities depend on several poorly known parameters of the major faults we estimate uncertainties of the probabilities by monte carlo simulation this enables us to include uncertainties on the elapsed time since the last earthquake the repeat time and its variability and the period of aftershock decay we estimate that a calculated 3 bar 0 3 mpa stress increase on the eastern section of the arima takatsuki tectonic line attl near kyoto causes fivefold increase in the 30 year probability of a subsequent large earthquake near kyoto a 2 bar 0 2 mpa stress decrease on the western section of the attl results in a reduction in probability by a factor of 140 to 2000 the probability of a mw 6 9 earthquake within 50 km of osaka during 1997 2007 is estimated to have risen from 5 6 before the kobe earthquake to 7 11 afterward during 1997 2027 it is estimated to have risen from 14 16 before kobe to 16 22

an ion microprobe study of diagenetic carbonates in the devonian nisku formation of alberta canada abstract diagenetic calcites and dolomites of the upper devonian nisku formation in central alberta canada were analyzed for trace elements by ion microprobe the ion microprobe permits analyses on sample spots comparable in size 20 m to those of conventional electron probes detection limits on the ion microprobe are 1 ppm for many trace elements of interest trace element data obtained by ion microprobe are comparable to those obtained by icp trace element variations in and between upper devonian diagenetic calcites from the nisku formation aid in the interpretation of the fluid composition during precipitation and or recrystallization as well as in the interpretation of primary carbonate mineralogy e g high mg calcite vs aragonite using the ion probe microenvironments as well as temporal variations in diagenetic fluid composition can be resolved the presence of significant trace element variations in nisku carbonates on a scale of 100 m indicates that fluid rock interaction during burial of up to 4000 m and during more than 300 m y was very limited although several of the measured trends probably reflect incomplet retention of primary compositional variations trace element variations in some paleozoic limestones and dolostones reflect variations in fluid composition during primary precipitation as opposed to fluid compositions during recrystallization these findings encourage the use of trace element compositions for diagenetic interpretations even in very old and deeply buried carbonates

post 1906 stress recovery of the san andreas fault system calculated from three dimensional finite element analysis 1 the m 7 8 1906 san francisco earthquake cast a stress shadow across the san andreas fault system inhibiting other large earthquakes for at least 75 years the duration of the stress shadow is a key question in san francisco bay area seismic hazard assessment this study presents a three dimensional 3 d finite element simulation of post 1906 stress recovery the model reproduces observed geologic slip rates on major strike slip faults and produces surface velocity vectors comparable to geodetic measurements fault stressing rates calculated with the finite element model are evaluated against numbers calculated using deep dislocation slip in the finite element model tectonic stressing is distributed throughout the crust and upper mantle whereas tectonic stressing calculated with dislocations is focused mostly on faults in addition the finite element model incorporates postseismic effects such as deep afterslip and viscoelastic relaxation in the upper mantle more distributed stressing and postseismic effects in the finite element model lead to lower calculated tectonic stressing rates and longer stress shadow durations 17 74 years compared with 7 54 years all models considered indicate that the 1906 stress shadow was completely erased by tectonic loading no later than 1980 however the stress shadow still affects present day earthquake probability use of stressing rate parameters calculated with the finite element model yields a 7 12 reduction in 30 year probability caused by the 1906 stress shadow as compared with calculations not incorporating interactions the aggregate interaction based probability on selected segments not including the ruptured san andreas fault is 53 70 versus the noninteraction range of 65 77

analysis of the infiltrative metasomatic relationships controlling skarn mineralization at the abbas abad fe cu deposit isfahan north zefreh fault central iran abstract the abbas abad volcano sedimentary hosted fe cu skarn deposit ne isfahan is one of the most important skarns in the central urumieh dokhtar magmatic arc it was formed along the contact with the dorojin granitoid massif next to the zefreh fault the plutonic rocks are of i type volcanic arc affinity with normal k metaluminous calc alkaline to calcic quartz diorite tonalite and granodiorite similar to many other fe type skarn related granitoids worldwide the parent magma involved in this skarn system is high temperature and relatively oxidized amphibole geobarometery in quartz diorite yielded a crystallization pressure lower than 200 mpa 2 kb 7 km at 724 to 785 c granitoid compositions around the ore deposit are mainly granodiorite u pb zircon dating yields early miocene ages of 23 0 1 6 ma for a quartz dioritic rock and 21 3 1 5 ma for a tonalitic sample the injection and cooling of the granodiorite produced a hornblende hornfels aureole with endoskarn paragenetic relationships and microprobe data indicate that abbas abad calcic skarn evolution can be subdivided into three stages as follow i prograde skarn associated andradite rich garnet adr93 98grs0 4spe1 2 and pyroxene ii retrograde skarn starting with garnet adr53 69grs28 43spe2 4 magnetite and sulfide minerals associated with calcic alteration and iii post ore with pyrite chalcedony epidote quartz calcite and zeolite veinlets textural and compositional studies of garnet and magnetite from the garnet bearing exoskarn zone reveal the multiple events associated with skarn formation garnets are characterized by low tio2 and relatively high cao that are indicative of a calcareous wall rock among eocene volcaniclastic rocks they are grouped into garnet 1 low w r and garnet 2 inverse zoning at high w r with notable cu contents up to 743 ppm petrographically magnetite morphology is divided into fine grained granular needle like and polycrystalline aggregates mineral chemistry of needle like type reveals impure components al2o3 cao and sio2 this type formed from dissolution reprecipitation processes during a stage of reequilibration in the skarn system mixing with cooler external fluid rich in oxygen and poor in fe2 is reflected in individual features during infiltration metasomatism during garnet and magnetite growth such as oscillatory zoning and needle like textures thus we infer increasing ph decreasing acidity and decreasing t related to carbonate neutralization reactions affecting fe and cu chloride complexing as the main controls on mineralization the structural studies of the area show that movement of the dextral transtensional zefreh fault provide local zones for emplacement of dorojin granitoid during the early miocene consequently the dextral transtensional zefreh fault and dextral transpression associated with the marbin rangan fault uplifted the skarn and host units and dorojin body under the roughly n s directed maximum compression direction furthermore the interplay of zefreh and marbin rangan faults within the n s regional compressional regime formed an anticlinal structure that exposed the dorojin body within the core