temporal variations in coda duration of local earthquakes in the wellington region new zealand temporal variations of coda duration relative to event magnitude for local earthquakes near wellington have been investigated the region is one of plate convergence and subduction the data consist of routinely made observations for events from 1978 through 1985 1552 events magnitude 1 6 to 5 2 depth 0 5 to 90 0 km the observed average over time correspondence between duration as measured from the origin time and magnitude is reasonably well predicted by the single backscattering theory of coda formation for events of magnitude 4 or less for larger events the observed durations are longer than predicted this theory predicts that a temporal increase in scattering attenuation will reduce the coda duration relative to magnitude thus any temporal changes in the duration magnitude relation can be interpreted in terms of changes inq however it is necessary to consider spatial biases since the observed durations are relatively long for shallow events and for events of all depths at stations situated in the south eastern half of the region usually believed part of the accretionary border for both these situations other evidence would suggest that the scattering coefficient would be relatively high lowq these observations may be due to a relatively high component of surface wave scattering and the importance of multiple scattering in the later part of the coda in regions of lowq as suggested by finite element studies of coda formation despite the lack of any significant earthquakes during the 1978 1985 period there is nevertheless a significant temporal change in duration observed in the wellington region a change from relatively long to relatively short codas occurred in mid 1981 this change correlates well with changes in the rate of activity b value radon emission and ground tilt as derived from lake levels it is not yet clear how all these parameters are related physically but an episode of aseismic slip or creep along the plate interface below the region may have been the cause

high frequency site effects at two parkfield downhole and surface stations abstract using stacked ratios of microearthquake source spectra recorded at the surface and 200 m downhole we have established the p and s wave site effect at two locations in parkfield california the frequency responses of both sites are bimodal being completely dominated by multiples and amplification below 10 hz and by attenuation above 30 hz the low frequency amplification factors show roughly three to five times more uphole motion compared to that downhole the multiples produce peaks with a maximum of nearly 10 times more uphole motion above 50 hz the downhole motion is always larger approaching a factor of 5 at the high frequency limits of our study when fit with a linear attenuation model the high frequency ratios yield compressional and shear q values between 6 and 19 the data were divided into subsets based on event location and time of year statistical comparison of these subsets shows no systematic variation with azimuth or season the results of our study accounts for the lack of high frequency surface reflections in the parkfield downhole data but not for the lack of source scaling of parkfield microearthquakes

evidence for stability in coda q associated with the egion central greece earthquake of 15 june 1995 one hundred seventy two seismograms recorded at one seismological station located close to the source region of the egion ms 6 2 15 june 1995 earthquake were used to measure values of q from the decay of the earthquake coda the collected data were compared between events that occurred before and after the main event the analysis showed no significant temporal variation in the value of coda q for the region

temporal change in coda q before the tangshan earthquake of 1976 and the haicheng earthquake of 1975 a new earthquake precursor called coda q is demonstrated for the tangshan earthquake of 1976 and for the haicheng earthquake of 1975 the precursor is based on the measurement of coda decay rate for small local earthquakes in the general area that is preparing for a major earthquake during the 3 year period preceding the tangshan earthquake the coda q was about 3 times lower than it was before or after this period a comparable change also occured at the time of the haicheng earthquake the observed change cannot be due to the change in the source parameters such as the focal depth or the source spectrum the coda q precursor appears to detect the same physical process detected by other precursors such as b value quiescence radon water quality vp vs and animal behavior but has advantages over them in its clearer physical mechanism easier sampling and better defined anomalous region

small scale stress heterogeneity in the anza seismic gap southern california focal mechanism inversions reveal significant lateral variations in stress orientations along the anza segment of the san jacinto fault zone the most notable stress anomaly is within the 20 km aseismic seismic gap portion of the fault zone where 1 the maximum compressive stress is nearly horizontal and is oriented at 74 13 relative to the fault strike this contrasts with orientations ranging from 62 11 to 49 7 along the more seismically active portions of the fault zone immediately to the northwest and southeast of the seismic gap regional stress results found by inverting all focal mechanisms simultaneously indicate that 1 is horizontal and trends north south while 3 is horizontal and trends east west approximately 15 km west of the seismic gap in the off fault cahuilla swarm area 1 and 3 solutions are rotated clockwise by about 25 relative to the regional model roughly 10 km southeast of the seismic gap near the buck ridge fault 1 and 3 are rotated counterclockwise by about 10 relative to the regional solution northwest of the seismic gap along the fault zone 3 plunges about 30 from the horizontal correlating with a local increase in reverse faulting between the hot springs and san jacinto faults southeast of the seismic gap 1 plunges about 45 from the horizontal correlating with a local increase in normal faulting in the trifurcation region of the buck ridge clark and coyote creek faults we propose a simple mechanical model in which a block rotation superimposed on the dominant right lateral strikeslip motion of the fault zone satisfies the first order observations of stress orientation faulting and horizontal surface strain under this model the anza seismic gap is the region of zero convergence between the northeast and southwest sides of the fault and the fault zone strength within the seismic gap is either comparable to or exceeds the fault zone strength adjacent to the gap

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

changes in attenuation related to eruptions of mt ruapehu volcano new zealand abstract temporal variations of seismic attenuation have been observed at different volcanoes around the world and are often claimed to correlate with volcanic activity seismic attenuation and its variation in time at mt ruapehu volcano new zealand was measured for the period october 1990 to may 2005 using local earthquakes originating from a nearby cluster of earthquakes called the waiouru swarm as recorded on 5 permanent seismometer stations cross correlation of p and s waves reveals a similarity of events from this ongoing seismic source which suggests that alterations due to source and path effects are minimized therefore the swarm is suitable for the study of temporal changes in seismic attenuation the attenuation q c 1 of coda waves following the direct p and s waves are calculated for five frequency bands centred at 1 5 3 0 6 0 9 0 and 12 0 hz using the single scattering model a best fit equation of q c q 0 f with q 0 54 7 and 1 02 0 06 shows an overall high frequency dependence of coda attenuation which is characteristic for tectonically active regions small fluctuations of q c 1 are observed at all stations over the entire time period and do not act as an apparent indicator of volcanic activity relative changes in integrated direct wave attenuation t along the whole path are obtained using a spectral ratio method in which spectra of individual 1 second p wave windows are compared to a reference spectrum during the time of volcanic activity the following changes were significant at the 95 confidence level in the low frequency band 1 5 6 hz a high attenuation anomaly with an abrupt increase of t by 0 23 s was detected in waveforms that have travelled through the volcano and a shift from negative to positive t by 0 25 s was observed at a station next to the volcano we suggest that these observations are related to variations detected in seismic anisotropy studies which propose a model of a change in stress caused by pressurisation of magma dykes under the volcano

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

temporal changes in attenuation associated with the 2004 m6 0 parkfield earthquake 1 elevated seismic attenuation is often observed in fault zones due to the high degree of fracturing and fluid content however temporal changes in attenuation at the time of an earthquake are poorly constrained but can give indications of fracture damage and healing in this study spectral ratios between earthquakes within repeating clusters are calculated in an attempt to resolve temporal variations in attenuation at the time of the 2004 m6 0 parkfield earthquake a sharp increase in attenuation is observed immediately after the earthquake which then decays over the next 2 years influences of intercluster magnitude variations time window length and previously reported postseismic velocity changes are investigated the postseismic decay is fit by a logarithmic function the timescale of the decay is found to be similar to that in gps data and ambient seismic noise velocities following the 2004 m6 0 parkfield earthquake the amplitude of the attenuation change corresponds to a decrease of approximately 10 in qp at the time of the earthquake the greatest changes are recorded on the northeast of the fault trace consistent with preferential damage in the extensional quadrant behind a north westerly propagating rupture tip our analysis suggests that significant changes in seismic attenuation and hence fracture dilatancy during coseismic rupture are limited to depths of less than about 5 km

stability of coda wave attenuation during the loma prieta california earthquake sequence the loma prieta california earthquake occurred in a densely instrumented region with a history of microearthquake recording beginning more than a decade before the october 1989 mainshock this affords an unprecedented opportunity to detect changes in seismic wave propagation in the earth s crust associated with a major earthquake in this study we use pairs of nearly identical earthquakes doublets to search for temporal changes of coda attenuation in the vicinity of the loma prieta earthquake we analyze 21 earthquake doublets recorded from 1978 to 1991 that span the preseismic coseismic and postseismic intervals and measure the change in coda q using a running window ratio of the doublet spectral amplitudes in three frequency bands from 2 to 15 hz this method provides an estimate of changes in coda q that is insensitive to other factors that influence coda amplitudes our observations place an upper bound of about 5 on preseismic coseismic and postseismic changes of coda q in the epicentral region of the loma prieta earthquake even at this low level the changes are neither spatially coherent nor correlated between adjacent frequency bands the only hint of a signal is in the preseismic data where there is a possible precursory increase in coda q of approximately 5 in the two years before the mainshock the stability of coda q throughout the loma prieta sequence is in sharp contrast to other studies that have reported much larger precursory changes in coda q for other earthquakes

differential analysis of coda q using similar microearthquakes in seismic gaps part 1 techniques and application to seismograms recorded in the anza seismic gap abstract a large but conflicting literature exists that suggests that the scattering properties of the earth in seismogenic areas may be temporally variable and that this variability could be correlated with the nucleation times of moderate to large earthquakes to search for temporal variations in coda q in the vicinity of an expected moderate earthquake nucleation region along the san jacinto fault zone pairs and clusters of earthquakes recorded by the anza seismic network between 1982 and 1992 are examined to minimize differences arising from path and source variability only the most similar examples of microearthquake wave fields are intercompared to assess coda q differences between similar microearthquake signals we search for systematic temporal changes in moving window spectral amplitude ratios for a single scattering coda model with an envelope decay function of the form t m e ft qc the relationship between the natural log amplitude spectral ratio and q 1 q 1 c 2 q 1 c 1 is linear i e ln r f t ft q 1 f w f where w f is a time independent relative source term to obtain robust uncertainty estimates of q 1 f and w f we utilize multi taper spectral analysis coupled with a nonparametric monte carlo confidence interval estimation procedure for the most similar events in the anza region coda cross correlation values of approximately 0 7 for 16 sec of coda we find that coda q as a function of time is stable at a typical 1 resolution of only between 25 and 50 of the reference coda q value for the area even in the best constrained frequency bands comparison of similar microearthquake coda signals with both short and long temporal separations indicates that all of this variability can be reasonably attributed to random fluctuations in the coda that are driven by source variability and is not indicative of any systematic temporal variability in coda q to obtain estimates of relative coda q that are more precise than this level the spectral ratio analysis technique requires significantly more similar earthquakes than are produced by seismogenic processes in the anza region such earthquakes have been observed to occur in other regions of the san andreas fault system and are analyzed in antolik et al 1996

contemporaneous formation of adjacent porphyry and epithermal cu au deposits over 300 ka in northern luzon philippines there is commonly a close spatial relation between porphyry cu au and high sulfidation epithermal cu au deposits throughout the world although a genetic association has not been proven nowhere is this spatial association better seen than in northern luzon philippines where the lepanto epithermal cu au deposit overlies the far southeast fse porphyry cu au deposit both world class orebodies fresh rock and hydrothermal mineral separates yield k ar ages indicating that premineralization and postmineralization volcanism occurred at 2 2 1 8 ma and 1 2 0 9 ma respectively and that the hydrothermal system was active from 1 5 to 1 2 ma k ar ages of alunite from lepanto have the same range as those of hydrothermal biotite and illite from the fse deposit indicating that both epithermal and porphyry mineralization formed from an evolving magmatic hydrothermal system that was active for about 300 ka this temporal relation strengthens the argument for a genetic link between these two styles of ore deposit and has implications for exploration where one style of mineralization is found there is potential for the other nearby

evolution of hydrothermal fluid characteristics at the santa rita new mexico porphyry copper deposit mineralogic and fluid inclusion investigations conducted in the laboratory combined with in situ observations of temporal relationships among geologic features demonstrate that systematic changes in hydrothermal fluid characteristics occurred with time during evolution of mineralization and alteration of the granodiorite stock at the santa rita porphyry copper deposit the earliest fluids to circulate are recorded in potassically altered orthoclase and biotite stable veins as vapor rich h 2 o co 2 inclusions and hypersaline 30 70 equiv wt nacl or kcl inclusions which homogenize over a wide temperature range from 240 degrees to greater than 800 degrees c the high salinity fluid inclusions are complex chloride brines with significant concentrations of sodium potassium copper iron and sulfur but sulfide minerals are not associated with the early potassic assemblage produced by this fluid oxygen isotope ratios of quartz in the orthoclase and biotite stable veins are identical to phenocryst quartz in the intrusion 8 2ppm later solutions circulated through newly formed fractures and older reopened veins and are recorded in low salinity less than 15 equiv wt nacl fluid inclusions which homogenize primarily in the temperature range of 220 degrees to 360 degrees c these hydrothermal fluids formed two distinct alteration assemblages as they reacted with potassically altered rock chlorite is the dominant silicate gangue mineral of the earlier chalcopyrite bearing orthoclase and clay stable assemblages and sericite characterizes the later phyllic alteration assemblage with quartz and pyrite oxygen isotope ratios of quartz of the later assemblages 8 6 10 4ppm are heavier than quartz of the earlier potassic assemblages it is concluded that the earliest hydrothermal fluids to circulate within the stock localizing the orebody at santa rita could have been derived by phase separations of fluids exsolved from crystallizing magma into condensed hypersaline liquids and h 2 o co 2 vapors as these fluids moved through fractures potassic alteration of rock occurred without concomitant deposition of sulfides later solutions of dominantly meteoric origin progressively formed hypogene copper mineralization associated with chlorite stable alteration and then phyllic alteration

a temporal change in coda wave attenuation observed during an eruption of mount st helens during the past few years there have been numerous reports of changes in coda wave attenuation occurring before major earthquakes these observations are important because they may provide insight into stress related structural changes taking place in the focal region prior to the occurrence of large earthquakes the results of these studies led us to suspect that temporal changes in coda wave attenuation might also accompany volcanic eruptions by measuring power decay envelopes for earthquakes at mount st helens recorded before during and after an eruption that took place during september 3 6 1981 we found that coda q sup 1 for frequencies between 6 and 30 hz was 20 30 higher before the eruption than after the change is attributed to an increase in the density of open microcracks in the rock associated with inflation of the volcano prior to the eruption q sup 1 was found to be only weakly dependent on frequency and displayed a slight peak near 10 hz the weak frequency dependence is attributed to the dominance of intrinsic attenuation over scattering attenuation since it is generally accepted that intrinsic attenuation is constant with frequency whereas scattering attenuation decreases strongly at higher frequencies the weak frequency dependence of q sup 1 more at mount st helens contrasts with results reported for studies in nonvolcanic regions the peak in q sup 1 near 10 hz at mount st helens is attributed to the scale length of heterogeneity responsible for generating backscattered waves results for nonvolcanic regions have shown this peak to occur near 0 5 hz thus a smaller scale length of heterogeneity is required to explain the 10 hz peak at mount st helens copyright american geophysical union 1988 less

thermal and dynamical regimes of single and two phase magmatic flow in dikes finite element calculations of magma flow in dikelike channels with length to width ratios of 1000 1 or more have been used to investigate the coupling between thermal and dynamical regimes due to temperature dependent viscosity and dissipation steady state solutions with realistic thermal and dynamical parameter values have been obtained the models show that the onset of solidification on the boundaries of a basaltic or andesitic dike as predicted by idealized laminar flow models can be prevented or significantly delayed by a small amount of transverse flow induced by rising bubbles boundary roughness or turbulence this effect will reduce the critical initial widths of dikes estimated by bruce and huppert 1989 in the absence of transverse flow the bulk temperature of the magma may actually increase slightly with distance along the dike as a result of viscous dissipation even while solidification is occurring on the walls of the dike with converging or necking dike walls it is found that boundary temperatures fall to a minimum and then increase with distance along a dike even if viscous heating is neglected for viscous heating to offset significant rates of heat loss 2 kw m2 in a plane parallel 1 m wide basaltic dike an average flow velocity of 2 7 m s driven by a pressure gradient of 1 7 mpa km is required a 7 void fraction caused by exsolution of volatiles or chamber gas in the magma will produce this pressure gradient the ease of producing such a gradient by reducing the density of the magmatic column with addition of a gas phase makes it likely that flows of basaltic magma could be maintained in dikes tens of kilometers long furthermore a gas phase may be important for the propagation of the fracture prior to the initial injection of magma during dike emplacement rapid transport of more silicic magmas through dikes is inhibited by the requirement of large driving pressure gradients exceeding several hundred megapascals per kilometer however the pressure gradient can be substantially reduced if the magma is a heterogenous mixture of a predominantly silicic component with a more mafic component pipe flow experiments involving molten polymers that exhibit dynamical similarity to magmas strongly suggest that unmixing occurs when a two component magma mixture in which the components have different viscosities rises within a dike within a few dike widths of the inlet the less viscous mafic component encapsulates the more viscous silicic part effectively lubricating the passage of the more viscous component compositional variations in the obsidian dome volcano support the occurrence of this pressure reduction or self lubrication mechanism such a self lubrication process often may be necessary to permit very viscous magmas to reach earth s surface if so chemical and lithologic zoning would be anticipated as a common feature of near surface intrusions or lava flows that are characterized by a high silica and or high crystal content such as at deadman dome in long valley california

temporal and spatial variation on coda q 1 associated with the north palm springs earthquake of july 8 1986 a temporal and spatial change of codaq 1 associated with the occurrence of the north palm springs earthquake of july 8 1986 was studied by using 242 small local earthquakes in the vicinity of the mainshock we found that the codaq 1 of earthquakes which occurred before the mainshock was significantly higher than that of the aftershocks in the mainshock area while the codaq 1 for the surrounding area remained almost constant throughout 1986 codaq 1 was determined separately for the lapse time windows of 10 to 20 sec and 15 to 40 sec for the period from 1981 to 1987 the result for the time window 10 to 20 sec showed a peak in codaq 1 before the time of mainshock at all frequencies the peak appeared earlier at lower frequencies there was no significant change in codaq 1 for the time window 15 to 40 sec probably because the change was restricted to a small area

variations in rupture process with recurrence interval in a repeated small earthquake in theory and in laboratory experiments friction on sliding surfaces such as rock glass and metal increases with time since the previous episode of slip1 this time dependence is a central pillar of the friction laws widely used to model earthquake phenomena2 3 on natural faults other properties such as rupture velocity4 5 porosity and fluid pressure6 11 may also vary with the recurrence interval eighteen repetitions of the same small earthquake separated by intervals ranging from a few days to several years allow us to test these laboratory predictions in situ the events with the longest time since the previous earthquake tend to have about 15 larger seismic moment than those with the shortest intervals although this trend is weak in addition the rupture durations of the events with the longest recurrence intervals are more than a factor of two shorter than for the events with the shortest intervals both decreased duration and increased friction are consistent with progressive fault healing during the time of stationary contact

seismic waveform attributes before and after the loma prieta earthquake scattering change near the earthquake and temporal recovery during 1987 1995 several clusters of nearly identical seismic events multiplets occurred near the loma prieta source region these multiplets allow us to investigate and demonstrate spatial and temporal changes in seismic wave character associated with the 1989 loma prieta main shock for seismogram pairs we use a moving window technique to compute coherencies depending on lapse time and frequency post loma prieta events have reduced coherencies with pre loma prieta events in a spatially limited region close to the loma prieta hypocenter while other paths remain nearly unaffected these changes gradually recover within a time interval of 5 years after the loma prieta earthquake a possible explanation for the time dependence is coseismically opened cracks which cause scattering increase for wavefields after the loma prieta event postseismic relaxation processes such as crack healing fluid diffusion or after deformations lead to progressive closure of these cracks with time after the main shock thus the scattering properties of the local crust approach the pre main shock state

plume spreading in groundwater by stretching and folding 1 this paper proposes a new approach to the hydraulics of in situ groundwater remediation in situ remediation promotes reactions between an injected treatment solution and the contaminated groundwater but without a hydraulic mechanism to promote spreading the laminar flows characteristic of porous media will keep the two fluids in approximately the same relative configuration as they travel through the aquifer limiting the opportunity for reactions to occur to address this fundamental limitation this paper borrows a key result from the fluid mechanics literature spreading in laminar flows is optimized by chaotic advection previous studies have applied this result to groundwater remediation using the pulsed dipole model but that model depends on reinjection of fluid which presents a number of theoretical and practical limitations accordingly this paper proposes a new conceptual model for plume spreading by chaotic advection using an engineered sequence of extractions and injections of clean water at an array of wells which generates plume spreading by stretching and folding the fluid interface between the injected treatment solution and the contaminated groundwater but does not require reinjection the paper includes an overview of the analytical techniques poincare sections periodic points stable and unstable manifolds heteroclinic points and lyapunov exponents used to demonstrate chaotic advection in the limiting case in which diffusion is negligible numerical simulations show that spreading by stretching and folding is complimentary to spreading resulting from aquifer heterogeneity

temporal changes in coda q 1 and b value due to the static stress change associated with the 1995 hyogo ken nanbu earthquake the seismicity in the tamba region northeast of the hyogo ken nanbu earthquake in japan january 17 1995 mjma 7 2 increased significantly following this earthquake this increase suggests that the static stress change due to a large earthquake causes a change in the crustal condition or dynamics in order to reveal the changes quantitatively we investigate the temporal variation in coda q l and b value in the tamba region we analyze the waveform data of many shallow microearthquakes m 1 5 3 0 in the region recorded in a period from 1987 to 1996 coda q 1 is estimated in 10 frequency bands in a range of 1 5 24 hz based on the single isotropic scattering model at frequencies between 1 5 and 4 0 hz the temporal variation in coda q 1 shows significant correlation with the occurrence of the hyogo ken nanbu earthquake coda q l increases after the event a variation in b value whose sign is opposite to that of coda q 1 is recognized the fracture dimensions of microearthquakes that contribute to the variation in b value are estimated to be 400 m this scale length is consistent with the characteristic scale length of scatterer 300 600 m which contributes effectively to a temporal variation in coda q 1 the crustal activity in the tamba region is possibly controlled by the heterogeneity with dominant scale of 102 m the stress sensitivity of the coda q 1 change is estimated to be 10 mpa 1 this value is an order of magnitude larger than the stress sensitivity of seismic velocity reported before

intensity of quartz cathodoluminescence and trace element content in quartz from the porphyry copper deposit at butte montana textures of hydrothermal quartz revealed by cathodoluminescence using a scanning electron microscope sem cl refl ect the physical and chemical environment of quartz formation variations in intensity of sem cl can be used to distinguish among quartz from superimposed mineralization events in a single vein in this study we present a technique to quantify the cathodoluminescent intensity of quartz within individual and among multiple samples to relate luminescence intensity to specific mineralizing events this technique has been applied to plutonic quartz and three generations of hydrothermal veins at the porphyry copper deposit in butte montana analyzed veins include early quartz molybdenite veins with potassic alteration pyrite quartz veins with sericitic alteration and main stage veins with intense sericitic alteration cl intensity of quartz is diagnostic of each mineralizing event and can be used to fingerprint quartz and its fluid inclusions isotopes trace elements etc from specific mineralizing episodes furthermore cl intensity increases proportional to temperature of quartz formation such that plutonic quartz from the butte quartz monzonite bqm that crystallized at temperatures near 750 c luminesces with the highest intensity whereas quartz that precipitated at 250 c in main stage veins luminesces with the least intensity trace element analyses via electron microprobe and laser ablation icp ms indicate that plutonic quartz and each generation of hydrothermal quartz from butte is dominated by characteristic trace amounts of al p ti and fe thus in addition to cl intensity each generation of quartz can be distinguished based on its unique trace element content aluminum is generally the most abundant element in all generations of quartz typically between 50 and 200 ppm but low temperature main stage quartz containing 400 to 3600 ppm al is enriched by an order of magnitude relative to all other quartz generations phosphorous is present in abundances between 25 and 75 ppm and p concentrations in quartz show little variation among quartz generations iron is the least abundant of these elements in most quartz types and is slightly enriched in cl dark quartz in pyrite quartz veins with sericitic alteration titanium is directly correlated with both temperature of quartz precipitation and intensity of quartz luminescence such that bqm quartz contains hundreds of ppm ti whereas main stage quartz contains less than 10 ppm ti our results suggest that ti concentration in quartz is controlled by temperature of quartz precipitation and that increased ti concentrations in quartz may be responsible for increased cl intensities

changes in source and site effects compared to coda q 1 temporal variations using microearthquakes doublets in california we analyse spectral ratio of the coda of doublets of microearthquakes our purpose is to find evidence for temporal changes of the attenuation in the crust before a large magnitude earthquake a moving window cross spectral analysis of the coda of doublets gives a plot of the spectral ratio as a function of lapse time along the seismogram for several frequency bands sr t f plot from a certain pattern in thesr t f plot we should infer a temporal change in coda attenuation several doublets recorded in central california by the usgs network are analysed

late quaternary rate of slip along the san jacinto fault zone near anza southern california the anza section of the san jacinto fault southern california has not experienced a groundbreaking earthquake since at least 1918 and probably since before 1899 leading previous workers to designate this 20 km long fault segment as a seismic gap study of displaced pleistocene and holocene alluvial fan and fluvial deposits across the san jacinto fault near anza california dated using 14c and soil development age control indicates a minimum right lateral slip rate of 9 2 2 mm yr since 9 5 ka and a slip rate of 11 9 5 mm yr since 14 ka 12 9 5 mm yr since 17 ka and 13 10 6 mm yr since 50 ka these estimates agree with a previously determined 700 ka to present minimum slip rate of 10 2 mm yr based on an estimated average slip rate of 12 mm yr from the longer term slip rate estimates about 0 8 m of potential slip has accumulated if the 1918 earthquake broke the anza segment over 1 1 m of potential slip has accumulated if the last earthquake occurred prior to 1899 these data attest to the potential for an earthquake m6 5 for this section of the fault

hypocenter migration as an explanation for temporal changes in coda q in the 1993 earthquake swarm near the norris lake community georgia qc coda q and b value exhibit systematic temporal variations on a scale of months and hours the long term monthly variations correlate with the swarm s growth and decay examination of the hypocenters demonstrates that q is a strong function of hypocenter and the temporal variations of q reflect a systematic migration of hypocenters the b value appears to vary in this swarm because the method of magnitude determination is dependent on qc throughout the duration of the swarm the active areas migrated from a high qc area eastward to a low qc area variations of qc over periods of hours were explained by a shifting ofhypocenters between high and low qc areas significant changes in qc occur for hypocenters that are separated by distances 10 km the nonuniform fractal distribution of relative scattering coefficients plays a major role in determining the spatial dependence of q by using forward coda modeling on the distribution of relative scattering coefficients derived for this earthquake swarm we can reproduce seismic coda with the same spatial dependence on q as found in the earthquakes throughout the swarm the relative locations of earthquakes associated with different q values and our ability to model different q values from a known distribution of relative scattering coefficients confirm that the migration of hypocenters and not a temporal change in attenuation properties determines the temporal variation of qc observed during the norris lake community earthquake swarm

site amplification of coda waves from local earthquakes in central california the goals of this study are two fold 1 to examine the site effect of coda waves believed to be the average site effect of shear waves in order to understand its spatial and frequency dependent behavior and 2 to learn what we can about the processes that generate the coda itself we use digital data from over 90 earthquakes each recorded by a subset of some 150 stations in the coast ranges of central california between san francisco and san luis obispo results from the band 1 5 to 24 hz indicate that site amplification depends strongly on surface geology and frequency at low frequencies 1 5 to 3 0 hz changes in amplification up to a factor of 20 are observed amplification generally varies inversely with deposit age at sediment sites and is lowest at granite and franciscan basement sites at high frequencies 6 to 24 hz the pattern changes many granite sites the majority in the gabilan range exhibit increasing amplification with frequency relative to the average station this behavior differs strikingly from that observed at sediment and franciscan sites which roll off at an intermediate rate and many sediment sites adjacent to the san andreas fault zone which decay away even more rapidly with frequency these results can be explained qualitatively by appealing to variable near site impedance and attenuation however complicating phenomena such as mode excitation in valley sediments must exist at low frequencies peaked behavior at a few hard rock sites at high frequency 12 hz currently lacks explanation at a few sediment sites the low frequency excitation is so strong that the coda envelopes begin to take on different shapes this contradicts the assumption based on previous observations that the coda shape is independent of source receiver location thus some site measurements may be artificially high the working model of coda waves as body wave energy backscattered from randomly distributed inhomogeneities must be modified to include the possibility of efficient near site resonance excited by incident direct and coda wave energy

seismological studies at parkfield ii search for temporal variations in wave propagation using vibroseis abstract for more than 3 years the propagation characteristics of shear waves have been monitored for paths near the 1966 hypocenter at parkfield the presumed nucleation site for the expected next m 6 earthquake there data have been collected repeatedly 33 sets as of april 1991 from eight s wave vibroseis source positions into the 10 borehole installed three component seismometers of the local high sensitivity digital network twenty second correlated records from a 6 to 24 hz sweep are acquired and the entire seismogram is viewed for analysis as the elastic response of the local crustal structure which includes the san andreas fault zone amplitudes travel times spectra and particle motions of the p and s waves are monitored for indications of any changes in these properties that may be attributed to processes associated with nucleation the horizontal vibrator at each source point is positioned at three surface orientations to study anisotropy unorthodox methods have been developed to display the waveform properties in time in order to visualize the resulting massive data sets the first order variations seen in some of the parameters are attributed to changes from dry to wet conditions in the shallow subsurface due to the seasonal rainfall which affects the source function of the vibrator corrections have been devised for these source specific variations secular variations not obviously coupled to seasonal near surface changes are also seen in some localized time intervals within the 20 sec records the most striking of such changes is a progressive travel time decrease at rates of 3 to 7 msec year seen for late arrivals 7 to 11 sec travel time on at least five paths into station vca which sample the region southeast of the anticipated epicenter at middle mountain this anomaly appears to be genuine and is now the subject of intensified study in the same general area along the fault in the southwestern block the direct s wave is clearly split with the faster of the split phases polarized parallel to the fault zone a result in agreement with that from the vsp survey in the varian well on the northeast side of the fault

the aitik cu au ag deposit in northern sweden a product of high salinity fluids the aitik cu au ag deposit is located in northern sweden and is hosted by strongly deformed 1 9 ga svecofennian volcano sedimentary rocks the main copper mineralization which occurs as disseminations and veinlets is hosted by garnet biotite schist subeconomic mineralization in the footwall to the ore is hosted by feldspar biotite amphibole gneiss and porphyritic quartz monzodiorite the deposit has been affected by post mineralization metamorphic and igneous activity fluid inclusions in six samples of copper mineralized quartz veins record the presence of three different fluid populations the main ore was deposited from an aqueous highly saline 31 37 eq wt nacl cacl2 fluid this fluid was trapped in inclusions intimately associated with the main chalcopyrite mineralization later bornite deposition took place from a less saline 18 27 eq wt nacl cacl2 aqueous fluid a third fluid composed of almost pure co2 interacted with the copper rich system during a post ore event the aitik cu au ag deposit shares some features with both porphyry type and fe oxide cu au deposits a high calcium content of the ore fluids similar to other cu au deposits in northern scandinavia suggests a contribution to the salinity of the mainly magmatic hydrothermal fluids from evaporitic rocks in stratigraphically lower units

quantitative measurements of shear wave polarizations at the anza seismic network southern california implications for shear wave splitting and earthquake prediction we analyze shear wave polarizations from local earthquakes recorded by the anza network in southern california using an automated method which provides unbiased and quantitative measurements of the polarization and the duration of linear motion following the shear wave arrival the linearity interval initial shear wave particle motions are strongly aligned at four stations a feature that is not predicted by focal mechanisms the particle motion alignment is most likely caused by shear wave splitting due to anisotropy beneath these stations a result supported by the clear shear wave splitting seen in a borehole recording near one of the anza stations these results are consistent with an earlier analysis of these data by peacock et al 1988 however our analysis does not support claims by crampin et al 1990 that shear wave splitting delay times at station knw exhibit temporal variations which can be correlated with the occurrence of the north palm springs earthquake ml 5 6 of july 8 1986 automatically determined linearity intervals scatter widely from 0 02 to 0 15 s and exhibit no clear temporal trends we find a correlation between earthquake moment and the linearity interval possibly a result of longer effective source time functions for the larger events the inability to identify a distinct slow quasi shear wave pulse for the vast majority of these events indicates that scattering strongly affects the particle motion even in the very early shear wave coda analysis of earthquake clusters with similar waveforms recorded at knw shows that seismic green functions are stable throughout the observational period and that most linearity interval variation is due to source and ray path differences between events if shear wave splitting is causing the observed delay times between horizontal components the waveform stability for events in these clusters restricts any temporal changes in shear wave splitting delay times to less than 5 10

seismic quiescence before the landers m 7 5 and big bear m 6 5 1992 earthquakes the landers earthquake of 28 june 1992 was preceded by a seismicity rate decrease of 75 in a volume approximately 11 by 23 by 15 km located adjacent to and north of the epicenter this anomaly started for all magnitude bands in january 1988 lasting 4 5 yr up to the mainshock a smaller volume 7 by 14 by 15 km to the south of the epicenter showed a seismicity rate decrease of 75 starting in november 1989 the big bear earthquake of the same day was preceded by a 100 decrease of the seismicity rate within a volume of approximately 13 by 22 by 15 km around the hypocenter this volume contained 192 earthquakes of m 1 6 during the background period of 9 yr but none during the 1 6 yr from december 1990 to 27 june 1992 the standard deviate z values characterizing these rate changes are very high 6 3 and 12 3 respectively and the anomalies are unique not surpassed in significance by any other rate decrease in portion of the southern california earthquake catalog examined 117 06 w to 115 40 w and 33 45 n to 35 10 n no seismicity rate change was found in the vicinity of the m 6 1 joshua tree earthquake of 23 april 1992 based on magnitude signatures and frequency magnitude analyses we conclude that the two quiescence anomalies could not have been due to a shift or a compression of the magnitude scale and we interpret them as precursor anomalies this analysis was carried out using the declustered earthquake catalog for the landers area with corrections of 0 2 and 0 1 august 1985 and may 1990 for two suspected magnitude shifts with a new visualization technique we can investigate the stability and changes of the seismicity rate as a function of time and space by mapping z values for rate changes at every time interval and in volumes centered on a dense grid of points latitude longitude this computer code furnishes an almost continuous sequence of smooth contour maps of the degree of rate changes any anomalies artificial or real may thus be defined accurately

site amplification and attenuation of strong ground motion abstract at the mcgee creek california site three component strong motion accelerometers are located at depths of 166 m 35 m and 0 m the surface material is glacial moraine to a depth of 30 5 m overlying hornfels accelerations were recorded from two california earthquakes round valley m l 5 8 23 november 1984 18 08 utc and chalfant valley m l 6 4 21 july 1986 14 42 utc anti plane shear strains for the round valley and chalfant valley events are less than 1 8 10 5 and 1 2 10 5 respectively by separating out the sh components of acceleration we were able to determine the orientations of the downhole instruments peak sh accelerations at the surface were 5 7 times greater than those at 166 m in both earthquakes a constant phase velocity haskell thomson model was applied to generate synthetic sh seismograms at the surface using the accelerations recorded at 166 m in the frequency band 0 10 to 10 0 hz we compared the filtered synthetic records to the filtered surface data the onset of the sh pulse and the reflections from the interface at 30 5 m are clearly seen in both the synthetics and the recorded data the synthetic records closely match the data in both amplitude and phase the fit between the synthetic accelerograms and the data indicates that the seismic amplification at the surface is a result of the resonance of the surface layers and the contrast of the impedances shear stiffness of the near surface materials the impedance contrast of the materials does not account for all of the amplification of the peak accelerations at the surface the resonances of the layer system below 10 hz contribute the most to this amplification we find that a linear model predicts the soil response for frequencies up to 10 hz material damping is added to the soil layers of the model in the form of a quality factor q the damping moderates the strong resonance effects by allowing energy to radiate into the half space the quality factor q 10 is constant in this frequency range but does not accurately model the attenuation at frequencies above 10 hz

mineralogic and stable isotope zonation at the surface over the el salvador porphyry copper deposit chile we examined in detail the mineralogic and stable isotope characteristics of alteration minerals exposed at the surface of the el salvador porphyry copper deposit a total of 276 samples was collected from 203 localities over an area of 5 km 2 at elevations between 2 900 and 3 300 m the alteration assemblages can be separated into two groups broadly corresponding to the stages previously identified from underground studies although the early stage k silicate alteration identified underground is not evident at the surface a transitional to late stage is characterized at the surface by assemblages of 1 muscovite andalusite with trace diaspore including some areas rich in andalusite and 2 muscovite with trace diaspore there is a sharp contact outward with a marginal propylitic assemblage chlorite calcite epidote pyrophyllite occurs as a retrograde overprint of muscovite in both of the transitional to late stage assemblages these assemblages are concentrically zoned and centered on a core of least altered granodiorite porphyry a late intramineral intrusion the muscovite andalusite assemblage occurs up to 500 m away from the granodiorite porphyry and andalusite rich zones are located near the brecciated margin of the porphyry further outward is the muscovite zone from 500 to 1 500 m wide the pyrophyllite overprint overlaps the contact of the muscovite andalusite and muscovite zones and occurs mainly above 3 000 m elevation such that its present distribution is controlled largely by topography very late alteration minerals occur in radial pebble dikes of hydrothermal breccia and their extensions and they are dominated by an advanced argillic assemblage of alunite aluminum phosphate sulfate minerals diaspore zunyite pyrophyllite dickite with residual muscovite in one case a breccia extends upward and appears to be the root of a 300 500 m outcrop 80 m thick of massive quartz alunite replacement of rhyolite pure mineral separates were prepared from these samples for o h and s isotope analysis including 48 samples of silicate minerals muscovite pyrophyllite dickite and supergene kaolinite and 20 samples of alunite some supergene in origin information on mineral assemblage was used to estimate temperatures of formation which then allowed calculation of the isotopic composition of associated hydrothermal fluids the fluid responsible for forming the muscovite had a relatively narrow range of isotopic composition 6 5 1 5 per mil 18 o and 40 10 per mil d the heaviest 18 o and d values about 8 and 35 per mil respectively were obtained from the samples with andalusite muscovite diaspore assemblage this composition is close to that expected for a magmatic fluid with 10 to 20 percent meteoric water component responsible for forming the other muscovite samples the fluid compositions calculated for the very late stage alunite range from 5 and 30 per mil to 1 and 40 per mil 18 o and d respectively this range in composition agrees with the trend predicted for magmatic vapor absorbed by local groundwater the latter similar in composition to that responsible for forming the supergene kaolinite there is no systematic spatial zonation of the alunite samples in terms of isotopic composition or paleotemperature the temperature estimates from s isotope geothermometry are higher than those based on mineral assemblage possibly caused by partial supergene replacement of some hypogene alunites there is no strong isotopic zonation of hydrothermal minerals from surface alteration assemblages at el salvador that can be applied to generate clear exploration guidelines by contrast mapping of alteration mineralogy in the field backed up by laboratory checking of mineralogy and examination of relict minerals and replacement textures in thin section clearly indicates the center of the late intramineral intrusion

origins of amplitude variations in seismic doublets source or attenuation process summary accurate estimates of spectral ratios of two doublets i e similar seismic events occurring along the san andreas fault in the hollister region have been computed using a cross spectral method both events of each doublet occurred within a 24 hr interval although both waveforms of a doublet are remarkably similar computed spectral ratios exhibit strong but steady variations with frequency in the first arrivals the attenuation process can explain neither the sign nor the order of magnitude of these variations on the contrary they are closely related to the source mechanism we show that the slope computed from the linear and coherent part of the spectral ratio is an estimation of the variation in the apparent rupture duration between the two events one doublet exhibits an azimuthal distribution of the spectral ratio variations that is interpreted as the result of a change in the position of the hypocentres relative to the rupture area for this doublet location of hypocentres varies only from 10 to 30 per cent of the source length this points out that small changes in rupture kinematics can lead to significant variations in the spectral ratio of earthquake doublets i e in the amplitude of each event for the other doublet the variations are related to a change in source length we also have computed spectral ratios all along the seismograms using a moving window technique when an azimuthal distribution of the spectral ratio is observed in the first arrivals we notice a decrease of the spectral ratio all along the seismograms the doublet with strong but non azimuthal variations of the spectral ratio in the first arrivals does not indicate such a decrease of the spectral ratio along the seismogram this implies that the variations of the coda decay are related not only to temporal or spatial changes of attenuation but also to source parameters these variations have the same order of magnitude as those provoked by a temporal change in coda q of 10 per cent they can occult time changes of spectral ratio for instance in case the attenuation in the crust would vary before a strong earthquake

seismicity of the hellenic subduction zone in the area of western and central crete observed by temporary local seismic networks temporary local seismic networks were installed in western crete in central crete and on the island gavdos south of western crete respectively in order to image shallow seismically active zones of the hellenic subduction zone more than 4000 events in the magnitude range between 0 5 and 4 8 were detected and localized the resulting three dimensional hypocenter distribution allows the localization of seismically active zones in the area of western and central crete from the mediterranean ridge to the cretan sea furthermore a three dimensional structural model of the studied region was compiled based on results of wide angle seismics surface wave analysis and receiver function studies the comparison of the hypocenter distribution and the structure has allowed intraplate and interplate seismicity to be distinguished high interplate seismicity along the interface between the subducting african lithosphere and the aegean lithosphere was found south of western crete where the interface is located at about 20 to 40 km depth an offset between the southern border of the aegean lithosphere and the southern border of active interplate seismicity is observed in the area of crete the offset varies laterally along the hellenic arc between about 50 and 70 km a southwards dipping zone of high seismicity within the aegean lithosphere is found south of central crete in the region of the ptolemy trench it reaches from the interface between the plates at about 30 km depth towards the surface in comparison the aegean lithosphere south of western crete is seismically much less active including the region of the ionian trench intraplate seismicity within the aegean plate beneath crete and north of crete is confined to the upper about 20 km between 20 and 40 km depth beneath crete the aegean lithosphere appears to be seismically inactive in western crete the southern and western borders of this aseismic zone correlate strongly with the coastline of crete

earthquake cluster what can we learn from waveform similarity abstract the seismograms of earthquakes which have closely spaced hypocenters tend to be similar due to the similarity of the green s functions characterizing the source receiver paths based on the 4 criterion it is frequently argued that similar earthquakes may represent repeated slip of the same patch of a fault because of the phenomenological nature of waveform similarity such interpretations are strongly dependent on seismic signal characteristics and on the way the waveform similarity is defined in this article we use two dimensional synthetic wave field simulations in lateral heterogeneous media to investigate how the waveform similarity of closely spaced hypocenters changes with interevent separation we analyze the influence of correlation window length signal frequency bandwidth and source receiver geometry on the waveform similarity and discuss under which conditions the 4 criterion can be applied to the synthetic data set with the correlation window length defined as 2 8 times the travel time difference between the s and p phase onsets we find a correlation threshold value of 0 95 independent of the signal frequency bandwidth we use the same threshold value for two field data examples that are similar to the synthetic data in frequency content and waveform complexity and we discuss the implications of the 4 criterion for three microearthquakes occurring during a fluid injection experiment at the german deep drilling site kontinentale tiefbohrung ktb the interevent separation constrained by the 4 criterion is sufficient to identify these events as a sequence of repeating earthquakes in the sense that at least a fraction of the source area experienced repeated slip for a second data example of four natural micro earthquakes occurring near the island of crete the 4 criterion does not sufficiently constrain the hypocenter location to identify these events as repeating earthquakes due to the lack of high frequency information

precise determination of the relative wave propagation parameters of similar events using a small aperture seismic array 1 we propose a method to determine accurately the relative wave propagation parameters apparent slowness and propagation azimuth of a cluster of seismic events with similar waveforms recorded on a seismic array this relative slowness estimate relse method is based on precise measurements of the delays among arrivals of different earthquakes to each of the array receivers delays are determined using interpolations of the cross correlation functions of the earthquake waveforms accurate relative slowness vectors are estimated using a least squares fit of the observed delays to the delays corresponding to the arrivals of plane wave fronts we tested the method using both synthetics and real data in order to understand its resolution capabilities in presence of seismic noise and to assess the uncertainty regions associated with the slowness vector estimates from these analyses we establish a procedure to determine the 90 uncertainty regions associated with the estimates of relative slowness vectors as an example of application of the relse method we analyzed a multiplet composed of 16 similar earthquakes recorded during the 1999 seismic crisis at deception island volcano antarctica using a conventional slowness estimate method produces virtually the same result for every earthquake because of the large uncertainties alternatively using the relse method reduces the uncertainties of the estimates and allows to resolve the detailed distribution of relative apparent slowness vectors our results show that the slowness vectors are aligned within a narrow north south trending band which represents a clue toward the features of the source region and or source distribution we repeated the procedure using different earthquakes as master events the estimated distribution of slowness vectors is similar in every case which demonstrates that our results are independent of the choice of reference event index terms 7299 seismology general or miscellaneous 7203 seismology body wave propagation 7215 seismology earthquake parameters 7230 seismology seismicity and seismotectonics 7280 seismology volcano seismology 8419 keywords seismic arrays slowness vectors multiplet analysis deception island volcano

metal fractionation between magmatic brine and vapor determined by microanalysis of fluid inclusions the major and trace element compositions of individual fluid inclusions from a range of magmatic hydrothermal ore deposits were analyzed by laser ablation inductively coupled plasma mass spectrometry to explore the behavior of ore forming components during fluid phase separation boiling in high temperature saline fluid systems data from 13 samples showing unambiguous evidence for coeval trapping of a liquid brine and a coexisting vapor phase identify two groups of elements with drastically different geochemical behavior na k fe mn zn rb cs ag sn pb and tl preferentially partition into the brine probably as cl complexes whereas cu as au probably as hs complexes and b selectively partition into the vapor fluid phase separation is probably a major previously underestimated process in the chemical differentiation that contributes to the extreme range of selective element enrichments in magmatic hydrothermal systems from deep plutons through porphyry style and greisen deposits to epithermal mineralization and volcanic fumaroles

spatial and temporal correlation between coda q 1 and seismicity and its physical mechanism from the analysis of local earthquake coda waves recorded by the benioff short period vertical seismograph at riverside california we found a surprisingly large and systematic temporal variation in coda q 1 in the southern california during the 55 year period from 1933 to 1987 comparison of the coda q 1 variation with the b value obtained for earthquakes with m 3 occurred in the area within 180 km from riverside corresponding to the area for which q 1 is estimated by the coda method led to an extraordinary result that coda q 1 correlates positively with b value with the correlation coefficient of 0 79 the significance of correlation cannot be rejected at the confidence level of 0 974 since the data used for measuring q 1 namely the coda part of seismograms and the data used for measuring b namely the seismicity catalog are totally independent the observed correlation supports strongly the physical reality of temporal change in both coda q 1 and b value the correlation between coda q 1 and b value has been reported for several other cases but the correlation was positive in some cases and negative in others our current preferred model for explaining the observed correlation is the following aseismic creep is going on from time to time over various sizes of cracks in the ductile part and in some cases in the brittle part of lithosphere at and near the plate boundary creep activities tend to increase the crack density and coda q 1 observed in the region if the creek occurs over distributed cracks with a certain predominant scale length spatial stress concentration may enhance seismicity for earthquakes with a similar size if this characteristic size is in the lower part of the magnitude range for which the b value is estimated the enhanced seismicity will increase b on the other hand if it is in the upper part of the magnitude range it will decrease b thus we can explain the observed strong correlation between coda q 1 and b value for both positive and negative cases the existence of such a characteristic crack size in a seismic region has been supported by various observations on earthquake scaling

comment on quantitative measurements of shear wave polarizations at the anza seismic network southern california implications for shear wave splitting and earthquake prediction by richard c aster peter m shearer and jon berger

constraints on temporal variations in velocity near anza california from analysis of similar event pairs similar earthquake pairs recorded by the anza seismic network in southern california are used as repeatable sources to place an upper limit on temporal changes in seismic velocity which occurred in the vicinity of the anza seismic gap in the last 9 yr relative arrival times for each pair of events are found using a cross correlation method and relative locations are calculated to verify that the pairs have nearly identical hypocenters the time separation between events in these pairs varies from less than a day to almost 7 yr the long term changes in seismic travel times as measured from the pairs with the longest time separation are not significantly greater than the noise level estimated from the short time separation event pairs almost all p wave paths show less than 0 06 0 007 sec change in travel time and all s wave paths have less than 0 03 0 004 sec change sensitivity tests place an upper bound on travel time changes that could be compensated by hypocenter mislocation at 0 2 there is no evidence that localized stress accumulation causes measurable changes in seismic velocity in the anza region

temporal change in attenuation intensity before and after the eastern yamanashi earthquake of 1983 in central japan a crutal earthquake of magnitude 6 0 took place on august 8 1983 in the middle of the kanto tokai microearthquake observation network of the national research center for disaster prevention in central japan by analyzing vertical seismograms of microearthquakes occurring in a small volume in the aftershock region we measured temporal change in attenuation intensity for a period from 22 months before to 9 months after the main shock attenuation change was estimated by using two different kinds of analyses in the first analysis station magnitude calculated from the maximum amplitude at each station was compared with the average of station magnitudes deviations of station magnitude from the average magnitude at five stations in the vicinity of the aftershock area are found to have increased after the main shock compared with that before in the second analysis s coda duration from the origin time was measured and was compared with the average magnitude the increase of s coda duration for the same average magnitude is found after the main shock at two stations close to the main shock epicenter the simplest interpretation of the results is that the attenuation intensity in the upper crust in the close vicinity of the focal region decreased after the main shock for frequencies f from 2 to 20 hz qs 1 1 4 10 2f 1 since other precursors appeared in the preparation stage it is possible to interpret the change in qs 1 as a precursor the attenuation intensity would have been anomalously large before the main shock

a model for attenuation and scattering in the earth s crust the mechanisms contributing to the attenuation of earthquake ground motion in the distance range of 10 to 200 km are studied with the aid of laboratory data coda waves rg attenuation strong motion attenuation measurements in the northeast united states and canada and theoretical models the frequency range 1 10 hz has been studied the relative contributions to attenuation of anelasticity of crustal rocks constant q fluid flow and scattering are evaluated scattering is found to be strong with an albedo b 0 0 8 0 9 and a scattering extinction length of 17 32 km the albedo is defined as the ratio of the total extinction length to the scattering extinction length the rg results indicate that q increases with depth in the upper kilometer or two of the crust at least in new england coda q appears to be equivalent to intrinsic anelastic q and indicates that this q increases with frequency as q q 0 f n where n is in the range of 0 2 0 9 the intrinsic attenuation in the crust can be explained by a high constant q 500 q 0 2000 and a frequency dependent mechanism most likely due to fluid effects in rocks and cracks a fluid flow attenuation model gives a frequency dependence q q 0 f0 5 similar to those determined from the analysis of coda waves of regional seismograms q is low near the surface and high in the body of the crust

millisecond accurate monitoring of seismic travel times over 13 and 18 kilometer baselines using a repeatable airgun source we have monitored the travel times of several seismic phases along 13 and 18 km baselines from bouquet reservoir to boreholes on the san andreas fault near palmdale california the first arriving phases refract at a depth of 2 3 km while one later arrival is possibly a reflection from 10 km the majority of some 200 travel time determinations for the most prominent phases were made between august 1979 and march 1980 isolated measurements were made in november 1978 and march 1981 there exists ample geodetic and other evidence for significant strain changes during this period allowing for source variation due to fluctuating reservoir water levels we observed no travel time changes to the limit of our precision of 1 2 ms for the first arrivals and 3 5 ms for secondary arrivals or about 0 1 of the total travel time an earlier study which monitored rays penetrating only 500 m into the crust found that travel times varied by up to 0 3 over a period of several days the variations showed some correlation with strain changes due to local seismic activity and were not permanent to understand this different behavior of crustal rocks between 500 and 2000 m we investigate the depth dependence of their velocity strain sensitivity using measured p and s velocity profiles to gauge the rate at which confining pressure increases velocity we find that 1 bar of overpressure at 500 m can vary the p velocity by 0 1 while 1 bar at 2000 m will vary the velocity by only 0 01 applying the o connell budiansky physical model for cracked rock to the velocity depth profiles we can further characterize the local crust as having a high crack density a mobile fluid component and an average crack aspect ratio of 2 5 10 3 the combination of a mobile fluid content and high crack density suggests that fluids play a role in the transient velocity anomalies observed at a depth of 500 m and argues against significant undersaturation phenomena at seismogenic depths on the san andreas fault

time space variation of seismic s wave coda attenuation qc 1 and magnitude distribution b values for the petatlan earthquake average s wave coda q qc at 6 hz and to about 10 sec after the s wave arrival shows 1 temporal variation positively correlated with the magnitude distribution parameter b for foreshocks and aftershocks of the 1979 petatlan mexico earthquake 2 spatial variation through the aftershock area positively correlated with b high qc b values at the two activity centers intermediate values in between and landward and low values toward the middle america trench which remain low for two weeks after the main shock and 3 five foreshock average qc 135 1 6 and eleven aftershock average qc 175 1 3 for the eastern asperity the b values and possibly qc values seem to correlate with the level of aftershock activity

coda q before and after the 1983 misasa earthquake of m 6 2 tottori prefecture japan to detect any temporal change in coda q associated with an earthquake of m 6 2 digitized data from analog magnetic records of microearthquakes for a small confined region just around its hypocenter have been processed with special attention to measuring errors the m 6 2 earthquake took place at the misasa town tottori prefecture in southwest japan with preceding anomalous seismicity changes theq values were elevated 20 around three years before the m 6 2 event for frequencies of 5 to 20 hz and tended to decrease around two years before data with high quality show undulated temporal variation with a period of 5 6 years before the earthquake which is correlated with the regional seismic activity there is a possibility that the observedq change stands for precursory effect of the medium scale earthquake the aftershock sequence also shows an undulated temporal variation ofq with a period of 150 days for around 10hz correlating also with the seismic activity the fracturing processes by numerous microearthquakes may be responsible for the attenuation property of randomly scattered seismic waves

monitoring rapid temporal change in a volcano with coda wave interferometry 1 multiply scattered waves typically dominate the late part of the seismic coda in local earthquake seismograms small medium changes that have no detectable influence on the first arrivals are amplified by multiple scattering and may thus be readily observed in the coda we exploit this idea using coda wave interferometry to monitor temporal changes at mount erebus volcano antarctica erebus is one of the few volcanoes on earth with a long lived convecting lava lake large exsolved gas bubbles generate impulsive strombolian explosions that provide a repeating seismic source of seismic energy propagating through the strongly scattering geology of the volcano we examined these signals during a particularly active eruptive two month period between december 1999 and february 2000 early seismograms are highly reproducible throughout this period during the first month this is also the case for the coda approximately midway through this period however the seismic coda decorrelates rapidly over a period of several days this indicates a rapid change in the scattering properties of the volcano likely reflecting subtle changes in the near summit magma conduit system that would not be discernible using direct or single scattered seismic wave methods

temporal stability of coda q 1 in southern california some studies of coda q 1 have found temporal changes that may be associated with earthquake activity but these analyses are subject to biases due to differences in source locations and other nonstationary behavior in earthquake catalogs these biases can be greatly reduced by using clusters of repeating earthquakes studies using this approach have generally found no resolvable changes in coda q 1 we examine coda q 1 variations across southern california using 22 similar event clusters identified from a recent large scale waveform cross correlation project to improve earthquake locations these clusters are found across the region and span the time period between 1981 and 2005 we apply the method of beroza et al 1995 to compute differential coda q 1 using waveforms from similar earthquake pairs and analyze the results to constrain any possible temporal variations results from individual event pairs show a great deal of scatter in differential coda q 1 but exhibit no clear temporal variations or changes associated with large earthquakes application of a median filter to smooth the results shows that any persistent large scale changes in coda q 1 during this time period are less than about 30

the anza array a high dynamic range broadband digitally radiotelemetered seismic array a small aperture seismic array has been deployed along a 30 km stretch of the san jacinto fault in the vicinity of the town of anza california the array was installed to study specifically the scaling laws of body wave spectra the character of high frequency ground motion the physical interpretation of seismic stress drops and the interaction of earthquakes this region was chosen for these studies due to its high rate of seismic activity in the 2 m 4 5 range the likelihood of a m 6 event in the next decade and the existence of the southern california batholith on either side of the fault reducing problems associated with attenuation and large scale anisotropy these studies employ an instrument package with a frequency response of 100 hz a dynamic range of 138 db a sampling rate of 250 times per second per component and a 16 bit a d converter the array consists of 10 three component stations telemetered via digital vhf radio to a nearby mountain peak and thence via a microwave link to la jolla california a minicomputer system monitors the array s performance detects events and records data upon demand initial results demonstrate the feasibility of digital transmission with an inherent increase in data quality over analog systems

telescoped porphyry cu mo au mineralisation advanced argillic alteration and quartz sulphide gold anhydrite veins in the thames district new zealand porphyry cu mo au mineralisation with associated potassic and phyllic alteration an advanced argillic alteration cap and epithermal quartz sulphide gold anhydrite veins are telescoped within a vertical interval of 400 800 m on the northeastern margin of the thames district new zealand the geological setting is jurassic greywacke basement overlain by late miocene andesitic dacitic rocks that are extensively altered to propylitic and argillic assemblages the porphyry cu mo au mineralisation is hosted in a dacite porphyry stock and surrounding intrusion breccia relicts of a core zone of potassic k feldspar magnetite biotite alteration are overprinted by phyllic quartz sericite pyrite or intermediate argillic chlorite sericite alteration assemblages some copper occurs in quartz magnetite chlorite pyrite chalcopyrite veinlets in the core zone but the bulk of the copper and the molybdenum are associated with the phyllic alteration as disseminated chalcopyrite and as molybdenite sericite carbonate veinlets the advanced argillic cap has a quartz alunite dickite core which is enveloped by an extensive pyrophyllite diaspore dickite kaolinite assemblage that overlaps with the upper part of the phyllic alteration zone later quartz sphalerite galena pyrite chalcopyrite gold anhydrite carbonate veins occur within and around the margins of the porphyry intrusion and are associated with widespread illite carbonate argillic alteration multiphase fluid inclusions in quartz stockwork veins associated with the potassic alteration trapped a highly saline 50 84 wt nacl equiv magmatic fluid at high temperatures 450 to 600 c these hypersaline brines were probably trapped at a pressure of about 300 bar corresponding to a depth of 1 2 km under lithostatic conditions this shallow depth is consistent with textures of the host dacite porphyry and reconstruction of the volcanic stratigraphy liquid rich fluid inclusions in the quartz stockwork veins and quartz phenocrysts trapped a lower salinity 3 20 wt nacl equiv moderate temperature 300 400 c fluid that may have caused the phyllic alteration fluid inclusions in the quartz sphalerite galena pyrite chalcopyrite gold anhydrite carbonate veins trapped dilute 1 3 wt nacl equiv fluids at 250 to 320 c at a minimum depth of 1 0 km under hydrostatic conditions oxygen isotopic compositions of the fluids that deposited the quartz stockwork veins fall within the 6 to 10 range of magmatic waters whereas the quartz sulphide gold anhydrite veins have lower 18owater values 0 6 to 0 5 reflecting a local meteoric water 6 influence a 18o versus d plot shows a trend from magmatic water in the quartz stockwork veins to a near meteoric water composition in kaolinite from the advanced argillic alteration data points for pyrophyllite and the quartz sulphide gold anhydrite veins lie about midway between the magmatic and meteoric water end member compositions the spatial association between porphyry cu mo au mineralisation advanced argillic alteration and quartz sulphide gold anhydrite veins suggests that they are all genetically part of the same hydrothermal system this is consistent with k ar dates of 11 6 10 7 ma for the intrusive porphyry for alunite in the advanced argillic alteration and for sericite selvages from quartz gold veins in the thames district

crustal shear wave anisotropy in southern hawaii spatial and temporal analysis split shear wave arrivals are analyzed in seismograms from local earthquakes in southern hawaii recorded at five temporary arrays and one permanent network station we identify split shear wave arrivals by their orthogonally polarized pulses linear particle motions and similar waveforms and estimate the delay time for the slow shear wave arrival s 2 using a waveform cross correlation method consistent leading shear wave polarizations were measured at the majority of our stations comparison of observed and predicted shear wave polarizations confirms that the former are due to anisotropy rather than earthquake source mechanism agreement between fast shear wave s 1 polarizations and independently estimated directions of the maximum horizontal compressive stress h for the ainapo and punaluu gulch arrays leads us to conclude that the predominant source of the observed anisotropy for these two areas is stress aligned cracks consistent with the extensive dilatancy anisotropy eda hypothesis two distinct s 1 polarization directions were observed over distances less than 1 km for the bird park and south flank arrays s 1 polarizations parallel to the ne striking kaoiki pali fault system for the bird park array combined with a nonhorizontal maximum principal stress 1 for the south flank region suggest stress induced cracks aligned by nearby faulting as a source for the observed anisotropy large station to station variations in s 1 polarization and the relationship between delay time and event depth for arrays in the kaoiki and south flank regions provide evidence for anisotropy that is predominantly shallow rather than pervasive average delay times for the five arrays vary from about 100 to 230 ms with standard deviations of the order of 30 ms estimated anisotropic velocity variations and crack densities exceeding 10 indicate that the upper crust of southern hawaii is highly fractured a search for possible temporal changes in delay time associated with the 1983 kaoiki main shock m l 6 6 at a station near the epicenter finds no evidence for change

phase relations and adiabats in boiling seafloor geothermal systems abstract observations of large salinity variations and vent temperatures in the range of 380 400 c suggest that boiling or two phase separation may be occurring in some seafloor geothermal systems consideration of flow rates and the relatively small differences in density between vapors and liquids at the supercritical pressures at depth in these systems suggests that boiling is occurring under closed system conditions salinity and temperature of boiling vents can be used to estimate the pressure temperature point in the subsurface at which liquid seawater first reached the two phase boundary data are reviewed to construct phase diagrams of coexisting brines and vapors in the two phase region at pressures corresponding to those of the seafloor geothermal systems a method is developed for calculating the enthalpy and entropy of the coexisting mixtures and results are used to construct adiabats from the seafloor to the p t two phase boundary results for seafloor vents discharging at 2300 m below sea level indicate that a 385 c vent is composed of a brine 7 nacl equivalent in equilibrium with a vapor 0 1 nacl brine constitutes 45 by weight of the mixture and the fluid first boiled at approximately 1 km below the seafloor at 415 c 330 bar a 400 c vent is primarily vapor 88 wt 0 044 nacl with a small amount of brine 26 nacl and first boiled at 2 9 km below the seafloor at 500 c 520 bar these results show that adiabatic decompression in the two phase region results in dramatic cooling of the fluid mixture when there is a large fraction of vapor

precursory seismic quiescence past present and future precursory seismic quiescence has played a major role in most of the succesful earthquake predictions made to date in addition to these successes the number of detailed post mainshock documentations of precursory quiescence is steadily growing these facts suggest that precursory quiescence will play an important role in earthquake prediction programs of the future for this reason it is important to critically evaluate the present state of knowledge concerning this phenomenon the history of observations of precursory seismic quiescence includes work on seismic gaps and seismic preconditions as well as actual studies of temporal quiescence these papers demonstrated the importance of quantitative evaluation of seismicity rates and the benefits of systematic analysis during the early 1980 s the impact of man made effects on seismicity rates was demonstrated for the first time despite progress in catalog understanding the identification and correction of man made seismicity changes remains as the major barrier to earthquake prediction using these data effects of man made changes are apparent in many past studies of seismicity patterns making the results difficult to evaluate recent experience with real time anomalies has demonstrated the necessity of determining the false alarm rates associated with quiescence precursors determination of false alarm rates depends on quantitative definitions of anomalies and statistical evaluations of their significance a number of successful predictions which have been made on the basis of seismic quiescence provide important lessons for present and future work there are many presently unanswered questions regarding seismic quiescence which must be answered before we can determine the reliability of this phenomena as a precursor

a precursorlike change in coda excitation before the western nagano earthquake ms 6 8 of 1984 in central japan temporal variations of coda duration were studied in relation to a crustal earthquake september 14 1984 which took place near the nw corner of the kanto tokai microearthquake observation network of the national research center for disaster prevention in japan vertical seismograms recorded at station ger close to the main shock epicenter 24 km between february 1982 and december 1984 were analyzed a precursorlike change was found in the relation between coda duration and average magnitude for 185 earthquakes which occurred in a small volume in the middle of the aftershock region the average magnitude is the arithmetic mean of station magnitudes which are calculated from the maximum amplitudes of direct waves coda durations for earthquakes of the same average magnitude were significantly longer during the 16 month period preceding the main shock than those before and after this period with a confidence level of 99 9 the increase in coda durations was about 3 s on average in this period the coda duration anomaly was significant for lapse time shorter than 30 s which corresponds to a travel radius less than 50 km although no clear temporal change was found in the residuals of station magnitude measured at ger from average magnitude an attenuation change in the preevent period can not be ruled out due to the large scatter of data crack formation however is the most plausible mechanism for an increase in scattering intensity around the focal region in the stress accumulation stage and is consistent with other precursory observations clusters of cracks in the heterogeneous earth medium might be big enough to scatter high frequency seismic waves even though each individual crack may be very small

seismic albedo from the total seismic energy dependence on hypocentral distance in southern california abstract scattering and absorption of seismic waves have been studied in southern california to determine their respective contributions to the measured apparent attenuation we measured the total seismic energy from the onset of the s waves for local earthquakes recorded at stations on granitic rock reduced to a common source by eliminating the source and site effect by the coda method then applied wu s method based on the radiative transfer theory which has the facility to separate the intrinsic absorption from the scattering effect the observed total energy as a function of hypocentral distance exhibits a striking behavior increasing to a maximum at about 50 km then decreasing exponentially as a function of hypocentral distance decay of the total energy as a function of distance is remarkably similar for all frequency bands centered at 1 5 3 0 6 0 and 12 0 hz in good agreement with earlier results on q of coda and s waves in southern california comparison with wu s theoretical plots which shows curves that differ in shape because of differences in seismic albedo if b 0 s s a where s and a are the scattering and absorption coefficients respectively leads to the conclusion that the s wave energy is primarily redistributed in space by scattering rather than intrinsically absorbed by the earth our results from southern california agree with those of toksoz et al who found seismic albedo b0 to be 0 8 0 9 in eastern north america coda q in southern california however closely agrees with scattering q using wu s model in disagreement with the conclusions of toksoz et al for eastern north america where coda q is close to the absorptive q obtained from the total energy study the agreement between wu s theoretical curves and our observations is not perfect departure of the observed curves from the theory may be due in part to inhomogeneous distribution of scatterers and absorbers as well as non isotropic scattering we need more realistic models which can also account for inhomogeneous bounded media

attenuation of high frequency shear waves in the crust measurements from new york state south africa and southern california we compare the attenuation of high frequency 3 30 hz shear waves for crustal paths in new york state south africa and southern california over source receiver distances of about 10 400 km the data consist of digital recordings of s waves 5 100 km and lg waves 100 400 km produced by earthquakes we use a coda normalization method to remove the effects of site amplification and source excitation from the amplitudes of the s and lg waves over the entire distance range studied 10 400 km the amplitude decay of 3 hz shear wave energy is considerably less for the tectonicaily stable areas of new york and south africa than for the tectonicaily active region of southern california high frequency 30 hz s wave attenuation is significantly less for new york and south africa than for southern california for distances between 15 and 90 km we parameterize the decay with distance r of coda normalized shear wave amplitudes with a frequency independent q and geometrical spreading exponent where geometrical spreading is proportional to r for new york state the s wave amplitude decay 3 30 hz is well described by a frequency independent q of 2100 330 490 and of 1 3 0 1 the decay of lg wave amplitudes from 3 to 15 hz in the new york state region is fit with a frequency independent q of 1600 280 330 of 0 70 0 2 the s wave amplitudes 3 30hz in south africa yield a q of 1500 190 380 and of 1 3 0 1 fixing the geometrical spreading at r 0 5 produces an lg wave q estimate at 3 hz in south africa of 360 50 80 this lg wave q is low considering that south africa is a cratonic tectonicaily stable area the s wave amplitudes from southern california are described with a frequency independent q of 800 150 240 and a large geometrical spreading exponent of of 1 9 0 2 we find an lg wave q at 3 hz of 260 30 for southern california after constraining the geometrical spreading at r 0 5

energy flux model of seismic coda separation of scattering and intrinsic attenuation a new model of seismic coda is presented based on the balance between the energy scattered from the direct wave and the energy in the seismic coda this energy flux model results in a simple formula for the amplitude and time decay of the seismic coda that explicitly differentiates between the scattering and intrinsic anelastic attenuation of the medium this formula is valid for both weak and strong scattering and implicitly includes multiple scattering the model is tested using synthetic seismograms produced in finite difference simulations of wave propagation through media with random spatial variations in seismic velocity some of the simulations also included intrinsic dissipation the energy flux model explains the coda decay and amplitude observed in the synthetics for random media with a wide range of scattering q in contrast the single scattering model commonly used in the analysis of microearthquake coda does not account for the gradual coda decay observed in the simulations for media with moderate or strong scattering attenuation scattering q less than or equal to 150 the simulations demonstrate that large differences in scattering attenuation cause only small changes in the coda decay rate as predicted by the energy flux model the coda decay rate is sensitive however more to the intrinsic q of the medium the ratio of the coda amplitude to the energy in the direct arrival is a measure of the scattering attenuation thus analysis of the decay rate and amplitude of the coda can in principle produce separate estimates for the scattering and intrinsic q values of the crust we analyze the coda from two earthquakes near anza california intrinsic q values determined from these seismograms using the energy flux model are comparable to coda q values found from the single scattering theory the results demonstrate that coda q values are at best measures of the intrinsic attenuation of the lithosphere and are unrelated to the scatteing q less

direct evolution of brine from a crystallizing silicic melt at the questa new mexico molybdenum deposit molybdenum mineralization in the southwest orebody at the questa deposit is associated with crystallization of aplite porphyry explosive brecciation and exsolution of magmatic hydrothermal fluids quartz k feldspar fluorophlogopite and molybdenite precipitated from exsolving aqueous fluids and cemented aplite porphyry and andesite wall rock clasts forming a magmatic hydrothermal breccia ore fluid inclusions in quartz in the breccia matrix trapped aqueous fluids that transported and precipitated molybdenum two fluid inclusion populations associated with molybdenite mineralization were identified the largest population commonly contains liquid vapor halite sylvite and one or more opaque daughter crystals these inclusions homogenize between 200 degrees and 500 degrees c and have a prominent mode at 360 degrees to 400 degrees c salinities vary from 31 to 57 wt percent nacl equiv low first ice melting temperatures suggest that additional fluid components possibly calcium or magnesium chlorides may be present approximately 80 percent of these inclusions homogenize by halite dissolution phase equilibria constraints require that these inclusions trapped fluids in the vapor absent field the remaining saline inclusions homogenize to liquid at temperatures above halite dissolution temperatures significantly the saline fluid did not coexist with a low density aqueous fluid a second population of inclusions contains fluids with salinities of 2 7 to 25 0 wt percent nacl equiv and homogenizes by vapor bubble disappearance vapor bubble expansion or critical behavior textural relationships and phase behavior during microthermometry indicate that these inclusions constitute a single population which formed as pressure and temperature fluctuated at near critical conditions pressure changes related to brecciation followed by crystallization and system resealing produced the observed fluids saline fluids were trapped as the system sealed following a major brecciation event these high salinity fluids were produced as the melt under pressure that increased from hydrostatic to lithostatic partitioned increasing amounts of chlorine into the exsolving aqueous fluid renewed fracturing and abrupt pressure decrease to hydrostatic conditions reduced the mass of chlorine partitioning to the exsolving fluid lower salinity fluids exsolved at near critical conditions and were trapped by inclusions that homogenize to liquid to vapor or by critical behavior the lack of cogenetic liquid and vapor rich fluid inclusions and phase equilibria constraints indicate that high salinity fluids or 57 wt nacl equiv were generated directly by the crystallizing magma and were not a product of aqueous fluid immiscibility

temporal change in coda associated with the round valley california earthquake of november 23 1984 seven thousand seismograms of small earthquakes in the mammoth lakes bishop area were used to measure values of q from the decay of the earthquake coda these measurements were compared between events that occurred before and after the round valley earthquake m 5 7 we found that in regions near the main shock epicenter measurements of coda q 1 for earthquakes that occurred after the main shock were higher than for those earthquakes that occurred prior to the main shock the opposite behavior was found for regions farther away from the main shock namely lower coda q 1 after the main shock than before measurements of coda q 1 in the long valley caldera outside of the immediate source region of the earthquake were higher than in surrounding areas before the main shock but the difference disappeared after the occurrence of the main shock this indicates that the temporal variation in coda q 1 is comparable to its spatial variation the doughnut model seismicity quiescence surrounded by a zone of activity which was invoked for explaining the precursory seismicity pattern appears to be similar with the observed coda q 1 variation associated with the round valley earthquake the observed spatial variations in coda q 1 also help to reconcile conflicting results published in previous studies of the coda q 1 precursor

a scattering model to explain seismic q observations in the lithosphere between 1 and 30 hz observations of lithospheric q for shear waves in the range 1 30 hz reported in the literature are examined using a scattering model consisting of randomly distributed spheres for the single scattering approximation i have assumed 1 q 1 q sub i gv omega where q sub i is the intrinsic q due to anelasticity v is the velocity of shear waves omega is angular frequency and g is the turbidity g is taken as a constant in this paper since g integral n a sigmada where n a da is the number of scattering spheres of radius a unit volume and sigma is the scattering cross section for a sphere this suggests that geometrical scattering dominates this will be true for ka 1 where k is wavenumber based on this criterion and the observation that q is large i e g small at a frequency of 0 05 hz a is of the order of magnitude 1 10 km fits of observations of shear wave q from japan and central asia indicate that q sub i 2000 500 for the lithosphere of both regions g 0 01 km for the japan observations and g 0 005 km sup 1 for central asia

evidence for shallow and pervasive seismic anisotropy in the wellington region new zealand the shear waves of local earthquakes were recorded during a 5 month deployment of seven three component digital seismographs on the wellington peninsula new zealand the seismographs were spaced an average of less than 5 km apart and over 300 local earthquakes were recorded with phase arrivals within the shear wave window a significant number 37 of the earthquakes recorded showed clear evidence of shear wave splitting identifiable fast and slow shear wave arrivals with similar pulse shapes consistent polarization directions at particular stations were also observed even when poor signal to noise ratio or scattering meant that no slow shear wave arrival could be identified however there were large station to station differences in the polarization directions correcting for the observed shear wave splitting improved the fit between the measured shear wave polarizations and those calculated assuming a double couple focal mechanism the cause of the observed shear wave splitting is therefore most likely to be seismic anisotropy large station to station differences in the polarization alignments ranging from 61 24 to 137 18 suggest that most anisotropy is confined to the top 2 3 km of the crust however there is evidence from one station for a small amount of pervasive anisotropy if such a trend existed on the other stations it could not be identified because of the large scatter in the data points the measured delay times between split shear waves vary from 0 02 to 0 22 s with a mean value of 0 1 0 06 s this translates to a near surface shear wave velocity anisotropy of about 10 with up to 2 pervasive anisotropy possible throughout the crust this data set indicates that extensive dilatancy anisotropy cannot be the sole cause of crustal seismic anisotropy and that foliations in the rock fabric and the fracture zones of active faults may also be important there is no evidence for temporal change in the shear wave splitting parameters during the period of the experiment

fluid immiscibility in natural processes use and misuse of fluid inclusion data abstract many occurrences of fluid immiscibility in natural geologic systems have been reported recently most often from fluid inclusion studies however the interpretation of fluid inclusion data in terms of immiscibility sometimes suffers from ambiguity of the vocabulary insufficient knowledge of the immiscibility constraints and insufficient knowledge of the topology in the tpx space of natural fluid systems for such reasons some authors have been misled to erroneous interpretations the term chemical immiscibility is unambiguously redefined as a multiphase multicomponent equilibrium the consequences of this definition are directly derived from the phase rule and concern the possible equations that relate the various parameters temperature pressure volumes compositions to each other these equations already put constraints on the topology of the phase equilibria in fluid systems a particular expression of the phase rule is proposed which takes into account the multiphase constant bulk volume constant bulk composition constraints in fluid inclusions the consequences of such an expression are of major importance in fluid inclusion studies the phase relations of some simple systems that approximate quite efficiently the natural complex fluids are then detailed h2o nacl co2 ch4 h2o co2 h2o co2 nacl the effects of these topologies and of the supplementary constraints constant bulk composition and constant bulk volume assumed for fluid inclusions isopleth isochoric systems are discussed

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering less

differential analysis of coda q using similar microearthquakes in seismic gaps part 2 application to seismograms recorded by the parkfield high resolution seismic network abstract nearly two thirds of the microseismicity occurring at parkfield california consists of repeating clusters of closely located events exhibiting waveform cross correlation values exceeding 0 95 this observation coupled with a high probability for an m 6 earthquake within the next decade working group on california earthquake probabilities 1988 make this segment of the san andreas fault system a prime location to search for temporal variations in coda q associated with crustal changes that may occur during the earthquake cycle the coda comparison analysis method described in part 1 of this study aster et al 1996 is applied to data from four borehole stations of the parkfield high resolution seismic network hrsn for the period january 1987 through february 1994 we examine 21 of the nearly 300 repeating clusters observed to date the restriction of the data set to only the most highly similar sources is observed to be critical small differences in the source process even for event pairs with centroid locations within approximately 20 m significantly increase the spurious noise level in the parameter estimates absolute 68 confidence bound estimates obtained on the repeatability of coda q for all microearthquake pairs are 10 for frequencies below 20 hz tighter constraints are obtainable by reconstructing the temporal history of coda q from the first difference measurements between microearthquake pairs these functional reconstructions show that the mean value of coda q has not varied by more than approximately 5 from 3 to 30 hz at the 1 level during the study period however other observables such as an increased level of microseismicity suggest that a preparatory stage for the next parkfield earthquake has begun indicating that coda q is so far showing no sign of sensitivity to preparatory processes at parkfield

high frequency borehole seismograms recorded in the san jcinto fault zone southern california part 2 attenuation and site effects we examine surface and downhole p and s wave spectra from local earthquakes recorded at two borehole seismometer arrays knw bh and pfo bh installed in the southern california batholith region of the san jacinto fault zone by the u s geological survey to assess the influence of the weathered layer on the spectral content of high frequency 2 to 200 hz seismic signals earthquake signals recorded downhole at both sites show significantly improved seismic bandwidth due to both a reduction in ambient noise levels and especially to dramatically increased levels of high frequency signal significant seismic signal is observed up to approximately 190 hz for p waves at knw bh stacked spectral ratios from these signals indicate that the highly weathered near surface between 0 and 150 m at knw bh and pfo bh exerts a much larger influence on seismic signals than deeper between 150 and 300 m material modeling of uphole downhole spectral ratio data suggests q 6 5 and q 9 between 0 and 150 m increasing to q 27 and q 26 between 150 and 300 m an outcrop mounted anza network station deployed approximately 0 4 km from knw bh displays roughly similar high frequency content to the knw bh downhole sensors but it exhibits spectra that are significantly colored by directional resonances low q and low velocity near surface material forms a lossy boundary layer at these borehole sites that is advantageous to the high frequency downhole environment not only are noise levels reduced but reflections from the surface and near surface are greatly attenuated as a result high frequency recordings from below the weathered zone more nearly resemble those recorded in a whole space than would otherwise be expected

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