a compositional classification scheme for meteoritic chondrules a taxonomic scheme is proposed for the main component of the primitive chondrite meteorites the chondrules the scheme provides insight into the variety of chondrules originally produced in the primordial solar nebula and the effects on them of secondary processes on meteorite parent bodies it may also contribute to understanding the origin of compositional diversity in the chondrites

composition of chondrule silicates in ll3 5 chondrites and implications for their nebular history and parent body metamorphism our petrologic studies of 75 type ia and type ii porphyritic olivine chondrules in nine selected ll group chondrites of type 3 3 to type 5 and comparisons with published studies of chondrules in semarkona ll3 0 show that compositions of silicates and bulk chondrules but not overall chondrule textures vary systematically with the petrologic type of the chondrite these compositional trends are due to diffusive exchange between chondrule silicates and other phases e g matrix such as those now preserved in semarkona during which olivines in both chondrule types gained fe2 and mn2 and lost mg2 cr3 and ca2 in a given ll4 5 chondrite the olivines from the two chondrule types are identical in composition enrichments of fe2 in olivine are particularly noticeable in type ia chondrules from type 3 3 3 6 chondrites especially near grain edges chondrule rims grain boundaries and what appear to be annealed cracks compositional changes in low ca pyroxene lag behind those in coexisting olivine consistent with its lower diffusion rates with increasing petrologic type low ca pyroxenes in type ia chondrules become enriched in fe2 and mn2 and depleted in mg2 cr3 and a13 these compositional changes are entirely consistent with mineral equilibration in chondritic material during metamorphism from these compositional data alone we cannot exclude the possibility that chondritic material was metamorphosed to some degree in the nebula but we see no evidence favoring nebula over asteroidal metamorphism nor evidence that the chondrule reacted with nebular gases after crystallization modelling of the equilibration of chondrule olivines suggests that heterogeneous feo concentrations in olivine could be preserved after cooling from 600 c at rates of 1 10 c ma for at least tens to hundreds of millions of years this is consistent with published estimates for the maximum metamorphic temperatures in type 3 chondrites thermal histories derived from metallographic and fission track cooling rates and 4 4 ga 40ar 39ar ages for ordinary chondrites since the lifetime of the solar nebula was not more than 106 years and there is abundant evidence that meteorite parent bodies were heated some even above their melting point we confidently conclude that the formation of type 3 3 5 ordinary chondrites from type 3 0 material by metamorphism occurred in parental asteroids not the solar nebula

dynamic crystallization of chondrule melts of porphyritic and radial pyroxene composition abstract dynamic crystallization experiments in which heterogeneous nucleation is an important variable have been completed on four melts of chondrule composition compositions were chosen to best represent chondrules with porphyritic pyroxene and radial pyroxene textures experimental results show that heterogeneous nucleation is essential for the formation of porphyritic textures without preexisting nuclei too much supercooling is established before crystallization is initiated and the textures are more likely to be dendritic or radial in the near total absence of nuclei radial textures can form at cooling rates as slow as 5 c hr in this study by varying the heterogeneous nucleation conditions and having a melt in which the appropriate phases are stable or metastable analogs to most of the recognized chondrule textures can be produced in a single melt composition olivine inclusions in pyroxene can form readily during an experiment from a starting material which did not initially contain olivine crystals thus care must be taken in the assumption that olivine inclusions in pyroxene represent preexisting crystals

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

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

evidence for the three stage cooling history of olivine porphyritic fluid droplet chondrules abstract three haplochondritic melts were experimentally examined to investigate thermal parameters in the pre accretionary chondrule environment the melts in the form of 2 mm diameter spherules were subjected to cooling rates of 220 460 or 1300 3700 c hr and either held at 1460 c for up to 90 minutes or continuously cooled to 600 c a fractional crystallization model designed to incorporate the effects of lattice diffusion in olivine but not volume diffusion of magnesium or iron in the melt was found to yield results in excellent agreement with olivine formed in experimental charges having a melt composition most similar to chondrules application of this numerical model to three olivine porphyritic chondrules from the tieschitz h3 chondrite indicates that their mean olivine phenocryst compositions are too fayalitic to have been derived from a continuous cooling event partial equilibration of the phenocrysts with the melt in a high temperature isothermal environment is postulated to explain the measured mean values from this investigation the following three stage model for the cooling of olivine porphyritic fluid droplet chondrules found in ordinary chondrites is proposed 1 a initial continuous cooling from at least liquidus temperatures at rates of 300 to 4000 c hr to about 1300 c a process that may have taken 5 60 minutes 2 b interruption of the initial cooling by a short duration isothermal event at 1300 c 3 c quenching thus the entire cooling history of fluid droplet chondrules is but a brief process in the early history of the solar system this thermal model suggests a rather specific and restricted physical setting for the origin of chondrules it is unlikely that such a severely constrained physical setting could have been achieved by repetitive small scale events such as impact splattering on planetary surfaces or volcanism rather a single large scale event is suggested

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

chondrule cooling rates inferred from diffusive profiles in metal lumps from the acfer 097 cr2 chondrite abstract cr chondrites contain metal lumps 300 m either attached to chondrule silicates or apparently isolated in the matrix here laser ablation microanalysis of six metal lumps from a polished thin section of the acfer 097 cr2 chondrite at 15 m spatial resolution revealed zoning profiles for the volatile elements cu and ga the mutual diffusivities of cu and ga were used to infer t 1473 100 k from the correlation of cu versus ga the cooling rates of the metal lumps were calculated to be 0 5 50 k h 1 for tp 1473 100 k with a maximum possible range of 0 1 400 k h 1 for tp 1200 1800 k overlapping the range of cooling rates inferred from petrological studies of type i chondrules 10 1000 k h 1 chondrule textures were established near the peak heating temperatures of chondrules approximately 1900 2000 k while the cu and ga diffusive profiles were established after solidification t 1500 k consistent with nonlinear cooling furthermore one chondrule n2 has a more complex zoning profile that is modeled as a three stage cooling history involving initial cooling at approximately 1 k h 1 followed by mild re heating t 1700 k that re evaporated cu and ga from the outer approximately 100 m of the metal lump and then cooled again at approximately 5 k h 1 the thermal effects of parent body and other preaccretionary heating events on the cu and ga zoning profiles are examined although cr parent bodies have experienced aqueous alteration the thermal effects of this process can neither produce nor erase the cu and ga diffusive profiles thus metal lumps in cr chondrites record the solid state thermal history of chondrules as they travelled away from the chondrule forming region

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

the rupture extent of low frequency earthquakes near parkfield ca the low frequency earthquakes lfes that constitute tectonic tremor are often inferred to be slow to have durations of 0 2 to 0 5 s a factor of 10 to 100 longer than those of typical m w 1 2 earthquakes here we examine lfes near parkfield ca in order to assess several proposed explanations for lfes long durations we determine lfe rupture areas and location distributions using a new approach similar to directivity analysis where we examine how signals coming from various locations within lfes finite rupture extents create differences in the apparent source time functions recorded at various stations we use synthetic ruptures to determine how much the lfe signals recorded at each station would be modified by spatial variations of the source station travel time within the rupture area given various possible rupture diameters and then compare those synthetics with the data our synthetics show that the methodology can identify inter station variations created by heterogeneous slip distributions or complex rupture edges and thus lets us estimate lfe rupture extents for unilateral or bilateral ruptures to obtain robust estimates of the sources similarity across stations we stack signals from thousands of lfes using an empirical green s function approach to isolate the lfes apparent source time functions from the path effects our analysis of lfes in parkfield implies that lfes apparent source time functions are similar across stations at frequencies up to 8 to 16 hz depending on the family the inter station coherence observed at these relatively high frequencies or short wave lengths down to 0 2 to 0 5 km suggest that lfes in each of the 7 families examined occur on asperities they are clustered in patches with sub 1 km diameters the individual lfes rupture diameters are estimated to be smaller than 1 1 km for all families and smaller than 0 5 km and 1 km for the two shallowest families which were previously found to have 0 2 s durations coupling the diameters with the durations suggests that it is possible to model these m w 1 2 lfes with earthquake like rupture speeds around 70 of the shear wave speed however that rupture speed matches the data only at the edge of our uncertainty estimates for the family with highest coherence the data for that family are better matched if lfes have rupture velocities smaller than 40 of the shear wave speed or if lfes have different rupture dynamics they could have long rise times contain composite sub ruptures or have slip distributions that persist from event to event

the solar nebula redox state as recorded by the most reduced chondrules of five primitive chondrites abstract mafic minerals in the most reduced chondrules of five primitive meteorites were analyzed with an electron microprobe to determine the lower limit on their feo contents the accuracy obtained was 0 01 weight percent feo the thermodynamic relationship between mole fraction fesio 3 and po 2 of the ambient nebular gas at the time of mineral equilibration was established and was used to infer the local o h ratio of the nebular gas during chondrule formation the lowest ferrosilite compositions reflected equilibration at 1500k with a gas 2 18 times more oxidizing than a gas of solar composition olivines in low feo uoc chondrules are uniformly more feo rich than coexisting pyroxenes this discrepancy suggests that a significant change in the o h ratio of the nebular gas occurred between the time of olivine and pyroxene crystallization in the region of the nebula where uocs formed mineral compositions in the chondrules of two c2 chondrites studied suggest they formed in a more homogeneous region of the nebula than the uocs

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

early solar system processes recorded in the matrices of two highly pristine cr3 carbonaceous chondrites met 00426 and que 99177 the mineralogy and bulk compositions of the matrices of the cr chondrites met 00426 and que 99177 have been studied using a combination of sem epma and tem techniques the matrices of these two chondrites are texturally chemically and mineralogically similar and are characterized by significant feo enrichments with respect to other cr chondrite matrices nearly flat refractory lithophile patterns variable volatile element patterns and a simple mineral assemblage dominated by amorphous silicate material and fe ni sulfides fine grained crystalline silicate phases such as olivine and pyroxene appear to be extremely rare in the matrices of both meteorites instead the mineralogy of matrices and fine grained rims of both meteorites consists of abundant amorphous feo rich silicate material containing nanoparticles of fe ni sulfides troilite pyrrhotite and pentlandite secondary alteration minerals that are characteristic of other cr chondrites e g renazzo and al rais such as phyllosilicates magnetite and calcite are also rare the texture and mineralogy of the matrices of met 00426 and que 99177 share many features with matrices in the primitive carbonaceous chondrites alh a77307 co3 0 and acfer 094 unique these observations show that met 00426 and que 99177 are very low petrologic type 3 chondrites that have escaped the effects of aqueous alteration unlike other cr chondrites which are typically classified as petrologic type 2 we suggest that these meteorites represent additional samples of highly primitive but extremely rare carbonaceous chondrites of petrologic type 3 00 according to the classification scheme of grossman and brearley 2005 the highly pristine nature of met 00426 and que 99177 provides important additional insights into the origins of fine grained materials in carbonaceous chondrites based on our new observations we infer that the amorphous silicate material and nanosulfide particles that dominate the matrices of these meteorites formed in the solar nebula by rapid condensation of material following high temperature events such as those that formed chondrules

temporal variation of body wave attenuation using earthquake doublets summary a technique to measure temporal variations of p and s body wave attenuation is presented spectral ratios of earthquake doublets recorded in the same station at different dates are computed doublets are pairs of earthquakes which share the same hypocentre and magnitude they have nearly identical wave forms and can be compared by using signal processing techniques three doublets were selected in the vicinity of the coyote lake california earthquake 1979 august 6 m 5 9 the doublet following the coyote lake earthquake does not show any variation in spectral ratio the doublet preceding the main shock by more than one year shows a small change in p spectral ratios and no change in s the largest variation in both p and s spectral ratios is observed for the doublet whose first event occurred two months before the coyote lake earthquake despite the difficulty in completely eliminating source and calibration effects the simplest interpretation of our data is to invoke temporal changes in p and s attenuation p attenuation was significantly higher by 8 per cent and s attenuation larger by 2 3 per cent two months before the m 5 9 shock than one year before and one month after such observations remind us of the possible role of the migration of fluids in the crust prior to an impending large earthquake and supports aki s plea for attenuation studies as a tool for earthquake prediction

the matrices of unequilibrated ordinary chondrites implications for the origin and history of chondrites abstract the matrices of sixteen unequilibrated ordinary chondrites all witnessed falls were studied microscopically in transmitted and reflected light and analyzed by electron microprobe selected specimens were also studied by scanning electron microscopy these studies indicate that the fine grained opaque silicate matrix of type 3 unequilibrated chondrites is compositionally mineralogically and texturally distinct from the chondrules and chondrule fragments and may be the low temperature condensate proposed by larimer and anders 1967 1970 examination of the matrices of unequilibrated chondrites also shows that each meteorite has been metamorphosed with the alteration ranging in intensity from quite mild where the matrix has been only slightly altered to a more severe metamorphism that has completely recrystallized the opaque matrix most of the metamorphic changes in the matrix occurred without significant effects on the compositions or textures of the chondrules the metamorphic alteration probably resulted from a combination of processes including thermal metamorphism and the passage of shock waves the present appearance of each unequilibrated chondrite is a result of the particular temperature and pressure conditions under which it and its components formed plus the subsequent metamorphic alteration it experienced

a seismological overview of the induced earthquakes in the duvernay play near fox creek alberta this paper summarizes the current state of understanding regarding the induced seismicity in connection with hydraulic fracturing operations targeting the duvernay formation in central alberta near the town of fox creek we demonstrate that earthquakes in this region cluster into distinct sequences in time space and focal mechanism using i cross correlation detection methods to delineate transient temporal relationships ii double difference relocations to confirm spatial clustering and iii moment tensor solutions to assess fault motion consistency the spatiotemporal clustering of the earthquake sequences is strongly related to the nearby hydraulic fracturing operations in addition we identify a preference for strike slip motions on subvertical faults with an approximate 45 p axis orientation consistent with expectation from the ambient stress field the hypocentral geometries for two of the largest magnitude m 4 sequences that are robustly constrained by local array data provide compelling evidence for planar features starting at duvernay formation depths and extending into the shallow precambrian basement we interpret these lineaments as subvertical faults orientated approximately north south consistent with the regional moment tensor solutions finally we conclude that the sequences were triggered by pore pressure increases in response to hydraulic fracturing stimulations along previously existing faults

dynamic crystallization of shock melts in allan hills 77005 implications for melt pocket formation in martian meteorites abstract a series of crystallization experiments have been performed on synthetic glasses matching the composition of a melt pocket found in allan hills alh 77005 in order to evaluate the heterogeneous nucleation potential of the melt and the effect of oxygen fugacity on crystallization the starting temperature of the experiments varied from superliquidus liquidus and subliquidus temperatures each run was then cooled at rates of 10 500 and 1000 c h at fmq the results of this study constrain the heating and cooling regime for a microporphyritic melt pocket within the melt pocket strong thermal gradients existed at the onset of crystallization giving rise to a heterogeneous distribution of nucleation sites resulting in gradational textures of olivine and chromite skeletal olivine in the melt pocket center crystallized from a melt containing few nuclei cooled at a fast rate nearer to the melt pocket margin elongate skeletal shapes progress to hopper and equant euhedral reflecting an increase in nuclei in the melt at the initiation of crystallization and growth at low degrees of supercooling cooling from post shock temperatures took place on the order of minutes an additional series of experiments were conducted for a melt temperature of 1510 c and a cooling rate of 500 c h at the fmq buffer as well as 1 and 2 log units above and below fmq variation in chromite stability in these experiments is reflected in crystal shapes and composition and place constraints on the oxygen fugacity of crystallization of the melt pocket we conclude that the oxygen fugacity of the melt pocket was set by the fe 3 fe 2 ratio imparted by melting of the host rock rather than external factors such as incorporation of co 2 rich martian atmosphere or melting and injection of oxidized surface e g regolith material comparison with previous crystallization experiments on melt pockets in martian basalts indicate that the predominance of dendritic crystal shapes reflects the likelihood that those melt pockets with lower liquidus temperatures will be more completely melted destroying most or all nuclei in the melt in this case crystal growth takes place at high degrees of supercooling yielding dendritic shapes it appears as though the melting process is just as important as cooling rate in determining the final texture of the melt pocket as this process controls elimination or preservation of nuclei at the onset of cooling and crystallization

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

dynamic cyrstallization of chondrule melts of porphyritic olivine composition textures experimental and natural abstract melts of the same composition as has been defined for porphyritic olivine chondrules have been crystallized under controlled cooling conditions dynamic crystallization the full range of textures observed in such chondrules has been duplicated in the experimentally produced analogs the primary controlling factor in producing this range of textuures is the heterogeneous nucleation behavior in general if nuclei are present when cooling begins growth starts immediately at low degrees of supercooling and porphyritic textures result the shapes of the phenocyrsts depend on the growth rate which in turn depends on the cooling rate with high nucleation densities and modest to low cooling rates the textures are microporphyritic with generally equant euhedral phenocrysts as the nucleatio density decreases the phenocrysts become larger and as the cooling rate increases they become increasingly skeletal if nuclei are not present when cooling begins growth is delayed until subcritical sized embryos graduate to supercritical nuclei growth usually begins at some significant degree of supercooling depending on the cooling rate and how long it takes the embryos to become nuclei the shapes of the crystals depend on the degree of supercooling when growth is initiated and on the subsequent cooling rate the resulting textures vary from plate dendrites barred olivine chondrules to randomly oriented elongated skeletal crystals as the degree of supercooling and cooling rates decreases the results of a matrix of experiments set limits on the maximum melting temperatures of chondrule forming materials and the subsequent cooling rates based primarily on crystal shape the porphyritic textures develop best for this composition at melting temperatures less than 1590 c and cooling rates near 100 c hr and definitely less than 1000 c hr at cooling rates significantly less than 100 c hr the phenocrysts are generally larger than observed in chondrules and as cooling rates approach 1000 c hr they become more skeletal barred olivine chondrule textures form best from materials melted at higher temperatures and cooling rates in the range 1000 to 3000 c hr

currents and transports of the great whirl socotra gyre system during the summer monsoon august 1993 from august 11 to 22 1993 a conductivity temperature depth acoustic doppler current profiler survey was carried out in the somali socotra region to investigate currents and transports associated with the great whirl and socotra gyre circulation during the height of the summer monsoon the monsoon circulation was confined to the upper 300 m depth with intense surface currents up to 2 2 m s 1 in the great whirl and up to 1 4 m s 1 in the socotra gyre deeper reaching flow was found in the northwestern part of the somali basin and in the passage between the shelf of somalia and abd al kuri the great whirl transport was 58 sv of which nearly 25 were due to ageostrophic flow components the northern part of the great whirl thereby appeared as a closed circulation cell in which the offshore transport was balanced by a southward transport of the same magnitude upwelled water was advected from the cold wedge of the upwelling regime at the somali coast along the edge of the gyre the water in the center of the gyre had the characteristics of indian equatorial water iew the socotra gyre carried 23 sv of modified arabian sea water asw with the transports in the two anticyclonic gyres nearly balanced the exchange of water masses between the somali basin west of the carlsberg ridge and the arabian sea occurred in two areas about 16 sv of warm and saline surface water of southern offshore origin entered the northern somali basin within a 120 km wide swift current between the great whirl and the socotra gyre the other key region for the exchange of water masses was the passage between somalia and abd al kuri there the total northward transport was 13 sv with contributions of iew of upwelled water close to the surface and asw underneath

pyroxene structures cathodoluminescence and the thermal history of the enstatite chondrites in order to explore the thermal history of enstatite chondrites we examined the cathodoluminescence cl and thermoluminescence tl properties of 15 eh chondrites and 21 el chondrites including all available petrographic types both textural types 3 6 and mineralogical types alpha delta the cl properties of el3 alpha and eh3 alpha chondrites are similar enstatite grains high in mn and other transition metals display red cl while enstatite with low concentrations of these elements show blue cl a few enstatite grains with greater than 5 wt feo display no cl in contrast the luminescent properties of the metamorphosed eh chondrites are very different from those of metamorphosed el chondrites while the enstatites in metamorphosed eh chondrites display predominantly blue cl the enstatites in metamorphosed el chondrites display a distinctive magenta cl with blue and red peaks of approximately equal intensity in their spectra the tl sensitivities of the enstatite chondrites correlate with the intensity of the blue cl and unlike other meteorite classes are not simply related to metamorphism the different luminescent properties of metamorphosed eh and el chondrites cannot readily be attributed to compositional differences but x ray diffraction data suggests that the enstatite in eh5 gamma delta chondrites is predominantly disordered orthopyroxene while enstatite in el6 beta chondrites is predominantly ordered orthopyroxene the difference in thermal history of metamorphosed el and eh chondrites is so marked that the use of single petrographic types is misleading and separate textural and mineralogical types are preferable our data confirm earlier suggestions that metamorphosed eh chondrites underwent relatively rapid cooling and the metamorphosed el chondrites cooled more slowly and experienced prolonged heating in the orthopyroxene field

a new asymptotic method for the modeling of near field accelerograms we study high frequency radiation from a dislocation model of rupture propagation at the earthquake source we demonstrate that in this case all the radiation emanates from the rupture front and by a change of variables that at any instant of time the high frequency waves reaching an observer come from a line on the fault plane that we call isochrone an asymptotic approximation to near source velocity and acceleration is obtained that involves a simple integration along the isochrones for every time step it is shown that wave front discontinuities critical or stopping phases are radiated every time an isochrone becomes tangent to a barrier this leads to what we call the critical ray approximation which is given in a closed form the previous results are compared with discrete wavenumber synthetics obtained by bouchon 1982 for the gilroy 6 recording of the coyote lake earthquake of 1980 the fit between the asymptotic and full numerical method is extremely good the critical ray approximation permits the identification of different phases in bouchon s synthetics and the prediction of the behavior of the signal in the vicinity of their arrival time

sulfur isotope composition of putative primary troilite in chondrules from bishunpur and semarkona the sulfur isotopic compositions of putative primary troilite grains within 15 ferromagnesian chondrules 10 feo poor and 5 feo rich chondrules in the least metamorphosed ordinary chondrites bishunpur and semarkona have been measured by ion microprobe some troilite grains are located inside metal spherules within chondrules since such an occurrence is unlikely to be formed by secondary sulfidization processes in the solar nebula or on parent bodies those troilites are most likely primary having survived chondrule forming high temperature events if they are primary they may be the residues of evaporation at high temperatures during chondrule formation and may have recorded mass dependent isotopic fractionations however the supposed primary troilites measured in this study do not show any significant sulfur isotopic fractionations 104 106 k h would be required to avoid a large degree of sulfur isotopic fractionation in the chondrule precursors this heating rate may provide a new constraint on the chondrule formation processes

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

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

complexities in high frequency seismic waveforms due to three dimensional structure in the new madrid seismic zone effects of three dimensional structure on 2 to 10 hz seismic signals in the new madrid seismic zone nmsz are investigated using waveforms from similar microearthquakes that occurred near ridgely tennessee slowness power spectral sps analysis is used to study the plane wave composition of p s and coda waves the observed sps at four stations suggest that the early s coda is composed mainly of wavelets leaving the source with slownesses of the direct s wave at greater lapse times coda is increasingly affected by random scattering sps observed on the vertical components and or near the s wave nodes are more comlplex due to practical limitations of the algorithm p coda and early s coda at a fifth station located southwest of the junction show the most complex sps analysis of that complexity together with waveform synthetics and travel time analysis strongly suggests that scattering multipathing due to source zone velocity heterogeneities occurs near the path probably due to dilatancy occurring southwest of the ridgely junction or due to internal fault zone complexities coda q when averaged over three components show no station variations we infer that 1 coda at 1 hz is mainly caused by scattering in the sedimentary layer where q is frequency independent 2 at higher frequencies the coda contains an increasing amount of scattered body waves and 3 the source radiation pattern and path variable scattering multipathing effects in early coda do not affect coda q

a review of the discrete wavenumber method we present a review of the discrete wavenumber dwn method the method introduced by bouchon and art 1977 allows the simple and accurate calculation of the complete green s functions for many problems in elastodynamics

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

formation and metamorphism of group a5 chondrules in ordinary chondrites abstract group a5 chondrules have feo rich olivines 4 wt feo and albite normative mesostases and thus are discrete from the major primary chondrule groups group a5 chondrules in six ll chondrites have been studied by cathodoluminescence optical microscopy electron micropobe and in the case of four chondrules removed from semarkona type 3 0 and krymka type 3 1 by instrumental neutron activation analysis olivine and pyroxene compositions vary with petrographic type in a manner resembling group bi chondrules they gain feo and mno lose cao mgo al2o3 and cr2o3 and become more homogeneous but the pyroxene trends are less marked because of lower diffusion rates there are no metamorphically related compositional trends in the mesostasis although compositional zoning is common in the mesostases of two type 3 4 3 7 chondrites group a5 chondrules contain unfractionated lithophile element bulk compositions but as is typical of all chondrules siderophile and chalcophile elements are depleted by about an order of magnitude group a5 chondrules are abundant in equilibrated 100 by number but rare in unequilibrated ordinary chondrites uocs 5 by number but their presence in uocs is not due to the emplacement of metamorphosed chondrules during brecciation because 1 olivine in group a5 chondrules is heterogeneous 2 the olivine displays all the compositional properties of olivine in low petrographic type ordinary chondrites and 3 the mesostasis is not recrystallized the chondrules display trends that are consistent with chondrule to chondrule and chondrule to matrix mineral homogenization and equilibration during metamorphism like the major chondrule groups a1 a2 and b1 in semarkona group a5 is a primary group whose presence provides further insights into chondrule formation process and diversity their bulk composition and redox state suggest that the conditions and temperatures of formation for groups a5 and b1 were similar however their different mesostasis compositions indicate that their post solidification histories were different either group b1 chondruues experienced slower cooling at low temperatures than group a5 during which albite crystallized in the mesostasis group b1 suffered a subsequent mild reheating that caused albite crystallization in the mesostasis or nucleation details for crystallization of albite in the residual melt were different group a1 and a2 chondrules could have been derived from group a5 or b1 like material by reduction and evaporative loss during chondrule formation

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

shear wave splitting in the anza seismic gap southern california temporal variations as possible precursors shear wave splitting above small earthquakes in the anza seismic gap on the san jacinto fault southern california displays the effective anisotropy of vertical fluid filled microcracks the delays between the split shear waves increase significantly over the 3 years of available records at the only station with arrivals from a wide range of azimuths and angles of incidence these changes can be modeled by increasing the aspect ratio bowing of stressoriented microcracks which is one of the expected elastic effects of an increase of stress on a rock mass containing a distribution of fluid filled microcracks this is the first time that temporal variations of shear wave splitting have been observed and suggests that shear wave splitting can be used to monitor the detailed changes in the buildup of stress before an earthquake

chemical zoning and homogenization of olivines in ordinary chondrites and implications for thermal histories of chondrules we studied the extent and degree of homogenization of chemical zoning of olivines in type 3 ordinary chondrites in order to obtain some constraints on cooling histories of chondrites based on mg fe and cao zoning olivines in type 3 chondrites are classified into four types a single chondrule usually contains olivines with the same type of zoning microporphyritic olivines show all four zoning types barred olivines usually show almost homogenized chemical zoning we have calculated cooling rates or burial depths needed to homogenize the chemical zoning by solving the diffusion equation using the zoning profiles as an initial condition mg fe zoning of olivine may be altered during initial cooling whereas cao zoning is hardly changed barred olivines may be homogenized during initial cooling because their size is relatively small to simulated microporphyritic olivine chondrules cooling from just below the liquidus at moderately high rates is preferable to cooling from above the liquidus at low rates for postaccumulation metamorphism of type 3 chondrites in order to keep mg fe zoning unaltered the maximum metamorphic temperature must be less than about 400 c if we assume cooling rates based on fe ni data calculated cooling rates for both fa and cao homogenization are consistent with those by fe ni data for type 4 chondrites a hot ejecta blanket several tens of meters thick on the surface of a parent body is sufficient to homogenize mg fe zoning if the temperature of the blanket is 600 700 c burial depths for petrologic types of ordinary chondrites in a parent body heated by 26al are broadly consistent with those previously proposed

compositions and textures of relic forsterite in carbonaceous and unequilibrated ordinary chondrites several percent of the olivine in the c2 c3 and unequilibrated ordinary chondrites uoc can be distinguished by blue cathodoluminescence cl and an unusual composition for forsterite this olivine has the following textural features 1 1 forms cores in single olivine grains 2 2 shows subhedral to euhedral boundaries against rim olivine 3 3 rarely contains inclusions 4 4 has embayments containing olivine like that of the rim 5 5 occurs within chondrules especially in uoc meteorites the blue olivine is always fe poor 0 25 feo 1 0 and shows the following average and maximum values al2o3 0 25 0 5 tio2 0 05 0 09 cao 0 5 0 8 cr2o3 0 15 0 5 and mno 0 02 0 15 vanadium is present within a single olivine and within all blue olivines al ca and ti are strongly positively correlated as are mn fe and cr in olivine surrounding the blue the blue cores are not zoned but each element shows a marked change at the boundary of the blue with al showing the most rapid change these are interpreted as diffusion profiles between rim and core olivine textures suggest initial free growth probably from a gas and later addition of olivine by liquid crystallization to form single crystals or chondrules the unusual olivine composition indicates high temperature growth from a refractory rich reservoir with al entering olivine in tetrahedral coordination vapor growth is suggested as the process allowing the high minor element levels the occurrence of blue olivine in all primitive meteorites indicates that it is relic material which was widespread prior to chondrule and hence meteorite formation similarities in composition exist between this relic olivine and olivine of cosmic dust and deep sea particles pointing to this olivine being a common component in all primitive extraterrestrial material

the importance of experiments constraints on chondrule formation models abstract we review a number of constraints that have been placed on the formation of chondrules and show how these can be used to test chondrule formation models four models in particular are examined the x wind model sudden exposure to sunlight 0 1 au from the proto sun with subsequent launching in a magnetocentrifugal outflow solar nebula lightning nebular shocks driven by eccentric planetesimals and nebular shocks driven by diskwide gravitational instabilities we show that constraints on the thermal histories of chondrules during their melting and crystallization are the most powerful constraints and provide the least ambiguous tests of the chondrule formation models such constraints strongly favor melting of chondrules in nebular shocks shocks driven by gravitational instabilities are somewhat favored over planetesimal bow shocks

estimation of arrival times in intense seismic sequences using a master events methodology based on waveform similarity summary intense seismic sequences involve a large number of earthquakes densely clustered in space and time their detailed analysis is important for the geometry of the activated faults which contributes to studies of the seismotectonic characteristics of an area the sheer number of small events as well as their low energy content renders their processing problematic in this work we have developed and applied a methodology to automatically pick the arrival times of p and s waves using a correlation detector event detection is performed using the waveform recordings of a reference station located close to the epicentral area of an intense seismic sequence such as aftershocks or swarms cross correlation matrices are constructed followed by nearest neighbour clustering and the formation of multiplets a master event is chosen from each cluster and its arrival times are picked manually the automatic algorithm uses the p o rs wave of each master event as a correlation detector searches the waveforms of the other events of the same multiplet and imposes the corresponding arrival time when the bestfit is achieved the picks are characterized by observation weights which derive from the quality of thefit the type of the available waveform components and the consistency between multiple measurements the proposed methodology was applied to an important seismic sequence that occurred between 2010 january 18 and 26 near the city of efpalio greece this procedure has the potential to increase 10 fold the amount of information and provide sufficient detail for a subsequent analysis of the spatiotemporal distribution of a seismic series

properties of scattered elastic waves in the lithosphere of kamchatka parameters and temporal variations abstract records of near earthquakes from the shipunsky station were used to estimate s wave absorption for seven frequency bands ranging from 0 4 to 24 hz three techniques were employed and three rows of consistent estimates were obtained two of the three techniques give estimates that are independent of q anisotropic scattering was studied by observing the broadening of the s wavelet the estimates obtained show that anisotropic scatter may be significant the time variation of the coda envelope shape was studied using the records of 1 s regional seismographs three epicentral regions were chosen in the kurile kamchatka zone where m 8 earthquakes have occurred time series of the parameter which is the anomaly of the logarithmic steepness of coda envelope were constructed for vertical and horizontal channels of several stations pronounced forerunner type variations of were revealed we show that the probable cause of these variations is a qs decrease in the vicinity of impending m 8 earthquake this decrease is about 20 with a lead time of about a year the forerunner anomaly is not of the bay type and recovers 1 2 years after a large earthquake

zoned chondrules in semarkona evidence for high and low temperature processing at least 15 of the 10w feo chondrules in semarkona ll3 0 have mesostases that are concentrically zoned in na with enrichments near the outer margins we have studied zoned chondrules using electron microprobe methods x ray mapping plus quantitative analysis ion microprobe analysis for trace elements and hydrogen isotopes cathodoluminescence imaging and transmission electron microscopy in order to determine what these objects can tell us about the environment in which chondrules formed and evolved mesostases in these chondrules are strongly zoned in all moderately volatile elements and h interpreted as water calcium is depleted in areas ofvolatile enrichment titanium and cr generally decrease toward the chondrule surfaces whereas al and si may either increase or decrease generally in opposite directions to one another mn follows na in some chondru1es but not in others fe and mg are unzoned d h ratios increase in the water rich areas of zoned chondrules mesostasis shows cathodoluminescence zoning in most zoned chondrules with the brightest yellow color near the outside mesostasis in zoned chondrules appears to be glassy with no evidence for devitrification systematic variations in zoning patterns among pyroxene and olivine rich chondrules may indicate that fractionation oflow and high ca pyroxene played some role in ti cr mn si ai and some ca zoning but direct condensation ofelements into hot chondrules secondary melting oflate condensates into the outer portions of chondrules and subsolidus diffusion of elements into warm chondrules cannot account for the sub parallel zoning profiles ofmany elements the presence ofh20 or elemental abundance patterns zoning ofmoderately volatile elements and ca may have been produced by hydration ofchondrule glass without devitrification during aqueous alteration on the parent asteroid this could have induced structural changes in the glass allowing rapid diffusion and exchange of elements between altered glass and surrounding matrix and rim material calcium was mainly lost during this process and other nonvolatile elements may have been mobile as well some unzoned 10w feo chondrules appear to have fully altered mesostasis

formation conditions of pyroxene olivine and magnesian olivine chondrules abstract dynamic crystallization experiments performed on a type i and an intermediate type ii iii composition demonstrate chondrule texture is controlled by the abundance of heterogeneous nuclei this factor is controlled by the maximum initial temperature relative to the olivine disappearance temperature for the given heating time glassy and excentroradial textures form from superheated melts with no nuclei and barred textures form with initial temperatures near the olivine disappearance temperature porphyritic and granular textures form with initial temperatures below the liquidus with abundant nuclei comparison of zoning characteristics of experimental olivines with those in natural porphyritic olivine chondrules indicates cooling rates of 100 to 1000 c h whereas olivine morphology indicates barred olivines cooled at rates of 250 to 1000 c h texture composition relationships suggest chondrules experienced initial temperatures below 1750 c these observations are consistent with the idea that chondrules formed by transient heating in dust rich regions i e in the midplane of the solar nebula

shear wave anisotropy spatial and temporal variations in time delays at parkfield central california summary shear wave splitting is analysed on data recorded by the high resolution seismic network hrsn at parkfield on the san andreas fault central california during the three year period 1988 1990 shear wave polarizations either side of the fault are generally aligned in directions consistent with the regional horizontal maximum compressive stress at some 70 to the fault strike whereas at station mm in the immediate fault zone shear wave polarizations are aligned approximately parallel to the fault normalized time delays at this station are found to be about twice as large as those in the rock mass either side this suggests that fluid filled cracks and fractures within the fault zone are elastically or seismically different from those in the surrounding rocks and that the alignment of fault parallel shear wave polarizations are associated with some fault specific phenomenon temporal variations in time delays between the two split shear waves before and after a ml 4 earthquake can be identified at two stations with sufficient data mm within the fault zone and vc outside the immediate fault zone time delays between faster and slower split shear waves increase before the ml 4 earthquake and decrease near the time of the event the temporal variations are statistically significant at 68 per cent confidence levels earthquake doublets and multiplets also show similar temporal variations consistent with those predicted by anisotropic poroelasticity theory for stress modifications to the microcrack geometry pervading the rock mass this study is broadly consistent with the behaviour observed before three other earthquakes suggesting that the build up of stress before earthquakes may be monitored and interpreted by the analysis of shear wave splitting

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

temporal change in scattering and attenuation associated with the earthquake occurrence a review of recent studies on coda waves the study of coda waves has recently attracted increasing attention from seismologists this is due to the fact that it is viewed as a new means by which the stress accumulation stage preceding a large earthquake can be measured since the scattering paths nearly uniformly cover a fairly large region around the focus and observation stations compared with the direct ray paths to date we have had many reports on the temporal variation of the relation between coda duration and amplitude magnitude and that of the coda attenuationq 1 which is estimated from coda amplitude decay some of these have shown a precursor like behavior however others seem to have shown a coseismic change we have critically reviewed these reports and discussed what these observational facts tell us about the change in the heterogeneous crust we found significant temporal variations not only in the mean but also in the scatter ofq 1 associated with the mainshock occurrence the formation of new cracks the reopening and growing of existing cracks the interaction of these cracks and the pore water movement through these cracks might correspond to such variations in addition we may expect an inhomogeneous distribution of crack clusters in a fairly large region compared with the aftershock region the gradual appearance of such crack clusters seems to be the most plausible mechanism by which coda decay gradients are caused to largely scatter in the stress accumulation stage

experimental studies of group a1 chondrules abstract dynamic crystallization and annealing experiments have been conducted using a group al chondrule bulk composition to examine the formation and alteration of mesostases that emit a bright yellow cathodoluminescence cl this type of mesostasis has only been observed in group al and a2 chondrules in the least altered chondritic meteorites the dynamic crystallization experiments produce yellow luminescing mesostases only in experiments cooled to their final quench temperatures at the slowest cooling rates the yellow cl is present only where low ca pyroxene grows from the melt so the remaining liquid is enriched in normative anorthite and diopside this composition is strongly associated with yellow luminescence in group al chondrule mesostases low temperature hydrothermal annealing experiments demonstrate that the yellow luminescence can only be destroyed and not enhanced or altered to blue luminescence by aqueous alteration annealing under dry conditions increased both the amount and intensity of the yellow luminescent material annealing experiments designed to further devitrify the mesostasis converted both yellow luminescing and nonluminescent mesostases to blue luminescing mesostases these results confirm that yellow luminescing mesostases are the result of the thermal history group al chondrues experienced prior to accretion and their alteration to blue luminescing mesostases is a direct result of their metamorphic history

chondrule formation metamorphism brecciation an important new primary chondrule group and the classification of chondrules abstract the recently proposed compositional classification scheme for meteoritic chondrules divides the chondrules into groups depending on the composition of their two major phases olivine or pyroxene and the mesostasis both of which are genetically important the scheme is here applied to discussions of three topics the petrographic classification of roosevelt county 075 the least metamorphosed h chondrite known brecciation an extremely important and ubiquitous process probably experienced by 40 of all unequilibrated ordinary chondrites and the group a5 chondrules in the least metamorphosed ordinary chondrites which have many similarities to chondrules in the highly metamorphosed equilibrated chondrites since composition provides insights into both primary formation properties of the chondrules and the effects of metamorphism on the entire assemblage it is possible to determine the petrographic type of rc075 as 3 1 with unique certainty similarly the new scheme can be applied to individual chondrules without knowledge of the petrographic type of the host chondrite which makes it especially suitable for studying breccias finally the new scheme has revealed the existence of chondrules not identified by previous techniques and which appear to be extremely important like group a1 and a2 chondrules but unlike group b1 chondrules the primitive group a5 chondrules did not supercool during formation but unlike group a1 and a2 chondrules and like group b1 chondrules they did not suffer volatile loss and reduction during formation it is concluded that the compositional classification scheme provides important new insights into the formation and history of chondrules and chondrites which would be overlooked by previous schemes

crustal structure of the southern calaveras fault zone central california from seismic refraction investigations a magnitude 5 7 earthquake on 6 august 1979 within the calaveras fault zone near coyote lake of west central california motivated a seismic refraction investigation in this area a northwest southeast profile along the fault as well as two fan profiles across the fault were recorded to examine the velocity structure of this region the analysis of the data reveals a complicated upper crustal velocity structure with strong lateral variations in all directions the near surface layers consist of recent sediments with seismic p wave velocities of 2 6 to 3 2 km sec these are underlain by rocks of the great valley sequence which have an average velocity of 4 5 km sec the great valley sequence is present along the whole profile depths range from 4 3 to 4 8 km in the northwest near anderson lake and in the southeast of the profile line near hollister in the middle of the profile near coyote lake however this layer thins and we find a laterally limited higher velocity layer 5 1 km sec between depths of 2 8 to 4 8 km the high velocity zone which coincides with a gravity high also correlates spatially with the hypocentral area of the 6 august earthquake and its aftershocks and may therefore represent an asperity on the fault velocities within the fault zone were determined from the fan profiles near anderson lake a pronounced delay of first arrivals on the fan records indicates a vertical 1 to 2 km wide near surface low velocity zone along the fault near coyote lake the delays observed in the fan records correlate with two subsurface en echelon fault planes which have been previously identified from lineations in the seismicity pattern the structure of the lower crust is similar to the neighboring diablo range a 8 to 9 km thick upper crustal layer with a seismic velocity of 5 7 to 6 3 km sec is underlain by a 3 km thick layer with velocity 6 8 km sec in accordance with previous studies of the diablo range there are indications of a pronounced lower crustal low velocity zone between a depth of 17 and 23 km the presence of this low velocity zone suggests that higher velocity igneous rocks of the middle crust have been thrust over sedimentary rocks

temporal change in p wave scatterer distribution associated with the m6 1 earthquake near iwate volcano northeastern japan summary temporal variation of the scatterer distribution has been detected around the focal area of an m6 1 earthquake northeastern japan by applying semblance analysis to seismic array data the variation was found in slant stacked waveforms of two explosions detonated just above the focal area one month before and two months after the m6 1 earthquake according to geodetic observations a pressure source that might be a magma reservoir exists beneath this region and its location changed during the observation period slant stacked waveforms are slightly different for the two explosions the difference suggests that a scatterer contributing to the coda part is shifted towards the east and to greater depths only after three months in this region seismic and volcanic activity was very active during the interval between the two explosions the volcanic activity of mt iwate just north of the m6 1 earthquake which started several months beforehand continued during this period it may be considered that scatterer change relates to seismic and or volcanic activity in the studied area

chemical and physical studies of chondrites x cathodoluminescence and phase composition studies of metamorphism and nebular processes in chondrules of type 3 ordinary chondrites abstract the cathodoluminescence cl properties of eight type 3 ordinary chondrites and one l5 chondrite have been determined and phenocryst and mesostasis compositions have been analyzed in the chondrules of four of them semarkona type 3 0 krymka 3 1 allan hills a77214 3 5 and dhajala 3 8 in order to investigate their origins and metamorphic history two major classes of chondrule with eight subdivisions have been identified mainly on the basis of cl properties and 95 of the chondrules can be assigned to these groups on the basis of phenocryst and mesostasis composition class a chondrules consisting of those with plagioclase normative mesostasis with bright cl are subdivided into groups a1 a2 a3 a4 and a5 class b chondrules with little or no cl and having quartz normative mesostases in the least metamorphosed chondrites which becomes feldspathic with metamorphism are subdivided into groups b1 b2 and b3 relationships between the eight chondrule groups can be deduced from their relative abundance in each of the nine chondrites groups a1 a2 b1 and a5 are present in semarkona 15 20 60 5 by number respectively group a5 chondrules in semarkona being more heterogeneous than a5 chondrules in chondrites of higher petrologic type chondrule group a1 evolves into a3 then a4 and then a5 during metamorphism while a2 evolves into a4 and then a5 chondrule group b1 evolves into b2 b3 and then a5 but higher levels of metamorphism are required to complete the series than for the a1 5 series conversion of a group to an adjacent group can be observed in allan hills a77214 3 5 where several chondrules are group b3 in their central regions and group a5 in their outer regions the present chondrule groups are essentially independent of texture since group a and group b chondrules differ in bulk composition redox state and possibly oxygen isotope systematics their relative abundance might be a factor in the creation of the nine chondrite classes

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

the semarkona meteorite first recorded occurrence of smectite in an ordinary chondrite and its implications abstract semarkona is an unshocked unequilibrated ordinary chondrite much of the interchondrule matrix and the mesostases of some chondrules and clasts have been hydrothermally altered analyses of altered materials and opaque matrix are presented ca and fe have been redistributed from primary anhydrous phases into calcite and na fe smectite respectively in semarkona the process possibly requires open system behavior inconsistent with the conventional view of metamorphism of the ordinary chondrites the low petrologic type previously assigned to semarkona is the result of retrograde metamorphism under aqueous conditions of a higher temperature mineral assemblage semarkona and possibly bishunpur should be assigned to petrologic type 2

changes in shear wave splitting at anza near the time of the north palm springs earthquake changes in shear wave splitting are observed at knw before and after the m 6 north palm springs earthquake of july 8 1986 knw is a station of the anza seismic network monitoring the anza seismic gap on the san jacinto fault southern california the gradual increase in the delays between the split shear waves over 3 years at knw reported by peacock et al 1988 ended in june 1986 the further 2 years of observations analyzed here show that the behavior of the delays changed abruptly near the time of the north palm springs earthquake 33 km north of knw peacock et al demonstrated that the increase in delays could be simulated by increasing the aspect ratio of stress aligned fluid filled inclusions and speculated that this increase might be the result of a buildup of stress before an impending earthquake the new data appear to confirm this speculation but the temporal variations require a more complex interpretation although they still suggest that the changes in shear wave splitting are caused by earthquake induced stress changes to the fluid filled inclusions throughout the rockmass central to interpretation of temporal changes in shear wave splitting is the well established existence throughout at leastmore the uppermost 10 to 20 km of the crust of small fluid filled cracks microcracks and pores the existence of such inclusions introduces a compliant quality to otherwise stiff crustal rock the authors term these distributions of inclusions extensive dilatancy anisotropy or eda and the individual inclusions eda cracks because although they may include a wide range of shapes many of the seismic properties can be simulated by distributions of thin parallel cracks less