active high resolution compressional wave attenuation tomography at newberry volcano central cascade range in this study we use the seismic data from a previous study at newberry to compute its three dimensional compressional wave attenuation structure the data consist of eight explosions recorded on an array of about 120 seismograph stations the shots are located on two concentric circles centered on the caldera with radii of 39 and 85 km attenuation is estimated using spectral ratios to compute t at each station for each shot the data are inverted using a least squares technique our results indicate that regions of inferred boiling water i e two phase pore fluid are correlated spatially with regions of high attenuation not corresponding to low velocities two regions are of particular interest one is underneath the newberry ii drill hole in the central part of the caldera where results from a flow test suggest that two phase fluid conditions existed in the bottom of the hole before the flow test the other region is beneath the west flank of the volcano which has been interpreted as an attractive geothermal prospect because of a shallow conductive anomaly our results are consistent with the suggestion made in an earlier paper by us that two phase geothermal reservoirs can be located within complex three dimensional structures by using jointly interpreted compressional wave velocity and attenuation images

size distribution analyses for estimating diamond grade and value abstract analysing the size frequency distributions sfds of both micro diamonds and macro diamonds from primary deposits shows that the distributions are continuous across all sizes and that there are two regions of different character with a transition about 1 2 mm using log axes the frequency curve is linear for the smaller sizes allowing slope and intercept parameters to be determined which are less ambiguous than stone counts and ratios of macro to micro populations that are generally reported modelling a diamond population that has undergone removal of a uniform thickness of the outer layer transforms a linear frequency curve into a quadratic form which is also the form of the frequency curve for macro diamonds diamonds grown synthetically also display a linear distribution across a smaller fraction of their size distribution curve

long period events the most characteristic seismicity accompanying the emplacement and extrusion of a lava dome in galeras volcano colombia in 1991 abstract since its reactivation in 1988 the principal eruptions of galeras volcano occurred on may 4 9 1989 july 16 1992 and january 14 march 23 april 3 april 14 and june 7 1993 the initial eruption was a phreatic event which clearly marked a new period of activity a lava dome was extruded within the main crater in october 1991 and subsequently destroyed in an explosive eruption on july 16 1992 the eruptions that followed were all vulcanian type explosions the seismicity accompanying the emplacement extrusion and destruction of the lava dome was dominated by a mix of long period lp events and tremor displaying a variety of waveforms repetitive lp events with dominant periods in the range 0 2 1 s were observed in october and november 1991 and visually correlated with short energetic pulses of gas venting through a crack bisecting the dome surface each lp event was characterized by a weak precursory signal with dominant periods in the range 0 05 0 1 s lasting roughly 7 s using the fluid driven crack model of chouet 1988 1992 we infer that two distinct cracks may have acted as sources for the lp and precursor signals spectral analyses of the data yield the following parameters for the lp source crack length 240 360 m crack width 130 150 m crack aperture 0 5 3 4 mm crack stiffness 100 500 sound speed of fluid 880 m s and excess pressure 0 01 0 19 mpa similar analyses yield the parameters of the precursor source crack length 20 30 m crack width 15 25 m crack aperture 2 3 8 7 mm crack stiffness 5 15 sound speed of fluid 140 m s and excess pressure 0 06 0 15 mpa combined with geologic and thermodynamic constraints obtained from field observations these seismic parameters suggest a gas release mechanism in which the episodic collapse of a foam layer trapped at the top of the magma column subjacent to the dome releases a slug of pressurized gas which escapes to the surface while dilating a preexisting system of cracks in the dome structure accordingly the fracture observed on the crystallized dome body is the surface extension of the lp source crack where lp activity is induced by the rapid emission and expansion of gas flowing through this conduit the width and aperture of the crack estimated in the model are in good agreement with the length and aperture of the fracture estimated from visual observations the source parameters of the precursor signal are suggestive of a nozzle like conduit connecting the lp source crack to the underlying magma reservoir excitation of this conduit segment is attributed to the rapid emission and acceleration of the frothy fluid resulting from the collapse of the foam layer at the top of the reservoir the calculated periodicity of foam collapse events is in agreement with the observed average rate of thirteen lp events per hour

locating tremor and shock sources recorded at bromo volcano abstract during a phase of high eruptive activity as well as high tremor activity seismic signals were recorded at bromo volcano east java for almost three months in 1995 the signals generated by the volcano cover a broad frequency range including long period signals with frequencies between 10 and 100 mhz tremor signals at about 5 hz and volcanic shocks with frequencies up to 25 hz seismic signals from volcanoes especially tremors have been classified and categorized in different ways but interpretation has always been limited by the difficulties in determining even approximate source locations volcanic tremor lacks an emergent first onset while the complex structure of the volcano makes it difficult to determine other phases from shock signals than first arrivals if the volcanic signal has been recorded in at least two stations the location of its seismic source can be estimated using a grid search method if we assume the source radiates isotropically in a homogeneous medium applying the grid method to data recorded at mt bromo we determine the locations of the sources of tremor and shock signals the sources for both types of signals are located in the northwestern part of the crater near the open vent and also near the source of long period signals gottschammer 1999 annal geofis 42 465 481

2d finite difference viscoelastic wave modelling including surface topography we have pursued two dimensional 2d finite difference fd modelling of seismic scattering from free surface topography exact free surface boundary conditions for the particle velocities have been derived for arbitrary 2d topographies the boundary conditions are combined with a velocity stress formulation of the full viscoelastic wave equations a curved grid represents the physical medium and its upper boundary represents the free surface topography the wave equations are numerically discretized by an eighth order fd method on a staggered grid in space and a leap frog technique and the crank nicholson method in time in order to demonstrate the capabilities of the surface topography modelling technique we simulate incident point sources with a sinusoidal topography in seismic media of increasing complexities we present results using parameters typical of exploration surveys with topography and heterogeneous media topography on homogeneous media is shown to generate significant scattering we show additional effects of layering in the medium with and without randomization using a von karman realization of apparent anisotropy synthetic snapshots and seismograms indicate that prominent surface topography can cause back scattering wave conversions and complex wave patterns which are usually discussed in terms of inter crust heterogeneities

models of tremor and low frequency earthquake swarms on montserrat recent observations from soufriere hills volcano in montserrat reveal a wide variety of low frequency seismic signals we discuss similarities and differences between hybrid earthquakes and long period events and their role in explosions and rockfall events these events occur usually in swarms and occasionally merge into tremor an observation that can shed further light on the generation and composition of harmonic tremor we use a 2d finite difference method to model major features of low frequency seismic signatures and compare them with the observations a depth dependent velocity model for a fluid filled conduit is introduced which accounts for the varying gas content in the magma and the impact on the seismic signals is discussed we carefully analyse episodes of tremor that show shifting spectral lines and model those in terms of changes in the gas content of the magma as well as in terms of a time dependent triggering mechanism of low frequency resonances in this way we explain the simultaneous occurrence of low frequency events and tremor with a spectral content comprising integer harmonics

seismicity associated with dome growth and collapse at the soufriere hills volcano montserrat varied seismicity has accompanied growth and collapse of the lava dome of the soufriere hills volcano montserrat earthquakes have been classified as either volcano tectonic long period or hybrid and daily variations in the numbers of events have mapped changes in the style of eruption repetitive hybrid earthquakes were common during the first months of dome growth in july 1996 the style of seismicity changed and regular short lived hybrid earthquake swarms became common this change was probably caused by an increase in the magma flux earthquake swarms have preceded almost all major dome collapses and have accompanied cyclical deformation thought to be due to a build up of pressure in the upper conduit which is later released by magma moving into the dome

modelling the growth of natural diamonds abstract in the following article we have reviewed the mineralogical chemical physical and isotopic evidence concerning the growth of coated diamonds and have combined it to produce a comprehensive model for their formation we suggest that the coatings formed during a period of metasomatic activity which preceded the eruption of their host kimberlites ultrapotassic co21bh2o rich fluids resulted from the crystallisation of diamond free kimberlitic magmas intruded into the deep lithosphere the kimberlite magmas were derived from an asthenospheric source which was globally quite uniform in terms of the isotopic composition of carbon and nitrogen 13c and 15n both being close to 5 the fluids produced during crystallisation invaded overlying diamondiferous lithosphere in which different regions could contain diamond populations with different mineralogical isotopic and physical characteristics depending on the history of their source region either intrinsic to their formation or due to reaction with reduced lithosphere the fluids were super saturated with carbon although not to such an extent as to allow for the nucleation of new diamonds when these super saturated fluids encountered older diamonds new and fibrous diamond growth commenced immediately this period of metasomatic activity was followed rapidly by one or more successful kimberlite eruptions which transported the now coated diamonds to the surface in the crust carbonates within hypabyssal facies kimberlites will have 13c values which reflect the deep seated source 5 whereas those within diatreme facies may be more variable due to outgassing of co2 during eruption finally we consider isotope fractionation related to growth we suggest that approaches based on equilibrium are not appropriate to diamonds but rather that it is better to consider the nature and kinetics of the surface reactions leading to growth where diamond growth is very rapid as may be the case for fibrous diamond we propose that there will be no difference in isotopic composition between the fluid and diamond and not the 3 4 13c depletion in the latter predicted by theoretical treatments octahedral diamonds are more problematic since far less is known about their growth conditions however we show in principle how the content and perhaps isotopic composition of nitrogen within a diamond may be controlled by its growth rate we are uncertain whether 13 c would be affected

the micro macro diamond relationship a case study from the artemisia kimberlite northern slave craton canada abstract size frequency distributions are the principal tool for predicting the macro diamond grade of new kimberlite discoveries based on micro diamonds i e diamond 0 5 mm recovered from small exploration samples lognormal size frequency distributions as observed for the artemisia kimberlite slave craton canada suggest a common source for micro and macro diamonds recovered from single samples an implication that has never been conclusively tested we analyzed 209 diamonds between 0 2 and 2 mm in size from the artemisia kimberlite for their carbon isotopic compositions and nitrogen characteristics to determine the nature of the micro macro diamond relationship despite overall similarity in the 13c distributions of micro and macro diamonds both are bimodal with peaks in classes 5 0 to 4 5 and 3 5 to 3 0 rare diamonds with 13c between 14 2 and 24 5 of presumed eclogitic origin are restricted to macro diamonds whereas positive values are only observed for micro diamonds in addition a shift in main mode and median value in 13c of about 1 is observed for micro relative to macro diamonds fundamental differences between micro and macro diamonds at artemisia were revealed through the analysis of nitrogen concentrations 68 of micro diamonds are type ii nitrogen free versus 21 of macro diamonds and only 19 of micro diamonds have nitrogen contents 100 atomic ppm versus 43 of macro diamonds similarly the presence of a detectable hydrogen related peak at 3107 cm 1 increases from 40 for micro diamonds to 94 for macro diamonds previous studies on diamond populations from individual deposits have documented that single batches of ascending kimberlite or lamproite magma sample multiple diamond subpopulations formed during distinct growth events in compositionally variable sources and at various depth levels the artemisia data clearly show that even over a fairly narrow size interval spanning the micro to macro diamond transition the specific diamond subpopulations present and their relative proportions may vary significantly with diamond size at artemisia we conclude that the observed lognormal size distribution is not a reflection of an entirely common origin of micro and macro diamonds

cosmic ray exposure histories of the lunar meteorites aau 012 and shisr 166 we measured the concentrations and isotopic compositions of the stable isotopes of he ne ar kr and xe in the two lunar impact melt breccias abar al uj aau 012 and shisr 166 to obtain information on their cosmic ray exposure histories and possible launch pairing the latter was suggested because of their similar chemical composition aau 012 has higher gas concentrations than shisr 166 and clearly contains implanted solar wind gases indicating a shallow to moderate shielding for this meteorite in the lunar regolith the maximum shielding depth of aau 012 was most likely 310 g cm 2 and its lunar regolith residence time was 420 70 ma our results indicate that in shisr 166 the trapped component is a mixture of air and solar wind the low concentration of cosmogenic and solar wind gases indicate substantial diffusive gas loss and a shielding depth of 700 g cm 2 on the moon for shisr 166 all differences seen in the concentrations and isotopic compositions of the noble gases suggest that aau 012 and shisr 166 are most likely not launch pairs although a different exposure history on the moon does not exclude the possibility that the two meteorites were ejected by a single large impact event

the geology and mineralogy of the anuri kimberlite nunavut canada abstract the 613 6 ma anuri kimberlite is a pipelike body comprising two lobes with a combined surface area of approximately 4 5 ha the pipe is infilled with two contrasting rock types volcaniclastic kimberlite vk and less common hypabyssal kimberlite hk the hk is an archetypal kimberlite composed of macrocrysts of olivine spinel mica rare eclogitic garnet and clinopyroxene with microphenocrysts of olivine and groundmass spinel phlogopite apatite and perovskite in a serpentine calcite phlogopite matrix the ba enrichment of phlogopite the compositional trends of both primary spinel and phlogopite as well as the composition of the mantle derived xenocrysts are also characteristic of kimberlite the present day country rocks are granitoids however the incorporation of sedimentary xenoliths in the hk shows that the archean granitoid basement terrain at least locally was capped by younger proterozoic sediments at the time of emplacement the sediments have since been removed by erosion hk is confined to the deeper eastern parts of the anuri pipe it is suggested that the hk was emplaced prior to the dominant vk as a separate phase of kimberlite the hk must have ascended to high stratigraphic levels to allow incorporation of proterozoic sediments as xenoliths most of the anuri kimberlite is infilled with vk which is composed of variable proportions of juvenile lapilli discrete olivine macrocrysts country rock xenoliths and mantle derived xenocrysts it is proposed that the explosive breakthrough of a second batch of kimberlite magma formed the western lobe resulting in the excavation of the main pipe much of the resulting fragmented country rock material was deposited in extra crater deposits pyroclastic eruption s of kimberlite must have occurred to form the common juvenile lapilli present in the vks the vk is variable in nature and can be subdivided into four types volcaniclastic kimberlite breccia magmaclast rich volcaniclastic kimberlite breccia finer grained volcaniclastic kimberlite breccia and lithic rich volcaniclastic kimberlite breccia the variations between these subtypes reflect different depositional processes these processes are difficult to determine but could include primary pyroclastic deposition and or resedimentation there is some similarity between anuri and the lac de gras kimberlites with variable types of vk forming the dominant infill of small steep sided pipes excavated into crystalline archean basement and sedimentary cover

location of long period events below kilauea volcano using seismic amplitudes and accurate relative relocation 1 we present methods for improving the location of long period lp events deep and shallow recorded below kilauea volcano by the permanent seismic network lp events might be of particular interest to understanding eruptive processes as their source mechanism is assumed to directly involve fluid transport however it is usually difficult or impossible to locate their source using traditional arrival time methods because of emergent wave arrivals at kilauea similar lp waveform signatures suggest the existence of lp multiplets the waveform similarity suggests spatially close sources while catalog solutions using arrival time estimates are widely scattered beneath kilauea s summit caldera in order to improve estimates of absolute lp location we use the distribution of seismic amplitudes corrected for station site effects the decay of the amplitude as a function of hypocentral distance is used for inferring lp location in a second stage we use the similarity of the events to calculate their relative positions the analysis of the entire lp seismicity recorded between january 1997 and december 1999 suggests that a very large part of the lp event population both deep and shallow is generated by a small number of compact sources deep events are systematically composed of a weak high frequency onset followed by a low frequency wave train aligning the low frequency wave trains does not lead to aligning the onsets indicating the two parts of the signal are dissociated this observation favors an interpretation in terms of triggering and resonance of a magmatic conduit instead of defining fault planes the precise relocation of similar lp events based on the alignment of the high energy low frequency wave trains defines limited size volumes

are euhedral microdiamonds formed during ascent and decompression of kimberlite magma implications for use of microdiamonds in diamond grade estimation abstract the relationship between euhedral microdiamonds we propose an alternative hypothesis based on published experimental studies showing there is a significant decrease in the c bearing volatile content of kimberlite magma as pressure decreases during ascent of the kimberlite magma this may result in a pressure related transition from conditions at depth at which diamond is unstable in fluid undersaturated kimberlite magma to shallower level conditions at which diamond becomes stable or metastable as the magma reaches fluid saturation in this scenario macrodiamond xenocrysts of an early generation entrained at asthenospheric or deep lithospheric depths may partially or totally dissolve into the undersaturated magma upon disaggregation of their host rocks upon ascent of the magma to shallower depths and under appropriate oxidation conditions the lowered capacity of the magma to dissolve c bearing volatiles may result in euhedral microdiamond precipitation probably immediately before final eruption although framed in qualitative terms our hypothesis has testable consequences which we discuss in view of these considerations and the multiple possible relationships within and between microdiamonds and macrodiamonds in individual deposits we suggest that the use of microdiamond abundances from small samples as a guide to economic macrodiamond grade is problematic as an exploration strategy

the polarization of volcanic seismic signals medium or source abstract with the proliferation of three component seismometers on volcanoes the temptation is great to use polarization analysis as we do in earthquake seismology to determine propagation direction and or wavetype in order to locate and characterize the wave s source in volcano seismology there are two impediments to such a procedure the complexity of the volcano s structure and the often long lasting volcanic seismic signals i develop a simple model of acoustic scattering and apply it to three simple theoretical source signals which represent the classes of signals encountered at volcanoes when the medium is strongly scattering the polarization at a receiver location for impulsive sinusoidal or square wave sources mimics the characteristics for volcanic shocks tornillos with a single frequency and multichromatic tremor or tornillos the polarization observed for the square wave source resembles that observed for multichromatic tremor at lascar volcano chile and multichromatic tornillos at galeras volcano colombia at low frequencies the particle motion is fairly linear and nearly constant but cannot necessarily be used directly to indicate the direction to the source at all frequencies the particle motion exhibits some characteristics of rayleigh waves namely ellipticity of varying degrees and an rz product that oscillates with twice the frequency of the mode if this model is correct the lack of change of fundamental wavefield parameters such as the polarization for low frequencies during any given tornillo and from one tornillo to the next implies that the location of the source is stable to within a resolution of about 200 m

assessing the diamond potential of kimberlites from discovery to evaluation bulk sampling the economic evaluation of diamond bearing kimberlites is usually carried out in four stages expenditure tends to increase by an order of magnitude at each successive stage at the end of each stage the sample results should be critically appraised before deciding to proceed to the next phase in the first stage even before individual kimberlite bodies have been discovered the indicator mineral geochemistry will give a first rough idea of the diamond potential the relative abundance of harzburgitic pyropes subcalcic chrome rich is often directly correlated with the diamond grade in the next stage when the kimberlite body has been discovered a relatively small sample of a few hundred kilograms will be enough to recover sufficient microdiamonds to allow an extrapolation of the size distribution towards the commercial sized diamonds and a rough estimate of their grade if positive the third stage should be a limited bulk sampling programme order of 200 tonnes to determine the commercial sized diamond grade expressed as carats per tonne the aim of the final stage is to obtain a parcel of the order of 1 000 carats to estimate the average commercial value of the diamonds the robustness and reliability of the grade and value estimates can be verified with extreme value analysis and by obtaining the confidence limits with bootstrapping

locating pyroclastic flows on soufriere hills volcano montserrat west indies using amplitude signals from high dynamic range instruments pyroclastic flows are located using amplitude signals from a seven station high dynamic range seismograph array located 1 9 6 1 km from soufriere hills volcano in montserrat west indies locations are determined by measuring the seismograph signal amplitude for an event recorded at several stations in a moving time window analysis for a given window the measured amplitudes are corrected to a trial source location by removing the effect of the surface wave geometric spreading instrument gain and the attenuation at calculated travel times the trial source location is then compared to other trial locations via an iterative localised grid search where the root mean squared amplitude residual a is minimised the process is repeated for subsequent time steps resulting in a best fit event location and size through time the method has been tested on four small events occurring on april 8 1999 august 12 1999 february 25 2001 and july 4 2001 when visual observations of pyroclastic flows coincided with good seismograph station coverage number of stations 5 azimuthal gap 160 based on the location results the four events propagated 0 5 1 4 1 3 and 1 0 km from the dome and had maximum attenuation corrected reduced displacements drq of 9 0 2 8 6 9 and 2 3 cm2 and maximum pyroclastic flow velocities of 7 30 20 and 8 ms 1 respectively a time lapse video of the event of august 12 1999 shows that amplitude based location through time closely matches the observed run out distance and velocity in contrast amplitude based locations for the events of april 8 1999 and july 4 2001 underestimated the actual flow run out by 1 5 km underestimation of the true run out distance is probably due to both the increased distribution of sources as coherent dome material disaggregates into many blocks and signal contamination from other sources results indicate that pyroclastic flows and rockfalls can be located using amplitude signals from high dynamic range seismograph stations yielding estimates of size and trajectory regardless of visibility conditions on the volcano this new method is being tested as a hazard mitigation and research tool on montserrat

shear modulus and internal friction of calcite rocks at seismic frequencies pressure frequency and grain size dependence abstract the shear modulus g and associated internal friction q 1 have been measured at seismic frequencies for a suite of four essentially monomineralic calcite rocks with grain sizes ranging from 4 to 1000 m the measurements are based on a previously described technique for the observation of forced torsional oscillations of a series combination of a rock cylinder and a steel standard under high confining pressure at room temperature the behaviour of each rock has been studied as a function of strain amplitude 10 8 10 6 maximum at surface pressure 0 300 mpa and oscillation period 1 300 s no evidence is found of any departure from linearity in the range of strain amplitudes studied corrections which are significant only at the shortest periods 1 3 s have been applied to the raw data to account for the influence of torques exerted on the specimen assembly by the gas pressure medium up to about 100 mpa increase in pressure results in a marked increase in g and decrease in q 1 attributable to the closure of crack porosity except in the fine grained solnhofen limestone in which both g and q 1 are insensitive to change in pressure indicative of the virtual absence of crack porosity at higher pressures g is much less pressure sensitive and q 1 is essentially pressure independent with values less than 0 001 in all four rocks since the rock specimens were jacketted under conditions of normal humidity these relatively low values of q 1 indicate a diminished role for adsorbed water in the anelasticity of rocks at high effective pressures within the pressure independent regime q 1 is essentially independent of frequency for periods of 3 100 s and increases by only 30 as the grain size decreases from 1000 to 4 m thus within this regime it is concluded that the observed value of q 1 results to a large degree from an intracrystalline mechanism with a broad range of relaxation times the possibility of significant dislocation damping will be discussed

mineral deposits of canada a synthesis of major deposit types district metallogeny the evolution of geological provinces and exploration methods wayne d goodfellow editor 1 068 pp geological association of canada mineral deposits division special publication no 5 2007 hardcover isbn 13 978 1 897095 24 9 price members cdn 60 00 non members cdn 80 00 following in the footsteps of other landmark reviews of major ore producing countries such as australia hughes 1990 solomon and groves 1994 and south africa anhaeusser and maske 1986 this substantial 1 000 pages monograph is a great achievement that should be in every geologic research library in the world in many ways it sets a new standard most notably in that all figures and photographs are in color and that the entire volume is available in electronic form both as an included dvd and mostly on the gac website it is common in such compendia to have a spectacular cover photo or frontispiece to catch the reader s attention and this book does not disappoint the frontispiece photo is of a 61 8 kg sample from the dome mine timmins ontario and is stated to contain 20 wt percent gold at today s prices the gold alone would be worth 1 5 million dollars

unusual low frequency volcanic seismic events with slowly decaying coda waves observed at galeras and other volcanoes abstract events with slowly decaying coda waves are observed in active andesitic volcanoes associated mainly with vulcanian type eruptions or large gas emissions however these signals are also recorded in some quiescent volcanoes these unusual signals are considered to be related to magmatic activity and generally occur beneath the active crater the signals have been observed to be a short term precursor galeras volcano colombia 1992 1993 asama yama volcano japan 1983 after eruption tokachi dake volcano japan 1989 during seismic swarms meakan dake volcano japan 1982 and during quiescence puracevolcano colombia 1994 1995 tarumai volcano japan 1970 1971 1975 spectral analysis reveals common characteristics for this type of signal the spectrum is characterized by one or several sharp frequency peaks fundamental frequencies are not affected by epicentral distance azimuth or travel time indicating a source effect the damping coefficient for coda waves ranges from 0 002 to 0 02 and is related to large values of the quality factor q c ranging from 250 to 25 respectively these parameters may be the result of large amounts of gas bubbles in the magma body

overview of the eruption of soufriere hills volcano montserrat 18 july 1995 to december 1997 the onset of phreatic volcanic activity at the soufriere hills volcano montserrat on 18 july 1995 followed a three year period of heightened volcano seismic activity beneath the island phreatic explosions gave way to continuous eruption of juvenile andesitic magma in the form of a lava dome on or around 15 november 1995 magma production rate has varied leading to changes in eruptive style an explosive eruption on 17 september 1996 followed a period of enhanced dome growth and large scale gravitational collapses from its eastern flank increasing dome volume led to stressing and overtopping of the confining crater walls to the southwest north and west during early 1997 sustained high magma production rate since june 1997 has led to three periods of major gravitational dome collapses followed by vulcanian explosive eruptions dome growth re started immediately after the cessation of the latest of these explosive phases in october 1997 and continues as of december 1997

deformation of foamed rhyolites under internal and external stresses an experimental investigation the style of magma eruption depends strongly on the character of melt degassing and foaming depending on the kinetics of these processes the result can be either explosive or effusive volcanism in this study the kinetics of foaming due to the internal stresses of gas expansion of two types of obsidian have been investigated in time series experiments 2 min 24 h followed by quenching the samples the volumetric gas melt ratio has been estimated through the density measurements of foamed samples

unusual mineral inclusions and carbon isotopes of alluvial diamonds from bingara eastern australia abstract a suite of diamonds from eastern australia group b are essentially eclogitic however mineral inclusion compositions are unlike eclogitic diamonds from other occurrences garnets are very ca rich gr 61 84 and clinopyroxenes are mostly diopsidic 16 10 mol jd other inclusions in these diamonds are sio 2 titanite olivine molybdenite and melilite a truly unique suite garnet and clinopyroxene are not accompanied by indications of fertile mantle conditions rather we find depletions in fe mn na k coupled with high ni and cr in some clinopyroxenes the chemistry of the garnets and clinopyroxenes suggests affinities with rodingites metasomatised mafic rocks that occur in ophiolites group b diamonds are 13 c enriched 13 c 1 1 1 3 1 s d internal structures include evidence of brittle failure and of rapid growth the diamonds have high nitrogen contents and positive nitrogen isotopes 15 n 10 1 4 7 this may indicate that the diamonds formed from 13 c enriched carbon 3 such as that derived from marine carbonates within the mafic rocks the many unusual features of these diamonds can be interpreted to indicate that the diamonds formed in a subduction environment however resorption on the surfaces of the diamonds indicates that they were brought to the upper crust by magmatic activity

parameterization of multichromatic tornillo signals observed at galeras volcano colombia in the past decade several of the ash eruptions at galeras volcano colombia have been preceded by tornillos these unusual tremor wavelets have quasi sinusoidal waveforms with screw like envelope profiles and can last up to several minutes a swarm of tornillos occurred at galeras volcano between 8 december 1999 and 12 february 2000 these tornillos appear to be more complex than those previously recorded with the broadband instruments or with the short period network of the observatorio vulcanologico y sismologico in pasto they are multichromatic with a varying number of narrow spectral peaks between 1 and 20 hz we describe a procedure for parameterizing the tornillo signals in the time and frequency domains to determine signal parameters in addition to wavelets like the tornillos the procedure can be applied to random signals such as volcanic tremor we derive distribution and correlation functions for the signal parameters determined from the swarm these provide along with the signal signature constraints for modelling variations of the source process from these observations we derive qualitative conclusions about the characteristics of differential equations which describe the underlying processes and excitation mechanisms as forced or self excited oscillators

precursory swarms of long period events at redoubt volcano 1989 1990 alaska their origin and use as a forecasting tool abstract during the eruption of redoubt volcano from december 1989 through april 1990 the alaska volcano observatory issued advance warnings of several tephra eruptions based on changes in seismic activity related to the occurrence of precursory swarms of long period lp seismic events dominant period of about 0 5 s the initial eruption on december 14 occurred after 23 years of quiescence and was heralded by a 23 hour swarm of lp events that ended abruptly with the eruption after a series of vent clearing explosions over the next few days dome growth began on december 21 another swarm with lp events similar to those of the first began on the 26th and ended in a major tephra eruption on january 2 eruptions continued over the next two weeks and then ceased until february 15 when a large eruption initiated a long phase of repetitive dome building and dome destroying episodes that continued into april warnings were issued before the major events on december 14 and january 2 but as the eruptive sequence continued after january 2 the energy of the swarms decreased and forecasting became more difficult a significant but less intense swarm preceded the february 15 eruption which was not forecast this eruption destroyed the only seismograph on the volcanic edifice and stymied forecasting until march 4 when the first of three new stations was installed within 3 km of the active vent from march 4 to the end of the sequence on april 21 there were eight eruptions six of which were preceded by detectable swarms of lp events although weak these swarms provided the basis for warnings issued before the eruptions on march 23 and april 6 the initial swarm on december 13 had the following features 1 short duration 23 hours 2 a rapidly accelerating rate of seismic energy release over the first 18 hours of the swarm followed by a decline of activity during the 5 hours preceding the eruption 3 a magnitude range from 0 4 to 1 6 4 nearly identical lp signatures with a dominant period near 0 5 s 5 dilatational first motions everywhere and 6 a stationary source location at a depth of 1 4 km beneath the crater this occurrence of long period events suggests a model involving the interaction of magma with groundwater in which magmatic gases steam and water drive a fixed conduit at a stationary point throughout the swarm the initiation of that sequence of events is analogous to the failure of a pressure relief valve connecting a lower supercharged magma dominated reservoir to a shallow hydrothermal system a three dimensional model of a vibrating fluid filled crack recently developed by chouet is found to be compatible with the seismic data and yields the following parameters for the lp source crack length 280 380 m crack width 140 190 m crack thickness 0 05 0 20 m crack stiffness 100 200 sound speed of fluid 0 8 1 3 km s compressional wave speed of rock 5 1 km s density ratio of fluid to rock 0 4 and ratio of bulk modulus of fluid to rigidity of rock 0 03 0 07 the fluid filled crack is excited intermittently by an impulsive pressure drop that varies in magnitude within the range of 0 4 to 40 bar such disturbance appears to be consistent with a triggering mechanism associated with choked flow conditions in the crack

the application of c isotope measurements to the identification of the sources of c in diamonds a review abstract in the past decade the isotopic compositions of c in 600 inclusion bearing diamonds have been determined such analyses have revealed the following isotopic characteristics 1 peridotitic diamonds which typically contain garnet chromite olivine and or orthopyroxene inclusions with refractory compositions high mg cr have 13 c values predominantly between 10 and 1 with a sharp peak in the distribution near 5 2 eclogitic diamonds which commonly contain inclusions of omphacitic clinopyroxene cr poor pyrope and or eclogitic accessory minerals such as rutile kyanite coesite or sanidine have 13 c values between 34 and 3 with a smaller peak near 5 3 the isotopic compositions obtained for suites of diamonds from individual occurrences are in general unique and do not resemble the range and distribution obtained by amalgamating the diamond isotope data from a number of localities 4 isotopic zoning patterns and heterogeneities are found in some diamonds cores of coated diamonds tend to be depleted in 13 c relative to the rims and within single octahedral diamonds 13 c variations of nearly 6 have been reported because expected c isotope fractionations at mantle temperatures are small attempts to model the full range of diamond isotope values through fractionating a homogeneous mantle c source have been unsuccessful nevertheless fractionation is probably responsible for some of the observed variation in 13 c values two other models have also been proposed to account for the diamond characteristics outlined above the primordial model suggests that the range and distribution of c isotope compositions are inherited from primordial c in the mantle which has an inhomogeneous isotopic composition such as that found in meteorites the subduction model suggests that subducted crustal c is the source of c in diamonds as organic and inorganic c compounds in the crust exhibit a range of 13 c values similar to that observed in diamonds this paper reviews the c isotope characteristics of diamonds and compares the models which have been proposed to explain the origins of these characteristics

linear and nonlinear inverse rheologies of rocks abstract the generalized constitutive equations of anelastic media are considered and discussed in three dimensions 3d and in terms of two material functions as a generalized standard linear solid sls the inverse problem is considered and it is seen that one may not determine the material functions using the data of one standard creep or relaxation experiment data from both experiments would be needed if the medium is a generalized viscoelastic one then the material function can be determined with one experiment only the creep is determined in the generalized viscoelastic 3d case simulating a 3d experiment using the creep compliance obtained from the relaxation modulus determined from constant strain rate uniaxial experiments caputo 1983 it is seen that the one dimensional 1d model mostly used to model rock mechanics laboratory experiments which in practice are 3d experiments and not rigorously 1d gives the same value of the creep rate obtained using as load the difference between 1 and the confining pressure 3 the case of nonlinear viscoelastic stress strain relation is also discussed and a relation is found to determine the creep rate from 3d experiments at constant strain rate a check made with polycrystalline halite at high pressure and large strain rate gives satisfactory results

qp melting temperature relation in peridotite at high pressure and temperature attenuation mechanism and implications for the mechanical properties of the upper mantle the anelastic properties of compressional waves in a peridotite have been determined in the laboratory at sufficiently high temperatures to 1280 c and pressures to 0 73 gpa to warrant comparison with seismic measurements of the earth a substantial decrease of qp is observed at temperatures well below the onset of partial melting qp systematically increases with increasing pressure over the entire temperature range of major significance is the finding that qp is dependent on the ratio of the temperatures to the melting solidus temperature i e qp depends on the homologous temperature the pressure dependence of qp appears through the pressure dependence of the solidus of the peridotite within the uncertainties of measurement of both qp and the phase diagram it appears that melting and high temperature anelastic properties have a common origin in peridotite the homologous temperature dependence of qp suggests that we may estimate the temperature and pressure dependence of qp for peridotites of different compositions and possibly even for hydrous peridotites if solidus temperatures are known as a function of pressure a far easier measurement than elastic and anelastic properties the activation volume of qp is greatly reduced at high pressure since the slope of solidus versus pressure rapidly decreases with increasing pressure pressure dependence of seismic velocity and melt fraction in peridotite also appears to be related to the homologous temperature the qp homologous temperature relation suggests a connection between qp and the properties of the grain boundaries that is the major loss of seismic energy occurs at the grain boundaries grain boundary relaxation or high temperature background attenuation is a possible mechanism for the grain boundary damping no frequency dependence of qp is resolved 0 0 2 in qp f over the pressure temperature and frequency ranges of the measurement the present results and the model of grain boundary relaxation suggest that an appropriate choice of grain size may give an ultrasonic q that is applicable to the earth experimentally determined anelastic properties of a peridotite are critical for modeling mechanical properties of the upper mantle implications of the results are as follows 1 seismic data commonly interpreted as indicating a partially molten asthenosphere may instead reflect a hot solid asthenosphere at 90 100 of the solidus temperature 2 partial melting may not produce any abrupt change of seismic velocity and q rather elastic and anelastic properties of the upper mantle will change gradually at the boundary where the geotherm crosses the solidus 3 there may be no sharp mechanical boundary between the lithosphere and the asthenosphere

composition and microstructure of magma bodies from effective medium theory summary the extent and seismic properties of magma bodies beneath the subsurface are normally ascertained via seismic methods the seismic properties of such bodies depend on the composition and microstructure of both melt and crystals using effective medium theory we assess the effect of microstructure geometry and orientation of melt and crystals on the seismic properties namely p and s wave velocities and anisotropy we find that s wave velocity and anisotropy are key observables in determining the composition and microstructure of magma bodies

seismic evolution of the 1989 1990 eruption sequence of redoubt volcano alaska abstract redoubt volcano in south central alaska erupted between december 1989 and june 1990 in a sequence of events characterized by large tephra eruptions pyroclastic flows lahars and debris flows and episodes of dome growth the eruption was monitored by a network of five to nine seismic stations located 1 to 22 km from the summit crater notable features of the eruption seismicity include 1 small long period events beginning in september 1989 which increased slowly in number during november and early december 2 an intense swarm of long period events which preceded the initial eruptions on december 14 by 23 hours 3 shallow swarms 0 to 3 km of volcano tectonic events following each eruption on december 15 4 a persistent cluster of deep 6 to 10 km volcano tectonic earthquakes initiated by the eruptions on december 15 which continued throughout and beyond the eruption 5 an intense swarm of long period events which preceded the eruptions on january 2 and 6 nine additional intervals of increased long period seismicity each of which preceded a tephra eruption hypocenters of volcano tectonic earthquakes suggest the presence of a magma source region at 6 10 km depth earthquakes at these depths were initiated by the tephra eruptions on december 15 and likely represent the readjustment of stresses in the country rock associated with the removal of magma from these depths the locations and time history of these earthquakes coupled with the eruptive behavior of the volcano suggest this region was the source of most of the erupted material during the 1989 1990 eruption this source region appears to be connected to the surface by a narrow pipe like conduit as inferred from the hypocenters of volcano tectonic earthquakes concentrations of shallow volcano tectonic earthquakes followed each of the tephra eruptions on december 15 these shocks may represent stress readjustment in the wall rock related to the removal of magma and volatiles at these depths this shallow zone was the source area of the majority of long period seismicity through the remainder of the eruption the long period seismicity likely reflects the pressurization of the shallow portions of the magmatic system

modelling the time dependent frequency content of low frequency volcanic earthquakes abstract low frequency volcanic earthquakes and tremor have been observed on seismic networks at a number of volcanoes including soufriere hills volcano on montserrat single events have well known characteristics including a long duration several seconds and harmonic spectral peaks 0 2 5 hz they are commonly observed in swarms and can be highly repetitive both in waveforms and amplitude spectra as the time delay between them decreases they merge into tremor often preceding critical volcanic events like dome collapses or explosions observed amplitude spectrograms of long period volcanic earthquake swarms may display gliding lines which reflect a time dependence in the frequency content using a magma filled dyke embedded in a solid homogeneous half space as a simplified volcanic structure we employ a 2d finite difference method to compute the propagation of seismic waves in the conduit and its vicinity we successfully replicate the seismic wave field of a single low frequency event as well as the occurrence of events in swarms their highly repetitive characteristics and the time dependence of their spectral content we use our model to demonstrate that there are two modes of conduit resonance leading to two types of interface waves which are recorded at the free surface as surface waves we also demonstrate that reflections from the top and the bottom of a conduit act as secondary sources that are recorded at the surface as repetitive low frequency events with similar waveforms we further expand our modelling to account for gradients in physical properties across the magma solid interface we also expand it to account for time dependence of magma properties which we implement by changing physical properties within the conduit during numerical computation of wave propagation we use our expanded model to investigate the amplitude and time scales required for modelling gliding lines and show that changes in magma properties particularly changes in the bubble nucleation level provide a plausible mechanism for the frequency variation in amplitude spectrograms

modelling low frequency volcanic earthquakes in a viscoelastic medium with topography summary magma properties are fundamental to explain the volcanic eruption style as well as the generation and propagation of seismic waves this study focusses on magma properties and rheology and their impact on low frequency volcanic earthquakes we investigate the effects of anelasticity and topography on the amplitudes and spectra of synthetic low frequency earthquakes using a 2 d finite difference scheme we model the propagation of seismic energy initiated in a fluid filled conduit embedded in a homogeneous viscoelastic medium with topography we model intrinsic attenuation by linear viscoelastic theory and we show that volcanic media can be approximated by a standard linear solid sls for seismic frequencies above 2 hz results demonstrate that attenuation modifies both amplitudes and dispersive characteristics of low frequency earthquakes low frequency volcanic earthquakes are dispersive by nature however if attenuation is introduced their dispersion characteristics will be altered the topography modifies the amplitudes depending on the position of the seismographs at the surface this study shows that we need to take into account attenuation and topography to interpret correctly observed low frequency volcanic earthquakes it also suggests that the rheological properties of magmas may be constrained by the analysis of low frequency seismograms

infrared spectral and carbon isotopic characteristics of micro and macro diamonds from the panda kimberlite central slave craton canada abstract one hundred and twenty one micro diamonds in addition sims carbon isotopic analyses for the micro diamonds were obtained 13c compositions range from 6 9 to 1 8 median 4 3 cl imaging reveals distinct growth layers that in some samples differ by 2 but mostly vary by the bimodal mantle residence temperature distribution may coincide with the transition from highly depleted shallow to more fertile deep lithospheric mantle observed beneath the central slave craton the increase in 13c with decreasing residence temperature proxy for decreasing depth is interpreted to reflect diamond formation from a carbonate bearing metasomatic fluid melt that isotopically evolves as it percolates upward through the lithosphere

the accuracy of estimating q from seismic data a major aim of seismic interpretation is the inference of petrophysical properties of reservoir rocks because the inversion from seismic to petrophysical characteristics is far from unique this task requires a range of seismic parameters prominent among which are seismic velocity impedance and poisson s ratio the inclusion of seismic absorption in this list could add desirable complementary information for example absorption may be more sensitive to clay content than seismic velocity klimento and mccann 1990 however seismic absorption is difficult to measure particularly over depth intervals as short as most reservoir intervals

using microdiamonds in kimberlite diamond grade prediction a case study of the variability in diamond population characteristics across the size range 0 2 to 3 4 mm in misery kimberlite ekati mine nwt canada first predictions of the macrodiamond grade of newly discovered kimberlites are commonly obtained using size frequency distributions of microdiamonds the success of this approach suggests a common origin of microdiamonds and macrodiamonds an implication not yet conclusively established or disproved in contrast to previous comparative studies on microdiamonds and macrodiamonds from single deposits here all diamonds analyzed originate from the same microdiamond samples 558 diamonds ranging from 0 212 to 3 35 mm the diamonds were analyzed for their carbon isotope compositions and nitrogen characteristics and based on this dataset statistical comparisons were conducted across the size range to assess cogenesis as a whole the misery diamond suite shows high nitrogen contents median 850 at ppm a bimodal distribution in time averaged mantle residence temperatures two distinct subpopulations in mantle residence temperatures 1 125 and 1 175 c a high degree of platelet degradation and 13 c compositions that are isotopically slightly heavier median 4 4 than the global median statistical comparisons of the various size classes indicate the presence of subtly different subpopulations at misery however the nature and magnitude of these geochemical differences are very small in the context of the global diamond database and are viewed as petrogenetically insignificant the general geochemical similarity of diamonds from different size fractions at misery reinforces the use of size frequency analysis to predict diamond grade in kimberlite diamond deposits

moment tensor analysis of near field broadband waveforms observed at aso volcano japan abstract locations and focal mechanisms of long period volcanic events observed at aso volcano japan are determined by waveform inversion near field broadband three component seismograms of four to seven stations are simultaneously inverted in the time domain in order to find the six component seismic moment tensor a linear inversion is performed at each point of a 3d grid located under the volcano in order to constrain the centroid position and the focal mechanism of the source the complete displacements including near field waves in a homogeneous half space for a general point source are taken into account inversions of 43 long period tremors and six phreatic eruptions exhibit mainly an isotropic mechanism with a minor deviatoric component that may originate from a north south trending crack these events are all located in a small region at about 1 3 km depth beneath the active crater the high accuracy both of locations a few hundred meters and of focal mechanisms given by the inversion is partly attributed to the rapid variation of the amplitude of the static displacement seen in the long period part of the near field seismograms