the influence of fluid type on elastic wave velocity and attenuation in volcanic rocks abstract volcano seismic signatures are the convolution of source and path effects the source signature provides important information about the dynamic rock deformation and fluid resonance processes within the volcano but path effects are the result of the volcanic plumbing the edifice physical conditions and the complex geological structure complicating the inversion of seismic data further is the influence of fluid properties here we use ultrasonic experiments to understand the effect of variable fluid viscosity and bulk modulus on p wave attenuation and velocity for volcanic rocks from white island volcano whakaari new zealand our experimental conditions for high porosity ash tuff and low porosity lava resemble shallow and deep volcano facies respectively p wave velocity vp and quality factor qp increase with the viscosity and bulk modulus of the saturating fluid and decrease with porosity and fracture volume tuffs are highly sensitive to saturating fluid with variations in vp of up to 67 and qp of 383 vp and qp in fractured lavas are slightly less sensitive to fluids 24 and 296 respectively but vp can be used to identify lithology for these tuff vs lavas comparison of the experimental data with rock physics models suggests that squirt flow is the dominant attenuation mechanism for viscosities greater than that of water while scattering losses may be important in gas saturated rocks our results have significant implications for the interpretation of seismic tomography studies and for volcano hazard monitoring based on the characteristics of detected seismicity

broadband seismic experiment at merapi volcano java indonesia very long period pulses embedded in multiphase earthquakes abstract multiphase mp and low frequency lf earthquakes with spectral peak amplitudes at 3 4 and 1 hz respectively are two common types of shallow volcanic earthquakes previously recognized at merapi volcano their mechanisms are poorly understood but mps have been temporally associated with lava dome growth we conducted a seismic experiment in january february 1998 using four broadband seismographs to investigate the nature of seismic activity associated with dome growth during our experiment merapi experienced mild dome growth with low level seismic activity we compare our data to that recorded on a local short period sp network with the following preliminary results mp and lf events as recorded and classified on the short period network instruments were recognized on the broadband network frequency spectrograms revealed similar patterns in the near summit region at widely separated broadband stations higher frequency spectra than previously recognized were identified for both mp and lf events and were strongly attenuated as a function of radial distance from the source thus the spectral characteristics of these events as recorded on far field stations are not fully indicative of the source processes in particular many events classified as lf type appear to have much high frequency energy near the source this aspect of these so called lf earthquakes and their association with very long period vlp pulses suggests that many events identified in the far field as lf events are in actuality a variety of the mp event and involve similar source processes broadband records indicated that simple large amplitude vlp pulses were embedded in mp and lf wavetrains from event to event these pulses were similar in their waveforms and had periods of 4 s vlp events embedded in lf and mp earthquakes were located using particle motions the epicenters were clustered in a central region of the dome complex and preliminary source depths were within about 100 m of the dome surface suggesting a source region deep within the dome or the uppermost conduit a similar source location was established by study of mp high frequency onsets our broadband data suggests that we have recorded both elastic seismic waves and a simple embedded pulse that is interpreted to represent a surface tilt at the seismometer site the inferred tilt indicates an inflation and subsequent deflation possibly caused by a gas pressure pulse or episodic shallow magma transport with stick slip movement of the conduit wall

origin distribution and alteration of asphalts at chapopote knoll southern gulf of mexico abstract following the discovery of asphalt volcanism in the campeche knolls a research cruise was carried out in 2006 to unravel the nature of the asphalt deposits at chapopote the novel results support the concept that the asphalt deposits at the seafloor in 3000 m of water depth originate from the seepage of heavy petroleum with a density slightly greater than water the released petroleum forms characteristic flow structures at the seafloor with surfaces that are ropy or rough similar to magmatic lava flows the surface structures indicate that the viscosity of the heavy petroleum rapidly increases after extrusion due to loss of volatiles consequently the heavy petroleum forms the observed asphalt deposit and solidifies detailed survey with a remotely operated vehicle revealed that the asphalts are subject to sequential alterations e g volume reduction leading to the formation of visible cracks in the asphalt surface followed by fragmentation of the entire deposit while relatively fresh asphalt samples were gooey and sticky older fragmented pieces were found to be brittle without residual stickiness furthermore there is evidence for petroleum seepage from below the asphalt deposits leading to local up doming and sometimes to whip shaped extrusions extensive mapping by tv guided tools of chapopote asphalt volcano indicates that the main asphalt deposits occur at the south western rim that borders a central crater like depression the most recent asphalt deposit at chapopote is the main asphalt field covering an area of 2000 m2 asphalt volcanism is distinct from oil and gas seepage previously described in the gulf of mexico and elsewhere because it is characterized by episodic intrusions of semi solid hydrocarbons that spread laterally over a substantial area and produce structures with significant vertical relief as chapopote occurs at the crest of a salt structure it is inferred that asphalt volcanism is a secondary result of salt tectonism

geologic framework of upper miocene and pliocene gas plays of the macuspana basin southeastern mexico this integrated study provides a geological and geochemical framework for upper miocene and pliocene siliciclastic gas plays in the macuspana basin structural controls for the plays are deep seated faults that tap mesozoic thermogenic gas sources areas of intense shale diapirism and folding and areas with structural inversion that could enhance trapping and reservoir productivity early neogene thrusting south of the basin triggered evacuation of oligocene shale along northwest dipping listric faults in the eastern and southeastern basin margin these faults are associated with large scale rollover structures and thick 500 m upper miocene shoreface and wave dominated deltaic complexes a second phase of extension in the early pliocene formed a set of broad southeast dipping listric faults in the western basin controlling thick accumulations of stacked pliocene shoreface deposits trap formation and enhancement in the southern basin margin are linked to late miocene to pliocene inversion the primary stratigraphic controls on play occurrence in the upper miocene in the onshore part of the basin are the regional facies distribution of northwest prograding shoreface and wave dominated deltaic systems there was a shift in pliocene sedimentation from the southeast to the west and northwest parts of the basin where thick successions of aggradational shoreface and wave dominated deltaic deposits accumulated in depocenters defined by shale evacuation along growth faults valley fill deposits in both the upper miocene and pliocene resulted from shortlived periods of base level change induced by either uplift on the southern basin margin or eustasy the offshore part of the basin is inferred to consist of deep water turbidite deposits that formed downdip westward of a hypothesized mixed clastic carbonate prograding complex from the yucatan platform three petroleum systems mesozoic paleogene lower neogene and upper miocene pliocene contributed to the hydrocarbon accumulations and hydrocarbon generation and migration in the basin principal upper jurassic lower cretaceous source rocks generated wet thermogenic gases and oil secondary lower tertiary source rocks generated dominantly dry biogenic gases mixtures of the two gas types are common numerous deep seated growth faults and faults serve as pathways for mesozoic sourced hydrocarbons surface seeps and abundant gas shows suggest that hydrocarbons are being generated today

repeated fracture and healing of silicic magma generate flow banding and earthquakes textures in an exceptionally preserved effusive rhyolite conduit at torfajokull iceland indicate that rising magma repeatedly fractured and healed at shallow levels in the conduit rfh process anastomosing tuffisite veins filled by fine grained juvenile clasts were generated by shear fracture of highly viscous magma in the glass transition interval welding of the particulate material during subsequent deformation led to thorough healing of veins allowing repeated fracture of the same body of magma we propose that the rfh process is a rechargeable trigger mechanism for hybrid seismicity and show that the time scale of the process and the fractures formed by it are consistent with the repeat time and magnitude of hybrid earthquakes during silicic eruptions the rfh process may also form the flow banding that is nearly ubiquitous in obsidian

textural heterogeneities in pumices from the climactic eruption of mount pinatubo 15 june 1991 and implications for magma ascent dynamics the climactic event of mount pinatubo represents one of the most thoroughly studied eruptions of the century and has provided important insights into the dynamics of explosive volcanism we have performed detailed textural analyses of the white and gray pumices of the plinian and pyroclastic flow deposits and found that differences in color and clast density reflect different crystal and vesicle amounts and size distributions white pumice has higher vesicularity deformed and highly coalesced vesicles with thin walls euhedral phenocrysts and microlite free groundmass gray pumice shows lower vesicularity wider ranges in vesicle number density limited coalescence vesicles with thick walls that are less deformed phenocrysts and microphenocrysts with abundant solution pitting and groundmass containing ubiquitous microlites and crystal fragments the presence of white and gray pumice varieties and the broad range in vesicularity and vesicle number density that characterizes both of them appear to record the complexities of conduit processes such as magma vesiculation and fragmentation and the development of conduit regions marked by different rheological behaviors in particular the results of this study suggest the likely importance of intense shear and viscous dissipation at the conduit walls a mechanism that may be responsible for the creation and discharge of the gray pumice of this eruption along with the dominant white variety

characterization of the san jacinto fault zone near anza california by fault zone trapped waves we installed three 350 m long seismic arrays each array consisting of 12 three component stations across the coyote creek fault ccf clark valley fault cvf and buck ridge fault brf of the san jacinto fault zone sjfz near anza california to record fault zone trapped waves from microearthquakes we observed trapped waves with relatively large amplitudes and long duration at stations close to the fault traces for earthquakes occurring within the fault zone the coda normalized amplitude spectra of trapped waves showed peaks at 4 7 hz which decreased sharply with the distance from the fault trace observations and three dimensional finite difference simulations of trapped waves revealed low velocity and low q waveguides on these active faults with the width of 75 100 m in which shear velocities are reduced by 25 30 from wall rock velocities and q values are 40 90 at depths between the surface and 18 km the locations of earthquakes for which we observed trapped waves delineate the most seismically active fault strands of the sjfz in a region with complicated slip planes near anza the low velocity waveguides inferred from trapped waves extend 15 to 20 km in the length on these active faults and are segmented by the fault discontinuities the waveguide on the brf dips south westward to connect the waveguide on the cvf which dips northeastward this waveguide extends at the seismogenic depth through anza slip gap to another low velocity waveguide on the casa loma fault clf which has been delineated in our previous study of the sjfz using trapped waves li et al 1997 the waveguide on the ccf in coyote mountain is nearly vertical and disconnected from the clf at the south edge of anza gap we interpret the low velocity waveguides on these active strands to partly result from recent prehistoric significant earthquakes on them and evaluate the future earthquake in the anza region

cold seeps at the salt front in the lower congo basin ii the impact of spatial and temporal evolution of salt tectonics on hydrocarbon seepage abstract this study investigates the distribution and evolution of seafloor seepage in the vicinity of the salt front i e the seaward boundary of salt induced deformation in the lower congo basin lcb seafloor topography backscatter data and tv sled observations indicate active fluid seepage from the seafloor directly at the salt front whereas suspected seepage sites appear to be inactive at a distance of 10 km landward of the deformation front high resolution multichannel seismic data give detailed information on the structural development of the area and its influence on the activity of individual seeps during the geologic evolution of the salt front region the unimpeded migration of gas from fan deposits along sedimentary strata towards the base of the gas hydrate stability zone within topographic ridges associated with relatively young salt tectonic deformation facilitates seafloor seepage at the salt front bright and flat spots within sedimentary successions suggest geological trapping of gas on the flanks of mature salt structures in the eastern part of the study area onlap structures associated with fan deposits which were formed after the onset of salt tectonic deformation represent potential traps for gas which may hinder gas migration towards seafloor seeps faults related to the thrusting of salt bodies seawards also disrupt along strata gas migration pathways additionally the development of an effective gas hydrate seal after the cessation of active salt induced uplift and the near surface location of salt bodies may hamper or prohibit seafloor seepage in areas of advanced salt tectonic deformation this process of seaward shifting active seafloor seepage may propagate as seaward migrating deformation affects congo fan deposits on the abyssal plain these observations of the influence of the geologic evolution of the salt front area on seafloor seepage allows for a characterization of the large variety of hydrocarbon seepage activity throughout this compressional tectonic setting

geometric and seismic interpretation of the perdido fold belt northwestern deep water gulf of mexico we interpret the perdido fold belt to be composed of detachment folds flanked by megascopic scale kink bands the two previous principal fold models for the perdido fold belt incorporated components of large scale faulting an imbricate fault bend fold model and a high angle reverse faulted detachment fold model we interpret the perdido fold belt to be fold dominated the belt consists of detachment folds overlying a ductile decollement layer the detachment fold crests are bounded by kink bands which are narrow zones of angularly folded strata the low reflectivity low signal to noise zones seen in seismic profiles across the perdido fold belt are poorly imaged sections of the folds that result from steeply dipping bedding in the kink bands the substantial width of these low reflectivity zones their subparallel edges in cross section and their orientation at a high angle to layering as well as their organized spacing and conjugate geometry support a kink band interpretation propagating reverse faults are unlikely in the folds because of the absence of backlimbs overlying the locations of hypothetical faults improved seismic imaging efforts have illuminated steeply dipping bedding that is not cut by faulting in many of the low reflectivity zones in the perdido fold belt

field based density measurements as tool to identify preeruption dome structure set up and first results from unzen volcano japan for an improvement in the quality of conduit flow and dome related explosive eruption models knowledge of the preeruption or precollapse density of the rocks involved is necessary as close investigation is impossible during eruption the best substitute comes from quantitative investigation of the eruption deposits the porosity of volcanic rocks is of primary importance for the eruptive behaviour and accordingly a key parameter for realistic models of dome stability and conduit flow fortunately this physical property may be accurately determined via density measurements we developed a robust battery powered device for rapid and reliable density measurements of dry rock samples in the field the density of the samples sealed in plastic bags at 250 mbar is determined using the archimedean principle we have tested the device on the deposits of the 1990 1995 eruption of unzen volcano japan short setup and operation times allow up to 60 measurements per day under fieldwork conditions the rapid accumulation of correspondingly large data sets has allowed us to acquire the first statistically significant data set of clast density distribution in block and ash flow deposits more than 1100 samples with a total weight of 2 2 tons were measured the data set demonstrates that the deposits of the last eruptive episode at unzen display a bimodal density distribution with peaks at 2 0 0 1 and 2 3 0 1 g cm3 corresponding to open porosity values of 20 and 8 vol respectively we use this data set to link the results of laboratory based fragmentation experiments to field studies at recently active lava domes

petrology of the 1991 1995 eruption at unzen effusion pulsation and groundmass crystallization abstract effusive eruption of dacite magma 2 1 108 m3 during 1991 1995 formed a lava dome at the summit of unzen volcano japan the effusion rate was highest at the beginning 4 0 105 m3 day 4 6 m3 s and decreased roughly with time to almost zero before this pattern was repeated with a second pulse of magma supply the whole rock chemistry of lavas shows significant variation attributable to variations in phenocryst abundance the more mafic the more abundant the phenocrysts the pattern of chemical variation with time shows some difference from that of the effusion rate all phenocrysts in dacite plagioclase hornblende biotite quartz and magnetite show evidence of disequilibrium with melt although a glomerophyric aggregation of phenocrysts suggests coexistence with each other phenocrysts are isotopically heterogeneous from species to species the calculated initial melt composition was rhyodacite and was nearly constant throughout the activity in contrast the bulk phenocryst population is andesite a model explaining the textures and the isotopic heterogeneity is the capture of diorite fragments or xenocrysts by parental rhyodacite magma it is suggested that when effusion rate was high less viscous crystal poor magma exited from the reservoir groundmass glass and plagioclase microlite rims show temporal chemical variations correlating with the effusion rate the higher the effusion rate the more evolved the compositions groundmass crystallinity increased with decreasing effusion rate from 33 to 50 textures in dome lavas suggest that groundmass crystallization had been mostly completed when magma reached the conduit top the fe ti oxide temperature 880 780 c was low when the crystallinity was high micropumice erupted before dome growth provided a sample recording magmatic foam in the conduit porosity of dome lavas was lower at lower effusion rates collapse of foam magma and simultaneous escape of volatiles through the conduit top were probably responsible for the accompanying low frequency earthquakes phenocrysts were broken and the breakdown rims on hornblende phenocrysts were torn off during collapse and successive compaction when effusion waned degassing and the resultant crystallization proceeded more completely so that the magma became too viscous to flow in the conduit top and behaved as a plug resulting in a temporary halt of effusion in turn groundmass crystallization in magma below the plug increased excess pressure in the upper parts of conduit due to slow cooling the plug was scavenged when rising excess pressure overcame its effective strength then the second pulse of magma supply began strong endogenous growth and extrusion of a lava spine in the later stage probably occurred for the same reason

pressure and temperature dependence of p and s wave velocities seismic anisotropy and density of sheared rocks from the sierra alpujata massif ronda peridotites southern spain seismic wave velocities and densities and their pressure and temperature dependence of rock samples recovered from surface exposures at the sierra alpujata were determined in order to better understand the petrological controls on velocity and density the rock samples studied are representative of the major lithologies of the ronda ultramafic body and its metamorphic aureole the suite of ultramafic rocks includes dunite harzburgite and lherzolite exhibiting different degrees of deformation and serpentinization the rocks representing the metamorphic aureole comprise coarse grained migmatites to ultramylonitic migmatites gneisses and eclogites the experimental data include measurements of elastic wave velocities vp vs and densities at confining pressures up to 600 mpa and temperatures up 600 c at 600 mpa the determination of the pressure and temperature derivatives of velocities and densities and the determination of velocity anisotropy average p and s wave velocities at 600 mpa for rocks of the ultramafic body vary from 6 47 to 8 22 km s 1 and 3 27 to 4 75 km s 1 respectively mainly due to different degrees of serpentinization maximum vp and vs anisotropy is about 8 0 and 9 5 respectively and is primarily related to the preferred orientation of olivine in rocks of the metamorphic aureole average p velocities are in the range 5 61 7 23 km s 1 and s velocities vary from 3 48 to 4 04 km s 1 p and s velocity anisotropy is highest about 6 4 and 4 6 in sheared rocks mylonites and is mainly due to the preferred orientation of biotite and sillimanite the geophysical significance of the experimental data is briefly discussed

a conceptual model for hydrocarbon accumulation and seepage processes around chapopote asphalt site southern gulf of mexico from high resolution seismic point of view 1 as part of the german r v meteor m67 2 expedition in 2006 to the southern gulf of mexico a set of 2d high resolution seismic profiles was acquired across the chapopote knoll to study seafloor asphalt occurrences on the basis of regional seismostratigraphic studies and dsdp drilling a more highly reflective coarse grained sediment unit of late miocene age is identified as a potential shallow hydrocarbon reservoir although a unit of that age would typically be buried by pliocene and pleistocene sediment cover at chapopote local salt tectonism has highly elevated the structure since the late miocene and the miocene reservoir is locally above present day regional datum the elevation resulted in a thin 100 200 m fine grained sediment cover on the crest of the knoll above the reservoir because oil and gas production can be expected at depth in jurassic cretaceous and tertiary source rocks the presence of high amplitude reflector packages within the reservoir unit is interpreted as an evidence of hydrocarbons this is variously supported by observations of crosscutting reflectors polarity reversal and drops in instantaneous frequency the thin seal above the reservoir unit facilitates leakage of trapped hydrocarbons hydrocarbons apparently invaded into the seal sediments in the wider vicinity around the crest of the knoll even extending beyond the area where seafloor asphalt is known the asphalt site thus may be a currently active spot while the rest of the crest may be temporarily sealed by solid phase hydrocarbons we propose that a shallow large reservoir with deeply sourced relatively heavy petroleum is principally responsible for the formation of asphalts on the seafloor

easternmost mediterranean evidence of the zanclean flooding event and subsequent surface uplift adana basin southern turkey according to the literature the adana basin at the easternmost part of the mediterranean basin in southern turkey records the pliocene stage with shallow marine to fluvial deposits our micropalaeontological analysis of samples from the adana basin reveal late lago mare biofacies with paratethyan ostracod assemblages pertaining to the loxocorniculina djafarovi zone grey clays rich in planktonic foraminifera lie above the lago mare deposits within the grey clays the continuous occurrence of the calcareous nannofossil reticulofenestra zancleana and the base of the reticulofenestra pseudoumbilicus paracme points to an early zanclean age 5 332 5 199 ma both ostracod and benthic foraminifera indicate epibathyal and bathyal environments 87 sr 86 sr measurements on planktonic and benthic foraminifera fall below the mean global ocean value for the early zanclean indicating potentially insufficient mixing of low 87 sr 86 sr mediterranean brackish lago mare water with the global ocean in the earliest pliocene we utilize the ages and palaeodepths of the marine sediments together with their modern elevations to determine uplift rates of the adana basin of 0 06 to 0 13 mm a 1 since 5 2 5 3 ma total uplift of 350 650 m from surface data and 0 02 0 13 mm a 1 since c 1 8 ma total uplift of 30 230 m from subsurface data

three dimensional seismic characterization of a venting site reveals compelling indications of natural hydraulic fracturing based on a three dimensional high resolution seismic survey off vancouver island canada we show that natural hydraulic fracturing is an efficient process to create permeable pathways for focused fluid upflow at submarine venting sites the pockmark structure examined in this study is located on top of an accreted ridge where the low permeability base of the gas hydrate stability field is also elevated and fluid overpressure will be induced tectonically elongated hydraulic fractures reveal decreased reflection amplitudes and are oriented along the maximum principal stress direction perpendicular to nearby fault planes a surface expression is created by fluid and material expulsion forming an irregular noncircular rim along the axis of the upflow zone our findings confirm a relationship between lateral variations in seismic reflectivity and sediment distribution regional tectonics episodic fluid flow and the formation and dissociation of gas hydrate they explain the presence of gas hydrate at the top of the upflow zone which requires transport of large volumes of gas through the gas hydrate stability field since hydraulic fracturing is not restricted to compressional regimes it is a likely explanation for the nature shape and orientation of upflow zones as well as for seismic blanking widely observed at both active and passive continental margins

shallow sediment deformation styles in north western campeche knolls gulf of mexico and their controls on the occurrence of hydrocarbon seepage during german r v meteor m67 2 expedition to campeche knolls southern gulf of mexico a set of 2d high resolution seismic data was acquired to study the near surface sediment structure and its relationship with hydrocarbon seepages in this salt province the comprehensive survey covered 20 individual bathymetric highs or ridges and identified three principle structural types passive type chaopopte type and asymmetric flap type the first type is the result of passive diapirism whereas the latter two were initialized by a regional compressional event in the miocene but are later differently modified by salt tectonism chapopote type structures appear as symmetrical domes with uplifted coarse grained miocene sediments in their cores and rather thin syn kinematic sediments covering the crests asymmetric flap type structures are also first folded as domes or ridges but one flap later subsided together with salt evacuation resulting in single uplifted monoclines with the coarse grained pre kinematic sediments as reservoir units both structural types can focus and accumulate hydrocarbons the geometries of the structures suggest that hydrocarbons are accumulated in the center of the chapopote type structures and in the subsided flaps of the asymmetric flap type structures hydrocarbon leakage from these thinly sealed reservoirs is regarded as the principle mechanism for the seepage in the study area and accordingly the most seepage prone positions are above these reservoirs the seep locations suggested by analysis of sea surface oil slick images of sar satellite data are also examined in this study these independently derived seep locations confirm the seepage prone positions to be above the shallow buried reservoirs this study suggest that the shallow sediment structures control the distribution of the hydrocarbon seeps of the north western campeche knolls although the hydrocarbons are sourced from the greater depth

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

temperature dependence of elastic p and s wave velocities in porous mt unzen dacite laboratory measurements of elastic properties of volcanic rocks are crucial for the modelling of volcano seismic activity compared to the large database reported in the literature for sedimentary igneous and metamorphic rocks the data set for volcanic rocks is limited and mostly restricted to basalts data for more silica rich rocks are sparse in particular velocity data for silica rich volcanic rocks measured at elevated temperature are lacking we measured the elastic p and s wave velocities and the velocity anisotropy of porous dacitic rocks from unzen volcano japan exhibiting an open porosity of 3 3 to 24 3 vol the measurements were done at temperatures of up to 600 c and confining pressures of 100 mpa corresponding to depths of 3000 4000 m samples with even higher porosities failed at the required pressures the measurements were carried out in a cubic multi anvil pressure apparatus using the pulse transmission technique in contrast to low porosity magmatic and metamorphic rocks the seismic velocities of the investigated volcanic rocks increased and the velocity anisotropies decreased with increasing temperature due to further sample compaction there is a close relationship between velocity density and porosity the higher the density and the lower the porosity the higher are the p and s wave velocities these results can contribute to a better understanding of the propagation of seismic energy through the volcanic edifice

volcano tectonic seismicity at unzen volcano japan 1985 1999 abstract the eruption of unzen volcano in southwestern japan began on november 17 1990 and an extrusion of a dacite lava dome lasted from may 20 1991 until early february 1995 the seismic network operated by the shimabara earthquake and volcano observatory of kyushu university sevo located about 4000 volcano tectonic earthquakes during the period from 1985 to 1999 the seismicity was greatest in the period between one year before the eruption and the start of the lava dome extrusion the hypocenters were mostly distributed within a 12 20 km area on the western side of the volcano an inclined seismic aseismic boundary shallows eastward to the summit probably reflecting the thermal structure beneath the volcano within 4 km west from the summit however the seismicity is very low it was suggested that the high temperature ductile and low q bodies exist there we obtained focal mechanism solutions for about 90 earthquakes among them orientations of p axes for the earthquakes occurring on the upper side of the inclined seismic aseismic boundary suggest a pressure source located below this boundary although most of the focal mechanisms have t axes nearly horizontal in the n s direction consistent with the n s extensional tectonic stress several earthquakes whose focal mechanisms are inconsistent with the tectonic stress were observed within a horizontal distance of 5 km from the summit this is because the pressurization of volcanic gas or magma beneath the summit produced a strong local stress in the summit surroundings

influence of maturity on distributions of benzo and dibenzothiophenes in tithonian source rocks and crude oils sonda de campeche mexico abstract the sureste basin is the most prolific oil producing area of mexico extending from the mainland into the sonda de campeche offshore region the tithonian sedimentary sequence is the most important source of hydrocarbons it contains sulphur rich kerogen which progressively cracks to form petroleum beginning at 0 53 rr maturity increases from northeast to southwest across the region sulphur compounds in the tithonian source rocks and in the petroleums they have generated have been studied by gas chromatography alkylbenzothiophenes are present in highest abundance at low maturity whereas the alkyldibenzothiophenes are most abundant at higher stages of maturity the relative abundance of specific c3 benzothiophene isomers are especially sensitive to changes in maturity of sulphur rich type ii organic matter a novel maturity parameter the c3 benzothiophene index c3bti shows a very good correlation to vitrinite reflectance values r2 0 96 n 10 the methyldibenzothiophene ratio mdr also has a wide dynamic range application of c3bti and mdr to the study area strongly supports a model involving localised vertical migration avenues though several possible scenarios may explain the filling history of reservoirs in the southwest part of the sonda de campeche

properties of seismic fault zone waves and their utility for imaging low velocity structures a two dimensional solution for the scalar wave equation in a model of two vertical layers between two quarter spaces is used to study properties of seismic waves in a laterally heterogeneous low velocity structure the waves referred to as seismic fault zone waves include head waves internal fault zone reflections and trapped waves the analysis aims to clarify the dependency of the waves on media velocities media attenuation coefficients layer widths and source receiver geometry additional calculations with extreme low velocity layers provide examples that may be relevant for volcanic and geothermal domains the interference patterns controlling seismic fault zone waves change with the number of internal reflections in the low velocity structure this number increases with propagation distance along the structure decreases with fault zone width and increases for given length scales with the velocity contrast the relative lateral position of the source within the low velocity layer modifies die length scales associated with internal reflections and influences the resulting interference pattern low values of q affect considerably the dominant period and overall duration of the waves thus there are significant tradeoffs between propagation distance along the structure fault zone width velocity contrast source location within the fault zone and q the lateral and depth receiver coordinates determine the particular point where the interference pattern is sampled and observed motion is a strong function of both coordinates the zone connecting sources generating fault zone waves and observation points with appreciable wave amplitude can be over an order of magnitude larger than the fault zone width calculations for cases with layer p wave velocity of 200 m s 1 modeling a vertical dike or crack with fluid and gas show conspicuous persisting oscillations the results resemble aspects of seismic data in volcanic domains if these waves exist in observed records their explicit recognition and modeling will help to separate source and structural effects and aid in the interpretation of volcano seismology signals although the tradeoffs in parameters governing seismic fault zone waves are significant each variable has its own signature and the parameters may be constrained by additional geophysical data simultaneous modeling of many waveforms with an appropriate solution can resolve the various parameters and provide a high resolution structural image

surface expression of eastern mediterranean slab dynamics neogene topographic and structural evolution of the southwest margin of the central anatolian plateau turkey 1 the southwest margin of the central anatolian plateau has experienced multiple phases of topographic growth including the formation of localized highs prior to the late miocene that were later affected by wholesale uplift of the plateau margin our new biostratigraphic data limit the age of uplifted marine sediments at the southwest plateau margin at 1 5 km elevation to 7 17 ma and regional lithostratigraphic correlations imply that the age is 6 7 ma single grain ca tims u pb zircon analyses from a reworked ash within the marine sediments yield dates as young as 10 6 ma indicating a maximum age that is consistent with the biostratigraphy our structural measurements within the uplifted region and fault inversion modeling agree with previous findings in surrounding regions with early contraction followed by strike slip and extensional deformation during uplift focal mechanisms from shallow earthquakes show that the extensional phase has continued to the present broad similarities in the change in the tectonic stress regime after 8 ma and the onset of surface uplift after 7 ma imply that deep seated process es caused post 7 ma uplift the geometry of lithospheric slabs beneath the plateau margin pliocene to recent alkaline volcanism and the uplift pattern with accompanying normal faulting point toward slab tearing and localized heating at the base of the lithosphere as a probable mechanism for post 7 ma uplift of the southwest margin considering previous work in the region there appears to be an important link between slab dynamics and surface uplift throughout the anatolian plateau s southern margin

application of strontium isotopes to late miocene early pliocene stratigraphy measurements of sup 87 sr sup 86 sr ratios of planktonic foraminifers from paleomagnetically dated deep sea drilling project dsdp cores indicate that the sup 87 sr sup 86 sr ratio of seawater increased linearly between 6 and 4 ma with a slope of 87 times 10 sup minus 6 m y this suggets that sup 87 sr sup 86 sr variation in this time interval are useful for estimating ages in marine sequences the theoretical stratigraphic resolution of the technique is 0 23 m y but the practical resolution is estimated to be 0 3 0 5 m y strontium isotope ratios of five samples at the base of the miocene pliocene m p boundary stratotype at capo rossello sicily have a mean sup 87 sr sup 86 sr value of 0 708995 plus minus 0 00002 applying the regression equation derived from our sup 87 sr sup 86 sr vs age data set for deep sea sequences yields an age of 4 94 plus minus 0 50 ma 95 confidence interval for the m p boundary stratotype similar to ages estimated by biostratigraphic and magnetostratigraphic methods correlation of this mean sup 87 sr sup 86 sr ratio to the section at dsdp site 519 suggests that the boundary is coincident with the onset of a major early pliocene transgression as recorded by a decrease in oxygen isotope values for benthic foraminifers this studymore demonstrates the potential application of strontium isotope stratigraphy for correlating and dating problematic sequences such as those deposited in restricted shallow water or high latitude environments less

source and propagation effects on near field co eruptive ground motion at santiaguito volcano guatemala abstract data from a december 2008 january 2009 seismometer deployment show substantial variation in seismic signal characteristics among different sites and eruptive events at santiaguito volcano a station on one of the inactive domes typically records higher amplitudes and a more peaked spectrum than does another station closer to the vent on lower ground amplitude ratios between the stations and spectral peakedness of the station on the dome vary substantially and depend on vertical signal polarity which is controlled by seismic source mechanism finite difference models considering two likely source mechanisms and several hypothetical subsurfaces show that the topography of the free surface and subsurface units can increase or decrease amplitudes by focusing or obstructing body waves a homogeneous velocity structure is shown not to be a close approximation to the actual shallow subsurface while a subsurface including a dipping reflective layer produces results that fit observations better these models also indicate that path effects act more strongly on waves originating from an implosion than from a downward force possibly due to differences in body and surface wave proportions and differing susceptibilities of body and surface waves to these path effects thus recorded data and models both indicate that the level of wave field distortion associated with propagation effects is controlled by the source mechanism

fault zone trapped seismic waves two instances of fault zone trapped seismic waves have been observed at an active normal fault in crystalline rock near oroville in northern california trapped waves were excited with a surface source and recorded at five near fault borehole depths with an oriented three component borehole seismic sonde at parkfield california a borehole seismometer at middle mountain recorded at least two instances of the fundamental and first higher mode seismic waves of the san andreas fault zone at oroville recorded particle motions indicate the presence of both love and rayleigh normal modes the love wave dispersion relation derived for an idealized wave guide with velocity structure determined by body wave travel time inversion yields seismograms of the fundamental mode that are consistent with the observed love wave amplitude and frequency applying a similar velocity model to the parkfield observations we obtain a good fit to the trapped wavefield amplitude frequency dispersion and mode time separation for an asymmetric san andreas fault zone structure a high velocity half space to the southwest a low velocity fault zone a transition zone containing the borehole seismometer and an intermediate velocity half space to the northeast in the parkfield borehole seismic data set the locations depth and offset normal to fault plane of natural seismic events which do or do not excite trapped waves are roughly consistent with our model of the low velocity zone we conclude that it is feasible to obtain near surface borehole records of fault zone trapped waves because trapped modes are excited only by events close to the fault zone proper thereby fixing these events in space relative to the fault a wider investigation of possible trapped mode waveforms recorded by a borehole seismic network could lead to a much refined body wave tomographic velocity model of the fault and to a weighting of events as a function of offset from the fault plane it is an open question whether near surface sensors exist in a stable enough seismic environment to use trapped modes as an earth monitoring device

the source of infrasound associated with long period events at mount st helens 1 during the early stages of the 2004 2008 mount st helens eruption the source process that produced a sustained sequence of repetitive long period lp seismic events also produced impulsive broadband infrasonic signals in the atmosphere to assess whether the signals could be generated simply by seismic acoustic coupling from the shallow lp events we perform finite difference simulation of the seismo acoustic wavefield using a single numerical scheme for the elastic ground and atmosphere the effects of topography velocity structure wind and source configuration are considered the simulations show that a shallow source buried in a homogeneous elastic solid produces a complex wave train in the atmosphere consisting of p sv and rayleigh wave energy converted locally along the propagation path and acoustic energy originating from the source epicenter although the horizontal acoustic velocity of the latter is consistent with our data the modeled amplitude ratios of pressure to vertical seismic velocity are too low in comparison with observations and the characteristic differences in seismic and acoustic waveforms and spectra cannot be reproduced from a common point source the observations therefore require a more complex source process in which the infrasonic signals are a record of only the broadband pressure excitation mechanism of the seismic lp events the observations and numerical results can be explained by a model involving the repeated rapid pressure loss from a hydrothermal crack by venting into a shallow layer of loosely consolidated highly permeable material heating by magmatic activity causes pressure to rise periodically reaching the pressure threshold for rupture of the valve sealing the crack sudden opening of the valve generates the broadband infrasonic signal and simultaneously triggers the collapse of the crack initiating resonance of the remaining fluid subtle waveform and amplitude variability of the infrasonic signals as recorded at an array 13 4 km to the nw of the volcano are attributed primarily to atmospheric boundary layer propagation effects superimposed upon amplitude changes at the source

natural oil slicks in the gulf of mexico visible from space natural oil seepage in the gulf of mexico causes persistent surface slicks that are visible from space in predictable locations a photograph of the sun glint pattern offshore from louisiana taken from the space shuttle atlantis on may 5 1989 shows at least 124 slicks in an area of about 15 000 km2 a thematic mapper tm image collected by the landsat orbiter on july 31 1991 shows at least 66 slicks in a cloud free area of 8200 km2 that overlaps the area of the photograph samples and descriptions made from a surface ship from aircraft and from a submarine confirmed the presence of crude oil in floating slicks the imagery data show surface slicks near eight locations where chemosynthetic communities dependent upon seeping hydrocarbons are known to occur on the seafloor additionally a large surface slick above the location of an active mud volcano was evident in the tm image in one location the combined set of observations confirmed the presence of a flourishing chemosynthetic community active seafloor oil and gas seepage crude oil on the sea surface and slick features that were visible in both images we derived an analytical expression for the formation of floating slicks based on a parameterization of seafloor flow rate downstream movement on the surface half life of floating oil and threshold thickness for detection applying this equation to the lengths of observed slicks suggested that the slicks in the atlantis photograph and in the tm image represent seepage rates of 2 2 30 m3 1000 km 2 d 1 and 1 4 18 m3 1000 km 2 d 1 respectively generalizing to an annual rate suggests that total natural seepage in this region is of the order of at least 20 000 m3 yr 1 120 000 barrels yr 1

eruption dynamics at mount st helens imaged from broadband seismic waveforms interaction of the shallow magmatic and hydrothermal systems 1 the current eruption at mount st helens is characterized by dome building and shallow repetitive long period lp earthquakes waveform cross correlation reveals remarkable similarity for a majority of the earthquakes over periods of several weeks stacked spectra of these events display multiple peaks between 0 5 and 2 hz that are common to most stations lower amplitude very long period vlp events commonly accompany the lp events we model the source mechanisms of lp and vlp events in the 0 5 4 s and 8 40 s bands respectively using data recorded in july 2005 with a 19 station temporary broadband network the source mechanism of the lp events includes 1 a volumetric component modeled as resonance of a gently nnw dipping steam filled crack located directly beneath the actively extruding part of the new dome and within 100 m of the crater floor and 2 a vertical single force attributed to movement of the overlying dome the vlp source which also includes volumetric and single force components is 250 m deeper and nnw of the lp source at the sw edge of the 1980s lava dome the volumetric component points to the compression and expansion of a shallow magma filled sill which is subparallel to the hydrothermal crack imaged at the lp source coupled with a smaller component of expansion and compression of a dike the single force components are due to mass advection in the magma conduit the location geometry and timing of the sources suggest the vlp and lp events are caused by perturbations of a common crack system

the effects of a decompression on seismic parameter profiles in a gas charged magma seismic velocities in a gas charged magma vary with depth and time relationships between pressure density exsolved gas content and seismic velocity are derived and used in conjunction with expressions describing diffusive bubble growth to find a series of velocity profiles which depend on time an equilibrium solution is obtained by considering a column of magma in which the gas distribution corresponds to the magmastatic pressure profile with depth decompression events of various sizes are simulated and the resulting disequilibrium between the gas pressure and magmastatic pressure leads to bubble growth and therefore to a change of seismic velocity and density with time bubble growth stops when the system reaches a new equilibrium the corresponding volume increase is accommodated by accelerating the magma column upwards and an extrusion of lava a timescale for the system to return to equilibrium can be obtained the effect of changes in magma viscosity and bubble number density is examined

climatic significance of holocene beachrock sites along shorelines of the red sea discussion the geologic record of climate change is currently a very active area of research the results of such studies have the potential to greatly improve our understanding of the different factors that influence climate and consequently may help to guide policy initiatives regarding global warming given the importance of such studies it is imperative that they be scientifically rigorous and thorough friedman 2005 falls short on both counts in this article friedman attempted to use the oxygen isotopic composition of a series of 14c dated beachrock samples to infer past changes in temperature on the basis of increasing 18o values for beachrock with decreasing age he concluded that global temperature has decreased dramatically during much of the holocene the conclusions of the study regarding changing temperature are not supported by the data presented alternative hypotheses not considered in the study are far more likely explanations for the observed isotopic trend than decreasing temperature the principal problems with the article are that 1 critical assumptions are unsupported and there is no discussion of alternative hypotheses 2 there is no description of the petrographic characteristics of the samples 3 no information on methodology is included 4 the existing literature on beachrock much directly relevant to the study is completely ignored and 5 the conclusions are contradicted by a large number of paleoclimate studies for the same period these problems are discussed in detail below friedman makes several important assumptions without adequately justifying them the first assumption is that cements in the beachrock precipitated from unaltered seawater he acknowledges that ground water discharge mixing with river water and evaporation effects particularly significant in the gulf of aqaba friedman 1968 can alter the isotopic composition of local seawater but proceeds to assume for the purpose of the subsequent

the use of a shear thinning polymer as a bubbly magma analogue for scaled laboratory experiments abstract analogue materials are commonly used in volcanology to perform scaled laboratory experiments analogue experiments inform on fundamental fluid dynamic structural and mechanical processes that are typically very difficult to observe and quantify directly in the natural volcanic system here we investigate the suitability of an aqueous solution of hydroxyethyl cellulose polymer hec for use as a lava magma analogue with a particular focus on its rheological behaviour we characterize a range of physical properties as functions of the concentration and temperature of the solution density specific heat capacity thermal diffusivity thermal conductivity surface tension as well as rheology hec has a non newtonian shear thinning rheology that depends on the concentration and temperature of the solution we show that the rheology is well described by the cross model which was originally developed for polymer solutions but has also been applied to bubbly magmas using this similarity an approach for scaling analogue experiments that use shear thinning polymers like hec to bubbly magma is presented a detailed workflow and a spreadsheet are provided to allow experimentalists to investigate the effects of non newtonian behaviour in their existing laboratory set ups this contribution will allow for the more complex but often more realistic case of bubble bearing magmas to be rigorously studied in experimental volcanology

p and s wave anisotropy and shear wave splitting at pressure and temperature in possible mantle rocks and their relation to the rock fabric the seismic properties and their directional dependence have been measured in three potentially mantle derived rocks peridotite ivrea zone italy lherzolitic xenolith massif central france serpentinite the experimental data include the measurement of elastic wave velocities and densities at confining pressures up to 600 mpa and temperatures up to 600 c 600 mpa and the determination of velocity anisotropy and shear wave splitting the petrophysical data can be related to mineral composition and to microstructural characteristics of the rocks macroscopic anisotropy of p and s wave velocities is strongly controlled in the peridodites by the olivine and in the serpentinite by the serpentine antigorite lattice preferred orientation lpo respectively shear wave splitting was found to be an important characteristic of the anisotropic rocks the study shows that for the interpretation of shear wave splitting the direction of wave propagation in relation to the lpos of the major minerals and to the symmetry of their lattice fabric is of great importance in the ivrea peridotite exhibiting rhombic symmetry there is practically no shear wave splitting to be observed for s waves propagating parallel to the olivine 100 axes and the maximum shear wave splitting is not coupled with the direction of highest p wave velocity in the transversely isotropic massif central xenolith shear waves do not split when propagating parallel to the olivine 010 maximum coinciding with the direction of the radial symmetry axis of the olivine fabric the experimental data are principally in accordance with velocity calculations based on the measured olivine lpo and the olivine single crystal stiffness coefficients implications for the interpretation of seismic data are discussed

dynamics of explosive volcanism at unzen volcano an experimental contribution knowledge of the dynamics of magma fragmentation is necessary for a better understanding of the explosive behaviour of silicic volcanoes here we have measured the fragmentation speed and the fragmentation threshold of five dacitic samples 6 7 53 5 vol open porosity from unzen volcano kyushu japan the measurements were carried out using a shock tube based fragmentation apparatus modified after alidibirov and dingwell 1996a b the results of the experimental work confirm the dominant influence of porosity on fragmentation dynamics the velocity of the fragmentation front increases and the value of the fragmentation threshold decreases with increasing porosity further we observe that the fragmentation speed is strongly influenced by the initial pressure difference and the texture of the dacite at an initial pressure difference of 30 mpa the fragmentation speed varies from 34 m s for the least porous sample to 100 m s for the most porous sample these results are evaluated by applying them to the 1990 1995 eruptive activity of unzen volcano emplacements of layered lava dome lobes merapi type pyroclastic flows and minor explosive events dominated this eruption the influence of the fragmentation dynamics on dome collapse and vulcanian events is discussed

mechanics of active salt diapirism abstract an active diapir forcefully intrudes its overburden driven by diapir pressure that overcomes the resistance of the overburden strength possible causes for the driving pressure are differential loading of the source layer and a density contrast with the overburden possible resisting forces derive from the mass of the roof block and resistance to the faulting and folding that accommodate the intrusion for a typical density contrast between salt and a sedimentary overburden a simple force balance demonstrates that the diapir height must be more than two thirds to three quarters the thickness of the surrounding overburden to initiate substantial active diapirism narrow diapirs must be even taller physical and numerical modeling show that typical structures of active diapirism are a central crestal graben flanked by relatively unstrained flaps that rotate upward and outward curved reverse faults can separate the flaps from the regional overburden normal faults in the crestal graben propagate downward with new faults created farther outward as the roof arches over the rising diapir thin wide roofs develop multiple grabens separating a relatively flat roof from the rotating flaps in cases leading to emergence the piercing diapir evolves from a pointed crest to a progressively rounded and widening crest as the flaps rotate outward the numerical models show that overburden flexure contributes to early formation of active diapir structures but piercement does not continue to emergence unless the diapir is very wide or tall relative to the overburden thickness active diapirism becomes progressively more difficult for diapir crests ranging from a rectangle a round cornered rectangle a semicircle to a triangle with a pointed crest

three dimensional p and s wave velocity structure below unzen volcano abstract unzen volcano located in southwestern japan erupted on november 17 1990 after 198 years of dormancy and has been ejecting lava since may 20 1991 in this paper we present three dimensional p and s wave velocity variations below unzen volcano using 22 473 p and 14 349 s wave arrival times from 3457 local earthquakes recorded on a local network of twelve seismic stations the model was parameterized by 24 000 approximately 2 0 km cubic blocks targeting a volume of 120 100 20 km a prominent low velocity anomaly greater than 4 slowness perturbation starting from 2 5 to 5 0 km depth beneath the volcano is observed on both the p and s wave inversions below unzen volcano slightly lower amplitude low velocity anomalies are further observed to a depth of 12 5 km for p and 7 5 km for s waves shallow low velocity anomalies are observed below the chijiwa bay area northwest of unzen and deeper anomalies are seen below shimabara bay southwest of shimabara peninsula this nw se trending feature represents an elongated system of dykes which supply the shallow magma reservoirs

marine seepage variability and its impact on evaluating the surface migrated hydrocarbon seep signal abstract detection of chemically identifiable hydrocarbon oil and gas seepage is an important tool in offshore exploration generated and or trapped oil and gas can leak to near surface sediments and ocean in detectable concentrations the seepage surface expression is controlled by hydrocarbon generation regional pressure regimes and migration pathways the migrated hydrocarbon concentration and composition varies due to seepage rates and near surface physical and biological processes that can alter the signal a seepage continuum exists from large volume oil and gas seeps known as macro seepage to lower volume seeps known as micro seepage only detectible with special sampling and analysis understanding the impact of migrated hydrocarbon concentration relative to in situ organic material and locally derived microbial hydrocarbons is critical this paper describes factors that control the near surface geochemical signal as well as the challenges in deciphering the migrated hydrocarbon signature to evaluate subsurface hydrocarbon generation and entrapment

asphalt volcanism and chemosynthetic life in the campeche knolls gulf of mexico in the campeche knolls in the southern gulf of mexico lava like flows of solidified asphalt cover more than 1 square kilometer of the rim of a dissected salt dome at a depth of 3000 meters below sea level chemosynthetic tubeworms and bivalves colonize the sea floor near the asphalt which chilled and contracted after discharge the site also includes oil seeps gas hydrate deposits locally anoxic sediments and slabs of authigenic carbonate asphalt volcanism creates a habitat for chemosynthetic life that may be widespread at great depth in the gulf of mexico

biogeochemical controls on authigenic carbonate formation at the chapopote asphalt volcano bay of campeche abstract the campeche knolls in the bay of campeche southern gulf of mexico were investigated through detailed seafloor mapping rov surveys and sediment and pore water sampling the knolls are elongated submarine hills created by salt tectonics with a positive relief of up to 800 m above the surrounding seafloor several of the knolls are associated with sea surface oil slicks identified from satellite data indicating the presence of hydrocarbon seeps on the seafloor one of the knolls named chapopote was studied in detail during two international research expeditions so174 2 and m67 2 and is characterized by extensive hydrocarbon seepage including large asphalt flows oil and gas seeps and seafloor gas hydrate deposits chemosymbiotic biological communities and authigenic carbonate deposits are associated with the seeps and are the result of both biogeochemical turnover and the interaction between downward diffusing seawater and hydrocarbon rich pore fluids at shallow sediment depth authigenic carbonates are characterized by aragonite exhibit a porous texture and are cemented by a matrix of microsparitic to sparitic aragonite macropores of the carbonates were completely filled with liquid oil carbonate microfabrics include peloidal or clotted fabrics that may indicate the existence of microenvironments resulting from microbial metabolism banded botryoidal aragonite cements line the intra and bioclasts and incompletely fill the pore spaces the stable carbon isotopic composition of authigenic aragonite varies between 28 6 and 17 9 pdb identifying oil oxidation as the primary source of carbon to the dic pool while lipid biomarker data demonstrate the concurrent existence of microbial communities responsible for anaerobic oxidation of methane aom these observations indicate the presence of additional aom independent reactions responsible for carbon sequestration at hydrocarbon seeps and demonstrate the complexity of biogeochemical processes at seep sites in the gulf of mexico basin oxygen isotope data of authigenic aragonite vary from 2 5 to 3 8 pdb indicating carbonate precipitation in slight disequilibrium with the surrounding pore fluids

rabaul volcano papua new guinea seismic tomographic imaging of an active caldera abstract the recently active rabaul volcano on the island of new britain in eastern papua new guinea is associated with a subduction zone located near the triple junction formed by the pacific south bismarck and solomon lithospheric plates analysis of our 1997 seismic tomography survey of the rabaul caldera reveals the p wave velocity structure to a depth of about 12 km using both explosive and earthquake seismic sources the rabaul volcanic complex is formed by a series of caldera collapse structures and a group of basalt andesite volcanic centres with two currently active dacitic intra caldera cones tavurvur and vulcan the 1994 eruption of these intra caldera cones caused major infrastructure damage and required the evacuation of rabaul township ongoing minor activity of tavurvur continues to the present the 1997 three dimensional seismic tomography imaging identifies a 30 35 km 3 low velocity region magma reservoir at 3 6 km depth beneath the central rabaul caldera and gives an insight into the geological features of the caldera plumbing system on scales of a few kilometres the seismic survey highlights the heterogeneity in p wave velocity both laterally and vertically within the rabaul caldera indicating significant complexity within quite a small area the structural complexity is consistent with that observed in outcrop of palaeozoic eroded calderas in other parts of the world the low velocity region at rabaul 6 0 km s rock units around the caldera rims that are interpreted to indicate large volumes of mafic intrusive rock at shallow

experimental volcanology on eruptive products of unzen volcano abstract protracted dome building eruptions may be profitably investigated using laboratory based experiments density distribution studies on the pyroclastic flow deposits of unzen 1990 1995 allow us to apply the results of experimental investigations on unzen samples to the interpretation of the last eruption of unzen here primary laboratory experiments have focused on several aspects of the degassing permeability and the fragmentation behavior threshold speed and efficiency those investigations have been flanked by analyses of flexural strength fracture toughness and seismic velocities to provide new insights into eruption related processes here we present a review of these results and their application to the eruption dynamics of unzen volcano we propose that efforts be made to incorporate routinely such comprehensive experimental analyses into the response to emerging volcanic crises in future

three dimensional structural model of the cantarell and sihil structures campeche bay mexico the cantarell and sihil fields are located in a complex system of compressive structures in the offshore campeche bay province in mexico the geometry of the cantarell sihil structure varies along trend from a simple fault related structure in the south to a duplex consisting of the cantarell and sihil structures in the central part to a more complex system consisting of compressive blocks separated by tertiary normal faults in the north the cantarell sihil structures formed during three main episodes of deformation 1 jurassic to early cretaceous extension resulting in the formation of normal faults that displace tithonian kimmeridgian and lower cretaceous units 2 miocene compression during which the cantarell sihil thrust system was formed and 3 pliocene to holocene extension during which several of the preexisting jurassic normal faults were reactivated the cantarell field produces out of three separate fault bounded allochthonous blocks the akal nohoch and kutz blocks the main field is located in the akal structure secondary fields in the allochthonous block include kutz which formed on the crest of a downthrown fault block and nohoch which formed above a west vergent backthrust the recently discovered sihil field is located in a subthrust compressive structure and consists of two structural lobes formed above the sub sihil fault the chac structure is formed at the updip edge of a tilted fault block in the autochthonous block the detailed three dimensional structural model is being used for future production of the remaining reserves in the cantarell field as well as for the delineation of the sihil field

choking the mediterranean to dehydration the messinian salinity crisis strait uplift due to isostasy played a pivotal role in the development and maintenance of a desiccated mediterranean basin during the late miocene messinian salinity crisis new three dimensional flexure models for the western mediterranean suggest that most of the giant evaporite body was deposited before sea level lowering any mechanism that subsequently caused a mediterranean sea level lowering by a few hundred meters during several thousand years sufficed to cause isostatic uplift and closure of the gateways thus choking the mediterranean to desiccation due to this isostatic feedback multiple desiccation and reflooding phases driven by milankovitch cycles are unlikely when the atlantic connection had been lost and sea level had dropped a sizeable regional uplift of the strait of gibraltar developed that presented a formidable obstacle to reflooding rollback and steepening of the gibraltar slab may have played a key role at the end of the miocene by dynamically lowering the sill region thus reinstating the oceanic connection

seismic stratigraphy of veracruz tongue deep southwestern gulf of mexico the veracruz tongue is a region of continental slope and rise sediments bounded bathymetrically by the mexican ridges fold belt to the west and the campeche knolls salt province to the east study of two multichannel seismic lines and single fold sparker data enables five post early miocene seismic stratigraphic sequences to be distinguished in the tongue sedimentary processes responsible for deposition of each sequence are inferred on the basis of external geometry internal reflection configuration and where possible core data the five sequences are each interpreted to consist of turbidites grading laterally into hemipelagites these primary deposits may be modified later by downslope creep or sliding and slumping because bathymetry is a major control on location of turbidity current flows slides and slumps the depositional history of the veracruz tongue provides indirect evidence of tectonic evolution of the mexican ridges fold belt and the campeche knolls salt province salt domes first formed a barrier to turbidity current flow from the east at the close of the middle miocene the mexican ridges fold belt evolved gradually until it formed a complete barrier to turbidity current flow from the west at the close of the pliocene as a result of shift in direction of turbidity current flow through time potentially sand prone miocene turbidites are overlain by hemipelagic clays and clayey oozes a situation favorable to hydrocarbon entrapment

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

propagation of p and s waves in magmas with different crystal contents insights into the crystallinity of magmatic reservoirs abstract increasing amount of crystals tends to reduce the mobility of magmas and modifies its elastic characteristics e g caricchi l et al 2007 non newtonian rheology of crystal bearing magmas and implications for magma ascent dynamics earth and planetary science letters 264 402 419 bagdassarov n dingwell d b and webb s l 1994 viscoelasticity of crystal and bubble bearing rhyolite melts physics of the earth and planetary interior 83 83 99 to quantify the effect of crystals on the elastic properties of magmas the propagation speed of shear and compressional waves have been measured at pressure and temperatures relevant for natural magmatic reservoirs the measurements have been performed in aggregates at variable particle fractions 0 0 7 the measurements were carried out at 200 mpa confining pressure and temperatures between 300 k and 1273 k i e across the glass transition temperature tg from glass to melt the specimens were mixtures of a haplogranitic melt containing 5 25 wt h2o and variable amounts of sub spherical alumina particles additional experiments were carried out on a sample containing both crystals and air bubbles the temperature derivatives of the shear dvs dt and compressional wave dvp dt velocities for pure glass and samples with a crystal fraction of 0 5 are different below and above the glass transition temperature for a crystal fraction 0 7 only dvp dt changed above the tg in the presence of gas bubbles vp and vs decrease constantly with increasing temperature the bubble bearing material yields a lower bulk modulus relative to its shear modulus the propagation velocities of compressional and shear waves increase non linearly with increasing crystal fraction with a prominent raise in the range 0 5

velocity structure and a seismic model for nevado del ruiz volcano colombia abstract a seismic tomographic study was performed for nevado del ruiz volcano nrv using more than 1500 high quality local and regional three low p wave velocity low v p and low s wave velocity low v s zones were found one low v s zone at depths 2 4 km located beneath the volcano a second low v p and low v s zone at depths 5 10 km located beneath the crater elongated and dipping to the e se and a third low v p and low v s zone at 10 to 12 km farther to the east these three low v p and low v s zones are believed to be the location of heat sources a high velocity zone for both p and s waves was found at shallow depths 0 5 km around the active crater the upper part 0 2 km depth of the high v p and high v s zone was characterized by low v p v s ratios v p v s ratios 1 80 the low v p v s zone is correlated with a steam dominated geothermal system the high v p v s is interpreted as an intrusive body of magmatic origin which includes partial melting zones associated with low v s anomalies a small low v p zone in which long period lp earthquakes were clustered was found to the southwest of the volcano based on the data obtained with the tomography in combination with seismicity geochemistry geology and gravimetry we suggest a model for the seismic activity of nrv volcano tectonic vt earthquakes that occur very often in swarm like patterns located in several clusters around the volcano seem to be due to changes in stress produced by the passing of fluids and or gas through many small cracks a fault and a caldera like structure separate the vt swarms located to the west of the volcano from the source of lp earthquakes

three dimensional modeling of the 1983 1984 eruption at piton de la fournaise volcano reunion island displacement vectors on 125 points over a 6 km 2 area were calculated zlotnicki et al 1990 for piton de la fournaise volcano reunion island from photogrammetric surveys conducted in september 1981 and again in september 1984 an eruptive crisis with two episodes occurred during the 3 years between the surveys we modeled the displacements from the photogrammetric surveys using a three dimensional mixed boundary element method the model shows that both eruptive episodes were fed by a single dike oriented 165 from north as the dike approached the ground surface it divided into segments that rotated into an en echelon pattern the model that best fits all observations suggests that the stress state within the volcano is quasi isotropic such that horizontal stresses equal the overburden these high horizontal stresses are incompatible with an elastic edifice loaded merely by gravitational forces however they may be attributed to the cumulative effect of repeated dike intrusions

relationship between anisotropy of p and s wave velocities and anisotropy of attenuation in serpentinite and amphibolite velocities and q values of p and s waves as functions of pressure and temperature at 100 and 600 mpa are presented for a serpentinite and an amphibolite both rocks exhibit a strong lattice preferred orientation lpo of the major mineral phases antigorite and hornblende respectively velocities and q values increase with pressure the rate of increase is different in the three orthogonal directions normal and parallel to foliation and lineation and closely related to progressive closure of microcracks increasing temperature decreases velocities and q values only slightly as long as thermal cracking is prevented by the applied confining pressure substantial anisotropy of velocities and q in p and s waves is observed in both rocks but is found to be different in origin anisotropy of p and s wave velocities is highest at low pressure and basically caused by constructive interference of effects related to oriented microcracks and to the lpo of major minerals increasing confining pressure decreases velocity anisotropy at a smaller and smaller rate the residual anisotropy of p and s wave velocities shear wave splitting at high confining pressure is mainly a result of preferred mineral orientation by contrast anisotropy of q is very low at low confining pressure and markedly enhanced as pressure is increased at high confining pressure substantial anisotropy of q in p waves is apparent but reversed from that of p wave velocities qp is highest in the direction normal to the foliation plane whereas vp and vs is lowest in this direction the generation of a pronounced anisotropy of qp by increasing pressure is due to a directionally dependent increase of contact areas on the oriented grain boundaries of the platy minerals defining the foliation the increase of q with pressure in the direction normal to foliation is mainly caused by the decrease of energy loss due to compressive strain relative to shear strain the reverse is true for the x and y directions serpentinite and x direction amphibolite parallel to the foliation plane

three dimensional calculations of fault zone guided waves in various irregular structures summary the detailed structure of fault zones fzs plays an important role in problems related to fault mechanics earthquake rupture wave propagation and seismic hazard fzs are thought to consist of an o 10 100 m wide region of decreased seismic velocity but structural details such as their depth extent lateral and vertical variations etc are elusive the small spatial scales involved make such structures difficult to image with ray theoretical methods such as tomography however seismic energy trapped inside fz layers can provide dispersive wave trains that carry information on the fz structure these waves can travel many kilometres inside the fz before reaching the surface and are therefore strongly altered by its properties candidate trapped waves have been observed above several active faults inversion algorithms exist that can model these observations in terms of planar fault zone structures however at present it is not clear how reliable these estimates are as the effects of even small 3 d variations on trapped waves are not well understood the goal of this study is to distinguish 3 d structures that do and do not significantly affect fz waves to achieve this we perform numerical calculations of wave propagation in various fz geometries and analyse the waveforms spectra and envelopes of the synthetic seismograms the main results are that 1 moderate changes of the shape of fz or 2 small scale heterogeneities or 3 depth dependent properties do not strongly affect the observed fz waves in contrast strong effects are to be expected from 4 breaks in the continuity of fz structure e g offsets which may at some point allow imaging of such features at depth

dissolution methods for strontium isotope stratigraphy whole rock analysis the preparation of samples for strontium isotope stratigraphy sis by whole rock dissolution results in contributions of sr from contaminant phases as well as from the target carbonate phase here we highlight and quantify the errors in 87sr 86sr values that might result when calcium carbonate is dissolved using an inappropriate method we report the variation in 87sr 86sr value of sr released from four samples of differing calcite content and degrees of cementation when subject to different methods of dissolution we show that errors of up to 0 000076 in 87sr 86sr which correspond to errors of 3 68 ma in age can be avoided by careful preleaching of the samples

significance of hydrocarbon seepage relative to petroleum generation and entrapment near surface indications of migrating hydrocarbons provide the petroleum systems analyst critical information about source organic matter type maturation organic maturity migration migration pathway delineation and in selected geologic settings specific prospect hydrocarbon charge all petroliferous basins exhibit some type of near surface signal but the hydrocarbon leakage to surface is not always detectable with conventional seep detection methods understanding the petroleum seepage system hence petroleum dynamics of a basin is key to understanding and using near surface geochemical methods for basin assessment and prospect evaluation the relationships between near surface hydrocarbon seepage and subsurface petroleum generation and entrapment are often complex the petroleum seepage system contain four key elements seepage activity qualitative expressions of relative leakage rates active vs passive and episodic vs continuous seepage type concentration of migrated thermogenic hydrocarbon relative to in situ material macro vs micro migration focus major direction of bulk flow leakage relative to the subsurface hydrocarbon generation and or entrapment and near surface seep disturbances near surface processes which can greatly alter or block seepage signals the rate and volume of hydrocarbon seepage to the surface greatly control near surface geological and biological responses and thus are the best method of sampling and analysis to detect hydrocarbon leakage effectively to properly predict subsurface petroleum properties interpretation of near surface geochemical data must recognize many potential problems including recent organic matter input transported hydrocarbons bacterial alteration mixing contamination and fractionation effects surface geochemical data should always be integrated with other geological data calibration datasets to determine the utility of near surface geochemical techniques within particular basinal settings are essential when evaluating prospects for hydrocarbon charge