sedimentary trace element constraints on the role of north atlantic igneous province volcanism in late paleocene early eocene environmental change abstract a growing body of geologic evidence suggests that emplacement of the north atlantic igneous province naip played a major role in global warming during the early paleogene as well as in the transient paleocene eocene thermal maximum petm event a 5 million year record of major and trace element abundances spanning 56 to 51 ma at deep sea drilling project sites 401 and 549 confirms that the majority of naip volcanism occurred as subaerial flows thus the trace element records provide constraints on the nature and scope of the environmental impact of the naip during the late paleocene early eocene interval subaerial volcanism would have injected mantle co2 directly into the atmosphere resulting in a more immediate increase in atmospheric greenhouse gas abundances than co2 input through submarine volcanism the lack of significant hydrothermalism contradicts recently proposed mechanisms for thermally destabilizing methane hydrate reservoirs during the petm any connection between naip volcanism and petm warming had to occur through the atmosphere

inferences on the lithospheric structure of campi flegrei district southern italy from seismic noise cross correlation abstract lithospheric v s models are defined in the campi flegrei district southern italy through the non linear inversion of the group velocity dispersion curves of fundamental mode rayleigh waves extracted from ambient noise cross correlations between two receivers and the regional group and phase velocities of the italian cellular lithospheric model 1 1 cells four paths are investigated of which one ischia mis across two adjoining cells the distribution of v s shows a pyroclastic covering with v s increasing from 0 3 0 7 km s to 2 1 km s it rests on a lava or carbonate basement about 5 6 km thick with v s increasing from 2 1 km s to 3 1 km s at about 2 km of depth and rising to 0 6 km towards the island of procida a metamorphic layer is detected at an average depth of 7 7 km with v s of 3 8 3 9 km s about 5 km thick overlying a low velocity layer v s of 3 5 km s at about 11 12 km of depth the v s model along the ischia mis path as average of the models obtained by combining local and regional dispersion data of the two adjoining cells is well consistent with the other paths the moho discontinuity is retrieved at about 23 km of depth with v s of 4 2 km s

a gravity and magnetic study of the volcanic island of ischia naples italy abstract gravity and magnetic data for the volcanic island of ischia naples italy have been analyzed and interpreted in light of recent geological and volcanological data to define a model of the island s shallow and deep structures from the interpretation of the gravity data it appears that the shallow structures consist of pyroclastic material p 2 0 g cm 3 within these pyroclastics there are domes and lava flows of higher density and eruptive centres filled with lower density material the basement is a horst with the shallowest depth at about 1 0 km south of the centre of the island if we assign a density contrast of 0 5 g cm 3 relative to the above pyroclastics interpretation of magnetic data measured at 725 stations showed that the basement derived from the gravity interpretation is magnetized moreover this basement is less magnetized on the western side of ischia which may be caused by the anomalous thermal state of the area as indicated by surface fumaroles hot springs etc and temperature measurements in deep drillings

assessing the utility of fe al and fe speciation to record water column redox conditions in carbonate rich sediments abstract geochemical proxies based on fe abundance fe al and fe speciation have been widely applied to marine sediments in order to unravel paleo depositional redox conditions though geological time to date however these fe proxies have only been calibrated in relation to modern and ancient fine grained siliciclastic marine sediments this clearly limits their use particularly in relation to carbonate rich sediments and rocks to address this we here explore the applicability of fe based redox proxies in carbonates through three approaches first we have compiled fe al data for modern marine sediments to investigate variability in fe enrichments as a function of carbonate content and depositional setting second we have expanded this approach with a compilation of new and existing fe speciation data for modern and ancient marine sediments deposited under oxic and euxinic anoxic sulfidic water column conditions finally we show new data from paired limestone and dolomite sample sets to demonstrate the potential significance of deep burial dolomitization on the fe speciation redox proxy modern marine sediments deposited under oxic conditions show no relationship between fe al and carbonate content these sediments have an average fe al ratio of 0 55 0 11 with some higher values potentially being attributable to steady state early diagenetic remobilization of fe towards the sediment water interface in contrast significant fe al enrichments occur as a consequence of water column fe mineral formation and deposition either under anoxic conditions or due to input of anoxic hydrothermal fluids into oxic seawater iron speciation data also show no direct correlation with carbonate content and instead three groups can be distinguished based on total fe fe t and organic c contents sediments deposited under oxic water column conditions with fe t 0 5 wt generally plot below the lower fe hr fe t siliciclastic reference threshold 0 38 for distinguishing anoxic environments regardless of carbonate content also consistent with siliciclastic calibrations carbonate rich sediments deposited under anoxic water column conditions tend to have fe hr fe t ratios 0 38 in contrast oxic carbonate rich sediments with low fe t hr fe t ratios suggesting that the use of fe speciation for such samples is not appropriate for evaluating water column redox conditions taken together our data suggest that an fe t content of 0 5 wt rather than carbonate content represents the most suitable basis for identifying whether carbonate rich sediments are appropriate for fe based redox proxy analyses analysis of burial dolostones suggests that the fe speciation proxy may also be compromised by deep burial dolomitization where there has been a source of mobile fe to enrich rocks during recrystallization however pre screening can identify such samples this new assessment expands the utility of fe based redox proxies to also incorporate appropriate carbonate rich rocks provided that care is taken to assess the possible impact of deep burial dolomitization

shear wave velocity and attenuation structure of ischia island using broad band seismic noise records abstract in volcanic areas accurate localization of earthquakes requires detailed velocity and possibly attenuation models taking into account wide lithological variability and high geothermal gradients ischia island campania region italy is a seismically active volcano recently affected by a mw 3 9 event casamicciola august 21 2017 1 km depth due to the lack of a specific velocity model the earthquakes occurred on the island were localized using the one developed for the nearby campi flegrei caldera the aim of this work is the definition of a mean representative 1d shear wave velocity vs and attenuation q model of the shallower crust up to 2 km depth of ischia seismic noise array and spectral ratios techniques were applied to broad band seismic signals recorded by temporary and permanent networks updated after the august 2017 earthquake the values of both shear wave velocity vs and quality factor q are realistic with q values comparable with those obtained for campi flegrei and stromboli volcanic areas by taking into account stratigraphic information from deep wells and ultrasonic measurements of velocity on granite and trachytic lava samples a geological interpretation of the resulting velocity model is provided such a model can have significant implications for understanding the dynamics of a volcano mainly those leading to seismic activity

plume dispersed hydrothermal particles a time series record of settling flux from the endeavour ridge using moored sensors abstract settling particles collected with moored sediment traps near an area of active hydrothermal venting in the northeast pacific ocean provide information about the deep sea distribution of hydrothermal material results of an 8 day near field single trap experiment and a 340 day multi instrument 5 trap deployment two kilometers from the endeavour ridge vent field show variability in the quantity and composition of the plume to sediment particle flux over time with depth and with distance from the vent field hydrothermal elemental fluxes vary by a factor of two among the four sampling intervals of the longer experiment a factor of three variation in fe s among these periods reflects temporal changes in phase composition changes in flux with depth for example a 200 fold increase in cu and zn between above and below plume traps are evidence of hydrothermal input comparison of fluxes determined in the near and far field experiments reveals the spatial influence of vent effluent near field particle flux exceeds that measured two kilometers away by a factor of 10 to 20 and is relatively enriched in fe cu and organic carbon but depleted in mn calculations of the residence time of the plume with respect to settling indicate that more than 90 percent of the particulate material is transported farther than two kilometers from the vent field interpretation of elemental mineralogical and grain size analyses suggest that chemical precipitation kinetics other physical and biological particle forming processes changes in vent output and lateral transport of hydrothermal material by abyssal currents are tenable explanations for our observations our findings suggest that these rate interdependent processes be included in realistic models of hydrothermal particle flux

analysis of seismic driven instability of mt nuovo in the ischia island italy abstract ischia is a volcanic island located at the margin of the gulf of naples in the southeastern tyrrhenian sea italy in this article we investigate the stability of the deep seated block known as mt nuovo in the northwestern flank of the mt epomeo volcano under a combined gravitational and seismic load mt nuovo is bounded by a number of active seismic faults and is placed close to the epicentral area of the 1883 casamicciola earthquake i mcs x m w 5 8 that is the largest shock occurring in the island in historical times we explore the hypothesis that a casamicciola like earthquake might occur with an epicenter in the mt nuovo block area using relationships between maximum seismic intensity and peak ground acceleration found in the literature as well as a new relationship derived specifically for this study we apply the minimum lithostatic deviation method which is a variant of the limit equilibrium method to assess the stability of the block the main finding is that mt nuovo would be mobilized if such an earthquake took place on a fault very close to the block which would give rise to a catastrophic mass failure and to a disastrous tsunami this calls for the need of continuous monitoring of the volcano seismicity and deformation pattern

the ischia volcanic island southern italy inferences from potential field data interpretation abstract in this paper we present a study of the structural setting of the volcanic island of ischia by the analysis and interpretation of high resolution aeromagnetic and self potential data recently acquired over the island the magnetic data allowed us to locate the main anomaly sources and lineaments of the island and its offshore surroundings while the self potential sp data provided information on both the structural pattern of the resurgent caldera and the high temperature fluid circulation an inversion of the acquired magnetic and sp data and a joint modelling of the magnetic data and of a previous gravity data set along a sw ne profile allowed us to build a model of the island the model is characterized by the presence of an igneous very likely trachytic structure whose top is located at 1200 1750 m b s l such a body possibly formed by several neighbouring intrusions has a density contrast with the pyroclastic cover of about 0 4 gr cm 3 and its central western part below mt epomeo seems to be demagnetized the demagnetization should be connected to the high geothermal gradient measured in this portion of the island and may be due to hydro chemical alteration processes and or to the possible presence of partially melted spots within the intrusion our outcome is consistent with the results of previous geophysical geo volcanological and geothermal studies

processes affecting the isotopic composition of dissolved iron in hydrothermal plumes a case study from the vanuatu back arc abstract hydrothermal discharge is one of multiple fe sources contributing to the marine dissolved fe budget but its relative importance remains controversial and largely unconstrained isotopic characterization of fe sources and mass balance calculations are considered as a potential tool to unravel the complex interplay of various fe fluxes but require a more profound knowledge of the processes that fractionate fe isotopes in hydrothermal plumes we present dissolved fe isotope data from two buoyant plumes and profiles traversing the non buoyant plume above the nifonea vent field in the vanuatu back arc our findings support opposing controls from precipitation of fe sulfides and fe oxyhydroxides that either enrich the heavy or the light isotopes within the residual dissolved fe fraction but also suggest significant influence from size partitioning of oxidized fe following precipitation as well as potential effects from organic complexation at low aggregation of precipitated fe oxyhydroxides or stabilization of significant fe iii aq dissolved 56 fe is only marginally affected by fe ii oxidation which strengthens the role of fe sulfide precipitation during early plume rise in determining the isotope signature of hydrothermal fe exported to the open ocean dissolved 56 fe range from 0 73 0 05 to 0 16 0 05 and suggest that sulfide rich basalt hosted hydrothermal systems and slow oxidation kinetics in the pacific favor export of stabilized dissolved fe with heavier 56 fe values than the true vent fluids 56 fe of 0 5

piston core record of late paleogene 31 ma to recent seafloor hydrothermal activity in the southwest pacific basin a large diameter piston core containing 8 35 m of metalliferous sediment has been recovered from a small abyssal valley in the remote southwest pacific basin 31 42 194 s 143 30 331 w 5082 m water depth providing unique insight into hydrothermal activity and eolian sedimentation there since the early oligocene a combination of fish teeth sr isotope stratigraphy and inaa geochemical data reveals an exponentially decreasing hydrothermal flux 31 ma to the present although hydrothermal sedimentation related to seafloor spreading explains this trend a complex history of late eocene early oligocene ridge jumps propagating rifts and plate tectonic reorganization of south pacific seafloor could have also played a role a possible hiatus in deposition as recorded by changes in core composition just below 2 m depth is beyond the resolution of the fish teeth sr isotope dating method employed here however the timing of this interval may be coincident with extinction of the pacific farallon ridge at 20 ma a low flux eolian component accumulating at this site shows an increase relative to the hydrothermal component above 2 m depth consistent with dust generating continental sources far to the west australia new zealand this is the first long term paleoceanographic record obtained from within the south pacific bare zone rea et al 2006 an anomalous region where pacific seafloor has largely escaped sediment accumulation since the late cretaceous

v s profiles from noise cross correlation at local and small scale ambient noise measurements have been performed at local and small scales in the neapolitan and surrounding areas campania southern italy by employing two broad band kinemetrics q330 stations equipped with episensor es t three component accelerometers in both experiments frequency time analysis ftan method has been performed on the vertical and radial components of noise cross correlations to retrieve the rayleigh wave dispersion green s function at local scale over an interstation distance of about 26 km the group velocity dispersion values have been compared with those obtained from ftan analysis on recordings of two earthquakes with similar path at small scale measurements have been carried out over an interstation distance of about 440 m in the public gardens of scampia the northernmost quarter of naples the rayleigh wave group velocity dispersion data obtained from noise cross correlation have been combined with those from active seismic experiment along the same alignment but shorter 120 m offset the non linear inversion of such a dispersion curve has allowed the definition of v s models to depths of 100 m in agreement with nearby stratigraphy moreover a good agreement has resulted for the resonance frequency among the h v ratio the ellipticity of the fundamental mode computed for the chosen v s model and the average two dimensional 2d spectral amplification computed along a cross section representative of the scampia quarter

oceanic ridge crest processes oceanic ridge crest processes constitute a vigorous frontier of multidisciplinary research with global ramifications in the earth atmospheric and biologic sciences this deep ocean frontier is gradually opening in response to investigations which are elucidating the role of these processes in the lithosphere hydrosphere atmosphere and biosphere and the application of advanced instrumental and interpretive techniques which are increasing the quality and quantity of data these techniques include crustal drilling with borehole logging deep sea drilling project reports high resolution bathymetry sea beam etc side scan sonar seamarc i and ii gloria etc imagery with video and photography multichannel seismics determination of water column properties ctd with rosette sampler etc and submersible applications

dissolved and particulate 230 th 232 th in the central equatorial pacific ocean evidence for far field transport of the east pacific rise hydrothermal plume we assess the distribution of 230th and 232th along a latitudinal gradient in the central equatorial pacific ocean 155 w 159 w at two sites 8 n and the equator the dissolved 230th concentration profile at 8 n increases nearly linearly from the surface to 2000 m exhibiting behavior consistent with thermodynamic reversible scavenging however from 2000 m to 3000 m the dissolved 230th concentrations exhibit little change before increasing slightly from 3000 m to the bottom at this site dissolved 230th concentrations range from 1 1 fg kg at 100 m to 55 2 fg kg at 4600 m at the equator dissolved 230th concentrations are slightly lower and range from undetectable at 25 m to 19 1 fg kg at 3038 m the pattern in the dissolved 230th concentration profile at the equator is indistinguishable from that at 8 n the mid depth water deviation from equilibrium reversible scavenging between 2 and 3 km in the 230th profiles lower concentrations than expected at both sites occurs in the interval of the water column that is consistent with an interval that has high concentrations of 3he and dissolved fe at other nearby sites this 3he and fe rich signal has been traced to hydrothermal plumes from the east pacific rise thousands of kilometers away we hypothesize that the lower concentrations of 230th in mid depth waters of the central equatorial pacific are a result of a 5000 km transit of waters that have had their 230th scavenged by fe mn particulates close to the epr oceanic residence times of thorium combined with dissolved 232th concentrations suggest dust fluxes of about 0 5 0 6 gm 2yr 1 to the sea surface these fluxes are in agreement with other empirical studies in the pacific but are higher than those suggested by global atmospheric circulation models

seismic risk mitigation at ischia island naples southern italy an innovative approach to mitigate catastrophic scenarios abstract ischia island in the province of naples is a densely populated volcanic island in which small to moderate magnitude earthquakes occur due to the very shallow depth of such events the maximum acceleration recorded for this earthquake exceeded by more than a factor of two the reference acceleration that should be sustained by edifices according to official hazard maps we propose here a complete procedure to assess and mitigate the risk which can be rapid and economically affordable and at the same time can avoid further grief due to possible occurrence of other destructive earthquakes within a short time interval we describe the most likely building collapse and casualty scenarios in case that low to moderate magnitude earthquakes would occur before the edifices would be appropriately reinforced and secured our scenarios demonstrate the urgent need for securing operations the proposed procedures for assessing seismic hazard and for securing urban areas provide an example that is potentially applicable to the whole italian peninsula they may allow in fact the mitigation of the destructive impact of a large number of earthquakes which in italy are often characterized by low or moderate magnitudes

33 000 yr k ar dating of the volcano tectonic horst of the isle of ischia gulf of naples the gulf of naples corresponds to a tectonic sink connected with recent volcanic activity in the south campanian area phlegrean fields ischia and vesuvius at its extreme northwest the isle of ischia was early recognized as a volcano tectonic horst by rittmann1 previous data2 concluded that its uplift ended around 300 000 yr and that the green tuff formation of which it is predominantly composed had an age of some 700 000 yr but tectonic and morphological studies together with original tephrostratigraphical observations on the slope of the horst led us to do some new k ar datings these revealed that the 780 m uplift of the horst from the sea level is younger than 33 000 yr the green tuff which was considered to be the oldest volcanic unit in the island is now dated at 56 000 yr its eruption following the dismantlement of a first volcanic complex now dated as not older than 130 000 yr

on the post 25 ma geodynamic evolution of the western mediterranean during the neogene and quaternary western mediterranean geodynamics were dominated by the eastward migration of the apenninic arc and associated back arc basins the migration was controlled by retreat of the apenninic slab and was associated with boudinage of the lithosphere in the back arc area palaeo reconstruction of the kinematics of the arc suggests about 775 km of migration from the late oligocene to present along a transect from the gulf of lions to calabria a maximum of 135 km of n s converge occurred between africa and europe during the same time span the western mediterranean was thus mainly shaped by the migration of the slab related to west directed subduction it is hypothesized that minor n s convergence deformed the arc but was not the cause of its formation 1998 elsevier science b v all rights reserved

time dependent effects in elastoviscoplastic models of loaded lithosphere summary we conducted a plane strain finite element analysis of topographic loading on a 40 km thick compositionally homogeneous wet olivine oceanic lithosphere the rheological model was elastoviscoplastic evp and accommodated elastic deformation steady state dislocation creep as well as frictional slip via a drucker prager yield surface from the model results we analyse the development of thrust and normal faulting zones that evolve with the growth of a 150 mpa spatially uniform topographic load as well as the interaction between frictional slip and creep in the normal faulting zone that exists at about 20 km depth beneath the load the spatial extent of this zone is shown to be a function of the load growth rate and during loading the lowest 3 km of this region demonstrates simultaneous pressure sensitive frictional slip and pressure insensitive temperature and strain rate dependent creep this dual mechanism deformation is similar to descriptions of semi brittle deformation because of the combined cataclastic and crystal plastic nature that characterizes semi brittle flow the models also show a feature that we refer to as palaeoslip within the two normal faulting regions in the lithosphere and after the load has reached its maximum part of each region maintains active faulting while nearby the faulting has long since ceased the active faulting is enabled by the migration of stress due to post loading creep in high temperature regions of the plate these three phenomena cannot be realized in elastic plastic or viscoelastic rheologies

a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

seismic characterization of neapolitan soils detailed shear wave velocity profiles versus depth have been obtained in typical lithostratigraphies of napoli ftan and hedgehog methods have been applied to rayleigh surface waves recorded in refraction seismic surveys the comparison with literature measurements shows good agreement with nearby down and cross hole tests

the east pacific rise near 21 n 13 n and 20 s inferences for along strike variability of axial processes of the mid ocean ridge abstract data obtained along various segments of the mid ocean ridge mor are used to construct an idealized model for crustal accretion the model seeks to predict the topographic volcanic tectonic and hydrothermal characteristics of any given spreading segment of the mor as a function of distance away from the bounding transform faults this model is based on a series of detailed mapping efforts carried out on segments of the mor having a broad range of spreading rates between 2 and 16 cm yr this paper includes the results of the french searise program carried out during the summer of 1980 aboard the n o jean charcot and two american cruises conducted in 1981 aboard the r v melville

energetics of a two phase model of lithospheric damage shear localization and plate boundary formation summary the two phase theory for compaction and damage proposed by bercovici et al 2001a j geophys res 106 8887 8906 employs a nonequilibrium relation between interfacial surface energy pressure and viscous deformation thereby providing a model for damage void generation and microcracking and a continuum description of weakening failure and shear localization here we examine further variations of the model which consider 1 how interfacial surface energy when averaged over the mixture appears to be partitioned between phases 2 how variability in deformational work partitioning greatly facilitates localization and 3 how damage and localization are manifested in heat output and bulk energy exchange microphysical considerations of molecular bonding and activation energy suggest that the apparent partitioning of surface energy between phases goes as the viscosity of the phases when such partitioning is used in the two phase theory it captures the melt compaction theory of mckenzie 1984 j petrol 25 713 765 exactly as well as the void damage theory proposed in a companion paper ricard bercovici submitted calculations of 1 d shear localization with this variation of the theory still show at least three possible regimes of damage and localization at low stress is weak localization with diffuse slowly evolving shear bands at higher stress strong localization with narrow rapidly growing bands exists and at yet higher shear stress it is possible for the system to undergo broadly distributed damage and no localization however the intensity of localization is strongly controlled by the variability of the deformational work partitioning with dilation rate represented by the parameter f or 1 extreme localization is allowed with sharp profiles in porosity weak zones nearly discontinuous separation velocities and effectively singular dilation rates finally the bulk heat output is examined for the 1 d system to discern how much deformational work is effectively stored as surface energy in the high stress distributed damage cases heat output is reduced as more interfacial surface energy is created yet in either the weak or strong localizing cases the system always releases surface energy regardless of the presence of damage or not and thus slightly more heat is in fact released than energy is input through external work moreover increased levels of damage represented by the maximum work partitioning f make the localizing system release surface energy faster as damage enhances phase separation and focusing of the porosity field thus yielding more rapid loss of net interfacial surface area however when cases with different levels of damage are compared at similar stages of development say the peak porosity of the localization it is apparent that increased damage causes smaller relative heat release and retards loss of net interfacial surface energy the energetics and energy partitioning of this damage and shear localization model are applied to estimating the energy costs of forming plate boundaries and generating plates from mantle convection

meridional distribution of dissolved manganese in the tropical and equatorial pacific abstract the distribution of dissolved mn dmn was studied in the tropical and equatorial pacific along a meridional transect beginning at station aloha 22 45 n 158 w extending southwards to 7 s along 158 w results show that in the surface ocean 6000 km from the continents which suggests that dmn in the deep open ocean is strongly affected by remineralization the dmn aou linear relationship n 37 r 0 87 that we found in this work is consistent with culture studies and can be applied to mn models to reproduce the observed open ocean mn concentrations in deep waters

the role of slab detachment processes in the opening of the western central mediterranean basins some geological and geophysical evidence abstract a review of the geological and geophysical data from the central and western mediterranean region and the present day upper mantle structure derived from tomographic studies are utilized in order to define the oligocene recent geodynamic evolution for the area in line with previous work we suggest that the miocene quaternary opening of the western and central mediterranean basins is the result of back arc extension due to the roll back toward the southeast of a northwestward subducting african slab in a geodynamic setting pinned between the alpine and betic collisional zones we find however that this general pattern is complicated by four different detachment events which occurred beneath the alps early oligocene the betic chain aquitanian northern africa langhian and the apennines late miocene pliocene we show that each of these events determines a major tectonic reorganization within the european plate

seismology speed and size of the sumatra earthquake we now have a clearer picture of the seismic features of last year s gigantic event our seismological results reveal that indonesia s devastating sumatra andaman earthquake on 26 december 2004 was 2 5 times larger than initial reports suggested second only to the 1960 chilean earthquake in recorded magnitude they indicate that it slowly released its energy by slip along a 1 200 km fault generating a long rupture that contributed to the subsequent tsunami now that the entire rupture zone has slipped the strain accumulated from the subduction of the indian plate beneath the burma microplate has been released and there is no immediate danger of a similar tsunami being generated on this part of the plate boundary although large earthquakes on segments to the south still present a threat

the geochemistry of inorganic germanium in natural waters we present the initial results from a survey of the distribution of dissolved inorganic germanium in rivers in the oceans and in hydrothermal vents and plumes in the ocean germanium cycling mimics that of silica since siliceous organisms incorporate ge as a trace constituent in biogenic opal the vertical and horizontal distributions of ge concentrations in seawater are thus identical to those of silica ge si 0 7 10 6 and reflect uptake into and dissolution from the frustules of siliceous organisms germanium enters the ocean via dissolution of continental and seafloor silicates the naturally weathered flux from continents to oceans carries a dissolved ge si atom ratio in rivers of about 0 7 10 6 which reflects the ratio in average continental granites rivers draining industrial regions with significant coal combustion are contaminated with ge leached from fly ash particles resulting in ge si ratios up to tenfold above the naturally weathered background the flux to the oceans via high temperature alteration of seafloor basalts hot springs produces a ge anomaly in hydrothermal plumes over the east pacific rise crest 20 s combining the observed ge and 3he anomalies in plumes with 3he si observations in hot springs suggests that the ge si hydrothermal flux to the oceans is about 4 10 6 near the ratio for average oceanic basalts 2 6 10 6 vent effluents from the galapagos hot springs measured directly display ge si ratios of 16 10 6 suggesting that the ratio is variable between vent fields metalliferous sediments accumulating on the epr crest 17 s are enriched in germanium suggesting that a fraction of the hydrothermal germanium source on the rise crest is scavenged into these rapidly accumulating iron and manganese hydroxyoxide phases

co diagenesis of iron and phosphorus in hydrothermal sediments from the southern east pacific rise implications for the evaluation of paleoseawater phosphate concentrations abstract we present a detailed study of the co diagenesis of fe and p in hydrothermal plume fallout sediments from 19 s on the southern east pacific rise three distal sediment cores from 340 1130 km from the ridge crest collected during dsdp leg 92 were analysed for solid phase fe and p associations using sequential chemical extraction techniques the sediments at all sites are enriched in hydrothermal fe oxyhydr oxides but during diagenesis a large proportion of the primary ferrihydrite precipitates are transformed to the more stable mineral form of goethite and to a lesser extent to clay minerals resulting in the release to solution of scavenged p however a significant proportion of this p is retained within the sediment by incorporation into secondary goethite by precipitation as authigenic apatite and by readsorption to fe oxyhydr oxides molar p fe ratios for these sediments are significantly lower than those measured in plume particles from more northern localities along the southern east pacific rise and show a distinct downcore decrease to a depth of 12 m molar p fe ratios are then relatively constant to a depth of 35 m the fe and p speciation data indicate that diagenetic modification of the sediments is largely complete by a depth of 2 5 m and thus depth trends in molar p fe ratios can not solely be explained by losses of p from the sediment by diffusion to the overlying water column during early diagenesis instead these sediments are likely recording changes in dissolved p concentrations off the sepr possibly as a result of redistribution of nutrients in response to changes in oceanic circulation over the last 10 million years furthermore the relatively low molar p fe ratios observed throughout these sediments are not necessarily solely due to losses of scavenged p by diffusion to the overlying water column during diagenesis but may also reflect post depositional oxidation of pyrite originating from the volatile rich vents of the southern east pacific rise this study suggests that the molar p fe ratio of oxic fe rich sediments may serve as a proxy of relative changes in paleoseawater phosphate concentrations particularly if fe sulfide minerals are not an important component during transport and deposition

a model for ischia hydrothermal system evidences from the chemistry of thermal groundwaters abstract ischia volcano in central italy has long been known for its copious surface hydrothermal manifestations signs of a pervasive circulation of hot fluids in the subsurface because of the significant chemical heterogeneity of fumarolic gas discharges and hot spring discharges evidences of a complex hydrothermal setting a definite model of fluid circulation at depth is currently unavailable in spite of the several previous efforts here we report on the chemical and isotopic composition of 120 groundwater samples collected during several sampling surveys from 2002 to 2007 the acquired data suggest that the composition of surface manifestations reflect contributions from meteoric water sea water and thermal fluids rising from two distinct hydrothermal reservoir with equilibrium temperatures of respectively 150 c and 270 c and depths of 150 300 m and 300 m but possibly 1000 m we also make use of an isotopic characterization of the dissolved gas phase in thermal waters to demonstrate that the ischia hydrothermal system is currently supplied by a deep rising gas component dgc characterized by co2 97 7 1 2 vol on a water free basis 13cco2 3 51 0 9 and helium isotopic ratio of about 3 5 ra 3he 4he ratio normalized to the air ratio ra likely magmatic in origin an assessment of the thermal budget for ischia hydrothermal system is also presented in the attempt to derive a first estimate of the size and rate of degassing of the magmatic reservoir feeding the gas emissions we calculate that a heat flow of about 153 222 mw presently drives hydrothermal circulation on the island which we suggest is supplied in convective form e g by the ascent of a high t magmatic vapour phase by complete degassing of 2 2 3 3 107 m3 yr 1 of trachytic magma with 2 1 wt dissolved h2o content if extrapolated to entire period of quiescence lasting since the arso eruption in 1302 a d this volume corresponds to 1 6 2 3 1010 m3 of magma degassed in about 700 years of quiescent activity

the interaction between regional and local tectonics during resurgent doming the case of the island of ischia italy abstract the volcanic island of ischia is located on the tyrrhenian margin of central italy characterized by plio quaternary nw se and ne sw trending extensional fractures ischia displays a resurgent dome uplifted by at least 800 m in the last 33 ka remote sensing and field data have been collected to study the structural setting of the island the deformation pattern associated with resurgence and the superimposition of the regional and the resurgence induced stress fields nw se and ne sw extensional fracture systems predominate throughout the island and around the resurgent block suggesting a relationship with the regional extensional structures these systems were formed before resurgence and were partly reactivated during resurgence the reactivation of pre existing regional systems during resurgence confined the extent of the uplifted area n s and e w trending systems have been found exclusively at the borders of the dome and are interpreted as being induced by resurgence the topmost resurgent block shows an octagonal shape in map view and is tilted at an angle of 15 around a ne sw trending horizontal axis the block is partly bordered by high angle inward dipping regional faults more than 90 in volume of the volcanic products coeval with resurgence on ischia have been erupted outside the resurgent block area suggesting that the resurgence process locally replaced volcanic activity in the last 33 ka

iron enrichments in hydrothermal plumes over the east pacific rise abstract manganese iron and helium isotopes have been measured in samples taken near the crest of the east pacific rise at 19 s samples were enriched in mn and in he isotopes as is typical for waters of this area samples were also enriched in fe fe enrichments covary with mn and 3 he enrichments the fe mn ratio at four sites ranged from about 2 to 9 spanning the average value found for metalliferous sediments 3 5

subsidence due to crack closure and depressurization of hydrothermal systems a case study from mt epomeo ischia island italy levelling surveys carried out between 1990 and 2003 on the mt epomeo resurgent block ischia island record negative dislocations on its northern and southern flanks with a maximum subsidence rate of 1 27 cm yr 1 this deformation is not associated with the cooling crystallization or lateral drainage of magma and cannot be explained by a pressure point or prolate ellipsoid source results from dislocation models and the available structural and geochemical information indicate that the subsidence is due to crack closure processes along two main ene wsw and e w preexisting faults which represent the preferred pathway of co2 degassing from the hydrothermal system located beneath mt epomeo the monitoring of the dislocations and co2 flux along these faults could give useful information on the dynamics of the hydrothermal system

thermal structure and seismicity of subducting lithosphere it has recently been suggested that the mechanical behaviour of the oceanic and continental uppermost mantle depends on temperature alone and that there is no strong evidence for compositional effects it seems in the majority of cases that if uppermost mantle temperatures exceed 600 c any deformation that occurs does so in the absence of significant seismicity this observation apparently applies irrespective of whether that mantle material underlies an ocean or a continent this paper investigates whether the same behaviour exists for earthquakes occurring in descending lithospheric slabs namely whether there is some limiting temperature above which deformation occurs without significant seismicity and whether that limiting temperature is consistent with the behaviour seen in the uppermost mantle beneath oceans and continents by re examining the thermal structure in subducting slabs accounting for the temperature dependence of the relevant physical parameters teleseismically recorded seismicity is shown to be limited to material having potential temperatures less than not vert similar570 600 c or homologous temperatures less than not vert similar0 42 the exceptions to this pattern occur in the subhorizontally subducting regions of the nazca plate in which temperatures are probably affected by the relatively cold overriding plate

numerical models of lithospheric deformation forming the southern alps of new zealand compression of the entire continental lithosphere is considered using two dimensional numerical models in order to study the influence of the lithospheric mantle on the geometry of continental collision in its initial stages the models are based on the central section of new zealand southern alps where continental collision has occurred along the alpine fault since about 7 ma they incorporate brittle elastic ductile rheology heat transfer surface processes and fault localisation the models are compared to the surface relief the gps convergence velocity the measured electrical conductivity and the geometry of the crustal root imaged from seismic velocity measurements the crustal deformation is characterized by localized uplift at the plate boundary alpine fault and by two secondary zones of faulting one is located about 60 to 80 km east of the alpine fault at the start of upper crust bending or tilting and the other is located about 100 to 130 km east of the alpine fault as a result from shear strain propagating to the surface through the ductile lower crust the observed asymmetric shape of the crustal root is best reproduced for a mantle lithosphere strength of the order of 200 mpa and an intermediate rate of strain softening a lower strength of the mantle lithosphere can produce symmetric thickening but provides an amplitude of the crustal root too small when compared to observations the observed 20 km offset between the maximum in surface relief and the crustal root was not satisfactorily reproduced this offset is most likely due to the three dimensionality of oblique collision in new zealand southern alps

surface wave tomography of the western united states from ambient seismic noise rayleigh and love wave phase velocity maps summary we present the results of rayleigh wave and love wave phase velocity tomography in the western united states using ambient seismic noise observed at over 250 broad band stations from the earthscope usarray transportable array and regional networks all available threecomponent time series for the 12 month span between 2005 november 1 and 2006 october 31 have been cross correlated to yield estimated empirical rayleigh and love wave green s functions the love wave signals were observed with higher average signal to noise ratio snr than rayleigh wave signals and hence cannot be fully explained by the scattering of rayleigh waves phase velocity dispersion curves for both rayleigh and love waves between 5 and 40 speriod were measured for each interstation path by applying frequency time analysis the average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station triplets we find that empirical green s functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross correlation without explicit knowledge of the source distribution the average traveltime uncertainty is less than 1 s at periods shorter than 24 s we present rayleigh and love wave phase speed maps at periods of 8 12 16 and 20 s the maps show clear correlations with major geological structures and qualitative agreement with previous results based on rayleigh wave group speeds

strain localisation and weakening of the lithosphere during extension we explore the sensitivity of extensional systems to the thermal structure of the lithosphere using numerical simulations that fully couple the energy momentum and continuity equations the rheology of the lithosphere is controlled by weakening processes such as shear heating that localises strain into shear zones and faults numerical models show that during extension of an initially unpatterned lithosphere structures develop spontaneously out of basic thermodynamic energy fluxes and without the imposition of ad hoc rules on strain localisation this contrasts with the classical mohr coulomb theory for brittle localisation which prescribes the angles of faults by a mathematical rule our results show that the mode of extension is sensitive to subtle changes in rheology heat flux and geometry of the system this sensitivity lies at the core of the variety and complexity observed in extensional systems localisation processes make the lithosphere weaker than previously estimated from the brace goetze quasi static approach consequently typical estimates for plate tectonic forces are capable of splitting the lithosphere under extension even without the role of active magmatism

hydrothermal manganese plumes in the mid atlantic ridge rift valley the concentration of dissolved manganese in sea water can be used as a chemical tracer of hydrothermal activity on the underlying sea floor here we present vertical profiles of seawater manganese concentrations above the rift valley of the mid atlantic ridge mar the values obtained indicate the presence of plumes that are presently active generated by hydrothermal vents in the rift valley these plumes are confined to the rift valley and do not spill over into the adjacent deep ocean basins differences between them suggest that there are at least five hydrothermal sources along this 1 700 km long section of mid ocean ridge

the effects of continental margins and water mass circulation on the distribution of dissolved aluminum and manganese in drake passage a total of 232 samples were analyzed for concentrations of dissolved aluminum al and manganese mn in drake passage both al and mn were extremely low similar to 0 3 and 0 1 nm respectively in the surface layer of the middle drake passage most likely due to limited input and biological uptake scavenging elevated al 14 nm and mn 2 nm over the south american continental shelf are related to land run off whereas elevated concentrations 1 nm and 2 nm respectively near the antarctic peninsula are most likely related to sediment re suspension re suspension of sedimentary particles and pore waters influences the distribution of al and mn over the continental slopes on both sides of drake passage the influence of the continental margins and accumulated dust input potentially explains the higher al observed eastward in the atlantic section of the southern ocean in the northern drake passage elevated al similar to 0 8 nm and mn similar to 0 3 nm near the seafloor are most likely the result of bottom sediment re suspension by the relatively strong currents in the deep southern drake passage sediment re suspension associated with the inflow of weddell sea deep water appears to cause elevated al 1 nm and mn similar to 0 4 nm in the deep northern drake passage north atlantic deep water brings in elevated al and southeast pacific deep slope water brings in the signature of pacific hydrothermal vents elevated mn and delta he 3 were correlated in this water layer and are most likely originating from the volcanically active ridges in the pacific ocean

crustal rheology from focal depths in the north china basin abstract in order to investigate earthquakes in the lower crust of north china basin ncb we develop a new method of resolving very accurately the focal depth for local earthquakes in the sedimentary regions by using p and s to p converted wave sp at the sedimentary interface theoretical analysis shows clearly that the travel time difference between the sp and p wave almost linearly correlates with the focal depth this finding provides tight constraints on the depth with this method we obtain well constrained depths of 44 events in the ncb with uncertainties in the depth of about 2 km such a fine resolution can have great potential in asking questions regarding the crustal rheology the depth distribution shows abundance of earthquakes in depth interval of 20 km with some events in the lower crust but also reveals the absence of seismicity deeper than 25 km we find a good fit between the depth frequency distribution in this region and the yield strength envelope yse in the baikal rift systems brs we infer that the seismogenic thickness is 25 km in the ncb and the main deformation mechanism is brittle fracture we further hypothesize that 1 the rheological layering of dominant rheology in the ncb is similar to that of the brs which can be explained with a quartz rheology at 0 10 km depth and a diabase rheology at 10 35 km depth 2 the temperature is moderate in the seismogenic zone of crust we emphasize that many accurately resolved earthquake locations can shed light on the local nature of the crustal rheology and this strategic method can be employed in other sedimentary regions which are seismically active

diagenesis of oxyanions v u re and mo in pore waters and sediments from a continental margin this research tests the hypothesis that trace metals respond to the extent of reducing conditions in a predictable way we describe pore water and sediment measurements of iron fe manganese mn vanadium v uranium u rhenium re and molybdenum mo along a transect off washington state usa sediments become less reducing away from the continent and the stations have a range of oxygen penetration depths depth to unmeasurable o2 concentration varying from a few millimeters to five centi meters when oxygen penetrates 1 cm or less fe is reduced in the pore waters but reoxidized near the sediment water interface preventing a flux of fe 2 to overlying waters whereas mn oxides are reduced and mn 2 diffuses to overlying waters both re and u authigenically accumulate in sediments only at the most reducing location where the oxygen penetrates 0 3 cm below the sediment water interface does the surface 30 cm of sediments become reducing enough to authigenically accumulate mo stations in close proximity to the juan de fuca ridge crest are enriched in mn and fe from hydrothermal plume processes both v and mo clearly associate with mn cycling whereas u may be associating with either mn oxides and or fe oxyhydroxides rhenium is uncomplicated by adsorption to mn oxides and or fe oxyhydroxides and re accumulation in sediments appears to be due solely to the extent of reducing conditions therefore authigenic sediment re enrichment appears to be the best indicator for intermediate reducing conditions where oxygen penetrates less than 1 cm below the sediment water interface when coupled with negligible authigenic mo enrichment copyright 2005 elsevier ltd 1 introduction oceanic and atmospheric carbon cycles are strongly coupled with the ocean reservoir of dissolved inorganic carbon being 60 times larger than that of the atmosphere broecker and peng 1987 models that couple both ocean and atmosphere have been used to investigate why atmospheric carbon dioxide pco2 atm was reduced during the last glacial age and thus may be useful in predicting the environmental impact of future changes in pco2 atm some of these models require a large increase in organic carbon export through the more efficient use of nutrients to predict the lower pco2 atm observed during

earthquake cycle fault zones and seismicity patterns in a rheologically layered lithosphere we study the coupled evolution of earthquakes and faults in a model consisting of a seismogenic upper crust governed by damage rheology over a viscoelastic substrate the damage rheology has two types of functional coefficients 1 a generalized internal friction separating states associated with material degradation and healing and 2 damage rate coefficients for positive degradation and negative healing changes the evolving damage modifies the effective elastic properties of material in the upper crust as a function of the ongoing deformation this simulates the creation and healing of fault systems in the upper seismogenic zone in addition to the vertically averaged thin sheet approximation we introduce a green function for three dimensional elastic half space for the instantaneous component of deformation the formulation accounts in an internally consistent manner for evolving deformation fields evolving fault structures aseismic energy release and spatiotemporal seismicity patterns these developments allow us to simulate long histories of crustal deformation and to study the simultaneous evolution of regional earthquakes and faults for various model realizations to focus on basic features of a large strike slip fault system we first consider a simplified geometry of the seismogenic crust by prescribing initial conditions consisting of a narrow damage zone in an otherwise damage free plate for this configuration the model generates an earthquake cycle with distinct interseismic preseismic coseismic and postseismic periods model evolution during each period is controlled by a subset of physical properties which may be constrained by geophysical geodetic rock mechanics and seismological data in the more generic case with a random initial damage distribution the model generates large crustal faults and subsidiary branches with complex geometries the simulated statistics depend on the space time window of the observational domain the results indicate that long healing timescale h describing systems with relatively long memory leads to the development of geometrically regular fault systems and the characteristic frequency size earthquake distribution conversely short h relatively short memory leads to the development of a network of disordered fault systems and the gutenberg richter earthquake statistics for intermediate values of h the results exhibit alternating overall switching of response from periods of intense seismic activity and the characteristic earthquake distribution to periods of low seismic activity and gutenberg richter statistics

mode of crustal extension determined by rheological layering the results of numerical modelling show that the mechanical stratification of the crust provides the fundamental control on fault spacing and ultimately the mode of extension macroscopic pre existing structures and weaknesses are often thought to govern the behaviour of continental crust under extension and many prior studies have focussed on the effect of heterogeneities in triggering faulting and exhumation of lower crustal material the role played by such features is in fact subordinate to that exerted by the rheological contrast from upper to lower crust in our numerical model the temperature gradient dictates the transition from a strong brittle upper crust to a weaker ductile lower crust we see two distinct extension modes that depend on this vertical rheological contrast the distributed faulting mode and the metamorphic core complex mode the ratio of the integrated strength of the upper to lower crust is an indicator of the resulting mode of extension when this strength ratio is small i e the lower crust is relatively strong the result is distributed densely spaced faulting with limited slip on each fault and no exposure of lower crustal rocks an example could be faulting in the north sea a large strength ratio hence a weak lower crust that flows easily leads to stretching being strongly localised onto relatively few normal fault zones each fault accommodates large displacements eventually dissecting the upper crust and resulting in exhumation of the lower crust this is representative of the metamorphic core complexes of the western u s a and the aegean the actual critical strength ratio for the transition between modes will depend upon secondary factors such as the relative thickness of the lower crust with respect to the upper crust and the degree of fault weakening d 2005 elsevier b v all rights reserved

mineralogy bulk and rare earth element geochemistry of massive sulphide associated hydrothermal sediments of the brunswick horizon bathurst mining camp new brunswick massive sulphides are spatially and temporally associated with iron formation if and other hydrothermal sedimentary rocks in the vicinity of the brunswick no 12 brunswick no 6 and austin brook deposits bathurst mining camp sulphide carbonate oxide and silicate predominant if is present carbonate predominant if is best developed in and around the brunswick no 12 deposit whereas hematite bearing if is absent here but prominent in the austin brook brunswick no 6 area the if is composed dominantly of si co2 fe mn and ca minor constituents include mg p ti al and s statistically significant interelement correlations between eu fe mn pb zn cd au ca sr ba p co2 and s indicate that these elements were precipitated from hydrothermal fluids vented onto the seafloor positive interelement correlations between si ti al mg k zr rare earth elements ree s except eu se v y yb co ni and cr reflect the presence of detrital clastic mafic and aluminosilicate minerals and

dispersal patterns for hydrothermal plumes in the south pacific using manganese as a tracer abstract manganese profiles over the spreading axis of the east pacific rise epr between 22 15 s and 19 25 s disclose a series of plumes which are formed by buoyant emanations of hot hydrothermal vent fluids the plume ceilings or anomaly maxima can occur several hundred meters above the sea floor these plumes are dispersed laterally and are detectable as mid depth manganese anomalies 2000 km from the spreading axis along this section the plumes are dispersed mainly westward but at 30 s the plumes are advected eastward the asymmetrical dispersal pattern inferred from these data is coincident with the asymmetrical distribution of metalliferous sediments about the epr which suggests that plumes generated by high temperature venting play a dominant role in the formation of these sediments

the uppermost crust structure of ischia southern italy from ambient noise rayleigh waves abstract ambient noise measurements were performed at the island of ischia southern italy along alignments of 2 4 7 km by using two three component seismic stations synchronous noise recordings of 2 20 h were cross correlated over 20 30 s windows stacked and iteratively band pass filtered to enhance the dispersive wave trains frequency time analysis was performed on the vertical and radial components of cross correlations and the fundamental mode rayleigh wave group velocity was obtained validation of the dispersion data was possible with those obtained from an earthquake recording along a close path the non linear inversion of average rayleigh wave group velocity dispersion curves along 13 paths receiver inter distances allowed the definition of shear wave velocity models in the uppermost 1 2 km of the crust the correlation of vs profiles vs depth and drilling stratigraphy allowed to attribute vs lower than 1 km s to tuffs and vs of 1 41 km s to very fractured lavas higher vs are found in the central area of the island in correspondence of the resurgent area the top of the trachytic lava basement with vs of 2 2 2 4 km s and density of 2 3 g cm3 is about 0 6 0 7 km deep b s l in the centre of ischia below altered very fractured lava or thermally altered tuff

scaling relations of strike slip earthquakes with different slip rate dependent properties at depth abstract empirical observations suggest that earthquake stress drop is generally constant to investigate the effect of rupture width on earthquake scaling relations we analyze synthetic seismicity produced by a 3d vertical strike slip fault model using two different profiles of frictional slip rate behavior below the seismogenic zone within the rate and state framework a relatively abrupt transition of the a b profile from velocity weakening to strengthening at the base of the seismogenic crust produces increasing slip and stress drop with increasing event size choosing a smoother transition allows large earthquakes to propagate deeper leading to similar slip length scaling but constant stress drop scaling our numerical experiments support the idea that the maintenance of constant stress drop across the entire range of observed earthquake magnitudes may be achieved by allowing coseismic slip to rupture to depths below the seismogenic layer

iron and copper enrichment of suspended particles in dispersed hydrothermal plumes along the mid atlantic ridge particulate fe and cu concentrations are used in conjunction with dissolved mn values to identify hydrothermal venting at several sites along the mid atlantic ridge mar in dispersed hydrothermal plumes as defined by dissolved mn anomalies suspended matter fe and cu values were as high as 15 8 and 1100 g g respectively relative to al at 1 7 suspended matter fe and cu values correlate well with dissolved mn concentrations tracing the intensity of dispersed plumes in contrast with fe and cu particulate mn values in vent plumes were low at 700 1200 g g calculated al fe mn al ratios for mar particles increase with increasing dissolved mn concentrations this ratio is used to estimate the percent hydrothermal component of the suspended matter these sensitive tracers identify a 2 20 hydrothermal contribution to the 10 2 g of total suspended matter 1 found along the rift valley

rapid conversion of elastic energy into plastic shear heating during incipient necking of the lithosphere an important and novel mechanism for ductile failure of the lithosphere is identified here which is intrinsic to the thermal mechanical feedback in a temperature dependent plastic body with coupled elastic fields both a temperature dependent power law visco elasto plastic rheology and a temperature dependent elasto plastic rheology are employed to study in a self consistent fashion the deformation of the lithosphere subject to extension by means of a two dimensional finite element code a structural perturbation initially localizes elasto plastic deformation only in its immediate vicinity however after 800 000 years have elapsed the localized zone of deformation takes off in a crack like fashion and travels to the bottom of the lithosphere in about 50 000 years time when the plate is severed thermal runaway is caused by mechanical heating triggered by the rapid energy transfer of the globally stored elastic energy into localized plastic dissipation in the ductile fault

ambient noise tomography of katla volcano south iceland abstract a shear wave velocity model of subglacial katla volcano southern iceland has been developed using ambient seismic noise tomography based on data from a temporary network operating between may 2011 and august 2013 and permanent stations around the volcano phase velocity dispersion curves were obtained using cross correlations of vertical components of 136 station pairs and non linearly inverted for phase velocity maps between 1 7 and 7 5 s local dispersion curves were inverted for shear velocity variation with depth using a grid search imposing a fixed ice layer at the top the resulting one dimensional 1 d velocity models were combined to obtain a pseudo three dimensional 3 d model with estimated lateral resolution of 8 km and depth resolution varying from close to 1 km near the surface to about 8 km at 10 km depth shear wave velocities are generally higher within the katla central volcano than in its surroundings the most striking feature of the model is a high velocity anomaly beneath the caldera at 6 km depth interpreted to be due to cumulates resulting from differentiation of shallower magma intrusions and remelting of subsiding upper crust no shallow low velocity anomaly is resolved beneath the central caldera but a low velocity region is found at 2 4 km depth beneath the western half of the caldera v p v s ratios estimated from average velocity depth profiles from surface wave data and higher frequency p wave data are anomalously high 1 9 compared to average icelandic crust particularly in the top 2 3 km this is argued not to be an artifact due to lateral refraction or topography instead this anomaly could be explained as an artifact caused by velocity dispersion due to attenuation and a difference in frequency content and possibly to a degree by the compositional difference between the transalkalic fe ti basalts of katla and average tholeiitic icelandic crust

thermomechanical evolution of a thinned continental lithosphere under compression implications for the pyrenees in order to demonstrate the interactions between plate boundary forces and preexisting zones of weakness and how those control the localization of continental deformation inside the lithosphere the thermomechanical evolution of an initially thinned and thermally perturbed continental lithosphere in compression was analyzed within the framework of the pyrenees while a concensus exists as to the shallow structures the extent and geometry of deformation at depth have been the subject of great controversy the thermomechanical implications of recent geological hypotheses on the initial state prior to the compression recently derived from balanced cross section reconstructions are here quantified and compared to the recent ecors deep seismic reflection profile across the pyrenees a thermomechanical model based on finite elastoplastic viscoplastic deformations has therefore been formulated using phenomenological constitutive equations derived from experimental studies the thermally coupled problem is solved by an appropriate vertical two dimensional plane strain finite element approximation in those models most of the shortening is accommodated inside a local zone of intense plastic shearing that creates a sharp wedge shaped root progressively sinking deep into the mantle the main thickening takes place inside the lower crust where it can reach a factor 2 this indentation and crustal imbrication process is controlled by a buckling instability occuring inside the uppermost part of the mantle the evolution of the topography can be related to these phenomena lateral conductive heat transfer overtakes the advective transfer in the vicinity of the inflow of colder crustal material inside a warmer mantle the deformation pattern can be explained by a three layer mechanical lithosphere with a soft ductile internal layer of potential decoupling between two more competent layers characterized by a significant elastic stored energy the overall response of this composite plate is not much influenced by smaller scale variations of crustal rheology but is very much dependent on the contrast in rates of viscous dissipation between the lower crust and the upper mantle and on the possibility of singling out a layer of significant elastic stored energy by the balance between rate of loading and rate of dissipation inside the uppermost mantle predicted deformation pattern is found to agree with the seismic reflection and gravity data even though extrapolation to other rates of shortening must be verified by appropriate numerical modelling these physical mechanisms may be regarded as a paradigm for other crustal imbrication phenomena found in the himalayas tibet or the alps

extracting time domain green s function estimates from ambient seismic noise 1 it has been demonstrated experimentally and theoretically that an estimate of the green s function between two seismic stations can be obtained from the time derivative of the long time average cross correlation of ambient noise between these two stations this tdgf estimate from just the noise field includes all tensor components of the green s function and these green s function estimates can be used to infer earth structure we have computed cross correlations using 1 to 30 continuous days of ambient noise recorded by over 150 broadband seismic stations located in southern california the data processing yielded thousands of cross correlation pairs for receiver separations from 4 500 km which clearly exhibit coherent broadband propagating dispersive wavetrains across frequency band 0 1 2 hz

fumarolic and diffuse soil degassing west of mount epomeo ischia italy abstract fumarolic fluid compositions and diffuse soil emissions of hydrothermal fluids of the donna rachele area 0 86 km 2 western flank of mt epomeo ischia island have been studied in order to develop a conceptual geochemical model of the hydrothermal system the degassing area was mapped and the total release of hydrothermal gas and heat associated with the diffuse emission of hydrothermal fluids was estimated a mesostructural study was carried out in order to investigate the relations between the brittle structures and the main pathways of the uprising vapor the fumarolic compositions are typical of hydrothermal fluids and water 99 represents the major component all gas species in the h 2 o h 2 co ch 4 co 2 h 2 s system are close to equilibrium concentrations at temperatures of 300 c and at redox conditions slightly more oxidizing than expected the compositions of the donna rachele fumarolic gas approach the pure liquid equilibrium composition this indicates a high fraction of separated vapor and suggests the presence of a highly energetic hydrothermal system at depth the pure liquid equilibrium compositions of the donna rachele fumaroles along with the historical records of shallow seismicity the explosion of a well in 1995 the occurrence of intense acoustic phenomena and of shallow wells discharging vapor indicate that the internal pressure of the hydrothermal system is occasionally larger than the hydrostatic pressure to quantify the energy dissipated in the donna rachele area by the emission of fumarolic fluids the hydrothermal diffuse degassing was studied by means of 336 soil co 2 flux measurements the highest co 2 fluxes were measured in hydrothermally altered areas along the faults that border mt epomeo structural data indicate that the vapor rises up along nw se striking normal faults related to gravity induced stresses and affecting highly fractured lavas the older faults which are related to the mt epomeo resurgence act as a permeability barrier and bound the donna rachele diffuse degassing structure the total hydrothermal co 2 output was estimated to be 9 t d 1 assuming that the h 2 o co 2 ratio of the fluids that feed the diffuse degassing is the same as that of fumarolic effluents the calculated heat flux is 40 mw this value which represents an important energy release is only a part of the total thermal energy release of ischia where other fumarolic areas occur the results obtained at ischia indicate the importance of thermal energy released by diffuse degassing structures in the energy balance of quiescent volcanoes values of the thermal energy release from the ischia hydrothermal system are comparable with those estimated on other quiescent volcanoes

continental extension from core complexes to rigid block faulting extension of overthickened continental crust is commonly characterized by an early core complex stage of extension followed by a later stage of crustal scale rigid block faulting these two stages are clearly recognized during the extensional destruction of the alpine orogen in northeast corsica where rigid block faulting overprinting core complex formation eventually led to crustal separation and the formation of a new oceanic backarc basin the ligurian sea here we investigate the geodynamic evolution of continental extension by using a novel fully coupled thermomechanical numerical model of the continental crust we consider that the dynamic evolution is governed by fault weakening which is generated by the evolution of the natural state variables i e pressure deviatoric stress temperature and strain rate and their associated energy fluxes our results show the appearance of a detachment layer that controls the initial separation of the brittle crust on characteristic listric faults and a core complex formation that is exhuming strongly deformed rocks of the detachment zone and relatively undeformed crustal cores this process is followed by a transitional period characterized by an apparent tectonic quiescence in which deformation is not localized and energy stored in the upper crust is transferred downward and causes self organized mobilization of the lower crust eventually the entire crust ruptures on major crosscutting faults shifting the tectonic regime from core complex formation to wholesale rigid block faulting

rare earth element concentrations and nd isotopes in the southeast pacific ocean 1 three vertical profiles of rare earth element concentrations and nd isotopic compositions have been measured in the remote southeast pacific ocean the three stations represent contrasting environments the oligotrophic center of the gyre station gyr the transition zone east of the south tropical front station egy and the peru chile upwelling marked by a pronounced oxygen minimum station upx rare earth concentrations display nutrient like vertical profiles except at upx where surface waters are enriched at this station nd isotopic compositions are clearly more radiogenic than in the open ocean suggesting that boundary exchange process is releasing lithogenic rare earth element from the volcanic andes unexpected radiogenic values end reaching 3 7 are also observed at 2000 m at station gyr in the upper circumpolar deep water that commonly have end values around 6 exchange processes related to hydrothermal activity are suspected to produce this increase in end in the vicinity of the east pacific rise these results provide some guidance for higher resolution studies planned in this region by the international geotraces program

tutorial on seismic interferometry part 1 basic principles and applications seismic interferometry involves the crosscorrelation of responses at different receivers to obtain the green s function between these receivers for the simple situation of an impulsive plane wave propagating along the x axis the crosscorrelation of the responses at two receivers along the x axis gives the green s function of the direct wave between these receivers when the source function of the plane wave is a transientas in exploration seismology or a noise signalas in passive seismology then the crosscorrelation gives the green s function convolved with the autocorrelation of the source function direct wave interferometry also holds for 2d and 3d situations assuming the receivers are surrounded by a uniform distribution of sources in this case the main contributions to the retrieved direct wave between the receivers come from sources in fresnel zones around stationary points the main application of direct wave interferometry is the retrieval of seismic surface wave responses from ambient noise and the subsequent tomographic determination of the surfacewave velocity distribution of the subsurface seismic interferometry is not restricted to retrieving direct waves between receivers in a classic paper claerbout shows that the autocorrelation of the transmission response of a layered medium gives the plane wave reflection response of that medium this is essentially 1d reflected wave interferometry similarly the crosscorrelation of the transmission responses observed at two receivers of an arbitrary inhomogeneous medium gives the 3d reflection response of that medium one of the main applications of reflected wave interferometry is retrieving the seismic reflection response from ambient noise and imaging of the reflectors in the subsurface a common aspect of direct and reflected wave interferometry is that virtual sources are created at positions where there are only receivers without requiring knowledge of the subsurface medium parameters or of the positions of the actual sources

multiscale brittle ductile coupling and genesis of slow earthquakes we present the first attempt to explain slow earthquakes as cascading thermal mechanical instabilities to attain this goal we investigate brittle ductile coupled thermal mechanical simulation on vastly different time scales the largest scale model consists of a cross section of a randomly perturbed elasto visco plastic continental lithosphere on the order of 100 9 100 km scale with no other initial structures the smallest scale model investigates a km scale subsection of the large model and has a local resolution of 40 9 40 m the model is subject to a constant extension velocity applied on either side we assume a free top surface and with a zero tangential stress along the other boundaries extension is driven by velocity boundary conditions of 1 cm a applied on either side of the model this is the simplest boundary condition and makes it an ideal starting point for understanding the behavior of a natural system with multiscale brittle ductile coupling localization feedback is observed as faulting in the brittle upper crust and ductile shearing in an elasto viscoplastic lower crust in this process brittle faulting may rupture at seismogenic rates e g at 10 2 10 3 ms 1 whereas viscous shear zones propagate at much slower rates up to 3 9 10 9 ms 1 this sharp contrast in the strain rates leads to complex short time scale interactions at the brittle ductile transition we exploit the multiscale capabilities from our new simulations for understanding the underlying thermo mechanics spanning vastly different time and length scales

temporal and spatial variability of hydrothermal manganese and iron at cleft segment juan de fuca ridge a unique data set for hydrothermal mn and fe was collected at cleft segment on the juan de fuca ridge between 1983 and 1991 the data set includes observations of focused and diffuse venting fluids and neutrally buoyant plumes formed by chronic and episodic venting manganese heat and iron heat ratios for plumes from the north end of the cleft segment were combined with independently determined estimates of plume heat flux to yield annually averaged chronic venting fluxes for mn of 0 36 0 17 mol s 1 and for fe of 0 61 0 34 mol s 1 over 6 years of plume measurements at north cleft segment observed episodic hydrothermal discharge accounted for 15 of the total vented mn and 35 of vented fe the chronic fluxes for mn and fe at a second venting center located at the south end of the cleft segment were estimated to be approximately equal to the fluxes at north cleft segment chronic plumes at north cleft segment are mixtures of focused and diffuse discharge that contribute heat mn and fe in variable proportions similar examination of south cleft segment data strongly suggests the presence of an as yet unobserved venting source relatively depleted in mn and fe but contributing substantially to the overall heat temporal and spatial variations in the concentrations of mn and fe and in mn heat and fe heat ratios for focused seafloor vents were difficult to resolve within complex chronic plumes manganese heat and iron heat ratios of megaplumes suggest they may have derived from reservoirs of diffuse fluids while smaller event plumes may have formed by different processes and have properties similar to chronic plumes the accurate assessment of segment scale hydrothermal fluxes of mn and fe requires coordinated measurements of representative seafloor sources and the neutrally buoyant plume that integrates all seafloor discharge

subsurface geophysics of the phlegrean fields new insights from downhole measurements 1 the volcanic complex of phlegrean fields located northwest of naples italy has been the site of deep geothermal exploration in the 1980s several wells were drilled by an agip enel joint venture with downhole continuous physical properties acquired in each well the main purpose of this study is to map and describe the spatial variations of the volcanic deposits in terms of their nature thickness and in situ physical properties we apply fuzzy k means classification of the well logging data available in the wells cored in the san vito area fuzzy set theory provides an approach that quantitatively assigns individuals to physically continuous classes the optimal number of classes is found by minimization of three mathematical functions thus reducing subjectivity the resulting classifications are found 1 to reflect the main lithologies in the san vito plain 2 to provide more detail on the geological stratigraphy allowing a more precise volcanic history and 3 to differentiate between transition zones and interbedded well defined deposits in addition to discriminating between lithologies that have different physical properties this study gives information on the degree of homogeneity of each lithologic unit and the range of variation for the measured properties finally using the physical classification of the deposits we are able to propose a detailed two dimensional compressional acoustic velocity structure of the studied area

compositional variability in the ascending fluxes from a hydrothermal plume 1 sequentially sampling sediment traps set with 33 day sampling intervals were deployed with current meters on three moorings in the northeast pacific ocean between july 1994 and may 1995 one mooring was deployed near the main vent field on endeavour ridge on axis site 47 57 0 n 129 05 7 w a second 3 km west of the main vent site west site and the third 43 km northeast of the main vent site east or background site ascending and descending particles were collected near 1600 and 2000 m depth well above and within the top of laterally spreading hydrothermal plumes the elemental composition of particles was used to evaluate their origins biogenic fluxes were indicated by elevated ca or si hydrothermal fluxes by elevated fe mn and cu and lithogenic fluxes by elevated ti we link temporal variability in both the ascending and descending particle composition and flux to variations in lateral transport of hydrothermal constituents and to seasonal drawdown of hydrothermal plume particles by biogenic material from the upper ocean the relatively low hydrothermal fe content of ascending material late in the experiment is thought to be due to uptake by descending biogenic material these results suggest that seasonal productivity and particle export from the ocean surface can modulate the hydrothermal flux of elements to the waters above and to the sediments below

velocity models and site effects at kawah ijen volcano and ijen caldera indonesia determined from ambient noise cross correlations and directional energy density spectral ratios abstract two different ambient seismic noise techniques allow the determination of velocity models at ijen caldera and kawah ijen volcano at ijen caldera two average velocity models are constrained down to a depth of 3 km by inverting the stacked dispersion curve obtained by ambient noise cross correlation in addition four local velocity models were obtained by inverting the horizontal to vertical spectral ratio of the directional energy densities of ambient noise dedhvr i e computed through auto correlation of ambient noise this set of velocity models is then compared to the geology of the caldera and the local discontinuities are evidenced at kawah ijen volcano a map of local dominant frequencies is provided by the dedhvr measurements recorded at 87 sites around kawah ijen volcano the horizontality of the shallow layers and the great outcrop of the crater rim facilitate the interpretation of the dedhvrs furthermore the inversion of several juxtaposed dedhvrs provided a complete 2 d velocity model of the flank of the crater unlike other stratovolcanoes the kawah ijen appears to have a remarkably homogeneous structure the dedhvr technique is used for the first time in a volcanic environment and shows a great potential for an accurate and fast computation of the velocity model on volcanoes

landslides ice quakes earthquakes a thermodynamic approach to surface instabilities the total rate of rock deformation results from competing deformation processes including ductile and brittle mechanisms particular deformation styles arise from the dominance of certain mechanisms over others at different ambient conditions surprisingly rates of deformation in naturally deformed rocks are found to cluster around two extremes representing coseismic slip rates or viscous creep rates classical rock mechanics is traditionally used to interpret these instabilities these approaches consider the principle of conservation of energy we propose to go one step further and introduce a nonlinear far from equilibrium thermodynamic approach in which the central and explicit role of entropy controls instabilities we also show how this quantity might be calculated for complex crustal systems this approach provides strain rate partitioning for natural deformation processes occurring at rates in the order of 10 3 to 10 9 s 1 we discuss these processes using examples of landslides and ice quakes or glacial surges we will then illustrate how the mechanical mechanisms derived from these near surface processes can be applied to deformation near the base of the seismogenic crust especially to the phenomenon of slow earthquakes

radioisotopic studies of submarine hydrothermal vents the importance of mid ocean ridge hydrothermal systems has been recognized for their role in the regulation of ocean and sediment chemistry as well as for providing a chemosynthetic source of carbon which drives a unique population of animals found at hydrothermal vents despite the importance of these systems the rates length and depth scale of submarine hydrothermal processes are not precisely known because they are for the most part inaccessible to observational tools we must therefore rely on indirect methods to quantify these processes one way of investigating the rates or timescales of processes in a hydrothermal or any natural system is through the study and modeling of naturally occurring radioisotopes disequilibria among the naturally occurring radioactive decay series in vent fluids associated mineral deposits and overlying effluent plume have provided geochemical tools to investigate the rates of various processes occurring in submarine hydrothermal systems because the half lives of the radioisotopes vary from days to many years processes which encompass a wide range of spatial and temporal scales can be studied this paper presents a review of methods that estimate the residence time of hydrothermal fluids in the ocean crust establish the geochronology of seafloor sulfide deposits investigate the rates of chemical reactions within hydrothermal effluent plumes and derive the heat and mass flux from seafloor hydrothermal areas

quartz rheology and short time scale crustal instabilities we present numerical results of thermal mechanical feedback in crustal quartz rheology and contrast this behavior to the vastly different character of an olivine mantle in the numerical experiments quartz is found to have a very strong tendency for short time scale instabilities while our numerical experiments show that olivine has a decisive tendency for a stable thermally lubricated slip at the same time olivine can also go through a transitional period of creep bursts which are physically caused by multiple interacting ductile faults at various length and time scales which collocate quickly into a major shear zone since olivine has this strong propensity to self organize in a large apparently stable fault system it lacks the dynamics of interacting ductile faults evident in other minerals quartz behaves totally different and keeps its jerky slip behavior for prolonged deformation an example is shown here in which a 30 50 km piece of a wet quarzitic crust is extended for about 2 ma the associated total displacement field clearly shows the unstable slipping events which have a characteristic time frame of one to several years in contrast olivine is very stable and has a much longer time scale for thermal instability of 100 kyrs

peculiarities of surface wave propagation across central eurasia abstract the recent installation of six broadband digital iris ida seismic stations in the ussr has provided new opportunities for studying surface wave propagation across eurasia group velocities of fundamental rayleigh and love modes between epicenters and these stations were determined for 35 events that occurred since april 1989 to the middle of july 1990 near eurasia differential phase velocities were found for the same arrivals along paths between several pairs of stations group and phase velocities were obtained in the period range from 15 to 300 sec frequency time polarization analysis was used for studying polarization properties of surface waves in some cases significant anomalies in the particle motion for periods up to 100 sec were observed they are attributed to surface wave refraction and scattering due to lateral inhomogeneities at the boundaries and inside the eurasia continent

new insights into late pleistocene explosive volcanic activity and caldera formation on ischia southern italy a new pyroclastic stratigraphy is presented for the island of ischia italy for the period 75 50 ka bp the data indicate that this period bore witness to the largest eruptions recorded on the island and that it was considerably more volcanically active than previously thought numerous vents were probably active during this period the deposits of at least 10 explosive phonolite to basaltic trachyandesite eruptions are described and interpreted they record a diverse range of explosive volcanic activity including voluminous fountain fed ignimbrite eruptions fallout from sustained eruption columns block and ash flows and phreatomagmatic eruptions previously unknown eruptions have been recognised for the first time on the island several of the eruptions produced pyroclastic density currents that covered the whole island as well as the neighbouring island of procida and parts of the mainland the morphology of ischia was significantly different to that seen today with edifices to the south and west and a submerged depression in the centre the largest volcanic event the monte epomeo green tuff megt resulted in caldera collapse across all or part of the island it is shown to comprise at least two thick intracaldera ignimbrite flow units separated by volcaniclastic sediments that were deposited during a pause in the eruption extracaldera deposits of the megt include a pumice fall deposit emplaced during the opening phases of the eruption a widespread lithic lag breccia outcropping across much of ischia and procida and a distal ignimbrite in south west campi flegrei during this period the style and magnitude of volcanism was dictated by the dynamics of a large differentiated magma chamber which was partially destroyed during the megt eruption this contrasts with the small volume holocene and historical effusive and explosive activity on ischia the timing and distribution of which has been controlled by the resurgence of the monte epomeo block the new data contribute to a clearer understanding of the long term volcanic and magmatic evolution of ischia

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

geophysical and petrological modelling of the structure and composition of the crust and upper mantle in complex geodynamic settings the tyrrhenian sea and surroundings abstract information on the physical and chemical properties of the lithosphere asthenosphere system las can be obtained by geophysical investigation and by studies of petrology geochemistry of magmatic rocks and entrained xenoliths integration of petrological and geophysical studies is particularly useful in geodynamically complex areas characterised by abundant and compositionally variable young magmatism such as in the tyrrhenian sea and surroundings a thin crust less than 10 km overlying a soft mantle where partial melting can reach about 10 is observed for magnaghi vavilov and marsili which belong to the central tyrrhenian sea backarc volcanism where subalkaline rocks dominate similar characteristics are seen for the uppermost crust of ischia a crust about 20 km thick is observed for the majority of the continental volcanoes including amiata vulsini roccamonfina phlegraean fields vesuvius vulture stromboli vulcano lipari etna and ustica a thicker crust is present at albani about 25 km and at cimino vico sabatini about 30 km the structure of the upper mantle in contrast shows striking differences among various volcanic provinces volcanoes of the roman region vulsini sabatini alban hills sit over an upper mantle characterised by vs mostly ranging from about 4 2 to 4 4 km s at the alban hills however slightly lower vs values of about 4 1 km s are detected between 60 and 120 km of depth this parallels the similar and rather homogeneous compositional features of the roman volcanoes whereas the lower vs values detected at the alban hills may reflect the occurrence of small amounts of melts within the mantle in agreement with the younger age of this volcano the axial zone of the apennines where ultrapotassic kamafugitic volcanoes are present has a mantle structure with high velocity lid vs 4 5 km s occurring at the base of a 40 km thick crust beneath the campanian volcanoes of vesuvius and phlegraean fields the mantle structure shows a rigid body dipping westward a feature that continues southward up to the eastern aeolian arc in contrast at ischia the upper mantle contains a shallow low velocity layer vs 3 5 4 0 km s just beneath a thin but complex crust the western aeolian arc and ustica sit over an upper mantle with vs 4 2 4 4 km s although a rigid layer vs 4 55 km s from about 80 to 150 km occurs beneath the western aeolian arc in sardinia no significant differences in the las structure are detected from north to south the petrological geochemical signatures of italian volcanoes show strong variations that allow us to distinguish several magmatic provinces these often coincide with mantle sectors identified by vs tomography for instance the roman volcanoes show remarkable similar petrological and geochemical characteristics mirroring similar structure of the las the structure and geochemical isotopic composition of the upper mantle change significantly when we move to the stromboli campanian volcanoes the geochemical signatures of ischia and procida volcanoes are similar to other campanian centres but sr pb isotopic ratios are lower marking a transition to the backarc mantle of the central tyrrhenian sea the structural variations from stromboli to the central vulcano and lipari and western aeolian arc are accompanied by strong variations of geochemical signatures such as a decrease of sr isotope ratios and an increase of nd pb isotope and lile hfse ratios the dominance of mafic subalkaline magmatism in the tyrrhenian sea basin denotes large degrees of partial melting well in agreement with the soft characteristics of the uppermost mantle in this area in contrast striking isotopic differences of plio quaternary volcanic rocks from southern to northern sardinia does not find a match in the las geophysical characteristics the combination of petrological and geophysical constraints allows us to propose a 3d schematic geodynamic model of the tyrrhenian basin and bordering volcanic areas including the subduction of the ionian adria lithosphere in the southern tyrrhenian sea and to place constraints on the geodynamic evolution of the whole region

thermal mechanical effects of low temperature plasticity the peierls mechanism on the deformation of a viscoelastic shear zone we studied for the first time the effects of low temperature plasticity on the formation of shear zones a thermal mechanical model has been developed for describing the shear deformation of maxwell viscoelastic material with a rheology close to dry olivine we employed a one dimensional model with a half width of l deforming under a constant velocity u at the boundary and the spatially averaged strain rate u l was set to o 10 14 s 1 in addition to diffusion and power law creep we included deformation by low temperature plasticity called the peierls mechanism which is significant at low temperatures and has a strong exponential dependence on the stress when a sufficient magnitude of heat is generated by the rapid conversion from elastically stored energy into viscous dissipation thermal instability takes place and the deformation localizes in a narrow region by comparing the condition for thermal instability we found that the low temperature plasticity inhibits the development of thermal instability in shear zones in case of constant strain rate the peierls mechanism enhances deformation at a significantly lower stress compared to the rheology with solely diffusion creep and power law creep the enhanced deformation by low temperature plasticity produces lower amount of dissipative heating and thus stabilizes the shear zone comparing the stability between constant strain rate and constant stress boundary conditions we found that the peierls mechanism exerts an opposite destabilizing effect in the case of constant stress for dry olivine rheology and realistic magnitude of the strain rate the effect of low temperature plasticity is significant for temperatures between around 800 k and 1000 k this finding suggests that the low temperature plasticity may be crucial in determining the thermal mechanical stability in the shallow portion of slabs

s waves profiles from noise cross correlation at small scale abstract cross correlations of ambient seismic noise recordings are studied to infer shear wave velocities vs profiles versus depth experiments are performed over inter station distances ranging from 60 m to about 400 m in the crowded and noisy historical centre of napoli where the conditions for the use of active controlled source seismic spreadings are prohibitive even for just one receiver from the noise cross correlation group velocity dispersion curves are extracted with ftan method and their non linear inversion supplies vs profiles versus depth the information of nearby stratigraphies and the range of vs variability for samples of neapolitan soils and rocks confirms the validity and reliability of the results obtained with our expeditious procedure if successfully tested in other geological settings the proposed approach is a low cost methodology to get reliable vs velocity profiles versus depth

hydrothermal methane and manganese variation in the plume over the superfast spreading southern east pacific rise abstract onboard analyses of dissolved ch4 and mn were conducted on the water column along the southern east pacific rise between 13 50 and 18 40 s during the 1993 ridge flux cruise many hydrothermal plumes were identified by chemical anomalies which overlie more than half of the surveyed ridge crest the ch 4 mn ratio in the plumes shows wide variability ranges from about 0 05 to 3 9 due to wide range of ch 4 concentration the ch 4 rich plumes were detected in the region of 16 00 18 40 s where vigorous magmatic budget was confirmed by previous studies moreover the ch 4 mn ratio of the plumes is highly correlated with other volatile metal parameters such as the s fe ratio in plume particulate these results strongly suggest that volatile input caused by magmatic perturbation to hydrothermal systems is responsible for the ch 4 mn variability in the southern epr plumes based on analogy of the case at the epr 9 50 n site the detection of several volatile rich plumes and the extensive hydrothermal flux of volatile species are attributed to frequent magmatic events in the superfast spreading southern epr

dehydration induced porosity waves and episodic tremor and slip episodic tremor and slip ets along the subduction interface takes place where there is abundant evidence for elevated near lithostatic pore pressures at sufficiently great depths 30 45 km that chemical dehydration reactions must act as their dominant source we simulate fluid and heat flow while tracking the location of a vertically oriented one dimensional column of material as it subducts through the slow slip and tremor zone the material in the column is transformed through a pressure dependent and temperature dependent dehydration reaction that we describe with a generalized nonlinear kinetic rate law column deformation is largely dominated by viscous creep with a closure rate that depends linearly on porosity this behavior causes the dehydration reaction to generate traveling porosity waves that transport increased fluid pressures within the slow slip region to explore the possibility that the observed periodicity of slow slip and tremor in subduction zones can be explained by the migration of such porosity waves we derive a dispersion relation that accurately describes our numerical results we also obtain an expression for how the thickness of the dehydrating layer is expected to vary as a function of the parameters in the reaction rate law although the amplitudes of pore pressure perturbations rival those that are produced by known external forcings e g tides or passing surface waves our analysis suggests that given reasonable estimates of rock viscosity permeabilities in the range 6 5 10 15 to 5 10 10 m2 are required for porosity wave trains to form at periods comparable to those of slow slip and tremor

how ductile are ductile shear zones three premises of ductile deformation in the middle and lower crust are widely accepted 1 rocks flow with power law viscous rheology 2 localization in ductile shear zones involves strain softening and 3 fluid flows into and is channelized within ductile shear zones ductile viscous shear zones should therefore initially develop along planes of maximum shear stress strain soften and rotate as material planes into the field of progressive extension however the mean stress or pressure within a weak elongate viscous band being stretched is higher than the surrounding matrix and this is difficult to reconcile with premise 3 in contrast mohr coulomb brittle faults always have lower pressure within the fault zone flow of fluid and melt into high temperature shear zones therefore implies that ductile shear zones are not perfectly viscous but have a pressure dependent viscoplastic rheology the continued pressure dependence may reflect significant microcracking on the grain scale even when localized deformation does not produce larger scale discrete fractures

laboratory measurements of ultrasonic wave velocities in rocks from the campi flegrei volcanic system and their relation to other field data the campi flegrei caldera located near the city of naples italy has shown signs of unrest characterized by large ground deformation seismic activity and changes in the hydrothermal system since 1970 any attempt to model the processes giving rise to these phenomena requires some knowledge of the subsurface structure and of the physical properties of the rocks at depth in this study we report the results of laboratory measurements of ultrasonic compressional and shear wave velocities in rock samples cored in 4 different geothermal wells reaching a maximun depth of 3 km the wells are located in the san vito sv and mofete mf areas at about 3 km north and 4 km west respectively from the center of the caldera we selected 10 core samples 7 from the sv wells and 3 from the mf wells the attention being focused on the most important rock formations underneath campi flegrei and on the lower sections of the wells where data had been lacking the measurements involved the transmission of ultrasonic waves along three orthogonal directions through dry and water saturated rocks at room conditions the samples are only moderately anisotropic 13 for one sv sample and 8 for all the other samples wave velocities generally increase with the depth of the sample the range of velocities is 3 5 4 km s 1 for p waves and 1 5 2 9 km s 1 for s waves for the sv samples water saturation generally implies slightly larger 10 vp values and smaller 20 vs values as compared with dry velocities for the mf samples water saturation implies both higher vp and vs velocities up to 35 and 18 respectively these results may be explained by the different type of porosity of the sv samples vesicular and the mf samples fissurai the ultrasonic measurements on water saturated samples are slightly higher than the available in situ vp sonic measurements 25 for one sv sample and 15 for all the other samples these differences can be explained by velocity dispersion between ultrasonic and sonic frequencies and by the different pressure temperature conditions existing at depth

modeling shear zones in geological and planetary sciences solid and fluid thermal mechanical approaches abstract shear zones are the most ubiquitous features observed in planetary surfaces they appear as a jagged network of faults at the observable brittle surface of planets and in geological exposures of deeper rocks they turn into smoothly braided networks of localized shear displacement leaving centimeter wide bands of mylonitized reduced grain sizes behind the overall size of the entire shear network rarely exceeds kilometer scale at depth although mylonitic shear zones are only visible to the observer when uplifted and exposed at the surface they govern the mechanical behavior of the strongest part of the lithosphere below 10 15 km depth mylonitic shear zones dissect plates thus allowing plate tectonics to develop on the earth we review the basic multiscale physics underlying mylonitic ductile shear zone nucleation growth and longevity and show that grain size reduction is a symptomatic cause but not necessarily the main reason for localization we also discuss a framework for analytic and numerical modeling including the effects of thermal mechanical couplings thermal elasticity the influence of water and void volatile feedback the physics of ductile shear zones relies on feedback processes that turn a macroscopically homogenously deforming body into a heterogeneously slipping solid medium positive feedback can amplify strength heterogeneities by cascading through different scales we define basic intrinsic length scales of strength heterogeneity such as those associated with plasticity grain size fluid inclusion and thermal diffusion length scale for an understanding ductile shear zones we need to consider the energetics of deformation shear heating introduces a jerky flow phenomenon potentially accompanied by ductile earthquakes additional focusing due to grain size reduction only operates for a narrow parameter range of cooling rates for the long time scale deformational energy stored inside the shear zone through plastic dilation or crystallographic and shape preferred orientation consumes only a maximum of 10 of energy dissipated in the shear zones but creates structural anisotropy shear zones become long living features with a long term memory a special role is attributed to the presence of water in nominally anhydrous minerals we show that water directly affects the mechanical equation of state and has the potential to synchronize viscous and plastic flow processes at geological time scale we have shown that fully coupled finite element calculations using mechanical data from the laboratory can reproduce the basic mode of deformation of an entire mylonitic shear zone the next step of modeling lies in benchmarking basic feedback mechanism in field studies and zooming into the braided network of shear zone structure without losing the large scale constraint numerical methods capable of fulfilling the goal are emerging these are adaptive wavelet techniques and hybrid particle finite element codes which can be run over a computational grid across the net

geochemistry of a hydrothermal sediment core from the obs vent field 21 n east pacific rise abstract we report a geochemical investigation of near vent hydrothermal sediment from the east pacific rise collected in a short 11 cm core by submersible from the obs vent site at 21 n the sediment has high concentrations of fe 23 25 cu 10 22 zn 4 13 and s 22 30 but low mn concentrations 108 279 ppm indicating a much fresher sulfidic input than in previously reported near vent sediments from the mid atlantic ridge further studies are required to fully characterise near field hydrothermal sediments but the data in this study allow the first comparisons with similar near vent material collected previously from the mid atlantic ridge as well as ridge flank data from the epr and juan de fuca ridge compared to ridge flank sediments the near field sediments exhibit high ratios of fe mn cu fe and zn fe unlike cu and zn pb is not so significantly enriched pb isotope compositions are indistinguishable from local morb indicating a dominant hydrothermal source for this element in these sediments this may not necessarily be the case for ridge flank sediments however where scavenging from seawater may also be important ree distributions throughout the core exhibit low concentrations and characteristics typical of vent fluids with lree enrichments and pronounced positive eu anomalies these patterns are similar to those of relatively fresh sulfides but there is also evidence for progressive oxidation downward into the core by ingressing seawater

14c geochronological constraints for the volcanic history of the island of ischia italy over the last 5000 years abstract the chronology of the most significant eruptions at the island of ischia in the last 5000 years has been studied by means of accelerator mass spectrometry to obtain 14 c data the results are in good agreement with stratigraphical and archeological constraints this allows interpretation of the measured dates as ages of the eruptions which produced the deposits overlying or incorporating the sampled paleosols and charcoal fragments respectively these ages define the timing of volcanism in the last 5000 years suggesting that the recent volcanic activity at ischia is characterized by periods of very intense volcanism alternating to periods of quiescence this timing of the volcanism is correlated with the behaviour of the magmatic system and dynamics of resurgence of the mt epomeo block

modes and times of caldera resurgence the 10 ka evolution of ischia caldera italy from high precision archaeomagnetic dating abstract ischia is a well exposed and densely populated late quaternary caldera in the campanian magmatic province of italy ischia caldera experienced an average uplift rate of 3 3 cm year in the last ca 30 ka and is still actively resurging during the last 10 ka coeval with the resurgence a volcanic field of alkali trachytic to trachyandesitic lava domes lava flows tuff and scoria rings and pumice cones developed mainly on the eastern sector of the caldera along both resurgence related faults and regional nnw and ne striking faults in order to improve both our understanding of the recent volcanic history and the evaluation of future risks on ischia island a high precision archaeomagnetic dating method was applied to the products of 12 volcanic centres with probable age 14 c ages archaeomagnetic and other geochronological data as well as stratigraphic constraints show that during the studied time interval ischia volcanism occurred in five periods separated by phases of quiescence and coeval with earthquake and landslide events this fact suggests a pulsating mode of uplifting and deformations of the ischia resurgence during the two oldest periods of activity 7200 6800 bc and 4100 2300 bc resurgence probably produced a dome shaped structure location and geometry of vents suggest the occurrence of magma uprise along the fractures produced by bending of the overburden crustal block most of magma was emplaced as intrusions at the interior of the resurgent block whereas volcanism was represented by very viscous differentiated and crystallized lavas that emplaced as domes and high aspect ratio flows the resurgent dome caused recurrent lateral collapses that removed about 2 5 km 3 of rocks during the three youngest periods of activity 1800 1000 bc 650 bc 355 ad and 1302 ad resurgence affected a fault bounded asymmetric block this resulted from both a hydrostatic rebound of the crustal block after removal of material involved into huge slope instability triggering an increase in uplift rate and b new influxes of less evolved magma batches into the shallow reservoir that in turn favoured the intense volcanism of the last 4000 years

a major helium 3 source at 15 s on the east pacific rise an extensive plume of water enriched with helium 3 has been discovered in the deep pacific ocean at latitude 15 s on the east pacific rise in the core of the plume at a depth of 2500 meters over the ridge crest the helium 3 helium 4 ratio is 50 percent higher than the ratio in atmospheric helium indicating a strong injection of mantle or primordial helium at the spreading center axis through local hydrothermal systems the helium 3 plume is completely absent east of the rise but it can be traced over 2000 kilometers to the west above a newly observed physical feature a density discontinuity here caled the ridge crest front the injected plume provides a unique deep sea tracer with an asymmetric distribution which shows that the deep circulation across the rise is from east to west the striking intensity and lateral extent of this helium 3 anomaly compared to observations at known oceanic hydrohrmal sites suggest that the largest hydrothermal fields in the ocean are yet to be discovered and that they will be found near 15 s on the east pacific rise

testing constitutive equations for brittle ductile deformation associated with faulting in granitic rock uncertainty in constitutive equations for brittle ductile deformation limits our understanding of earthquake nucleation and propagation at the base of the seismogenic lithosphere to reduce this uncertainty we investigate exhumed strike slip faults and related deformation features in the lake edison granodiorite central sierra nevada ca that developed at 250 500 c and 250 mpa the seven gables outcrop contains a 10 cm wide contractional fault step separating two meter scale left lateral faults within the step a 4 cm thick leucocratic dike is stretched and rotated thus constraining the kinematics of deformation and the dike and surrounding granodiorite are strongly mylonitized petrographic and electron backscatter diffraction analyses reveal evidence for brittle and plastic deformation mechanisms including dislocation creep diffusion creep microfracturing and cataclasis we present a 2d finite element model of the seven gables outcrop that tests a series of candidate constitutive equations von mises elastoplasticity drucker prager elastoplasticity power law creep viscoelasticity two layer elastoviscoplasticity and coupled elastoviscoplasticity models based on von mises yielding most accurately match the outcrop deformation frictional plastic yield criteria i e drucker prager are incapable of reproducing the outcrop deformation due to the elevated mean compressive stress and reduced plastic yielding within the model fault step furthermore the power law creep viscoelastic model requires a high strain rate 10 4 s 1 to resolve slip on faults and fails to localize strain within the step region comparing model results and elastic stress fields with field observations suggests that deformation localizes in regions of elevated mean compressive stress and mises equivalent stress