determination of space time structure of a deep earthquake source by means of power moments abstract for a planar shear earthquake source with monotonous slip at a given point power moments of the slip rate function provide a useful means of reconstructing a space time source structure in theory even a smoothed source function can be uniformly estimated power moments are linear functions of the processed data we have developed a practical technique for estimating the source power moment of degrees 1 and 2 from the body wave pulses of deep earthquakes the technique is applied to a moderate m b 5 7 event in the fiji islands we determined the source plane elongation direction length and duration values degree of asymmetry and possible rupture velocity most estimates are independent from any particular parametric source model although the haskell aki partly bilateral model agrees well with our observations

seasonal changes in silica deposition in hot spring systems abstract monthly monitoring of water chemistry at octopus spring yellowstone national park reveals no changes in the chemical composition over this eight month study differences in silica deposition are attributed to flow dynamics and seasonal air temperatures colder air temperatures in winter promote visible accumulation of siliceous sinter probably as a result of decreased solubility periodic drying promotes accumulation and subsequent dehydration of the silica this combination of intermittent supply and periodic dehydration may account for the laminated siliceous deposits observed in the geological record the processes described herein are important in the siliceous preservation of microbial fossils but the following observations underscore the difficulty in preserving microbial fabrics in the geological record pools populated by cyanobacteria are bounded by margins built of silicified microbial mats silicification of the pool margins occurs through an evaporative process called wicking silica rich water is transported upward through the microbial mats by capillary action depositing silica at the surface of the mat as water evaporates the upper surface of such wicking deposits is extremely resistant to brecciation but the underlying support is highly friable and would be difficult to preserve intact in winter months temporary isolation of some pools from active flow causes fragile silica deposition around biological and other debris film coated gas bubbles on the surfaces of microbial mats are observed during all seasons and probably are filled with oxygen released during photosynthesis although this has not been confirmed they become coated with silica during winter months presumably because of increased cooling possibly forming thin discontinuous silica sheets as observed in the geological record

stability of earthquake moment tensor inversions effect of the double couple constraint abstract we show that spurious large non double couple components can be obtained in inversions for the full deviatoric moment tensor for shallow crustal earthquakes due to inaccurate earth models the traditional best double couple solution does not in general provide an optimal estimate of a double couple mechanism and is only reliable when the non double couple component of the full deviatoric solution is small the inverse problem for the moment tensors of the 1998 antarctic plate and 2000 wharton basin strike slip earthquakes is shown in each case to have two well fitting minima in the misfit function of pure double couple solutions such pairs of solutions are most likely to exist for earthquakes which are close either to vertical strike slip or to dip slip on a fault plane dipping at 45 it is shown theoretically that these pairs of solutions arise from the combination of the pure double couple constraint and the instability of two elements of the moment tensor no significant non double couple component is found for the shallow thrusting 1996 biak indonesia earthquake

the growth of siliceous sinter deposits around high temperature eruptive hot springs abstract siliceous hot spring deposits sinter are of interest as they are indicative of hydrothermal resources at depth and may provide evidence for early life on earth and possibly mars numeric models of concurrent evaporation and opal a precipitation around high temperature 73 c eruptive hot spring vents such as geysers show that silica is most efficiently precipitated by complete evaporation owing to very sluggish growth kinetics for silica precipitation from supersaturated hydrothermal water where evaporation is complete between geyser events areas of initially deeper water precipitate more silica that over time fill in topographic lows to produce a smooth surface in contrast incomplete evaporation in which water is left in low areas prior to being washed away by the next geyser event or equivalently where there is continuous surface flow in topographic low areas tends to enhance the growth of minor topographic highs and leads to an increase in surface roughness such as seen in the development of knobby geyserite sinter texture around vents

physico chemical and environmental controls on siliceous sinter formation at the high altitude el tatio geothermal field chile abstract el tatio geothermal field is located 4270 m above sea level in the altiplano northern chile siliceous sinter deposits from el tatio were studied to understand the influence of water chemistry and the extreme climatic conditions on their textures and mineralogy the results of this study show that the mineralogy of el tatio sinters include of opal a and accessory minerals such as halite gypsum and cahnite ca 4 b 2 as 2 o 12 4h 2 o which precipitate by full evaporation of high arsenic boron and calcium thermal waters el tatio sinters show a high degree of structural disorder probably linked to cation incorporation into the silica structure and or the occurrence of micro to nano scale accessory minerals the high content of cations in the thermal waters is strongly tied to relatively high silica precipitation rates considering silica concentration in water 147 285 mg l sio 2 precipitation rate reach 2 5 kg m 2 per year based on in situ precipitation experiments the particular environmental conditions of this high altitude geothermal area that produce high water cooling rate and high evaporation rate may also be responsible for the fast silica precipitation low environmental temperatures create freezing related sinter textures i e silica platelets and micro columns ridges silicified microbial filaments are also characteristic of el tatio sinters and they are indicative of water temperature and hydrodynamic conditions at the moment of sinter formation however sinter textural interpretation in a high altitude andean context must be done carefully as specific relationships between microbial and hydrodynamic textures are found

long period seismic source inversions using global tomographic models summary we investigate the effect of laterally varying earth structure on centroid moment tensor inversions using fundamental mode mantle waves theoretical seismograms are calculated using a full formulation of surface wave ray theory calculations are made using a variety of global tomographic earth models results are compared with those obtained using the so called great circle approximation which assumes that phase corrections are given in terms of mean phase slowness along the great circle and which neglects amplitude effects of heterogeneity synthetic tests suggest that even source parameters which fit the data very well may have large errors due to incomplete knowledge of lateral heterogeneity the method is applied to 31 shallow large earthquakes for a given earthquake the focal mechanisms calculated using different earth models and different forward modelling techniques can significantly vary we provide a range of selected solutions based on the fit to the data rather than one single solution difficulties in constraining the dip slip components of the seismic moment tensor often produce overestimates of seismic moment leading to near vertical dip slip mechanisms this happens more commonly for earth models not fitting the data well confirming that more accurate modelling of lateral heterogeneity can help to constrain the dip slip components of the seismic moment tensor

source mechanism of mining induced seismic events resolution of double couple and non double couple models abstract traditional assumption about a seismic source as a double couple dc can represent a serious limitation for describing mechanisms of mining induced seismic events in mining conditions more general process than a shear slip can occur due to stress concentration on mined out areas we assume both non dc components within the dipole description of the source the moment tensor and a single force we processed five seismic events recorded at driefontein gold mine in south africa to demonstrate that waveform modeling is not successful enough due to poor information about the medium inversion of amplitudes of direct p and s waves is more prospective due to their smaller sensitivity to detail of the medium and possibility to correct them for ray bending and shear wave splitting prior to the inversion moreover we are able to estimate the error of the resulting mechanism due to neglect of ray bending all five events processed display non dc mechanisms which are significant at 95 considering the mismodelling of the rock mass by a homogeneous isotropic medium the source mechanisms are in agreement with the underground mining and geological structures one event has a sub vertical pressure single dipole complemented by an implosion which is the body force equivalent of a collapsing horizontal crack or a burst of a pillar supporting the hangingwall of a mined out area two events have mechanisms close to a pressure single couple all three events are located on pillars two out of these three events can be assigned with a downward single force as an alternative mechanism which matches the amplitude data successfully it is the force equivalent of a mined out area collapse when a rock mass falls from the hangingwall to the footwall the events are however rather strong which would require too large rock mass fallen one of the remaining events is a nearly horizontal tensile single couple corresponding to a vertical tensional fault it could be originated by a break of the hangingwall of a mined out area however the hypocenter of this event is deep into the footwall were there is no mining taking place the last event is mostly dc accompanied by a compensated compressive dipole which may be associated to nearly vertical dip slip along a fault in the hangingwall this event is located on the margin of a wide pillar which supports the interpretation

investigating δ 18 o of turbo sarmaticus l 1758 as an indicator of sea surface temperatures abstract the large marine gastropod turbo sarmaticus was and still is an important food item for coastal foragers along the south coast of south africa opercula of this species are well preserved in both holocene and pleistocene archaeological sites offering the opportunity to reconstruct past sea surface temperatures from 18o of shell carbonate over much of the last glacial cycle we have analysed 18o and 13c in 16 opercula and one shell of modern animals collected alive from an area with good sst records in order to explore how reliably this species records water temperature through the year and to investigate possible vital effects that may influence the isotope record we find that t sarmaticus deposits aragonite in both operculum and shell in oxygen isotopic equilibrium with seawater operculum 18o values of this species reliably reflect water temperatures between c 14 and 24 c although they do not always capture temperature extremes especially in winter likely due to slower growth under stressful growth conditions these thresholds probably alter according to factors such as variations in nutrient supply the averaged maximum and minimum values across the set of sixteen serially sampled opercula very closely approximate the temperatures of the warmest and coolest months and therefore provide a good measure of the seasonal temperature range and of mean annual sst 18o of edge increments can to some extent be used to indicate season of collection within the broad categories of warmer cooler seasons

calculation of synthetic seismograms in a laterally varying medium by the boundary element discrete wavenumber method abstract we investigate the propagation of lg waves in laterally varying crustal structures by numerical simulation the method of calculation is formulated in terms of boundary integral equations where the green9s functions are evaluated by wavenumber summation the approach is well suited to study the propagation of seismic waves in a layered medium where the interfaces are flat in some regions and irregular in others we investigate the effect of a crustal fault with vertical offset and study the case of a lateral change in crustal thickness the results show that the lg wave amplitude is only slightly affected by the presence of these heterogeneities they confirm the robustness of lg wave propagation in presence of lateral heterogeneities observed in other numerical simulations they show that large scale geometric features of the crust cannot account alone for the strong attenuation of lg waves observed in many regions the results also suggest a possible relation between the level of lg wave coda and the degree of roughness of the moho they further indicate the importance of backscattering and suggest a possible use of the backscattered wave field to map strong crustal heterogeneities

global tectonic significance of the solomon islands and ontong java plateau convergent zone abstract oceanic plateaus areas of anomalously thick oceanic crust cover about 3 of the earth s seafloor and are thought to mark the surface location of mantle plume heads hotspot tracks represent continuing magmatism associated with the remaining plume conduit or tail it is presently controversial whether voluminous and mafic oceanic plateau lithosphere is eventually accreted at subduction zones and therefore 1 influences the eventual composition of continental crust and 2 is responsible for significantly higher rates of continental growth than growth only by accretion of island arcs the ontong java plateau ojp of the southwestern pacific ocean is the largest and thickest oceanic plateau on earth and the largest plateau currently converging on an island arc solomon islands for this reason this convergent zone is a key area for understanding the fate of large and thick plateaus on reaching subduction zones this volume consists of a series of four papers that summarize the results of joint us japan marine geophysical studies in 1995 and 1998 of the solomon islands ontong java plateau convergent zone marine geophysical data include single and multi channel seismic reflection ocean bottom seismometer obs refraction gravity magnetic sidescan sonar and earthquake studies objectives of this introductory paper include 1 review of the significance of oceanic plateaus as potential contributors to continental crust 2 review of the current theories on the fate of oceanic plateaus at subduction zones 3 establish the present day and neogene tectonic setting of the solomon islands ontong java plateau convergent zone 4 discuss the controversial sequence and timing of tectonic events surrounding ontong java plateau solomon arc convergence 5 present a series of tectonic reconstructions for the period 20 ma early miocene to the present day in support of our proposed timing of major tectonic events affecting the ontong java plateau solomon islands convergent zone and 6 compare the structural and deformational pattern observed in the solomon islands to ancient oceanic plateaus preserved in precambrian and phanerozoic orogenic belts our main conclusion of this study is that 80 of the crustal thickness of the ontong java plateau is subducted beneath the solomon island arc only the uppermost basaltic and sedimentary part of the crust 7 km is preserved on the overriding plate by subduction accretion processes this observation is consistent with the observed imbricate structural style of plateaus and seamount chains preserved in both precambrian and phanerozoic orogenic belts

inversion for parameters of tensile earthquakes the tensile source model generalizes the shear source model by assuming that the slip vector can be arbitrarily oriented with respect to the fault and is not constrained to lie within the fault plane the proposed inversion for the parameters of tensile sources is based on the evaluation of the isotropic iso compensated linear vector dipole clvd and double couple dc components in seismic moment tensors the most significant parameters inverted are the ratio at the fault denoted as the parameter and the inclination of the slip vector from the fault the parameter is significant for discriminating noisy moment tensors of shear earthquakes from those of tensile earthquakes the inclination can be accurately determined from the dc component in the moment tensor because the dc component rapidly decreases with increasing for example the inclination of 20 causes dc being 50 60 only the inversion is applied to earthquakes which occurred in january 1997 in west bohemia czech republic it is shown that some of these earthquakes display tensile faulting the parameter is 0 1 the inclination of the slip from the fault attains values of up to 20 this inclination is a result of tensile traction and reduced shear traction along the fault and high fluid pressure in the region

determination of sea surface temperatures using oxygen isotope ratios from phorcus lineatus da costa 1778 in northern spain implications for paleoclimate and archaeological studies changes in oxygen isotope ratios from shell carbonates are mainly dependent on sea surface temperature which enables the estimation of temperatures during periods of shell growth and helps to dete

a quantitative comparison between 1d and 3d source inversion methodologies application to the middle east we present a quantitative comparison between seismic moment tensor mt inversion solutions using 1d and 3d synthetic seismograms at two frequency bands for events in the middle east to assess the effects of 3d models on source studies complex geology associated with the active continental convergent margin leads to a scarcity of reliable available data necessitating a thorough examination of solution stability and robustness to assure an accurate description of sources with well characterized source parameters solutions were calculated for 195 events m w 5 5 using a full waveform mt inversion matching both phase and amplitude seismic data processed at two frequency bands compares short and long period performance for 1d and 3d synthetic seismograms an improvement in fit between data and synthetics is seen using 3d over 1d synthetic seismograms especially for complex body wave propagation and surface wave dispersion at short periods 3d synthetics provide a more robust solution compared with 1d showing a reduction in error of the source mechanism the percentage of double couple components increases with the addition of 3d structure and suggests the percentage of non double couple components is a result of poorly constrained earth structure event solutions contained in the catalog graphic 1 table s1 in the electronic supplement to this paper have an average cross correlation value of 0 87 with good amplitude ratios and are improved i e increased variance reduction yet consistent with longer period solutions from the global centroid moment tensor cmt catalog online material table of 184 event solutions from 3d moment tensor inversion 1 embed inline graphic 1 gif

resolution of non double couple mechanisms simulation of hypocenter mislocation and velocity structure mismodeling mechanisms of earthquakes and induced seismic events are frequently found using the moment tensor description rather than the traditional double couple dc as it allows for nonshear source phenomena however non dc source components are sensitive to event mislocations and inexact velocity models of the crust inaccuracies such as these can generate spurious non dc components in the mechanism which should be taken into account during the interpretation we perform a synthetic case study simulating seismic observations at soultz sous forets alsace hot dry rock hdr site synthetic p and s amplitudes for several shear tensile source models are inverted assuming hypocenter mislocation and velocity structure mismodeling in several types of station coverage satisfactory reconstruction of the source mechanism is achieved except for rather extreme model simplification and extremely poor station coverage thus our results suggest that non dc mechanisms can be successfully resolved in local studies with reasonable station configuration when errors in event location and velocity profile are realistic

oxygen isotope constraints on surface ocean temperatures published oxygen isotope results from benthic and planktonic foraminifera are used to constrain the extent to which surface ocean temperatures in the tropics changed between glacial and interglacial time the possible impacts of bioturbation and of the redistribution of 18o16o ratios within the sea putting aside the oxygen isotope results are consistent with the climap project conclusion that tropical ocean temperatures remained within 2 c of their present value

resolving fault plane ambiguity for small earthquakes summary we have developed an automated procedure to resolve fault plane ambiguity for small to medium sized earthquakes 2 5 ml 5 using synthetic green s tensors computed in a 3 d earth structure model and applied this procedure to 35 earthquakes in the los angeles area for 69 per cent of the events we resolved fault plane ambiguity of our cmt solutions at 70 per cent or higher probability for some earthquakes the fault planes selected by our automated procedure were confirmed by the distributions of relocated aftershock hypocentres in regions where there are no precisely relocated aftershocks or for earthquakes with few aftershocks we expect our method to provide the most convenient means for resolving fault plane ambiguity our procedure does not rely on detecting directivity effects therefore it is applicable to any types of earthquakes

cryogenic opal a deposition from yellowstone hot springs sub zero winter temperatures on the yellowstone plateau alter the opal a precipitation pathway offluid erupting from hot springs and geysers frozen fluid often only meters from boiling pools contains abundant opal a particles comprising sheet and filamentlike aggregations of opal a microspheres which are formed by opal a precipitation in brine pockets channels and veins by natural cryogelling unconsolidated cryogenic opal a sediment accumulates in and below water ice where it is locked until spring thaw conditions sediment is then either remobilized contributing large volumes of opal a particulate to geothermally influenced wetlands or becomes adhered in situ by dehydration and cementation this strongly seasonal opal a precipitation regime has been overlooked in investigations of sinter deposition accretion rates and microbe mineral interactions natural opal a textures recorded fromyellowstonemaybereplicatedsimplybyfreezingandthawingsyntheticsilica saltsolutioninthelaboratory cryogenicprocess may have influenced mineral precipitation and sediment accumulation in many other geothermal areas particularly active terrestrial springs located at high altitude latitude fossil systems influenced by ancient glaciations plus potential astrobiological targets e g mars and europa 2007 elsevier b v all rights reserved

cryogenic silicification of microorganisms in hydrothermal fluids silica rich hydrothermal fluids that experience freezing temperatures precipitate cryogenic opal a coa within ice bound brine channels we investigated cryogenic silicification as a novel preservation pathway for chemo and photo lithotrophic bacteria and archaea we find that the co partitioning of microbial cells and silica into brine channels causes microorganisms to become fossilised in coa rod and coccoidal form bacteria and archaea produce numerous cell casts on coa particle surfaces while chloroflexus filaments are preserved inside particle interiors coa particles precipitated from natural icelandic hot spring fluids possess similar biomorphic casts including those containing intact microbial cells biomolecules and inorganic metabolic products are also captured by coa precipitation and are detectable with a combination of visible shortwave infrared reflectance ftir and raman spectroscopy we identify cryogenic silicification as a newly described mechanism by which microbial biosignatures can be preserved within silica rich hydrothermal environments this work has implications for the interpretation of biosignatures in relic hydrothermal settings and for life detection on mars and enceladus where opaline silica indicative of hydrothermal activity has been detected and freezing surface conditions predominate

delta o 18 of fissurella maxima as a proxy for reconstructing early holocene sea surface temperatures in the coastal atacama desert 25 degrees s abstract fissurella maxima is a keyhole limpet that is abundant and well preserved in archaeological shell midden sites along the coast of chile making it an appropriate species to use for reconstructions of past sea surface temperature sst in the present study we evaluate the potential of f maxima shells as a proxy of sst by analysing 18o of modern shells collected alive from the atacama desert area of taltal 25 s and archaeological shells from two early holocene rockshelter sites 224a and paposo norte 9 reconstructed sst from modern f maxima shells were related to sst obtained from in situ thermometers supporting the use of this mollusc species as a paleotemperature archive mean sst reconstructed from early holocene archaeological shells 14 13 c was 2 86 c cooler than mean temperature recorded in modern shells 16 99 c mean sst reconstructed from modern shells was 1 04 c warmer than the mean temperature of in situ thermometers 15 95 c hence the paleo sst data from archaeological sites 224a and paposo norte 9 enrich the early holocene nearshore paleoceanographic scenario of the pacific coast of south america with mean sst cooler than present day sst our results validate the use of f maxima shells as a sst proxy and contribute to a better understanding of the latitudinal distribution of the coastal upwelling regime during the early holocene temporal changes in the structure of the humboldt current along the holocene and its influence on human adaptation through the prehistory of south america

strontium to calcium ratios in the marine gastropod conus ermineus growth rate effects and temperature calibration here we investigate the potential of sr ca ratios in the marine gastropod conus ermineus for reconstructing seawater temperatures we present annually resolved records of sr ca and 18o for four shells collected alive from the flower garden banks national marine sanctuary in the gulf of mexico our results show that variations in sr ca and 18o covary with the in situ seasonal temperature cycle sr ca and temperature are positively correlated in contrast with the inverse relationship found in inorganically precipitated aragonite the seasonal sr ca variability is superimposed on a long term trend of increasing sr ca with age both the seasonal and long term ontogenetic changes in sr ca are associated with variations in growth rate defined here as the shell linear extension rate ler the seasonal variability in ler is superimposed on a long term decrease with ontogeny thus the covariance of sr ca ratios with temperature and ler suggests that sr incorporation is likely driven by temperature influence on growth rate rather than by thermodynamic effects unlike the seasonal variability the ontogenetic effect is characterized by inverse covariation between sr ca and ler suggesting that sr ca variability is not controlled by growth rate alone but probably by two different biomineralization mechanisms one related to temperature and the other related to age we use the seasonal sr ca signal of four shells to construct a temperature calibration to minimize the ontogenetic effects we separate the records into juvenile and adult growth stages and calculate the sr ca temperature t relationships juvenile sr ca mmol mol 1 0 042 0 008 t c 0 24 0 21 r2 0 66 adult sr ca mmol mol 1 0 072 0 014 t c 0 05 0 34 r2 0 68 applying the calibration to a single specimen provides mean annual temperature estimates within 1 c of the in situ temperature record but resolves the seasonal variability only within 3 5 c the large error in the seasonal estimates reflects the high variability among specimens to reduce the uncertainty on seasonal temperatures we propose combining records from multiple shells to generate an average temperature record the potential of this approach needs however to be validated in other locations

non double couple mechanisms of microearthquakes induced during the 2000 injection experiment at the ktb site germany a result of tensile faulting or anisotropy of a rock abstract moment tensors of microearthquakes induced during the 2000 injection experiment at the ktb deep drilling borehole at a depth level of 5 4 km are studied a family of 37 most reliable moment tensors contains significant non double couple non dc components the dc is on average 60 and the non dc is 40 fault plane solutions computed from the dc part show preferred strike slip mechanisms with small normal or reverse components a predominant azimuth of p and t axes is in the range of n320 340 e and of n230 250 e respectively the non dc components contain both the isotropic iso and compensated linear vector dipole clvd components the mean value of iso is 1 5 the mean value of clvd is 5 7 the predominantly negative clvd components are inconsistent with the concept of the non dc mechanisms as a result of tensile faulting due to fluid injection into the rock the main origin of the non dc components is probably anisotropy in the focal area the other origins are errors produced by mismodelling of the medium when calculating the green functions and numerical errors produced by noise and limitations of input data adopting four alternative models of anisotropy obtained by other seismic measurements at the ktb we have employed the non dc components for estimating an optimum orientation of anisotropy in the focal area the optimum orientation of the symmetry plane of anisotropy is nearly vertical with a strike of n335 340 e this strike coincides well with the strike of 330 typical for many major lithological units and faults and with the orientation of the transversely isotropic model inferred by other authors after removing the anisotropy effects from the moment tensors by calculating the source tensors the distribution of iso is significantly narrowed this indicates predominantly shear but not tensile faulting

oxygen isotopes from phorcus osilinus turbinatus shells as a proxy for sea surface temperature in the central mediterranean a case study from malta abstract the marine topshell phorcus osilinus turbinatus is a common component of many archaeological sites in the mediterranean this species has been successfully used as a palaeoclimate proxy in italy to test whether 18 o from p turbinatus shells can serve as a reliable palaeoclimate archive for other regions of the mediterranean we collected live p turbinatus from the northeast coast of malta each month for a year the 18 o shell values of the outermost growth increments of these live collected shells ranged between 0 4 and 2 4 these values correspond to growing temperatures calculated from shell edge 18 o of between 15 c and 27 c calculated shell edge sea surface temperatures are highly correlated with instrumental records of sea surface temperature recorded over the period of collection the individuals analysed for this study are smaller than p turbinatus from populations studied elsewhere in the mediterranean nonetheless 18 o shell provides a robust record of sea surface temperatures suggesting that smaller younger shells in archaeological deposits can still provide reliable palaeothermometry records this study extends the upper growth limit p turbinatus by 2 c compared with the previous studies of p turbinatus in the mediterranean and suggests that contrary to the previous studies growth shutdown does not occur in all p turbinatus when sea surface temperatures exceed 25 c this may reflect the higher sample resolution that can be obtained from smaller faster growing shells or it may reflect actual higher growth tolerances of p turbinatus populations in malta by showing that p turbinatus precipitate their shells in 18 o equilibrium with surrounding sea water this study reinforces the potential for the stable isotope chemistry of p turbinatus shells preserved in mediterranean archaeological sites to provide a window into the climate and seasonality regimes of the past

significance of non double couple components of deep and intermediate depth earthquakes implications from moment tensor inversions of long period seismic waves abstract analysis of long period seismic waves suggests that non double couple components in source moment tensors of intermediate depth and deep earthquakes are significant and appear to respond to the state of predominant strain release within slabs the strain regime is partially or fully induced by the sources themselves or by slab structures near the sources we observe consistency in the non double couple components from three different seismic wave inversions among 21 earthquakes studied 17 events have the same sign in the three non double couple components and the signs show a correlation with the state of strain release within the slabs the effects of unmodeled propagation structure and instability of the inversion procedure are unlikely to be responsible for the consistent non double couple components because the suites of seismic waves traverse different paths and the various inversion schemes have the different resolvabilities of the moment tensors

estimating finite source properties of small earthquake ruptures many of the most fundamental questions in earthquake science are currently limited by a lack of knowledge about small earthquake ruptures small earthquakes are difficult to study owing to the poor constraints placed on many of the interesting physical parameters by bandlimited far field seismic data traditionally dynamic models such as an expanding circular crack have been utilized to bridge the gap between the easily measurable quantities for small earthquakes and more interesting physical parameters such as stress drop and rupture velocity here i present a method for estimating the basic finite source properties of a rupture that is independent of any a priori model and utilizes the description of a finite source the second moments that far field waves are inherently sensitive to application to two magnitude 5 events in southern california demonstrates the ability of an empirical green9s function approach to estimating the second moments to resolve the fault plane ambiguity rupture length and overall directivity additional results are presented for two example m 2 7 events from the creeping section of the san andreas fault to examine the likely lower bound on event size that can be studied with surface seismometers the creeping section earthquakes have very similar rupture areas but would be improperly interpreted as significantly different using the traditional methodology one of these events presents a relatively clear interpretation of the velocity of rupture front propagation which is about 0 8 of the rayleigh speed suggesting little difference in rupture velocity between it and typical large earthquakes

high resolution in situ thermal imaging of microbial mats at el tatio geyser chile shows coupling between community color and temperature 1 microbial mats have spatially heterogeneous structured communities that manifest visually through vibrant color zonation often associated with environmental gradients we report the first use of high resolution thermal infrared imaging to map temperature at four hot springs within the el tatio geyser field chile thermal images with millimeter resolution show drastic variability and pronounced patterning in temperature with changes on the order of 30 c within a square decimeter paired temperature and visual images show that zones with specific coloration occur within distinct temperature ranges unlike previous studies where maximum minimum and optimal temperatures for microorganisms are based on isothermally controlled laboratory cultures thermal imaging allows for mapping thousands of temperature values in a natural setting this allows for efficiently constraining natural temperature bounds for visually distinct mat zones this approach expands current understanding of thermophilic microbial communities and opens doors for detailed analysis of biophysical controls on microbial ecology

depositional evolution of an extinct sinter mound from source to outflow el tatio chile siliceous sinter deposits from el tatio chile preserve a wide variety of depositional environments and biosignatures from high temperature 85 c vent proximal facies to distal deposits dominated by silicified microbial mats four cores were drilled into an el tatio sinter mound and associated distal apron to investigate changes in hydrothermal environments over geologic timescales sedimentary and geochemical analysis of multiple sinter cores records the initiation and accretion of diverse depositional features still observed today in el tatio facies adjacent to hydrothermal vents are dominated by laminated sinter crusts on the steep margins of a high temperature pool with sparse microbial preservation outer margins of the same pool contain extensive sinter columns up to ten centimeters in length precipitated during repeated cycles of pool overflow and subsequent evaporation low relief hydrothermal pools also form minor deposits within distal debris aprons and analogous pools are still active close to sampling locations debris aprons are dominated by palisade tufted and arborescent microbial fabrics with distinct mat textures revealing well preserved microfossils surficial deposits in all cores feature detrital rich and microbially influenced sinters overlying higher temperature facies indicating a relative decrease in hydrothermal activity over time geochemical proxies for hydrothermal fluids and de trital input match depositional interpretations based on sedimentary structures 14 c ages from core deposits extend the mound s history by 11 000 years recording at least three thousand years of sinter deposition on top of glacial sandstones 13 337 10 232 y cal bp importantly this work provides a detailed depositional model unavailable through surficial sedimentology alone

new constraints on the rupture process of the 1999 august 17 izmit earthquake deduced from estimates of stress glut rate moments summary this paper illustrates the use of integral estimates given by the stress glut rate moments of total degree 2 for constraining the rupture scenario of a large earthquake in the particular case of the 1999 izmit mainshock we determine the integral estimates of the geometry source duration and rupture propagation given by the stress glut rate moments of total degree 2 by inverting long period surface wave lpsw amplitude spectra kinematic and static models of the izmit earthquake published in the literature are quite different from one another in order to extract the characteristic features of this event we calculate the same integral estimates directly from those models and compare them with those deduced from our inversion while the equivalent rupture zone and the eastward directivity are consistent among all models the lpsw solution displays a strong unilateral character of the rupture associated with a short rupture duration that is not compatible with the solutions deduced from the published models with the aim of understand this discrepancy we use simple equivalent kinematic models to reproduce the integral estimates of the considered rupture processes including ours by adjusting a few free parameters controlling the western and eastern parts of the rupture we show that the joint analysis of the lpsw solution and source tomographies allows us to elucidate the scattering of source processes published for this earthquake and to discriminate between the models our results strongly suggest that 1 there was significant moment released on the eastern segment of the activated fault system during the izmit earthquake 2 the apparent rupture velocity decreases on this segment

geochemistry of metals and metalloids in siliceous sinter deposits implications for elemental partitioning into silica phases abstract sinter deposits are formed by precipitation of silica from hydrothermal fluids that have reached the surface environment they are commonly found around hot springs and represent surface expressions of underlying geothermal systems and or low sulfidation epithermal gold silver hydrothermal deposits several studies have reported ppm to weight percent concentrations of metals e g au ag cu and metalloids e g as sb b in sinters capping geothermal systems and epithermal gold silver deposits however the relation between the maturity of the siliceous sinter and its metal enrichment remains unknown here we use geochemical and mineralogical data that link the silica crystallinity degree with trace metal and metalloid contents in sinter in this paper we provide in situ trace element data in metal rich silica sinter samples from the puchuldiza geothermal field in the altiplano of northern chile that record the complete diagenetic sequence from non crystalline opal a to microcrystalline quartz combined sem xrd and la icp ms data show that the concentration of metals and metalloids in sinters from puchuldiza display a strong correspondence with silica crystallinity while arsenic and boron are predominantly enriched in the more amorphous silica phases opal a ct gold and silver show higher concentrations in the more crystalline phases opal c quartz silica structural morphological and geochemical transformations from its initial precipitation to its final maturation after diagenesis are responsible for this differential enrichment during the initial stages gold and silver are incorporated into silica microspheres as cationic species and or metal nanoparticles or colloids while arsenic and boron incorporation is controlled by as bearing accessory minerals and fe oxyhydroxides as diagenesis progresses and the crystallinity of silica increases diffusion driven processes such as ostwald ripening may progressively enrich gold and silver in the sinter while metalloids are depleted owing to the low retention of arsenic by silica these findings indicate that the diagenetic transitions of silica defined by significant structural changes that involve generation of surface defects and the creation of reactive sites may play an important role in elemental uptake by silica in near surface environments

dating silica sinter geyserite a cautionary tale abstract we describe a new effort to date hydrothermal silica sinter deposits geyserite from the upper geyser basin of yellowstone national park using 14c of co deposited organic matter u series and cosmogenic 10be methods a majority of the samples were collected from stratigraphic sections mainly at riverside giant and castle geysers ages obtained from 41 14c analyses range from modern to 12 1 cal ka bp nearly all the 14c ages show inconsistencies with their stratigraphic positions and several replicate 14c analyses from the same sample result in significantly different ages the 13c values of the organic material in the sinter range from 26 6 to 12 7 the more enriched values are attributed to microbial fixation of dissolved inorganic carbon dic which has heavier 13c values and is 14c depleted relative to atmospheric co2 leading to an apparent older age u series analyses on 4 samples yielded ages between 2 2 and 7 4 ka large 230th u age uncertainties in the sinter due to low uranium concentrations along with elevated 232th and associated initial 230th make these ages imprecise for use on holocene deposits a single cosmogenic 10be exposure age of 596 18 ka is considerably older than the age of underlying rhyolite and is thus unreliable this apparent old age results from contamination by meteoric 10be trapped in the opal that overprints the very small amount of cosmogenic 10be by presenting the problems we encountered and discussing their probable cause this paper highlights the difficulty in obtaining reliable high precision geochronological data necessary to use sinter deposits as paleoenvironmental and paleo hydrothermal archives

oxygen isotope fractionation in marine aragonite of coralline sponges oxygen isotope values of the extant caribbean coralline sponge ceratoporella nicholsoni are compared with published temperatures and 18o of water calculated from salinities the measured values from aragonitic sponge skeletons have a mean offset of 1 0 0 1 from calculated calcite equilibrium values aragonite calcite 1 0010 this is in good agreement with published values from synthetic aragonite they further agree with published near equilibrium oxygen isotope values of temperate and cold water molluscs and foraminifera extrapolated to the temperature range of the coralline sponges these results and the mode of skeleton formation of ceratoporella nicholsoni suggest that these sponges precipitate aragonite close to isotopic equilibrium the temperature dependence of oxygen isotopic fractionation between the aragonite of ceratoporella nicholsoni and water is only roughly constrained by the available data due to the narrow temperature range of the caribbean reef sites however as the data suggest oxygen isotopic equilibrium we can calculate a well constrained temperature equation combining temperate and cold water equilibrium values from molluscs and foraminifera with our sponge data full size image 1 k and full size image 1 k

experimental studies on new zealand hot spring sinters rates of growth and textural development to study the rate of growth of sinters in new zealand hot springs field experiments were conducted in seven geothermal areas at wairakei fan shaped subaqueous deposits of amorphous silica grow rapidly 350 kg a 1 m 2 of drain wall and are composed of silicified filaments with subordinate bacillus and spirillium shaped organisms characterization of bacteria revealed isolates sharing 97 16s rrna gene sequence homologies affiliated with thermus meiothermus bacillus tepidomonas thermomonas porphyrobacter thermonema and hydrogenophilus spp as well as previously uncultured bacteria at rotokawa microstromatolites have a slow growth rate 0 004 mm day 1 that is attributed to low ph capillary rise and evaporation at champagne pool sinter growth 0 023 mm day 1 is dominated by wave action building alternating microbe rich and microbe poor layers silica sinter was not observed at waikite where slides developed a layer of calcite 0 026 mm day 1 sinter growth at ngatamariki 0 016 mm day 1 forms by capillary rise evaporation and diffusion and at tokaanu subaqueous growth is slow 0 002 mm day 1 and contains silicified microbes textures at orakei korako indicate similar mechanisms to ngatamariki except that growth is more rapid 0 023 mm day 1 due to a splash contribution silica and calcite saturation indices adequately explain the growth of the sinters and calcite indicating that microbes are not inducing precipitation where it should not occur the rate of precipitation is correlated with silica supersaturation but ph effects can alter this relationship the degree of preservation of microbial material is explained by the effect of ostwald ripening on silica spherules subaqueous growth allows coarsening of spherules and poor preservation of smaller microbes while subaerial nucleation is rapid ostwald ripening is inactive and better preservation can be expected

predominance of unilateral rupture for a global catalog of large earthquakes the manner in which an earthquake rupture propagates across a fault reflects both the initial properties of the fault and the dynamical stresses produced by the rupture we quantify the propagation of an earthquake rupture using the second moments of the earthquake space time distribution in particular the second moments provide a simple way to differentiate between approximately bilateral and predominantly unilateral ruptures we determined the second moments for a catalog of m w 7 earthquakes that have occurred since 1994 the results show that approximately 80 of large shallow ruptures are predominantly unilateral our result agrees well with strong motion inversions from previous studies on moderate and large earthquakes the predominance of unilateral propagation in large earthquakes is explained by a simple characteristic earthquake model in which large events rupture an entire structurally defined fault segment and nucleation points are uniformly distributed along the fault the predominance of unilateral rupture may also be enhanced by the dynamic stress field produced by contrasts in the elastic properties between the two sides of plate boundary faults manuscript received 16 november 2001

moment tensors of the january 1997 earthquake swarm in nw bohemia czech republic double couple vs non double couple events abstract we investigated moment tensors mts of 70 events of the earthquake swarm which occurred in january 1997 in nw bohemia a refined location using the master event procedure shows that all the foci clustered in a volume of less than 0 5 km3 comprising two compact clusters the southern and northern ones the results of single source absolute moment tensor inversion of the p and sh peak amplitudes reveal two types of the source mechanisms a and b in our denotation which dominated in the swarm type a implies an oblique normal faulting with a nearly pure double couple dc source for the b type an oblique thrust faulting and a combined source double couple combined with the isotropic iso and compensated linear vector dipole clvd components are typical magnitudes of the non double couple components of mt appear unrelated to the ml magnitude of the event the proximity of hypocentres of a and b events guarantees the non double couple source mechanisms of the b events not to be an artefact of a mismodelling of the medium to exclude finiteness of the focus or station site effects as possible causes of spurious non double couple components of mts of the b events the residuals of the peak amplitudes across the set of the b events were analysed and the jack knife test was applied the a and b events separate in time and space consequently three major phases of swarm activity can be distinguished in the first only the southern cluster was active and a events prevailed while b events dominated in the northern cluster in the third phase both a and b events occurred the former in the southern cluster the latter in the northern one during the second phase the initiation of the b events in the northern cluster are reflected in a pronounced increase in the non double couple components of the mts which points to tensile source mechanisms as a consequence of a hypothesised fluid injection

formation of silica oncoids around geysers and hot springs at el tatio northern chile siliceous oncoids up to 4 cm in diameter are common on the laterally extensive sinter aprons that surround the spectacular geysers and hot springs at el tatio in northern chile many of these complex oncoids developed close to geyser and spring vents that discharge boiling water internally the oncoids which are composed of precipitated amorphous silica are formed of complex arrays of spicules and concentric laminae as well as detrital volcanic grains spicular growth is dominant in most examples the formation and growth of the spicules and concentric laminae were mediated by a microbial community which included filamentous microbes mucus and possibly bacteria the microbes and mucus were silicified by replacement and encrustation in some laminae the filamentous microbes lay parallel to the growth surface in other laminae most filaments forming the thin mats were suberect amorphous silica precipitated between the filaments occluded porosity and commonly disguised the microbial fabric the oncoids grew on the proximal sinter aprons around the geyser vents and hot spring pools most growth took place subaerially with the silica delivered to the precipitation sites by splashing water from the geysers and or periodic shallow flooding of the discharge aprons unlike silica oncoids at other geothermal sites vertical growth of oncoids that formed in some rimstone pools was not limited by water depth

the hot spring and geyser sinters of el tatio northern chile abstract the siliceous sinter deposits of el tatio geothermal field in northern chile have been examined petrographically and mineralogically these sinters consist of amorphous silica opal a deposited around hot springs and geysers from nearly neutral silica saturated sodium chloride waters water cooling and evaporation to dryness are the main processes that control the opal a deposition in both subaqueous and subaerial settings in close spatial relation to microbial communities all fingerprints of organisms observed in the studied sinter samples represent microbes and suggest that the microbial community is moderately diverse cyanobacteria green bacteria and diatoms the most important ecological parameter is the temperature gradient which is closely related to the observed depositional settings 1 geyser setting water temperature 70 86 c boiling point at el tatio 4200 m a s l coarse laminated sinter macrostructure with rapid local variations biota comprises non photosynthetic hyperthermophilic bacteria 2 splash areas around geysers water temperature 60 75 c laminated spicule and column macrostructure locally forming cupolas

source process of the 1995 kobe earthquake determination of spatio temporal slip distribution by bayesian modeling the kobe hyogo ken nanbu earthquake ms 6 8 occurred on 16 january 1995 in western japan bringing about a tremendous disaster we constructed its source model by determining a spatio temporal slip distribution using strong motion seismograms recorded at a number of stations near the hypocenter the source area is expressed using both a rough and a detailed subfault discretization system and a source time function expanded with a finite number of basis functions at each subfault is determined to perform stable inversions with many parameters we construct a bayesian model with unknown hyperparameters incorporating prior constraints on the smoothness of spatio temporal slip distribution in the observation equation using akaike s bayesian information criterion abic the optimal set of hyperparameters are objectively determined from observed data which enables us to uniquely determine a spatio temporal slip distribution after rough analysis in which the actual rupture area is estimated as 45 20 km we carried out a detailed analysis with a finer subfault discretization system 5 5 km in our final source model most of the slip exists beneath awaji island and the rupture below the city of kobe where the damage was most serious is relatively smaller the large slips of about 2 m in the shallowest subfaults located southwest of the hypocenter correspond to the surface offsets observed along the nojima fault the overall focal mechanism of the source is right lateral strike slip with a small thrust component while total seismic moment is 2 0 1019 nm the source time functions at shallow subfaults show a longer duration than those at deeper ones being hypothesized to represent a possible combined effect of low rupture propagation velocity and varying friction behavior in shallow regions of crust

relationship between spring and geyser activity and the deposition and morphology of high temperature 73 c siliceous sinter yellowstone national park wyoming u s a abstract six classes of alkaline hot springs and geysers are here distinguished in yellowstone national park based on activity and eruptive style 1 non surging non boiling springs 2 gently surging non boiling springs 3 non surging to gently surging boiling springs 4 strongly surging springs 5 fountain geysers and 6 cone geysers each displays morphologically distinctive siliceous sinter deposits in the high temperature 73 c parts of the vent and outflow systems non surging and gently surging non boiling springs that do not overflow their rims develop thin digitate to lilypad like sinter rims that grow horizontally over the pool surfaces similar springs with rim overflow have rims that accrete vertically boiling springs often have nearly circular steep sided pools and rims dominated by splash and rim overflow and composed mainly of spicular and columnar sinter fountain geysers characterized by broad fountain like eruption bursts have a central vent surrounded by a zone of spicular sinter beyond which is a broad flat bottomed moat but lack steep sinter cones cone geysers have narrow vents jet like discharges that cool rapidly and fall close to the vent and steep sided spicule dominated sinter cones sinter deposition takes place within three main zones 1 fully subaqueous sides and bottoms of vent pools outflow basins and outflow channels 2 periodically wetted splash zones surrounding hot springs and geysers and 3 largely subaerial parts of the rim and outflow areas wetted mainly by overflow and surging and that dry quickly fully subaqueous surfaces are covered by fine earthy particulate siliceous sediment pss composed largely of amorphous silica spherules and spherule aggregates that appear to have precipitated around heterogeneous nuclei including microbes splash zones of hot springs and geysers are characterized by spicular sinter largely subaerial zones wetted mainly by rim overflow and surging with little or no splash show complex varieties of terraced columnar and knobby sinter the highest silica deposition rates occur where surfaces are wetted frequently and evaporate to dryness such as the tops of spicules columns and knobs associated lower areas and crevices that remain wet or moist show slow accumulation of pss most continuously wet surfaces in high temperature 73 c hot spring and geyser vent and outflow systems are probably covered by microbial biofilms although microbes may locally influence rates of silica deposition and sinter microstructure the results of this study suggest that the depositional sites morphology and macrostructuring of high temperature sinter are controlled largely by the processes of surface wetting evaporation and drying

detection of high frequency tensile vibrations of a fault during shear rupturing observations from the 2008 west bohemia swarm summary the analysis of 12 earthquakes of magnitudes between 1 7 and 3 7 that occurred in 2008 in west bohemia czech republic reveals that shear rupturing along a fault is accompanied by weak tensile vibrations of the fault the vibrations are of a narrow frequency band with frequencies distinctly higher than those of shear rupturing the tensile vibrations decay slowly in time and often resemble resonant waves they complicate the radiated p waveforms and the p wave radiation pattern the tensile vibrations can be observed in waveforms in directions near the nodal lines where the dominance of shear faulting radiation is lost the tensile vibrations are probably generated by opening of the fault during shear rupturing or by creating a wing tensile crack at the tip of the fault when shear fracturing stops

disputable non double couple mechanisms of several strong earthquakes second degree moment approach the earthquake source mechanism description of the geometry of the source and its strength in terms of forces equivalent to rupturing of the rock mass is routinely modeled as a moment tensor mt describing the earthquake focus as a point however sometimes this approximation is not satisfied and seismic radiation keeps the directivity due to the finite extent of the source inversion into the mt then may yield a biased mechanism synthetic study in the adamova and silen 2010 demonstrated the appearance of spurious non double couple components in the mechanism even for a pure double couple dc source their method was designed to reduce the spurious source components by using the second degree moments to evaluate their contribution into the records and subtract it from the data here we applied the procedure to five moderate to large regional events with large nonshear components they are mostly located on large tectonic faults where predominantly pure shear slip is expected we studied one event on the prominent north anatolian fault three events in the pacific area and one event in bolivia in most cases the non dc components essentially were reduced and the geometry of the mechanism remained largely unchanged this confirms the hypothesis that part of the non dc components in regional mt solutions may be spurious due to the neglect of the source finiteness in the routine procedure of the mt retrieval in addition the geometrical and kinematical characteristics of the foci provided by the second degree moments the source ellipsoid and rupture velocity vector are mostly consistent with the fault geometry aftershock distribution and estimates of rupture speed from available previous studies

implosive earthquakes at the active accretionary plate boundary in northern iceland non double couple earthquake focal mechanisms imply a mode of seismic failure other than simple shear and movements perpendicular to the fault plane reports of such events are rare and it is controversial whether such failure can occur at depth in the earth following reports of such earthquakes from the hengill and reykjanes volcanic systems on the accretionary plate boundary in iceland1 3 a seismological survey was conducted in the krafla system iceland to explore whether such earthquakes occur elsewhere along the boundary here we report the observation of a mixed suite of focal mechanisms at krafla including shear events explosive tensile crack events such as were observed at hengill and reykjanes and implosive events these last represent cavity collapse and constitute an entirely new class of earthquake the krafla system had undergone a crustal spreading episode4 10 during the decade before the observations were made and our results indicate that immediately after such an episode the accretionary plate boundary is characterized by a heterogeneous stress regime with shear extensional and compressional sources in close juxtaposition

oxygen isotopic composition of limpet shells from the beagle channel implications for seasonal studies in shell middens of tierra del fuego abstract shell middens distributed along the coastal areas of the beagle channel tierra del fuego testify the primary role of marine resources in the successful social dynamic of hunter gatherer fisher societies hgf in extreme high latitude environmental conditions intertidal and subtidal limpet species are frequently identified taxa of these archaeological deposits we investigated whether shell 18o of the limpet species nacella deaurata is a valuable record of local sea surface temperature sst and ambient water 18o 18ow fluctuations and in turn can be used to estimate the season of its exploitation by holocene hgf sequential shell 18o of modern species track seasonal changes of sst and 18ow the comparison of shell 18o profiles of n deaurata and nacella magellanica a coexisting species suggests the occurrence of distinct growth rate and physiological adaptations between species shell 18o of zooarchaeological specimens of n deaurata from lanashuaia ii suggests that animals were exploited predominantly in winter and that experienced similar environmental conditions of present day at 1320 years bp results also indicate that n deaurata is a valuable candidate for studying past seasonal changes in sst and 18ow in this southernmost part of south america

radiocarbon dating of silica sinter deposits in shallow drill cores from the upper geyser basin yellowstone national park abstract to explore the timing of hydrothermal activity at the upper geyser basin ugb in yellowstone national park we obtained seven new accelerator mass spectrometry ams radiocarbon 14 c ages of carbonaceous material trapped within siliceous sinter five samples came from depths of 15 152 cm within the y 1 well and two samples were from well y 7 depths of 24 cm and 122 cm these two wells at black sand and biscuit basins respectively were drilled in 1967 as part of a scientific drilling program by the u s geological survey white et al 1975 even with samples as small as 15 g we obtained sufficient carbonaceous material a mixture of thermophilic mats pollen and charcoal for the 14 c analyses apparent time of deposition ranged from 3775 25 and 2910 30 14 c years bp at the top of the cores to about 8000 years bp at the bottom the dates are consistent with variable rates of sinter formation at individual sites within the ugb over the holocene on a basin wide scale though these and other existing 14 c dates hint that hydrothermal activity at the ugb may have been continuous throughout the holocene

stable isotope aspects of modern molluscs brachiopods and marine cements from cool water carbonates lacepede shelf south australia the isotopic composition of some modern gastropods bivalves and brachiopods from the lacepede shelf of south australia were investigated to determine the isotopic equilibrium and dis equilibrium states of biogenic and non biogenic inorganic carbonates and to understand the kinetic and metabolic isotopic effects on precipitating carbonates and the isotopic fractionation between these different carbonates and dissolved bicarbonate seawater and high mg calcite hmc marine cements from different depths were also analyzed to determine equilibrium isotopic composition this study shows that the shells of some cool water gastropods and bivalves precipitate in isotopic equilibrium with their ambient waters while brachiopod shells show 18o values heavier than equilibrium values and coralline algae and ahermatypic corals exhibit significant metabolic and kinetic effects the isotopic equilibrium precipitation seen in these biogenic carbonates results from lower precipitation rates that are in turn caused by the lower bottom temperatures in this area

source rupture process of the kocaeli turkey earthquake of august 17 1999 obtained by joint inversion of near field data and teleseismic data the rupture process of the 1999 turkey earthquake is examined using both near field strong motion data and teleseismic body wave data the derived source parameters are as follows strike dip slip 268 86 180 nearly pure strike slip the seismic moment mo 1 7 1020 nm mw 7 4 the source duration 20 sec the fault length 70 km the fault width 15 km the rupture process is characterized by an asymmetric bilateral rupture propagation and smooth slip it consists of two major fault segments a rupture propagating to the west and a second rupture propagating to the east the maximum dislocation and the maximum dislocation velocity are 6 3 m and 2 7 m s respectively both found at the former segment the average dislocation is about 4 m the extent of the coseismic rupture suggests that a considerable part of the anticipated seismic gap remains unruptured

geyserite in hot spring siliceous sinter window on earth s hottest terrestrial paleo environment and its extreme life siliceous hot spring deposits or sinters typically form in active terrestrial on land volcanic terrains where magmatically heated waters circulating through the shallow crust emerge at the earth s surface as silica charged geothermal fluids geyserites are sinters affiliated with the highest temperature 75 100 c natural geothermal fluid emissions comprising localized lithologically distinctive hydrothermal silica precipitates that develop around geysers spouters and spring vents they demarcate the position of hot fluid upflow zones useful for geothermal energy and epithermal mineral prospecting near vent areas also are extreme environment settings for the growth of microbial biofilms at near boiling temperatures microbial biosignatures e g characteristic silicified microbial textures carbon isotopes genetic material lipid biomarkers may be extracted from modern geyserite however because of strong taphonomic filtering and subsequent diagenesis fossils in geyserite are very rare in the pre quaternary sinter record which in and of itself is patchy in time and space back to about 400 ma only a few old examples are known such as geyserite reported from the devonian drummond basin australia devonian rhynie cherts scotland and a new example described herein from the spectacularly well preserved late jurassic 150 ma yellowstone style geothermal landscapes of patagonia argentina there geyserite is associated with fossil vent mounds and silicified hydrothermal breccias of the claudia sinter which is geologically related to the world class cerro vanguardia gold silver deposit of the deseado massif a part of the chon aike siliceous large igneous province tubular filament like micro inclusions from claudia were studied using integrated petrographic and laser micro raman analysis the results of which suggest a biological origin the putative fossils are enclosed within nodular geyserite a texture typical of subaerial near vent conditions overall this worldwide review of geyserite confirms its significance as a mineralizing geological archive reflecting the nature of earth s highest temperature habitable terrestrial sedimentary environment hot spring depositional settings also may serve as analogs for early earth paleoenvironments because of their elevated temperature of formation rapid mineralization by silica and morphologically comparable carbonaceous material sourced from prokaryotes adapted to life at high temperatures

characterization of aftershock fault plane orientations of the 1999 izmit turkey earthquake using high resolution aftershock locations 1 joint inversion for hypocentral parameters and the velocity field is nowadays a state of the art tool to obtain high resolution images of seismically active regions in this study we focus on the location accuracy of aftershocks of the 1999 mw 7 4 izmit nw turkey earthquake we obtained a new velocity model for the region and depicted its improvement on absolute locations in terms of uncertainty and misfit two well developed aftershock clusters located in the akyazi area and karadere duzce region were analyzed in detail based on a waveform cross correlation approach that allowed improving the location accuracy by a factor of 6 relocation results reveal that hypocenters form narrow planes of activity that can be correlated with focal mechanisms of the larger aftershocks as well as nearby clouds of activity with no internal structure down to the resolved scale of 300 m

sclerochronology and geochemical variation in limpet shells patella vulgata a new archive to reconstruct coastal sea surface temperature 1 climate archives contained in shells of the european limpet patella vulgata accumulated in archaeological deposits can potentially provide much needed information about holocene environmental change in midlatitude coastal areas before reconstructing climate information preserved in these zooarchaeological records we studied the controls on oxygen and carbon isotope ratios 18o and 13c respectively in modern specimens we tested the hypothesis that p vulgata precipitates its shell in isotopic equilibrium with the ambient water by comparing 18oshell with predicted values predicted 18oshell was constructed using observed sea surface temperature sst records and the equilibrium fractionation equation for calcite and water we assumed a constant 18owater value of 0 10 vsmow based on published regional measurements comparison of 18oshell with predicted values revealed that 18oshell values were higher than expected by 1 01 0 21 consequently estimated sst calculated from 18oshell was 4 2 2 3 c lower than observed sst however because of the relatively uniform offset between observed and expected 18o an adjustment can be made to account for this predictable vital effect thus past climate can be reliably reconstructed using this temperature proxy once the offset is taken into account 13c values have a similar cyclicity to the 18o variation and therefore vary seasonally however 13c is slightly out of phase relative to 18o an overall negative shift in 13cshell over the lifetime of the individual indicates a vital effect associated with ontogeny further study of environmental and ecological factors that influence shell 13c is required to evaluate fully the potential of carbon isotope ratios as a useful environmental proxy

new research on the development of high resolution palaeoenvironmental proxies from geochemical properties of biogenic carbonates abstract geochemical signatures from biogenic carbonates are being increasingly employed as palaeoenvironmental proxies in turn many of these proxy archives including mollusc shells corals and otoliths have periodic growth structures which allow the reconstruction of chronologically constrained records of palaeoenvironmental variability at unparalleled high temporal resolution studying the growth and chemistry of these periodic growth structures is known as sclerochronology biogenic hard parts accumulate in geological or archaeological deposits and can be directly dated using radiometric and racemisation methods they therefore offer the opportunity for high resolution palaeoenvironmental reconstructions across many time intervals all over the globe such data are important for several reasons 1 understanding past climate and environmental change provides a means of contextualising current and future climate change and ecological disturbance 2 high resolution palaeoenvironmental records are essential for constraining testing and validating global and regional numerical climate models 3 palaeoenvironmental records from biogenic carbonates can provide an environmental framework from which to understand the behavioural changes and interactions of peoples with their environment however inter and intra species differences in growth rate physiology and environmental response can cause variations in the chemical profiles of biogenic carbonates before geochemical data is employed for palaeoenvironmental reconstructions it is thus necessary to examine modern specimens of the target species or related taxa to understand how geochemical variations are influenced by local environmental conditions kinetic and vital effects this allows the generation of quantitative and more reliable proxy records of environmental change this special issue brings together the latest research on palaeoenvironmental proxy development and validation in biogenic carbonates it includes studies on marine freshwater and estuarine organisms molluscs corals and echinoderms and on traditional as well as novel geochemical proxies the papers presented here include in situ field calibration studies laboratory growth experiments as well as methodological studies into the effects of sampling and pre treatment the geographical scope is broad encompassing both the northern and southern hemispheres including south africa south america australia asia the mediterranean sea and the north atlantic

automatic regional moment tensor inversion in the european mediterranean region summary we produce fast and automatic moment tensor solutions for all moderate to strong earthquakes in the european mediterranean region the procedure automatically screens near real time earthquake alerts provided by a large number of agencies each event with magnitude m 4 7 triggers an automatic request for near real time data at several national and international data centres moment tensor inversion is performed using complete regional long period 50 100 s waveforms initially the data are inverted for a fixed depth to remove traces with a low signal tonoise ratio the remaining data are then inverted for several trial depths to find the best fitting depth solutions are produced within 90 min of an earthquake we analyse the results for the period 2000 april to 2002 april to evaluate the performance of the procedure for quality assessment we compared the results with the independent swiss regional moment tensor catalogue srmt and divided the 87 moment tensor solutions into three groups 38 a quality solutions with well resolved m w depth and focal mechanism 21 b quality solutions with wellresolved m w and 28 unreliable c quality solutions the non homogeneous station and event distributions varying noise level and inaccurate earthquake locations affected solution quality for larger events m w 5 5 we consistently obtained a quality solutions for m w 4 5 5 5 we obtained a and b quality solutions solutions that pass empirical rules mimicking the a posteriori quality for our data set are automatically disseminated

tracking crystallinity in siliceous hot spring deposits siliceous hot spring deposits sinters entrap paleoenvironmentally significant components and are used as extreme environment analogs in the search for early earth and extraterrestrial life however sinters undergo a series of textural and mineralogical changes during diagenesis that can modify and overprint original environmental signals for ancient hydrothermal settings including those close to the dawn of life these transformations have long since occurred so that study of diagenetic processes and effects is best undertaken in much younger deposits still undergoing change three young sinters preserve the entire diagenetic sequence of silica phases from opal a to quartz the 6000 to 11 500 years bp 70 years sinter at steamboat springs nevada the 1600 1900 160 years bp opal mound sinter at roosevelt hot springs utah and the 456 35 years bp deposit at sinter island taupo volcanic zone new zealand provide an opportunity to track crystallographic mineralogic and morphologic transitions of sinter diagenesis using standard and new analytical approaches worldwide sinter forms from cooling alkali chloride waters as noncrystalline opal a transforming first into noncrystalline opal a ct then paracrystalline opal ct moganite paracrystalline opal c and eventually to microcrystalline quartz in this study these changes were identified by the novel and combined application of electron backscatter diffraction x ray powder diffraction and scanning electron and optical microscopy techniques we show that mineralogical changes precede morphological and accompanied crystallographic transformations during this modification silica particles grow and shrink several times from the micron to nano meter scales via dissolution reprecipitation and recrystallization and diagenesis follows the ostwald step rule all deposits followed nearly identical diagenetic pathways with time as the only variable in the march toward physicochemically stable quartz crystals diagenesis alters original environmental signatures trapped within sinters after five silica phase changes filamentous microfossils are modified but still remain recognizable within sinter from the opal mound and steamboat springs deposits and during the opal a to opal ct silica phase transformations at sinter island therefore delineating diagenetic components and how they affect sinters is necessary to accurately identify biosignals from ancient hot spring deposits

joint inversion of insar and teleseismic data for the slip history of the 1999 izmit turkey earthquake the slip history of the izmit earthquake is investigated by jointly inverting sar and teleseismic data with a multi segment variable slip finite fault model surface offsets are used as an added constraint the highest slip values 5 to 7 m of right lateral displacement are associated with a strong central asperity surrounding the hypocenter the bilateral breaking of this main asperity which lasted about 10 sec dominates the source time function from the golcuk izmit area to lake sapanca a relatively good correspondence is observed between slip at depth and at the surface but farther to the west and to the east slip tends to be confined to the near surface slip in the easternmost part of the rupture duzce segment is not well resolved our analysis finds the insar and teleseismic data to be compatible and complementary this study shows the potential of the joint inversion of both data sets for a rapid determination of the spatio temporal history of large earthquakes

changing patterns of eastern mediterranean shellfish exploitation in the late glacial and early holocene oxygen isotope evidence from gastropod in epipaleolithic to neolithic human occupation layers at the haua fteah cave libya abstract the seasonal pattern of shellfish foraging at the archaeological site of haua fteah in the gebel akhdar libya was investigated from the epipaleolithic to the neolithic via oxygen isotope 18 o analyses of the topshell phorcus osilinus turbinatus to validate this species as faithful year round palaeoenvironmental recorder the intra annual variability of 18 o in modern shells and sea water was analysed and compared with measured sea surface temperature sst the shells were found to be good candidates for seasonal shellfish forging studies as they preserve nearly the complete annual sst cycle in their shell 18 o with minimal slowing or stoppage of growth during the terminal pleistocene early epipaleolithic locally known as the oranian with modeled dates of 17 2 12 5 ka at 2 probability douka et al 2014 analysis of archaeological specimens indicates that shellfish were foraged year round this complements other evidence from the archaeological record that shows that the cave was more intensively occupied in this period than before or afterwards this finding is significant as the period of the oranian was the coldest and driest phase of the last glacial cycle in the gebel akhdar adding weight to the theory that the gebel akhdar may have served as a refugium for humans in north africa during times of global climatic extremes mollusc exploitation in the latest pleistocene and early holocene during the late epipaleolithic locally known as the capsian c 12 7 to 9 ka and the neolithic c 8 5 to 5 4 ka occurred predominantly during winter other evidence from these archaeological phases shows that hunting activities occurred during the warmer months therefore the timing of holocene shellfish exploitation in the gebel akhdar may have been influenced by the seasonal availability of other resources at these times and possibly shellfish were used as a dietary supplement when other foods were less abundant

a simple method to establish calcite aragonite ratios in archaeological mollusc shells oxygen isotope thermometry from archaeological mollusc shells relies on preservation of the original crystal structure in particular that metastable aragonite has not undergone recrystallization to calcite conventional methods for detecting recrystallization however require large sample sizes and extensive calibration so that they cannot address variable shifts across sampling surfaces and in practice are rarely fully applied here we show that attenuated total reflectance fourier transform infrared spectroscopy ftir atr can be applied to rapidly quantify biogenic aragonite and recrystallized calcite contents in mollusc shells at a sufficient level of accuracy we established a series of calibration curves based on artificial mixtures of calcite and aragonite for comparison with archaeological samples this method offers an improvement over existing tools most importantly spectra can be determined from small samples that can be recovered for subsequent isotope analysis thus allowing assessments of crystal structure at high spatial resolution across the shell surface and within an entire assemblage

a late quaternary record of seasonal sea surface temperatures off southern africa the southern cape coastal region is important for understanding both the behavioural history of modern humans and regional and global climate dynamics because it boasts a long archaeological record and occupies a key geographical location near the intersection of two major oceans the western boundary agulhas current implicated in global heat exchange dynamics is an important modulator of southern african climates and yet we understand its past behaviour only broadly as the current itself scours the coastal shelf and marine sediment core records necessarily provide little detail numerous archaeological sites from both the late pleistocene and holocene provide the opportunity for reconstruction of near shore seasonal sst records which respond both to localized wind driven upwellings and agulhas temperature shifts corresponding in turn with terrestrial precipitation trends in the near coastal and summer rainfall regions here we present a record of seasonal ssts extending over mis5 mis4 and the holocene from serial 18o measurements of a single gastropod species turbo sarmaticus the results show that mean sst shifts accord well with global sst trends although they are larger than those recorded in the agulhas current from coarser scale marine sediment records comparison with a record of antarctic sea ice suggests that annual sst amplitude responds to antarctic sea ice extent reflecting the positioning of the regional wind systems that drive upwelling dynamics along the coast thus near shore sst seasonality reflects the relative dominance of the westerly and easterly wind systems these data provide a new climate archive for an important but understudied climate system

space and time evolution of rupture and faulting during the 1999 izmit turkey earthquake we use the records of the ground motion obtained at near fault accelerometers to study the space and time evolution of rupture and faulting during the izmit earthquake we find that the rupture propagated at the sub rayleigh speed of about 3 km sec on the western and eastern segments of the fault but that the central segment izmit sapanca lake sakarya nearly 50 km long broke at the supershear speed of about 4 8 km sec this value within the range of uncertainties is the one theoretically predicted sqrt 2 v mathrm s in fracture dynamics for stable shear crack growth at intersonic speed we infer an average fault slip of about 2 9 m over a total rupture length of about 150 km with the largest values of up to 6 m occurring in the golcuk area to the west and in the sakarya region to the east the strong motion data also indicate that the slip diminished gradually to the west beyond the hersek peninsula over about 30 km whereas it stopped abruptly at depth at the termination of the eastern karadere segment the slip duration is between 2 and 4 sec except in the hypocentral area which slipped in about 1 sec the seismic moment inferred is about 2 5 10 20 n m

mineralogical characterization of silica sinters from the el tatio geothermal field chile silica sinters deposited from alkali chloride waters in the el tatio geothermal field in northern chile 22 20 s 68 01 w have been characterized by xrd sem tg dta and ftir the dominant silica phase is opal a minor contents of opal a ct and opal ct are also present together with halite nacl sylvite kcl and realgar ass accessory phases include teruggite ca4mgas2b12o22 oh 12 12 h2o sassolite h3bo3 and detrital quartz sio2 fwhm values reflect the immature nature of the studied opal a dta heating experiments of opal a show cristobalite crystallization at 1000 c whereas dta cooling experiments show the cristobalite transformation at 200 c the total weight loss is related to changes in the sinter microtextures mineral phases and organic matter contents ftir spectra show the effects of silica maturation as consequence of the loss of trapped and absorbed water attached to silanols

non double couple earthquakes 1 theory historically most quantitative seismological analyses have been based on the assumption that earth quakes are caused by shear faulting for which the equiv alent force system in an isotropic medium is a pair of force couples with no net torque a double couple or dc observations of increasing quality and coverage however now resolve departures from the dc model for many earthquakes and find some earthquakes especially in volcanic and geothermal areas that have strongly non dc mechanisms understanding non dc earth quakes is important both for studying the process of faulting in detail and for identifying nonshear faulting processes that apparently occur in some earthquakes this paper summarizes the theory of moment tensor expansions of equivalent force systems and analyzes many possible physical non dc earthquake processes contrary to long standing assumption sources within the earth can sometimes have net force and torque components described by first rank and asymmetric sec ond rank moment tensors which must be included in analyses of landslides and some volcanic phenomena non dc processes that lead to conventional symmetric second rank moment tensors include geometrically complex shear faulting tensile faulting shear faulting in an anisotropic medium shear faulting in a heteroge neous region e g near an interface and polymorphic phase transformations undoubtedly many non dc earthquake processes remain to be discovered progress will be facilitated by experimental studies that use wave amplitudes amplitude ratios and complete waveforms in addition to wave polarities and thus avoid arbitrary assumptions such as the absence of volume changes or the temporal similarity of different moment tensor com ponents

non double couple mechanisms of microearthquakes induced by hydraulic fracturing 1 we have inverted polarity and amplitude information of representative microearthquakes to investigate source mechanisms of seismicity induced by hydraulic fracturing in the carthage cotton valley east texas gas field with vertical arrays of four and eight three component geophones in two monitoring wells respectively we were able to reliably determine source mechanisms of the strongest events with the best signal to noise ratio our analysis indicates predominantly non double couple source mechanisms with positive volumetric component consistent with opening cracks oriented close to expected hydraulic fracture orientation our observations suggest the induced events are directly the result of opening cracks by fluid injection in contrast to many previous studies where the seismicity is interpreted to be primarily shearing caused by pore pressure diffusion into the surrounding rock or associated with shear stresses created at the hydraulic fracture tip

stable isotopes and sclerochronology of the bivalve mesodesma donacium potential application to peruvian paleoceanographic reconstructions reconstructing the past enso el nino southern oscillation interannual variability requires very high resolution sea surface temperature sst proxies in order to compensate for the lack of coral archive in the eastern pacific cold tongue we studied the potentiality of the bivalve species mesodesma donacium as a sst tracer for the peruvian coast biomineralisation cycles and growth line formation in the shells are shown to be controlled by tides the sclerochronology based on fortnightly cycles allowed us to compare local sst data with high resolution shell records as a result of the high correlation between sst and aragonite delta 18 o we calculated a linear sst fractionation relationship for the 14 20 degrees c range t degrees c 17 41 1 15 3 66 0 16 delta 18 o arag pdb delta 18 o wat smow the difference from the commonly used grossman and ku 1986 grossman e l ku t l 1986 oxygen and carbon fractionation in biogenic aragonite temperature effect chemical geology 59 59 74 equation suggests the potential existence of a species dependence of vital effect within bivalves this preliminary equation allows monthly scale sst reconstructions with a 1 5 degrees c precision using m donacium archaeological shells from southern peru giving potential insights into the problem of past enso behaviour c 2005 elsevier b v all rights reserved

structural analysis and paleoenvironmental potential of dog cockle shells glycymeris glycymeris in brittany northwest france to compensate for the lack of high resolution data on variation in environmental parameters before the establishment of monitoring networks we evaluated dog cockle shells glycymeris glycymeris mollusca bivalvia as archives for temperature and climate perturbations such as the north atlantic oscillation nao over the last 50 years oxygen isotope compositions were measured from annual increments of shells collected from the bay of brest and the chausey islands in northwestern france simultaneously sclerochronological analyses were performed on the same shells oxygen isotopic ratios measured in shells collected from the bay of brest were compared to in situ temperature and salinity data from monitoring stations and buoys in order to build a specific paleotemperature equation r2 0 87 p 0 001 for the dog cockle the specific equation was used to estimate sea surface temperatures around the chausey islands between 1966 and 1994 standardized growth indices sgi calculated through sclerochronological methods were strongly correlated to oxygen isotope derived temperatures the sgi however did not capture the area s predominant climate pattern the nao this study demonstrates that dog cockle shells can be used for long term high resolution reconstructions of past sea surface temperatures

progressive glacial retreat in the southern altiplano uturuncu volcano 22 s between 65 and 14 ka constrained by cosmogenic 3he dating this work presents the first reconstruction of late pleistocene glacier fluctuations on uturuncu volcano in the southern tropical andes cosmogenic 3he dating of glacial landforms provides constraints on ancient glacier position between 65 and 14 ka despite important scatter in the exposure ages on the oldest moraines probably resulting from pre exposure these 3he data constrain the timing of the moraine deposits and subsequent glacier recessions the uturuncu glacier may have reached its maximum extent much before the global lgm maybe as early as 65 ka with an equilibrium line altitude ela at 5280 m then the glacier remained close to its maximum position with a main stillstand identified around 40 ka and another one between 35 and 17 ka followed by a limited recession at 17 ka then another glacial stillstand is identified upstream during the late glacial period probably between 16 and 14 ka with an ela standing at 5350 m this stillstand is synchronous with the paleolake tauca highstand this result indicates that this regionally wet and cold episode during the heinrich 1 event also impacted the southern altiplano the ela rose above 5450 m after 14 ka synchronously with the bolling allerod

imaging hydraulic fractures in a geothermal reservoir 1 an injection experiment at the coso geothermal field in eastern california in march 2005 caused a swarm of microearthquakes that was recorded by a local network of three component digital seismometers high resolution relative hypocenter locations propagated upward and northward on a 700 600 m plane striking n 20 e and dipping 75 to the wnw this plane is a pre existing fault whose surface projection coincides with an active scarp the earthquakes have similar non double couple mechanisms that involve volume increases and the fault plane bisects their dilatational fields implying a process dominated by tensile failure the source types require the additional involvement of subsidiary shear faulting however events before and after the swarm have variable orientations and volume changes of both signs similar tensile shear failure is observed in some natural microearthquake swarms for example at long valley caldera california its occurrence under low fluid pressure may imply a heterogeneous stress field or the induction of thermal stresses by introduction of cold fluid

coseismic and early post seismic slip associated with the 1999 izmit earthquake turkey from sar interferometry and tectonic field observations summary we use combined tectonic field observations and sar data to determine an improved model of the slip associated with the 1999 izmit earthquake which ruptured the north anatolian fault at the eastern end of the sea of marmara the leading goal is to understand the main features of the coseismic and post seismic deformation which are captured together in the sar data to achieve this we make a critical analysis of the ers1 2 sar data which allows atmospheric effects to be identified and removed we also use detailed field mapping and measurements of the earthquake surface rupture dislocations in elastic half space and a forward modelling strategy allow us to obtain a slip model by steps a trial and error approach is combined with conventional inversion techniques to determine the slip in the different regions of the fault the sar data are well explained with three main zones of high slip along the fault releasing a total moment of 2 3 10 20 nm mw 7 6 which is higher than the seismological estimates 1 7 2 0 10 20 n m the inhomogeneous slip distribution correlates with fault segments identified at the surface the izmit rupture appears to have extended 30 km west of the hersek peninsula into the sea of marmara with slip tapering fro m2mt ozero the western end of the rupture is located 40 km sse from istanbul we show that some features seen near to mudurnu and gevye and previously interpreted as slip on secondary faults are explained mostly as atmospheric effects correlated with the topography using our approach and the available gps data we obtain a slip model that represents the coseismic slip alone which suggests that the moment release during the main shock was 1 9 10 20 nm mw 7 5 consistent with the seismological estimates we conclude that the sar data include the effects of 2 m of fast after slip during the month following the main shock within a zone of the fault located 12 24 km below the epicentral region near the hypocentre at a depth of 18 km the fault appears to have experienced dynamic slip of 1 m associated with the main shock followed by 2 m of rapidly decelerating post seismic shear during the following month we suggest that the distribution of heterogeneous slip and loading along the different fault segments may be important factors controlling the propagation of large earthquake ruptures along the north anatolian fault

microbial silica interactions in icelandic hot spring sinter possible analogues for some precambrian siliceous stromatolites silicified deposits such as sinters occur in several modern geothermal environments but the mechanisms of silicification and crucially the role of microorganisms in their construction are still largely unresolved detailed examination of siliceous sinter in particular sections of microstromatolites growing at the krisuvik hot spring iceland reveals that biomineralization contributes a major component to the overall structure with approximately half the sinter thickness attributed to silicified microorganisms almost all microorganisms observed under the scanning electron microscope sem are mineralized with epicellular silica ranging in thickness from 5 lm coatings on individual cells to regions where entire colonies are cemented together in an amorphous silica matrix tens of micrometres thick within the overall profile there appears to be two very distinct types of laminae that alternate repeatedly throughout the microstromatolite microbial layers are predominantly consisting of filamentous intact vertically aligned biomineralized cyanobacteria identified as calothrix and fischerella sp and weakly laminated silica layers which appear to be devoid of any microbial component the microbial layers commonly have a sharply defined base overlying the weakly laminated silica and a gradational upper surface merging into the weakly laminated silica these cyclic laminations are probably explained by variations in microbial activity active growth during spring summer allows the microorganisms to keep pace with silicification with the cell surfaces facilitating silicification while during their natural slow growth phase in the dark autumn winter months silicification exceeds the bacteria s ability to compensate i e grow upwards at this stage the microbial colony is probably not essential to microstromatolite formation with silicification presumably occurring abiogenically when conditions once again become favourable for growth recolonization of the solid silica surface by free living bacteria occurs cell motility is not responsible for the laminations we have also observed that microbial populations within the microstromatolite some several mm in depth appear viable i e they still have their pigmentation the trichomes are not collapsed cell walls are unbroken cytoplasm is still present and they proved culturable this suggests that the bulk of silicification occurred rapidly probably while the cells were still alive surprisingly however measurements of light transmittance through sections of the microstromatolite revealed that photosynthetically active light pal only transmitted through the uppermost 2 mm therefore the deeper microbial

depositional facies and diagenetic alteration in a relict siliceous hot spring accumulation examples from yellowstone national park u s a abstract siliceous precipitates from portions of an 11 m long core drilled through a relict yellowstone hot spring deposit provide valuable insights into the diagenetic facies in this hydrothermal environment most of the core consists of relatively low temperature siliceous sinter containing abundant plant diatom and microbial fossilized remains derived from the distal debris apron and discharge channel flowpath of the hot spring a few intervals contain stromatolitic horizons analogous to modern siliceous pool margin and discharge channel flowpath facies despite the abundance of silicified microbial remains e g silicified stromatolitic horizons as well as individual filamentous microbes diatoms distinctive organic biomarkers are not preserved in the core the apparent lack of distinctive organic biomarkers is attributable to pervasive diagenetic alteration in the presence of high temperature chemically reactive fluids numerous diagenetic features have been superimposed on the siliceous sinter especially considering the relatively shallow depths of burial the uppermost interval 0 to 1 2 m consists of highly porous siliceous sinter opal a and interbedded travertine amorphous manganese oxides and sparry calcite cements are present and are irregularly distributed throughout this interval below is a diagenetic facies 4 8 to 5 3 m that consists of opal ct and minor chalcedony the most pervasive diagenetic alteration in the core is the 6 8 to 11 2 m depth interval where abundant zeolites mordenite heulandite bladed cristobalite lepispheres chalcedony cements and calcite veins are present judging by the assemblage of plant and diatom remains most of this pervasive alteration is superimposed on relatively low temperature siliceous sinters and is likely the result of migration of hot waters through this interval the paragenesis of all these intervals is very complex involving numerous episodes of mineral precipitation and dissolution this diagenetic alteration is facilitated by the porous nature of the siliceous sinter thermal convection of superheated fluids or steam strongly oxidizing spring waters and fluctuating hydrochemical regimes rapid dissolution and or replacement of organic matter indicates that standard morphological means e g petrographic identification of body fossils may be the best method by which to identify that organisms were previously present in ancient hot spring accumulations

three dimensional seismic structure and moment tensors of non double couple earthquakes at the hengill grensdalur volcanic complex iceland summary the volcanic and geothermal areas of iceland are rich sources of non double couple non dc earthquakes a state of the art digital seismometer network deployed at the hengill grensdalur volcanic complex in 1991 recorded 4000 small earthquakes we used the best recorded of these to determine 3 d v p and v p v s structure tomographically and accurate earthquake moment tensors the v p field is dominated by high seismic wave speed bodies interpreted as solidified intrusions a widespread negative 4 per cent v p v s anomaly in the upper 4 km correlates with the geothermal field but is too strong to be caused solely by the evect of temperature upon liquid water or the presence of vapour and requires in addition mineralogical or lithological diverences between the geothermal reservoir and its surroundings these may be caused by geothermal alteration well constrained moment tensors were obtained for 70 of the best recorded events by applying linear programming methods to p and s wave polarities and amplitude ratios about 25 per cent of the mechanisms are within observational error consistent with dc mechanisms consistent with shear faulting the other 75 per cent have significantly non dc mechanisms many have substantial explosive components one has a substantial implosive component and the deviatoric component of many is strongly non dc many of the non dc mechanisms are consistent within observational error with simultaneous tensile and shear faulting however the mechanisms occupy a continuum in source type parameter space and probably at least one additional source process is occurring this may be fluid flow into newly formed cracks causing partial compensation of the volumetric component studying non shear earthquakes such as these has great potential for improving our understanding of geothermal processes and earthquake source processes in general

rupture process of the 1999 kocaeli turkey earthquake estimated from strong motion waveforms the multiple time window linear waveform inversion is applied to study the source process of the 1999 kocaeli turkey earthquake using strong motion data two peculiar observations characterize this event the first one is a conflicting observation of the long surface ruptures and short source duration resulting from the observed strong motion waveforms the second is an anomalously short s p time observed at a station skr considering its hypocentral distance a supershear rupture propagation ellsworth and celebi 1999 and the p wave triggering of an asperity anderson et al 2000 were both proposed to explain the record at skr our waveform inversion study is aimed to examine these possibilities in order to clarify the relation between the spatial distribution of the surface ruptures and coseismic slips we divide the assumed fault plane into three parts and look for the first time window front propagation velocity propagation velocity of triggering front of the first time window at each subfault in each part by performing numerous inversions changing the first time window front propagation velocity separately in each part and selecting the best first time window propagation velocities that give largest variance reduction at the same time appropriate smoothness of spatiotemporal slip distribution is searched for by performing inversions with different strength of smoothing constraints against the observational equations and judging the relative appropriateness of inversion results in terms of the akaike s bayesian information criterion the best source model is characterized by an asperity that is about 35 km east of the epicenter and near a segment boundary at sapanca lake triggered by the first time window front with 5 8 km sec close to p wave velocity the time progression of the rupture suggests a scenario where a p wave arriving from the hypocenter or somewhere around the hypocenter triggered the second largest asperity near the junction of the segments at sapanca lake which is a preferable interpretation the first time window propagation velocities west of the hypocenter and east of skr are expected to be 3 0 km sec manuscript received 20 august 2000

corals paleotemperature records and the aragonite calcite transformation oxygen isotopic records from corals play an increasing role in paleoclimatic research and climatic modeling proxy records of sea surface temperature are produced by isotopically analyzing samples drilled from aragonitic caco 3 coral skeletons however drilling aragonite causes a polymorphic inversion to calcite accompanied by 18 o enrichment the isotopic enrichment may occur through atmospheric exchange co 2 degassing or fractionation during digestion regardless of the mechanism dry drilling produced isotopic shifts as large as 0 8 corresponding to an erroneous temperature decrease of 3 c this error is larger than the global temperature rise since the industrial revolution and a substantial part of the global temperature variation over the past 10 ka because the isotopic shift is inconsistent and can occur without the production of measurable calcite detecting and correcting the isotopic shift may be difficult

sea surface temperature fluctuations during the holocene off the south coast of africa implications for terrestrial climate and rainfall models of southern african palaeoclimate implicate surface atmospheric circulation anoma lies as forcing large scale changes during the late quaternary the available proxy data are insufficient to test the models since they provide information about temperature and rainfall rather than surface circulation a conceptual model is proposed which links coastal ocean temperatures with atmospheric circulation and allows a history of surface circulation to be inferred from sea temperature data a holocene sea surface temperature sst record was constructed by measuring the oxygen isotope composition of marine mollusc shells preserved in an archaeological cave deposit on the coast of the eastern agulhas bank southern africa radiocarbon dating of individual shells allowed definition of the timing and timespan of events in the record by serially sampling along the growth axis of each shell information was obtained about intra annual variability as well as millennial scale trends during the early holocene th