ocean drilling program leg 112 peru continental margin part 1 tectonic history studies of ocean drilling program leg 112 cores and geophysical data define early eocene quaternary normally faulted continental sediment sequences across the peru margin to the middle slope and a 15 km wide late miocene quaternary accretionary complex beneath the lower slope the eocene shelf and upper slope sea floor were eroded during the oligocene and in middle miocene the seaward part had subsided to lower slope depths this subsidence and the missing paleogene continental slope indicate tectonic erosion during normal plate convergence subduction of the nazca ridge locally accelerated tectonic erosion leaving a scarp but no associated compressional structure nearby late miocene sediment accreted against the erosional scarp local tectonic mechanisms of forearc basin subsidence are suggested by the rapid subsidence of a late miocene forearc basin and stability of the adjacent one despite similar histories of plate convergence

sediment dewatering in the makran accretionary prism abstract sediments within the makran accretionary prism are considerably more compacted than the material entering the subduction zone due to the additional tectonic stresses resulting from plate convergence and accretionary processes tectonic compaction of the offscraped sediments has been documented by deriving in situ porosities in the upper 4 km from their seismic velocities wide angle seismic reflection refraction profiles were analysed from a transect crossing both the makran accretionary prism and the undeformed abyssal plain sediments to the south the 6 7 km thick abyssal plain sediments exhibit normal compaction with depth the sediments incorporated into the accretionary prism have higher seismic velocities at all depths corresponding to reductions in porosity of 30 40 mapping the porosity depth gradient across the prism shows that there is a marked change in porosity at the seaward toe of the prism the frontal fold there is then little further change until further folding begins to occur 70 km landward of the toe the dewatering and consolidation of the sediments is an important control on deformation occurring within the sedimentary prism

subduction induced pore fluid venting and the formation of authigenic carbonates along the cascadia continental margin implications for the global ca cycle abstract pore fluid venting associated with subduction induced sediment deformation causes precipitation of calcium carbonate as prominent carbonate chimneys or cement in the accreted sediments across the active continental margin off oregon and washington a depletion of interstitial ca 2 with a maximum decrease of 50 relative to seawater ca 2 over only 1 5m depth and reduction in porosity in the deformed sediments suggest that interstitial ca 2 is removed to form calcium carbonate cement in contrast the pore waters of the undeformed abyssal plain sediments show no depletion in dissolved ca 2 they are either enriched to a maximum of 5 or show no change in dissolved ca 2 here the background level of caco 3 content in the sediment is only 0 1 to 1 calcium carbonate precipitation in the deformed sediments probably occurs as the result of upward migration and oxidation of biogenic methane and of the increase in carbonate saturation due to release of excess pore pressure during fluid venting upward advection of fluids at rates of 1 28 cm y 1 is predicted from diffusion advection reaction models applied to the downcore concentration profiles of dissolved ca 2 and nh 4 in the tectonically deformed sediments the range of predicted flow rates is related to the type of calcium carbonate lithification i e slow rates generate cement and fast rates generate chimneys carbonate mineral precipitation associated with pore fluid venting requires direct transfer of ca 2 from the oceanic basement to the accretionary complex such a mechanism leads us to propose that the accretionary complexes of the global plate subduction zones are a major sink for crustal ca 2 a global flux of crustal ca 2 that is removed by carbonate mineral precipitation may be as muc3 as the hydrothermal ca input this significant ca flux not previously considered in the global geochemical budget implies that pore fluid venting in subduction zones may also act as a global sink or source for other elements

tectonic implications of a dense continuous gps velocity field at yucca mountain nevada 1 a dense continuous gps network was established in the yucca mountain area in 1999 to provide the most reliable measurements possible of geodetic strain patterns across the nation s only proposed permanent repository for high level radioactive waste the network lies astride a boundary between the geodetically stable central great basin and the active western great basin which at the latitude of yucca mountain is undergoing distributed right lateral shear at a rate of 60 nstrain yr monitoring from 1999 to 2003 3 75 years yields a velocity field characterized by nearly homogenous n20 w rightlateral shear of 20 2 nstrain yr net velocity contrast of 1 2 mm yr across a 60 km aperture in the vicinity of the proposed repository site comparison of time series of continuous results with earlier campaign surveys indicating 50 nstrain yr of westnorthwest extension from 1991 to 1997 suggests that the more rapid rates were in part transient motions associated with the 1992 ms 5 4 little skull mountain earthquake postseismic motions do not appear to affect the 1999 2003 velocity field in either campaign or continuous data the magnitude of the velocity contrast across the area the overall linearity of the gradient and the large area of undeforming crust to the east of yucca mountain are difficult to explain by elastic bending of the crust associated with the death valley fault zone a major right lateral strike slip fault about 50 km west of the repository site these observations along with apparent local variations in the velocity gradient suggest that significant right lateral strain accumulation with displacement rate in the 1 mm yr range may be associated with structures in the yucca mountain area the absence of structures in the area with equivalent late quaternary displacement rates underscores the problem of reconciling discrepancies between geologic and geodetic estimates of deformation rates index terms 1208 geodesy and gravity crustal movements intraplate 8110 1243 geodesy and gravity space geodetic surveys 8107 tectonophysics continental neotectonics 8109 tectonophysics continental tectonics extensional 0905 keywords geodesy tectonics yucca mountain

retrospective investigation of geophysical data possibly associated with the ms8 0 wenchuan earthquake in sichuan china abstract the ms8 0 wenchuan earthquake is one of the most catastrophic earthquakes occurred recently although the geophysical network around the epicentral region is not dense enough partially due to the inactivity of the longmenshan fault the retrospective investigation of geophysical data in and around the epicentral region would be helpful for strengthening the understanding of the seismogenic process of the wenchuan earthquake this paper summarized some preliminary results of the retrospective investigation especially focusing on the seismic and electromagnetic data possibly associated with the wenchuan earthquake and its aftershocks the spatio temporal investigation of the seismicity changes indicated that there is an intermediate term seismic quiescence around the epicenter during 2006 2007 the electromagnetic data also showed some anomalous changes including co seismic electromagnetic changes which may be related with the wenchuan earthquake and its aftershocks although further work is definitely required to enhance the reliability of the relationship between the above geophysical changes and the seismogenic process the above preliminary results would provide some useful information for the related study and stimulate further validation study on the precursors of the wenchuan earthquake

variation of lithium isotope composition in the marine environment a preliminary report the li isotopic compositions of ocean waters lake water hydrothermal solutions altered and unaltered basalts have been determined using the technique of thermal ionization mass spectrometry of lithium tetraborate seawater appears to be homogeneous in li isotopic composition the mean delta sup 6 li value is minus 32 3 plus minus 0 5 per thousand relative to an isotopic standard three lakes studied lake tanganyika caspian sea and dead sea yield delta sup 6 li similar to the seawater isotopic composition a fresh basalt glass from 21 degree n east pacific rise displays a delta sup 6 li value of minus 4 7 per thousand a hydrothermal solution from a 21 degree n vent field has delta sup 6 li of minus 10 per thousand indicating incomplete extraction of li from the igneous minerals or partial retention in secondary phases the alteration margin of a basalt from the mid atlantic ridge has delta sup 6 li of minus 8 4 per thousand the isotope data of submarine basalts suggest preferential removal of sup 6 li from seawater into alteration minerals during low temperature weathering the delta sup 6 li values of two hydrothermal solutions from guaymas basin were found to be minus 5 per thousand and minus 10 per thousand the results can be interpreted as the net effect of li addition from basalt and sediments and incorporation in hydrothermal precipitates as the hydrothermalmore fluids interact with basin sediments the observed enrichment of sup 7 li in seawater relative to submarine hydrothermal solutions its principal li input is tentatively attributed to isotopic fractionation associated with low temperature alteration of sea floor basalt and incorporation in authigenic sediments it appears that the li isotope system may have characteristics that can resolve the mass balance of li in the ocean less

lithium in waters of a polar desert abstract lithium li concentrations were measured in a series of stream and lake samples from a cold dry desert the mcmurdo dry valleys mdv in southern victoria land antarctica li geochemistry has been of great interest and utility in part because of its solubility and mobility during rockwater interactions in general the values determined for the streams and the dilute lake waters in this polar desert environment are similar to those found in temperate streams and lakes the source of li to these waters is a combination of marine aerosol and crustal weathering within the stream channels the hypersaline hypolimnion of lake bonney has extremely high concentrations of li which has been concentrated via a previous drawdown of the lake and its subsequent evapoconcentration the different distributions of li within the lakes is also due to past climatic changes and their effects on the chemical evolution of the lakes the high relative mobility of li controls its distribution within the aquatic systems of this cold desert environment

the behavior of lithium and its isotopes in oilfield brines evidence from the heletz kokhav field israel twenty four brine samples from the heletz kokhav oilfield israel have been analyzed for chemical composition and li isotope ratios the chemical composition of the brines together with geological evidence suggests derivation from messinian seawater by evaporation that proceeded well into the gypsum stability field but failed to reach the stage of halite crystallization the present salinity of the samples 18 47 g cl l was achieved by dilution of the original evaporitic brine by local fresh waters like brines from other sedimentary basins the li cl ratios in the heletz kokhav samples show a prominent li enrichment five fold to eight fold relative to modern seawater the isotopic ratios of li expressed in the 6 li notation vary from 26 3 to 17 9 all values being significantly higher than that of modern seawater 32 irrespective of their corresponding li concentration 1 0 2 3 mg l the isotopic composition of li and the li cl ratio in the oilfield brines were acquired in two stages a the original evaporated seawater gained isotopically light li during the diagenetic interaction between the interstitial messinian brine and the basin sediments a parent brine with an elevated li cl ratio was formed the brine was later diluted in the oilfields b the 6 li values of the final brines were determined during epigenetic interaction with the heletz kokhav aquifer rocks at the same time the li cl ratio inherited from stage a remained largely unchanged this work represents the first use of lithium isotopic composition to elucidate the origin and evolution of formation waters in sedimentary basins copyright 2002 elsevier science ltd

halogen and 129i systematics in gas hydrate fields at the northern cascadia margin iodp expedition 311 insights from numerical modeling we measured halogen concentrations and i 129 i ratios in five drilling sites of integrated ocean drilling program expedition 311 offshore vancouver island canada in order to identify potential sources of fluids and methane in gas hydrate fields iodine is dominated by organic decomposition and transports with fluids in reducing environments and the presence of the cosmogenic radioisotope i 129 t 1 2 15 7 ma allows the age determination of organic sources for iodine here we report halogen concentrations in 135 pore water samples i concentrations in 48 sediment samples and i 129 i ratios measured in a subset of 20 pore water samples most i 129 i ratios fall into a range around 500 x 10 15 corresponding to a minimum age of 25 ma and the lowest ratio of 188 x 10 15 t min 47 ma was observed at 208 m below sea floor mbsf in site 1326 these ages are considerably older than that of the local sediments in the gas hydrate fields and that of the subducting sediments on the juan de fuca plate indicating that old accreted sediments in the accretionary wedge contribute a significant amount of iodide and by association of methane to the gas hydrate occurrences a geochemical transport reaction model was applied to simulate the advection of deeply sourced fluids and the release of iodide bromide and ammonia in the host sediments due to organic matter degradation the model was first tested with data from two well studied areas ocean drilling program site 1230 peru margin and site 1245 hydrate ridge the model results for the expedition 311 sites indicate that the in situ release of young iodine is relatively minor in comparison to the contribution of migrating fluids carrying large amounts of old iodine from deep sources the comparison between the sites demonstrates that the total organic content has a strong effect on the rate of in situ iodine release and that lateral flows along fractures can have a significant influence on pore water chemistry especially at the cascadia margin the iodine results indicate that mobilization and transport of methane from sources in the upper plate of active margins is an important process which can also play a substantial role in the formation of gas hydrate fields

the transformation of sediment into rock insights from iodp site u1352 canterbury basin new zealand abstract at integrated ocean drilling program iodp expedition 317 site u1352 east of the south island new zealand we continuously cored a 1927 m thick holocene to eocene section where we can uniquely document downhole changes in induration and lithification in siliciclastic to calcareous fine grained sediment using a wide range of petrological physical property and geochemical data sets porosity decreases from around 50 at the surface to 5 10 at the base of the deepest hole with a corresponding increase in density from 2 to 2 5 g cm 3 there are progressive bulk mineral changes with depth including an increase in carbonate and decrease in quartz and clay content grain compaction is first seen in thin section at 347 m below sea floor and intensifies downhole pressure solution chemical compaction begins at 380 m and is common below 1440 m with stylolite development below 1600 m and sediment injection features below 1680 m porewater geochemistry and petrographic observations document two active zones of cementation one shallow eogenetic down to 50 m as evidenced by micritic nodules and pore water geochemistry driven by methane oxidation by sulfate and another burial related cementation zone mesogenetic starting at 300 m a transitional zone occurs between 50 and 300 m our results quantify downhole diagenetic changes and verify depth estimates for these processes inferred from outcrop studies and provide an actualistic example of cementation and compaction trends in a slope setting

lithium in foraminiferal shells implications for high temperature hydrothermal circulation fluxes and oceanic crustal generation rates the lithium content of planktonic foraminiferal calcite has been determined to evaluate temporal variability of seawater li concentrations over the past 116 m y mean foraminiferal calcite lithium calcium in each time interval is no more than 16 greater nor 25 less than the mean li ca of all samples li ca minima are observed for samples from 50 60 m y and 80 90 m y with li ca about 25 lower than in adjacent time intervals at no time during the past 40 m y does mean li ca appear to be higher than that at present subject to the limitations imposed by sample coverage and diagenesis a similar conclusion holds for the past 116 m y coupled with an oceanic mass balance model for li these data suggest that 1 oceanic li concentrations and therefore high temperature hydrothermal circulation fluxes during the past 40 m y and perhaps the past 100 m y have not been more than perhaps 30 40 greater than at present for intervals any longer than a million years at most and 2 these fluxes werenot a factor of two higher 100 m y ago by inference variations in oceanic crustal generation rates over these time periods are similarly limited decreases in hydrothermal circulation fluxes and crustal generation rates or fluctuations up to 20 in these rates of a few million years duration arenot necessarily ruled out by the li ca data the lack of variability in li ca over time is not unequivocal evidence that hydrothermal fluxes have not varied because the rates of removal processes may be linked to changes in input fluxes

marine geochemical cycles of the alkali elements and boron the role of sediments abstract we have analysed the concentrations of li k rb cs and b and the isotopic ratios of li and b of a suite of pore fluids recovered from odp sites 1037 leg 169 escanaba trough and 1034 leg 169s saanich inlet in addition we have analysed dissolved k rb and cs concentrations for estuarine mixing of the ganges brahmaputra river system together these data sets have been used to assess the role of sediments in the marine geochemical cycles of the alkali elements and boron uptake onto clay minerals during estuarine mixing removes 20 30 of the riverine input of dissolved cs and rb to the oceans prior to this study the only other recognised sink of rb and cs was uptake during low temperature alteration of the oceanic crust even with this additional sink there is an excess of inputs over outputs in their modern oceanic mass balance pore fluid data show that li and rb are transferred into marine sediments during early diagenesis however modeling of the li isotope systematics of the pore fluids from site 1037 shows that seawater li taken up during marine sedimentation can be readily returned to solution in the presence of less hydrated cations such as nh4 this process also appears to result in high concentrations of pore fluid cs relative to local seawater due to expulsion of adsorbed cs from cation exchange sites flux calculations based on pore fluid data for a series of odp sites indicate that early diagenesis of clay sediments removes around 8 of the modern riverine input of dissolved li although nh4 rich fluids do result in a flux of cs to the oceans on the global scale this input only augments the modern riverine cs flux by 3 nevertheless this may have implications for the fate of radioactive cs in the natural environment and waste repositories

magnetic and electric fields associated with changes in high pore pressure in fault zones application to the loma prieta ulf emissions we determined the electric and magnetic fields generated during failure of faults containing sealed compartments with pore pressures ranging from hydrostatic to lithostatic levels exhumed fault studies and strain measurement data limit the possible size of these compartments to less than 1 km in extent rupture of seals between compartments produces rapid pore pressure changes and fluid flow and may create fractures that propagate away from the high pressure compartment along the fault face nonuniform fluid flow results from pressure decrease in the fracture from crack generated dilatancy partial blockage by silica deposition and clearing as pressure increases a direct consequence of this unsteady fluid flow may be associated transient magnetic signals caused by electrokinetic piezomagnetic and magnetohydrodynamic effects models of these processes for fault geometries with 1 km high pressure compartments show that electrokinetic effects are several orders of magnitude larger than the other mechanisms the electrokinetic signals produced by this unsteady flow are comparable in magnitude and frequency to the magnetic signals observed prior to the ml 7 1 loma prieta earthquake of october 18 1989 provided fracture lengths are less than 200 m

detection of ultra low frequency emissions connected with the spitak earthquake and its aftershock activity based on geomagnetic pulsations data at dusheti and vardzia observatories abstract ulf electromagnetic emissions from the spitak armenia earthquake site have been detected observations were carried out at the dusheti and vardzia georgia observatories at distances 120 200 km from the epicentre in a frequency range 0 005 1 hz it is shown that the emission appears several hours before the main shock and some of the powerful aftershocks and is not connected with geomagnetic pulsations of magnetospheric sources

secondary grain size effects on li and cs concentrations and appropriate normalization procedures for coastal sediments the sediment grain size effect gse a fundamental factor relevant to the interpretation of elemental concentrations and isotopic compositions has been normalized using conservative elements such as aluminum al cesium cs and lithium li c al c cs c li which serve as proxies for the natural metal controlling variables of grain size mineralogy and organic matter however a secondary gse reportedly remains even after compensation by the al normalization procedure particularly for the concentrations of transition metals c t m this secondary effect also occurred in the c li c cs c al ratios of the korean coastal sediments examined in this study the primary and secondary gses on cs and li concentrations can be explained by the quartz dilution effect and the cs and li incorporation effect of phyllosilicate minerals respectively based on a model involving three component end members a cs and li free sand dominated sediment component consisting mostly of quartz and feldspar a cs and li bearing silt dominated component of mica and a cs and li enriched clay dominated component of illite although the primary and secondary gses on the concentrations of transition metals particularly cu and ni in coastal sediments might be normalized by dividing the metal concentrations by the square of the al concentration c t m c al 2 the gses can also be normalized by dividing the concentrations by the exact cs or li concentration c t m c cs c 2016 elsevier ltd all rights reserved

iodine ages of pore waters at hydrate ridge odp leg 204 cascadia margin implications for sources of methane in gas hydrates hydrate ridge off the coast of oregon usa is a prime example for gas hydrate occurrences in active margin settings it is part of the cascadia margin and was the focus of ocean drilling program odp leg 204 which successfully recovered fluids from nine sites from the southern part of the ridge iodide concentrations in pore fluids associated with gas hydrates are strongly enhanced by factors up to 5000 compared to seawater which allows the use of this biophilic element as tracer for organic source regions we applied the cosmogenic isotope 129 i t 1 2 15 7 ma system to determine the age of the organic source formation responsible for the iodide enrichment in all sites at odp leg 204 129 i i ratios were found to decrease with depth to values around 250 10 15 corresponding to minimum ages of 40 ma but in several sites maxima in the 129 i i ratios point to the local addition of young iodide the results indicate that a large amount of iodide was derived from deep accreted sediments of eocene age and that additional source regions provide iodide of late miocene age the presence of old iodide in the pore waters suggests that fluid pathways are open to allow transport over large distances into the gas hydrate fields the strong correlation between iodide and methane in hydrate fields coupled with the similarity in transport parameters in aqueous solutions suggests that a large fraction of methane in gas hydrates also has old sources and is transported into the present locations from source regions of eocene age

porosity of sediments in accretionary prisms and some implications for dewatering processes rapid dewatering largely through loss of porosity is one of the most striking changes affecting deformed sediments in accretionary prisms analysis of porosity from sample and seismic data confirms that porosity in accretionary prisms is significantly less than that in basinal strata of similar lithology more specifically the porosity depth gradient increases arcward across the prism until porosities less than 10 occur within a few kilometers of the surface in deeper parts of the prism dewatering and volume reduction occur not only during loss of porosity but also during dehydration and metamorphic reactions calculations involving volume change lead us to define a function which reflects total volume reduction the distribution of the relative intensity of dewatering within the prism can be calculated from the porosity contours and trajectories of sediment elements an initial attempt indicates that in the toe region the rate of dewatering is accelerated at depth relative to the basinal section and may be greatest near the base of the prism toward the rear of the prism the maximum rate of dewatering occurs at progressively shallower depths several lines of evidence suggest that in addition to gradual diffuse dewatering localized zones of strong dewatering are associated with zones of intense shear this model of shear dewatering based on critical state soil mechanics suggests that sediments adjacent to the basal decollement should be strongly dewatered

fluid expulsion from the dvurechenskii mud volcano black sea part i fluid sources and relevance to li b sr i and dissolved inorganic nitrogen cycles significant sediment ocean chemical fluxes are produced by the expulsion of sedimentary fluids at continental margins although such fluxes could play a role in global geochemical cycles few quantitative estimates of their global or even regional significance exist we carried out a pore water geochemical study of fluids expelled from the dvurechenskii mud volcano dmv in the black sea with the aim of understanding the role played by mud volcanoes in black sea geochemical cycles the dmv is presently expelling highly saline fluids particularly enriched in geochemically important species such as li 1 5 mm b 2 17 mm ba2 0 57 mm sr2 0 79 mm i 0 4 mm and dissolved inorganic nitrogen din 22 mm a combination of geochemical indicators shows that this geochemical signature was acquired via organic matter and silicate alteration processes in the subsurface down to 3 km depth and near surface gas hydrate formation we used a simple transport model to estimate the benthic fluxes of these solutes at the dmv our results show that the dmv is expelling fluids at a rather low seepage rate 8 25 cm year 1 resulting in a total water flux of 9 4 10 5 km3 year 1 this gentle regime of fluid expulsion results in li b sr2 i and din fluxes between 3 8 104 and 2 1 106 mol year 1 surface biogeochemical processes affect the benthic fluxes of ba2 such that the deep ba2 flux is completely consumed through the precipitation of authigenic barite baso4 in surface sediments the black sea i cycle is likely to be affected by mud volcanism if the 50 known black sea mud volcanoes share the rather sluggish activity of the dmv mud volcano fluxes of li b sr and din instead are too small to affect black sea geochemical cycles on a global scale mud volcanism could play a role in the marine cycles of li b sr i and din if current estimates of mud volcano abundance are correct

fractal analysis of ulf geomagnetic data associated with the guam earthquake on august 8 1993 this paper presents a fractal analysis of the ulf electromagnetic data obtained at guam observatory during a strong ms 8 0 earthquake occurred on august 8 1993 near the guam island we have already reported the presence of seismogenic ulf emissions for this quake hayakawa et al grl 1996 the chosen period covered four months before and two months after the earthquake it was found that the spectrum of emissions at noon exhibited a power law behavior f which is typical for self organized critical dynamics the slope of the spectrum in the noon sector fluctuates in a range from 2 5 to 0 7 with a tendency to gradually decrease during the process of the earthquake preparation we consider this to be a candidate for a precursory signature the similar effect was found for the night sector we suggest that the focal zone was at the critical stage of self organized criticality process before the quake related to active microfracturing processes followed by the generation of ulf emissions as we detected

reconstructing the history of fluid flow at cold seep sites from ba ca ratios in vesicomyid clam shells hydrogen sulfide discharge at cold seep sites is recorded as enrichment in the barium to calcium ba ca ratio in shells of vesicomyid clams collected live from cold seeps in monterey canyon and the cascadia margin a direct relationship between increased ba fluxes from cold seeps and ba incorporation into shells was established for the cascadia margin site for the monterey canyon site a 2 yr episode of high fluid flow centered on 1992 was inferred from coherent changes in the ba ca profiles of threecalyptogena kilmerishells comparison with precipitation and d 18 o data indicates that this high flow period may have been driven by an increase in rainfall after the 1988 1990 california drought high resolution records preserved in clam shells are shown to be useful in elucidating characteristics history and possible mechanisms driving fluid discharge at continental margin seeps thus establishing their potential use as paleotracers of fluid seepage events an extensive set of geophysical and geochemical measurements is currently available to document the flow and expulsion of fluids at transform and convergent margins it is now recognized that such fluid discharge has far reaching implications that include hydrocarbon prospecting benthic ecosystem structure and function and groundwater research moore 1999 at present we are unable to incorporate geochemical data from cold seeps to models quantifying their effects on marine geochemical budgets because we lack a clear understanding of the spatial and temporal variability of these systems and of the mechanisms responsible for the advective transport however vent macrofauna may afford such an opportunity by recording in their shells the immediate environment in which they grow and thereby allowing us to reconstruct the variability in fluid discharge rates vesicomyid clams live in association with sites of sulfide 1

pre seismic geomagnetic anomaly and earthquake location article i nfo many researchers studied the relationships between appearances of geomagnetic anomalies and their distances to earthquake epicenters or faults yet occasionally some magnetometer stations located nearby earthquake epicenters and or faults do not observe geomagnetic anomalies in this paper a new hybrid system which simultaneously takes the hypocenter and fault plane solution into account is constructed to examine 38 earthquakes interpreted to be associated with geomagnetic anomalies during the period 1988 2001 in taiwan the surface magnetic anomaly reference tip smart of the new system is used instead of the epicenter or the fault to investigate statistically the distance relationship between the anomalies and the earthquake parameters results show that the anomalies gather along the fault and in the belt zone to the smart possible mechanisms causing the anomalies in the two zones are proposed and discussed characteristics of the anomaly might shed some light on locations of faults before earthquake occurrences

compositions and sources of fluids in sediments of the peru subduction zone sediments of the middle to lower slope regions of the peru continental margin drilled during ocean drilling program odp leg 112 contain interstitial waters with chloride concentrations as low as 454 mm cl equivalent to 20 dilution of seawater with fresh water strontium isotope data suggest that two separate fluid regimes are present a northerly one in which fluids contain more radiogenic sr than seawater 87sr 86sr up to 0 70996 possibly originating from continental crust and a southerly regime where fluids contain sr less radiogenic than seawater 87sr 86sr down to 0 70722 and which are also enriched in ca2 and depleted in mg2 and 18o that appear to have interacted with oceanic basement o c and he isotopic data support these interpretations

spatial variation in fluid flow and geochemical fluxes across the sediment seawater interface at the carlos ribeiro mud volcano gulf of cadiz submarine mud volcanism is an important pathway for transfer of deep sourced fluids enriched in hydrocarbons and other elements into the ocean numerous mud volcanoes mvs have been discovered along oceanic plate margins and integrated elemental fluxes are potentially significant for oceanic chemical budgets here we present the first detailed study of the spatial variation in fluid and chemical fluxes at the carlos ribeiro mv in the gulf of cadiz to this end we combine analyses of the chemical composition of pore fluids with a 1 d transport reaction model to quantify fluid fluxes and fluxes of boron lithium and methane across the sediment seawater interface the pore fluids are significantly depleted in chloride but enriched in lithium boron and hydrocarbons relative to seawater pore water profiles of sulphate hydrogen sulphide and total alkalinity indicate that anaerobic oxidation of methane occurs at 34 180 cm depth below seafloor clay mineral dehydration and in particular the transformation of smectite to illite produces pore fluids that are depleted in chloride and potassium profiles of boron lithium and potassium are closely related which suggests that lithium and boron are released from the sediments during this transformation pore fluids are expelled into the water column by advection fluid flow velocities are 4 cm yr 1 at the apex of the mv but they rapidly decrease to 0 4 cm yr 1 at the periphery the associated fluxes of boron lithium and methane vary between 7 301 0 5 6 and 0 806 mmol m 2 yr 1 respectively we demonstrate that fluxes of li and b due to mud volcanism may be important on a global scale however release of methane into the overlying water column is suppressed by microbial methanotrophy

statistical analysis of ulf seismomagnetic phenomena at kakioka japan during 2001 2010 to clarify and verify the ultralow frequency ulf seismomagnetic phenomena we have performed statistical studies on the geomagnetic data observed at the kakioka kak station japan during 2001 2010 we investigated the energy of ulf geomagnetic signals of the frequency around 0 01 hz using wavelet transform analysis to minimize the influences of artificial noises and global geomagnetic perturbations we used only the geomagnetic data observed at nighttime lt 2 30 a m to 4 00 a m and utilized observations from a remote station kanoya as a reference statistical results of superposed epoch analysis have indicated that ulf magnetic anomalies are more likely to appear before sizable earthquake events es 108 rather than after them especially 6 15 days before the events further statistical investigations show clearly that the ulf geomagnetic anomalies at kak station are more sensitive to larger and closer events finally we have evaluated the precursory information of ulf geomagnetic signals for local sizable earthquakes using molchan s error diagram the probability gain is around 1 6 against a poisson model the above results have indicated that the ulf seismomagnetic phenomena at kak clearly contain precursory information and have a possibility of improving the forecasting of large earthquakes

lithium sources in pore fluids of peru slope sediments and implications for oceanic fluxes high li concentrations up to a maximum of 1155 m are observed in the pore fluids of the peru convergent margin slope sediments at ocean drilling program sites 683 and 685 9 s the li concentration depth gradients are twice as steep as at site 682 and 688 11 s within the sediments the most important li sources are from aluminosilicate minerals biogenic opal a contains little li and thus dilutes the li concentration of the bulk sediments the sediment compositions and the thermal regimes are similar at 9 and 11 s suggesting there is an additional non sedimentary source for the observed high li concentrations in the northern pore fluids at 9 s the 87sr 86sr ratios reach a maximum value of 0 709958 the observed radiogenic 87sr 86sr values in the pore fluids support the suggestion that the additional li may derive from exchange reactions with underlying continental crust the high concentrations of li at 11 s may derive from basalt alteration at moderate to high temperatures as suggested by the non radiogenic 87sr 86sr ratios in these pore fluids which reach a minimum value of 0 707218 based on 1 li concentrations in the pore fluids in slope sediments from peru and several other margins and 2 an approximate estimate of fluid flux from continental margins into the ocean continental margins provide an estimated 1 to 3 1010 moles li yr to the ocean this source of oceanic li which has not been considered previously is of the same order of magnitude as some estimates of hydrothermal and river li fluxes and may have important consequences for the oceanic li isotope budget the sink is unknown for this newly discovered and possibly large li source but it may be more pervasive low temperature alteration of oceanic basement than previously estimated or burial of mineral phases such as authigenic clay minerals or metal oxyhydroxides which may be li rich

potential relationships between seismo deformation and seismo conductivity anomalies abstract this study examines the relationships between seismo deformation and seismo conductivity anomalies during two m6 earthquakes that occurred on march 27th and june 2nd 2013 in taiwan the hilbert huang transform is applied on surface displacement data to remove the effects of noise semi annual and annual cycles and the long term plate movements the residual displacements have similar orientations when earthquake related stress accumulates in the crust once the accumulated stress approaches the threshold for fault rupture the orientations of the residual displacements generally become random except in a small region near the epicenter interestingly high conductivity anomalies which can be detected from the 3 component magnetic data via the magnetic transfer function exist in places very close to this small region near the epicenter spatial and temporal correlations between the high conductivity anomalies and the small region of seismo deformation anomalies suggest that electric charges may migrate and become trapped in the region during seismogenic processes due to differential stress accumulation these electric charges form a high conductivity material that affects the parkinson vector of the geomagnetic field

shear wave polarizations and subsurface stress directions at lost hills field 2 2 s wave data matrix accomplished by computationally rotating sources and receivers although polarization directions obtained by assuming a homogeneous subsurface were moderately consistent with depth considerable improvement in consistency resulted from analytically stripping off a thin near surface layer whose fast s wave polarization direction was about n 6 e s wave birefringence for vertical travel averaged 3 percent in two zones 200 700 ft and 1200 2100 ft 60 210 m and 370 640 m which had closely similar s wave polarizations between those zones the polarization direction changed and the birefringence magnitude was not well defined s wave polarizations from two concentric rings of offset vsps were consistent in azimuth with one another and with polarizations of the near offset vsp this consistency argues strongly for the robustness of the s wave polarization technique as applied in this area the s wave polarization pattern in offset data fits a model of vertical cracks striking n 55 e

crustal displacements due to continental water loading the effects of long wavelength 100 km seasonal variability in continental water storage on vertical crustal motions are assessed the modeled vertical displace ments arm have root mean square rms values for 1994 1998 as large as 8 mm with ranges up to 30 mm and are predominantly annual in character regional strains are on the order of 20 nanostrain for tilt and 5 nanostrain for hori zontal deformation we compare arm with observed global positioning system gps heights aro which include ad justments to remove estimated effects of atmospheric pres sure and annual tidal and non tidal ocean loading for 147 globally distributed sites when the aro time series are ad justed by arm their variances are reduced on average by an amount equal to the variance of the arm of the aro time series exhibiting a strong annual signal more than half

cesium and rubidium in submarine hydrothermal fluids evidence for recycling of alkali elements abstract cs rb and k concentrations have been measured in hydrothermal fluids from the east pacific rise epr southern juan de fuca ridge and mid atlantic ridge mar the results of a time series from 21 n epr show a fall in the cs rb ratios from 1979 to 1985 together with results from other areas the data are consistent with a cracking front moving from weathered oceanic crust into fresh basalt within the magma chamber that supplies the heat for hydrothermal convection interaction of hydrothermal fluids with basalts that have undergone low temperature weathering results in recycling of the alkalis and other elements between oceanic crust and seawater these data demonstrate that the concentration of alkali elements in hydrothermal fluids do not represent a rigid constraint on the global magnitude of the circulation of seawater through axial high temperature hydrothermal systems

strontium and its isotopic composition in interstitial waters of marine carbonate sediments abstract the concentrations and isotopic compositions of strontium in interstitial waters from several dsdp sites where sediments consist chiefly of carbonate oozes and chalks are used as indicators of carbonate diagenesis by reference to a recently produced curve showing detailed variations in the87sr 86sr ratio of seawater with time carbonate sediments of the walvis ridge show increases in interstitial sr2 concentrations in the upper carbonate ooze sections with the highest concentrations near the ooze chalk boundary where maximum rates of carbonate recrystallization occur below this in situ production of sr2 diminishes and there is a diffusive flux of sr to an underlying sink presumably volcanogenic sediments or basalts leading to sr isotopic disequilibrium between carbonates and interstitial waters in some other sites however there is no apparent sr sink at depth and isotopic equilibrium is retained overall diffusive smoothing of profiles exerts an important control on the87sr 86sr ratios although lower ratios than contemporaneous seawater values in the carbonate oozes often correlate with zones of mg2 loss and reflect a combination of a flux of sr2 from the zone of maximum recrystallization rates together with a contribution from the in situ alteration of volcanic matter

anomalous behaviors of geomagnetic diurnal variations prior to the 2011 off the pacific coast of tohoku earthquake mw9 0 there have been many reports on ultra low frequency ulf electromagnetic phenomena associated with earthquakes in a very wide frequency range in this study unusual behaviors of geomagnetic diurnal variations prior to the 2011 off the pacific coast of tohoku earthquake mw9 0 have been reported ratios of diurnal variation range between the target station esashi esa which is about 135 km from the epicenter and the remote reference station kakioka kak about 302 km distant to the epicenter have been computed the results of 10 day running mean of the ratios showed a clear anomaly exceeding the statistical threshold in the vertical component about 2 months before the mega event this anomaly is unique over a 3 year background and the further stochastic test indicates that this anomaly is unlikely a random anomaly which is highly suggestive of correlation with the mega event the original records of geomagnetic fields of the esa station also exhibit continuous anomalous behaviors for about 10 days in the vertical component approximate 2 months prior to the mw9 0 earthquake

temporal record of lithium in seawater a tracer for silicate weathering abstract this paper presents multi species records of the li ca ratio and li isotopic composition 7 li of planktonic foraminifera from the pacific and atlantic oceans for the past 18 ma the li ca record is corrected for interspecific offsets determined from recent holocene foraminifera interspecific offsets in 7 li are not significant despite different diagenetic histories the records produced from both oceans are remarkably consistent corrected planktonic foraminiferal li ca ratios range from 6 3 to 10 9 mol mol while planktonic foraminiferal 7 li ranges from 25 to 31 both records are interpreted in terms of long term changes in seawater li ca and 7 li enabling issues related to higher resolution variability in li ca and 7 li to be ignored by assuming that the hydrothermal flux of li into the oceans and the flux of li removed from the oceans during low temperature uptake by marine basalts and sediments have not changed significantly since 18 ma and using published records for the seawater calcium concentration the seawater li ca and 7 li records can be used to estimate global average river 7 li and li fluxes our records indicate that the river flux of dissolved li decreased between 16 and 8 ma while the 7 li value of the river input increased these data imply that both silicate weathering rates and weathering intensity decreased over this interval which may have been responsible for putative increases in levels of atmospheric co 2 in contrast the riverine flux of li has increased since 8 ma while its 7 li value has increased this implies that the silicate weathering rate has increased while weathering intensity has decreased since that time

bromine and iodine in peru margin sediments and pore fluids implications for fluid origins at the peruvian convergent margin two distinct pore fluid regimes are recognized from differences in their cl concentrations the slope pore fluids are characterized by low cl concentrations but elevated br and i concentrations due to biogenic production the shelf pore fluids exhibit elevated cl and br concentrations due to diffusive mixing with an evaporitic brine in the slope pore fluids the br i and nh4 concentrations are elevated following bacterial decomposition of organic matter but the i concentrations are in excess of those expected based on mass balance calculations using nh4 and br concentrations the slope sediment organic matter which is enriched in iodine from oxidationreduction processes at the oxygenated sediment water interface is responsible for this enrichment the increases in dissolved i and the i enrichments relative to nh4 and br correlate well with sedimentation rates because of differential trapping following regeneration the pore fluid i br ratios suggest that membrane ion fiitration is not a major cause of the decreases in cl concentrations other possible sources for low cl water including meteoric water clathrate dissociation and or mineral dehydration reactions imply that the diluting component of the slope low cl fluids has flowed at least 1 km through the sediment the low bottom water oxygenation in the shelf is responsible for the low if any enrichment of iodine in the shelf sediments fluctuations in bottom water oxygen concentrations in the past however may be responsible for the observed variations in the sediment ibr ratios comparison of na cl and br cl molar ratios in the pore fluids shows that the shelf high cl fluid formed from mixing with a brine that formed from seawater concentrated by twelve to nineteen times and probably was modified by halite dissolution this dense brine located below the sediment sections drilled appears to have flowed a distance 500 km through the sediment

observation of surface displacements from gps analyses before and after the jiashian earthquake m 6 4 in taiwan abstract a blind thrust fault with a unique strike which is orthogonal to the strike of most tectonic structures in taiwan triggered the jiashian earthquake on march 4 2010 m 6 4 22 96 n 120 70 e this study utilizes 100 global positioning system stations to examine changes of surface displacements during the jiashian earthquake we mitigate effects of short term noise and long term plate movements from surface displacement data using a frequency dependent filter via the hilbert huang transform and compute the horizontal azimuth i e gps azimuth using residual data at the ns component relative to residual data at the ew component analytical results show that orientations of horizontal azimuths were aligned and orthogonal to the strike of the blind thrust fault meanwhile inverse orientations are observed before and after the earthquake that agrees well with the seismic rebound theory as stress disturbed on strata a few days before the earthquake an impeded region can be clearly identified by disordered orientations of horizontal azimuths for anticipating the mainshock these results provide an additional view to explore stress disturbance associated with earthquakes and offer more information to examine diverse models of tectonic evolution in this region

chemistry of hydrothermal solutions from the southern juan de fuca ridge fluids from three vent fields on the southern juan de fuca ridge were sampled in september 1984 using the dsrv alvin the fluids are uniquely high in both chloride which ranges up to twice the seawater value and in metal content simple vapor liquid phase separation could not have produced both the high chlorinity and gas concentrations observed in these fluids the cause of the elevated chlorinity can not be uniquely identified but may be the result of either or a combination of two processes 1 subsurface formation of a degassed brine and subsequent mixing of a small amount of this brine with a hydrothermal seawater which has not undergone a phase separation and 2 dissolution of a chloride rich phase combined with a possible small loss of gas during sampling procedures although measured temperatures were all less than 300 sup 0 c quartz geothermometry suggests that the fluids have equilibrated at greater than 340 sup 0 c quartz geobarometry is also in agreement with geophysical estimates of depth to the local magma chamber copyright american geophysical union 1987

fluid venting in the eastern aleutian subduction zone fluid venting has been observed along 800 km of the alaska convergent margin the fluid venting sites are located near the deformation front are controlled by subsurface structures and exhibit the characteristics of cold seeps seen in other convergent margins the more important characteristics include 1 methane plumes in the lower water column with maxima above the seafloor which are traceable to the initial deformation ridges 2 prolific colonies of vent biota aligned and distributed in patches controlled by fault scarps over steepened folds or outcrops of bedding planes 3 calcium carbonate and barite precipitates at the surface and subsurface of vents and 4 carbon isotope evidence from tissue and skeletal hard parts of biota as well as from carbonate precipitates that vents expel either methane or sulfide dominated fluids a biogeochemical approach toward estimating fluid flow rates from individual vents based on oxygen flux measurements and vent fluid analysis indicates a mean value of 5 5 0 7 l m 2 d 1 for tectonics induced water flow wallmann et al 1997b a geophysical estimate of dewatering from the same area von huene et al 1997 based on sediment porosity reduction shows a fluid loss of 0 02 l m 2 d 1 for a 5 5 km wide converged segment near the deformation front our video guided surveys have documented vent biota across a minimum of 0 1 of the area of the convergent segment off kodiak island hence an average rate of 0 006 l m 2 d 1 is estimated from the biogeochemical approach the two estimates for tectonics induced water flow from the accretionary prism are in surprisingly good agreement

genesis of mud volcano fluids in the gulf of cadiz using a novel basin scale model approach abstract mud volcanism and fluid seepage are widespread phenomena in the gulf of cadiz sw iberian margin in this seismically active region located at the boundary between the african and eurasian plates fluid flow is typically focused on deeply rooted active strike slip faults the geochemical signature of emanating fluids from various mud volcanoes mvs has been interpreted as being largely affected by clay mineral dehydration and recrystallization of upper jurassic carbonates here we present the results of a novel fully coupled 1d basin scale reactive transport model capable of simulating major fluid forming processes and related geochemical signatures by considering the growth of the sediment column over time compaction of sediments diffusion and advection of fluids as well as convective and conductive heat flow the outcome of the model is a realistic approximation to the development of the sediment pore water system over geological time scales in the gulf of cadiz combined with a geochemical reaction transport model for clay mineral dehydration and calcium carbonate recrystallization we were able to reproduce measured concentrations of cl strontium and 87sr 86sr of emanating mud volcano fluids these results support previously made qualitative interpretations and add further constraints on fluid forming processes reaction rates and source depths the geochemical signature at porto mv posed a specific problem because of insufficient constraints on non radiogenic 87sr 86sr sources at this location we favour a scenario of basement derived fluid injection into basal upper jurassic carbonate deposits hensen et al 2015 although the mechanism behind such basement derived flow e g along permeable faults remains speculative at this stage it provides an additional source of low 87sr 86sr fluids and offers an idea on how formation water from the deepest sedimentary strata above the basement can be mobilized and eventually initiate the advection of fluids feeding mvs at the seafloor the dynamic reactive transport model presented in this study provides a new tool addressing the combined simulation of complex physical geochemical processes in sedimentary systems the model can easily be extended and applied to similar geological settings and thus help us to provide a fundamental understanding of fluid dynamics and element recycling in sedimentary basins

geochemistry of a chert breccia a complex history of diagenetic interactions between a siliceous sediment seawater and fresh water is revealed by intraformational chert breccias chert breccias were formed in the campanian mishash formation in israel by practically contemporaneous fracturing of lithified cherty layers followed by silicification and lithification of the matrix pairs of fragments and matrix were compared with respect to their chemical ca sr na k mg li b so4 ba and isotopic 18 o d 11 b composition 11 b was analyzed by ion probe and includes a profile across a fragment matrix contact the epicontinental cherts of the mishash fm are enriched by a factor of 10 to 50 in all elements other than o and si in comparison with deep sea cherts all results are compatible with the proposition that the lithification of the matrix occurred in contact with fresh water as opposed to seawater in which the fragments as well as most of the mishash sediments were formed the strongest evidence for this difference is in the higher concentration of b in the fragments 27 70 ppm vs 11 21ppm in the matrix and higher 18 o 29 to 35 vs 21 to 33 d is a less efficient discriminator though compatible with fresher water diagenesis of the matrix 115 to 76 for hydrogen in the chert of the fragments compared to 141 to 85 for the matrix 11 b in the matrix shows some of the lowest values recorded in sediments 11 b 33 but varies strongly suggesting that the source of boron in the matrix is a mixture of a freshwater and a marine component both seawater and the freshwater that has equilibrated with the cherts underwent varying degrees of evaporation ca sr and so4 are carried by apatite trapped as detritus in the matrix the concentration of lithium in the matrix is high 11 16 ppm whereas in the adjacent fragments it is mostly only within 1 2 ppm li probably enters the matrix from the interstitial solution during the opal 3 quartz transformation the second prolonged transformation takes place in a freshwater flow through open system this allows a much larger mass of li to be scavenged by the transforming silica despite its low concentration in freshwater copyright 2005 elsevier ltd

results of ultra low frequency magnetic field measurements during the guam earthquake of 8 august 1993 we report the results of measurements of ultra low frequency magnetic noise during a large earthquake ms 7 1 at guam of 8 august 1993 depth 60 km the ulf observing system is located in the guam island about 65 km from the epicenter several distinct features of this analysis are summarized 1 we have proposed rather sophisticated statistical analyses monthly mean standard deviation in order to estimate the wave intensity and polarization i e ratio z h 2 a comparison between the ulf wave activity and kp is useful in distinguishing between the space geomagnetic pulsations and non space emissions 3 then the use of the ratio z h is found to be of essential importance in discrimating the emissions presumably of seismic origin from space plasma waves 4 the statistical analysis of the temporal evolution of this ratio has yielded that it shows a broad maximum only about one month before the earthquake and this suggests that the emissions during this period are very likely to be magnetic precursors 5 the temporal variation of z component is similar to that for the loma prieta earthquake such that it shows a broad maximum ten days two weeks before the earthquake and another increase a few days before the earthquake 6 the emissions presumably associated with the earthquake are of noise like nature and their main frequency is 0 02 0 05 hz with maximum intensity 0 1 nt

low frequency magnetic field measurements near the epicenter of the ms 7 1 loma prieta earthquake the authors report the results of measurements of low frequency magnetic noise by two independent monitoring systems prior to the occurrence of the m sub s 7 1 loma prieta earthquake of 17 october 1989 their measurements cover 25 narrow frequency bands in the more than six decade frequency range 0 01 hz 32 khz with a time resolution varying from a half hour in the ulf range 0 01 10 hz to one second in the elf vlf range 10 hz 32 khz the ulf system is located near corralitos about 7 km from the epicenter the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf data has revealed no precursor activity that they can identify at this time however the ulf data have some distinctive and anomalous features first a narrow band signal appeared in the range 0 05 0 2 hz around september 12 and persisted until the appearance of the second anomalous feature which consisted of a substantial increase in the noise background starting on 5 october and covering almost the entire frequency range of the ulf system third there was an anomalousmore dip in the noise background in the range 0 2 5 hz starting one day ahead of the earthquake finally and perhaps most compelling there was an increase to an exceptionally high level of activity in the range 0 01 0 5 hz starting approximately three hours before the earthquake there do not appear to have been any magnetic field fluctuations originating in the upper atmosphere that can account for this increase further while the systems are sensitive to motion seismic measurements indicate that there were no significant shocks preceding the quake thus the various anomalous features in the data and in particular the large amplitude increase in activity starting three hours before the quake may have been magnetic precursors less

lithium isotope geochemistry of marine pore waters insights from cold seep fluids lithium concentration and isotope data 7li are reported for pore fluids from 18 cold seep locations together with reference fluids from shallow marine environments a sediment hosted hydrothermal system and two mediterranean brine basins the new reference data and literature data of hydrothermal fluids and pore fluids from the ocean drilling program follow an empirical relationship between li concentration and 7li 7li 6 0 0 3 ln li 51 1 2 reflecting li release from sediment or rocks and or uptake of li during mineral authigenesis cold seep fluids display 7li values between 7 5 and 45 7 mostly in agreement with this general relationship ubiquitous diagenetic signals of clay dehydration in all cold seep fluids indicate that authigenic smectite illite is the major sink for light pore water li in deeply buried continental margin sediments deviations from the general relationship are attributed to the varying provenance and composition of sediments or to transport related fractionation trends pore fluids on passive margins receive disproportionally high amounts of li from intensely weathered and transported terrigenous matter by contrast on convergent margins and in other settings with strong volcanogenic input li concentrations in pore water are lower because of intense li uptake by alteration minerals and most notably adsorption of li onto smectite the latter process is not accompanied by isotope fractionation as revealed from a separate study on shallow sediments a numerical transport reaction model was applied to simulate li isotope fractionation during upwelling of pore fluids it is demonstrated that slow pore water advection order of mm a 1 suffices to convey much of the deep seated diagenetic li signal into shallow sediments if carefully applied li isotope systematics may thus provide a valuable record of fluid mineral interaction that has been inherited several hundreds or thousands of meters below the actual seafloor fluid escape structure

isotopic evidence 87sr 86sr δ7li for alteration of the oceanic crust at deep rooted mud volcanoes in the gulf of cadiz ne atlantic ocean the chemical and isotopic composition of pore fluids is presented for five deep rooted mud volcanoes aligned on a transect across the gulf of cadiz continental margin at water depths between 350 and 3860 m generally decreasing interstitial li concentrations and sr 87 sr 86 ratios with increasing distance from shore are attributed to systematically changing fluid sources across the continental margin although highest li concentrations at the near shore mud volcanoes coincide with high salinities derived from dissolution of halite and late stage evaporites clayey terrigenous sediments are identified as the ultimate li source to all pore fluids investigated light delta li 7 values partly close to those of hydrothermal vent fluids delta li 7 11 9 parts per thousand indicate that li has been mobilized during high temperature fluid sediment or fluid rock interactions in the deep sub surface intense leaching of terrigenous clay has led to radiogenic sr 87 sr 86 ratios similar to 0 7106 in pore fluids of the near shore mud volcanoes in contrast non radiogenic sr 87 sr 86 ratios similar to 0 7075 at the distal locations are attributed to admixing of a basement derived fluid component carrying an isotopic signature from interaction with the basaltic crust this inference is substantiated by temperature constraints from li isotope equilibrium calculations suggesting exchange processes at particularly high temperatures 200 degrees c for the least radiogenic pore fluids of the most distal location advective pore fluids in the off shore reaches of the gulf of cadiz are influenced by successive exchange processes with both oceanic crust and terrigenous fine grained sediments resulting in a chemical and isotopic signature similar to that of fluids in near shore ridge flank hydrothermal systems this suggests that deep rooted mud volcanoes in the gulf of cadiz represent a fluid pathway intermediate between mid ocean ridge hydrothermal vent and shallow marginal cold seep due to the thicker sediment coverage and slower fluid advection rates the overall geochemical signature is shifted towards the sediment diagenetic signal compared to ridge flank hydrothermal environments c 2009 elsevier ltd all rights reserved

temporal changes in shear wave splitting during an earthquake swarm in arkansas shear wave splitting has been observed in seismograms of two aftershock and one foreshock sequence recorded over 12 days by a local network of nine three component digital seismometers during the 1982 enola arkansas earthquake swarm polarizations of the faster split shear wave show alignments within the shear wave window which correlate with the regional stress field the time delay between split shear waves appears to increase before and to decrease at or after the time of each main shock this behavior is similar to observations before and after a m 6 0 event near the anza seismic gap southern california and may correspond to variations in crack geometry caused by changes in the stress field before and after the earthquakes there are indications that the decrease in delay may occur a few hours before the main shock and could be a possible precursor for earthquake prediction

a successfully stress forecast earthquake summary a m 5 earthquake in iceland has been successfully stress forecast by using variations in time delays of seismic shear wave splitting to assess the time and magnitude at which stress modified microcracking reaches fracture criticality within the stressed volume where strain is released local investigations suggested the approximate location of the forecast earthquake we report the criteria on which this stress forecast was based

chemical and isotopic evidence for sources of fluids in a mud volcano field seaward of the barbados accretionary wedge chemical isotopic and heat budgets are controlled by fluid flow and venting at convergent margins fluids vent from accretionary complex sediments via numerous pathways including mud volcanoes which are common at the barbados convergent margin chemical and isotopic compositions of fluids collected from four mud volcanoes located east of the barbados deformation front at 13 50 n indicate venting is sufficiently rapid to prevent diffusion from seawater in sediments surrounding the mud volcanoes the rate of nonfocused fluid flow is 0 26 cm yr although this rate is 3 orders of magnitude slower than the flow from the mud volcanoes significantly more fluid vents from the sediments surrounding the mud volcanoes than from the restricted areas of rapid flow from the volcanoes chloride concentrations are depleted to a minimum of 211 mm 45 of seawater value primarily by mixing diagenetically altered pore fluids with an 18o enriched fresh water released from the dissociation of methane hydrate this reaction is accompanied by the release of sufficient methane to form a free gas phase and initiate eruption of the mud volcanoes the geochemical compositions of the diagenetically altered pore fluids reflect the interplay between five major reactions 1 clay mineral dehydration which releases h2o and influences a range of chemical and isotopic compositions 2 organic matter regeneration which increases alkalinity nh4 and br and decreases so42 concentrations 3 cation exchange with clay minerals which increases na and decreases nh4 concentrations 4 carbonate recrystallization and precipitation which decrease ca2 but increase sr2 concentrations and 5 conversion of volcanic ash to clay minerals which utilizes h2o and decreases mg2 concentrations the geochemistry of the pore fluids suggests that these reactions occurred at temperatures ranging from 75 to 115 c thus at the regional geothermal gradients of 27 to 40 c km these temperatures indicate that the source regions are at 2 to 4 5 km depth

results of ulf magnetic field measurements near the epicenters of the spitak ms 6 9 and loma prieta ms 7 1 earthquakes comparative analysis the characteristics of the ulf magnetic field emissions measured at two magnetic observatories in the republic of georgia prior to and after the ms 6 9 earthquake that occurred near spitak armenia on december 7 1988 are compared with the apparently similar emissions associated with the ms 7 1 earthquake that occurred near loma prieta california on october 17 1989 the main features of the spitak measurements according to observations made at the dusheti station 128 km to the spitak epicenter as compared with the loma prieta measurements which were made at corralitos california 7 km to the loma prieta epicenter are the following 1 the intensity of ulf background activity started growing 3 to 5 days before the spitak earthquake whereas the corresponding increase in activity began 12 days before the loma prieta earthquake 2 a substantial ulf emission burst was recorded at dusheti starting 4 hours prior to the main shock a similar large burst of ulf activity commenced 3 hours before the loma prieta event and continued until the occurrence of the main shock 3 ulf activity remained high for about two weeks after the spitak earthquake and for several months after the loma prieta earthquake 4 ulf noise bursts were observed 1 to 6 hours before powerful aftershocks at spitak during the period of enhanced activity but there was no conclusive link between the ulf noise at corralitos and the after shocks a major difference in the ulf activity preceding the two earthquakes is a difference in amplitude 0 2 nt at spitak and 5 nt at loma prieta but this is easily explained as being caused by the different distances of the observation stations from the epicenters

sources of mud volcano fluids in the gulf of cadiz indications for hydrothermal imprint mud volcanism in the gulf of cadiz occurs over a large area extending from the shelf to more than 3500 m water depth and is triggered by compressional stress along the european african plate boundary affecting a deeply faulted sedimentary sequence of locally more than 5 km thickness the investigation of six active sites shows that mud volcano mv fluids on average are highly enriched in ch4 li b and sr and depleted in mg k and br the purity of the fluids is largely controlled by the intensity of upward directed flow flow rates could be constrained by numerical modelling and vary between 0 05 and 15 cm yr 1 application of d 18o systematics identifies clay mineral dehydration most likely within mesozoic and tertiary shales and marls as the major source of fluids hence cl and na in the pore fluids are mostly depleted below seawater values following a general trend of dilution however deviations from this trend occur and are likely caused by the dissolution of halite in evaporitic deposits other secondary processes overprinting the original fluid composition may occur along the flow path such as dissolution of anhydrite or gypsum and or the formation of calcite and dolomite different sources of fluids are also indicated by variations in 87sr 86sr which range from 0 7086 to 0 7099 at the different sites dehydration may be induced primarily by overburden and tectonic compression however very high concentrations of li and b specifically at captain arutyunov mv camv indicate additional leaching at temperatures above 150 c which could be explained by the injection of hot fluids along deep penetrating major e w strike slip fault systems this hypothesis is supported by the occurrence of generally thermogenic but significantly ch4 enriched light volatile hydrocarbon gases at camv which cannot be explained by shallow microbial methanogenesis li and li b ratios from different types of hot and cold vents are used to infer that high temperature signals seem to be preserved at various cold vent locations and indicate a closer coupling of both systems in continental margin environments than outlined in previous studies

chemical and isotopic evidence of gas influenced flow at a transform plate boundary monterey bay california chemical and isotopic compositions of pore fluids document upward flow through communities of vesicomyid clams in monterey bay california within the clam communities the sulfate reduction zone is only 10 cm thick and ca and mg concentrations decrease to values as low as 2 2 mm and 34 5 mm respectively at depths less than 30 cm below the sediment water interface less than 5 m outside the communities the base of the sulfate reduction zone is deeper than the greatest penetration of the cores 30 cm and ca and mg exhibit only minor changes from seawater values the sediment exhibits no significant variation in grain size mineralogy organic carbon nitrogen or carbonate content throughout the region the composition of pore fluid within clam communities results from upward flow of altered fluid rather than different diagenetic reactions within and outside the communities isotopically light dissolved inorganic carbon dic with 13c values ranging from 3 2 to 54 1 could reflect carbon sources from either oxidized thermogenic methane and or a mixture of oxidized microbial methane and solid organic carbon the c1 c2 c3 ratios ranging from 34 to 1142 and the hydrogen and carbon isotopic compositions of methane d values of 109 to 156 13c values of 30 6 to 86 6 suggest that methane is primarily microbial but that a minor component could be thermally generated any thermogenic methane would have migrated from great depths possibly 2 km the presence of methane is likely to contribute to fluid flow by reducing the density of the fluids past fluid migration and venting are reflected by widespread carbonate mineralization at the sediment water interface this mineralization and the geographic distribution and proportions of microbial and thermogenic methane suggest that vent sites migrate when permeability is reduced during carbonate cementation these results demonstrate that along with convergent and divergent plate boundaries transform plate boundaries are characterized by fluid flow and that the flow may be widespread occurring at sites away from fault zones

constraints on 2004 sumatra andaman earthquake rupture from gps measurements in andaman nicobar islands the 26 december 2004 sumatra andaman earthquake mw 9 0 9 3 is the greatest earthquake of the modern seismological era the rupture characteristics of the earthquake particularly in the andaman nicobar region are not well resolved from seismological or far field geodetic data here in this article we present campaign mode global positioning system gps measurements of coseismic displacements at 13 sites in the andaman nicobar islands before and after the 2004 sumatra andaman earthquake these measurements provide improved estimates of rupture characteristics in the region coseismic horizontal ground displacement of 1 5 6 5 m towards the southwest and coseismic vertical displacement mostly subsidence of 0 5 2 8 m occurred along the andaman nicobar islands with maximum displacements in the nicobar islands we estimate coseismic slip under the andaman and nicobar islands as 3 8 7 9 m and 11 15 m respectively the length of the rupture is estimated to be about 1500 km with a width varying from 120 km under middle andaman island to 160 km under great nicobar island gps measurements during january 11 22 2005 from port blair suggest rapid afterslip in the postseismic period limited gps data available from 1995 measurements at two sites in andaman provide evidence of strain accumulation that varied significantly in the 10 yr preceding the earthquake d 2005 elsevier b v all rights reserved

exploring the importance of authigenic clay formation in the global li cycle abstract lithium isotopic 7li and elemental concentrations of pore fluids and carbonates from iodp site u1338 hole a eastern equatorial pacific ocean suggest that clay authigenesis i e in situ precipitation is a significant sink for li in carbonate rich sedimentary sections systematic variations in pore fluid 7li with depth in the section suggest that clay authigenesis can i strongly decrease pore fluid li concentrations with depth and ii fractionate li isotopically to a considerable degree 5 21 relative to seawater we hypothesize that clay authigenesis in carbonate rich sections occurs due to the presence of reactive biogenic silica and reactive transport modeling supports the contention that the pore fluid 7li depth profile at site u1338 is best explained by faster authigenesis at depth the significance of clay authigenesis in carbonate rich sediments is two fold if global in scale i it can generate sizeable output fluxes in the global li cycle and ii the evolution of the sedimentary system over time can markedly impact the isotopic composition of the global li output flux we compile odp and iodp pore fluid li data from 267 sites of these 207 have li pore fluid concentration gradients in the upper 50 100 meters that indicate the sites as diffusive sinks of li we then estimate that clay authigenesis in carbonate rich sediments could reasonably generate a li output flux on the order of 1 2 1010 moles year which is comparable to the gross input fluxes in the modern li cycle a series of reactive transport simulations illustrate how clay authigenesis might impact the isotopic composition of the output flux of li from the global ocean the suggestion is that applying a constant fractionation factor from the global ocean over time is likely incorrect and that secular changes in the 7li of the output flux will be driven by rates of authigenesis burial rates and the depth extent of authigenesis in the sedimentary section utilizing a time dependent depositional diagenetic model the 7li values of bulk carbonate are shown to be a consequence not of recrystallization alone but recrystallization in the presence of clay authigenesis further our model results are used to illustrate how carbonate 7li may be used to constrain the temporal evolution of clay authigenesis in the sedimentary section ultimately this work suggests that the li isotopic composition of bulk carbonates can be altered diagenetically however such alteration is not a detriment but provides useful information on those diagenetic processes in the sedimentary column that impact the global li cycle thus li isotopes in bulk carbonates have the potential to elucidate diagenetic controls on the global li cycle over long time scales

evidence for the submarine weathering of silicate minerals in black sea sediments possible implications for the marine li and b cycles 1 the role of sediment diagenesis in the marine cycles of li and b is poorly understood because li and b are easily mobilized during burial and are consumed in authigenic clay mineral formation their abundance in marine pore waters varies considerably exchange with the overlying ocean through diffusive fluxes should thus be common nevertheless only a minor li sink associated with the low temperature alteration of volcanic ash has been observed we describe a low temperature diagenetic environment in the black sea dominated by the alteration of detrital plagioclase feldspars fluids expelled from the odessa mud volcano in the sorokin trough originate from shallow 100 400 m deep sediments which are poor in volcanic materials but rich in anorthite these fluids are depleted in na k li b and 18o and enriched in ca2 and sr2 indicating that anorthite is dissolving and authigenic clays are forming using a simple chemical model we calculate the ph and the partial pressure of co2 pco2 in fluids associated with this alteration process our results show that the ph of these fluids is up to 1 5 ph units lower than in most deep marine sediments and that pco2 levels are up to several hundred times higher than in the atmosphere these conditions are similar to those which favor the weathering of silicate minerals in subaerial soil environments we propose that in black sea sediments enhanced organic matter preservation favors co2 production through methanogenesis and results in a low pore water ph compared to most deep sea sediments as a result silicate mineral weathering which is a sluggish process in most marine diagenetic environments proceeds rapidly in black sea sediments there is a potential for organic matter rich continental shelf environments to host this type of diagenesis should such environments be widespread this new li and b sink could help balance the marine li and li isotope budgets but would imply an apparent imbalance in the b cycle

effect of annual signals on geodetic velocity 1 our analysis of global positioning system gps site coordinates in a global reference frame shows annual variation with typical amplitudes of 2 mm for horizontal and 4 mm for vertical with some sites at twice these amplitudes power spectrum analysis confirms that gps time series also contain significant power at annual harmonic frequencies with spectral indices 1 2 which indicates the presence of repeating signals van dam et al 2001 showed that a major annual component is induced by hydrological and atmospheric loading unless accounted for we show that annual signals can significantly bias estimation of site velocities intended for high accuracy purposes such as plate tectonics and reference frames for such applications annual and semiannual sinusoidal signals should be estimated simultaneously with site velocity and initial position we have developed a model to calculate the level of bias in published velocities that do not account for annual signals simultaneous estimation might not be necessary beyond 4 5 years as the velocity bias rapidly becomes negligible minimum velocity bias is theoretically predicted at integer plus half years as confirmed by tests with real data below 2 5 years the velocity bias can become unacceptably large and simultaneous estimation does not necessarily improve velocity estimates which rapidly become unstable due to correlated parameters we recommend that 2 5 years be adopted as a standard minimum data span for velocity solutions intended for tectonic interpretation or reference frame production and that we be skeptical of geophysical interpretations of velocities derived using shorter data spans

ulf electromagnetic precursors for an earthquake at biak indonesia on february 17 1996 ulf electromagnetic emissions associated with a large earthquake occurred at biak island indonesia at 5h 59m ut on february 17 1996 magnitude mw 8 2 and depth 20 km from usgs catalog have been investigated on the basis of ulf magnetic observations at two stations biak and darwin in australia about 1 200 km apart though a simple analysis of magnetic field intensity horizontal and vertical magnetic field components at both stations was found to be closely correlated with geomagnetic kp activity a detailed analysis of the difference of h and z components at the two stations the polarization analysis z h and fractal analysis frequency spectrum slope at these two stations has yielded that the ulf emissions in the frequency range from 5 mhz to 30 mhz about 1 5 1 0 months before the quake are likely to be a precursory signature of the quake with its intensity on the order of 0 2 0 3 nt

alteration of the oceanic crust implications for geochemical cycles of lithium and boron abstract fresh tholeiitic basalt glass has been reacted with seawater at 150 c water rock mass ratio of 10 and fresh diabase has been reacted with a na k ca cl fluid at 375 c water rock mass ratios of 1 2 and 5 to understand better the role of temperature basalt composition and water rock mass ratio on the direction and magnitude of b and li exchange during basalt alteration at 150 c slight but nevertheless significant amounts of b and li were removed from seawater and incorporated into a dominantly smectite alteration phase at 375 c however b and li were leached from basalt b behaved as a soluble element and attained concentrations in solution limited only by the b concentration in basalt and the water rock mass ratio li however was less mobile for example at water rock mass ratios of 1 2 and 5 the percent of li leached from basalt was 58 70 and 92 respectively this suggests some mineralogic control on li mobility during hydrothermal alteration of basalt especially at low water rock mass ratios in general these results as well as those for b are consistent with the temperature dependent chemistry of altered seafloor basalt and the chemistry of ridge crest hydrothermal fluids based on the distribution and chemistry of products of seafloor weathering low 150 c and high temperature hydrothermal alteration of basalt and the chemistry of ridge crest hydrothermal fluids it was estimated that alteration of the oceanic crust is a li source for seawater this is not true for b however since the hot spring flux estimated for b is balanced by low temperature basalt alteration these data coupled with b and li flux estimates for other processes e g continental weathering clay mineral adsorption authigenic silicate formation and formation of siliceous skeletal material yield new insight into the b and li geochemical cycles calculations performed here indicate relatively good agreement between the magnitude of b and li sources and sinks the geochemical cycle of b however may be affected by serpentinization of mantle derived peridotite in oceanic fracture zones serpentinites are conspicuously enriched in b and if the b source for these rocks is seawater then an additional b sink exists which must be integrated into the b geochemical cycle however until more data are available in terms of areal extent of serpentinization serpentite chemistry and isotopic composition the importance of b in these rocks with respect to the b geochemical cycle remains speculative at best

lithium isotope geochemistry of sediments and hydrothermal fluids of the guaymas basin gulf of california abstract lithium isotopic compositions of hydrothermally altered sediments of deep sea drilling project dsdp site 477 477a as well as high temperature vent fluids of the guaymas basin have been determined to gain an understanding of lithium exchange during fluid sediment interaction at this sediment covered spreading center unaltered turbidite of the basin has a 6 li value of 10 5 7 heavier than fresh oceanic basalts contact metamorphism induced by a shallow sill intrusion results in a decrease of the lithium content of the adjacent sediments and a lighter isotopic value 8 below the sill sediments altered by a deep seated hydrothermal system show strong depletions in lithium while lithium isotopic compositions vary greatly ranging from 11 to 1 the shift to lighter composition is the result of preferential retention of the lighter isotope in recrystallized phases after destruction of the primary minerals the complexity of the isotope profile is attributed to inhomogeneity in mineral composition the tortuous pathway of fluids and the temperature effect on isotopic fractionation the range of lithium concentration and 6 li values for the vent fluids sampled in 1982 and 1985 overlaps with that of the sediment free mid ocean ridge systems the lack of a distinct expression of sediment input is explained in terms of a flow through system with continuous water recharge the observations on the natural system agree well with the results of laboratory hydrothermal experiments the experimental study demonstrates the importance of temperature pressure water rock ratio substrate composition and reaction time on the lithium isotopic composition of the reacted fluid high temperature authigenic phases do not seem to constitute an important sink for lithium and sediments of a hydrothermal system such as guaymas are a source of lithium to the ocean the ready mobility of lithium in the sediment under elevated temperature and pressure conditions also has important implications for lithium cycling in subduction zones

current plate movements across the mid atlantic ridge determined from 5 years of continuous gps measurements in iceland 1 we analyze data spanning up to 5 years from 18 continuous gps stations in iceland computing daily positions of the stations with three different high level geodetic processing software packages we observe large scale crustal deformation due to plate spreading across iceland the observed plate divergence between the north american and the eurasian plates is in general agreement with existing models of plate motion spreading is taken up within a 100 150 km wide plate boundary zone that runs through the island of the two parallel branches of the plate boundary in south iceland the eastern volcanic zone is currently taking up the majority of the spreading and little is left for the western volcanic zone the plate boundary deformation field has been locally and temporarily affected in south iceland by two mw 6 5 earthquakes in june 2000 inflation at katla volcano during 2000 to 2004 and an eruption of hekla volcano in february 2000 all stations with significant vertical velocities are moving up relative to the reference station reyk with the highest velocity exceeding 20 mm yr in the center of the island

sr isotopes in interstitial waters of marine sediments from deep sea drilling project cores sr isotopic compositions of interstitial sea waters have been documented in detail with cores from 37 deep sea drilling project sites the 87sr 86sr ratios are sensitive indicators of diagenetic reactions involving alteration of volcanic matter dispersed in sediments and recrystallization of carbonates effects of basalt alteration reactions except possibly for hydrothermal signals and of alteration of continental debris are minimal carbonate recrystallization has a significant effect on the geochemical mass balance of sr but diffusion of unradiogenic strontium from interstitial waters has only a small effect on the 87sr 86sr ratio of ocean water

interstitial water chemistry of sediments of the costa rica accretionary complex off the nicoya peninsula interstitial water analyses from numerous piston gravity and alvin push cores show that fluid flow at the costa rica accretionary prism is spatially limited and can only be detected by visually directed cores in zones of biogenic activity most of the sites cored show evidence for normal diagenetic processes in rapidly deposited organic carbon rich sediments with little evidence for fluid advection however in visually directed alvin push cores obtained from black sulfidic sediments characterized by the presence of calyptogena clams or tubeworms evidence for fluids advected upward from greater depth horizons is shown these zones are associated with a large mudvolcano on the prism and with the zoes of out of sequence thrusts as changes from sea water concentrations are still relatively small substantial mixing with sea water must have occurred during this upward fluid movement

geochemical mass balance for lithium boron and strontium in the gulf of papua papua new guinea project tropics a mass balance has been calculated for the elements li b and sr in the gulf of papua from sampling undertaken during 1993 to 1999 parameters measured included fly kikori and purari river inputs of dissolved and particulate phases removal flux to sediment traps at the base of the continental shelf slope and century scale accumulation rates in shelf and slope sediments derived from excess 210pb profiles in sediment cores about 91 of river input li was in particulate form and there was conservative behavior of dissolved li in the salinity gradient of the estuaries li accumulation rate in inner shelf sediments was slightly less than river inputs suggesting that more than 90 of li river inputs were trapped in rapid aluminosilicate mud accumulation zones of the inner shelf 50 m depth li removal rate to sediment traps at the base of the slope at 1000 m water depth was an order of magnitude smaller than the inner shelf sedimentation export of li to deep water coral sea was estimated to be 1 2 108 mol yr 1 and this amount is equivalent to the riverine dissolved li annual supply rate about 66 of river input of b was in the particulate phase and low dissolved b concentrations in freshwater were conservatively mixed with higher concentrations of b in seawater across the salinity gradient removal of b to inner shelf sediments was about 83 of the total river input indicating a small export of b 1 2 108 mol yr 1 to the coral sea about half of the dissolved b input from rivers is sorbed to particles and trapped in inner shelf sediments only 24 of river input of sr was in particulate form and low freshwater concentrations of dissolved sr were conservatively mixed with higher concentrations of sr in seawater across the salinity gradient only 20 of total river inputs of sr were buried in shelf sediments and there was a large export 7 3 108 mol yr 1 of sr off the shelf to the coral sea a sediment core from a rapidly accumulating mud deposition zone of the inner shelf shows twofold sympathetic variations in li b and sr ca supply rates over 200 to 1000 yr time intervals

the fracture criticality of crustal rocks summary the shear wave splitting observed along almost all shear wave ray paths in the earth s crust is interpreted as the effects of stress aligned fluid filled cracks microcracks and preferentially oriented pore space once away from the free surface where open joints and fractures may lead to strong anisotropy of 10 per cent or greater intact ostensibly unfractured crustal rock exhibits a limited range of shear wave splitting from about 1 5 to 4 5 per cent differential shear wave velocity anisotropy interpreting this velocity anisotropy as normalized crack densities a factor of less than two in crack radius covers the range from the minimum 1 5 per cent anisotropy observed in intact rock to the 10 per cent observed in heavily cracked almost disaggregated near surface rocks this narrow range of crack dimensions and the pronounced effect on rock cohesion suggests that there is a state of fracture criticality at some level of anisotropy between 4 5 and 10 per cent marking the boundary between essentially intact and heavily fractured rock when the level of fracture criticality is exceeded cracking is so severe that there is a breakdown in shear strength the likelihood of progressive fracturing and the dispersal of pore fluids through enhanced permeability the range of normalized crack dimensions below fracture criticality is so small in intact rock that any modification to the crack geometry by even minor changes of conditions or minor deformation particularly in the presence of high pore fluid pressures may change rock from being essentially intact below fracture criticality to heavily fractured above fracture criticality this recognition of the essential compliance of most crustal rocks and its effect on shear wave splitting has implications for monitoring changes in any conditions affecting the rock mass these include monitoring changes in reservoir evolution during hydrocarbon production and enhanced oil recovery and in monitoring changes before and after earthquakes amongst others

instantaneous global plate motion model from 12 years of continuous gps observations 1 we estimate a global plate motion model for 17 major and minor tectonic plates solely on the basis of analysis of data from 106 globally distributed continuous gps stations spanning the period from january 1991 to july 2003 site positions estimated from 24 hour segments of data are aligned day by day to the international gps service igs realization of the itrf2000 reference frame using a similarity transformation thereby ensuring that the itrf2000 no net rotation condition is preserved linear velocities of a carefully selected set of stations are estimated from the position time series along with annual and semiannual fluctuations and position offsets due to gps instrument changes a white noise plus flicker noise model is applied to estimate realistic uncertainties for the site velocities which are then propagated into the derived plate motion model parameters we also examine the vertical velocities in the site selection process at the scripps orbit and permanent array center we have implemented a procedure whereby the plate motion model is updated on a regular monthly basis to improve its precision and reliability as new data become available and as a baseline against which anomalous motions can be detected

lithium isotope geochemistry of pore waters from ocean drilling program sites 918 and 919 irminger basin the distribution of li isotopes in pore waters to a depth of 1157 m below seafloor is presented for odp sites 918 and 919 in the irminger basin offshore greenland lithium isotope data are accompanied by strontium isotope ratios to decipher diagenetic reactions in the sediments which are characterized by the pervasive presence of volcanic material as well as by very high accumulation rates in the upper section the lowering of the 87sr 86sr ratio below contemporaneous seawater values indicates several zones of volcanic material alteration the li isotope profiles are complex suggesting a variety of exchange reactions with the solid phases these include cation exchange with nh4 and mobilization from sediments at depth in addition to the alteration of volcanic matter lithium isotopes are therefore a sensitive indicator of sediment water interaction 6li values of pore waters at these two sites vary between 42 and 25 at shallow depths 100 mbsf rapid decreases in the li concentration accompanied by a shift to heavier isotopic compositions indicate uptake of li into alteration products a positive anomaly of 6li observed at both sites is coincident with the nh4 maximum produced by organic matter decomposition and may be related to ion exchange of li from the sediments by nh4 in the lower sediment column at site 918 dissolved li increases with depth and is characterized by enrichment of 6li the li isotopic compositions of both the waters and the solid phase suggest that the enrichment of li in deep interstitial waters is a result of release from pelagic sediments the significance of sediment diagenesis and adsorption as sinks of oceanic li is evaluated the maximum diffusive flux into the sediment due to volcanic matter alteration can be no more than 5 of the combined inputs from rivers and submarine hydrothermal solutions adsorption on to sediments can only account for 5 10 of the total inputs from rivers and submarine hot springs