a sea floor spreading event captured by seismometers two thirds of earth s surface is formed at mid ocean ridges yet sea floor spreading events are poorly understood because they occur far beneath the ocean surface at 9 50 n on the east pacific rise ocean bottom seismometers recently recorded the microearthquake character of a mid ocean ridge eruption including precursory activity a gradual ramp up in activity rates since seismic monitoring began at this site in october 2003 suggests that eruptions may be forecast in the fast spreading environment the pattern culminates in an intense but brief 6 hour inferred diking event on 22 january 2006 followed by rapid tapering to markedly decreased levels of seismicity

influence of tidal effects on the periodicity of earthquake activity in diverse geological settings with particular emphasis on submarine hydrothermal systems abstract hydrothermal earthquakes may be defined as earthquakes caused by the hydrofracturing of the oceanic crust by submarine hydrothermal fluids it is suggested that they correspond to the cracking of the ocean crust at the brittle ductile transition that marks the downward limit of seawater circulation into the ocean crust semi diurnal variations in submarine hydrothermal discharge in backarc settings and at the crests of mid ocean ridges have been detected by hydrophone but no influence of tidal effects on the periodicity of microearthquakes around submarine hydrothermal vents has been observed so far although tidal stresses are too small to initiate earthquakes themselves they may trigger earthquake activity when imposed on slowly increasing tectonic stress these effects therefore tend to be observed in geologically active regions where stress levels in the earth s crust are high the influence of tides on the periodicity of microearthquakes tends to be complex because the effects of ocean and earth tides are not uniform at the surface of the earth and because the microearthquakes occur in a wide variety of geological settings earth tides cause compression and dilatation of the oceanic crust which may be the most significant factor in initiating changes in fluid flow rate and microseismicity in submarine hydrothermal systems much of the information now available on the tidal periodicity of microearthquakes is based on relatively short term monitoring which lacks statistical validity the development and installation of deep sea monitoring stations will permit rigorous long term monitoring programmes to be carried out which will lead to a better understanding of the nature and periodicity of microearthquakes around submarine hydrothermal vents

sea ice production over the laptev sea shelf inferred from historical summer to winter hydrographic observations of 1960s 1990s the winter net sea ice production nsip over the laptev sea shelf is inferred from continuous summer to winter historical salinity records of 1960s 1990s while the nsip strongly depends on the assumed salinity of newly formed ice the nsip quasi decadal variability can be linked to the wind driven circulation anomalies in the laptev sea region the increased wind driven advection of ice away from the laptev sea coast when the arctic oscillation ao is positive implies enhanced coastal polynya sea ice production and brine release in the shelf water when the ao is negative the nsip and seasonal salinity amplitude tends to weaken these results are in reasonable agreement with sea ice observations and modeling

origin of freshwater and polynya water in the arctic ocean halocline in summer 2007 extremely low summer sea ice coverage in the arctic ocean in 2007 allowed extensive sampling and a wide quasi synoptic hydrographic and 18o dataset could be collected in the eurasian basin and the makarov basin up to the alpha ridge and the east siberian continental margin with the aim of determining the origin of freshwater in the halocline fractions of river water and sea ice meltwater in the upper 150 m were quantified by a combination of salinity and 18o in the eurasian basin two methods applying the preformed phosphate concentration po and the nitrate to phosphate ratio n p were compared to further differentiate the marine fraction into atlantic and pacific derived contributions while po based assessments systematically underestimate the contribution of pacific derived waters n p based calculations overestimate pacific derived waters within the transpolar drift due to denitrification in bottom sediments at the laptev sea continental margin within the eurasian basin a west to east oriented front between net melting and production of sea ice is observed outside the atlantic regime dominated by net sea ice melting a pronounced layer influenced by brines released during sea ice formation is present at about 30 to 50 m water depth with a maximum over the lomonosov ridge the geographically distinct definition of this maximum demonstrates the rapid release and transport of signals from the shelf regions in discrete pulses within the transpolar drift the ratio of sea ice derived brine influence and river water is roughly constant within each layer of the arctic ocean halocline the correlation between brine influence and river water reveals two clusters that can be assigned to the two main mechanisms of sea ice formation within the arctic ocean over the open ocean or in polynyas at the continental slope where relatively small amounts of river water are found sea ice formation results in a linear correlation between brine influence and river water at salinities of about 32 to 34 in coastal polynyas in the shallow regions of the laptev sea and southern kara sea sea ice formation transports river water into the shelf s bottom layer due to the close proximity to the river mouths this process therefore results in waters that form a second linear correlation between brine influence and river water at salinities of about 30 to 32 our study indicates which layers of the arctic ocean halocline are primarily influenced by sea ice formation in coastal polynyas and which layers are primarily influenced by sea ice formation over the open ocean accordingly we use the ratio of sea ice derived brine influence and river water to link the maximum in brine influence within the transpolar drift with a pulse of shelf waters from the laptev sea that was likely released in summer 2005

assessment of mineralogical and petrographic factors affecting petro physical properties strength and cracking processes of volcanic rocks abstract microtextural features influence the petrophysical and mechanical properties of rocks including the elastic properties and cracking processes under axial loads volcanic rocks with varying microtextural characteristics and compositions were evaluated to assess the effect of the main constituents mineralogical petrographic and micro structural features on the petrophysical properties elastic properties and strength furthermore detailed analyses were also used to understand the cracking processes under axial loads the analyses of the cracking processes were completed on thin sections obtained from the mechanically tested specimens the results from the quantitative mineralogical and petrographic studies and observations from thin sections revealed that the mineral mass fractions have an effect on the specific gravity and loss on ignition loi values on the other hand unconfined compressive strength ucs and elastic properties are mostly affected by petrographic variables e g mineral content the ucs values tend to decrease with a relative increase in the groundmass with respect to the phenocryst content and vice versa biotite is the only mineral that influences the ucs individually geometric features e g feret s diameter and perimeter of opaque minerals and biotite are determined to be important constituents influencing the young s modulus under axial loads crack propagation is strongly dependent on the proportional distribution of the phenocryst and groundmass it was observed that increasing groundmass content leads to predominantly axial cracks the cracks tend to bend or propagate as a boundary crack when they reach the boundary of an unaltered phenocryst thus axial and shear cracks co exist with increasing amounts of phenocrysts which hinders crack propagation occasionally cracks can penetrate the altered or opaque phenocrysts depending on the degrees of orientation with respect to applied load of the same minerals furthermore the synthesis of the measurements obtained from ucs tests and thin section observations reveals that an increase in the amount of phenocrysts which promote the formation of more shear cracks in addition to axial cracks causes an increase in the radial strain and poisson s ratio the other factors investigated had minor effects on physical and mechanical properties of studied rocks

tomographic image of the magma chamber at 12 50 n on the east pacific rise the east pacific rise at 12 50 n fig 1 is a fast spreading ridge with intense hydrothermal activity1 and ophiolite studies2and thermal modelling3 indicate that this is a likely setting for a magma chamber a recent seismic reflection experiment4 imaged the top of the magma chamber at this site at a depth of 1 4 km below the sea floor and found that it is continuous for tens of kilometres along the rise axis here we examine a large set of accurate p wave travel times from a detailed seismic refraction experiment at the same site5 the patterns observed in the travel times demonstrate that a zone of low seismic velocities exists beneath the rise axis throughout the region studied the best fitting two dimensional structure obtained from linear inversion of the travel times includes an axial low velocity zone magma chamber only 6 km wide in which velocities are depressed by more than 0 5 km s 1

a new observation of dynamically triggered regional seismicity earthquakes in greece following the august 1999 izmit turkey earthquake the m w 7 4 izmit turkey earthquake triggered widespread regional seismicity in greece over a study region extending from 400 km to nearly 1000 km away from the epicenter small events began immediately after the passage of the mainshock surface waves suggesting that the transient stresses of the seismic waves were the trigger the increase in cataloged earthquakes in ordinary continental crust is a new observation and is statistically significant at the 95 level unlike the previous example of distant triggering during the landers earthquake the activated seismicity occurred entirely in non volcanic areas the greek sites were triggered by waves with amplitudes at least a factor of 3 lower than the observed triggering threshold for imperial valley we speculate that dynamic triggering on a regional scale results in countrywide episodes of increased seismicity or superswarms in regions with low triggering thresholds such as greece

effect of heterogeneity of brittle rock on micromechanical extensile behavior during compression loading a grain based universal distinct element code model was developed to generate a deformable polygonal grain like structure to simulate the microstructure of brittle rock it takes into account grain scale heterogeneity including microgeometric heterogeneity grain scale elastic heterogeneity and microcontact heterogeneity the microgeometric heterogeneity can be used to match the grain size distribution of the rock the discrete element approach is able to simulate the microheterogeneity caused by elastic variation and contact stiffness anisotropy the modeling approach was evaluated using lac du bonnet granite and a aspo diorite the microheterogeneity played an important role in controlling both the micromechanical behavior and the macroscopic response when subjected to uniaxial compression loading the crack initiation stress was found to be controlled primarily by the microscale geometric heterogeneity while the microcontact heterogeneity controlled the strength characteristics the effect of heterogeneity on the distribution and evolution of tensile stresses and associated extension cracks was also examined

geological and hydraulic characterisation of the excavation disturbed zone in the opalinus clay of the mont terri rock laboratory abstract the fracture network in the excavation disturbed zone edz of an argillaceous formation the opalinus clay in the mont terri rock laboratory in northwest switzerland is characterised using structural and hydrogeological techniques sampling of unloading fractures is done by analysing resin injected overcores taken from the edz resulting in a structural data set of fracture orientations frequencies and extent of the edz these parameters are derived in tunnel sections which were excavated by blasting pneumatic hammering and road header techniques pneumatic and hydrogeological tests are subsequently carried out to derive hydraulic parameters such as permeability and transmissivity distributions of the fracture network synthesis of the structural and hydrogeological data led to a conceptual model of the edz in the mont terri rock laboratory which is defined by a 2 m plastically deformed zone around the tunnel this plastic zone is further divided into an inner 1 m zone consisting of an air filled fracture network and an outer zone with mostly saturated and isolated fractures transmissivities in the inner zone are orders of magnitude higher than those of the undisturbed opalinus clay finally a methodology is proposed for the structural and hydrogeological characterisation of the edz this methodology is not site specific and is thus applicable at any argillaceous underground facility

freshwater balance and the sources of deep and bottom waters in the arctic ocean inferred from the distribution of h218o data from sections across the eurasian basin of the arctic ocean occupied in 1987 and 1991 are used to derive information on the freshwater balance of the arctic ocean and on sources of the deep waters of the nansen amundsen and makarov basins using salinity h218o and mass balances we estimate the river runoff and the sea ice melt water fractions contained in the upper waters of the arctic ocean and infer pathways of the river runoff signal from the shelf seas across the central arctic ocean to fram strait the average mean residence time of the river runoff fraction contained in the arctic ocean halocline is determined to be about 11 to 14 years pacific water entering through bering strait is traced using silicate and its influence on the halocline waters of the canadian basin is estimated water column inventories of river runoff and sea ice melt water are calculated for a section just north of fram strait and implications of these inventories for sea ice export through fram strait are discussed comparison of the 18o 16o ratios of shelf water atlantic water and the deep waters of the arctic ocean indicate that the sources of the deep and bottom waters of the eurasian basin are located in the barents and kara seas

dipole anomaly in the winter arctic atmosphere and its association with sea ice motion abstract this paper identified an atmospheric circulation anomaly dipole structure anomaly in the arctic atmosphere and its relationship with winter sea ice motion based on the international arctic buoy program iabp dataset 1979 98 and datasets from the national centers for environmental prediction ncep and the national center for atmospheric research ncar for the period 1960 2002 the dipole anomaly corresponds to the second leading mode of eof of monthly mean sea level pressure slp north of 70 n during the winter season october march and accounts for 13 of the variance one of its two anomalous centers is stably occupied between the kara sea and laptev sea the other is situated from the canadian archipelago through greenland extending southeastward to the nordic seas the dipole anomaly differs from one described in other papers that can be attributed to an eastward shift of the center of action of the north atlantic oscillation the finding shows that the dipole anomaly also differs from

breaking new ground estimates of crack depth along the axial zone of the east pacific rise 9 12 54 n using simple fracture mechanics models the depths of fissures that were observed along the axial zone of the east pacific rise epr from 9 12 to 54 n with the deep towed argo z vehicle are estimated the widest cracks 4 8 m along this fast spreading portion of the epr are the deepest and are spatially correlated with the broadest youngest and most hydrothermally active portions of the ridge crest if the widest deepest cracks are not primarily eruptive they should be most abundant in areas of older lava flows having increased in width with time this is not observed some of the widest cracks are located where the 1991 eruption of the ridge crest occurred at 9 45 52 n and may be deep enough to reach the sheeted dikes of layer 2b these cracks may have tapped melt during the eruption and facilitated the flux of vapor rich hydrothermal fluids through overlying lava flows the narrowest presumably shallowest cracks correspond to the narrowest oldest and least hydrothermally active portions of the ridge crest we interpret the wide deep cracks as primarily eruptive in origin and suggest that they may be associated with the inflation of an axial magma chamber whereas the narrow shallow cracks are interpreted as primarily tectonic and are thought to be associated more with far field plate stresses

is the dipole anomaly a major driver to record lows in arctic summer sea ice extent recent record lows of arctic summer sea ice extentare found to be triggered by the arctic atmospheric dipoleanomaly da pattern this local second leading mode ofsea level pressure slp anomaly in the arctic produced astrong meridional wind anomaly that drove more sea ice outof the arctic ocean from the western to the eastern arcticinto the northern atlantic during the summers of 1995 1999 2002 2005 and 2007 in the 2007 summer the daalso enhanced anomalous oceanic heat flux into the arcticoceanviaberingstrait whichacceleratedbottomandlateralmelting of sea ice and amplified the ice albedo feedback acoupled ice ocean model was used to confirm the historicalrecord lows of summer sea ice extent

seismogenic structure and processes associated with magma inflation and hydrothermal circulation beneath the east pacific rise at 9 50 n a dense ocean bottom seismometer array recorded more than 7 300 microearthquakes between october 2003 and april 2004 on the fast spreading east pacific rise at 9 50 n a previous initial analysis of these data revealed the general structure of an along axis oriented hydrothermal circulation cell with an inferred down flow zone near a 4th order axial discontinuity a horizontal band of seismicity overlying the axial magma chamber amc and an upflow zone that correlates with activity patterns of hydrothermal vents here we present cross correlation based double difference hypocenter locations that reveal further insight into the detailed structure and kinematics that control seismic failure we find that the majority of events within the inferred down flow pipe occur near the surface where the entrenched seawater presumably lowers the frictional strength of faults generated by local tectonic stresses beneath the eastern side of the ridge axis just above the amc at 1 4 km depth we observe repeated shear failure along well defined steeply east dipping faults composite focal mechanisms indicate reverse motion suggesting that slip on these faults is caused by amc inflation and possibly injection of magma into a narrow sill we resolve a small counterclockwise skew in the strike of the reverse faults relative to the direction of the ridge axis consistent with nuvel 1a spreading direction suggesting that the regional tectonic stress field may be controlling the seismogenic structures at depth earthquakes on the reverse faults occur preferentially during peak extensional tidal stresses indicating that these faults are critically stressed

arctic dipole anomaly and its contribution to sea ice export from the arctic ocean in the 20th century 1 the winter dipole anomaly da in the arctic atmosphere and its contribution to sea ice export are investigated by using a high resolution coupled global general circulation model the spatial distributions of the first two leading eof modes of winter mean sea level pressure slp and geopotential height at 500 hpa north of 70n obtained by the long term simulation 1900 2010 are highly similar to those derived from the national center for environmental prediction and the national center for the atmospheric research ncep ncar reanalysis datasets 1948 2004 the first leading mode corresponds to the arctic oscillation ao the da is defined as the second leading mode the ao and da account for 59 and 19 of the total variance respectively composite spatial patterns of slp sea ice thickness and velocity in the extreme years when both the absolute values of principal component pc1 and pc2 exceed 1 0 standard deviation indicate that the da plays a great important role in sea ice export from the arctic ocean to the greenland sea due to its strong meridionality sea ice export is highly promoted restricted in the positive negative da phase the dependence of sea ice export on the da is comparable to or rather larger than that on the ao citation watanabe e j wang a sumi and h hasumi 2006 arctic dipole anomaly and its contribution to sea ice export from the arctic ocean in the 20th century geophys res lett 33 l23703 doi 10 1029 2006gl028112

fine scale seismic structure of the shallow volcanic crust on the east pacific rise at 9 50 n upper crust in a 3 3 km field area centered on the east pacific rise at 9 50 0 n we detonated 18 explosive shots 18 sources in a circular pattern 1 5 km radius on the rise axis and recorded seismic arrivals with eight ocean bottom seismometers eight receivers we observed 30 40 hz compressional body waves from all shots 144 p waves and 1 3 hz stoneley interface waves on a subset of source receiver pairs 58 interface waves using a station correction inversion we find that roughly half of the variance in the p wave first arrival times results from lateral variations in the thickness of the surface low velocity layer slvl a layer of extremely porous lava and basalt breccia with an average p wave velocity of 2 2 km s 1 the slvl thickness increases from 20 m along the axial summit trough ast to 120 m at near axis lava depocenters which are not symmetric about the rise axis depocenters are located 0 5 km to the west and 1 5 km to the east of the rise axis tomographic inversion of the stoneley wave first arrivals reveals that shear velocities in the slvl covary with the layer thickness exhibiting a similar asymmetric pattern with shear velocities increasing from 320 m s 1 near the ast to 520 m s 1 at the near axis depocenters our analysis demonstrates that the seismic characteristics of the extrusive layer near the rise axis are related primarily to volcanic features and processes the thickness and velocity of the slvl are low on the axis and within channel networks that deliver lava flows away from the axis and then increase rapidly at the distal ends of the channels where the lavas are deposited we find that azimuthal anisotropy exerts only a weak influence on our p wave first arrival times which we model as weak 4 seismic azimuthal anisotropy in the upper dikes with a fast axis oriented n23 32 w we find no evidence for seismic azimuthal anisotropy in the extrusive layer index terms 3025 marine geology and geophysics marine seismics 0935 3035 marine geology and geophysics midocean ridge processes 7220 seismology oceanic crust

hydrothermal seismicity beneath the summit of lucky strike volcano mid atlantic ridge abstract we present two years july 2007 july 2009 of earthquake locations from a local seismological network on the lucky strike volcano mid atlantic ridge whose summit hosts one of the most active and largest deep sea hydrothermal fields known two clusters of small m l

faulting patterns near 19 30 s on the east pacific rise fault formation and growth at a superfast spreading center 1 structural mapping from high resolution sonar and bathymetric data collected near 19 30 s on the southern east pacific rise epr reveals multiple packets of small closely spaced outward dipping faults that form antithetic to larger inward dipping faults the mean spacing and height of inward dipping scarps are 1 6 and 1 9 times greater than those of outward dipping faults and the median spacing and height of inward dipping scarps are 2 0 and 1 7 times greater respectively accordingly inward dipping faults are less abundant 35 45 but accommodate more 50 55 of the roughly 4 0 strain although previous studies have shown that epr fault populations exhibit exponential size frequency distributions one dimensional throw and spacing data from the 19 30 s region are not described well by this model the first major 40 m scarp height fault is observed within 1 4 km of the ridge crest and invariably dips inward further off axis a transition from greater inward dipping to greater outward dipping fault abundance constrains the minimum half width of the active plate boundary zone to be 5 15 km inspection of additional data sets from 16 and 18 30 s indicates a pattern of large inward dipping faults with associated hanging wall deformation similar to that observed in the 19 30 s region this pattern is distinct from the horst and graben morphology observed along the fast spreading northern epr the pervasive hanging wall deformation observed on the flanks of the southern epr suggests master fault geometries that are more sharply curved or kinked at depth relative to their abyssal hill equivalents on the northern epr boundary element modeling indicates the pattern and geometry of faulting observed along the southern epr is consistent with fault nucleation above a shallow sill like magma chamber with internal overpressure since the influence of the sill on fault growth is strongly dependent on the depth of the sill the different patterns of faulting observed along the northern and southern epr may reflect the small difference in axial magma chamber depth between these two regions with a slightly shallower chamber beneath the southern epr

pulse of the seafloor tidal triggering of microearthquakes at 9 50 n east pacific rise 1 unequivocal evidence of tidal triggering is observed for microearthquakes 0 4 to 2 0 ml recorded between october 2003 to april 2004 near 9 50 n on the east pacific rise epr although semidiurnal tidal stress changes are small 99 9 nonrandom temporal distribution with events occurring preferentially near times of peak extension due to the proximity of this site to an ocean tidal node where changes in sea surface height are minimal periodic stress changes are dominated by the solid earth tide in contrast previous studies on the juan de fuca ridge have shown microearthquake triggering to be a response to seafloor unloading during times of low ocean tide the modulation of 9 50 n microearthquakes by small amplitude periodic stresses is consistent with earthquake nucleation within a high stressing rate environment that is maintained near a critical state of failure by on axis magmatic and hydrothermal processes

short and long baseline tiltmeter measurements on axial seamount juan de fuca ridge abstract long term observations of seismic activity and ground deformation at mid ocean ridges and submarine volcanoes are required for an understanding of the spatial and temporal characteristics of magma transport and intrusion to make precise records of tilt on the seafloor we have installed short baseline tiltmeters in six ocean bottom seismometers tilt obs and developed a long baseline 100 500 m two fluid tiltmeter lbt in the tilt obs the seismometer platform is levelled to better than 1 after deployment the tiltmeter consists of a pair of electrolytic bubble sensors mounted on a secondary levelling stage on the seismometer platform the levelling stage uses two motor driven micrometers on a triangular mounting plate to bring the sensors to null the sensitivity of these tiltmeters is 0 05 rad at a dynamic range of 0 2 mrad a long baseline instrument was developed to achieve a better spatial average of deformation most approaches used on land to measure stable long baseline tilt cannot be applied to a submarine instrument but tiltmeters in which the pressure of a fluid in tubes is measured are amenable to installation on the seafloor the development resulted in a device that is essentially a center pressure instrument folded back on itself with fluids of different densities in the two tubes during july to september 1994 these instruments were deployed on axial seamount on the juan de fuca ridge off washington state for a test of their relative performance on volcanic terrain yielding 9 weeks of continuous data seismic tilt and temperature from five tilt obs and one long baseline instrument drift on all instruments was of the order of 1 rad day with higher frequency variations of order 5 10 rad initial drift on the tilt obs is shown to be associated with platform settling rather than with the sensor or its mounting high frequency noise is coherent across instruments and tidal in character and we conclude that tidal currents moving the sensors are responsible

the petrographic and geomechanical properties of some sandstones from the newspaper member of the natal group near durban south africa abstract sandstones are by far the most important rock type in the natal group which is mainly a terrestrial succession formed during ordovician silurian times the most notable member of the group is the newspaper member from which sample material was obtained most of the material sampled was fine to medium grained arkosic sandstone they are well cemented with generally low porosity accordingly sandstones of the newspaper member tend to be very strong and of low deformability few of the petrological properties of these sandstones have a notable influence on the mechanical properties however increasing clay content tends to lower the unconfined compressive strength whilst increasing quartz content tends to enhance it on the other hand many of the mechanical properties are interrelated significant or highly significant relationships occur amongst the strength parameters and between hardness and strength young s modulus also has significant relationships with strength and hardness another property which has a significant influence on strength and deformability is porosity

the impact of climatic and atmospheric teleconnections on the brine inventory over the laptev sea shelf between 2007 and 2011 export of brine enriched water from siberian shelves is thought to be a key parameter in maintaining the arctic halocline which isolates the fresh and cold surface water from the warm atlantic water and thus prevent dramatic change in the arctic sea ice thermodynamic in this study we used five years of oxygen isotope and hydrological summer surveys to better understand the factors controlling the brine inventory and distribution over the laptev sea shelf the inventory was maximal in 2011 and 2007 and minimal in 2010 the brine inventory interannual variations are coherent with the winter arctic oscillation index that was maximal in 2011 and 2007 and minimal in 2010 which is known to modulate arctic winds and sea ice export pattern while we should remain cautious since our record is limited to 5 years our results suggest that the combined effect of the arctic oscillation and of the arctic dipole is the main factor controlling the annual variations in the inventory of brine enriched waters from the laptev sea shelf between 2007 and 2011 especially during extreme negative arctic oscillation and arctic dipole conditions as in 2010

poisson s ratio values for rocks abstract compared to other basic mechanical properties of rocks poisson s ratio is an elastic constant of which the significance is generally underrated yet in rock mechanics there is a considerable number of diverse areas which require a prior knowledge or estimation of the value of poisson s ratio this paper examines the values and applications of poisson s ratio in rock mechanics following an historical account of the initial controversy whether it was a material constant or not the effects of poisson s ratio in the elastic deformation of materials intact rocks and rock masses are briefly reviewed also the reported values of poisson s ratio for some elements materials and minerals are compiled while typical ranges of values are presented for some rocks and granular soils finally poisson s ratio classifications are recommended for isotropic intact rocks

a poroelastic model for the tidal modulation of seafloor hydrothermal systems 1 time series measurements of the temperature and exit velocity of hydrothermal effluent suggest that seafloor hydrothermal systems are modulated by tidal processes here we apply the theory of poroelasticity to predict the magnitude and phase of tidally induced changes in the temperature and flow rate of hydrothermal effluent at the seafloor we construct a model in which the steady state upwelling of buoyant fluid in the crust is modulated by tidal loading of a one dimensional seafloor by the overlying water column the nature of the solution is controlled by the relative magnitudes of three length scales these are 1 the depth h of the heat source below the seafloor 2 the skin depth d over which pore pressure signals can diffuse during one tidal cycle and 3 the advective length scale a over which the upwelling flow advects thermal signals during one tidal cycle we consider the likely magnitude of the parameters in a real system as well as the limitations of a one dimensional representation of that system we then discuss how observational data on the magnitude and phase lag of temperature and flow rate could be used to constrain the subseafloor parameters that govern hydrothermal circulation within the seafloor

relationship between textural petrophysical and mechanical properties of quartzites a case study from northwestern himalaya abstract the quantification of various textural parameters and petrophysical mechanical properties of quartzites located in the lesser and higher himalayas has been carried out a dimensionless quantity texture coefficient representing rock texture incorporates various textural parameters like grain shape orientation degree of grain interlocking and relative proportion of grain and matrix packing density has been measured besides shape preferred orientation and grain suturing fractal dimension these have been correlated with the seismic properties like p and s wave velocities and attenuation characteristics and unconfined compressive strength it has been noted that seismic velocity in rocks is a function of various textural parameters like with the increase of aspect ratio grain size and shape preferred orientation velocity increases and with the increase of suturing fractal dimension the velocity decreases the texture coefficient is noted to be inversely proportion to the velocity and there exits strong positive relationships r 0 71 between texture coefficient and the unconfined compressive strength however the relation between the velocity and the unconfined compressive strength is meaningless

analysis and application of in situ pore pressure measurements in marine sediments recent measurements of in situ subseafloor pore pressure in sediment ponds on the flank of the mid atlantic ridge using a pop up pore pressure instrument have provided important information regarding fluid exchange processes at the seafloor as well as in situ estimates of physical properties of marine sediments the in situ pore pressure recordings of 4 5 days duration contain three distinct components the early part of the record is dominated by the decay of a pressure pulse associated with probe penetration the rate of decay of this pulse is used to estimate in situ permeabilities which range from 3 1 10 16 m2 to 6 5 10 15 m2 the recording also exhibits a low amplitude oscillation that is associated with tidal pressure variation on the seafloor a study based on biot s theory shows that amplitudes and phases of tidally induced pore pressure oscillations are determined by both the frame compressibility and the permeability of the sediments and thus the oscillation components are used to estimate these parameters the frame compressibilities and the permeabilities estimated from tidal oscillations range from 1 2 10 8 pa 1 to 4 1 10 8 pa 1 and from 1 1 10 15 m2 to 4 8 10 15 m2 respectively laboratory measured permeabilities range from 7 6 10 16 m1 to 1 2 10 15 m2 permeabilities determined by these three methods are comparable the third component is the ambient equilibrium pore pressure negative pore pressure gradients were identified on all deployments when combined with the permeabilities of the sediments the estimated average rates of drawdown of water through the sedimentary layers in the ponds are 2 7 mm yr the pore pressure gradient near the seafloor can be used to construct a pore pressure profile through the sediment extrapolated pore pressure at the top of the basement is about 80 kpa 0 8 bar below the hydrostatic pressure

systematic along axis tidal triggering of microearthquakes observed at 9 50 n east pacific rise 1 hydrothermal fluid circulation at mid ocean ridges facilitates the exchange of heat and chemicals between the oceans and the solid earth and supports chemosynthetic microbial and macro faunal communities the structure and evolution of newly formed oceanic crust plays a dominant role in controlling the character and longevity of hydrothermal systems however direct measurements of subsurface processes remain technologically challenging to obtain previous studies have shown that tidally induced stresses within the subseafloor modulate both fluid flow and microearthquake origin times in this study we observe systematic along axis variations between peak microearthquake activity and maximum predicted tidal extension beneath the hydrothermal vent site at 9 50 n east pacific rise we interpret this systematic triggering to result from pore pressure perturbations propagating laterally through the hydrothermal system based on our observations and a one dimensional pore pressure perturbation model we estimate bulk permeability at 10 13 to 10 12 m2 within layer 2b over a calculated diffusive lengthscale of 2 0 km

impact of the arctic ocean atlantic water layer on siberian shelf hydrography this paper examines the role of the arctic ocean atlantic water aw in modifying the laptev sea shelf bottom hydrography on the basis of historical records from 1932 to 2008 field observations carried out in april may 2008 and 2002 2009 cross slope measurements a climatology of bottom hydrography demonstrates warming that extends offshore from the 30 50 m depth contour bottom layer temperature time series constructed from historical records links the laptev sea outer shelf to the aw boundary current transporting warm and saline water from the north atlantic the aw warming of the mid 1990s and the mid 2000s is consistent with outer shelf bottom temperature variability for april may 2008 we observed on shelf near bottom warm and saline water intrusions up to the 20 m isobath these intrusions are typically about 0 2 c warmer and 1 1 5 practical salinity units saltier than ambient water the 2002 2009 cross slope observations are suggestive for the continental slope upward heat flux from the aw to the overlying low halocline water lhw the lateral on shelf wind driven transport of the lhw then results in the bottom layer thermohaline anomalies recorded over the laptev sea shelf we also found that polynya induced vertical mixing may act as a drainage of the bottom layer permitting a relatively small portion of the aw heat to be directly released to the atmosphere finally we see no significant warming up until now over the laptev sea shelf deeper than 10 15 m in the historical record future climate change however may bring more intrusions of atlantic modified waters with potentially warmer temperature onto the shelf which could have a critical impact on the stability of offshore submarine permafrost

seismic tremor at the 9 50 n east pacific rise eruption site ocean bottom seismic observations within the 9 50 n region of the east pacific rise indicate persistent low amplitude tremor activity throughout the october 2003 through february 2007 period of monitoring these signals exhibit either monochromatic or polychromatic spectral characteristics with a 6 hz fundamental frequency and up to two harmonics individual events cannot be correlated between nearby 1 km stations implying the presence of multiple small amplitude sources positioned within the shallow crust tremor exhibits a semidiurnal periodicity with some stations recording activity during times of increasing tidal extension and others detecting tremor signals during times of increasing compression the amplitude duration and rate of activity also correlate positively with fortnightly changes in the amplitude of the tides these spatiotemporal patterns are consistent with tremor generation in response to tidally modulated fluid flow within a network of shallow cracks tremor energy flux is spatially and temporally heterogeneous however there are extended periods of greater and lesser activity that can be tracked across portions of the array despite their shallow crustal origin changes in tremor amplitude and spectral character occur in the months prior to a major microearthquake swarm and inferred seafloor spreading event on 22 january 2006 with an increase in the degree of correlation between tremor activity and tidal strain in the weeks leading up to this event after the spreading event two eruption surviving stations near the axis continue to show high rates of tremor activity whereas these signals are suppressed at the single station recovered from the near axis flanks this off axis quiescence may result from the dike induced closing of cracks or perhaps from the emplacement of impermeable flows near the station

the examination of fracturing process subjected to triaxial compression test in inada granite the behavior of a granite subject to a triaxial compression test ranging from the prefailure stage to the postfailure stage was studied using a fluorescent technique from the geological point of view microscopic observations of the specimens at different stages showed changes in the failure process the start of formation of new microcracks paralleled the compression direction through their propagation until the onset of faulting and ended with the failure of shear zones after the strength failure point pores chiefly identified in the feldspar increased in length and width in the early stages but not in number it seems that the effect of pore spaces did not have any effect of failure the microcracks generated on angular edges of quartz or feldspar grains and around biotite grains with increasing compression force the phenomenon appearing on the crystal boundaries among biotite and quartz or feldspar agrees with the result calculated based on the theory on stress fields with ellipsoidal inhomogeneity suggested by eshelby

distribution of magma beneath the east pacific rise between the clipperton transform and the 9 17 n deval from forward modeling of common depth point data we have reprocessed seven cross axis common depth point cdp profiles between the clipperton transform and the 9 17 n deval deviation in axial linearity on the east pacific rise epr to understand the relationship between axial magma chamber amc width and seafloor morphology forward modeling of cross axis cdp profiles suggests a segmented amc in which significant variations in width occur across minor rise axis discontinuities e g devals the modeled rise segment widths bounded by the 9 53 n 9 35 n devals the 9 35 n 9 17 n devals and south of the 9 17 n deval were 0 7 km 1 0 1 2 km and 4 15 km respectively transition in amc width across these discontinuities is unclear due to the sparseness of cross axis line spacing however a simple association of devals with decreased magma supply is doubtful the minimum 250 m and maximum 4150 m amc widths are found near the 9 35 n and 9 17 n devals respectively the reprocessing of cdp profiles included repicking stacking velocities to ensure a proper stack of the amc reflector and its associated diffractions imaging postcritical reflections from the base of layer 2a finite difference time migration ray theoretical depth migration and travel time modeling of amc diffraction patterns constraints on amc width were derived from forward modeling techniques based on analytic raytracing velocity models were constructed from seabeam bathymetry and modified expanding spread profile esp velocity depth functions esp velocity models were altered to compensate for off axis thickening of layer 2a as imaged in the cdp reflection data continuous two dimensional velocity models constructed from modified esp velocity depth functions and seabeam bathymetry should account for ray bending at the seafloor basalt interface and any lateral velocity gradients induced by a thickening layer 2a stacked data were time migrated using a finite difference algorithm and extrapolated to depth using ray theoretical depth migration reflector positions were input into our forward modeling scheme to produce a zero offset travel time response of our migrated solution the travel time response was then overlain on the stacked section to ensure an adequate match especially to diffractions generated at the amc edge forward modeling of amc diffraction patterns reveals that original amc width estimates were too large the under migration of the amc reflector resulted from the conversion of stacking to interval velocities without accounting for topographic effects on individual cmp gathers thus resulting in improperly collapsed diffraction hyperbolae ship wandering relative to the amc edge can account for variations in amc reflector amplitude and dropout on the along axis cdp line the continuity of the amc appears unbroken across several ridge axis discontinuities between the clipperton transform and the 9 17 n deval which suggests an amc whose along axis dimension exceeds 75 km reflectivity modeling of cmp gathers suggests that the available data are consistent with a magma chamber comprising only a thin layer of melt overlying a zone of partially solidified crystal mush such a thin layer of melt might inhibit along axis mixing of magmas and thereby account for variations in magma composition along the rise crest this melt lens model for the amc would also produce strong diffraction patterns as imaged in the cdp data

statistical analysis of the el nino southern oscillation and sea floor seismicity in the eastern tropical pacific we present statistical evidence for a temporal link between variations in the el nino southern oscillation enso and the occurrence of earthquakes on the east pacific rise epr we adopt a zero inflated poisson regression model to represent the relationship between the number of earthquakes in the easter microplate on the epr and enso expressed using the southern oscillation index soi for east pacific sea level pressure anomalies from february 1973 to february 2009 we also examine the relationship between the numbers of earthquakes and sea levels as retrieved by topex poseidon from october 1992 to july 2002 we observe a significant 95 confidence level positive influence of soi on seismicity positive soi values trigger more earthquakes over the following 2 to 6 months than negative soi values there is a significant negative influence of absolute sea levels on seismicity at 6 months lag we propose that increased seismicity is associated with enso driven sea surface gradients rising from east to west in the equatorial pacific leading to a reduction in ocean bottom pressure over the epr by a few kilopascal this relationship is opposite to reservoir triggered seismicity and suggests that epr fault activity may be triggered by plate flexure associated with the reduced pressure

termination of a 6 year ridge spreading event observed using a seafloor seismic network on the endeavour segment juan de fuca ridge 1 we present automatically determined epicenters and magnitudes for 36 523 earthquakes recorded along the endeavour segment between august 2003 and october 2006 using a local ocean bottom seismometer obs network the catalog is dominated by two swarm sequences in january and february 2005 in the vicinity of the endeavour overlapping spreading center which included earthquakes in west valley the northern portion of the endeavour segment southwest endeavour valley and the endeavour vent fields these swarms are attributed to volcanism including a dike intrusion on the northern endeavour in february 2005 and smaller diking events on the propagating tip of the west valley segment in both swarms the dike on the northern endeavour propagated to the south which is inconsistent with magma sourced from the axial magma chamber beneath the elevated central portion of the segment following the swarms seismic activity on the endeavour segment decreased on average to 15 of pre swarm values and almost ceased at the segment ends we infer that a 6 year non eruptive event that started with a swarm in 1999 and finished with the 2005 swarms ruptured the entire segment and relieved plate spreading stresses the inferred coupling between the 1999 and 2005 events the observation of extensive precursory activity prior to the 2005 swarms and the interaction between seismically active regions during the swarms is consistent with static triggering with delays influenced by viscoelastic relaxation hydraulic diffusion and magma withdrawal and replenishment

influence of fortnightly tides on earthquake triggering at the east pacific rise at 9 50 n the study of tidal forcing provides an opportunity to view the response of the solid earth to known changes in stress earthquakes triggered by diurnal and semidiurnal tidal forces have been well documented for the deep ocean and some terrestrial environments however few studies examine the influence of fortnightly tides on earthquake triggering and only in terrestrial environments we assess triggering of microearthquakes related to true fortnightly tides and fortnightly tidal modulations along the east pacific rise at 9 50 n where strong diurnal and semidiurnal triggering of earthquakes has been observed an ocean bottom seismograph experiment collected microearthquake data between october 2003 and january 2007 a time period that included a well documented submarine eruption culminating in january 2006 we examine how triggering changed through the build up to and aftermath of this seafloor spreading event results show that earthquakes occur preferentially during times of increasing peak volumetric stress leading up to the eruption with strong statistical significance schuster test p values up to 2 22e 31 however the correlation loses its strength immediately prior to and during the eruptive period p value as high as 0 2837 when competing tectonic and magmatic stresses may occur post eruption triggering reappears p value 1 45e 26 but with opposite phase statistical significance is also explored using monte carlo method highlighting limitations of swarm dominated time series for the schuster test nevertheless the observations are consistent with a shift in the dominating stress triggering the earthquakes from extensional tectonics to magmatic processes followed by a post eruption period of cooling relaxation and possibly magma chamber refilling

impact of siberian coastal polynyas on shelf derived arctic ocean halocline waters hydrographic and stable oxygen isotope h218o h216o sampling was carried out within the west new siberian wns coastal polynyas in the southern laptev sea in late winters 2008 and 2009 the impact of sea ice formation on the water column was quantified by a salinity lower case delta 18o mass balance several stations had vertically homogeneous physical properties in april may 2008 and featured polynya formed local bottom water with elevated signals of brine released during sea ice formation and elevated fractions of river water the polynya formed bottom water was fresher than surrounding bottom waters at other stations salinity lower case delta 18o correlation showed well defined mixing lines for bottom and surface layers in march april 2009 surface waters were strongly influenced by lena river water and local polynya activity with elevated brine signals reached to intermediate depth but did not penetrate the bottom layer in the highly stratified water column inventory values of sea ice formation were comparable in both years but freshwater distributions from the preceding summers were different therefore the observed difference in the impact of polynya activity on the water column is not primarily controlled by the amount of sea ice formed during winter but by preconditioning from the preceding summer only in years when the river plume is mostly absent in the polynya region stratification is weak and allows winter sea ice formation to reach the bottom layer thus summer stratification controls the influence of local polynya water on the shelf s bottom hydrography and as bottom water is exported impacts on the source water of shelf derived halocline waters

exchange of laptev sea and arctic ocean halocline waters in response to atmospheric forcing combined delta o18 salinity data reveal a distinctive water mass generated during winter sea ice formation which is found predominantly in the coastal polynya region of the southern laptev sea export of the brine enriched bottom water shows interannual variability in correlation with atmospheric conditions summer anticyclonic circulation is favoring an offshore transport of river water at the surface as well as a pronounced signal of brine enriched waters at about 50 m water depth at the shelf break summer cyclonic atmospheric circulation favors onshore or an eastward alongshore water transport and at the shelf break the river water fraction is reduced and the pronounced brine signal is missing while on the middle laptev sea shelf brine enriched waters are found in high proportions residence times of bottom and subsurface waters on the shelf may thereby vary considerably an export of shelf waters to the arctic ocean halocline might be shut down or strongly reduced during onshore cyclonic atmospheric circulation while with offshore anticyclonic atmospheric circulation brine waters are exported and residence times may be as short as 1 year only

cross shelf transport of warm and saline water in response to sea ice drift on the laptev sea shelf 1 oceanographic moorings and conductivity temperature depth ctd surveys from september 2009 to september 2010 are used to describe recent changes in the laptev sea hydrography and to highlight wind and ice driven surface ekman transport as the mechanism to translate these changes from the outer to the inner shelf bottom waters in february 2010 moored oceanographic instruments recorded a sudden increase in temperature 0 8 c and salinity 3 near the bottom of the inner laptev sea shelf such warm and saline waters had not been previously observed on the inner shelf in winter they likely originated from the basin and were first observed during a summer 2009 ctd survey in the northwestern shelf break region subsequently spreading east and shoreward across the laptev sea shelf the changes were introduced to the mooring site by the first of a series of bottom intensified flow events with velocities reaching 20 cm s 1 topographically guided along a relic submarine river valley each of the flow events coincided with negative pressure anomalies at the mooring site and offshore directed upwelling favorable winds and ice drift we suggest that the observations to first order resemble a simplified two dimensional two layered ocean where offshore surface ekman transport is compensated for by a barotropic shoreward response flow near the bottom in this paper we use one of the first comprehensive long term laptev sea datasets to highlight ice ocean atmosphere interactions in early and late winter and discuss the role of freshwater stratification and ice mobility on under ice circulation on the laptev sea shelf

circulation of summer pacific halocline water in the arctic ocean 1 we present an analysis of arctic ocean hydrographic and sea ice observations from the 1990s with a focus on the circulation of water that originates in the north pacific ocean previous studies have shown the presence of two varieties of relatively warm summer halocline water in the vicinity of the chukchi sea i e the relatively fresh alaskan coastal water acw and the relatively saltier summer bering sea water sbsw here we extend these studies by tracing the circulation of these waters downstream into the arctic ocean we find that acw is generally most evident in the southern beaufort gyre while sbsw is strongest in the northern portion of the beaufort gyre and along the transpolar drift stream we find that this separation is most extreme during the early mid 1990s when the arctic oscillation was at historically high index values this leads us to speculate that the outflow to the north atlantic ocean through the canadian archipelago and fram strait may be similarly separated as arctic oscillation index values fell during the later 1990s acw and sbsw began to overlap in their regions of influence these changes are evident in the area north of ellesmere island where the influence of sbsw is highly correlated with a 3 year lag with the arctic oscillation index we also note the presence of winter bering sea water wbsw which underlies the summer varieties all together this brings the number of distinct pacific water types in our arctic ocean inventory to three acw sbsw and wbsw

modeling the effects of tidal loading on mid ocean ridge hydrothermal systems 1 tidal signals are observed in numerous time series measurements obtained from mid ocean ridge hydrothermal systems in some instances these tidal signals are clearly the result of ocean currents but in other instances it appears that the signals may originate in the subseafloor formation in order to explore the effect of ocean tidal loading on mid ocean ridge hydrothermal systems we apply a one dimensional analytical model of tidal loading on a poroelastic half space and develop a two dimensional numerical model of tidal loading on a poroelastic convection cell the one dimensional models show that for a reasonable range of fluid elastic and hydrological properties the loading efficiency may vary from near zero to near unity and the diffusive penetration depth for tidal pressure signals may vary from tens of meters to kilometers the two dimensional models demonstrate that tides may generate significant vertical and horizontal pressure gradients in mid ocean ridge hydrothermal systems as a result of spatial variations in fluid temperatures and the elastic and hydrological properties of the crust these continuum models predict that outflow temperature perturbations will be very small 10 4 c but in real systems where the continuum hypothesis does not always apply the perturbations may be on the order of 0 1 c the models predict relatively large perturbations to fluid velocity at the seafloor for high temperature vents the outflow perturbations normalized to the mean flow velocity increase as the permeability decreases flow reversals at the seafloor are predicted in some regions of net low temperature outflow and net inflow during the tidal cycle in the subseafloor tidally induced flow perturbations are likely to significantly enhance mixing and fluid exchange below the seafloor in regions of slow flow and in regions where there are strong gradients in temperature or in the mechanical and hydrological properties of the crust tidally enhanced mixing and fluid exchange may significantly influence the extent and character of microbial production in the subseafloor

the recent shift in early summer arctic atmospheric circulation 1 the last six years 2007 2012 show a persistent change in early summer arctic wind patterns relative to previous decades the persistent pattern which has been previously recognized as the arctic dipole ad is characterized by relatively low sea level pressure over the siberian arctic with high pressure over the beaufort sea extending across northern north america and over greenland pressure differences peak in june in a search for a proximate cause for the newly persistent ad pattern we note that the composite 700 hpa geopotential height field during june 2007 2012 exhibits a positive anomaly only on the north american side of the arctic thus creating the enhanced mean meridional flow across the arctic coupled impacts of the new persistent pattern are increased sea ice loss in summer long lived positive temperature anomalies and ice sheet loss in west greenland and a possible increase in arctic subarctic weather linkages through higheramplitude upper level flow the north american location of increased 700 hpa positive anomalies suggests that a regional atmospheric blocking mechanism is responsible for the presence of the ad pattern consistent with observations of unprecedented high pressure anomalies over greenland since 2007 2012 american geophysical union all rights reserved

observations of static coulomb stress triggering of the november 2011 m5 7 oklahoma earthquake sequence in november 2011 a m5 0 earthquake occurred less than a day before a m5 7 earthquake near prague oklahoma which may have promoted failure of the mainshock and thousands of aftershocks along the wilzetta fault including a m5 0 aftershock the m5 0 foreshock occurred in close proximity to active fluid injection wells fluid injection can cause a buildup of pore fluid pressure decrease the fault strength and may induce earthquakes keranen et al 2013 links the m5 0 foreshock with fluid injection but the relationship between the foreshock and successive events has not been investigated here we examine the role of coseismic coulomb stress transfer on earthquakes that follow the m5 0 foreshock including the m5 7 mainshock we resolve the static coulomb stress change onto the focal mechanism nodal plane that is most consistent with the rupture geometry of the three m 5 0 earthquakes as well as specified receiver fault planes that reflect the regional stress orientation we find that coulomb stress is increased e g fault failure is promoted on the nodal planes of 60 of the events that have focal mechanism solutions and more specifically that the m5 0 foreshock promoted failure on the rupture plane of the m5 7 mainshock we test our results over a range of effective coefficient of friction values hence we argue that the m5 0 foreshock induced by fluid injection potentially triggered a cascading failure of earthquakes along the complex wilzetta fault system

channelized lava flows at the east pacific rise crest 9 10 n the importance of off axis lava transport in developing the architecture of young oceanic crust 1 submarine lava flows are the building blocks of young oceanic crust lava erupted at the ridge axis is transported across the ridge crest in a manner dictated by the rheology of the lava the characteristics of the eruption and the topography it encounters the resulting lava flows can vary dramatically in form and consequently in their impact on the physical characteristics of the seafloor and the architecture of the upper 50 500 m of the oceanic crust we have mapped and measured numerous submarine channelized lava flows at the east pacific rise epr crest 9 10 n that reflect the high effusion rate and high flow velocity end member of lava eruption and transport at mid ocean ridges channel systems composed of identifiable segments 50 1000 m in length extend up to 3 km from the axial summit trough ast and have widths of 10 50 m and depths of 2 3 m samples collected within the channels are n morb with mg indicating eruption from the ast we produce detailed maps of lava surface morphology across the channel surface from mosaics of digital images that show lineated or flat sheets at the channel center bounded by brecciated lava at the channel margins modeled velocity profiles across the channel surface allow us to determine flux through the channels from 0 4 to 4 7 103 m3 s and modeled shear rates help explain the surface morphology variation we suggest that channelized lava flows are a primary mechanism by which lava accumulates in the off axis region 1 3 km and produces the layer 2a thickening that is observed at fast and superfast spreading ridges in addition the rapid high volume flux eruptions necessary to produce channelized flows may act as an indicator of the local magma budget along the epr we find that high concentrations of channelized lava flows correlate with local across axis ridge morphology indicative of an elevated magma budget additionally in locations where channelized flows are located dominantly to the east or west of the ast the ridge crest is asymmetric and layer 2a appears to thicken over a greater distance from the ast toward the side of the ridge crest where the channels are located

tectonically induced coastal uplift mechanism of gokceada island northern aegean sea turkey abstract this paper presents evidence of coastal uplift on gokceada formerly imbros island situated in the northern aegean sea in proximity to a deep trough along the seismically active north anatolian fault naf the island comprises 2 km thick sedimentary strata underlain by metamorphic rocks which are similar to those observed 170 km to the north in the strandzha rhodope mountains the sedimentary strata begin at the bottom with eocene turbidites and limestones continue upward with oligocene lower miocene detritial rocks and andesitic volcanoclastics and end with loosely consolidated sandstones of the upper miocene pliocene at the top the island at its extreme eastern coast has a peneplain form however at its northern part it is mountainous and has steeply inclined coastal cliffs uplifted paleo shore notches hanging valleys springs waterfalls uncemented slope deposits travertine formations and exposed fault scarps field evidence of many coastal morphological geological and tectonic features together with corresponding seismic reflection data suggest that the island has experienced a rapid uplift i e vertical displacement with respect to the saros trough along the naf total uplift is on the order of a few kilometers since the initiation of the naf during pliocene or late pleistocene as suggested by some studies and the yearly rate varies from a few millimeters to a centimeter according to the age assumed for this major fault

wind driven summer surface hydrography of the eastern siberian shelf 1 high interannual variability of summer surface salinity over the laptev and east siberian sea shelves derived from historical records of the 1950s 2000s is attributed to atmospheric vorticity variations in the cyclonic regime positive vorticity the eastward diversion of the laptev sea riverine water results in a negative salinity anomaly to the east of the lena delta and farther to the east siberian sea and a positive anomaly to the north of the lena delta anticyclonic negative vorticity results in negative salinity anomalies northward from the lena delta due to freshwater advection toward the north and a corresponding salinity increase eastward

seismic triggering by rectified diffusion in geothermal systems widespread seismicity was triggered by the june 28 1992 landers california earthquake at a rate which was maximum immediately after passage of the exciting seismic waves rectified diffusion of vapor from hydrothermal liquids and magma into bubbles oscillating in an earthquake can increase the local pore pressure to seismically significant levels within the duration of the earthquake in a hydrothermal system modeled as a two component h 2o co 2 fluid in porous rock the pressure initially increases linearly with time the rate of pressure buildup depends sensitively on the mean bubble radius and is large for small bubbles the diffusion induced pressure is relaxed by percolation and resorption of vapor into the liquid solution the induced seismicity itself also relieves stress values of parameters used in the present calculations give results consistent with observations of triggered seismicity at long valley caldera after the landers earthquake for one representative condition at 250 c and 5 6 km depth oscillating strain acting on 10 m diameter bubbles increases pore pressure at the rate of 151 pa s resulting in a pressure increase of 12 kpa in the 80 s duration of the landers earthquake the elevated pressure induced by a single 26 m diameter cloud of bubbles in saturated rock relaxes by percolation through soil of 0 2 mdarcy permeability in 53 6 hours observations of earthquake swarms at other locations suggest that self induced buildup of pore pressure by rectified diffusion can provide a positive feedback mechanism for amplifying seismicity

tidal modulation of eruptive activity at open vent volcanoes evidence from stromboli italy terra nova 24 233 237 2012 abstract the role of earth tides as a relevant controlling factor of a variety of geological processes including seismicity and volcanism is widely debated stromboli volcano italy is well known for its persistent explosive activity and represents an ideal setting to investigate tidal effects on the energy release and eruptive behaviour of volcanoes herein we report new evidence that tidal stresses may modulate the timing of eruptive activity at volcanoes in an open vent state we report statistically significant correlations of the peak eruption frequencies to fortnightly tidal maxima i e full and new moon during a 17 month long period of activity in 2010 2011 in fact the number of explosive events per hour increases by 85 during tidal maxima with respect to the average values we suggest that tidally induced cycles of compression decompression of country rocks controls fluctuating magma supply rate from the shallow plumbing system and thus eruption frequency

micro textural effects on crack initiation and crack propagation of andesitic rocks abstract the onset of dilation and uniaxial compressive strength ucs of rocks are known to be affected by mineralogical petrographic and microstructural features therefore micro textural variations are essential for understanding variation in strength and failure behaviour of rocks in this study volcanic rock samples with different micro textural characteristics from different locations in turkey were evaluated the mechanical tests revealed considerable variations in unconfined uniaxial compressive strength and the crack initiation ci threshold the ucs ranges between 108 289 mpa and ci ranges between 46 130 mpa detailed quantitative petrographic and mineralogical analyses were carried out on each tested specimen to understand these strength variations additionally microstructural studies were carried out on thin sections before and after mechanical perturbation to analyze 1 the effect of the main constituents of the rock specimens and mineral heterogeneity on crack initiation and propagation and 2 the orientation and distribution of micro and macro cracks formed during laterally unconfined compression the synthesis of mechanical mineralogical petrographic and microstructural data suggests that both the crack initiation threshold and peak strength are influenced by the ratio of the area of fine grain groundmass grains smaller than 200 m to amphibole and plagioclase phenocrysts in addition ci and ucs decrease with an increasing normalized area of biotite phenocryst

changes in distribution of brine waters on the laptev sea shelf in 2007 combined salinity and 18o data from summer 2007 reveal a significant change in brine production in the laptev sea relative to summer 1994 the distribution of river water and brine enriched waters on the laptev sea shelf is derived based on mass balance calculations using salinity and 18o data while in 1994 maximal influence of brines is seen within bottom waters bauch et al 2009a in 2007 the influence of brines is highest within the surface layer and only a moderate influence of brines is observed in the bottom layer in contrast to 2007 salinity and 18o data from summer 1994 clearly identify a locally formed brine enriched bottom water mass as mixing endmember between surface layer and inner shelf waters on one side and with higher salinity water from the outer laptev sea on the other side in 2007 the brine enriched waters are predominantly part of the surface regime and the mixing endmember between surface layer and outer shelf waters is replaced by a relatively salty bottom water mass this relatively salty bottom water probably originates from the western laptev sea the inverted distribution of brines in the water column in 2007 relative to 1994 suggests a less effective winter sea ice formation in winter 2006 2007 combined with advection of more saline waters from the western laptev sea or the outer shelf precedent to 1 the climatically extreme summer 2007 the observed changes result in an altered export of waters from the laptev sea to the arctic ocean halocline

distribution of magma beneath the east pacific rise near the 9 03 n overlapping spreading center from forward modeling of common depth point data we have reprocessed six cross axis and three along axis common depth point cdp profiles near the 9 03 n overlapping spreading center osc to understand the relationship between axial magma chamber amc width and seafloor morphology travel time modeling of the amc reflector reveals an asymmetric distribution of melt across the 9 03 n osc the variation of modeled amc width beneath either osc limb is minimal but the width increases nearly fourfold across the offset attaining an estimated maximum width of 4 15 km near the 9 17 n ridge axis discontinuity additionally melt distribution underlying the eastern rise limb is not symmetric with respect to the rise axis neovolcanic zone but is displaced toward the western rise flank depth migration based on a continuum velocity model consistent with postcritical reflections from the base of layer 2a places the skewed amc reflector beneath a nearly constant thickness sheeted dike section which dips 10 away from the rise axis to confirm amc continuity beneath the western rise flank we use the maslov synthetic seismogram method to show that amplitude enhancement of the amc reflector is consistent with a continuous melt body underlying a thickening extrusive layer analysis of along strike cdp profiles indicates an amc which is neither overlapping nor discontinuous when projected onto the along strike plane identifying intracrustal events on along axis cdp lines however requires extreme caution we have modeled out of plane scattering using a kirchhoff formulation and we show that a coherent event identified beneath the overlap basin results from diffraction off the amc which lies nearly 3 km to the west of the profile we attribute the asymmetric pattern of melt to a decoupling of melt supply from preexisting weaknesses in the brittle upper crust in this model melt ascends upward buoyancy forces until deflected by the impermeable sheeted dike complex melt then migrates updip beneath the base of the sheeted dikes toward the neovplcanic zone where fissuring produces a temporary conduit for emplacement discrete jumps in modeled amc width toward the overlap basin represent a further displacement defocusing of melt supply western amc edge relative to the neovolcanic zone eastern amc edge the asymmetric pattern of melt therefore represents a gradual en echelon accommodation of melt supply across the 9 km of ridge axis offset at 9 03 n thus for asymmetric configurations amc width may not correlate solely with magmatic robustness but may signify the amount of decoupling which exists between melt supply and extrusive emplacement within the neovolcanic zone here we present a new model for osc development which invokes a significant component of cross axis melt migration moreover abrupt changes in amc width near ridge axis discontinuities e g 9 17 n deviation in axial linearity suggest that any along axis melt migration is confined to subsegments of the ridge and seem to preclude the segment length migration of melt proposed in some current models the transition of melt supply beneath the overlap basin might favor a continuous low velocity zone underlying this feature if true basin development may be related to the subsidence of a mechanically weak crustal lid the proposed model for osc development therefore views ridge axis discontinuities as the surficial response of misalignment and or defocusing of melt supply in the uppermost mantle