rupture mechanics of complex earthquakes in southern mexico abstract long period p waveforms of the three most important events of the sequence of earthquakes which occurred near the coast of chiapas mexico commencing on april 29 1970 were analysed using synthetic seismograms those synthetics were computed by the haskell thomson matrix method which allows an investigation of reflections from near source layering some perturbations in the wave forms are shown to be caused by near source structure while other are produced by complexities in the earthquake source time functions the results show that the aftershock of april 30 1970 at 0833 gmt m s 6 4 is a simple earthquake and consequently can be modelled by a single point source with a seismic moment of 6 6 10 25 dyn cm the foreshock of april 29 at 1122 gmt m s 6 3 consisted of two simple events having approximately the same seismic moment of 4 1 10 25 dyn cm four events were identified within a 15 second interval prior to the main rupture m s 7 3 for which the seismic moment was 9 9 10 26 dyn cm rather small fault areas and low rupture velocities seem to be characteristic of these earthquakes the direction of rupture does not show a clear pattern although there is a tendency for it to occur approximately in a ne sw direction

isostasy of fracture zones in the atlantic ocean the cross spectral method of studying the isostasy was applied to profiles of gravity and topography which run across fracture zones in the atlantic ocean between 40 sup 0 n and 40 sup 0 s 30 section in total were used each section 400 km long in wavelengths 25 to 80 km the coherence of the free air gravity anomaly and topography attains 0 8 while the phase is close to zero which indicates that the disturbances in gravity are controlled by the topography and its isostatic compensation the experimental isostatic response function admittance deduced in this study is compared with previous results which relied on different spatial distribution of data a single mechanism of isostasy can explain well the gravity anomalies across fraction zones and across the median valley of the mid atlantic ridge a basic feature of this mechanism is the elastic lithosphere 6 to 9 km in thickness we show that the topography and gravity anomalies over the mid atlantic ridge crest are essentially three dimensional nevertheless the admittance is reliable computed from a set of profiles by using the method of d mckenzie and c bowin this possibility is provided by the favorable pattern of the topography spectrum in the area under consideration

internal waves across the pacific 1 the long range propagation of the semidiurnal internal tide northward from the hawaiian ridge and its susceptibility to parametric subharmonic instability psi at the critical latitude c 28 8 n were examined in spring 2006 with intensive shipboard and moored observations spanning 25 37 n along a tidal beam velocity and shear at c were dominated by intense vertically standing inertially rotating bands of several hundred meters vertical wavelength these occurred in bursts following spring tide contrasting sharply with the downward propagating wind generated features seen at other latitudes these marginally stable layers which have inverse 16 meter richardson number ri16 1 0 7 are interpreted as the inertial waves resulting from psi of the internal tide elevated near inertial energy and parameterized diapycnal diffusivity and reduced asymmetry in upgoing downgoing energy were also observed at and equatorward of c yet simultaneous moored measurements of semidiurnal energy flux and 1 km deep velocity sections measured from the ship indicate that the internal tide propagates at least to 37 n with no detectable energy loss or phase discontinuity at c our observations indicate that psi occurs in the ocean with sufficient intensity to substantially alter the inertial shear field at and equatorward of c but that it does not appreciably disrupt the propagation of the tide at our location

recent developments in element concentration and isotope ratio analysis of individual fluid inclusions by laser ablation single and multiple collector icp ms abstract laser ablation inductively coupled plasma mass spectrometry la icp ms has become a most powerful technique for the elemental analysis of individual polyphase inclusions completely enclosed in minerals be they solid or a solid liquid gas mixture at the time of measurement simultaneous accurate quantification of major to ultra trace element concentrations from li to u by well controlled ablation of the entire fluid or melt inclusion content and successful use of largely matrix independent external calibration protocols are unique features of this method this contribution reviews fluid inclusion fundamentals relevant for their bulk analysis by la icp ms and discusses key aspects of the analytical protocol emphasis is on figures of merit precision accuracy obtained from the analysis of individual inclusions and fluid inclusion assemblages and procedures and technical developments to improving data quality are elaborated a new equation for the calculation of detection limits for la icp ms analysis is presented which closely follows iupac conventions applications are reviewed with emphasis on the use of synthetic fluid inclusions in constraining metal solubility and distribution between co existing phases new data for natural bismuth fluid inclusions document the seamless transition to melt inclusion analysis by la icp ms thus highlighting the fact that the procedures presented here are generally applicable to the analysis of inclusions in complex host minerals isotope ratio analysis of individual fluid inclusions by multicollector icp ms mc icp ms is a recent development that requires fast transient signals to be accurately recorded by instrumentation designed for high precision static measurements of long lasting stable ion beams we address the general principles based on pb isotopes and review a first application to the bingham canyon porphyry cu au mo deposit a pilot study using about 50 synthetic fluid inclusions containing srm 987 sr and variable nacl ca and rb concentrations demonstrates that accurate 87 sr 86 sr isotope ratios can be obtained on an individual rb poor fluid inclusion at absolute 2 precisions of 0 0003 to 0 002 a residual trend in 87 sr 86 sr as a function of the rb sr abundance ratio in the fluid inclusions suggests that interference correction of 87 rb on mass 87 assuming identical mass bias coefficients for the two elements may be inaccurate however the offset can be accurately corrected for by regressing the data to zero 87 rb the versatility and detection power of la icp ms makes this technique the method of choice for solute abundance and isotope ratio analysis of individual fluid inclusions significant future progress can be achieved by improvements in ion production transmission and data recording efficiency and by further improving control on inclusion ablation by pulsed laser beams data quantification strategies may also have to be further refined to keep pace with instrumental progress and innovation

observations of energetic high wavenumber internal waves in the kuroshio abstract intense and spatially coherent shear layers were detected in and under the kuroshio in an april 2000 survey in the east china sea the sloping layers revealed by shipboard doppler sonars on the r v roger revelle appeared to cross isopycnal surfaces except in a small region near the kuroshio shelfbreak front the rms finescale shear associated with the layers significantly exceeded the geostrophic shear an april 2002 follow on cruise was organized to establish whether these motions were propagating internal waves shipboard and lowered adcps were both operated from the r v melville in addition to ctd sonar transects a 30 h time series of currents and shear was obtained in the core of the kuroshio near the island of kyushu japan the shear structures were indeed found to be propagating with both up and down going internal wave motions present in comparison with the nearby open ocean the finescale 160 m vertical shear variance is increased by a factor of 3 in the kuroshio and by a fact

annual cycle and depth penetration of wind generated near inertial internal waves at ocean station papa in the northeast pacific abstractthe downward propagation of near inertial internal waves following winter storms is examined in the context of a 2 yr record of velocity in the upper 800 m at ocean station papa the long time series allow accurate estimation of wave frequency whereas the continuous data in depth allow separation into upward and downward propagating components near inertial kinetic energy kein dominates the record at all measured depths energy in downgoing motions exceeds that of upward propagating motions by factors of 3 7 whereas kein is elevated by a factor of 3 5 in winter relative to summer the two successive winters are qualitatively similar but show important differences in timing and depth penetration energy is seen radiating downward in a finite number of wave groups which are tagged and catalogued to determine the vertical group velocity cgz which has a mean of about 1 5 10 4 m s 1 13 m day 1 case studies of three of these are presented in detail downward energy flux is estimated as cgz

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

east pacific rise 8 10 30 n evolution of ridge segments and discontinuities from seamarc ii and three dimensional magnetic studies magnetic bathymetric and seamarc ii side scan sonar data from the ridge flanks adjoining the overlapping spreading center osc at 9 03 n on the east pacific rise epr are used to establish the evolution of this ridge axis discontinuity and adjacent ridge segments within the past 2 4 m y a three dimensional inversion for magnetization shows the discontinuity evolved from one of small offset 2 km to an 8 km offset osc within the past approximately 1 0 m y the osc has left a v shaped discordant zone indicating an average southward migration of 42 km m y since the beginning of anomaly 2 time 1 8 m y the west flank discordant zone consists of discrete abandoned overlap basins bounded by highly magnetized ridge tips with anomalous lineations while the east flank discordant zone is a broad swath of high magnetization anomalous lineations and greater depths kinematic modelling indicates that southward migration has not been steady but has been accomplished by a series of episodic propagation events with rates ranging from 500 mm yr ridge tips have been abandoned at intervals of approximately 50 000 100 000 years both by linkage of neighboring ridge segments and by self decapitation magnetic modelling suggests rotations of overlap basins of 25 consistent with predictions of kinematic modelling orientation of magnetic isochrons indicate a 3 6 counterclockwise change in pacifie cocos plate motion within the past 1 m y assuming orthogonal spreading throughout this time although the discontinuity currently located at 9 03 n existed prior to this change in plate motion its growth into a right stepping 8 km offset osc may be causally related to this change the current configuration of intratransform spreading within the siqueiros has developed since onset of the brunhes anomaly 0 73 m y possibly in response to this recent counterclockwise change in plate motion in addition to the osc there is evidence for several small discontinuities offsetting the ridge during anomaly 2 time which have since migrated along the ridge and vanished an axial magnetization high is observed along the crest of the epr change in the magnitude of the axial magnetization high or shifts in its location relative to the bathymetric axis coincide with several devals within the area magnetization maxima are found at ridge transform intersections and the osc these highs may reflect presence of highly fractionated feti basalts erupted from magma chambers with restricted supply located adjacent to both large and short offset ridge axis discontinuities discrete magnetization highs are found off axis adjacent to clipperton and siqueiros fracture zones indicating that production of feti basalts at ridge transform intersections is episodic magnetizations are higher north of clipperton than south of it possibly reflecting a long lived starvation in magma supply north of clipperton and more abundant supply to the south most seamounts within the area have the same magnetization polarity as surrounding seafloor indicating that seamount formation occurs near the ridge axis the exceptions lie near magnetic reversal boundaries and are consistent with seamount formation as close as 10 km from the ridge axis few pronounced magnetization highs are associated with seamounts indicating that the magnetized source layer is no thicker beneath them than surrounding seafloor or that seamount basalts are substantially less magnetic than normal mid ocean ridge basalts

the partitioning behavior of silver in a vapor brine rhyolite melt assemblage abstract the partitioning of silver in a sulfur free rhyolite melt vapor brine assemblage has been quantified at 800 c pressures of 100 and 140 mpa and f o 2 nno nickel nickel oxide silver solubility 2 in rhyolite increases 5 fold from 105 21 to 675 98 g g as pressure increases from 100 to 140 mpa nernst type partition coefficients d ag i j 2 describing the mass transfer of silver at 100 mpa between vapor and melt brine and melt and vapor and brine are 32 30 1151 238 and 0 026 0 004 respectively at 140 mpa values for d ag i j 2 for vapor and melt brine and melt and vapor and brine are 32 10 413 172 and 0 06 0 03 respectively apparent equilibrium constant values 2 describing the exchange of silver and sodium between vapor and melt k ag na v m at 100 and 140 mpa are 105 68 and 14 6 the average values 2 for silver and sodium exchange between brine and melt k ag na b m at 100 and 140 mpa are 313 288 and 65 12 these data indicate that the mass transfer of silver from rhyolite melt to an exsolved volatile phase s is enhanced at 100 mpa relative to 140 mpa suggesting that decompression increases the silver ore generative potential of an evolving silicate magma model calculations using the new data suggest that the evolution of low density aqueous fluid i e vapor may be responsible for the the silver tonnage of many porphyry type and perhaps epithermal type ore deposits for example halter et al halter w e pettke t and heinrich c a 2002 the origin of cu au ratios in porphyry type ore deposits science 296 1842 1844 used detailed silicate and sulfide melt inclusion and vapor and brine fluid inclusions analyses to estimate a melt volume on the order of 15 km3 to satisfy the copper budget at the bajo de la alumbrera copper gold silver ore deposit using their melt volume estimate with the data presented here model calculations for a 15 km3 felsic melt saturated with pyrrhotite and magnetite suggest that a low salinity magmatic vapor may scavenge on the order of 7 1012 g of silver from the melt this quantity of silver exceeds the discovered 2 109 g of ag at alumbrera calculated tonnages for numerous other deposits yield similar results the excess silver in the vapor remaining after porphyry formation is then available to precipitate at lower ptconditions in the stratigraphically higher epithermal environment these data suggest that silver and perhaps other ore metals in the porphyry epithermal continuum may be derived solely from the time integrated flux of dominantly low salinity vapor exsolved from a series of sequential magma batches

morphologic and geologic effects of the subduction of bathymetric highs morphologic and geologic observations suggest that subduction of bathymetric highs such as aseismic ridges chains of seamounts and fracture zones are important in the development of many forearc features and that those features form during relatively brief episodes of intense tectonism a bathymetric high obliquely entering a subduction zone tends to compress sediments along its leading edge resulting in arcward compression of the accretionary wedge a landward deflection of the trench axis and a steepened inner wall result from this deformation if a significant component of oblique slip occurs along the subduction zone then along strike movement of the accretionary wedge may also occur stresses resulting from subduction of bathymetric features with sufficient buoyancy or high relief extend farther landward than in the case of smaller less buoyant features inducing uplift of the leading edge of the overriding plate tectonic erosion of the base of the overriding plate and along strike transport of are material may also occur the accelerated tectonism observed along several convergent margins can be attributed to the consumption of bathymetric irregularities on the seafloor rather than temporally abrupt changes in rates and directions of plate motions or other episodic events in the accretionary prism

trapped near inertial waves and enhanced chlorophyll distributions waves with near inertial frequencies were observed along a front associated with a large mesoscale feature in the sargasso sea during the late summer of 1987 high subsurface chlorophyll concentrations occurred on the edge of this front coincident with the wave packets the amplitude of the waves increased with time and kinetic energy propagated downward reducing 20 m richardson numbers in the thermocline to 1 or less chlorophyll levels were episodic showing no periodicity coincident with wave dynamics however on two occasions chlorophyll concentration increased from 1 mg chl m 3 several hours after the waves penetrated the thermocline it was hypothesized that mixing associated with shear instabilities stimulated new production a diffusivity model combined with nutrient data produced a phytoplankton bloom that accounted for only one of the maxima the other increase in chlorophyll may have been the result of horizontal advection of the wave packets near the front

forced ocean response during the frontal air sea interaction experiment a central hypothesis of the frontal air sea interaction experiment fasinex was that the strong gradients in the upper ocean associated with ocean fronts would spatially modulate the response of the ocean to local atmospheric forcing to test this hypothesis measurements of near surface meteorology and upper ocean variability were made for 5 months from an array of moorings and for one of those 5 months from two ships a number of fronts passed through the moored array and the moored meteorological and current meter data were used to examine the response of the upper ocean to atmospheric forcing at subinertial and near inertial frequencies at low frequencies an ekmanlike frictionally driven component in the mixed layer and a more deeply penetrating component thought to be forced by ekman pumping were found strong near inertial response was found in the mixed layer the near inertial motion showed considerable spatial variability in the seasonal thermocline here it was evident that the structure of the front influenced the downward propagating near inertial internal waves data were also obtained by profiling instruments deployed along cross frontal sections these data were used to examine the spatial and temporal variability of the internal waves microstructure and dissipation and the relation of that variability to oceanic fronts and atmospheric events the spectral densities of the components of the internal waves that rotated clockwise with increasing depth were higher in regions of negative relative vorticity than those predicted by garrett and munk munk 1981 and estimates of clockwise and total shear were highest in regions of negative relative vorticity in the strong shear of the ocean front significant anisotropy of the internal wave field was observed and kinetic energy dissipation levels relative to the rate of work by the wind were higher than previously reported

boundary layer upper ocean and ice observations in the greenland sea marginal ice zone during the 1984 marginal ice zone experiment a coordinated ocean boundary layer and mixed layer experiment was carried out in concert with a complete heat and mass balance study in the summer marginal ice zone miz of the greenland sea the measurements were made at two drifting ice stations and included observations of ocean boundary layer turbulence profiles of water temperature salinity and velocity ice ablation ice concentration solar radiation and spectral albedos ocean conditions were found to be extremely variable the ice and water velocities were heavily influenced by tidal and inertial motions with amplitudes from 6 to 12 cm s 1 in the course of the drift a 30 km eddy was crossed wherein ice and water velocities exceeded 15 cm s 1 the northern extension of the east greenland polar front was encountered and a northward flow of atlantic water into the arctic basin was observed below the eastern edge of the front but the drift station never moved quite far enough west to be caught in the southward transport of arctic surface water heat from the ocean was a major factor in ice melt and when the ice was over atlantic water it was the dominant factor the events that had the greatest impact on the ice were two outbreaks during which off ice winds blew the ice across warm ice edge ocean fronts once south of these fronts and over surface water as warm as 1 c the ice bottom melted at rates up to 100 kg m 2 d 1 the rapid changes in stratification associated with the outbreaks had a dramatic impact on the drag and heat transfer coefficients the drag coefficient relative to the square of the relative water velocity at 30 m ranged from 0 002 to 0 02 and averaged 0 006 the heat transfer coefficient relative to the friction velocity u and the mixed layer temperature elevation above freezing ranged from 0 0025 to 0 009 and averaged 0 0038 in agreement with the idea that stratification inhibits turbulent exchange the heat transfer coefficient decreased when stratification increased in fact the observed melt rates can be simulated well if molecular heat and salt transfer through a thin near surface laminar boundary layer are accounted for as well as transfer through the turbulent outer boundary layer also in agreement with turbulent boundary layer theory the drag coefficient decreased when stratification increased slightly above neutral however for the large increases in surface stratification the drag coefficient increased this was due to the generation of internal gravity waves by ice bottom roughness because the surface exchange coefficients are so sensitive to surface stratification which is in turn highly variable in the miz accurate simulations of ice motion and ice melt will require realistic estimates of stratification and a good understanding of the relation between the ice ocean interactions and upper ocean conditions

geology of the northern colima and zacoalco grabens southwest mexico late cenozoic rifting in the mexican volcanic belt the south trending northern colima graben intersects two other grabens the northwest trending zacoalco graben and the east trending chapala graben to form a rift rift rift triple junction 50 km south southwest of guadalajara in southwest mexico the northern colima graben represents the northernmost extension of the 190 km long 20 to 65 km wide colima rift which overlies the projection of the subducting boundary of the rivera and cocos plates and represents a rift of probable pliocene pleistocene age of the east trending mexican volcanic belt mvb associated with the northernmost 90 km of the rift there are 4 6 m y old to holocene alkaline volcanic rocks rarely found in continental volcanic arc environments and which are more typically associated with either continental intraplate rifting or oceanic islands these alkaline lavas have erupted side by side with 10 m y old to holocene calc alkaline lavas that represent typical arc volcanism it is proposed that the grabens are associated with the initiation of a rifting of a portion of southwest mexico away from the mexican mainland similar to the rifting of baja california away from the mexican mainland the calc alkaline k ar dates are consistent with post mid miocene development of east trending mvb volcanism

northern east pacific rise evolution from 25 m y b p to the present the northeast pacific topography and magnetic lineations 25 m y b p to the present record the traces of three major spreading reorganizations only one spreading center is observed today but there is evidence for several ephemeral episodes of twin spreading accompanying the evolution from an extensive pacific guadalupe plate boundary to a much shortened pacific cocos and pacific rivera plate boundary the 25 m y b p plate reorganization culminated with the formation of the guadalupe plate bound by the murray fracture zone to the north and the cocos nazca spreading ridge to the south between 25 and 12 5 m y b p spreading continued while the plate retained the same general outline the 12 5 11 m y b p reorganization resulted in the creation of a much shortened pacific cocos plate boundary located in its early stages over the mathematician seamounts and a much reduced cocos plate the last reorganizaton 6 5 3 5 m y b p resulted in the abandonment of the mathematician spreading ridge as a pacific cocos plate boundary in favor of the east pacific rise

present day kinematics of the rivera plate and implications for tectonics in southwestern mexico we model the present day motion of the rivera plate relative to the pacific north america and cocos plates and combine the results with the nuvel i model for cocos north america motion to examine present day deformation in southwestern mexico the pacific rivera data which include 25 three m y average spreading rates determined from original surface ship magnetic data and 22 azimuthal data along the rivera transform are systematically misfit by the nuvel i pacific north america and pacifie cocos euler vectors indicating that the rivera plate is kinematically distinct from north america and cocos an f test shows that the improvement in fit to the pacific rivera data from a model with a distinct rivera plate exceeds that expected solely from adding three model parameters the rivera north america euler vector derived from closure of the rivera pacific north america plate circuit predicts slower and more trenchnormal convergence along the acapulco trench than prior models in addition the model predicts convergence normal to the eastern tamayo fracture zone at a rate 60 slower than the right lateral strike slip predicted by prior models an observed systematic misfit of the pacific rivera euler vector to azimuths from the western rivera transform fault may have several causes there may be a time averaging problem between the 3 0 m y average rates and the shorter time average transform fault azimuths and earthquake slip vectors alternatively rivera transform trends may be biased by deformation within lithosphere adjacent to the transform valley or future detailed mapping of the transform may reveal the misfit to be an artifact of the presently available bathymetry along the entire pacific rivera rise spreading rates averaged over the past 0 7 m y are systematically faster than 3 0 m y average rates with the difference increasing southward along the rise the post 3 ma change in the rate gradient has caused a southward migration of the pacific rivera euler pole since 3 ma possibly in response to the 3 ma completion of a spreading reorganization that doubled the length of the rivera transform fault and halved the area of the rivera plate we hypothesize that deformation in southwestern mexico including opening along the colima rift is related to oblique subduction of the cocos plate along the northern middle america trench three unes of evidence support this hypothesis first the sense of oblique subduction predicted by nuvel i along the middle america trench is consistent with a model in which part of western mexico located southeast of the colima rift moves to the southeast relative to north america second field geologic data and landsat imagery suggest that in the past few million years the chapala oaxaco fault zone has accommodated several kilometers of sinistral motion and sinistral transtension has occurred along the trans mexican volcanic belt either or both of these fault zones could accommodate any southeastward coastal block motion that might result from oblique subduction third the observation that earthquake slip vectors from the northern middle america trench trend systematically counterclockwise from the predicted cocos north america convergence direction is also consistent with southeastward motion the discrepancy between the observed and predicted slip directions along the middle america trench suggests sinistral slip is 0 10 mm yr 1 if oblique subduction is driving southeastward transport of a coastal sliver the colima rift is a passive pull apart zone at the northwestern end of this sliver rather than an incipient spreading ridge that will replace the pacific rivera rise

relationship between subduction and seismicity in the mexican part of the middle america trench two catalogs of earthquakes in the mexican part of the middle america trench are analyzed to elucidate principal relations between structure of the subducting cocos plate and seismicity a catalog of historical events that have occurred during the last two centuries with large magnitudes ms 6 0 is used to obtain cumulative seismic moment mo and seismic moment release rate m 0 distributions along the mexican subduction zone the catalog of instrumentally observed earthquakes from 1963 to 1990 international seismological center and u s geological survey with 4 5 mb 6 0 is applied to investigate background seismicity for the region the strength of coupling between the cocos and north american plates would be expected to grow gradually from the southeast to the northwest according to the variation of convergence rate v and age a of the cocos plate this correlates in general with a steady reduction in background seismicity and a slight average increase of m 0 and seismic energy release rate w at the sites where the main fracture zones of the cocos plate tehuantepec o gorman orozco and rivera undergo the subduction the general correlation breaks down the background seismicity increases at fracture zones while m0 and m 0 decrease significantly this feature is interpreted as a drop of the coupling at the areas where transform faults are being subducted seismic slip rates along the trench obtained from m 0 are lower then the values of plate convergence rates but the average seismic slip is in agreement with the estimates from the v model interaction between lithospheric plates at convergent zones through the viscous layer of subducted sediments variability of m 0 and seismic slip rate in relation with tectonics should be taken into account when the seismic gap model is being used for the prediction of strong earthquakes an examination of space time plots for the historical catalogs supposes a probable tendency of northwest migration of strong events with a rate of 10 km yr

observations of near inertial surface currents off oregon decorrelation time and length scales 1 high resolution km in space and hourly in time surface currents observed by an array of high frequency radars off oregon are analyzed to quantify the decorrelation time and length scales of their near inertial motions the near inertial surface currents are dominantly clockwise with amplitudes of 9 12 cm s 1 however they appear asymmetric and elliptical as a result of counterclockwise inertial motions with magnitudes in a range of 2 5 cm s 1 the decorrelation time and length scales are computed from the decay slope of the near inertial peak and the spatial coherence in the near inertial frequency band respectively decorrelation time scales of clockwise near inertial motions increase from 2 days nearshore within 30 km from the coast to 6 days offshore and their length scales increase from 30 to 90 km seaward possibly due to coastal inhibition the local spatial coherence has an exponentially decaying structure for both clockwise and counterclockwise rotations and their phases propagate northwestward offshore for clockwise and northeastward onshore for counterclockwise rotations

synthetic fluid inclusions in natural quartz i compositional types synthesized and applications to experimental geochemistry synthetic fluid inclusions having a wide range of geologically applicable compositions in the c o h s na k ca cl cu fe system have been formed by healing fractures in inclusion free natural quartz and by precipitating new quartz overgrowths on an original seed crystal inclusion types synthesized include 1 1 liquid rich pure h2o inclusions of primary and secondary origin 2 2 pure h2o inclusions with the critical density 3 3 liquid rich inclusions containing undersaturated aqueous solutions of nacl or kcl or cacl2 or mixtures of the three salts 4 4 h2o nacl inclusions containing halite daughter minerals 5 5 h2o nacl kcl inclusions containing halite and sylvite daughter minerals 6 6 h2o co2 inclusions of various compositions containing liquid h2o and either co2 vapor or co2 liquid or both at 25 c 7 7 h2o co2 nacl inclusions containing an aqueous phase liquid and vapor co2 and halite at 25 c 8 8 c o h inclusions containing liquid h2o a co2 ch4 liquid phase and graphite daughter minerals at 25 c 9 9 h2o nacl inclusions that contain a chalcopyrite daughter mineral and 10 10 inclusions representing trapping of the coexisting immiscible fluids in the h2o nacl h2o co2 nacl and na c o h systems the inclusions exhibit uniform phase ratios at room temperature and the temperatures of various phase changes within individual inclusions agree with those predicted from experimental and theoretical data indicating that the inclusion fluid has the same composition and density as the parent solution these miniature autoclaves thus may be used to study various problems related to fluid inclusion research to calibrate analytical equipment used to study natural inclusions and to study phase equilibria solubility and pvt relations of a variety of chemical systems

interaction of superinertial waves with submesoscale cyclonic filaments in the north wall of the gulf stream abstracthigh resolution nearly lagrangian observations of velocity and density made in the north wall of the gulf stream reveal banded shear structures characteristic of near inertial waves niws here the current follows submesoscale dynamics with rossby and richardson numbers near one and the vertical vorticity is positive this allows for a unique analysis of the interaction of niws with a submesoscale current dominated by cyclonic as opposed to anticyclonic vorticity rotary spectra reveal that the vertical shear vector rotates primarily clockwise with depth and with time at frequencies near and above the local coriolis frequency f at some depths more than half of the measured shear variance is explained by clockwise rotary motions with frequencies between f and 1 7f the dominant superinertial frequencies are consistent with those inferred from a dispersion relation for niws in submesoscale currents that depends on the observed aspect ratio of the wave shear as well as the vertical vorticity

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

nonuniform seismic slip rates along the middle america trench revised estimates of seismic slip rates along the middle america trench are lower on the average than plate convergence rates but match them locally for example oaxaca along the cocos north american plate boundary this can be explained by nonuniformities in slip at points of aseismic ridge or fracture zone subduction for at least 81 yr and possibly several hundred years no major m sub s or 7 5 shallow earthquake is known to have occurred near the orozco fracture zone and tehuantepec ridge areas compared with the average recurrence periods for large earthquakes 33 8 yr since 1898 and 35 24 yr between 1542 and 1979 this suggests that either a large m or 8 4 event may be anticipated at such locations or that these are points of aseismic subduction large coastal terraces and evidence suggesting tectonic uplift are found onshore near the orozco fracture zone the larger discrepancy between plate convergence and seismic slip rates along the cocos carribbean plate boundary is more likely due to decoupling and downbending of the subducted plate we used the limited statistical evidence available to characterize both spatial and temporal deficiencies in recent seismic slip the observations appear consistent with a possible forthcoming episodemore of more intense seismic activity based on a series of comparisons with carefully delineated aftershock zones we conclude that the zones of anomalous seismic activity can be indentified by a systematic automated analysis of the worldwide earthquake catalog m sub b or 4 less

space time scales of shear in the north pacific abstractthe spatial temporal and directional characteristics of shear are examined in the upper 1400 m of the north pacific during late spring with an array of five profiling moorings deployed from 25 to 37 n 1330 km and simultaneous shipboard transects past them the array extended from a regime of moderate wind generation at the north to south of the critical latitude 28 8 n where parametric subharmonic instability psi can transfer energy from semidiurnal tides to near inertial motions analyses are done in an isopycnal following frame to minimize contamination by doppler shifting approximately 60 of rms shear at vertical scales 20m and 80 for vertical scales 80 m is contained in near inertial motions an inertial back rotation technique is used to index shipboard observations to a common time and to compute integral time scales of the shear layers persistence times are o 7 days at most moorings but o 25 days at the critical latitude simultaneous shipboard transects show that these sh

role of near inertial internal waves in subthermocline diapycnal mixing in the northern gulf of mexico abstractmoored adcp data collected in the northern gulf of mexico are analyzed to examine near inertial internal waves and their contribution to subthermocline diapycnal mixing based on a finescale parameterization of deep ocean mixing the focus of the study is on the impact of near inertial internal waves generated by an extreme weather event that is hurricane katrina and by month to month variation in weather patterns on the diapycnal mixing the inferred subthermocline diapycnal mixing exhibits pronounced elevation in the wake of katrina both the increased near inertial 0 8 1 8f where f is the coriolis frequency and superinertial 1 8f shear variances contribute to the elevated diapycnal mixing but the former plays a more dominant role the intense wind work on near inertial motions by the hurricane is largely responsible for the energetic near inertial shear variance energy transfer from near inertial to superinertial internal waves however appears to play an important role in elevating th

the upper ocean response to monsoonal forcing in the arabian sea seasonal and spatial variability abstract observations from four towed profiler surveys undertaken between december 1994 and october 1995 examine the seasonal and spatial variability of the upper ocean response to the monsoon cycle in the arabian sea although observed atmospheric forcing agrees well with modern climatologies cross basin patterns of mixed layer depth and water properties observed in 1994 1995 are not entirely consistent with an upper ocean response dominated by ekman pumping during the winter monsoon the mixed layer deepens dramatically with distance offshore surface cooling intensifies with offshore distance and a one dimensional response dominated by convective overturning could explain observed wintertime mixed layer depths except for waters associated with a filament extending offshore from the omani coast mixed layer depths and water properties show only modest cross basin contrasts during the southwest monsoon filament waters differ from surrounding mid basin waters having shallow mixed layers and water properties similar to those of waters upwelled near the omani coast in september following the southwest monsoon waters within 1000 km of the omani coast have cooled and freshened with marked changes in stratification extending well into the pycnocline estimates of ekman pumping and wind driven entrainment made using the southampton oceanographic center 1980 1995 surface flux and the levitus mixed layer climatologies indicate that during the southwest monsoon wind driven entrainment is considerably stronger than ekman pumping inshore of the windstress maximum ekman pumping partially counters wind driven entrainment while offshore the two processes act together to deepen the mixed layer as ekman pumping is too weak to counter wind driven mixed layer deepening inshore of the windstress maximum another mechanism must act to maintain the shallow mixed layers seen in our observations and in climatologies offshore advection of coastally upwelled water offers a mechanism for maintaining upper ocean stratification that is consistent with observed changes in upper ocean water properties ekman upwelling will modulate wind driven entrainment but these results indicate that the primary mechanisms acting inshore of the windstress maximum are wind driven mixing and horizontal advection

near inertial wave propagation in the western arctic abstract from october 1997 through october 1998 the surface heat budget of the arctic sheba ice camp drifted across the western arctic ocean from the central canada basin over the northwind ridge and across the chukchi cap during much of this period the velocity and shear fields in the upper ocean were monitored by doppler sonar near inertial internal waves are found to be the dominant contributors to the superinertial motion field typical rms velocities are 1 2 cm s 1 in this work the velocity and shear variances associated with upward and downward propagating wave groups are quantified patterns are detected in these variances that correlate with underlying seafloor depth these are explored with the objective of assessing the role that these extremely low energy near inertial waves play in the larger scale evolution of the canada basin the specific focus is the energy flux delivered to the slopes and shelves of the basin available for driving mixing at the ocean boundaries the energy and

northern east pacific rise magnetic anomaly and bathymetric framework the oceanic crust in the eastern pacific between 7on and 30on and east of 127ow contains a fairly complete history of the spreading centers associated with the east pacific rise since 25 m y b p late oligocene in this paper we have summarized the seafloor spreading magnetic anomaly data and the bathymetric data that reflect the record of this tectonic history the well defined magnetic lineations north of the clarion fracture zone in the mouth of the gulf of california and on the east flank of the east pacific rise epr are carefully examined and used to provide a guide for interpreting the spreading pattern between the clarion and clipperton fracture zones southward of the rivera fracture zone over the mathematician ridge and over the entire epr east of the mathematician ridge between the rivera and siqueiros fracture zones the bathymetric data provide a trace of the fracture zone pattern in each of the above mentioned areas the fracture zone bathymetry and the seafloor spreading magnetic lineations on the epr south of the rivera fracture zone have a distinctive fanning pattern caused by close poles of rotation and plate boundary reorganizations all these data provide a good record of the plate reorganizations in the middle miocene at magnetic anomaly 5a time 12 5 to 11 m y b p in the late miocene at magnetic anomaly 3 4 time 6 5 m y b p and in the pliocene at magnetic anomaly 2 3 time 3 5 m y b p several abandoned spreading centers including the mathematician ridge were left behind as a result of these reorganizations the mathematician ridge is shown to be a set of ridges and trough whose origin is related to the tectonic activity associated with each of the above mentioned reorganizations since anomaly 5a

transfer of volatiles and metals from mafic to felsic magmas in composite magma chambers an experimental study abstract in order to determine the behavior of metals and volatiles during intrusion of mafic magma into the base of silicic upper crustal magma chambers fluid rock partition coefficients dfluid rock of li b na s cl k mn fe rb sr ba ce cu zn ag cd mo as se sb te w tl pb and bi were determined experimentally at 2 kbar and 850 c close to the solidus of mafic magma in a first step volatile bearing mafic glasses were prepared by melting a natural basaltic trachyandesite in the presence of volatile bearing fluids at 1200 c 10 kbar in piston cylinder presses the hydrous glasses were then equilibrated in subsequent experiments at 850 c 2 kbar in cold seal pressure vessels which caused 80 90 of the melt to crystallize after 0 5 2 0 days of equilibration the exsolved fluid was trapped by means of in situ fracturing in the form of synthetic fluid inclusions in quartz both the mafic rock residue and the fluid inclusions were subsequently analyzed by laser ablation icp ms for major and trace elements reverse experiments were conducted by equilibrating metal bearing aqueous solutions with rock powder and then trapping the fluid in two additional experiments information on relative element mobilities were obtained by reacting fluids that exsolved from crystallizing mafic magma with overlying silicic melts the combined results suggest that under the studied conditions s cl cu se br cd and te are most volatile dfluid rock 10 followed by li b zn as ag sb cs w tl pb and bi dfluid rock 1 10 less volatile are na mg k ca mn fe rb sr mo and rb dfluid rock 0 1 1 and the least fluid mobile elements are al si ti zr ba and ce dfluid rock

baroclinic energy flux at the hawaiian ridge observations from the r p flip abstract estimates of baroclinic energy flux are made in the immediate nearfield september october 2002 and 450 km offshore farfield october november 2001 of the kaena ridge an active barotropic to baroclinic conversion site the flux estimates are based on repeated profiles of velocity and density obtained from the research platform floating instrument platform flip as an aspect of the hawaii ocean mixing experiment energetic beams associated with both semidiurnal and diurnal internal waves are observed in the kauai channel beam depths and orientations are consistent with generation along the upper flanks of the ridge at the far field site the baroclinic energy flux is borne primarily by first mode semidiurnal waves the energy flux associated with the entire spectrum of internal waves is computed by cross spectral analysis significant energy fluxes are found in the inertial diurnal semidiurnal and twice semidiurnal frequency bands the semidiurnal energy flux strongly dominates the s

geometry of subduction and depth of the seismogenic zone in the guerrero gap mexico the western coast of guerrero in southern mexico has been identified as a seismic gap on the middle american trench in which no large earthquakes have occurred at least since 1908 it has been suggested that the seismic energy accumulated since 1908 will eventually be released by a large earthquake a permanent seismic network was installed to monitor the seismicity of this mature seismic gap and to understand the geometry of the subducted slab beneath this region the seismicity defines an unusual distribution along two bands of seismic activity parallel to the coast the resulting geometry of the subduction zone shows that the cocos plate dips at a shallow angle beneath the north american plate to a depth of 40 km from there the subducted slab is bent upward following a subhorizontal trajectory extending inland at a depth of 50 km this plate geometry is reminiscent of that found in peru and central argentina two other regions where a young oceanic plate is being subducted in mexico however the slab underplates an overriding plate which is only half as thick as that observed in south america a possible oceanic origin of the allochtonous terranes comprising southern mexico may explain the presence of the anomalously thin lithosphere in this region

influence of varying upper ocean stratification on coastal near inertial currents the influence of varying horizontal and vertical stratification in the upper layer o 10 m associated with riverine waters and seasonal atmospheric fluxes on coastal near inertial currents is investigated with remotely sensed and in situ observations of surface and subsurface currents and realistic numerical model outputs off the coast of oregon based on numerical simulations with and without the columbia river cr during summer the directly wind forced near inertial surface currents are enhanced by 30 60 when the near surface layer has a stratified condition due to riverine water inputs from the cr comparing model results without the cr for summer and winter conditions indicates that the directly wind forced near inertial surface current response to a unit wind forcing during summer are 20 70 stronger than those during winter depending on the cross shore location which is in contrast to the seasonal patterns of both mixed layer depth and amplitudes of near inertial currents the model simulations are used to examine aspects of coastal inhibition of near inertial currents manifested in their spatial coherence in the cross shore direction where the phase propagates upward over the continental shelf bounces at the coast and continues increasing upward offshore toward surface and then downward offshore at the surface with magnitudes and length scales in the near surface layer increasing offshore this pattern exhibits a particularly well organized structure during winter similarly the raypaths of clockwise near inertial internal waves are consistent with the phase propagation of coherence showing the influence of upper layer stratification and coastal inhibition

stress accumulation and release since 1882 in ometepec guerrero mexico implications for failure mechanisms and risk assessments of a seismic gap we found evidence that four episodes of large shallow h 60 km the time intervals between extensional and subsequent compressional events range from 1 6 to 9 9 years with an average of 6 3 3 7 years this apparent pattern which initiates at depth was further documented for the final 2 3 of the last seismic cycle from the spatiotemporal distribution of seismicity during this final period we identified three general stages of stress release stage i from 1964 to january 1980 was characterized by scattered seismicity stage ii from february 1980 to june 6 1982 showed a significant increase in downdip seismic activity while the shallow zone became quiescent there was also a period of apparent seismic quiescence from mid 1975 to early 1978 most seismic energy in stage ii was released on october 24 1980 by a downdip normal fault earthquake at intermediate depth ms 7 0 h 65 km stage iii began on june 7 1982 with the occurrence of two large interplate thrust fault earthquakes at shallow depths ms 6 9 h 18 km and ms 7 0 h 19 and 23 km the documentation of stage iii through june 1986 shows subsidence of previous downdip activity and an aftershock zone which is spatially coincident with the shallow quiet zone identified in stage ii the spatiotemporal characteristics of the 1982 main shock after shock sequence suggests that rupture propagated to the northwest toward the site of the 1957 ms 7 5 acapulco san marcos earthquake this propagation is of interest because the latter site is presently considered to possess high seismic potential we suggest that downdip normal fault seismic activity at intermediate depths reflects a symptomatic state of stress associated with some basic mechanism of plate interaction prior to interplate slippage in a large earthquake this mechanism may have an important bearing on the generation and possible intermediate term forecasts of large shallow interplate earthquakes along the subduction zone in mexico

near inertial current oscillations off the mid east coast of korea abstract near inertial current oscillations were observed at depths of 620 and 790 m at a current meter mooring station in water 840 m deep off the mid east coast of korea the oscillatory inertial motions with an amplitude of up to 8 cm s existed during 73 days between august 27 and november 7 of 1986 with a large temporal variation in speed spectral analysis of the data was conducted and the result showed that the most dominant signal in the records was clockwise rotation whose frequency was close to the inertial frequency the peak frequency of the near inertial oscillations was slightly greater than the local inertial frequency f 0 0511 cph by 2 5 these clockwise oscillations had the mean amplitude of about 2 5 cm s reaching an instantaneous maximum of 7 5 cm s the mean ratio of the semi major axis to the semi minor one was found to be about 1 2 and the mean direction of the major axis was nearly parallel to the isobaths around the mooring station high near inertial energy parallel continuously during the first 15 days and then appeared in the form of group wave packets lasting several days during the remaining period three prominent events of wave packets were more energetic at the deeper depth the phase difference between the two horizontal near inertial current vectors changed largely with time but it remained relatively constant during each of the three energetic events changing its sign from one event to another the horizontal near inertial current vector rotated clockwise with increasing depth during one event but counterclockwise during the other two events the corresponding phase propagation was upward with a phase speed of 2 5 cm s for the clockwise polarization with depth but downward with 1 8 and 1 1 cm s for the counterclockwise rotating events

an evaluation of synthetic fluid inclusions for the purpose of trapping equilibrated coexisting immiscible fluid phases at magmatic conditions we report data that allow us to evaluate the method of trapping immiscible saline aqueous fluids i e vapor and brine in the nacl kcl hcl fecl2 auhcl2 h2o system as synthetic fluid inclusions in pre fractured quartz cores in order to quantify the concentrations of au fe k and na among coexisting three phase immiscible fluids i e haplogranite melt brine and vapor at magmatic conditions coexisting vapor and brine were trapped experimentally at 800 c and 100 110 mpa as synthetic fluid inclusions in both quartz microfractures and quenched silicate melt i e glass and also sampled indirectly using the recovered quenched aqueous fluid quartz hosted and glass hosted brine inclusions were analyzed by laser ablation inductively coupled plasma mass spectrometry la icpms and instrumental neutron activation analysis inaa respectively quenched aqueous fluid from each experiment containing a quartz core was recovered and analyzed by atomic absorption spectrophotometry aas the composition of aqueous fluids trapped as quartz hosted inclusions glass hosted inclusions and those recovered after quench yield consistent and precise data at the 2 uncertainty level for the elements of interest the overlapping au fe k and na concentrations in aqueous fluids trapped and analyzed via three entirely different instrumental techniques i e la icpms inaa and aas suggest strongly that quartz microfractures heal on a slow enough time scale to permit entrapment of fully equilibrated aqueous fluids at our experimental ptx conditions the data evince clearly that the chemical composition of fluids in quartz microfractures at the time of self healing represents equilibrium conditions hence synthetic fluid inclusions in experiments with low thermal gradients across the charge provide a reasonable estimate of fluid composition at least at the experimental conditions examined in this study

conditional probabilities for the recurrence of large and great interplate earthquakes along the mexican subduction zone abstract time dependent conditional probabilities for the recurrence of large and great interplate earthquakes along the mexican subduction zone are presented for time intervals of 5 10 and 20 yr duration i e 1986 1991 1986 1996 and 1986 2006 at present the central oaxaca 97 3 to 97 7 w ometepec san marcos 98 2 to 99 5 w and central guerrero 100 to 101 w segments stand out as having the highest probability for the recurrence of large and great earthquakes in the near future segmentation of the margin is delineated by the rupture zones of the most recent earthquakes occurring in each area for segments of the mexican margin with one or more known recurrence intervals probability estimates are based on the observed average recurrence time for each segment and the lognormal probability distribution function use of a generic distribution function nishenko and buland 1987 allows a more stable estimate of average recurrence times than are available from a few observations a long term prediction time window is also defined based on the 90 per cent confidence interval for our estimates of the recurrence time use of a predetermined confidence interval conveys valuable additional information as to the precision and information content of the forecast for those segments of the margin with only one prior event and hence no historically observed recurrence times repeat times are estimated by extrapolating the observed recurrence time behavior in oaxaca subject to the assumptions that recurrence time scales only as a function of the ratio of seismic displacement and convergence rate and that all events are characterized as simple sources i e involve the rupture of a single asperity

the determination of phase relations in the ch4h2onacl system at 1 kbar 400 to 600 c using synthetic fluid inclusions synthesis of fluid inclusions in the ch4 h2o nacl system was accomplished by subjecting fractured quartz along with known quantities of ch4 h2o and nacl to a pressure of 1 kbar and temperatures of 400 500 or 600 c in sealed au capsules under the elevated p t conditions some of the fractures healed trapping fluids as inclusions microthermometric measurements conducted on the fluid inclusions show that at 1 kbar and 400 to 600 c there are very broad regions of fluid unmixing in the ch4 h2o nacl system for those bulk fluid compositions that lie in the two phase i e immiscible fluids field the high density phase is enriched in nacl whereas the low density phase is enriched in ch4 for any given bulk composition the degree of nacl enrichment in the high density phase increases whereas the degree of ch4 enrichment in the low density phase decreases as temperature increases from 4 00 to 600 c

submesoscale water mass spectra in the sargasso sea submesoscale stirring contributes to the cascade of tracer variance from large to small scales multiple nested surveys in the summer sargasso sea with tow yo and autonomous platforms captured submesoscale water mass variability in the seasonal pycnocline at 20 60 m depths to filter out internal waves that dominate dynamic signals on these scales spectra for salinity anomalies on isopycnals were formed salinitygradient spectra are approximately flat with slopes of 20 2 6 0 2 over horizontal wavelengths of 0 03 10km while the two to three realizations presented here might be biased more representative measurements in the literature are consistent with a nearly flat submesoscale passive tracer gradient spectrum for horizontal wavelengths in excess of 1km a review of mechanisms that could be responsible for a flat passive tracer gradient spectrum rules out i quasigeostrophic eddy stirring ii atmospheric forcing through a relict submesoscale winter mixed layer structure or nocturnal mixed layer deepening iii a downscale vortical mode cascade and iv horizontal diffusion because of shear dispersion of diapycnal mixing internal wave horizontal strain appears to be able to explain horizontal wavenumbers of 0 1 7 cycles per kilometer cpkm but not the highest resolved wavenumbers 7 30cpkm submesoscale subduction cannot be ruled out at these depths though previous observations observe a flat spectrum well below subduction depths so this seems unlikely primitive equation numerical modeling suggests that nonquasigeostrophic subinertial horizontal stirring can produce a flat spectrum the last need not be limited to mode one interior or surface rossby wavenumbers of quasigeostrophic theory but may have a broaderband spectrum extending to smaller horizontal scales associated with frontogenesis and frontal instabilities as well as internal waves

a near inertial internal wave spectrum for the sargasso sea in late summer abstract independent estimates of the frequency wavenumber spectrum of near inertial waves for the sargasso sea in late summer were made using 8 time series of horizontal velocity from a single moored vertical array and 58 vertical profiles of horizontal velocity from a horizontal array of expendable velocity profilers the profiler data were analyzed to produce an internal wave frequency wavenumber spectrum with sufficient resolution to resolve the details of the inertial peak and compute the vertical energy flux comparison with the lower resolution spectrum from the moored array shows qualitative agreement the differences are most likely due to biases in both techniques and to intermittency of the internal wave field these data reveal a marked asymmetry of the near inertial internal wave field with a net downward enemy flux of 0 12 0 12 ergs cm 2 s 1 the downward propagating waves have more energy a larger horizontal scale and a lower frequency than the upward propagating waves the magnitude of t

recent large earthquakes along the middle american trench and their implications for the subduction process several large shallow earthquakes ms 7 0 have occurred along the middle american trench since the installation of the wwssn network included are the 1965 1968 and 1978 oaxaca events the 1970 chiapas event the 1973 colima event and the 1979 petatlan event these earthquakes have been studied in an attempt to identify similarities and differences between them that may lead to a better understanding of fracture and subduction processes the events have seismic moments ranging from 1 0 1027 dyne cm for the 1968 event to 3 2 1027 dyne cm for the 1978 event all events are of predominantly thrust type consistent with subduction to the northeast of the cocos plate body waves for the 1965 1968 1978 and 1979 events along the trench indicate rather simple faulting processes these events all had focal depths of 15 to 20 km and stress drops of the order of 10 bars the 1970 and 1973 events the easternmost and westernmost respectively of the events studied here are located close to triple junctions for the cocos north america caribbean plates 1970 and the cocos north america rivera plates 1973 these two events generated more complex body waves than the oaxaca and petatlan quakes this source complexity may have been related to the more complicated tectonics near the 1970 and 1973 epicenters this may offer a new perspective to viewing source complexity in relation to subduction zones

inertial wave dynamics in the north atlantic subtropical zone doppler current profiler observations of an inertial wave packet are presented from a region where a cold core ring impinges on a front in this intense current a drogue is deployed to mark one region of the fluid as the drogue is advected by the current the ship follows it zigzagging across the drogue s trajectory along this ship track vertical rotary velocity spectra indicate the presence of a downgoing intertial wave with a vertical wavelength which slowly changes from 50 to 100 m as time progresses the wave s intrinsic frequency was measured for the first time ever a horizontally synoptic data set is obtained at the drogue depth by correcting for frontal advection and the temporal rotation of the wave velocity examination of these synoptic data indicates the presence of a southgoing near inertial wave with horizontal wavelength 20 km the wave is confined to a 25 km region supplementary ray tracing calculations through objective maps of the ring flow field indicate that the wave is strongly influenced by doppler shifting this is accompanied by a slow counterclockwise turning of the horizontal wave number vector a decrease in the intrinsic frequency and an increase in the vertical wavelength in qualitative agreement with the data a companion paper marmorino et al this issue details the effect of this inertial wave upon the small scale temperature activity with horizontal length scales of 1 3 m

near inertial mixing in the central arctic ocean observations were made in april 2007 of horizontal currents hydrography and shear microstructure in the upper 500m from a drifting ice camp in the central arctic ocean an approximately 4 day long time series collected about 10 days after a storm event shows enhanced near inertial oscillations in the first half of the measurement period with comparable upward and downward propagating energy rough estimates of wind work and near inertial flux imply that the waves were likely generated by the previous storm the nearinertial frequency band is associated with dominant clockwise rotation in time of the horizontal currents and enhanced dissipation rates of turbulent kinetic energy the vertical profile of dissipation rate shows elevated values in the pycnocline between the relatively turbulent underice boundary layer and the deeper quiescent water column dissipation averaged in the pycnocline is near inertially modulated and its magnitude decays approximately at a rate implied by the reduction of energy over time observations suggest that near inertial energy and internal wave induced mixing play a significant role in vertical mixing in the arctic ocean

experimental study of the behavior of copper and zinc in a boiling hydrothermal system vapor liquid partitioning coefficients for cu and zn in aqueous fluid were determined under boiling conditions at 500 650 c and 35 100 mpa in sulfur bearing and sulfur free systems a synthetic fluid inclusion technique was used to sample the experimental system of coexisting vapor rich and liquid rich fluid inclusions the cu and zn concentrations in individual fluid inclusions were then analyzed by synchrotron radiation x ray fluorescence the vapor liquid distribution constant of cu k d m cu vapor m cu liquid where m denotes the molality of metal is found to be strongly dependent on the sulfur content in the experimental solutions in sulfur bearing systems cu preferentially partitions into the vapor phase whereas zn preferentially fractionates into the hypersaline liquid the k d values for cu and zn obtained in this study correspond well with those obtained from natural fluid inclusions in hydrothermal ore deposits the results suggest that differential volatility of metals is an important factor affecting the enrichment of certain metals in different hydrothermal ore deposits

observations of shear and vertical stability from a neutrally buoyant float measurements of 1 to 5 m shear and strain from a neutrally buoyant float are used to examine the statistics and causes of shear instability in a 9 day record unstable conditions defined as vz n 2 where vz vz are due to higher than average shear rather than lower than average buoyancy frequency and there are no instances of unstable buoyancy frequency or overturns on the 0 5 m spacing of the thermistors shear is dominated by upward propagating near inertial motions unstable events were more frequent when a near inertial wave packet occupied the water parcel tracked by the float groups of unstable events occur roughly every 5 7 hours at scales 2 5 m and much less often at larger scales events typically last 10 min one buoyancy period or longer these time scales appear to be controlled by vertical advection of 1 m fine structure past the float sensors so do not represent the intrinsic time scales of instability turbulent and mixing quantities are estimated from these fine scale measurements giving a dissipation rate of e 2 3 16 10 10 w kg and an eddy diffusivity of k 3 10 6 m2 s in agreement with direct microstructure estimates therefore the float adequately resolves those quantities needed to estimate turbulent dissipation and could be used to monitor turbulent mixing in the ocean

shallow ocean response to tropical cyclones observed on the continental shelf of the northwestern south china sea based on observed temperature and velocity in 2005 in northwestern south china sea the shallow ocean responses to three tropical cyclones were examined the oceanic response to washi was similar to common observations with 2 degrees c cooling of the ocean surface and slight warming of the thermocline resulted from vertical entrainment moreover the wavefield was dominated by first mode near inertial oscillations which were red shifted and trapped by negative background vorticity leading to an e folding timescale of 12 days the repeated reflections by the surface and bottom boundaries were thought to yield the successive emergence of higher modes the oceanic responses to vicente appeared to be insignificant with cooling of the ocean surface by only 0 5 degrees c and near inertial currents no larger than 0 10 m s as a result of a deepened surface mixed layer however the oceanic responses to typhoon damrey were drastic with cooling of 4 5 degrees c near the surface and successive barotropic like near inertial oscillations during the forced stage the upper ocean heat content decreased conspicuously by 11 65 and the stratification was thoroughly destroyed by vertical mixing in the relaxation stage the water particle had vertical displacement of 20 30 m generated by inertial pumping the current response to damrey was weaker than washi due to the deepened mixed layer and the destroyed stratification our results suggested that the shallow water oceanic responses to tropical cyclones varied significantly with the intensity of tropical cyclones and was affected by local stratification and background vorticity

stress transfer and nonlinear stress accumulation at subduction type plate boundaries application to the aleutians a study of stress accumulation in seismic gaps and of stress transfer along linear plate boundaries is presented time dependent reloading of plate boundaries following seismic ruptures is modeled by a modified elsasser model of a coupled lithosphere asthenosphere plate system this model is applied to study a series of large earthquakes in the aleutian islands and the alaska peninsula in 1938 1965 it is found that the rat island earthquake and the 1948 earthquake in the central aleutians are likely to have been triggered by adjacent ruptures in the sense that their occurrence would have come at a later time had their neighboring segments not been ruptured stresses in the unalaska gap and the shumagin gap are at a relatively high level and these segments of the plate boundary may be expected to rupture in the near future in general in the ten years about 16 of the earthquake cycle for the aleutians following an earthquake the stress recovery in the rupture zone is highly nonlinear resulting in a much more rapid stress accumulation than the linear case even at a later stage of an earthquake cycle adjacent ruptures can cause an acceleration of loading rate in addition to the coseismic stress jump a good example is the influence of the 1964 alaska earthquake on the 1938 rupture zone a general conclusion of this work is that long term earthquake prediction models must take into account the nonlinear stress accumulation behavior in seismic gaps also we have shown the interaction of adjacent plate boundary segments which suggests that some large earthquakes may have been triggered by nearby ruptures

seismic strain release in the mexican subduction thrust abstract in this paper the seismic strain release in the mexican subduction zone is discussed the paper is based on a revised catalog of large earthquakes in mexico new in this catalog are estimates of the seismic moment for many of the larger pre 1962 earthquakes of this century based on instrumental recordings from uppsala sweden a regression between moment and magnitude is established and used to estimate moments for the remaining events of this and the previous century the envelopes of the cumulative seismic moment curves can thus be developed consistent with the nineteenth century seismicity these indicate that the guerrero region is currently the most likely within the mexican subduction zone to experience one great event or several large events with a moment deficit approaching 20 10 27 dyn cm this is comparable with the moment released between 1899 and 1912 in the region in guerrero and also perhaps in michoacan the seismic strain release is consistent with plate tectonic expectations for a seismogenic zone 50 km in width in oaxaca either the seismogenic zone is much narrower and there is considerable aseismic slip or events to rupture the downdip extremes of the subduction zone have not occurred so far this century this last alternative arises because in guerrero the 1907 and 1957 earthquakes have relatively strong 40 s surface waves recorded at uppsala compared with all the other events such events which we infer are deeper present new problems for seismic hazard estimation in mexico since they are not represented in the available strong motion records

turbulent mixing induced by upgoing near inertial waves in the seasonal thermocline of the norwegian sea acoustic doppler current profiler and towed thermistor chain measurements made in the seasonal thermocline in the norwegian sea are examined for evidence that near inertial shear leads to small scale turbulent mixing as inferred from meter scale temperature fluctuations for the 1 day of data examined here spatial variability in shear is dominated by near inertial waves having upward energy propagation 30 m vertical wavelength and 5 to 10 km horizontal extent 20 km wavelength repeated samples of one of these waves had high froude number and enhanced small scale variability dominated by 20 m long waveforms which we conjecture are kelvin helmholtz instabilities arising from the near inertial shear

gold diffusion into and out of quartz hosted fluid inclusions during re equilibration experiments at 600 800 c and 2 kbar abstract fluid inclusions were synthesized in quartz and subsequently re equilibrated in fluids of different compositions to investigate whether the au content of fluid inclusions can be modified via au diffusion through the host quartz in one experiment fluid inclusions containing 5 wt kcl were synthesized in platinum capsules at 2 kbar 800 c and then re equilibrated at the same conditions for 4 days in a fluid containing 20 1 wt nacl 3 5 wt hcl and 100 ppm cs enclosed in a gold capsule la icp ms analyses of 5 10 fluid inclusions before and after the re equilibration experiment demonstrate that the inclusions gained up to 570 ppm au and up to 0 23 wt na during the re equilibration process their unchanged high k content and the absence of cs within the inclusions proves that they remained physically closed during the re equilibration and thus that na and au were gained by diffusion through the quartz lattice in a similar experiment conducted at 600 c the fluid inclusions gained up to 140 ppm au within 14 days reverse experiments were conducted by synthesizing au bearing fluid inclusions in gold capsules and then re equilibrating them in platinum capsules which caused the inclusions to lose up to several hundred ppm au in both type of experiments au diffusion appears to have been driven by chemical potential gradients of au between the fluid inclusions and the external fluid additional experiments were performed to test whether au is able to diffuse into fluid inclusions in response to loss of h or indirectly as a consequence of diffusional cu gain and corresponding formation of cu rich sulfide daughter crystals however no evidence for au uptake via such mechanisms was found if au concentrations in natural quartz hosted fluid inclusions from magmatic hydrothermal ore deposits are affected then they likely lost au rather than gained it at temperatures below 400 c diffusional loss or gain of au is considered unlikely in magmatic hydrothermal systems but potentially was significant in samples from orogenic au gold deposits

a method to synthesize large fluid inclusions in quartz at controlled times and under unfavorable growth conditions a new synthesis technique allows large fluid inclusions to be produced at conditions under which one normally would obtain only small inclusions with the additional advantage that the timing of fluid entrapment can be controlled in the first step primary fluid inclusions are grown at p t conditions under which it is relatively easy to produce large inclusions in the second step which can be performed either during the same experiment or during a separate experiment after a desired time of pre equilibration some of the primary inclusions produced during the first step are re opened by in situ fracturing causing partial replacement of the inclusion content the sample is then left at high pressure and temperature until the cracks leading to the re opened inclusions are healed to test the method and quantify the efficiency of fluid replacement in the re opened inclusions we produced primary inclusions at 700 c 200 mpa and re opened them during a second experiment in the presence of a compositionally different fluid at 500 c 70 mpa laser ablation icp ms la icp ms analyses of eight primary and 11 refilled inclusions demonstrate that in the latter more than 97 of the original fluid was replaced by new fluid thus the refilled inclusions are representative of the surrounding fluid at the time of in situ fracturing

seismic coupling and uncoupling at subduction zones seismic coupling has been used as a qualitative measure of the interaction between the two plates at subduction zones kanamori 1971 introduced seismic coupling after noting that the characteristic size of earthquakes varies systematically for the northern pacific subduction zones a quantitative global comparison of many subduction zones reveals a strong correlation of earthquake size with two other variables age of the subducting lithosphere and convergence rate the largest earthquakes occur in zones with young lithosphere and fast convergence rates while zones with old lithosphere and slow rates are relatively aseismic for large earthquakes results from a study of the rupture process of three great earthquakes indicate that maximum earthquake size is directly related to the asperity distribution on the fault plane asperities are strong regions that resist the motion between the two plates the zones with the largest earthquakes have very large asperities while the zones with smaller earthquakes have small scattered asperities this observation can be translated into a simple model of seismic coupling where the horizontal compressive stress between the two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface while the variation in asperity size is used to establish a connection between earthquake size and tectonic stress it also implies that plate age and rate affect the asperity distribution plate age and rate can control asperity distribution directly by use of the horizontal compressive stress associated with the preferred trajectory i e the vertical and horizontal velocities of subducting slabs are determined by the plate age and convergence velocity indirect influences are many including oceanic plate topography and the amount of subducted sediments all subduction zones are apparently uncoupled below a depth of about 40 km and we propose that the basalt to eclogite phase change in the down going oceanic crust may be largely responsible this phase change should start at a depth of 30 35 km and could at least partially uncouple the plates by superplastic deformation throughout the oceanic crust during the phase change

near surface frontal zone trapping and deep upward propagation of internal wave energy in the japan east sea the full depth current structure in the japan east sea was investigated using direct velocity measurements performed with lowered and shipboard acoustic current doppler profilers rotary spectral analysis was used to investigate the three dimensional energy distribution as well as wave polarization with respect to vertical wavenumbers yielding information about the net energy propagation direction highly energetic near inertial downward propagating waves were found in localized patches along the southern edge of the subpolar front between 500 and 2500 m depth the basin average energy propagation was found to be upward with the maximum of relative difference between upward and downward propagating energy lying at about 1500 m depth this difference was most pronounced in the southeastern part of the basin

synthetic fluid inclusions in natural quartz ii application to pvt studies synthetic fluid inclusions have been used to determine volumetric properties of h2o and a 20 wt kcl solution from 300 700 c and 1 3 kb comparison of results obtained for h2o with previously published data indicates that the synthetic fluid inclusion technique provides pvt data that are within a few percent of those obtained from conventional pvt studies this technique thus provides a fast relatively simple means of determining pvt properties of many fluids of geologic interest

internal wave observations from the arctic environmental drifting buoy a free drifting buoy serving as an ice anchor and flotation sphere for a 125 m instrumented mooring line was deployed in the arctic pack ice by the r v polarstern in august 1987 at the northernmost point achieved by the arktis iv expedition current measurements were made from this arctic environmental drifting buoy aedb using a 150 khz acoustic doppler current profiler adcp attached to the mooring line at a depth of 16 m below the flotation sphere with the transducers facing downward velocity profiles spanning depths between 35 and 327 m with 15 m resolution were collected at half hour intervals over a period of 216 days while the buoy drifted from its starting point near 86 n 22 e to about 70 n 16 w the full experimental record was separated into three sections corresponding to periods of the drift spent in the nansen basin over the yermak plateau and in the greenland sea velocity time series and spectra were computed and results for the three analysis sections were compared spectra in the nansen basin were found to have energy levels significantly less than those typical for mid latitudes roughly one third of the canonical garrett munk gm level and a spectral slope between and 2 5 that was significantly flatter than that expected from the gm model between 83 n and 81 n as the buoy passed over the yermak plateau internal wave energy increased to levels comparable to gm isolated energetic near inertial wave packets with upward group velocity were observed in this portion of the record presumably generated by interaction of the barotropic tide with the bottom topography of the plateau estimates of the upward energy flux from these near inertial packets were comparable to the downward fluxes from typical surface sources interpretation of the greenland sea section was complicated by adcp sampling problems and a lack of argos fixes but the available data showed internal wave spectral levels that were intermediate between those of the nansen basin and yermak plateau and no evidence of upward propagating near inertial energy

near inertial current oscillations in the vicinity of the bering sea marginal ice zone near inertial current oscillations with 10 20 cm s amplitudes were prevalent over the bering sea shelf during november 1982 and again in march and april 1983 and also evident at reduced amplitudes during the intervening winter spectral peak frequencies were consistently within 1 of the local inertial frequency in contrast to the more superinertial 5 above frequencies commonly reported elsewhere a superinertial secondary energy peak at 1 038 was evident corresponding to the first mode wave amplitudes decreased with distance shoreward from the shelf break consistent with the effects of decreasing bottom depth and increasing mixed layer depth the oscillations were highly coherent over 100 km distances similar to observations reported by thomson and huggett 1981 for the british columbia coast whereas near inertial oscillations have been commonly reported to be uncoupled over much shorter 10 km distances in other regions vigorous near inertial ringing was associated with rapidly passing weather systems the decline in near inertial oscillation amplitudes during winter was partially due to a significant reduction in both cyclone frequency and occurrence of wind events causing clockwise wind shifts the decline was enhanced by reduction in the vertical stratification needed to support inertio gravity internal waves as the shelf waters apparently became mixed from top to bottom the loose mobile sea ice in the winter marginal ice zone miz did not appear to inhibit wind generation of the inertial oscillations the presence of sea ice appears in fact to have contributed to the spring increase of near inertial current amplitudes through restratification of the water column caused by melting ice our observations particularly the spatial coherency and spectral properties were generally consistent with kundu and thomson s 1985 model for inertio gravity waves generated in the wake of a translating weather front the half wavelength typical of these waves forced by transiting weather fronts on the bering shelf appears to be 150 km or approximately the width of the winter miz the associated near inertial currents are 180 out of phase with those a half wavelength away in the direction of phase propagation thus a storm passing perpendicular to the ice edge can excite waves at near inertial frequencies which compress deform and dilate the ice pack by up to a few percent of the miz width we suggest that this mechanism in conjunction with near inertial interfacial shear which can increase upward heat flux influences the width scale of the miz

textural evolution of synthetic fluid inclusions in quartz during reequilibration with applications to tectonic reconstruction experimental reequilibration of synthetic 10 wt nacl h2o inclusions in natural quartz reveals that reequilibration textures show distinct differences depending upon the p t path followed by the inclusion after formation these differences combined with other geological information may be used to determine whether the sample rock followed a dominantly isothermal or isobaricp t path following entrapment the intensity and style of inclusion reequilibration features is related to the direction and magnitude of the departure of thep t path from the original isochore for the inclusion thus fluid inclusion reequilibration textures not only permit inclusionists to determine whether the rocks followed an isothermal or isobaric retrogradep t path but also the magnitude of departure of this path from one that is isochoric