seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing water and hydrous minerals play a key role in geodynamic processes at subduction zones however there are few seismological constraints on the presence of water within the subducting plate audet et al model converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle their observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip this study models converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle the observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip water and hydrous minerals play a key part in geodynamic processes at subduction zones1 2 3 by weakening the plate boundary aiding slip and permitting subduction and indeed plate tectonics to occur4 the seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization5 6 7 however seismological observations bearing on the presence of water within the subducting plate itself are less well documented here we use converted teleseismic waves to obtain observations of anomalously high poisson s ratios within the subducted oceanic crust from the cascadia continental margin to its intersection with forearc mantle on the basis of pressure temperature and compositional considerations the elevated poisson s ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values combined with observations of a strong negative velocity contrast at the top of the oceanic crust our results imply that the megathrust is a low permeability boundary the transition from a low to high permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization these results may have important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip

the climatology of zonal wave numbers 1 and 2 planetary wave structure in the mlt using a chain of northern hemisphere superdarn radars the zonal wave components 1 and 2 were extracted from the meridional wind along the latitude band of 51 66 n for the years 2000 2008 using eight super dual auroral radar network superdarn radars spanning longitudes from 25 e to 150 w each extracted zonal component represents the superposition of all temporal periods with that zonal structure and indicates the total planetary wave energy available with that wave number the hovmoller diagrams show stationary as well as eastward and westward traveling planetary waves propagating in the background wind the method used to detect the zonal planetary wave components in the superdarn data are detailed and validated using uk meteorological office data which allows the evolution of s1 and s2 planetary wave energy between the stratosphere and mesosphere to be assessed the climatology of zonal wave number 1 and 2 planetary wave activity in the mesosphere lower thermosphere mlt is presented and compared to the activity in the stratosphere the mlt climatology of the mean wind anomalies shows stronger planetary wave activity during winter and weaker activity during summer with enhancement around midsummer and autumn equinox the climatology of the mean wind displays similar amplitudes apart from very strong s1 planetary wave amplitudes during summer in addition planetary wave activity during winters with major and minor stratospheric warming events are examined and contrasted

a study of a self generated stratospheric sudden warming and its mesospheric lower thermospheric impacts using the coupled time gcm ccm3 1 a stratospheric sudden warming episode was self consistently generated in the coupled national center for atmospheric research thermosphere ionosphere mesosphere and electrodynamics general circulation model climate community model version 3 time gcm ccm3 taking advantage of the unique vertical range of the coupled model ground to 500 km we were able to study the coupling of the lower and upper atmosphere in this warming episode planetary wave 1 is the dominant wave component in this warming event analysis of the wave phase structure and the wave amplitude indicates that the wave may experience resonant amplification prior to the peak warming the mean wind in the high latitude winter stratopause and mesosphere decelerates and reverses to westward due to planetary wave forcing and forms a critical layer near the zero wind lines the wind deceleration and reversal also change the filtering of gravity waves by allowing more eastward gravity waves to propagate into the mesosphere and lower thermosphere mlt which causes eastward forcing and reverses the westward jet in the mlt this also changes the meridional circulation in the upper mesosphere from poleward downward to equatorward upward causing a depletion of the peak atomic oxygen layer at 97 km and significant reduction of green line airglow emission at high latitudes and midlatitudes planetary waves forced in situ by filtered gravity waves in the mlt grow in the warming episode their growth and interaction with tides create diurnal and semidiurnal variabilities in the zonal mean zonal wind

strain partitioning and progressive deformation history in a transpressive belt northern appalachians abstract syntectonic fibres within rocks of the gaspetrough a mid paleozoic slate belt within part of the acadian orogen of the canadian appalachians record the complex structural evolution of a transpressive belt the fibres occur around pyrite framboids and can be divided into five segments which record four distinct structural stages all four structural stages are related to a single progressive deformation since fibre segments can be traced continuously from the first segments to the last fibre growth patterns within the gaspetrough clearly indicate that folding occurred during coaxial deformation during the first three structural stages these structural stages are 1 layer parallel shortening 2 combined flattening and rigid body rotation and 3 cleavage development strain associated with vertical extension during these three stages accounts for approximately 50 shortening within the slate belt during the last structural stage deformation resulting from regional simple shear continued to affect the entire slate belt as local flattening within cleavage planes produced horizontal extension and brought about further tightening of folds strain recorded by the horizontal fibre increments produced during simple shear accounts for 25 shortening in this part of the appalachians oblique convergence during the acadian orogeny was partitioned in time between strike slip and reverse faulting convergence was accommodated by folding flattening and reverse faulting during the first part of the deformation and later on by flattening and dextral transcurrent faulting

solar and lunar tidal variabilities in gps tec and geomagnetic field variations seasonal as well as during the sudden stratospheric warming of 2010 the global positioning system gps deduced total electron content tec data at 15 n geomagnetic which is the northern crest region of equatorial ionization anomaly are used to study solar and lunar tidal variabilities during the years 2008 and 2009 and also during the 2009 2010 winter when a major sudden stratospheric warming ssw event has occurred the diurnal and semidiurnal tidal amplitudes show semiannual variation with maximum amplitudes during february march and september november whereas terdiurnal tide is larger during april september they show significant longitudinal variability with larger smaller amplitudes over 250 e 150 e 200 e 250 e lunar semidiurnal tidal amplitudes show sporadic enhancements during northern winter months and negligible amplitudes during northern summer months they also show notable longitudinal variabilities the solar migrating tides dw1 and sw2 show semiannual variation with larger amplitudes during spring equinox months whereas tw3 maximizes during northern summer dw2 shows larger amplitudes during summer months during the ssw except tw3 the migrating tides dw1 and sw2 show considerable enhancements among solar nonmigrating tides sw1 tw2 and ds0 show larger enhancements solar tides in tec and equatorial electrojet strength over tirunelveli vary with the time scale of 60 days during october 2009 march 2010 similar to ozone mass mixing ratio at 10 hpa and this confirms the vital role of ozone in tidal variabilities in ionospheric parameters lunar tidal amplitudes in changes in horizontal component of geomagnetic field h are larger over tirunelveli a station near dip equator solar semidiurnal tides in h have larger amplitudes than lunar tides over polar stations mawson and godhavn

seismic anisotropy tracing plate dynamics in the mantle elastic anisotropy is present where the speed of a seismic wave depends on its direction in earth9s mantle elastic anisotropy is induced by minerals that are preferentially oriented in a directional flow or deformation earthquakes generate two seismic wave types compressional p and shear s waves whose coupling in anisotropic rocks leads to scattering birefringence and waves with hybrid polarizations this varied behavior is helping geophysicists explore rock textures within earth9s mantle and crust map present day upper mantle convection and study the formation of lithospheric plates and the accretion of continents in earth history

base metal skarns and au occurrences in the southern gaspe appalachians distal products of a faulted and displaced magmatic hydrothermal system along the grand pabos restigouche fault system in the southern gaspe appalachians base metal and au occurrences are spatially associated with the acadian dextral strike slip grand pabos and restigouche faults mineralization occurs as veins replacement zones and disseminations along the main structures and subsidiary faults with orientations compatible with the dextral strike slip kinematics along the main faults limestone of the upper ordovician lower silurian white head formation hosts numerous base metal skarns and au occurrences that are surrounded by halos of argillaceous alteration the reboul prospect is a type example of base metal skarns and consists of three types of mineralization 1 early strata bound disseminated cu zn ag associated with marble hornfels and skarn 2 northeast and northwest trending cu zn pb ag au and ag cu zn pb au sb veins parallel and perpendicular to the regional folding and 3 late ag au zn pb mineralized zones in quartz breccia veins parallel to the grand pabos fault crosscutting relationships fluid inclusion microthermometry mineralogy of the three types of mineralization and alteration patterns were used to define the timing of mineralizing processes which are 1 prograde metamorphism 2 metasomatism and hydrothermal alteration with high temperature skarn formation and cu zn ag mineralization 3 retrograde alteration with cu zn pb ag au and ag cu zn pb au sb veins and 4 late au precipitation at low temperature the saint andre de ristigouche prospect is the best example of au mineralization spatially associated with a base metal skarn in the area it consists of au sb as extensional veins and stockwork hosted by limestones felsic dikes associated with base metal skarns and a magmatic hydrothermal breccia at the reboul prospect are evidence for magmatic activity coincident with the mineralizing events argillaceous alteration high temperature and high salinity fluid inclusions and the pb isotope compositions of galena are compatible with a model linking the skarns and au occurrence to early to middle devonian magmatic activity at depth along the grand pabos and restigouche faults a palinspastic pre acadian strike slip reconstruction of the southern gaspe appalachians shows that all mineral occurrences hosted by the white head formation belong to the same mineralized area that might represent distal components of a magmatic hydrothermal system at depth

planetary waves and variability of the semidiurnal tide in the mesosphere and lower thermosphere over esrange 68 n 21 e during winter 1 the main features of the planetary waves and the variability of the semidiurnal tide with planetary wave periods observed by meteor radar over esrange 68 n 21 e have been investigated the interval of 39 months covering continuous measurements from october 1999 to december 2002 has been examined the planetary waves most frequently observed by meteor radar measurements in the mesosphere and lower thermosphere 80 100 km over esrange are 5 8 to 10 16 and 23 day waves the quasi 2 day wave is excluded in this study they are strongly amplified in the winter some differences between high and middle latitude planetary waves notwithstanding the 5 10 and 16 day waves are most probably related to the well known normal mode there are some reasons to believe that the vertically upward propagating 23 day wave could be generated by solar forcing the variability of the semidiurnal tide with periods of planetary waves has been thoroughly studied as well it is found that in the winter when the planetary waves are significantly amplified a very strong periodic variability of the semidiurnal tide is observed as well this result indicates that the most probable mechanism responsible for the periodic tidal variability during winter is in situ nonlinear coupling between tides and planetary waves two winter periods have been examined 1999 2000 and 2001 2002 in order to find strong evidence supporting this suggestion the validity of the frequency phase and vertical wavenumber wavelength relationship between the prime the planetary wave and semidiurnal tide and secondary waves has been established the novel aspect of this work is that we show for the first time that the calculated vertical structures vertical wavelengths of the sum and difference secondary waves which have very close periods are actually very different

stationary planetary waves inferred from windii wind data taken within altitudes 90 120 km during 1991 96 abstract a climatology of stationary planetary waves spws in horizontal winds at latitudes 70 s 70 n and altitudes 90 120 km is obtained from wind imaging interferometer windii green line measurements in december january and march april of 1991 96 the observed solstitial spw fields are relatively stronger and dominated by zonal wavenumber 1 variations in contrast the equinoctial spw fields are weaker and characterized by zonal wavenumber 2 variations the zonal amplitude maxima of 10 25 m s 1 are generally centered at the midlatitudes of 35 40 in both hemispheres around 96 km with the eastward perturbation velocity maxima around 90 e for wavenumber 1 and 60 and 240 e for wavenumber 2 the meridional amplitude maxima are about 5 15 m s 1 and show more variabilities in their latitude height distributions the meridional phases indicated that eliassen palm ep fluxes were downward poleward for the winter maxima vertically varying poleward for the summer maxima and more variable during march apr

the average behavior of large scale westward traveling disturbances evident in the northern hemisphere geopotential heights abstract the average structure of westward traveling disturbances that contribute to relative maxima found in space time spectra from 13 32 days at northern latitudes is determined for each season a compositing method used employs a minimum of space and time filtering in order to avoid biasing the results the average latitudinal structure is global in that it is discernible in the southern hemisphere during december february and september november it is primarily confined to northern latitudes during march august in all seasons the disturbance is out of phase between northern high latitudes and subtropical and tropical latitudes the longitudinal structure is primarily zonal wavenumber 1 in all seasons further work is suggested to confirm the structures determined here and to learn if they reflect the superposition of a number of occasionally excited rossby normal modes

reconstruction of taconian and acadian paleostress regimes in the quebec and northern new brunswick appalachians a numerical analysis of fault populations was applied in the quebec and northern new brunswick appalachians to characterize paleostress fields attributed to the taconian and acadian orogenies the first brittle deformation documented in the external domain of the humber zone is associated with the thin skinned tectonics of the taconian orogen the taconian brittle deformation characterized by north south to ne sw reverse conjugated brittle faults evolved under a pure shear compressional regime vertical 3 axes with 1 axes oriented ese wnw the ene wsw dextral and nw se sinistral faults that are observed in the st lawrence lowlands are also attributed to taconian compression the first brittle deformation recognized in the dunnage zone and the gaspe belt is attributed to an ese wnw compression during the acadian orogeny in the dunnage zone of southern quebec the acadian paleostress axes are similar to the directions of 1 axes and to the pure shear compressional regime computed for the silurian and devonian rocks of the gaspe belt in the gaspe peninsula the acadian stresses are oriented ese wnw and are mechanically compatible with transpressional regimes reverse brittle faults and pure shear stress are identified along regional and secondary sets of ne sw brittle faults whereas a strike slip stress regime is reconstructed along major east west faults in the humber zone of the quebec appalachians a second compression is identified it is characterized by conjugate ene wsw dextral and nw se sinistral strike slip faults that crosscut taconian thrust faults this late deformation event is attributed to a distal expression of the acadian orogeny

diurnal nonmigrating tides from timed doppler interferometer wind data monthly climatologies and seasonal variations 1 timed doppler interferometer tidi measurements of zonal and meridional winds in the mesosphere lower thermosphere are analyzed for diurnal nonmigrating tides june 2002 to june 2005 climatologies of monthly mean amplitudes and phases for seven tidal components are presented at altitudes between 85 and 105 km and latitudes between 45 s and 45 n westward propagating wave numbers 2 3 and 4 the standing diurnal tide and eastward propagating wave numbers 1 2 and 3 the observed seasonal variations agree well with 1991 1994 uars results at 95 km comparisons between the tidi results and global scale wave model gswm and thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm tidal predictions indicate that the large eastward propagating wave number 3 amplitude is driven by tropical tropospheric latent heat release alone in contrast latent heating and planetary wave migrating tidal interactions are equally important to westward 2 and standing diurnal tidal forcing there is good quantitative agreement between tidi and the model predictions during equinox but the latter tend to underestimate the westward 2 and standing diurnal tide during solstice neither model reproduces the observed seasonal variations of the eastward propagating components

structure and elasticity of serpentine at high pressure abstract serpentines occur in the subduction zone settings both along the slab and within the mantle wedge they are candidates for transporting water in to the deep earth their presence is manifested by serpentine mud volcanoes high electrical conductivities magnetic and seismic anomalies using theoretical methods we predict a pressure induced structural transformations in serpentine the transformations are related to the behavior of the silicate framework and misfit between octahedral and tetrahedral layers as the structure is compressed the octahedral layer and tetrahedral layers are compressed at different rates at 7 gpa the misfit between the layers vanishes this causes non linear pressure dependence of tetrahedral rotational angle this is also manifested by the onset of anomalous pressure dependence of the elastic constants c 11 c 33 c 12 c 13 beyond 7 gpa the misfit between the layers grows again reaching extremum at 22 gpa this is also manifested by discontinuity in average si o bond length volume of tetrahedron and re orientation of hydroxyl vector the symmetry of the crystal structure however remains unaffected evidence of pressure induced hydrogen bonding is absent in serpentine as evident from reduction of o h bond length upon compression results of compression for the low pressure regime p k 0 79 gpa k 0 12 and k 0 2 where k is the bulk modulus prime indicates pressure derivatives and o refers to zero pressure our best estimates of k 0 k 0 and the gruneisen parameter at 300 k and zero pressure based on our results are 61 gpa 17 and 0 77 respectively at low pressures serpentine structure is anisotropic with c 11 2 4 c 33 the pressure derivative of elastic constants c ij p are such that around 22 gpa c 11 c 33 an elastic instability c 66 50 gpa is also noted the elastic constant tensor reveals large acoustic anisotropy 41 in v p and seismic wave velocities that are significantly higher than those inferred from experiments on serpentinites

subduction zone anisotropy beneath corvallis oregon a serpentinite skid mark of trench parallel terrane migration 1 we studied the back azimuth dependence of ps converted phases at gsn station cor corvallis oregon using broadband p receiver functions computed from 602 teleseismic earthquakes the amplitudes and polarities of the transverse ps phases are largely two lobed which indicates anisotropy with a tilted symmetry axis a double peaked ps conversion at 4 5 6 5 s delay has the moveout of a dipping slab but is not consistent with simple deflection of the ps converted phase by the dipping interface a polarity flip on the transverse receiver function near north south back azimuth indicates an anisotropic symmetry axis aligned north south far from the convergence direction n68 e the ps phase is modeled using reflectivity synthetics with a highly anisotropic layer of depressed wave speed vp 6 0 6 5 km s near 40 km depth at the slab interface with the overriding north american plate one dimensional modeling suggests 10 anisotropy in the supraslab layer with a slow symmetry axis oriented n5 w at a 60 tilt from the vertical adjustments for the effect of slab interface dip on ps amplitude suggest a somewhat lower 7 anisotropy we infer a thin 7 km anisotropic detachment zone for the northward slippage of the siletz forearc terrane along the top of the descending slab a motion consistent with gps measurements and models of regional lithospheric dynamics serpentinite is a likely constituent for the deep anisotropic layer owing to its reduced vp and high poisson ratio the ductile rheology and hydrated composition of serpentinite make it a plausible lithology for a mechanical detachment zone

paleogeography and tectono sedimentary history at the margin of laurentia during silurian to earliest devonian time the gaspe belt quebec the silurian lower devonian sequence of the gaspe belt at the laurentia margin south of the quebec reentrant and st lawrence promontory was deposited during the period between the two main orogenies that created the northern appalachians the late ordovician taconian and the middle devonian acadian orogenies although this sequence is traditionally considered to have been deposited during a period of quiescence between both orogenies significant tectonic activity attributed to the salinic disturbance began during late llandoverian telychian time and persisted until the acadian orogeny this tectonic activity has profoundly influenced the composition and distribution of the silurian earliest devonian sedimentary facies the shelf and shelf edge history at the laurentia margin along the quebec reentrant st lawrence promontory is summarized according to four broad phases phase 1 is a llandoverian wenlockian regressive phase r1 related to post taconian successor basin filling that culminated with extensive carbonate platform development phase 2 is a late wenlockian ludlovian transgressive phase t1 phase 3 corresponds to a later ludlovian pridolian second regressive phase r2 phases 2 and 3 were accompanied by extensional tectonics that produced shelf faulting and block tilting on top of which block reefs and reef complexes settled and built a reef tract all the way along the gaspe temiscouata shelf phase 4 is an early devonian phase of accelerated subsidence transgression t2 affecting the northwestern part of the segment quebec reentrant area while the southeastern part st lawrence promontory area was already uplifted due to the ongoing collision between laurentia and the western margin of gondwana related terranes to the south composition and distribution of sedimentary facies were controlled by the interaction of tectonics sediment influx and sea level fluctuations construction of a post taconian pre acadian palinspastic map to plot facies has proven to be basic to obtaining a realistic picture of the paleogeography of the shelf and shelf edge of the gaspe temiscouata segment at the margin of the laurentia craton during the silurian earliest devonian time interval

carlin type gold mineralization at saint andre de ristigouche gaspe peninsula quebec canadian appalachians the gaspe peninsula in the canadian appalachians hosts a variety of mineral occurrences that are spatially associated with the grand pabos and restigouche faults among these occurrences the saint andre de ristigouche gold sar au showing has peculiar features comparable with carlin type gold deposits at the regional district and prospect scales the most striking ones are 1 the calcareous nature of the host rocks 2 the au as sb hg metallic signature with absence of base metals and ag 3 the association with a crustal scale fault zone 4 the hydrothermal alteration characterized by silicification calcite and quartz veinlets at the margin of the au bearing zones and the occurrence of kaolinite in large halos of argillic alteration 5 numerous felsic dikes 6 the occurrence of au in as rich pyrite forming overgrowths on premineralization as free pyrite and in arsenopyrite 7 hydrothermal fluids equilibrated with host rocks at high temperature 200 which cooled to precipitate arsenopyrite and then mixed with evolved meteoric water to precipitate stibnite in veins although the sar au showing is relatively small analogies with carlin type mineralization encourage exploration in the gaspe peninsula and in similar settings elsewhere in the appalachians

subducting slab ultra slow velocity layer coincident with silent earthquakes in southern mexico great earthquakes have repeatedly occurred on the plate interface in a few shallow dipping subduction zones where the subducting and overriding plates are strongly locked silent earthquakes or slow slip events were recently discovered at the down dip extension of the locked zone and interact with the earthquake cycle here we show that locally observed converted sp arrivals and teleseismic underside reflections that sample the top of the subducting plate in southern mexico reveal that the ultra slow velocity layer usl varies spatially 3 to 5 kilometers with an s wave velocity of 2 0 to 2 7 kilometers per second most slow slip patches coincide with the presence of the usl and they are bounded by the absence of the usl the extent of the usl delineates the zone of transitional frictional behavior

supplemental material zircon and monazite geochronology in the palmer zone of transpression south central new england usa constraints on timing of deformation high grade metamorphism and lithospheric foundering during late paleozoic oblique collision in the northern appalachian orogen analytical methods for zircon u pb and monazite th pb sims geochronology zircon u pb la icp ms geochronology data tables and supporting previous work

an observational study of traveling planetary waves in the southern hemisphere abstract southern hemisphere analyses from the surface to 2 mb and from 20 to 80 s for the period may september 1979 have been used to study the structure of traveling planetary waves space time cross spectral analysis of the height field has been employed to define the amplitude and phase for both the eastward and westward moving components of particular combinations of zonal wavenumber and frequency band latitude height contour plots of power phase and coherence squared show that westward moving waves have structure characteristic of barotropic external modes and are coherent across a broad range of latitudes and from the surface to 2 mb the highest level analyzed eastward moving waves on the other hand have more rapid phase variations especially in the troposphere and appear more baroclinic the tropospheric structure of the moving components of wavenumbers 1 4 is as one would expect for baroclinically unstable modes of the charney type wavenumbers 1 and 2 both have double amplitude maxima i

climatology of the stationary planetary waves seen in the saber timed temperatures 2002 2007 1 the paper focuses on the global spatial structure seasonal and interannual variability of the stationary planetary waves spw with zonal wavenumber s 1 spw1 and s 2 spw2 derived from the saber timed temperature measurements for 6 full years january 2002 december 2007 the monthly mean climatological multiyear average 2002 2007 depictions of spw temperature field extending between 20 and 120 km altitude and 50 latitude are derived a special attention is paid to the spw temperature field in the lower thermosphere where the spw1 amplifies in may and december january in the northern hemisphere nh and in april may and november in the southern hemisphere sh amplitudes in both hemispheres are similar in strato mesosphere however in the lower thermosphere sh amplitudes are significantly larger 30 k than those in nh 20 k the nh spw1 is able to propagate up to 115 km altitude contributing to the winter amplification of the lower thermospheric spw1 but that from the sh cannot penetrate above 90 100 km in the lower thermosphere above h 100 km mainly trapped spw signal is observed the spw1 are almost out of phase in both hemispheres the average 2002 2007 phases are 100 w in nh and 120 e in sh strong evidence indicates that auroral heating is a main origin of the lower thermospheric spw temperature field

the southern andes between 36 and 40 s latitude seismicity and average seismic velocities abstract the project issa 2000 integrated seismological experiment in the southern andes consists of a temporary seismological network and a seismic refraction profile a network of 62 seismological stations was deployed across the southern andes at 38 s three hundred thirty three local seismic events were observed in a 3 month period p and s arrival times of a subset of high quality data were inverted simultaneously for 1 d velocity structure hypocentral coordinates and station delays seismic refraction data along a transect at 39 s provide further constraints on the crustal structure low crustal velocities beneath the forearc may be either due to subducted trench sediments or serpentinized mantle material of the continental lithosphere the continental moho is not clearly observed in this region average velocities of the crust beneath the arc are higher than those beneath the forearc crustal thickness is about 40 km crustal seismicity concentrates in the forearc region along the bio bio and gastre fault zones the area between these two prominent fault zones seems to be nearly devoid of crustal seismicity but shows highest uplift and topography in the forearc region benioff seismicity is observed down to 150 km depth resulting in the first accurate image of the benioff zone in the southern andes a maximum of seismicity at 60 km depth may be caused by dehydration embrittlement

nonmigrating diurnal tides in mesospheric and lower thermospheric winds and temperatures abstract this paper presents analyses of nonmigrating diurnal tide signatures in high resolution doppler imager mesospheric and lower thermospheric winds and temperatures a global comparison of both winds and temperature reveals equatorial features corresponding to nonmigrating tides structures interpreted as zonal mean and eastward nonmigrating diurnal tides display consistency between horizontal winds and temperatures the second symmetric mode is prominent in the zonal mean and wavenumber 1 the gravest antisymmetric mode and the gravest symmetric or kelvin mode are the main features in zonal wavenumbers 2 and 3 the amplitudes of the tides generally increase with altitude and maximize within 90 110 km

climatological features of mesosphere and lower thermosphere stationary planetary waves within 40 latitude 1 zonal and meridional wind measurements from the high resolution doppler imager hrdi and wind imaging interferometer windii instruments on the upper atmosphere research satellite uars are used to construct monthly average stationary planetary wave spw structures from 15 km to 110 km over the period december 1991 to september 1994 because of viewing constraints of the instruments intercomparisons between northern hemisphere nh and southern hemisphere sh structures and seasonal evolutions are mainly confined to 40 latitude the largest zonal wave number s 1 amplitudes 10 25 m s 1 in the stratosphere and mesosphere at 40 exist in the zonal wind fields and occur during september january in the nh and july october in the sh spw s 2 structures are much less prevalent especially above 80 km because of more restrictive filtering effects due to the mean winds above about 70 km s 1 wave amplitudes 5 10 m s 1 are more uniform extending over all nonsummer months in both hemispheres up to 80 90 km with similar amplitudes existing throughout the year at higher altitudes our interpretation is that the spw above about 80 90 km during summer owe their existence to ducting from the winter hemisphere in agreement with numerical simulations by pogoreltsev and sukhanova 1993 the origin of spw above about 80 km during winter at midlatitudes is not possible to determine unambiguously phase structures undergo a transition from vertical propagation with long vertical wavelengths hundreds of kilometers below 80 km to either evanescent behavior or an extreme shortening of vertical scale at higher altitudes this change in phase behavior may be connected with negative values in refractive index q for quasi geostrophic wave propagation which occur over a narrow height region near 80 km during almost every month this interruption of normal phase progression makes it impossible to distinguish the origin of the planetary wave oscillations from 1 those that tunnel through the q 0 region and 2 those that might be excited in situ by zonally asymmetric momentum deposition from gravity waves which have undergone filtering by the stratospheric planetary wave wind field in addition quantitative estimates of aliasing due to the diurnal tide indicate that it may be of sufficient magnitude to contaminate retrieved spw structures between 80 90 km and 100 110 km where local time coverages are incomplete comparisons are made between the observed spw structure and those from the horizontal wind model hedin et al 1993 1996 this model is found to provide a reasonable approximation to nh winter spw s 1 structures below 80 km but severely underestimates the amplitudes of spw in the sh

climatology of normal mode rossby waves abstract three years of twice daily nmc global operational analyses were projected onto normal mode rossby waves to produce a climatology of these waves for zonal wavenumbers 1 through 4 annual average geopotential amplitudes at 50 kpa are about 5 gpm for the gravest symmetric meridional mode and 10 and 20 gpm for the next two meridional model although the amplitude for a given time and latitude can greatly exceed the average seasonal average amplitudes differ by less than 25 from the annual average the modes frequencies drift during the course of a year but this variation is not correlated with season autocorrelations of rossby wave time series become negligible for lags greater than approximately ten days which is of the order of the wave period for all ten modes examined geopotential fluctuations exist in both northern and southern hemispheres

stability and dynamics of serpentinite layer in subduction zone abstract the hydrous phyllosilicate serpentines have a strong influence on subduction zone dynamics because of their high water content and low strength at shallow and intermediate depths in the absence of data newtonian rheology of serpentinites has been assumed in numerical models yet experimental data show that serpentine rheology is best described by a power law rheology recently determined in subduction zone conditions hilairet n et al 2007 high pressure creep of serpentine interseismic deformation and initiation of subduction science 318 5858 1910 1913 using a simple 1d model of a serpentinized channel and as opposed to previous models in this power law rheology we examine the influence of channel thickness temperature and subduction angle on serpentine flow driven by density contrast serpentinization degree with the surroundings at temperatures of 200 500 c relevant to intermediate depths a fully serpentinized channel is unlikely to be thicker than 2 3 km for channel thicknesses of 2 km upward velocities are comparable to those using a constant viscosity of 10 18 pa s the velocity profile using power law rheology shows shear zones at the edges of the channel and a low strain rate region at its centre consistent with the frequent observation of weakly deformed hp rocks upward velocities estimated for channels 1 to 3 km thick are comparable to the serpentinization rates for maximum estimates of fluid velocities within shear zones in the literature competition between the upward flow and serpentinization may lead to intermittent behavior with alternating growth periods and thinning by exhumation at shallower levels the thickness allowed for a channel may be up to 8 10 km if the rheology has a higher dependence on stress we therefore propose that the exhumation of hp oceanic units in serpentinite channels is organized in two levels the deepest and fastest motion being driven by density contrast with the surrounding mantle and the shallowest circulation being driven by forced return flow the thicknesses estimated here for serpentinized layers at intermediated depths are similar to the precision of seismic studies the deepest serpentinite channel may thus be difficult to detect by seismic methods but it will have a strong influence on the mechanical coupling between the slab and mantle wedge

imaging the source region of cascadia tremor and intermediate depth earthquakes the subduction of hydrated oceanic crust releases volatiles that weaken the plate boundary interface trigger earthquakes and regulate transient phenomena such as episodic tremor and slip ets it is not clear how dehydration can separately induce earthquakes within the subducting plate and ets partly because few data exist on their relationship to subduction zone structures we present results of a seismic experiment in the washington cascades united states that images a region producing both earthquake types migration of scattered teleseis mic waves provides images of low velocity subducting crust at depths 40 45 km with sharp boundaries above and below it the sharp upper boundary indicates a layer of weak sediment or an overpressured fault zone that terminates abruptly downdip at 40 45 km depth regular earthquakes are at the top of the mantle within the downgoing plate everywhere the plate is 95 km deep but ets only exists where the sharp upper boundary occurs the ets location supports models of slow slip that require near lithostatic fluid pressure whereas regular earthquakes nucleate closer to the origin of metamorphic dehydration very low shear stresses on the plate boundary may limit seismicity to ets and similar phenomena

late neoproterozoic to permian tectonic evolution of the quebec appalachians canada abstract due to the unique location of the quebec appalachians in a re entrant of the paleo north american margin and to the fact that the area largely escaped late paleozoic deformation this segment of the orogen preserves evidence of the early orogenic stages that are partly obscured elsewhere despite diachronicity both along and across strike of the orogen five tectonic events of regional significance are recognized 1 the earliest event is mainly recorded by neoproterozoic to early ordovician normal faults associated with extension of the laurentian craton and the establishment of a passive continental margin 2 the second event the ordovician taconian orogeny is marked by foreland directed deformation and corresponds to the principal deformational and metamorphic events recorded by the laurentian margin 3 the third event early salinic is early silurian it is restricted to the southern part of the quebec appalachians and consists of hinterland se directed thrusts folds and retrograde metamorphism 4 the fourth event late salinic is recorded by regional scale late silurian to early devonian normal or transtensional faults and is associated with the formation of the connecticut valley gaspe trough and 5 the last event the devonian acadian orogeny affects with variable intensity all the pre carboniferous lithologies this tectonic synthesis implies that the subdivision of the peri laurentian oceanic tracts proposed in other segments of the appalachians should be applied with caution in quebec and that the structural style the number of oceanic domains and possibly the vergence of subduction change along the strike of the orogen in particular the similarities of the thetford mines and boil mountain ophiolitic complexes and sedimentary covers and the lack of evidence for a major intervening suture are consistent with the maximum allochtony hypothesis i e the assumption that the southern quebec ophiolites are rooted east of the chain lake massif a geodynamic model involving the taconian obduction of a large ophiolitic nappe s the docking of a peri gondwanan gander medial new england terrane in early salinic the formation of large sedimentary basins connecticut valley gaspe and merrimack troughs due to trench rollback and or delamination during the late salinic event and collision at the outer margin of composite laurentia during the acadian orogeny can account for the protracted structural and metamorphic history of the quebec appalachians

the vertical connection of the quasi biennial oscillation modulated 11 year solar cycle signature in geopotential height and planetary waves during northern hemisphere early winter 1 we analyzed observational geopotential height data to provide some new insights on the 11 year solar cycle signal in the northern hemisphere early winter and its modulation by the quasi biennial oscillation qbo the signals are strongest in the upper stratosphere when the qbo is in its easterly phase qboe it appears to move gradually eastward and poleward resulting in a predominantly positive signal over the pole with a weaker vertically connected negative signal over the icelandic low when the qbo is in its westerly phase qbow the polar stratospheric signal is mainly negative and appears connected to a negative anomaly in the troposphere over the aleutian low a spectral analysis of the stratospheric response in planetary waves showed a reduction of wave number 2 power under qboe and an enhancement of wave number 3 under qbow these responsesarecharacterizedbyanoverallincrease decreaseinwaveactivityatmiddletohigh latitudes rather than a latitudinal shift of wave activity there is no clear stratosphere troposphere connection under qboe but under qbow there is a vertically coherent increase in wave power at wave numbers 1 3 with a period of 5 6 6 9 days we suggest that the differences in response under qboe and qbow can be explained through differences in initial vortex strength resulting in either a stronger influence from the low latitude upper stratosphere qboe or from the troposphere qbow on the polar stratosphere

stationary planetary waves in upper mesospheric winds abstract quasi stationary planetary scale longitudinal variations are found in the upper mesospheric winds measured during winter by the hrdi satellite instrument these are negatively correlated with eddy winds in the stratosphere two different mechanisms are proposed to explain the mesospheric perturbation winds and their anticorrelation with stratospheric winds 1 planetary waves propagate through the stratosphere and into the mesosphere with a phase shift of one half cycle and 2 mesospheric perturbations are forced in situ by gravity waves whose spectrum has longitudinal asymmetries due to filtering by planetary waves in the stratosphere the first mechanism is more consistent with the observations during southern hemisphere late winter august and also may explain the observations during northern hemisphere early winter december the second mechanism gives a more consistent explanation for the northern hemisphere late winter observations as previously shown by the author the hemispheric diff

global temperature stationary planetary waves extending from 20 to 120 km observed by timed saber version 1 07 temperature measurements from saber instrument on board of timed satellite during 2006 2007 are used to study the temperature stationary planetary waves spws from 20 to 120 km to cover the high latitudes in both hemispheres 80 degrees s 80 degrees n and most local times 120 day data are combined together into one data set the most pronounced spw features are the large amplitudes in the upper mesosphere and lower thermosphere umlt while the spws below 90 95 km share common features with previous observations in both hemispheric umlt spws amplitudes are large at middle and high latitudes throughout the year while their amplitudes in tropics are small wave 1 activity is generally stronger than the corresponding wave 2 activity with maximum amplitudes larger than 15 k occurring at about 60 degrees 70 degrees north or south at the altitudes between 112 km and 119 km wave 1 amplitudes are larger in the southern hemisphere sh than in the northern hemisphere nh their phases are normally tilt westward with increasing height below similar to 110 km above this altitude the wave 1 and wave 2 phases remain nearly unchanged with height indicating the in situ generations and no propagations comparisons between the observed spw structures and those from the nrlmsise 00 model have been done result shows their consistent features below similar to 80 km and that nrlmsise 00 model gives no spw information from 95 to 125 km but does have longitudinal variations above similar to 125 km that are similar to the observed spw features above similar to 110 km

seasonal interannual and short term variability of planetary waves in met office stratospheric assimilated fields met office stratospheric assimilated data have been used to study the variability of travelling planetary waves in the upper stratosphere during the last decade 1992 2001 to distinguish the various travelling and quasi standing waves a new space time filtering method has been developed the results of this analysis show that longer period planetary waves 10 t 20 days have significant amplitudes mainly during winter in both hemispheres westward propagating waves are dominant in the northern hemisphere but in the southern hemisphere eastward and westward propagating waves have comparable amplitudes and sometimes eastward propagating waves are dominant it is suggested that the main forcing of longer period travelling waves is an internal variability of the quasi stationary planetary waves in the tropo stratosphere and that the substantial activity of eastward propagating waves in the southern hemisphere is associated with seasonal changes of the general circulation of the middle atmosphere in the shorter period part of the wavelet spectra t 10 days westward propagating waves are dominant and the observed maxima in amplitude spectra can be identified with the first symmetric normal atmospheric modes the so called 5 and 4 day waves these waves present in the stratosphere during most of the year increase in amplitude during seasonal transitions analysis of the behaviour of wavelet amplitudes at different pressure levels shows that these normal mode waves propagate upward from the lower atmosphere and their amplitudes increase with altitude there exists also a substantial long period modulation of the 5 day wave amplitude with quasi period of about 30 days copyright 2004 royal meteorological society

quasi 10 day wave and semidiurnal tide nonlinear interactions during the southern hemispheric ssw 2019 observed in the northern hemispheric mesosphere

properties of the quasi 16 day wave derived from eos mls observations 1 this paper describes the use of eos microwave limb sounder mls data to observe the field of traveling planetary waves with quasi 16 day periods this study utilizes mls v2 2 temperature and geopotential data between 1 january 2005 and 31 december 2008 in the range 316 hpa to 0 001 hpa approximately 8 to 97 km to examine these waves analysis demonstrates that the quasi 16 day wavefield is made up of a number of components with westward and eastward propagating s 1 and s 2 waves generally dominant in the northern hemisphere the westward and eastward propagating s 1 waves have similar magnitudes and are larger than the other modes while in the southern hemisphere the eastward propagating s 1 and s 2 waves are larger than the westward propagating wave modes all of the modes examined display strong seasonal patterns in the temperature amplitude significant variability in the wave activity from year to year and the presence of strong pulse like patterns in the activity all of the modes also display large median temperature amplitudes poleward of 40 degrees in both hemispheres our analysis also demonstrates that the variability in winter from year to year is larger in the northern hemisphere than the southern hemisphere detailed study also suggests that the exclusion of waves from regions of negative refractive index squared likely forms much of the seasonal pattern observed thus regions of strong westward wind speeds effectively exclude vertically propagating waves as expected from theory the reflection and absorption of waves associated with critical lines is also likely to explain the frequent occurrence of standing wave patterns in the eos mls temperature observations this study highlights the potential of mls observations for observing waves from the upper troposphere to the lower mesosphere

september 2019 antarctic sudden stratospheric warming quasi 6 day wave burst and ionospheric effects an exceptionally strong stationary planetary wave with zonal wavenumber 1 led to a sudden stratospheric warming ssw in the southern hemisphere in september 2019 ionospheric data from esa s swarm

upper mantle structure in the south central chilean subduction zone 30 to 36 s 1 regional p and s wave travel time data were used to obtain three dimensional seismic tomography models for vp vs and vp vs above the subducting slab in central chile and argentina in this region there is an abrupt change from a normal subduction geometry south of 33 s to a flat subduction geometry to the north we find low vp low vs and high vp vs ratios in the southern half of our study area directly beneath the modern active volcanic arc which we interpret as localized pockets of melt in the northern half of our study area above where the subducting nazca plate flattens at 100 km depth we find low vp high vs and low vp vs ratios these unusual results point to a lack of melt or hydrated mineralogies such as serpentine both of which are characterized by high vp vs values the only mantle rocks that have low vp vs and high vs are mg rich compositions such as dehydrated serpentinite or orthopyroxenite we suggest that significant portions of the mantle overlying the flat slab consist of orthopyroxenite formed by a transient fluxing of silica rich fluids such fluids may have come from sediments that were subducted during the initiation of flat subduction at this latitude at 10 ma this would imply that the hydration of mantle material above a flat slab can be a transient phenomenon which leaves little residual free water behind but significantly alters the mantle chemistry

the quasi 2 day wave observed in the polar mesosphere 1 using mf radar data obtained at tromso 69 6 n 19 2 e for 37 months between 1 november 1998 and 8 december 2001 we have examined characteristics of the quasi 2 day wave q2dw in the polar mesosphere in the height range from 70 to 91 km the activity of the q2dw is higher in winter months november february than in summer months may august over this height region the maximum values of the amplitude are 25 m s 1 in winter and 15 m s 1 in summer between 70 and 82 km the amplitude appears to maximize near winter solstice over the 3 years the average ratio of meridional to zonal amplitudes is 1 1 1 2 over the height region thus there is no significant preference towards either components the variations of the periods of maximum amplitude are also examined and periods with 45 2 and 54 9 hours occur more frequently than those with 48 0 and 51 2 hours however no clear seasonal trend of the variation of the period is found in addition the amplitude is modulated at 4 10 day rate with simultaneous observational data from the mf radar and the eiscat uhf radar colocated in tromso we have examined whether or not the q2dw was able to penetrate to the lower thermosphere for the period of 1 9 july 1999 it is found that the amplitude of the q2dw with period of 51 2 hours maximized at 95 km height with values of 25 m s 1 in both meridional and zonal components the q2dw was attenuated above 95 km but it appears to survive up to 108 km height in the meridional component between 85 and 95 km for the meridional component during this 8 day interval the q2dw and semidiurnal tide were the strongest among the periodic components

elasticity of antigorite seismic detection of serpentinites and anisotropy in subduction zones abstract serpentinization of the mantle wedge is an important process that influences the seismic and mechanical properties in subduction zones seismic detection of serpentines relies on the knowledge of elastic properties of serpentinites which thus far has not been possible in the absence of single crystal elastic properties of antigorite the elastic constants of antigorite the dominant serpentine at high pressure in subduction zones were measured using brillouin spectroscopy under ambient conditions in addition antigorite lattice preferred orientations lpo were determined using an electron back scattering diffraction ebsd technique isotropic aggregate velocities are significantly lower than those of peridotites to allow seismic detection of serpentinites from tomography the isotropic v p v s ratio is 1 76 in the voigt reuss hill average not very different from that of 1 73 in peridotite but may vary between 1 70 and 1 86 between the voigt and reuss bonds antigorite and deformed serpentinites have a very high seismic anisotropy and remarkably low velocities along particular directions v p varies between 8 9 km s 1 and 5 6 km s 1 46 anisotropy and 8 3 km s 1 and 5 8 km s 1 37 and v s between 5 1 km s 1 and 2 5 km s 1 66 and 4 7 km s 1 and 2 9 km s 1 50 for the single crystal and aggregate respectively the v p v s ratio and shear wave splitting also vary with orientation between 1 2 and 3 4 and 1 3 and 2 8 for the single crystal and aggregate respectively thus deformed serpentinites can present seismic velocities similar to peridotites for wave propagation parallel to the foliation or lower than crustal rocks for wave propagation perpendicular to the foliation these properties can be used to detect serpentinite quantify the amount of serpentinization and to discuss relationships between seismic anisotropy and deformation in the mantle wedge regions of high v p v s ratios and extremely low velocities in the mantle wedge of subduction zones down to about 6 and 3 km s 1 for v p and v s respectively are difficult to explain without strong preferred orientation of serpentine local variations of anisotropy may result from kilometer scale folding of serpentinites shear wave splittings up to 1 1 5 s can be explained with moderately thick 10 20 km serpentinite bodies

a statistical analysis of the propagating quasi 16 day waves at high latitudes and their response to sudden stratospheric warmings from 2005 to 2018

gaspe belt subsurface geometry in the northern quebec appalachians as revealed by an integrated geophysical and geological study 1 potential field mapping abstract together recent gravity and high resolution aeromagnetic datasets are used to qualitatively investigate the upper and middle crustal geometry of the middle paleozoic gaspe belt in the northern appalachians long wavelength potential field anomalies define two sub basins that are divided by northeast trending gravity highs for each sub basins gravity lows correlate with the youngest rock units maps that highlight anomalies associated with near surface features at the expense of those related to deeper sources provide an important supplement to the spatially discrete observations derived from bedrock mapping analysis of such maps indicates that the sub basins are characterized by different structural patterns and that faults trending obliquely compared to the main structural grain have been previously underestimated the geometry of the gaspe belt as revealed by this integrated geophysical and geological study bears similarities with orogens exhibiting lateral extrusion this geometry is interpreted as the result of a heterogeneous strain regime in front of an indenter corresponding to the early paleozoic gander dunnage crustal block the indentation tectonic model is supported by 1 the various strike and kinematic of faults that suggest a strongly heterogeneous strain regime 2 the greater geological complexity and the occurrence of faults with a significant thrust component in front of the indenter 3 the predominance of dextral strike slip faults in the eastern gaspe peninsula that result in lateral material transport away from the indenter 4 the location of abundant devonian magmatic dykes sills and stocks in a fault bounded zone that experienced local extension 5 the occurrence of block rotation

vertical and fold axis parallel extension within a slate belt in a transpressive setting northern appalachians abstract an incremental and finite strain study of a mid paleozoic slate belt in a transpressive setting in gaspe canadian appalachians has been undertaken using syntectonic fibers from pyrite type pressure shadows regionally strain estimates are quite consistent and reflect only slightly higher strain in the central part of the anticlinorial structure defining the slate belt extensions of up to 160 vertically and 110 parallel to the fold axis were recorded in the slate belt combined with an estimated overall regional shortening of 80 the fibers first rotated toward the final position of the cleavage within a vertical section normal to the cleavage and then rotated from a vertical to a horizontal orientation this change in fiber orientation observed in cleavage parallel sections indicates an abrupt change in the incremental stretching direction from sub vertical to sub horizontal fold axis parallel the vertical extension is related to folding and cleavage development during coaxial flattening the horizontal extension reflects the strain imposed on the rocks during regional simple shear which produced strike slip faulting and further tightening of the folds folding cleavage development fold axis parallel extension and faulting are all related to oblique convergence during the middle devonian acadian orogeny in this part of the canadian appalachians and clearly indicate an overall transition from a pure shortening deformation to a simple shear dominant deformation in an overall transpressive setting

on the seasonal cycle of stratospheric planetary waves quasi stationary planetary waves exhibit different seasonal behaviour in the two winter stratospheres whereas in a climatological sense wave amplitudes are large throughout northern winter in the southern hemisphere there is a climatological minimum in midwinter it is suggested here that the southern hemisphere behaviour is basically linear the midwinter minimum arising from the opacity of the strong westerlies of southern midwinter to stationary wave propagation on the other hand it is further suggested that in the northern hemisphere winter the westerlies are prevented from becoming so strong in a climatological sense by the action of the waves themselves on the mean state and that the penetration of large scale waves into the midwinter northern stratosphere thus depends on a nonlinear feedback process preliminary tests of this hypothesis are conducted using a highly truncated beta plane model of the stratospheric flow

phase relations of a serpentine composition between 5 and 14 gpa significance of clinohumite and phase e as water carriers into the transition zone run products from high pressure experiments at 800 1 200 c and 5 14 gpa corresponding to depths of 150 to 420 km on a serpentine bulk composition close to mg3si2o5 oh 4 were analysed by optical microscopy micro raman spectroscopy and electron microprobe all charges exhibit strong chemical zoning fluid melt and hydrous solids were mostly concentrated at the top bottom and along the wall of the capsules the central part of the charge was devoid of h2o both fluid and hydrous magnesian phases exhibit a mg si ratio higher than forsterite in contrast the centre of the capsule was enriched in sio2 the observed zoning can neither be explained by gravitational settling nor by a thermal gradient alone most likely the fluid was separated from the solids by surface forces and thereby established the chemical gradient by preferentially dissolving mgo if strong chemical zoning is taken into account the occurrence of more phases than allowed by the phase rule can be explained by separating the bulk into several domains of different bulk compositions results indicate that small amounts of f increase the stability field of clinohumite mg9si4o16 oh f 2 compared to oh clinohumite in pure msh previously reported clinohumite coexists with enstatite up to 975 c at 5 gpa and up to 1 100 c at 12 gpa at 14 gpa close to the mg2sio4 transition phase e becomes the most important water carrier the new results indicate that clinohumite could be an important mantle mineral for transporting water into the earth s transition zone due to its high thermal stability compared to other important water carriers such as serpentine and phase a

longitudinal variations in mesospheric winds evidence for gravity wave filtering by planetary waves abstract mesospheric horizontal wind data from the high resolution doppler image hrdi satellite instrument are used to investigate the longitudinal variation of nontidal winds in the upper mesosphere and their relationship with winds in the stratosphere the period covered by the study is late winter february mid march for 1992 1994 the results indicate that there is a negative correlation between longitudinal variations of the zonal winds in the stratosphere and those in the mesosphere and between longitudinal variations of the meridional winds in the stratosphere and mesosphere the data are examined to determine which of several possible causes is responsible the possibilities are 1 that planetary scale disturbances are produced in situ by gravity wave drag in the mesosphere that is not zonally symmetric because of filtering by the planetary waves in the stratosphere 2 that asymmetries are caused by longitudinal variations in gravity wave drag due to azonal source distributions that are coinc

a statistical analysis of sporadic e layer occurrence in the midlatitude china region a statistical analysis of sporadic e layer recorded from september 2011 to september 2015 at four chinese ionospheric sounding stations of mohe 122 37 e 53 50 n beijing 116 25 e 40 25 n wuhan 114 61 e 30 53 n and hainan 109 13 e 19 52 n are presented to investigate the characteristics of sporadic e layer at the middle latitudes over china the occurrence of the sporadic e layer in mid latitude china region shows strong dependence on local time and season consistent with previous studies the occurrence of the mid latitude sporadic e layer is prominent at local daytime in summer season the results also reveal that the post sunset sporadic e layer is statistically pronounced in mid latitude china region possibly related to the nighttime mid latitude e region irregularities the mid latitude sporadic e layer is modulated by atmospheric tidal waves and planetary waves at different latitudes the occurrence of the mid latitude sporadic e layer also tends to increase with the level of geomagnetic activity on basis of both the statistical analysis and case study

zonally symmetric oscillations in the northern hemisphere stratosphere during the winter of 2003 2004 1 the paper presents clear evidence of zonally symmetric planetary waves with very large amplitudes present in the uk met office zonal wind data of the northern hemisphere stratosphere in the winter of 2003 2004 the spectral analysis reveals that three prevailing periods of 23 17 and 11 days contribute to the observed zonally symmetric oscillations these waves are extracted from the data and their amplitudes and phases are studied in detail depending on height and latitude the wave amplitudes particularly those of the 11 and the 17 day zonally symmetric waves clearly indicate the presence of two latitudinal branches of amplifications centred at 50 60 n and 20 30 n the phase analysis shows that these waves are vertically upward propagating waves and that the waves from the high latitude and tropical branches are almost out of phase a possible forcing mechanism is suggested the zonally symmetric waves play an important role in coupling the dynamical regimes of the high and low latitude stratosphere particularly during the major stratwarm event in the arctic winter of 2003 2004

elasticity of serpentines and extensive serpentinization in subduction zones 1 elastic constants of lizardite mg3si2o5 oh 4 were computed using first principles quantum mechanical calculations within the density functional theory the predicted c axis compressibility is much larger than measured modeling of the weak o h o interactions between layers must be improved in order to better predict layered hydrated mineral elastic properties the large computed bulk modulus range is consistent with equation of state and seismic velocities in chrysotile lizardite serpentinites but shear wave velocities are lower than the lowest theoretical estimate the low seismic velocities measured for chrysotile serpentinites can be attributed to specific contribution of the nanotube textured chrysotile for antigorite the data from acoustic and eos measurements are consistent if used for interpreting seismic velocities the inferred degrees of serpentinization of the mantle wedge are higher than with the commonly used calibrations using chrysotile serpentinite properties serpentine is likely a dominant phase in low velocity areas of the mantle wedge at 30 50 km depths

role of grain size in phyllonitisation insights from mineralogy microstructures strain analyses and numerical modeling abstract brittle y and p planes exist in an exposure of greywacke in the garhwal lesser himalaya india although y planes are well developed throughout the p planes are prominent only in some parts domain a and not elsewhere domain b to investigate why the p planes developed selectively the following studies were undertaken 1 clay separated xrd analyses clinochlore and illite are present in both the domains 2 strain analyses by rf method it deduces strain magnitudes of 1 8 for the ductile deformed quartz grains from both the domains a and b 3 grain size analyses of quartz clasts domain a is mostly composed of finer grains area up to 40 000 m2 whereas domain b consists of a population of coarser grains area 45 000 m2 a 2d finite element modeling of linear elastic material was performed using comsol software to investigate the control of grain size variation on the generation brittle shear planes the results of numerical modeling corroborate the known fact that an increase in grain size reduces the elastic strain energy density a broader grain size distribution increases the effects of diffusion creep and resists the onset of dislocation creep thus rocks with coarser grain population domain b tend to resist the generation of shear fractures unlike their fine grained counterpart domain a

shear wave anisotropy in the mariana subduction zone to determine the location strength and orientation of seismic anisotropy in the mariana subduction zone beneath guam we evaluated shear wave splitting in local s regional s and scs and teleseismic core phases such as sks recorded at station gumo fast directions from the local s phases have an average azimuth of 45 and splitting times range from 0 1 s to 0 4 s for local s phases from events within the southeastern half of the subducting slab splitting parameters manifest minimal frequency dependence in both fast direction and splitting time however for the remaining local s phases in the data set fast directions vary with frequency content no well constrained splitting parameters were obtained for the regional and teleseismic phases but the particle motions of these unsplit phases are consistent with an average anisotropic fast direction of 45 anisotropy due solely to olivine oriented by slab entrained flow in the mantle wedge would produce local s fast directions at 66 and anisotropy due solely to fossil seafloor spreading in the subducting slab would yield fast directions at 20 to 30 neither of these predictions is consistent with the observed fast directions however the observed splitting including the frequency dependent fast directions can be explained by models containing anisotropy in both the slab and wedge and possibly although not necessarily anisotropy due to recent extension in the overriding philippine sea plate

electrical conductivity of the serpentinised mantle and fluid flow in subduction zones in the mantle wedge of subduction zones electromagnetic profiles reveal high electrical conductivity bodies in hot areas 700 degrees c water released by dehydration of the slab induces melting of the mantle under volcanic arcs that can explain the observed high conductivities in the cold 1 m fluids during progressive serpentinisation of the mantle wedge these fluids can mix with arc magmas at depths and account for high chlorine water ratios in arc lavas

high pressure creep of serpentine interseismic deformation and initiation of subduction the supposed low viscosity of serpentine may strongly influence subduction zone dynamics at all time scales but until now its role could not be quantified because measurements relevant to intermediate depth settings were lacking deformation experiments on the serpentine antigorite at high pressures and temperatures 1 to 4 gigapascals 200 to 500 c showed that the viscosity of serpentine is much lower than that of the major mantle forming minerals regardless of the temperature low viscosity serpentinized mantle at the slab surface can localize deformation impede stress buildup and limit the downdip propagation of large earthquakes at subduction zones antigorite enables viscous relaxation with characteristic times comparable to those of long term postseismic deformations after large earthquakes and slow earthquakes antigorite viscosity is sufficiently low to make serpentinized faults in the oceanic lithosphere a site for subduction initiation

a description of low frequency atmospheric oscillations over the extratropical northern hemisphere using singular spectrum analysis the method of singular spectrum analysis ssa is used to describe low frequency atmospheric variability over the extratropical northern hemisphere nh from 500 hpa geopotential heights analysis reveals significant intraseasonal and interannual oscillations confined principally to eastern sections of the pacific ocean and northern sections of the atlantic ocean generally where earlier studies have identified persistent anomalies from the results it is suggested that persistent anomalies may undergo significant modulation on the quasi biennial time scale

double seismic zone of the nazca plate in northern chile high resolution velocity structure petrological implications and thermomechanical modeling this paper presents an interdisciplinary study of the northern chile double seismic zone first a high resolution velocity structure of the subducting nazca plate has been obtained by the tomodd double difference tomography method the double seismic zone dsz is observed between 80 and 140 km depth and the two seismic planes is 20 km apart then the chemical and petrologic characteristics of the oceanic lithosphere associated with this dsz are deduced by using current thermal petrological seismological models and are compared to pressure temperature conditions provided by a numerical thermomechanical model our results agree with the common hypothesis that seismicity in both upper and lower planes is related to fluid releases associated with metamorphic dehydration reactions in the seismic upper plane located within the upper crust these reactions would affect material of basaltic morb composition and document different metamorphic reactions occurring within high p 2 4 gpa and low t 130 km lawsonite amphibole eclogite conditions the lower plane lying in the oceanic mantle can be associated with serpentinite dehydration reactions the vp and vs characteristics of the region in between both planes are consistent with a partially 25 30 vol antigorite 0 10 vol brucite and 4 10 vol chlorite hydrated harzburgitic material discrepancies persist that we attribute to complexities inherent to heterogeneous structural compositions while various geophysical indicators evidence particularly cold conditions in both the descending nazca plate and the continental fore arc thermomechanical models indicate that both seismic planes delimit the inner slab compressional zone around the 400 c 50 c isotherm lower plane earthquakes are predicted to occur in the slab s flexural neutral plane where fluids released from surrounding metamorphic reactions could accumulate and trigger seismicity fluids migrating upward from the tensile zone below could be blocked in their ascension by the compressive zone above this plane thus producing a sheeted layer of free fluids or a serpentinized layer therefore earthquakes may present either downdip compression and downdip tensile characteristics numerical tests indicate that the slab s thermal structure is not the only factor that controls the occurrence of inner slab compression 1 a weak ductile subduction channel and 2 a cold mantle fore arc both favor inner slab compression by facilitating transmission of compressional stresses from the continental lithosphere into the slab 3 decreasing the radius of curvature of the slab broadens the depth of inner slab compression whereas 4 decreasing upper plate convergence diminishes its intensity all these factors indicate that if dszs indeed contour inner slab compression they cannot be linked only to slab unbending but also to the transmission of high compressional stresses from the upper plate into the slab

antigorite high pressure stability in the system mgosio2h2o msh abstract the breakdown reactions of antigorite 1 forming talc forsterite water at low pressures and 2 forming forsterite clinoenstatite water at high pressures were determined in reversed equilibrium experiments results on reaction 1 were found to be in good agreement with former experimental determinations by both johannes johannes w 1975 zur synthese und thermischen stabilitat von antigorit fortschr mineral beih 53 36 and evans et al evans b w johannes w oterdoom h trommsdorff v 1976 stability of crysotile and antigorite in the serpentinite multisystem schweiz mineral petrogr mitt 56 79 93 from our experiments the invariant point i1 interconnecting the two reactions can be located at about 15 kbar 650 c this is consistent with the thermodynamic calculations using the dataset of berman berman r g 1988 internally consistent thermodynamic data for minerals in the system j petrol 29 445 522 however it is in contrast to recent experimental studies of ulmer and trommsdorff ulmer p trommsdorff v 1995a serpentine stability to mantle depths and subduction related magmatism science 268 858 861 who determined i1 at 21 kbar 730 c our pt conditions for i1 could be confirmed by equilibrium experiments on reaction 10 talc forsterite clinoenstatite water which is generated at i1 as well up to about 25 kbar the breakdown reaction 2 is nearly pressure independent towards still higher pressures the dp dt slope of reaction 2 bends and becomes negative schreinemakers analysis as well as thermodynamic calculations of the upper pressure stability of antigorite show that the possible antigorite breakdown reaction 3 antigorite clinoenstatite brucite water and reaction 4 brucite clinoenstatite forsterite water could originate at a new invariant point i2 provided that the reactions 2 and 11 brucite antigorite forsterite water intersect bracketing equilibrium 4 and combining these results with those on reaction 2 i2 was located at only about 51 kbar 490 c compared to 77 kbar 680 c according to berman s data however when taking into account the dense hydrous magnesium silicate dhms phase a mg7si2o8 oh 6 the phase relations of antigorite are changed resulting i in the metastability of i2 and reaction 3 and ii in a new invariant point i7 at about 44 kbar and 580 c generating the new antigorite breakdown reaction 16 antigorite phase a clinoenstatite water on the basis of these new data on the stability of antigorite earlier conclusions about dehydration depths in subducted serpentine bearing oceanic lithosphere have to be reconsidered the maximum pressure stability of antigorite according to reaction 16 extends between 44 and 55 kbar that is between about 130 and 160 km depths as opposed to about 75 kbar 220 km following ulmer and trommsdorff see above because many different thermal regimes are possible in subduction zones no specific dehydration depth can be expected but rather more continuous dehydration fronts in space and time

crustal structure study at the izu bonin subduction zone around 31 n implications of serpentinized materials along the subduction plate boundary abstract the izu bonin trench ibt has characteristics different from other trenches in many aspects a chain of serpentine seamounts is exposed at the forearc slope 40 50 km west of the izu bonin trench axis in this area few large earthquakes m7 0 have occurred at shallow depths 0 100 km and many large earthquakes have occurred at greater depths 400 km to reveal the mechanism of serpentine diapiring and the relation between heterogeneity in earthquake occurrence and plate subduction seismic refraction reflection studies at the forearc slope with two lines perpendicular and parallel to the izu bonin trench axis were carried out in 1998 detailed seismic velocities were obtained for both lines by seismic tomography using refracted first arrivals and reflected arrivals on the e w line the subducting plate interface and the moho of the subducting oceanic plate were recognized the velocity of the mantle wedge is lower than that of the average velocity of oceanic mantle along the subducting plate a layer between the two plates plate boundary layer pbl with a low velocity appears just beneath the serpentine diapir and forms a sill shape which becomes thicker with increasing velocity from the diapir toward the west and connects to the mantle wedge the low velocity materials in the pbl are interpreted as chrysotile which is a low temperature phase of serpentine produced by the hydration of peridotite by water supplied by the subducting slab the chrysotile in the pbl might act as a lubricant and decrease seismic activity along the subduction zone and this can explain the characteristics of seismicity in the izu bonin subduction zone ibsz in contrast to the e w line the crustal structure along the n s line is rather homogeneous

paleostress analysis of atlantic crustal extension in the quebec appalachians abstract a paleostress analysis using normal fault slip data and jurassic dike trends has been conducted in the quebec and new england appalachians stress tensor analysis of fault slip by a numerical inversion method has distinguished homogeneous and directionally consistent e w and nw se oriented extensional stress regimes in the quebec appalachians and st lawrence lowlands the directions of extension compare well with the mean direction of extensional stress inferred from the jurassic dolerite dike trend in new england both extensions are interpreted as the result of rift related stress associated with the separation of north america and africa early in the late triassic early jurassic fragmentation of pangea the paleostress field configuration is assumed to be related to the direction of divergent plate motion the n s and ne sw late proterozoic faults that bordered the quebec reentrant and taconian acadian structures of the quebec appalachians appear to have played a significant role in the dis

coupling between mesosphere and ionosphere over beijing through semidiurnal tides during the 2009 sudden stratospheric warming 1 sudden stratospheric warming ssw in the winter of 2008 2009 is the strongest recorded ssw event the enhancement in semidiurnal variation of ionospheric tec total electron content with phase shift forward is shown during 22 to 27 january 2009 based on the tec observations in beijing 40 30 n 116 19 e geographic 39 73 n dip latitude we focus on finding the reason for the tec variation winds observed by an all sky meteor radar in the same observatory are used to study mesospheric variation the semidiurnal solar tide in the mesosphere starts to increase before the ssw and maintains oscillation with period 16 20 days during the ssw the semidiurnal lunar tides in tec and wind start to increase on 17 and 15 january respectively although the semidiurnal lunar tide in tec over beijing almost dies out on 1 february that over equatorial ionospheric anomaly crest does not vanish until 15 february when lunar tide in wind tends to be very weak the maximum of lunar tide in wind appears on 2 february at 96 km with amplitudes of 15 m s and 21 m s for zonal and meridional winds the phase comparison shows that lunar tides in tec and zonal wind reach their maxima at almost the same time which is 2 4 h lag behind the meridional wind the coupling between the mesosphere and ionosphere contributes to the semidiurnal variation of tec through both solar and semidiurnal lunar tides the enhancement in semidiurnal lunar tide is responsible for the tec peak shift forward during the ssw

tomographic imaging of hydrated crust and mantle in the subducting pacific slab beneath hokkaido japan evidence for dehydration embrittlement as a cause of intraslab earthquakes abstract we estimate detailed three dimensional seismic velocity structures in the subducting pacific slab beneath hokkaido japan using a large number of arrival time data from 6902 local earthquakes a remarkable low velocity layer with a thickness of 10 km is imaged at the uppermost part of the slab and is interpreted as hydrated oceanic crust the layer gradually disappears at depths of 70 80 km suggesting the breakdown of hydrous minerals there we find prominent low velocity anomalies along the lower plane of the double seismic zone and above the aftershock area of the 1993 kushiro oki earthquake m7 8 since seismic velocities of unmetamorphosed peridotite are much higher than the observations hydrous minerals are expected to exist in the lower plane as well as the hypocentral area of the 1993 earthquake on the other hand regions between the upper and lower planes where seismic activity is not so high compared to the both planes show relatively high velocities comparable to those of unmetamorphosed peridotite our observations suggest that intermediate depth earthquakes occur mainly in regions with hydrous minerals which support dehydration embrittlement hypothesis as a cause of earthquake in the subducting slab

planetary waves in coupling the stratosphere and mesosphere during the major stratospheric warming in 2003 2004 1 the vertical coupling of the stratosphere mesosphere system through quasi stationary and traveling planetary waves during the major sudden stratospheric warming ssw in the arctic winter of 2003 2004 has been studied using three types of data the uk met office ukmo assimilated data set was used to examine the features of the global scale planetary disturbances present in the winter stratosphere of the northern hemisphere sounding the atmosphere using broadband emission radiometry saber satellite measurements were used as well for extracting the stationary planetary waves in the zonal and meridional winds of the stratosphere and mesosphere radar measurements at eight stations four of them situated at high latitudes 63 69n and the other four at midlatitudes 52 55n were used to determine planetary waves in the mesosphere lower thermosphere mlt the basic results show that prior to the ssw the stratospheremesosphere system was dominated by an upward and westward propagating 16 day wave detected simultaneously in the ukmo and mlt zonal and meridional wind data after the onset of the ssw longer period 22 24 days oscillations were observed in the zonal and meridional mlt winds these likely include the upward propagation of stationary planetary waves from below and in situ generation of disturbances by the dissipation and breaking of gravity waves filtered by stratospheric winds citation pancheva d et al 2008 planetary waves in coupling the stratosphere and mesosphere during the major stratospheric warming in 2003 2004 j geophys res 113 d12105 doi 10 1029 2007jd009011

high pressure elasticity of serpentine and seismic properties of the hydrated mantle wedge 1 a subset of the single crystal elastic moduli of natural antigorite has been measured using brillouin scattering at high pressure up to 9 gpa aggregate properties and axial compressibilities are in good agreement with equation of state results from x ray diffraction stiffness along the c axis increases becoming close to those within the silicate layer near 7 gpa a slight discontinuity in the evolution of the elastic moduli near 7 gpa is associated with a phase transition raman spectroscopy shows that the transition does not occur in subducting slabs except in the core of the coldest slabs where serpentine may be subducted to depths of about 200 km varying temperature and pressure has limited effects on the interpretation of seismic velocities principally because of the limited depth range of serpentine stability mostly above 100 km depth and also due to the compensating effects of pressure and temperature that maintain velocity variations well within the uncertainties and statistical variability of seismological studies serpentinites are excellent candidates for explaining low velocities in the hydrated mantle wedge inversion of the moho and thin anisotropic low velocity layers at the plate interface serpentinite layers provide an alternative explanation to fluid saturated oceanic crust for explaining these phenomena and account for a transition to an aseismic decoupled plate interface

three dimensional p and s wave velocity structures beneath the japan islands obtained by high density seismic stations by seismic tomography abstract we construct fine scale 3d p and s wave velocity structures of the crust and upper mantle beneath the whole japan islands with a unified resolution where the pacific pac and philippine sea phs plates subduct beneath the eurasian eur plate we can detect the low velocity low v oceanic crust of the pac and phs plates at their uppermost part beneath almost all the japan islands the depth limit of the imaged oceanic crust varies with the regions high vp vs zones are widely distributed in the lower crust especially beneath the volcanic front and the high strain rate zones are located at the edge of the extremely high vp vs zone however vp vs at the top of the mantle wedge is not so high beneath northern japan we can image the high v subducting pac plate using the tomographic method without any assumption of velocity discontinuities we also imaged the heterogeneous structure in the pac plate such as the low v zone considered as the old seamount or the highly seismic zone within the double seismic zone where the seismic fault ruptured by the earthquake connects the upper and lower layer of the double seismic zone beneath central japan thrust type small repeating earthquakes occur at the boundary between the eur and phs plates and are located at the upper part of the low v layer that is considered to be the oceanic crust of the phs plate in addition to the low v oceanic crust the subducting high v pac plate is clearly imaged to depths of approximately 250 km and the subducting high v phs zone to depths of approximately 180 km is considered to be the phs plate beneath southwestern japan the iso depth lines of the moho discontinuity in the phs plate derived by the receiver function method divide the upper low v layer and lower high v layer of our model at depths of 30 50 km beneath kyushu the steeply subducting phs plate is clearly imaged to depths of approximately 250 km with high velocities the high vp vs zone is considered as the lower crust of the eur plate or the oceanic crust of the phs plate at depths of 25 35 km and the partially serpentinized mantle wedge of the eur plate at depths of 30 45 km beneath southwestern japan the deep low frequency nonvolcanic tremors occur at all parts of the high vp vs zone within the zone the seaward side and the landward side where the phs plate encounters the mantle wedge of the eur plate we prove that we can objectively obtain the fine scale 3d structure with simple constraints such as only 1d initial velocity model with no velocity discontinuity

evidence for serpentinization of the forearc mantle wedge along the nicoya peninsula costa rica 1 characterizing the hydration state of the forearc mantle wedge yields valuable information on frictional stability at the downdip edge of subduction megathrusts simultaneous inversion of p and s wave arrival times collected as part of the costa rica seismogenic zone experiment yields 1d and 3d p and s wave velocity models vp and vs for the nicoya peninsula segment of the middle america trench nicoya peninsula 1d velocity models show similar velocity gradients to country wide 1d velocity models from 5 30 km depth but diverge at expected moho depths due to proximity to the subducting cocos plate 3d vp values range from 7 2 7 6 km sec in the forearc mantle wedge receiver functions computed at global seismic network station jts in northwestern costa rica confirm these vp values yield vp vs of 1 85 and place the continental moho at 36 4 km depth vp and vp vs are consistent with 15 25 serpentinization of the forearc mantle wedge

palinspastic restoration of a post taconian successor basin deformed within a transpressive regime northern appalachians restoration of transpressional orogens requires a three dimensional analysis of the strain state in order to take into account both the pure shear and simple shear components of the deformation and assess their relative contribution throughout the deformation history restoration of the post taconian successor basin the gaspe belt located within the external part of the acadian orogen in the canadian appalachians was performed by using a step by step method based on the successive removal of strain increments the pure shear component contributed 70 of the total strain during the first stages of the deformation whereas the simple shear component contributed 30 of the total strain during the last stages three retrodeformation steps are defined starting with restoration of the last deformation stage and working back to the first deformation stage the first step is to restore slip along acadian strike slip faults the second step is to restore shortening related to the horizontal extension during the acadian regional simple shear event finally the third step is to restore vertical extension related to the pure shear event by removing slip along the reverse faults unfolding and removing internal strain associated with cleavage development retrodeformation of the simple shear component of the transpressive deformation during the first two steps is performed on a horizontal view of the gaspe belt basin which contains the horizontal extension direction and which is perpendicular to the acadian nw se directed compression likewise restoration of the pure shear component is performed in vertical sections which contain the vertical extension and which are perpendicular to the acadian nw se directed compression the palinspastic map presented here is a much more appropriate base map for the basin and allows for a more realistic paleogeographic interpretation of the gaspe belt

mesospheric planetary waves over antarctica during 2002 1 wind measurements from a series of atmospheric radars located around antarctica have been used to characterize the mesospheric planetary wave field during the winter of 2002 combining winds from the medium frequency mf radar at rothera 68 s 68 w and the superdarn high frequency meteor wind radars at halley 76 s 27 w sanae 72 s 3 w and syowa 69 s 40 e stations we have been able to measure the period wavenumber and propagation direction of the most prominent planetary waves the results show that the planetary wave field before the unusual stratospheric warming in 2002 was dominated by a very long period 43 days westward and upward propagating zonal planetary wavenumber 1 however after the stratospheric warming events began in late winter the character of the wave field changed and a shorter period 14 days westward zonal wavenumber 1 became established it would appear that the previously reported oscillations of the mesospheric hydroxyl airglow temperatures at rothera and halley which were strongly anti correlated to the meridional wind were the result of these planetary waves

across strike geometry of the grand pabos fault zone evidence for devonian dextral transpression in the quebec appalachians the principal faults of southeastern gaspe peninsula in quebec consist of a central high strain zone that is characterized by mainly ductile deformation structures and bordered by low strain zones each dominated by brittle deformation structures the overall geometry of shear fractures within the low strain zones is quite similar to the expected geometry of riedel shear fractures the brittle structures overprint the dominant c s type fabric of the high strain zone which implies that brittle deformation outlasted ductile deformation the asymmetry of local micro to meso scale deformation features along the fault zones reflects the non coaxiality of the shear other features described within the fault zone stylolitic cleavage shear bands and reverse faults are evidence for a component of shortening perpendicular or oblique to the fault zone the geometry of the grand pabos fault zone gpfz a major fault of southern gaspe indicates that deeper seated fault rocks high strain zone have been brought

large scale rossby normal modes during some recent northern hemisphere winters abstractlarge scale rossby normal modes are studied for the northern hemisphere winters of 2005 2006 2008 and 2009 using global observational meteorological analyses spanning the 0 92 km altitude range spectral analysis of geopotential height fields shows pronounced peaks at westward propagating zonal wavenumber 1 near the theoretical locations of the free rossby waves at 25 16 10 and 5 days that in some cases have amplitudes significantly larger than the estimated background spectrum evidence is also found for a wavenumber 2 free mode near 4 days a coherence analysis is used to extract the amplitude and phase of the waves and to isolate those regions of the latitude altitude plane where the signals are statistically significant although the spectral location temporal evolution and vertical structure of several of these waves are suggestive of the presence of rossby normal modes this study shows that in the real atmosphere the waves only occasionally have the global properties of classical

paleomagnetic constraints on siluro devonian laurentian margin tectonics from northern appalachian volcanics abstract paleomagnetic analyses of silurian mafic volcanics from the overstep sequence of sedimentary and volcanic rocks deposited over the central mobile belt of the northern appalachians provide insight into the mid paleozoic tectonic history of the laurentian margin stepwise thermal demagnetization of the subaerial mafic volcanics of the ludlovian fivemile brook formation of northwestern maine reveals two ancient high temperature dual polarity remanences a tilt corrected mean direction yields an inclination of 41 i 3 9 n 4 sites and the magnetization is interpreted as a near primary magnetization acquired well before the end of early devonian deformation an in situ mean direction d 165 i 35 95 6 k 65 n 10 entries from 8 sites is interpreted as a secondary overprint with a pole 22 s 306 e near the early carboniferous segment of the north american apparent polar wander path apwp conglomerate and fold tests of the high temperature characteristic remanence preserved in wenlockian subaerial mafic volcanics of the bryant point formation and a red bed of the south charlo formation both of the chaleur group of northeastern new brunswick constrain paleolatitude and deformational age the inclination only fold test peaks at 50 unfolding with a mean inclination of 35 i 8 5 n 148 synfolding acquisition of magnetization is wenlockian based on a negative conglomerate test at the base of the section and a positive conglomerate test at the top of the section clockwise streaking of site mean directions away from a predominantly northerly declination is consistent with post middle wenlockian dextral shear in the chaleur bay region comparison of a locus of paleomagnetic pole positions with the north american apwp supports a silurian age of the magnetization of the chaleur group the age and synfolding nature of this remanence furthermore requires that deformation associated with the acadian orogeny in new brunswick began by mid silurian times moreover inclinations from these units indicate that within paleomagnetic resolution there has been no significant latitudinal displacement with respect to stable north america since the silurian

receiver function study of the cascadia megathrust evidence for localized serpentinization 1 we characterize the crustal and upper mantle structure of the cascadian fore arc using receiver function analysis of data from long running observatories located along the north american margin in oregon and washington we identify coherent sv polarized phases consistent with p s conversion from the top of the subducting juan de fuca plate throughout the area west of the volcanic arc in many instances we also find evidence for deeper features likely associated with the subducted oceanic crust at many locations sh polarized energy in receiver functions is associated with the surface of the subducting plate these sh polarized phases display significant directional variation and show clear polarity reversals consistent with the presence of seismic anisotropy previously a layer of serpentinized material within the megathrust has been proposed to explain an anisotropic low velocity high poisson s ratio layer identified by receiver function analysis at corvallis oregon global seismic network station cor our new results suggest that this feature is widespread in cascadia but the specific receiver function signature varies this anisotropic supraslab layer is supported by receiver function estimates beneath seismic stations which similar to cor are 100 km from the coast and 40 km above the slab surface however the orientation of rock fabric implied by the anisotropy varies greatly from station to station modeling with synthetic seismograms supports the existence of serpentinite beneath station gnw green mountain washington closer to the coast where the slab is shallower an anisotropic layer is likely beneath some stations but the evidence is less conclusive we propose that the anisotropic signature beneath the inland stations is related to serpentinization of the mantle wedge at greater depths best explained by the presence of the polymorph antigorite hypothetically suctioned upward by slab rollback a deformed sliver of serpentinite rich rock above the slab interface would likely display the observed large spatial variation in anisotropic symmetry axis within the layer consistent with our observations

relationship between anisotropy of p and s wave velocities and anisotropy of attenuation in serpentinite and amphibolite velocities and q values of p and s waves as functions of pressure and temperature at 100 and 600 mpa are presented for a serpentinite and an amphibolite both rocks exhibit a strong lattice preferred orientation lpo of the major mineral phases antigorite and hornblende respectively velocities and q values increase with pressure the rate of increase is different in the three orthogonal directions normal and parallel to foliation and lineation and closely related to progressive closure of microcracks increasing temperature decreases velocities and q values only slightly as long as thermal cracking is prevented by the applied confining pressure substantial anisotropy of velocities and q in p and s waves is observed in both rocks but is found to be different in origin anisotropy of p and s wave velocities is highest at low pressure and basically caused by constructive interference of effects related to oriented microcracks and to the lpo of major minerals increasing confining pressure decreases velocity anisotropy at a smaller and smaller rate the residual anisotropy of p and s wave velocities shear wave splitting at high confining pressure is mainly a result of preferred mineral orientation by contrast anisotropy of q is very low at low confining pressure and markedly enhanced as pressure is increased at high confining pressure substantial anisotropy of q in p waves is apparent but reversed from that of p wave velocities qp is highest in the direction normal to the foliation plane whereas vp and vs is lowest in this direction the generation of a pronounced anisotropy of qp by increasing pressure is due to a directionally dependent increase of contact areas on the oriented grain boundaries of the platy minerals defining the foliation the increase of q with pressure in the direction normal to foliation is mainly caused by the decrease of energy loss due to compressive strain relative to shear strain the reverse is true for the x and y directions serpentinite and x direction amphibolite parallel to the foliation plane

trench parallel anisotropy produced by serpentine deformation in the hydrated mantle wedge although seismic anisotropy in the upper mantle is generally attributed to the crystal preferred orientation of olivine the strong trench parallel anisotropy observed in several subduction systems is difficult to explain in terms of olivine anisotropy even if the entire mantle wedge were to act as an anisotropic source using high pressure deformation experiments ikuo katayama and colleagues show that the crystal preferred orientation of serpentine the main hydrous mineral in the upper mantle can produce the strong trench parallel seismic anisotropy observed in such subduction systems although seismic anisotropy in the upper mantle is generally attributed to the crystal preferred orientation of olivine the strong trench parallel anisotropy observed in several subduction systems is difficult to explain in terms of olivine anisotropy using high pressure deformation experiments it is now shown that the crystal preferred orientation of serpentine the main hydrous mineral in the upper mantle can produce the strong trench parallel seismic anisotropy observed in such subduction systems seismic anisotropy is a powerful tool for detecting the geometry and style of deformation in the earth s interior as it primarily reflects the deformation induced preferred orientation of anisotropic crystals1 2 although seismic anisotropy in the upper mantle is generally attributed to the crystal preferred orientation of olivine3 the strong trench parallel anisotropy delay time of one to two seconds observed in several subduction systems4 5 is difficult to explain in terms of olivine anisotropy even if the entire mantle wedge were to act as an anisotropic source here we show that the crystal preferred orientation of serpentine the main hydrous mineral in the upper mantle can produce the strong trench parallel seismic anisotropy observed in subduction systems high pressure deformation experiments reveal that the serpentine c axis tends to rotate to an orientation normal to the shear plane during deformation consequently seismic velocity propagating normal to the shear plane plate interface is much slower than that in other directions the seismic anisotropy estimated for deformed serpentine aggregates is an order of magnitude greater than that for olivine6 and therefore the alignment of serpentine in the hydrated mantle wedge results in a strong trench parallel seismic anisotropy in the case of a steeply subducting slab this hypothesis is also consistent with the presence of a hydrous phase in the mantle wedge as inferred from anomalously low seismic wave velocities7

global structure and seasonal and interannual variability of the migrating diurnal tide seen in the saber timed temperatures between 20 and 120 km 1 the present paper is focused on the global spatial altitude and latitude structure and seasonal and interannual variability of the migrating diurnal tide derived from the sounding of the atmosphere using broadband emission radiometry thermosphere ionosphere mesosphere energetics and dynamics saber timed temperature measurements for 6 full years january 2002 to december 2007 the tidal results are obtained by a new analysis method where the tides migrating and nonmigrating and the planetary waves zonally traveling and stationary are simultaneously extracted from the satellite data it has been found that above 70 km height the saber migrating diurnal tide reflects mainly the distinctive features of the first symmetric propagating 1 1 mode while below this height it reflects the features of the first symmetric trapped 1 2 mode the trapped component amplifies near 50 km and its phase is close to 1600 lt the seasonal behavior of the diurnal tide over the equator is dominated by semiannual variation with a primary maximum in february march 18 k average amplitude for 6 years and a secondary maximum in august september 15 k the tidal amplitude grows rapidly in the mesosphere lower thermosphere however it undergoes some decay near 90 km defining ubiquitous double peaked vertical structure a very rapid reduction in amplitude is detected at heights near 115 km however above this level the diurnal tide amplifies again the vertical wavelength of the propagating diurnal tide is 20 km over the equator at middle latitudes it is not very different from that over the equator but its magnitude depends on the season in the winter it is longer than that in summer the interannual variability of the diurnal tide indicates a clear correlation with the stratospheric quasi biennial oscillation

an inverted continental moho and serpentinization of the forearc mantle volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back arc region but the forearc mantle in the corner of the wedge is thought to be significantly cooler here we explore the structure of the mantle wedge in the southern cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers we find very low shear wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an inverted continental moho which reverts to normal polarity seaward of the cascade arc this observation provides compelling evidence for a highly hydrated and serpentinized forearc region consistent with thermal and petrological models of the forearc mantle wedge this serpentinized material is thought to have low strength and may therefore control the down dip rupture limit of great thrust earthquakes as well as the nature of large scale flow in the mantle wedge

nonmigrating diurnal tides in the thermosphere 1 horizontal wind measurements from the hrdi and windii instruments on the upper atmosphere research satellite are analyzed to reveal the most prominent nonmigrating diurnal tidal components at 95 km the eastward propagating diurnal tide with zonal wave number s 3 de3 the standing s 0 diurnal oscillation d0 and the westward propagating diurnal tide with s 2 dw2 the strongest de3 occurs primarily during northern hemisphere summer fall with maximum eastward winds near the equator of order 15 ms 1 and is a vertical extension of the s 3 kelvin wave the first antisymmetric mode of de3 dominates during october april with maximum meridional winds near the equator of order 8 ms 1 d0 exists during nearly all months and is nonsymmetric about the equator with maximum northward wind amplitudes in the southern hemisphere of order 7 10 ms 1 dw2 closely resembles the first symmetric propagating mode from classical tidal theory with maximum northward wind amplitudes of order 10 12 ms 1 during september through february the combination of de3 d0 and dw2 with dw1 gives rise to significant longitude variations in the diurnal tide between 40 latitude forcing in the global scale wave model gswm is calibrated according to the above observations thus enabling global estimates of nonmigrating tidal temperatures and other fields for instance it is estimated that the temperature and eastward wind perturbations associated with de3 may be as large as 20k and 35 ms 1 at 145 km and 115 km respectively over the equatorial region during july

taconian and acadian transpression between the internal humber zone and the gaspe belt in the gaspe peninsula tectonic history of the shickshock sud fault zone the shickshock sud fault has a history of ordovician taconian silurian salinic and devonian acadian movements taconian deformation involving ductile dextral oblique slip faulting is recorded in cambrian rocks in the footwall of the shickshock sud fault metabasalt and metaarkose at amphibolite grade are converted into phyllonite and mylonitic schist shear bands asymmetric garnet porphyroclasts c s fabrics and mica fish textures indicate dextral shearing the regional sense of shear is top to west and southwest on generally southeast dipping shear zones hornblende of metabasalt yielded an 40ar 39ar age of 455 9 2 ma and muscovite from the mylonitic schist yielded an 40ar 39ar age of 454 3 0 9 ma which indicate metamorphism and deformation during the taconian orogeny evidence for silurian activity is indicated by the salinic unconformity to the south related to normal block faulting deformation features in the ordovician and silurian devonian rocks in the hanging wall were predominantl

along strike acadian structural variations in the quebec appalachians consequence of a collision along an irregular margin the quebec appalachians have been shaped by two major orogenies the middle to late ordovician taconian and the middle devonian acadian thrust faults and nappe structures characterized the taconian deformation throughout the quebec appalachians whereas structural styles pertaining to the acadian orogeny differ from southern quebec to the gaspe peninsula structural analysis of late ordovician to middle devonian supracrustal rocks shows two different acadian deformational regimes strike slip tectonics in the gaspe peninsula and thrust or dip slip tectonics in southern quebec in southern quebec acadian regional deformation produced folds which vary from upright to overturned and tight to isoclinal from the nw to the se major faults e g la guadeloupe are northwestward directed thrust faults marked by highly ductile shear zones outlined by mylonite in the gaspe peninsula structural trend is ne and major e w dextral strike slip faults transect this trend folds are open and upright inclined and tighter near the major faults where they have a clockwise rotation like the regional cleavage major faults e g grand pabos follow corridors delimiting high strain zones where the fabrics developed are indicative of a ductilebrittle regime of deformation in the temiscouata region major structural features of both southern quebec and the gaspe peninsula are recognized structures of this region consist of ene trending dextral strike slip faults and high angle wnw verging reverse faults parallel to major nne folds these structures reflect the transition from purely horizontal movement along major strike slip faults of the gaspe peninsula to vertical movement along thrust faults in southern quebec acadian structural variations within the quebec appalachians are interpreted in terms of a continental collision of gondwana along the irregular margin of laurentian and its taconian accreted terranes

trench parallel anisotropy and large delay times elasticity and anisotropy of antigorite at high pressures 1 using theoretical methods we calculate the full elastic constant tensor and equation of state of antigorite up to 10 gpa a pressure range that encompasses its experimentally observed stability field at ambient conditions the elastic constant tensor reveals significantly large acoustic anisotropy 38 in vp 35 in vs compared to the dominant mantle phase olivine the shear anisotropy is enhanced upon compression upon compression the full elastic constant tensor reveals anomaly at 2 69 gm cm 3 at 2 69 gm cm 3 we find that the pressure volume results for antigorite are well represented by a third order birch murnaghan formulation with k0 52 gpa k0 8 5 and v0 3037 a3 0 2 48 gm cm 3 our results on elasticity and anisotropy at conditions relevant to the mantle wedge indicates that a 10 20 km layer of antigorite might account for the observed shear polarization anisotropy with fast polarization parallel to the trench and associated large delay times of 1 2 sec observed in some subduction zone settings