discontinuity structure of the mantle transition zone beneath the north china craton from receiver function migration 1 a better understanding of the significant phanerozoic tectonic reactivation and destruction of the north china craton ncc demands a detailed knowledge of the deep structural features of the region we applied the wave equation based poststack migration technique to a combined receiver function data set from more than 250 broadband seismic stations to construct the structural image of the mantle transition zone beneath the ncc our imaging results reveal a relatively simple and flat 410 km discontinuity but a structurally complicated 660 km discontinuity beneath the region double discontinuities and a 30 km depression of the 660 km discontinuity are observed locally in the southern part of the eastern ncc in contrast to the smoothly varying structure to the north and in the central and western parts of the craton distinctly rapid variations in both the 660 km discontinuity structure and mantle transition zone thickness were found across the northsouth gravity lineament nsgl near the boundary between the eastern and central ncc which probably reflects different thermal and probably chemical properties on the two sides of the nsgl these differences are possibly associated with the pacific slab which is imaged tomographically as a flat lying structure in the mantle transition zone under the region east of the nsgl the structural variation in the deep upper mantle appears to coincide with the sudden changes in surface topography gravity field and crustal and lithospheric structures as well indicating that the two domains may have tectonically deformed differently throughout the whole upper mantle during the phanerozoic cratonic destruction the mantle transition zone on the eastern side of the nsgl is up to 30 40 km thicker than the global average this thickness and the complex structure of the 660 km discontinuity in this region may reflect the strong influence that the deep subduction and stagnancy of the pacific slab and its possible sporadic penetration into the lower mantle have had on mantle dynamics and lithospheric reactivation in the eastern ncc since the mesozoic time on the other hand the less variable structure and normal to thin mantle transition zone imaged beneath the central and western ncc may indicate that the indiaeurasia collision has had a relatively weak effect on the cenozoic tectonics of these regions

accurate tremor locations from coherent s and p waves nonvolcanic tremor is an important component of the slow slip processes which load faults from below but accurately locating tremor has proven difficult because tremor rarely contains clear p or s wave arrivals here we report the observation of coherence in the shear and compressional waves of tremor at widely separated stations which allows us to detect and accurately locate tremor events an event detector using data from two stations sees the onset of tremor activity in the cascadia tremor episodes of february 2003 july 2004 and september 2005 and confirms the previously reported south to north migration of the tremor event detectors using data from three and four stations give sand p arrival times of high accuracy the hypocenters of the tremor events fall at depths of 30 to 40 km and define a narrow plane dipping at a shallow angle to the northeast consistent with the subducting plate interface the s wave polarizations and p wave first motions define a source mechanism in agreement with the northeast convergence seen in geodetic observations of slow slip tens of thousands of locations determined by constraining the events to the plate interface show tremor sources highly clustered in space with a strongly similar pattern of sources in the three episodes examined the deeper sources generate tremor in minor episodes as well the extent to which the narrow bands of tremor sources overlap between the three major episodes suggests relative epicentral location errors as small as 1 2 km

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

high resolution rayleigh wave group velocity tomography in north china from ambient seismic noise abstract this study presents the results of the rayleigh wave group velocity tomography in north china performed using ambient seismic noise observed at 190 broadband and 10 very broadband stations of the north china seismic array all available vertical component time series for the 14 months span between january 2007 and february 2008 are cross correlated to obtain empirical rayleigh wave green functions that are subsequently processed with the multiple filter method to isolate the group velocity dispersion curves of the fundamental mode of rayleigh wave tomographic maps with a grid spacing of 0 25o 0 25o are computed at the periods of 4 5s 12s 20s 28s the maps at short periods reveal an evident lateral heterogeneity in the curst of north china quite well in agreement with known geological and tectonic features the north china basin is imaged as a broad low velocity area while the taihangshan and yanshan uplifts and ordos block are imaged as high velocity zones and the quaternary intermountain basins show up as small low velocity anomalies the group velocity contours at 4 5s 12s and 20s are consistent with the bouguer gravity anomalies measured in the area of the taihangshan fault that cuts through the lower crust at least most of the historical strong earthquakes m 6 0 are located where the tomographic maps show zones with moderate velocity gradient

equatorial anisotropy in the inner part of earth s inner core from autocorrelation of earthquake coda the speed of seismic waves passing through the earth s inner core varies with direction analysis of earthquake seismic data suggests that this directional dependence differs between innermost and outer inner core

imaging the upper mantle transition zone with a generalized radon transform of ss precursors we demonstrate the feasibility of using inverse scattering for high resolution imaging of discontinuities in the upper mantle beneath oceanic regions far from sources and receivers using broadband wavefield observations consisting of ss and its precursors the generalized radon transform grt that we developed for this purpose detects in the broadband data signals due to scattering from elasticity contrasts in earth s mantle synthetic tests with realistic source receiver distributions demonstrate that the grt is able to detect and image deep mantle interfaces even in the presence of noise depth phases ghosts phase conversions and multiples generated by reverberation within the transition zone as a proof of concept we apply the grt to 50 000 broadband seismograms to delineate interfaces in the depth range from 300 to 1000 km beneath the northwest pacific we account for smooth 3d mantle heterogeneity using first order perturbation theory and independently obtained global tomography models the preliminary results reveal laterally continuous but undulating scatter zones near 410 and 660 km depth and a weaker broader and more complex structure near 520 km depth the images also suggest the presence of multiple laterally intermittent interfaces near 350 km and between 800 and 1000 km depth that is above and below the transition zone sensu stricto filtering of the data we consider four pass bands 20 50 s 10 50 s 5 50 s and 2 50 s reveals a prominent frequency dependence of the magnitude width and complexity of the interfaces in particular of the scatter zone near 520 km depth such dependencies may put important constraints on the mineralogy and phase chemistry of the transition zone

complex evolution of transient slip derived from precise tremor locations in western shikoku japan transient slip events which occur more slowly than traditional earthquakes are increasingly being recognized as important components of strain release on faults and may substantially impact the earthquake cycle surface based geodetic instruments provide estimates of the overall slip distribution in larger transients but are unable to capture the detailed evolution of such slip either in time or in space accompanying some of these slip transients is a relatively weak extended duration seismic signal known as nonvolcanic tremor which has recently been shown to be generated by a sequence of shear failures occurring as part of the slip event by precisely locating the tremor we can track some features of slip evolution with unprecedented resolution here we analyze two weeklong episodes of tremor and slow slip in western shikoku japan we find that these slip transients do not evolve in a smooth and steady fashion but contain numerous subevents of smaller size and shorter duration in addition to along strike migration rates of 10 km d observed previously much faster migration also occurs usually in the slab dip direction at rates of 25 150 km h over distances of up to 20 km we observe such migration episodes in both the updip and downdip directions these episodes may be most common on certain portions of the plate boundary that generate strong tremor in intermittent bursts the surrounding regions of the fault may slip more continuously driving these stronger patches to repeated failures tremor activity has a strong tidal periodicity possibly reflecting the modulation of slow slip velocity by tidal stresses

global propagation of body waves revealed by cross correlation analysis of seismic hum 1 seismic interferometry has now been applied to the exploration of the earth s interior at scales ranging from local to global most studies have used surface wave propagation recently some studies have focused on body wave propagation on local and regional scales but not on a global scale in this study we succeed in extracting global body wave propagation of p pp pkp s ss scs p p etc waves using seismic hum with frequency wave number filtering in the range of 5 to 40 mhz although the observed body wave propagation is similar to that of the corresponding components of green s functions there are two differences between them the lack of reflection phases in the observation and the dominance of shear coupled pl waves in the observation these differences originate from the dominance of shear traction sources on the earth s surface which causes the breakdown of equipartition among modes with different radial orders for further studies of body wave exploration by seismic interferometry these differences should be considered

low friction and fault weakening revealed by rising sensitivity of tremor to tidal stress at subduction zones deep parts of the fault can slip slowly generating tremor analysis of tremor in cascadia reveals increasing sensitivity of slip to tidal stresses over several days implying that the fault is weak and weakens as it slips

alteration of nuclear glass in contact with iron and claystone at 90 c under anoxic conditions characterization of the alteration products after two years of interaction abstract the present study investigates the alteration of a fractured glass block in contact with iron and callovo oxfordian claystone at 90 c under anoxic and water saturated conditions the alteration rates and the nature of glass alteration products at the different compact interfaces glass clay glass iron and in cracks were assessed by solution chemistry and microscopic scale techniques scanning electron microscopy coupled with energy dispersive x ray microscopy microraman spectroscopy and x ray absorption fine structure spectroscopy a significant but modest two fold increase in glass alteration in contact with steel was observed leading to an average alteration rate over the experiment of about 0 007 0 014 g m2 d this rate is significantly lower than forward rate r0 in clay equilibrated groundwater 1 7 g m2 d indicating that a decrease of the alteration rate was not hindered by the steel presence the corrosion alteration interface was made up of successive layers of corrosion products in contact with iron a layer of fe silicates and an altered glass layer enriched in fe characterization of the glass block in direct contact with claystone revealed that the thickness of altered glass was much more important than at the glass iron interface the altered glass layer in contact with clay was slightly enriched in fe and mg and depleted in alkali cations altered glass layers in cracks were usually limited to fringes thinner than 2 m with a thickness decreasing from the crack mouth indicating that alteration is controlled by transport in the cracks the fractures were partially filled with calcite and lanthanide hydroxocarbonate precipitates these results contribute to the understanding of nuclear vitrified waste iron corrosion products interactions in a deep geological repository

retrieval of moho reflected shear wave arrivals from ambient seismic noise theoretical studies on ambient seismic noise asn predict that complete green s function between seismic stations can be retrieved from cross correlation however only fundamental mode surface waves emerge in most studies involving real data here we show that moho reflected body wave sms and its multiples can be identified with asn for station pairs near their critical distances in the short period band 1 5 s we also show that an uneven distribution of noise sources such as mining activity and wind topography interaction can cause surface wave precursors which mask weaker body wave phases

destruction of the eastern north china craton in a backarc setting evidence from crustal deformation kinematics abstract the eastern north china craton ncc west of the pacific ocean has a long history of rifting from early cretaceous to the end of paleogene when the craton experienced destruction and significant thinning of the lithosphere the cause and geotectonic environment for this destruction remain controversial we use a set of field observation including basin patterns fault geometry and kinematics fault plane slip data dike distribution and fabric data from metamorphic core complexes to determine the kinematic evolution of the deformation in the eastern ncc during this period we show that the principal extension direction in the eastern ncc evolved from wnw ese in the earliest middle early cretaceous via nw se in the latest early cretaceous to nearly n s in the late cretaceous paleogene the movement history from late mesozoic to early cenozoic of the oceanic plates in the pacific ocean with respect to the eastern ncc is available from previous studies the izanagi plate first subducted nearly orthogonally wnw wards during earliest middle early cretaceous time and then moved obliquely nnw wards in the latest early cretaceous while the relaying pacific plate moved generally northwards from the late cretaceous to paleogene both the movement direction of oceanic plates and the principal extension direction of the continental deformation rotated clockwise we suggest that such a correlation can be explained by the eastern ncc being in a backarc setting in the cretaceous paleogene period the results support the backarc extensional model for the destruction and significant lithospheric thinning of the eastern ncc

rapid continuous streaking of tremor in cascadia nonvolcanic tremor is a recently discovered weak seismic signal associated with slow slip on a fault plane and has potential to answer many questions about how faults move its spatiotemporal distribution however is complex and varies over different time scales and the causal physical mechanisms remain unclear here we use a beam backprojection method to show rapid continuous slip parallel streaking of tremor over time scales of several minutes to an hour during the may 2008 episodic tremor and slip event in the cascadia subduction zone the streaks propagate across distances up to 65 km primarily parallel to the slip direction of the subduction zone both updip and downdip at velocities ranging from 30 to 200 km h we explore mainly two models that may explain such continuous tremor streaking the first involves interaction of slowly migrating creep front with slip parallel linear structures on the fault the second is pressure driven fluid flow through structurally controlled conduits on the fault both can be consistent with the observed propagation velocities and geometries although the second one requires unlikely condition in addition we put this new observation in the context of the overall variability of tremor behavior observed over different time scales

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

complex characteristics of slow slip events in subduction zones reproduced in multi cycle simulations 1 since the discovery of slow slip events along subduction zone interfaces worldwide dense geodetic and seismic networks have illuminated detailed characteristics of these events and associated tremor high resolution observations of tremor where the spatial temporal evolution is presumed to reflect that of the underlying slow slip events show highly complex patterns in which the origins remain poorly understood we present a new computationally efficient modeling technique that reproduces many features of observed slow slip events including slow initiation coalescence of separate events and rapid back propagation of renewed slip over previously slipped regions rapid back propagation speeds are explained as a consequence of rate and state dependent frictional healing consistent with analytical solutions developed in support of the simulations

constraining seismic velocity and density for the mantle transition zone with reflected and transmitted waveforms we examine stacks of several seismic phases having different sensitivities to mantle transition zone structure when analyzed separately underside p and s reflections pdp and sds are suggestive of very different structures despite similar raypaths and data coverage by stacking the radial component of pdp rather than the vertical pdp we show that this difference does not result from interference from other more steeply inclined phases such as pkp and ppdpdiff in general stacks of p to s converted phases pds appear to lack evidence of a 520 km discontinuity when examined without other phases when these phases and stacked topside p reflections ppdp are analyzed jointly using a nonlinear inversion method consistent but nonunique seismological models emerge these models show that a discontinuity at 653 km depth has smaller contrasts in density and velocity than found in most previous studies a sub 660 gradient can account for the majority of this difference a 1 6 0 5 p velocity contrast and a 2 2 0 3 density contrast at 518 km depth without a s velocity contrast can explain the lack of a p520s together with robust pp520p and s520s phases for models parameterized with a finite thickness for each discontinuity the 410 km discontinuity is consistently 3 times thicker than the 660 km discontinuity

global scale analysis of the mantle pds phases a global scale analysis of travel times of the mantle pds phases converted from p to s from the discontinuity at a depth d beneath the receiver is presented most of the data are related to p 410 s and p 660 s recorded by the broadband stations of geoscope incorporated research institutions for seismology iris and other networks in order to provide a good global scale coverage published measurements at 37 stations are complemented by our measurements at 45 stations lateral resolution of our data is many times higher than that of ss and its precursors previously used for similar purposes but we have fewer data in the oceans lateral variations of travel times of the major pds phases are strongly correlated with the lateral p and s velocity variations in the uppermost mantle as revealed by tomographic studies the scaling coefficient between the teleseismic s and p residuals as found from the variations of travel times of the major pds phases is around 3 7 for north america and around 3 3 for the rest of the world almost all the differential travel times t p 660 s t p 410 s are in the range of 1 s relative to the average value of 24 0 s if the lateral variations of the velocities within the mantle transition zone mtz can be neglected the corresponding variations of thickness of the mtz are in the range of 10 km relative to the standard depth of 250 km and do not show significant correlation with either velocities in the upper mantle above the mtz or with the variations of thickness of the mtz as found in some recent studies of precursors to ss there is a weak but marginally significant positive correlation between the variations of thickness of the mtz inferred from our data and the s velocity variations in the mtz as given by su et al 1994 this correlation suggests that both variables contain temperature dependent components lateral variability of the mtz is also manifested by extreme weakness of p 410 s at several locations this may indicate either anomalous topography on 410 km discontinuity or strong broadening of the otherwise sharp discontinuity at some stations there are arrivals that can be interpreted as p 520 s this interpretation implies that the strengh and or sharpness of 520 km discontinuity as well as its depth are laterally variable in a broad range

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

laterally propagating slow slip events in a rate and state friction model with a velocity weakening to velocity strengthening transition we investigate the behavior of simulated slow slip events using a rate and state friction model that is steady state velocity weakening at low slip speeds but velocity strengthening at high slip speeds our simulations are on a one dimensional line fault but we modify the elastic interactions to mimic the elongate geometry frequently observed in slow slip events simulations exhibit a number of small events as well as periodic large events the large events propagate approximately steadily along strike and stress and slip rate decay gradually behind the propagating front their recurrence intervals can be determined by considering what is essentially an energy balance requirement for long distance propagation it is possible to choose the model parameters such that the simulated events have the stress drops slip velocities and propagation rates observed in cascadia

depth variations of 410 km and 660 km discontinuities in eastern north china craton revealed by ambient noise interferometry recent studies have demonstrated that body waves between pairs of stations can be successfully retrieved from ambient noise cross correlation at both regional and global scales although surface waves are the dominant signals however it is still difficult to use these retrieved body wave signals to map lateral depth variations of main structural discontinuities or velocity contrasts because of its low signal to noise ratio snr in this research based on a dense seismic array in eastern north china craton reflected p wave signals from 410 km and 660 km discontinuities can be successfully recovered from ambient noise cross correlation to improve snr the cross correlations are stacked within each bin with the phase weighted stack pws method the retrieved p410p and p660p phases from stacked correlations reveal lateral variations of both depths and sharpness of the 410 km and 660 km discontinuities along two profiles which may be related with hot material upwelling and the effect of stagnant pacific plate in the transition zone beneath north china craton the imaging results are generally consistent with the results from teleseismic receiver functions which demonstrate the possibility of mapping high resolution topography and sharpness of deep internal discontinuities without earthquake station geometric limitations

body wave imaging of earth s mantle discontinuities from ambient seismic noise ambient seismic noise correlations are widely used for high resolution surface wave imaging of earth s lithosphere similar observations of the seismic body waves that propagate through the interior of earth would provide a window into the deep earth we report the observation of the mantle transition zone through noise correlations of p waves as they are reflected by the discontinuities associated with the top 410 kliometers km and the bottom 660 km of this zone our data demonstrate that high resolution mapping of the mantle transition zone is possible without using earthquake sources

imaging slow slip fronts in cascadia with high precision cross station tremor locations 1 we apply a new method to obtain accurate locations of tremor sources beneath southern vancouver island unlike more standard cross time methods which compare waveforms from different time windows at the same station this cross station method compares waveforms from the same time window at widely separated stations it performs well relative to cross time methods when the response to an impulsive tremor source is dominated by the main arrival rather than coda and when multiple colocated sources are active within the time window examined we focus on a region roughly 10 km across that was monitored by the polaris deployment from 2003 to 2006 relative location errors appear to be 1 km allowing us to image in great detail rapid and small scale tremor migrations that arise behind the main slow slip front the secondary fronts tend to a start at or within about 1 km of the main tremor front and propagate back along strike at rates of 10 20 km h b less commonly do the reverse ending at the main front or c propagate up or downdip at or within 1 2 km of the main front estimated stress drops in the secondary events are comparable to that in the main event implying that their 25 50 times greater propagation speed results from a similarly greater slip speed

seismic and geodetic constraints on cascadia slow slip 1 automatically detected and located tremor epicenters from episodic tremor and slip ets episodes in northern cascadia provide a high resolution map of washington s slow slip region thousands of epicenters from the past four ets events from 2004 to 2008 provide detailed map view constraints that correlate with geodetic estimates of the simultaneous slow slip each of these ets events exhibits remarkable similarity in the timing and geographic distribution of tremor density and geodetically inferred slip analysis of the latest 15 month inter ets period also reveals ageodetic tremor activity similar both in duration and extent to ets tremor epicenters from both ets and inter ets tremor are bounded between the 30 and 45 km plate interface depth contours and locate approximately 75 km east of previous estimates of the locked portion of the subducting juan de fuca plate inter ets tremor overlaps but is generally downdip of ets tremor and does not yet correlate with geodetically observed slip but this is likely because the slip is below current gps detection levels based on the tremor and slip correlation and the tremor duration and slip magnitude relationship we suggest that the well resolved sharp updip edge of tremor epicenters reflects a change in plate interface coupling properties the region updip of this boundary may accumulate stress with the potential for coseismic shear failure during a megathrust earthquake alternatively plate convergence in this region could be accommodated by continuous slow slip with no detectable tremor or by slow slip events with sufficiently long recurrence intervals that none have been detected during the past 10 years of gps observations

impact of iron on nuclear glass alteration in geological repository conditions a multiscale approach abstract interactions between nuclear glass and fe were investigated in a clayey environment to better understand the mechanisms and driving forces controlling the long term behavior of high level waste glass in a geological repository an integrated experiment involving a glass iron clay gic stack was run at a laboratory scale in anoxic conditions for 2 years and the interfaces were characterized by a multiscale approach using scanning electron microscopy coupled with energy dispersive spectroscopy transmission electron microscopy raman microspectroscopy and scanning transmission x ray microscopy at the sls synchrotron the characterization of glass alteration patterns on cross sections revealed an increase in glass alteration with the fe content and the proximity between the glass and fe the alteration layers are polyphase and stratified with an inner porous gel layer incorporating fe and an outer layer composed of nanocrystalline fe silicates several mechanisms which could affect the glass alteration kinetics and the transport properties of the alteration layer are proposed to explain this pattern i consumption of hydrolyzed silica by precipitation of fe silicates ii penetration of fe within the gel porosity probably as precipitates such as fe oxyhydroxide or fe silicates these new data may imply some consequences when considering the long term behavior of glass in geological disposal conditions

dolomite effect on borosilicate glass alteration dolomite camg co3 2 is one of the common rock forming minerals in many geological media in particular in clayey layers that are currently considered as potential host formations for a deep radioactive waste disposal facility magnesium in solution is one of the elements known to potentially enhance the alteration of nuclear glasses the alteration of borosilicate glasses with dolomite as a mg bearing mineral source was investigated for 8 months in batch tests at 90 c glass composition effects were investigated through two compositions sibnaalcazro and sibnaalzro differing in their ca content the ca rich glass alteration is slightly enhanced in the presence of dolomite compared to the alteration observed in pure water this greater alteration is explained by the precipitation of mg silicate phases on the dolomite and glass surfaces in contrast the ca free glass alteration decreases in the presence of dolomite compared to the alteration observed in pure water this behavior is explained by ca incorporation in the amorphous layer formed during glass alteration coming from dolomite dissolution calcium acts as a layer reorganizer and limits glass alteration by reducing the diffusion of reactive species through the altered layer modeling was performed using the graal model implemented within the chess hytec geochemical code to discriminate and interpret the mechanisms involved in glass dolomite interactions magnesium released by dolomite dissolution reacts with silica provided by glass alteration to form mg silicates this reaction leads to a ph decrease the main mechanism controlling glass alteration is the ability of dolomite to dissolve during the experiment the quantities of secondary phases formed were very small but for longer time scales this mechanism could supply sufficient mg in solution to form large amounts of mg silicates and sustain glass alteration the ability of the graal model to reproduce the concentrations of elements in solution and solid phases regardless of the amount of dolomite and the glass composition strongly supports the basic modeling hypothesis

imaging the d reflector with noise correlations the lowermost mantle of the earth is characterized by seismic structures that range from a few tens to thousands of kilometers at present it is difficult to test hypotheses put forward to explain seismic observations due to poor seismic coverage as particular earthquake station geometries are needed we demonstrate here that seismic noise correlations can be used to robustly image deep mantle reflections with larger stacked amplitudes of reflected waves compared with earthquake data in a comparison between noise and earthquake data we find that the arrival times and the slowness of reflected waves both sampling a region beneath siberia agree with those for a reflector at 2530 km depth and the small amplitude reflections are sufficiently clear in the noise correlations to compare them reliably with synthetic data our data open exciting prospects for illuminating new target zones in the deep mantle to further constrain the dynamics and mineralogy of the deep earth

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

high resolution imaging of rapid tremor migrations beneath southern vancouver island using cross station cross correlations we develop a cross station method to detect and locate tremor and low frequency earthquakes lfes based on the original work of armbruster et al 2014 that compares waveforms from the same time window at stations separated by roughly 10 km to improve the signal to noise ratio we first rotate the horizontal components into the empirical shear wave particle motion direction the large scale rapid tremor reversals beneath southern vancouver island are best recorded by stations that exhibit pronounced shear wave splitting which obscures this optimal direction we correct for splitting using the stacked templates of 11 low frequency earthquake families obtained in this region by bostock et al 2012 we find that the style of rapid tremor migrations rtms evolves as the main front passes over a region very close to the main front numerous small scale migrations occur with recurrence intervals far shorter than tidal periods these usually propagate along the main front even when that is not parallel to dip several larger rtms propagating along the main front have prominent elongation orthogonal to the propagation direction inconsistent with the interpretation that their large propagation speed is an apparent velocity caused by the slow main front intersecting a preexisting linear structure on the plate interface farther behind the main front rtms gradually progress to being tidally modulated and have generally slower propagation speeds many reversal like rtms are observed some of which evolve from fronts initially propagating along the main front these reversals are sometimes coherent across regions of low tremor density

a fractured roman glass block altered for 1800 years in seawater analogy with nuclear waste glass in a deep geological repository fractured archaeological glass blocks altered 1800 years in seawater are investigated because of their morphological analogy with vitrified nuclear waste they provide an opportunity for understanding glass alteration in variable confined media cracks by studying an actual ancient system in a known stable natural environment characterization of the crack network from two dimensional trace maps length alteration thickness orientation allows us to determine the three dimensional geometric parameters crack density fracture ratio and the percentage of alteration using stereological relations this methodology could be applied to nuclear glass from a representative archaeological glass block we showed that the surface developed by the cracks is 86 27 times greater than the geometric surface but the volumetric alteration is 12 2 4 1 which is only 12 times greater than the volumetric alteration of the block periphery about 1 vol this unexpected low value is explained by the large variation of the alteration thicknesses in the different types of cracks in relation with their location in the block the alteration thickness is usually smaller in the internal zone than in the border zone the alteration layers resulted from three main mechanisms interdiffusion glass dissolution and secondary phase precipitation leading to two different alteration products a sodium depleted layer and mainly a mg smectite geometric parameters such as the glass surface area solution volume ratio and transport parameters renewal of the alteration solution strongly affected the glass dissolution kinetics the confined conditions and the diffusive transport of reactive species favor low alteration kinetics the precipitation of secondary phases also results in sealing of the cracks consequently although it is not known if subcritical crack growth occurred internal cracks account for only a minor contribution to the overall alteration these results improve our understanding of alteration in cracks for assessing the predominant physical and chemical parameters that must be considered in long term nuclear glass modeling

iron clay interactions detailed study of the mineralogical transformation of claystone with emphasis on the formation of iron rich t o phyllosilicates in a step by step cooling experiment from 90 c to 40 c abstract iron minerals water interactions are of primary importance in the contexts of underground structure engineering e g reactive barriers or deep geological storage and for the understanding of secondary alteration processes in primitive meteorites to improve our understanding of these systems we determine the mineralogical transformations induced by the association of iron and silicates during a cooling through an experimental simulation of iron clay interactions with a step by step procedure in the range of 90 c to 40 c the run products and solutions are well characterised by means of different techniques x ray diffraction scanning and transmission electron microscopy manocalcimetry inductively coupled plasma optical emission spectrometry and ion chromatography and the thermodynamic data concerning fe bearing phyllosilicates are well tested comparing the modelling and experimental results therefore the main mineralogical modifications observed include the remarkable formation of cronstedtite and greenalite as well as the formation of magnetite at all temperatures along with a significant dissolution of quartz mixed layer illite smectite clays illite affecting more than 70 of each mineralogical phase and a partial alteration of chlorite kaolinite and dolomite the experimental results confirm the reaction path predicted by thermodynamic modelling i e the formation of iron rich t o phyllosilicates cronstedtite and greenalite and magnetite at the expense of metal iron and silicates both the experimental and thermodynamic results presented in this study provide important constraints to well predict the impact of nuclear waste canister corrosion in a claystone media and to better understand secondary alteration processes which could also affect the mineralogical and chemical composition of primitive meteorites

evidence for tidal triggering of high amplitude rapid tremor reversals and tremor streaks in northern cascadia 1 we provide a new link between tectonic tremor propagation tremor amplitude and tidal stresses by analyzing high resolution tremor locations and amplitudes determined by multibeam backprojection of data from an array of subarrays for two cascadia episodic tremor and slip events we observe repeating high amplitude rapid tremor reversals rtrs and tremor streaks they tend to occur when tremor amplitudes are highest and occur almost exclusively during periods of thrust encouraging tidally induced shear stress on the fault we speculate that thrust encouraging shear stress from tidal loading forces trigger rtrs and streaks that energetically rerupture the weakened fault behind the slow slip front the high rate and amplitude of tremor during rtrs and streaks stands in contrast to the hypothesis that activity at the leading edge of the slow slip zone is the most energetic and loudest this implies that the spatiotemportal pattern of slow earthquake slip migration is even more intricate than previously reported

using systematically characterized low frequency earthquakes as a fault probe in guerrero mexico studies of low frequency earthquakes lfes have focused on detecting events within previously identified tectonic tremor however the principal lfe detection tools of matched filter searches are intrinsically incapable of detecting events that have not already been characterized previously as a template event in this study we therefore focus on generating the largest number possible of lfe templates by uniformly applying a recently developed lfe template detection method to a 2 5 yearlong data set in guerrero mexico using each of the detected templates in a matched filter search we then form event families that each represents a single source we finally develop simple empirical statistics to select the event families that represent lfes our resulting catalog contains 1120 unique lfe sources and a total of 1 849 486 detected lfes over the 2 5 yearlong data set the locations of the lfe sources are then divided into subcatalogs based on their distance from the subduction trench considering each lfe as a small unit of slip along the subduction interface we observe discrete episodes of lfe activity in the region associated with large slow slip events this is in direct contrast to the near continuous activity observed 35 km farther downdip within the previously identified lfe tremor sweet spot

space time correlation of slip and tremor during the 2009 cascadia slow slip event 1 episodic tremor and slip ets involving transient deformations accompanied by emergent low frequency tremor occurs in subduction zones around the world ets events increase the shear stress on locked megathrusts and may potentially trigger damaging earthquakes despite the clear association of tremor and slip the physical relationship between them is unresolved tremor appears to result from slip on small asperities on the plate interface due to either creep on the surrounding fault or stress increases ahead of the propagating slow slip front previous studies of migrating slow slip events have not had sufficient spatial and temporal resolution to differentiate between these two models to address this we invert gps data from the august 2009 ets event in central cascadia for the space time evolution of fault slip rate we find a correlation in both space and time between tremor epicenters and the independently determined position of high fault slip rate this supports the first hypothesis that tremor asperities are loaded directly by slow slip rather than by stress increases ahead of the slip front and provides new insights into the mechanics of ets

distinct lateral variation of lithospheric thickness in the northeastern north china craton abstract a detailed knowledge of the thickness of the lithosphere in the northeastern north china craton ncc is important for understanding the significant tectonic reactivation of the craton in the mesozoic and cenozoic time we achieve this goal by applying the newly proposed wave equation based migration technique to the s receiver functions recently collected in the region distinct negative signals are identified below the moho in all the s receiver function migrated images and stacks which we interpret as representing the s to p conversions from the lithosphere asthenosphere boundary lab the imaged lab is as shallow as 60 70 km in the southeast basin and coastal areas and deepens to no more than 140 km in the northwest mountain ranges and continental interior these observations indicate widespread lithospheric thinning in the study region in comparison with the 180 km lithospheric thicknesses typical of most cratonic regions the revealed topography of the lab generally agrees with the lateral variation in upper mantle seismic anisotropy previously measured through sks splitting analysis in particular a sharp lab step of 40 km is detected at the triple junction of the basin and mountains at almost the same place where an abrupt change from nw se to ne sw in fast polarization direction of shear waves was found these findings suggest a close correlation between the seismic anisotropy and hence deformation of the upper mantle the lithospheric thickness and the surface tectonics of the northeastern ncc while the thinned lithosphere and the nw se fast shear wave polarizations in the east areas probably are related to the dominant nw se tectonic extension in the late mesozoic cenozoic time the thicker lithosphere and the ne sw fast polarization direction in the west mountain ranges may reflect earlier contractional deformations of the region synthetic tests indicate that the lab beneath the northeastern ncc is a well defined zone 10 20 km thick combined with seismic tomography results and geochemical and petrological data this suggests that complex modification of the lithosphere probably accompanied significant lithospheric thinning during the tectonic reactivation of the old craton

global variability of transition zone thickness 1 we analyze recordings from more than 3000 shallow earthquakes and measure s410s s660s differential travel times on a global scale these differential times are obtained using a novel cross correlation technique that eliminates effects associated with a priori assumptions of crustal thickness and velocity variations above the upper mantle transition zone our measurements show absolute perturbations up to 8 s from the global average 242 km which imply transition zone thickness variations of 20 km on a length scale of 2000 km the transition zone under major subduction zones e g the western pacific and south america is significantly thicker than the global average this could be associated with large scale depressions of the 660 km discontinuity due to the accumulation of cold oceanic lithosphere at the base of the upper mantle a narrow transition zone is observed under the central pacific and northern atlantic oceans we also observe a modest anticorrelation between s410s s660s times and the delay times of shear waves predicted using s12 wm13 su et al 1994 in the transition zone which suggests considerable thermal influence on the large scale topography of the 410 and 660 km discontinuities the lack of a stronger anticorrelation suggests that 1 compositional heterogeneities may be present and 2 a significant fraction of thermal anomalies near the transition zone do not extend through the transition zone and influence both the 410 and the 660 km discontinuities a regional analysis shows that the transition zone is on average 6 8 km thicker under continents than under oceans this implies a temperature difference of 50 70 c however we do not observe a clear correlation between thickness and the age of the crust

a detailed receiver function image of the sedimentary structure in the bohai bay basin abstract if the site at which receiver functions are constructed is filled by sediments then the waveforms from these receiver functions are dominantly controlled by the sedimentary structures within the first few seconds after the direct p arrival based on this observation waveform data collected at 44 temporary seismic stations have been used to image the sedimentary structure of the bohai bay basin a major continental petroliferous basin in eastern china an adapted hybrid global waveform inversion method was applied to the receiver functions to extract structural information beneath each of the stations the derived s velocity structure provides for the first time a basin scale seismic image of detailed sedimentary stratification the sedimentary cover of the basin is about 2 12 km thick consisting of cenozoic mesozoic and paleozoic strata from top to bottom the structural features presented in the s velocity image coincide quite well with the depression uplift type of tectonic system in the bohai bay basin the reconstructed morphology of the sedimentary layers provides seismological evidence for the two stage evolution of the intracontinental basin that were caused by an intensive tectonic regime transition in late mesozoic immediately following the lithospheric reforming of the eastern china continent

seismic interferometry of teleseicmic s wave coda for retrieval of body waves an application to the philippine sea slab underneath the japanese islands summary the reconstruction of surface waves from the cross correlation of random wavefields has recently been extensively inspected by theoretical and experimental approaches however the reconstruction of body waves has not been extensively studied in this study we present a method for extracting body waves that is direct p and s waves and reflected waves from the philippine sea slab we use the cross correlation of the wavefield generated by the teleseismic s waves observed by hi net tiltmeters with a passband of 0 07 0 5 hz to enhance the contribution of the s coda we reduced the source time function and the deterministic phases ss scs and ss and the surface wave in s coda the records of the processed s coda observed at every station pair are cross correlated for each teleseismic event the cross correlation functions ccfs of different earthquakes are stacked to retrieve wavefields propagating between the station pairs as a result direct p s and the reflected waves could be extracted when the stacked ccfs are aligned as a function of distance of separation between two stations the gradients of the traveltime curves for the direct p and s waves are approximately 5 7 and 3k m s 1 respectively these velocities correspond to the seismic velocities of the crust or the p wave velocity of the uppermost mantle in order to enhance the reflected waves we searched for the reflection points by assuming that the later phases in the ccfs are ss reflections and map the amplitudes onto the depth sections as a result the negative phases dipping to the north can be traced right below the region of hypocentre distribution these negative phases probably correspond to the oceanic moho within the philippine sea slab we also show that the oceanic moho can also be traced by assuming pp reflections these results indicate that the ccfs plausibly contain information regarding both p and s waves propagating between the two receivers and are capable of detecting reflected phases in addition to the direct waves

interactions and triggering in a 3 d rate and state asperity model we present a 3 d continuous quasi dynamic rate and state model of multiple seismic asperities forced by surrounding aseismic creep and motivated by observations of coplanar multiplets our model allows to study the physics of interactions among a set of asperities first we show that the amount of interactions and clustering characterized by the omori law and interevent time distribution depends on how far the system is from a critical density of asperities which is related to the friction properties of the barriers separating the sources this threshold controls the ability of a population of asperities to destabilize the creeping barriers between them and therefore determines whether dynamic sequences including several asperities in the same event might occur in agreement with what is expected from observed magnitude frequency distributions therefore the concept of critical density of asperity provides a mechanical interpretation of statistical properties of seismicity as an illustration we used our numerical results in the specific case of parkfield in the period preceding the mw 6 2004 earthquake in order to infer the steady state friction parameter a b characterizing the creep of this part of the san andreas fault we estimate a value of a b that locally exceeds 0 001 which is in the upper range of what has already been proposed for the postseimic period of the mw 6 2004 parkfield earthquake

upwelling mantle plume and lithospheric delamination beneath the north china craton abstract various models have been proposed for the destruction of the eastern north china craton ncc however it is still a highly controversial scientific issue in this study abundant teleseismic data recorded by permanent and temporary stations in the ncc were collected and p wave tomography and common conversion point ccp stacking of receiver functions were performed the results from this study reveal an upwelling mantle plume and a shallow lehmann discontinuity or the lower boundary of a low velocity zone beneath the eastern ncc additionally a large scale plate like high velocity anomaly is defined under the eastern ncc that might be related to the delamination of a lithospheric keel based on the above results and assessment ncc destruction might include two causes lithospheric keel removal or delamination and mantle plume upwelling