the q structure of the upper mantle constraints from rayleigh wave amplitudes 1 the three dimensional shear attenuation or q structure of the upper mantle is still poorly understood despite the increasing accuracy and sophistication of velocity models of the same part of the earth here we present a set of three dimensional q models of the upper mantle based on amplitude measurement of minor and major arc rayleigh waves in the period range 70 170 s the models show that areas of low attenuation underlie continents to a depth of around 300 km and areas of high attenuation are associated with oceans and plate boundaries particularly in the top 200 km below 350 km the sensitivity of the data to attenuation structure decreases rapidly it is well known that the amplitudes of surface waves can be strongly influenced by factors other than attenuation in particular focusing due to elastic structure and errors in source mechanisms we consider the effects of focusing by discussing the implications of the results of selby and woodhouse 2000 comparisons with focusing predictions using phase velocity maps allow us to identify features due to focusing in maps of attenuation distribution the influence of the source on the observed attenuation distribution is investigated by including a source term in the model inversion we find that successfully combining the data at each frequency into one three dimensional model requires that this source term must vary with frequency suggesting that a simple correction to the scalar moment of each event cannot explain the observations although the effects of focusing and the source can be significant we find that the observed attenuation pattern is robust up to degree 8 however shorter wavelength structure can be strongly influenced by other controls finally we use one of the models to predict the degree 2 attenuation pattern for 250 s rayleigh waves the observed pattern suggests that existing normal mode observations may be explainable in terms of structure above 350 km depth

anisotropic shear wave velocity structure of the earth s mantle a global model 1 we combine a new large data set of surface wave phase anomalies long period waveforms and body wave travel times to construct a three dimensional model of the anisotropic shear wave velocity in the earth s mantle our modeling approach is improved and more comprehensive compared to our earlier studies and involves the development and implementation of a new spherically symmetric reference model simultaneous inversion for velocity and anisotropy as well as discontinuity topographies and implementation of nonlinear crustal corrections for waveforms a comparison of our new three dimensional model s362ani with two other models derived from comparable data sets but using different techniques reveals persistent features 1 strong 200 km thick high velocity anomalies beneath cratons likely representing the continental lithosphere underlain by weaker fast anomalies extending below 250 km which may represent continental roots 2 weak velocity heterogeneity between 250 and 400 km depths 3 fast anomalies extending horizontally up to 2000 3000 km in the mantle transition zone beneath subduction zones 4 lack of strong long wavelength heterogeneity below 650 km suggesting inhibiting character of the upper mantle lower mantle boundary and 5 slow velocity superplumes beneath the pacific and africa the shear wave radial anisotropy is strongest at 120 km depth in particular beneath the central pacific lateral anisotropic variations appreciably improve the fit to data that are predominantly sensitive to the uppermost and lowermost mantle but not to the waveforms that control the transition zone and midmantle depths tradeoffs between lateral variations in velocity and anisotropy are negligible in the uppermost mantle but noticeable at the bottom of the mantle

global models of surface wave attenuation 1 a large data set of fundamental mode rayleigh wave amplitudes is analyzed to derive global models of surface wave attenuation 1 q the data set consists of measurements of rayleigh wave amplitude anomalies in the period range 50 250 s for 347 earthquakes observed at 179 seismic stations the amplitude anomalies are considered to depend on four factors intrinsic attenuation along the ray path elastic focusing effects along the ray path a source factor accounting for uncertainties in the strength of excitation and a receiver factor accounting for uncertainties in the response at the station the amplitude data are inverted simultaneously for global maps of attenuation expanded in spherical harmonics up to degree 12 global maps of phase velocity expanded to degree 20 and source and receiver correction factors all four variable types are shown to be important in explaining the amplitude anomalies a data set of phase delay measurements provides additional constraints on velocity structure the maps of attenuation obtained by simultaneous inversion for elastic and anelastic models contain important features that are not robustly imaged when the effect of focusing on wave amplitude is ignored these include high attenuation along western north america and along the east pacific rise and other ridge systems and low attenuation associated with stable continental interiors the global attenuation maps exhibit a strong correlation with phase velocity maps corrected for the effect of the crust particularly for periods 200 s the correlation suggests that the variability in both q and velocity in the shallow upper mantle is primarily thermal in origin

formation timescales of large martian valley networks abstract assessing timescales for formation of the ancient martian valley networks is key to interpreting the early climate on mars we determined the likely formation times for seven of the largest ancient valley networks on mars using the darcy weisbach equation for average flow velocity three different sediment transport models and a range of input parameters to encompass possible formation conditions with runoff rates similar to intense storms in arid regions on earth the minimum formation timescales of these martian valley networks range from 10 5 to 10 7 yr depending on the specific valley network shorter formation timescales require hurricane scale flows that if minimized with assumptions of continuous formation unlike even terrestrial rates could complete large valley network formation in as little as 200 to 5000 yr though this is not the preferred interpretation while these results do not support impact induced climate change as the sole mechanism for creating precipitation sufficient to incise the large valley networks neither do they extend the amount of time required to form the networks beyond their range in age consistent with hypotheses that valley incision was constrained to a relatively short period of martian history near the noachian hesperian boundary approximately 3 6 to 3 8 ga

rayleigh wave phase velocities small scale convection and azimuthal anisotropy beneath southern california 1 we use rayleigh waves to invert for shear velocities in the upper mantle beneath southern california a one dimensional shear velocity model reveals a pronounced low velocity zone lvz from 90 to 210 km the pattern of velocity anomalies indicates that there is active small scale convection in the asthenosphere and that the dominant form of convection is three dimensional 3 d lithospheric drips and asthenospheric upwellings rather than 2 d sheets or slabs several of the features that we observe have been previously detected by body wave tomography these anomalies have been interpreted as delaminated lithosphere and consequent upwelling of the asthenosphere beneath the eastern edge of the southern sierra nevada and walker lane region sinking lithosphere beneath the southern central valley upwelling beneath the salton trough and downwelling beneath the transverse ranges our new observations provide better constraints on the lateral and vertical extent of these anomalies in addition we detect two previously undetected features a high velocity anomaly beneath the northern peninsular range and a low velocity anomaly beneath the northeastern mojave block we also estimate the azimuthal anisotropy from rayleigh wave data the strength is 1 7 at periods shorter than 100 s and decreases to below 1 at longer periods the fast direction is nearly e w the anisotropic layer is more than 300 km thick the e w fast directions in the lithosphere and sublithosphere mantle may be caused by distinct deformation mechanisms pure shear in the lithosphere due to n s tectonic shortening and simple shear in sublithosphere mantle due to mantle flow

early mars volcanic sulfur storage in the upper cryosphere and formation of transient so2 rich atmospheres during the hesperian in a previous paper chassefiere et al 2013 we have shown that most volcanic sulfur released to the early mars atmosphere could have been trapped in the upper cryosphere under the form of co2 so2 clathrates huge amounts of sulfur up to the equivalent of an 1 bar atmosphere of so2 would have been stored in the noachian upper cryosphere then massively released to the atmosphere during the hesperian due to rapidly decreasing co2 pressure it could have resulted in the formation of the large sulfate deposits observed mainly in hesperian terrains whereas no or little sulfates are found at the noachian in the present paper we first clarify some aspects of our previous work we discuss the possibility of a smaller cooling effect of sulfur particles or even of a net warming effect we point out the fact that co2 so2 clathrates formed through a progressive enrichment of a pre existing reservoir of co2 clathrates and discuss processes potentially involved in the slow formation of a so2 rich upper cryosphere we show that episodes of sudden destabilization at the hesperian may generate 1000 ppmv of so2 in the atmosphere and contribute to maintaining the surface temperature above the water freezing point

early mars serpentinization derived ch4 reservoirs h2 induced warming and paleopressure evolution ch4 has been observed on mars both by remote sensing and in situ during the past 15 yr it could have been produced by early mars serpentinization processes that could also explain the observed martian remanent magnetic field assuming a cold early mars a cryosphere could trap such ch4 as clathrates in stable form at depth the maximum storage capacity of such a clathrate cryosphere has been recently estimated to be 2 x 10 19 to 2 x 10 20 moles of methane we estimate how large amounts of serpentinization derived ch4 stored in the cryosphere have been released into the atmosphere during the noachian and the early hesperian due to rapid clathrate dissociation and photochemical conversion of ch4 to h 2 these episodes of massive ch4 release may have resulted in transient h 2 rich atmospheres at typical levels of 10 20 in a background 1 2 bar co2 atmosphere the collision induced heating effect of h 2 present in such an atmosphere has been shown to raise the surface temperature above the water freezing point we show how local and rapid destabilization of the cryosphere can be induced by large events such as the hellas basin or tharsis bulge formation and lead to such releases our results show that the early mars cryosphere had a sufficient ch4 storage capacity to have maintained h 2 rich transient atmospheres during a total time period up to several million years or tens of million years having potentially contributed to the formation of valley networks during the noachian early hesperian

the zh ratio method for long period seismic data sensitivity kernels and observational techniques summary amplitude ratio between vertical and horizontal components of rayleigh waves is controlled by structure beneath a seismic station this ratio measured as a function of frequency has been extensively analysed for shallow crustal structure study in earthquake engineering and applied seismology this quantity termed the zh ratio in this paper may be useful for deep earth structure study and its feasibility for the frequency range between 0 004 and 0 05 hz period 20 250 s is explored in this paper for depth sensitivity kernels we demonstrate that a numerical approach is practical and provides sufficient accuracy for structural inversion depth extent of sensitivity kernels are about half of depth extent in phase velocity kernels indicating that the zh ratio is useful for studying the lithospheric structure two observational approaches for measurement of the zh ratio are presented the first approach uses simple envelope amplitude ratio and the second approach uses waveform correlation technique between vertical and horizontal components the zh ratio data alone only constrains structure beneath seismic stations but recent densification of seismic networks may make it possible to extend the analysis to regional scale structure a greater opportunity may exist in combination of the zh ratio method and the phase and group velocity measurements

a shear displacement criterion for soil infilled rock discontinuities an infilled rock joint is likely to be the weakest plane in a rock mass the most pronounced effect of the presence of infill material is the reduction in friction of the discontinuity boundaries i e rock to rock contact of the joint walls the thicker the infill the smaller the shear strength of the rock joint once the infill reaches a critical thickness the joint walls rock play no significant role in the overall shear strength several models have been proposed to predict the peak shear strength of infilled joints under both constant normal load and constant normal stiffness boundary conditions taking into account the ratio of infill thickness t to the height of the joint wall asperity a that is the t a ratio models based on the constant normal stiffness condition provide a much more accurate representation of the infilled joint behaviour in the field but only a limited number of studies have focused on the more realistic constant normal stiffness stress strain behaviour this paper pre

dynamic response of a rock fracture filled with viscoelastic materials rock fractures filled with viscoelastic materials such as sand usually contribute to rock mass instability under the influence of seismic waves and dynamic loads the purpose of this study is to verify that the specific fracture stiffness and the specific initial mass of the filling sand are two key fracture parameters in interrelating the physical mechanical and seismic properties of a rock fracture filled with dry sand a series of dynamic tests using a split hopkinson rock bar was conducted on a simulated sand filled fracture the experimental results show that stress wave attenuation across the filled fracture is strongly affected by wave reflection and transmission at the fracture interfaces and the dynamic compaction of the filling sand with the comparison between the analytical predictions by the displacement discontinuity model and the displacement and stress discontinuity model and the experimental results from the laboratory tests it is found that both models can predict a filled fracture with a smaller thickness i e less than 10 mm the displacement and stress discontinuity model may be used to predict a fracture with a larger thickness by considering the specific initial mass of filling materials the wave transmission coefficient for a filled fracture generally increases with increasing specific fracture stiffness

experimental study of stress wave propagation across a filled rock joint abstract dynamic properties of rock joints are of great interest to mining engineers seismologists and geoscientists in characterizing the dynamic mechanical behavior of discontinuous rock mass an experimental study of stress wave propagation across filled rock joints has been carried out using a modified split hopkinson pressure bar shpb apparatus two granitic bars cored from a rock site were used as the incident and transmitter pressure bars in the shpb tests while a sand layer of different widths and water contents sandwiched between the two bars was adopted to simulate the filled joint each pressure bar was mounted with two strain gauges with a specific spacing a wave separation method was used to process the test data the dynamic stress strain relation of the filled rock joints was derived from the separated strain waves finally the dynamic stress strain relations from the tests were curve fitted by using the least square regression method and compared with a traditional joint model it was found that the wave separation method is very effective for the shpb tests using short granitic pressure bars it was also concluded that the joint width and water content had significant effects on the dynamic stress strain relation of the filled rock joints existing joint models were not able to sufficiently describe such dynamic properties of the filled rock joints

new bulk sulfur measurements of martian meteorites and modeling the fate of sulfur during melting and crystallization implications for sulfur transfer from martian mantle to crust atmosphere system abstract sulfur storage and transport between different reservoirs such as core mantle crust and atmosphere of mars are tied to igneous processes martian meteorites carry a record of mantle melting and subsequent differentiation history of martian magmas investigation of s geochemistry of martian meteorites can thus provide an understanding of how s is transferred from the martian interior to the exosphere in this study we measured bulk s concentration of 7 martian meteorites and modeled the behavior of s during both isobaric crystallization of primary martian magmas and isentropic partial melting of martian mantle comparisons between measured data and modeled results suggest that 1 sulfides may become exhausted at the source during decompression melting of the mantle and mantle derived basalts may only become sulfide saturated after cooling and crystallization at shallow depths and 2 in addition to degassing induced s loss mixing between these differentiated sulfide saturated basaltic melts and cumulus minerals with without cumulate sulfides could also be responsible for the bulk sulfur contents in some martian meteorites in this case a significant quantity of s could remain in martian crust as cumulate sulfides or in trapped interstitial liquid varying from 2 to 95 percent by weight our modeling also suggests that generation of sulfide undersaturated parental magmas requires that the mantle source of martian meteorites contain

new images of the earth s upper mantle from measurements of surface wave phase velocity anomalies 1 the sensitivity of a surface wave to the lateral structure of the earth s mantle depends on the local structure and thickness of the crust particularly at short periods the strong lateral heterogeneity of the crust has a significant nonlinear effect on the surface wave sensitivity functions thus far this effect has not been quantified and tomographic studies of the upper mantle based on surface wave observations have not taken it into account on the basis of a jeffreys wentzel kramers brillouin jwkb description of surface wave propagation we find and discuss the lateral variations of the sensitivity of love and rayleigh waves to mantle seismic anomalies associated with a realistic model of the crust mooney et al 1998 we then use the resulting laterally varying sensitivity kernels to determine a new tomographic image of horizontally and vertically polarized shear velocity in the upper mantle from love and rayleigh wave phase velocity measurements periods from 35 to 300 s in terms of large scale patterns of high and low velocity our model is similar to previously published ones confirming among other features the anomalous anisotropy underlying the central pacific ekstrom and dziewonski 1998 we find however that the lateral dependence of the surface wave sensitivity kernels has a significant effect on the absolute amplitude of the anomalies which should not be neglected as we attempt to obtain higher resolution images of the upper mantle

carbon sequestration on mars on earth carbon sequestration in geologic units plays an important role in the carbon cycle scrubbing co 2 from the atmosphere for long term storage while carbonate is identified in low abundances within the dust and soils of mars at 1 wt in select meteorites and in limited outcrops no massive carbonate rock reservoir on mars has been identified to date here we investigate the largest exposed carbonate bearing rock unit the nili fossae plains combining spectral thermophysical and morphological analyses to evaluate the timing and carbon sequestration potential of rocks on mars we find that the olivine enriched 20 25 basalts have been altered by low temperature in situ carbonation processes to at most 20 fe mg carbonate thus limiting carbon sequestration in the nili fossae region to 0 25 12 mbar of co 2 during the late noachian early hesperian before or concurrent with valley network formation while this is large compared to modern day co 2 reservoirs the lack of additional comparably sized post late noachian carbonate bearing deposits on mars indicates ineffective carbon sequestration in rock units over the past 3 7 b y this implies a thin atmosphere 500 mbar during valley network formation extensive post noachian atmospheric loss to space or diffuse deep sequestration by a yet to be understood process in stark contrast to earth s biologically mediated crust atmosphere carbon reservoir ratio of 10 4 10 5 mars ratio is a mere 10 10 3 even if buried pre noachian crust holds multiple bars

local amplification of rayleigh waves in the continental united states observed on the usarray abstract we develop a method based on ratios of amplitudes measured at adjacent stations to determine local amplification of surface waves across an array of seismic stations we isolate the effects of local structure from those of the earthquake and propagation by systematic averaging of ratios corresponding to many sources we apply the method to data recorded on the usarray for the years 2006 2011 and determine amplification factors at each station of the array for rayleigh waves at periods between 35 s and 125 s local amplification factors are spatially coherent and display variations of 10 at a period of 125 s and greater variations at shorter periods maps of local amplification exhibit spatial correlation with topography and geologic structures in the western and central united states at long periods the observed amplification factors correlate well with predictions from a regional crust and mantle model of north america at short periods correlations are weaker suggesting that the local amplification factors can be useful for constraining shallow structure better

experimental studies on the effects of fracture on the p and s wave velocity propagation in sedimentary rock calcarenite del salento abstract experimental studies were carried out in laboratory in order to investigate the effects of fracture on compressional p wave and shear s wave velocity propagation and therefore the relations between seismic properties and rock mass parameters the discontinuity index i d fracture density parameter c linear fracture parameter and the rock quality designation rqd were used to describe the rock mass parameters these parameters are analyzed and then related to the seismic properties four vertical aligned fractures were created on an intact calcarenite block 0 6 m long 0 4 m thick and 0 4 m width by sawing the measures were carried out in four different blocks of cacarenite having the same physical properties and in four different phases in first block the fractures were filled with air in the second block the fractures were filled with terra rossa in third block the fractures were filled with wet terra rossa and in the fourth block the fractures were filled with clay the test results were statistically analysed using the method of least squares regression and polynomial relationships with high correlation coefficient were found between the fractured rock parameters and p wave s wave velocities and v p v s ratio the investigations suggest that the p wave and s wave velocities decrease with increasing the fracture parameters while the v p v s ratio increases with decreasing the fracture parameters furthermore the results of the experimental studies were applied on the seismic refraction tomography data acquired in a great measurements campaign undertaken in the adriatic salentina coast south italy in order to monitor the coastal erosion the geophysical results using the polynomial relationships between the fractured rock parameters and p wave velocity are in good agreement with the geomorphological and geological results

global love wave phase velocity variation and its significance to plate tectonics abstract global love wave phase velocity variation was constructed for periods between 80 and 200 s by using approximately 9000 paths from 971 earthquakes with m 5 5 the data set was from gdsn and geoscope networks between 1980 and 1987 we examined both the spherical harmonic expansion method and the block parameterization method with a simple constant damping parameter approach synthetic tests showed that more accurate results were obtained by the block parameterization method than by the spherical harmonic expansion method we adopted the block inversion method with a nearly equal area block 5 5 near the equator discretization the general pattern of the resulting maps were consistent with previous global and local studies with a discretization of 5 by 5 the maps were detailed enough to test some plate tectonic models for the pacific atlantic and indian oceans surface wave velocities increased smoothly to plate ages older than 100 ma simple forward modeling showed that seismic phase velocity variation with a continuous thickening of lithosphere up to about 150 ma fits the present observation disagreeing with the model deduced from the heat flow and ocean depth data which change variations at about 60 80 ma the seismic phase velocity variations in different oceans showed systematic differences at younger ages and convergence beyond 100 ma the difference at younger ages implies a failure of scaling derived from a simple thermal boundary layer model for oceanic plates age seismic phase velocity relationships on each side of ridges were also examined and asymmetric velocity variations were found which suggests differences in thermal states from one side of the ridge to the other in order to further examine the thermal state of the lithosphere average age phase velocity relations were established for each ocean and subtracted from phase velocity variation maps the results indicated broad low velocity regions in the south pacific super swell region the south and west indian ocean and high velocity regions east of the east pacific rise and in the north to northeast indian ocean the results reflect the asymmetry of phase velocity variation about ridges there is some correlation between hot spot locations and low velocity anomalies but additional large scale thermal anomalies exist under old oceanic plate

photochemical and climate consequences of sulfur outgassing on early mars abstract ancient mars might have been warm and wet compared to today but climate models have trouble reproducing this warmth partly because of the faintness of the young sun and partly because of inherent limitations to co2 h2o greenhouse warming in particular rayleigh scattering of incoming sunlight by a dense co2 rich atmosphere leads to a high planetary albedo thereby reducing the amount of sunlight absorbed by the planet it has been recently suggested that the presence of 1 100 ppmv so2 in mars early atmosphere might have provided enough additional greenhouse warming to maintain a warm wet early mars we show however that this warming should have been more than offset by cooling from sulfate and sulfur aerosols in early martian atmosphere hence the paradox of mars early climate remains unresolved

low palaeopressure of the martian atmosphere estimated from the size distribution of ancient craters the decay of the martian atmosphere which is dominated by carbon dioxide is a component of the long term environmental change on mars from a climate that once allowed rivers to flow to the cold and dry conditions of today the minimum size of craters serves as a proxy for palaeopressure of planetary atmospheres because thinner atmospheres permit smaller objects to reach the surface at high velocities and form craters the aeolis dorsa region near gale crater on mars contains a high density of preserved ancient craters interbedded with river deposits and thus can provide constraints on atmospheric density at the time of fluvial activity here we use high resolution images and digital terrain models from the mars reconnaissance orbiter to identify ancient craters in deposits in aeolis dorsa that date to about 3 6 gyr ago and compare their size distribution with models of atmospheric filtering of impactors we obtain an upper limit of 0 9 0 1 bar for the martian atmospheric palaeopressure rising to 1 9 0 2 bar if rimmed circular mesas interpreted to be erosionally resistant fills or floors of impact craters are excluded we assume target properties appropriate for desert alluvium if sediment had rock mass strength similar to bedrock at the time of impact the paleopressure upper limit increases by a factor of up to two if mars did not have a stable multibar atmosphere at the time that the rivers were flowing as suggested by our results then a warm and wet co 2 h 2o greenhouse is ruled out and long term average temperatures were most likely below freezing

role of filling materials in a p wave interaction with a rock fracture the purpose of this study is to investigate the role of filling materials e g quartz sand and kaolin clay in the interaction between a p wave and a rock fracture the specific fracture stiffness reflects the seismic response of a filled fracture while the wave transmission coefficient describes p wave transmission across the filled fracture a series of experimental tests using a split hopkinson rock bar technique are conducted on artificial rock fractures that are filled with pure quartz sand sand clay mixtures with 30 50 and 70 clay weight fractions and a pure clay matrix the boundary conditions of the filled fracture i e the displacement and stress discontinuities are used in the method of characteristic lines to calculate the wave transmission coefficient in the time domain the analytical results agree well with the experimental results the specific fracture stiffness and the wave transmission coefficient decrease with increasing filling material thickness when the clay matrix completely fills the void space of the quartz sand the filled fracture exhibits the largest specific fracture stiffness and promotes p wave transmission in general the wave transmission coefficient is strongly related to the specific fracture stiffness regardless of the filling material composition or the filling material thickness c 2014 elsevier b v all rights reserved

a further study on seismic response of a set of parallel rock fractures filled with viscoelastic materials the purpose of this study is to further investigate the seismic response of a set of parallel rock fractures filled with viscoelastic materials following the work by zhu et al dry quartz sands are used to represent the viscoelastic materials the split hopkinson rock bar shrb technique is modified to simulate 1 d p wave propagation across the sand filled parallel fractures at first the displacement and stress discontinuity model dsdm describes the seismic response of a sand filled single fracture the modified recursive method mrm then predicts the seismic response of the sand filled parallel fractures the shrb tests verify the theoretical predictions by dsdm for the sand filled single fracture and by mrm for the sand filled parallel fractures the filling sands cause stress discontinuity across the fractures and promote displacement discontinuity the wave transmission coefficient for the sand filled parallel fractures depends on wave superposition between the fractures which is similar to the effect of fracture spacing on the wave transmission coefficient for the non filled parallel fractures