rayleigh wave tomography at coronation field canada the topography effect within reflection seismology surface waves or ground roll are often considered a form of unwanted source generated noise unlike body waves surface waves propagate exclusively in the lateral direction and are virtually insensitive to structure deeper than one wavelength for a nominal frequency of 5 hz and phase velocity of 500 m s this means that a surface wave of the rayleigh or love type only feels the upper 100 m of the subsurface as a result surface waves cannot be used for imaging deep reflectors however they can be used to estimate near surface properties xia et al 1999 ross et al 2008 in particular the shear wave velocity knowledge of near surface velocity structure in turn can be used to estimate shear wave statics in reflection seismology estimating statics in the presence of laterally varying structure i e obtaining the long wavelength static component can be challenging

numerical models on the influence of partial melt on elastic anelastic and electrical properties of rocks part ii electrical conductivity abstract partial melting influences both the elastic and electrical properties of mantle rocks significantly but in a different manner a set of theoretical models of the electrical conductivity of partially molten rocks is developed for different geometries of the melt distribution the models correspond to a similar set on elasticity and anelasticity presented in a preceding paper part i both model sets allow combined interpretations of seismic and geoelectric observations from anomalous hot mantle regions by a systematic variation of the melt geometry the following melt geometries are assumed in the conductivity models melt films tubes isolated ellipsoidal inclusions films and ellipsoidal inclusions with a variable degree of interconnection distributed geometries and superpositions of spheres with films and with tubes unexplored conduction mechanisms near the melting temperature film thicknesses of molecular sizes or effects of volatiles are not considered resistor network theory is utilized to account for a variable degree of interconnection and distributed geometries thereby a new possible interpretation of archie s law is found in terms of varying interconnection furthermore it is found that a reduced degree of interconnection may have an important influence on the conductivity at melt fractions characteristic for a weak to moderate decrease in seismic velocity the model results are compiled together with the elastic models of part i in a set of diagrams which may be applied systematically to observed electrical and seismic data to find constraints on the state of melting

electrical conductivity of fluid bearing quartzite under lower crustal conditions abstract the electrical conductivity of fluid bearing quartzite was determined as function of temperature and fluid fraction at 1 gpa in order to assess the origin of the high conductivity anomalies observed in the middle to lower crustal levels dihedral angles of quartz fluid quartz determined from recovered samples were below 60 suggesting that fluid forms an interconnected network through the quartz aggregate the electrical conductivity of quartzite increases with increasing temperature which can be approximately expressed by arrhenius equation the apparent activation enthalpy decreases from 0 70 to 0 25 ev with increasing fluid fraction in volume from 0 00043 to 0 32 the electrical conductivity of the fluid bearing quartzite increased with fluid fraction proportionally to a power law 0 56 0 71 within the temperature range of 900 1000 k the electrical conductivity of the aqueous fluid bearing quartzite with the maximum fluid fraction 0 32 was found to be about three orders of magnitude higher than that of dry quartzite at 1000 k however its electrical conductivity was definitely lower than the geophysically observed values of high conductivity anomalies even if the quartzite contained large fluid fractions 0 32 the present results suggest that fluid bearing quartzite is unable to account for the high conductivity anomalies in terms of fluid fraction a significant amount of other ionic species such as na cl and al in aqueous fluid in addition to silica phases dissolved in fluid is required to increase conductivity

premelting polymerization of crustal and mantle fluids as indicated by the solubility of albite paragonite quartz in h2o at 1 gpa and 350 620 c abstract the composition and structure of dissolved silicates in model crustal and upper mantle fluids was assessed by measuring the solubility of the assemblage albite paragonite quartz in h 2 o from 350 to 620 c at 1 gpa natural low albite and quartz were equilibrated with h 2 o paragonite grew in all experiments due to incongruent dissolution of albite quartz melting occurred at 635 5 c solute concentrations at subsolidus conditions were determined by analysis of quenched fluids or mineral weight loss and mass balance bulk solubility of the mineral assemblage increased from 1 to 8 oxide wt with rising temperature si al and na all increase in concert the solutions were slightly peralkaline and possess si na al 1 5 molar at all conditions studied extrapolated thermodynamic data were used to predict solubility at the conditions investigated experimentally calculated solubility agreed with that measured from 350 to 500 c however above 500 c the calculations underpredict solubility to an increasing degree as the hydrothermal melting point is approached the excess measured solubility points to increasing abundance of aqueous si al si and na al si polymers polymerized solutes predominate in all near solidus solutions rising to 80 of total dissolved solids at the melting point the observations support a conceptual model in which as the temperature of the system rises isobarically at 1 gpa the silicate components dissolved in the aqueous phase begin to polymerize significantly within 100 c of the melting point the polymerized solutes may facilitate condensation of more polymerized hydrous silicate liquid at the hydrothermal melting point from the perspective of isobaric cooling the fluid crossing the solidus retains na al si o clusters or fragments that are less polymerized than those which comprised the melt but more polymerized than has previously been inferred for the aqueous phase the high concentrations of na al and si in the form of polymeric clusters will yield substantial mass transfer by near solidus metamorphic and magmatic fluids in the crust and mantle and likely promote dissolution transport and precipitation of nominally insoluble refractory rock components

electrical conductivity anisotropy of deformed talc rocks and serpentinites at 3 gpa abstract the electrical conductivity anisotropy of deformed natural talc rocks and serpentinites was investigated using a kawai type multi anvil press in the temperature range of 500 1000 k at 3 gpa the electrical conductivities of the samples were measured by an impedance analyzer with a frequency range of 10 3 10 6 hz along three sample directions the direction parallel to the lineation of oriented minerals x direction the direction perpendicular to the lineation on the foliation plane y direction and the direction perpendicular to the foliation z direction for both rock types electrical conductivities parallel to the x and the z directions were the highest and the lowest respectively electrical conductivities of talc rocks and serpentinites were at least two orders of magnitude lower than previous reports electrical conductivities of the serpentinites were higher than those of the talc rocks electrical conductivity anisotropy for the talc rocks was stronger than that for the serpentinites at the same oxygen buffer condition electrical conductivity and its anisotropy of the serpentinites become higher with higher oxygen fugacity the activation enthalpy of talc rocks was the lowest 0 59 ev in the x direction and highest 0 68 ev in the z direction the activation enthalpies of the serpentinites in different directions show similar values about 0 74 ev and 0 68 ev for the experiments using mo and ni electrodes respectively impedance spectra for both rock types show the presence of two conduction paths grain interior and grain boundary conductions the total electrical conductivities were reduced by grain boundary conduction electrical conductivities of hydrous minerals show strong dependence on hydrogen concentration and hydrogen mobility the conduction mechanism probably was proton migration through extrinsic vacancies derived from a presence of ferric iron perpendicular to the c axis of the crystals and through interstitial mechanisms parallel to the c axis in both warm and cold subduction zones high electrical conductors 10 1 5 s m cannot be explained by the presence of talc or serpentinites the electrical conductivity anisotropy in a subduction zone would be inconspicuously small within one order unless we consider other well aligned high conductive phases

electrical properties of granite with implications for the lower crust the electrical properties of granite appear to be dominantly controlled by the amount of free water in the granite and by temperature minor contributions to the electrical properties are provided by hydrostatic and lithostatic pressure structurally bound water oxygen fugacity and other parameters the effect of sulfur fugacity may be important but is experimentally unconfirmed in addition to changing the magnitude of electrical properties the amount and chemistry of water in granite significantly changes the temperature dependence of the electrical properties with increasing temperature changes in water content retain large but lessened effects on electrical properties near room temperature a monolayer of water will decrease the electrical resistivity by an order of magnitude several weight percent water may decrease the electrical resistivity by as much as 9 orders of magnitude and decrease the thermal activation energy by a factor of 5 at elevated temperatures just below granitic melting a few weight percent water may still decrease the resistivity by as much as 3 orders of magnitude and the activation energy by a factor of 2 above the melting temperature 650 to 1100 c depending upon water pressure a few weight percent water will decrease the resistivity by less than an order of magnitude and will barely change the activation energy remarkably the few weight percent water must be present as free water experiments with hydrated hornblende schist with structural water indicate an electrical resistivity very similar to that for dry granite the implications of these results together with the findings of deep magnetic sounding and magnetotelluric surveys suggest much more free water than is commonly associated with the lower crust and possibly into the upper mantle

electrical conductivity and temperature in the canadian cordilleran crust abstract high electrical conductivity and high heat flow coexist in much of the canadian cordillera a region of recent accretion of crustal terranes to north america the relationship between temperature and electrical conductivity in the crust is investigated by means of results from 251 heat flow determinations and 301 magnetotelluric mt soundings we first compared maps of mt phase at period 10 s and of heat flow larger phases correlate with higher heat flows in some areas but the relationship is complicated by other causes of variation in these two parameters to give a more focussed comparison we map the depth d 450 to the 450 c isotherm for two assumed distributions of reduced heat flow and the depth d c to the top of the lower crustal conductor at mt sites away from major fracture zones the map of d c visually resembles both of the maps of d 450 and readings at 76 points of a grid give correlation coefficient 0 80 this supports a relationship between high conductivity in the crust and temperatures above 450 c both the lower crustal conductor and the 450 c isotherm occur at depths near 30 km above the subducting oceanic plate under vancouver island at 15 20 km in the intermontane belt and of 10 15 km in the omineca belt if there is an upcurrent in the mantle beneath the continent behind the subduction as proposed elsewhere its axis may now be under the omineca belt this location is in harmony with evidence of recent extension and uplift there

detection of widespread fluids in the tibetan crust by magnetotelluric studies magnetotelluric exploration has shown that the middle and lower crust is anomalously conductive across most of the north to south width of the tibetan plateau the integrated conductivity conductance of the tibetan crust ranges from 3000 to greater than 20 000 siemens in contrast stable continental regions typically exhibit conductances from 20 to 1000 siemens averaging 100 siemens such pervasively high conductance suggests that partial melt and or aqueous fluids are widespread within the tibetan crust in southern tibet the high conductivity layer is at a depth of 15 to 20 kilometers and is probably due to partial melt and aqueous fluids in the crust in northern tibet the conductive layer is at 30 to 40 kilometers and is due to partial melting zones of fluid may represent weaker areas that could accommodate deformation and lower crustal flow

characteristics of the horizontal component of rayleigh waves in multimode analysis of surface waves in surface wave analysis s wave velocity estimations can be improved by the use of higher modes of the surface waves the vertical component of p sv waves is commonly used to estimate multimode rayleigh waves although rayleigh waves are also included in horizontal components of p sv waves to demonstrate the advantages of using the horizontal components of multimode rayleigh waves we investigated the characteristics of the horizontal and vertical components of rayleigh waves we conducted numerical modeling and field data analyses rather than a theoretical study for both components of rayleigh waves as a result of a simulation study we found that the estimated higher modes have larger relative amplitudes in the vertical and horizontal components as the source depth increases in particular higher order modes were observed in the horizontal component data for an explosive source located at a greater depth similar phenomena were observed in the field data acquired by using a dynamite source at 15 m depth sensitivity analyses of dispersion curves to s wave velocity changes revealed that dispersion curves additionally estimated from the horizontal components can potentially improve s wave velocity estimations these results revealed that when the explosive source was buried at a greater depth the horizontal components can complement rayleigh waves estimated from the vertical components therefore the combined use of the horizontal component data with the vertical component data would contribute to improving s wave velocity estimations especially in the case of buried explosive source signal

geochemical constraints on the origin and migration of palaeofluids at the northern margin of the variscan foreland southern belgium three major fracture types in the dinantian of the namur syncline at the northern margin of the variscan foreland in southern belgium have been investigated by fluid inclusion and stable isotope analysis the oldest and volumetrically most important fracture type is characterized by conjugated and sigmoidal en echelon calcite veins which formed during the variscan folding these veins and the surrounding limestones have both a similar dull brown orange luminescence and stable isotopic composition 18o 11 to 8 pdb and 13c 0 to 3 pdb this indicates precipitation of the calcite cement from a fluid buffered by the rock in the area studied only a limited amount of fluids was expelled through the dinantian during the main phase of variscan compressional tectonism fractures filled with ferroan calcites cross cut the variscan folds fluid inclusion and stable isotopic evidence indicates that the calcites precipitated at 40 60 c from a saline fluid 9 2 to 23 2 eq wt nacl with an estimated 18o composition between 2 0 and 0 6 smow the most likely origin of these high salinity fluids with a relatively low oxygen isotopic composition is a gravity driven meteoric water which underwent an intense water rock interaction the topographic relief created by the variscan tectonism could have allowed groundwater to penetrate into the deeper subsurface and to migrate towards the margin of the foreland basin non ferroan fracture filling calcites formed later during the mesozoic or tertiary low salinity meteoric waters and high salinity cacl2 nacl brines with a temperature around 50 c migrated through this fracture system along these fractures meteoric water migrated down into the subsurface and the brines could have flowed upward from the basement

peculiarities of surface wave propagation across central eurasia abstract the recent installation of six broadband digital iris ida seismic stations in the ussr has provided new opportunities for studying surface wave propagation across eurasia group velocities of fundamental rayleigh and love modes between epicenters and these stations were determined for 35 events that occurred since april 1989 to the middle of july 1990 near eurasia differential phase velocities were found for the same arrivals along paths between several pairs of stations group and phase velocities were obtained in the period range from 15 to 300 sec frequency time polarization analysis was used for studying polarization properties of surface waves in some cases significant anomalies in the particle motion for periods up to 100 sec were observed they are attributed to surface wave refraction and scattering due to lateral inhomogeneities at the boundaries and inside the eurasia continent

comments on the paper by preat et al 1983 caractere epigenetique etranger des gites filoniens pb zn ba f du bord sud du synclinorium de dinant belgique

deep electrical structure of the northern cascadia british columbia canada subduction zone implications for the distribution of fluids long period magnetotelluric data have been used to image the deep electrical structure of the cascadia subduction zone in british columbia canada zones of elevated electrical conductivity were found in both the forearc and backarc regions and are interpreted as a consequence of the fluid release from subducting slab a shallow zone of high conductivity beneath vancouver island is likely due to fluids that are trapped above the subducting plate east of this structure is a conductive 0 03 s m forearc mantle wedge that also exhibits low seismic velocities and may be serpentinized a free fluid phase is required to account for this enhanced conductivity elevated conductivities are observed in the upper mantle throughout the backarc 0 01 s m and strongly support the hypothesis of a shallow convecting asthenosphere this enhanced upper mantle conductivity can be explained by either hydrogen ion diffusion in olivine minerals or by a few percent partial melting 4

electrical conductivity of albite quartz water and albite water nacl systems and its implication to the high conductivity anomalies in the continental crust abstract the electrical conductivities of albite water albite quartz water and albite water nacl systems have been measured in terms of impedance spectroscopy at 1 gpa and 400 1000 k the relationship between electrical conductivity and temperature in the albite quartz water system cannot be expressed by the arrhenian formula whereas that in the brine bearing system follow the arrhenian law showing small temperature dependence the electrical conductivity of the albite quartz water samples decreased with decreasing temperature from 1000 to 800 k then increased rapidly upon further cooling from 800 to around 550 k the bulk conductivities of the albite quartz water system are consistent with variation of the total concentration of the dissolved electric charge carriers of h oh na alo 2 and hsio 3 in aqueous fluid with temperature based on the thermal dynamic calibration there is a small negative dependence of bulk conductivity on aqueous fluid fraction electrical conductivity of the albite water nacl samples is higher than that of the albite quartz water samples which shows the following features 1 small dependence of conductivity on the temperature 2 increase of electrical conductivity with the fluid fraction and the salinity our results suggest that the high conductivity anomalies of 10 1 s m typically observed in the continental crust can be explained by the presence of albite and quartz with fluid fraction as low as 0 014 at temperatures lower than 650 k in the case that the geotherm is higher than 650 k the observed value of 10 1 s m can be explained by the brine bearing albite with a fluid fraction of 1 vol if the salinity is similar to the seawater

melting of albite and dehydration of brucite in h 2 o nacl fluids to 9 kbars and 700 900 c implications for partial melting and water activities during high pressure metamorphism the melting reaction albite solid h2o fluid albite h2o melt has been determined in the presence of h2o nacl fluids at 5 and 9 2 kbar and results compared with those obtained in presence of h2o co2 fluids to a good approximation albite melts congruently at 9 kbar indicating that the melting temperature at constant pressure is principally determined by water activity at 5 kbar the temperature t mole fraction x h2o melting relations in the two systems are almost coincident by contrast h2o nacl mixing at 9 kbar is quite non ideal albite melts 70 c higher in h2o nacl brines than in h2o co2 fluids for x h2o 0 8 and 100 c higher for x h2o 0 5 the melting temperature of albite in h2o nacl fluids of x h2o 0 8 is 100 c higher than in pure water the p t curves for albite melting at constant h2o nacl show a temperature minimum at about 5 kbar water activities in h2o nacl fluids calculated from these results from new experimental data on the dehydration of brucite in presence of h2o nacl fluid at 9 kbar and from previously published experimental data indicate a large decrease with increasing fluid pressure at pressures up to 10 kbar aqueous brines with dissolved chloride salt contents comparable to those of real crustal fluids provide a mechanism for reducing water activities buffering and limiting crustal melting and generating anhydrous mineral assemblages during deep crustal metamorphism in the granulite facies and in subduction related metamorphism low water activity in high pressure temperature metamorphic mineral assemblages is not necessarily a criterion of fluid absence or melting but may be due to the presence of low a h2o brines

peloids in stratabound zn pb deposits and their genetic importance peloids from sediment hosted zn pb deposits in belgium ireland and poland are composed of zn calcite siderite smithsonite silica pyrite melnikovite sphalerite galena thiosulphates and zn as bearing limonite the size of peloids is between 7 and 60 m the core and the shell of peloids are composed of different minerals and the shell is usually coarsely crystalline peloids are present in collapse breccias of karst cavities stromatactis cavities debris flow breccias and fractures cross cutting carbonates hosting the mineralization in places peloids form a major microtexture of the sulfide mineralization peloids are cemented and replaced by sulfides organic acids extracted from sulfide peloids are composed of amido acids considered to be characteristic of bacterial origin the size and specific texture of peloids are independent of mineralogy location and age of the mineralization therefore the peloids disussed are considered as forms induced by bacterial activity rather than forms precipitated inorganically

the effect of feldspar on quartz h 2 o co 2 dihedral angles at 4 kbar with consequences for the behaviour of aqueous fluids in migmatites an investigation was made of the effect of trace amounts of feldspar na and or k on dihedral angles in the quartz h2o co2 system at 4 kbar and 450 1050 c quartz quartz h2o dihedral angles in feldspar bearing quartz aggregates are observed to be the same as those in pure quartz aggregates at temperatures below 500 c above this temperature they decrease with increasing temperature until the solidus the final angle at the inception of melting is about 65 for microcline quartz h2o and microcline albite quartz h2o and much less than 60 the critical value for formation of grain edge fluid channels in an isotropic system for the albite quartz h2o system co2 was observed to produce a constant quartz quartz fluid dihedral angle of 97 in feldspar bearing quartz aggregates at all temperatures studied also examined were the dihedral angles for the two co existing supersolidus fluids in quartz aggregates in all systems the quartz volatile fluid angle is greater than 60 whereas the quartz melt angle is lower than 60 both supersolidus angles decrease with increasing temperature the transition from nonconnected to connected porosity with increasing temperature observed in the quartz albite h2o system some tens of degrees below the solidus termed a permeability transition if a common feature of rocks near their melting points will play an important role in controlling the permeability of high grade rocks to aqueous fluids

fluid and deformation regime of an advancing subduction system at marlborough new zealand newly forming subduction zones on earth can provide insights into the evolution of major fault zone geometries from shallow levels to deep in the lithosphere and into the role of fluids in element transport and in promoting rock failure by several modes the transpressional subduction regime of new zealand which is advancing laterally to the southwest below the marlborough strike slip fault system of the northern south island is an ideal setting in which to investigate these processes here we acquired a dense high quality transect of magnetotelluric soundings across the system yielding an electrical resistivity cross section to depths beyond 100 km our data imply three distinct processes connecting fluid generation along the upper mantle plate interface to rock deformation in the crust as the subduction zone develops massive fluid release just inland of the trench induces fault fracture meshes through the crust above that undoubtedly weaken it as regional shear initiates narrow strike slip faults in the shallow brittle regime of interior marlborough diffuse in width upon entering the deeper ductile domain aided by fluids and do not project as narrow deformation zones deep subduction generated fluids rise from 100 km or more and invade upper crustal seismogenic zones that have exhibited historic great earthquakes on high angle thrusts that are poorly oriented for failure under dry conditions the fluid deformation connections described in our work emphasize the need to include metamorphic and fluid transport processes in geodynamic models

salinity of oceanic hydrothermal fluids a fluid inclusion study abstract an extensive microthermometric study of quartz epidote plagioclase anhydrite and sphalerite hosted fluid inclusions from ophiolitic semail oman and trinity california ophiolites and oceanic east pacific rise hydrothermal vents gorringe bank odp leg 111 hole 504b crust has been carried out in order to constrain a model accounting for wide salinity variations measured in the oceanic hydrothermal fluids recorded salinities in fluid inclusions vary between 0 3 and 52 wt nacl eq however more than 60 of the mean standard deviation salinities of the samples are within the range 3 2 0 3wt nacl eq microthermometric error and the mean salinity of all fluid inclusions without the brines is 4 0 wt nacl eq with a standard deviation of 1 6 wt nacl eq whereas most samples display slightly higher salinities than seawater several samples exhibit very high salinities more than two times that of seawater these high salinities are restricted to the plagiogranites semail and trinity ophiolites which mark the top of the fossil magma chamber in the transition zone between the plutonic sequence and the sheeted dyke complex the fluid inclusion population studied in the plagiogranites is characterized by the occurrence of four major fluid inclusion families 1 low to medium salinity liquid vapor fluid inclusions which homogenize into the liquid phase 2 low salinity liquid vapor fluid inclusions with pseudocritical homogenization 3 low to medium salinity liquid vapor fluid inclusions which homogenize into the vapor phase and 4 high salinity liquid vapor halite fluid inclusions which homogenize into the liquid phase by halite dissolution and exhibit salinities as high as 52 wt nacl eq these fluid inclusion families are interpreted as resulting from phase separation occurring in hydrothermal or magmatic fluids within the transition zone between the hydrothermal system and the magma chamber at temperatures higher than 500 c very low salinities less than half that of seawater have been found only in one dioritic sample from the gorringe bank mineralogical and petrological data from the semail ophiolite shows the absence of cl rich minerals furthermore hydration of the crust although very important cannot account for the large salinity variations thus the large salinity variations measured are interpreted as resulting from phase separation and generation of brine rich fluids at the top of the magma chamber this phase separation and subsequent phase segregation and brine accumulation may result in a double diffusive convection of the fluids in the hydrothermal system

improving surface wave group velocity measurements by energy reassignment surface waves are increasingly used for shallow seismic surveys in particular in acoustic logging environmental and engineering applications these waves are dispersive and their dispersion curves are used to obtain shear velocity profiles with depth the main obstacle to their more widespread use is the complexity of the associated data processing and interpretation of the results our objective is to show that energy reassignment in the time frequency domain helps improve the precision of group velocity measurements of surface waves to show this full waveform seismograms with added white noise for a shallow flat layered earth model are analyzed by classic and reassigned multiple filter analysis mfa classic mfa gives the expected smeared image of the group velocity dispersion curve while the reassigned curve gives a very well constrained narrow dispersion curve systematic errors from spectral fall off are largely corrected by the reassignment procedure the subsequent inversion of the dispersion curve to obtain the shear wave velocity with depth is carried out through a procedure combining linearized inversion with a nonlinear monte carlo inversion the diminished uncertainty obtained after reassignment introduces significantly better constraints on the earth model than by inverting the output of classic mfa the reassignment is finally carried out on data from a shallow seismic survey in northern belgium with the aim of determining the shear wave velocities for seismic risk assessment the reassignment is very stable in this case as well the use of reassignment can make dispersion measurements highly automated thereby facilitating the use of surface waves for shallow surveys

a systematic error in estimating surface wave group velocity dispersion curves and a procedure for its correction abstract a systematic error is known to occur in estimating surface wave group velocity dispersion when the multiple filter analysis technique is applied the error comes from the fall off of the amplitude spectra at long periods we propose a method for correcting this error it consists of using a centroid frequency of the filtered spectrum instead of the central frequency of the gaussian window the method is especially useful when the group velocity curve is obtained from stacking of individual frequency time diagrams we apply this technique to two data sets the first one consists of nine seismograms of coastal subduction zone earthquakes recorded by a broadband station located in mexico city this data set has been previously used to estimate an average crustal structure of southern mexico the second data set consists of broadband seismograms recorded in india and has been used to determine an average structure of the indian peninsular region our results show that in the first case the systematic error is negligible this is due to the relatively low decay rate of the spectral amplitudes at long periods however in the case of the indian data the systematic error of the multiple filter analysis cannot be neglected since it changes significantly the measured dispersion curves and leads to errors in the estimated crustal structure our tests show that the proposed method successfully corrects a major part of the systematic error