new relationships between vs thickness of sediments and resonance frequency calculated by the h v ratio of seismic noise for the cologne area germany noise measurements were carried out in the cologne area germany and the resonance frequency of each site was estimated from the main peak in the spectral ratio between the horizontal and vertical component for 32 of these sites the thickness of the sedimentary cover was known from boreholes and a clear correlation between resonance frequency and sediment thickness was observed a formula that correlates cover thickness with frequency of the main peak in the horizontal to vertical spectral ratio was derived in addition a best fitting shear wave velocity distribution with depth vs z as well as a relationship between average shear wave velocity vs and thickness of the sedimentary cover was calculated by using all of the noise measurements and applying the derived relationships we obtained a subsoil classification for the cologne area

subsurface profiling along banni plains and bounding faults kachchh western india using microtremors method the present article is a maiden attempt to map shallow subsurface rheological interfaces laterally across the banni plains and to decode geometry of the antecedent faults associated with the kachchh mainland fault using the microtremor method we conducted microtremor data acquisition for thirty one sites along n s transect from loriya in mainland kachchh to bhirandiara towards patcham island results from h v spectral ratio technique show presence of two distinct rheological interfaces characterised by the resonant frequency f r ranges 0 23 0 27 hz and 0 8252 1 5931 hz respectively the above frequency ranges are correlated with the depths of the mesozoic basement m b interface and the quaternary tertiary q t interface using either the velocity vs of seismic waves at the m b and q t interfaces calculated as 1830 m s and 411 m s respectively or the standard non linear regression relationship derived for the banni plains h 110 18f r 1 97 we estimate the depth range for m b interface to be 1442 1965 m and for q t interface to be 44 160 in the subsurface profile across the banni plains educe cluster of four faults that develop an array of imbricate faults at the forefront of the kachchh mainland fault within the banni footwall syncline the geometry of the faults suggests a positive flower structure indicating step overs and strain restraining bends displaying push ups resulting from localized shortening between converging bends of kachchh mainland fault and the south wagad fault the banni footwall syncline preserves evidence of two episodes of deformations the initial deformation event led to subsidence within the kachchh mainland fault zone bringing mesozoic sequence juxtaposed to the basement rocks whereas the later event is dominated by an uplift developing a positive flower structure in the kachchh mainland fault zone finally the present study provides a mechanism to investigate faults and fault geometries correlating surface structural grains with subsurface structures

comparison of site classification from vs30 vs10 and hvsr in italy the aim of this work is to verify if 1 the average of shear wave velocity from the surface to 30 m depth vs30 is a good proxy of site amplification in a country with complex geology like italy 2 the grouping of vs30 in different soil classes and relevant spectra in the italian seismic codes is adequate and 3 shallow shear wave profiles vs10 could be a more economical tool for site classification to answer the first two questions we examined 40 estimates of vs30 derived from microzonation projects we performed in italy 27 obtained with downhole measurements plus 13 ve locity profiles obtained with surface techniques in all the sites we installed seismic instrumentation to record earthquakes and to estimate site response using horizontal to vertical spectral ratios hvsr the comparison between hvsr and vs30 showed in about one third of the sites that vs30 is not a good proxy of observed amplification effects if the site does not have a monotonically increasing velocity profile the reason vs30 does not provide satisfactory estimates in italy is linked to peculiar geological settings that are widespread in the country we then compared the observed ampli fications from earthquake hvsr data with the ones provided by the italian seismic code noting a substantial underestimation by the code a somewhat unsettling situa tion because hvsr is usually considered to be a lower bound for amplification es timated with other techniques finally we studied 45 vs downhole profiles to 30 m depth performed also at sites where earthquake recordings are not available on this data set we noticed that vs10 could predict site classification with the same performances of vs30 we consider al ternative soil classification schemes that include soil frequency besides the velocity profile in this two parameter approach vs10 could be substituted for vs30

microtremors as a geophysical exploration tool applications and limitations the usefulness of microtremors as a geophysical exploration tool has been analyzed this application is possible due to the relationship between the main resonance frequency of a given soil obtained from the h v spectral ratios of microtremors its thickness and average shear velocity we first measured the ambient noise at 33 sites and determined their main resonance frequency detailed geotechnical information was available for 23 of the sites thereby allowing us to establish a quantitative relationship between the resonance frequency and the thickness of the soil and indirectly between either of them and the shear velocity of the soil the practical application of this relationship has revealed its usefulness in determining the surface structure of a valley with excellent accuracy with an error of only 15 in the depths calculated these errors are due to the simplification of the problem that this method implies it requires that the shear velocity vary constantly with depth throughout the study region which is evidently not always so and that the input data themselves intrinsically have a certain degree of uncertainty this method is therefore not valid when there is no mechanical contrast between the study soil and the underlying layer or when the shear velocity varies irregularly with depth in the study area

water exsolution from quartz implications for the generation of retrograde metamorphic fluids available data from the literature suggest that the solubility of h2o in nominally anhydrous minerals such as quartz should increase with increasing metamorphic grade if this is the case water should precipitate from the host mineral during cooling and uplift of regionally metamorphosed terranes calculations indicate that this mechanism could result in the release of significant quantities of h2o which would then be available to participate in retrograde hydration reactions and the formation of fluid inclusions

staurolite growth and metamorphic zones in the kalak nappe complex of northeastern porsangerhalvoya north norway abstract four main thrust units have been differentiated in the kalak nappe complex of northeastern porsangerhalvoya all exhibit barrovian type prograde metamorphism although the metamorphic grade increases up the nappe pile the development of planar and non kinematic fabrics is the same in relation to the deformation sequence in each of the thrust sheets early porphyroblast growth preserves a planar fabric developed during burial as a result of overthrusting this was superseded by a randomly oriented and equidimensional non kinematic fabric which developed by recrystallization associated with increased fluid concentrations due to prograde metamorphic dehydration reactions these fabric developments have been preserved in textures associated with the prograde alteration of staurolite and muscovite porphyroblasts with increased fluid concentrations the shear strength of the rock declined and thrust propagation occurred the associated shear stresses caused rotational fabrics in some garnets and aligned mineral growth

ambient noise measurements for preliminary site effects characterization in the urban area of florence italy abstract environmental noise measurements and borehole data were used for a preliminary seismic characterization of the plio quaternary sedimentary basin underlying the city of florence italy an extensive survey of ambient vibrations was conducted by using the seismic noise horizontal to vertical h v spectral ratio technique hvsr to map the fundamental resonance frequency of the sedimentary cover in order to use this information to infer main features of the basin subsurface geometry an estimate of the s wave velocity profile in the sediment layer was obtained from array noise recordings along with information on resonance frequency and direct measurements of the sediment thickness available at 23 borehole sites a first order reconstruction of the seismic bedrock topography in the area was provided which shows a good consistency with available geological log data from these pieces of information a preliminary soil classification of the whole area was attempted in order to identify situations where possible seismic amplification effects are expected during future earthquakes and where more accurate investigations are needed to parameterize the local seismic response

analysis of spectral ratios for estimating ground motion in deep basins abstract use of nakamura9s spectral ratio horizontal versus vertical components is investigated theoretically for deep sedimentary basins by considering semi circular and semi spherical valleys the ratio is evaluated from the steady state surface response for different incident waves based on this ratio both the resonant frequencies and ground motion amplification are determined the results based on nakamura9s ratio are compared with those based on the sediment to bedrock spectral ratios kagami9s ratio the results show that for both two and three dimensional models nakamura9s technique predicts well the fundamental resonant frequency but it could not determine higher resonant frequencies of the basins the error in nakamura9s estimate of the fundamental resonant frequency increases for stations near the valley center for alluvial valleys considered in this article nakamura9s ratio failed to predict accurately surface ground motion amplification

the penetration of convection electric fields to the latitude of millstone hill λ 56 incoherent scatter observations of e and f region drifts over millstone hill 56 were made routinely from may 1976 to november 1977 at monthly intervals some 667 hours of data gathered over this 19 month period has been analyzed to yield the f region polarization electric field in the magnetic south and magnetic east directions in an effort to determine what part of the observed fields can be attributed to the penetration of auroral convection fields to the latitude of millstone these data have been used to construct an analytical model of these two field components having a time of day and kp dependence wand this issue to guide the interpretation mean convection fields also were constructed for 60 65 70 and 75 using data gathered between may 1978 and december 1978 from a separate series of experiments evans et al 1979 1980 the results suggest that under quiet magnetic conditions there is no significant penetration of the magnetospheric electric field to the latitude of millstone at any time of day except possibly for the southward component of the field at night during magnetically disturbed periods the incremental fields observed over millstone exhibit all the gross characteristics associated with convection fields seen at higher latitudes the results also indicate an eastward rotation of the convection pattern of about 4 hours in local time in going from quiet or moderate conditions kp 2 at 65 to disturbed conditions kp 5 at 56

on the horizontal to vertical spectral ratio in sedimentary basins the horizontal to vertical spectral ratio hvsr has been used by many researchers to characterize local conditions in terms of the dynamic response of the soil one of its variants is that proposed by nakamura 1989 in which records of microtremors are used usually the analysis is aimed to obtain the predominant period of the site under study in this work we explore what can be achieved by using this method we study the response of different configurations under incident waves coming from an explosive source using the indirect boundary element method ibem we investigate two cases low and high velocity contrast holding constant the physical properties inside the basin and changing only the properties of the bedrock then we compute the seismic response using the horizontal sediment to bedrock spectral ratio sbsr at various locations on the free surface of the basins and compare it with the one calculated by the hvsr at the same locations the comparison shows that in general the predominant period computed with the hvsr is not the same as that obtained by the sbsr in all the locations on the other hand the hvsr approximation can reasonably well predict the fundamental local frequencies when the impedance contrast between the basin and the bedrock is low however hvsr cannot be used in sedimentary basins having a high impedance contrast with respect to the bedrock below

application of integrated methods in mapping waste disposal areas an integrated suite of environmental methods was used to characterize the hydrogeological geological and tectonic regime of the largest waste disposal landfill of crete island the fodele municipal solid waste site msw to determine the geometry of the landfill depth and spatial extent of electrically conductive anomalies to define the anisotropy caused by bedrock fabric fractures and to locate potential zones of electrically conductive contamination a combination of geophysical methods and chemical analysis was implemented for the characterization and management of the landfill five different types of geophysical surveys were performed 1 2d electrical resistance tomography ert 2 electromagnetic measurements using very low frequencies vlf 3 electromagnetic conductivity em31 4 seismic refraction measurements sr and 5 ambient noise measurements hvsr the above geophysical methods were used with the aim of studying the subsurface properties of the landfill and to define the exact geometrical characteristics of the site under investigation

insights on the structural control of a neogene forearc basin in northern chile a geophysical approach abstract the comprehensive study of intramountain basins located in the coastal cordillera of the continental emergent andean forearc in northern chile enables the better understanding of the nature and evolution of the upper crustal deformation during the neogene and quaternary a case study is the extensive extensional half graben alto hospicio basin the basin is cut by the coastal cliff which exposes the deformed neogene basin fill also exposed are several structural systems some of which affect quaternary surfaces the results of the integrated geophysical surveys electromagnetic transient and gravity allow us to fully constrain the geometry of the alto hospicio basin and the lithological relationship between the subsurface geological units the structural geology analysis assesses the deformation regimes affecting the faults present in the basin and surrounding area altogether evidence a change in the deformation regime from an ew extensional deformation during the miocene pliocene to a ns compression in the quaternary as is presented in this study we suggest this deformation change is related to a small change in the convergence vector orientation during the pliocene

metamorphic and structural diachroneity in the finnmarkian nappes of north norway two periods of garnet growth gt1 and gt2 have been found in the finnmarkian nappes of north norway in the kolvik nappe the lowest nappe gt1 has preserved an s2 syntectonic spiral inclusion fabric in the olderfjord nappe an earlier s1 fabric and an interkinematic inter d1 d2 fabric have been preserved in gt1 whilst only the s1 fabric has been found in gt1 in the brennsvik nappe the highest nappe in each nappe gt2 overgrew a penetrative fabric s2 wrapped around gt1 in the kolvik nappe inclusion fabrics may be continuous from gt1 into gt2 but in the higher nappes there is a distinct break gt2 may have been partially syntectonic with d3 in the brennsvik nappe chemically gt1 in the kolvik nappe and in parts of the olderfjord and brennsvik nappes has antithetic fe mn zoning in all nappes xca and xmg are weakly zoned in gt1 xmg increases outwards and is greater in the higher nappes in gt1 suggesting higher nucleation temperatures in the olderfjord and brennsvik nappes gt2 is marked by increasing xca probably due to changing garnet plagioclase equilibria although the fe mg ratio remains constant xmg is higher in gt2 than gt1 basement rocks within the nappe pile have an early pre finnmarkian growth gt1 and a later finnmarkian growth gth correlated with gt2 on the basis of chemical zoning patterns the diachroneity of gt1 is ascribed to progressively earlier compared to the structural development cessation of overstepping of garnet forming reactions before peak metamorphism in the higher nappes resulting in earlier structural events being preserved

integrating ambient noise with gis for a new perspective on volcano imaging and monitoring the case study of mt etna abstract the timely estimation of short and long term volcanic hazard relies on the availability of detailed 3d geophysical images of volcanic structures high resolution seismic models of the absorbing uppermost conduit systems and highly heterogeneous shallowest volcanic layers while particularly challenging to obtain provide important data to locate feasible eruptive centres and forecast flank collapses and lava ascending paths here we model the volcanic structures of mt etna sicily italy and its outskirts using the horizontal to vertical spectral ratio method generally applied to industrial and engineering settings the integration of this technique with web based geographic information system improves precision during the acquisition phase it also integrates geological and geophysical visualization of 3d surface and subsurface structures in a queryable environment representing their exact three dimensional geographic position enhancing interpretation the results show high resolution 3d images of the shallowest volcanic and feeding systems which complement 1 deeper seismic tomography imaging and 2 the results of recent remote sensing imaging the study recovers a vertical structure that divides the pre existing volcanic complexes of ellittico and cuvigghiuni this could be interpreted as a transitional phase between the two systems a comparison with recent remote sensing and geological results however shows that anomalies are generally related to volcano tectonic structures active during the last 17 years we infer that seismic noise measurements from miniaturized instruments when combined with remote sensing techniques represent an important resource to monitor volcanoes in unrest reducing the risk of loss of human lives and instrumentation

measuring the sediment thickness in urban areas using revised h v spectral ratio method abstract for the sake of safety it is crucial for civil engineers to determine the thickness of the sediment layers in the urban areas however the noisy detection environment in a city presents a significant challenge to the traditional artificial source geophysical methods which are used to estimate and monitor of sediment thickness given this otherwise challenging detection environment the h v spectral ratio method provides an effective and cheap means of detecting sediment thickness it exploits microtremor signals to obtain the resonant frequency of the surface layer which is then used to determine site sediment thickness with an empirical equation using the data from a single observation station in this study we collected microtremor data at 109 locations in the aoshan bay area of the shandong peninsula and determined the resonant frequency and analysed the morphological features of the h v spectral ratio curves in order to calibrate the frequency bedrock depth equation accurately to the local conditions vs profile estimation is used to fine tune the frequency bedrock depth equation by comparing the s wave velocity structure obtained using the microtremor spac method with that found from borehole samples we were able to verify the reliability and accuracy of application of the microtremor spac method by using the h v spectral ratio method and the modified equation that transforms resonance frequencies to sediment thickness we generated a thickness map of the sedimentary layers in the aoshan bay area of the shandong peninsula the map provides useful information for ensuring the safe construction of the city s infrastructure we conclude that the use of microtremor signals can provide important geological information as a cheaper and quick way for the construction and development of urban infrastructure

influence of a sedimentary basin infilling description on the 2 d p sv wave propagation using linear and non linear constitutive models numerical modelling is a useful tool to understand the role of different parameters site geometry impedance contrast material properties constitutive model input motion governing site effects we focus here on the 2 d p sv seismic wave propagation in a simple shaped asymmetric model we consider two ways of describing the sedimentary infilling properties the basin is either composed of distinct homogeneous geological layers or is described through properties progressively changing as a function of depth smooth model in order to study the wave propagation in the two basins with similar soil properties p and s velocities of the layered basin are deduced from the smooth basin ones making both models compatible in a kinematic point of view p and s velocities globally increase with depth following epri non linear properties are considered as constant in layers for the two basins we assess the influence of the model choice on the wave propagation while taking into account linear and non linear constitutive models we test the influence of the input motion by propagating two different input motions the first being a simple impulsive one and the second a real complex accelerogram we find that transfer functions computed in each basin are quite similar irrespective of the soil constitutive behaviour and the input motion moreover we show that the maximum shear strain spatial distribution depends on the input motion frequency content and maximum values depend on the input motion strength and complexity maximum shear strains are generally higher for superficial layers than for deeper ones we show that the highest shear strain values are located above discontinuities where velocities are lower and the soil is more non linear than in the underlying layer regardless of the input motion indeed in a layered basin the shear strain is higher above interfaces for all the soil constitutive models that were used in the smooth visco elastoplastic model a kind of layering appears absent in a viscoelastic model due to the different non linear properties in each layer moreover no matter what the model structure and the input motion used maximum shear strain levels are higher in the visco elastoplastic soil than in the viscoelastic one such a numerical study helps to understand the non linearity location and therefore the consequences of a model choice when performing a site specific study

empirical evidence of orthogonal relationship between directional site effects and fracture azimuths in an active fault zone the case of the mt etna lower eastern flank abstract mt etna in eastern sicily is a composite active volcano whose eastern flank is affected by several normal and strike slip active faults in this study geological structural field survey and ambient vibration measurements are performed in the lower eastern flank of mt etna in order to define the role of the tectono stratigraphic setting in the seismic site response the sites of measurements are mainly distributed inside the few hundreds of meters long s caterina graben which is located between two main seismogenic active faults of this volcano sector the acireale and the fiandaca faults our study aims at defining the contribution of the fault related active deformation in determining the local ground motion amplification also providing a subsoil geological model based on the integration of geological and geophysical investigation therefore structural measurements were made in seven sites revealing coseismic and aseismic extensional fractures mainly striking nnw the seismic site response was studied processing the ambient vibration measurements through horizontal to vertical spectral ratio the measured fundamental frequency falls in the range 1 0 4 0 hz that we linked to the presence of a velocity contrast at depth of 80 200 m by calibrating a frequency depth function moreover the seismic site effect is due to the stratigraphic setting and is markedly directional showing maximum amplification along the direction orthogonal to the strike of the observed isooriented extensional fracture field produced by the activity of the s caterina graben it is noteworthy that far from the graben on sites of measurements located near the fiandaca fault we observed directional effects parallel to the direction of maximum extension inferred for this tectonic lineament our results suggest a linkage between directional site effects and local stress tensors and fractures field orientation

reflection and refraction by tilted layers an explanation for vhf auroral backscatter at large aspect angles auroral structures are often accompanied by tilts to the electron density contours on the underside of the e region by including the effects of these tilts on radio wave refraction and reflection it is possible to understand many of the previously puzzling observations of vhf auroral backscatter at large angles away from perpendicularity to the earth s magnetic field it is shown that many of the characteristics of echoes from the vhf canadian bistatic auroral radar system bars are consistent with this process for bars observations for which the tilt hypothesis is correct the resulting doppler velocities can be interpreted in the same way as those from stare and used to give electric fields and convection patterns over the bars field of view

assessment of the stability of h v spectral ratios from ambient noise and comparison with earthquake data in the cologne area germany abstract situated in an active tectonic region the highly industrialised cologne area germany suffers from moderate sized earthquakes our contribution to the mitigation of earthquake risk includes a microzonation study using ambient seismic noise and earthquake recordings from two field campaigns an analysis of these data using the horizontal to vertical h v as well as the classical spectral ratio csr technique led to the following observations and conclusions 1 the spatial variation in the thickness of the sedimentary cover is reliably retrieved using the fundamental resonance frequency estimated from the peak in the h v ratio of ambient noise 2 this fundamental resonance frequency is stable in time but the amplitude of the peak the amplification factor is not 3 the relative amplification variation of the h v ratio in the area should therefore be checked systematically with repeated measurements before drawing conclusions about its significance 4 the analysis of the h v ratio of ambient noise provides the lower frequency bound above which amplification may occur 5 the shapes of the spectral ratios obtained by the different methods are generally in good agreement however the analysis of earthquake data shows that significant amplification of ground motion may also occur at frequencies higher than the fundamental one even when thick sediments are present

simultaneous chatanika radar and s3 2 satellite measurements of ionospheric electrodynamics in the diffuse aurora simultaneous chatanika radar and s3 2 satellite measurements have been used to investigate the spatial variation of the auroral zone ionosphere near the equatorward edge of the diffuse aurora during early evening satellite passes on 2 days in february 1976 the equatorward boundary of the diffuse aurora was nearly overhead at chatanika the configurations of e region ionization and conductivity were nearly identical in both passes but the latitudinal variations of f region ionization were quite dissimilar during both passes the ionospheric electric field in the diffuse aurora was directed northward as a result the closing current of the field aligned current system was primarily a pedersen current and the eastward electrojet was larger than the northward ionospheric current although the morphology of ionospheric conductivity was very similar on the 2 days different patterns were observed for the latitudinal distribution of electric field and field aligned current

site effect evaluation in the basin of santiago de chile using ambient noise measurements summary we performed extensive ambient vibration measurements in the basin of santiago de chile chile and we look for testing the reliability of the horizontal to vertical amplitude spectra ratio method h v as a tool to provide qualitative and quantitative information of site effects in complex geological media the interpretation of the h v data was carried out conformably to the sesame project consensus criteria and outlines three major patterns 1 clear peaked h v curves related to sharp underground velocity contrast 2 h v peak of low amplitude and flat curve related to weak contrast and 3 broad h v peak indicating the presence of strong lateral variations of underground structure h v measurements however reveal a discrepancy between the computed soil resonance frequencies and the expected building resonance therefore not leading to a straight interpretation of the intensity distribution derived from observed damage to one storey houses in santiago after the 1985 valparaiso earthquake indeed the h v technique mostly maps the first fundamental frequency however it fails to show higher resonance modes in the case of the city of santiago this method works well for assessing the seismic hazard for high rise buildings but is questionable for smaller structures as is the case of a great percentage of constructions in the city

p t paths from garnet zoning a new technique for deciphering tectonic processes in crystalline terranes a procedure to calculate quantitative rock pressure temperature p t paths based on chemical zoning profiles in garnet combined with mineral chemistry from the other minerals in the assemblage has been applied to samples from diverse tectonic settings with the result that the calculated p t path is shown to be a sensitive monitor of tectonic processes terranes where metamorphic recrystallization paths are controlled by uplift and erosion show heating during decompression in the prograde p t path and cooling during decompression in the retrograde path in nappe terranes where hot rocks are emplaced over cool rocks the upper plate shows cooling during decompression whereas the lower plate shows heating during compression in nappe terranes where cool rocks are emplaced over hot the lower plate shows cooling during compression calculation of p t paths from mineral zoning should provide a powerful new tool for deciphering tectonic processes in crystalline terranes

characteristics of long period microtremors and their applicability in exploration of deep sedimentary layers abstract applicability of long period microtremors in inferring subsurface structure is examined using measurements of microtremors in the northwestern part of the kanto plain in japan short term continuous measurements of long period microtremors at both sediment and basement sites were taken a spectral peak at a period of 4 to 5 sec is stable with time while peaks at periods less than 2 sec are time variant suggesting a variation of microtremor sources however it was found that the spectral ratio between vertical and horizontal microtremors ellipticity at each site is stable with time good agreement was found between ellipticities of microtremors at the sediment site and those computed for rayleigh waves in which the structure of the sediments beneath the site was taken into account we also found that the ellipticities of rayleigh waves in earthquake ground motions were consistent with those of the microtremors these comparisons provide strong evidence that long period microtremors in the area studied consist mainly of rayleigh waves the ellipticity of microtremors was investigated by observing microtremors at temporary observation sites in the kanto plain where the sediment thickness varied from 0 to 1 km the subsurface structures were deduced by trial and error fitting of observed ellipticities with theoretical ellipticities that were calculated assuming rayleigh waves these results show that ellipticity of long period microtremors is effective for deducing structure from microtremor data at a single site

dual radar investigation of e region plasma waves in the southern polar cap origins and characteristics of small scale plasma irregularities in the polar ionosphere are investigated using a dual radar setup in which the e region is probed from opposite directions by two super dual auroral radar network superdarn facilities at the mcmurdo and dome concordia antarctic stations in certain time intervals velocity agreement is observed when velocities are compared at the same physical location in the horizontal plane such an agreement is widely expected if velocity at a given location is largely controlled by the convection electric field in other cases however velocity agreement is unexpectedly observed when measurements are considered at the same slant range distance along the radar beam for both radars this implies that it is not the electric field at a given location that is a controlling factor raytracing results show that the same range agreement may be explained for certain e region density conditions when echo altitude increases with radar range backscatter observations under generally unfavorable conditions for irregularity generation and the critical role of propagation conditions in the polar cap are discussed the observed e region velocity in the polar cap is demonstrated to depend indirectly on the plasma density distribution which is important for establishing the fundamental dependence on the convection electric field

the diurnal and latitudinal variation of auroral zone ionospheric conductivity the great spatial and temporal variability of auroral ionospheric conductivity significantly influences the ionospheric closure path for high latitude field aligned currents because these closure paths can extend to low latitudes changes in auroral zone conductivity can influence the global electric field distribution in this paper synoptic chatanika radar observations of auroral zone conductivity that cover 62 to 68 geomagnetic latitude are presented they are representative of quiet winter active winter and equinoctial conditions during the daytime the solar contribution to the height integrated conductivity is well represented by p h 5 10 cos1 2 where is the solar zenith angle the nighttime height integrated pedersen and hall conductivities p and h in the electron density trough are at times below our detection threshold of 0 5 mho following magnetic substorm onset enhanced conductivity regions move southward and intensify as the recovery phase begins the conductivity pattern recedes northward and diminishes the onset and cessation of precipitation associated with these events can be as abrupt as a few minutes in one example the behavior of p and h are examined in the vicinity of the harang discontinuity which was quite sharp 30 min in local time at the harang discontinuity on that day the ratio of h to p decreased indicating a softening of the precipitating energy distribution

hvsr deep mapping tested down to 1 8 km in po plane valley italy abstract the horizontal to vertical spectral ratio hvsr of seismic noise is extensively used in seismic microzonation for its capability to provide a good approximation to the subsoil main resonance frequencies of geotechnical and seismic engineering interest this implies in turn that it has also an approximate passive subsoil mapping capability independent of the level of noise illumination albeit limited to relatively shallow depths since tilt sensitivity makes hvsr unreliable below 0 1 hz however we have experimentally verified that hvsr subsoil mapping capability extends to depths in the kilometer range by applying it to the largest sedimentary basin of italy the po plain valley there we were able to resolve the major stratigraphic discontinuities down to the sediment bedrock interface for which we estimated a depth of 1 6 km with a 25 uncertainty while the surface mapped from oil exploration indicates a depth of 1 8 km quarter of an hour recordings gave always stable signals that fitted to synthetic curves using as a constraint the parameters of the shallow subsoil provided a stratigraphic map consistent with the independent survey this candidates hvsr as a fast and inexpensive first order subsoil mapping tool down to depths of geological and exploration interest

insights into bedrock paleomorphology and linear dynamic soil properties of the cassino intermontane basin central italy abstract seismic amplifications are dictated by the depth of the bedrock and the stratigraphy and dynamic properties of the soil deposits quantifying these properties together with their uncertainty is a necessary task to perform a reliable assessment of the seismic risk at an urban scale in this paper a multidisciplinary analysis is presented where information of different nature is combined borehole logs geophysical geological and geotechnical surveys are interpreted with the aid of analytical numerical and geostatistical techniques to characterise the complex shape of the bedrock and the linear dynamic properties of the sedimentary deposits filling the cassino basin a quaternary intermontane basin located in central italy the regional and local seismic hazard is firstly identified with geological surveys that reveal an active seismogenic fault capable of producing earthquakes with estimated magnitudes up to 6 7 6 8 boreholes reaching depths variable up to a maximum of 180 m and microtremor measurements revealing the sharp impedance contrast at the transition between the sedimentary arenaceous bedrock and the soft quaternary infilling are combined to identify the depth of the bedrock and the linear dynamic properties of soil deposits these are one of the key factors governing the propagation to the ground level of seismic waves and their assessment represents the first step for the seismic hazard characterisation of the plain

inverted isograds at sulitjelma norway the result of shear zone deformation at sulitjelma norway there is a major inversion of metamorphic isograds beneath an inverted but undisrupted ophiolite the flysch like furulund schist in which the inverted isograds occur is also inverted and the early folds in it are downward facing the isograds cut across the axial surfaces of early folds and across the schistosity these relationships are explained as the consequence of metamorphism during the progressive development of a large overfold the inverted limb of the overfold is regarded as a major thick gently dipping shear zone separating the lower grade lower part of the caledonian allochthon below from the higher grade upper part of the allochthon above the association between stratigraphical inversion downward facing of syn schistosity folds and metamorphic inversion is explained by the progressive development of the shear zone it is suggested that the presence of such shear zones is a common feature of orogenic belts formed by continental collision

simulation based comparison of four site response estimation techniques abstract recent earthquakes have triggered renewed interest to understand better earthquake site response most of the studies comparing various techniques for estimating site response were based on real data from earthquakes nuclear blasts and seismic noise a theoretical approach using synthetic data generated with the pseudospectral method is used to compare four site response estimation techniques the limits of applicability of each method were determined by modeling microtremors and incoming sv waves with different incidence angles and analyzing the site amplifications the first two techniques investigated consist of dividing the spectrum of the horizontal motion at a site by that of a reference site using either incident s waves or microtremors the latter was unable to reveal either the resonant frequencies or peak amplitudes in any cases the two other techniques are based on the horizontal to vertical h v spectral ratio using s waves or microtremors these techniques were found to reveal at least the fundamental resonant frequency and amplitude former method only within 10 error in the case of simple geology flat layers however the results show that these techniques are unable to take into account 2d effects such as focusing effects and basin edge effects and yield unreliable or incorrect results in such cases

on the limitation of the h v spectral ratio using seismic noise as an exploration tool application to the grenoble valley france a small apex ratio basin the h v spectral ratio method based on seismic noise hvsrn was used in the grenoble basin france an alpine valley characterized by a small apex ratio the resonance frequencies obtained in the experiments were compared to the thickness of the sediments deduced from a microgravimetric survey and to the 1 d theoretical assessment of site responses given the abundance of data on the sediments and depth of the basin the values of the theoretical resonance frequency fo can be determined quite accurately however it has been observed that the effects of basin geometry can disturb fo measurements using the hvsr method in particular for a case like the grenoble basin which has a small apex ratio w h and strong suspected 2 d and or 3 d effects interpretation of fo values in terms of bedrock depth gives rise to estimation errors of about 10 in certain cases with the most significant errors 50 occurring on the edges of the basin where subsurface layers are characterised by larger heterogeneities and where the basin topography is accentuated this study suggests that great care must be taken when using the hvsrn method as an exploration tool at least in valleys with a small apex ratio

spatial relationship between large aspect angle vhf radio aurora and 557 7 nm emissions evidence for refraction a recently proposed explanation for large aspect angle vhf backscatter observations based on refraction through auroral ionization structures in the e region moorcroft 1989 has been confirmed by an experimental comparison of observations of auroral e region coherent backscatter at 48 5 mhz made with the bistatic auroral radar system or bars with simultaneous 557 7 nm emissions detected with a ccd based all sky imager the apparently large aspect angle radio auroral echoes are found to occur predominantly on the side of the visual aurora away from the radar for both the premidnight and the postmidnight sectors for the red lake bars radar this means that the strongest echoes occur to the north of the visual form in sharp contrast with previous comparisons particularly for the premidnight sector which found that radar echoes occur predominantly southward of the visual aurora these results are consistent with the proposed explanation based on refraction in the auroral e region

thrust tectonics a mechanistic view from the west and central alps abstract two modern models of thin skinned thrust tectonics by elliott 1976 and chapple 1978 are reviewed and found to be of restricted application following possible variations of surface and basal slope and based on published alpine cross sections eight elementary two dimensional mechanical models are set up these include the possibility of a weak basal layer a common feature of alpine thrust sheets and an externally applied subhorizontal compression six of these have two variants depending on if the maximum shear stress in the sheet attains the yield stress in which case there is permanent deformation and the sheet changes shape perhaps to that of a different elementary model the long ignored analysis by goguel 1948 of stresses in a relaxed plastic material at depth below an inclined surface is outlined stress components resulting from this analysis are used together with supplementary stresses derived by hafner 1951 to represent an externally applied subhorizontal compression to suggest ways in which decollement possibilities of the models can be investigated some specific examples are considered

subsurface profiling of granite pluton using microtremor method southern aravalli gujarat india we report using the microtremor method a subsurface granitic pluton underneath the narukot dome and in its western extension along a wnw profile in proximity of eastern fringe of cambay rift india the dome and its extension is a part of the champaner group of rocks belonging to the mesoproterozoic aravalli supergroup the present finding elucidates development of an asymmetric double plunge along narukot dome microtremor measurements at 32 sites were carried out along the axial trace n95 of the dome fourier amplitude spectral studies were applied to obtain the ratio between the horizontal and vertical components of persisting rayleigh waves as local ambient noise fundamental resonant frequencies with amplitude 1 sigma for each site are considered to distinguish rheological boundary two distinct rheological boundaries are identified based on frequency ranges determined in the terrain 1 0 2219 10 364 hz recorded at 31 stations identified as the champaner metasediment and granite boundary and 2 10 902 27 1119 hz recorded at 22 stations identified as the phyllite and quartzite boundary the proposed equation describing frequency depth relationship between granite and overlaying regolith matches with those already published in the literature the morphology of granite pluton highlights the rootless character of champaner group showing sharp discordance with granitic pluton the findings of manifestation of pluton at a shallower depth imply a steep easterly plunge within the champaner metasediments whereas signature of pluton at a deeper level implies a gentle westerly plunge the present method enables to assess how granite emplacement influences the surface structure

microtremor survey in talchir india to ascertain its basin characteristics in terms of predominant frequency by nakamura s ratio technique abstract the talchir basin one of india s oldest basins has been a subject of interest because of its rich coal deposits the maximum thickness of the basin is about 1500 m beyond the basin is the hard metamorphic rocks of precambrian age the ambient noise survey data have been analyzed for the talchir basin using nakamura s technique of horizontal vertical spectral ratio hvsr to ascertain the basin structure in terms of the predominant frequency the predominant frequency varies from 0 25 hz to 7 8 hz but a major portion of the basin comes under the range of 0 3 hz 2 4 hz while on the metamorphic rocks it is as high as 7 8 hz the variation in predominant frequency shows a good correlation with the sediment thickness of the basin the results have been compared with the previous studies by other researchers and it shows consistency with the northerly dip of the basin the present study has also been compared with the results of the synthetic seismogram that was performed for the talchir basin the predominant frequency obtained from hvsr technique complements well with the frequency at which the peak response spectra ratio is observed the present study of the predominant frequency identifies quite well the characteristics of talchir basin and is in good agreement with the synthetic ground motion modeling of the region

combining borehole log stratigraphies and ambient vibration data to build a 3d model of the lower var valley nice france abstract in seismic hazard studies site effects assessment is based on an accurate knowledge of mechanical properties and geometry of superficial geological formations the lower var valley nice southeastern france is a 2 km wide fluvial sedimentary basin where site effects have been observed on earthquake recordings in addition this area is a significant economically developing zone including the second largest airport of france therefore it is highly important to define a 3d sub surface model of the basin to understand the ground motion amplifications based on the compilation of several years of geotechnical and geophysical studies the quaternary alluvial deposits of the lower var valley were investigated using 331 borehole log stratigraphies and 439 ambient vibration measurements these data were combined in a commercial software that models and allows to visualize geoscientific data and geological models in 3d the borehole log stratigraphies helped to define a representative lithostratigraphic soil profile and the geometry of the different sedimentary layers only few boreholes are reaching the engineering bedrock pliocene conglomerates characterized by a s wave velocity larger than 800 m s 1 from the ambient vibration data the fundamental resonance frequency identified from h v curves indicates the bedrock depth using the well known f0 vs 4h relationship these h v curves were interpreted using geological knowledge of the studied zone our results show that the bedrock depth varies in the center of the valley between 50 m in the northern part of the studied zone and more than 100 m on the river estuary first the average s wave velocity in the alluvial deposits is estimated according to combined analysis of the borehole log stratigraphies and h v calculations on ambient vibration measurements the spatial variability of this velocity has been translated into a velocity zonation of the valley second this zonation allows us to extrapolate the quaternary pliocene limit in the whole valley the 3d model of the lower var valley will be useful in future numerical simulations of seismic ground motions in order to evaluate and mitigate seismic risk in the area

structures associated with superimposed inhomogenous shearing of basic dykes from finnmark norway abstract metadolerites within the olderfjord nappe of the kalak nappe complex of north norway show a wide range of structural relationships during d2 simple shear rotated the dykes from an initially orthogonal relationship towards parallelism with the sedimentary layering and boudinaged those dykes that rotated to within 25 of the sedimentary layering during d3 dykes which had been rotated to within 5 of the layering were folded those lying between 5 and 25 were boudinaged whilst those at angles between 25 and 75 had folds developed against their margins at higher angles of discordance little evidence of d2 or d3 deformation has been observed in other thrust sheets within the kalak nappe complex metabasites have generally been sheared into parallelism with the compositional banding by comparison with the olderfjord nappe the average d2 shear strain within the kalak nappe complex ranges between 5 and 10 the anomalous preservation of high angle discordant relationships in the olderfjord nappe reflects the preservation of a large scale low strain block mega boudin within the nappe samples taken from the mega boudin are more suitable for geochemical analysis for tectonic setting discrimination

effects of surface geology on seismic ground motion deduced from ambient noise measurements in the town of avellino irpinia region italy the effects of surface geology on ground motion provide an important tool in seismic hazard studies it is well known that the presence of soft sediments can cause amplification of the ground motion at the surface particularly when there is a sharp impedance contrast at shallow depth the town of avellino is located in an area characterised by high seismicity in italy about 30 km from the epicentre of the 23 november 1980 irpinia earthquake m 6 9 no earthquake recordings are available in the area the local geology is characterised by strong heterogeneity with impedance contrasts at depth we present the results from seismic noise measurements carried out in the urban area of avellino to evaluate the effects of local geology on the seismic ground motion we computed the horizontal to vertical h v noise spectral ratios at 16 selected sites in this urban area for which drilling data are available within the first 40 m of depth a rayleigh wave inversion technique using the peak frequencies of the noise h v spectral ratios is then presented for estimating vs models assuming that the thicknesses of the shallow soil layers are known the results show a good correspondence between experimental and theoretical peak frequencies which are interpreted in terms of sediment resonance for one site which is characterised by a broad peak in the horizontal to vertical spectral ratio curve simple one dimensional modelling is not representative of the resonance effects consistent variations in peak amplitudes are seen among the sites a site classification based on shear wave velocity characteristics in terms of vs30 cannot explain these data the differences observed are better correlated to the impedance contrast between the sediments and basement a more detailed investigation of the physical parameters of the subsoil structure together with earthquake data are desirable for future research to confirm these data in terms of site response

oceanic lithospheric s wave velocities from the analysis of p wave polarization at the ocean floor our knowledge of the absolute s wave velocities of the oceanic lithosphere is mainly based on global surface wave tomography local active seismic or compliance measurements using oceanic infragravity waves the results of tomography give a rather smooth picture of the actual s wave velocity structure and local measurements have limitations regarding the range of elastic parameters or the geometry of the measurement here we use the p wave polarization apparent p wave incidence angle of teleseismic events to investigate the s wave velocity structure of the oceanic crust and the upper tens of kilometres of the mantle beneath single stations in this study we present an up to our knowledge new relation of the apparent p wave incidence angle at the ocean bottom dependent on the half space s wave velocity we analyse the angle in different period ranges at ocean bottom stations obs to derive apparent s wave velocity profiles these profiles are dependent on the s wave velocity as well as on the thickness of the layers in the subsurface consequently their interpretation results in a set of equally valid models we analyse the apparent p wave incidence angles of an obs data set which was collected in the eastern mid atlantic we are able to determine reasonable s wave velocity depth models by a three step quantitative modelling after a manual data quality control although layer resonance sometimes influences the estimated apparent s wave velocities the apparent s wave velocity profiles are well explained by an oceanic prem model in which the upper part is replaced by four layers consisting of a water column a sediment a crust and a layer representing the uppermost mantle the obtained sediment has a thickness between 0 3 km and 0 9 km with s wave velocities between 0 7 km s 1 and 1 4 km s 1 the estimated total crustal thickness varies between 4 km and 10 km with s wave velocities between 3 5 km s 1 and 4 3 km s 1 we find a slight increase of the total crustal thickness from 5 km to 8 km towards the south in the direction of a major plate boundary the gloria fault the observed crustal thickening can be related with the known dominant compression in the vicinity of the fault furthermore the resulting mantle s wave velocities decrease from values around 5 5 km s 1 to 4 5 km s 1 towards the fault this decrease is probably caused by serpentinization and indicates that the oceanic transform fault affects a broad region in the uppermost mantle conclusively the presented method is useful for the estimation of the local s wave velocity structure beneath ocean bottom seismic stations it is easy to implement and consists of two main steps 1 measurement of apparent p wave incidence angles in different period ranges for real and synthetic data and 2 comparison of the determined apparent s wave velocities for real and synthetic data to estimate s wave velocity depth models

the early caledonian finnmarkian event reassessed in finnmark 40ar 39ar cleavage age data from nw varangerhalvoya n norway abstract the relative significance of early finnmarkian and late scandian caledonian deformation in n norway is uncertain early studies suggested pervasive finnmarkian deformation whilst later results indicated a restricted finnmarkian domain the present work suggests it was more widespread than accepted and that inter finnmarkian scandian deformation occurred 40 ar 39 ar dating of 2 6 and 6 11 m pelitic fractions from the lower to mid greenschist facies tanahorn nappe five samples base middle allochthon and the epizone lokvikfjellet and barents sea groups three samples north varanger region in the north scandinavian caledonides show slightly discordant spectra most spectra from the tanahorn nappe preserve possible evidence of an early caledonian event in the high temperature steps with recoil excess ar effects in the low temperature steps no pre caledonian relict component has been recorded the results indicate finnmarkian deformation continued to 460 ma with scandian reactivation at 425 415 ma from the north varanger region a strongly crenulated sample yielded plateau ages 444 442 ma means of combined young steps from weakly to uncrenulated samples gave 470 450 ma suggesting penetrative strike slip deformation occurred in the late finnmarkian to inter finnmarkian scandian period no scandian ages were recorded in the north varanger region reassessment of published data from the laksefjord nappe and gaissa thrust belt suggests they were affected by finnmarkian deformation

basement topography of the kathmandu basin using microtremor observation abstract kathmandu valley an intermontane basin of the himalaya has experienced many destructive earthquakes in the past the observations of the damage pattern during the 1934 earthquake m w 8 1 in particular suggest that the spectral ground amplification due to fluvio lacustrine sediments plays a major role in intensifying the ground motion in the basin it is therefore imperative to conduct a detailed study about the floor variation of sediments in the basin in this paper a preliminary attempt was made to estimate the thickness of soft sediment in the kathmandu basin using microtremor observations the measurements of microtremors were carried out at 172 sites spaced at a grid interval of 1 km the results showed that the predominant frequency varies from 0 488 hz to 8 9 hz a non linear regression relationship between resonance frequency and sediment depth was proposed for the kathmandu basin the thickness of lacustrine sediments at various points in the basin was estimated using the proposed equation and then the estimated thickness was used to plot a digital elevation model of the basement topography and cross profiles of the sediment distribution in the basin the results were validated by correlating the estimated sediment thickness with geology and geomorphology of the study area

characterizing surface geology liquefaction potential and maximum intensity in the kachchh seismic zone western india through microtremor analysis abstract this study presents results of microtremor analysis carried out over diverse geological formations and liquefaction sites in the kachchh seismic zone of western india which is host to the deadliest intraplate earthquake m w 7 7 microtremors were recorded at 36 sites with single stations and 7 sites with an array the microtremor array measurements were made using triangular arrays with sensors kept at 30 90 m radii the rayleigh wave velocities are estimated from the array data using high resolution frequency wavenumber f k analysis and the 1d shear wave velocity structure is determined by inversion we found a good correlation between surface geology resonant frequency and amplitude of the horizontal to vertical spectral ratio hvsr curve and shear wave velocity the ground vulnerability index k g values in the liquefied areas are found to be higher than those in the adjacent areas devoid of liquefaction broad or multiple peaks in the hvsr curves and large variations in the shear velocity models could be attributable to the structural and tectonic complexity in the maximum intensity area further our results show that the average fundamental frequencies are around 0 32 hz for the quaternary 0 80 hz for tertiary 1 8 hz for cretaceous 1 8 hz for jurassic and 2 3 hz for the deccan trap formations the inverted s wave velocity varies from 190 to 1350 m s down to a depth of 200 m for the quaternary 220 to 680 m s down to 100 m for tertiary 236 to 1160 m s for cretaceous 670 to 1780 m s for jurassic and 260 to 2440 m s for the deccan trap sites the results of microtremor analysis corroborate the observations from the available geophysical geological and borehole data

are microtremors useful in site response evaluation we have reviewed the applicability of microtremor measurements to evaluate site response of soft soils to this end we evaluated three different techniques commonly used to estimate site effects from microtremor measurements interpretation of fourier amplitude spectra computation of spectral ratios relative to a firm reference station and finally computation of spectral ratios of horizontal components relative to the vertical component of ground motion nakamura s technique these techniques are applied to microtremor records obtained in three cities in mexico mexico city oaxaca and acapulco these cities differ in their local geological conditions and in their seismotectonic environment in order to evaluate the results obtained from microtremor measurements we compare them with standard spectral ratios of the intense s wave part of weak or strong motion records obtained at the same sites our results showed that microtremor measurements can be used to estimate the dominant period of a site with very acceptable reliability in the range 0 3 to 5 hz the best results were obtained with nakamura s technique which also gives a rough estimate of amplification of seismic waves when the local geology is relatively simple simple numerical simulations indicate that the underlying assumptions of nakamura s technique are consistent with the propagation of rayleigh waves these simple numerical simulations also explain why different researchers have been able to successfully characterize 1d site effects using microtremor records regardless of whether they consider microtremors to consist of surface or body waves our results strongly suggest that the technique by nakamura effectively compensates for source effects in microtremor measurements which eliminates a major limitation to their application in earthquake engineering

microtremor measurements used to map thickness of soft sediments the observations about the behavior of microtremor spectra presented here show that noise measurements can be used as a powerful tool to determine the thickness of soft cover layers the most suitable method for this determination is nakamura s technique which is the ratio of the horizontal component noise spectrum and that of the vertical component i i v spectrum the frequency of the main peak in these spectral ratios correlates well with the sediment thickness at the site using an extensive database of microtremor measurements carried out in the western lower rhine embayment germany it was possible to show that this correlation is clearly valid for a wide range of thickness namely from tens of meters to more than 1000 m a simple formula was derived that for the sediments to be found in the area investigated directly calculates the cover thickness from the frequency of the main peak in the h v spectrum a comparison with calculated resonant frequencies sug gests the relation derived from the noise measurements depending on the velocity depth function of the shear wave classical spectral ratios are shown to be strongly influenced by the noise level and are therefore less reliable in determining the res onant frequency of the subsoil the practical relevance of the investigation is illus trated by means of cross sections constructed from results of the microtremor anal yses which provide a convincing image of the surficial structure of the areas investigated

basin related effects on ground motion for earthquake scenarios in the lower rhine embayment summary the deterministic calculation of earthquake scenarios using complete waveform modelling plays an increasingly important role in estimating shaking hazard in seismically active regions here we apply 3 d numerical modelling of seismic wave propagation to m 6 earthquake scenarios in the area of the lower rhine embayment one of the seismically most active regions in central europe using a 3 d basin model derived from geology borehole information and seismic experiments we aim at demonstrating the strong dependence of ground shaking on hypocentre location and basin structure the simulations are carried out up to frequencies of ca 1 hz as expected the basin structure leads to strong lateral variations in peak ground motion amplification and shaking duration depending on source basin receiver geometry the effects correlate with basin depth and the slope of the basin flanks yet the basin also affects peak ground motion and estimated shaking hazard thereof outside the basin comparison with measured seismograms for one of the earthquakes shows that some of the main characteristics of the wave motion are reproduced cumulating the derived seismic intensities from the three modelled earthquake scenarios leads to a predominantly basin correlated intensity distribution for our study area

the distribution of topside spread f from in situ measurements by defense meteorological satellite program f2 and f4 on the basis of 331 equatorial passes of two defense meteorological satellite program satellites at 840 km we have determined that two distinct types of topside ion depletions occur in the evening sector during equinoctial periods first during the early evening 1854 lt a smooth type of depletion occurs with over 80 probability of observation per pass this feature is aligned parallel to the magnetic equator and is probably related to the equatorial fountain effect and general f region dynamics second we have seen irregular depletions later in the evening 1936 2154 hours which are the topside signatures of spread f their total probability of occurrence per pass increases from 20 at 1936 hours to 60 at 2154 hours a statistical study of the entire data set has shown that spread f depletions occur only when the topside ion density surpasses a seasonally controlled threshold therefore longitudinal and local time variations of topside ion density are reflected in similar variations in the occurrence probability of spread f as reported both here and earlier a detection model including orbit feature intersection geometry the above mentioned threshold and poisson statistics has been empirically verified

multi textured garnets from a single growth event an example from northern norway textural relationships between porphyroblasts of biotite and garnet in metasediments in the nordkinn peninsula area of the finnmarkian caledonides of north norway are apparently complex there is evidence for two textural zones in both mineral phases and superficially the development of these appears to have overlapped at least in part in time and space this apparently complex porphyroblast growth history can be considerably simplified if only one period of garnet growth occurred and if different inclusion fabrics developed where garnet replaced biotite porphyroblasts and where it overgrew the matrix foliation the possibility that porphyroblasts with textural evidence for multiphase growth histories actually grew during a single crystallization event is of importance in the interpretation and elucidation of tectonometamorphic relationships