contrasting styles of welding observed in the proximal askja 1875 eruption deposits i regional welding abstract as an alternative to classical welding models of fall deposits due to the progressive accumulation of hot tephra which then weld we describe here welded deposits on the northern 1875 caldera rim of askja volcano that have welded due to the influence of hot discrete spatter bombs impacting into and supplying heat to a halo of surrounding tephra this style of welding we term local welding in contrast to regional welding which is described elsewhere carey r j houghton b f thordarson t 2008 contrasting styles of welding observed in the proximal askja 1875 eruption deposits i regional welding j volcanol geotherm res 171 1 19 doi 10 1016 j jvolgeores 2007 11 020 locally welded deposits are associated with the rhyolitic plinian phase of the 1875 eruption of askja volcano two distinct welding units w1 and w2 are interbedded with plinian fall on the northern caldera rim and grade outwards to weakly dispersed non welded fall spatter bombs are found in both welding units but vary in their characteristic sizes and internal features in the w1 unit simple bombs with homogeneous internal characteristics up to 60 cm in diameter are found in the w2 unit large discrete spatter bombs with complex internal features range up to 9 m in diameter we describe here two case studies showing the effects of a single small spatter bombs b multiple small spatter bombs and c large discrete spatter bombs varying in size vertical and lateral profiles through welding zones reveal that the primary controls on local welding are the availability of supplied or added heat and the loading capacity of the spatter bomb local welding grades are much higher than that of regional welding as the combined effects of heat compaction and insulation can provide suitable conditions which lead to dense welding and proximal to the spatter bomb rheomorphic flowage if heating and loading exceed the critical requirement for welding porosity loss via matrix welding and vesicle collapse occurs to a point where further strain must be accommodated as shearing and ductile flowage the spatter bombs are found only within the weakly dispersed welding units and are the final erupted products of each fountaining phase their low viscosities are evident by their deformation on impact and fluidal forms and hold some important clues to eruption dynamics in the shallow conduit and vent regions

the development of the central european continental crust since the early archaean based on conventional and ion microprobe dating of up to 3 84 b y old detrital zircons abstract archaean components up to 3 84 b y old have been detected by ion microprobe dating of zircon from various sediments and metasediments of the european hercynides moldanubian of northeastern bavaria and the massif central the early archaean age of 3 84 b y was obtained within the euhedral core of a detrital grain from a moldanubian paragneiss the same detrital zircon grain reveals at least three metamorphic overprints at 2 59 b y b p 1 94 b y b p and 460 m y b p and at least two cycles of mechanical abrasion during surface recycling in the early proterozoic and after the pan african cycle it is thus the crystal with the most complex geological history ever detected further archaean ages for the crystallization of primary magmatic zircons probably in the course of continental crust formation in the first cycle provenances of the two studied areas were found at 3 15 2 9 2 76 and 2 65 b y b p and in a few cases between 2 6 and 2 5 b y b p early proterozoic crust forming events between about 1 75 and 2 15 b y b p play an important role especially for the sediments and metasediments of the montagne noire at the southern rim of the massif central middle and late proterozoic ages cluster around 1 0 b y b p and 600 m y b p for all analysed samples therefore the deposition of the metasedimentary precursors took place after the pan african cycle which is in line with the rb sr whole rock systematics of central european metasediments the ages of metamorphism in the different source areas could be inferred in some cases by lower intercept ages obtained on single detrital grains the following sequence coinciding with times of magmatic events has been so far established 2 59 1 94 and 1 0 b y b p and 600 m y b p thus ion probe dating is also capable of defining secondary effects in the respective provenances which are typical for orogenic cycles the ubiquitous presence of pan african detrital zircons in european metasediments is a strong indication that the detrital material was derived from gondwana however from the presence of metamorphic units including eclogitefacies rocks which probably formed at different continental margins and at various times between about 500 m y and 330 m y ago it is probable that various gondwana derived microcontinental plates contributed to the different basin fillings the gondwana derived detritus is also supported by the observation of two periods of relative quiescence or non activity around 2 3 b y ago and especially around 1 5 b y ago which is a typical feature observed in gondwana cahen et al 1984 but not in laurasia the other possible source of the detritus the lack of zircons crystallized between 3 84 and 3 15 b y ago might have different causes thus the continental crust of the european hercynides probably developed since the early archaean and grew via many crustal accretion events to its present state

large scale experiments on the mechanics of pyroclastic flows design engineering and first results 1 a newly designed apparatus for experimental studies of pyroclastic flows consists of a cylindrical conduit that is filled with samples of natural volcanic products tephra blowing nozzles in the base plate of the conduit are connected to a volume of highly pressurized gas opening of fast solenoid valves results in impulse like coupling of the released gas to the sample the system was designed so that the range of mechanical energy transferred to the particle mass in the conduit reflects the mechanical energy observed and measured during fragmentation experiments with melts of similar composition depending on the specific mechanical energy sme of the system which results from pv m where p is gas overpressure i e pressure atmospheric v is gas volume and m is sample mass different behaviors are observed if sme 2 6 kj kg a dilute plume develops and particles are sedimented by fallout exclusively if sme 106 implying that flows are fully turbulent and that particle coupling to gas turbulence of natural pyroclastic flows is replicated by the experiments the measured shear current velocities are proportional to the impact mass flow rate i e the product of mixture density and impact velocity experimental data and grain size analysis of the produced particle deposits suggest that the scale of the experiment is large enough to reproduce the transport dynamics of natural pyroclastic flows

subcrustal lithosphere around the saxothuringian moldanubian suture zone a model derived from anisotropy of seismic wave velocities abstract we have modelled the thickness and large scale fabric of the subcrustal lithosphere from the variations of p wave delay times and the shear wave splitting observed at seismological observatories and four mobile stations in central europe the saxothuringian s lithosphere is characterized by a total thickness of 90 120 km and by a coherent fabric in its mantle part with olivine a c foliation planes dipping to the north northwest the moldanubian m lithosphere is generally thicker 120 140 km on the average and characterized by a c foliations dipping to the south the divergently dipping anisotropic structures may represent remnants of successive paleosubductions of the ancient oceanic lithosphere frozen in the subcrustal lithosphere of both units a long time before their variscan collision the deep s m contact is marked by a lithosphere thinning to about 80 90 km beneath the s m surface boundary within the subcrustal lithosphere a complex structure of the transition of both units extends to about 150 km toward the south as indicated by the anisotropic characteristics of body waves

comparative proximal features of the main plinian deposits campanian ignimbrite and pomici di base of campi flegrei and vesuvius abstract the proximal plinian fall deposits of the campanian ignimbrite ci 38 ky fedele et al 2008 and pomici di base pdb 18 ky bertagnini et al 1998 have been investigated in order to understand the contribution of each part of the plume to the proximal sedimentation following houghton et al 2004b we consider three main transport regimes jet phase producing facies fb buoyant region of the plume producing facies fa and direct lateral ejection producing facies fc as well documented in medial locations sparks et al 1992 1997 ernst et al 1996 transport regimes can develop different facies even in proximal locations according to the dynamics of the eruptive column our proximal deposits show stratification and diffuse bedding allowing us to introduce two new facies stratified fa sfa and diffuse bedded fb dbfb these facies retain the transport regime previously proposed for fa buoyant plume and fb jet phase but their lithological features are influenced by near vent depositional conditions lithology and sedimentological data grain size componentry maximum clasts suggest that most of the sedimentation occurred mainly from the buoyant plume with simultaneous contribution from the other two different dynamic regimes coarse clasts falling from the lower margins of the plume strongly affected the sedimentation of the ci proximal fall deposit with a minor contribution from lithic clasts ballistically emplaced and partial collapses of the plume forming pyroclastic density currents in contrast the pdb proximal fall deposit was strongly affected by coarse clasts emplaced directly from the vent through parabolic trajectories with very little contribution of material emplaced from the lower part of the plume these differences can be attributed to different vent conduit processes acting during the eruptions

complexities of plinian fall deposition at vent an example from the 1912 novarupta eruption alaska abstract an extremely proximal ejecta ring with exposures to within 100 m of vent was deposited during later stage plinian fall activity during the 1912 novarupta eruption in alaska one bed in the ejecta ring bed s contains predominantly andesitic clasts which serve to delineate the striking contrast in thinning rates along dispersal axis of the ejecta ring pyle bt values of 70 m bed s alone or 190 m whole ejecta ring and the coeval dacitic plinian fall deposits pyle bt values of 4 km proximal and 37 km medial distal the locally deposited andesitic and dacitic clasts of the ejecta ring are interpreted as products of an irregular collar of low fountaining ejecta partially sheathing the core of higher velocity dacitic ejecta that fed the stable converting 23 km high column the presence of such an extremely proximal accumulation of ejecta appears to be a feature common to several other historic eruptions that generated widespread fall deposits this feature in part accounts for conflicts between measured and calculated values for thickness maxima in plinian fall deposits and suggests that modifications may be required of existing models for plinian eruption columns

formation of scoria cone during explosive eruption at izu oshima volcano japan 1 scoria cones have been regarded to be formed by accumulation of ballistic bombs ejected by mild eruptions however more recent geological investigations show that some scoria cones could be formed during explosive eruptions here we demonstrate how the scoria cone of the 1986 izu oshima eruption was formed during the explosive eruption we measured particle fractionation of the cone and propose a theoretical model to explain the observation the model considers lateral transport of particles by turbulent eddies particles that reached characteristic column radius l are laterally transported to l where they starts to free fall we obtained 1 2 and 2 5 for larger and smaller particles respectively which is consistent to the observation in the model extensive fallout takes place at the base of the column where it expands rapidly we suggest that lateral particle projection and the rapid column expansion are the key processes to form the cones

large scale 3 d gravity analysis of the inhomogeneities in the european mediterranean upper mantle methods and the results of estimating the anomalies characterising the density inhomogeneities in the european mediterranean upper mantle are described these anomalies were obtained by subtracting the gravity effect of a crustal density model derived from seismic velocities from the observed gravity field averaging over an area of 1o 1o the 3 d density model of the study region comprises two regional layers of varying thickness with lateral variation of average density the sedimentary cover and the crystalline crust the average densities for model layers were evaluated by using a velocity density conversion function and taking into account sediment consolidation with depth clear correlation between residual gravity anomalies and both velocity heterogeneities and thermal regime data of the upper mantle has been revealed an agreement of positive anomalies over the alps the adriatic plate and the calabrian arc with high velocity domains in the upper mantle and reduced temperatures at the subcrustal layer are caused by lithospheric roots and thickened lithosphere below these structures gravity residual lows revealed over the western mediterranean basin and pannonian basin are in correspondence with both low velocities and high temperatures in the upper mantle these anomalies are the result of the presence of asthenosphere in shallow near moho depths below these basins

the 0 57 ma plinian eruption of the granadilla member tenerife canary islands an example of complexity in eruption dynamics and evolution the granadilla member is one of the most widely dispersed and largest volume pyroclastic units at tenerife canary islands and represents the culminating eruption to a second cycle of explosive volcanism of the las canadas edifice the member dared at 0 57 ma comprises a plinian fall deposit the granadilla pumice which is overlain by ignimbrite up to 30 m thick the granadilla pumice is up to 9 m thick approximately 10 km from sourer pyle b t value is 5 35 km and is subdivided into four fail units unit 1 is up to 1 2 m thick and is further divisible into another four pumice fall subunits based on bedding and grainsize differences unit 2 is a thin but distinctive ash layer similar to2 cm thick and its wide dispersal 550 km 2 constant thickness planar laminations and ash aggregate textures collectively indicate a phreatoplinian fall origin the lithic rich nature and abundance of unaltered lithic fragments reflect magma interaction with aquifer derived water at depth unit 3 less than or equal to1 8 m thick records a reversal to dry plinian eruptive activity unit 4 the thickest of the fall units up to 6 3 m thick records the maximum dispersal and intensity of the eruption pyle b t and b c values are 5 7 and 6 3 km respectively best illustrated by the presence of large pumice bombs up to 30 cm diameter at distances up to 20 km from vent and reverse grading of lithic and pumice clasts the widespread 500 km 2 nonwelded and pumice rich granadilla ignimbrite unit 5 records the collapse of the plinian eruption column the ignimbrite has a simple sheet like geometry but exhibits a complex internal stratigraphy the base of the ignimbrite locally cuts down through the underlying granadilla pumice removing it entirely indicating up to 9 m of erosion by the pyroclastic flows a coarse vent derived lithic breccia horizon towards the top of the ignimbrite is interpreted to record the onset of caldera collapse late in the eruption minimum volume estimates for the granadilla pumice and ignimbrite are 5 2 and 5 km 3 respectively the dispersal area deposit characteristics and exponential thickness and clast size decay relationships with isopach area 1 2 are consistent with dispersal and fallout from the umbrella region of a moderately high similar to 17 to greater than or equal to 25 km plinian column we propose that the eruption involved two vents probably aligned along a ne sw fissure within the las canadas caldera c 2000 elsevier science b v all rights reserved

a new ichnotaxon classification of large mammaliform trackways from the lower cretaceous botucatu formation parana basin brazil abstract during the early cretaceous a large area in brazil and other south american countries was covered by an extensive paleoerg field the botucatu desert the araraquara county sao paulo state brazil contains some of the most diverse ichnological assemblages in the botucatu formation mammaliform trace fossils from the botucatu formation are of great interest as they may represent the only record of lower cretaceous mammaliamorpha from brazil these trace fossils can be grouped into two distinct classes based on the dimensions of the footprints the larger morphotype is described and classified as a new ichnotaxon aracoaraichnium leonardii igen nov isp nov with a discussion of preservational features and paleoecological aspects this morphotype can be differentiated from brasilichnium leonardi 1981 by digit morphology with digits iii and iv being larger and sub equal in size the tracks are mesaxonic unlike brasilichnium which is ectaxonic and the stride is proportionally smaller suggesting a trackmaker with shorter limbs in relation to body length another characteristic that reinforces the new ichnotaxon is the larger size of the footprints of aracoaraichnium igen nov footprints representing intermediate ontogenetic stages between brasilichnium and the larger morphotype are not observed suggesting that the two track types were made by different taxa compared with others tetrapod ichnotaxa the new ichnotaxon is characterized by differences in the number and morphology of the digits track morphology the degree of heteropody and locomotor parameters tracks with good preservation quality were likely originally produced in the humid subsurface below the surficial dry sand layer tracks with smaller dimensions and trackways with the presence or absence of the manus may be due to variable degrees of impression into subsurface layers and substrate heterogeneity the aracoaraichnium igen nov trackmakers probably inhabited areas near the desert making occasional incursions into desert areas while brasilichnium trackmakers may have been mostly nocturnal residents of the desert environment

reconstruction of eruption column dynamics on the basis of grain size of tephra fall deposits 1 methods two inversion methods are developed to reconstruct eruption column dynamics from granulometric data of plinian deposits they are based on the steady tephra dispersal model from umbrella clouds which spread as gravity currents the methods provide 1 expansion rate of an umbrella cloud 2 grain size distribution at the top of the eruption column and 3 total amount of ejecta including very fine particles which are extensively dispersed in the atmosphere the first quantity is correlated to the magma discharge rate the second quantity provides information about sorting processes during column rise and hence about deceleration in the gas thrust region of the eruption column and the timing of column collapse the third quantity together with the estimated magma discharge rate provides the effective duration of the eruption the two methods are based on the same dispersal model but use different averaging combining the two methods can provide additional information about eruption dynamics such as minor flow structures of the umbrella cloud and fluctuations of eruption rate the methods are applicable to large scale eruptions where the radial expansion velocity of the umbrella cloud exceeds wind velocity the applicability of the methods is tested from the viewpoint of comparison with real time observations in the companion paper paper 2

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

spatial variations of p residuals and deep structure of the european lithosphere spatial variations of these normalized residuals as large as 2 s were derived from events in different focal regions an average residual at each station was calculated from 23 selected groups compiled from 181 events evenly distributed as to their azimuths and distances the 3 d inversion of the residuals yielded very much the same picture of the relatively high and low velocity provinces for the upper layer of the mantle as compared with the map of average residuals the map of average residuals mainly reflects variations in the thickness of the lithosphere and its thermal state regions of low velocities include the pannonian basin and central carpathians the northern apennines and the po plain as well as the rhine graben the rhenish massif and the north german polish platform high velocities are observed in the south western margin of the east european platform and in three well defined zones situated in the inner part of the western alps in the eastern part of the austrian alps and in the eastern carpathians besides the effects of inhomogeneities also anisotropic effects are anticipated from the spatial diagrams of the residuals which show a similar pattern within large tectonic provinces r

azimuthal anisotropy beneath the bohemian massif from broad band seismograms of sks waves abstract shear wave splitting in sks phases recorded by the two broad band stations khc south bohemia and ksp lower silesia is used to determine the anisotropic properties of the lithosphere beneath the marginal regions of the bohemian massif directions of fast velocity of 80 and 120 clockwise from north were obtained for khc and ksp respectively these directions are consistent with the predominantly e w direction of fast velocity found by different authors using similar techniques in some regions of western europe they disagree however with the directions found for the investigated region by other authors on the basis of teleseismic p wave traveltime residuals the value of the time delay between the two splitted shear waves is close to 1 s for both stations implying that the thickness of the anisotropic zone in the upper mantle essentially exceeds 80 km

three dimensional gravity modelling of the european mediterranean lithosphere summary residual gravity anomalies characterizing the density heterogeneities in the upper mantle of the alpine belt of western europe are determined residual anomalies were calculated on a 1 x 1 grid by subtracting the gravity effect of the density model for the earth s crust from the observed gravity field our 3 d density model consists of two regional layers of varying thicknesses with a lateral variation in average density the sedimentary cover and the crystalline crust offshore the model is supplemented by a sea water layer this 3 d density model is based on a generalized velocity model represented by structure maps of the main seismic horizons the seismic basement and the moho boundary and a map of the average p wave velocity in the consolidated crust the density distribution within the model layers was obtained using the correlation functions between p wave velocity and density for sediments sediment consolidation with depth was taken into account the gravity effect of the model approximated by parallelepipeds 1 x 1 in planar size was calculated by a program designed for solving 3 d gravity problems the program takes into account the spherical configuration of the earth this method also permits the estimation of the isostatic state of the crust a mantle origin of residual gravity anomalies is confirmed by their close correlation with upper mantle velocity heterogeneities established by both seismic tomography and thermal regime data the residual gravity field is inverted into the distribution of anomalous density within the uppermost mantle layer between the moho and a bottom level at 200 km depth the most important anomalies are the high density domains caused by the thick lithosphere of the adriatic plate and by the lithosphere roots beneath the alps and the calabrian arc negative density anomalies over the pannonian basin and the western mediterranean basins reach 0 04 to 0 05 x lo3 kg m 3 due to thermal expansion of the asthenosphere

teleseismic p residual study in the iberian peninsula abstract teleseismic p wave residuals cleared of the effects of various source regions and deep mantle paths reflect the composition and structure of the lithosphere and asthenosphere beneath seismological stations we use a method with which we compute two components of the relative residuals for each station namely a directionally independent average and azimuth incidence angle dependent terms and also the ach 3 d inversion method the representative averages show consistent variations over the iberian peninsula with a relatively steep gradient in some areas the iberian massif and the betic cordillera these changes attain values around 1 s over a distance of about 200 km the lateral variations of these residual averages are transformed into a tentative model of the lithosphere thickness a thick lithosphere is observed beneath the iberian massif the pyrenees and beneath part of the betic cordillera waves from events at different teleseismic distances and various azimuths provide consistent residual patterns and a systematic directional dependence of the relative residuals especially at stations in the betic cordillera

stratigraphy and physical parameters of the plinian phase of the campanian ignimbrite eruption the campanian ignimbrite eruption 39 ka was the most powerful eruptive event of the campi flegrei caldera southern italy this event coincided with the onset of a cold climatic phase and the paleolithic transition from neanderthals to modern humans the eruption started with a sustained column that emplaced a widespread pyroclastic fall deposit covering an area 4000 km2 within the 15 cm isopach for the first time we present the complete longitudinal variation from the coarse and 10 m thick proximal down to 15 km sequence through the well stratified pumice lapilli deposit in medial areas 30 80 km to the distal tephra hundreds to thousands of kilometers distant the plinian pumice fall deposit shows a strong lateral heterogeneity due to variations in stratification grading and abundance of components all campanian ignimbrite fall layers display plinian dispersal variation of grain size with stratigraphic height suggests that the convective plume was far from steady state initially the plume dispersed 1 3 km3 of tephra toward the ene n75 e from a height of 29 km layer a a gradual increase in intensity resulted in inverse grading of layer b column height increased from 26 to 37 km at a vertical velocity of 3 6 m s it had a main dispersal axis to the east n97 e and a secondary lobe to the southeast n137 e during this phase a maximum volume of 1 73 km3 of tephra was emplaced accessory lithics concentrated in layer c are possibly due to vent clearing after partial blockage of the vent the 33 km high column dispersed ejecta to the east n95 e with only 0 2 km3 of tephra erupted during this phase during the successive gradual decline in eruption intensity column height decreased from 38 to 32 km at a velocity of 4 2 m s a normally graded layer d with a volume of 1 km3 accumulated to the east n95 e the sustained column phase ended with a pulsating and partially collapsing column that reached 23 km in height and dispersed 1 1 km3 of a stratified and lithic rich succession layer e to the southeast n112 e if we include the distal co plinian deposit a total volume of 7 8 km3 dense rock equivalent dre of magma was released containing 0 09 km3 of accessory lithics tephra mass for the single layers is on the order of 1011 kg and the total mass is 2 1012 kg 2 1013 kg including the co plinian ash mass discharge rates ranged from 0 9 to 6 7 108 kg s the calculated magnitude of the sustained column phase is 6 3 the duration of the plinian phase of this eruption based on the ratio of two parameters erupted mass divided by discharge rate is estimated to have been 20 h including co plinian ash this study shows that plinian deposits are not always homogeneous and as for pyroclastic current deposits can show an articulate architecture only the complete reconstruction of vertical and lateral variations in components stratification and grading might provide insights into the temporal and spatial evolution of the sustained plume

seismic signature and tectonic cross section of the variscan crust in western france deep seismic reflection profiling ecors program vertical and wide angle survey coupled with field and subsurface geology are used to propose a complete nne ssw section of the variscan belt in western france from belgium to southern brittany on this 800 km long profile which probably crosses two paleozoic sutures the variscan belt appears as a broad fanlike orogen characterized by large 100 km northward and southward overthrusts with polyphase deformation and metamorphism the central part of the belt central armorican zone suffered a simpler dextral shearing parallel to the strike of the belt with only green schist metamorphism deep reflection profiling shows that all the large thrusts visible at the surface root deeply in the lower crust or even crosscut the moho in the same way all the large strike slip faults parallel to the belt appear at depth as narrow discontinuities which crosscut the whole crust and in some cases the moho the seismically well layered crust develops essentially at depth in the most deformed and metamorphic internal parts of the belt in contrast with the relatively transparent brabant foreland basement which escaped the variscan deformation the moho appears as a relatively flat boundary at an average depth of 35 km with different characters it is sharp and strongly reflective both by wide angle and vertical seismics below the internal thrust zones much less distinct in the central armorican zone and only defined by low frequency signals at wide angle below the brabant foreland all these characteristics led us to consider the layering of the lower crust and the moho itself as initially tectonometamorphic features essentially produced by shearing and crust mantle decollement during the variscan stacking of the crust by intracontinental lithospheric subduction

the decompression of volcanic jets in a crater during explosive volcanic eruptions during explosive volcanic eruptions fragmented silicic magma and volatiles exit the vent with pressures typically in the range 10 100 atm and at the speed of sound of the mixture we show that for magmatic volatile contents no in the range 0 03 no 0 06 this has the approximate value 0 95 0 05 nort 12 where r is the gas constant and t is the eruption temperature this speed is nearly independent of the vent pressure and vent radius by assuming there is negligible mixing with the air we have modelled the decompression of such jets following eruption from the vent for free decompression into the atmosphere the velocity of the decompressed jet has the approximate value 1 85 0 05 nort 12 this is nearly independent of the eruption rate for decompression into a crater the process is more complex at low eruption rates with low vent pressure the material becomes underpressured as it rises in the crater a shock then forms in the crater this recompresses the magma volatile mixture which then issues from the crater as a relatively slow subsonic jet at atmospheric pressure as the eruption rate increases such shocks move towards the top of the crater and ultimately cannot form in the crater instead the material issues from the crater as a high speed supersonic jet the upward thrust provided by the crater walls on this high pressure jet then increases the upward velocity above that of a freely decompressing jet the presence of a crater may therfore cause collapse in relatively small eruptions whereas it may promote formation of buoyant eruption columns at higher eruption rates if a crater grows through erosion during an eruption column collapse will typically ensue even if the mass flux remains steady

the timing of caldera collapse at mount katmai in response to magma withdrawal toward novarupta several thin layers of nonjuvenile lithic rich tephra from mount katmai are intercalated with 1912 plinian pumice fall deposits that originated at novarupta 10 km away demonstrating that caldera collapse at katmai and eruption at novarupta were synchronous emplaced by phreatic explosions and avalanche generated dustclouds each katmai derived layer is thickest and coarsest at the caldera rim and pinches out within 5 8 km in contrast thicknesses and clast sizes of plinian layers a g decrease radially away from novarupta the first katmai derived layer lies between novarupta derived layers b2 and b3 indicating that collapse began after release of 6 9 km of magma at novarupta the first major earthquake ms 6 5 at 2356 h on 6 june 11 hours after the eruption began may have marked the onset of collapse the katmai river landslide and several debris flow deposits are also sandwiched within the plinian deposits indicating that they too were emplaced during the eruption

the deep lithosphere in the alps a model inferred from p residuals abstract the tomographic studies of the alps and their surroundings based on the relative p residuals indicated two lithosphere roots attaining depths over 200 km separated by an upwelling of the lithosphere asthenosphere transition beneath the central part of this mountain range the directional dependence of relative p velocities indicates an anisotropic wave propagation in the subcrustal lithosphere beneath the alps and their surroundings the presented model of the deep lithosphere structure suggests several phases of the tectonic development of this region collision of a tip of the adriatic plate with europe in the eastern alps and dextral strike slip movement of the adriatic ending with underthrusting of europe beneath the western alps and counterclockwise rotation the latter contributes to a steep plunge of both plates beneath the eastern alps and to stress accumulation in the friuli region a model with delamination of the rigid upper crust and its rotation resolves some of the inconsistencies between the near surface and deep tectonics and also explains the distribution of seismicity

recently formed elastic anisotropy and petrological models for the continental subcrustal lithosphere in southern germany this paper advances new evidence for elastic anisotropy in the continental subcrustal lithosphere in southern germany the range of petrological models compatible with the observed azimuthal variation of seismic p wave velocity is explored the azimuthal distribution of amplitudes of mantle phases and the observed increase of p velocity with depth both indicate a continuation of anisotropy with depth together with an increase of preferred orientation even depletion of the upper mantle in basaltic components as suggested by mantle xenoliths from various parts of germany cannot explain the velocity depth and azimuthal amplitude observations without an increase of anisotropy with depth preferred orientation of olivine is the most likely mechanism for the observed phenomena its fast a axis at the moho level is directed towards n22 5 e the b axis is also required to be horizontal i e the b plane one of the preferred glide planes of olivine is vertical with a strike of n22 5 e therefore this preferred glide plane of olivine practically coincides with the plane of maximum horizontal shear stress deduced from fault plane solutions of earthquakes in western germany this is a strong indication that the preferred orientation of olivine is formed in the recent west european crustal stress field leaking into the upper mantle the distribution of velocities to a depth of at least 50 km requires slight horizontal rotation of the a axis with depth by 10 towards n32 e and a change in the modal composition towards a depletion increasing with depth compatible with the composition of mantle xenoliths from western germany further experiments are needed to substantiate this suggestion which could lead to a better understanding of the interaction of crustal and upper mantle stress strain fields

the plinian eruptions of 1912 at novarupta katmai national park alaska the three day eruption at novarupta in 1912 consisted of three discrete episodes episode i began with plinian dispersal of rhyolitic fallout layer a and contemporaneous emplacement of rhyolitic ignimbrites and associated proximal veneers the plinian column was sustained throughout most of the interval of ash flow generation in spite of progressive increases in the proportions of dacitic and andesitic ejecta at the expense of rhyolite accordingly plinian layer b which fell in unbroken continuity with purely rhyolitic layer a is zoned from 99 to 15 rhyolite and accumulated synchronously with emplacement of the correspondingly zoned ash flow sequence in mageik creek and the valley of ten thousand smokes vtts only the andesiterichest flow units that cap the flow sequence lack a widespread fallout equivalent indicating that ignimbrite emplacement barely outlasted the plinian phase on near vent ridges the passing ash flows left proximal ignimbrite veneers that share the compositional zonation of their valley filling equivalents but exhibit evidence for turbulent deposition and recurrent scour episode ii began after a break of a few hours and was dominated by plinian dispersal of dacitic layers c and d punctuated by minor proximal intraplinian flows and surges after another break dacitic layers f and g resulted from a third plinian episode iii intercalated with these proximally are thin intraplinian ignimbrites and several andesite rich fall flow layers both cd and fg were ejected from an inner vent 400 m wide nested within that of episode i into which the rhyolitic lava dome novarupta was still later extruded two finer grained ash layers settled from composite regional dust clouds layer e which accumulated during the d f hiatus includes a contribution from small contemporaneous ash flows and layer h settled after the main eruption was over both are distinct layers in and near the vtts but distally they merge with cd and fg respectively they are largely dacitic but include rhyolitic shards that erupted during episode i and were kept aloft by atmospheric turbulence published models yield column heights of 23 26 km for a 22 25 km for cd and 17 23 km for fg and peak mass eruption rates of 0 7 1x108 0 6 2x108 and 0 2 0 4x108 kg s 1 respectively fallout volumes adjusted to reflect calculated redistribution of rhyolitic glass shards are 8 8 km3 4 8 km3 and 3 4 km3 for episodes i ii and iii microprobe analyses of glass show that as much as 0 4 km3 of rhyolitic glass shards from eruptive episode i fell with cde and 1 1 km3 with fgh most of the rhyolitic ash in the dacitic fallout layers fell far downwind se of the vent near the rhyolite dominated ignimbrite however nearly all of layers e and h are dacitic showing that the downwind rhyolitic ash is of co plinian rather than co ignimbrite origin

continental scale rheological heterogeneities and complex intraplate tectono metamorphic patterns insights from a case study and numerical models abstract continental plates are built over long periods of time through successive extensional and compressional cycles they are therefore rheologically heterogeneous this heterogeneity should significantly influence the mechanical response of the continental lithosphere during collision processes the study of the neoproterozoic borborema shear zone system of northeast brazil highlights a systematic link between marked changes in its tectono metamorphic pattern and the pre existing structure of the plate that is characterized by juxtaposition of continental domains either comprising an old basement palaeo to eoproterozoic or accreted during an extensional event between 1 0 and 0 7 ga in neoproterozoic time when the shear zone system was developed these domains displayed different geotherms and lithospheric thicknesses and therefore contrasted rheological behaviours we use numerical models simulating the mechanical evolution of a continental plate comprising multiple thermally induced rheological heterogeneities submitted to compression to investigate how these heterogeneities may affect strain localization and the distribution of deformation regimes and vertical strain within the plate from the very beginning of the deformation weak and stiff heterogeneities induce strain localization due to a lower initial effective viscosity or to stress concentrations at their tips respectively shear zones propagate from the heterogeneities and finally coalesce forming a network of high strain zones bounding almost underformed blocks within this network shear zones transfer strain between the different heterogeneities and model boundaries the evolution of the system depends essentially on the geometrical distribution of heterogeneities and on their strength contrast relative to the surrounding lithosphere the resulting finite strain field is heterogeneous and displays rapid lateral variations in vertical and or rotational deformation such a heterogeneous strain distribution may induce contrasted magmatic metamorphic and uplift evolutions within an orogenic belt as observed in the borborema shear zone system and other collisional belts

observations of laterally inhomogeneous anisotropy in the continental lithosphere elastic anisotropy may be an important factor when seismic data are used to determine the structure composition and dynamics of the earth s interior1 2 azimuthal anisotropy has been found in the oceanic and although less definitely in the continental lithosphere from field experiments where the pn wave velocity was observed to vary with direction3 5 these studies suggest a 180 periodicity in travel time variations as the only criterion of the presence of azimuthal anisotropy this criterion however may fail to distinguish between anisotropy and lateral inhomogeneity of the isotropic medium a new method for measuring azimuthal anisotropy has been described recently6 based on the phenomenon of shear wave splitting in anisotropic media which suggests three criteria instead of one to identify azimuthal anisotropy we have now applied this method to the records of permanent seismograph stations in southern germany our results provide strong evidence for the presence of azimuthal anisotropy in the lithosphere of the region and reveal pronounced lateral variations in the parameters of anisotropy on a scale of about 200 km

sequence and eruptive style of the 1783 eruption of asama volcano central japan a case study of an andesitic explosive eruption generating fountain fed lava flow pumice fall scoria flow and forming a cone the 3 month long eruption of asama volcano in 1783 produced andesitic pumice falls pyroclastic flows lava flows and constructed a cone it is divided into six episodes on the basis of waxing and waning inferred from records made during the eruption episodes 1 to 4 were intermittent vulcanian or plinian eruptions which generated several pumice fall deposits the frequency and intensity of the eruption increased dramatically in episode 5 which started on 2 august and culminated in a final phase that began on the night of 4 august lasting for 15 h this climactic phase is further divided into two subphases the first subphase is characterized by generation of a pumice fall whereas the second one is characterized by abundant pyroclastic flows stratigraphic relationships suggest that rapid growth of a cone and the generation of lava flows occurred simultaneously with the generation of both pumice falls and pyroclastic flows the volumes of the ejecta during the first and second subphases are 0 21 km3 dre and 0 27 km3 dre respectively the proportions of the different eruptive products are lava cone pumice fall 84 11 5 in the first subphase and lava cone pyroclastic flow 42 2 56 in the second subphase the lava flows in this eruption consist of three flow units l1 l2 and l3 and they characteristically possess abundant broken phenocrysts and show extensive welding texture these features as well as ghost pyroclastic textures on the surface indicate that the lava was a fountain fed clastogenic lava a high discharge rate for the lava flow up to 106 kg s may also suggest that the lava was initially explosively ejected from the conduit the petrology of the juvenile materials indicates binary mixing of an andesitic magma and a crystal rich dacitic magma the mixing ratio changed with time the dacitic component is dominant in the pyroclasts of the first subphase of the climactic phase while the proportion of the andesitic component increases in the pyroclasts of the second subphase the compositions of the lava flows vary from one flow unit to another l1 and l3 have almost identical compositions to those of pyroclasts of the first and second subphases respectively while l2 has an intermediate composition suggesting that the pyroclasts of the first and second subphases were the source of the lava flows and were partly homogenized during flow the complex features of this eruption can be explained by rapid deposition of coarse pyroclasts near the vent and the subsequent flowage of clastogenic lavas which were accompanied by a high eruption plume generating pumice falls and or pyroclastic flows

paleomagnetic constraints on a time stratigraphic framework for the evolution of ohachidaira volcano and the summit caldera central hokkaido japan we present a revised stratigraphy of the proximal deposits around ohachidaira volcano and their paleomagnetic directions obtained from 21 sites 193 samples we identify four proximal pyroclastic members from ohachidaira volcano that were produced after the early edifice building effusive volcanism from older to younger 1 vent opening mafic pyroclastic density current pdc deposits kobachidaira ignimbrite 2 maar forming mafic tephra ring deposits mamiyadake tephra ring 3 mafic to silicic caldera forming deposits sounkyo member and 4 mafic pdc deposits kumonotaira ignimbrite well grouped paleomagnetic directions obtained from the kobachidaira ignimbrite and the sounkyo member indicate that each deposit was formed over a short time interval compared to geomagnetic secular variation that is less than a century conversely scattered paleomagnetic directions of the mamiyadake tephra ring record the secular variation of the geomagnetic field that took place over a longer time interval that is at least 750 yr probably more the kumonotaira ignimbrite which has a similar paleomagnetic direction to the underlying sounkyo member may have been produced during the sounkyo eruption from comparison between our data and the previously reported paleomagnetic directions of two petrologically distinct distal ignimbrites we conclude that the sounkyo member is a proximal correlative of the distal pyroxene rich ignimbrite and that the distal hornblende rich ignimbrite may not be of an ohachidaira origin the revised stratigraphy suggests that ohachidaira volcano is a maar caldera complex volcano and that the summit caldera is a flaring funnel formed incrementally by explosive erosion and syn eruptive collapse of the vent walls volume estimates imply that the sounkyo eruption fundamentally enlarged the vent and formed the caldera our data confirm that the comparison of paleomagnetic directions can offer a useful identification and correlation tool for the ohachidaira pyroclastic sequences

magnetotelluric and seismological determination of the lithosphere asthenosphere transition in central europe abstract we assembled all available magnetotelluric mt sounding curves that cover characteristic provinces of europe the depths of layers with increased electrical conductivities estimated from mt sounding curves by the respective authors were compared with a model of the lithosphere thickness derived from seismic p residuals regions of a relatively thin and thick lithosphere are characterized by positive and negative p residuals respectively we have found a good correspondence with both sets of results in the central part of the pannonian basin the depth of the lithosphere asthenosphere transition is estimated at 60 80 km and 100 120 km at the flanks the results for the bohemian massif show deeper levels of this transition between 100 and 200 km these depths seem to be typical of the lithosphere base beneath the variscan domain of central europe

sedimentation from turbulent jets and plumes theoretical models are developed for the sedimentation from the margins of a particle laden axisymmetric turbulent buoyant plume in a still environment and for an axisymmetric turbulent momentum jet the models assume that the mass of each individual size fraction of sediment carried in a parcel of fluid decreases exponentially with time for relatively coarse particles the fallout models predict that the sediment deposition beyond a distance r on the ground expressed in log units should decay linearly with distance away from the vent for the momentum jet and should decrease with r1 3 for the buoyant plume the exponential decay constant j is proportional to the terminal fall velocity vt of the particles in both cases and inversely proportional to the square root of the initial momentum flux m0 for the jet fallout jj vtmo 1 2 and to the third power of the initial buoyancy flux fo for the plume fallout jp vtfo 1 3 smaller particles are affected by reentrainment caused by the turbulent eddies sweeping ambient fluid back into the plume or jet and thus reincorporating some particles that were released from the flow at greater heights this is taken into account by introducing a reentrainment coefficient into the theoretical models with the assumption that the coefficient has a constant value for a plume of given strength in new experiments fallout occurs from the margins of particle laden fresh water buoyant jets and plumes in a tank of salty water and sedimentation is measured on the tank floor two experiments were weakly affected by reentrainment and show excellent agreement with the simple theory for smaller particles and increasingly buoyant plumes and strong jets particle reentrainment is important the experimental data are fitted by the new reentrainment theory confirming that values of the reentrainment coefficient are approximately constant for a given flow a settling number is defined as the ratio of the characteristic velocity of the jet or plume to the particle settling velocity for 1 reentrainment seems to reach an equilibrium state for which the reentrainment coefficient is a constant of value 0 1 for jets and 0 4 for plumes irrespective of flow strength or particle size the plume experiments indicate that the value of the reentrainment coefficient is strongly dependent on plume strength and particle size for slightly less than 1 the general principles of sedimentation from turbulent plumes and jets are applied to the fallout of pumice from volcanic eruption columns and of metalliferous particles from black smokers on the ocean floor for volcanic eruptions the results provide an explanation for the near vent overthickening of tephra fall deposits and imply that lithic and pumice fragments from small lapilli up to at least 1 m diameter blocks are efficiently reentrained into eruption columns the size of particles reentrained in hydrothermal plumes is predicted to vary from less than 100 m in weakly buoyant plumes up to over 1000 m in megaplumes

neotectonics and intraplate continental topography of the northern alpine foreland research on neotectonics and related seismicity has hitherto been mostly focused on active plate boundaries that are characterized by generally high levels of earthquake activity current seismic hazard estimates for intraplate domains are mainly based on probabilistic analyses of historical and instrumental earthquake catalogues the accuracy of such hazard estimates is limited by the fact that available catalogues are restricted to a few hundred years which on geological time scales is insignificant and not suitable for the assessment of tectonic processes controlling the observed earthquake activity more reliable hazard prediction requires access to high quality data sets covering a geologically significant time span in order to obtain a better understanding of processes controlling on going intraplate deformation the alpine orogen and the intraplate sedimentary basins and rifts in its northern foreland are associated with a much higher level of neotectonic activity than hitherto assumed seismicity and stress indicator data combined with geodetic and geomorphologic observations demonstrate that deformation of the northern alpine foreland is still on going and will continue in the future this has major implications for the assessment of natural hazards and the environmental degradation potential of this densely populated area we examine relationships between deeper lithospheric processes neotectonics and surface processes in the northern alpine foreland and their implications for tectonically induced topography for the environmental tectonics project entec the upper and lower rhine graben urg and lrg and the vienna basin vb were selected as natural laboratories the vienna basin developed during the middle miocene as a sinistral pull apart structure on top of the east alpine nappe stack whereas the upper and lower rhine grabens are typical intracontinental rifts the upper rhine graben opened during its late eocene and oligocene initial rifting phase by nearly orthogonal crustal extension whereas its neogene evolution was controlled by oblique extension seismic tomography suggests that during extension the mantle lithosphere was partially decoupled from the upper crust at the level of the lower crust however whole lithospheric folding controlled the mid miocene to pliocene uplift of the vosges black forest arch whereas thermal thinning of the mantle lithosphere above a mantle plume contributed substantially to the past and present uplift of the rhenish massif by contrast oblique crustal extension controlling the late oligocene initial subsidence stage of the lower rhine graben gave way to orthogonal extension at the transition to the neogene the entec project integrated geological geophysical geomorphologic geodetic and seismological data and developed dynamic models to quantify the societal impact of neotectonics in areas hosting major urban and industrial activity concentrations the response of europe s intraplate lithosphere to late neogene compressional stresses depends largely on its thermo mechanical structure which in turn controls vertical motions topography evolution and related surface processes

the magnitude symmetry and origin of upper mantle anisotropy based on fabric analyses of ultramafic tectonites summary seismic anisotropy within the upper mantle originates from the preferred orientation of highly anisotropic single crystals the symmetry and magnitude of anisotropy depend upon 1 the volume percentages of the minerals constituting the upper mantle 2 the degree and symmetry of preferred orientation of each mineral and 3 the alignment of the minerals crystallographic axes relative to one another the nature of upper mantle anisotropy can be examined by studying mineral orientations within ultramafic rocks which were once part of the mantle petrofabric data for olivine and pyroxene have been used to obtain velocity anisotropy patterns over large regions of ultramafic rocks from the samail ophiolite oman the troodos ophiolite cyprus the bay of islands ophiolife newfoundland the twin sisters ultramafic washington usa the dun mountain ophiolite new zealand the red hills ophiolite new zealand and the red mountain ophiolite new zealand the compressional wave anisotropy calculated for these massifs ranges from 3 to 8 per cent in excellent agreement with observed seismic anisotropy in the upper continental and oceanic mantle the symmetry varies from orthorhombic to axial with the axial symmetry axis corresponding to the olivine a axes maxima and subparallel to spreading directions in oceanic upper mantle pyroxene a b and c axes maxima generally parallel olivine b c and a axes respectively and anisotropy decreases with increasing pyroxene content shear wave splitting is predicted for all propagation directions within the upper mantle symmetry is also orthorhombic or axial with the minimum difference in velocity between the two shear waves parallel to the maximum compressional wave velocity

structural model for the saxothuringian moldanubian suture in the variscan basement of the oberpfalz northeastern bavaria f r g interpreted from geophysical data abstract the moldanubian saxothuringian boundary marks a prominent subduction zone in the internal parts of the european variscides in the oberpfalz area deep reflection seismic profiles show a high density of various reflectors mainly in the upper crust indicating a complex polyphase deformation during the collision process seismic structures and related data from surface geology suggest that the moldanubian saxothuringian collision consisted of two main phases the first phase is marked by extensive nw directed overthrusting of moldanubian onto saxothuringian crust along se dipping master decollements some of which can be traced down to the moho during an advanced stage progressive overthrusting led to the development of wedge structures associated with se directed backthrusting and backfolding in the upper structural levels subsequently some of these wedges and their related decollements were folded to form the main ne striking anticlines the first phase of crustal imbrication correlates with a regional low pressure high temperature metamorphism at about 320 ma decreasing in grade northwestward the second phase is characterized by a reorientation of the main direction of crustal shortening from nw se to sw ne which is interpreted as the result of the n directed indentation of the vindelician terrane into the moldanubian this event is recorded by conjugate systems of overthrusting and subsequent strike slip faulting in the oberpfalz and the bavarian forest and the black forest vosges area in the area of the southern german block between these basement outcrops the indentation front is marked by the arc shaped axes of gravimetric and magnetic anomalies and permo carboniferous troughs

post variscan evolution of the lithosphere in the rhine graben area constraints from subsidence modelling in the area of the cenozoic rhine rift system crustal and lithospheric thicknesses range between 24 and 35 km and 60 and 120 km respectively this rift system transects the deeply truncated variscan orogen and superimposed permo carboniferous wrench induced troughs and late permian and mesozoic thermal sag basins at the time of its westphlian consolidation the variscan orogen was probably characterized by 45 60 km deep crustal roots that were associated with its rheno hercynian saxo thuringian saxo thuringian bohemian and bohemian moldanubian sutures all of which are transected by the cenozoic rhine rift system during the stephanian early permian wrench induced disruption of the variscan orogen subducted lithospheric slabs were detached causing upwelling of hot mantle material during the resulting thermal surge partial delamination and or thermal thinning of the continental mantle lithosphere induced regional uplift at the same time the variscan orogenic roots were destroyed and crustal thicknesses reduced to 28 35 km in response to the combined effects of mantle derived melts interacting with the lower crust regional erosional unroofing of the crust and on a more local scale by its mechanical stretching towards the end of the early permian the potential temperature of the asthenosphere returned to ambient levels with this regional long term thermal subsidence of the lithosphere commenced controlling the development of a new system of late permian and mesozoic thermal sag basins however the evolution of these basins was repeatedly overprinted by minor short term subsidence accelerations that reflect the build up of far field stresses related to rifting in the tethyan and atlantic domains comparison of observed and modelled subsidence curves suggests that in the area of the rhine rift system the lithosphere had equilibrated with the asthenosphere at the end of the cretaceous at depths of 100 120 km before it became thermally destabilized again by cenozoic rifting and plume related magmatism modelled subsidence curves indicate that by the end of early permian times the thermal thickness of the remnant mantle lithosphere ranged between 10 and 50 km in areas that were later incorporated into mesozoic thermal sag basins this corresponds to mid permian thermal lithosphere thicknesses of 40 80 km the geological society of london 2004

complex proximal deposition during the plinian eruptions of 1912 at novarupta alaska proximal 3 km deposits from episodes ii and iii of the 60 h long novarupta 1912 eruption exhibit a very complex stratigraphy the result of at least four transport regimes and diverse depositional mechanisms they contrast with the relatively simple stratigraphy and inferred emplacement mechanisms for the previously documented better known medial distal fall deposits and the valley of ten thousand smokes ignimbrite the proximal products include alternations and mixtures of both locally and regionally dispersed fall ejecta and numerous thin complex deposits of pyroclastic density currents pdcs with no regional analogs the locally dispersed component of the fall deposits forms sector confined wedges of material whose thicknesses halve radially from and concentrically about the vent over distances of 100 300 m cf several kilometers for the medial distal fall deposits this locally dispersed fall material and many of the associated pdc deposits is rich in andesitic and banded pumices and richer in shallow derived wall rock lithics in comparison with the coeval medial fall units of almost entirely dacitic composition there are no marked contrasts in grain size in the near vent deposits however between locally and widely dispersed beds and all samples of the proximal fall deposits plot as a simple continuation of grain size trends for medial distal samples associated pdc deposits form a spectrum of facies from fines poor avalanched beds through thin bedded landscape mantling beds to channelized lobes of pumice block rich ignimbrite the origins of the novarupta near vent deposits are considered within a spectrum of four transport regimes 1 sustained buoyant plume 2 fountaining with co current flow 3 fountaining with counter current flow and 4 direct lateral ejection the novarupta deposits suggest a model where buoyant stable regime 1 plumes characterized most of episodes ii and iii but were accompanied by transient and variable partitioning of clasts into the other three regimes only one short period of vent blockage and cessation of the plinian plume occurred separating episodes ii and iii which was followed by a single pdc interpreted as an overpressured blast involving direct lateral ejection in contrast regimes 2 and 3 were reflected by spasmodic sedimentation from the margins of the jet and perhaps lower plume which were being strongly affected by short lived instabilities these instabilities in turn are inferred to be associated with heterogeneities in the mixture of gas and pyroclasts emerging from the vent of the parameters that control explosive eruptive behavior only such sudden and asymmetrical changes in the particle concentration could operate on time scales sufficiently short to explain the rapid changes in the proximal 1912 products

complex proximal sedimentation from plinian plumes the example of tarawera 1886 the 1886 eruption of tarawera new zealand was unusual for a plinian eruption because it involved entirely basaltic magma originated in a 17 km long fissure and produced extremely overthickened proximal deposits with a complex geometry this study focuses on an 8 km long segment cutting across mount tarawera where over 50 point source vents were active during the 5 5 h eruption a detailed characterization of the proximal deposits is developed and used to interpret the range of styles and intensities of the vents including changes with time we identify the four vents that contributed most heavily to the plinian fall and evaluate the extent to which current volcanic plume models are compatible with the depositional patterns at tarawera three proximal units are mapped that have phreatomagmatic magmatic and phreatomagmatic characteristics respectively within the magmatic proximal unit beds of like character are grouped into packages and delineated on scaled cross sections package dispersal is quantified by measuring the linear thickness half distance t1 2 in the planes of the fissure walls most packages have localized dispersals low t1 2 indicating that strombolian style activity dominated most vents the more widely dispersed packages high t1 2 reflect contributions from additional transport regimes that were more vigorous but still contributed considerable material to the proximal region we conclude that the geometry of the observed proximal deposits requires three modes of fall transport 1 fallout from the upper portions of the plinian plumes produced principally by vents in four craters 2 sedimentation from the margins of the lower portions of the plinian plumes including the jets and possibly the lower convective regions and 3 ejection by weak strombolian style explosions from vents that did not contribute significant volumes of particles to the high plume we suggest that the curvature of the velocity profile across the jet region of each plume 1 4 km height was important and that the lower velocity at the margins allowed proximal deposition of a large volume of material with a wide grain size range

volcanic facies architecture of an intra arc strike slip basin santa rita mountains southern arizona the three dimensional arrangement of volcanic deposits in strike slip basins is not only the product of volcanic processes but also of tectonic processes we use a strike slip basin within the jurassic arc of southern arizona santa rita glance conglomerate to construct a facies model for a strike slip basin dominated by volcanism this model is applicable to releasing bend strike slip basins bounded on one side by a curved and dipping strike slip fault and on the other by curved normal faults numerous very deep unconformities are formed during localized uplift in the basin as it passes through smaller restraining bends along the strike slip fault in our facies model the basin fill thins and volcanism decreases markedly away from the master strike slip fault deep end where subsidence is greatest toward the basin bounding normal faults shallow end talus cone alluvial fan deposits are largely restricted to the master fault proximal deep end of the basin volcanic centers are sited along the master fault and along splays of it within the master fault proximal deep end of the basin to a lesser degree volcanic centers also form along the curved faults that form structural highs between sub basins and those that bound the distal ends of the basin abundant volcanism along the master fault and its splays kept the deep master fault proximal end of the basin overfilled so that it could not provide accommodation for reworked tuffs and extrabasinally sourced ignimbrites that dominate the shallow underfilled end of the basin this pattern of basin fill contrasts markedly with that of nonvolcanic strike slip basins on transform margins where clastic sedimentation commonly cannot keep pace with subsidence in the master fault proximal end volcanic and subvolcanic rocks in the strike slip basin largely record polygenetic explosive and effusive small volume eruptions from many vents in the complexly faulted basin referred to here as multi vent complexes multi vent complexes like these reflect proximity to a continuously active fault zone where numerous strands of the fault frequently plumb small batches of magma to the surface releasing bend extension promotes small multivent styles of volcanism in preference to caldera collapse which is more likely to form at releasing step overs along a strike slip fault

investigation of inhomogeneities and anisotropy in the crust and upper mantle of central europe by means of teleseismic p waves abstract travel time residuals from global samples as well as azimuth and slowness deviations of teleseismic p wave arrivals have been analysed both at the individual seismic stations brg cll mox and pru and using the g d r station network the main results of the analysis are as follows 1 1 azimuth and incidence angle deviations of short period p waves have been observed at individual stations by means of three component measurements their transformations into the slowness space reveal a mislocation pattern at all stations which suggests the superimposition of regional and strong local effects on wave propagation 2 2 the mean station residuals as well as the azimuth dependence of the residuals with a period of 2 indicate a rising of the upper mantle discontinuities to the north of central europe to the east european platform 3 3 this general trend is confirmed by the mislocation patterns observed at various subnetworks of the telemetric system of seismic stations of the g d r the refined model assumes a dipping of flat discontinuities or isotachs in the upper mantle down to the 20 discontinuity with a dip angle of about 11 2 north of the network centre and a zero dip south of it the dip direction is 192 5 4 4 fourier analysis of the azimuth dependence of travel time residuals revealed almost the same phase of the second azimuthal term at all individual stations this fact could be interpreted in terms of an anisotropic layer of some 200 km thickness in the upper mantle assuming a coefficient of anisotropy of 6 the azimuth of maximum velocity is 10 180 and agrees well with the results derived by bamford 1977 from pn wave measurements

azimuthal anisotropy in the earth from observations of sks at geoscope and nars broadband stations abstract we have analyzed observations of low frequency sks waves recorded on horizontal components at several broadband stations of the geoscope and nars arrays splitting of sks is consistently observed and in good agreement with a hypothesis of azimuthal anisotropy due to transverse anisotropy with a horizontal axis in the upper mantle beneath the receivers we have designed an inversion method which takes advantage of observations made simultaneously at different azimuths and which permits us to obtain estimates of the direction of fast axis of anisotropy as well as the time delay between the orthogonal quasi shear waves in general the directions of fast velocity obtained both for stations around the atlantic and around the pacific appear to be related to directions of past and present plate motions

3 d velocity structure beneath france in different frequency bands abstract the 3 d velocity structure beneath france is investigated by using a method based upon teleseismic waveform analysis and a block inversion technique in this method the p wave travel time is computed exactly in cach block for a spherical earth model and the p wave arrival times are obtained by cross correlating the waveforms observed in 26 stations of the ldg network one image is obtained directly from the observed signals the other two are obtained from low pass filtered waveforms with 0 5 and 0 25 hz cut off frequencies the results show that the 3 d velocity image depends weakly but significantly on the cut off frequency of the low pass filter in addition to possible changes in the signal to noise ratio this may indicate a dependence of the tomographic images on the seismic wavelength the best fit to the data is obtained from the 0 5 hz image the main features of this image are a clear indication of a lithospheric root beneath switzerland a general large scale w e variation of velocity within the lithosphere and a diffuse low velocity area beneath the french massif central and the western part of the alps in the 100 250 km layer

the variscan belt in central europe main structures geodynamic implications open questions abstract the variscan belt of europe originated from the confrontation of northern europe and gondwana with intervening pre variscan blocks cadomian and older armorica tepla barrandean moravo silesian though a strike slip component cannot be excluded geological evidence suggests a subduction collision process newly discovered features include basaltic rocks with morb affinities high pressure metamorphic rocks trench deposits and large scale allochthonism which also affects the pre variscan basement and has often led to an inversion of the metamorphic isogrades large scale thrusting is evident at all crustal levels and is also observable by geophysical methods the structure of the variscan crust is best described as horizontal tectonic layering late ordovician through carboniferous convergence closed one rhenohercynian and one saxo thuringian basin to the north and at least one mediterranean basin to the south of the pre variscan blocks subduction occurred from the north as well as from the south down under the dorsal core region the exact timing and the driving mechanism of this bilateral activity remains a problem likewise uncertain are the exact limination of the pre variscan blocks and the existence and width of oceanic areas in the saxothuringian zone and in the south facing part of the moldanubian zone there is good evidence of early palaeozoic rifting and of late ordovician through carboniferous plate convergence palaeomagnetic and palaeoclimatic constraints however suggest only a limited extent of oceanic basins in these areas while they appear to allow a wider ocean at the rhenohercynian saxothuringian boundary which is relatively unobtrusive from the geological point of view research during the past decade has produced a wealth of information on the variscan fold belt in europe the resulting geodynamic models however are extremely diverging evidently it is not the time yet for definitive statements the present paper intends to review the state of knowledge to deduce such basic items of a geodynamic model as appear reasonably well documented and to point out the most urgent open questions stress will be laid on central europe which offers a complete cross section through the northern flank of the variscan belt and where we have carried out most of our studies during the last years

the arce tephra two subsequent paroxysmal plinian eruptions from coatepeque caldera el salvador abstract the coatepeque volcanic complex in el salvador produced at least four plinian eruptions within the last 80 kyr the eruption of the 72 ka old arce tephra formed the coatepeque caldera and was one of the most powerful explosive eruptions in el salvador hitherto it was thought that the arce tephra had been emplaced only by one mostly plinian eruptive event that ended with the deposition of a thick ignimbrite however our stratigraphic geochemical and zircon data reveal a temporally closely spaced double eruption separated by a gap of only a couple of hundred years and we therefore distinguish lower and upper arce tephras both eruptions produced in the beginning a series of fallout units generated from fluctuating eruption columns and turning wind directions the final phase of the upper arce eruption produced surge deposits by several eruption column collapses before the terminal phase of catastrophic ignimbrite eruption and caldera collapse mapping of the individual tephra units including the occurrences of distal marine and lacustrine ash layers in the pacific ocean the guatemalan lowlands and the caribbean sea result in 25 6 km3 tephra volume areal distribution of 4 105 km2 and eruption column heights between 20 33 km for the lower arce eruption and 40 5 km3 tephra volume including 10 km3 for the ignimbrite distributed across 6 105 km2 and eruption column heights of 23 28 km for the upper arce eruption these values and the detailed eruptive sequence emphasize the great hazard potential of possible future highly explosive eruptions at coatepeque caldera especially for this kind of double eruption

upper mantle anisotropy at the transition zone of the saxothuringicum and moldanubicum in southeast germany revealed by shear wave splitting summary the main structures of the mid european lithosphere crossing europe from the iberian peninsula to the bohemian massif are predominantly formed by the variscan orogeny to investigate the anisotropy of the mantle at the transition zone between the two variscan units the saxothuringicum and the moldanubicum we carried out a field experiment in se germany in 1995 1996 23 mobile broad band stations were installed for 6 months in the vogtland oberpfalz bavarian forest area the station profile crossed the suture zone of the saxothuringicum and moldanubicum near the ktb borehole german continental deep drilling program with a mean station spacing of about 10 km we intended to obtain a high lateral resolution of the anisotropy parameters and to resolve possible changes when passing the suture zone the analysis of the observed birefringence of sks phases shows e w directions for the fast polarization therefore the directions deviate only slightly from the strike of the hercynian mountain belt and from the direction of the absolute plate motion in that region indications for the transition zone come from a rotation of the fast polarization direction from 86 13 in the northern part of the profile saxothuringicum to 110 15 in the southern part moldanubicum as well as from strong variations of the splitting parameters with respect to the azimuths of the incoming waves in the middle of the profile we interpret these variations as an expression of a complex mantle structure formed either by several anisotropic layers with inclined symmetry axes in at least one layer or by a model consisting of inhomogeneous anisotropic layers a comparison of the azimuthal variations of the splitting parameters in the middle of the profile with those observed at the grafenberg station gra1 situated in the central part of the transition zone approximately 100 km to the west shows remarkable differences which may reflect lateral variations in the direction and inclination of the symmetry axes in the transition zone even on a small scale both observations the change in the fast polarization direction from the northern to the southern part as well as the variations with respect to different azimuths in the middle of the profile suggest that the transition zone between the saxothuringicum and the moldanubicum continues down into the upper mantle

sedimentation of tephra by volcanic plumes i theory and its comparison with a study of the fogo a plinian deposit sao miguel azores sedimentation of ejecta from volcanic plumes has been studied as a function of distance from the source in the fogo a plinian deposit sao miguel azores the fogo a trachytic pumice deposit is reversely graded and can be divided into two parts on the basis of pumice colour abundance of syenite accessory lithic clasts and distribution the lower syenite poor part was dispersed to the south and was clearly influenced by wind the upper syenite rich part is coarsegrained and has a nearly symmetrical distribution around the vent elongation of isopachs to the east indicate a weak wind influence the grain size variations of lithic and crystal components in the upper coarse part were studied total accumulation and accumulation per unit area expressed in kg m2 show good fits to a gaussian function at distances greater than 7 km for grain diameters less than 2 cm these results agree with a theoretical model for a radially spreading turbulent current moving over a quiescent fluid the gaussian coefficient is shown to be a function of grain size and the flow rate of material into the umbrella region of the eruption column the coefficient is therefore also a function of column height the column height deduced from these data is 21 km which is in broad agrrement with the column height of 27 km deduced from maximum clast dispersal using the method of carey and sparks 1986 the accumulation of clasts larger than 2 cm agrees with a theory for the fallout of clasts from the margins of the ascending eruption column which treats the plume as a succession of large eddies that decrease their mass of particles as an exponential function of time calculations are also presented for the influence of the radial inflow of surrounding air into the column on the deposition of clasts these calculations constrain the wind speed during the later part of the fogo a eruption to be at most a few metres per second the study has allowed four different dynamic categories of clast behaviour to be recognised in eruption columns

europe from the bottom up a statistical examination of the central and northern european lithosphere asthenosphere boundary from comparing seismological and electromagnetic observations abstract the lithosphere asthenosphere boundary lab is a fundamental boundary in the plate tectonic paradigm it is the most pervasive on the planet yet comparatively it is one we know little about defined initially on the basis of the mechanical response of the earth to loading its usage has become ubiquitous across the geosciences but the natural differences in its definition due to differences in thermal physical and chemical parameters cause confusion to advance this debate comparisons are made both qualitatively and quantitatively between the delineation of the lab for europe based on seismological and electromagnetic observations we examine statistically using robust methods the labs derived from independent datasets and methods essentially all definitions of the lab as an impedance contrast from receiver functions slabrf a seismic anisotropy change slaba and an increase in conductivity from magnetotellurics elab are consistent with a deeper lab beneath precambrian europe and a shallower lab beneath phanerozoic europe with some exceptionally deep regions in phanerozoic europe such as the alps all three labs increase in depth significantly and rapidly at a location consistent with the surface expression of the trans european suture zone tesz which separates precambrian europe to the north and east from phanerozoic europe in the centre two of the definitions slabrf and elab are consistent for phanerozoic europe with mean values of 90 100 km compared to an average slabrf of 135 km a different two slaba and slabrf are consistent for precambrian europe with mean values of 170 180 km compared to an elab mean of 250 km the deeper elab depths for precambrian europe are more consistent with body wave and surface wave tomography models than are the slaba and slabrf ones suggesting that the lower lithosphere beneath precambrian europe between 170 to 250 km is responding to shearing on the base of the lithosphere from plate driving forces taken together the definitions provide strong constraints on the nature of the lab for example the electrical elab beneath the tesz is anomalously thick to possibly the transition zone whereas slaba and slabrf seismological definitions would place it at far shallower depths given the sensitivity of electrical conductivity to partial melt and water content the thick elab beneath the tesz excludes interpretation of the seismic lab in that location in terms of a thermal structure that would induce partial melting or of hydration

tarawera 1886 new zealand a basaltic plinian fissure eruption abstract new zealand s biggest and most destructive volcanic eruption of historical times was that of tarawera in 1886 the resulting scoria fall has a dispersal very similar in extent to that of the vesuvius a d 79 pumice fall and is one of the few known examples of a basaltic deposit of plinian type a new estimate of the volume 2 km 3 is significantly greater than previous estimates the basalt came mainly from a 7 km length of fissure and emission and exit velocity were fairly uniform along at least 4 km of it this is one of the few documented examples of a plinian eruption from a fissure vent primary welding of the scoria fall resulted where the accumulation rate exceeded about 250 mm min 1 a model of the eruption dynamics is proposed which leads to an estimate of 28 km for the height of the eruption cloud and implies a magma volatile fraction of 1 5 3 violent phreatic explosions occurred in the southwestern extension of the fissure across the rotomahana geothermal field and it is thought that some of the water responsible for the power of the plinian eruption came from this source though its amount was not sufficient to turn the eruption into a phreatoplinian one

variability of plinian fall deposits examples from okataina volcanic centre new zealand abstract plinian eruptions are intense sustained open vent volcanic outbursts that produce extensive beds of generally well sorted and generally highly vesicular pumice fallen from eruption plumes up to 55 km high their deposits tend to be almost homogeneous throughout their thickness although inverse grading commonly occurs here we detail departures from this near homogeneity that we observed among the mangaone subgroup a group of 12 plinian pumice fall deposits from okataina volcanic centre one of the dormant rhyolitic volcanoes in the taupo volcanic zone new zealand we propose that plinian eruptions may pass through seven states ranging from inception commencement of activity or renewed activity following a shutdown waxing steady discharge climax and waning leading to column collapse or shutdown decrease to zero intensity some deposits include intercalated water flushed ash rich beds having a bimodal grain size other examples of non homogeneity include phreatoplinian ashes that may alternate with the plinian pumice as though modulated by a delicate balance in water flux and still other eruptions may switch completely from dry to wet conditions when the column wanes towards the latest stages of the eruptions pink pumice occurs in some deposits and is totally absent in others we infer that it oxidized during temporary storage in or around the vent lithics are ubiquitous and concentrations of them may indicate vent wall collapses and explosive ejection of some of the resulting debris some lithic rich horizons neither coincide with apparent variations in the plinian discharge nor interrupt it as is the case with some rain flushed bimodal beds the events that produced these incongruent beds proceeded synchronously with but independent of the main plinian discharge in an isolated portion of the vent system such as a subsidiary vent other variations of density vesicularity and crystallinity among the eruption products record the pre and syn eruptive history of the magma a local inverse relationship between pumice density and crystallinity of one eruptive unit is inferred to reflect a control by crystals on vesiculation and fragmentation

lithosphere thickness in the contact zone of the moldanubicum and saxothuringicum in central europe abstract the analysis of the time residuals of p waves and their 3 d inversion show strong lateral velocity variations beneath the grf array situated above the contact zone of two important tectonic units the saxothuringicum and moldanubicum variations of teleseismic p residuals have provided data for constructing a detailed model of the lithosphere asthenosphere boundary in the region assuming the effects of lateral changes of average velocities in the subcrustal lithosphere to be much smaller than the effects of lithosphere thickness variations we relate the changes of representative average residuals in direct proportionality to changes of the lithosphere thickness under this assumption we can explain the variations of average residuals over the grf array by a relatively high increase in the thickness of the lithosphere of about 50 km from the northernmost to the southernmost stations the lithosphere asthenosphere boundary dips steeply to the sse and the isopachyte contours follow the general direction of the variscan fold belt in central europe fitting a general pattern of the lithosphere thickness derived for central europe

two dimensional anisotropic tomography of lithosphere beneath france using regional arrival times this paper presents an anisotropic tomography study beneath france travel times of pn waves were inverted in order to simultaneously retrieve lateral variations of both seismic velocity and seismic anisotropy within the subcrustal lithosphere the parameterization scheme uses a classical approach the subcrustal lithosphere is modeled using a two dimensional horizontal grid of nonoverlapping cells 0 5 0 5 each cell being characterized by an average slowness the isotropic term of slowness and an azimuthal anisotropy term the velocity and anisotropy perturbation amplitudes do not exceed 2 in the paris basin and in the aquitaine basin more significant perturbations can be observed in the tectonically active regions the images of the modeled subcrustal lithosphere emphasize the not recently reactivated areas of the hercynian range by high velocities 2 to 5 from the armorican massif to the west part of the massif central and from the northeast massif central to the vosges mountains and black forest mountains regions these areas are also characterized by an anisotropy of 2 5 with the fast directions parallel to the hercynian structures low velocities 2 to 4 are observed in the neogene volcanic areas of the massif central which confirm the results obtained from a short wavelength teleseismic tomography these low velocities are most probably caused by high temperatures another low velocity region 3 to 4 roughly follows the alpine belt and is interpreted as the image of the crustal root of the range in the inner part of the alps fast pn directions lie perpendicular to the belt with an anisotropy amplitude of 3 while in the outer part they are parallel to the range with amplitudes ranging from 3 to 5 to the east and from 2 to 3 to the west the anisotropy feature of the pyrenean range follows a simple pattern one observes high amplitudes up to 5 and a fast direction which is parallel with the strike of the range the observations show seismic anisotropy for most of the tectonically active zones across france recently formed structural units and old hercynian structures as well and the amplitudes reach the same order as the amplitudes of the velocity perturbations

possible distinguishing characteristics of very deepwater explosive and effusive silicic volcanism recent seafloor exploration has shown that volcanic hosted massive sulfides vhms occur in modern silicic calderas formed by highly explosive eruptions at substantial water depths sampling of these has so far been restricted to surficial deposits ancient analogs provide a time integrated view of the structure and fill of deepwater calderas but constraints on paleo water depths have previously been lacking the ordovician bald mountain vhms northern maine usa is unique in its degree of preservation not only permitting detailed textural and structural analysis of the enclosing volcanic rocks but also allowing fluid inclusion analysis to determine a paleo water depth of eruption of greater than 1 45 km the deposits that result from very deepwater explosive eruptions have distinctive textural characteristics recognized in other ancient examples where paleo water depths are less well constrained i propose that hydrostatic pressure suppresses the explosivity of the eruption sufficiently to retard the formation of fine ash producing ignimbrite composed largely of pumice lapilli it also inhibits exsolution of dissolved water in the magma producing fluidal rhyolite eruptions and intrusions these include silicic fire fountaining to produce proximal cones of hyalotuff or spatter accumulations and intrusions of globular peperite

post rift compressional reactivation potential of passive margins and extensional basins poly phase deformation of a compressional nature is a common feature in the post rift evolution of passive margins and rifts the compressional mode of deformation in these sedimentary basins originally formed by extension in an intraplate setting is characterized by a spectrum of spatial wavelengths spanning several tens of kilometres up to several hundreds of kilometres the actual mode of compressional deformation appears to be strongly affected by the rheological structure of the underlying lithosphere the level of the regional intraplate stress field and the geometry of the rifted basin configuration prior to late stage compressional reactivation the interplay of plumes and intraplate compressional deformation can lead to temporal transitions from basin inversion to lithospheric folding these modes of deformation lead to substantial differential vertical motions late stage anomalies in subsidence and uplift patterns the development of innovative combinations of numerical and analogue modelling techniques is the key to differentiating different modes of compressional deformation of passive margins and extensional basins the geological society of london 2008

intraplate deformation and 3d rheological structure of the rhine rift system and adjacent areas of the northern alpine foreland the lithosphere of the northern alpine foreland has undergone a polyphase evolution during which interacting stress induced intraplate deformation and upper mantle thermal perturbations controlled folding of the thermally weakened lithosphere in this paper we address relationships among deeper lithospheric processes neotectonics and surface processes in the northern alpine foreland with special emphasis on tectonically induced topography we focus on lithosphere memory and neotectonics paying special attention to the thermo mechanical structure of the rhine graben system and adjacent areas of the northern alpine foreland lithosphere we discuss implications for mechanisms of large scale intraplate deformation and links with surface processes and topography evolution

the lithosphere in central europe seismological and petrological aspects abstract the lithosphere thickness in the variscan belt of central europe varies between about 60 and 150 km with typical values of 100 120 km our estimates derived from directionally independent representative p wave residuals are in good agreement with magnetotelluric determinations of a layer with increased conductivity in the upper mantle the large scale anisotropies of the subcrustal lithosphere beneath four seismological stations determined from spatial variations of relative p residuals vary between 6 5 and 15 2 for p velocities the s wave anisotropies determined from sks polarizations vary between 2 2 and 6 7 these values are in reasonable agreement with the anisotropies of peridotites determined in laboratory systematic spatial variations of the directional terms of relative residuals in dependence on azimuths and incidence angles suggest the existence of large dipping anisotropic structures in the subcrustal lithosphere the residual patterns at most stations in the saxothuringicum rhenohercynicum and in the massif central imply northwesterly orientated dips of the anisotropic structures while stations in the moldanubicum the alpine foredeep and most of the alps north of the insubric line suggest southeasterly orientated dips in our interpretation the dipping anisotropic structures may represent paleosubductions which retain olivine preferred orientations originating from an ancient oceanic lithosphere the variscides of central europe may thus represent a collision zone characterized by two systems of paleosubductions divergent relative to the suture between the moldanubicum and the saxothuringicum

anisotropy and p wave tomography a new approach for inverting teleseismic data from a dense array of stations summary a new formulation is given for inverting teleseismic p wave residuals in terms of both 3 d variations of seismic velocity and anisotropy of the subcrustal lithosphere two restrictive assumptions are made on the anisotropic elastic tensor to reduce the number of model parameters first the upper mantle anisotropy is modelled by a preferred orientation of olivine crystals with b and c axes randomly distributed around the a axis and second the elastic properties of polycrystalline aggregates are computed according to the voigt averaging rule the latter assumption allows us to link linearly the observed p wave residuals to the proportion of oriented crystals in a realistic polycrystalline assemblage in the inversion process the orientation of the symmetry axis is fixed either by a trial procedure or by using a priori hypotheses from independent data a linear inversion scheme is then applied to the data to retrieve the 3 d variations of two scalar parameters giving the isotropic velocity perturbation and the amount of anisotropy the inversion algorithm is tested for different source receiver configurations using several idealistic ray geometries it is concluded that the teleseismic p wave residuals could potentially carry enough information for retrieving both the 3 d isotropic velocity variations and the amount of anisotropy however from a more practical point of view by looking at the distributions of rays for two recent tomographic experiments in the southern rhine graben area and in the pyrenees it is concluded that the distributions of rays in these experiments do not fulfil the necessary requirements for retrieving reliable information about the lithospheric anisotropy additional data are thus needed to constrain the anisotropic model if the symmetry axis is set as horizontal the inversion of the p wave residual of the pyrenees leads to an east west fast p wave velocity orientation the resulting anisotropy is compatible with sks observations made in the pyrenees whatever the anisotropy is the numerical tests performed with the actual ray configurations show the robustness of the isotropic components in the inverted model a long wavelength anisotropy in the lithosphere if present should not drastically alter the isotropic 3 d velocity distributions that are obtained from classical methods of teleseismic tomography