alternating field characteristics of pseudo single domain 2 14 μm and multidomain magnetite abstract we report normalized af demagnetization curves of anhysteretic remanences arm s produced by 1 10 and 40 oe steady fields and of saturation isothermal remanence irm s in a suite of dispersed unannealed magnetite powders with median sizes of 2 4 6 10 and 14 m pseudo single domain or psd size range and 100 m multidomain or md size interpreted in the light of the domain structure test first proposed by lowrie and fuller 12 the relative stability trend of curves for the 2 m sample is of single domain sd type the 1 oe arm being most resistant to demagnetization followed by the 10 oe and 40 oe arm s and irm s for the 100 m sample the trend is exactly reversed and is of md type in the 4 14 m samples hitherto undescribed transitional trends between sd type and md type occur at 6 m 1 oe 10 oe and 40 oe arm s preserve an sd type trend but for all af s 75 oe irm s is more resistant than any of these remanences at 10 m this trend is unmistakable and only at 14 m do the 1 oe 10 oe and 40 oe arm curves merge we conclude 1 that the lowrie fuller test distinguishes between small md grains enhanced by psd remanence and large md grains lacking psd remanence rather than between sd and md structures per se and 2 that in the psd transition region from 6 to 14 m in magnetite irm s changes over to md type relative stability around 6 m whereas 10 oe and 40 oe arm s achieve an md type trend around 14 m in accord with the predicted field dependence of the psd threshold size our theoretical interpretation assumes that the intrinsic internal field coercive force spectra of weak field and strong field remanences are identical but that the observed external field spectrum is shifted to lower fields as a result of the internal demagnetizing field nj r of the remanence j r the effect is slight for weak field j r s but substantial for irm s since all coercivities high as well as low are shifted the result of the lowrie fuller test is determined simply by the shape of the intrinsic coercivity spectrum or the corresponding af demagnetization curve depending on the model of self demagnetization used either subexponential or sublinear af decay curves of weak field remanence will automatically lead to an md type trend whereas by either model the decay curves that characterize sd and psd remanences decaying slowly initially and then more rapidly will always produce and sd type trend

inferring domain state from magnetic hysteresis in high coercivity dolerites bearing magnetite with ilmenite lamellae abstract hysteresis loops were measured for 16 dolerite samples from separate precambrian dykes whose remanence is probably primary remanence is carried by grains of magnetite subdivided into fine particles usually by ilmenite lamellae as seems common in mafic igneous rocks of high coercivity coercive force h c ranges from 9 to 40 10 3 a m 110 500 oe the ratio j rs j s of saturation remanence to saturation magnetization ranges from 0 10 to 0 45 j rs j s varies in approximate proportion to h c with a constant of proportionality appropriate for pseudo single domain magnetite with one or two domain walls per particle a cooling cycle to 77k causes large 40 on average demagnetization of j rs in most samples supporting the dominance of pseudo single domain magnetite most samples also show a large 29 on average decrease in h c on cooling to 140k suggesting magnetostrictive control of h c perhaps through internal stresses opposing domain wall motion only the three dolerites with h c greater than 30 10 3 a m 380 oe show little change in h c on cooling suggesting dominance by single domain particles with shape anisotropy in magnetite grains subdivided into single domain particles by ilmenite lamellae magnetic interaction may lower j rs j s from the expected 0 5 some theories 1 2 suggests that this is due to a self demagnetizing field from magnetic poles on the surface of each grain of magnetite subdivided by ilmenite and should be corrected for another theory 3 suggests that this correction is not necessary because the self demagnetizing field is already approximately cancelled due to magnetic poles inside each subdivided grain at the ends of magnetite particles the latter suggestion is favoured by our three highest h c dolerites whose j rs j s averages 0 42 0 04 before and 0 66 0 06 after correction for the self demagnetizing field from poles on the surface of magnetite ilmenite grains applying this correction to our other dolerites usually raises j rs j s significantly above 0 5 which is unreasonable for pseudo single domain magnetite hence correcting for self demagnetizing fields from poles on the surface of magnetite ilmenite grains in rocks is not recommended whatever the domain state

a new rock magnetic approach to selecting sediments for geomagnetic paleointensity studies application to paleointensity for the last 4000 years the hypothesis that the ratio of detrital remanent magnetization to anhysteretic remanent magnetization drm arm for sediment samples is a measure of relative geomagnetic paleointensity is critically evaluated by two distinct approaches one approach is a detailed rock magnetic examination of the implicit assumptions of the drm arm method and the construction of a selection process by which to identify sediments that conform to requirements satisfying these assumptions sediments are uniform with respect to drm arm ratio if they contain magnetite in the 1 15 ym particle size range as the predominant magnetic mineral and have variations in magnetite content of less than 20 30 times the minimum concentration the drm arm ratios of these sediments should provide estimates of relative geomagnetic paleointensity relative particle size variations in magnetite are detected with a plot of anhysteretic susceptibility xarm versus low field susceptibility x and the size range 1 15 m is approximately identified by high field hysteresis parameters a rock magnetic evaluation of leboeuf lake sediments with these techniques indicates that these sediments are suitable for a relative plaeointensity study the second approach to evaluating the drm arm ratio as a measure of relative paleointensity is direct comparison with absolute paleointensity data a comparison between the leboeuf lake estimates and thellier thellier results from the western united states supports the conclusion that suitable sediments can record geomagnetic paleointensity fluctuations

three dimensional finite difference waveform modeling of strong motions observed in the sendai basin japan we perform three dimensional 3d finite difference fd waveform modeling of strong motions in the frequency range 0 2 to 1 67 hz observed in the sendai basin japan during the japan meteorological agency magnitude m j 5 0 1998 miyagiken nanbu earthquake in a previous we estimated s wave velocity structures above the pre tertiary bedrock at six sites in the sendai basin based on array records of microtremors to interpolate these velocity structures in space we conduct single station microtremor measurements at a total of 61 locations and estimate the s wave velocity structure at each site by modeling the horizontal to vertical spectral ratio of fundamental mode rayleigh waves an initial 3d model of the basin is constructed using the velocity structures estimated from both array and single station microtremor measurements along with other information such as surface geology this model encompasses a region 33 km long 30 km wide and 19 km deep the final model is obtained through a trial and error process by fitting 3d fd synthetic waveforms to the bandpass filtered 0 2 hz to 1 67 hz displacement records 12 stations for the 1998 miyagiken nanbu earthquake we compute the synthetics using a fourth order staggered grid 3d fd method with variable grid spacing as the 3d model is modified the source parameters strike dip rake and seismic moment are estimated by a grid search method using 1d site specific models derived from the modified 3d model the observed waveforms are reproduced well at most stations by the final 3d basin model this agreement suggests the validity of the final 3d basin model for theoretical strong motion prediction of large earthquakes in the frequency range from 0 2 to 1 67 hz manuscript received 7 june 2000

assessing the ability of first order reversal curve forc diagrams to unravel complex magnetic signals 1 first order reversal curve forc diagrams for mixtures of different magnetic phases and bimodal distributions have been measured to examine the efficiency of the forc method at unraveling complex magnetic signals the forc distributions for various magnetic minerals including magnetite maghemite hematite and goethite and their linear additivity are assessed mixtures containing only hard magnetic minerals like hematite or goethite which have relatively small spontaneous magnetizations ms and large magnetocrystalline anisotropies can be adequately described by a linear addition of the two end members because there are virtually no magnetostatic interactions between the phases mixtures dominated by softer minerals like magnetite and maghemite are more susceptible to interactions and exhibit nonlinear behavior when a hard phase with low ms like hematite is mixed with a softer phase with high ms like magnetite it can still be identified using the forc technique whereas it is impossible to do so using standard magnetic hysteresis measurements when the weaker phase can be identified then weak strong mixes add linearly however beyond a certain critical concentration the mineral with high ms swamps the magnetic signal and linearity breaks down it is suggested that the forc method is highly suitable for identifying small traces of hard magnetic minerals like hematite and goethite in the presence of minerals with high ms such as magnetite

hybrid modeling of p sv seismic motion at inhomogeneous viscoelastic topographic structures a new hybrid two step method for computation of p sv seismic motion at inhomogeneous viscoelastic topographic structure is presented the method is based on a combination of the discrete wavenumber dw finite difference fd and finite element fe methods in the first step the dw method is used to calculate the source radiation and wave propagation in the background 1d medium in the second step the fd fe algorithm is used to compute the wave propagation along the topographic structure the accuracy of the method has been separately tested for inclusion of the attenuation and for inclusion of the free surface topography through numerical comparisons with analytical and independent numerical methods the method is a generalization of the hybrid dw fd method of zahradnik and moczo 1996 for localized structures with a flat free surface numerical computations for a ridge sediment valley and the ridge neighboring the sediment valley show that a ridge can considerably influence the response of the neighboring sediment valley this means that the neighboring topographic feature should be taken into account even when we are only interested in the valley response

estimates of shear wave q and κ0 for unconsolidated and semiconsolidated sediments in eastern north america measured and calculated values of the effective quality factor qef and the site attenuation parameter 0 for unconsolidated and semiconsolidated sediments in eastern north america ena indicate that the latter is strongly dependent on sediment thickness estimates of 0 for national earthquake hazard reduction program nehrp bc site profiles sediment plus hard rock in the mississippi embayment and the atlantic coastal plain were found to increase from about 9 to 31 msec for sedi ment thicknesses ranging from 116 to 600 m stochastic simulations using the 175 m thick hypothetical nehrp bc site profile used to estimate ena ground motions in the nationalseismichazardmapsbytheu s geologicalsurvey usgs indicatethat 0 20 msec provides a smaller estimate of amplification that agrees more closely with the low strain short period site coefficients in the nehrp recommended provisions for seismic regulations for new buildings and other structures nehrpprovisions than the10msecvalueusedbytheusgs alinearregressionofthe 0 estimatescompiledin this study indicates that 0 20 msec corresponds to a relatively thick bc sediment thickness of 460 116 m these same stochastic simulations indicate that the rela tivelyshallowusgssiteprofileprovidesestimatesofamplificationthataresmallerthan thelow strainlong periodsitecoefficientsinthenehrpprovisions thedependenceof bothsiteattenuationandsiteamplificationonsedimentthicknesssuggeststhattheuseof a single reference site condition for hazard mapping might not be appropriate instead theseresultsimplythateitheraregionalsetofreferencesiteprofilesshouldbedeveloped or that a more uniform site condition such as hard rock should be used to define a more stable reference site condition in ena

simulations of ground motion in the los angeles basin based upon the spectral element method we use the spectral element method to simulate ground motion generated by two recent and well recorded small earthquakes in the los angeles basin simulations are performed using a new sedimentary basin model that is constrained by hundreds of petroleum industry well logs and more than 20 000 km of seismic reflection profiles the numerical simulations account for 3d variations of seismic wave speeds and density topography and bathymetry and attenuation simulations for the 9 september 2001 m w 4 2 hollywood earthquake and the 3 september 2002 m w 4 2 yorba linda earthquake demonstrate that the combination of a detailed sedimentary basin model and an accurate numerical technique facilitates the simulation of ground motion at periods of 2 sec and longer inside the basin model and 6 sec and longer in the regional model peak ground displacement velocity and acceleration maps illustrate that significant amplification occurs in the basin

near fault earthquake ground motion simulation in the grenoble valley by a high performance spectral element code near fault effects are known to produce specific features of earthquake ground motion such as long period velocity pulses and directivity that cannot be predicted by numerical approaches involving vertical plane wave propagation in one dimensional 1d soil models that are used as a standard in engineering applica tions coupling near fault conditions with site effects induced by complex geological structures such as deep alluvial basins or steep topographic irregularities further con tributes to the complexity of earthquake ground motion and to the difficulty to provide reliable predictions without making use of large size 3d numerical simulations in this article we present a parametric study of the seismic response of the grenoble valley france due to an mw 6 seismic source at some 10 km epicentral distance from the urban area that was carried out in the framework of an international benchmark for earthquake ground motion prediction the spectral element code geoelse for seismic wave propagation analyses in 3d heterogeneous media in the linear and non linear range was used for this purpose full advantage was taken of its implementation on parallel computer architectures after introducing geoelse and its parallel per formance and after introducing some of its validation benchmarks the spatial varia bility of the seismic response of the grenoble valley is quantitatively investigated taking into account two effects i the hypocenter location and ii the nonlinear soil behavior through a nonlinear viscoelastic soil model finally numerical results are compared with available data and attenuation relationships of peak values of ground motion in the near fault region based on the results of this work the unfavorable interaction between fault rupture radiation mechanism and complex geological con ditions may give rise to large values of peak ground velocity exceeding 1 m sec even in low to moderate seismicity areas it may therefore considerably increase the level of seismic risk especially in highly populated and industrially active regions such as the alpine valleys

ground motion observations at hotel montana during the m 7 0 2010 haiti earthquake topography or soil amplification unusually severe structural damage was reported during the 2010 m 7 0 haiti earthquake in the vicinity of hotel montana located on top of a ridge in the district of petionville prompted by the observations u s geological survey seismic stations were deployed and aftershock recordings indicated ground motion amplification on the top of the hill compared to adjacent stations on reference site conditions the presence of topographic relief has been shown to significantly aggravate the consequences of strong ground motion during past events and topographic effects were brought forward to explain the observations in this paper we test the hypothesis of topographic amplification as the dominant factor that contributed to the damage concentration in the vicinity of hotel montana we initially conduct numerical simulations of the ridge seismic response assuming elastic homogeneous site conditions and show that numerical predictions of topographic amplification disagree with the field data both in amplitude and in frequency conversely while 1d ground response analyses for the site conditions at the hilltop predict amplification in the same frequency range as the field data they significantly underestimate the recorded amplitude we then conduct numerical simulations of the foothill ridge response to seismic motion while accounting for soil layering and qualitatively demonstrate that the recorded amplification is most likely attributed to coupled site topographic amplification effects namely to seismic waves trapped in the soft soil layers of the near surface amplified as a consequence of reverberations and further modified due to diffraction and scattering upon incidence on the irregular ground surface parametric investigations of the topography soil amplification coupling effects are then conducted and our results show that when accounting for a hypothetical soil bedrock interface at 100 m depth predictions are in excellent agreement with the observed motion

effects of topography on seismic wave propagation an example from northern taiwan topography influences ground motion and in general increases the amplitude of shaking at mountain tops and ridges whereas valleys have reduced ground motions as is observed from data recorded during and after real earthquakes and from numerical simulations however recent publications have focused mainly on the implications for ground motion in the mountainous regions themselves whereas the impact on surrounding low lying areas has received less attention here we develop a new spectral element mesh implementation to accommodate realistic topography as well as the complex shape of the taipei sedimentary basin which is located close to the central mountain range in northern taiwan spectral element numerical simulations indicate that high resolution topography can change peak ground velocity pgv values in mountainous areas by 50 compared to a half space response we further demonstrate that large scale topography can affect the propagation of seismic waves in nearby areas for example if a shallow earthquake occurs in the i lan region of taiwan the central mountain range will significantly scatter the surface waves and will in turn reduce the amplitude of ground motion in the taipei basin however as the hypocenter moves deeper topography scatters body waves which subsequently propagate as surface waves into the basin these waves continue to interact with the basin and the surrounding mountains finally resulting in complex amplification patterns in taipei city with an overall pgv increase of more than 50 for realistic subduction zone earthquake scenarios off the northeast coast of taiwan the effects of topography on ground motion in both the mountains and the taipei basin vary and depend on the rupture process the complex interactions that can occur between mountains and surrounding areas especially sedimentary basins illustrate the fact that topography should be taken into account when assessing seismic hazard

the effects of annealing and concentration on the hysteresis properties of magnetite around the psd md transition abstract hysteresis parameters h cr h c j rs j s and their ratios h cr h c j rs j s have been measured for a large number of accurately prepared grain size fractions of magnetite in the range between 5 and 150 m for several grain size fractions three different concentrations of magnetite are used 100 0 1 and 0 002 vol most of the measurements were repeated after annealing the specimens to 600 c for some specimens in the pseudo single psd and multidomain md range h c and h cr have been measured as functions of temperature plots of the results from h c h cr h c and j rs j s versus the grain size reveal curves with a convex and a concave part concentration and annealing affects the values of the hysteresis parameters especially for grains coarser than 25 m but the shape of the curves remains the same the inflection point from convex to concave for all curves occurs at 25 m and it appears to be independent of concentration and annealing it is therefore proposed to define the transition from psd to md as the inflection point of these curves

relationship between median destructive field and remanent coercive forces for dispersed natural magnetite titanomagnetite and hematite summary remanent acquisition curves remanent hysteresis curves and alternating field demagnetization curves were determined for a number of artificial rock specimens containing well defined grain size fractions between 5 and 250 m of natural magnetite titanomagnetite and hematite from these curves the remanent acquisition coercive force h cr the remanent coercive force hcr and the median destructive field of irm h i were determined theoretically these parameters should be the same for an assembly of non interacting homogeneously distributed randomly oriented single domain grains for a given hematite specimen h cr hcr and h i have about the same value in spite of the strong grain size dependence of these parameters for each specimen of magnetite and titanomagnetite the value of h cr is larger than hcr which again is larger than h i however the ratios h cr hcr and h i hcr appear to have a different constant value an interesting relationship which appears to hold for dispersed magnetite titanomagnetite or hematite grains between 5 and 250 m independently of grain size quantity and packing density of the magnetic material is

genesis of the assif el mal zn pb cu ag vein deposit an extension related mesozoic vein system in the high atlas of morocco structural mineralogical and geochemical evidence the assif el mal zn pb cu ag vein system located in the northern flank of the high atlas of marrakech morocco is hosted in a cambro ordovician volcaniclastic and metasedimentary sequence composed of graywacke siltstone pelite and shale interlayered with minor tuff and mudstone intrusion of synorogenic to postorogenic late hercynian peraluminous granitoids has contact metamorphosed the host rocks giving rise to a metamorphic assemblage of quartz plagioclase biotite muscovite chlorite amphibole chloritoid and garnet the assif el mal zn pb cu ag mineralization forms subvertical veins with ribbon fault breccia cockade comb and crack and seal textures two phase liquid vapor fluid inclusions that were trapped during several stages occur in quartz and sphalerite primary inclusion fluids exhibit t h mean values ranging from 104 c to 198 c final ice melting temperatures range from 8 1 c to 12 8 c corresponding to salinities of 15 wt nacl equiv halogen data suggest that the salinity of the ore fluids was largely due to evaporation of seawater late secondary fluid inclusions have either ca rich saline 26 wt nacl equiv or very dilute 3 5 wt nacl equiv compositions and homogenization temperatures ranging from 75 c to 150 c the 18o and d fluid values suggest an isotopically heterogeneous fluid source involving mixing between connate seawater and black shale derived organic waters low 13cvpdb values ranging from 7 5 to 7 7 indicate a homogeneous carbon source possibly organic matter disseminated in black shale hosting the zn pb cu ag veins the calculated 34sh2s values for reduced sulfur 22 5 to 24 3 are most likely from reduction of so4 2 in trapped seawater sulfate or evaporite in the host rocks reduction of sulfate probably occurred through thermochemical sulfate reduction in which organic matter was oxidized to produce co2 which ultimately led to precipitation of saddle dolomite with isotopically light carbon lead isotope compositions are consistent with fluid rock interaction that leached metals from the immediate cambro ordovician volcaniclastic and metasedimentary sequence or from the underlying paleo neoproterozoic crustal basement geological constraints suggest that the vein system of assif el mal formed during the jurassic opening of the central atlantic ocean

grain size dependence of initial susceptibility and saturation magnetization related parameters of four natural magnetites in the psd md range summary initial susceptibility coercive force and several types of remanent coercive forces were measured on a set of artificial rock specimens containing grain size fractions of a natural magnetite and titanomagnetite both of which are optically homogeneous and a natural titanomagnetite and titanomaghemite both of which show exsolution phenomena it was found subsequently that the optically homogeneous titanomagnetite contains some submicroscopic fe rich inclusions these inclusions are magnetically screened in coarse grains only for the lower grain sizes studied they have an appreciable influence on the data the size of the fractions varied from 5 to 250 m the parameters and several parameter ratios are plotted as a function of grain size several of these parameters can be used as mineralogical and grain size indicators the varying degree of exsolution of the minerals is reflected in the gradients of the plots from plots of initial susceptibility versus grain size it is concluded that the shape of the grains does not play a dominant role in determining the change of this parameter with grain size variation of the various parameters with grain size is explained in terms of a gradual transition from large psd grains to md grains without there being any sharp transition for titanomagnetite x 0 55 the transition takes place at grain sizes that are about 15 m larger than for magnetite

modeling strong ground motion in the wellington metropolitan area new zealand the wellington metropolitan area new zealand about 35 km by 10 km is crossed by the southernmost segment of the wellington fault striking roughly in the northeast southwest direction numerical modeling of m 6 7 earthquakes due to ruptures on this fault intended to characterize the 3d effects of the region9s main geological features on the ground motion are performed by using a finite differences scheme with staggered grid for frequencies up to 1 5 hz we consider the part of the wellington fault that crosses the wellington metropolitan region as an almost vertical strike slip fault 30 km long and with slip distribution history taken from the slip history of the 1992 m 7 3 landers california earthquake the 3d stratigraphy of the region has been built by integrating all available geological and geophysical data results of the modeling show several dominant features when the fault ruptures from south to north resonance occurs within a small area close to the harbor where the depth of the basin is largest this resonance produces a train of seismic waves traveling northward with dominant frequency of about 0 5 hz as the rupture propagates into the harbor the radiated wavefield focuses on the lower hutt valley to the north due to the presence of a ridge that rises up from the bottom of the harbor to emerge as somes island this effect considerably enhances the incident seismic energy in the valley particularly the horizontal motions further focusing occurs due to the triangular shape of the lower hutt valley whose alluvial deposits exhibit large impedance contrasts with the surrounding bedrock the combined focusing effects produce amplification factors in the valley of about 5 between 0 5 hz and 0 7 hz in wellington city the amplification factors are between 0 5 deamplification and 2 except for an area on reclaimed land in the harbor which shows an amplification factor as large as 9 after the rupture has stopped higher frequency waves between 1 and 1 2 hz appear trapped reverberating in the harbor for the remaining duration of the seismograms up to 60 sec on the other hand when the rupture is from north to south none of the focusing effects occur only the long lasting reverberations in the harbor seem a characteristic of the wave propagation common to both rupture directions nevertheless the amplification factors in this north to south scenario are about the same as for the south to north rupture online material movies of wellington fault rupture scenarios

three dimensional simulation of earthquakes on the los angeles fault system we have used a 3d finite difference method to simulate ground motion from elastodynamic propagating ruptures with constant slip on faults in the metropolitan area of los angeles california simulations are carried out for hypothetical m 6 75 earthquakes on the palos verdes and elysian park faults and for comparison an approximation to the 17 january 1994 m 6 7 northridge earthquake the dominant subsurface features of this area are the deep sedimentary los angeles basin and the smaller and shallower san fernando basin simulated ground motions are restricted to the frequency range 0 0 to 0 4 hz ground motion time histories show that in general sites associated with the largest particle velocities and cumulative kinetic energies are located 1 in the epicentral area 2 above the deepest parts of the basins and 3 near the steepest edges of the los angeles basin we find maximum particle velocities for the palos verdes elysian park and northridge simulations of 0 44 0 67 and 0 58 m sec respectively in each case both the directivity of the rupture and the lower impedance of the basins significantly amplify the ground motion although the gross radiation pattern from these ruptures is observable the 3d basin structure distorts the wave field and becomes a source for edge generated waves signal durations at some basin sites last beyond 90 sec due to love waves and refracted s waves that propagate into the sediments from the basin edges compared with the palos verdes event the durations are generally smaller for the elysian park earthquake due to a smaller amount of love waves generated at the basin edges a simple approximation to the northridge earthquake reproduces the overall spatial pattern of the long period particle velocities successfully predicts the timing of late arriving waves and matches the peak velocities with discrepancies generally less than a factor of 2 however for localized areas immediately north and south of the santa monica mountains the computed ground motion underpredicts the observed horizontal peak velocities but matches the vertical ones the pattern of simulated total cumulative kinetic energies is similar to that for the damage intensities observed near the epicenter of the northridge event while the northridge earthquake caused damage in the los angeles area the 3d simulations show that earthquakes with the same magnitude on the palos verdes or elysian park faults produce more severe ground shaking in the los angeles basin

possible mechanisms causing failure of thellier palaeointensity experiments in some basalts summary the normally magnetized zone of the jurassic lesotho basalts although providing apparently quite reliable palaeofield directions kosterov perrin 1996 shows anomalous behaviour when studied in vacuum using the thellier palaeointensity method typically the slope of the natural remanent magnetization thermoremanent magnetization nrm trm curves is very steep at intermediate temperatures 200 to 400 460 c in order to elucidate the reasons for such an anomalous behaviour six representative samples from a total of 74 studied using this method were subjected to a variety of analyses these experiments indicate that the magnetic properties are dominated by pseudo single domain psd magnetite grains some 1 mm in size resulting from high temperature oxidation of titanomagnetite laboratory heatings in vacuum up to the curie point do not change significantly the roomtemperature hysteresis characteristics or the initial susceptibility k similarly the k t curves in vacuum are with a single exception rather reproducible since the laboratory trms yield almost ideal nrm trm plots the anomalous nrm trm plot is presumably due to some peculiarity of the natural trm the partial trm ptrm acquisition capacity in the moderate temperature range cooling from 200 to 20 c is generally very strongly reduced after heating to 270 c which indicates that some magnetic alteration has already occurred at these temperatures hysteresis measurements between room temperature and the curie temperature t c show that some small less than 10 per cent but significant irreversible changes in hysteresis characteristics also occur during heating in particular the coercive force h c0 at room temperature is typically reduced after heating at a moderate temperature 175 c but increases after treatments at 475 c and more pronouncedly at 580 c the saturation magnetization j s0 remains unchanged except for a very small decrease less than 5 per cent occurring in some samples after the two latter treatments these changes are most clearly seen on h c t j s t bilogarithmic plots which show that the moderate temperature change in coercivity can extend up to 200 250 c thus hysteresis measurements as a function of temperature over a promising tool for sample pre selection for thellier experiments alternating field demagnetization and cycling of ptrms at liquid nitrogen temperature suggest that the blocking mechanism is largely multidomain like near room temperature but becomes less so as the curie point is approached the main reason for the failure of the thellier experiments is the loss of a fraction of the nrm natural trm at temperatures apparently lower than the blocking temperatures in nature it is suggested that this anomalous behaviour results from the reorganization of the domain structure of the psd grains during heating this transformation which seems to be triggered by the coercivity decrease observed at very moderate temperatures can reduce the nrm intensity without requiring any correlated ptrm acquisition

review of the low temperature magnetic properties of magnetite from a rock magnetic perspective the low temperature magnetic properties of magnetite are reviewed and implications for rock magnetism considered the behaviour of fundamental properties of magnetite at low temperatures near the verwey transition tv are documented and attention is given to various verwey transition theories the low temperature behaviour of the magnetic energies that control domain structure is reviewed in detail for the first time in rock magnetic literature the low temperature anomaly in spontaneous magnetization ms is documented and the differences between the saturation magnetization and ms near the verwey transition are discussed it is argued that the low temperature behaviour of the magnetocrystalline anisotropy and in particular the anomaly at tv is most likely to affect multidomain remanence during low temperature cycling for multidomain crystals it is calculated that the large increase in magnetocrystalline anisotropy intensity and reduction in symmetry on cooling through tv is likely to reduce the stability of closure domains

a nodal discontinuous galerkin method for site effects assessment in viscoelastic media verification and validation in the nice basin we present a discontinuous galerkin method for site effects assessment the p sv seismic wave propagation is studied in 2 d space heterogeneous media the first order velocity stress system is obtained by assuming that the medium is linear isotropic and viscoelastic thus considering intrinsic attenuation the associated stress strain relation in the time domain being a convolution which is numerically intractable we consider the rheology of a generalized maxwell body replacing the convolution by a set of differential equations this results in a velocity stress system which contains additional equations for the anelastic functions expressing the strain history of the material our numerical method suitable for complex triangular unstructured meshes is based on centred numerical fluxes and a leap frog time discretization the method is validated through numerical simulations including comparisons with a finite difference scheme we study the influence of the geological structures of the nice basin on the surface ground motion through the comparison of 1 d and 2 d soil response in homogeneous and heterogeneous soil at last we compare numerical results with real recording data the computed multiple sediment basin response allows to reproduce the shape of the recorded amplification in the basin this highlights the importance of knowing the lithological structures of a basin layers properties and interface geometry

magnetic properties of natural goethite iii magnetic behaviour and properties of minerals originating from goethite dehydration during thermal demagnetization summary the magnetic behaviour during stepwise demagnetization of a set of artificial samples containing well defined natural goethite from five localities chemical composition crystallite size and grain size are known is reported differential scanning calorimetry measurements indicated that the goethites converted to haematite between 260 and 360 c in this temperature range a small decrease in initial susceptibility and an additional remanence decay leading toward an extra bending point in the thermal decay curve are observed because titanomagnetite or pyrrhotite are absent in the samples this extra bending point is tentatively interpreted as being due to recrystallization of the minor haematite already present in the original goethite concentrates facilitated by water made available through the goethite haematite conversion at much higher temperatures at some 600 c a self reversal of the remanence is observed in most specimens the haematite derived from the goethites between 260 and 360 c appeared to be prone to further alteration at successive higher demagnetization temperatures chemical alterations in the magnetic mineral suite starting at temperatures from 380 c upward depending on the grain size of the original goethite were inferred from an increase in initial susceptibility the susceptibility behaviour showed an appreciable variation due to the creation of varying trace amounts of magnetite which appeared to be already present after the 400 c step after the final 685 c demagnetization step the magnetic mineralogy was usually dominated by magnetite the observed variation is thought to be the result of local within specimen differences in availability of the amount and possibly also the composition of the vapour phase the vapour phase is due to chemical reactions between the matrix constituents waterglass and calcite leading to a c02 h20 vapour phase reducing capacity necessary for the magnetite formation is envisaged to be created by decomposition of trace amounts of organic matter at relatively low temperatures up to some 400 c at higher temperatures over 550 c decomposition of traces of ferrous iron bearing clayminerals presumably donates the ferrous iron differences in the magnetite haematite ratio as well as in the properties of both minerals were assessed in some detail with more or less routine rockmagnetic methods acquisition of the isothermal remanent magnetization at room temperature in fields up to 11 2mam or 14t af demagnetization and low temperature cycling of the saturation remanence this was done after the 400 c step to study the magnetic properties of the newly formed haematite and after the 685 c step to evaluate the properties of the magnetite and more evolved haematite after the 400 c step the haematite appeared to be very fine crystalline and magnetically extremely hard its saturation remanence is considerably lower than that of well crystalline haematite after the 685 c step its hardness has decreased and its saturation remanence slightly increased chemical differences between the

some aspects of source characteristics of the 19 september 1985 michoacan earthquake and ground motion amplification in and near mexico city from strong motion data abstract the fourier amplitude ratio of the 19 september m s 8 1 to the 21 september 1985 m s 7 6 michoacan earthquakes obtained from data in and near mexico city increases from about 3 5 at 0 5 hz to about 10 at 0 2 hz this increase is neither seen in the coastal data nor in the teleseismic broadband gdsn p wave spectra it is also not predicted by 2 or gusev9s scaling laws we tentatively attribute the increase at frequencies of less than 0 5 hz to a special path and or a depth of energy release effect for the 19 september earthquake the damage to mexico city is mostly related to 0 5 hz energy since at f 0 5 hz the fourier amplitude ratios in and near mexico city along the coast and at teleseismic distances are nearly equal we attribute this energy to the source characteristics of the 19 september earthquake the evidence suggests that the 19 september was about twice more energetic at f 0 5 hz than expected from scaling laws and from spectral regression of coastal earthquakes recorded in mexico city the analysis of strong motion data recorded in mexico city shows that the ground motions in the lake bed zone are amplified by 8 to 50 times with respect to a hill zone site in ciudad universitaria the frequency at which the maximum relative amplification occurs varies from site to site and lies between 0 2 and 0 7 hz the data suggest that f o 4 h where f o frequency at which maximum relative amplitude occurs and and h are the shear wave velocity and the thickness of the clay layer respectively relatively small if any nonlinear behavior of the clay is found at strains of about 0 2 per cent during the great 19 september earthquake for a given lake bed site maximum relative amplitude and f o are roughly constant independent of magnitude depth and azimuth of sources located more than about 200 km ground motion at lake bed sites in mexico city with f o 0 5 hz appear to be amplified 75 times with respect to hard rock coastal sites at equal distances from the source this is also confirmed by m l calculation of the 19 and 21 september earthquakes for the 19 and 21 september earthquakes the average values of m l at hard rock coastal sites 100 distance 250 km are 7 4 and 6 7 whereas they are 8 7 and 8 4 in the lake bed zone distance 300 km respectively

first order reversal curve forc diagrams for pseudo single domain magnetites at high temperature abstract the recently developed first order reversal curve forc technique for rapidly examining magnetic domain state has great potential for paleomagnetic and environmental magnetic investigations however there are still some gaps in the basic understanding of forc diagrams in particular the behavior of pseudo single domain psd grains and the contribution of magnetostatic interactions in this paper we address some of these problems we report the first forc diagrams measurements on narrowly sized and well characterized synthetic psd through multidomain md magnetite samples the forc diagrams evolve with grain size from single domain sd like to md like through the psd grain size range since each sample contains grains of essentially a single size individual psd grains evidently contain contributions from both sd like and md like magnetic moments in proportions that vary with grain size the evolving forc diagrams cannot be due to physical mixtures of sd and md grains of widely different sizes the forc diagrams were all asymmetric small psd samples have forc diagrams with a distinctive closed contour structure the distributions of the larger md grains display no peak and lie closer to the interaction field axis to assess the effect of magnetostatic interactions we measured forc diagrams between room temperature and the curie temperature on heating the forc distributions contract without changing shape until 500 c above this temperature the diagrams become more md like and in addition become more symmetric the temperature dependence of the interaction field parameter is proportional to that of the saturation magnetization in accordance with neel s interpretation of the preisach diagram the decrease in asymmetry with heating suggests that the origin of the asymmetry lies in magnetostatic interactions the magnetic hysteresis parameters as a function of temperature were determined from the forc curves as the grain size decreased the normalized coercive force was found to decrease more rapidly with temperature