intensity of the geomagnetic field in western europe over the past 2000 years new data from ancient french pottery 1 we studied 14 groups of french pottery fragments dated between the 4th and 16th centuries the potsherds were analyzed using the thellier and thellier 1959 method revised by coe 1967 intensity values were corrected for thermoremanent magnetization trm anisotropy and cooling rate dependence of trm acquisition we first analyzed modern ceramics produced following ancient techniques and fired in a wood burning kiln inside of which field intensity was measured the recovered mean intensity is within 3 of the expected value which proves the reliability of our experimental procedure thermal experiments carried out at rapid and slow cooling rates clearly indicate that the cooling rate correction is critical in archeointensity studies our data indicate that large variations in intensity occurred in france over the last 2000 years two relative maxima in intensity are observed one between the 8th and 10th centuries and the second between the 14th and 15th centuries similarities are observed between the archeointensity data from france and ukraine yielding some evidence for eastward drift of geomagnetic sources between western and eastern europe from a d 800 to a d 1700 we also show that the dipole moment evolution proposed by mcelhinny and senanayake 1982 and yang et al 2000 for the last two millennia is likely biased toward higher values mainly because of the absence of correction for the cooling rate dependence of trm acquisition in most published archeointensity studies we finally underline a possible relationship valid at least in western europe between changes in direction and intensity of the geomagnetic field

the magnetic properties of baked clays and their implications for past geomagnetic field intensity determinations summary burnt clays provide a vital source of information about the archaeomagnetic field but their magnetic properties and the dependency of these on thermal history are diverse complex and poorly understood here we attempt to shed light on this problem through the investigation of artificial clay samples prepared from three different clay types repeatedly heated in known magnetic field to two different temperatures 400 and 700 c combined rock magnetic and x ray analyses were carried out to obtain information about the mineralogical content and magnetic properties of the diverse raw and heated clays and also their evolution during the course of multiple heating cooling treatments the magnetic behaviour of the three clay types evolved significantly during the course of being repeatedly heated to both 400 and 700 c phyllosilicates containing iron substitutions in their matrix apparently played an important role in supplying iron oxides during the heatings and the iron oxides themselves underwent progressive oxidation the samples heated to the higher temperature exhibited more ideal magnetic behaviour but even those heated only to 400 c achieved magnetic stabilization after multiple heatings after 10 reheating treatments samples heated to both peak temperatures yielded reliable palaeointensity results and a grand mean intensity value fa 48 57 1 19 twhichdiffersbylessthan2 t orabout3percent fromtheknownintensity of the inducing field the results confirm that the thermoremanent magnetization produced as a result of multiple heatings even to moderate temperature in the antiquity can give reliable palaeointensity determination they also highlight that materials from repeatedly used baked clay structures kilns hearths etc may be far more appropriate for archaeointensity study than singly baked clay structures destruction layers floor plasters etc

direction of resolved shear stress a construction and discussion abstract a simple construction facilitates identification of the direction of resolved shear stress for andersonian conditions in which one principal axis is vertical a constructed horizontal rake guide for specific stress and strike will project perpendicularly onto any dipping plane as the direction of resolved shear stress consideration of rake guides for different strikes for each fixed stress state illustrates that tectonic regimes are identifiable by ranges but not by individual values of rake the tectonic regime parameter and the rake guide angle are useful parameters for andersonian stress

a numerical method for determining the state of stress using focal mechanisms of earthquake populations application to tibetan teleseisms and microseismicity of southern peru the numerical method described in this paper enables the study in terms of stress of the kinematics of seismic faults provided by focal mechanisms this method assumes a mean state of stress in the source region and is based on the simple mechanical model used for fault population analysis which supposes slip in the direction of the resolved shear stress acting on the fault plane the proposed algorithm first defines compressional and tensional zones resulting from superimposition of the compressional and tensional quadrants limited by the nodal planes this enables one to test the data homogeneity furthermore this restricts the space where the principal stress axes have to be searched then for each principal stress reference whose location is constrained by above confined zones the r value chosen equal to 2 1 3 1 is computed which fits the slip vector on each nodal plane this permits one to select a set of preferred seismic fault planes from a set of auxiliary planes finally a state of stress is computed from the preferred seismic fault plane set using the non linear simplex method already applied to fault populations this algorithm is constructed so as to avoid two major difficulties misleading estimation of the deviatoric stress tensor which may result from excessive emphasis by minimizing the residuals by a least squares method if some of the data are wrong and a lengthy prospection of the stress references over all the space of directions this calculation does not take into account possible changes of the strike and dip of the nodal planes however we use rotations of nodal planes in agreement with the first arrival data to test the compatibility of these data with the computed state of stress tibetan teleseisms and southern peruvian microseisms are analyzed and results are compared with kinematics of superficial recent and active faults measured in field in the same regions this suggests that major seismic events may give a good evaluation of the regional mean state of stress focal mechanisms of the small events are also modelled by a mean stress deviator but this differs significantly from the regional state of stress in southern peru deduced from quaternary faulting this may be due to imprecise location of the small events however some movements are strongly different from those predicted by the computed mean stress deviator this suggests that small fault kinematics surely depend on the regional state of stress but that local effects may control the small deformations

significance of first order faults in folding mechanically isotropic layers evidence from the sudbury basin canada abstract the sudbury basin is a non cylindrical fold basin demarcated by the layered sudbury igneous complex sic the eastern part of which is transected by prominent curved faults folding of the sic and adjacent rock units occurred in the brittle field and is peculiar due to its petrographically distinct but initially mechanically similar layers overall the layers are characterized by low levels of solid state strain raising the question how the layer contacts acquired their curvature we addressed this question by developing a g i s based workflow to analyze the orientation and slip vectors of the faults slip vectors form clusters of normal and reverse slip along a given fault the clustering is best interpreted in terms of successive slip events during folding of the sic as the faults formed most likely as planar reverse faults prior to folding of the sic they subsequently served as mechanically anisotropic elements to fold the sic the results contribute to 1 better understand the folding mechanisms of thick melt sheets in the upper crust 2 explain apparently incompatible principal strain axes during progressive deformation and 3 efficiently analyze the orientation and kinematics of fault zones close to the earth s surface

late pliocene pleistocene stress field in the teruel and jiloca grabens eastern spain contribution of a new method of stress inversion samples of non striated fracture surfaces within clastic materials of late pliocene pleistocene age from the teruel grabens eastern spain have been analysed using a stress inversion method based on observations of slip sense the results obtained at 21 sites are compared with late miocene early pliocene extensional stress tensors previously inferred from striated faults in the same area the similarity between both sets of stress states suggests that the extensional miocene pliocene stress field essentially continues with minor changes into pliocene pleistocene times the main changes involve a the dominant trend of 3 trajectories which evolve from ese to ene b the waning of the compressional component caused by europe iberia africa convergence and c the progressive trend towards a multidirectional extension regime stress deflection caused by large scale extensional faults as well as switching of 2 and 3 axes induced by fracture development are common within this stress field they produce groups of local stress ellipsoids with 3 axes orthogonal to each other and either orthogonal or parallel to the faults bounding the grabens the regional consistency of the new results gives support to the new inversion method and demonstrates its utility in research on young sedimentary rocks where gaps in palaeostress records may exist due to absence of striated faults

the tr method the use of slip preference to separate heterogeneous fault slip data in compressional stress regimes the surface rupture of the 1999 chi chi taiwan earthquake as a case study abstract synthetic contractional fault slip data have been considered in order to examine the validity of widely applied criteria such as the slip preference slip tendency kinematic p and t axes transport orientation and strain compatibility in different andersonian compressional stress regimes radial compression rc radial pure compression rc pc pure compression pc pure compression transpression pc trp and transpression trp are examined with the aid of the win tensor stress inversion software furthermore the validity of the recently proposed graphical tr method which uses the concept of slip preference for the separation of heterogeneous fault slip data is also examined for compressional stress regimes in these regimes only contractional faults can be activated and their slip preferences imply the distinction between real i e rc rc pc and pc and hybrid i e pc trp and trp stress regimes for slip tendency values larger than 0 6 the activated faults dip at angles from 10 to 50 but in the hybrid regimes faults can dip with even higher angles the application of the tr method is here refined by introducing two controlling parameters the coefficient of determination r2 of the final tensor ratio line ftrl and the normal or inverse distribution of the faults plotted within the final tensor ratio belt ftrb the application of the tr method on fault slip data of the 1999 chi chi earthquake taiwan allowed the meaningful separation of complex heterogeneous contractional fault slip data into homogeneous groups in turn this allowed the identification of different compressional stress regimes and the determination of local stress perturbations of the regional or far stress field generated by the 1999 chi chi earthquake this includes clear examples of stress permutation and stress partitioning caused by pre existing fault structures such as the n s trending chelungpu thrust and the ne sw trending shihkang shangchi fault zone

on the suitability of baked clay for archaeomagnetic studies as deduced from detailed rock magnetic studies summary extensive rock magnetic investigations have been carried out on baked clays from four kilns two from bulgaria and two from switzerland found in archaeological sites of different age knowledge of the magnetic characteristics of the grains responsible for the archaeomagnetic signal enables us to determine which baked clays have the stablest magnetization and why this is so this is important in directional studies but even more so in painstaking palaeointensity studies that require a very careful evaluation of the suitability of the burnt clay material the proposed rock magnetic experiments enable the identification of the carriers responsible for the remanence and an adequate interpretation of the experimental results connected with the palaeointensity evaluation the experimental methods employed are illustrated with the particular results obtained from each of the four kilns studied the preliminary elucidation of the magnetic mineralogy of the archaeological samples helps first by obtaining a more reliable palaeointensity result and secondly by explaining some of the discrepancies in the palaeodirectional results examples of successful and failed palaeointensity experiments are given in relation to the magnetic properties previously established for each oven the burnt clay materials in this present study satisfy the essential condition of carrying a thermoremanence in spite of that it is shown that there are many factors that can produce undesirable magnetic properties and thus restrict the suitability of these materials for archaeomagnetic analysis the most important factors influencing the magnetic behaviour during magneto diagnostic experiments are the degree of heating in antiquity the initial composition of the unbaked material and the burial conditions the large difference in heating temperatures within a particular archaeological feature is a major cause of variation in magnetic behaviour amongst individual specimens and so preventing a successful pre selection of specimens for palaeointensity experiments nevertheless the study has shown a very good coincidence between the determined rock magnetic characteristics and the success rate in palaeointensity evaluation

breddin s graph for tectonic regimes abstract a simple graphical method is proposed to infer the tectonic regime from a fault and slip data set an abacus is overlaid on a plot of the rake versus strike of the data this yields the horizontal principal stress directions and a constraint on the stress tensor aspect ratio in a manner similar to breddin s graph for two dimensional strain analysis the main requirement is that one of the principal stress directions is close to the vertical this method is illustrated on monophase synthetic and natural data but is also expected to help sort out multiphase data sets

linear and nonlinear thellier paleointensity behavior of natural minerals 1 we tested single domain sd and multidomain md theories of the acquisition and thermal demagnetization of thermoremanent magnetization trm and partial trm ptrm in thellier paleointensity determination using as samples plagioclase and mafic minerals extracted from matachewan diabase dikes susceptibility hysteresis and coercivity data indicate that the plagioclase contains mainly sd grains of magnetite while the mafic minerals clinopyroxene biotite and actinolite contain mainly md magnetite the extracted minerals were used in simulated thellier experiments with laboratory trm as a proxy for natural remanent magnetization nrm the plagioclase behaved ideally as predicted by neel sd theory giving a linear nrm ptrm arai plot with positive ptrm checks the mafic minerals behaved nonideally with strongly curved arai plots sagging below the ideal sd line in accord with observations for md magnetites and with predictions that in heating to moderate temperatures t more trm is lost than can be regained as ptrm causing convex down arai plots in experiments with ptrm parallel to nrm all ptrm tail checks were zero but ptrm checks increasingly deviated from the arai curve toward the sd line as t increased however in repeat thellier experiments ptrms at all t agreed with the original ptrms the negative ptrm checks were therefore not due to physicochemical alteration but rather to departure from initial states with different magnetic histories than those of the original ptrms the inability of ptrm checks to reliably distinguish between md behavior and irreversible alteration could lead to overestimates of paleointensity from straight line fits to the low t unaltered part of the arai curve or underestimates from fits to high t data alternating field cleaning to 15 mt before each thellier step made the arai plot only marginally less curved low temperature demagnetization ltd zero field cycling through the 120 k verwey transition hardly changed the curvature of the arai plot for ptrm parallel to nrm for ptrm perpendicular to nrm ltd led to an inflected arai curve straddling the ideal sd line data of either form would not give reliable paleointensity values no presently available pretreatment renders the paleointensity data of md grains usable sd and nearly sd grains which behave ideally in the thellier experiment remain the only useful recorders of absolute paleointensity

different mechanisms of magnetisation recorded in experimental fires archaeomagnetic implications abstract we present here the archaeomagnetic and rock magnetic results obtained from the experimental recreation of prehistoric fires on a clayish soil substratum by using a system of thermocouples that allows the control of temperatures and heat penetration with depth the magneto mineralogical transformations as well as the ability to acquire magnetic remanences are studied a detailed set of rock magnetic analyses carried out both on surface and depth with a millimetre scale resolution shows the creation of post burn magnetite over the entire surface of the hearth thus promoting a distinguishable magnetic enhancement on the basis of a detailed control of temperatures interesting differences between areas centre vs periphery were observed and two different mechanisms of magnetisation have been recorded the central area which exceeded 600 c acquired a thermal remanent magnetisation trm and the periphery which was heated up to 300 c recorded a thermo chemical tcrm remanent magnetisation the most noticeable mineralogical changes are focused to the first centimetre of the central area where single domain magnetite has been created the implications of these results for archaeomagnetic and palaeointensity studies as well as their utility for the detection of fire in archaeological sites are discussed

regional state of stress and characteristic fault kinematics instabilities shown by aftershock sequences the aftershock sequences of the 1978 thessaloniki greece and 1980 campania lucania italia earthquakes as examples abstract usual analysis of fault kinematics in terms of stress supposes that the slip occurs in the direction of the shear stress resolved on the fault plane due to an homogeneous state of stress however as a block moves this yields perturbations of the static stress conditions the resulting displacement may produce interactions of blocks and may induce complex fault motions such as those demonstrated by the aftershock sequences of the thessaloniki and campania lucania earthquakes each of which shows a main group of focal mechanisms whose normal fault motions are modelled using a stress deviator tm in agreement both with the motion of the main seismic fault and with the regional stress pattern deduced from quarternary and recent faults it is therefore considered as representative of the mean state of stress acting in the epicentral area but two other families of fault motions are also demonstrated one shows reverse motions explained by a compressional stress deviator tc the other involving normal motions is explained by a tensional stress deviator te these deviators are not representative of the mean regional state of stress the compressional 1 axis of tc and the tensional 3 axis of te are roughly orthogonal to the 3 axis of the mean state of stress tm these tc and te deviators may be deduced from the mean state of stress tm by adding respectively td1 and td2 deviators to this latter this means that on each fault plane having a reverse c or a normal e motion this motion may be deduced from the normal kinematics m it should have occurred in the mean regional state of stress tm by adding local pushes d1 and d2 respectively the deviator td2 being nearly axisymmetric around a vertical 3 axis the local reverse pushes d1 are nearly dip slip and td2 having a high angle dipping 2 axis the local pushes d2 are essentially strike slip approximated solutions of these td1 and td2 deviators have been calculated by taking tm td1 tc and tm td2 te the mean state of stress tm being divided into two parts tv and ts which respectively produce the dip slip and essentially strike slip components of the stress resolved on the fault plane a first approximation of the data shows that td1 kv tv and td2 ks ts with kv and ks equal to 2 this approximation supposes that tm tc and te are coaxial and that td1 and td2 are respectively axisymmetric around the vertical 3 axis and planar in the horizontal plane actually the data give kv 2 and ks in the order of 4 5 it is suggested that the local reverse and strike slip pushes are induced by the reaction of the rocky body surrounding small blocks moving as a consequence of a motion on a major fault particularly as there are incompatibilities of motion of adjacent small blocks however data are not sufficient to demonstrate the mechanical and geometric conditions which control the observed different behaviors of the small seismic faults numerical simulations or experiments could probably precise these conditions whatever under certain conditions the stable solution m is replaced by kinematics instabilities e and c however it is usually observed that faults studied in the field in a simple way often yield a single stress deviator this is probably due to the nature of the measured striations which are often growth fibers and oblique stylolithes resulting from creep fault motions in this case incompatibilities of block motions are probably accommodated by a pressure dissolution phenomena therefore it is suggested that the bifurcation parameter which controls the occurrence of the characteristic instabilities possibly depends on a ratio of the deformation rate versus the pressure dissolution rate of the material a question remains unanswered are these instabilities scale invariant or is there a changeover in the behavior between minor and major faults

analysis of a gradual change in stress regime example from the eastern iberian chain spain abstract the compression extension passage in the eastern iberian chain during the miocene is analyzed structural data suggest that it is a gradual change in stress regime which does not involve rotation but interchange of 1 and 2 axes one of them remaining always vertical the gradual stress evolution is interpreted by a numerical graphic method y r diagram which optimizes combinations of y azimuth of the maximum horizontal axis and r stress ratio explaining groups of fault movements the y r diagrams of some fault populations measured in the castellon region provide optimum tensors appearing within a continuous cloud of solutions from the compressional field to the extensional one movement sequences obtained from superimposed striations indicate a systematic stress change between these two regimes

a reliable absolute palaeointensity determination obtained from a non ideal recorder reliable measurements of the intensity of the palaeomagnetic field are notoriously difficult to obtain the approach generally taken is to produce multiple estimates per rock unit and assume that those which meet certain minimum standards of technical quality will combine to produce an accurate mean however here using results produced from a package of 20th century basaltic lava flows from mount etna in sicily we demonstrate that this approach can fail in this case the application of typical sets of selection criteria actually introduces bias into the mean determination that we measure we demonstrate that this is caused by two types of non ideal behaviour acting in combination the first is a result of the multidomain grains that the samples contain and the second is caused by differences in the natural and laboratory cooling rates we discuss means of avoiding these sources of error in future palaeointensity studies performed on ancient rocks we also develop a new more general reliability criterion which is effective here and which we argue should be applied wherever possible in future palaeointensity studies in conjunction with standard criteria it requires two distinct types of materials which both produce some good quality palaeointensity measurements and uses their range of overlap to constrain the true palaeointensity both the application of this criterion and general reliability considerations require that future palaeointensity studies should measure many samples per cooling unit and that these should be as diverse in terms of their rock magnetic properties and cooling histories as possible

from orientation to magnitudes in paleostress determinations using fault slip data abstract determinations of reduced stress tensors using fault slip data yield the orientation of principal stress axes and the ratio of the differences between principal stress magnitudes the use of rupture and friction laws allows determination of the two remaining unknowns that is the reconstruction of the complete stress tensor taking into account the depth of overburden brings an additional constraint the method is applied and discussed in the case of the hoover dam site western u s a where large data sets and rock mechanics information are available differences between intact sample and rock mass properties account for apparent disagreements between paleostress levels determined in similar tectonic environments pore pressure plays an important role where information about pore pressure is absent zero and hydrostatic pore pressure cases should be considered as limits

partial anhysteretic remanence and its anisotropy applications and grainsize dependence the distribution of remanence coercivities in a rock sample can be obtained by differentiating alternating field af demagnetization curves of anhysteretic remanent magnetization arm however significant errors can be introduced by grain interactions and by the noise inherent in differentiation we have found that 1 this error can be significantly reduced by measuring partial arm s parm s and 2 parm patterns show a strong empirical correlation with grain size parm s are imparted by exposing a sample to a small direct magnetic field in the presence of a large decreasing af the direct field is switched on over a specified range of af s thus magnetizing a fraction of the magnetite grains in the corresponding coercivity range we have further found in both synthetic and natural sediments that measurement of the anisotropy of parm enables us to detect the preferred orientations of distinct subpopulations of magnetite particles related to the size and shape of the grains

toward an optimal geomagnetic field intensity determination technique 1 paleointensity determinations based on double heating techniques in field zero field cooling zero field in field cooling and two in field steps with opposite laboratory fields are generally considered to be functionally interchangeable producing equally reliable paleointensity estimates to investigate this premise we have developed a simple mathematical model we find that both the zero field first and in field first methods have a strong angular dependence on the laboratory field parallel orthogonal and anti parallel while the two in field steps method is independent of the direction of the laboratory produced field contrary to common practice each method yields quite different outcomes if the condition of reciprocity of blocking and unblocking temperatures is not met even with marginal 10 tails of partial thermoremanence our calculations suggest that the zero field first method with the laboratory produced field anti parallel to the natural remanence nrm is the most robust paleointensity determination technique when the intensity of the lab induced field is smaller than ancient field however the zero field first method with the laboratory field parallel to the nrm is the optimum approach when the intensity of the lab induced field is larger than the ancient field by far the best approach however is to alternatethe infield zerofield iz steps with zerofield infield zi steps

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

favoured states of palaeostress in the earth s crust evidence from fault slip data abstract in a major survey of published palaeostress estimates obtained by the use of fault slip data over 2000 stress tensors from shallow crustal levels have been compiled the results are derived from regions where deformation is dominated by brittle processes and consist of incomplete stress tensors in which the orientations of the principal stresses 1 2 3 are known together with the stress ratio 2 3 1 3 the orientations of the stress axes display a preferred orientation with a tendency for one of the axes to be vertical this accords with anderson s assumed standard state stress configuration near to the earth s free surface although the tendency is strong there are frequent deviations from the arrangement in 25 of cases the steepest stress axis deviates by more than 25 from the vertical in undertaking studies of palaeostress it would be therefore unwise to use methods that assume a priori one vertical stress axis unless previous local results indicate this to be the case normal strike slip and thrust stress arrangements with 1 2 and 3 as the steepest stress respectively occur in the database with frequencies approximately in the ratio 2 2 1 in the compiled results the raw stress ratios which have a theoretical range from 0 to 1 show a lack of very high values and to a lesser extent very low values this suggests that triaxial stress states are more common than axial compression deviatoric stress and axial tension deviatoric stress however this relative abundance of triaxial stress states is considered to be a natural feature of a uniform distribution of stress tensors in addition there is a marked bias in the collated ratios towards values less than 0 5 and this is expressed by an overall mean of 0 39 several possible explanations for the distribution of stress ratios are discussed these explanations are related to the tendency for tectonic deformation to be of plane strain type coupled with volume change and to the fact that gravitational loading makes an important contribution to the state of stress in the crust

stress ratio determinations from striated faults a spherical plot for cases of near vertical principal stress for stress regimes with one principal axis z vertical the stress ratio is best represented by an angular function f arctan 3 z x1 x2 z 3 x1 x2 or if the larger of the horizontal principal stresses x1 and x2 is designated y by f arctan 3 z x y z 3 y x traditional palaeostress regimes normal wrench reverse represent equal angular sectors of f or f and may be subdivided on a spherical projection of f against 2y where y is the bearing of maximum horizontal stress the locus of all combinations of stress orientation and stress ratio capable of generating one datum known slip direction on a known fault plane is a great circle since tanf cos 2y 2s b 3 cosb where tanb tan cosd and s d and are the fault strike dip and striation pitch respectively stereographic construction is simple using pencil and paper and gives a visual appreciation of the definition of palaeostress states which could have generated the fault motions it facilitates better than previous methods 1 the identification of radially symmetrical stress states 2 recognition of suspect or incompatible data and 3 delimiting the palaeostress state according to sense of shear where this is known great circle and pole representations are suited to different purposes and data types for which examples are given

forty years of paleostress analysis has it attained maturity abstract powerful methods of paleostress analysis from fault slip data have been used since the 1970 s and have demonstrated their capacity for reconstructing stress fields with tectonic significance however in some cases these methods have been applied to samples that do not fulfill basic requirements or developed on the basis of unsound conceptual models most methods of fault slip are based on the wallace bott principle dynamic paradigm while others invoke the necessity of remaining within the alternative kinematic paradigm therefore inferring only finite strain or strain rate axes the scientific community shares neither standard procedures for applying these methods nor standard parameters for assessing the quality of results this indicates that paleostress analysis has not attained maturity it is necessary to see back to the conceptual and methological bases following accurate procedures of data collection using additional field observations and critically assessing the results within the tectonic setting spatial and temporal heterogeneity of stress fields over all scales makes the mean stress tensor obtained from site analysis just an abstract notion though indispensable for understanding lithosphere dynamics

slip preference on pre existing faults a guide tool for the separation of heterogeneous fault slip data in extensional stress regimes abstract synthetic fault slip data have been considered in the present paper in order to examine through a simple graphical manner the validity and use of the widely mentioned and applied criteria such as the slip preference slip tendency kinematic p and t axes transport orientation and strain compatibility the examination and description concern extensional stress regimes whose greatest principal stress axis 1 always remains in vertical position as in andersonian stress states in particular radial extension re radial pure extension re pe pure extension pe pure extension transtension pe trn and transtension trn are examined with the aid of the win tensor stress inversion software in all of these extensional stress regimes only extensional faults can be activated the lower dip angle of the reactivated faults is about 40 assuming that the coefficient of friction is no smaller than 0 6 the increase of the stress ratio and or the fault dip angle up to 70 results in the increase of the slip deviation from the normal activation based on the present examination of the slip preference and slip tendency in different extensional stress regimes a new simple and practical method is proposed herein in order to separate originally heterogeneous fault slip data into homogeneous fault groups by which different extensional stress regimes could be determined the application of the method on the already published fault slip data of lemnos island supports its validity since over 90 the resulted fault groups and stress regimes coincide to the already published ones

thellier paleointensity theory and experiments for multidomain grains 1 we extend theories of thermoremanent magnetization trm and partial trm ptrm in multidomain md grains to model thermal demagnetization and ptrm acquisition steps in thellier paleointensity determination because of the interleaving of zero field and in field heating cooling steps to increasing temperatures the initial state for any step is complex and theoretical modeling is more intricate than for ptrm production or thermal demagnetization separately at low to moderate temperature t trm lost exceeds ptrm regained causing convex down arai plots sagging below the ideal single domain sd line at moderate to high t ptrm acquisition outweighs trm loss as t approaches tcurie ptrm gain exactly equals trm loss and the arai plot becomes ideal when ptrms are produced perpendicular to the original trm and measured directly rather than by differencing field on and field off results there is less deviation from ideality at low to moderate t our theory agrees semiquantitatively with results for parallel and perpendicular ptrms for large md magnetites 135 m smaller md magnetites 6 and 20 m have less curved arai plots and the smallest magnetites 0 6 and 1 m have almost linear plots positive ptrm checks demonstrate that curved arai plots of md grains are reproducible unlike curved plots for rocks that alter physicochemically in the thellier experiment while negative ptrm tail checks indicate undemagnetized ptrm residuals low temperature demagnetization improves linearity only slightly practical applications of this work include using the predicted threshold t below which no net ptrm is produced in a parallel thellier experiment to screen data used for paleointensity fits straight line fits through low and medium t points in arai plots of md 135 m grains overestimated the paleofield by as much as 100 and for small pseudo single domain psd 0 6 and 1 m grains overestimated by about 25 however by using linear segments of medium to high t data with f values 0 5 it may be possible to obtain reasonable paleointensity estimates even for larger psd 6 and 20 m and md grains middle to high t fits for 0 6 m grains gave paleointensities within 4 of the correct value utilizing essentially the entire data set f 0 9 perpendicular data always gave superior linear fits orienting samples with their natural remanent magnetizations perpendicular to the laboratory field is therefore recommended for rocks containing psd and md grains however double heatings are preferable to single heatings because they allow ptrm tail checks to be carried out

first order symmetry of weak field partial thermoremanence in multi domain md ferromagnetic grains 2 implications for thellier type palaeointensity determination two models derived in very different ways but both incorporating the symmetry constraints outlined in the previous paper are developed for use in simulating thellier type palaeointensity experiments these are then tested against experimental data which endorse them both as powerful tools they predict that non ideal behaviour due to md grain content is sensitive not only to the protocol employed and the vector difference between the partial thermoremanent magnetisations ptrms imparted in the laboratory and the natural remanent magnetisation nrm but also to the spacing of the temperature steps and the type of ptrm imparted during the remagnetisation stages consistent with experimental studies the models predict that ptrm checks may fail despite no alteration occurring and that any double stage experimental protocol will produce non ideal results to some degree provided that md grains are present a single heating perpendicular or high angle single heating protocol is predicted to remove non ideal effects provided that the grains obey the symmetry constraints perfectly however this remains to be experimentally tested and does not allow for the use of ptrm checks five straightforward recommendations for future palaeointensity studies to follow are outlined these are designed to minimise non ideal behaviour due to md grains as far as possible while retaining the capacity to detect and reject those samples which will nonetheless produce significant errors

a simple stress inversion of fault slip data assuming andersonian stress state 1 stress inversion from fault slip data is an important modern technique for structural geologists the parameter or sigma space may be reduced from five to three dimensions if an andersonian stress state having a vertical principal direction is assumed in such a case associated fault slip data can be displayed after some transformation on a stereonet homogeneous fault slip data tend to lie in a great circle while heterogeneous data lie in no less than two great circles visual appreciation thus becomes fairly easy in particular separation of the heterogeneous fault slip data set into many homogeneous subsets the unit vectors normal to the great circles are the solutions giving the controlling reduced stress vectors v permitted solutions to a homogeneous set or subset are v and v the acceptability of each solution depends upon the fit between calculated and measured fault slip senses several examples of applications of this method are used for its validation these examples also illustrate the potential value of the method in making a rough simple and visual appreciation of fault slip data under approximately andersonian stress we believe the method will have a broad applicability as andersonian stress represents the ideal states for the various tectonic regimes

are ceramics and bricks reliable absolute geomagnetic intensity carriers a detailed rock magnetic and archeointensity study was carried out on materials baked by a western mexican artisan following traditional techniques to produce faithful reproductions of archeological pieces of the michoacan region western mesoamerica the field strength at the site 41 0 0 5 lt was measured with a fluxgate magnetometer and the temperature of the furnace during the baking process was monitored continually by means of a thermocouple placed in the middle of the baking cavity rock magnetic experiments performed on the raw material clay and paste and on in situ prepared baked ceramics and bricks included measurement of thermomagnetic curves susceptibility and strong field magnetization versus temperature first order reversal curves forc anisotropy of magnetic susceptibility ams and anisotropy of thermoremanent magnetization a trm magnetite and probably hematite are present in the samples as carriers of the remanence hysteresis ratios suggest that the samples fall in the pseudo single domain grain size region which may indicate a mixture of multidomain and a significant amount of single domain grains ceramic pieces and brick fragments were subjected to the thellier coe archeointensity method and to an alternative paleointensity experiment with a triaxe magnetometer in order to check whether they are faithful recorders of the local geomagnetic field strength mean raw intensity of sample m1 pottery overestimates a 7 the expected site intensity while those corresponding to the brick samples lq1 and lq2 underestimate it 15 brick sample lnq shows a slightly lower intensity 7 but agrees with the expected site intensity within the experimental uncertainty the intensity retrieved from the volcanic fragment also included closely reproduces the expected intensity after a trm and cooling rate corrections all mean raw values move closer to the expected intensity measurement of temperatures at different parts inside the kiln bottom and upper parts of both central and peripheral parts revealed the existence of significant thermal gradients similar to those observed in ovens from other localities different cooling rates are then expected in a single oven the scatter in the intensity determinations observed in this study retrieved from pieces elaborated together in the same oven could arise from this differentiated cooling rate within the oven and thus to an inappropriate cooling rate correction in the archeointensity protocol as this situation was probably reproduced in the baking of ancient ceramic artifacts a better knowledge of the temperature distribution inside these types of kiln would be desirable in order to choose the appropriate cooling rate correction 2011 elsevier b v all rights reserved

a geometric test for possible andersonian stress using striated faults a graphical compilation of the rake guides of fault striations of known sense facilitates a simple test for their compatibility with andersonian stress conditions a compilation of negative double strike angles on tracing paper is superimposed on the rake guide plot if the two register the candidate generating stress is given by the relative position and orientation of the two plots

effect of multi cycle heat treatment and pre history dependence on partial thermoremanence ptrm and ptrm tails abstract we test two fundamental assumptions embedded in thellier experiments the initial state dependence and the effect of multi cycle heat treatment we observe that the magnitude of partial thermoremanent magnetizations ptrms imparted on an initial state of thermal demagnetization is larger than those of ptrms in the presence of a trm when the field used to impart ptrm is equal in magnitude and parallel to that used to produce trm a multi cycle thellier analysis on coarse grained magnetites progressively produces more intense ptrms and progressively erases more of the ptrm tails both pre history and multi cycle dependence will likely enhance the non linear features of the arai plot for coarse grained magnetites

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

palaeostresses associated with thrust sheet emplacement and related folding in the southern central pyrenees huesca spain brittle mesostructures have been studied in the detached mesozoic and lower tertiary cover rocks of the south central pyrenees huesca province spain in order to reconstruct the state of stress within the thrust sheets during tertiary compression the structure of the area studied consists of nw se to e w striking south verging thrust sheets located west of the south pyrenean central unit the palaeostresses obtained show dominant n s to ene wsw compression directions for stress tensors with horizontal 1 axes and e w to nw se extension directions for stress tensors with vertical l axes the values of the stress ellipsoid ratios for stress tensors with horizontal 1 are predominantly between 0 and 0 5 indicating uniaxial compression to wrench regime regarding their relationship with macro structures the palaeostresses show transport parallel compression in most sites although thrust parallel compression is also found there are no differences between palaeostresses found in the hanging walls and the footwalls of thrusts stress tensors with vertical 1 do not show systematic relations with macro structures but transport parallel extension and thrust parallel extension are found in some sites the analysis of palaeostresses in areas of fold and thrust belts shows a high degree of complexity and the results are not easy to interpret the continuous variation from n s to ene wsw in the orientation of the compression axes is here interpreted in two ways 1 as the result of the clockwise rotation of the mesozoic and tertiary cover which was pushed in the east by the south pyrenean central unit with a constant n to nne regional compression and 2 due to ne sw compression resulting from a sw directed local transport of minor thrusts palaeostress analysis can therefore reveal important information about thrust kinematics at high structural levels where ductile deformation is absent

detecting multidomain magnetic grains in thellier palaeointensity experiments the thellier technique is the most commonly used method for absolute palaeointensity studies it is based on thellier s laws stating that partial thermoremanent magnetisations ptrms are independent and additive which however only are true for non interacting single domain sd grains for multidomain md grains individual ptrms are not independent and thellier palaeointensity experiments on rocks with a significant proportion of md grains may therefore lead to erroneous palaeofield estimates by introducing a ptrm tail check in the coe version of the thellier technique j geophys res 72 1967 3247 we present a simple method to detect and discard such rocks the usefulness of the ptrm tail check is exemplified by thellier palaeointensity experiments performed on two palaeomagnetic sample collections with different magnetomineralogy miocene baked sediments from french massif central are shown to be ideal for thellier studies with the remanent magnetisation residing in thermally stable sd grains for palaeocene eocene basaltic lavas from faeroe islands 64 of otherwise acceptable palaeointensity estimates are discarded due to the failure of ptrm tail checks indicating the presence of significant concentrations of md grains 2001 elsevier science b v all rights reserved

the inverse problem in microtectonics and the separation of tectonic phases abstract the algorithm of inverse problems is applied to three cases in microtectonics a collection of striations measured on pre existing faults may be processed automatically and interpreted in terms of tectonic stress a comparison is made between two different methods formerly proposed by the authors both methods are tested with field data the theoretical results agree with independent field criteria for a separation of tectonic phases

a stress inversion method requiring only fault slip sense in numerous cases the use of standard methods of palaeostress inversion from fault slip data is prevented by the absence of structures that indicate the direction of slip on the fault in such instances however the offset of planar markers such as beds matched in the footwall and hanging wall often allows the sense of dip separation normal or reverse to be observed where such displaced markers are horizontal or at least where their cut off lines are horizontal it can be readily demonstrated that the sense of the dip slip component of net slip is the same as the sense of dip separation ways are explored for characterizing the stress tensor from data consisting of the orientations of a collection of faults each with known dip slip sense normal or reverse on the basis of properties of the stress quadric the relationship between dip slip sense fault plane orientation and the stress tensor is discovered this relationship is used as the basis of a grid search method of stress inversion in which a large number of stress tensors differing in orientation and shape are systematically considered those tensors that successfully explain the senses of offset on the observed faults are considered potential solutions to the palaeostress problem examples of different applications of the new stress inversion method are described including the analysis of fault data from boreholes these examples illustrate the way the new method potentially broadens the scope of palaeostress analysis

factors determining magnetic enhancement of burnt clay from archaeological sites abstract the magnetic susceptibility of a collection of 212 archaeological samples of burnt clay of different origin burnt soil ovens and bricks taken from 60 archaeological sites from bulgaria were studied in order to determine factors which may have affected their magnetic enhancement the highest magentic susceptibility values were obtained for bricks and the lowest for burnt soils suggesting that the firing temperature and the duration of burning are important conditions for determining magnetic enhancement specific spatial pattern of the low field magnetic susceptibility was also observed characterized by separation of sites situated in northern and southern parts of the country divided by the west east trending mountain chain stara planina maximum susceptibility values are obtained for burnt soils in southern bulgaria and minima in northern bulgaria in contrast burnt clay plasters and bricks show the opposite picture it is supposed that the observed pattern is due to differences in the outcropped geological formations and variable climate conditions between the two regions which determine different iron supply during burning of initial clay material results from the thermomagnetic analyses show that the dominant ferrimagnetic mineral in all burnt clay materials studied is magnetite titanomagnetite with low ti content and different grain sizes high values of frequency dependent magnetic susceptibility indicate the presence of significant amount of fine grained d

tectonic regime and slip orientation of reactivated faults the slip orientation of reactivated faults is predicted by assuming that one principal stress direction is vertical that faulting occurs on pre existing planes of weakness with a slip direction along the applied shear stress and by extending the original concept of tectonic regime so as to include the stress tensor aspect ratio the predicted rake of slip is then analysed so as to reveal the respective influence of the fault plane orientation strike and dip and of the tectonic regime the analysis of this direct problem allows one to describe the geometry of the slip directions within any given tectonic regime its evolution as the tectonic regime varies and the constraints provided by slip direction data on the tectonic regime however the question of what fault orientations would satisfy a failure criterion and thus be preferentially reactivated is not addressed in any tectonic regime pure strike slip occurs on vertical planes and only on them except in wrench regimes where it also occurs on all fault planes along four strikes that are determined by the tectonic regime pure dip slip occurs on planes striking along one of the horizontal principal stress directions and only on them except in radial compression and radial extension regimes where it occurs on all planes except vertical ones at fixed strike but varying dip the slip direction is closest to dip slip for zero dip and pure strike slip for vertical dip at fixed dip and varying strike the slip direction is pure dip slip for strikes along one of the horizontal principal stress directions and closest to strike slip for four strikes that are determined by the tectonic regime the horizontal principal stress directions separate four quadrants two where the slip direction is dextral and two where it is sinistral the slip directions of all fault planes of the same dip can be easily deduced from those of subhorizontal planes and can be constructed geometrically as the tectonic regime varies continuously from radial compression to radial extension the domain of fault plane orientations where steep reverse slip directions are possible shrinks and disappears when the extensional regime is entered conversely the domain where steep normal slip directions are possible appears when the wrench regime is entered and grows thereafter the strike slip domain first grows towards shallow dip until the wrench regime is entered and then shrinks after the extensional regime is entered whereas in the model of failure in isotropic rocks dip slip or strike slip data fully determine the original tectonic regime in the model of failure on pre existing planes of weakness constraints on the extended tectonic regime require additional information the sense of shallow slip direction data which are to be found on steeply dipping planes constrains the horizontal principal stress directions and the steepness of slip direction data on shallow dipping planes striking away from the principal stress directions constraints the extended tectonic regime in the case of wrench regimes an extra constraint arises from the fact that the extended tectonic regime also controls the strike at which the dip component of slip changes from normal to reverse these constraints can be quantified by superposing a simple plot of the data rake versus strike with an abacus that is called breddin s graph for tectonic regimes while this graph does not replace inverse techniques it may help in detecting tectonic phases in complex data sets without using this graph or resorting to inverse techniques the transition from wrench to either compressional or extensional regime is difficult to infer from data that display a limited range of fault plane strikes and the same sense of dip component of the slip direction

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

how much does slip on a reactivated fault plane constrain the stress tensor given a fault plane and its slip vector the stress tensor which caused the displacement is sought two constraints are considered first a geometrical constraint that the shear stress applied to the fault plane is parallel to the slip wallace 1951 bott 1959 second a frictional constraint that the shear to normal stress ratio equals tan 0 coulomb 1776 in a first step the stress tensors that satisfy the geometrical constraint are sought for tensors belonging to the vectorial space of solutions shear and normal stress magnitudes become a function of the orientation of the principal stresses and are mapped extending a study by mckenzie 1969 in a second step it is investigated which of these tensors also satisfy the frictional constraint within this more restricted vectorial space there is a relationship between the magnitudes 1 2 1 3 and s 1 3 1 and the orientations of the principal stresses both the range of s and the spatial distribution of are more restricted than when the geometrical constraint alone is considered as when the geometrical constraint is solely considered mckenzie 1969 the orientations of the principal stresses may lie significantly away from and up to right angle to the p b t axes however this can happen only in two cases 1 either the effective stress difference s has reached a high value which is unlikely to happen if enough preexisting fractures are available to release the stress or 2 2 becomes close to either 1 or 3 and therefore barely distinguishable from it in that case the delocalization of the orientations of the principal stresses is best described by a tendency for to exchange role with either or when the stress difference remains small and 2 reasonably away from 1 and 3 approach positions that we define as the pf b tf axes and that are obtained from the p b t axes by a rotation of angle 0 2 around b and toward the slip vector this explains why the p b t axes gives reasonable estimates of the orientations of the principal stresses scheidegger 1964 despite objections mckenzie 1969 however whenever the fault plane can be distinguished from the auxiliary plane pf b tf should give a better estimate raleigh et al 1972 in an area where many fault planes are available and a uniform tensor is assumed the scatter in the plane orientations contains information about both the relative position of 2 represented by and the relative stress difference s the higher s or the closer to either 0 or 1 the more scatter this information could then be extracted by inverse methods because a friction law would constrain these inverse method more tightly it may show the necessity of nonuniform tensor to explain scattered fault plane

storage or cooking pots inferring pottery use through archaeomagnetic assessment of palaeotemperatures abstract in this paper we report the results of an archaeomagnetic and rock magnetic study performed on a set of neolithic and chalcolithic potsherds from el portalon de cueva mayor site sierra de atapuerca burgos spain to investigate their thermal history and obtain information about their function during ancient times two types of palaeomagnetic behaviour have been observed one yields stable and univectorial magnetization diagrams type 1 while the other yields multivectorial diagrams with an intermedium component interpreted as a partial thermoremanence p trm type 2 acquired during a partial reheating of the pottery during their use to investigate the connection of these two types with the ancient function of the potsherds a set of modern pots was experimentally fired and then partially reheated al known temperatures the results obtained reproduced patterns similar to those observed in the archaeological samples type 1 univectorial samples that reached only a high heating temperature 600 c during their manufacture were most probably used as storage vessels by contrast type 2 multivectorial samples probably recorded a p trm acquired during their last use reheating related to cooking activities

reliability of geomagnetic paleointensity data the effects of the nrm fraction and concave up behavior on paleointensity determinations by the thellier method abstract to test the reliability of the thellier method for paleointensity determinations we studied six historic lavas from hawaii and two gauss age lava flows from raiatea island french polynesia our aim is to investigate the effects of the nrm fraction and concave up behavior of nrm thermal remanent magnetization trm diagrams on paleointensity determinations for the hawaiian samples the paleointensity results were investigated at both sample and site levels for consistency and confidence in the paleointensity results it is important to measure multiple samples from each cooling unit the results from the raiatea island samples confirm that reliable paleointensities can be obtained from nrm trm diagrams with concave up curvature provided the data are accompanied by successful partial trm ptrm checks and no significant chemical remanent magnetization crm production we conclude that reliable determinations of the paleofield strength require analyses of linear segments representing at least 40 50 of the total nrm this new criterion has to be considered for future studies and for evaluating published paleointensities for calculating average geomagnetic field models using this condition together with other commonly employed selection criteria the observed mean site paleointensities are typically within 10 of the definitive geomagnetic reference field dgrf our new results for the hawaii 1960 lava flow are in excellent agreement with the expected value in contrast to significant discrepancies observed in some earlier studies overestimates of paleointensity determinations can arise from cooling rate dependence of trm acquisition viscous remanent magnetization vrm at elevated temperatures and trm properties of multidomain md particles these outcomes are exaggerated at lower temperature ranges therefore we suggest that provided the ptrm checks are successful and there is no significant crm production it is better to increase the nrm fraction used in paleointensity analyses rather than to maximize correlation coefficients of line segments on the nrm trm diagrams we introduce the factor q n q to assess the quality of the weighted mean paleointensity hw for each cooling unit

what do the hirm and s ratio really measure in environmental magnetism the hard isothermal remanent magnetization hirm and the s ratio are widely used in environmental magnetism to quantify the absolute and relative concentrations respectively of antiferromagnetic minerals hematite and goethite in mineral mixtures we demonstrate that synthetic al substituted hematite and goethite exhibit a wide range of coercivities which significantly influences the hirm and s ratio these parameters are therefore not necessarily straightforward indicators of the absolute and relative concentrations of hematite goethite to circumvent this problem we propose a new parameter the l ratio which is the ratio of two remanences after alternating field af demagnetization of an irm imparted in a 1 t field with a peak af of 100 mt and 300 mt irmaf 300mt irmaf 100mt these parameters are easily measured using modern vibrating sample or alternating gradient magnetometers changes in hirm only reflect changes in the absolute concentration of hematite and or goethite if the l ratio is relatively constant conversely l ratio fluctuations indicate variable coercivities that possibly reflect changes in the source of hematite goethite corresponding hirm and s ratio variations should be interpreted with caution in such cases the l ratio can be determined using equivalent terms depending on available instrumentation and measurement protocols for example the hirm is equivalent to irmaf 300mt likewise 0 5 sirm irm 100mt where irm 100mt represents the remanent magnetization obtained by first saturating the sample in a high field and then applying a back field of 100 mt is equivalent to irmaf 100mt the hirm 0 5 sirm irm 100mt ratio is therefore a suitable substitute for the l ratio when measurements are made with a long core magnetometer the newly proposed l ratio is straightforward to measure on a wide range of instruments and can provide significant new insights and reduce ambiguities associated with interpretation of two widely used parameters in environmental magnetism the hirm and s ratio

magnetic field intensity study of the 1960 kilauea lava flow hawaii using the microwave palaeointensity technique summary it is extremely valuable to study historic lava flows where the geomagnetic field at their time of extrusion is well known in this study two vertical sections 16 m apart have been sampled from the approximately 1 m thick 1960 kilauea lava flow hawaii variations are seen in the rock magnetic and palaeomagnetic properties between and within the two sections indicating that there are small scale lateral and vertical variations in the lava flow the two sections showed dierent responses to microwave palaeointensity analysis section h6001 generally gave ideal linear behaviour on plots of natural remanent magnetization nrm lost against microwave induced thermoremanent magnetization t m rm gained whilst the majority of samples from h6002 showed anomalous two slope behaviour when all plots were interpreted by taking the best fitting line through all points the flow mean intensity for h6001 was 31 6 3 6 mt and that for h6002 was 37 1 6 4 mt compared with the expected intensity of 36 mt additional historic flows need to be studied in order to ascertain whether this behaviour is typical of all lava and whether it is best to always interpret nrm lost t m rm gained plots by taking the line of best fit regardless of shape

the 1978 borden tracer experiment analysis of the spatial moments a reanalysis of the 1978 tracer experiment at borden ontario is performed using spatial moments the tracer experiment involved the uniform injection of chloride ions into an aquifer and the resulting plume was allowed to migrate under natural gradient conditions detailed monitoring of the evolving plume was then performed in three dimensions the work of sudicky et al 1983 showed that the solute cloud evolved as two plumes owing to variations in hydraulic conductivity at the site in this paper we compute the zeroth through the fourth spatial moments of the plume in the lower hydraulic conductivity zone from these moments the solute mass of the plume the velocity of the center of mass the dispersion the skew and the kurtosis of the plume are calculated these results are compared with the results of sudicky et al as well as with the theoretical results of gelhar et al 1979 and naff 1990 our computed plume velocity and apparent horizontal transverse macrodispersivity are in agreement with the estimates of sudicky et al however our apparent longitudinal macrodispersivity estimate exceeds that of sudicky et al by a factor of 2 the apparent horizontal transverse macrodispersivity obtained is also quite similar to that of freyberg 1986 at early times the plume is found to be positively skewed as well as platykurtic this supports the findings of gelhar et al and contradicts those of naff

determination of domain structure in igneous rocks by alternating field and other methods abstract af alternating field demagnetization arm anhysteretic remanent magnetization and strong field hysteresis properties of a large collection of mostly continental igneous rocks are reported here the collection included rocks whose magnetic carriers were believed from previous work to be of one of three types md multidomain sd psd single domain pseudo single domain or a bimodal mixture of md grains e g discrete opaques and sd psd material e g silicate inclusions two series of subaerial basalts with a full range of deuteric oxidation classes included examples of all three classes of behaviour sd psd rocks have relatively hard inflected af decay curves decay rate initially increasing then decreasing md rocks have soft exponential like decay curves and bimodal rocks have a combination of these characteristics relative hardnesses of normalized decay curves of remanences acquired in weak intermediate and strong fields the lowrie fuller test are also distinctively different for the three classes and the results support the theory developed in an accompanying paper 1 that lowrie fuller characteristics are an expression of the shapes of decay curves the lowrie fuller test although its result can be expressed as a numerical parameter is not capable of fine scale classification of domain structure or grain size the shape of the arm induction curve does have a quasi continuous variation with grain size however the parameter ar j rs initial anhysteretic susceptibility normalized to saturation remanence which is easily measured with standard paleomagnetic instrumentation is potentially useful for magnetic granulometry although ar itself was not diagnostic of grain size

deflection of a compressional stress field by large scale basement faults a case study from the tertiary almazan basin spain abstract palaeostresses deduced from brittle mesostructures more than 50 sites and 1500 structures measured in the mesozoic and tertiary rocks of the almazan basin located in the northwestern iberian chain indicate a regional nne sse directed compression that lasted during all the tertiary shortening stage the stress regime corresponding to this compression ranges from thrust to wrench n s directed compression was the responsible for most macrostructures folds and thrusts forming a s vergent system with ne sw to e w and nw se orientations and mesostructures mainly faults stylolytes and impressed pebbles we propose that the stress trajectories are deflected following anderson s model in the western part of the almazan basin by the ne sw striking left lateral strike slip soria fault this basement fault was inherited from the late variscan fracturing stage and controlled the deposition in the mesozoic basins as well as the location of tertiary compressional macrostructures in the eastern border of the almazan basin palaeostress trajectories were deflected both by right lateral strike slip faults and nw se trending thrusts near which the regional n s directed compression becomes perpendicular to them three minor compression directions have also been recorded in several sites ne sw e w and nw se the ne sw directed compression is interpreted as a deviation of the main n s directed compression at a regional scale whereas the nw se directed stress field corresponds to the regional field responsible for the main tertiary shortening stage in the spanish central system the age of compression ranges from eocene to miocene

new archeomagnetic secular variation data from central europe ii intensities abstract variations of the geomagnetic field during the past millennia can be obtained by investigating archeological material the spatial distribution of the available data across europe is rather uneven and only about 15 of the sites provide a full vector record of the geomagnetic field here we report 39 new reliable paleointensity data for sites from austria germany and switzerland with ages ranging between 1500 bce and 1900 ce for 31 of them directional information is available too paleointensities were determined with thellier type techniques with the multiple specimen domain state corrected paleointensity protocol or with both techniques corrections for anisotropy of thermoremanent magnetization were carried out for the structures showing small variations of only a few per cent in most cases cooling rate dependence was tested for 16 structures often strong alteration during the experiments was observed seven successful cooling rate corrections were applied which lowered the paleointensity values by about 10 values obtained from the multiple specimen technique are generally somewhat lower than those from the thellier experiments rock magnetic measurements revealed magnetite type minerals mostly in pseudo single domain range as main magnetic carrier but also high coercive mineral components like hematite or epsilon iron oxide are present the new data are mostly in good agreement with published paleointensities they support the presence of strong intensity variations around 800 ce and in the millennium bce the new full vector data reveal that the deep paleointensity minimum observed from german data around 850 bce is accompanied by large variations in direction with declinations up to 50

inferring stress from faulting from early concepts to inverse methods abstract we review the evolution of concepts on and methods of estimating the state of stress from fault movements theories of failure in isotropic materials suggested a simple geometrical construction of optimal principal stress directions from a fault plane and its associated slip these optimal directions align shear stress and slip directions and maximize the difference between shear stress and frictional resistance on the fault plane optimal stress directions for calcite twinning are obtained by a similar construction with the difference that they maximize shear stress force representation of seismic sources independently introduced pressure p and tension t axes at positions that also maximize shear stress on both nodal planes frictional slip theory and the constraint that slip and shear stress directions be parallel allowed to address reactivation of pre existing faults this suggested that stress could also be inverted from reactivated fault and slip data or earthquake focal mechanisms early methods relied on geometrical constructions as a substitute for calculations whereas later methods relied on software as these calculations became tractable with the help of computers similar methods were developed for the inversion of stress from crystal twin gliding with non optimal geometry with a different criterion that relies on a threshold of the component of shear stress along the gliding line even though these methods seek a common stress tensor compatible with fault and slip data their main use is to separate polyphase data into homogeneous subsets and help deciphering complex tectonic histories fault and slip data can also be analyzed to constrain the strain rather than the stress tensor in most cases this involves a summation and yields an average strain for the considered rock volume stress inversion thus appears better suited for differentiating heterogeneous data whereas strain analysis appears better suited for homogenizing them

kinematic indicators in fault gouge tectonic analog for soft bedded ice sheets abstract polished slip planes resulting from basin and range detachment faulting of mid tertiary volcaniclastics are well exposed at lake pleasant arizona u s a slip planes show erosional features formed by abrasion below moving sheets of gouge coarse grained diamict during repeated faulting and shearing tectonically generated forms are identical to those found in glaciated terrains slip planes show rat tail ridges and grooves ridge in groove structures nail head striations and wear tracks a prominent morphological element consists of flute ridges up to 30 cm wide and at least 7 m long formed of gouge preserved in the lee of boulders projecting as obstacles above slip surfaces crescentic scours around the stoss side of such boulders record enhanced abrasion by streams of gouge debris clasts are striated and show shapes comparable to flat iron clasts produced by glacial abrasion kinematic indicators at lake pleasant are directly comparable in form to flutes and drumlins in glaciated terrains the data presented here not support a recent hypothesis arguing that glacial striations flutes and drumlins are the product of turbulent subglacial meltwater instead diamict produced along fault planes gouge by low grade shearing is directly comparable to diamict facies deformation till formed by pervasive shear at the base of soft bedded ice sheets both facies are tectonically generated cataclastites produced in low grade shear zones and display genetically related but differently scaled streamlined bedforms

are systematic differences between thermal and microwave thellier type palaeointensity estimates a consequence of multidomain bias in the thermal results a meta analysis which directly compares 13 datasets of microwave and thermal thellier palaeointensity measurements obtained from igneous rocks is reported the results clearly indicate systematic differences in the measurements made using the two approaches the thermal results tend to be higher often by several tens of percent and associated with slightly noisier arai plots additionally in nearly half of the cases considered higher thermal palaeointensity estimates were reported to be calculated from the lowtemperature portions of concave up arai plots while microwave measurements made on specimens from the same core sample or rock unit were derived from more linear arai plots the most plausible explanation for the bulk of these differences appears to be that non ideal behaviour caused by multidomain vortex state and or interacting ferrimagnetic grains is exaggerated in the results of the thermal experiments over their microwave counterparts a detailed investigation of the individual studies concludes that such effects may be adversely affecting some of the measurements thermal and or microwave in 10 of the 13 datasets considered it is probable that these non ideal effects are enhanced in the thermal results over their microwave counterparts at least in part because of the different thellier type protocols that are used in the two types of study the findings of this study suggest that biasing of absolute palaeointensity estimates by multidomain effects may be much more prevalent than previously thought and that this effect might be responsible for certain discrepancies that have been observed in the geomagia50 database they also clearly indicate that in addition to taking the steps they already do to avoid biasing from secondary overprints and thermally induced alteration future absolute palaeointensity studies of