fluid dynamical implications of anastomosing slope streaks on mars 1 the mars global surveyor mission has imaged slope streaks some of which have formed in periods as short as 109 days these features are one of the most currently active surface processes on mars some slope streaks have flow like morphologic characteristics which include anastomosing patterns influenced by small topographic barriers in order to understand what processes gave rise to these specific features we applied viscoplastic flow numerical modeling techniques to simulated martian surfaces we simulate martian surfaces with observed slope streaks by using mars orbiter laser altimeter measurements to obtain large scale slope measurements and a photoclinometry technique on mars orbiter camera images to obtain meter scale topographic information our numerical simulations of slow moving plastic flows show that a fluid rheology and a short formation period are necessary to explain these features we estimate that the typical values of bulk viscosity and bulk yield strength are less than 10 pa s and less than 10 pa respectively the fluid rheology can be explained by a water related flow with a solid content less than about 20 an alternative explanation is a dry grain flow with extremely low cohesion and friction angle supported by dispersive pressure or a lubricant such as electric conditions of particles the continuous nature of anastomosing slope streaks that originate from point sources is best explained by continuous discharges of material or lubricant in this case the estimated flow rate is less than several cubic meters per second and the flow duration is estimated to be less than a day

recovery of small strain stiffness following blast induced liquefaction based on shear wave velocity measurements changes in soil fabric following liquefaction have been studied using various in situ methods and often return inconclusive or conflicting observations the time rate variation of stiffness when

interaction of viscous free surface flows with topography the interaction of gravitationally driven free surface flows of viscous fluid with topographic features is investigated theoretically the motion is studied in the regime where the depth of the flow is much smaller than the streamwise extent of the topography a lubrication model of the motion is developed integrated numerically and analysed asymptotically for small mounds it is shown that the flow surmounts the obstacles but for larger mounds the flow is deflected around it and can form dry zones in its wake into which fluid does not flow as well as forming deeper ponded regions upstream which of these phenomena prevails is shown to depend upon the amplitude of the mound height and the thickness of the oncoming flow relative to the streamwise length scale over which the topography varies by using numerical and asymptotic results we demonstrate that relatively wide mounds lead to the development of deep ponds of material upstream which may lead to flow overtopping if the mound is not sufficiently high these insights can be used to inform the design of barriers that defend built infrastructures from lava flows and it is shown how this model can also provide an upper bound on the force exerted by the flow on them

liquefaction evidence for strong earthquakes of holocene and latest pleistocene ages in the states of indiana and illinois usa abstract sand and gravel filled clastic dikes of seismic liquefaction origin occur throughout much of southern indiana and illinois nearly all of these dikes originated from prehistoric earthquakes centered in the study area in this area at least seven and probably eight strong prehistoric earthquakes have been documented as occurring during the holocene and at least one during the latest pleistocene the recognition of different earthquakes has been based mainly on timing of liquefaction in combination with the regional pattern of liquefaction effects but some have been recognized only by geotechnical testing at sites of liquefaction most paleo earthquakes presently recognized lie in indiana but equally as many may have occurred in illinois studies in illinois have not yet narrowly bracketed the age of clastic dikes at many sites which sometimes causes uncertainty in defining the causative earthquake but even in illinois the largest paleo earthquakes probably have been identified prehistoric magnitudes were probably as high as about moment magnitude m 7 5 this greatly exceeds the largest historic earthquake of m 5 5 centered in indiana or illinois the strongest paleo earthquakes struck in the vicinity of the concentration of strongest historic seismicity elsewhere paleo earthquakes on the order of m 6 7 have occurred even where there has been little or no historic seismicity both geologic and geotechnical methods of analysis have been essential for verification of seismic origin for the dikes and for back calculating prehistoric magnitudes methods developed largely as part of this study should be of great value in unraveling the paleoseismic record elsewhere

visco plastic models of isothermal lava domes the dynamics of expanding domes of isothermal lava are studied by treating the lava as a viscoplastic material with the herschel bulkley constitutive law thin layer theory is developed for radially symmetric extrusions onto horizontal plates this provides an evolution equation for the thickness of the fluid that can be used to model expanding isothermal lava domes numerical and analytical solutions are derived that explore the eects of yield stress shear thinning and basal sliding on the dome evolution the results are briefly compared with an experimental study it is found that it is dicult to unravel the combined eects of shear thinning and yield stress this may prove important to studies that attempt to infer yield stress from morphology of flowing lava

recurrence rates of large earthquakes in the south carolina coastal plain based on paleoliquefaction data we present a reanalysis of results of 15 years of paleoliquefaction investigations in the south carolina coastal plain all earlier radiocarbon age data and locations of organic material collected by various investigators were reviewed and recalibrated to obtain a uniform data set the calibrated dates and the spatial extent of the sandblows having similar dates were used to estimate ages and magnitudes of prehistoric earthquake episodes the results of this analysis suggest seven episodes episodes a g of prehistoric liquefaction in the past 6000 years and two possible scenarios for their occurrence in the first scenario three seismic sources exist within the coastal plain of south carolina at charleston a b e and g with magnitudes m 71 georgetown c and f and bluffton d with magnitudes m 6 in the second scenario episodes c and d are combined into one episode episode c9 in this scenario all earthquakes occurred at charleston and with m 71 episodes a and b seem to be more representative of the earthquake cycle and suggest a recurrence time of 500 600 years for m 71 earthquakes at charleston the recurrence times and magnitudes for episodes c and d are estimated at 2000 years and 6 0 respectively the older episodes are less frequent a fact that may be attributable to times of low ground water table before 6000 years b p the ground water table was too low to permit observable liquefaction features to develop at the surface

paleomagnetic constraints on eruption patterns at the pacaya composite volcano guatemala pacaya volcano is an active composite volcano located in the volcanic highlands of guatemala about 40 km south of guatemala city volcanism at pacaya alternates between strombolian and vulcanian and during the past five years there has been a marked increase in the violence of eruptions the volcano is composed principally of basalt flows interbedded with thin scoria fall units several pyroclastic surge beds and at least one welded tuff between 400 and 2000 years bp the w sw sector of the volcano collapsed producing a horseshoeshaped amphitheater 0 65 km3 and providing a window into the cone s infrastructure lava flows and tephra exposed in the amphitheater are more then 200 m thick and when combined with flows erupted recently represent between 30 and 40 of the cone s history pacaya is ideally suited for a paleomagnetic study into the timing and duration of eruption episodes at a large composite volcano we drilled 27 paleomagnetic sites 25 aa flows 1 dike and 1 welded tuff from four lava flow sequences with between 4 and 14 sites per sequence the four sequences represent initial through historic activity at pacaya we resolved what appear to be 22 time independent paleomagnetic sites by averaging together directions from successive sites where the sitemean directions were indistinguishable at the 95 level of confidence however mean sequence directions of individual lava flow sequences yielded unusually high fisher precision parameters k 44 224 and small circles of 63 confidence a63 1 6 6 1 suggesting as few as three or four time independent sites were collected this indicates that activity as pacaya is strongly episodic and that episodes are characterized by voluminous outpouring of lavas modelling the data using holocene psv rates confirms this and shows that differences in within sequence directions 6 11 5 are consistent with emplacement of lava flow sequences in less than 100 years to as many as 300 years relatively larger differences in directions 18 23 between subjacent lava flow sequences indicates that repose is at least 300 500 years and could be even longer

the static shape of yield strength fluids slowly emplaced on slopes a theoretical solution is presented for the static three dimensional shape of a fluid having a finite yield strength after it is extruded slowly from a small source on an inclined plane the solution is compared to the shapes obtained in laboratory experiments in which slurries of kaolin in polyethylene glycol wax were ejected slowly and in small incremental volumes onto a slope this study is aimed at understanding the shape of highly silicic lava flows such as large rhyolite flows which occur on steep mountain sides or on gentle slopes and the role of a finite yield strength in governing the slow spreading and the final static shape the results indicate that it is possible to obtain an estimate of the yield strength of a fluid which is emplaced under such circumstances using only horizontal aspect ratios and the slope of the underlying ground

effect of aging on the penetration resistance of sands the main objective of this study was to understand the effect of aging on the penetration resistance of freshly deposited sands two types of sand locally available river sand used as masonry sand and beaufort sea sand were selected for the study the sands were allowed to age under a constant stress of 100 kpa in a specially designed apparatus in a dry state as well as submerged in distilled water and in simulated sea water penetration resistance of the sand beds was measured periodically by pushing 4 probes into the sand bed mineralogical and fabric studies on freshly deposited and aged sand samples were conducted to detect the effect of aging if any on sand grains the results indicate that aging significantly increases the penetration resistance of sands the rate of increase in penetration resistance was higher for the submerged sand as compared with the dry sand the increase in penetration resistance of the sand in a dry state was attributed to rearrangement of sand grains in the submerged

archaeomagnetic secular variation in the uk during the past 4000 years and its application to archaeomagnetic dating this paper examines the limitations and deficiencies of the current british archaeomagnetic calibration curve and applies several mathematical approaches in an attempt to produce an improved secular variation curve for the uk for use in archaeomagnetic dating the dataset compiled is the most complete available in the uk incorporating published results phd theses and unpublished laboratory reports it comprises 620 archaeomagnetic directional data and 238 direct observations of the geomagnetic field and includes all relevant information available about the site the archaeomagnetic direction and the archaeological age a thorough examination of the data was performed to assess their quality and reliability various techniques were employed in order to use the data to construct a secular variation sv record moving window with averaging and median as well as bayesian statistical modelling the sv reference curve obtained for the past 4000 years is very similar to that from france most differences occurring during the early medieval period or dark ages two examples of dating of archaeological structures medieval and pre roman are presented based on the new sv curve for the uk and the implications for archaeomagnetic dating are discussed

liquefaction lateral stress consolidation state and aging abstractin 1986 1989 jackson lake dam wyoming was removed after standard penetration tests indicated that the foundation soil was subject to liquefaction part of a subsequent research program involved measuring lateral in situ stresses at various depths in the foundation soil by use of the ko stepped blade a device that introduces a stepwise lateral displacement of soil so contact pressures can be extrapolated to give the hypothetical pressure on a zero thickness step the foundation soil was cohesionless mix of alluvial and deltaic silts and sands with some sharp edged gravel the lateral stress measurements established relationships between the four topics in the title of this paper a normal consolidation state meaning that a soil is in equilibrium with its own weight can be established when ko is constant with depth and lateral effective stresses extrapolate to zero at the ground surface on this basis three stress zones were identified 1 based on limited data an uppermost zone to a depth

liquefaction evidence for the strength of ground motions resulting from late holocene cascadia subduction earthquakes with emphasis on the event of 1700 a d during the past decade paleoseismic studies done by many researchers in the coastal regions of the pacific northwest have shown that regional downdropping and subsequent tsunami inundation occurred in response to a major earthquake along the cascadia subduction zone this earthquake occurred almost certainly in 1700 a d and is believed by many to have been of m 8 5 9 or perhaps larger in order to characterize the severity of ground motions from this earthquake we report on a field search and analysis of seismically induced liquefaction features the search was conducted chiefly along the banks of islands in the lowermost columbia river of oregon and washington and in stream banks along smaller rivers throughout southwestern washington to a lesser extent the investigation included rivers in central oregon numerous small to moderate sized liquefaction features from the earthquake of 1700 a d were found in some regions but there was a notable lack of liquefaction features in others the regional distribution of liquefaction features is evaluated as a function of geologic and geotechnical factors in different field settings near the coast our use of widely different field settings each in which we independently assess the strength of shaking and arrive at the same conclusion enhances the credibility of our interpretations our regional inventory of liquefaction features and preliminary geotechnical analysis of liquefaction potential provide substantial evidence for only moderate levels of ground shaking in coastal washington and oregon during the subduction earthquake of 1700 a d additionally it appears that a similar conclusion can be reached for an earlier subduction earthquake that occurred within the past 1100 years which also has been characterized by others as being m 8 or greater on the basis of more limited data for older events collected in our regional study it appears that seismic shaking has been no stronger throughout holocene time our interpreted levels of shaking are considerably lower than current estimates in the technical literature that use theoretical and statistical models to predict ground motions of subduction earthquakes in the cascadia region because of the influence of estimated ground motions from cascadia subduction zone earthquakes on seismic hazard evaluations more paleoliquefaction and geotechnical field studies are needed to definitively bracket the strength of shaking with further work it should be possible to extend the record of seismic shaking through much of holocene time in large portions of washington and oregon

accounting for soil aging when assessing liquefaction potential it has been recognized that liquefaction resistance of sand increases with age due to processes such as cementation at particle contacts and increasing frictional resistance resulting from particle rearrangement and interlocking as such the currently available empirical correlations derived from liquefaction of young holocene sand deposits and used to determine liquefaction resistance of sand deposits from in situ soil indices standard penetration test spt cone penetration test cpt shear wave velocity test vs are not applicable for old sand deposits to overcome this limitation a methodology was developed to account for the effect of aging on the liquefaction resistance of old sand deposits the methodology is based upon the currently existing empirical boundary curves for holocene age soils and utilizes correction factors presented in the literature that comprise the effect of aging on the in situ soil indices as well as on the field cyclic strength crr this paper describes how to combine currently recorded spt cpt and vs values with corresponding crr values derived for aged soil deposits to generate new empirical boundary curves for aged soils the method is illustrated using existing geotechnical data from four sites in the south carolina coastal plain sccp where sand boils associated with prehistoric earthquakes have been found these sites involve sand deposits that are 200 000 to 450 000 years in age this work shows that accounting for aging of soils in the sccp yields less conservative results regarding the current liquefaction potential than when age is not considered the modified boundary curves indicate that old sand deposits are more resistant to liquefaction than indicated by the existing empirical curves and can be used to evaluate the liquefaction potential at a specific site directly from the current in situ properties of the soil

benchmarking lava flow models prediction of the emplacement of volcanic mass flows lava flows pyroclastic density currents debris avalanches and debris flows is required for hazard and risk assessment and for the planning of risk mitigation measures numerical computer based models now exist that are capable of approximating the motion of a given volume of volcanic material from its source to the deposition area with these advances in technology it is useful to compare the various codes in order to evaluate their respective suitability for real time forecasting risk preparedness and post eruptive response a benchmark compares codes or methods all aimed at simulating the same physical process using common initial and boundary conditions and outputs but using different physical formulations mathematical approaches and numerical techniques we set up the basis for a future general benchmarking exercise on volcanic mass flow models and more specifically establish a benchmark series for computational lava flow modelling we describe a set of benchmarks in this paper and present a few sample results to demonstrate output analysis and code evaluation methodologies the associated web based communal facility for sharing test scenarios and results is also described

computer synthesis of geomagnetic palaeosecular variations computer models designed to synthesize palaeosecular variations of the geomagnetic field cast doubt on some widely accepted palaeomagnetic dogmas westward or eastward drift cannot be uniquely deduced from the sense of rotation of the geomagnetic vector the use of unit vectors in statistical analyses leads to systematic errors which render investigation of the global symmetry of the palaeofield more difficult than previously supposed at least some geomagnetic excursions may be regarded as large amplitude secular variations

effect of surface solidification on the emplacement of lava flows on a slope 1 the emplacement dynamics of lava flows on a slope is investigated using theoretical analyses and laboratory experiments for the case where a fixed volume of lava is rapidly released and propagates downhill as a two dimensional flow when the lava has no internal yield strength we identify four dynamical flow regimes that can arise an inertial slumping regime a horizontal viscous regime a sloping viscous regime and a crust yield strength regime that finally stops the flow when the lava has an internal yield strength it can also flow in a sloping viscoplastic regime which is accurately predicted by a simple box model that we derive our results are applied to predict the propagation downhill of various volumes of two typical lavas a hawaiian lava with no internal yield strength and a mount etna lava with an internal yield strength in particular we find that sloping flows of the mount etna lava are stopped by the surface crust strength rather than the internal yield strength

congruent paleomagnetic and archeomagnetic records from the western united states a d 750 to 1450 two independently dated high resolution paleomagnetic records one lacustrine and one archeological record the passage across western north america of the same nondipole feature of the geomagnetic field during the time interval from a d 750 to 1450 although these sequences indicate that correlation between paleomagnetic and archeomagnetic records is feasible under certain conditions differences between the records underscore the difficulty of dating accurately an archeological site by correlation of a single archeomagnetic direction with a secular variation curve

holocene secular variation in western north america paleomagnetic record from fish lake harney county oregon an 8 9 m composite section of lake sediment from fish lake steens mountain southeastern oregon has provided a high resolution record of holocene geomagnetic secular variation in western north america the section is composed of overlapping core segments with stratigraphic control based on six tephra layers and other thin distinct bands and with age control from 37 radiocarbon dates the 455 paleomagnetic samples possess a strong and stable magnetic remanence which is carried by pseudo single domain magnetite paleomagnetic records for individual core segments show low scatter and high serial correlation and where the segments overlap there is excellent agreement between records the azimuthal orientation of the composite section was recovered from the known direction of the geomagnetic field at the time of the climactic eruption of mount mazama tephra which is present in fish lake both internal and external evidence including the correspondence with an archaeomagnetic record from the southwestern united states support the conclusion that the fish lake record represents the history of geomagnetic field behavior during at least the last 10 000 years b p analysis of that record reveals that the average geomagnetic direction can not be distinguished from that of a geocentric axial dipole field and that the overall circularity of the field was clockwise but the detailed behavior was quite complex angular standard deviations of both field directions and virtual geomagnetic poles differ significantly from the values predicted from theoretical models of secular variation but are consistent with those of other holocene records when the record from fish lake is compared to the proposed type curve for east central north america there is excellent agreement for the past 6000 years provided the curves are offset by about 400 years this offset corresponds to a rate of westward drift of about 0 062 yr beyond about 6000 radiocarbon years ago good agreement between the two curves occurs when there is no offset suggesting that the field was standing rather than drifting during this time

late quaternary paleomagnetic field secular variation from two minnesota lakes detailed paleomagnetic records from the wet sediments of two minnesota lakes are the basis for estimating the local secular variation of the earth s magnetic field during late quaternary time results from lake st croix cover the interval 0 9500 years b p and results from kylen lake cover the interval 4000 14 000 years b p paleomagnetic data were recovered from two replicate cores in each lake by sampling the sediments at 3 to 10 cm intervals analysis of the potential errors in the results indicates that all cores were correctly oriented in the vertical plane but that some azimuthal offsets of individual core segments did occur various methods for correcting the occasional azimuthal offsets are described the final paleomagnetic data sets from each lake show a high degree of internal consistency these results also show close correspondence 1 between the two lakes 2 with the known historic magnetic field variation and 3 with paleomagnetic results from dated archeological material and lava flows from the western united states rock magnetic analysis of the lake sediments indicates that the natural remanent magnetization is the result of a physical remanence acquisition process detrital remanent magnetization active at or near the sediment water interface there is no evidence for a systematic inclination error in the results statistical analysis of vector time series determined from the paleomagnetic data indicates that both the field vector and virtual geomagnetic pole vgp distributions are non fisherian and essentially axial dipolar when averaged over 10 000 years spectral analysis of the scalar inclination and declination suggests that the field behavior is separable into a dominant low frequency dipolelike waveform period of 9500 years and a higher frequency band irregular waveform fundamental period of 2400 years with multiples at 1200 800 and 600 years that may represent the nondipole field this irregular waveform is interpreted as resulting from zonal drift of the nondipole field past minnesota on the basis of waveform morphology and vgp circularity zonal drift of the nondipole field plus a low frequency dipole variation can account for almost all of the observed paleomagnetic field variation

geomagnetic secular variation from recent lake sediments ancient fireplaces and historical measurements in southeastern australia abstract compilations of historical observations archaeomagnetic data from ancient fireplaces and palaemagetic results from short cores of sediment from lakes in southeastern australia particularly lake keilambete provide a detailed record of the geomagnetic secular variation during the last 3000 years the independent sets of data are in good agreement if the radiocarbon time scale for the lacustrine record is about 450 years too old the error is attributed to systematic incorporation of ancient carbon into the lake floor sediments mainly through erosion of sediment on the crater walls at times of low water level a significant lag between deposition and the acquisition of stable magnetic remanence is ruled out inclination has been abnormally steep during the last 500 years but remained fairly close to the axial dipole field value prior to that during the last 1000 years the predominant sense of looping of the magnetic vector corresponds to westward drift of the nondipole field secular variations on a time scale of 100 years can be resolved by the lacustrine record

open channel flow of bingham fluids applications in debris flow research the results of a numerical simulation of open channel flow of bingham fluids provide improved capabilities for analyzing muddy debris flows and their depositis and for routing debris flows because of limitations of the phenomenonological bingham model results are deemed applicable to mud rich debris flows only most published field estimates of debris flow rheological bingham properties depend on application to natural channels of analytical solutions for flow through channels with either circular or very wide channel cross sections lack of a general solution for flow of bingham fluids in channels with realistic shapes has restricted capabilities in debris flow modeling and field data analysis numerical solutions permit generalization and extension of analytical solutions to channels of arbitrary cross sectional form without loss of accuracy the numerical model fidap utilizes a well established finite element formulation of the non newtonian fluid flow problem and reproduces available analytical

use of explosives to investigate liquefaction resistance of aged sand deposits abstract current methods of predicting liquefaction potential were largely developed using data from relatively young deposits or deposits that have been frequently disturbed i e areas of high seismicity while engineers recognize that these prediction methods are overly conservative for assessing liquefaction potential in geologically aged deposits there is no widely accepted method for quantitatively accounting for age in these assessments because a major disturbance such as an earthquake or explosion that causes liquefaction resets a deposit s geological age data from explosive compaction projects in aged deposits are used herein to provide information about both the aged and fresh deposits a recent explosive compaction project performed in griffin in as well as four other explosive compaction projects is used to develop an aging correction relationship for liquefaction resistance using a log linear trend frequently proposed in previous studies the method proposed herein predicts an approximate 20 gain in liquefaction resistance per time log cycle the proposed relationship can be used directly if the time since deposition or last disturbance is known or in conjunction with the measured to estimated velocity ratio mevr relationship proposed by andrus et al if the deposit s age is unknown

compaction of alluvial sands by deep blasting the jebba hydroelectric development nigeria presently under construction features a 42 m high zoned rockfill embankment founded on river alluvium up to 70 m in depth the riverbed alluvium comprises fine to medium to coarse grained quartzitic sands with traces of gravel the relative densities of the sands vary appreciably in both the vertical and horizontal directions during the dam design it was found that it would be necessary to densify the loose to medium dense portion of the river sands to maintain settlements within acceptable limits and to withstand design earthquake forces the top 25 m of the river alluvium is densified by the vibrocompaction method and below this level down to depths of 40 m the alluvium is densified by blasting there is no precedent found in the literature for densification by blasting at such depth this paper presents details of a test program and the production work test results conclusively show increases in static cone penetration resistance in loose sand layers

evaluation of installation effects on set up of field displacement piles in sand the paper presents results from a new series of tests on displacement piles in sand involving different installation modes and combines these with results from previous tests at the same site as

cpt based evaluation of liquefaction and lateral spreading in centrifuge two series of centrifuge model tests were conducted using nevada sand four saturated models placed in a mildly inclined laminar box and simulating a 6 m thick deposit were shaken inducing liquefaction effects and lateral spreading the sand was deposited at a relative density dr 45 or 75 two of the 45 models were subjected to overconsolidation or preshaking the second series involved in flight measurements of static cone tip penetration resistance qc simulating the standard cone penetration test cpt 36 mm cone values of qc increased with dr overconsolidation and preshaking a normalized resistance qc1n was assigned to each of the four liquefaction lateral spreading models increases in dr overconsolidation and preshaking decreased liquefaction and ground deformation but relative density alone captured these effects rather poorly conversely qc1n predicted extremely well the liquefaction and lateral spreading response of the four models confirming seed s hypothesis to explain the s

the paleomagnetism and u th dating of mexican stalagmite das2 a 72 cm high stalagmite from mexico das2 has been analyzed for its paleomagnetism and has provided a record of secular variation beginning about 1200 years ago to present the stalagmite did not grow uniformly and a low content of magnetic material has rendered the record less precise in some parts a topographic test involving the magnetic measurement of coeval specimens from the sides of the stalagmite has shown that the record is detectably free from depositional errors age data were provided by the u th method and concordancy checked by14c and226ra methods shallow inclinations at the base of the record are followed by a partial anticlockwise loop in the declination inclination plot there is good agreement between the das2 data and the southwest u s a archeomagnetic record and with a lacustrine record from oregon from 750 to 1400 ad comparison of the record with the present field at the site latitude shows that westward drift of the field has persisted for at least 1200 years at a drift rate of about 0 30 yr 1 a close match in declinations with the present field at the site latitude suggests that the stalagmite may have recorded the passing of the northern edge of the gulf of guinea negative anomaly about 1000 years ago though the corresponding inclination feature is not present in the record an archeomagnetic synthesis by merrill and mcelhinny of worldwide data to estimate positions of the main dipole shows that it was tilted away from mexico from 500 to 1250 ad and this may account for the shallow inclinations seen at the start of the record

a robust least squares gondwanan apparent polar wander path and the question of palaeomagnetic assessment of gondwanan reconstruction abstract two hundred and nineteen palaeomagnetic results are combined in calculating gondwanan apparent polar wander paths their confidence intervals and the residual mean square errors about the paths for six reconstructions a quantitative assessment of the six reconstructions of gondwanaland is made on the basis of the consistency of palaeomagnetic pole positions using a new statistical technique smith and hallam s 1 gondwanan reconstruction is the most effective in accounting for the distribution of the palaeomagnetic data and is used in calculating our preferred apparent polar wander path

high resolution paleomagnetic record of geomagnetic field fluctuations from the varved sediments of elk lake minnesota measurements of samples taken from three parallel cores from elk lake in northern minnesota have been combined to produce a high quality record of recent variations in the local magnetic field annual laminations in the sediment provide excellent time control for the record and evidence for a consistent depositional environment the elk lake paleomagnetic record contributes significantly to our understanding of the recent history of the magnetic field in central north america modifying several previous conclusions

archaeomagnetism and magnetic anomalies in the american southwest magnetic surveying is probably the most widely used geophysical technique at archaeological sites weymouth and huggins 1985 it is useful for locating features in which the magnetic susceptibility contrasts with the magnetic susceptibility of the surroundings because of induced and or remanent magnetization a contrast in magnetic induction can arise for example when the disturbed soil fill inside a formerly occupied room has a different magnetic susceptibility from the subsoil outside the room tite and mullins 1971 a contrast in magnetic remanence most commonly occurs when a baked clay artifact or feature such as a hearth has acquired a thermoremanent magnetization after being heated to several hundred degrees celsius

liquefaction at moss landing during loma prieta earthquake a study of liquefaction at five sites in the moss landing area during the 1989 loma prieta earthquake is presented results of this case history study include 1 a large set of cone penetration test cpt data for sites where evidence of liquefaction was and was not observed 2 information regarding the influence of thin soil strata on overall site behavior 3 inclinometer data on deformations at depth due to lateral spreading of a shoreline 4 a description of the apparent liquefaction of a marshland clayey silt deposit 5 seismic shear wave velocity data at sites where evidence of liquefaction was and was not observed and 6 an evaluation of how interpretation methods affect the development and use of cpt based liquefaction correlations

archaeomagnetic paleointensity in the american southwest during the past 2000 years abstract an archaeomagnetic paleointensity study was carried out on pottery samples from the hohokam anasazi and mogollon cultures of the american southwest the thellier thellier paleointensity experiment was used on 187 specimens from 77 different sherds derived from 23 archaeological sites interpretations were made for 127 specimens from 54 sherds about a two thirds success rate the median value for the quality factor was 12 the results were corrected for magnetic anisotropy owing to a fabric in the pottery using an easy plane model of magnetization the anisotropy of the hard axis relative to the easy plane of magnetization averaged 31 the correction factor for the paleointensity was typically 5 4 and systematically increased the paleointensities because the laboratory heatings were applied within the easy plane the sample average paleointensities were compiled along with other data from north america the hohokam data were kept as a separate set because of uncertainties concerning the hohokam chronology curves of the virtual axial dipole moment vadm variation for the hohokam and non hohokam data sets were derived using a moving window smoothing technique the hohokam and non hohokam curves show good agreement regardless of which hohokam chronology is used relative paleointensity records from north american lake sediments are also congruent with the archaeointensity results despite the scatter in the archaeomagnetic data the correlation of these records suggests that the secular variation pattern is being recovered the field strength at 300 bc is 30 40 higher than at present a low from 250 to 1250 ad is 10 15 weaker than at present and a peak at 1500 ad is about 30 higher than at present the low from 250 to 1250 ad in comparison with global paleointensity compilations suggests a substantial non dipole field in north america at that time the rate of change of the archaeomagnetic vadm is similar to rates observed today

engineering geologic and geotechnical analysis of paleoseismic shaking using liquefaction effects field examples abstract the greatest impediments to the widespread acceptance of back calculated ground motion characteristics from paleoliquefaction studies typically stem from three uncertainties 1 the significance of changes in the geotechnical properties of post liquefied sediments e g aging and density changes 2 the selection of appropriate geotechnical soil indices from individual paleoliquefaction sites and 3 the methodology for integration of back calculated results of strength of shaking from individual paleoliquefaction sites into a regional assessment of paleoseismic strength of shaking presented herein are two case studies that illustrate the methods outlined by olson et al engineering geology this issue for addressing these uncertainties the first case study is for a site near memphis tennessee wherein cone penetration test data from side by side locations one of liquefaction and the other of no liquefaction are used to readily discern that the influence of post liquefaction aging and density changes on the measured in situ soil indices is minimal in the second case study 12 sites that are at scattered locations in the wabash valley and that exhibit paleoliquefaction features are analyzed the features are first provisionally attributed to the vincennes earthquake which occurred around 6100 years bp and are used to illustrate our proposed approach for selecting representative soil indices of the liquefied sediments these indices are used in back calculating the strength of shaking at the individual sites the results from which are then incorporated into a regional assessment of the moment magnitude m of the vincennes earthquake the regional assessment validated the provisional assumption that the paleoliquefaction features at the scattered sites were induced by the vincennes earthquake in the main which was determined to have m 7 5 the uncertainties and assumptions used in the assessment are discussed in detail

archeomagnetic dating in western north america an updated reference curve based on paleomagnetic and archeomagnetic data sets 1 a robust database of paleomagnetic pm and archeomagnetic am data for western north america covering the past 4 millennia is assembled from three data sets 1 published pm data for dated lava flows 2 recently published am data generated by r l dubois and 3 published am data generated by j l eighmy chronologic information for the am data sets has been reassessed and the data points have been assigned to age ranges depending on their archeological contexts we have selected the computer program archeocourbe available from m le goff http www ipgp fr legoff or the auxiliary material see also http earthref org to construct am reference curves and to quantitatively estimate am dates for archeological and geological samples the updated curve provides a more detailed record of prehistoric secular variation for western north america than was previously available and shows a short interval of rapid secular variation sv in the 10th or 11th centuries at near excursional rates similar and coeval features in the hawaiian and to a lesser extent arkansan sv data sets possibly indicate a rapid amplitudinal shift in the regional nondipole field at that time

a revision to the u s southwest archaeomagnetic master curve abstract recently two problems have been recognized with the united states southwest archaeomagnetic master curve eighmy 1991 labelle eighmy 1997 sternberg 1989 one of these problems the damping problem is inherent to the moving window method of curve construction proposed by sternberg 1989 the other is due to the fact that the small number of independently dated virtual geomagnetic pole determinations available for the period between ad 900 1100 are not representative of secular variation during this period the analyses presented here confirm the existence of these two problems and suggest that they distort the curve by less than 1 0 and between 1 0 and 2 0 respectively based on these findings a new curve is proposed for the u s southwest

the pre ad 585 extension of the u s southwest archaeomagnetic reference curve a set of 104 independently dated archaeomagnetic directions was used to extend the u s southwest reference curve back to 375 cal bc and to calculate isolated mean vgps centered on 960 cal bc and 2390 cal bc prior to this study most u s southwest reference curves extended to only ca ad 585 this study employed sternberg s moving window technique with variably sized windows rather than fixed windows to smooth the dataset into a continuous curve the size of each averaging window was determined by the density of data captured by the window such that each window had a minimum data density of 5 0 and a minimum window size of 50 years this approach differs from previous studies in the u s southwest which have applied a uniformly sized averaging window to a dataset regardless of the temporal distribution of the data

a comparison of geomagnetic secular variation as recorded by historical archaeomagnetic and palaeomagnetic measurements palaeomagnetic methods can extend the documentary record of changes in the earth s magnetic field far into the past tolerable agreement is found between various methods demonstrating the geophysical value of palaeomagnetic experiments combining results from the different approaches of investigating secular change can lead to a better perspective and to superior models of geomagnetic field behaviour lake sediments have recently been found to hold remarkably detailed signatures of past field changes a mathematical approach to formulating an empirical description of global geomagnetic field behaviour is proposed and applied to palaeomagnetic data spanning the last 10 ka

densification of pond ash by blasting fly ash from thermal power plants is disposed in huge quantities in ash ponds which occupy large land areas otherwise useful for agriculture housing or other development for effective rehabilitation of ash ponds densification of the slurry deposit is essential to increase the bearing capacity and to improve its resistance to liquefication extensive field trials were carried out to evaluate the effectiveness of deep blasting for densification of deposited fly ash ninety explosions comprising 15 single blasts with varying depths and quantities of charges and 3 group blasts each having 25 charges placed at various spacings were carried out the compaction achieved in terms of an increase in relative density was evaluated from surface settlement measurements extensive field monitoring was undertaken through pore water pressure measurements vibration measurements penetration tests and block vibration tests for the average charge of 2 4 g of explosive per cubic meter of untreated deposit the average relative density was found to improve from 50 to 56 58 analysis of the test results indicates that deep blasting may be an effective technique for modest compaction of loose fly ash deposits the field testing program presented in this paper provides valuable information that can be used for planning blast densification of fly ash deposits

three dimensional surface deformation derived from airborne interferometric uavsar application to the slumgullion landslide author s delbridge bg burgmann r fielding e hensley s schulz wh abstract 2016 american geophysical union all rights reserved in order to provide surface geodetic measurements with landslide wide spatial coverage we develop and validate a method for the characterization of 3 d surface deformation using the unique capabilities of the uninhabited aerial vehicle synthetic aperture radar uavsar airborne repeat pass radar interferometry system we apply our method at the well studied slumgullion landslide which is 3 9 km long and moves persistently at rates up to 2 cm day a comparison with concurrent gps measurements validates this method and shows that it provides reliable and accurate 3 d surface deformation measurements the uavsar derived vector velocity field measurements accurately capture the sharp boundaries defining previously identified kinematic units and geomorphic domains within the landslide we acquired data across the landslide during spring and summer and identify that the landslide moves more slowly during summer except at its head presumably in response to spatiotemporal variations in snowmelt infiltration in order to constrain the mechanics controlling landslide motion from surface velocity measurements we present an inversion framework for the extraction of slide thickness and basal geometry from dense 3 d surface velocity fields we find that the average depth of the slumgullion landslide is 7 5 m several meters less than previous depth estimates we show that by considering a viscoplastic rheology we can derive tighter theoretical bounds on the rheological parameter relating mean horizontal flow rate to surface velocity using inclinometer data for slow moving clay rich landslides across the globe we find a consistent value for the rheological parameter of 0 85 0 08

effects of hydromechanical loading history and antecedent soil mechanical damage on shallow landslide triggering evidence suggests that the sudden triggering of rainfall induced shallow landslides is preceded by accumulation of local internal failures in the soil mantle before their abrupt coalescence into a landslide failure plane the mechanical status of a hillslope at any given time reflects competition between local damage accumulated during antecedent rainfall events and rates of mechanical healing e g rebonding of microcracks and root regrowth this dynamic interplay between damage accumulation and healing rates determines the initial mechanical state for landslide modeling we evaluated the roles of these dynamic processes on landslide characteristics and patterns using a hydromechanical landslide triggering model for a sequence of rainfall scenarios the progressive nature of soil failure was represented by the fiber bundle model formalism that considers threshold strength of mechanical bonds linking adjacent soil columns and bedrock the antecedent damage induced by prior rainfall events was expressed by the fraction of broken fibers that gradually regain strength or mechanically heal at rates specific to soil and roots results indicate that antecedent damage accelerates landslide initiation relative to pristine undamaged hillslopes the volumes of first triggered landslides increase with increasing antecedent damage however for heavily damaged hillslopes landslide volumes tend to decrease elapsed time between rainfall events allows mechanical healing that reduces the effects of antecedent damage this study proposed a quantitative framework for systematically incorporating hydromechanical loading history and information on precursor events e g such as recorded by acoustic emissions into shallow landslide hazard assessment

palaeomagnetic studies of burned rocks an assemblage of rocks such as comprising a fireplace will acquire a remanent magnetization upon cooling parallel to the ambient geomagnetic field and thus will share a common direction of magnetization detailed palaeomagnetic analyses of oriented samples will reveal whether these rocks have remained in situ since the last heating event or whether these rocks have moved or represent discard material thermal demagnetization makes it possible in many cases to estimate the maximum temperature which a given rock has experienced the direction of magnetization can be used to reposition rocks to their cooling position and the cooling history of boiling stones can be reconstructed for some rocks this paper presents results obtained from burned rocks from various archaeological sites

blast densification multi instrumented case history a comprehensive blast densification field study was conducted at a test site in south carolina to densify a loose soil layer at a depth between z 8 13 m the study included extensive laboratory and field characterizations and four carefully monitored blast events results revealed that densification is not an instantaneous phenomenon underlying time dependent processes involve resedimentation drainage of excess pore pressure as the granular skeleton deforms and the effective stress recovers and secondary settlement effects which do not involve excess pore pressure dissipation the degree of densification decreased in successive blasting events and the soil gradually evolved toward an asymptotical terminal density associated with blast densification the blasting sequence and detonation delays appeared to have a minor effect on shear induced movements the increase in penetration resistance manifested 2 years after four blasting drainage events instead surface settlement using standard surveying te

near east paleomagnetic secular variation recorded in sediments from the sea of galilee lake kinneret abstract paleomagnetic records of declination and inclination from sediments recovered from the bed of lake kinneret 32 4 n 35 7 e have been dated by radiocarbon techniques the sediments span the last 5000 yr the changes in inclination down the sediment cores are more pronounced than the declination fluctuations and are repeatable between the three coring sites which are several kilometers apart magnetic susceptibility logs display 13 maxima in the 5 m long sequences with a pronounced susceptibility minimum about 1000 yr b p many of the susceptibility maxima and minima can be easily correlated between coring sites and are shown to be dominantly related to changes in sediment carbonate content the natural remanent magnetization intensity follows a similar pattern to that of susceptibility and the natural remanence of the kinneret sediments is presumed to reside in detrital magnetite grains carried into the lake by the river jordan from the basalt rich bedrock of the rift floor and the golan heights the 14c chronology is strongly supported by a pollen study in which pronounced changes in the proportion of olive pollen were interpreted as being due to extensive cultivation of olives around galilee in the hellenistic and byzantine periods the kinneret paleosecular variation records if accurately dated point to a complex spatial pattern of holocene secular variation with significant variations over distances as small as 1000 2000 km

archaeomagnetic investigations of geomagnetic secular variations bulgarian archaeomagnetic directions and intensities show a satisfactory agreement with those for ukraine and paris bauer plots of declination against inclination show both clockwise and anticlockwise looping through the last eight millennia the necessity for accurate dating of samples studied is stressed

effects of geologic time on the initial stiffness of clays abstract the paper addresses the effect of geologic aging on the initial stiffness of clays through the analysis of in situ shear stiffness data obtained using a seismic cone penetrometer at three sites in boston blue clay bbc a 12 000 14 000 year old post glacial marine clay deposit the effects of this aging period are estimated using as reference for the unaged behavior the results of over 90 triaxial shear phases conducted on specimens of resedimented boston blue clay rbbc a soil prepared in the laboratory from natural bbc and tested after 1 day of laboratory aging at the same ocr and effective stress level the natural clay displays an initial stiffness which on the average is approximately 50 greater than that of the laboratory resedimented clay based on the estimated age of the natural deposit this corresponds to an increase of the stiffness per log cycle of time of 7 this value of the aging coefficient ng is at the low end of values presented in the literature for clays which are however all based on shorter aging durations days to weeks

shallow viscoplastic flow on an inclined plane evolving viscoplastic flows upon slopes are an important idealization of many flows in a variety of geophysical situations where yield stress is thought to play a role for such models asymptotic expansions suitable for slowly moving shallow fluid layers lubrication theory reduce the governing equations to a simpler problem in terms of the fluid thickness we consider the version of the theory for fluids described by the herschel bulkley constitutive law and provide a variety of solutions to the reduced equation both numerical and analytical for extruded inclined domes we derive the characteristic temporal behaviour of measures of the dome s dimensions

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

archaeomagnetic dating of santorini volcanic eruptions and fired destruction levels of late minoan civilization archaeomagnetic dating on the minoan ash horizons of the santorini volcano and on fired destruction levels at late minoan sites on crete demonstrates that the basal plinian air fall ash of the first minoan pumice is contemporaneous with the destruction levels on central crete while the higher minoan ashes are contemporaneous with the destruction levels in extreme eastern crete these destruction levels were almost certainly caused by seismic activity rather than the ash fall the determination of a time gap between these events lead to a reappraisal of the archaeological evidence and is important volcanologically

use of small amplitude paleomagnetic fluctuations for correlation and dating of continental climatic changes abstract recent advances in field and laboratory methods have made possible the study of paleomagnetic fluctuations recorded with high resolution in lake sediments of relatively small amplitude and short period 102 years to 104 years foremost among these methods are sediment coring techniques that allow azimuthally oriented long cores 25 m to be raised with small orientation errors 3 and the use of cryogenic magnetometers to measure weakly magnetized m 10 9 a m2 sediment samples accurately with these methods records of inclination declination and relative paleointensity nrm arm have been obtained in north america that span the last 20 000 years substantial agreement in declination and inclination features is seen on a scale of 103 km in north america for the last 10 000 years these paleomagnetic features can be useful in determining the relative age of paleoclimatic features particularly in those situations where 14c dating is unreliable similar agreement is seen for the last 4000 years between relative paleointensity estimates obtained from pennsylvania lake sediments and absolute paleointensity estimates obtained from 14c dated lava flows and potsherds from the western united states similar paleointensity fluctuations to those occurring from 0 to 4000 yr b p in the western united states are observed for the last 12 500 yr b p in lake sediments from new york and pennsylvania such relative paleointensity records from lake sediments if independently confirmed considerably extend the range and resolution of paleointensity data and have important implications for the study of secular variation models variations in atmospheric radiocarbon concentration and the proposed relationships between geomagnetism and climate an absolute secular variation chronology for the varved sediments of elk lake minnesota can be used to date magnetically the secular variation records of unvarved sediments elsewhere in north america

the origin of consolidation laminae and dish structures in some deep water sandstones abstract consolidation laminae and dish structures form high density zones that are interpreted to have formed by disruption of primary structures during gravitational collapse of the grain framework during water escape and consolidation they are not associated with higher contents of clay size material than adjacent units but the chloritic clay minerals associated with consolidation laminae and dish structures have a different microtexture than observed elsewhere clay mineral texture has a direct effect on petrophysical characteristics in particular water saturation and conductivity in hydrocarbon saturated intervals ct scans identify consolidation laminae and dish structures as zones of high density that correspond to tighter packing of sand grains and are unrelated to clay distribution dish structures may form independently of consolidation laminae or by further modification of fragmented consolidation laminae

use of liquefaction induced features for paleoseismic analysis an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of holocene paleo earthquakes abstract liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the holocene these features include dikes craters vented sand sills and laterally spreading landslides the relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo earthquakes this state of the art summary for using liquefaction induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives the driving mechanism for formation of the features is primarily the increased pore water pressure associated with liquefaction of sand rich sediment the role of this mechanism is often supplemented greatly by the direct action of seismic shaking at the ground surface which strains and breaks the clay rich cap that lies immediately above the sediment that liquefied discussed in the text are the processes involved in formation of the features as well as their morphology and characteristics in field settings whether liquefaction occurs is controlled mainly by sediment grain size sediment packing depth to the water table and strength and duration of seismic shaking formation of recognizable features in the field generally requires a low permeability cap above the sediment that liquefied field manifestations are controlled largely by the severity of liquefaction and the thickness and properties of the low permeability cap criteria are presented for determining whether observed sediment deformation in the field originated by seismically induced liquefaction these criteria have been developed mainly by observing historic effects of liquefaction in varied field settings the most important criterion is that a seismic liquefaction origin requires widespread regional development of features around a core area where the effects are most severe in addition the features must have a morphology that is consistent with a very sudden application of a large hydraulic force this article discusses case studies in widely separated and different geological settings coastal south carolina the new madrid seismic zone the wabash valley seismic zone and coastal washington state these studies encompass most of the range of settings and the types of liquefaction induced features likely to be encountered anywhere the case studies describe the observed features and the logic for assigning a seismic liquefaction origin to them also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin two independent methods for estimating prehistoric magnitude are discussed briefly one method is based on determination of the maximum distance from the epicenter over which liquefaction induced effects have formed the other method is based on use of geotechnical engineering techniques at sites of marginal liquefaction in order to bracket the peak accelerations as a function of epicentral distance these accelerations can then be compared with predictions from seismological models

construction of type curves of geomagnetic secular variation for dating lake sediments from east central north america type curves of palaeomagnetic secular variations of declination and inclination through the last 12 000 radiocarbon years have been constructed by combining data from the minnesota lakes with paral

geotechnical analysis of paleoseismic shaking using liquefaction features a major updating a new methodology is proposed for the geotechnical analysis of strength of paleoseismic shaking using liquefaction effects the proposed method provides recommendations for selection of both individual and regionally located test sites provides techniques for validation of field data for use in back analysis and presents a recently developed energy based solution to back calculate paleoearthquake magnitude and strength of shaking the proposed method allows investigators to qualitatively assess the influence of post earthquake density change and aging the proposed method also describes how the back calculations from individual sites should be integrated into a regional assessment of paleoseismic parameters

archeomagnetism of ontario potsherds from the last 2000 years an archeomagnetic study was carried out on potsherds samples from sites in ontario with ages ranging from a d 90 to a d 1640 as determined by 14c dating thellier double heating paleointensity experiments were performed in air on 65 specimens of 52 samples from seven sample sets reliable paleointensity estimates were obtained for 49 specimens alternating field and thermal demagnetization temperature dependence of weak field susceptibility and hysteresis measurements indicate that magnetite of pseudo single domain grain size is the carrier of natural remanent magnetization the paleointensity results follow a half cycle sine curve with a steady decrease from 54 0 5 9 t to 37 6 5 7 t between a d 90 and a d 885 and a monotonic increase from 52 0 6 1 t to 59 4 1 7 t between a d 1200 and a d 1900 the paleointensities determined yield virtual axial dipole moments vadms of the earth s magnetic field that agree well with those from other parts of north america except between a d 900 and a d 1400 when they are systematically lower this discrepancy is probably caused by a substantial non dipole field in southwestern north america from the tenth to the fifteenth century since secular variation studies using potsherds from arizona and lake sediments from minnesota show different inclination variations during that period

secular variation of archaeomagnetic direction in the american southwest a d 750 1425 oriented archaeomagnetic samples were collected from 158 in situ features at 33 archaeological sites in the southwestern united states seventy three independently dated features were used for analysis of secular variation a moving window technique with outlier rejection was developed to compute a smoothed secular variation curve this technique incorporates weighted fisher statistics to account for imprecision in both the age of remanence acquisition and the direction of magnetization for each feature a mean direction and measure of dispersion is generated for each window of time the secular variation record covers the period a d 750 1425 during which time the virtual geomagnetic pole vgp moves in a generally counterclockwise fashion from 86 n 83 e at a d 750 to the lowest latitude position of 74 n 192 e at a d 1075 and then to 85 n 236 e at a d 1425 the median rate of vgp movement is 0 036 yr 1 similar to present day rates the southwestern record shows close correspondence to other north american archaeomagnetic limnomagnetic and speleomagnetic records the archaeomagnetic record can serve as the master curve for the derivation of archaeomagnetic dates

attempts to date salt making activity in iron age britain using magnetic inclinations briquetage describes all the ceramic equipment used in extracting sea salt in prehistoric and roman europe it includes semi cylindrical desiccating troughs and the stands supports and clips used to stabilize them over hearths in many cases the baked hearth linings or superstructures are included under briquetage upon first inspection archeomagnetic dating seems inappropriate because the briquetage is broken and disoriented material although the ancient magnetic declination cannot be referred to the present north direction the desiccating troughs acted as water level gauges so that a tilt correction permits one to estimate the archaeoinclination the range of inclinations brackets the age of the saltern use within the last two centuries bc this is compatible with ceramic styles and two radiocarbon ages of charcoal from a supposedly contemporaneous hearth the archeodeclination of 7 95 10 from a contemporary in situ hearth confirms this age range thus we attribute the lincolnshire salterns to late iron age activity the paleosecular variation for southern britain over the last two millennia is sufficiently characteristic in many time periods to permit the use of inclinations alone to bracket ages this requires material with some original horizontal reference e g masonry fragments disrupted sedimentary layers or pot bases