archeomagnetic study of seven contemporaneous kilns from murcia spain new archeointensity values have been determined from seven spanish kilns sampled at the same archeological site and dated by archeological constraints as between 1100 and 1200 a d the directions of the characteristic remanent magnetization and paleointensities have been obtained from classical thellier experiments conducted on 69 samples collected from the walls of the kilns thermoremanent magnetization trm anisotropy and the cooling rate effect upon trm intensity acquisition have been investigated in all the samples differences between mean archeointensities per site before and after corrections for cooling rate are between 3 and 17 the study of these seven contemporaneous kilns coming from the same archeological site and treated in the same way in the laboratory allows us to discuss the different factors that can cause the dispersion between sites generally observed in archeointensity studies the results confirm on one hand the need for cooling rate corrections in this kind of study and on the other hand the need to obtain several archeointensity determinations per century in order to construct a reliable archeointensity curve finally the new data provide a robust mean intensity 60 3 3 3 t at the latitude of paris for the middle of the xii century in western europe and constrain better the evolution of the geomagnetic field intensity during medieval times in this area

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

new archeointensity data from nw argentina 1300 1500 ce abstract a good characterization of the geomagnetic field strength at centennial to millennial time scales in the southern hemisphere is particularly crucial to disentangle the long term evolution of the south atlantic anomaly saa an intriguing geomagnetic feature currently observed at the earth s surface here we present 59 new archeointensities obtained from four well dated groups of potteries with ages ranging between 1300 and 1500 ce and collected in northwest argentina the new data were obtained in accordance with the thellier paleointensity method including partial thermoremanent magnetization ptrm checks and trm anisotropy and cooling rate corrections we have also performed a comparative study of the efficiency of magnetic susceptibility arm and trm anisotropy tensors to correct the trm anisotropy effect upon intensity estimates our results suggest that the magnetic susceptibility tensor systematically underestimates the trm anisotropy effect by 10 30 our new data together with selected archeointensities already published confirm that the decrease of the geomagnetic field intensity in south america started around 1600 1650 ce due to the arrival of the saa

two thousand years of archeointensity from west africa this study presents 17 archeointensity estimates from senegal and mali two neighboring countries in west africa for the period 1000 bce to 1000 ce the archeological artifacts used in this study were collected during the course of two separate projects together spanning 22 years and across 8 separate excavations a primary objective of this study was to get accurate dates hence only samples with independent age constraints from pottery style detailed stratigraphy and 14c dates were used a total of 236 specimens from 63 samples were subjected to a double heating paleointensity experiment izzi method from which 95 specimens were selected using a set of very strict selection criteria the paleointensity results were corrected for differential cooling rate effects and remanence anisotropy additionally we demonstrate the equivalence of using tensors derived from anhysteretic and thermal remanences for correcting remanent anisotropy of the specimens and use the former for the anisotropy correction our data show good agreement with the most recent paleosecular variation model but are lower than the pre existing data which are mostly from egypt and morocco the presence of substantial non axial dipolar contributions in the region is evident when virtual axial dipole moments vadms from the published literature are calculated for 20 latitudinal bands and compared with our data the average vadm values show a distinct latitudinal gradient a prominent feature of this dataset is an intensity high observed prior to 700 ce in both senegal and mali comparing this peak with existing records from regions further to the north suggests a small but significant temporal offset and is interpreted to be additional evidence for a geomagnetic field with a significant and rapidly changing non axial dipolar contribution

geomagnetic field for 0 3 ka 2 a new series of time varying global models 1 steadily increasing numbers of archeomagnetic and paleomagnetic data for the holocene have allowed development of temporally continuous global spherical harmonic models of the geomagnetic field extending present and historical global descriptions of magnetic field evolution the current work uses various subsets of improved data compilations details of which are given in a companion paper by donadini et al 2009 and minor modifications of standard modeling strategies using temporally and spatially regularized inversion of the data and cubic spline parameterizations for temporal variations to produce five models with enhanced spatial and temporal resolution for 0 3 ka spurious end effects present in earlier models are eliminated by enforcing large scale agreement with the gufm1 historical model for 1650 1990 a d and by extending the model range to accommodate data older than 3 ka age errors are not considered as a contribution to data uncertainties but are included along with data uncertainties in an investigation of statistical uncertainty estimates for the models using parametric bootstrap resampling techniques we find common features but also significant differences among the various models indicating intrinsic uncertainties in global models based on the currently available holocene data model cals3k 3 based on all available archeomagnetic and sediment data without a priori quality selection currently constitutes the best global representation of the past field the new models have slightly higher dipole moments than our previous models virtual axial dipole moments vadms calculated directly from the data are in good agreement with all corresponding model predictions of vadms these are always higher than the spherical harmonic dipole moment indicating the limitations of using vadms as a measure of geomagnetic dipole moments

non dipole and regional effects on the geomagnetic dipole moment estimation the study of the temporal evolution of the dipole moment variations is a forefront research topic in earth sciences it constrains geodynamo simulations and is used to correct cosmogenic isotope production which is evidence of past solar activity and it is used to study possible correlations between the geomagnetic field and the climate in this work we have analysed the main error sources in the geomagnetic dipole moment computation from palaeomagnetic data the influence of the non dipole terms in the average approach the inhomogeneous distribution of the current palaeomagnetic database and the averaging procedure used to obtain the evolution of the dipole moment to evaluate and quantify these effects we have used synthetic data from a global model based on instrumental and satellite data the international geomagnetic reference field 11th generation results indicate that the non dipole terms contribute on a global scale of 6 in the averaged dipole moment whereas the regional non dipole contribution can show deviations of up to 35 in some regions such as oceania and different temporal trends with respect to the global dipole moment evolution in other ones such as europe and asia a regional weighting scheme seems the best option to mitigate these effects in the dipole moment average approach but when directional and intensity palaeomagnetic information is available on a global scale and in spite of the inhomogeneity of the database global modelling presents more reliable values of the geomagnetic dipole moment

geomagnetic intensity spike recorded in high resolution slag deposit in southern jordan article i nfo in paleomagnetism periods of high field intensity have been largely ignored in favor of the more spectacular directional changes associated with low field intensity periods of excursions and reversals hence questions such as how strong the field can get and how fast changes occur are still open in this paper we report on data obtained from an archaeometallurgical excavation in the middle east designed specifically for archaeomagnetic sampling we measured 342 specimens from 72 samples collected from a 6 1 m mound of well stratified copper production debris at the early iron age 12th 9th centuries bce site of khirbat en nahas in southern jordan seventeen samples spanning 200 yr yielded excellent archaeointensity results that demonstrate rapid changes in field intensity in a period of overall high field values the results display a remarkable spike in field strength with sample mean values of over 120 t compared to the current field strength of 44 t a suite of 13 radiocarbon dates intimately associated with our samples tight control of sample location and relative stratigraphy provide tight constraints on the rate and magnitude of changes in archaeomagnetic field intensities

new archeointensity data from novgorod north western russia between c 1100 and 1700 ad implications for the european intensity secular variation abstract reconstructing the secular variation of europe s geomagnetic field over the past millennium is challenging because of the lack of recently acquired archeomagnetic data from western russia in this paper we report on nine new archeointensity values obtained from groups of brick fragments sampled in novgorod north western russia and its vicinities these fragments were collected from churches whose precise ages range from the beginning of the 12th century to the end of the 17th century ad all the archeointensity measurements were carried out using the triaxe experimental protocol which takes into account the thermoremanent magnetization trm anisotropy effect intensity determinations were performed using fast and slow cooling rates for laboratory trm acquisition the results confirm that the triaxe protocol overcomes the trm cooling rate dependence the new data shows that geomagnetic field intensities in north western russia have decreased in the past millennium comparisons were made with other data previously obtained in western europe the balkans and russia as well as with intensity values expected in novgorod from global geomagnetic field models these comparisons yielded three main results 1 the new archeointensity data do not show the occurrence of large intensity variations in north western russia as those observed in the balkan dataset conversely they appear more compatible with western european results which suggests a limited non dipole field effect across europe during the past millennium 2 our data are weaker than the intensity values expected in novgorod from the available global geomagnetic field models this suggests that the field models are inaccurate for the novgorod area 3 a constant linear decrease of the geocentric axial dipole moment since 1600 ad does not appear compatible with our younger data

estimates of dinosaur speeds from a new trackway site in texas a method for estimating the speed of a dinosaurian trail maker from the size of its footprints and stride has been described by alexander1 however when applied to known trackways this method gave rather low speeds 1 0 3 6 m s 1 russell and beland2 estimated a speed of 1 77 m s 1 for a slowly moving ornithomimid and 7 54 m s 1 for an allegedly rapidly running ornithopod the latter estimate is questionable as there is some doubt concerning the number of prints and thus the stride length of the trail3 4 dinosaurs responsible for trackways in british columbia5 south wales6 and queensland7 all seem to have been moving slowly thus reliable estimates of dinosaur speeds are all rather low here i report dinosaur speeds based on trails at a new site from the lower cretaceous of texas some of which appear quite fast by alexander s method1

intensity of the geomagnetic field in europe for the last 3 ka influence of data quality on geomagnetic field modeling one of the main challenges of paleomagnetic research is to obtain high resolution geomagnetic field intensity reconstructions for the last millennia these reconstructions are mostly based on archeomagnetic data however the quality of the intensity data available in the databases is very variable and the high scatter observed in the records clearly suggests that some of them might not be reliable in this work we investigate how the geomagnetic field intensity reconstructions and hence our present knowledge of the geomagnetic field in the past are affected by the quality of the data selected for modeling the earth s magnetic field for this purpose we rank the european archeointensity data in four quality categories following widely accepted paleomagnetic criteria based on the methodology used during the laboratory treatment of the samples and on the number of specimens retained to calculate the mean intensities four geomagnetic field regional models have been implemented by applying the revised spherical cap harmonic analysis to these four groups of input data geomagnetic field models strongly depend on the used data set the model built using all the available data without any preselection appears to be the less accurate indicating some internal inconsistencies of the data set in addition some features of this model are clearly dominated by the less reliable archeointensity data suggesting that such features might not reflect real variations of the past geomagnetic field on the contrary the regional model built on selected high quality intensity data shows a very consistent intensity pattern at the european scale confirming that the main intensity changes observed in europe in the recent history of the geomagnetic field occurred at the continental scale

new late neolithic c 7000 5000 bc archeointensity data from syria reconstructing 9000years of archeomagnetic field intensity variations in the middle east we present new archeomagnetic intensity data from two late neolithic archeological sites tell halula and tell masaikh in syria these data from 24 groups of potsherds encompassing 15 different time levels are obtained using the triaxe experimental protocol which takes into account both the thermoremanent magnetization anisotropy and cooling rate effects on intensity determinations they allow us to recover the geomagnetic intensity variations in the middle east between 7000 bc and 5000 bc i e during the so called pre halaf proto halaf halaf and halaf ubaid transitional cultural phases the data are compared with previous archeointensity results of similar ages from northern iraq yarim tepe ii and tell sotto and bulgaria we find that previous dating of the iraqi material was in error when corrected all northern mesopotamian data show a relatively good consistency and also reasonably match with the bulgarian archeointensity dataset using a compilation of available data we construct a geomagnetic field intensity variation curve for the middle east encompassing the past 9000 years which makes it presently the longest known regional archeomagnetic intensity record we further use this compilation to constrain variations in dipole field moment over most of the holocene in particular we discuss the possibility that a significant dipole moment maximum occurred during the third millennium bc which cannot easily be identified in available time varying global geomagnetic field reconstructions

fault activation by hydraulic fracturing in western canada hydraulic fracturing has been inferred to trigger the majority of injection induced earthquakes in western canada in contrast to the midwestern united states where massive saltwater disposal is the dominant triggering mechanism a template based earthquake catalog from a seismically active canadian shale play combined with comprehensive injection data during a 4 month interval shows that earthquakes are tightly clustered in space and time near hydraulic fracturing sites the largest event moment magnitude mw 3 9 occurred several weeks after injection along a fault that appears to extend from the injection zone into crystalline basement patterns of seismicity indicate that stress changes during operations can activate fault slip to an offset distance of 1 km whereas pressurization by hydraulic fracturing into a fault yields episodic seismicity that can persist for months

a new three axis vibrating sample magnetometer for continuous high temperature magnetization measurements applications to paleo and archeo intensity determinations we have developed a new three axis vibrating sample magnetometer which allows continuous high temperature magnetization measurements of individual cylindrical 0 75 cm3 samples up to 650 c and the acquisition of thermoremanent magnetization trm in any direction and field intensity up to 200 t we propose a fast less than 2 5 h automated experimental procedure adapted from boyd s nature 319 1986 208 209 modified version of the thellier and thellier ann geophys 15 1959 285 376 method which provides continuous intensity determinations over a large typically 300 c temperature interval for each sample this procedure allows one to take into account both the cooling rate dependence of trm acquisition and anisotropy of trm several examples of analyses of ancient magnetization demonstrate the quality and reliability of the data and illustrate the promising potential of this new instrument in paleo and archeomagnetism

new constraints on the most significant paleointensity change in western europe over the last two millennia a non dipolar origin over the last years new evidences of several short lived regional maxima of the geomagnetic field intensity at various times and locations have been defined these features have important implications both for geomagnetic field modeling and for earth s dynamo simulations however the nature extent and underlying causes of these variations are still poorly understood the major constraint for an adequate description of these important features is the absence of continuous detailed records and the current limited availability of precisely dated geomagnetic field recorders in this context archeological materials from superimposed strata covering long sequences of occupation provide a powerful tool to investigate the temporal variability of geomagnetic field strength at decadal and centennial time scales in this work we report the archeomagnetic study of 79 potteries from southeastern spain collected in 14 different stratigraphic units the chronological framework of the studied collection ranging from the 9th to the 12th centuries is based on historical archeological data such as written sources and well established typological and archeometric documentation on ceramics found on reference contexts in the area additionally two radiocarbon dates obtained from two different stratigraphic units confirm the proposed chronological intervals from classical thellier and thellier experiments including partial thermoremanent magnetization ptrm checks and trm anisotropy and cooling rate corrections height new high quality mean intensities were derived the new data provide an improved description of the sharp abrupt intensity decay that took place in western europe after the 800 ad intensity maximum the most significant geomagnetic field intensity feature observed in europe over the last two millennia the new results confirm that several rapid intensity changes with rates higher than 10 t century took place in western europe during the recent history of the earth the comparison between the regional curve of western europe and the sha dif 14k global field model predictions suggests that the 800 ad event observed in europe is probably controlled by non dipolar geomagnetic sources

two archaeomagnetic intensity maxima and rapid directional variation rates during the early iron age observed at iberian coordinates implications on the evolution of the levantine iron age anomaly abstract variations of geomagnetic field in the iberian peninsula prior to late iron age times are poorly constrained here we report 14 directional and 10 palaeointensity results from an archaeomagnetic study carried out on 17 combustion structures recovered from six archaeological sites in eastern spain the studied materials have been dated by archaeological evidences and supported by radiocarbon dates 8th 5th centuries bc rock magnetic experiments indicate that the characteristic remanent magnetization is carried by a low coercivity magnetic phase with curie temperatures of 500 575 c most likely titanomagnetite maghemite with low titanium content archaeointensity determinations were carried out by using the classical thellier thellier experiment including ptrm checks and magnetic anisotropy corrections a new full vector iberian paleosecular variation curve for the iron age is presented high fluctuation rates on both directions and intensities are observed during the early iron times that seems to be related with the levantine iron age anomaly liaa the most prominent anomaly of the geomagnetic field of the last three millennia two intensity maxima were observed at iberian coordinates the oldest around 750 bc associated with easterly declinations of around 23 and the second 275 yrs later 475 bc with northerly directions the related virtual axial dipole moment was up to 14 10 22 am2 for the oldest materials 750 bc and reaching 16 10 22 am2 for the materials corresponding to the end of the early iron age in order to investigate the origin of the unusually high fluctuations of the palaeofield we have developed a new global geomagnetic field reconstruction the shawq ironage model which is based on a critical revision of the global archeomagnetic and volcanic dataset the new model provides an improved description of the evolution of the liaa which is related to a normal flux patch at the core mantle boundary cmb below arabian peninsula clearly observed at around 950 bc this flux patch expanded towards the north west while decreasing in intensity reaching iberia at around 750 bc around 600 500 bc it underwent a revival below the european continent after that it seems to vanish in situ

the cardston earthquake swarm and hydraulic fracturing of the exshaw formation alberta bakken play more than 60 small earthquakes m l 0 7 3 0 were detected from december 2011 to march 2012 north of cardston alberta an area with little evidence for previous seismic activity the timing of these events closely correlates 99 7 confidence with hydraulic fracturing completions of the devonian mississippian age exshaw formation at a nearby horizontal well unanimous waveform multiplicity within the swarm suggests that the events share a similar origin and source mechanism this observation is corroborated by the point like collocation of hypocenters within the crystalline basement during robust double difference relocations furthermore the presence of a pre existing fault is confirmed via formation top offset mapping and interpreted to be a late cretaceous extensional fault the confirmation of this fault at depth provides a plausible pathway for rapid hydraulic communication from the fracturing interval into the crystalline basement consistent with structural interpretations and available stress information moment tensor inversion of the largest magnitude event m w 3 0 indicates reactivation of a basement fault with normal slip we conclude that the genesis of this earthquake swarm was likely caused by increased pore pressure within the basement fault as a result of fracturing stimulation online material figure showing frequency magnitude distribution of earthquakes and table of the velocity models used in the study

the steens mountain oregon geomagnetic polarity transition 2 field intensity variations and discussion of reversal models we carried out an extensive paleointensity study of the 15 5 0 3 m y miocene reversed to normal polarity transition recorded in lava flows from steens mountain south central oregon one hundred eighty five samples from the collection whose paleodirectional study is reported by mankinen et al this issue were chosen for paleointensity investigations because of their low viscosity index high curie point and reversibility or near reversibility of the strong field magnetization curve versus temperature application of the thellier stepwise double heating method was very successful yielding 157 usable paleointensity estimates corresponding to 73 distinct lava flows after grouping successive lava flows that did not differ significantly in direction and intensity we obtained 51 distinguishable complete field vectors of which 10 are reversed 28 are transitional and 13 are normal the record is complex quite unlike that predicted by simple flooding or standing nondipole field models it begins with an estimated several thousand years of reversed polarity with an average intensity of 31 5 8 5 t about one third lower than the expected miocene intensity this difference is interpreted as a long term reduction of the dipole moment prior to the reversal when site directions and intensities are considered truly transitional directions and intensities appear almost at the same time at the beginning of the transition and they disappear simultaneously at the end of the reversal large deviations in declination occur during this approximately 4500 1000 year transition period that are compatible with roughly similar average magnitudes of zonal and nonzonal field components at the site the transitional intensity is generally low with an average of 10 9 4 9 t for directions more than 45 away from the dipole field and a minimum of about 5 t the root mean square of the three field components x y and z are of the same order of magnitude for the transitional field and the historical nondipole field at the site latitude however a field intensity increase to pretransitional values occurs when the field temporarily reaches normal directions which suggests that dipolar structure could have been briefly regenerated during the transition in an aborted attempt to reestablish a stationary field changes in the field vector are progressive but jerky with at least two and possibly three large swings at astonishingly high rates each of those transitional geomagnetic impulses occurs when the field intensity is low less than 10 t and is followed by an interval of directional stasis during which the magnitude of the field increases greatly for the best documented geomagnetic impulse the rapid directional change corresponds to a vectorial intensity change of 6700 2700 nt yr 1 which is about 15 50 times larger than the maximum rate of change of the nondipole field observed during the last centuries the occurrence of geomagnetic impulses seems to support reversal models assuming an increase in the level of turbulence within the liquid core during transitions the record closes with an estimated several thousand years of normal polarity with an average intensity of 46 7 20 1 t agreeing with the expected miocene value however the occurrence of rather large and apparently rapid intensity fluctuations accompanied by little change in direction suggests that the newly reestablished dipole was still somewhat unstable

fluid injection and seismic activity in the northern montney play british columbia canada with special reference to the 17 august 2015 mw 4 6 induced earthquake in this article we analyzed the recent seismic activity in the northern montney play of british columbia in 2015 and its connection with fluid injection hydraulic fracturing and long term injection of gas and wastewater disposal in the region the earthquake sequence used in this study includes 676 events from 3 october 2014 to 31 december 2015 from the progress energy earthquake catalog with moment magnitude as small as 1 spatial and temporal correlation of seismic activity with the fluid injection in the region revealed that these events are better correlated with hydraulic fracturing correlation coefficient of 0 17 at confidence level close to 99 7 with a lag time between 0 and 2 days than other types of injection using the double difference relocation technique we obtained depth constraints for some of the events for which supplementary industry provided waveforms were available the depths of these events range from 0 5 to 2 5 km and are mostly constrained above the target zone where hydraulic fracturing was taking place the best fit moment tensor solution for the event on 17 august 2015 gives a moment magnitude of 4 6 and a predominantly thrust mechanism in the northwest southeast direction with a shallow focal depth of 4 km this is consistent with that obtained through double difference relocation for this event 1 3 km given the depth uncertainty of the moment tensor inversion electronic supplement 1 tables of injection volumes and seismicity parameters and figure of monthly distribution of seismic events and location of fluid injection sites in the vicinity of the 17 august 2015 m w 4 6 event 1 http www bssaonline org lookup suppl doi 10 1785 0120160175 dc1

biomechanics dinosaur locomotion from a new trackway ardley quarry in oxfordshire uk contains one of the most extensive dinosaur trackway sites in the world with individual trackways extending for up to 180 metres we have discovered a unique dual gauge trackway from a bipedal theropod dinosaur from the middle jurassic in this locality which indicates that these large theropods were able to run and that they used different hindlimb postures for walking and running our findings have implications for the biomechanics and evolution of theropod locomotion

control of hazard due to seismicity induced by a hot fractured rock geothermal project in 2003 hydraulic stimulations were carried out in a geothermal field in eastern el salvador central america as part of a project to explore the feasibility of commercial hot fractured rock energy generation a key requisite for this environmentally friendly energy source is that the fracturing of the hot rocks at depths of 1 2 km must not produce levels of ground shaking at the surface that would present a serious disturbance or threat to the local population thresholds of tolerable ground motion were inferred from guidelines and regulations on tolerable levels of vibration and from correlations between instrumental strong motion parameters and intensity considering the vulnerability of the exposed housing stock the thresholds were defined in terms of peak ground velocity pgv and incorporated into a traffic light system that also took account of the frequency of occurrence of the induced earthquakes the system was implemented through a dedicated seismograph array and locally derived predictive equations for pgv the traffic light was used as a decision making tool regarding the duration and intensity of pumping levels during the hydraulic stimulations the system was supplemented by a small number of accelerographs and re calibrated using records obtained during the rock fracturing

ensembles of low degree archeomagnetic field models for the past three millennia abstract we introduce ensembles of time varying archeomagnetic field models consisting of a reference model a mean model and a thousand individual models we present a set of three such ensembles built from archeomagnetic volcanic and sedimentary data sets that cover the past three millennia these ensembles can be used to describe the field at any location from the core surface to the magnetosphere and assess the way uncertainties due to the limited distribution and quality of the data affect any of its component or parameter such as individual gauss coefficients they provide alternative and we argue more complete descriptions of the archeomagnetic field to those provided by previously published archeomagnetic field models being better suited to existing and emerging needs such as those of geomagnetic data assimilation we present the data sets we rely on essentially the same as those used by other recent archeomagnetic field models and describe how errors affecting the data and errors due to non modelled small spatial scales of the field are taken into account we next explain our modeling strategy and motivation for building low degree spherical harmonic degree ensembles of models we carry on a number of end to end simulations to both illustrate the usefulness of such ensembles and point at the type of errors one should expect practical illustrations of what can be done with these three ensembles of models with examples of geomagnetic inferences are also described northern high latitude flux patches for instance appear to be the most robust features of all these patches tend to fluctuate but clearly have some favored locations resulting in the same clear signature with three tongues over northern america europe and asia in the time averaged field at the core mantle boundary similar to what had been found in earlier models inferences about the field behavior in the southern hemisphere are more difficult to draw still some suggestions that the well known present south atlantic reversed patch could have arisen as early as in 1500 a d are found in some of the ensembles we otherwise confirm that most of the current archeomagnetic field model limitations are related to a number of sediment cores identified as producing frequent outliers in the modeling process we provide evidence that such cores are likely affected by timing errors and timing delays between magnetization lock in and sediment deposition that future more advanced treatment should be able to handle all source files for the three ensembles of models together with appropriate matlab applications can be downloaded from http geomag ipgp fr download archeo fm zip

decadal scale variations in geomagnetic field intensity from ancient cypriot slag mounds geomagnetic models based on direct observations since the 1830s show that the averaged relative change in field intensity on earth s surface over the past 170 years is less than 4 8 per decade it is unknown if these rates represent the typical behavior of secular variations due to insufficient temporal resolution of archaeomagnetic records from earlier periods to address this question we investigate two ancient slag mounds in cyprus skouriotissa vouppes su1 fourth to fifth centuries ce 21 m in height and mitsero kokkinoyia mk1 seventh to fifth centuries bce 8 m in height the mounds are multilayered sequences of slag and charcoals that accumulated near ancient copper production sites we modeled the age height relation of the mounds using radiocarbon dates and estimated paleointensities using thellier type izzi experiments with additional anisotropy cooling rate and nonlinear trm assessments to screen out ambiguous paleointensity interpretations we applied strict selection criteria at the specimen sample levels to ensure objectivity consistency and robust error estimation we employed an automatic interpretation technique and put the data available in the magic database the analyses yielded two independent subcentury scale paleointensity time series the mk1 data indicate relatively stable field at the time the mound accumulated in contrast the su1 data demonstrate changes that are comparable in magnitude to the fastest changes inferred from geomagnetic models we suggest that fast changes observed in the published archaeomagnetic data from the levant are driven by two longitudinally paired regions the middle east and south africa that show unusual activity in geomagnetic models

a seismological overview of the induced earthquakes in the duvernay play near fox creek alberta this paper summarizes the current state of understanding regarding the induced seismicity in connection with hydraulic fracturing operations targeting the duvernay formation in central alberta near the town of fox creek we demonstrate that earthquakes in this region cluster into distinct sequences in time space and focal mechanism using i cross correlation detection methods to delineate transient temporal relationships ii double difference relocations to confirm spatial clustering and iii moment tensor solutions to assess fault motion consistency the spatiotemporal clustering of the earthquake sequences is strongly related to the nearby hydraulic fracturing operations in addition we identify a preference for strike slip motions on subvertical faults with an approximate 45 p axis orientation consistent with expectation from the ambient stress field the hypocentral geometries for two of the largest magnitude m 4 sequences that are robustly constrained by local array data provide compelling evidence for planar features starting at duvernay formation depths and extending into the shallow precambrian basement we interpret these lineaments as subvertical faults orientated approximately north south consistent with the regional moment tensor solutions finally we conclude that the sequences were triggered by pore pressure increases in response to hydraulic fracturing stimulations along previously existing faults

critical analysis of the holocene palaeointensity database in central america impact on geomagnetic modelling abstract thanks to its rich archaeological heritage central america is a key region to recover the past secular variation of the geomagnetic field this article presents 13 new palaeointensity data on epiclassic 650 900 ce pottery sherds from central mexico archaeointensities were determined using the thellier thellier protocol with anisotropy and cooling rate corrections average results between 25 and 42 t reveals a fast secular variation in the second half of the first millennium ce but are not in agreement with global geomagnetic models that predict a higher geomagnetic field strength to check the reasons of this discrepancy we compiled all intensity data over the last millennia published in central america the bayesian curve calculated from 194 data covering the last 4 millennia highlights a rapid succession of oscillations of the geomagnetic field strength between 20 and 80 t but a critical analysis of the dataset shows a large influence of data quality 74 of them having a poor cooling unit consistency and experimental quality the small number of specimens per cooling unit and the anisotropy correction absent or incorrectly made increase the scatter between data whereas the absence of cooling rate correction biases the dataset towards higher palaeointensity discarding these data results in a lower secular variation by removing most extreme values and several intensity oscillations the weaknesses of the dataset are likely the main reason of the limitations of global models in central america pending the acquisition of new high quality data archaeomagnetic dating seems premature in central america

updated iberian archeomagnetic catalogue new full vector paleosecular variation curve for the last three millennia authors acknowledge the spanish ministry of economy cgl2014 54112 r and cgl2017 87015 p projects bes 2015 074575 and bes 2016 077257 grants the spanish ministry of education fpu14 02422 grant and the autonomous community of madrid through the european youth employment initiative pej15 amb ai 0203 m g p and m r acknowledge the ramon y cajal program and the cgl2015 63888 r project of the spanish ministry of economy and competitiveness financial support was also given by the pics international program for scientific cooperation cnrs france and csic spain

geomagnetic paleointensity between 1300 and 1750 a d derived from a bread oven floor sequence in lubeck germany geomagnetic paleointensities have been determined from a single archaeological site in lubeck germany where a sequence of 25 bread oven floors has been preserved in a bakery from medieval times until today age dating confines the time interval from about 1300 a d to about 1750 a d paleomagnetic directions have been published from each oven floor and are updated here the specimens have very stable directions and no or only weak secondary components the oven floor material was characterized rock magnetically using thellier viscosity indices median destructive field values curie point determinations and hysteresis measurements magnetic carriers are mixtures of sd psd and minor md magnetite and or maghemite together with small amounts of hematite paleointensity was measured from selected specimens with the double heating thellier method including ptrm checks and determination of trm anisotropy tensors corrections for anisotropy as well as for cooling rate turned out to be unnecessary ninety two percent of the thellier experiments passed the assigned acceptance criteria and provided four to six reliable paleointensity estimates per oven floor mean paleointensity values derived from 22 oven floors show maxima in the 15th and early 17th centuries a d followed by a decrease of paleointensity of about 20 until 1750 a d together with the directions the record represents about 450 years of full vector secular variation the results compare well with historical models of the earth s magnetic field as well as with a selected high quality paleointensity data set for western and central europe

geomagnetic field hemispheric asymmetry and archeomagnetic jerks abstract we investigate the origin of the so called archeomagnetic jerks detected in the french archeomagnetic record over the past three millennia although only very large scale global archeomagnetic field models are currently available we show that the occurrence of archeomagnetic jerks is intimately linked to what we define as most eccentric events i e periods of time when a simple description of the geomagnetic field in terms of an eccentric dipole reveals the center of this eccentric dipole to strongly move away from the earth s center from the behavior of the much better known historical field we interpret the evolution of the center of the eccentric dipole as reflecting the production and gathering of flux patches at the core mantle boundary within preferential hemispheres archeomagnetic jerks would thus correspond to episodes of maximum geomagnetic field hemispheric asymmetry such most eccentric events could also provide an explanation for some of the properties previously reported in the long term paleomagnetic field

intensity of the earth s magnetic field in greece during the last five millennia new data from greek pottery abstract new archaeointensity results have been obtained from the study of four ceramic collections coming from four different archaeological sites in greece the ages of the ceramic fragments based on archaeological constrains and radiocarbon analysis range from 2200 bc to 565 ad low field magnetic susceptibility versus temperature reveals a good thermal stability for most of the samples however for some samples the thermomagnetic curves are not reversible indicating mineralogical changes during heating isothermal remanent magnetisation irm acquisition curves and thermal demagnetisation of three orthogonal irm components have also been performed the rock magnetic results identify magnetite and or ti magnetite as the main magnetic carriers in the studied samples classical thellier experiments with regular partial thermoremanent magnetisation ptrm checks have been conducted on 125 specimens belonging to 34 independent ceramic fragments only 61 archaeointensity determinations at specimen level that correspond to linear nrm trm plots were used for the calculation of the site mean archaeointensities the effect of the anisotropy of the thermoremanent magnetisation trm and cooling rate upon trm intensity acquisition have been investigated in all specimens the maximum difference between the trm anisotropy corrected and uncorrected intensities is around 30 at specimen level confirming that the trm effect can be very important in ceramic samples cooling rate correction factors determined per specimen are up to 10 with only one exception that reaches 35 despite the moderate success rate of archaeointensity determination around 50 reliable mean site intensities have been obtained with in situ intensities ranging from 53 6 4 1 to 69 3 3 9 t corresponding to virtual axial dipole moments from 9 2 0 7 to 11 9 0 7 10 22 am 2 the new data are reasonably consistent with other available data for the studied region as well as with the sv reference curves for greece and the south balkan peninsula and the regional and global geomagnetic field models combined with previously published data from the area they confirm that important changes of the earth s magnetic field intensity occurred in greece during the last five millennia for some periods the available archaeointensity data for the balkan area show a large dispersion even for data corresponding to high quality intensity standards whereas for other periods their limited number prevents an accurate description of geomagnetic field intensity changes this evidences the need of new reliable and well dated archaeointensity data in order to obtain a robust description of geomagnetic field intensity changes during the last five millennia in this area

newly emerging cases of hydraulic fracturing induced seismicity in the duvernay east shale basin abstract hydraulic fracturing hf in the duvernay formation near fox creek alberta canada has produced some of the most prolific clusters of induced seismicity in this paper we describe newly emerging clusters of events occurring in previously quiescent and undeveloped areas of the duvernay formation in the duvernay east shale basin an industry supplemented waveform database is examined using a variety of seismological techniques here strike slip events as large as 4 18 ml have been felt in nearby cities temporal relationships suggest these clusters are almost certainly 99 7 confidence caused by nearby hf spatially these earthquakes tend to occur in the strata directly overlying the duvernay formation and laterally near a horizontal well one exceptional cluster clearly delineates a 1 5 km offset between its centroid and the inducing horizontal well raising questions about the earthquake triggering mechanism westward in the duvernay two minor clusters within the willesden green region appear to be tenuously related to hf completions this study also places constraints on the structural geology of faulting occurring in the rocky mountain house seismogenic zone a region of induced seismicity related to secondary recovery in the strachan d 3a pool here our moment tensors and double difference relocations describe thrust slip on a fault underlying the target formation last the largest event 4 27 ml in our study area was likely natural due to its deeper hypocentral depth 15 km and non correspondence with industrial operations overall the newly emerging clusters are consistent with reactivation of basement rooted faults

extended and revised archaeomagnetic database and secular variation curves from bulgaria for the last eight millennia the efforts of geophysicists to describe geomagnetic field behaviour in the past lead to creation of different geomagnetic field models on the other hand the established regional palaeosecular variations of geomagnetic elements are increasingly used for dating purposes in archaeology both of these goals can be achieved if sufficient amounts of long archaeomagnetic data sets exist for different geographical regions the accumulation of archaeomagnetic determinations began at the middle of the last century parallel with the progressive development of experimental methodology and acceptance criteria the presence of great number of old determinations requires their critical assessment the important question about the reliability of the associated dating intervals should be also re assessed all this requires the continuous refinement and extension of the accumulated databases this paper presents the last synthesis of bulgarian archaeomagnetic database and the local palaeosecular variation curves obtained using a statistical treatment based on bayesian approach rencurve software the rock magnetic characteristics of the newly included non published results are summarized

improving geomagnetic field reconstructions for 0 3 ka global geomagnetic field reconstructions on millennial time scales can be based on comprehensive paleomagnetic data compilations but especially for older data these still suffer from limitations in data quality and age controls as well as poor temporal and spatial coverage here we present updated global models for the time interval 0 3 ka where additions to the data basis mainly impact the south east asian alaskan and siberian regions we summarize recent progress in millennial scale modelling documenting the cumulative results from incremental modifications to the standard algorithms used to produce regularized time varying spherical harmonic models spanning 1000 bc to 1990 ad from 1590 to 1990 ad gauss coefficients from the historical gufm1 model supplement the paleomagnetic information in addition to absolute paleointensities calibrated relative paleointensity data from sediments are now routinely included iterative data rejection and recalibration of relative intensity records from sediments ensure stable results bootstrap experiments to generate uncertainty estimates for the model take account of uncertainties in both age and magnetic elements and additionally assess the impact of sampling in both time and space based on averaged results from bootstrap experiments taking account of data and age uncertainties we distinguish more conservative model estimates cals3k nb representing robust field structure at the core mantle boundary from relatively high resolution models cals3k n for model versions n 3 and 4 we assess the impact of newly available data and modifications to the modelling method by comparing the previous cals3k 3 the new cals3k 4 and the conservative new model cals3k 4b we conclude that with presently available data it is not feasible to produce a model that is equally suitable for relatively high resolution field predictions at earth s surface and robust reconstruction of field evolution avoiding spurious structure at the core mantle boundary cmb we presently consider cals3k 4 the best high resolution model and recommend the more conservative lower resolution version for studies of field evolution at the cmb

archaeomagnetic study of five mounds from upper mesopotamia between 2500 and 700 bce further evidence for an extremely strong geomagnetic field ca 3000 years ago the distribution of archaeomagnetic data in eastern europe and the near and middle east shows a remarkable gap in turkey this study presents the first archaeomagnetic results from five different mounds in southeast turkey the northern part of mesopotamia the rock magnetic experiments indicate that in the majority of the samples the dominant magnetic carrier is magnetite which is stable to heating to temperatures of 700 1c in general the demagnetization diagrams are single component and all five sets display well defined characteristic magnetizations and clustered directions for the period between 2500 and 700 bce the declinations are between 3501 and 201 while inclinations are in the range of 49 641 the directional results are compared with the global geomagnetic field models cals7k 2 arch3k cst 1 and cals3k 4 and the data from the archaeomagnetic database geomagia50v2 the results are coherent with both the data and the models except for two nearcontemporaneous sets dating 2000 bce which are offset to the east by more than 201 with respect to cals7k 2 archaeointensity measurements were made using the microwave and conventional thermal thellier methods applied to five sets of samples four furnaces and a mud brick wall these yielded comparable and intriguing results while those from the furnaces are slightly higher than the cals7k 2 model and in agreement with the geomagia50v2 and the middle east data the results from the mud brick wall suggest a high intensity of 100 8 mt 17 7 10 22 am 2 a t 1000 bce this result is

on the possible occurrence of archaeomagnetic jerks in the geomagnetic field over the past three millennia abstract archaeomagnetism can provide a high resolution full vector description of the earth s magnetic field for the past several thousand years we analyse the bulk of archaeomagnetic data both direction and intensity obtained recently in western europe and the eastern mediterranean covering the past three millennia we demonstrate a remarkable coincidence between sharp cusps in geomagnetic field direction and intensity maxima two clear ones at ad 200 and 1400 two presently less well constrained at 800 bc and ad 800 these sharp changes may constitute a new feature of geomagnetic secular variation archaeomagnetic jerks with time characteristics intermediate between geomagnetic jerks and magnetic excursions

refined 3600 years palaeointensity curve for mexico abstract our knowledge of the earth s magnetic field intensity changes over the past few thousand years is still limited because of the uneven spatial and temporal distribution of data which also includes the americas the present study reports 41 new palaeointensity data covering the past 3600 years which together with 38 previously published data of similar quality are used to construct a palaeointensity secular variation curve for central mexico these new data are an important contribution to the global intensity database and will also improve the application of palaeomagnetic dating in mexico which is of interest because of the many holocene monogenetic volcanoes within the trans mexican volcanic belt and of its archaeological heritage the most conspicuous feature of the new intensity curve is the rapid increase between 400 and 250 bce from about 45 to 65 t other relative intensity highs of 45 55 t were found around 1600 bce 370 ce and 1200 ce and relative intensity lows of 30 35 t around 1350 bce and 700 ce comparing the virtual axial dipole moment of our intensity curve with global vadm vdm dipole estimates indicates that non dipole components in central mexico have been observed at several times from 1600 bce to 1000 ce while the dipole field was prevalent from 1000 to 1800 ce a comparison of our results with selected data from southern usa shows a significant difference between the two regions which indicates an important nondipole feature of the magnetic field during the last few thousands of years and or undetected problems in the age palaeointensity data accuracy

performance assessment of the induced seismicity traffic light protocol for northeastern british columbia and western alberta abstract in response to the increasing concern of possible seismic risk due to injection operations during development of unconventional hydrocarbon resources regulators in both british columbia bc and alberta ab canada have adopted varying aspects of a traffic light protocol as part of their individual oversight and risk mitigation strategies in this study we compare the regional seismicity pattern with the database of injection parameters to assess the performance of the individual induced seismicity traffic light protocols is tlp the red light threshold in both bc and ab is set at local magnitude ml 4 which appears to be adequate in characterizing the potential seismic risk from induced earthquakes since 2014 there were three red light events each in bc and ab all related to hydraulic fracturing in the three ab cases and one bc case at least one 2 ml 4 seismic event characterized in ab as a yellow light event preceded the red light event suggesting that an is tlp based on e

geomagnetic field intensity during the last 60 000 years based on 10be and 36cl from the summit ice cores and 14c abstract based on 10 be 36 cl and 14 c records we reconstruct past changes in the geomagnetic field intensity under the assumption that radionuclide records are mainly influenced by changes in their production rates subsequent comparison of these records with independent geomagnetic field reconstructions allows us to assess the reliability of our approach and to identify periods where our method or the geomagnetic field reconstructions might be problematic the geomagnetic field derived from the 10 be flux to summit in central greenland agrees well with independent geomagnetic field intensity reconstructions however compared to independent palaeomagnetic data the radionuclide record suggests increased geomagnetic field intensities especially for the period from 20 000 to 30 000 years bp 36 cl from the grip ice core agrees well with the 10 be record for the last ice age and hence also the reconstructed geomagnetic field based on the tree ring radiocarbon record it is possible to reconstruct geomagnetic field intensity changes during the holocene a comparison of radiocarbon based and independent geomagnetic field reconstructions indicates that changes in the carbon cycle significantly influenced the atmospheric radiocarbon concentration before 10 000 years bp

core flow constraints on extreme archeomagnetic intensity changes abstract recent studies ben yosef et al 2009 shaar et al 2011 propose extreme archeomagnetic intensity changes termed spikes in the range 4 5 t year c a 1000 bc in the near east around 40 to 50 times larger than values typical of the present day in order to investigate whether such extreme changes are consistent with a model of the source region of the magnetic field namely the fluid flow at the surface of earth s core we construct upper bounds for instantaneous magnetic intensity change at an arbitrary site on the earth s surface these bounds are constrained by the amount of kinetic energy available to sustain the change taken here to be a prescribed value for the root mean squared surface velocity of 13 km yr as inferred from the current state of the core further we focus attention on two end members of optimised core surface flow structure unrestricted and purely toroidal as the derivation of the bounds demands complete knowledge of the geomagnetic field at the core surface we model the unknown field by means of a monte carlo approach extending to high degree the chaos 4 epoch 2010 ad and cals10k1 b epoch 1000 bc geomagnetic field models using 2000 realisations for each family of stochastic field models we find that optimised core flows are always large scale and that they tend to generate a non dipole quadrupole dominated secular variation at the earth s surface the dependence of the upper bounds as a function of site location reflects the large scale structure of the intensity itself stronger field permits more rapid change for the site in the near east purely toroidal flows have upper bounds of approximately 0 62 0 02 t year whereas unrestricted flows increase this bound to 1 20 0 02 t year we favour the former as more geophysically sound on the account of a large body of previous results from core surface flow inversions and consistency with the existence of a stratified layer at the top of the core even if we allow for a generous threefold increase in the prescribed rms velocity and a concomitant threefold increase in the bound we conclude that the reported occurrences of extreme intensity changes as suggested in the near east are not compatible with the commonly accepted structure of core surface flow however it may be that an explanation for spikes lies beyond our current perception of core dynamics and future work would be further motivated by seeking corroborative evidence of rapid intensity change from sites elsewhere on earth s surface we therefore also discuss the form that the secular variation would take in the case of simultanenous archeomagnetic spikes

decay rate of fluid induced seismicity after termination of reservoir stimulations we present a model describing the seismicity rate of fluid injection induced seismicity we put the focus on seismicity induced after termination of fluid injections here our primary objective is the identification of parameters controlling the decay rate of seismicity the particular importance of a theoretical model for postinjection seismicity is underlined by observations after stimulations of geothermal reservoirs at different locations for instance the postinjection phase is relevant for a seismic risk which up to now has been difficult to control because processes leading to postinjection events are not well understood based on the assumption of pore pressure diffusion as the governing mechanism leading to the triggering of seismic events we develop a method to calculate the seismicity rate during and after fluid injections we find that the decay rate of seismicity after termination of injection is very similar to the omori law which describes the decay rate of aftershock activity after t

geomagnetic intensity variations for the past 8 kyr new archaeointensity results from eastern china abstract in this study we have carried out paleointensity experiments on 918 specimens spanning the last 7 kyr including pottery fragments baked clay and slag collected from shandong liaoning zhejiang and hebei provinces in china approximately half of the specimens yielded results that passed strict data selection criteria and give high fidelity paleointensities the virtual axial dipole moments vadms of our sites range from 2 10 22 to 13 10 22 am 2 at 2250 bce our results suggest a paleointensity low of 2 10 22 am 2 which increases to a high of 13 10 22 am 2 by 1300 bce this rapid less than 1000 yrs six fold change in the paleointensity may have important implications for the dynamics of core flow at this time our data from the last 3 kyr are generally in good agreement with the arch3k 1 model but deviate significantly at certain time periods from the cals3k 4 and cals10k 1b model which is likely due to differences in the data used to constrain these models at ages older than 3 ka where only the cals10k 1b model is available for comparison our data deviate significantly from the model combining our new results with the published data from china and japan we provide greatly improved constraints for the regional model of eastern asia when comparing the variations of geomagnetic field in three global representative areas of eastern asia the middle east and southern europe a common general trend of sinusoidal variations since 8 ka is shown likely dominated by the dipole component however significant disparities are revealed as well which we attribute to non dipolar components caused by movement of magnetic flux patches at the core mantle boundary

improving our knowledge of rapid geomagnetic field intensity changes observed in europe between 200 and 1400 ad vailable archaeomagnetic data indicate that during the past 2500 yr there have been periods of rapid geomagnetic field intensity fluctuations interspersed with periods of almost constant field strength despite europe being the most widely covered region in terms of archaeomagnetic data the occurrence and the behaviour of these rapid geomagnetic field intensity changes is under discussion and the challenge now is to precisely describe them the aim of this study is to obtain an improved description of the sharp intensity change that took place in western europe around 800 ad as well as to investigate if this peak is observed at the continental scale for this purpose 13 precisely dated early medieval spanish pottery fragments four archaeological french kilns and three collections of bricks used for the construction of different french historical buildings with ages ranging between 335 and 1260 ad have been studied classical thellier experiments performed on 164 specimens and including anisotropy of thermoremanent magnetisation and cooling rate corrections gave 119 reliable results the 10 new high quality mean archaeointensities obtained confirm the existence of an intensity maximum of 85 t at the latitude of paris centred at 800 ad and suggest that a previous abrupt intensity change occurred around 600 ad together with previously published data from western europe that we deem to be the most reliable the new data also suggest the existence of two other abrupt geomagnetic field intensity variations during the 12th century and around the second half of the 13th century ad high quality archaeointensities available from eastern europe indicate that very similar geomagnetic field intensity changes occurred in this region european data indicate that very rapid intensity changes of at least 20 t century took place in the recent history of the earth s magnetic field the results call for additional high quality archaeointensities obtained from precisely dated samples and for a selection of the previously published data if a refined description of geomagnetic field intensity changes at regional scales is to be obtained

geomagnetic field variations in western europe from 1500 bc to 200 ad part ii new intensity secular variation curve abstract in order to extend the secular variation curve svc of archaeointensity in western europe to the first millennium bc we studied 24 kilns and hearths in place two displaced hearths and six sets of pottery sherds from french archaeological sites archaeological artefacts radiocarbon and dendrochronology dated the acquisition of the thermoremanent magnetization trm carried by the studied objects rock magnetism experiments suggest that the main carrier of the magnetization is a ti poor titanomagnetite archaeointensity was determined by the thellier thellier classical protocol with ptrm checks a strict criteria set was applied to select only the most reliable results with linear nrm trm diagrams 55 of total specimens this study demonstrates that pottery sherds with two trms give reliable archaeointensities in the low temperature interval if the nrm trm diagram is adequately adjusted eighteen new mean archaeointensities 14 corrected from the anisotropy of trm and 16 from cooling rate were computed the comparison with previously published western europe paleointensities show a strong dispersion between data primarily due to their variable quality western europe data were weighted following the archaeointensity protocol the number of specimens per site and the type of studied materials in order to better highlight the secular variation of archaeointensity during the first millennium bc the svc built with sliding windows of 160 years shifted every 50 years presents at paris a maximum of 90 t around 800 bc and a minimum of 60 t around 250 bc these archaeointensity maximum and minimum correspond to cusps of the geomagnetic field direction in western europe this new curve is consistent with mesopotamian and eastern europe data the archaeointensity secular variation in western europe predicted by global geomagnetic models cals3k 4 arch3k 1 and arch3k cst 1 is smoother than our svc we used our directional dataset herve et al 2013 to build a new western europe vgps and vdms mean curves comparison with the predictions given by the global models points out a possible persistent non dipole fields effect over europe between 1000 bc and 600 500 bc finally we note that the strong variations of intensity of the geomagnetic field with a mean decrease rate per century close to 6 t will be useful for archaeomagnetic dating purposes

a geomagnetic field model for the holocene based on archaeomagnetic and lava flow data abstract we propose a new geomagnetic field model for the holocene period based on archaeomagnetic and lava flow data avoiding the use of lake sediment data the source of data comes from the geomagia50v2 database which has been updated with the new archaeomagnetic and volcanic studies published during the last 3 yr the model called sha dif 14k allows us to analyse the behaviour of the geomagnetic field for the last 14 000 yr from 12 000 bc to 1900 ad for the model construction we use the spherical harmonic analysis in space and the penalized cubic b splines in time both spatial and temporal regularization norms are used to constrain the inversion problem and applied at the core mantle boundary cmb to assure the convergence of the model for the last 3 ka the model predictions agree with those given by the global model arch3k 1 and the european model scha dif 3k for older epochs the new model presents a clear improvement in field resolution with respect to other current models of the geomagnetic field for the holocene for the last 9 ka the time evolution of the dipolar moment obtained from the dipole field shows a clear minimum between 5500 bc and 3000 bc and the well known continuous decreasing trend of the geomagnetic field strength for the last millennium and a half a general view of the time average evolution of the geomagnetic field flux lobes at the cmb for the northern hemisphere suggests a marked lobe of positive magnetic flux when the dipole moment was maximum this lobe vanishes when the dipolar field is decreasing the north polar wander paths of both north magnetic dip and geomagnetic poles were obtained showing an average rate of motion of 5 1 km yr and 3 7 km yr respectively the model shows that the geomagnetic field can be averaged as axial dipolar in 2000 yr within an error of 5 the typical uncertainty of the palaeomagnetic studies finally and following the recent definition of archaeomagnetic jerks we found 8 critical events in the time evolution of the geomagnetic field for the last 8 ka characterized by a maximum in the hemispheric asymmetry of the proposed model the model is available in the earth ref digital archive at http earthref org erda 1897

an investigation of seismicity clustered near the cordel field west central alberta and its relation to a nearby disposal well historically seismicity documented in the western canada sedimentary basin has been relatively quiescent and earthquakes are usually restricted to the foreland belt of the rocky mountains however exceptional clusters of events which have remained active for decades are recognized in alberta in this study we investigate the seismicity in this region using data obtained from recently established regional arrays emphasizing the relationship between a disposal well in the cordel field and a nearby cluster of previously reported earthquakes we explore temporal correlations of wastewater pumping rates and local seismic activity dating back to 1960 we find that the first statistically significant increase in seismicity lags the onset of wastewater injection october 1991 by 3 33 years in particular the waveform similarity of 32 events are analyzed from continuous data recorded at nor a nearby 30 km station operated by the university of alberta starting in september of 2006 results from this analysis suggest that many events are well correlated in the characteristics of the waveforms and thus are likely to share a similar origin and source mechanism the most prolific of these multiplets repeats more than 10 times sporadically throughout the entire duration of recorded data from october 2006 to march 2012 despite the limited availability of nearby stations which adversely affects the resolution of our analysis hypocenter depths could be relatively accurately determined from waveform synthesis and double difference methods the results of our analysis provide first order evidence that the seismicity is consistent with fluid injection induced events

speeds and gaits of dinosaurs abstract the known relationships of speed gait and body size derived mainly from mammals are used to determine the gaits and theoretical maximum speeds of dinosaurs speed estimates are made for 62 dinosaurs representing 51 genera and are supplemented with information from comparative anatomy and from dinosaur trackways it is concluded that smaller bipedal dinosaurs were capable of running at speeds up to 35 or 40 km h the so called ostrich dinosaurs are credited with maximum speeds less than 60 km h and possibly as low as 35 or 40 km h larger bipedal dinosaurs were probably restricted to walking or slow trotting gaits with maximum speeds in the range 15 20 km h most quadrupedal dinosaurs seem to have been restricted to a walking gait stegosaurs and ankylosaurs may have had maximum speeds as low as 6 8 km h sauropods may have attained 12 17 km h and some ceratopsians may have been capable of trotting at speeds up to 25 km h on a weight for weight basis the speeds of dinosaurs are generally lower than those of mammals

geomagnetic field intensity variations in western europe over the past 1100 years 1 ten archeointensity results have been obtained from brick and ceramic fragments collected in france and precisely dated to between the tenth and eighteenth centuries intensity experiments were performed using the triaxe protocol taking into account cooling rate and thermoremanent magnetization anisotropy effects together with our previous results from france and belgium we computed a geomagnetic field intensity variation curve for western europe covering the past 1100 years this curve is characterized by a general decreasing trend at the millennial timescale punctuated by three short intensity peaks during the twelfth century around 1350 1400 ad and 1600 ad a similar evolution but with smoother variations due to data scatter is also observed in western europe and to a lesser extent in eastern europe when all available archeointensity data fulfilling quality criteria are used comparison of our archeointensity variation curve with the climatic record derived from fluctuations in length of the swiss glaciers shows a good temporal concordance between all geomagnetic field intensity maxima detected in western europe over the past millennium and colder episodes a comparison is further discussed between these intensity maxima and episodes of low rates of 14c production a common pattern of variations between both records is recognized between the middle of the tenth and of the beginning of eighteenth centuries if significant such coincidences suggest a dual geomagnetic and solar origin for the century scale climate and radionuclide production variations during at least the past millennium

archeoint an upgraded compilation of geomagnetic field intensity data for the past ten millennia and its application to the recovery of the past dipole moment 1 this paper presents a compilation of intensity data covering the past 10 millennia archeoint this compilation which upgrades the one of korte et al 2005 contains 3648 data and incorporates additional intensity and directional data sets a large majority of these data 87 were acquired on archeological artifacts and the remaining 13 correspond to data obtained from volcanic products the present compilation also includes important metadata for evaluating the intensity data quality and providing a foundation to guide improved selection criteria we show that 50 of the data set fulfill reasonable reliability standards which take into account the anisotropic nature of most studied objects potsherds the stability of the magnetization and the data dispersion the temporal and geographical distributions of this sub data set are similar to those of the main data set with 72 of the data dated from the past three millennia and 76 obtained from western eurasia approximately half of the selected intensity data are associated with at least an inclination value to constrain the axial and full dipole evolution over the past three millennia requires that we avoid any overrepresentation of the western eurasian data we introduce a first order regional weighting scheme based on the definition of eight widely distributed regions of 30 width within which the selected data are numerous enough the regional curves of virtual axial dipole moments vadm and of mixed vadm virtual dipole moments vdm averaged over sliding windows of 200 years and 500 years testify for strong contributions from either equatorial dipole or nondipole components the computation of global vadm and mixed vadm vdm variation curves assuming an equal weight for each region yields a dipole evolution marked by a distinct minimum around 0 b c a d followed by a maximum around the third fourth century a d a second minimum is present around the eighth century a d this variation pattern is compatible with the one deduced from earlier more

archaeomagnetic and rock magnetic study of six kilns from north africa tunisia and morocco new full vector archaeomagnetic data for north africa recovered from the study of six kilns five from tunisia and one from morocco are presented archaeological and historical considerations along with three radiocarbon dates indicate that the age of the kilns ranges between the 9th and 15th centuries ad rock magnetic analyses showed that the principal magnetic carriers are magnetite and low ti titanomagnetite along with variable contributions of thermally stable maghemite and a high coercivity phase with low unblocking temperatures the magnetic mineralogy of the studied material is thermally stable and behaves ideally during archaeointensity experiments stepwise alternating field demagnetization isolated a single stable characteristic remanence component with very well defined directions at both specimen and structure levels mean archaeointensities have been obtained from successful classical thellier experiments conducted on between five and eight independent samples per kiln thermoremanent magnetization trm anisotropy and cooling rate effects upon trm intensity have been investigated the results showed that these effects are low for four of the six studied kilns with differences between the uncorrected and corrected means of less than 3 per cent for the other two structures differences between the uncorrected and corrected mean site intensities are 4 4 per cent and 5 8 per cent these results highlight the necessity for trm anisotropy and cooling rate corrections in archaeomagnetic studies if accurate archaeointensities are to be obtained the new results suggest that high intensities occurred in northwest africa during the 9th century although more data are clearly needed to define this period of high intensity the results are in agreement with the available european archaeointensity data acomparison between the newdata other available archaeomagnetic determinations in nearby locations and palaeosecular variation psv curves derived from the regional scha dif 3k and global arch3k 1 geomagnetic field models shows good agreement between the new data and directional results derived from the models however some differences are observed between geomagnetic field models intensity results and available archaeointensity data for the studied regions this highlights the need for new data for unexplored regions such as north africa the new data presented here better constrains the evolution of the geomagnetic field during historical times in this region they represent a new step towards the construction of a reference psv curve for northwest africa once established this curve will represent a new dating method for this region

fast geomagnetic field intensity variations between 1400 and 400 bce new archaeointensity data from germany abstract thirty five mean archaeointensity data were obtained on ceramic sherds dated between 1400 and 400 bce from sites located near munich germany the 453 sherds were collected from 52 graves pits and wells dated by archaeological correlation radiocarbon and or dendrochronology rock magnetic analyses indicate that the remanent magnetization was mainly carried by magnetite data from thellier thellier experiments were corrected for anisotropy and cooling rate effects triaxe and multispecimen msp dsc protocols were also measured on a subset of specimens around 60 of the samples provide reliable results when using stringent criteria selection the 35 average archaeointensity values based on 154 pots are consistent with previous data and triple the western europe database between 1400 and 400 bce a secular variation curve for central western europe built using a bayesian approach shows a double oscillation in geomagnetic field strength with intensity maxima of 70 t around 1000 900 bce and another up to 90 t around 600 500 bce the maximum rate of variation was 0 25 t yr circa 700 bce the secular variation trend in western europe is similar to that observed in the middle east and the caucasus except that we find no evidence for hyper rapid field variations i e geomagnetic spikes virtual axial dipole moments from western europe the middle east and central asia differ by more than 2 1022 a m2 prior to 600 bce which signifies a departure from an axial dipole field especially between 1000 and 600 bce our observations suggest that the regional levantine iron age anomaly has been accompanied by an increase of the axial dipole moment together with a tilt of the dipole

variations in the geomagnetic dipole moment during the holocene and the past 50 kyr all absolute paleointensity data published in peer reviewed journals were recently compiled in the geomacia50 database based on the information in geomagia50 we reconstruct variations in the geomagnetic dipole moment over the past 50 kyr with a focus on the holocene period a running window approach is used to determine the axial dipole moment that provides the optimal least squares fit to the paleointensity data whereas associated error estimates are constrained using a bootstrap procedure we subsequently compare the reconstruction from this study with previous reconstructions of the geomagnetic dipole moment including those based on cosmogenic radionuclides be 10 and c 14 this comparison generally lends support to the axial dipole moments obtained in this study our reconstruction shows that the evolution of the dipole moment was highly dynamic and the recently observed rates of change 5 per century do not appear unique we observe no apparent link between the occurrence of archeomagnetic jerks and changes in the geomagnetic dipole moment suggesting that archeomagnetic jerks most likely represent drastic changes in the orientation of the geomagnetic dipole axis or periods characterized by large secular variation of the non dipole field this study also shows that the holocene geomagnetic dipole moment was high compared to that of the preceding similar to 40 kyr and that similar to 4 10 22 am 2 appears to represent a critical threshold below which geomagnetic excursions and reversals occur c 2008 elsevier b v all rights reserved less

investigation of regional seismicity before and after hydraulic fracturing in the horn river basin northeast british columbia we systematically re analyzed historical seismograms to verify the existence of background seismicity in the horn river basin of northeast british columbia before the start of regional shale gas development we also carefully relocated local earthquakes that occurred between december 2006 and december 2011 to delineate their spatiotemporal relationship with hydraulic fracturing hf operations in the region scattered seismic events were detected in the horn river basin throughout the study periods the located seismicity within 100 km of the fort nelson seismic station had a clearly increasing trend specifically in the etsho area where most local hf operations were performed the number of events was increased from 24 in 2002 2003 prior to hf operations to 131 in 2011 peak period of hf operations in addition maximum magnitude of the events was shifted from ml 2 9 to ml 3 6 as the scale of hf operation expanded from 2006 2007 to 2011 based on our relocated earthquake catalog the overall b value i

new archaeomagnetic data recovered from the study of roman and visigothic remains from central spain 3rd 7th centuries summary new archaeomagnetic results from four heated combustion structures recovered from two archaeological sites in central spain are reported they have been dated by archaeological evidence and in two cases by radiocarbon dating rock magnetic experiments indicate low coercivity magnetic phases such as magnetite and thermally stable maghaemite as the main carriers of the remanent magnetization haematite has been observed in poorly heated baked clays archaeomagnetic directions have been obtained from either alternating field or thermal demagnetization experiments performed on 57 specimens coming from 46 independently oriented samples the four well defined archaeomagnetic directions obtained are in good agreement with previous archaeomagnetic data and with recent regional and global field models they define the beginning of easterly declination drift that was initiated around 350 400 ad and culminated around 800 850 ad and delineate the maximum in inclination that took place around 600 650 ad in addition classical thellier thellier experiments including thermal remanent magnetization anisotropy and cooling rate corrections were conducted on 23 specimens only 13 specimens corresponding to well defined single component behaviour gave reliable results new mean archaeointensities have been obtained for two of the four studied structures vbk1 64 2 5 0 t and vbt1 62 4 2 6 t the new data suggest that two relative intensity maxima occurred in western europe around 320 and 630 ad being of lower magnitude that observed in eastern europe

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

new archeointensity data from spain and the geomagnetic dipole moment in western europe over the past 2000 years archeomagnetic studies on 14 kilns a group of jar fragments and a collection of baked bricks dated between 1000 and 1959 ad plus one roman pottery kiln have been conducted in order to obtain high quality archeointensity data to enhance the western european database the thellier method with corrections for anisotropy of thermoremanent magnetization trm and for cooling rate dependence upon trm acquisition was used the effect of trm anisotropy is only important for the bricks where the corrected and uncorrected mean intensities differ by more than 5 cooling rate correction factors determined per sample are up to 15 and per site up to 7 7 our 17 new data together with 62 previously published results were used to obtain by bayesian modeling the geomagnetic field intensity over the past two millennia for western europe our results indicate that geomagnetic intensity remained more or less constant between the 1st and 4th centuries and between the 14th and 16th centuries mean values at paris around 65 and 57 t respectively whereas an important decrease occurs between 1600 and 1800 ad the detailed evolution of geomagnetic field intensity during the high middle ages is not yet well established despite their differences geomagnetic global models predict our results reasonably well this work indicates the need to obtain a number of archeointensity data for each time interval in order to reliably record variations of the geomagnetic field and to test whether any relationship exists between field intensity and climate

analysis of the acceleration phase of a theropod dinosaur based on a cretaceous trackway from korea abstract well preserved trackways of carnivorous dinosaurs belonging to small sized theropods have been reported from the cretaceous neungju group in south korea the site at hwasun seoyu ri quarry represents the most extensive and diverse theropod trackway ichnofauna in south korea among them one theropod trackway is unique in that it demonstrates that theropods were able to increase stride lengths to reach maximum speed during the running phase fossilized track evidence of the acceleration ability of dinosaurs is scant despite this the evidence shown in our findings suggests a theropod running near the limit of its capabilities and shows evidence of a temporary acceleration of speed while running

globally strong geomagnetic field intensity circa 3000 years ago abstract high fidelity geomagnetic field intensity determination was carried out using 191 baked fragments collected from 20 kilns or hearths with ages ranging between 1200 bc and ad 1725 in south korea geomagnetic field intensity variation displayed three narrow minima at 800 700 bc ad 700 and ad 1600 and two maxima at 1200 1100 bc and ad 1000 1100 in most time intervals virtual axial dipole moment vadm variation is confined within 20 of the present vadm however geomagnetic field intensity circa 3000 yr ago is nearly 40 larger than the present value such high vadms circa 3000 yr ago are in phase with those in other longitudinal bands in northern hemisphere centered at 5e france 30e the middle east and 200e hawaii although strong geomagnetic field intensity circa 3000 yr ago is globally synchronous the highest vadm occurs at slightly different time intervals in different locations hence it is possible that the globally strong geomagnetic field intensity circa 3000 yr ago reflects the migration of persistent hemispheric flux in northern hemisphere or an episode of geomagnetic field hemispheric asymmetry

evidence for rapid geomagnetic field intensity variations in western europe over the past 800 years from new french archeointensity data abstract the number of reliable archeointensity determinations obtained from western europe for the past millennium remains limited moreover the large scatter between different datasets available is puzzling the present study analyzed 31 new groups of baked clay ceramic or brick fragments sampled in france 29 groups and in belgium 2 groups these groups contain several fragments collected from different artefacts and are precisely dated principally from historical constraints between the xiiith and the xixth centuries additionally we re evaluated 14 intensity values that we previously obtained from the same time period the fragments were analyzed using two different thermal methods 1 the in field zero field iz or the izzi version of the classical thellier and thellier method and 2 the triaxe protocol that involves high temperature magnetization measurements data were corrected for the anisotropy of thermoremanent magnetization trm and the dependence of trm acquisition on the cooling rate was taken into account in the different protocols archeointensity data obtained on twin specimens sampled from the same fragment and using both experimental techniques generally show a good agreement i e within 5 at the fragment and at the site level all retained site level averaged intensity results 43 of 45 groups have standard deviations of less than 5 t furthermore groups of approximately the same age have very consistent archeointensity altogether the data presented herein recover a detailed and smoothed geomagnetic field intensity variation curve characterized by two peaks in intensity the first during the second half of the xivth century and the second around ad 1600 followed by a significant decreasing trend in intensity during most the xviith and xviiith centuries this evolution does not satisfactorily fit with the expected intensity values for france derived from geomagnetic field models relying on a different evolution of the axial dipole moment our results lead us to propose that the axial dipole moment decreased from ad 1600 to the end of the xviiith century then slightly increased up to ad 1850 before decreasing again to present day

geomagnetic field intensity how high can it get how fast can it change constraints from iron age copper slag article the intensity of the geomagnetic field varies over different time scales yet constraints on the maximum intensity of the field as well as for its maximum rate of change are inadequate due to poor temporal resolution and large uncertainties in the geomagnetic record the purpose of this study is to place firm limits on these fundamental properties by constructing a high resolution archaeointensity record of the levant from the 11th century to the early 9th century bce a period over which the geomagnetic field reached its maximum intensity in eurasia over the past 50 000 years we investigate a 14 c dated sequence of ten layers of slag material which accumulated within an ancient industrial waste mound of an iron age copper smelting site in southern israel depositional stratigraphy constrains relative ages of samples analyzed for paleointensity and 14 c dates from different horizons of the mound constrain the age of the whole sequence the analysis yielded 35 paleointenisty data points with accuracy better than 94 and precision better than 6 covering a period of less than 350 years most probably 200 years we construct a new high resolution quasi continuous archaeointensity curve of the levant that displays two dramatic spikes in geomagnetic intensity each corresponding to virtual axial dipole moment vadm in excess of 200 zam 2

holocene paleointensities thellier experiments on submarine basaltic glass from the east pacific rise a complete description of the geomagnetic field requires both paleodirectional and paleointensity data although the paleointensity data base has grown steadily over the last three decades it remains limited in time and space the majority of data are of holocene age and come from europe furthermore it has been difficult to assess the reliability of the paleointensity determinations here we present paleointensity determinations on precisely dated holocene 0 to 3500 years old submarine basaltic glass from the east pacific rise 15 s to 22 s although hysteresis measurements and low temperature isothermal remanent magnetization irm acquisition experiments document a significant contribution of superparamagnetic grains high blocking temperatures above 400 c and curie temperatures between 490 c and 550 c indicate a single domain low ti magnetite as the carrier of the remanent magnetization this notion is further supported by the fact that saturation of remanence is achieved in moderate fields of about 200 300 mt submarine basaltic glass proves to be nearly ideal for paleointensity determinations in that it produces a high success rate for thellier experiments twenty six out of 30 samples resulted in acceptable paleointenisty determinations multiple experiments on splits from the same sample show good reproducibility the paleointensities for zero age glasses correspond precisely with the present field intensity at the site of recovery the results of the remaining samples range from 16 7 to 53 9 t with corresponding virtual axial dipole moments vadm of 3 61 1022 to 11 9 1022 a m2 the intensities vary rapidly with time excluding a westward drifting nondipole component as the source for these fluctuations basaltic glass is frequently recovered in both dredged and drilled material from the ocean floor the availability of submarine basaltic glass throughout the world oceans therefore holds great potential for a better distribution of paleointensity data through time and space