a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

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

very low frequency earthquakes indicate a transpressional stress regime in the nankai accretionary prism 1 we investigated the stress field within the nankai accretionary prism of southwestern japan where very low frequency vlf earthquakes occur associated with thrust faulting a northwest southeast azimuth of the maximum horizontal principal stress previously estimated from borehole breakouts in wells drilled in the region by deep sea drilling vessel chikyu suggests trench normal shortening although strike slip and normal faulting are also possible within a thrust dominated tectonic environment we estimated stress orientations and stress ratios by using stress tensor inversion to derive moment tensor solutions for vlf earthquakes in three regions along the nankai trough off kumano off muroto and hyuga nada the stress orientations we obtained indicate that the regions off kumano and off muroto are within a transpressional stress regime with trench normal shortening whereas the hyuga nada region on the westernmost edge of the nankai accretionary prism is in a reverse faulting regime

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

two dimensional probabilistic cell automaton model for broadband slow earthquakes slow tectonic events such as deep tectonic tremor low frequency earthquakes very low frequency earthquakes and slow slip events are regarded as broadband slow earthquakes various observational properties of these events have previously been explained using a one dimensional 1d stochastic model that mimics brownian motion in the time domain here we present a simple two dimensional 2d slow earthquake model using a probabilistic cell automaton pca where each cell possesses one of two states slip or hold at a given time step the status of each cell is updated as a markov process dependent on its own status and that of neighboring cells the seismic moment rate of the event in the 2d pca model is assumed to be proportional to the number of slipping cells which is approximated using a stochastic differential equation equivalent to the previous 1d brownian model approach this 2d pca model is therefore able to explain the various observational properties of slow earthquakes moreover it includes an additional degree of freedom to separate the effects of loading and dissipation which enables us to explain the variations in episodic slow slip activity the size of the slow earthquake is limited by either the system size or the characteristic size which is controlled by the degree of dissipation such a simple representation of slow earthquakes is useful for characterizing the broad spectrum of slow earthquake behavior in different environments

first archaeomagnetic secular variation curve for the iberian peninsula comparison with other data from western europe and with global geomagnetic field models 1 a first secular variation sv curve for the iberian peninsula was computed by hierarchical bayesian method using a total of 134 archaeomagnetic directions with ages ranging from 775 to 1959 a d a general agreement is observed between the iberian curve and the french and german sv curves although some interesting differences were found such as the occurrence of lower inclinations between the 11th and 14th centuries in the iberian curve the analysis of these three reference curves indicates that sv in western europe is characterized by three major directional changes at 125 200 and 1350 a d it is suggested that these cusps are regional features of the geomagnetic field the iberian curve has been compared with the predictions of the jackson calsk7k 2 and hongre global models despite large differences recognized between these models even for the dipolar terms they predict reasonably well the iberian archaeomagnetic sv

recurring and triggered slow slip events near the trench at the nankai trough subduction megathrust the discovery of slow earthquakes has revolutionized the field of earthquake seismology defining the locations of these events and the conditions that favor their occurrence provides important insights into the slip behavior of tectonic faults we report on a family of recurring slow slip events sses on the plate interface immediately seaward of repeated historical moment magnitude mw 8 earthquake rupture areas offshore of japan the sses continue for days to several weeks include both spontaneous and triggered slip recur every 8 to 15 months and are accompanied by swarms of low frequency tremors we can explain the sses with 1 to 4 centimeters of slip along the megathrust centered 25 to 35 kilometers km from the trench 4 to 10 km depth the sses accommodate 30 to 55 of the plate motion indicating frequent release of accumulated strain near the trench

consistent treatment of errors in archaeointensity implies rapid decay of the dipole prior to 1840 we present a meta analysis of 223 archaeo and palaeointensities spanning the period 1840 1990 and compare these data with the geomagnetic field model gufm1 jackson et al 2000 philos trans r soc lond a 358 957 990 we find that the principal source of uncertainty in all the data regardless of experimental method or number of samples is due to systematic error this error is quantified and it is shown that the data is capable of estimating the magnitude of the geomagnetic field for the period with reasonable accuracy but only if errors are estimated on the basis of the field strength rather than the measured intensity the findings are then applied to archaeointensity data from the period 1590 1840 and it is shown that the most likely behaviour of the field was a decay of the axial dipole at a similar rate to that observed since 1840 we show that underestimation of the field s magnitude can be an artefact of inconsistent error estimation

secular variation of the earth s magnetic field in the balkan region during the last eight millennia based on archaeomagnetic data summary the first archaeomagnetic secular variation sv curves for the whole southern balkan peninsula are presented these are based on all data within a 700 km circle centred at thessaloniki 40 60on 23 00oe this data set consists of 325 directional and 625 intensity data mainly from greece bulgaria serbia and southern hungary some data from southern italy are also included the sliding moving window technique was used to calculate a continuous sv curve for intensity while the directional sv curves were calculated using the bivariate extension of the fisher statistics these curves are well constrained and clearly show the main features of the geomagnetic field variation in this region during the last eight millennia comparisons with the predictions of the scha dif 3k and scha dif 8k regional and the cals7k 2 and arch3k 1 global geomagnetic field models show a good agreement for the last 3000 years but differences for older times the balkan sv curves identify several rapid changes of the geomagnetic field in eastern europe and can be used as reference curves for archaeomagnetic dating in the balkan peninsula

a german catalogue of archaeomagnetic data summary a catalogue has been compiled of existing published and unpublished archaeomagnetic directional data from sites in germany the data comprise 125 results dated mainly in the past two millennia the stability of the natural remanent magnetization was proven for most structures with at least a thellier viscosity test although for the majority of the data the direction is based on the characteristic remanent magnetization obtained from demagnetization experiments rock magnetic experiments carried out on the samples from many of the sites reveal that the dominant magnetic carrier is magnetite often oxidized or with impurities for many sites the archaeological age estimate is supported by physical dating methods while the roman epoch 0 400 ad and the period from medieval to modern times 800 1700 ad are reasonably well covered with data the time interval in between and the first millennium bc are only poorly covered the geographical distribution of data throughout germany shows a concentration along the rhine valley during roman times with in general a better coverage to the north nevertheless this data set clearly shows the secular variation during the past three millennia and it extends the european archaeomagnetic data set considerably

archeointensities in greece during the neolithic period new insights into material selection and secular variation curve numerous archeomagnetic studies have provided high quality data for both the direction and the intensity of the geomagnetic field essentially in europe for the last 10 millennia in particular greece supplies a lot of archeological materials due to its impressive cultural heritage and volcanic activity so that numerous data have been obtained from burnt clays or historical lava flows the most recent greek secular variation curves are available for the last 8 millennia for the intensity and the last 6 millennia for the direction nevertheless the coverage still presents several gaps for periods older than 2500 bc in an effort to complete the greek curve and extend it to older times we present the archeointensity results from three neolithic settlements in northern greece the samples are of two different natures burnt structures from avgi 5250 150 bc and vasili 4800 200 bc as well as ceramics from dikili tash 4830 80 bc and vasili 4750 250 bc the samples have been subjected to standard rock magnetic analyses in order to estimate the thermal stability and the domain state of the magnetic carriers before archeointensity measurements surprisingly very few ceramic samples provided reliable archeointensities whereas samples from burnt structures presented a very good success rate complementary studies showed that a detailed examination of the matrix color following archeological information and classification standards can be a decisive test for pre selection of sherds in spite of these unsuccessful measurements from ceramics we obtained an intensity value of 73 5 1 1 t for dikili tash a higher value than the other data obtained in the same area during the same period however we do not have evidences for a technical artefact during the experiment the burnt structures yielded two reliable archeointensities of 36 1 1 8 t and 46 6 3 4 t for avgi and vasili respectively finally we achieved a new archeomagnetic dating for these sites by comparing these new archeointensity values combined to the directional measurements already published with the bulgarian secular variation curve these new results contribute to extend the greek secular variation reference curve towards older periods

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

very low frequency earthquakes spatiotemporally asynchronous with strong tremor during the 2014 episodic tremor and slip event in cascadia we find very low frequency earthquakes vlfes in cascadia during the 2014 episodic tremor and slip event under washington and vancouver island using a grid search centroid moment tensor inversion method the very low frequency earthquakes occur when and where there is no strong tremor detected contrasting with previous findings where tremor and very low frequency earthquakes have a clear spatiotemporal relationship this challenges our current understanding of the dynamic relationship between the different types of slow earthquakes and their relationship to slow slip we interpret these findings to suggest that vlfes and tremor may have their own seismic cycles resulting from asperities of different sizes or characteristics that respond pseudo independently to stress loading we propose that very low frequency earthquakes and tremor are subject to asynchronous seismic cycles

long term variations in palaeointensity we compile a dataset of reliable palaeointensity estimates based both on published work and on new data from basaltic glass the basaltic glass data more than double the number of reliable thellie

estimation of high frequency wave radiation areas on the fault plane by the envelope inversion of acceleration seismograms we have developed an inversion method to estimate high frequency wave radiation areas on the fault plane it is very difficult to perform a source inversion for seismic waveforms whose frequencies are higher than 1 hz because of two problems one is the difficulty in obtaining green s functions that are accurate enough for such high frequencies and the other is that involved in doing a waveform inversion for such oscillatory data we overcame these problems by using aftershock records as empirical green s functions and by using the envelopes of acceleration seismograms as the inversion data instead of waveforms envelopes were calculated by smoothing the acceleration seismograms with a running root mean square time window we applied this method to the 1993 kushiro oki japan earthquake mw 7 6 which occurred on a horizontal fault plane inside the pacific plate subducting beneath the north american plate we adopted the mjma 4 9 aftershock as the empirical green s function event we bandpass filtered 2 0 10 0 hz the strong motion acceleration seismograms at three stations and calculated the envelopes by smoothing with a 5 0 s window length the 40 km 60 km fault plane was divided into 4 6 meshes and the acceleration radiation intensity and rupture time of each mesh were obtained by the inversion the results are as follows 1 high frequency waves radiated weakly around the rupture starting point but radiated mainly near the periphery of the fault plane an area with particularly strong radiation intensity of high frequency waves is seen at the edge of the fault plane about 30 km southwest of the rupture starting point its size is about 20 km 20 km 2 the distribution of high frequency radiation intensity and slip distribution are complementary to each other that is the radiation of high frequency waves was strong in those areas where that of low frequency waves was weak

shallow dynamic overshoot and energetic deep rupture in the 2011 mw 9 0 tohoku oki earthquake strong spatial variation of rupture characteristics in the moment magnitude mw 9 0 tohoku oki megathrust earthquake controlled both the strength of shaking and the size of the tsunami that followed finite source imaging reveals that the rupture consisted of a small initial phase deep rupture for up to 40 seconds extensive shallow rupture at 60 to 70 seconds and continuing deep rupture lasting more than 100 seconds a combination of a shallow dipping fault and a compliant hanging wall may have enabled large shallow slip near the trench normal faulting aftershocks in the area of high slip suggest dynamic overshoot on the fault despite prodigious total slip shallower parts of the rupture weakly radiated at high frequencies whereas deeper parts of the rupture radiated strongly at high frequencies

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

further evidence of the levantine iron age geomagnetic anomaly from georgian pottery recent archaeomagnetic data from ancient israel revealed the existence of a so called levantine iron age geomagnetic anomaly liaa which spanned the first 350 years of the first millennium before the common era b c e and was characterized by a high averaged geomagnetic field virtual axial dipole moments vadm 140 z am2 nearly twice of today s field short decadal scale geomagnetic spikes vadm of 160 185 z am2 fast field variations and substantial deviation from dipole field direction the geographic constraints of the liaa have remained elusive due to limited high quality paleointensity data in surrounding locations here we report archaeointensity data from georgia showing high field values vadm 150 z am2 in the tenth or ninth century b c e low field values vadm 60 z am2 in the twelfth century b c e and fast field variation in the fifth and fourth centuries b c e high field values in the time frame of liaa have been observed so far only in three localities near the levant eastern anatolia turkmenistan and now georgia all located east of longitude 30 e west of this in the balkans field values in the same time are moderate to low these constraints put geographic limits on the extent of the liaa and support the hypothesis of an unusually intense regional geomagnetic anomaly during the beginning of the first half of the first millennium b c e comparable in area and magnitude but of opposite sign to the presently active south atlantic anomaly

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

paleointensity of the geomagnetic field recovered on archaeomagnetic sites from france abstract twenty new paleointensity determinations have been obtained from archaeomagnetic sites from france time intervals investigated range from 65 to 380 ad and from 1370 to 1700 ad two hundred forty two samples of tiles and bricks were treated with the classical thellier method for paleointensity determination rock magnetic studies identify magnetite substituted maghemite and hematite as the main magnetic minerals as is usual with archaeomagnetic samples especially tiles magnetic anisotropy was observed in all samples the effect of thermoremanent magnetization trm anisotropy upon the paleointensity values was corrected after the determination of the tensor of trm anisotropy in each sample these determinations allow corrections of the field strength obtained which are usually lower than 20 the effect of the cooling rate on the trm intensity acquired was also determined and seems relatively low on our samples most frequently eight to 10 samples per site were used to calculate the mean intensity standard deviations are typically lower than 7 of the average value during the roman period small variations of the field intensity in paris are observed between 62 and 70 t while during the more recent period the intensity of the field decreases from 62 to 52 t an analysis of the paleointensity data available for the last 2000 years obtained from sites in western europe was performed using a weighing factor which takes into account the number and type of the samples studied as well as the technique used for the paleointensity determination this weighing factor clearly shows that most of the existing data might not be reliable the analysis performed indicates that more data is needed especially from the time interval 500 to 1400 ad before it would be possible to determine a reference curve of the time variations of the archaeomagnetic intensity of the field in western europe

secular variation of the geomagnetic dipole during the past 2000 years we have constructed a very simple model of a time varying geocentric dipole based on the archeomagnetic records obtained at four widely separated sites on the globe for the past 2 ka the predictions of the model in terms of directional variations have been tested against actual archeomagnetic data from 12 sites distributed over the globe they were also compared with the hongre et al 1998 time varying spherical harmonic model and with the cals7k 2 model by korte et al 2005 we find that the misfits between the predictions of our simple dipole model and the data are equivalent to those of the spherical harmonic models for the european sites and not strikingly larger for the rest of the world many discrepancies can be accounted for by uncertainties inherent to the archeomagnetic records which along with the small number and poor geographical distribution of sites leads us to conclude that the present state of the database does not allow the extraction of secular variations described by terms going beyond degree 2 it appears also that dipole tilt could be responsible for the main part of the secular variation associated with time constants exceeding 102 years in a second step we used the paleointensity records contained in the same database to construct the curve depicting the variations of the true dipole moment the present decrease of the dipole did not begin prior to 1000 years ago and the dipole was actually increasing from 0 until a d 500 the dipole moment of cals7k is lower than the present estimate probably due to large repartition of energy to higher harmonics to minimize the misfit between the inversion and the data the tilt and strength of the dipole can predict the dipole field at any site and were used to derive the contribution of the nondipole field to values of paleointensity at paris during the past 2 ka the results show that the archeomagnetic jerks are associated with various configurations depending on the phase relationship between the nondipolar and dipolar parts of the field

friction experiments under in situ stress reveal unexpected velocity weakening in nankai accretionary prism samples abstract the nankai trough hosts diverse fault slip modes ranging from slow slip events to megathrust earthquake ruptures we performed laboratory friction experiments on samples collected by the integrated ocean drilling program offshore kii peninsula japan this study systematically investigates the effect of effective normal stress on frictional strength and the velocity dependence of friction for natural fault zone and wall rock samples collected from depths of 270 to 450 meters below seafloor mbsf and over a range of shearing velocity spanning from 0 01 30 m s in addition cohesive strength was determined before and after each velocity step experiment while the sample was unloaded we tested both powdered and intact specimens at estimated in situ effective stresses as well as at higher stresses representing deeper portions of the megasplay fault sites c0004 c0010 and the frontal thrust zone sites c0007 c0006 the apparent coefficient of sliding friction s varies between 0 22 0 53 and correlates inversely with clay content direct measurements of cohesive strength show that on average 11 of the residual shear strength and up to 30 for some specimens can be attributed to cohesion friction coefficient slightly decreases as a function of increasing effective normal stress attributed to a decreasing proportion of cohesive strength the lowest s values are observed for samples from the frontal thrust zone site c0007 and the megasplay fault site c0010 all samples show a combination of velocity strengthening and velocity weakening behavior but intact samples tested under in situ effective normal stress and low shearing velocities a b we propose that fault zones in the nankai subduction zone are likely to be velocity weakening and thus potentially able to host the nucleation of unstable slip from seismogenic depths to the seafloor we also find that testing disaggregated fault zone samples and employing effective stresses exceeding those in situ lead to overestimation of a b emphasizing the importance of testing intact samples under in situ conditions in laboratory friction studies

slow earthquakes and nonvolcanic tremor nonvolcanic tremor is observed in close association with geodetically observed slow slip events in subduction zones accumulating evidence points to these events as members of a family of slow earthquakes that occur as shear slip on the downdip extensions of fault zones in a regime that is transitional between a frictionally locked region above and a freely slipping region below by virtue of their locations and their properties slow earthquakes are certain to provide new insights into the behavior of earthquakes and faulting and into the hazard they embody

large scale response of the pacific ocean subarctic front to momentum transfer a numerical study abstract a numerical four layer hydrodynamical model is implemented to investigate the role the atmosphere exerts on the dynamics of the subarctic front while the effect of the westerly winds causes a southward shift of the front the effect of a negative curl shows convergence at the front this convergence strongly favors frontogenesis the salient features at the wake of a strong cyclone can be summarized as follows i upwelling of 20 m of the four interfaces occurs ii the water remains upwelled for several weeks iii the e folding time scale of the vertical oscillations induced by the storm s passage is of the order of 10 days iv a region of relative maximum convergence is observed in the lower layers below a region of relative maximum upwelling in the upper layer and v the along and cross front velocity fields are in quadrature in time with the cross front velocity lagging the along front velocity with the exception of the cyclone case it is established that the effects of the atmos

split philippine sea plate beneath japan 1 the shape of the philippine sea plate subducting beneath western japan is a crucial factor in understanding earthquakes and volcanic activity we propose that the subducted plate was split along an extinct ridge due to an abrupt change of subduction direction followed by elastic deformation of the plate and an accumulation of stress near the ridge this shape is consistent with receiver function images the distribution of deep tremor sources the seismicity and focal mechanisms of intraplate earthquakes and the distribution of anomalous ratios of helium isotopes in ground water the movement history of the plate can explain active tectonics in western japan in the last 2 4 ma the location history of the volcanic front and the tear control where fluids ascend in the crust and these fluids are responsible for the generation of large earthquakes and volcanoes

a catalogue of spanish archaeomagnetic data a total of 58 new archaeomagnetic directions has been determined from archaeological structures in spain together with five previous results they allow the compilation of the first archaeomagnetic catalogue for spain which includes 63 directions with ages ranging between the 2nd century bc and the 20th century ad characteristic remanence directions have been obtained from stepwise thermal and alternating field demagnetization the hierarchical structure has been respected in the calculation of the mean site directions rock magnetic experiments reveal that the main magnetic carrier is magnetite or titanomagnetite with different titanium contents the age estimate of the studied structures is generally well justified by archaeological constraints for six structures the proposed date is also supported by physical methods the data are in close agreement with the french secular variation sv curve this catalogue represents the first step in the construction of a sv curve for the iberian peninsula which will be of much use in archaeomagnetic dating and in modelling of the earth s magnetic field in western europe

continuous geomagnetic field models for the past 7 millennia 2 cals7k 1 we present two continuous global geomagnetic field models for recent millennia cals3k 2 covering the past 3000 years and cals7k 2 covering 7000 years from 5000 bc to 1950 ad the models were determined by regularized least squares inversion of archeomagnetic and paleomagnetic data using spherical harmonics in space and cubic b splines in time they are derived from a greatly increased number of paleomagnetic directional data compared to previous efforts and for the first time a significant amount of archeointensity data is used in this kind of global model allowing the determination of evolution of geomagnetic dipole strength while data accuracy and dating uncertainties remain a limitation reliable low resolution global models can be obtained the results agree well with previous results from virtual axial dipole moment vadm studies from archeomagnetic intensity data apart from a systematic offset in strength a comparison of model predictions with the previous 3000 year model cals3k 1 gives general agreement but also some significant differences particularly for the early epochs the new models suggest that the prominent two northern hemisphere flux lobes are more stationary than cals3k 1 implied extending considerably the time span of stationary flux lobes observed in historical models between 5000 bc and 2000 bc there are time intervals of weak dipole moment where dipole power is exceeded by low degree nondipole power at the core mantle boundary model coefficients and evaluation code can be obtained from the earthref digital archive erda together with animations and snapshots plots for every 100 years at http www earthref org detailed urls for the different material are listed in appendix a

striations duration migration and tidal response in deep tremor deep tremor in subduction zones is thought to be caused by small repeating shear slip events on the plate interface with significant slow components it occurs at a depth of about 30 kilometres and provides valuable information on deep plate motion and shallow stress accumulation on the fault plane of megathrust earthquakes tremor has been suggested to repeat at a regular interval migrate at various velocities and be modulated by tidal stress here i show that some time invariant interface property controls tremor behaviour using precise location of tremor sources with event duration in western shikoku in the nankai subduction zone japan in areas where tremor duration is short tremor is more strongly affected by tidal stress and migration is inhibited where tremor lasts longer diffusive migration occurs with a constant diffusivity of 10 4 m 2 s 1 the control property may be the ratio of brittle to ductile areas perhaps determined by the influence of mantle wedge serpentinization on the plate interface the spatial variation of the controlling property seems to be characterized by striations in tremor source distribution which follows either the current or previous plate subduction directions this suggests that the striations and corresponding interface properties are formed through the subduction of inhomogeneous structure such as seamounts for periods as long as ten million years

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

archaeomagnetic results on three early iron age salt kilns from moyenvic france variations of the earth fs magnetic field during the first millennium bc in western europe remain poorly constrained especially archaeointensity changes three salt kilns moa mob and moc sampled in moyenvic lorraine eastern france have been studied to provide new reference data each kiln has been dated by radiocarbon to originate from the early iron age or hallstatt period between viii and vth century bc rock magnetic experiments and hysteresis results suggest the predominance of pseudo single domain psd ti poor magnetite archaeomagnetic directions obtained by thermal and alternating field demagnetizations have high mean inclination close to 70 and declination between 19 and 31 a first set of classical thellier thellier experiments was conducted on 46 samples with a laboratory field almost parallel to the direction of the characteristic remanent magnetization chrm only 24 of these specimens present a linear nrm trm plot for other specimens nrm trm plots are concave up with positive ptrm checks the very large dispersion observed between the determined palaeointensity values suggests some artefacts have not been fully recognized a second set of thellier experiments was conducted on 34 sister specimens with the laboratory field applied quasi perpendicular to the chrm in these cases mineralogical evolutions during heating and chemical remanent magnetization acquisitions have been clearly recognized despite positive ptrm checks the concave up shapes of nrm trm plots appear mainly due to mineralogical alteration rather than to the presence of psd md grains for the entire set of samples the success rate of the palaeointensity determinations is very low with 80 per cent of the samples rejected nevertheless reliable mean archaeointensities have been obtained for two of the three kilns moa 80 1 14 5 et and mob 86 6 6 9 et at the latitude of paris the high field strength and the archaeomagnetic directions determined combined with previous published data provide further evidence for important changes of the earth magnetic field in europe during the first half of the first millennium bc these large variations of the geomagnetic field during the iron ages indicate that archaeomagnetism is highly suitable for dating of structures from this period

three stage rupture process of the 28 december 1994 sanriku oki earthquake we investigated the rupture process of the 28 december 1994 sanriku oki earthquake mw 7 7 using broadband seismograms recorded at local distances the earthquake rupture nucleated at the eastern end of the aftershock area as it propagated towards the west a major subevent occurred near the center of the aftershock area about 26 s after the initial rupture releasing most of the seismic energy of this earthquake about 24 s later another subevent followed at the western end of the aftershock area emitting large high frequency waves the whole rupture time is about 55 sec the three stage rupture process is very similar to the earlier stage rupture process of the 1968 tokachi oki earthquake mw 8 2 the difference is that the rupture of the tokachi oki earthquake further propagated towards the north in the following stage instead of terminating at the western end the occurrence of the sanriku oki earthquake is critical to the validity of the characteristic earthquake so far believed to exist in this part of the plate boundary

reconstructing the holocene geomagnetic field abstract knowledge of the holocene evolution of earth s magnetic field is important for understanding geodynamo processes in the core is necessary for studying long term solar terrestrial relationships and can provide useful age constraints for archeologicaland stratigraphic applications continuous time varying global field models based on archeo and paleomagnetic data are useful tools in this regard we use a comprehensive data compilation and recently refined modelling strategies to produce cals10k 1b the first time varying spherical harmonic geomagnetic field model spanning 10 ky the model is an average obtained from bootstrap sampling to take account of uncertainties in magnetic components and ages in the data and hence has version number 1b instead of 1 this model shows less spatial and temporal resolution than earlier versions for 0 3 ka and particularly aims to provide a robust representation of the large scale field at the core mantle boundary cmb we discuss the geomagnetic dipole evolution and changes in holocene magnetic field morphology at the cmb as shown by the new reconstruction the results are compatible with earlier models cals3k 3 and cals3k 4 for 0 3 ka but reveal some clear deficiencies in the 0 7 ka cals7k 2 model prior to 3 ka cals10k 1b is able to resolve mobile and structurally evolving high latitude radial field flux lobes at the cmb in both hemispheres as well as persistent non zonal structure in the 10 ky average contributions to the average field from time varying structures in the equatorial indonesian australian region are particularly striking

archaeomagnetic secular variation in germany during the past 2500 years summary the german archaeomagnetic data set was supplemented with 35 new directions from ger man sites mainly dating from the past 3000 yr together with archaeomagnetic data from the neighbouring countries of germany a database of 166 reliable archaeomagnetic directions has been compiled for the reference area which is defined by a 500 km radius circle around gottingen the retrieved directions come from well dated archaeological structures and about 40 per cent of the dating relay on natural science methods such as radiocarbon thermolumines cence dendrochronology dating or historical documents from this data set a secular variation sv reference curve has been calculated using a bivariate algorithm which fits a natural cubic spline based on roughness penalty to declination inclination and time simultaneously the error tube surrounding this curve was obtained from bayesian modelling of the experimental errors which can also take stratigraphic information into account the obtained sv reference curve for the past 2500 yr is similar to that from france but also significant differences are seen comparison of the curves does not show a simple westward drift of the sv pattern the german reference curve allows archaeomagnetic dating in the reference area and extends this dating technique to sites situated in middle europe

a regional archeomagnetic model for europe for the last 3000 years scha dif 3k applications to archeomagnetic dating 1 the available european database of archeomagnetic field values and instrumental data has been used to produce a regional model for the geomagnetic field in europe for the last 3000 years from 1000 b c to 1900 a d connecting with the epoch covered by the igrf models this new model scha dif 3k constitutes an improvement with respect to the previous regional archeomagnetic model scha di 00 f which used relocated values and was only valid for the last 2000 years the new model has been obtained by least sums of absolute deviation inversion of paleomagnetic data using spherical cap harmonics for the spatial representation of the field and sliding windows in time an algorithm has been developed to jointly model the three archeomagnetic elements declination inclination and intensity the resulting model provides the direction and intensity of the earth s magnetic field over the european continent northern africa and western asia for the last 3000 years the fit to the european archeomagnetic database is more accurate than that provided by global archeomagnetic models in addition this model represents a step forward in archeomagnetic dating studies since the relocation error is avoided and can also be used to study the rapid changes of the geomagnetic field archeomagnetic jerks that have been recently proposed

large geomagnetic field anomalies revealed in bronze to iron age archeomagnetic data from tel megiddo and tel hazor israel abstract geomagnetic field measurements from the past few centuries show heightened secular variation activity in the southern hemisphere associated with the south atlantic anomaly saa it is uncertain whether geomagnetic anomalies at a similar scale have existed in the past owing to limited coverage and uncertainties in the paleomagnetic database here we provide new evidence from archaeological sources in the levant suggesting a large positive northern hemisphere anomaly similar in magnitude to the saa during the 9th 8th centuries bce called levantine iron age anomaly we also report an additional geomagnetic spike in the 8th century the new dataset comprises 73 high precision paleointensity estimates from ca 3000 bce to 732 bce and five directional measurements between the 14th and the 9th centuries bce well dated pottery and cooking ovens were collected from twenty archaeological strata in two large contemporaneous stratigraphical mounds tells in israel tel megiddo and tel hazor the new data are combined with previously published data and interpreted automatically using the pmagpy thellier gui program the tel megiddo and tel hazor data sets demonstrate excellent internal consistency and remarkable agreement with published data from mesopotamia syria the data illustrate the evolution of an extreme geomagnetic high that culminated in at least two spikes between the 11th and the 8th centuries bce iron age in the levant the paleomagnetic directional data of the 9th century bce show positive inclination anomalies and deviations of up to 22 from the averaged geocentric axial dipole gad direction from comparison of the levantine archaeomagnetic data with igrf model for 2015 we infer the levantine iron age anomaly between the 10th and the 8th centuries bce is a local positive anomaly the eastward extent of the anomaly is currently unknown

geomagnetic field for 0 3 ka 1 new data sets for global modeling 1 paleomagnetic and archeomagnetic records are used in both regional and global studies of earth s magnetic field we present a description and assessment of five newly compiled data sets also used in the companion paper by korte et al 2009 to produce a series of time varying spherical harmonic models of the geomagnetic field for the last 3000 years data are drawn from our compilation of lake sediment records and from the online database geomagia50v2 the five selections are available from the earthref digital archive at http earthref org cgi bin erda cgi n 944 data are grouped according to the source of material and we conducted separate assessments of reliability for archeomagnetic artifacts and lava flows the arch3k dat data set and for sediments sed3k dat the overall number of data is 55 greater than in previous compilations constrained data sets were selected using different criteria for each group winnowing of archeological data was based on uncertainties supplied by the original data providers the lake sediment data assessment relied on preassigned age uncertainties and one or more of the following comparisons with archeomagnetic data from the same region regional consistency among several lakes and consistency with global archeomagnetic models we discuss relative merits of a larger unconstrained data set or a smaller possibly more reliable one the constrained data sets eliminate a priori up to 35 of the available data in each case and rely on potentially subjective assessments of data quality given the limited data available our analyses indicate that iterative rejection of a small number 1 1 5 of outlying data during global field modeling is a preferable approach specific regional comparisons among the models and data support the conclusion that korte et al s outlier free cals3k 3 model based on all available measurements from sediments and archeological artifacts currently provides the best global representation of the 0 3 ka field the arch3k 1 model provides a better fit to the denser european archeomagnetic data and may be better in that region

new archaeointensity data from italy and geomagnetic field intensity variation in the italian peninsula we present new archaeointensity results from three italian kilns situated at ascoli satriano vagnari and fontanetto po obtained with the thellier modified by coe double heating method these data complement the directional results previously published all sites are dated on the basis of archaeological information and or thermoluminescence dating the results are corrected for the anisotropy of the thermoremanent magnetization and the cooling rate effects the new data are compared with previously published archaeointensity data from italy and nearby countries within 900 km radius from viterbo an initial data set including archaeointesity data mainly coming from italy france switzerland czech republic slovakia hungary greece and bulgaria has been compiled after the application of strict selection criteria the most reliable data have been used for the calculation of a preliminary italian intensity secular variation sv curve for the last 3000 yr the new curve covers the 300 bc 400 ad and 1200 1900 ad periods it is established by means of sliding windows of 200 yr shifted by 100 yr the lack of reliable data for the 1000 200 bc and 400 1200 ad time intervals does not permit the calculation of a continuous curve clearly more high quality archaeointensity data from italy and europe are still needed to draw a robust intensity sv curve for the italian peninsula that could be used for archaeomagnetic dating in combination with the directional data

a brownian walk model for slow earthquakes 1 along some subduction plate boundaries slow deformation is observable as seismically detected deep low frequency tremor and geodetically detected slow slip events these phenomena are considered as different manifestations of slow earthquakes characterized by fairly constant seismic moment rate this paper presents a simple model of slow earthquakes that can explain wide variety of observed features including the steady moment rate and scaled energy characteristics of tremor signals both in time and frequency domains and the migration of the source location in this model slow earthquakes are represented as shear slip on circular faults whose radius is a random variable that is governed by a langevin equation and three parameters a diffusion coefficient a damping coefficient and a slip rate coefficient this model expands on a previous scaling law for the slow earthquakes by providing a specific image of kinematics allowing for spatial variations of the parameters could potentially explain differences in behavior of slow slip events worldwide

slow earthquakes coincident with episodic tremors and slow slip events we report on the very low frequency earthquakes occurring in the transition zone of the subducting plate interface along the nankai subduction zone in southwest japan seismic waves generated by very low frequency earthquakes with seismic moment magnitudes of 3 1 to 3 5 predominantly show a long period of about 20 seconds the seismicity of very low frequency earthquakes accompanies and migrates with the activity of deep low frequency tremors and slow slip events the coincidence of these three phenomena improves the detection and characterization of slow earthquakes which are thought to increase the stress on updip megathrust earthquake rupture zones

regional modeling of the geomagnetic field in europe from 6000 to 1000 b c we have developed a first low degree regional geomagnetic model for the european continent valid for the period 6000 1000 b c from a selected compilation of sedimentary and archeomagnetic data the scha dif 8k model this model provides information about both direction declination and inclination and intensity of the earth s magnetic field by connecting it with our previous model scha dif 3k valid from 1000 b c to 1900 a d and the igrf we furnish continuous geomagnetic field information for the last 8000 years in europe it has been developed using the revised spherical cap harmonic analysis in 2 dimensions technique r scha2d and using the norm of the earth s magnetic field to constrain the inversion problem the size of the cap is 22 and the maximum degree of the expansion is 2 the linearization problem was solved by using the truncated taylor s series applied to the expressions representing the relationship between the declination inclination and intensity data and the cartesian components of the geomagnetic field we used the geocentric axial dipole gad field as our initial or reference field for time we used the classical sliding overlapping window method the size of the window was set to 100 years shifted by 50 years we compared the model s prediction with the input data with the global cals7k 2 model and with new independent data the regional model shows a better fit to the input and to the independent data than the global model especially in terms of intensity and agrees with the virtual axial dipole moment given by other studies for the last 8000 years the european geomagnetic field has recorded rapid changes or archeomagnetic jerks the average field for the last 8000 years in europe is indistinguishable from the gad field

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

bridging the gap between seismically and geodetically detected slow earthquakes 1 recently observed unusual seismic events deep low frequency earthquakes and tremor very low frequency earthquakes and slow slip events form a family of slow earthquakes that are governed by a scaling law different from ordinary earthquakes guided by this scaling law we have observed previously unknown events with source duration of 20 200 s and moment magnitude of 3 4 under the kii peninsula in western japan these events radiate seismic energy in the 2 8 hz band in direct proportion to their seismic moment rate though the constant of proportionality is 4 5 orders of magnitude smaller than for ordinary earthquakes slow earthquakes in this region may be comprised of numerous shear slip events which in aggregate are manifest seismically as tremor or isolated longer events up to 200 s and geodetically as slow slip events

three millennia of directional variation of the earth s magnetic field in western europe as revealed by archeological artefacts directional secular variation of the geomagnetic field over the last 2000 years has been defined in western europe from numerous archeomagnetic studies however the number of archeomagnetic results for older periods is much more limited for this reason we present new data obtained from fired archeological structures found in two french sites loupiac and aspiran dated within the first millennium b c latest bronze earliest iron age transition 850 700 b c and iron age 525 475 b c respectively from a compilation of archeomagnetic results from western europe great britain italy and france and northern africa tunisia we propose a directional secular variation curve for western europe that covers the entire first millennium b c this curve exhibits a large clockwise motion with rapid changes during the first half of the millennium while the last four centuries b c are characterized by weak variations

shallow episodic tremor near the nankai trough axis off southeast mie prefecture japan we analyzed long term continuous seismic records from september 2015 to april 2016 of dense ocean floor network system for earthquake and tsunamis an ocean floor observation system deployed around the fore arc slope of the nankai subduction zone to investigate shallow tremor near the trough axis we found that the activity of shallow tremor was concentrated in two time periods 6 days in october 2015 and 2 weeks in april 2016 during the episode in april 2016 migration and triggering of tremor were observed these characteristics are similar to those of tremor in the deeper part of the subduction zone the triggering of tremor indicates that the tremor activity is very sensitive to nearby stress perturbation in the area of this study which is near the initiation points of past large earthquakes along the nankai trough therefore it is very important to monitor tremor activity in this region for understanding the stress accumulation process of megathrust earthquakes

near field observations of an offshore mw 6 0 earthquake from an integrated seafloor and subseafloor monitoring network at the nankai trough southwest japan an mw 6 0 earthquake struck 50 km offshore the kii peninsula of southwest honshu japan on 1 april 2016 this earthquake occurred directly beneath a cabled offshore monitoring network at the nankai trough subduction zone and within 25 35 km of two borehole observatories installed as part of the international ocean discovery program s nantroseize project the earthquake s location close to the seafloor and subseafloor network offers a unique opportunity to evaluate dense seafloor geodetic and seismological data in the near field of a moderate sized offshore earthquake we use the offshore seismic network to locate the main shock and aftershocks seafloor pressure sensors and borehole observatory data to determine the detailed distribution of seafloor and subseafloor deformation and seafloor pressure observations to model the resulting tsunami contractional strain estimated from formation pore pressure records in the borehole observatories equivalent to 0 37 to 0 15 strain provides a key to narrowing the possible range of fault plane solutions together these data show that the rupture occurred on a landward dipping thrust fault at 9 10 km below the seafloor most likely on the plate interface pore pressure changes recorded in one of the observatories also provide evidence for significant afterslip for at least a few days following the main shock the earthquake and its aftershocks are located within the coseismic slip region of the 1944 tonankai earthquake mw 8 0 and immediately downdip of swarms of very low frequency earthquakes in this region illustrating the complex distribution of megathrust slip behavior at a dominantly locked seismogenic zone

tsunamigenic potential of the shallow subduction plate boundary inferred from slow seismic slip at subduction zones slip along the shallowest parts of the plate boundary is generally thought to be aseismic observations of very low frequency earthquakes occurring at shallow levels on the plate boundary of the nankai trough subduction zone imply that slow but seismic slip can occur there and could potentially generate tsunamigenic earthquakes

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

space time correlation of slip and tremor during the 2009 cascadia slow slip event 1 episodic tremor and slip ets involving transient deformations accompanied by emergent low frequency tremor occurs in subduction zones around the world ets events increase the shear stress on locked megathrusts and may potentially trigger damaging earthquakes despite the clear association of tremor and slip the physical relationship between them is unresolved tremor appears to result from slip on small asperities on the plate interface due to either creep on the surrounding fault or stress increases ahead of the propagating slow slip front previous studies of migrating slow slip events have not had sufficient spatial and temporal resolution to differentiate between these two models to address this we invert gps data from the august 2009 ets event in central cascadia for the space time evolution of fault slip rate we find a correlation in both space and time between tremor epicenters and the independently determined position of high fault slip rate this supports the first hypothesis that tremor asperities are loaded directly by slow slip rather than by stress increases ahead of the slip front and provides new insights into the mechanics of ets

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

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

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

low frequency tremors associated with reverse faults in a shallow accretionary prism abstract the shallow part of a seismogenic subduction zone is thought to play an important role in tsunami genesis during large interplate thrust earthquakes near the updip portion of the seismogenic zone along the nankai trough splay faults which are major active reverse faults in the accretionary prism likely rupture during large interplate earthquakes such as the 1944 m w 8 2 tonankai earthquake off kii peninsula we observed low frequency tremors associated with reverse faults in a shallow accretionary prism off kii peninsula at close range by using ocean bottom seismographs the tremors were characterized by a dominant frequency range of 2 8 hz and a lack of energy in the frequency range above 10 hz their duration ranged from tens of seconds to a few minutes their source locations lay in three clusters on the landward slope of the nankai trough activity in each cluster continued for from one day to two weeks many of the low frequency tremors were located near the shallowest part of a major splay fault the episodic activity of low frequency tremors and of previously reported very low frequency earthquakes which indicate reverse faulting in the shallow accretionary prism suggests that the reverse faults in the accretionary prism are conditionally stable faults that can become unstable under sufficiently strong dynamic loading such as that caused by a large earthquake such reverse faults as typified by a splay fault can rupture during large interplate earthquakes and generate large tsunamis

bayesian approach for detecting dynamically triggered very low frequency earthquakes in the nankai subduction zone and application to the 2016 mw 5 9 off kii peninsula earthquake japan

quantifying the time function of nonvolcanic tremor based on a stochastic model 1 nonvolcanic tremor is the seismically observable component of slow earthquakes which have been recently discovered in subduction zones around the world including major study areas at the nankai and cascadia subduction zones although tremor appears to occur randomly in both areas cascadia tremor has a longer duration than nankai tremor in the present study this difference in tremor duration is quantified using a brownian slow earthquake model that explains several features of tremor and slow earthquakes a previous brownian model is improved and applied to explain the cumulative distribution function of tremor amplitude which is approximated by a 2 distribution the model also shows that the power spectrum of tremor amplitude has a simple analytic formula including a characteristic time an inversion method is developed to measure the characteristic time from the tremor spectrum in the presence of non gaussian background noise the method is applied to several tremor sequences in the nankai and cascadia subduction zones to quantitatively confirm the apparent differences in tremor behavior between the two areas the constants for cascadia and nankai tremor are 1000 3000 s and 100 1000 s respectively with temporal increases in these values observed over the course of 1 day records of activity the difference in characteristic time between the two areas may reflect geometric constraints such as the width of the tremor region