characteristics of short term slow slip events estimated from deep low frequency tremors in shikoku japan 1 we have investigated the characteristics of short term slow slip events sses recurrence interval and size distribution and the slip rate at the transition zone on the plate interface beneath the shikoku region japan using nonvolcanic deep low frequency dlf tremors on the basis of a proportional relationship between the seismic moment of sse observed geodetically and the total size of dlf tremors of the corresponding episode we estimated the seismic moment due to the slip on the plate interface from the dlf tremors and a temporal variation in the cumulative seismic moment the recurrence interval of major short term sses is 6 months in the western area and 3 months in the central and the eastern areas the size distribution of short term sses as well as dlf tremors is approximated by an exponential law rather than by a power law showing a different scaling for regular earthquakes the average slip rate at the transition zone estimated from the cumulative seismic moment with time of sses is 4 2 cm yr 3 3 cm yr and 4 9 cm yr in the western central and eastern areas respectively these values compensate for the difference between the convergence rate at the trench and the slip deficit rate at the transition zone of the subducting philippine sea plate in other words the slip rate estimated from the dlf tremors provides a constraint of the slip deficit rate at the transition zone on the plate interface

grain size dependence of sediment composition and environmental bias in provenance studies abstract this article investigates both experimentally and theoretically the compositional changes associated with textural effects and hydraulic sorting during sediment transport and deposition which cause systematic distortion in quantitative provenance analysis environmental bias traditional procedures aimed at eliminating textural noise find limited success the gazzi dickinson method cannot remove hydrodynamic related modal variability multiple size window strategies are time consuming narrow or moving size window strategies represent misleading or impractical short cuts being less convenient options than simply analysing each sample in bulk new concepts introduced here unravel the superposed causes of compositional variability in modern sediments intrasample modal variability fundamentally explained by settling equivalence relationships can be accurately modelled mathematically intersample modal variability principally resulting from selective entrainment can be assessed and removed by a simple principle in absence of provenance changes and environmental bias the weighted average density of terrigenous grains srd index should be equal for each sample and each grain size class of each sample to the weighted average density of source rocks by correcting relative abundances of detrital minerals in proportion to their densities we can restore the appropriate srd index for any provenance and subprovenance type in each sample or grain size class modal variability is effectively reduced by this procedure which can be applied confidently to modern sediments deposited by tractive currents in any environment good results are obtained even for placer sands and finest classes where heavy mineral concentration is strongest such srd correction also successfully compensates for biased narrow window modes thus providing a numerical solution of general validity to the problem of environmental bias in sedimentary petrology after compensating for settling equivalence and selective entrainment effects residual size dependent compositional variability may be provenance related minor in ganga brahmaputra sediments provenance related effects are spectacularly displayed in the nile basin where volcaniclastic silt mixes with basement derived quartzofeldspathic sand and wind blown saharan quartz

localized seismic deformation in the upper mantle revealed by dense seismic arrays seismicity along continental transform faults is usually confined to the upper half of the crust but the newport inglewood fault nif a major fault traversing the los angeles basin is seismically active down to the upper mantle we use seismic array analysis to illuminate the seismogenic root of the nif beneath long beach california and identify seismicity in an actively deforming localized zone penetrating the lithospheric mantle deep earthquakes which are spatially correlated with geochemical evidence of a fluid pathway from the mantle as well as with a sharp vertical offset in the lithosphere asthenosphere boundary exhibit narrow size distribution and weak temporal clustering we attribute these characteristics to a transition from strong to weak interaction regimes in a system of seismic asperities embedded in a ductile fault zone matrix

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

processes of selective grain transport and the formation of placers on beaches placers are found on many beaches of the oregon coast in the beach that is the focus of this study the principal placer minerals are ilmenite 22 0 epidote 20 0 garnet 18 7 augite 15 5 hypersthene 8 1 hornblende 5 8 and zircon 2 0 the ilmenite fraction actually being partly chromite a series of beach face sand samples was obtained along a profile when sand was being eroded from the upper beach and transported to offshore bars since the processes of grain selective sorting leading to placer formation were probably most active at such a time the landward most sample contained 96 heavy minerals being part of the placer this concentration systematically decreased offshore to a 6 heavy mineral content in the seaward most sample 54 m offshore determinations of individual heavy mineral concentrations revealed that although they all tended to become concentrated within the placer with light quartz and feldspar dominating the offshore transport the sorting processes were m

very low frequency earthquakes related to small asperities on the plate boundary interface at the locked to aseismic transition 1 very low frequency vlf seismic signals observed in southwestern japan are evidently radiated from shear slips on the upper surface of the subducting philippine sea plate we used grid moment tensor inversion and centroid moment tensor inversion to calculate 242 moment tensor solutions with moment magnitudes between 3 1 and 3 8 from continuous seismograms recorded over a 5 year period by using a very dense broadband seismic network at least 5 10 sequences of repetitive activity were observed during the 5 years the vlf events formed clustered distributions along the 35 km isodepth contour of the subducting plate surface the nodal planes which dip landward of moment tensor solutions of the vlf events reflected the configuration of the subducting plate interface the slip vectors were consistent with the direction of movement of the subducting plate the dip and strike of the slip vectors clearly reflected the configuration of the upper surface of the subducting plate we found that the rates of seismic moment release per unit area associated with five major vlf clusters were very similar although both the seismic magnitudes and sizes of the clusters varied considerably the rate of seismic moment released from detectable vlf sources was 0 1 of the rates of short term slow slip events suggesting that the source areas occupied only 0 1 of the fault segment on which the short term slow slip events occurred

dynamic modeling of slow slip coupled with tremor 1 we theoretically study the generation mechanism of slow slip in a dynamical framework assuming a fault in a fluid saturated thermoporoelastic medium the fluid flow is taken into consideration dynamic slip is assumed to create pores and cause shear heating on the fault key parameters in the modeling are su and su the nondimensional parameter su represents the relative dominance of the effect of pore creation on the fluid pressure change over that of shear heating while su is associated with the dominance of fluid flow effect over the effect of shear heating our calculation shows that we have to assume su 1 and relatively small values for su to simulate rupture speed that is negligibly small compared to the shear wave velocity although this was also found in our former paper our new finding here is the simulation of slow slip coupled with tremor we find that frozen slip is reactivated sporadically because the fluid inflow triggered by the pore creation elevates the fluid pressure on the fault the slip reactivation actually occurs if su is smaller than a threshold such sporadic reactivation of slips can be a model for slow slip coupled with tremor we also show that the moment evolution curves are categorized into two separate groups when su 0 1 one of them represents slow slips while the other represents ordinary earthquakes

detransformation of the british geomagnetic secular variation record for holocene times in this note we replot the british post glacial secular variation curve in terms of actual values of declination and inclination rather than the transformed declination and inclination system used in our original paper turner thompson 1981 this should facilitate the comparison of our record with contemporaneous european archaeomagnetic data our composite record was obtained by averaging the dated records from 10 cores of lake sediment the sequence of unit vectors describing the magnetic direction record of each core was rotated so as to place its mean direction the mean over the section of core dated between 0 and 7000 bp the time span of the shortest core at zero transformed declination and inclination dt o it 0 the transformed coordinate frame of each core is thus derived from its mean direction assumed to represent the mean geomagnetic field direction over the 7000 yr period rather than from the core tube and its orientation during coring hence the problem of not knowing the azimuthal orientation and inclination of the corer during core collection is avoided and the 10 records can be averaged in this coordinate system transformed coordinates then provide a convenient generalised method of plotting averaged sediment records however in the archaeomagnetic method sample orientation is straightforward and the results can readily be plotted as absolute declination and inclination values so for consistency when comparing the two we have attempted here to detransform our record the following procedures assumptions and approximations were taken to produce the detransformed magnetograms and bauer type plots of figs 1 and 2 1 amplitude correction although the combination of 10 data sets produces a good estimate of the signature of the geomagnetic variations the following factors contribute to an overall loss of amplitude in both declination and inclination a the quality of magnetic recording varies widely between different sediments depending on the porosity of the sediment the size and shape distributions and the nature of the magnetic carrier verosub 1979 the loch lomond sediments carry a good high amplitude pattern of remanent directions of which the most recent closely follow the london observatory records the much wetter and less compacted sediments of llyn geirionydd on the

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

evidence for a scale limited low frequency earthquake source process we calculate the seismic moments for 34 264 low frequency earthquakes lfes beneath the olympic peninsula washington lfe moments range from 1 4 1010 to 1 9 1012 n m mw 0 7 2 1 while regular earthquakes follow a power law moment frequency distribution with a b value near 1 the number of events increases by a factor of 10 for each unit increase in mw we find that while for large lfes the b value is 6 for small lfes it is 1 the magnitude frequency distribution for all lfes is best fit by an exponential distribution with a mean seismic moment characteristic moment of 2 0 1011 n m the moment frequency distributions for each of the 43 lfe families or spots on the plate interface where lfes repeat can also be fit by exponential distributions an exponential moment frequency distribution implies a scale limited source process we consider two end member models where lfe moment is limited by 1 the amount of slip or 2 slip area we favor the area limited model based on the observed exponential distribution of lfe moment and geodetically observed total slip we estimate that the total area that slips within an lfe family has a diameter of 300 m assuming an area limited model we estimate the slips subpatch diameters stress drops and slip rates for lfes during episodic tremor and slip events we allow for lfes to rupture smaller subpatches within the lfe family patch models with 1 10 subpatches produce slips of 0 1 1 mm subpatch diameters of 80 275 m and stress drops of 30 1000 kpa while one subpatch is often assumed we believe 3 10 subpatches are more likely

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

on archeomagnetic secular variation curves and archeomagnetic dating abstract secular variation sv of the earth s magnetic field can be used for dating purposes by comparing archeomagnetic directions of unknown ages with a well dated reference curve in this study we propose a dating technique based on the statistics of mcfadden and mcelhinny geophys j int 103 1990 725 for testing the hypothesis that two fisherian distributions of individual directions share a common mean direction the statistics are adapted to test the degree of compatibility between one individual fisherian mean direction and a reference curve constructed using the bivariate extension of the fisher distribution furthermore as the density of the data which define the archeomagnetic reference curve varies in time we suggest that one computes the mean directions with moving windows of varying duration where both the window widths and the time shifts between successive mean directions are fixed when a minimum threshold density of data is reached within each time interval in our paper we apply this new procedure to the french archeomagnetic data set

geomagnetic secular variation as recorded in british lake sediments and its application to archaeomagnetic studies abstract lake sediments can play an important role in understanding and reconstructing temporal characteristics of the geomagnetic field as they potentially offer near continuous high resolution archives of magnetic information extending throughout the holocene to date lake sediment geomagnetic data has typically been excluded from british archaeomagnetic secular variation curves svc due to uncertainties with the acquisition of magnetisation by lake sediments this paper presents the argument that with regards to british datasets the real problem lies with poor chronological control and sets out to illustrate that with british archaeomagnetic data some progress has been made the results indicate that it is not currently possible to resolve secular variation on a time scale of 100 years from published british lake sediment data but more success has been made with data from archaeological sediments this level of detail has been considered necessary for the incorporation of lake sediment data into the british archaeomagnetic dataset as the ability to resolve short term geomagnetic changes is critical for the integration of any dataset into the british svc as the latter is predominantly employed to date archaeological architecture and artefacts requires that it has the ability to resolve changes over timescales relevant to human lifetimes using currently available data this retrospective critique confirms that in archaeological sediments depositional and thermoremanent magnetisation can record the same direction over the same time interval

imaging widespread seismicity at midlower crustal depths beneath long beach ca with a dense seismic array evidence for a depth dependent earthquake size distribution we use a dense seismic array composed of 5200 vertical geophones to monitor microseismicity in long beach california poor signal to noise ratio due to anthropogenic activity is mitigated via downward continuation of the recorded wavefield the downward continued data are continuously back projected to search for coherent arrivals from sources beneath the array which reveals numerous previously undetected events the spatial distribution of seismicity is uncorrelated with the mapped fault traces or with activity in the nearby oil fields many events are located at depths larger than 20 km well below the commonly accepted seismogenic depth for that area the seismicity exhibits temporal clustering consistent with omori s law and its size distribution obeys the gutenberg richter relation above 20 km but falls off exponentially at larger depths the dense array allows detection of earthquakes two magnitude units smaller than the permanent seismic network in the area because the event size distribution above 20 km depth obeys a power law whose exponent is near one this improvement yields a hundred fold decrease in the time needed for effective characterization of seismicity in long beach

deep low frequency tremors as a proxy for slip monitoring at plate interface 1 we propose a new method to monitor slip at the plate interface using non volcanic deep low frequency dlf tremors we assume that a dlf tremor is the superposition of frequently excited intermittent events meaning that the envelope of the reduced displacement of the dlf tremor provides an apparent moment rate function we estimate a conversion factor from the apparent moment to the seismic moment with an assumption that a total size of dlf tremors of an episode is proportional to the size of corresponding slow slip event sse the cumulative seismic moment estimated by dlf tremors is consistent with that estimated from geodetic methods and provides appropriate slip and slip rate at the plate interface this proves our assumptions and demonstrates that dlf tremors are useful tool for real time monitoring of the slip at the plate interface

the rupture extent of low frequency earthquakes near parkfield ca the low frequency earthquakes lfes that constitute tectonic tremor are often inferred to be slow to have durations of 0 2 to 0 5 s a factor of 10 to 100 longer than those of typical m w 1 2 earthquakes here we examine lfes near parkfield ca in order to assess several proposed explanations for lfes long durations we determine lfe rupture areas and location distributions using a new approach similar to directivity analysis where we examine how signals coming from various locations within lfes finite rupture extents create differences in the apparent source time functions recorded at various stations we use synthetic ruptures to determine how much the lfe signals recorded at each station would be modified by spatial variations of the source station travel time within the rupture area given various possible rupture diameters and then compare those synthetics with the data our synthetics show that the methodology can identify inter station variations created by heterogeneous slip distributions or complex rupture edges and thus lets us estimate lfe rupture extents for unilateral or bilateral ruptures to obtain robust estimates of the sources similarity across stations we stack signals from thousands of lfes using an empirical green s function approach to isolate the lfes apparent source time functions from the path effects our analysis of lfes in parkfield implies that lfes apparent source time functions are similar across stations at frequencies up to 8 to 16 hz depending on the family the inter station coherence observed at these relatively high frequencies or short wave lengths down to 0 2 to 0 5 km suggest that lfes in each of the 7 families examined occur on asperities they are clustered in patches with sub 1 km diameters the individual lfes rupture diameters are estimated to be smaller than 1 1 km for all families and smaller than 0 5 km and 1 km for the two shallowest families which were previously found to have 0 2 s durations coupling the diameters with the durations suggests that it is possible to model these m w 1 2 lfes with earthquake like rupture speeds around 70 of the shear wave speed however that rupture speed matches the data only at the edge of our uncertainty estimates for the family with highest coherence the data for that family are better matched if lfes have rupture velocities smaller than 40 of the shear wave speed or if lfes have different rupture dynamics they could have long rise times contain composite sub ruptures or have slip distributions that persist from event to event

is it possible to identify temporal differences among combustion features in middle palaeolithic palimpsests the archaeomagnetic evidence a case study from level o at the abric romani rock shelter capellades spain abstract archaeomagnetic dating is probably one of the most known applications of magnetic methods to archaeology but there are others still underutilized and of particular interest to palaeolithic archaeology here we report a novel application of archaeomagnetism as a technique to determine temporal diachronies among combustion features from the same surface within palaeolithic palimpsests the approach is based on the subtle directional changes of the earth s magnetic field through time secular variation sv and on the ability of burned materials to record such variations under certain conditions three middle palaeolithic hearths from level o ca 55 ka bp at the abric romani rock shelter ne spain were archaeomagnetically investigated the studied surface black homogeneous carbonaceous facies recorded the magnetic enhancement produced by fire with a tenfold increase in concentration dependent magnetic parameters in the uppermost centimetre with respect to its unburned or deeper counterparts pseudo single domain psd ti low titanomagnetite was identified as the main remanence carrier the irreversibility of thermomagnetic curves suggests that these samples did not undergo enough high temperatures as to record a full thermoremanence trm additionally the occasional occurrence of maghaemitized magnetite is interpreted as an indication of a thermochemical remanent magnetization tcrm making these samples unsuitable for absolute palaeointensity determinations two well defined 95

a slow thrust slip event following the two 1996 hyuganada earthquakes beneath the bungo channel southwest japan we report a slow thrust slip event that occurred beneath the bungo channel region southwestern japan on oct and dec 1996 two hyuganada earthquakes both mw 6 7 followed by afterslips occurred in addition a crustal movement characterized by an extremely slow rise was observed around the bungo channel about 200 km north from the epicenters and continued for about 300 days long assuming a slow slip on the plate boundary we estimate its duration and surface displacements from gps time series data by curve fitting and then determine the fault slip distribution we found that a slow slip without any earthquakes continued for nearly one year and released the seismic moment comparable to that of the hyuganada earthquakes occurrence of the slow thrust slip event suggests that this kind of event may be a characteristic mode of stress release at a transition region of interplate coupling

magnitudes and moment duration scaling of low frequency earthquakes beneath southern vancouver island we employ 130 low frequency earthquake lfe templates representing tremor sources on the plate boundary below southern vancouver island to examine lfe magnitudes each template is assembled from hundreds to thousands of individual lfes representing over 269 000 independent detections from major episodic tremor and slip ets events between 2003 and 2013 template displacement waveforms for direct p and s waves at near epicentral distances are remarkably simple at many stations approaching the zero phase single pulse expected for a point dislocation source in a homogeneous medium high spatiotemporal precision of template match filtered detections facilitates precise alignment of individual lfe detections and analysis of waveforms upon correction for 1 d geometrical spreading attenuation free surface magnification and radiation pattern we solve a large sparse linear system for 3 d path corrections and lfe magnitudes for all detections corresponding to a single ets template the spatiotemporal distribution of magnitudes indicates that typically half the total moment release occurs within the first 12 24 h of lfe activity during an ets episode when tidal sensitivity is low the remainder is released in bursts over several days particularly as spatially extensive rapid tremor reversals rtrs during which tidal sensitivity is high rtrs are characterized by large magnitude lfes and are most strongly expressed in the updip portions of the ets transition zone and less organized at downdip levels lfe magnitude frequency relations are better described by power law than exponential distributions although they exhibit very high b values 5 we examine lfe moment duration scaling by generating templates using detections for limiting magnitude ranges mw 1 5 mw 2 0 lfe duration displays a weaker dependence upon moment than expected for self similarity suggesting that lfe asperities are limited in fault dimension and that moment variation is dominated by slip this behavior implies that lfes exhibit a scaling distinct from both large scale slow earthquakes and regular seismicity

deep volcanic tremor and magma ascent mechanism under kilauea hawaii deep harmonic tremor originating at depths around 40 km under kilauea was studied using records accumulated since 1962 at the hawaii volcano observatory of the u s geological survey the deep source of the tremor was determined by onset times and confirmed by the relative amplitude across the island wide network of seismometers the period of tremor was conclusively shown to be determined by the source effect and not by the path or station site effect because the period would change considerably in time but maintained uniformity across the seismic net during the tremor episode the tremor appeared to be primarily composed of p waves we interpret the observed period and amplitude in terms of the stationary crack model of aki et al 1977 and find that the seismic moment rates for deep tremors are considerably larger than those for shallow tremors suggesting more vigorous transport for the former we propose a kinematic source model which may be more appropriate for deep tremor according to this model a measurable quantity called reduced displacement is directly proportional to the rate of magma flow a systematic search for deep tremor episodes was made for the period from 1962 through 1979 and the amplitude period and duration of the tremor were tabulated we then constructed a cumulative reduced displacement plot over the 18 year period the result shows a generally steady process which does not seem to be significantly affected by major eruptions and large earthquakes near the surface the total magma flow estimated from the reduced displacement is however one order of magnitude smaller than that estimated by swanson 1972 it may be that most channels transport magma aseismically and only those with strong barriers generate tremor

investigating the expected archaeomagnetic dating precision in europe a temporal and spatial analysis based on the scha dif 3k geomagnetic field model abstract archaeomagnetic dating is a chronometric dating technique based on the ability of baked clay archaeological structures and artifacts to acquire a thermal remanent magnetization trm when heated at high temperatures and cooled in the presence of the earth s magnetic field the precision of archaeomagnetic dating depends on several factors among others the availability of a detailed reference secular variation sv curve for a given territory in this study we investigate the precision that archaeomagnetic dating can reach in europe we used the scha dif 3k european geomagnetic field model to calculate the dating uncertainties for the last 3000 years taking into consideration only the uncertainties depending on the change rate of the geomagnetic field in the past and the reference sv curve s uncertainty envelope such uncertainties were calculated both in time and space they are usually asymmetrically distributed around the considered year and it have been represented as dynamic maps of uncertainties the obtained results show that archaeomagnetic dating based solely on directional data declination and inclination can be very precise for the last four centuries with total uncertainties being almost always lower than 100 years all around europe inherent dating uncertainties are also low for the last millennium with values ranging from 50 to 300 years these results underline the great potential of archaeomagnetism on dating baked clays belonging to the last 1000 years for older periods the uncertainty maps show that the dating precision may importantly vary from place to place but with local non symmetric uncertainty ranges generally below 400 years the obtained maps also show that adding the intensity to the computation of the inherent uncertainties does not always reduce the uncertainty the temporal and spatial analysis presented here does not give the total dating imprecision of archaeomagnetic dating that definitely depends on numerous often uncontrollable factors but aims at offering a useful tool to archaeomagnetic and archaeological research to check the feasibility of archaeomagnetic dating for determining the age of an archaeological structure below a desired precision

detection and monitoring of ongoing aseismic slip in the tokai region central japan analysis of global positioning system data shows that the rate of crustal deformations in the tokai region of japan a seismic gap area changed over the past 18 months kalman filtering analysis shows aseismic slip on the plate boundary in the western tokai region centered on lake hamana adjacent to the anticipated tokai earthquake source area the cumulative moment magnitude reaches 6 7 in june 2002 with a relative slip increase northeast of lake haman from january 2002 an existence of aseismic slip in the western tokai supports the hypothesis of a silent event as the cause of uplifting several days before the 1944 tonankai earthquake

tidal sensitivity of tectonic tremors in nankai and cascadia subduction zones tectonic tremors in subduction zones which result from slip at the deep plate interface are known to exhibit a 12 4 h periodicity in their activity due to tidal influence because tidal stress can be calculated quantitatively the response of the plate interface can yield quantitative information about its frictional property the relation between tremor rate and tidal stress is investigated and an exponential relation is widely confirmed as observed by previous studies this study particularly focuses on spatial variations of tidal sensitivity which are compared with spatial variations of tremor duration and amplitude the sensitivity is quantitatively defined by the exponent of the exponential relation which can be related to the parameter a or a b in the rate and state friction law where is effective normal stress on the shallower tremor zone short duration and large amplitude tremors occur followed by more sensitive tremors meanwhile deeper tremors with longer duration and smaller amplitude show lower sensitivity although along strike variation also exists typical and maximum sensitivities estimated here imply values for a or a b of about 3 and 1 kpa respectively these correlations are consistent with a model in which the plate interface consists of a velocity strengthening background with embedded velocity weakening regions the frictional heterogeneity may be statistically characterized by cluster size and density of the velocity weakening regions and controls the overall slip behavior the observed depth dependency of tremor duration amplitude and sensitivity implies that frictional heterogeneity is controlled by physical quantities varying with depth such as temperature or fluid amount

episodic tremor and slip on a frictional interface with critical zero weakening in elastic solid summary non volcanic tremor nvt and related relatively weak and slow slip events termed episodic tremor and slip ets are observed below the seismogenic sections of numerous subduction zones and several major strike slip faults these events have various characteristics that distinguish them from regular tectonic earthquakes here we show that a frictional fault in elastic solid with a region below the seismogenic zone having on average a critical near zero weakening during slip provides a simple unified explanation for the diverse observed phenomenology of nvt ets the results imply that nvt ets have little predictive power on the occurrence of large events in the overriding seismogenic zone additional model predictions that may be tested with future high resolution observations are fractal slip distributions and failure areas discrete power law frequency moment statistics with exponent 3 2 and exponential tapering overall scale invariant potency moment magnitude time histories triggered periodic nvt with evolving size and rate correlated with the stressing rate of the periodic triggering mechanisms and parabolic or exponential source time functions for event sizes measured by duration or moment potency

the frequency size scaling of non volcanic tremors beneath the san andreas fault at parkfield possible implications for seismic energy release abstract we analyse the frequency size distribution of non volcanic tremors observed along the parkfield section of the san andreas fault we suggest that these non volcanic tremors follow a power law scaling typical of scale invariant stick slip tectonic earthquakes but with an unusually high scaling exponent of more than 2 0 and a systematic depth dependency while each individual non volcanic tremor releases only a minuscule amount of energy and slip this is more than compensated by their sheer numbers consequently the integrated contribution of this largely invisible seismicity non volcanic tremors and nano earthquakes is non negligible and could potentially account in selected patches along the san andreas fault for up to 100 of the plate motion

short term slow slip and correlated tremor episodes in the tokai region central japan 1 we observe the related phenomenon of short term slow slip event sse and low frequency nonvolcanic tremor on the deeper extension of the 1944 tonankai and the anticipated tokai earthquake rupture areas central japan japan nation wide seismometer and tiltmeter array nied hi net has recorded these correlated episodes of sse and tremor known as episodic tremor and slip ets in 2004 and 2005 the events are located on two areas in the tokai region one is near the shima peninsula and the other is around the aichi area both episodes have a typical duration of 2 3 days and released seismic moment corresponding to mw 6 0 moreover these episodes repeatedly occur with a recurrence interval of about six months in both areas this evidence suggests that the coincidence between the sse and the tremor is a characteristic behavior in the whole tremor belt like zone in the nankai trough subduction zone

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

tidal modulation of continuous nonvolcanic seismic tremor in the chile triple junction region 1 we located continuous seismic tremor with coherent amplitude wave trains in the chile ridge subduction region 46 5 s in two clusters north and south of the chonos archipelago between the chile trench and the north patagonian fore arc tremor persisted from december 2004 to february 2007 the entire period of the chile ridge subduction project temporary seismic deployment and lasted 17 h on six occasions tremor in the more active southern cluster reached a maximum duration of 48 h and we observed no more than 3 continuous days without tremor activity the cluster locations coincide with the surface projections of subducted transform faults formed at the chile ridge we also detected simultaneous colocated low frequency microearthquakes with well defined impulsive waves within the tremor signals distributed from the surface to 40 km depth suggesting tremors and earthquakes are part of the same process the periodicity of tremor duration is strongly correlated with semidiurnal diurnal and long period tides m2 n2 k1 o1 p1 and mm 12 421 h 12 000 h 23 934 h 25 819 h 24 066 h and 27 555 days respectively we found a significant correlation between tremor occurrence and earth tides when tidal stress is calculated for the slip plane of a right lateral strike slip fault with strike n95 e which is near parallel to subducted transform faults n78 e of the chile ridge indicating that the very small stresses resulting from the combination of ocean loading and solid earth tides 1 kpa are sufficient to facilitate or suppress tremor production tremors occur when shear stresses are maximum and wane or are low when shear stresses are minimum

three archaeomagnetic applications of archaeological interest to the study of burnt anthropogenic cave sediments abstract recent archaeomagnetic studies carried out on mid to late holocene burnt anthropogenic cave sediments have shown that under certain conditions these materials are suitable geomagnetic field recorders archaeomagnetic analyses carried out on these contexts constitute a rich source of information not only for geophysical purposes in terms of reconstructing the variation of earth s magnetic field in the past but also from the archaeological point of view for example by archaeomagnetic dating here we report three different archaeomagnetic applications to the study of burnt cave sediments i archaeomagnetic dating ii determining palaeotemperatures and iii assessing post depositional processes the first case study is a dating attempt carried out on a late holocene bronze age burnt level from el mirador cave burgos spain using the directional european secular variation curve several dating intervals were obtained for the last burning of this combustion feature considering the archaeological evidence and the independent radiometric 14 c dating available the possible ages obtained are discussed this is the first archaeomagnetic dating obtained in these contexts so far the second case study is an application of the method to determine the last heating temperatures reached by the carbonaceous facies of these fires stepwise thermal demagnetization of oriented samples can be used to quantitatively estimate heating temperatures an intermediate normal polarity component interpreted as a partial thermo remanence ptrm with maximum unblocking temperatures of 400 450 c was systematically identified revealing the last heating temperatures experienced by this facies these temperatures were confirmed with partial thermomagnetic curve experiments finally archaeomagnetic analyses on a partially bioturbated burning event were performed in order to evaluate until what spatial extent the burnt sediments were affected by post depositional mechanical alteration processes for each case study the archaeological implications are discussed highlighting the potential of archaeomagnetic methods to retrieve archaeological information

archaeomagnetic research in the andean highlands abstract eleven archaeomagnetic samples were collected from several sites near porco bolivia as part of the proyecto arqueologico porco potosi these samples were collected in order to 1 explore the availability of appropriate sample materials in the bolivian andes and 2 assess the feasibility of pursuing reference curve research for this region in addition this research explored the archaeomagnetic dating application of reference curves constructed from the global geomagnetic field model gufm1 jackson et al 2000 which covers the period from ad 1590 1990 this model is particularly applicable to our project since many of the project sites are late prehispanic pre ad 1532 and early historic ca ad 1532 1825 in age of the 11 samples three appeared to contain an insufficient amount of ferromagnetic minerals to provide reliable results while eight samples produced acceptable to good results the data from the eight good samples were compared to a reference curve for the period of ad 1600 2000 that was calculated for this project from the global field model gufm1 the archaeomagnetic dates obtained for two of the samples agreed with archaeological expectations while those for four other samples marginally or greatly postdated the archaeological age expectations two additional samples produced significantly different directions and could not be dated against the reference curve it is likely that the age discrepancies for four of the samples stem from inaccuracies in the archaeomagnetic data the archaeological age expectations the calculated reference curve or some combination of these factors

the direction of the earth s magnetic field at london 1570 1975 the observations of magnetic declination and dip made in london over the past 400 years comprise one of the longest and most complete series of such data for anywhere in the world they give an indication of secular change on a time scale intermediate between that of recent observatory measurements and of archaeomagnetic measurements we have attempted to catalogue all direct measurements of declination and dip paying particular attention to completeness in the earlier years and tracing the data to their original source wherever possible sufficient details of the observations are given for an assessment of their reliability and accuracy the data are then corrected to a single site fitted with a continuous smooth curve and discussed

seismic tremor at the 9 50 n east pacific rise eruption site ocean bottom seismic observations within the 9 50 n region of the east pacific rise indicate persistent low amplitude tremor activity throughout the october 2003 through february 2007 period of monitoring these signals exhibit either monochromatic or polychromatic spectral characteristics with a 6 hz fundamental frequency and up to two harmonics individual events cannot be correlated between nearby 1 km stations implying the presence of multiple small amplitude sources positioned within the shallow crust tremor exhibits a semidiurnal periodicity with some stations recording activity during times of increasing tidal extension and others detecting tremor signals during times of increasing compression the amplitude duration and rate of activity also correlate positively with fortnightly changes in the amplitude of the tides these spatiotemporal patterns are consistent with tremor generation in response to tidally modulated fluid flow within a network of shallow cracks tremor energy flux is spatially and temporally heterogeneous however there are extended periods of greater and lesser activity that can be tracked across portions of the array despite their shallow crustal origin changes in tremor amplitude and spectral character occur in the months prior to a major microearthquake swarm and inferred seafloor spreading event on 22 january 2006 with an increase in the degree of correlation between tremor activity and tidal strain in the weeks leading up to this event after the spreading event two eruption surviving stations near the axis continue to show high rates of tremor activity whereas these signals are suppressed at the single station recovered from the near axis flanks this off axis quiescence may result from the dike induced closing of cracks or perhaps from the emplacement of impermeable flows near the station

low frequency earthquakes reveal punctuated slow slip on the deep extent of the alpine fault new zealand we present the first evidence of low frequency earthquakes lfes associated with the deep extension of the transpressional alpine fault beneath the central southern alps of new zealand our database comprises a temporally continuous 36 month long catalog of 8760 lfes within 14 families to generate this catalog we first identify 14 primary template lfes within known periods of seismic tremor and use these templates to detect similar events in an iterative stacking and cross correlation routine the hypocentres of 12 of the 14 lfe families lie within 10 km of the inferred location of the alpine fault at depths of approximately 20 30 km in a zone of high p wave attenuation low p wave speeds and high seismic reflectivity the lfe catalog consists of persistent discrete events punctuated by swarm like bursts of activity associated with previously and newly identified tremor periods the magnitudes of the lfes range between ml 0 8 and ml 1 8 with an average of ml 0 5 we find that the frequency magnitude distribution of the lfe catalog both as a whole and within individual families is not consistent with a power law but that individual families frequency amplitude distributions approximate an exponential relationship suggestive of a characteristic length scale of failure we interpret this lfe activity to represent quasi continuous slip on the deep extent of the alpine fault with lfes highlighting asperities within an otherwise steadily creeping region of the fault

dynamic deformation of the accretionary prism excites very low frequency earthquakes 1 we have detected anomalous very low frequency earthquakes within the accretionary prism along the nankai trough southwestern japan centroid moment tensor inversion analysis reveals that the earthquake hypocenters are distributed at 10 km depth above the upper surface of the subducting philippine sea plate and within 50 70 km landward of the trough axis the focal mechanisms indicate reverse faulting their hypocenters are distributed beneath a deformation zone of an accretionary prism in sea floor topography these observations suggest that the occurrence of very low frequency earthquakes is related to numerous reverse fault systems within the accretionary prism and that the earthquakes reflect the dynamics of deformation within this accretionary prism

model of deep nonvolcanic tremor part i ambient and triggered tremor there is evidence of triggering of tremor by seismic waves emanating from distant large earthquakes the frequency content of triggered and ambient tremor are largely identical suggesting that tremor does not depend directly on the nature of the source we show here that the model of plate dynamics developed earlier by us is an appropriate tool for describing the onset of tremor in the framework of this model tremor is an internal response of a fault to failure triggered by external disturbances the model predicts generation of radiation in a frequency range defined by the fault parameters other specific features predicted are 1 the upper limit of the size of the emitting area is a few dozen kilometers 2 tremor accompanies earthquakes and aseismic slip 3 the frequency content of tremor depends on the type of failure the model also explains why a tremor has no clear impulsive phase in contrast to earthquakes a comparatively small effective normal stress hence a high fluid pressure is required to make the model consistent with observed tremor parameters our model indicates that tremor is not necessarily a superposition of low frequency earthquakes as commonly assumed although the latter may trigger tremor the approach developed complements the conventional viewpoint which assumes that tremor reflects a frictional process with low rupture speed essentially our model adds the hypothesis that resonant type oscillations exist inside a fault this addition may change our understanding of the nature of tremor in general and the methods of its identification and location in particular

an earthquake like magnitude frequency distribution of slow slip in northern cascadia 1 major episodic tremor and slip ets events with mw 6 4 to 6 7 repeat every 15 2 months within the cascadia subduction zone under the olympic peninsula although these major ets events are observed to release strain smaller tremor swarms without detectable geodetic deformation are more frequent an automatic search from 2006 2009 reveals 20 000 five minute windows containing tremor which cluster in space and time into 96 tremor swarms the 93 inter ets tremor swarms account for 45 of the total duration of tremor detection during the last three ets cycles the number of tremor swarms n exceeding duration follow a power law distribution n 0 66 if duration is proportional to moment release the slip inferred from these swarms follows a standard gutenberg richter logarithmic frequency magnitude relation with the major ets events and smaller inter ets swarms lying on the same trend this relationship implies that 1 inter ets slip is fundamentally similar to the major events just smaller and more frequent and 2 despite fundamental differences in moment duration scaling the slow slip magnitude frequency distribution is the same as normal earthquakes with a b value of 1

a family of repeating low frequency earthquakes at the downdip edge of tremor and slip we analyze an isolated low frequency earthquake lfe family located at the downdip edge of the main episodic tremor and slip ets zone beneath western washington state the 9000 individual lfes from this repeating family cluster into 198 swarms that recur roughly every week cumulative lfe seismic moment for each swarm correlates strongly with the time until the next swarm suggesting that these lfe swarms are time predictable precise double difference relative locations for 700 individual lfes within this family show a distribution that is approximately 2 km long and 500 m wide elongated parallel to the relative plate convergence direction the distribution of locations 300 m vertical spread lies within a few hundred meters of two different plate interface models and has a similar dip peak to peak lfe s wave amplitudes range from 0 2 to 18 nm individual lfes exhibit a trend of increasing magnitude during swarms with smaller events at the beginning and the largest events toward the end the largest lfes cluster in a small area 300 m radius coincident with maximum lfe density we propose that the less concentrated smaller lfes act to unlock this patch core allowing it to fully rupture in the largest lfes usually toward the end of a swarm we interpret the patch responsible for producing these lfes as a subducted seamount on the downgoing juan de fuca jdf plate lfe locking efficiency slip estimated during 5 years from summing lfe seismic moment divided by plate rate determined slip is at most 20 and is highly concentrated in two 50 m radius locations in the larger patch core estimated individual lfe stress drops range from 1 to 20 kpa but could also be significantly larger

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

a method for correcting geographically separated remanence directions for the purpose of archaeomagnetic dating summary spatial variations in the geomagnetic field must be taken into account if secular variation master curves and directional magnetic dates are to be optimized two methods for relocating remanence vectors have been proposed and in this paper their relative accuracies are compared using a numerical model based on the present day field a method which converts archaeomagnetic directions via a virtual geomagnetic pole is shown to be the more efficient transformation for an archaeomagnetic region the size of the british isles 900 km radius the maximum error in relocating vectors to a central location is predicted to be of the order of 1 2

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

precise tremor source locations and amplitude variations along the lower crustal central san andreas fault 1 we precisely locate 88 tremor families along the central san andreas fault using a 3d velocity model and numerous p and s wave arrival times estimated from seismogram stacks of up to 400 events per tremor family maximum tremor amplitudes vary along the fault by at least a factor of 7 with by far the strongest sources along a 25 km section of the fault southeast of parkfield we also identify many weaker tremor families which have largely escaped prior detection together these sources extend 150 km along the fault beneath creeping transitional and locked sections of the upper crustal fault depths are mostly between 18 and 28 km in the lower crust epicenters are concentrated within 3 km of the surface trace implying a nearly vertical fault a prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6 0 parkfield earthquake

a regional archaeomagnetic model for the palaeointensity in europe for the last 2000 years and its implications for climatic change the scha di 00 directional model for the geomagnetic field in europe for the last 2000 years pavo n carrasco et al 2008 has been updated by modelling the palaeointensity this model scha di 00 was developed from available bayesian european palaeosecular variation curves using the regional spherical cap harmonic analysis technique the comparison of the palaeosecular variation curves given by the regional model with available archaeomagnetic data not used in its development showed an improvement with respect to the fit obtained by global archaeomagnetic models in this paper advantage is taken of recently published palaeointensity databases to develop a complete direction and intensity regional archaeomagnetic model for the last 2000 years valid for the european region the scha di 00 f model not only does this complete model provide an improvement for example for archaeomagnetic data studies but it is also shown that this new regional model can be used to study the recently proposed link between the centennial secular variation of the geomagnetic field and climate change the pattern of the archaeosecular variation of the field intensity obtained by scha di 00 f seems to verify the hypothesis presented by gallet et al 2005 about a possible causal connection between changes in the geomagnetic field intensity and in climate parameters opening the door for more discussions on this challenging subject

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

continuous global geomagnetic field models for the past 3000 years abstract several global geomagnetic field models exist for recent decades but due to limited data availability models for several centuries to millennia are rare we present a continuous spherical harmonic model for almost 3 millennia from 1000 b c to 1800 a d based on a dataset of directional archaeo and paleomagnetic data and axial dipole constraints the model named continuous archaeomagnetic and lake sediment geomagnetic model for the last 3k years cals3k 1 can be used to predict both the field and secular variation comparisons and tests with synthetic data lead to the conclusion that cals3k 1 gives a good general large scale representation of the geomagnetic field but lacks small scale structure due to the limited resolution of the sparse dataset in future applications the model can be used for comparisons with additional new data for that time span for better resolved regions the agreement of data with cals3k 1 will provide an idea about the general compatibility of the data with the field and secular variation in that region of the world for poorly covered regions and time intervals we hope to iteratively improve the model by comparisons with and inclusion of new data animations and additional snapshot plots of model predictions as well as the model coefficients and a fortran code to evaluate them for any time can be accessed under http www mahi ucsd edu cathy holocene holocene html the whole package is also stored in the earthref digital archive at http www earthref org

spatial temporal patterns of seismic tremors in northern cascadia 1 we study in detail the two consecutive episodic tremor and slip ets events that occurred in the northern cascadia subduction zone during 2003 and 2004 for both sequences the newly developed source scanning algorithm ssa is applied to seismic waveform data from a dense regional seismograph array to determine the precise locations and origin times of seismic tremors in map view the majority of the tremors occurred in a limited band bounded approximately by the surface projections of the 30 km and 50 km depth contours of the plate interface the horizontal migration of tremor occurrence is from southeast to northwest with an average speed of 5 km d in cross section tremors in both sequences span a depth range of over 40 km across the interface with the majority occurring in the overriding continental crust in particular 50 55 of them are located within 2 5 km from the strong seismic reflector bands above the plate interface the lack of vertical migration implies that a slow diffusion process in the vertical direction cannot be responsible for tremor occurrences the source spectra of tremors clearly lack high frequency content 5 hz relative to local earthquakes we propose two possible models to explain the relationship between slip and tremors the first one regards ets tremors as the manifestation of hydroseismogenic processes in response to the temporal strain variation associated with the episodic slip along the lower portion of the plate interface downdip from the locked zone in the second model tremors and slip are associated with the same process along the same structure in a distributed deformation zone across the plate interface neither model can be dismissed conclusively at this stage

the sieving of heavy mineral sands abstract an investigation has been undertaken of the sieving of natural heavy mineral sands from a beach placer to determine the effects of the differing shapes of the several mineral types the measurements agree with an equation derived by sahu 1965 based on the passage of ellipsoidal grains through a square sieve opening demonstrating that the ratio of the grain s smallest axial diameter dc to its intermediate diameter db controls grain passage through the sieves empirical relationships are established between the average db values of the grains and the sieve size on which they are captured during sieving these relationships are sufficiently close to that for quartz grains to conclude that there would be little separation of the several minerals by s ape during the sieving process the results further permit evaluations of the db distributions of the heavy mineral sands rather than the standard practice of reporting distributions in terms of sieve sizes

scaling relationship between the duration and the amplitude of non volcanic deep low frequency tremors 1 we investigate a duration amplitude relation of non volcanic deep low frequency dlf tremors in the tokai region southwest japan to constrain the source process of the tremors we apply two models to the distribution one is an exponential model as a scale bound distribution and the other a power law model as a scale invariant distribution the exponential model shows a better fit to the duration amplitude distribution of the tremors than a power law model implying that the dlf tremors are caused by a scale bound source process the source process of the dlf tremors therefore differs from those for earthquakes we suggest that the non volcanic dlf tremor is possibly caused by a fixed source dimension with variable excess pressure of fluid or variable stress drop

low frequency continuous tremor around the moho discontinuity away from volcanoes in the southwest japan 1 recent enhancement of seismic networks in the japan islands revealed occurrence of low frequency continuous tremors of a beltlike distribution in the southwest japan where the subducting philippine sea plate reaches depths of 30 40 km source depth of the tremor is estimated by selecting tremor segments with relatively clear p wave onsets the source region of the tremor is assumed to correspond to lowermost parts of crust close to a triple boundary of the crust mantle wedge and the subducting slab the long duration of the phenomenon indicates existence of fluid relating to the generation of the tremor the most probable fluid is considered to be water produced by dehydration process of chlorite and amphibole in the slab on the basis of data from high pressure and temperature experiments the northern border of the beltlike distribution is possibly rimmed by the edge of the mantle wedge because serpentine formation absorbs fluid water

lake sediment record of the geomagnetic secular variation in britain during holocene times summary a palaeomagnetic record of the geomagnetic secular variation during the last 10000 years has been obtained from 10 cores of sediment from loch lomond scotland lake windermere north england and llyn geirionydd north wales a time scale is provided by 30 radiocarbon age determinations and pollen analyses on several of the cores the main swings and much fine detail of both declination and inclination records repeat well between cores and between lakes and the overall record is much more detailed than previous european records the new record shows that neither declination nor inclination swings have been periodic over the past 10000 years but that the main swings have become progressively shorter in duration during that time each swing is characterized by fine detail which enables use of the record as a secondary method of dating other european sediments the motion of the geomagnetic vector has been predominantly clockwise throughout the time period spanned but confirms a period of anticlockwise motion from 1100 to 600 bp first discovered by british archaeomagnetic investigations the record agrees with british and czechoslovakian archaeomagnetic records but not with japanese archaeomagnetic or north american lake sediment records this suggests that the secular changes are controlled by local growing and decaying drifting sources rather than by wobbling of the main geomagnetic dipole

combining an archaeomagnetic and radiocarbon study dating of medieval fireplaces at the muhlegasse zurich abstract during the restoration of the radium cinema located in the old town of zurich a stratigraphic sequence of medieval fireplaces came to light based on ceramic finds a preliminary age of about 1000 ad was assigned in this paper we show the results from archaeomagnetic and radiocarbon dating which combined with the stratigraphic information yield a better constrain of the period of use of these fireplaces whilst the radiocarbon technique continues to be the most widespread methodology for dating young archeological artifacts archaeomagnetic dating is becoming increasingly more established in europe thanks to the increased number of available measurements a bayesian model on the period of use of these fireplaces was produced with oxcal by a combination of magnetic and radiocarbon ages together with the stratigraphic information the results show that the fireplaces were probably used during 1 to 2 generations e g 20 40 years each and are in good agreement with the archaeological context of this site to make use of the magnetic measurements for future reconstructions of the field we carried out an additional age model using only the radiocarbon and the stratigraphic information although some of the structures show large directional scatter due to poor baking in antiquity the results confirm the trend of the geomagnetic field around 1000 ad

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

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

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses

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