effect of fault rupture characteristics on near fault strong ground motions the effect of fault rupture characteristics on near fault strong ground motions is investigated using a kinematic modeling approach in an attempt to identify physical processes that lead to specific ground motion patterns the shear stress distribution on the causative fault plane of four well documented seismic events i e 1979 imperial valley 1985 michoacan 1989 loma prieta and 1999 izmit is calculated based on fault slip models available in the literature using the methodology proposed by bouchon 1997 for stress field computations in order to associate the fault rupture characteristics i e slip rupture velocity state of stress of the investigated earthquakes with near fault ground motions generated by the events forward ground motion simulations are performed using the discrete wavenumber representation method and the concept of the s wave isochrones is exploited the results indicate that the seismic energy radiated from the high isochrone velocity region of the fault arrives at the receiver within a time interval that coincides with the time window of the long period ground motion pulse recorded at the site furthermore the near fault ground motion pulses are strongly correlated with large slip on the fault plane locally driven by high stress drop in addition the local rupture velocity seems to be inversely correlated to the spatial distribution of the strength excess over the fault plane confirming findings of previous studies for various events the area of the fault that contributes to the formation of the near fault pulse encompasses more than one patch of significant moment release subevent e g 1979 imperial valley 1989 loma prieta this observation explains why a dislocation model with average properties i e slip rise time etc reproduces successfully near fault ground motions for strike slip faults and for dip slip faults with intermediate to large earthquake magnitudes aki 1979 however for very large earthquakes such as megathrust events on subduction zones e g 1985 michoacan the fault region that contributes to the pulse formation encompasses individual subevents and consequently cracklike slip functions rather than dislocation models may be more appropriate for the simulation of the near fault ground motions

ground motion prediction equations in the san jacinto fault zone significant effects of rupture directivity and fault zone amplification we present a new set of ground motion prediction equations gmpes for horizontal peak ground acceleration peak ground velocity and 5 damped pseudo spectral acceleration psa developed for the san jacinto fault zone sjfz area besides using these equations to quantify seismic shaking in the area the results allow us to examine the physics and local properties controlling the observed ground motions the analyzed dataset includes 30 000 observations from 800 events spanning a magnitude range of 1 5 m 6 0 and recorded by up to 140 stations at epicentral distances ranging from essentially zero to 150 km the local gmpe is developed for the sjfz by applying classical regression techniques with predictive variables that include first distance and magnitude and then site characteristics rupture directivity and fault zone amplification the significance of these effects is determined by measuring the uncertainty reduction of the gmpe due to each factor the results show that in contrast to many regional studies traditional site characteristic has a relatively minor effect on peak amplitudes in our study area however rupture directivity is a significant factor controlling the amplitudes of ground motion even for small events the dense seismic network and newly developed directivity tool enable us to extract efficiently directivity effects with statistical significance using the ground motion dataset during the regression analysis process the obtained rupture directivities are consistent with the main focal mechanism orientations and surface trace orientations known from other studies and predictions for bimaterial ruptures in the trifurcation area of the sjfz fault zone amplification is a second important factor showing strong impact on the peak ground motion values with increasing role for the lower frequency range 10 hz examined in the 5 damped psa values we also observe signatures of large amplitude variances which indicate additional source related control on the distribution of amplitudes besides rupture directivity for aftershocks close in time and location to the m l 5 1 earthquake of march 2013 using the full set of records we present the most complete set of gmpes for the sjfz area including a higher amplitude prediction for regions in the direction of rupture

complexity of the mw 6 3 2009 l aquila central italy earthquake 2 broadband strong motion modeling 1 near fault strong ground motions 0 1 10 hz recorded during the mw 6 3 2009 l aquila earthquake exhibit great spatial variability modeling the observed seismograms allows linking distinct features of the observed wavefield to particular source and propagation effects and provides insights on strong motion complexity from this moderate magnitude event we utilize a hybrid integral composite approach based on a k square kinematic rupture model combining low frequency coherent and high frequency incoherent source radiation and providing omega squared source spectral decay several source model features proven to be stable by means of an uncertainty analysis in the preceding low frequency 2 hz

complexity of the rupture process during the 2009 l aquila italy earthquake summary in this study we investigate the rupture history of the 2009 april 6 mw 6 1 l aquila normal faulting earthquake by using a non linear inversion of strong motion gps and dinsar data both the separate and joint inversion solutions reveal a complex rupture process and a heterogeneous slip distribution slip is concentrated in two main asperities a smaller shallow patch of slip located updip from the hypocentre and a second deeper and larger asperity located southeastwards along strike direction the key feature of the source process emerging from our inverted models concerns the rupture history which is characterized by two distinct stages the first stage begins with rupture nucleation and with updip propagation at relatively high 4 0 km s 1 but still subshear rupture velocity the second stage starts nearly 2 0 2 5 s after nucleation and it is characterized by the along strike rupture propagation the largest and deeper asperity fails during this stage of the rupture process the rupture velocity is larger in the updip than in the along strike direction the updip and along strike rupture propagation are separated in time and associated with a mode ii and a mode iii crack respectively the comparison between the source models inferred in this study with the poisson ratio anomalies in the crustal volume containing the fault plane allows the interpretation of the delay in along strike rupture propagation in terms of a structural control of the rupture history our results show that the l aquila earthquake featured a very complex rupture with strong spatial and temporal heterogeneities suggesting a strong frictional and or structural control of the rupture process

control of the 2009 l aquila earthquake central italy by a high velocity structure a receiver function study 1 receiver functions rfs analyzed at two permanent broadband seismic stations operating in the epicentral area of the mw 6 3 2009 l aquila earthquake central italy yield insight on crustal structure along the fault rupture the harmonic decomposition of rfs highlights a subsurface structure in which both isotropic and anisotropic features are present we model the waveforms using recently developed monte carlo methods the retrieved models display a common depth structure between 10 and 40 km depth consistent with the under thrusting of the adria lithosphere underneath the apennines belt along the fault in the uppermost crust the s wave velocity structure is laterally heterogeneous right above the hypocenter we find a 4 6 km thick very high s wave velocity body vs as high as 4 2 km s that is absent in the se portion of the fault where the earthquake propagated the high vs body is coincident with the area of fewer aftershocks and is anticorrelated with the maximum slip patches of the earthquake as modeled by differential interferometric synthetic aperture radar dinsar and strong motion data we interpret this high vs body as a high strength barrier responsible for the high peak ground motion in the near field observed in the l aquila city and surroundings and for the complexity in the rupture evolution the retrieved seismic s wave velocity of this body far exceeds common vs values in the upper crust and it is more compatible with values observed in mafic basement rocks

further studies for uranium series dating of fossil bone abstract in an earlier paper the authors suggested that bones from well sealed depositional matrices might be deteable by the u series method this paper presents the results of further case studies on bones from archaeological sites and also in vitro laboratory studies of the u bone system these suggest that the u series method may only be of limited use for bones and that in most sites samples are exposed to an unknown number of wetting events over their period of deposition the laboratory experiments indicate a more complex process than the simple diffusion of u through the bone cross section

the 2009 l aquila central italy mw6 3 earthquake main shock and aftershocks 1 a m w 6 3 earthquake struck on april 6 2009 the abruzzi region central italy producing vast damage in the l aquila town and surroundings in this paper we present the location and geometry of the fault system as obtained by the analysis of main shock and aftershocks recorded by permanent and temporary networks the distribution of aftershocks 712 selected events with m l 2 3 and 20 with m l 4 0 defines a complex 40 km long nw trending extensional structure the main shock fault segment extends for 15 18 km and dips at 45 to the sw between 10 and 2 km depth the extent of aftershocks coincides with the surface trace of the paganica fault a poorly known normal fault that after the event has been quoted to accommodate the extension of the area we observe a migration of seismicity to the north on an echelon fault that can rupture in future large earthquakes

analysis of the ground accelerations radiated by the 1980 livermore valley earthquakes for directivity and dynamic source characteristics the strong motion accelerograph recordings of the 24 january 1980 main shock and the 27 january 1980 aftershock of the livermore valley earthquake sequence are analyzed for systematic variations with azimuth or station location the variation of the peak accelerations with epicentral azimuth is apparently reversed for the two events the main shock accelerations are larger to the south and the aftershock accelerations are larger to the northwest we eliminate the site effects by forming the ratio of the peak accelerations recorded at the same station after correcting for the epicentral distance this analysis indicates that source directivity caused a total variation of a factor of 10 in the peak accelerations comparison of this variation with the spatial extent of the aftershock sequences suggests that the strong directivity in the radiated accelerations is the result of unilateral ruptures in both events the accelerograms recorded at 10 stations within 35 km of the events were digitized to analyze the azimuthal variation of the rms acceleration the peak velocity and the radiated energy flux the variation of rms acceleration correlates almost exactly with the variation of the peak accelerations this correlation is analyzed using both deterministic and stochastic models for the acceleration waveforms the peak velocities corrected for epicentral distance vary with azimuth by a factor of 5 for both events while the radiated energy flux varies by a factor of 30 for the main shock and 15 for the aftershock the peak velocities are strongly correlated with the radiated energy flux the radiated seismic energies are estimated to be 2 6 0 9 1020 dyne cm for the main shock and 1 5 0 3 1020 dyne cm for the aftershock

a new asymptotic method for the modeling of near field accelerograms we study high frequency radiation from a dislocation model of rupture propagation at the earthquake source we demonstrate that in this case all the radiation emanates from the rupture front and by a change of variables that at any instant of time the high frequency waves reaching an observer come from a line on the fault plane that we call isochrone an asymptotic approximation to near source velocity and acceleration is obtained that involves a simple integration along the isochrones for every time step it is shown that wave front discontinuities critical or stopping phases are radiated every time an isochrone becomes tangent to a barrier this leads to what we call the critical ray approximation which is given in a closed form the previous results are compared with discrete wavenumber synthetics obtained by bouchon 1982 for the gilroy 6 recording of the coyote lake earthquake of 1980 the fit between the asymptotic and full numerical method is extremely good the critical ray approximation permits the identification of different phases in bouchon s synthetics and the prediction of the behavior of the signal in the vicinity of their arrival time

magnitude scaling of the near fault rupture directivity pulse abstract current ground motion models all assume monotonically increasing spectral amplitude at all periods with increasing magnitude however near fault recordings from recent earthquakes confirm that the near fault fault normal forward rupture directivity velocity pulse is a narrow band pulse whose period increases with magnitude this magnitude dependence of the period of the near fault pulse is expected from theory because the period of the pulse is related to source parameters such as the rise time duration of slip at a point on the fault and the fault dimensions which generally increase with magnitude this magnitude dependence of the pulse period causes the response spectrum to have a peak whose period increases with magnitude such that the near fault ground motions from smaller earthquakes may exceed those of larger earthquakes at intermediate periods around 1 s this paper presents preliminary equations relating the period of the fault normal component of the forward rupture directivity velocity pulse to the earthquake magnitude and a preliminary model for the acceleration response spectra of near fault fault normal ground motions that includes the magnitude dependence of the period of the response spectral peak

estimation of response spectra and simulation of nonstationary earthquake ground motions abstract italian strong motion data were used to study the attenuation of response spectra and to simulate artificial accelerograms as a function of magnitude distance and site geology the database has already been utilized for the study of the atten uation of peak ground acceleration pga and velocity and consists of 95 accelero grams from 17 earthquakes of magnitudes ranging from 4 6 to 6 8 using multiple regressions we developed empirical predictive equations for the vertical and hori zontal components of response spectra corresponding to 14 frequencies ranging from 0 25 to 25 hz predictive equations aimed at the ground motion simulation were also estimated for time dependent frequency parameters strong ground motion du ration and arias intensity the shape of the predicted spectra is strongly dependent on magnitude and nearly independent of distance alluvium sites show an amplification effect with respect to stiff sites in different frequency ranges according to the thickness of the soil deposit the vertical horizontal spectral ratio in far field varies with magnitude and frequency from 0 35 to 0 85 the resulting response spectra are compared with the predictions of some recent attenuation relationships and with those proposed by the eurocode ec8 the simulation of nonstationary strong ground motions is achieved through an empirical method where time and frequency features of the motion are represented through the physical spectrum extending the spectral moments theory to the nonsta tionary case the simulated time histories fit the recorded accelerograms in terms of several ground motion amplitude measures such as peak acceleration peak velocity fourier spectra and response spectra the principal advantage of the proposed method consists in correlating the simulation parameters with earthquake magnitude source distance and soil conditions introduction in the field of seismic risk assessment the prediction of shaking intensity in future earthquakes plays a key role re liable estimates of the ground motions that structures must be designed to withstand are obtained mainly through em pirical predictive relationships developed after statistical analysis of data recorded during strong earthquakes many predictive equations are by now available in dif ferent regions of the world campbell 1985 1993 for the prediction of peak ground acceleration pga many fewer are the relationships developed for the prediction of response spectral values idriss 1991 boore

spatial variability of the directivity pulse periods observed during an earthquake the ground velocity pulses generated by rupture directivity effects in the near fault region can cause a large amount of damage to structures proper estimation of the period of such velocity pulses is of particular importance in characterizing near fault seismic hazard and mitigating potential damage we propose a simple equation to determine the pulse period as a function of the site location with respect to the fault rupture defined by the hypocentral distance hypd the closest distance to the rupture area clsd and the length of the rupture area that breaks toward the site d and some basic rupture properties average rupture speed and average rise time our equation is first validated from a dataset of synthetic velocity time histories deploying simulations of various strike slip extended ruptures in a homogeneous medium the analysis of the synthetic dataset confirms that the pulse period does not depend on the whole rupture area but only on the parameter d it also reveals that the pulse period is not sensitive to the level of slip heterogeneity on the fault plane our model is tested next on a real dataset build from the next generation attenuation west2 project database compiling 110 observations of velocity pulse periods from 10 strike slip events and 6 non strike slip events the standard deviation of the natural logarithm residuals between observations and predictions is 0 5 furthermore the correlation coefficient between observations and predictions equals 0 8 indicating that despite its simplicity our model explains fairly well the spatial variability of the pulse periods

high frequency seismic radiation from a buried circular fault summary we propose a simplified method for the calculation of near field accelerograms it is based upon the hypothesis that in the course of dynamic faulting the dominating part of the seismic radiation is emitted by the rupture front as the rupture moves smoothly it radiates continuously generating the low frequency part of the field high frequency waves are produced by jumps in the rupture velocity and abrupt changes in the stress intensity factor the wave front discontinuities created in this fashion are evaluated by asymptotic methods and may be propagated away from the source by ray theoretical methods we apply our technique to the evaluation of asymptotic near field accelerograms for a circular fault buried in a half space the agreement with numerical accelerograms calculated by full wave theory is very satisfactory two problems are given particular emphasis 1 the phase shifts introduced by focusing and 2 a simpler method based on dislocation theory is proposed for the calculation of the radiation coefficients from a discontinuously moving rupture front

precise timing of the last interglacial period from mass spectrometric determination of thorium 230 in corals the development of mass spectrometric techniques for determination of 230 th abundance has made it possible to reduce analytical errors in 238 u 234 u 230 th dating of corals even with very small samples samples of 6 x 10 8 atoms of 230 th can be measured to an accuracy of 3 percent 2 and 3 x 10 10 atoms of 230 th can be measured to an accuracy of 0 2 percent the time range over which useful age data on corals can be obtained now ranges from about 50 to about 500 000 years for young corals this approach may be preferable to 14 c dating the precision with which the age of a coral can now be determined should make it possible to critically test the milankovitch hypothesis concerning pleistocene climate fluctuations analyses of a number of corals that grew during the last interglacial period yield ages of 122 000 to 130 000 years the ages coincide with or slightly postdate the summer solar insolation high at 65 n latitude which occurred 128 000 years ago this supports the idea that changes in pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth s orbit and rotation axis

erosional characteristics and behavior of large pyroclastic density currents factors influencing the erosive behavior of large pyroclastic density currents pdcs both mainly massive and thinly stratified are not well understood to investigate the parameters influencing the erosive behavior of pdcs produced during the flowing phase of large caldera forming plinian campanian ignimbrite and phreatoplinian neapolitan yellow tuff eruptions we use scoured fall deposits at the base of or interstratified with pdc deposits from the campanian region of italy at several localities we calculated the depth of pdc erosion by comparing the measured thickness of eroded remnants to reconstructed thickness at each site estimated by isopach mapping and recorded the 1 distance from vent 2 elevation of the locality and 3 paleoslopes furthermore we have considered how these factors can be influenced by outcrop exposure depth of erosion correlates with distance from the vent in low relief landscape while across very rugged topography the only related parameter is elevation the different erosive patterns appear to show how pyroclastic currents interact with the topography in the surrounding terrain when a pdc crosses relatively flat surfaces it decelerates away from the vent decreasing its erosive capacity but when moving through steep terrain a pdc accelerates down the valley increasing its erosive capacity

source mechanism and rupture directivity of the 18 may 2009 mw 4 6 inglewood california earthquake on 18 may 2009 an m w 4 6 earthquake occurred beneath inglewood california and was widely felt though source mechanism and its location suggest that the newport inglewood fault nif may be involved in generating the earthquake rupture directivity must be modeled to establish the connection between the fault and the earthquake we first invert for the event s source mechanism and depth with the cut and paste method in the long period band 5 s because of the low velocity shallow sediments in the los angeles la basin we use two velocity models in the inversion for stations inside and outside the la basin however little difference is observed in the resolved source mechanism m w 4 6 strike 246 145 dip 50 77 rake 17 138 and depth 7 to 9 km compared to an inversion using the standard southern calfornia model with the resolved source parameters we calibrate the amplitude anomaly of the short period 0 5 2 hz p waves with amplitude adjustment factors aaf these aafs are used as corrections when retrieving source mechanisms of the smaller aftershocks using short period p waves alone most of the aftershocks show similar source mechanisms as that of the mainshock providing ideal empirical green s functions egfs for studying its rupture process we use a forward modeling approach to retrieve rupture directivity of the mainshock consistent with movement on the nif with rupture toward the southeast although we focus on p waves for analyzing rupture directivity the resolved unilateral pattern is also confirmed with the azimuthal variation of the duration of sh waves observed in the basin the high rupture velocity near the shear velocity and relatively low stress drop are consistent with the hypothesis of rupture on a mature fault

electron spin resonance esr dating abstract esr dating has been systematically applied in earth sciences and archaeology since 1975 when ikeya dated a stalactite from the akiyoshi cave in japan in the meantime this new technique has been successfully applied to the dating of materials such as speleothems spring deposited travertines mollusc shells corals and tooth enamel the present research focuses on the dating of quartz which allows the age assessment of heated ceramics volcanic rocks intrafault material or windblown sediments esr dating is based on the measurement of the number of paramagnetic centers in a mineral these centers are generated by alpha beta and gamma radiation of the matural radioelements such as u th and k and have accumulated over time two parameters have to be determined the accumulated dose ad and the dose rate d to which the sample was exposed this review comprises three major parts a introduction into esr dating b application of the method and c appendices giving detailed description of dose rate calculation physical basis of electron spin resonance the esr spectrometer and esr lines the major emphasis lies on the outline of the application of esr dating this includes the discussion of the esr signals of the various materials sampling sample preparation and measurement techniques

directivity effects for moderate magnitude earthquakes mw 5 6 6 0 during the 1997 umbria marche sequence central italy abstract the colfiorito mw 6 0 september 26 1997 09 40 utc and the sellano mw 5 6 october 14 1997 normal faulting earthquakes are the two strongest events of the 1997 1998 umbria marche seismic sequence central italy they provided accelerograms recorded at epicentral distances within nearly two fault lengths previous studies on these events revealed clear evidence of unilateral rupture propagation and directivity effects on the source time functions we developed an approximate procedure to correct the observed peak ground motion for the site effects and we found a systematic increase of peak ground acceleration pga and peak ground velocity pgv at sites located in the direction of the rupture propagation respect to the stations located to the backward in particular we showed that for the colfiorito earthquake the average pgv at the north west sites is 2 8 times larger than the pgv at south east sites 2 1 for pga an opposite behaviour is found during the sellano earthquake with an amplification factor of about 1 9 for pgv 1 5 for pga recorded at south east sites respect to the north west stations we explained these behaviours in terms of directivity effect by comparing recorded ground accelerations with synthetics simulated by a deterministic stochastic technique this method computes high frequency ground motions f 0 5 hz from extended faults generalizing the point source stochastic method to capture the essence of near source effects the synthetic pgas decrease with distance in agreement with the ground motion empirical predictive model available for the area and describe the azimuthal variation of recorded data in terms of source effects

rupture history of the 2009 l aquila italy earthquake from non linear joint inversion of strong motion and gps data 1 we image the rupture history of the 2009 l aquila central italy earthquake using a nonlinear joint inversion of strong motion and gps data this earthquake ruptured a normal fault striking along the apennines axis and dipping to the sw the inferred slip distribution is heterogeneous and characterized by a small shallow slip patch located up dip from the hypocenter 9 5 km depth and a large deeper patch located southeastward the rupture velocity is larger in the up dip than in the along strike direction this difference can be partially accounted by the crustal structure which is characterized by a high velocity layer above the hypocenter and a lower velocity below the latter velocity seems to have affected the along strike propagation since the largest slip patch is located at depths between 9 and 14 km the imaged slip distribution correlates well with the on fault aftershock pattern as well as with mapped surface breakages

continuum of earthquake rupture speeds enabled by oblique slip earthquake rupture speed can affect ground shaking and thus seismic hazard seismological observations show that large earthquakes span a continuum of rupture speeds from slower than rayleigh waves up to p wave speed and include speeds that are predicted to be unstable by 2d theory this discrepancy between observations and theory has not yet been reconciled by a quantitative model here we present numerical simulations that show that long ruptures with oblique slip both strike slip and dip slip components can propagate steadily at various speeds including those previously suggested to be unstable the obliqueness of slip and the ratio of fracture energy to static energy release rate primarily control the propagation speed of long ruptures we find that the effects of these controls on rupture speed can be predicted by extending the 3d theory of fracture mechanics to long ruptures with oblique slip we propose that this model provides a quantitative framework to interpret supershear earthquakes to constrain the energy ratio of faults based on observed rupture speed and rake angle and to relate the potential rupture speed and size of future earthquakes to the observed slip deficit along faults

broadband numerical simulations in complex near field geological configurations the case of the 2009 mw 6 3 l aquila earthquake abstract a numerical study on the 2009 m w 6 3 l aquila earthquake is here presented using a high performance spectral element se code to clarify the issues regarding the generation of physics based deterministic ground motion scenarios in near fault conditions and over a broad range of frequencies numerical simulations provide reliable ground motion scenarios up to about 2 5 hz in the epicentral region of the l aquila earthquake as confirmed by the good agreement between the simulated peak ground velocity pgv wave field and the observed distribution of damage moreover the synthetic waveforms fit reasonably well the strong motion recordings within the town of l aquila and the surrounding areas nevertheless some discrepancies are found in the upper aterno valley associated to a considerable extent with the details of the rupture process improvements on the source modeling are obtained through the definition of stochastically but realistically varying kinematic source parameters that may play a relevant role in propagating high frequency hf components of ground motion poorly controlled by numerical approaches finally the proposed hybrid scheme to generate broadband bb synthetic waveforms by combining the low frequency lf synthetics from se simulations f

new approach for coupling k 2 and empirical green s functions application to the blind prediction of broad band ground motion in the grenoble basin summary we present a new approach for performing broad band ground motion time histories 0 1 30 hz of a future earthquake in a sedimentary basin synthetics are computed with an hybrid scheme combining reciprocity based 3 d spectral element method simulations at low frequencies and empirical green s functions egf at high frequencies the combination between both deterministic and empirical parts results in a set of hybrid green s functions summed according to a new k 2 kinematic model algorithm the summation technique enables to remove the high frequency artefacts that appear above the egf corner frequency the ground motion variability is assessed by generating a variety of source parameter sets selected from ap rioriprobability density functions this leads to a population of response spectra from which the median spectral acceleration and standard deviation values are derived the method is applied to simulate a m w 5 5 event in the deep grenoble basin french alps the comparison with ec8 regulations suggests the need of specific design spectra in the grenoble valley

open system modelling for u series and esr dating of teeth abstract the study of the constituents of teeth dentine and enamel by a combination of esr and u series techniques offer unique constraints on the history of uranium migration into these materials our results imply that it is inappropriate to assume a simplified u uptake model for neither the components of a single tooth nor for the faunal remains of a given site however the combination of both methods may provide a new technique for establishing reliable chronologies for archaeological quaternary sites of up to several hundred thousand years

successful application of uranium series dating of fossil bone abstract a novel approach to uranium series disequilibrium dating is presented and used successfully to date bones from several european archaeological and palaeontological sites a method is described based on a proposed mechanism of uranium uptake and fixation derived from present understanding of the biochemistry of fossilizing bones and the geochemistry of uranium stability of uranium in fossil bone is predicted under particular conditions of local depositional environment and the importance of the inhomogeneous distribution of uranium through bone to uranium series dating is explained sample bones from several different sites have been examined taking into account the three factors of uptake mechanism uranium distribution and sedimentary environment and have yielded ages in good agreement with those derived by alternative dating methods or from chronologically fixed stratigraphical positions