evidence for inner core rotation from possible changes with time in pkp coda 1 inner core grazing pkp waves from seven french nuclear tests on mururoa island recorded at norsar appear to change over a decade we compared filtered and stacked signals from the explosions which took place from 1977 to 1987 and were separated by less than 10 km the pkp energy 3 to 10 s after the first arrivals differs greatly between the norsar subarrays and evolves over time the small time shifts of coda arrivals a few tenths of a second are qualitatively consistent with shifts predicted for point scatterers in an inner core that rotates in the range 0 05 to 0 10 per year there are also visible changes in the envelope of the pkp energy although the alternative of systematic shifts in source location cannot be ruled out the apparent time evolution of pkp supports claims of slow inner core rotation song and richards 1996 creager 1997 laske and masters 1999 vidale et al 2000 and offers a powerful new tool for its assessment

molybdenum isotope constraints on the extent of late paleoproterozoic ocean euxinia abstract the expansion of anoxic and sulfidic euxinic deep oceans may explain the termination of global large iron formation if deposition at 1 85 ga but the areal extent of late paleoproterozoic ocean euxinia is poorly constrained here we use the molybdenum mo isotope composition 98 95 mo of black shales from the hr fe t typically 0 38 and ratios of pyrite fe to highly reactive fe fe py fe hr typically 2 rich because the fe py fe hr ratios do not imply sustained water column euxinia the conversion of molybdate moo 4 2 to tetrathiomolybdate mos 4 2 in bottom waters and sediments was probably not quantitative and thus the 98 95 mo 0 1 to 0 8 from these shales provides only a minimum estimate for coeval seawater by contrast black shales from the middle rove formation have high fe py fe hr 0 8 and fe hr fe t 0 38 which implies persistent water column euxinia concentrations of free sulfide may have been sufficient to result in near quantitative formation of tetrathiomolybdate and its removal from bottom waters the observed narrow range in 98 95 mo of 1 19 0 28 2sd defined by most euxinic shales is thus inferred to represent the mo isotope composition of late paleoproterozoic global seawater mass balance modeling suggests that organic rich sediments deposited beneath euxinic bottom waters represented a substantial fraction of the oceanic mo sink at 1 8 ga the modeling results suggest that euxinic marine environments were common along late paleoproterozoic ocean margins these environments could have served as efficient sinks for fe 2 aq upwelling from anoxic deeper waters hence the mo isotope data are consistent with fe speciation and other geochemical evidence that suggest an expansion of euxinic environments led to the cessation of global large if deposition after 1 85 ga

detection of small scale heterogeneities at the inner core boundary 2018 elsevier b v the hemispherical pattern of seismic velocities in the uppermost inner core has been described at the global scale in many studies in this paper we investigate shorter scale heterogeneities in the vicinity of the inner core boundary icb using differential travel time and amplitude measurements between the pair of core phases pkp df and pkikp seismic events occurring close to sumatra and recorded at usarray stations in the distance range 132 142 are used to investigate the velocity and attenuation structure at the icb and in the uppermost 100 km of the inner core beneath eastern russia in this distance range pkp df and pkikp are difficult to separate due to their proximity in travel time we present a new method based on the envelope of the seismic signal to identify them following which we measure differential travel time residuals and amplitude ratios by comparison with synthetics computed using the direct solution method which allows us to take into account the correct phase shift of the pkikp we found that in our region of study the compressional velocity is slower in the uppermost inner core than the ak135 model however the sampled region is located in the eastern hemisphere generally considered as faster and more attenuating than the ak135 model this suggests significant regional departures from the simple hemispherical pattern reported in the literature we also deduce from the amplitude ratios that the attenuation is stronger than the global average at the top of the inner core in this region as expected from its location in the eastern hemisphere our results confirm the presence of a low attenuation zone at the top of the inner core followed by a highly attenuating layer centered around 35 km depth in the inner core as found in the eastern hemisphere in previous studies this zone is however thinner 15 km and more attenuating q reaching values less than 50

molybdenum behavior during early diagenesis insights from mo isotopes 1 we present molybdenum isotope and concentration data from 14 sites in the eastern pacific from the central california to the peru margin the environments studied have been chosen to represent a broad range in oxidation reduction redox potential which provide a framework for the behavior of this redox sensitive element manganese rich hemipelagic sediments from the eastern tropical pacific have a mean characteristic mo isotope signature 98 95mo 0 49 0 04 two times the standard deviation of the mean 2 sdom with n 14 that reflects fractionation between ocean water and authigenic mo associated with mn oxides authigenic fe mo s deposits from reducing continental margin settings also have a characteristic mo isotopic signature 98 95mo 1 64 0 04 2 sdom with n 136 both of these values are in contrast to highly sulfidic 11 m h2saq restricted basin environments which contain mo isotope values analytically indistinguishable from seawater in terms of the mo isotope composition the modern oceanic mo sink is dominated by continental margin type environments where 98 95mo 1 6 and mn rich sediments where 98 95mo approximately 0 5 with a minor contribution from euxinic settings where h2saq 11 m

directional properties of van s ses and ulf mt signals at ioannina greece abstract in order to examine the validity of the earthquake prediction technique developed in greece by van varotsos alexopoulos and nomicos and elucidate the underlying physical processes we performed a magnetotelluric mt recording of the ulf band 3 200 s in the vicinity of van s sensitive station ioannina ioa by comparing mt electric field of ionospheric or magnetospheric origin electric field of lightning origin and van s seismic electric signals ses the following facts were revealed 1 the mt electric field always varies in the ene wsw direction indicating existence of significant electrical conductivity contrast near the site 2 the lightning electric field orientation is somewhat more scattered but still holds the same preferred direction as that of the mt electric field the scatter is larger for larger lightning field probably due to closer location of lightning stroke to the station and or due to no linear saturation of the recording signals 3 the ses electric field orientation is even more scattered than that of the lightning origin these observations suggest that the sources of the ses are in the neighborhood of the station it is still unclear how the ses associated with distant earthquakes are emitted from the sources near the ioa station

localized temporal change of the earth s inner core boundary compressional waves of an earthquake doublet two events occurring in the south sandwich islands on 1 december 1993 and 6 september 2003 recorded at three seismic stations in russia and kyrgyzstan and reflected off earth s inner core boundary arrived at least from 39 to 70 milliseconds earlier in the 2003 event than in the 1993 event such changes indicate that earth s inner core radius enlarged locally beneath middle africa by 0 98 to 1 75 kilometers between the times of these two events changes of the inner core radius may be explained by either a differential motion of the inner core assuming that irregularities are present at the inner core boundary and fixed to the inner core or a rapid growth of the inner core by this amount

structure of the earth s inner core jacobs1 proposed that the earth s inner core is growing through the freezing of outer core material as the earth gradually cools2 recent studies have shown that compositional effects associated with this freezing process can release energy at a rate sufficient to power the geodynamo3 4 and may be crucial in determining the dynamic state of the outer core5 here we investigate the effects of composition on the freezing process itself drawing on metallurgical experience and speculate on the structure and state of the inner core we propose that the interface separating the inner and outer core is dendritic and argue that the region in which freezing takes place may extend throughout the entire inner core consequently the compositionally driven convective motions which stir the outer core and sustain the geodynamo also occur within the interdendritic spaces of the inner core the seismic evidence which corroborates this proposal is briefly reviewed

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

s coda and rayleigh waves from a decade of repeating earthquakes reveal discordant temporal velocity changes since the 2004 sumatra earthquake temporal changes in the subsurface seismic velocity structure reflect the physical processes that modulate the properties of the media through which seismic waves propagate these processes such a

paleoproterozoic basin development and sedimentation in the lake superior region north america abstract the peneplaned archean craton in the lake superior region was the platform upon which a continental margin assemblage was deposited extension resulted in localized rifts that received thicker accumulations of sediments and volcanic rocks than did adjacent parts of the platform seas transgressed onto the continent several times and an ocean basin opened south of the present day lake superior island arcs that formed during subduction collided with the craton margin as the ocean basin closed oceanic crust is poorly preserved as a dismembered ophiolite sequence the arc volcanics are preserved as the wisconsin magmatic terranes the collision resulted in a fold and thrust belt known as the penokean orogen to the north of the fold and thrust belt a northward migrating foreland basin the animikie basin developed thick turbidite successions were deposited along the basin axis and terrigenous clastics and lake superior type iron formation were deposited on the shelf along the northern margin of the basin the primary paleoclimatic indicators are 1 glaciogenic rocks at the base of the paleoproterozoic succession in michigan indicating ice house conditions 2 remnants of a paleosol on the glaciogenic rocks indicative of deep weathering probably under subtropical conditions and therefore of greenhouse conditions and 3 carbonate minerals after gypsum halite and anhydrite in stromatolitic dolomite indicative of aridity three second order depositional sequences are bounded by major unconformities and can be correlated throughout the lake superior region

natural mass dependent variations in the isotopic composition of molybdenum we present the first observations of natural mass dependent fractionation of the isotopic composition of molybdenum mo using multi collector inductively coupled plasma mass spectrometry variations in the isotopic composition of mo are reported as 97 95mo 97mo 95mo sample 97mo 95mo standard 1 1000 external analytical precision of 97 95mo is 1 between sediments deposited under anoxic conditions 97 95mo 1 02 to 1 52 relative to our in house standard and ferromanganese nodules 97 95mo 0 63 to 0 42 97 95mo of pacific ocean seawater 97 95mo 1 48 lies within the range of values for anoxic sediments closest to modern black sea anoxic sediments molybdenites from continental ore deposits have intermediate 97 95mo ranging from 0 26 to 0 09 variations in the abundances of 92mo 95mo 96mo 97mo and 98mo are consistent with mass dependent fractionation a sporadic unidentified interference occurs at mass 94 and 100mo is not measured we hypothesize that the 97 95mo offset between anoxic sediments and ferromanganese nodules results from mo isotope fractionation during inefficient scavenging of mo from seawater by mn oxides under oxic conditions the similarity in 97 95mo of anoxic sediments and seawater is consistent with the very efficient removal of mo from seawater under anoxic conditions in the presence of h2s the data can be interpreted in terms of a steady state mass balance between the mo flux into the oceans from the continents and the mo flux out of the oceans into oxic and anoxic sediments such an interpretation is quantitatively consistent with existing estimates of the removal fluxes of mo to anoxic and oxic sediments these findings suggest that 97 95mo in seawater may co vary with changes in the relative proportions of anoxic and oxic sedimentation in the oceans and that this variation may be recorded in 97 95mo of anoxic sediments hence the mo isotope system may be useful in paleoredox investigations

anomalously strong observations of pkikp pcp amplitude ratios on a global scale the inner core boundary marks the phase transition between the solid inner core and the fluid outer core as the site of inner core solidification the boundary provides insight into the processes generating the seismic structures of the inner core in particular it may hold the key to understanding the previously observed hemispherical asymmetry in inner core seismic velocity anisotropy and attenuation here we use a large pkikp pcp amplitude ratio and travel time residual data set to investigate velocity and density contrast properties near the inner core boundary although hemispherical structure at the boundary has been proposed by previous inner core studies we find no evidence for hemispheres in the amplitude ratios or travel time residuals in addition we find that the amplitude ratios are much larger than can be explained by variations in density contrast at the inner core boundary or core mantle boundary this indicates that pkikp is primarily observed when it is anomalously large due to focusing along its raypath using data in which pkikp is not detected above the noise level we calculate an upper estimate for the inner core boundary icb density contrast of 1 2 kg m 3 the travel time residuals display large regional variations which differ on long and short length scales these regions may be explained by large scale velocity variations in the f layer just above the inner core boundary and or small scale topography of varying magnitude on the icb which also causes the large amplitudes such differences could arise from localized freezing and melting of the inner core

detection of motion and heterogeneity in earth s liquid outer core 1 the lateral variations in the fluid outer core are believed to be very small from fluid dynamics calculations seismological studies on the issue have been limited and controversial a great challenge is to sort out influences from heterogeneity in the mantle or the inner core using high quality earthquake waveform doublets we found that waves passing through the fluid core over a few years are significantly more variable than those passing through the mantle only we interpret the temporal variability as the result of the fluid motion of the heterogeneous materials in the outer core the level of heterogeneity in the fluid outer core is constrained to be 0 022 s 95 confidence in seismic travel times through the core negligible for most seismological studies however the estimated velocity perturbation about 10 3 for small scale heterogeneity 10 km or 10 4 for large scale heterogeneity 1000 km borders or exceeds the high end estimates of the lateral variations that can be supported by dynamic forces within the fluid core the source of the heterogeneity is not clear at present

origin of temporal changes of inner core seismic waves abstract temporal changes of inner core ic seismic phases have been confirmed with high quality waveform doublets however the nature of the temporal changes is still controversial we investigated systematically the temporal changes of ic refracted pkikp and reflected pkikp waves with a large data set of waveform doublets we used non ic reference phase mainly skp which eliminated ambiguity where the temporal changes come from we found that the temporal changes have always started at refracted pkikp and the travel time changes correlate better with pkikp changes in reflected pkikp can be easily contaminated by the strong and time varying pkikp and coda wave trains and therefore are not reliable indicators for ic boundary changes combining with previous observations we conclude that the temporal changes come mostly if not all from the ic interior and ic surface changes as the sole source suggested previously can be ruled out the differential rotation of the ic shifting its heterogeneous uppermost structures is the simplest and most reasonable explanation for the origin of the time varying ic waves a rotation rate of about 0 05 0 1 per year with possible decadal fluctuation can reconcile all temporal change observations from body waves ic scattering and normal mode data

global large deep focus earthquakes source process and cascading failure of shear instability as a unified physical mechanism abstract we apply a multiple source inversion method to systematically study the source processes of 25 large deep focus depth 400 km earthquakes with mw 7 0 from 1994 to 2012 based on waveform modeling of p pp sh and ssh wave data the earthquakes are classified into three categories based on spatial distributions and focal mechanisms of the inferred sub events 1 category one with non planar distribution and variable focal mechanisms of sub events represented by the 1994 mw 8 2 bolivia earthquake and the 2013 mw 8 3 okhotsk earthquake 2 category two with planar distribution but focal mechanisms inconsistent with the plane including eighteen earthquakes and 3 category three with planar distribution and focal mechanisms consistent with the plane including six earthquakes we discuss possible physical mechanisms for earthquakes in each category in the context of plane rupture transformational faulting and shear thermal instability we suggest that the inferred source processes of large deep focus earthquakes can be best interpreted by cascading failure of shear thermal instabilities in pre existing weak zones with the perturbation of stress generated by a shear instability triggering another and focal mechanisms of the sub events controlled by orientations of the pre existing weak zones the proposed mechanism can also explain the observed great variability of focal mechanisms the presence of large values of clvd compensated linear vector dipole and the super shear rupture of deep focus earthquakes in the previous studies in addition our studies suggest existence of relationships of seismic moment source duration 3 and moment source dimension 3 in large deep focus earthquakes

wide scale detection of earthquake waveform doublets and further evidence for inner core super rotation summary we report on more than 100 earthquake waveform doublets in five subduction zones including an earthquake nest in bucaramanga colombia each doublet is presumed to be a pair of earthquakes that repeat at essentially the same location these doublets are important for studying earthquake physics as well as temporal changes of the inner core particularly our observation from one south sandwich islands ssi doublet recorded at station ink in canada shows an inner core traveltime change of 0 1 s over 6 yr confirming the innercore differential motion occurring beneath central america observations from one aleutian islands doublet recorded at station bosa in south africa and from one kuril islands doublet recorded at station bdfb in brazil show an apparent inner core traveltime change of 0 1 s over 7 yr and 6 yr respectively providing evidence for the temporal change of inner core properties beneath central asia and canada respectively on the other hand observations from one tonga fiji solomon islands doublet recorded at station ptga in brazil and from one bucaramanga doublet recorded at station wrab in australia and station chto in thailand show no little temporal change no more than 0 005 syr 1 if any of inner core traveltimes for the three corresponding ray paths for which the path in the inner core is nearly parallel to the equatorial plane such a pattern of observations showing both presence and possible absence of inner core traveltime change can be explained by the geometry and relative directions of ray path lateral velocity gradient and inner core particle motion due to an eastward super rotation of a few tenths of a degree per year

the behavior of molybdenum and its isotopes across the chemocline and in the sediments of sulfidic lake cadagno switzerland abstract molybdenum mo isotope studies in black shales can provide information about the redox evolution of the earth s oceans provided the isotopic consequences of mo burial into its major sinks are well understood previous applications of the mo isotope paleo ocean redox proxy assumed quantitative scavenging of mo when buried into sulfidic sediments this paper contains the first complete suite of mo isotope fractionation observations in a sulfidic water column and sediment system the meromictic lake cadagno switzerland a small alpine lake with a pronounced oxygen sulfide transition reaching up to h 2 s 200 m in the bottom waters or about 300 m total sulfide s 2 h 2 s hs s 2 we find that mo behaves conservatively in the oxic zone and non conservatively in the sulfidic zone where dissolved mo concentrations decrease from 14 nm to 2 8 nm across this transition dissolved mo in the upper oxic waters has a 98 mo oxic 0 9 0 1 which matches that of the riverine input 98 mo river 0 9 0 1 in the deeper sulfidic waters a subaquatic source delivers mo at 1 55 0 1 but the dissolved mo is even heavier at 98 mo sulfidic 1 8 sediment traps in the sulfidic zone of the lake collect particles increasingly enriched in mo with depth with 98 mo values significantly fractionated at 0 8 to 1 2 both near the chemocline and in the deepest trap suspended particulates in the sulfidic waters carry lighter mo than the ambient dissolved mo pool by 0 3 1 5 sedimentary mo concentrations correlate with total organic carbon and yield mo levels which are two orders of magnitude higher than typical crustal values found in rocks from the catchment area solid phase mo in the sediment shows a slightly positive 98 mo trend with depth from 98 mo 1 2 to 1 4 while the pore waters show dramatic enrichments of mo 2000 nm with a relatively light isotope signature of 98 mo 0 9 1 0 these data are explained if mo is converted to particle reactive oxythiomolybdates in the sulfidic waters and is fractionated during removal from solution onto particles isotope fractionation is expressed in the water column despite the high sulfide concentrations because the rate of mo removal is fast compared to the slow reaction kinetics of thiomolybdate formation however elemental and isotopic mass balances show that mo is indeed quantitatively removed to the lake sediments and thus the isotopic composition of the sediments reflects sources to the sulfidic water this efficient mo drawdown is expected to occur in settings where h 2 s is very much in excess over mo or in a restricted setting where the water renewal rate is slow compared to the mo burial rate we present a model for the mo isotope fractionation in sulfidic systems associated with the slow reaction kinetics and conclude that quantitative removal will occur in highly sulfidic and restricted marine systems

a cascading failure during the 24 may 2013 great okhotsk deep earthquake on 24 may 2013 the largest ever recorded deep earthquake occurred beneath sea of okhotsk a multiple point source inversion procedure is applied to constrain source process of this earthquake based on waveform modeling of both direct p and sh waves and near surface reflected pp and ssh waves our results indicate that the earthquake consists of six major subevents separated in space and time encompassing a horizontal dimension of 64 4 km along n160 e and a downward depth extension of 35 4 km the geographic distribution and focal mechanisms of the inferred subevents and foreshock aftershock locations do not fit into plane rupture we suggest that the earthquake can be best explained by a cascading failure of shear instability within preexisting weak zones in the region with the perturbation of stress generated by a shear instability triggering another

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

inner core boundary topography explored with reflected and diffracted p waves abstract the existence of topography of the inner core boundary icb can affect the amplitude phase and coda of body waves incident on the inner core by applying pseudospectral and boundary element methods to synthesize compressional waves interacting with the icb these effects are predicted and compared with waveform observations in pre critical critical post critical and diffraction ranges of the pkikp wave reflected from the icb these data sample overlapping regions of the inner core beneath the circum pacific belt and the eurasian north american and australian continents but exclude large areas beneath the pacific and indian oceans and the poles in the pre critical range pkikp waveforms require an upper bound of 2 km at 1 20 km wavelength for any icb topography higher topography sharply reduces pkikp amplitude and produces time extended coda not observed in pkikp waveforms the existence of topography of this scale smooths over minima and zeros in the pre critical icb reflection coefficient predicted from standard earth models in the range surrounding critical incidence 108 130 this upper bound of topography does not strongly affect the amplitude and waveform behavior of pkikp pkikp at 1 5 hz which is relatively insensitive to 10 20 km wavelength topography height approaching 5 km these data however have a strong overlap in the regions of the icb sampled by pre critical pkikp that require a 2 km upper bound to topography height in the diffracted range 152 topography as high as 5 km attenuates the peak amplitudes of pkikp and pkpcdiff by similar amounts leaving the pkpcdiff pkikp amplitude ratio unchanged from that predicted by a smooth icb the observed decay of pkpcdiff into the inner core shadow and the pkikp pkpcdiff differential travel time are consistent with a flattening of the outer core p velocity gradient near the icb and iron enrichment at the bottom of the outer core

inner core rotation and its variability from nonparametric modeling 1 we present a new approach for studying the inner core rotation and its variability by separating the underlying structure from its time evolution this is achieved by fitting a large set of existing seismic bc df traveltime data with a smoothing spline analysis which is implemented in the statistics package r this method allows us to separate the time independent mantle contribution from the time dependent core contribution without any a priori constraints and to also estimate the error of the fit we add our newly acquired seismic data from the passcal experiment arctic in northern alaska to pkp differential traveltime measurements previously obtained from south sandwich islands earthquakes and recorded at college col and the alaskan seismic network this nearly doubles the number of measurements to a total of 1165 and increases the data coverage of the inner core structure and our time coverage to about 55 years the large number of measurements allows us to use the standard statistical method of bootstrapping to derive the rotation rate and thus to further separate the core structure from its time evolution this approach has been successfully tested with synthetic data sets that feature both a nonlinear structure and variable rotation rates while sharing the same earthquakes and stations geometry as our real data applying this method to the real data yields an average rotation rate of 0 39 0 090 22 yr 1 at 68 confidence level our results also suggest a nonzero acceleration of the inner core with an apparent change in the rotation rate from 0 24 to 0 56 yr 1 within the last 55 years the minimum torque acting on the inner core is estimated 1 19 1016 n m which could result from the imbalance of the electromagnetic and gravitational torques

seismological evidence for differential rotation of the earth s inner core the travel times of seismic waves that traverse the earth s inner core show a small but systematic variation over the past three decades this variation is best explained by a rotation of the inner core that moves the symmetry axis of its known seismic anisotropy the inferred rotation rate is on the order of 1 per year faster than the daily rotation of the mantle and crust

high precision location and yield of north korea s 2013 nuclear test 1 using north korea s 2009 nuclear test as reference and satellite imagery we show that the location and yield of north korea s 2013 nuclear test can be quickly and accurately determined based on seismic data north korea s 2013 nuclear test site is pinpointed by deriving relative location of north korea s 2009 and 2013 nuclear tests and using the previously determined location of the 2009 nuclear test while its yield is estimated based on the relative amplitude ratios of the lg waves recorded for both events the previously determined lg magnitude of 2009 nuclear test and burial depth inferred from satellite imagery north korea s 2013 test site is determined to be located at 41 17 26 88 n 129 4 34 68 e about 345 m south and 453 m west of its 2009 nuclear test site with a geographic precision of 94 m its yield is estimated to be 12 2 3 8 kt

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

official earthquake prediction procedure in greece abstract since jan 19 1983 the authors have been operating a telemetric network of electrotelluric stations in greece the real time observation of specific pre seismic variations in the electric field of the earth seismic electric signals ses allows us to predict the time epicenter and magnitude of an impending earthquake eq initially the predictions were announced by expediting telegrams prior to the event after the ministry of public works established the earthquake prediction council epc in september 1985 predictions were dealt with in special sessions of the council prior to the occurrence of an earthquake it was decided to announce only eq s with an expected magnitude ms 4 8 for epicenters predicted within or near the perimeter surrounding the network of measuring stations and ms 5 for eq s predicted outside the perimeter this procedure was followed from september 1985 to march 18 1986 with the following results 1 1 within the network only one eq with ms 4 9 occurred during the period mentioned the prediction of the magnitude was accurate to within a few tenths of a magnitude unit while the epicenter was predetermined to within some tens of kilometers no predictions were made that were not followed by earthquakes 2 2 outside the network three eq s with ms 5 4 5 2 and 5 3 occurred on nov 9 dec 18 and dec 23 1985 respectively the first was missed the magnitudes of the other two were predicted to be ms 5 2 and 5 5 respectively the corresponding epicentral coordinates were forecast with an accuracy of 150 and 160 km respectively the sessions were discontinued on march 18 1986 on march 24 1986 a ms 6 1 eq was predicted and directly announced to the ministry of public works the event occurred on march 29 with the predicted magnitude and less than 50 km from the predicted epicenter

complex seismic anisotropy in the top of the earth s inner core beneath africa 1 we report complex seismic anisotropy in the top 80 km of the earth s inner core beneath africa the anisotropy in the top 80 km of the inner core is constrained using differential travel times amplitude ratios and waveforms of the pkikp pkikp phases sampling africa along various directions the differential pkikp pkikp time residuals relative to the preliminary reference earth model prem along the polar paths are larger than those along the equatorial paths by 0 1 4 s indicating the presence of seismic anisotropy in the top 80 km of the inner core furthermore the observations along the polar paths show complex regional variations beneath africa the differential pkikp pkikp travel time residuals vary from 1 2 s beneath eastern africa to 0 1 s beneath central africa and to 0 2 to 0 8 s beneath western africa a correlation between small pkikp pkikp amplitude ratios and large differential pkikp pkikp travel time residuals is observed the waveform data are spatially binned into six groups to constrain the regional dependence of velocity and attenuation anisotropy in the top 80 km of the inner core overall the seismic data can be explained by an isotropic upper inner core uic overlying an anisotropic lower inner core lic in the top 80 km of the inner core across africa the thickness of the isotropic uic varies from 0 to 50 km and the p velocity transition from the isotropic uic to the anisotropic lic is sharp with velocity increases laterally varying from 1 6 to 2 2 the attenuation structure along the polar paths has a q value of 600 for the isotropic uic and q values varying from 150 to 400 for the anisotropic lic the complex seismic anisotropy in the top of the inner core is found in a region where a rapid change of the inner core boundary icb between 1993 and 2003 was discovered wen 2006 and may be explained by complex alignments of iron crystals resulting from a localized anomalous solidification of the inner core

sub million year age resolution of precambrian igneous events by thermal extraction thermal ionization mass spectrometer pb dating of zircon application to crystallization of the sudbury impact melt sheet a new approach to zircon dating is described that potentially offers a considerable improvement in the accuracy of 207 pb 206 pb ages on a wider variety of samples and at less cost than that generally available from conventional techniques zircon is first preheated in a vacuum to evaporate pb from altered domains leaving predominantly pb with isotopes that preserve the primary age of the sample refractory pb is removed from the zircon by thermal extraction at higher temperature directly into a silica melt ionization activator within a thermal ionization mass spectrometer this produces strong ion beams that allow 207 pb 206 pb isotope ratios to be measured to high precision 10 4 with almost negligible contamination from common pb isotope fractionation appears to be more reproducible than with conventional solution analysis allowing routine age determinations with precision of 0 2 m y for the precambrian as a test application zircon from a noritic boundary phase of the sudbury impact melt gives 1849 53 0 21 ma while a phase from several hundred meters higher in the noritic layer is resolvably younger at 1849 11 0 19 ma 95 confidence errors the enhanced precision and ease of application of this method should greatly increase the scientific power and availability of zircon dating

century long record of mo isotopic composition in sediments of a seasonally anoxic estuary chesapeake bay abstract a double spike method was used to obtain mo isotope data for sediments and waters of the seasonally anoxic chesapeake bay and its primary tributary the susquehanna river the dissolved mo distribution in the estuary is non conservative reflecting minor mo loss to the sediments although removal of mo to the sediments does not have a large influence on the isotopic composition of the water column the 98mo of dissolved mo in most of the estuary is dominated by seawater six samples with salinity 15 have an average 98mo 2 17 0 12 which agrees well with a 98mo value for the cass 4 seawater standard of 2 23 a single sample of susquehanna river water has a 98mo of 1 02 consistent with recent findings of positive 98mo in rivers worldwide susquehanna river sediments in contrast have 98mo 0 1 the difference between the river water and sediment values implies that isotopic fractionation occurs within the river basin the 98mo values for estuarine sediments are offset from values in the overlying water most samples deposited before 1925 have 98mo less than 0 similar to the susquehanna sediments subsequently there is an increase in the variability of 98mo with values ranging up to 0 8 the transition to increased variability coincides with the onset of authigenic mo deposition which was previously attributed to escalating summertime anoxia authigenic mo concentrations correlate poorly with 98mo in core samples suggesting that independent mechanisms influence the two parameters authigenic mo concentrations may be controlled by shifting pore water h2s levels while 98mo may be primarily affected by annual variations in mn refluxing

repeating aftershocks of the great 2004 sumatra and 2005 nias earthquakes abstract we investigate repeating aftershocks associated with the great 2004 sumatra andaman mw 9 2 and 2005 nias simeulue mw 8 6 earthquakes by cross correlating waveforms recorded by the regional seismographic station psi and teleseismic stations we identify 10 and 18 correlated aftershock sequences associated with the great 2004 sumatra and 2005 nias earthquakes respectively the majority of the correlated aftershock sequences are located near the down dip end of a large afterslip patch we determine the precise relative locations of event pairs among these sequences and estimate the source rupture areas the correlated event pairs identified are appropriately referred to as repeating aftershocks in that the source rupture areas are comparable and significantly overlap within a sequence we use the repeating aftershocks to estimate afterslip based on the slip seismic moment scaling relationship and to infer the temporal decay rate of the recurrence interval the estimated afterslip resembles that measured from the near field geodetic data to the first order the decay rate of repeating aftershocks as a function of lapse time t follows a power law decay 1 t p with the exponent p in the range 0 8 1 1 both types of observations indicate that repeating aftershocks are governed by post seismic afterslip

on the physical background of the van earthquake prediction method abstract seismic electric signals ses have been used as precursors of earthquakes for the van method of earthquake prediction in greece its generation is theoretically expected from the thermodynamics of point defects in rock forming minerals this paper reviews the theoretical and observational basis of the van method and points out several unsolved problems in its physical background the problems can be classified into three source energetics signal generation mechanism and signal transmission further investigations on the geological and geoelectrical structure laboratory experiments and theoretical aspects are recommended to solve these problems and to establish a better understanding of the physics of the focal process

tomographic inversion for three dimensional anisotropy of earth s inner core abstract seismological studies generally suggest that the earth s inner core is anisotropic and the anisotropic structure changes significantly both laterally and with depth previous body wave studies of the inner core have relied on ray tracing or waveform modeling using one dimensional 1d models here we present non linear tomographic inversions of the inner core anisotropy using three dimensional 3d ray tracing spline parameterization and a large collection of pkp differential travel times we adapt a pseudo bending ray tracing pbr method in spherical coordinates for seismic rays that traverse the inner core pkp df phase the method iteratively perturbs each discontinuity point and continuous segment of the ray through 3d earth structure so that its travel time is minimum the 3d anisotropic structure of the inner core is approximated to the first order as 3d heterogeneous but isotropic structure for a given ray the data are corrected using a scaled mantle tomographic model the inner core anisotropy model obtained has the following major features 1 the model has strong hemispherical and depth variation the isotropic velocity in the topmost inner core is greater in quasi eastern hemisphere qeh 40 160 e than in quasi western hemisphere qwh other longitudes the anisotropy is weak in qeh to the depth of 600 700 km below the inner core boundary icb while in qwh the anisotropy increases at much shallower depth about 100 200 km below the icb to about 3 4 then remains at about 2 4 throughout the rest of the inner core 2 the anisotropy form changes abruptly over a depth range of about 150 km at the radius of about 600 km slightly less than half of the inner core radius forming a distinct inner inner core iic the velocity in the iic has maximums at equatorial and polar directions and minimum at an angle of about 40 from the equatorial plane the velocity in the outer inner core oic however changes little for ray directions 0 40 from the equatorial plane 3 despite large variation of the anisotropy the isotropic velocity voigt average throughout the inner core is nearly uniform the results suggest that the oic is likely composed of the same type of iron crystals with uniform chemistry but the iic may be composed of a different type of crystal alignment a different iron phase or a different chemical composition our tests on model parameterization mantle correction and linear and non linear inversion suggest the main features of our model are very robust however fine scale structures are likely to differ particularly in the major transition zones e g in the topmost qwh isotropy to anisotropy between oic and iic change in the form of anisotropy and between qeh and qwh in oic difference in anisotropy strength searches for possible waveform complications from these boundaries need to be aware of the directional dependence and geographical variation to be successful

inner core rotation rate from small scale heterogeneity and time varying travel times the time it takes seismic waves to propagate from south atlantic earthquakes through the inner core to station col in alaska has decreased systematically over the past 30 years travel times from three earthquakes in 1991 to an array of 37 seismometers in alaska suggest that lateral gradients in seismic wavespeeds are steep in this part of the inner core this combination of observations can be explained by postulating that the inner core is rotating 0 2 to 0 3 per year faster than the mantle

small scale structure of the geodynamo inferred from oersted and magsat satellite data the geodynamo in the earth s liquid outer core produces a magnetic field that dominates the large and medium length scales of the magnetic field observed at the earth s surface1 2 here we use data from the currently operating danish oersted3 satellite and from the us magsat2 satellite that operated in 1979 80 to identify and interpret variations in the magnetic field over the past 20 years down to length scales previously inaccessible projected down to the surface of the earth s core we found these variations to be small below the pacific ocean and large at polar latitudes and in a region centred below southern africa the flow pattern at the surface of the core that we calculate to account for these changes is characterized by a westward flow concentrated in retrograde polar vortices and an asymmetric ring where prograde vortices are correlated with highs and retrograde vortices with lows in the historical 400 year average magnetic field4 5 this pattern is analogous to those seen in a large class of numerical dynamo simulations6 except for its longitudinal asymmetry if this asymmetric state was reached often in the past it might account for several persistent patterns observed in the palaeomagnetic field7 8 9 10 we postulate that it might also be a state in which the geodynamo operates before reversing

deep focus repeating earthquakes in the tonga fiji subduction zone abstract deep focus earthquakes in the tonga fiji subduction zone make up greater than 66 of the globally recorded deep seismicity the high number of deep focus seismicity in this active subduction zone allows us to search for deep focus similar earthquake pairs and repeating earthquakes we compile a waveform dataset for deep earthquakes with magnitude above 4 7 occurring in the tonga fiji kermadec subduction zone recorded teleseismically between 1990 and 2009 we identify 8 similar clusters and 18 similar doublets with an average cross correlation coefficient greater than 0 8 among more than 45 000 potential earthquake pairs these similar doublets and clusters are located in the central part of the tonga fiji slab at the depth range of 480 650 km a master event relocation algorithm is used to determine the precise relative location and depth among these similar earthquake pairs we estimate and superpose circular fault areas for these similar clusters and doublets and find that one similar doublet appears to be a deep repeating earthquake pair this deep doublet has a small separation less than 0 4 km and overlapping rupture areas indicating that the same fault appears to slip other deep similar earthquake pairs are spatially offset or do not exhibit overlapping rupture areas time separation is on the order of years for the majority of similar earthquake pairs thermal plastic shear instability is more likely to explain these deep repeating earthquakes and similar earthquake pairs

irregular topography at the earth s inner core boundary compressional seismic wave reflected off the earth s inner core boundary icb from earthquakes occurring in the banda sea and recorded at the hi net stations in japan exhibits significant variations in travel time from 2 to 2 5 s and amplitude with a factor of more than 4 across the seismic array such variations indicate that earth s icb is irregular with a combination of at least two scales of topography a height variation of 14 km changing within a lateral distance of no more than 6 km and a height variation of 4 8 km with a lateral length scale of 2 4 km the characteristics of the icb topography indicate that small scale variations of temperature and or core composition exist near the icb and or the icb topographic surface is being deformed by small scale forces out of its thermocompositional equilibrium position and is metastable

the structure of the base of the outer core inferred from seismic waves diffracted around the inner core 1 we systematically searched for seismograms of waves diffracted around the inner core pkpcdiff from all the temporary seismic arrays with data currently available at the iris dmc as well as some permanent regional seismic arrays including f net in japan and grf in germany to assemble the largest high quality pkpcdiff database ever created pkpcdiff waves preferentially sample the base of the outer core and so contain important clues about earth structure in this region we measured pkpdf pkpcdiff differential traveltimes and pkpcdiff pkpdf amplitude ratios in the distance range of 154 160 and modeled the observations using grid searches and full wave theory synthetic seismograms the optimum model found by fitting the differential traveltimes has relatively low velocity at the base of the outer core as in ak135 which is consistent with many previous traveltime studies however the optimum model found by fitting the amplitude ratios pkpcdiff pkpdf does not exhibit this feature and instead is closer to prem the discrepancy may be explained by two likely causes one is that small scale topography or roughness on the icb tends to scatter energy away from pkpcdiff waves by generating trailing coda waves the other is that there exists a thin layer with relatively low q at the base of the outer core this might be expected if there are suspended solid particles at the base of the outer core as proposed decades ago both mechanisms could generate smaller pkpcdiff amplitudes without significantly affecting pkpcdiff traveltimes

the molybdenum isotopic composition in river water constraints from small catchments we report molybdenum isotope compositions and concentrations in water samples from a variety of river catchment profiles in order to investigate the influence of anthropogenic contamination catchment geology within river precipitation and seasonal river flow variations on riverine molybdenum our results show that the observed variations in 98 95mo from 0 to 1 9 are primarily controlled by catchment lithology particularly by weathering of sulfates and sulfides erosion in catchments dominated by wet based glaciers leads to very high dissolved molybdenum concentrations in contrast anthropogenic inputs affect neither the concentration nor the isotopic composition of dissolved molybdenum in the rivers studied here seasonal variations are also quite muted the finding that catchment geology exerts the primary control on the delivery of molybdenum to seawater indicates that the flux and isotope composition of molybdenum to seawater has likely varied in the geologic past

piezoelectric effects in quartz rich rocks abstract piezoelectricity a polarization of charge produced by an applied stress occurs in many minerals it is particularly strong in quartz aggregates of piezoelectric grains are themselves piezoelectric if the grains are suitably aligned such aggregates may be said to have a piezoelectric fabric thus quartz rich rocks may possess a piezoelectric fabric and this paper discusses the various possible fabrics to test whether a piezoelectric fabric might be detected in a quartz rich rock apparatus was built that hydraulically applied a sinusoidal stress to cubic specimens the three resulting orthogonal polarizations of charge were measured via a charge amplifier a specimen of pure quartz was used to verify the experimental method and to ensure that absolute piezoelectric moduli were being measured rocks with and without preferred orientation were tested of the latter types those containing little or no free quartz marble basalt did not exhibit measurable piezoelectric effects however all quartz rich rocks quartzites granites gneisses mylonites did show piezoelectric effects when stressed these effects were in two categories 1 1 effects due to piezoelectric fabrics called true piezoelectric effects 2 2 effects due to random distributions of the piezoelectric vectors called statistical effects to distinguish between these two effects three criteria were used firstly the measured effects were compared with the expected statistical effect for a rock of that grain size and composition secondly where possible multiple specimens were cut from the one rock sample all specimens with the same orientation specimens from a rock with a piezoelectric fabric should show similar results thirdly the optically observed c axis distribution and orientation was compared with the piezoelectrically predicted fabric and orientation this paper shows that while most rocks gave results consistent with statistical effects from a non polar or random distribution some rocks exhibited a true piezoelectric effect due to fabric this effect may be used with some imprecision to locate the a axes and c axes of quartz in the aggregate the polarities of the a axes are also obtained

does the paleoproterozoic animikie basin record the sulfidic ocean transition comment pufahl et al 2010 1 question the interpretation of data in poulton et al 2004 2 showing a transition from ferruginous to euxinic conditions on the continental shelf of a major ocean basin at ca 1840 ma in contrast with poulton et al 2004 2 and also johnston et al 2006 3

two decades of temporal change of earth s inner core boundary we report two decades of changing behavior of the earth s inner core boundary icb which provides the simplest explanation for the observed temporal change of the compressional seismic waves that are reflected from the icb pkikp and refracted in the inner core pkikp from earthquake doublets occurring in south sandwich islands between 1993 and 2013 in the early period before 2003 the icb is enlarged beneath the western coast of gabon republic of congo and southwest tanzania in the reflected points of the pkikp observed at seismic stations obn aak and aru while it experiences little change beneath zimbabwe or and kenya and beneath west angola or and north central african republic in the pkikp entry or and exit points of aak and aru observations respectively in the later period after 1998 the icb regions beneath the western coast of gabon republic of congo and southwest tanzania either shrink or remain unchanged and the temporal change migrates to beneath zimbabwe or and kenya and beneath west angola or and north central african republic with a decrease of inner core surface by 5 59 km between 1998 and 2009 beneath zimbabwe or kenya and by 1 73 km beneath west angola or north central african republic between 1998 and 2013 these results indicate that icb temporal change occurs in localized regions and is episodic rapidly migrating and alternately enlarged and shrunk

molybdenum isotope fractionation during adsorption by manganese oxides the isotopic composition of mo 97 95mo in seawater is 2 heavier than mo in marine ferromanganese crusts and nodules barling et al earth planet sci lett 193 2001 447 457 siebert et al earth planet sci lett 211 2003 159 171 to explore this phenomenon we have conducted an experimental investigation into the mass dependent fractionation of mo isotopes during adsorption onto mn oxyhydroxide two series of experiments were carried out a time series in which adsorption proceeded for 2 96 h and a ph series in which ph varied from 6 5 to 8 5 the extent of mo adsorption by mn oxyhydroxides decreases with increasing ph a trend typical of anion adsorption and takes 48 h to reach steady state lighter mo isotopes are preferentially adsorbed experimentally determined fractionation factors soln mnox exhibit no systematic variation with either time or experimental ph the mean soln mnox for all experiments is 1 0018 0 0005 2 s d comparison of the mo isotopic data for experimental solutions and mo adsorbed to mn oxyhydroxide with predictions for closed system equilibrium and rayleigh fractionation models indicates that isotope fractionation occurs as a result of closed system equilibrium exchange between dissolved and adsorbed mo the isotopic offset between dissolved and adsorbed mo is comparable to that observed between mo in seawater and mo in ferromanganese nodules and crusts it is therefore likely that adsorption of mo to mn oxyhydroxides is a significant factor in the fractionation of mo isotopes in the oceans

comment on the existence of an inner core super rotation questioned by teleseismic doublets by georges poupinet annie souriau and olivier coutant abstract poupinet et al j geophys res 89 1984 5719 presented a new methodology for testing whether the pkp travel times observed at college alaska station from south sandwich islands earthquakes indicate inner core rotation they applied the method to seven events and concluded that there is no evidence for pkp df times increasing systematically with event dates and therefore no reason to postulate that the inner core rotates at a different rate than the mantle in a reanalysis of the same seven events i find that their results are systematically biased by the choice of radial earth models and by incorrectly assuming that one of the phases had reversed polarity i also question their choice of events but upon correcting for these biases conclude that these seven events are consistent with the previous model of inner core rotation

discovery of distal ejecta from the 1850 ma sudbury impact event a 25 70 cm thick laterally correlative layer near the contact between the paleoproterozoic sedimentary gunflint iron formation and overlying rove formation and between the biwabik iron formation and overlying virginia formation western lake superior region contains shocked quartz and feldspar grains found within accretionary lapilli accreted grain clusters and spherule masses demonstrating that the layer contains hypervelocity impact ejecta zircon geochronologic data from tuffaceous horizons bracketing the layer reveal that it formed between ca 1878 ma and 1836 ma the sudbury impact event which occurred 650 875 km to the east at 1850 1 ma is therefore the likely ejecta source making these the oldest ejecta linked to a specific impact shock features particularly planar deformation features are remarkably well preserved in localized zones within the ejecta whereas in other zones mineral replacement primarily carbonate has significantly altered or destroyed ejecta features

inner core differential rotation inferred from antipodal seismic observations abstract the earth s inner core may rotate at a different speed than earth s crust mantle we use observations for antipodal earthquake and station pairs to examine the arrival time shift of the whispering gallery wave which propagates tangentially along the top of the inner core observations of these waves for earthquakes which occurred at the same location reveal that travel times vary by 0 2 s over the past 20 years we propose that these time shifts are caused by the interaction of a zero rigidity patch lateral heterogeneity at the inner core surface with the inner core differential rotation the simplest interpretation infers a rotation rate of 0 05 year which is one order of magnitude smaller than those reported by previous studies our result may also give constraint to the provenance of a zero rigidity patch at the inner core surface the fresnel zone coverage of whispering gallery pkiikp antipodal measurements beneath the inner core boundary extend over 60 of the boundary surface in contrast to pkikp pkp paths which individually measure specular reflections 1 hz from the top of the icb over fresnel zones each encompassing 0 002 of the inner outer core boundary

on waveform correlation measurement uncertainty with implications for temporal changes in inner core seismic waves abstract we address the uncertainty related to cross correlation waveform time shift measurements particularly related to temporal changes in inner core seismic waves details of the cross correlation measurement including data processing window length pick time sampling rate and the algorithm itself all affect the calculated time shift by systematically varying measurement parameters for a set of earthquake doublets we find time shift uncertainties of 0 01 s and 0 02 s for differential times and double differential times respectively the uncertainty is of a similar magnitude to reported double differential times of pkikp and pkikp inner core phases accounting for measurement uncertainty results in 80 of values published in a recent study being below the measurement resolution yang and song 2020a while the temporal variations in inner core phases is not in dispute properly accounting for uncertainties is needed for robust data interpretation a re assessment for the origin of inner core temporal changes is therefore warranted and future studies should account for measurement uncertainty

spatial variability in oceanic redox structure 1 8 billion years ago the deposition of iron formations ceased about 1 84 billion years ago reconstructions of ocean chemistry suggest that the advent of euxinic conditions along ocean margins preferentially removed dissolved iron from the water column in the form of the mineral pyrite inhibiting widespread iron oxide mineral deposition

using repeated sources to quantitatively determine temporal change of medium properties theory and an example 1 we develop a theory of using difference wavefields of repeated sources to locate and quantify temporal medium change and apply the theory to locate temporal change of seismic properties beneath the japan subduction zone using repeated earthquakes our theory states the difference wavefields of two repeated sources in a temporally changed medium can be equivalently treated as wavefields propagating from conceptual sources with their location at the place of temporal change and their strengths equal to the product of magnitude of medium property change and magnitude of the initial wavefields from the repeated sources when the medium change extends to a finite region the conceptual sources become volumetric sources distributed over the region of the medium change and propagating in the direction of the initial wave the conceptualization establishes a theoretical framework for possible applications of using difference wavefields to locate and quantify temporal medium changes in geological sciences ultrasonic experiments civil engineering and medical imaging we search repeating earthquakes occurring in the japan subduction zone formulate an empirical procedure to extract the difference wavefields between repeating earthquakes and determine temporal change of seismic properties using a back projection method we locate the temporal change of seismic properties beneath the japan subduction zone to be at 37 2 n 142 e and estimate the magnitude of the conceptual body force associated with the temporal change to be 1 15 1010n or as a reference a 0 87 density change for an assumed volume of temporal change of 103 km3

inner core differential motion confirmed by earthquake waveform doublets we analyzed 18 high quality waveform doublets with time separations of up to 35 years in the south sandwich islands region for which the seismic signals have traversed the inner core as pkp df the doublets show a consistent temporal change of travel times at up to 58 stations in and near alaska and they show a dissimilarity of pkp df coda using waveform doublets avoids artifacts of earthquake mislocations and contamination from small scale heterogeneities our results confirm that earth s inner core is rotating faster than the mantle and crust at about 0 3 degrees to 0 5 degrees per year

topography of earth s inner core boundary from high quality waveform doublets summary precise determination of the topography of a major internal boundary of the earth is difficult because of the trade off with the unknown velocity structure above it however the discoveries of the inner core ic rotation and high quality teleseismic waveform doublets make the precise mapping of the topography of the inner core boundary icb possible here we examine ic refracted pkp df and reflected pkp cd waves recorded at the yellowknife array and other global stations from 14 high quality doublets among a large collection of doublets in s sandwich islands that are recently discovered our results show clear evidence for spatial and temporal variations of ic reflections in traveltimes and in waveforms if the time separation dt between the two members of the doublet is less than 3 yr the ic arrivals show little temporal change in traveltimes or waveforms if dt is greater than about 6 yr some doublets show large variations but some others do not the icb regions beneath atlantic and indian oceans show little temporal change the regions that show large variations are beneath africa and the central america which coincide with large seismic anomalies at the core mantle boundary cmb inside these two icb regions there are fine scale km scale variations the largest temporal changes of ic reflections are about 0 10 to 0 14 s corresponding to a topographic variation of up to about 3 7 to 5 2 km the results suggest icb topography of a few kilometres on fine to regional scales the geographical coincidence of the icb and cmb anomalies may suggest strong thermal coupling of the mantle and the core dynamic models include a bumpy icb rotating with the ic itself or a transient slurry boundary containing a mixture of molten materials and solidified patches of iron crystals which is rapidly modified by the turbulence at the base of the convecting outer core if the former is the main cause of the observed temporal change of the topography the ic rotation is required to be an oscillation whose half period has an upper limit of a few hundred years

convection current generated prior to rupture in saturated rocks laboratory experiments were performed to study the generation mechanism of electric signals during deformation and rupture of rock with the focus on the effects of pore water movement we have developed a triaxial apparatus that is specially designed for this purpose within the framework of the international frontier program on earthquake research of the institute of physical and chemical research riken this apparatus can deform a rock specimen that is electrically isolated from the surroundings at a very slow strain rate using a cylindrical specimen of intact rock inada granite makabe granite muroto gabbro and fujieda sandstone saturated with distilled water we carried out triaxial deformation tests under a constant pore pressure at room temperature during a deformation test we continuously measured the electric current generated in the specimen in addition local strains pore pressure and pore fluid movement from the intensifier were recorded at a sampling frequency up to 1 khz the volume change due to dilatancy was obtained from the average of the local strain measurements at four positions we found that the convection current flowed before the main fracture showing good correlation with the dilatancy rate and the water flow rate the current density of the signal was about 1 ma m2 this result demonstrated that the electric current is caused by an electrokinetic effect due to the water flow associated with accelerating evolution of dilatancy before the fracture

physical properties of the variations of the electric field of the earth preceding earthquakes i abstract in an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field the present letter clarifies a few points that were not properly emphasized in our previous publications furthermore recent results like that of the destructive kalamata earthquake on september 13 1986 indicate that the duration of a preseismic electric signal may reach considerably high values lasting up to several hours

the existence of an inner core super rotation questioned by teleseismic doublets abstract the first evidence for a differential rotation of the earth s inner core with respect to the mantle comes from the detection of a variation over 30 years of the differential travel time anomalies of seismic core phases song x richards p g 1996 seismological evidence for differential rotation of the earth s inner core nature 382 221 224 the comparison of teleseismic doublets provides a powerful means to measure such differential travel times and to test their temporal variation contrary to direct measurements of differential travel times this technique does not require to have an accurate location of the seismic events this method is first checked on examples of doublets for which no differential travel time is expected these tests allow us to point out the difficulties such as polarity reversals which may be encountered in the use of the doublet method it is then applied to deep tonga events recorded in france and to the south sandwich islands events recorded at station college col alaska which led song and richards to propose an inner core rotation for the first path we find no time variation in agreement with previous studies for the path from south sandwich island to col the doublet analysis shows that no significant temporal change in pkp travel time can be detected within the resolution of the method which is about 0 05 s the variation of the residuals observed by song and richards about 0 3 s over 30 years is in a large extent ascribable to hypocenter mislocations consequently present seismological observations do not detect the inner core differential rotation because if it exists it is smaller than about 0 2 year the present detection capacity of seismology

reconciling the hemispherical structure of earth s inner core with its super rotation earth s solid inner core grows through solidification of material from the fluid outer core onto its surface at rates of about 1 mm per year1 freezing in core properties over time and generating an age depth relation for the inner core a hemispherical structure of the inner core is well documented an isotropic eastern hemisphere with fast seismic velocities contrasts with a slower anisotropic western hemisphere2 3 4 independently the inner core is reported to super rotate at rates of up to 1 per year5 6 7 considering the slow growth steady rotation rates of this magnitude would erase frozen in regional variation and cannot coexist with hemispherical structure here we exploit the age depth relation using the largest available pkikp pkikp seismic travel time data set to confirm hemispherical structure in the uppermost inner core and to constrain the locations of the hemisphere boundaries we find consistent eastward displacement of these boundaries with depth from which we infer extremely slow steady inner core super rotation of 0 1 1 per million years our estimate of long term super rotation reconciles inner core rotation with hemispherical structure two properties previously thought incompatible it is in excellent agreement with geodynamo simulations8 9 while not excluding the possibility that the much larger rotation rates inferred earlier5 6 7 correspond to fluctuations in inner core rotation on shorter timescales10

geomagnetic secular variation we analyse over 175000 magnetic observations from an interval spanning 1695 1980 to produce a sequence of maps of the magnetic field at the core mantle boundary we find that even the earlier data enable us to determine reliable maps we produce these maps at approximately 60 year intervals through the eighteenth and nineteenth centuries and at 10 year intervals in the twentieth century this span of maps is long enough to render straightforward the distinction between static and drifting features in the field we observe that some features show no sign whatsoever of drift over the entire 285 year time interval although others drift westwards in particular we observe that the secular variation is very low beneath the pacific ocean but beneath southern africa and the south atlantic ocean we observe rapid secular variation we interpret the morphology of the static field in terms of a simple model of the dynamo and conjecture that interactions between the core and the mantle are an important element of the process as part of the static field we identify four main concentrations of flux two in each hemisphere at high latitudes these features largely account for the earth s axial dipole moment we find unequivocal evidence that magnetic flux has not remained frozen over the time span of our models much of the diffusive behaviour that we identify is associated with the formation of a pair of flux spots a core spot beneath southern africa early in this century nevertheless we are able to construct maps that satisfy a set of necessary conditions for frozen flux and use these maps to construct maps of the core surface fluid flow based on the steady flow hypothesis although we find no strong evidence against the steady flow hypothesis we do find some grounds on which to doubt the validity of the flow maps

high isotope fractionations during sulfate reduction in a low sulfate euxinic ocean analog a detailed record of the early earth sulfur s cycle is chronicled by the s isotope values of sulfide and sulfate preserved in the rock record interpretation of this record rests on our understanding of sulfur cycling in modern systems experiments and the resulting isotopic signatures very large fractionations in 34s of 70 are commonly measured between sulfide and sulfate in modern systems and in ancient sediments theoretical calculations suggest that sulfate reducing prokaryotes are capable of producing such large fractionations during the reduction of sulfate to sulfide although they have only been demonstrated to generate fractionations up to 48 here we report the first direct determination of 60 70 fractionations by natural populations of sulfate reducers these high fractionations occur under the relatively low sulfate conditions 1 1 2 mm of meromictic lago di cadagno in switzerland the major and minor isotopic composition of sulfide and sulfate in the lake water is consistent with sulfide produced by sulfate reduction with little evidence for modification by further oxidative sulfur cycling these observations help us to constrain the evolution of seawater sulfate concentrations

the inner inner core of the earth texturing of iron crystals from three dimensional seismic anisotropy abstract we present a three dimensional model of the seismic anisotropy and texturing of iron crystals in the inner core the form of the anisotropy changes suddenly at slightly less than half of the inner core radius the outer part is composed of iron crystals of a single phase with different degrees of preferred alignment along the spin axis of the earth the inner part may be composed of a different phase of crystalline iron or have a different pattern of alignment

inner core rotation from event pair analysis abstract the last decade has witnessed an animated debate on whether the inner core rotation is a fact or an artifact here we examine the temporal change of inner core waves using a technique that compares differential travel times at the same station but between two events the method does not require precise knowledge of earthquake locations and earth models the pairing of the events creates a large data set for the application of statistical tools using measurements from 87 events in the south sandwich islands recorded at college alaska station we conclude the temporal change is robust the estimates of the temporal change range from about 0 07 to 0 10 s decade over the past 50 yr if we used only pairs with small inter event distances which reduce the influence of mantle heterogeneity the rates range from 0 084 to 0 098 s decade nearly identical to the rate inferred by zhang et al zhang j song x d li y c richards p g sun x l waldhauser f inner core differential motion confirmed by earthquake waveform doublets science 309 5739 2005 1357 1360 from waveform doublets the rate of the df change seems to change with time which may be explained by lateral variation of the inner core structure or the change in rotation rate on decadal time scale

using pre critical pkikp pcp phases to constrain the regional structures of the inner core boundary beneath east asia abstract we collected 177 pre critical pkikp pcp records assembling a wealth of traveltime and amplitude data these observations sample the inner core boundary icb beneath east asia with good spatial coverage combined with previous studies our results demonstrate a 100 km wide anomaly with positive pkikp pcp traveltime residuals surrounded by negatives beneath the yellow sea area 123 e 33 n yellow sea anomaly after correcting the elliptic effects and mantle vp heterogeneities based on the tomography models the residuals of the yellow sea anomaly remain at least 0 6 s faster than those of the surrounding areas suggesting a thickening of 2 3 km between the icb and core mantle boundary cmb due to the negative cmb topography along the western pacific rim we attribute this anomaly mainly to negative icb topography across the northern border of the yellow sea anomaly pkikp pcp amplitude ratios increase by approximately 50 from north to south which can be explained by an approximately 0 6 g cm3 raise in icb density contrast these traveltime and amplitude features suggest a mosaic structure at the icb beneath the yellow sea areas

the shuffling rotation of the earth s inner core revealed by earthquake doublets earth s inner core rotates at a different rate than the mantle and discrepancies exist between rotation rates derived from geophysical observations and geodynamical simulations an inverse analysis of seismic data from repeating earthquakes over the past 50 years suggests that the rotation rate of the inner core fluctuates on decadal timescales