relative paleointensity in sediments a pseudo thellier approach we present a method for normalizing sedimentary records for estimating relative paleointensity of the geomagnetic field similar to that successfully used to obtain absolute paleointensity from thermally blocked remanences it has the advantages that it is more effective in removing unwanted viscous remanence thereby improving agreement among various records and that it allows the estimation of the uncertainty in the relative paleointensity calculated

inference of postseismic deformation mechanisms of the 1923 kanto earthquake 1 coseismic slip associated with the m7 9 1923 kanto earthquake is fairly well understood involving slip of up to 8 m along the philippine sea honshu interplate boundary under sagami bay and its onland extension postseismic deformation after the 1923 earthquake however is relatively poorly understood we revisit the available deformation data in order to constrain possible mechanisms of postseismic deformation and to examine the consequences for associated stress changes in the surrounding crust data from two leveling lines and one tide gage station over the first 7 8 years postseismic period are of much greater amplitude than the corresponding expected interseismic deformation during the same period making these data suitable for isolating the signal from postseismic deformation we consider both viscoelastic models of asthenosphere relaxation and afterslip models a distributed coseismic slip model presented by pollitz et al 2005 combined with prescribed parameters of a viscoelastic earth model yields predicted postseismic deformation that agrees with observed deformation on mainland honshu from tokyo to the izu peninsula elsewhere southern miura peninsula boso peninsula the considered viscoelastic models fail to predict observed deformation and a model of 1 m shallow afterslip in the offshore region south of the boso peninsula with equivalent moment magnitude mw 7 0 adequately accounts for the observed deformation using the distributed coseismic slip model layered viscoelastic structure and a model of interseismic strain accumulation we evaluate the post 1923 stress evolution including both the coseismic and accumulated postseismic stress changes and those stresses contributed by interseismic loading we find that if account is made for the varying tectonic regime in the region the occurrence of both immediate first month post 1923 crustal aftershocks as well as recent regional crustal seismicity is consistent with the predicted stress pattern this suggests that the influence of the 1923 earthquake on regional seismicity is fairly predictable and has persisted for at least seven decades following the earthquake

evolution of the geomagnetic field prior to the matuyama brunhes transition radiometric dating of a 820 ka excursion at la palma we present cassignol technique k ar dating of lava flows from la palma canary islands spain that bracket the matuyama brunhes transition an age of 821 13 ka obtained for a transitionally magnetized flow ls118 provides the first volcanic evidence for a geomag netic excursion occurring about 40 kyr prior to the transition this interval has been successfully correlated with intensity minima present in high resolution deep sea records before the matuyama brunhes transition this study along with the growing number of well dated excursions reported for the brunhes and matuyama chrons shows that the occurrence of excursions is a common feature of the evolution of the geomagnetic field during stable polarity intervals however the presence of two successive excursional states within 40 kyr prior to the actual reversal conjugated with moderate averaged palaeointensity in this interval as deduced from deep sea records could suggest that favorable conditions for the reversal to occur existed since about 820 ka the present study highlights the importance of detailed chronological constraints for our understanding of the transition of the geomagnetic field from a stable polarity to a reversal state

mantle flow in subduction systems the subslab flow field and implications for mantle dynamics 1 the character of the mantle flow field in subduction zones remains poorly understood despite its importance for our understanding of subduction dynamics in particular little attention has been paid to mantle flow beneath subducting slabs in order to identify processes that make first order contributions to the global pattern of subslab mantle flow we have compiled shear wave splitting measurements from subduction zones worldwide from previously published studies and estimated average splitting parameters for the subslab region globally the subslab region is overwhelmingly dominated by trench parallel fast splitting directions we tested for relationships between splitting delay time a measure of the strength of anisotropy and parameters that are indicators of tectonic processes such as trench migration velocity convergence velocity and obliquity age of subducting lithosphere and slab dip curvature seismicity and thickness we used several different plate motion models to describe plate and trench motions and evaluated the differences among the models we find that only one parameter namely the trench migration velocity in a pacific hot spot reference frame appears to correlate well with the strength of the subslab splitting signal this finding supports a model in which the mantle beneath subducting slabs is dominated by three dimensional flow induced by trench migration we explore several implications of our model for various aspects of mantle dynamics including the choice of a suitable reference frame s for mantle flow the existence of a thin decoupling zone between slabs and the subslab mantle and consequences for mass transfer between the upper and lower mantle

rapid rotation of southwest japan palaeomagnetism and k ar ages of miocene volcanic rocks of southwest japan summary miocene volcanic rocks have been sampled from the san in district in the central part of southwest japan reliable palaeomagnetic direction and k ar dating data have been obtained from 28 localities a clockwise deflection in declination d 38 5 is observed in the kawai formation having an age of 16 1 1 4 ma whereas a northerly declination is observed in formations younger than 14 2 0 6 ma these data indicate that southwest japan had ceased rotational motion by about 14 ma when compared with the amount of rotation estimated from cretaceous palaeomagnetic data it is apparent that more than 80 per cent of the overall clockwise rotation occurred between about 16 and 14 ma we conclude that the angular velocity of southwest japan about a rotation pole at 129 e 34 n reached 20 myr 1 at about 15 ma the corresponding rate of linear motion of the eastern part of southwest japan was 21 cm yr 1

reconstructing recent relative sea level changes in west greenland local diatom based transfer functions are superior to regional models we present the results of an investigation into the potential of salt marshes in the aasiaat area west greenland for recent relative sea level rsl reconstruction we use 64 modern diatom samples to develop a transfer function that has a rmsep of 0 16 m and an r2 of 0 84 we combine these with a similar data set from sisimiut 250 km south of aasiaat standardising the data to account for tidal range differences an aasiaat sisimiut and a combined model is used to reconstruct rsl change from two recently deposited sediment sections all three models predict similar rsl change for sediment deposited in low marsh settings but for sediment deposited in high marsh environments the models differ our preferred aasiaat model reconstructs rsl rise from c 0 6 m at c 570 cal yr bp to stabilise within 0 20 m of present after 400 cal yr bp model differences are related to variations in the high marsh upland vegetation zones diatom assemblages and organic content between sites that are likely related to differences in tidal range we conclude that a local transfer function model is superior to a combined site model for rsl reconstruction in west greenland

the 1995 kobe japan earthquake a long delayed aftershock of the offshore 1944 tonankai and 1946 nankaido earthquakes the 1995 kobe earthquake produced predominantly right lateral slip along the northeast southwest trending nojima fault approximately 200 km landward of the nankai trough southwest japan the last major earthquakes along the nankai trough the m 8 0 1944 tonanakai and m 8 2 1946 nankaido earthquakes involved about 4 m of interplate slip each releasing about 100 years of accumulated stress from the northwest southeast convergence of the philippine sea phs plate by calculating the change in coulomb failure stress on the nojima fault due to 1944 46 to 1995 postseismic relaxation of a thin low viscosity channel beneath southwest japan we show that stress diffusion from the 1940s interplate earthquakes increased the likelihood of future failure on the nojima fault by slowly but progressively unloading the normal stress on the fault over a 50 yr period

holocene environmental variability in southern greenland inferred from lake sediments abstract sediments from qipisarqo lake provide a continuous holocene paleoenvironmental record from southern greenland following deglaciation and glacio isostatic emergence of the basin from the sea 9100 cal yr b p proxies of lake paleoproductivity including biogenic silica and organic matter increased markedly until 6000 cal yr b p and thereafter remained stable over the ensuing warm three millennia subsequent decreases in these proxies most dramatically between 3000 and 2000 cal yr b p show the lake s responses to initial neoglacial cooling intervals of ameliorated limnological conditions occurred between 1300 and 900 and between 500 and 280 cal yr b p briefly interrupting the decreasing trend in productivity that culminated in the little ice age increased lake productivity during the latter half of the 20th century which reflects the limnological response to circum arctic warming still has not reached peak holocene values the neoglacial climate of the last 2000 yr includes the most rapid high amplitude environmental changes of the past nine millennia the norse thus migrated around the north atlantic ocean region in the most environmentally unstable period since deglaciation lacustrine sediment records provide a context with which to consider future environmental changes in the labrador sea region in particular any future warming will be superposed on a regional climate system that is currently exhibiting highly unstable behavior at submillennial timescales

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

early holocene history of the west greenland ice sheet and the gh 8 2 event abstract the margin of the greenland ice sheet retreated rapidly during the first few thousand years of the holocene during this period of relative warmth known as the holocene thermal maximum ice core records identify a significant short lived cooling event at approximately 8 4 8 0 ka cal yr bp the gh 8 2 event associated with a 5 7 c fall in mean annual air temperature over the centre of the ice sheet in this paper we constrain the history of the ice sheet margin in disko bugt west greenland and that of a major ice stream jakobshavns isbrae during the early holocene which incorporates the interval of the gh 8 2 event our work is based on a new relative sea level curve and minimum age estimates for the timing of deglaciation from two field sites combined with a review of previously published research from the study area we identify important differences in the chronology of ice margin recession during the early holocene most noticeably the margin of jakobshavns isbrae retreated well inland of the adjacent ice sheet at this time we conclude that the early holocene fjord stade moraines in disko bugt do not record a uniform ice sheet margin response to the gh 8 2 event rather these moraines are diachronous and formed between c 10 8 ka cal yr bp their age varying as a function of the interplay between topography and ice sheet ice stream dynamics we hypothesise that one cause for the lack of an identifiable response to the gh 8 2 event is because topographic controls dominated ice sheet behaviour at this time in lowland areas any increase in ice sheet mass balance was probably associated with an increase in calving rather than any major advance of a grounded ice sheet margin

holocene climate changes in southern greenland evidence from lake sediments a holocene lake sediment record is presented from lake n14 situated on angissoq island 15 km off the main coast of southern greenland the palaeoclimatic development has been interpreted on the basis of flux and percentage content of biogenic silica clastic material organic material and sulphur as well as sedimentation rate moss content and magnetic susceptibility a total of 43 radiocarbon dates has ensured a reliable chronology it is argued that varying sediment composition mainly reflects changing precipitation by analogy with the present meteorological conditions in southern greenland holocene climate development is inferred between 11550 and 9300 cal yr bp temperature and precipitation increase markedly but this period is climatically unstable from 9300 yr bp conditions become more stable and a holocene climatic optimum characterised by warm and humid conditions is observed from 8000 to 5000 cal yr bp from 4700 cal yr bp the first signs of a climatic deterioration are observed and from 3700 cal yr bp the climate has become more dry and cold superimposed on the climatic long term trend is climate variability on a centennial time scale that increases in amplitude after 3700 cal yr bp a climatic scenario related to the strength and position of the greenland high pressure cell and the iceland low pressure cell is proposed to explain the holocene centennial climate variability a comparison of the lake n14 record with a terrestrial as well as a marine record from the eastern north atlantic ocean suggests that the centennial climate variability was uniform over large areas at certain times less

late holocene atlantic bottom water variability in igaliku fjord south greenland reconstructed from foraminifera faunas a high resolution record of late holocene subsurface water mass characteristics in outer igaliku fjord south greenland is presented based on benthic foraminifera faunas from core po 243 451 collected from a water depth of 304 m strati cation with atlantic water masses present in the lower part of the water column is suggested to have prevailed during the last 3200 cal years except for a period referred to as the mediaeval warm period mwp during the mwp c ad 885 1235 the outer part of igaliku fjord experienced enhanced vertical mixing and a high hydrodynamic energy level which we ascribe to increasing wind stress through this period corresponding to the period of the norse settlement the transition from the mwp to the little ice age lia shows a two step pattern with a short climatic amelioration around ad 1520 before maximum cooling occurred the intensified wind stress and the overall environmental change are suggested to have contributed to the loss of the norse settlement in greenland periods with strong stratification and marked in uence of atlantic subsurface water masses around 2 6 1 3 ka bp and during the lia are correlated to north atlantic holocene ice rafting events reported by bond et al 1997

greenland gisp2 ice core and historical indicators of complex north atlantic climate changes during the fourteenth century the paper uses greenland gisp2 ice core data together with historical documentary information to investigate the nature of climate changes that took place between ad 1270 and 1450 across the north atlantic region detailed deuterium and deuterium excess time series resolved to c 8 10 samples per year are used to reconstruct relative changes in greenland air temperature and past changes in sea surface tem perature across the western north atlantic the data show that sea surface temperatures during the late thirteenth century and the majority of the fourteenth century were characterized by relatively high amplitude warming and cooling events these changes preceded a marked reduction in the amplitude of the sea surface temperature changes c 30 40 years before the well known change in northern hemisphere tropospheric circulation characterized by a marked increase in regional storminess that started between c ad 1400 and 1420 the time interval between ad 1270 and 1450 also appears over greenland to have fea tured several short lived phases of marked air temperature lowering that were rarely ever equalled during succeeding centuries we believe that the climate changes described here are of considerable importance in understanding climate dynamics of the north atlantic region since they took place at a time when the north atlantic oscillation nao may have been weak the results also show that the marked change in atmospheric circulation coincident with a significant increase in north atlantic storminess at c ad 1400 1420 possibly the biggest such change in the holocene took place after the strong perturbations in north atlantic sea surface temperature both warming and cooling described here as well as after several episodes of air temperature lowering over greenland

viscoelastic postseismic rebound from strike slip earthquakes in regions of oblique plate convergence according to the slip partitioning concept the trench parallel component of relative plate motion in regions of oblique convergence is accommodated by strike slip faulting in the overriding continental lithosphere the pattern of postseismic surface deformation due to viscoelastic flow in the lower crust and asthenosphere following a major earthquake on such a fault is modified from that predicted from the conventional elastic layer over viscoelastic half space model by the presence of the subducting slab the predicted effects such as a partial suppression of the postseismic velocities by 1 cm yr or more immediately following a moderate to great earthquake are potentially detectable using contemporary geodetic techniques

11 million years of oligocene geomagnetic field behaviour summary an 11 million year long record of the oligocene geomagnetic field has been obtained from pelagic sediments of dsdp hole 522 an average sample spacing of 4 cm yielded approximately one specimen per 4 to 8 kyr the rock magnetics are remarkably consistent across the entire interval previous work demonstrated a magnetic mineralogy dominated by magnetically stable magnetite the natural remanent magnetism nrm carries an oligocene polarity timescale that is in excellent agreement with the oligocene reversal record as determined from marine magnetic anomalies mmas including many of the so called crypto chrons normalized nrm intensities from the undisturbed portions of the record yield a time series of variations with features consistent with a number of other palaeointensity time series derived from both sedimentary and lava sequences these features include consistent major decreases in palaeointensity dips at reversal boundaries and occasional dips between reversal boundaries that could correspond to lineated tiny wiggles in the mma records the data set suggests that the overall field strength was 40 per cent higher in the first half of the oligocene when the average reversal frequency was 1 6 myr l than in the second half when the reversal frequency was 4myr there is also a weak dependence of average field strength on length of polarity interval finally in the three cores suited to spectral analysis of coherent polarity and relative intensity independent of lithological contamination there is a persistent ca 30 50 ka periodicity in the variations of the relative intensity suggesting that the geomagnetic field pulses at about this frequency not only during the brunhes as demonstrated by tauxe shackleton 1994 but in the oligocene as well

diagnostic study of the fram strait marginal ice zone during summer from 1983 and 1984 marginal ice zone experiment lagrangian observations from 1984 marginal ice zone experiment observations in fram strait three main results concerning large scale mesoscale and summer marginal ice zone miz features are presented and discussed in this paper regarding the large scale the main conclusion is that the east greenland current egc is a narrow stable current in contradiction with past results presenting the egc as a broad and unstable current in the mesoscale the west spitsbergen current wsc and the norwegian current are the main generators for eddies in fram strait these eddies propagate northwestward preferentially following topographic features like fracture zones which are quite abundant in this region in our opinion these wsc eddies represent an important part of the atlantic water recirculation in fram strait when approaching the east greenland continental slope they interact with the egc and they form well developed eddies these ice edge eddies associated with ice edge tongues are quite recognizable with remote sensing techniques the summer marginal ice zone in fram strait is clearly characterized by sea ice concentrations from 1 10 to 3 10 and floe sizes limited to 1 km or less there is a well defined limit which separates the pack ice from the miz where no big ice floes are ever recorded the breaking action of waves and swell propagating into the ice are likely to be the only mechanisms explaining such a drastic filtering effect according to their amplitudes and directions winds and eddies act in the miz in shrinking or stretching this zone

persistent positive north atlantic oscillation mode dominated the medieval climate anomaly the medieval climate anomaly mca was the most recent pre industrial era warm interval of european climate yet its driving mechanisms remain uncertain we present here a 947 year long multidecadal north atlantic oscillation nao reconstruction and find a persistent positive nao during the mca supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker nao conditions into the little ice age lia globally distributed proxy data suggest that this nao shift is one aspect of a global mca lia climate transition that probably was coupled to prevailing la nina like conditions amplified by an intensified atlantic meridional overturning circulation during the mca

relative sea level change in west greenland during the last millennium relative sea level rsl data provide important long term century to millennial scale constraints on ice load history in greenland in this paper we present the results of a litho bio and chronostratigraphic study designed to reconstruct rsl during the last millennium from salt marsh deposits recovered from a field site near to the town of sisimiut west greenland the stratigraphy at three marshes typically records an upwards transition from freshwater to salt marsh deposits we use a quantitative transfer function and subjective model to reconstruct palaeomarsh elevation and changes in mean tide level mtl from 16 sediment profiles from these marshes these palaeomarsh elevations are placed in a chronological framework established by 18 radiocarbon dated index points both models yield similar results and show mtl rose from 0 60 0 20 m at c 600 cal a bp to reach 0 10 0 20 m at c 400 cal a bp after this time mtl remained close to present 0 20 m until the present day although low sedimentation rates limit the resolution of our reconstructions during this interval the initial rise in rsl can be explained by the dominance of non greenland processes notably the collapse of the laurentide forebulge over local greenland solid earth uplift caused by postglacial ice unloading this is despite some reloading of the crust that occurred during the neoglacial expansion of the greenland ice sheet in this part of west greenland the slow down in rsl at 400 cal a bp does not record either a change in the rate of laurentide forebulge collapse or a change in eustatic sea level we argue instead that this slow down records the effects of a sustained reduction in local greenland ice mass that persists over most of the past 400 years the latter interval is widely acknowledged as a period of generally cooler than present conditions associated with the later stages of the little ice age during this period field evidence suggests that in many areas the ice sheet had reached its maximum late holocene extent it is not obvious at this stage how to reconcile an expanding ice sheet with a reduction in ice load during this interval although we hypothesise it could reflect one or more of i a change in ice sheet dynamics ii reduced mass accumulation caused by cold and dry conditions and iii a lagged response to earlier periods of climate warming

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

asymmetrical saw tooth pattern of the geomagnetic field intensity from equatorial sediments in the pacific and indian oceans abstract a record of relative paleointensity from marine sediments in the equatorial indian ocean spanning the last 4 ma completes a previous dataset from ocean drilling program odp leg 138 sites in the equatorial pacific 1 the timescale was defined with a precision better than 20 kyr with different and independent methods most of the features present in the record from the equatorial pacific are confirmed the overall saw tooth pattern is observed across every field reversal and the short term fluctuations superimposed on the slow intensity decrease preceding the reversals appear to be similar at both sites the global character of these features reinforces their interpretation in terms of changes in dipole field intensity and provides new important constraints on models of the geodynamo a synthetic curve of field intensity changes during the last 4 ma is proposed as a first paleointensity timescale for future stratigraphic studies

postseismic deformation and stress diffusion due to viscoelasticity and comments on the modified elsasser model finite element techniques have been used to investigate the far field deformation and stress changes due to asthenospheric viscoelastic relaxation following a dip slip earthquake the diffusion of extensional stress toward the subduction zone following a thrust earthquake on land is qualitatively consistent with the modified elsasser model as proposed by rydelek and sacks 1988 1990 to explain the coupled occurrence of land and sea earthquakes near japan however the magnitude of the diffusing tensional signal is significantly smaller the nominal model consists of a partially faulted elastic lithosphere overlying a viscoelastic substrate other models consider thin channel flow rupturing of the entire elastic lithosphere and changes in the depth of faulting while some of these changes have significant impact on the magnitude and spatial features of the stress and deformation field the far field stress remains small numerical experiments demonstrate that the assumptions of the modified elsasser model accentuate uniaxial deformation when these assumptions are replicated in the finite element calculations reasonable agreement between the models is achieved

can heterogeneous core mantle electromagnetic coupling control geomagnetic reversals abstract an analytical model is developed for the electromagnetic torques exerted on the mantle by the poloidal magnetic field of the core interacting with a laterally heterogeneous conducting layer at the base of the mantle torques due to changes in both orientation and intensity of a dipolar poloidal field are included contrary to earlier suggestions our calculations predict that the trajectory of the magnetic pole during a polarity reversal is not strongly affected by heterogeneity in mantle electrical conductivity

salt marshes as archives of recent relative sea level change in west greenland abstract temperate latitude salt marshes are a proven environment from which high precision 0 10 0 20 m relative sea level rsl records can be developed over recent decades and centuries such records provide an important link between millennial histories of rsl change and instrumental records the high latitude salt marshes in greenland have not previously been explored as potential archives of recent rsl change here we develop four diatom based transfer functions using contemporary diatom data collected from three salt marshes located 40 km south of the coastal town of sisimiut west greenland our preferred model has a good fit between observed and predicted elevations r 2 0 94 and a root mean square error prediction of 0 19 m we apply the four models to a short sediment profile collected from one of the marshes that formed between c 600 cal year bp and the present three of the four models predict the same trend in which rsl rose from 0 55 0 19 m mean tide level mtl to 0 05 0 19 m mtl between c 600 and 400 cal year bp at a rate of c 2 7 mm year 1 after 400 cal year bp rsl slowed and remained stable until the present day the results of this study demonstrate that greenland salt marshes are potentially valuable archives of data for developing quantitative estimates of rsl change during the last few centuries thereby bridging the gap between existing millennial scale approaches and more recent direct observations of ice sheet behaviour and associated vertical land motions

detailed paleomagnetic study of two volcanic polarity transitions recorded in eastern iceland abstract two sequences of 45 and 49 individual lava flows respectively have been sampled in eastern iceland the two sections range in age from 12 09 to 10 21 ma as reported by watkins and walker watkins n walker g p l 1977 magnetostratigraphy of eastern iceland am j sci 277 513 584 and are labelled as profiles c and d stepwise alternating field af and thermal demagnetizations accompanied by investigations of rock magnetic properties indicate that the magnetization is primarily carried by titanomagnetite demagnetization experiments have identified eight and six transitional lavas respectively for these profiles the transitional virtual geomagnetic poles vgps of the r n profile c reversal are located mainly between patagonia and antarctica with a tendency of the virtual poles to move towards west coast of south america subsequently traveling to the northern hemisphere through several discrete steps located in the middle part of south america then to west africa and on to central asia before the poles settle into normal polarity the second and younger vgp path corresponding to profile d is a path characterized by a reverse to normal to reverse r n r motion of the virtual poles this path is characterized by poles located in west antarctica patagonia and the western and eastern part of south america the passage from the southern to the northern hemisphere is also through a discrete sets of steps along the southwestern pacific followed by a rapid motion to the northern siberian region continuing to the western equatorial part of south america before moving on to the central region of asia followed by a motion to the western pacific prior to the final move to the eastern part of antarctica the data from eastern iceland based on highly reliable transitional results as indicated by the demagnetizations and rock magnetic experiments derived from relatively spaced sites and different ages seem to indicate that the eastern icelandic high latitude 66 n profiles studied have several persistent transitional paleofield features that are uniquely observed at those sites particularly when compared to other volcanic records located at lower latitudes

gravitational viscoelastic postseismic relaxation on a layered spherical earth viscoelastic relaxation of a ductile asthenosphere underlying a purely elastic plate is a strong candidate process for explaining anomalous rates of crustal deformation observed following large earthquakes the nongravitational treatment of pollitz 1992 which is valid on a global scale and includes the effects of compressibility is here extended to permit the calculation of gravitational viscoelastic relaxation for a specified spherically layered viscoelastic rheology following an earthquake in an elastic layer the simple approximations we adopt make the resulting treatment particularly suitable for near field calculations for an asthenosphere with a maxwell rheology the effect of gravitational coupling is manifested only many relaxation times after the earthquake as obtained by previous investigators its effect is generally to speed up the long wavelength component of the relaxation process and attenuate the overall vertical displacement pattern several subtle features common to the relaxation behavior from several different fault types thrust rift and strike slip are identified the effect of gravitational coupling on horizontal displacements is consistent with flexure of the upper elastic plate driven by the corresponding effects on the vertical displacement stress diffusion away from the source region generally exhibits pulse like behavior which is dispersive in both space and time if the asthenosphere is confined to a relatively narrow channel then the dispersion branches governing relaxation are radically altered and stress diffusion effects far from the coseismic rupture zone exhibit a complicated time dependence reflecting the competing tendencies of toroidal and spheroidal mode relaxation

inelastic models of lithospheric stress 11 implications for outer rise seismicity and dynamics summary outer rise seismicity and dynamics are examined using inelastic models of lithospheric deformation which allow a more realistic characterization of stress distributions and failure behaviour we conclude that thrust and normal faulting outer rise earthquakes represent substantially different states of stress within the oceanic lithosphere specifically the normal faulting events occur in response to downward plate bending which establishes the standard bending dominated state of outer rise stress and the thrust faulting events occur in response to an elevated level of in plane compression which develops only in response to exceptional circumstances this interpretation accounts for the observation that normal faulting outer rise earthquakes occur more frequently and are more widely distributed than their thrust faulting counterparts an observation for which the simple bending model offers no explanation in addition attributing both thrust and normal faulting outer rise earthquakes to plate bending implies that both classes of events should occur within relatively close lateral proximity to one another because both are allegedly a manifestation of the same bendingdominated stress distribution whereas in reality this is not observed we propose that the tendency for thrust faulting outer rise earthquakes to exhibit greater source depths than their normal faulting counterparts an observation that is frequently cited in support of the bending interpretation of the former is merely a consequence of the fact that bending induced tension is confined to the upper lithosphere our model predicts that outer rise in plane force variations may promote thrust faulting outerrise activity prior to an underthrusting interplate subduction earthquake and normalfaulting outer rise activity following such an earthquake but that both forms of outerrise activity are unlikely to be associated with the same subduction earthquake a corollary implication of our model is that subduction earthquakes are likely to be either preceded by or followed by an absence of large outer rise earthquakes levels of in plane compression necessary to generate thrust faulting outer rise earthquakes are attributed to stress concentrations within the subducting plate that are induced by relatively localized resistance to regionally distributed plate driving forces resistance of this nature may result from either the attempted subduction of relatively buoyant i e isostatically compensated bathymetric features or the existence of strong interplate

deuterium excess record from central greenland over the last millennium hints of a north atlantic signal during the little ice age a stacked water isotope record for summit central greenland has been established covering approximately the last 900 years measurements of 18o and d in the grip deep ice core and the 230 m core s93 allow the reconstruction of a millennial record of the deuterium excess in a near annual resolution a short period of particularly high values of the deuterium excess at the beginning of the fourteenth century may be associated with the medieval warm period mwp the little ice age lia might be represented by a 100 year period of very low excess values in the sixteenth and seventeenth centuries using a simple isotope model 18o and deuterium excess are interpreted in terms of surface temperature variations over central greenland and over the subtropical north atlantic greenland s principal vapor source region an estimated cooling of 0 7 c of subtropical sea surface temperatures ssts during the little ice age and a warming of 0 6 c during the short warm period in the medieval is in agreement with previous studies over periods of about 100 years an antiphasing between gradually decreasing 18o and increasing deuterium excess is observed interannual to decadal scale variability associated to the north atlantic oscillation may be responsible for this anti phase relationship an alternative explication is a north south oscillation in north atlantic sea surface temperatures associated with short term changes in the thermohaline circulation

viscosity of oceanic asthenosphere inferred from remote triggering of earthquakes a sequence of large interplate earthquakes from 1952 to 1965 along the aleutian arc and kurile kamchatka trench released accumulated stresses along nearly the entire northern portion of the pacific plate boundary the postseismic stress evolution across the northern pacific and arctic basins calculated from a viscoelastic coupling model with an asthenospheric viscosity of 5 x 10 17 pascal seconds is consistent with triggering of oceanic intraplate earthquakes temporal patterns in seismicity at remote plate boundaries and space based geodetic measurements of anomalous velocity over an area 7000 by 7000 kilometers square during the 30 year period after the sequence

asthenospheric viscosity inferred from correlated land sea earthquakes in north east japan the viscosity of the earth s mantle has been estimated from studies of post glacial rebound1 2 post seismic deformations of the ground following large earthquakes3 4 and aftershock sequences5 7 here we derive a value for the viscosity of the asthenosphere from a correlation found in the historical catalogue of subduction induced seismicity between the intraplate land and interplate sea earthquakes in north east japan the correlation persists since the time of reliably reported earthquakes in ad 1600 land events precede sea events by 36 yr with a mean distance between land sea pairs of 200 km because of the visocoelastic coupling of the lithosphere to the asthenosphere a plausible mechanism to explain the correlation is stress migration governed by the viscosity of the asthenosphere large land shocks generate diffuse like stress pulses which sweep past and unlock the thrust fault in the subduction zone thus triggering the sea events the correlation time and distance provide a measure of the speed of diffusion 5 6 km yr 1 and hence an estimate of the viscosity 7 1018 pa s

new observations on the relative sea level and deglacial history of greenland from innaarsuit disko bugt relative sea level rsl data derived from isolation basins at innaarsuit a site on the south shores of the large marine embayment of disko bugt west greenland record rapid rsl fall from the marine limit ca 108 m at 10 300 9900 cal yr b p to reach the present sea level at 3500 cal yr b p since 2000 cal yr b p rsl rose ca 3 m to the present when compared with data from elsewhere in disko bugt our results suggest that the embayment was deglaciated later and more quickly than previously thought at or slightly before 10 300 cal yr b p the northern part of disko bugt experienced less rebound ca 10 m at 6000 cal yr b p compared with areas to the south submergence during the late holocene supports a model of crustal down warping as a result of renewed ice sheet growth during the neoglacial there is little evidence for west to east differences in crustal rebound across the southern shores of disko bugt

large earthquake occurrence affected by small stress changes abstract many observations suggest that relatively small changes in stress may trigger or inhibit earthquakes this result is surprising because the perturbing stress is only a small fraction of the stress drop from the affected earthquake we investigate this phenomenon by simulating the earthquake fault with a numerical model that is physically realistic a fault is not homogeneous and therefore the failure criteria will vary over the surface of the fault we model fault heterogeneity as simple coulomb failure on smaller but mostly uniform areas that comprise the fault as a result of multiple and repeated failures over these small areas the fault can have a very uneven stored stress we show that it is possible for small changes in confining stress of a few tenths of a bar to advance or retard the occurrence of large earthquakes by decades because such stress changes can be generated by nearby earthquakes and over much longer time scales by postseismic strain diffusion from large distant earthquakes estimates of the probabilities of earthquake occurrence must take into account these stress perturbations in order to be reliable

hydrography and climate of the last 4400 years in a sw greenland fjord implications for labrador sea palaeoceanography a multiproxy record including benthic foraminifera diatoms and xrf data of a marine sedi ment core from a sw greenland fjord provides a detailed reconstruction of the oceanographic and cli matic variations of the region during the last 4400 cal years the lower part of our record represents the final termination of the holocene thermal maximum after the onset of the neoglaciation at approxi mately 3 2 ka cal bp the fjord system was subject to a number of marked hydrographical changes that were closely linked to the general climatic and oceanographic development of the labrador sea and the north atlantic region our data show that increased advection of atlantic water irminger sea water from the west greenland current into the labrador sea was a typical feature of northeast atlantic cool ing episodes such as the little ice age and the european dark ages while the advection of irminger sea water decreased significantly during warm episodes such as the mediaeval warm period and the roman warm period whereas the mediaeval warm period was characterized by relatively cool climate as suggested by low meltwater production the preceding dark ages display higher meltwater runoff and consequently warmer climate when compared with european climate these regional climate anomalies indicate persisting patterns of advection of colder respectively warmer air masses in the study region dur ing these periods and thus a long term seesaw climate pattern between west greenland and europe

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

triggering and inhibition of great japanese earthquakes the effect of nobi 1891 on tonankai 1944 nankaido 1946 and tokai abstract there are two unusual features of the most recent great earthquakes off southwest honshu the tonankai and nankaido earthquakes were relatively early compared to the historical record of past occurrence and the tokai section of the tonankai fault did not fail in 1944 whereas it probably had for the previous 1000 years we show that both phenomena can be explained by postseismic strain diffusion from the great nobi japan earthquake m 8 0 in 1891 it is believed to have produced stress changes that influenced the time of occurrence of the great tonankai m 7 9 and nankaido m 8 0 earthquakes in the mid 1940 s the pattern of long term viscoelastic deformation following the nobi earthquake suggests that the failure threshold was reduced in the southwest section of the nankai trough which may have acted to trigger the tonankai and nankaido events in contrast the threshold was increased in the eastern tokai section of the thrust zone and therefore failure of this section may have been inhibited we model fault failure and show that the stress levels from nobi are adequate to account for the advance of tonankai and the inhibition of tokai

surface melt area variability of the greenland ice sheet 1979 2008 the surface melt area time series 1979 2008 of the greenland ice sheet gris shows large spatio temporal variability the overall melt area time series is characterized by a step like increase in 1995 the melt area trend for the entire ice sheet between 1979 1994 is 7 64 10 3 4 79 x 10 3 km 2 year which is 8 times higher than the period between 1995 2008 9 64 x 10 2 1 10 10 4 km 2 year this step like increase of melt area in 1995 coincides well with mean summer air temperature patterns at 8 coastal sites we find that the melt area and temperature change in 1995 both coincide to a general sign reversal in the north atlantic oscillation nao index in 1995 we also find that the northerly sectors of the ice sheet do not clearly coincide with changes in the nao suggesting the influence of nao is being felt predominantly on the central eastern and central western sectors of the ice sheet

a tensile flexural model for the initiation of subduction we argue that subduction may be initiated at passive continental margins without shortening the lithosphere overcoming the lithosphere s high compressive strength requires special circumstances and these make it difficult to explain the nearly complete recycling of old sea floor instead we present a model that predicts tensile decoupling of the continental and oceanic lithosphere passive rifting and foundering of the seafloor beneath material welling up in the rift this occurs because the lithosphere in a new ocean basin establishes mechanical continuity with the continent at a depth comparable to mid ocean ridges later subsidence at the margin is therefore inhibited by flexure which implies shear stresses that promote fault slip and tensile stresses necessary to balance the component of the plate s weight directed down the margin slope we show that this tension can more than offset ridge push in our model an important additional tension arises from basal shear tractions resisting the plate s motion away from the mid ocean ridge although these tractions cannot be evaluated with confidence slip on a high angle fault decouples the oceanic and continental lithosphere when shear stresses arising from flexure and the applied tension exceed the lithosphere s shear strength under these loads a passive rift then forms allowing a mantle column to rise to the height of mid ocean ridges over 3 km above the old seafloor and flow onto the surface in a gravity current this load flexes the plate downwards which enhances the flow and lets the old oceanic lithosphere founder this model is consistent with the presence of oceanic material in continental forearcs and the youth of ophiolites when they are obducted as both might be explained by rifting a margin and underthrusting the juvenile crust formed there boninites in ophiolite complexes and tectonites at their bases show depleted and hydrated geochemistries consistent with the melting of rifted mantle lithosphere that receives volatiles from foundering oceanic crust

stress triggering of the 1999 hector mine earthquake by transient deformation following the 1992 landers earthquake the m 7 3 june 28 1992 landers and m 7 1 october 16 1999 hector mine earthquakes california both right lateral strike slip events on nnw trending subvertical faults occurred in close proximity in space and time in a region where recurrence times for surface rupturing earthquakes are thousands of years this sug gests a causal role for the landers earthquake in triggering the hector mine earth quake previous modeling of the static stress change associated with the landers earthquake shows that the area of peak hector mine slip lies where the coulomb failure stress promoting right lateral strike slip failure was high but the nucleation point of the hector mine rupture was neutrally to weakly promoted depending on the assumed coefficient of friction possible explanations that could account for the 7 year delay between the two ruptures include background tectonic stressing dissi pation of fluid pressure gradients rate and state dependent friction effects and post landers viscoelastic relaxation of the lower crust and upper mantle by employing a viscoelastic model calibrated by geodetic data collected during the time period between the landers and hector mine events we calculate that postseismic relaxa tion produced a transient increase in coulomb failure stress of about 0 7 bars on the impending hector mine rupture surface the increase is greatest over the broad surface that includes the 1999 nucleation point and the site of peak slip further north since stress changes of magnitude greater than or equal to 0 1 bar are associated with documented causal fault interactions elsewhere viscoelastic relaxation likely con tributed to the triggering of the hector mine earthquake this interpretation relies on the assumption that the faults occupying the central mojave desert i e both the landers and hector mine rupturing faults were critically stressed just prior to the landers earthquake

comment on migration of historical earthquakes in california by c y king and z ma king c y and ma z 1988 migration of historical earthquakes in california pure appl geophys 127 627 639

relative sensitivity of the atlantic meridional overturning circulation to river discharge into hudson bay and the arctic ocean 1 increases in high latitude river discharge over the 20th century and projected continued increases during the 21st century may have an impact on the atlantic meridional overturning circulation amoc which could feed back to regional and global climate although the general trend in high latitude river discharge is positive there is important geographical spread in the trends while eurasian rivers draining into the arctic ocean show positive trends over the 20th century rivers draining into hudson bay show negative trends since 1964 here the sensitivity of amoc to changes in river discharge into hudson bay and the arctic ocean is studied with an intermediate complexity earth system model it is found that ocean freshening originating from arctic rivers is more effective in slowing down the amoc than freshening originating from hudson bay rivers given the same magnitude of freshening in both regions the lesser impact of hudson bay river discharge on amoc is the result of a buildup of freshwater anomalies in the labrador sea affecting the northward flow of the gulf stream this work highlights that not only the freshening magnitude but the region where this freshening takes place is crucial for the amoc response to altered river discharge climatology

revision of the late middle pleistocene stratigraphy and palaeoclimate in poland abstract the aim of this paper is a critical verification of the late middle pleistocene stratigraphy in poland in connection with stratigraphical schemes in the neighbouring countries although a terrestrial record of the middle pleistocene is almost complete in western and southern europe it is full of gaps in central and eastern europe eight key sites in poland and one in belarus were selected to compile environmental and palaeoclimate data for a revised stratigraphy from the termination of mis 12 to mis 6 and the chronology was based on correlation with oxygen isotope stratigraphy and osl ages the late middle pleistocene record starts with the holsteinian lake sequences some of which have been initiated already at the end of mis 12 persisted through mis 11 and terminated in mid mis 10 in the examined sites mis 11 is represented also by deposits of meandering rivers in a temperate climate in contrast there is no evidence for deposition in most of mis 10 and in mis 9 a warmer and presumably wet episode at the beginning of mis 8 lead to local erosion followed by development of small lakes modest ice sheet advance into central europe occurred in the second part of mis 8 as reflected by a till glaciofluvial and glaciolacustrine deposits and presumably also by permafrost and ice wedges in western belarus mis 7 seems to have been generally warm and wet when small lakes and meandering rivers could develop such mild conditions were interrupted with cool and probably drier episodes when braided rivers and limited pedogenesis occurred saalian ice sheet cover of central europe in mis 6 was widespread but even more importantly in this stage periglacial environments were dominant as shown by continuous permafrost intensive aeolian activity and development of ice wedges and involutions braided rivers developed during short wetter intervals

patterns of seismic release in the southern california region southern california experiences earthquakes on the san andreas system of vertical right lateral predominantly strike slip faults and on a second system of faults that includes thrusts oblique slip left lateral and other faults pattern recognition and cluster analysis are used to analyze the catalog of earthquakes with magnitudes 5 5 from 1915 to 1994 we use pattern recognition to find a suite of traits that would characterize each of these two systems and distinguish them from each other both pattern recognition and cluster analysis show that epochs of seismic release occur in which one or the other system is the predominant form of earthquake activity for the past 2 decades the second system has been the active one small changes in the direction of plate movements could account for this phenomenon seismic release on the san andreas system is preceded by episodes of activity in the great basin or in the gulf of california presumably these episodes would represent extension in the former region and spreading and slip on transform faults in the latter

k ar dating of an early middle pleistocene distal tephra in the interglacial varved succession of pianico sellere southern alps italy abstract a distal tephra has been discovered in the varved lacustrine succession of pianico sellere one of the best preserved interglacial sedimentary assemblages south to the italian alps the k ar dating of the juvenile glass fraction gives an age of 779 13 ka this age is supported by the observation of a reverse paleomagnetic direction probably recorded before the matuyama brunhes transition dated at 780 ka the tephra belongs to the shoshonite series and the volcanic source is likely located in southern italy the age of 779 13 ka is much older than that of the riss wurm interglacial which was previously suggested on the basis of geological setting and macroflora studies the pianico tephra represents the first stratigraphical marker of an interglacial so far unsettled in the southern alps

jakobshavn isbrae west greenland flow velocities and tidal interaction of the front area from 2004 field observations 1 during the summer of 2004 the front area of the jakobshavn isbrae was monitored using a geodetic photogrammetric survey with temporarily coincident precise observations of local ocean tides in the disko bay close to ilulissat the geodetic and photogrammetric observations were conducted at the southern margin of the glacier front the largest observed horizontal flow velocities are in the central part of the front with values up to 45 m d this is a factor of 2 greater than the average velocities at the front area observed in the last century our new observations confirm previous estimates of an acceleration of glacier flow during the last decade the photogrammetric survey provided flow trajectories for 4000 surface points with a time resolution of 30 min these flow trajectories were used to compare the vertical motion of the glacier with the observed tides the existence of a free floating glacier tongue in 2004 was confirmed by these data however it occupied only a small belt of at most a few 100 m width in the central part of the glacier front horizontal motion did not appear to depend on the tidal phase unlike some of the fast moving ice streams of west antarctica

link between excursions and paleointensity inferred from abnormal field directions recorded at la palma around 600 ka abstract an excursion of the geomagnetic field characterized by strongly abnormal directions associated with a field intensity as low as 7 t has been identified in a lava flow sequence from la palma canary islands the age of 602 12 ka obtained by k ar dating using the cassignol technique for a transitional flow represents our best estimate for the age of the occurrence of this episode of excursional directions this age is concordant with a minimum observed in the global sint800 composite record derived from worldwide deep sea records of relative paleointensity we show that a geomagnetic field model composed of a present day like non dipole field superimposed on an axial dipole reduced by a factor of 2 compared to its present value can account for excursional directions associated with low paleointensity in some areas while most other parts of the globe display apparently normal polarity directions we next generate through linear inversion a synthetic field model constrained by the actual la palma data and a set of directions at 30 sites distributed worldwide based on an axial dipole field with half present day intensity the energy spectrum of this synthetic field model is compatible with most of the non dipole part of the present day field and in that sense is earth like i e represents an acceptable configuration of the past geomagnetic field at 600 ka the model shows that very anomalous excursional directions covering 1 5 of the earth s surface may co exist with apparently normal directions elsewhere the new data and modeling strongly support the hypothesis that excursions are an integral aspect of secular variation there may be a continuum between normal sv and field reversals primarily controlled by the ratio of axial dipole field intensity relative to the remaining non axial dipole part

relative sea level change in greenland during the last 700 yrs and ice sheet response to the little ice age this paper presents new evidence regarding relative sea level rsl changes and vertical land motions at three sites in greenland since 1300 a d a time interval that spans the later part of the medieval climate anomaly mca and the little ice age lia we observe rsl rise at two sites in central west greenland from c 0 80 0 20 m at c 1300 a d to c 0 20 m 0 25 m at c 1600 a d after which rsl slowed and then stabilised at a third site in south greenland we observe rsl rise from c 1 40 0 20 m at c 1400 a d until c 1750 a d after which rsl slowed and was stable during at least the latter part of the 20th century the c 1600 a d rsl slow down seen at the two former sites is surprising because it occurs during the lia when one might expect the ice sheet to be gaining mass and causing rsl to rise we interpret this rsl slowdown to indicate a period of enhanced regional mass loss from central west greenland since c 1600 a d and propose two hypotheses for this loss first a reduction in precipitation during cold and dry conditions and second higher air temperatures and increased peripheral surface melt of the ice sheet from this date onwards the latter hypothesis is compatible with a well established temperature seesaw between western greenland and northern europe and potentially a previously identified shift from a positive to generally more negative nao conditions around 1400 to 1600 a d our study shows how rsl data from greenland can provide constraints on the timing of ice sheet fluctuations in the last millennium and challenges the notion that during cold periods in northern europe the ice sheet in west greenland gained mass

postseismic relaxation theory on the spherical earth abstract postseismic displacements and strains observed at the earth9s surface can be explained through the relaxation of a viscoelastic asthenosphere underlying a purely elastic crust a theory is presented for modeling the effects of postseismic relaxation on a spherically symmetric earth for an earthquake point source located in the upper elastic layer the displacement field is decomposed into its toroidal and spheroidal components a linear maxwell rheology in the viscoelastic layers is assumed enabling the use of the correspondence principle for the solutions of the equations of static equilibrium displacement and strain fields are then calculated using normal mode summation computational results are presented for two simple earthquake sources a strike slip fault and a uniaxial thrust fault the patterns of postseismic displacements and strains are found to depend strongly on both the earth model and earthquake source geometry in particular the elastic plate thickness asthenosphere thickness fault type and fault length each play a major role in determining the spatial pattern of postseismic relaxation effects asthenospheric viscosity controls the temporal pattern of relaxation

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

afterslip and viscoelastic relaxation following the 2011 tohoku oki earthquake mw9 0 inferred from inland gps and seafloor gps acoustic data we simultaneously estimate 2 5 years of afterslip and viscoelastic relaxation as well as coseismic slip for the 2011 tohoku oki earthquake displacements at inland gps and seafloor gps acoustic stations are inverted using viscoelastic green s functions for a model with an upper elastic layer and lower viscoelastic substrate the result shows that afterslip is isolated from the rupture area and possibly asperities of historical earthquakes and has almost decayed by 10 september 2013 2 5 years after the main shock the inversion result also suggests that observed landward postseismic displacements at the seafloor gps acoustic stations are caused by the viscoelastic relaxation whereas trenchward displacements at inland stations are mainly an elastic response to afterslip

consequences of stress changes following the 1891 nobi earthquake japan abstract great earthquakes along the philippine sea interplate boundary central honshu usually rupture a large portion of the nankai trough and suruga trough however the 1944 tonankai and 1946 nankaido earthquakes the most recent great philippine sea events did not rupture the suruga trough mogi proposed that strain release from the 1891 nobi earthquake is responsible for the apparently premature northeast termination of the 1944 rupture zone using a recently derived fault model of the 1891 earthquake combined with a suitable rheological model of central honshu we quantify both the inland and offshore consequences of the nobi earthquake north of the median tectonic line the co seismic plus postseismic stress changes of the nobi earthquake promoted the failure of faults which subsequently ruptured in the decades following 1891 in contrast along the philippine sea interplate boundary the co seismic plus postseismic strain release of the nobi earthquake during the decades following 1891 has delayed the anticipated tokai earthquake by at least 20 yr

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

isolation basin stratigraphy and holocene relative sea level change on arveprinsen ejland disko bugt west greenland this paper presents the results of an investigation into holocene relative sea level rsl change isostatic rebound and ice sheet dynamics in disko bugt west greenland data collected from nine isolation basins on arveprinsen ejland east disko bugt show that mean sea level fell continuously from ca 70 m at 9 9 ka cal yr bp 8 9 ka 14c yr bp to reach a minimum of ca 5 m at 2 8 ka cal yr bp 2 5 ka 14c yr bp before rising to the present day a west east gradient in isostatic uplift across disko bugt is confirmed with reduced rebound observed in east disko bugt however rsl differences up to 20 m at 7 8 ka to 6 8 ka cal yr bp 7 ka to 6 ka 14c yr bp also exist within east disko bugt suggesting a significant north south component to the area s isostatic history the observed magnitude and timing of late holocene rsl rise is not compatible with regional forebulge collapse instead rsl rise began first in the eastern part of the bay as might be expected under a scenario of crustal subsidence caused by neoglacial ice sheet readvance the results of this study demonstrate the potential of isolation basin data for local and regional rsl studies in greenland and the importance of avoiding data compilations from areas where the isobase orientation is uncertain copyright 1999 john wiley sons ltd

paleointensity across the reunion event in ethiopia abstract paleointensity experiments have been conducted on a volcanic series of 33 flows which recorded the geomagnetic reunion event successive determinations of absolute paleointensity from 20 flows indicate that the reunion event would actually be characterized by two successive periods of low field intensity with a total duration not in excess of 30 kyr the first period has a mean paleointensity of 12 t and shows significant deviations from initial reverse polarity but no signs of fully normal polarity it is followed by field recovery then a decrease prior to the second directional episode the second period has a mean paleointensity of 17 t and is associated with full normal directions and thus likely a dominantly dipolar configuration these results are compatible with a simple earthlike magnetic field model with a large decrease in dipole field strength which yields local emergence of relatively stronger non dipole components field characteristics from this configuration would be different at different locations and could explain the variability of the paleomagnetic records collected around the world we propose that the absence of field recovery following the event is responsible for not leading to a durable polarity interval

little ice age nivation activity in northeast greenland during the little ice age lia the periglacial landscape in northeast greenland responded rela tively quickly to the climatic deterioration with increased nivation activity resulting nivation landforms and associated sediment basins are used as palaeoclimatic archives documenting the significant geomorphological effect of nivation during the lia period in the zackenberg area a nival basin studied in detail showed the onset and dominance of niveo fluvial sedimentation in the period ad 1250 1420 followed by increasing niveo aeolian sedimentation between ad 1420 1500 1580 finally very rapid niveo aeolian sedimentation prevailed during the period ad 1500 1580 1690 in the same period some large nival fans accumulated in the zackenberg lowland as a result of increased niveo fluvial activity and niveo fluvial sediments were also deposited in pre existing fluvial valleys demonstrating the large areal extension of the nivation activity the chronology is based on nine ams 14c determinations the inte

joint estimation of afterslip rate and postseismic relaxation following the 1989 loma prieta earthquake global positioning system gps data from campaigns carried out over the 5 years following the 1989 loma prieta earthquake and leveling data measured in 1990 and 1992 define the postseismic velocity field around the loma prieta rupture zone subtraction of a background velocity field yields a residual velocity pattern which we interpret as the product of two physical processes 1 slow afterslip along distinct planes in the upper cru st and 2 viscoelastic relaxation of the lower crust and upper mantle biirgmann et al 1997 previously derived an afterslip model involving uniform afterslip on two optimally determined planes in cluding oblique reverse slip on the coseismic rupture and reverse slip on a shallow thrust fault to the northeast of the san andreas fault we further consider models of distributed slip on these two fault planes plus a viscoelastic relaxation pattern which depends on a suitable cose ismic rupture model and crust and mantle viscosities several fault models from the literature were considered for the 1989 coseismic rupture with nearly identical impact on the results simultaneous maximum likelihood inversion of the gps and leveling data for afterslip distri bution and viscosity yields the following results 1 a good fit to the data is obtained by smooth afterslip distributions without any viscoelastic relaxation being required 2 tangible broad scale viscoelastic relaxation of the lower crust and upper mantle are present in this data set at 97 confidence and a lower crustal viscosity of 1029 pa s is obtained however the viscosity of both the lower crust and upper mantle are poorly constrained 3 for a given misfit 20 less integrated afterslip and smoother afterslip distributions result when viscoelas tic relaxation is included 4 maximum slip rates on the slip distributed models are 3 5 crn yr the dominant patches estimated on the two planes fill in the entire depth range 4 13 km without significant overlap and deeper afterslip is not required the afterslip distribution on the coseismic rupture plane is strongly dominated by reverse slip immediately southeast of the main center of coseismic reverse slip