elevated pore pressure and anomalously low stress in regions of low frequency earthquakes along the nankai trough subduction megathrust 1 recent seismic reflection and ocean bottom seismometer obs studies reveal broad regions of low seismic velocity along the nankai subduction plate boundary megathrust offshore sw japan these low velocity zones lvz s extend 55 km landward from the trench corresponding to depths of 10 km below sea floor here we estimate the in situ pore pressure and stress state within these lvz s by combining p wave velocities obtained from the geophysical surveys with new well constrained empirical relations between p wave velocity porosity and effective mean stress defined by laboratory deformation tests on drill core samples of the incoming oceanic sediment we document excess pore pressures of 17 87 mpa that extend 55 km into the subduction zone indicating that trapped pore fluids support 45 91 of the overburden stress along the base of the upper plate and surrounding major fault zones the resulting effective stresses in the lvz are limited to 1 3 of the values expected for non overpressured conditions these low effective stresses should lead to a mechanically weak and predominantly aseismic plate boundary the region of lowest effective stress coincides with precisely located very low frequency earthquakes providing the first quantitative evidence linking these anomalous slip events to low stress and high pore pressure

greenland ice sheet surface melt extent and trends 1960 2010 observed meteorological data and a high resolution 5 km model were used to simulate greenland ice sheet surface melt extent and trends before the satellite era 1960 79 and during the satellite era through 2010 the model output was compared with passive microwave satellite observations of melt extent for 1960 2010 the average simulated melt extent was 15 5 for the period 1960 72 simulated melt extent decreased by an average of 6 whereas 1973 2010 had an average increase of 13 with record melt extent in 2010 the trend in simulated melt extent since 1972 indicated that the melt extent in 2010 averaged twice that in the early 1970s the maximum and mean melt extents for 2010 were 52 9 5 10 5 km 2 and 28 5 2 10 5 km 2 respectively due to higher than average winter and summer temperatures and lower than average winter precipitation for 2010 the southwest greenland melt duration was 41 60 days longer than the 1960 2010 average while the northeast greenland melt duration was up to 20 days shorter from 1960 to 1972 the melting period with a 10 melt extent decreased by an average of 3 days a 1 after 1972 the period increased by an average of 2 days a 1 indicating an extended melting period for the ice sheet of about 70 days 40 and 30 days in spring and autumn respectively

evidence for a weak and overpressured decollement beneath sediment dominated accretionary prisms we present structural data from several underthrust sequences in southwest alaska that suggest that the deformation regime beneath accretionary prisms is characterized by a subvertical 1 and regionally extensive layer parallel shearing these results contrast markedly with the results obtained from the more shallow parts of accretionary prisms and fold and thrust belts where 1 plunges gently seaward or toward the deformation front on the basis of mohr circle diagrams we propose that these different stress directions are consistent only with a model in which the two regimes are separated by a very weak decollement and calculate coefficient of friction values that range from 0 25 to 0 08 these values are significantly lower than coefficient of friction values calculated for the basal decollement in the taiwan fold and thrust belt e g 0 2 barr and dahlen 1989a and they are also lower than laboratory friction measurements for most rocks e g 0 6 0 8 byerlee 1978 consequently these low values suggest the presence of rocks with unusual material properties e g montmorillonite logan and rauenzahn 1987 or anomalous fluid pressures along the decollement on the basis of the occurrence of shale diapirs the distribution of early veins and the absence of montmorillonite in the underthrust sequences we propose that there was an anomalously high fluid pressure along the decollement fault instead of there being such a low coefficient of friction these results emphasize the importance of dewatering and fluid flow in controlling the position of the decollement which in turn determines how the accretionary prism grows in essence it is the development of a weak overpressured decollement within a thick sediment pile that allows plate convergence to be partitioned into offscraping and underthrusting regimes

greenland coastal air temperatures linked to baffin bay and greenland sea ice conditions during autumn through regional blocking patterns variations in sea ice freeze onset and regional sea surface temperatures ssts in baffin bay and greenland sea are linked to autumn surface air temperatures sats around coastal greenland through 500 hpa blocking patterns 1979 2014 we find strong statistically significant correlations between baffin bay freeze onset and ssts and sats across the western and southernmost coastal areas while weaker and fewer significant correlations are found between eastern sats ssts and freeze periods observed in the neighboring greenland sea autumn greenland blocking index values and the incidence of meridional circulation patterns have increased over the modern sea ice monitoring era increased anticyclonic blocking patterns promote poleward transport of warm air from lower latitudes and local warm air advection onshore from ocean atmosphere sensible heat exchange through ice free or thin ice covered seas bordering the coastal stations temperature composites by years of extreme late freeze conditions occurring since 2006 in baffin bay reveal positive monthly sat departures that often exceed 1 standard deviation from the 1981 2010 climate normal over coastal areas that exhibit a similar spatial pattern as the peak correlations

a self consistent mechanism for slow dynamic deformation and tsunami generation for earthquakes in the shallow subduction zone 1 dynamic pore pressure changes in the overriding wedge above a shallow dipping plate interface significantly affect the rupture dynamics of shallow subduction zone earthquakes and their tsunamigenesis for a wedge on the verge of coulomb failure everywhere including the basal fault the dynamic pore pressure increase due to up dip rupture propagation leads to widespread yielding within the wedge which is greatly enhanced by the shallow dip of the fault the widespread yielding reduces the stress drop slip velocity slip and rupture velocity giving rise to prolonged rupture duration thus explaining many anomalous features of shallow subduction zone earthquakes significant inelastic seafloor uplift occurs in the case of a shallow fault dip with the largest uplift located landward from the trench integrating this physical mechanism with existing seismic geodetic and tsunami observations can provide new insights into earthquake dynamics and deformation processes in shallow subduction zones

nonlinear seismo acoustic land mine detection and discrimination a novel technique for detection and discrimination of artificial objects such as land mines pipes containers etc buried in the ground has been developed and tested the developed approach utilizes vibration using seismic or airborne acoustic waves of buried objects remote measurements of soil surface vibration using laser or microwave vibrometers and processing of the measured vibration to extract mine s vibration signatures the technique does not depend upon the material from which the mine is fabricated whether it be metal plastic wood or any other material it depends upon the fact that a mine is a container whose purpose is to contain explosive materials and associated detonation apparatus the mine container is in contact with the soil in which it is buried the container is an acoustically compliant article whose compliance is notably different from the compliance of the surrounding soil dynamic interaction of the compliant container and soil on top of it leads to specific linear and nonlinear effects used for mine detection and discrimination the mass of the soil on top of a compliant container creates a classical mass spring system with a well defined resonance response besides the connection between mass soil and spring mine is not elastic linear but rather nonlinear due to the separation of the soil mine interface in the tensile phase of applied dynamic stress these two effects constituting the mine s vibration signature have been measured in numerous laboratory and field tests which proved that the resonance and nonlinear responses of a mine soil system can be used for detection and discrimination of buried mines thus the fact that the mine is buried is turned into a detection advantage because the seismo acoustic technique intrinsically detects buried containers it can discriminate mines from noncompliant false targets such as rocks tree roots chunks of metal bricks etc this was also confirmed experimentally in laboratory and field tests

seismic velocities from the barbados ridge complex indicators of high pore fluid pressures in an accretionary complex three wide aperture 0 5 km offset seismic profiles were shot perpendicular to the strike of the barbados ridge accretionary complex at 16 12 n line 465 14 23 n line 480 and 13 20 n line 484 to image the deep structure of the accretionary complex and obtain seismic velocity data velocity analyses on full fold common depth point cdp gathers were used to provide velocity depth functions at 1 km separation along each line to map the variation in velocity with depth and distance across the accretionary complex the sediments within the complex show consolidation increasing laterally with greater age of the complex as indicated by the increase in seismic velocity and the inferred decrease in porosity the velocity at the base of the wedge along line 480 is 2 4 km s at the toe the velocity at the wedge base at 60 km from the toe where the wedge thickness has increased from 1 8 km to 5 0 km has increased to greater than 3 0 km s however the velocities within the leading margins and within undeithrust sequences in each of the three sections are low as much as 1 0 km s less than velocities found in undeformed sedimentary sequences of equivalent thickness the low velocity regions are interpreted as sediments with high porosity where porosity is inferred to be high pore fluid pressures are also inferred to exceed hydrostatic and pore fluids actually support the increased lithostatic load produced by recent thrusting and thickening of the complex the correlation between the most rapidly thickened regions and the velocity anomalies suggests that a rapid rate of loading relative to the rate of pore fluid expulsion produced these overpressured sediments velocities in the underthrust sequences where the differences between loading histories of wedge sediments and the underthrust sequences are largest are sufficiently low to produce velocity inversions low velocities also occur in regions adjacent to the complex where the pore fluid pressures may be elevated by the pressure produced in the adjacent wedge west of the wedge in the forearc basin along line 480 and near a seismically imaged mud diapir velocities at a depth of 3 5 km below the seafloor are 0 5 km s less than what is expected in a more normal sedimentary section immediately seaward of the complex the deepest undeformed sequences have a velocity anomaly of 0 5 km s velocities remain low for at least 12 km seaward of the complex but they become closer to a more normal sediment section farther from the wedge

modern and ancient seismogenic out of sequence thrusts in the nankai accretionary prism comparison of laboratory derived physical properties and seismic reflection data 1 to investigate characteristics of a seismogenic out ofsequence thrust oost imaged as a strong reflection on seismic profiles in the nankai accretionary prism we determined acoustic properties of discrete samples from an fossil nobeoka oost outcrop under confining pressures and compared the acoustic properties with those of an active oost in the nankai accretionary prism we observed anisotropy of velocity and attenuation in the hanging wall of nobeoka oost attributed to foliation of pelitic phyllite in contrast the footwall is composed of brittlely deformed chaotic shales and fine sandstones and velocities in the footwall are lower than those in the hanging wall amplitude variation with offset avo modeling utilizing contrasts in p and s wave velocities and densities between the hanging wall and footwall of the nobeoka oost indicates that fractures filled with overpressured fluid likely account for angle dependent reflection amplitudes of the active oost in the nankai trough citation tsuji t g kimura s okamoto f kono h mochinaga t saeki and h tokuyama 2006 modern and ancient seismogenic out ofsequence thrusts in the nankai accretionary prism comparison of laboratory derived physical properties and seismic reflection data geophys res lett 33 l18309 doi 10 1029 2006gl027025

pore pressure distribution of a mega splay fault system in the nankai trough subduction zone insight into up dip extent of the seismogenic zone we use the pore pressure distribution predicted from a waveform tomography wt velocity model to interpret the evolution of the mega splay fault system in the nankai trough off kumano japan to map pore pressure around the mega splay fault and plate boundary decollement we integrate the high resolution wt velocities with laboratory data and borehole well log data using rock physics theory the predicted pore pressure distribution shows that high pore pressures close to lithostatic pressure along the footwall of the mega splay fault extend seaward to the trough region and the normalized pore pressure ratio is nearly constant over that extent this continuity of the overpressured zone indicates that a coseismic rupture can potentially propagate nearly to the trough axis we interpret a high pressure belt within an accretionary wedge on the landward side of the present mega splay fault as evidence of the ancient mega splay fault because the ancient mega splay fault soles into the active mega splay fault the active mega splay fault may function as a basal detachment fault and is directly connected to the seaward plate boundary decollement

influence of a subducted oceanic ridge on the distribution of shallow vlfes in the nankai trough as revealed by moment tensor inversion and cluster analysis

a low velocity zone with weak reflectivity along the nankai subduction zone three dimensional seismic reflection data reveal the presence of a low seismic velocity zone lvz with weak reflectivity character along the nankai accretionary prism this lvz is intercalated between an upper offscraped layer and a lower underthrusting layer in the outer accretionary wedge wide angle ocean bottom seismograph data also support the presence of the lvz which is estimated to be a maximum of 2 km thick 15 km wide and 120 km long the lvz could be an underthrust package underplated in response to the lateral growth of the nankai accretionary prism underplating of the underthrusting layer beneath the overlying offscraped layer would maintain a critical taper of the accretionary prism so that the offscraped layer can continue to grow seaward the lvz could have elevated fluid pressure leading to rigidity reduction of the entire outer accretionary wedge the rigidity lowered outer wedge containing the lvz may be more easily uplifted and thus eventually foster tsunami generation during a nankai megathrust earthquake if the fluid rich lvz supplies a significant amount of the fluid to the megasplay fault zone at depth it may affect stick slip behavior of the fault

has arctic sea ice loss contributed to increased surface melting of the greenland ice sheet abstractin recent decades the greenland ice sheet has experienced increased surface melt however the underlying cause of this increased surface melting and how it relates to cryospheric changes across the arctic remain unclear here it is shown that an important contributing factor is the decreasing arctic sea ice reduced summer sea ice favors stronger and more frequent occurrences of blocking high pressure events over greenland blocking highs enhance the transport of warm moist air over greenland which increases downwelling infrared radiation contributes to increased extreme heat events and accounts for the majority of the observed warming trends these findings are supported by analyses of observations and reanalysis data as well as by independent atmospheric model simulations using a state of the art atmospheric model that is forced by varying only the sea ice conditions reduced sea ice conditions in the model favor more extensive greenland surface melting the authors find a positive feedba

friction on subduction megathrust faults beyond the illite muscovite transition abstract previous experimental studies addressing subduction megathrust friction have focused on shallow fault gouges dominated by smectite illite and quartz here we aim to determine the effect of the transition to muscovite rich fault rock at depths beyond the illite dominated region of the seismogenic zone to achieve this rotary friction experiments were performed on simulated muscovite quartz 65 35 gouge at 100 600 c an effective normal stress of 170 mpa pore pressures of 100 and 200 mpa and sliding velocities of 1 100 m s we isolated the effects of muscovite by shearing pure muscovite gouge at 200 600 c under otherwise identical conditions at low shear strains 1 muscovite quartz gouge showed a friction coefficient of 0 4 0 5 while pure muscovite gouge exhibited 0 3 both gouges showed an increase in with and temperature the muscovite quartz gouge was characterised by velocity strengthening or neutral behaviour at 100 350 c velocity weakening at 350 500 c and velocity strengthening at 500 600 c in contrast pure muscovite gouge showed predominantly velocity strengthening or neutral behaviour demonstrating a key role of quartz in producing velocity weakening the velocity weakening regime in the mixed gouge extends that of 250 400 c recently reported for illite quartz gouge up to 500 c taking into account the observed effect of sliding velocity on a b the data for illite quartz and muscovite quartz together help explain the depth extent of seismogenesis on subduction megathrusts interestingly comparison with previous microphysical models suggests that the mechanism causing velocity weakening in phyllosilicate quartz gouges is one of granular flow involving competition between shear induced dilation and compaction through thermally activated quartz deformation

elevated fluid pressure and extreme mechanical weakness of a plate boundary thrust nankai trough subduction zone pore fluid pressure is a key parameter governing both the shear strength of faults and the conditions for seismic and tsunamigenic slip on subduction zone megathrusts however quantitative constraints on this parameter based on in situ data in these or any faults have proven elusive using seismic interval velocities derived from a three dimensional seismic reflection survey we compute porosity fluid pressure and effective stress at the plate interface in the nankai trough subduction zone offshore southwestern japan to 20 km down the fault dip using well constrained locally calibrated empirical relationships between velocity porosity and effective stress we show that the fault and immediately subjacent footwall are nearly undrained implying that the subduction megathrust slips under a shear stress of

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

the extreme melt across the greenland ice sheet in 2012 1 the discovery of the 2012 extreme melt event across almost the entire surface of the greenland ice sheet is presented data from three different satellite sensors including the oceansat 2 scatterometer the moderate resolution imaging spectroradiometer and the special sensor microwave imager sounder are combined to obtain composite melt maps representing the most complete melt conditions detectable across the ice sheet satellite observations reveal that melt occurred at or near the surface of the greenland ice sheet across 98 6 of its entire extent on 12 july 2012 including the usually cold polar areas at high altitudes like summit in the dry snow facies of the ice sheet this melt event coincided with an anomalous ridge of warm air that became stagnant over greenland as seen in melt occurrences from multiple ice core records at summit reported in the published literature such a melt event is rare with the last significant one occurring in 1889 and the next previous one around seven centuries earlier in the medieval warm period given its rarity the 2012 extreme melt across greenland provides an exceptional opportunity for new studies in broad interdisciplinary geophysical research

fluid induced rupture experiment on fontainebleau sandstone premonitory activity rupture propagation and aftershocks 1 a 14 porosity fontainebleau sandstone sample diameter 40 mm length 88 mm was loaded tri axially under 100 mpa confining pressure and 240 mpa differential stress in drained conditions and under constant load pore pressure water was raised until failure was triggered during the experiment elastic wave velocities and permeability were monitored while more than 3000 acoustic emissions ae were located prior and after failure ae locations show that macroscopic fracture propagated from a large nucleation patch at speeds comprised between 0 1 and 4 m s number of ae hits per second followed omori s law with exponents of 0 92 and 1 18 pre and post failure respectively no quiescence was observed post failure except where rupture initially nucleated from fast depressurization of the pore space induced secondary aftershocks located within the fracture plane possibly indicating a heterogeneous fault geometry after rupture of lower permeability that compacted during the release of pore pressure

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

coupled fluid flow and deformation modeling of the frontal thrust region of the kumano basin transect japan implications for fluid pressures and decollement downstepping 1 results of coupled fluid flow and deformation modeling illustrate the influence of frontal thrust slip on excess pore pressures and decollement downstepping in the kumano basin transect offshore japan although permeable trench sediments and a buried sandstone layer provide potential fluid escape pathways the numerical modeling suggests that excess pore pressure could build beneath the frontal thrust within hemipelagic clay of the shikoku basin facies simulated excess pore pressures range between 45 and 77 of the overburden weight 3 km landward of the deformation front and are very sensitive to the permeability of the shikoku basin clay and the coefficient of friction of the fault zone excess pore pressures increase as the fault coefficient of friction is increased suggesting that volume change due to shear within the footwall sediments is an important contributor to excess pore pressures raising the coefficient of friction also increases shear within the sediments beneath the fault zone suggesting downward migration of the decollement zone this shearing focuses in the weaker shikoku basin clays rather than an underlying turbidite unit suggesting that lithologic differences play an important role in controlling deformation location

earthquakes induced by water injection at 3 km depth within the rongchang gas field chongqing china 1 unwanted water amounting more than 1 million m 3 has been injected intermittently at a pumping pressure of 2 1 2 9 mpa over hydrostatic at 2 6 2 9 km depth within the rongchang gas field western chongqing china since july 1988 the injections have induced more than 32 000 surface recorded earthquakes including 2 of m l 5 14 of m l 4 and more than 100 of m l 3 up until the end of 2006 we examined the epidemic type aftershock sequence etas model and the temporal evolution of several statistics of the earthquake sequence the random component in the etas model can be considered as an indicator of fluid driven activity while the rate of omori law type aftershocks indicates stress triggering of the preceding earthquakes we observed three distinct seismic activity phases that were coincident with different injection periods phase i corresponds to initial injections with low injection rate long time interval and shows a vast majority of omori type events and only 8 externally forced activity phase ii corresponds to a period of high injection rates and shows intense earthquake activity characterized by a high percentage 45 of fluid driven earthquakes phase iii demonstrates decreasing seismicity as a result of a lowering in the injection rate more than 70 of earthquakes occurred randomly over time indicating the dominance of external triggering the physical mechanism that induced the rongchang earthquake sequence was a change in coulomb s failure stress caused by pore pressure diffusion and transformed from seismic slip of preceding earthquakes a pressure increase of 2 1 2 9 mpa at the injection well is more than sufficient to induce failure within the local formations

an improved mass budget for the greenland ice sheet extensive ice thickness surveys by nasa s operation icebridge enable over a decade of ice discharge measurements at high precision for the majority of greenland s marine terminating outlet glaciers prompting a reassessment of the temporal and spatial distribution of glacier change annualmeasurements for 178 outlet glaciers reveal that despite widespread acceleration only 15 glaciers accounted for 77 of the 739 29 gt of ice lost due to acceleration since 2000 and four accounted for 50 among the top sources of loss are several glaciers that have received little scientific attention the relative contribution of ice discharge to total loss decreased from 58 before 2005 to 32 between 2009 and 2012 as such 84 of the increase in mass loss after 2009 was due to increased surface runoff these observations support recentmodel projections that surface mass balance rather than ice dynamics will dominate the ice sheet s contribution to 21st century sea level rise

effective stress and pore pressure in the nankai accretionary prism off the muroto peninsula southwestern japan 1 we developed a theoretical method for predicting effective stress and pore pressure based on rock physics model we applied the method to reveal the pore pressure distribution within the nankai accretionary prism off southwestern japan and to investigate variations in pore pressure associated with evolution of the plate boundary decollement from the crack aspect ratio spectrum estimated from laboratory and well log data we calculated a theoretical relationship between acoustic velocity and mean effective stress by using differential effective medium theory by iteratively fitting the theoretically calculated velocity to the seismic velocities derived from 3d tomographic inversion we estimated in situ mean effective stress within the accretionary prism pore pressure is then the difference between the effective stress and the confining stress when we calculated pore pressure we considered compressive state of stress in the accretionary prism our results confirm that pore fluid pressure is high within the subducting sedimentary sequence below the decollement we determined a normalized pore pressure ratio of 0 4 0 7 abnormal pore pressures develop in the under thrust sequence as a result of the increase in overburden load because of the thickened overlying prism and a low permeability barrier across the decollement overpressuring within the accreted sequence is initiated at the deformation front and proceeds landward the increase in horizontal compaction within the accreted sequence may raise pore pressures within the accreted sequence and the pore pressure mean effective stress contrast at the decollement becomes smaller landward of the deformation front

seismic velocity anisotropy and fluid pressure in the barbados accretionary wedge from an offset vertical seismic profile with seabed sources 1 the state of compaction and fluid pressure in the barbados accretionary wedge near its toe at ocean drilling program site 949 were investigated by modeling travel times of seismic waves from ocean bottom shots to a borehole geophone array the model constrained by a three dimensional seismic survey and well logs shows 1 a velocity gradient of about 1 1 25 s 1 in the uppermost 180 230 m of the wedge 2 a zone of variable but no net change in velocity between 230 and 350 m depth 3 a low velocity zone 40 50 m thick just above the decollement at 391 m and 4 a displacement of the low velocity zone by thrust faults pore fluid pressure sections derived from p wave velocity show that the upper half of the wedge is normally pressured while the lower half is overpressured the 160 m thick underconsolidated basal zone shows anisotropy which increases downward the lowest 40 50 m has velocity varying 1 azimuthally 3 being fastest in the direction of plate convergence and 2 in the vertical plane 2 5 horizontal faster than vertical after correction for the effect of anisotropy in the derivation of effective stress from seismic velocity the calculated pore fluid pressure ratio does not exceed 0 9 and in the lowest 40 50 m of the basal zone is between 0 71 and 0 82 with fluid pressure hydrostatic lithostatic pressure hydrostatic between 0 5 and 0 65 in accordance with in situ measurements of fluid pressure in the decollement zone beneath these indicate that the accretionary wedge is stronger and less overpressured than was previously supposed

waveform tomography imaging of a megasplay fault system in the seismogenic nankai subduction zone abstract we apply frequency domain waveform tomography to form quantitative high resolution p wave velocity images of a megasplay fault system within the central nankai subduction zone offshore of southwest japan using controlled source ocean bottom seismometer obs data originally acquired in 2004 the waveform tomography method exploits recorded seismic waveforms beyond their first arrivals and thus achieves a much higher resolution of the order of a wavelength than that of conventional traveltime tomography methods frequency domain waveform tomography facilitates a multi scale approach to stabilize the inversion in which initial traveltime tomography results are sequentially improved on by first fitting low frequency components of the seismic records starting at 2 25 hz higher frequency components up to 8 5 hz are then introduced progressively our final waveform tomography image allows velocity anomalies as small as 700 m horizontally and 350 m vertically to be discerned and interpreted as confirmed by checkerboard modeling tests the improved explanatory power of the final images is verified by observing that synthetic waveforms calculated from the final results yield much better fit to the observed waveforms than those estimated from the original traveltime tomography image apparent lithological boundaries from waveform tomography agree well with corresponding reflections on seismic migration images providing further confidence in the validity of the results the megasplay fault is evident on the final waveform tomography image as a sharp velocity discontinuity delineating the upper surface of a velocity reduction of nearly 1 km s with respect to the regional 1d velocity trend the megasplay fault can be traced continuously throughout the entire image from a nearly horizontal section at the landward extent moving seaward through to a steeper angle penetrating the old accretionary prisms with several additional splays appearing to branch in the shallow subsurface the location of the low velocity zones imaged by our waveform tomography method coincides with two previously identified low velocity zones the image reveals a low velocity zone that is continuous from deeper to shallower portions of the subsurface suggesting that pore fluids may be transported from the inner wedge to the transition zone and to the surface through fluid conduits associated with the megasplay fault system

splay fault branching from the hikurangi subduction shear zone implications for slow slip and fluid flow gns science s mbie funded contracts grant number co5x1204 and c05x0908 gas hydrates resources marsden fund project grant number gns0902

positive feedback fracture process induced by nonuniform high pressure water flow in dilatant granite during forced water infiltration into a dry granite rock in the dilatant state migration of a water front and a clear positive feedback between acoustic activity and water flow into microcracks were revealed by means of ae hypocenter locations and velocity tomography water was injected into a cylindrical granite sample subjected to 40 mpa confining pressure and constant axial stress equal to about 70 of short term dry strength the injection water pressure was held constant at 17 mpa until failure occurred soon after water injection into the bottom end of the sample ae hypocenters began near the bottom end subsequently they moved up with a strong preference for the region where a weak concentration of ae events had been observed during a steady state creep stage before the water injection the p wave velocity structure was determined in the section parallel to the loading axis and crossing the cluster of ae hypocenters the velocity structure reconstructed by seismic tomography showed a nonsymmetric distribution of the velocity with regard to the loading axis during the injection the strong concentration of ae hypocenters suggests that water flow channels are preferentially formed in a very limited region in the dilatant rock the concentration of ae events and formation of these water channels marks a positive feedback process in which the local strength of the rock is reduced by the decrease of the effective confining pressure caused by increasing pore pressure which in turn triggers more microfracturing

greenland ice sheet melt extent 1979 1999 analysis of melt extent on the greenland ice sheet is updated to span the time period 1979 1999 and examined along with its spatial and temporal variability using passive microwave satellite data to acquire the full record the issue of continuity between the previous passive microwave sensors smmr ssm i f 8 and ssm i f 11 and the most recent ssm i f 13 sensor is addressed the f 13 cross polarized gradient ratio melt classification threshold is determined to be 0 0154 results show that for the 21 year record a positive melt trend of nearly 1 yr is observed but this trend falls just below the 90 significance level the observed melt increase does appear to be driven by conditions in the western portion of the ice sheet rather than the east where melt appears to have decreased slightly moreover the eruption of mount pinatubo in 1991 is likely to have had some impact on the melt but not so much as previously suspected the 1992 melt anomaly is 1 7 standard deviations from the mean finally the relationship between coastal temperatures and melt extent suggests an increase in surface runoff contribution to sea level of 0 31 mm yr for a 1 c temperature rise

recent changes in arctic sea ice melt onset freezeup and melt season length 1 in order to explore changes and trends in the timing of arctic sea ice melt onset and freezeup and therefore melt season length we developed a method that obtains this information directly from satellite passive microwave data creating a consistent data set from 1979 through present we furthermore distinguish between early melt the first day of the year when melt is detected and the first day of continuous melt a similar distinction is made for the freezeup using this method we analyze trends in melt onset and freezeup for 10 different arctic regions in all regions except for the sea of okhotsk which shows a very slight and statistically insignificant positive trend 0 4 d decade 1 trends in melt onset are negative i e toward earlier melt the trends range from 1 0 d decade 1 for the bering sea to 7 3 d decade 1 for the east greenland sea except for the sea of okhotsk all areas also show a trend toward later autumn freeze onset the chukchi beaufort seas and laptev east siberian seas observe the strongest trends with 7 d decade 1 for the entire arctic the melt season length has increased by about 20 days over the last 30 years largest trends of over 10 d decade 1 are seen for hudson bay the east greenland sea the laptev east siberian seas and the chukchi beaufort seas those trends are statistically significant at the 99 level

a sea ice free summer arctic within 30 years an update from cmip5 models interpreted as sea ice extent less than 1 0 million km 2 w e consider this estimate to be still valid based on projections of updated climate models cmip5 and observational data similar to previous models cmip3 cmip5 still shows a wide spread in hindcast and projected sea ice loss among different models further there is no consensus in the scientific literature for the cause of such a spread in results for cmip3 and cmip5 while cmip5 model mean sea ice extents are closer to observations than cmip3 the rates of sea ice reduction in most model runs are slow relative to recent observations all cmip5 models do show loss of sea ice due to increased anthropogenic forcing relative to preindustrial control runs applying the same technique of model selection and extrapolation approach to cmip5 as we used in our previous paper the interval range for a nearly sea ice free arctic is 14 to 36 years with a median value of 28 years relative to a 2007 baseline this suggests a nearly sea ice free arctic in the 2030s citation wang m and j e overland 2012 a sea ice free summer arctic within 30 years an update from cmip5 models geophys res lett 39 l18501

acoustic emission induced by pore pressure changes in sandstone samples an understanding of microseismicity induced by pore pressure changes in stressed rocks is important for applications in geothermal and hydrocarbon reservoirs as well as for co 2 sequestrations we have studied the triggering mechanisms of microseismicity or acoustic emission in the laboratory as a function of triaxial stress conditions and pore pressure changes in investigating the spatiotemporal distribution of acoustic emission activity in water saturated triaxially stressed flechtingen sandstone samples subjected to changes in pore pressure we assumed that acoustic events were triggered by pore pressure increase to estimate pore pressure changes in the sample we used an analytical solution of the 1d diffusion equation a theoretical analysis of the spatiotemporal distribution suggested that for initially insignificantly stressed samples acoustic events were triggered by the migration of a critical pore pressure level through the sample the critical level was controlled by the applied pore press

hydrogeology and mechanics of subduction zone forearcs fluid flow and pore pressure at subduction zones fluid flow pore pressure and tectonic processes are tightly interconnected excess pore pressure is driven by tectonic loading and fluids released by mineral dehydration and it has profound effects on fault and earthquake mechanics through its control on effective stress the egress of these overpressured fluids which is in part governed by the presence of permeable fault zones is a primary mechanism of volatile and solute transport to the oceans recent field measurements new constraints gained from laboratory studies and numerical modeling efforts have led to a greatly improved understanding of these coupled processes here we summarize the current state of knowledge of fluid flow and pore pressure in subduction forearcs and focus on recent advances that have quantified permeability architecture fluxes the nature and timing of transience and pressure distribution thus providing new insights into the connections between fluid metamorphic mechanical and fault slip proc

the melting arctic and midlatitude weather patterns are they connected abstractthe potential of recent arctic changes to influence hemispheric weather is a complex and controversial topic with considerable uncertainty as time series of potential linkages are short 10 yr and understanding involves the relative contribution of direct forcing by arctic changes on a chaotic climatic system a way forward is through further investigation of atmospheric dynamic mechanisms during several exceptionally warm arctic winters since 2007 sea ice loss in the barents and kara seas initiated eastward propagating wave trains of high and low pressure anomalous high pressure east of the ural mountains advected arctic air over central and eastern asia resulting in persistent cold spells blocking near greenland related to low level temperature anomalies led to northerly flow into eastern north america inducing persistent cold periods potential arctic connections in europe are less clear variability in the north pacific can reinforce downstream arctic changes and arctic amplification

surface melt induced acceleration of greenland ice sheet flow ice flow at a location in the equilibrium zone of the west central greenland ice sheet accelerates above the midwinter average rate during periods of summer melting the near coincidence of the ice acceleration with the duration of surface melting followed by deceleration after the melting ceases indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice bedrock interface interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting with larger increases accompanying higher amounts of summer melting the indicated coupling between surface melting and ice sheet flow provides a mechanism for rapid large scale dynamic responses of ice sheets to climate warming

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

greenland ice sheet surface melt and its relation to daily atmospheric conditions abstractmelt area is one of the most reliably monitored variables associated with surface conditions over the full greenland ice sheet gris surface melt is also an important indicator of surface mass balance and has potential relevance to the ice sheet s global sea level contribution melt events are known to be spatially heterogeneous and have varying time scales to understand the forcing mechanisms it is necessary to examine the relation between the existing conditions and melt area on the time scales that melt is observed here we conduct a regression analysis of atmospheric reanalysis variables including sea level pressure near surface winds and components of the surface energy budget with surface melt the regression analysis finds spatial heterogeneity in the associated atmospheric circulation conditions for basins in the southern gris there is an association between melt area and high pressure located south of the denmark strait which allows for southerly flow over the western half of th

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

melt induced speed up of greenland ice sheet offset by efficient subglacial drainage fluctuations in surface melting are known to affect the speed of glaciers and ice sheets but their impact on the greenland ice sheet in a warming climate remains uncertain although some studies suggest that greater melting produces greater ice sheet acceleration others have identified a long term decrease in greenland s flow despite increased melting here we use satellite observations of ice motion recorded in a land terminating sector of southwest greenland to investigate the manner in which ice flow develops during years of markedly different melting although peak rates of ice speed up are positively correlated with the degree of melting mean summer flow rates are not because glacier slowdown occurs on average when a critical run off threshold of about 1 4 centimetres a day is exceeded in contrast to the first half of summer when flow is similar in all years speed up during the latter half is 62 16 per cent less in warmer years consequently in warmer years the period of fast ice flow is three times shorter and overall summer ice flow is slower this behaviour is at odds with that expected from basal lubrication alone instead it mirrors that of mountain glaciers where melt induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient a model of ice sheet flow that captures switching between cavity and channel drainage modes is consistent with the run off threshold fast flow periods and later summer speeds we have observed simulations of the greenland ice sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage a simple model of basal lubrication alone misses key aspects of the ice sheet s response to climate warming

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

nonlinear rise in greenland runoff in response to post industrial arctic warming the greenland ice sheet gris is a growing contributor to global sea level rise1 with recent ice mass loss dominated by surface meltwater runoff2 3 satellite observations reveal positive trends in gris surface melt extent4 but melt variability intensity and runoff remain uncertain before the satellite era here we present the first continuous multi century and observationally constrained record of gris surface melt intensity and runoff revealing that the magnitude of recent gris melting is exceptional over at least the last 350 years we develop this record through stratigraphic analysis of central west greenland ice cores and demonstrate that measurements of refrozen melt layers in percolation zone ice cores can be used to quantifiably and reproducibly reconstruct past melt rates we show significant p 0 01 and spatially extensive correlations between these ice core derived melt records and modelled melt rates5 6 and satellite derived melt duration4 across greenland more broadly enabling the reconstruction of past ice sheet scale surface melt intensity and runoff we find that the initiation of increases in gris melting closely follow the onset of industrial era arctic warming in the mid 1800s but that the magnitude of gris melting has only recently emerged beyond the range of natural variability owing to a nonlinear response of surface melting to increasing summer air temperatures continued atmospheric warming will lead to rapid increases in gris runoff and sea level contributions

mechanical and hydraulic properties of nankai accretionary prism sediments effect of stress path 1 we have conducted triaxial deformation experiments along different loading paths on prism sediments from the nankai trough different load paths of isotropic loading uniaxial strain loading triaxial compression at constant confining pressure pc undrained pc reduction drained pc reduction and triaxial unloading at constant pc were used to understand the evolution of mechanical and hydraulic properties under complicated stress states and loading histories in accretionary subduction zones five deformation experiments were conducted on three sediment core samples for the nankai prism specifically from older accreted sediments at the forearc basin underthrust slope sediments beneath the megasplay fault and overthrust upper shikoku basin sediments along the frontal thrust yield envelopes for each sample were constructed based on the stress paths of pc reduction using the modified cam clay model and in situ stress states of the prism were constrained using the results from the other load paths and accounting for horizontal stress results suggest that the sediments in the vicinity of the megasplay fault and frontal thrust are highly overconsolidated and thus likely to deform brittle rather than ductile the porosity of sediments decreases as the yield envelope expands while the reduction in permeability mainly depends on the effective mean stress before yield and the differential stress after yield an improved understanding of sediment yield strength and hydromechanical properties along different load paths is necessary to treat accurately the coupling of deformation and fluid flow in accretionary subduction zones

contrasts in physical properties between the hanging wall and footwall of an exhumed seismogenic megasplay fault in a subduction zone an example from the nobeoka thrust drilling project 1 we examined the physical properties of an exhumed and fossilized subduction zone megasplay fault by analyzing geophysical logging data obtained by the nobeoka thrust drilling project which provide a high resolution transect of properties across the main fault zone the footwall cataclasite exhibits higher averages of neutron porosity 7 6 and lower values of electric resistivity 232 m compared to the hanging wall phyllite 4 8 453 m this clear contrast between the hanging wall and footwall may account for the difference in maximum burial and structural variation despite the contrast observed between the hanging wall and footwall in macroscopic scale the resistivity and porosity data from both the hanging wall and footwall can be fit with a single curve using archie s law suggesting the similarities in microstructures and mineralogy in this low porosity range above the main fault core of the nobeoka thrust a brittle damage zone in the hanging wall contains pseudotachylyte as evidence of the seismogenic slip and does not follow archie s law damage zones in the hanging wall are also observed in the modern splay fault at shallow depth in the nankai trough but with much thicker width whereas the footwall damage zone is more extensive in the nobeoka thrust splay faults may exhibit strong deformation in the hanging wall in the early stage and as fault rocks get buried deeper and as displacement and physical property contrast increase across the fault the damage effect may eventually be enlarged in the footwall

mechanics of seismic instabilities induced by the recovery of hydrocarbons we review earthquake distributions associated with hydrocarbon fields in the context of pore pressure diffusion models poroelastic stress transfer and isostasy theory these three mechanisms trigger or induce seismic instabilities at both local scale d 5 km and at regional scale d 20 km the modeled changes in stress are small 1 mpa whatever the tectonic setting each mechanism corresponds to different production processes 1 local hydraulic fracturing due to fluid injection induces seismic slip on cracks ml 3 within the injected reservoir through decreasing the effective stress 2 pure fluid withdrawal causes pore pressure to decrease within the reservoir it triggers adjustments of the geological structure to perturbations related to the reservoir response to depletion poroelastic mechanisms transfer this stress change from the reservoir to the surrounding levels whereml 5 seismic instabilities occur either above or below the reservoir 3 massive hydrocarbon recovery induces crustal readjustments due to the removal of load from the upper crust it can induce larger earthquakes ml 6 at greater distance from the hydrocarbon fields than the two other mechanisms

crustal velocity field of southwest japan subduction and arc arc collision we investigate crustal deformation in southwest japan over a 3 year period revealed by a permanent dense global positioning system gps array southwest japan is a part of the amurian plate a microplate moving about 10 mm yr toward the east with respect to the eurasian plate it overrides the philippine sea plate at the nankai trough and collides with the northeast japan arc in the central part of japan in this paper we first derive gps site velocities relative to the stable part of the amurian plate in order to isolate signals of crustal deformation caused by the subduction and or the collision the velocity field has a conspicuous feature indicating the interseismic elastic loading by the philippine sea plate slab at the nankai trough characterized by the northwestward movements of points throughout the studied area their amplitudes are the largest at the pacific coast and decay toward the japan sea coast with a subtle systematic shift of azimuths a model assuming an elastic half space the convergence rate at the nankai trough based on a refined euler vector and the strength of the coupling inferred from a thermal model could explain the velocity field in the western part of the studied area to a large extent those in the eastern part systematically deviate from them and the residual components there show east west shortening and north south extension this may represent crustal thickening and trenchward extrusion of crustal blocks caused by the collision between southwest and northeast japan this suggests that the collision between southwest and northeast japan gives rise to not only crustal thickening but also trenchward extrusion of crustal block a velocity contrast was found across the median tectonic line the largest inland active fault in japan but the current permanent gps network is not dense enough for us to discuss its coupling depth

mass balance of the greenland ice sheet from 1958 to 2007 we combine estimates of the surface mass balance smb of the greenland ice sheet for years 1958 to 2007 with measurements of the temporal variability in ice discharge d to deduce the total ice sheet mass balance during that time period we find a robust correlation r2 0 83 between anomalies in smb and in d which we use to reconstruct a continuous series of total ice sheet mass balance we find that the ice sheet was losing 110 70 gt yr in the 1960s 30 50 gt yr or near balance in the 1970s 1980s and 97 47 gt yr in 1996 increasing rapidly to 267 38 gt yr in 2007 multi year variations in ice discharge themselves related to variations in smb cause 60 20 more variation in total mass balance smb and therefore dominate the ice sheet mass budget copyright 2008 by the american geophysical union

broad weak regions of the nankai megathrust and implications for shallow coseismic slip abstract deep within the nankai trough subduction zone the plate boundary thrust slips along a well imaged megasplay fault system during the megathrust earthquakes that regularly strike southwest japan the routing of the active plate boundary thrust along an upward branching splay fault causes deep underthrusting of an unusually thick section of material attached to the subducting ocean crust here we present three dimensional seismic reflection data that shows this unusually thick section is fluid rich sediment that results in broad weakly coupled regions of the megathrust down into the updip end of the seismogenic zone the weakly coupled regions lie above an underthrust low seismic impedance presumed to be low velocity and low density sediment section that is between one and two kilometers thick and covers 3300 km2 at least one eighth of the total rupture area of the 1944 mw 8 1 tonankai earthquake this underthrust sediment section is broader and much deeper than inferred at other margins sediment underthrusting into the normally well coupled seismogenic zone likely releases fluids and elevates fluid pressure which reduces inter plate coupling along portions of the megasplay fault and allows coseismic rupture to propagate to unusually shallow depths and generate large tsunami as inferred for the 1944 tonankai event splay faults may be a common yet transient mechanism for developing weak subduction zone thrusts

assessing whether the 2017 mw 5 4 pohang earthquake in south korea was an induced event the moment magnitude m w 5 4 pohang earthquake the most damaging event in south korea since instrumental seismic observation began in 1905 occurred beneath the pohang geothermal power plant in 2017 geological and geophysical data suggest that the pohang earthquake was induced by fluid from an enhanced geothermal system egs site which was injected directly into a near critically stressed subsurface fault zone the magnitude of the mainshock makes it the largest known induced earthquake at an egs site

quantitative determination of stress by inversion of speckle interferometer fringe patterns experimental laboratory tests summary quantitative determination of crustal stress states remains problematic here we provide a synopsis of work that is leading towards the development of an optical interferometric method that may be applied in boreholes the major obstacle to the continued development of this technique has been the problem of determining the state of stress within a stressed continuum we demonstrate the solution of both the technical and analytical issues in this contribution specifically dual beam digital electronic speckle interferometry is used to record the stressrelief displacements induced by the drilling of blind holes into blocks subject to uniaxial compressive stresses speckle interferograms are produced at rates near 4 hz using a local pearson s correlation method and are stored for analysis this time lapse capability is useful when transient effects such as thermal expansion displacements produced by the heat of drilling or ongoing time dependent deformation are active four acrylic blocks subject to uniaxial compressions from 3 8 to 5 5 mpa with the compressions oriented at different angles with respect to the axes of the interferometry system were studied relative fringe phase information was extracted from appropriate interferograms and inverted to provide a quantitative measure of the 2 d stress field within the block in general the largest value of the stress obtained in the inversion agreed with the known stress to better than 70 per cent these measurements suggest the levels of uncertainty that might be expected by use of such optical interferometric techniques this technique may show promise for quantitative stress determination in the earth to complement existing techniques as well while the interferometric principles are not exactly the same as for the popular satellite based insar techniques the optical method here has the potential to be useful in analogue physical model laboratory studies of deformation in complex structures

greenland ice sheet melt from modis and associated atmospheric variability daily june july melt fraction variations over the greenland ice sheet gis derived from the moderate resolution imaging spectroradiometer modis 2000 2013 are associated with atmospheric blocking forming an omega shape ridge over the gis at 500 hpa height blocking activity with a range of time scales from synoptic waves breaking poleward 5 days to full fledged blocks 5 days brings warm subtropical air masses over the gis controlling daily surface temperatures and melt the temperature anomaly of these subtropical air mass intrusions is also important for melting based on the years with the greatest melt 2002 and 2012 during the modis era the area average temperature anomaly of 2 standard deviations above the 14 year june july mean results in a melt fraction of 40 or more though the summer of 2007 had the most blocking days atmospheric temperature anomalies were too small to instigate extreme melting

toward noncontacting seismology buried land mines and chemical waste may providethe contrast in elastic properties within the soil needed toachieve detection via near surface seismic methods thehazardous nature of these targets strongly indicates the useof noncontacting sources and receivers a home madeultrasonic parametric array allows us to insonify the soilwith an intense beam of sound this acoustic energy isconverted to elastic waves in the soil our noncontactingseismometer is a microwave doppler vibrometer that candetect seismic waves even through grass we believe thatdevelopments along these lines will ultimately lead to theability to probe large areas of the near surface in a safe andreliable fashion without physically touching the ground

substantial contribution to sea level rise during the last interglacial from the greenland ice sheet during the last interglacial period the eemian global sea level was at least three metres and probably more than five metres higher than at present1 2 complete melting of either the west antarctic ice sheet or the greenland ice sheet would today raise sea levels by 6 7 metres but the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the west antarctic ice sheet3 with model studies attributing only 1 2 m of sea level rise to meltwater from greenland4 5 this result was considered consistent with ice core evidence4 although earlier work had suggested a much reduced greenland ice sheet during the last interglacial period6 here we reconsider the eemian evolution of the greenland ice sheet by combining numerical modelling with insights obtained from recent central greenland ice core analyses our results suggest that the greenland ice sheet was considerably smaller and steeper during the eemian and plausibly contributed 4 5 5 m to the sea level highstand during that period we conclude that the high sea level during the last interglacial period most probably included a large contribution from greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the west antarctic ice sheet

glaciers dominate eustatic sea level rise in the 21st century ice loss to the sea currently accounts for virtually all of the sea level rise that is not attributable to ocean warming and about 60 of the ice loss is from glaciers and ice caps rather than from the two ice sheets the contribution of these smaller glaciers has accelerated over the past decade in part due to marked thinning and retreat of marine terminating glaciers associated with a dynamic instability that is generally not considered in mass balance and climate modeling this acceleration of glacier melt may cause 0 1 to 0 25 meter of additional sea level rise by 2100

consolidation state and strength of underthrust sediments and evolution of the decollement at the nankai accretionary margin results of uniaxial reconsolidation experiments 1 uniaxial reconsolidation experiments conducted on ocean drilling program drill cores along the muroto transect of the nankai accretionary margin demonstrate complex yield and postyield behavior and provide evidence for enhanced strengths within sediments beneath the decollement zone tests were conducted on samples collected from similar stratigraphic levels below the decollement and its seaward projection consolidation state of the samples increased landward and with depth and was tracked closely by sediment yield stress for all but one of the samples the sediments however exhibited substantial postyield strength up to 2 8 times the predicted in situ effective vertical stress beneath the protothrust zone this enhanced strength results from diagenesis that leads to matrix cementation during stable effective stress conditions within the underthrust section the close correspondence between yield stress and predicted in situ effective stress suggests that despite the cemented state the sediment matrix remains sensitive to in situ stress conditions the low yield stress of one sample collected within 40 m of the decollement fault at site 808 may reflect diagenesis under reduced effective stress conditions due to postconsolidation increases in pore pressure along the decollement due to their cemented state the strong underthrust sediments resist decollement downcutting beneath the toe of the prism leading to preferential incorporation of weaker continuously deforming accreted sediments during shear seismogenic slip along the decollement at depth may create stresses in excess of sediment strength causing shear failure and rapid release of trapped pore fluids feeding high pore fluid pressures along the decollement zone