drivers of holocene sea level change in the caribbean abstract we present a holocene relative sea level rsl database for the caribbean region 5 n to 25 n and 55 w to 90 w that consists of 499 sea level index points and 238 limiting dates the database was compiled from multiple sea level indicators mangrove peat microbial mats beach rock and acroporid and massive corals we subdivided the database into 20 regions to investigate the influence of tectonics and glacial isostatic adjustment on rsl we account for the local scale processes of sediment compaction and tidal range change using the stratigraphic position overburden thickness of index points and paleotidal modeling respectively we use a spatio temporal empirical hierarchical model to estimate rsl position and its rates of change in the caribbean over 1 ka time slices because of meltwater input the rates of rsl change were highest during the early holocene with a maximum of 10 9 0 6 m ka in suriname and guyana and minimum of 7 4 0 7 m ka in south florida from 12 to 8 ka following complete deglaciation of the laurentide ice sheet lis by 7 ka mid to late holocene rates slowed to

upper mantle electrical resistivity structure beneath the central mariana subduction system this paper reports on a magnetotelluric mt survey across the central mariana subduction system providing a comprehensive electrical resistivity image of the upper mantle to address issues of mantle dynamics in the mantle wedge and beneath the slow back arc spreading ridge after calculation of mt response functions and their correction for topographic distortion two dimensional electrical resistivity structures were generated using an inversion algorithm with a smoothness constraint and with additional restrictions imposed by the subducting slab the resultant isotropic electrical resistivity structure contains several key features there is an uppermost resistive layer with a thickness of up to 150 km beneath the pacific ocean basin 80 100 km beneath the mariana trough and 60 km beneath the parece vela basin along with a conductive mantle beneath the resistive layer a resistive region down to 60 km depth and a conductive region at greater depth are inferred beneath the volcanic arc in the mantle wedge there is no evidence for a conductive feature beneath the back arc spreading center sensitivity tests were applied to these features through inversion of synthetic data the uppermost resistive layer is the cool dry residual from the plate accretion process its thickness beneath the pacific ocean basin is controlled mainly by temperature whereas the roughly constant thickness beneath the mariana trough and beneath the parece vela basin regardless of seafloor age is controlled by composition the conductive mantle beneath the uppermost resistive layer requires hydration of olivine and or melting of the mantle the resistive region beneath the volcanic arc down to 60 km suggests that fluids such as melt or free water are not well connected or are highly three dimensional and of limited size in contrast the conductive region beneath the volcanic arc below 60 km depth reflects melting and hydration driven by water release from the subducting slab the resistive region beneath the back arc spreading center can be explained by dry mantle with typical temperatures suggesting that any melt present is either poorly connected or distributed discontinuously along the strike of the ridge evidence for electrical anisotropy in the central mariana upper mantle is weak

along axis gravity gradients at mid ocean ridges implications for mantle flow and axial morphology along axis gradients in mantle bouguer anomalies mbas were calculated for detailed gravity surveys at the southwest central and southeast indian ridges with half spreading rates of 0 9 2 3 and 3 1 cm yr respectively mba gradients at the very slow spreading southwest indian ridge are 0 4 0 7 mgal km similar to the gradients found at the slow spreading mid atlantic ridge whereas gradients at the central indian and southeast indian ridges are 0 2 0 35 mgal km the results of this study when combined with other published data show that axial mba gradients at ridge segments with an axial high are about 0 1 mgal km independent of spreading rate gradients at segments with a median valley are higher and generally decrease with increasing spreading rate the spreading rate independent mba gradient at ridge segments with an axial high represents the mantle gravity signal due to the focusing of upwelling within segments the larger gravity gradients at segments with an axial valley result from the superposition of intrasegment variations in crustal thickness on this mantle signal the consistent relation between along axis mba gradient and across axis axial morphology suggests that the axial morphology is related to the efficiency of along axis transport of melt

some theoretical predictions on the relationships among spreading rate mantle temperature and crustal thickness a series of numerical experiments on mantle flow and melting predict a positive relation between mantle temperature and crustal thickness the models also demonstrate that crust formed at slow spreading rates is more sensitive to variations in mantle temperature than crust formed at fast rates so that the range of calculated thicknesses is much greater for crust formed at slower rates an instantaneous mantle temperature increase results in a transient pulse of melt production that is also more pronounced at slower spreading rates the predicted behavior is caused by the interplay between mantle flow driven by plate separation and that driven by thermal compositional and melt related buoyancy a temperature increase results in a decrease in mantle viscosity and an increase in the depth at which melting begins a lower viscosity leads to stronger buoyancy driven flow that carries more mantle to shallow depths below the ridge thermal buoyancy effects which may result in cooling and mixing of depleted and undepleted material under the ridge appear to be of greater importance at slower spreading rates the steady state results are broadly consistent with global compilations of oceanic crustal thickness that show larger variations in crustal thickness at slower spreading rates than at faster rates thicknesses estimated from seismic refraction data from crust formed within a single segment of the mid atlantic ridge but at different spreading rates 1 0 to 1 9 cm yr are consistent with but do not prove the model results the transient pulse of melt production associated with a rapid increase in mantle temperature might occur when a ridge becomes proximal to a hot spot

changes in failure stress and stress transfer during the 1976 77 friuli earthquake sequence summary coulomb stress changes related to the sequence of strong earthquakes that affected the friuli area northeastern italy during the period 1976 77 have been investigated to explore the possibility of fault interaction and stress transfer mechanisms the seismic sequence that followed the mw 6 4 mainshock of 1976 may 6 consists of 5 events of mw between 5 2 and 6 0 during the same year and one event of mw 5 3 that occurred in 1977 september all characterized by thrust focal mechanisms the area is affected by a regional compressive stress which tends to activate n dipping thrust planes the goal of this study is to analyse and verify the relationship between the stress changes induced by the mainshock and the occurrence of subsequent events our results show that the mainshock induced a variation in the stress field in the area where most of the seismic events occurred our modelling shows a positive correlation between the areas of increased coulomb stress induced by the mainshock and the distribution of seismicity that followed this evidence suggests stress interaction and the possibility that the mainshock promoted the rupture of those faults associated with the event of 1976 may 9 mw 5 1 and the events of 1976 september 11 mw 5 2 and 5 6 1976 september 15 mw 6 0 and 1977 september 16 mw 5 3 the coulomb stress caused by co seismic dislocations decreased in the zone where an mw 5 9 earthquake occurred on september 15 at 03 15 when we included the contribution of the regional tectonic loading in the calculation of coulomb stress changes we found a positive correlation between the hypocentral area of the september 15 03 15 event and the area of coulomb stress increase aftershocks that occurred after the mainshock but before the september 15 03 15 event are also located in the area of coulomb stress increase

oceanic crustal thickness versus spreading rate a compilation of oceanic crustal thickness from seismic observations collected over the past two decades shows that the average crustal thickness away from plateaus is 6 km no systematic increase of crustal thickness with spreading rate is observed instead the data show large variations in crustal thickness at slow spreading ridges 3 8 km for half rates 30 mm yr the large variations at slow ridges and small variations at fast ridges are consistent with the results inferred from recent gravity studies of mid ocean ridges both data sets support the speculation of a transition from a 3 d structure of crustal accretion at slow ridges to a 2 d accretion pattern at fast ridges

modeling the influence of greenland ice sheet melting on the atlantic meridional overturning circulation during the next millennia a three dimensional earth system model of intermediate complexity including a dynamic ice sheet component has been used to investigate the long term evolution of the greenland ice sheet and its effects on the atlantic meridional overturning circulation amoc in response to a range of stabilized anthropogenic forcings our results suggest that the greenland ice sheet volume should experience a significant decrease in the future for a radiative forcing exceeding 7 5 w m 2 the modeled ice sheet melts away within 3000 years a number of feedbacks operate during this deglaciation implying a strong nonlinear relationship between the radiative forcing and the melting rate only in the most extreme scenarios considered the freshwater flux from greenland into the surrounding oceans of ca 0 1 sv during a few centuries induces a noticeable weakening of the amoc in the model

non transform offsets along the mid atlantic ridge south of the azores 38 n 34 n ultramafic exposures and hosting of hydrothermal vents ten contiguous non transform offsets ntos along the mid atlantic ridge mar south of the azores between 38 n and 35 40 n have been studied in detail using swath bathymetric acoustic backscatter and deep tow high resolution sidescan sonar tobi data in contrast with discontinuities studied elsewhere at slow spreading ridges these left lateral ntos are consistently broader and larger with complex structural fabrics accommodating the offset they are characterized by a range of elevated and faulted massifs detached from their segment flanks with an irregular acoustic backscatter pattern some of these massifs have been explored and sampled recently during dive cruises revealing that they are composed of upper mantle peridotites and lower crustal rocks and sometimes associated with high temperature hydrothermal venting water column surveys adjacent to these massifs show high ch4 and low tdm total dissolvable manganese concentrations possibly resulting from the process of serpentinization of ultramafic rocks the correlation between the shallow dome like shaped massifs and the high concentrations of ch4 associated with low levels of mn is of particular interest to predict the outcrop of ultramafic rocks within the ntos where no geological data are available the exposure of the ultramafic massifs within the ntos is favored by low magmatic supply and low angle detachment faulting occurring at segment ends the pervasive fracturing and faulting at these discontinuities favor circulation of hydrothermal fluids and occurrence of high temperature vent sites

palaeoclimate delayed holocene warming remnants of the laurentide ice sheet lasted until about 7 000 years ago climate simulations show that they caused the multimillennial delay between maximum early holocene solar radiation and temperatures evident in northern hemisphere proxy records

river gradient anomalies reveal recent tectonic movements when assuming an exponential gradient decrease along a river course abstract high resolution digital models combined with gis or other terrain modelling software allow many new possibilities in geoscience in this paper we develop describe and test a novel method the gla method to detect active tectonic uplift or subsidence along river courses it is a modification of hack s sl index method in order to overcome the disadvantages of the latter the core assumption of the gla method is that over geological time river profiles quickly adjust to follow an exponential decrease in elevation along the river course any large deviation can be attributed to active tectonic movement or to disturbances in erosion sedimentation processes caused by an anthropogenic structure e g artificial dam during the testing phase the locations of identified deviations were compared to the locations of faults identified on a 1 100 000 geological map results show that higher magnitude deviations are found within a maximum radius of 200 m from the fault and the majority of detected deviations within a maximum radius of 600 m from faults or thrusts however these results are not the best that could be obtained because the geological map that was used and the only one available for the area is not of the appropriate scale and was therefore not precise enough comparison of deviation magnitudes against psinsar measurements of vertical displacements in the vicinity revealed that in spite of the very few suitable points available a good correlation between both independent methods was obtained r 2 0 68 for the e research area and r 2 0 69 for the w research area the gla method was applied to the three test sites where previous studies have shown active tectonic movements it shows that deviations occur at the intersections between active faults and river courses as well as also correctly detected active uplift attributed to the increased sedimentation rate above an artificial hydropower dam and an increased erosion rate below the method gives promising results and it is acknowledged that the gla method needs to be tested in other locations around the world

electromagnetic constraints on a melt region beneath the central mariana back arc spreading ridge 1 an electrical resistivity profile across the central mariana subduction system shows high resistivity in the upper mantle beneath the back arc spreading ridge where melt might be expected to exist although seismic data are equivocal on the extent of a possible melt region the question arises as to why a 2 d magnetotelluric mt survey apparently failed to image any melt we have run forward models and inversions that test possible 3 d melt geometries that are consistent with the mt data and results of other studies from the region and that we use to place upper bounds on the possible extent of 3 d melt region beneath the spreading center our study suggests that the largest melt region that was not directly imaged by the 2 d mt data but that is compatible with the observations as well as the likely effects of melt focusing has a 3 d shape on a ridge segment scale focused toward the spreading center and a resistivity of 100 m that corresponds to 0 1 1 interconnected silicate melt embedded in a background resistivity of 500 m in contrast to the superfast spreading southern east pacific rise the 3 d melt region suggests that buoyant mantle upwelling on a ridge segment scale is the dominant process beneath the slow spreading central mariana back arc a final test considers whether the inability to image a 3 d melt region was a result of the 2 d survey geometry the result reveals that the 2 d transect completed is useful to elucidate a broad range of 3 d melt bodies

simulating arctic climate warmth and icefield retreat in the last interglaciation in the future arctic warming and the melting of polar glaciers will be considerable but the magnitude of both is uncertain we used a global climate model a dynamic ice sheet model and paleoclimatic data to evaluate northern hemisphere high latitude warming and its impact on arctic icefields during the last interglaciation our simulated climate matches paleoclimatic observations of past warming and the combination of physically based climate and ice sheet modeling with ice core constraints indicate that the greenland ice sheet and other circum arctic ice fields likely contributed 2 2 to 3 4 meters of sea level rise during the last interglaciation

a regionalized upper mantle rum seismic model seismic velocity heterogeneity in the earth s mantle is strongly concentrated near its top the shallow heterogeneity of the mantle correlates strongly with surface tectonics we use these observations as constraints of a tomographic experiment aimed at building a regionalized upper mantle rum reference model we use a select set of teleseismic travel times to minimize the mapping of mislocation into structure the data selection emphasizes the robustness of individual picks the form of the rum model is a set of velocity profiles as functions of depth through the upper mantle for each of the different tectonic provinces of earth together the profiles constitute a three dimensional model which incorporates considerable structural detail but is described by only 90 parameters and has only about 22 degrees of freedom this is achieved by irregularly sampling a detailed regionalization of the globe by detailed mapping of subducted lithosphere in the mantle as defined by seismicity and by combining these structures in an irregular grid in which bookkeeping is efficiently handled the resulting rum model includes subducting slabs as sharp fast features in the upper mantle old continents are fast young oceans are slow models have been derived for both compressional and shear velocity the rum model is designed to represent as much of upper mantle heterogeneity as seen by body wave travel times as possible with a simple model it can be useful as a reference model for individual tectonic regions travel times are efficiently generated for the rum model mislocations of explosions of known location are significantly reduced when corrections for the rum model are applied to travel time residuals for a spherically symmetrical earth model

geophysical characteristics of the southern mariana trough 11 50 n 13 40 n despite slow opening rates generally inferred for the mariana trough the southernmost part of the basin has fast spreading geophysical and morphologic characteristics that are unlike the features of the basin to the north a side scan sonar and geophysical survey maps the eastern part of the basin and the seafloor spreading center between 11 50 n and 13 40 n and identifies the following characteristics the ridge across axis profile forms a triangular to rounded high with relief of 100 to 500 m and cross sectional area variations of 1 to 7 km2 the along axis mantle bouguer gravity gradient is 0 2 mgal km axial segmentation occurs as overlapping axes and small deviation in trend no transform fault offsets exist despite significant changes in the trend of the spreading center characteristics of the surrounding basin include shallower overall depth than in the north no well developed frontal arc high in the southernmost trough the close proximity of submarine arc type volcanoes to the spreading center and tectonic fabric that is at a high angle to the trend of the spreading center on the eastern flank but is concordant on the western flank these characteristics imply different tectonic and magmatic conditions in the southern trough from the rest of the basin we propose that these effects are related to 1 the geometry of trench rollback in the southern trough leading to trench parallel extension generating inward radiating extensional faults 2 decoupling of the trench parallel extensional strain by the spreading center so that it primarily affects the eastern flank of the basin and 3 augmentation of the spreading center s magmatic budget by arc magmatic sources contributing to its fast spreading character although these effects may be accentuated in the southern mariana trough by the geometry of trench rollback and position of the slab which here underlies the spreading center they reflect distinct volcanic and tectonic processes which are varyingly expressed in back arc systems but are not normally found at mid ocean ridges

geomorphological variations at hydrothermal sites in the southern mariana trough relationship between hydrothermal activity and topographic characteristics abstract this study presents the first detailed geomorphological characterization of field scale geological features associated with hydrothermal systems in the southern mariana trough using near bottom swath mapping data collected by the autonomous underwater vehicle auv urashima during cruise yk09 08 and dive observation data acquired by the submersible shinkai6500 during cruise yk10 11 the motivation of this study is to examine the relationship between geomorphological characteristics and hydrothermal activity and to examine the nature of tectonic and volcanic controls on the hydrothermal system in this area two of the hydrothermal sites in the study area near 12 57 n 143 37 e are located on the active backarc spreading axis the snail and yamanaka sites one is located at the eastern foot of the axial high the archean site and two are located on an off axis knoll about 5 km from the spreading axis the pika and urashima sites the on axis area is divided into tectonically dominant and volcanically dominant zones volcanically dominant zones are characterized by mounds height 5 30 m diameter 250 320 m cut by fissures the snail and yamanaka sites are located adjacent to these fissures and are possibly represented local activity associated with a 4th order segment scale diking event on the basis of comparisons with previously studied cases on the east pacific rise with similar on axis geological characteristics in contrast to the on axis sites the off axis sites show no evidence of faulting the archean site at the foot of the axial high is characterized by a single mound height 50 100 diameter 250 300 m pronounced off axis lava flows and the presence of high amplitude rugged seafloor features the site is located at the top of the mound numerous ridge lines height mainly 2 6 m extend radially from the top of the mound and several chimney like structures up to approximately 6 m high occur on the top and slopes of the mound the pika site is located on the western peak of an off axis knoll and the newly discovered urashima site is located at the northern foot of the western peak of the same knoll the western peak is characterized by bumpy seabed textures formed by numerous smaller scale mounds and ridge lines however the eastern peak has a very smooth top and slope and shows no signs of hydrothermal activity numerous mounds heights 5 75 m diameters 50 350 m are developed on the comparatively gentle slope of the knoll in contrast to the numerous ridge lines height mainly 1 6 m developed on the relatively steep slopes of the knoll on the basis of the associated geomorphological features the three off axis sites archean pika and urashima were identified as localities created by relatively long term large scale hydrothermal activity as compared with sites in the on axis area the sustained activity at off axis sites appears closely related to an off axis upwelling magma system the three off axis hydrothermal sites are composed mainly of breccia assemblages that probably originated from hydrothermal activity with black smoker venting these areas are characterized by numerous ridge lines conical mounds and bumpy seabed texture whereas the on axis sites are characterized by the absence of ridge lines and the presence of white smoker and shimmering observed on dome shaped pillow mounds hence the distribution of ridge lines mound morphology and bumpy seabed texture is likely to correlate with hydrothermal activity

discovery of ancient and active hydrothermal systems along the ultra slow spreading southwest indian ridge 10 16 e 1 we report the discovery of active and fossil hydrothermal systems during r v knorr cruise 162 legs vii and ix along a 400 km long segment of the ultra slow southwest indian ridge swir between 10 and 16 e where the effective spreading rate for mantle upwelling is the slowest of any ocean ridge explored to date 8 4 mm yr 1 full rate eight of forty one optical temperature profiles contain hydrothermal plume characteristics that indicate firm evidence for two active vent sites and tentative evidence for as many as three others fossil hydrothermal material was recovered in 6 of the 38 dredge hauls and includes an occurrence of partially oxidized sulfide breccias four deposits ofsepiolite and silica as well as mn oxide and nontronite cemented breccias the massive sulfide deposit likely developed during mixing of upwelling hot fluids with cold seawater within a shallow permeable fault breccia along a deep seated normal fault bounding the southern rift valley wall silica and sepiolite deposits were found mostly on the rift valley walls and likely formed during low to moderate temperature ultramafic hosted hydrothermal activity the abundance of hydrothermal material and the frequency of localized hydrothermal activity is remarkable because the mantle upwelling and magma supply rates and hence the magmatic heat input along this section of the swir are lower than on any other explored segment of the global mid ocean ridge system this observation suggests that high mantle upwelling and magma supply rates are not required to drive mid ocean ridge hydrothermal systems and that a close relationship between magmatic heat input and hydrothermal activity may not be established at the ultra slow end of the ridge spreading spectrum the frequency and distribution of hydrothermal activity in the study area may reflect a largely tectonic control on fluid circulation with hydrothermal vent sites being preferentially associated with long lived faults that provide fluid pathways our results suggest the contribution of magma starved ridge segments to the global ocean lithosphere geochemical budget is potentially much larger than previously thought

high resolution magnetic signature of active hydrothermal systems in the back arc spreading region of the southern mariana trough high resolution vector magnetic measurements were performed on five hydrothermal vent fields of the back arc spreading region of the southern mariana trough using shinkai 6500 a deep sea manned submersible a new 3 d forward scheme was applied that exploits the surrounding bathymetry and varying altitudes of the submersible to estimate absolute crustal magnetization the results revealed that magnetic anomaly derived absolute magnetizations show a reasonable correlation with natural remanent magnetizations of rock samples collected from the seafloor of the same region the distribution of magnetic anomaly derived absolute magnetization suggests that all five andesite hosted hydrothermal fields are associated with a lack of magnetization as is generally observed at basalt hosted hydrothermal sites furthermore both the pika and urashima sites were found to have their own distinct low magnetization zones which could not be distinguished in magnetic anomaly data collected at higher altitudes by autonomous underwater vehicle due to their limited extension the spatial extent of the resulting low magnetization is approximately 10 times wider at off axis sites than at on axis sites possibly reflecting larger accumulations of nonmagnetic sulfides stockwork zones and or alteration zones at the off axis sites

chemical composition of hydrothermal fluids in the central and southern mariana trough backarc basin abstract we present a geochemical data set from hydrothermal fluids collected from the central and southern mariana trough during dive programs conducted in the 1990s the fluid samples were collected from two hydrothermal fields 1 the alice springs field 18 13 n 144 42 e water depth 3600 m on the axial ridge crest of the central marana trough and 2 the forecast field 13 24 n 143 55 e water depth 1470 m on peak b seamount one of a cluster of small volcanic seamounts which represents a unique tectonic setting in the southern mariana trough gas geochemistry of the alice springs fluid showed he and c isotope ratios in the range of morb whereas that of the forecast fluid showed a higher co 2 3 he ratio and 13 c enriched isotope ratio both of which are commonly recognized in hydrothermal fluids from intraoceanic arc volcanoes the major and minor element composition of the alice springs fluid is characterized by enrichment in mobile alkali elements such as k rb and cs this geochemical signature is in accordance with the well known characteristics of basaltic lava collected from the same area which show substantial enrichment in incompatible elements as interpreted in previous petrological studies this signature is considered to be an arc geochemical signal reflecting contribution from the subduction component the b concentration of the alice springs fluid is also high and is another arc geochemical signal the forecast fluid by contrast did not show enrichment in the mobile alkali elements although its b concentration is high the forecast fluid is characterized instead by enrichment in ca and sr coupled with depletion in na and li as discussed in previous studies this signature is attributed to hydrothermal reactions at rather low temperature due to the shallow water depth we recognize two different arc geochemical signals in these two hydrothermal fluids mobile alkali elements in the alice spring fluid and gaseous species in the forecast fluid this difference could reflect different behaviors of these species during magmatic processes in the mantle wedge beneath the mariana trough backarc spreading center

the spatial and temporal complexity of the holocene thermal maximum the holocene thermal maximum a period of relatively warm climate between 11 000 and 5 000 years ago1 2 is most clearly recorded in the middle and high latitudes2 3 of the northern hemisphere where it is generally associated with the local orbitally forced summer insolation maximum however proxy based reconstructions have shown that both the timing and magnitude of the warming vary substantially between different regions2 3 4 suggesting the involvement of extra feedbacks and forcings here we simulate the holocene thermal maximum in a coupled global ocean atmosphere vegetation model we find that before 7 000 years ago summers were substantially cooler over regions directly influenced by the presence of the laurentide ice sheet whereas other regions of the northern hemisphere were dominated by orbital forcing our simulations suggest that the cool conditions arose from a combination of the inhibition of labrador sea deep convection by the flux of meltwater from the ice sheet which weakened northward heat transport by the ocean and the high surface albedo of the ice sheet we thus conclude that interglacial climate is highly sensitive to relatively small changes in ice sheet configuration

back arc basin basalt systematics the mariana east scotia lau and manus back arc basins babs have spreading rates that vary from slow 100 mm yr and extension axes located from 10 to 400 km behind their island arcs axial lava compositions from these babs indicate melting of mid ocean ridge basalt morb like sources in proportion to the amount added of previously depleted water rich arc like components the arc like end members are characterized by low na ti and fe and by high h2o and ba la the morb like end members have the opposite traits comparisons between basins show that the least hydrous compositions follow global morb systematics and an inverse correlation between na8 and fe8 this is interpreted as a positive correlation between the average degree and pressure of mantle melting that reflects regional variations in mantle potential temperatures lau manus hotter than mariana scotia this interpretation accords with numerical model predictions that faster subduction induced advection will maintain a hotter mantle wedge the primary compositional trends within each bab a positive correlation between fe8 na8 and ti8 and their inverse correlation with h2o 8 and ba la are controlled by variations in water content melt extraction and enrichments imposed by slab and mantle wedge processes systematic axial depth as a proxy for crustal production variations with distance from the island arc indicate that compositional controls on melting dominate over spreading rate hydrous fluxing enhances decompression melting allowing depleted mantle sources just behind the island arc to melt extensively producing shallow spreading axes flow of enriched mantle components around the ends of slabs may augment this process in transform bounded back arcs such as the east scotia basin the re circulation by mantle wedge corner flow to the spreading axes of mantle previously depleted by both arc and spreading melt extraction can explain the greater depths and thinner crust of the east lau spreading center manus southern rifts and mariana trough and the very depleted lavas of east scotia segments e8 e9 the crust becomes mid ocean ridge mor like where the spreading axes further away from the island arc and subducted slab entrain dominantly fertile mantle

crustal structure of the mariana trough three seismic refraction profiles were shot in the mariana trough in the vicinity of the proposed axial rift spreading center one long east west trending line was shot across the axial high region the elevated portion of the trough associated with the rift zone the two other lines were shot in a rough north south orientation subparallel to the trend of the axial rift on crusts 1 and 5 6 m y old comparison of the results of the ray tracing analysis for these two profiles indicated that thinning of layer 2a velocity of 3 3 km s and development of a distinct layer 2b velocity of 5 3 km s and development of a distinct layer 2b velocity of 5 3 km s and layer 3a velocity of 6 7 km s takes place with increasing crustal age implying a process of crustal evolution the presence of large scale crustal faults was noted in several instances in addition a consistent but low upper mantle seismic velocity of 7 7 km s was measured for all three lines these characteristics correlate with those previously observed for other areas of young oceanic crust when compared with major active spreading centers such as the mid atlantic ridge and east pacific rise the mariana trough appears similar to the formermore in most respects both the mid atlantic ridge and mariana trough are slow spreading 1 2 cm yr half rate and are characterized by rough topography an axial rift and a thick layer sup 2 like the mid atlantic ridge the mariana trough also has no low velocity zone in the crust that could be interpreted as a magma chamber at the spreading center less

3 d configuration of subducted lithosphere in the western pacific summary computer graphics techniques are used to portray the shape of the subducted lithosphere as seen from different views the configuration of the subducted lithosphere is represented by a surface that approximately fits the upper envelope of the slab like spatial distribution of earthquake hypocentres in the benioff wadati zone regions considered include tonga kermadec izu bonin mariana japankuril kamchatka and sunda banda in the western pacific these regions include all known zones of deep focus earthquakes except the tectonically complex regions of new hebrides solomon new britain molucca sea phillipines the mediterranean and south america shown at the same scale and with the effect of earth s sphericity included the views are very useful for illustrating variations in the configuration of the subducted lithosphere between different regions and within the same region the results illustrate the segmentation of the upper several hundred kilometres of subducted lithosphere into major units of relatively uniform configuration these segments are also clearly defined by major features of surface morphology of the trench and upper plate the distribution of subduction related volcanism and by the intersection with the subduction zone of major bathymetric features of the subducting plate in contrast the deeper portions of the slabs have a more complex and variable configuration discordances between the deep and shallow structures are often important on a regional scale and suggest that there are relative horizontal movements between the surface trace of the subduction zone and the material at depth into which the subducted lithosphere is sinking these relative movements appear to be intimately associated with the tectonic evolution of the region and indicate a regional aspect of subduction that is often overlooked in an attempt to explain the global variability of the shapes of subducted lithosphere although earthquake activity ceases at 680 km possibly because of a phase transition the geometry of the deep portion of subducted lithosphere suggests that subducted lithosphere does penetrate to greater depth

controls on back arc crustal accretion insights from the lau manus and mariana basins abstract together the lau manus and mariana basins encompass a broad range of conditions of back arc basin development marine surveys have determined the tectonic setting and reconnaissance scale geophysical and geochemical properties of the extension axes in these basins we review these data to examine crustal accretion characteristics in the back arc setting in each basin magmatism is enhanced in spreading centres near the arc volcanic front but decreases becoming deficient in axes further from the arc in the lau and manus basins the axes extend far behind the arc and develop typical mid ocean ridge mor like characteristics we propose that these variations are controlled by the subducting slab which shapes composition and flow within the mantle wedge water released from the slab lowers the mantle solidus and increases in concentration toward the volcanic arc spreading centres near the arc advect the hydrated mantle material enhancing melt production slab induced flow carries melt depleted mantle material back beneath the basin where it mixes with ambient mantle spreading centres further from the arc advect this mantle mixture and produce thinner than normal crust far from the arc spreading centres advect essentially mid ocean ridge basalt morb source mantle and their characteristics are mor like thus in addition to spreading rate effects on mantle melting that predominate at mors in back arc basins the subducting slab introduces additional systematic effects

sedimentary volcanic and tectonic processes of the central mariana arc mariana trough back arc basin formation and the west mariana ridge 1 we present new multichannel seismic profiles and bathymetric data from the central marianas that image the west mariana ridge wmr remnant arc both margins of the mariana trough back arc basin the modern arc and eocene frontal arc high these data reveal structure and stratigraphy related to three periods of arc volcanism and two periods of arc rifting we interpret the boundary between accreted back arc basin and rifted arc crust along the mariana trough and support these findings with drilling results and recent seismic refraction and gravity studies we show that with the exception of a few volcanoes behind the volcanic front that straddle the boundary between crustal types the modern mariana arc is built entirely on rifted arc crust between 14 and 19 n our data indicate that there is more accreted back arc seafloor to the west of the mariana trough spreading axis than to the east confirming previous evidence for an asymmetric basin the rifted margin of the wmr remnant arc forms a stepped pattern along the western boundary of the mariana trough between 15 30 and 19 n in this region linear volcanic cross chains behind the wmr are aligned with the trend of mariana trough spreading segments and the wmr ridges extend into the back arc basin along the same strike these ridges are magmatic accommodation zones which to the north along the izu bonin arc punctuate tectonic extension for the wmr we hypothesize that rift basins are more commonly the sites where spreading segment offsets nucleate whereas magmatic centers of spreading segments are sites where magmatism continues from arc volcanism through rifting to back arc spreading the mariana trough is opening nonrigidly and is characterized by two predominant abyssal hill trends nnw sse in the north and n s in the south between the only two basin crossing fracture zones at 15 5 and 17 5 n s axes propagated north at the expense of nnw axes

a seismic stratigraphic analysis of mariana forearc basin evolution new seismic data collected in the 14 5 18 5 n mariana segment of the izu bonin mariana island arc system image six seismic stratigraphic sequences that can be mapped throughout the inner forearc these sediments were most likely deposited from 35 ma to the present the oldest stratigraphic units 1 2 and 3 are syn rift volcaniclastic deposits unit 4 deposits accumulated during a period of mild structural inversion which resulted in several isolated reverse faulted anticlines within the forearc sedimentary basin a late period of extensional deformation began near the end of unit 5 deposition and continued through unit 6 sedimentation to the present seismic lines show that the basement of the forearc is composed of large rotated fault blocks and half grabens with ne nw and nne trends fault offset calculations show that basement faults with dips between 45 and 50 account for only 4 total extension in the forearc south of 16 3 n normal growth faults initiated during basement extension offset the frontal arc high from a deep forearc basin from correlations with the known geologic history we hypothesize that extension during deposition of units 1 through 3 corresponds to rifting of the eo oligocene arc between 35 ma and 29 ma older deposits being too thin to be seismically resolvable localized compression during unit 4 accumulation occurred some time after eo oligocene rifting in the early miocene late stage normal faulting near the end of deposition of unit 5 and throughout unit 6 accumulation may be associated with the opening of the mariana trough backarc basin from 8 ma years to the present there is a higher density of these later faults in the inner forearc between 15 5 and 17 n and in the outer forearc between 14 n and 18 n recent extension is at least partially accommodated by reactivation of older basement faults with the same ne nw and nne trends stratigraphic relationships indicate that the inner forearc south of 16 3 n has differentially subsided and tilted trenchward possibly as a result of a recent change in subducting slab geometry or subducted relief under the forearc

constraints on the location and mechanism of the 1511 western slovenia earthquake from active tectonics and modeling of macroseismic data abstract the 1511 western slovenia earthquake m 6 9 is the largest event occurred so far in the region of the alps dinarides junction though it strongly influences the regional seismic hazard assessment the epicenter and mechanism are still under debate the complexity of the active tectonics of the alps dinarides junction is reflected by the presence of both compressional and transpressional deformations this complexity is witnessed by the recent occurrence of three main earthquake sequences the 1976 friuli thrust faulting events the 1998 bovec krn mountain and the 2004 kobarid strike slip events the epicenters of the 1998 and 2004 strike slip earthquakes ms 5 7 and ms 4 9 respectively lie only 50 km far from the 1976 thrust earthquake ms 6 5 we use the available macroseismic data and recent active tectonics studies to assess a possible epicenter and mechanism for the 1511 earthquake and causative fault according with previous works reported in the literature we analyze both a two and a single event case defining several input fault models we compute synthetic seismograms up to 1 hz in an extended source approximation testing different rupture propagations and applying a uniform seismic moment distribution on the fault segments we extract the maximum horizontal velocities from the synthetics and we convert them into intensities by means of an empirical relation a rounded to integer misfit between observed and computed intensities is performed considering both a minimized and a maximized databases built to avoid the use of half degree macroseismic intensity data points our results are consistent with a 6 9 magnitude single event rupturing 50 km of the idrija right lateral strike slip fault with bilateral rupture propagation

no slab derived co2 in mariana trough back arc basalts implications for carbon subduction and for temporary storage of co2 beneath slow spreading ridges the southern mariana trough is particularly well suited to study mass balance in subduction zones because the flux of material recycled from the subducted slab has been shown to diminish to negligible levels in the southernmost part of the area we present new he and ar concentration and isotopic data for 16 back arc basaltic glasses and combine these with previously published co2 and h2o concentration and 13c data to explore the recycling of carbon and light noble gases in the mariana back arc degassing has affected all samples and is particularly extensive in more water rich samples i e those containing the largest recycled component the degassing history features three stages 1 deep degassing which commenced when the melt reached saturation of co2 and noble gases in the mantle 2 preeruptive degassing during storage in the crust mantle transition zone which involved addition of extraneous co2 to the vapor phase and 3 eruption co2 released during stage 1 was at least partially incorporated into wall rock and subsequently remobilized during stage 2 degassing of later magma batches reconstructed parental values for 3he 4he 13c co2 3he and co2 40ar are indistinguishable from those of mid ocean ridge basalt this implies that there is negligible recycling of subducted carbon helium or argon into the source of mariana trough basalt

distinct regional differences in crustal thickness along the axis of the mariana trough inferred from gravity anomalies we have compiled extensive gravity and bathymetry data for the whole mariana trough which were collected during several japanese scientific cruises over the last few years this study aims to clarify the lateral distribution of the local differences in geochemical signatures which have been observed locally in the mariana trough shipboard free air gravity anomaly data from eight japan agency for marine earth science and technology jamstec cruises were compiled with those crossover errors of 2 85 mgal mantle bouguer anomalies mba were calculated by subtracting the predictable gravity signal due to the seawater crust and crust mantle density boundaries the crustal thickness variation along the spreading axis was estimated from the mba different features in crustal thickness its variation and segment length for each segment allow us to identify four distinct regional differences in magmatic activity along the spreading axis of the mariana trough segment in region a to the north of 20 35 n shows the largest sectional dimensions of crust along the axis and it is probably affected by an additional supply from island arc magma sources a variety of crustal thickness values and of along axis crustal thickness variations in region b between 15 38 n and 20 35 n suggests two types of segments one is similar to a slow spreading ridge segment that has a plume like mantle upwelling under the spreading axis and the other is a magma starved segment region c between 14 22 n and 15 38 n is a less magmatic region individual crustal thickness averages of 3 4 4 1 km region d to the south of 14 22 n has higher individual crustal thickness averages of 5 9 6 9 km suggesting higher magmatic activity with a sheet like mantle upwelling under the spreading axis different features in the mba for off axis areas suggest that these four regions have existed since the mariana trough started spreading moreover comparison between our results of crustal thickness and previous geochemical results indicates that less magmatic spreading segments with thin crust which are locally distributed in both regions b and c probably result from mantle source depleted of water and incompatible elements this suggests that lateral compositional variation of water and incompatible elements exists on a segment scale in the mantle source beneath the spreading axis of the mariana trough

a two and three dimensional analysis of gravity anomalies associated with the east pacific rise at 9 n and 13 n we have used a unique data set collected during the 1985 east pacific rise multichannel seismic experiment to reevaluate the constraints that gravity data can place on the crustal structure of the east pacific rise epr the close spacing of track lines within the two main survey areas 8 45 n 9 55 n and 12 20 13 30 n allowed us to perform three dimensional analyses of high quality gravity data 1 mgal uncertainity obtained with the bell aerospace bgm 3 gravity meter our gravity modeling was enhanced by the availability of high resolution sea beam bathymetric data and by independent structural constraints provided by seismic reflection and refraction data to model the crustal and upper mantle density structure at the ridge axis we first calculated the gravity anomalies due to the density contrasts at the water crust and crust mantle boundaries and the changes in density caused by the cooling of the lithosphere with age and subtracted these predictable signals from the observed free air anomaly the residual anomalies were then used to place constraints on the magnitude and distribution of anomalous mass at the epr our results show that over 90 of the power in the observed free air anomaly can be modeled by these predictable components of the gravity signal the amplitude and wavelength of the small residual anomaly can be modeled by a broad region 20 km wide centered on the rise axis of slightly lower than normal crustal and or upper mantle densities 0 03 mg m 3 this region of anomalous mass and density variations in the underlying mantle provide the principle isostatic support for the axial topographic high the anomalies are consistent with but do not require the presence of a low density crustal magma chamber at the rise axis if a largely molten magma chamber exists then the gravity data require that it be a narrow volumetrieally small body there are first order differences in the distribution of anomalous mass between the two survey areas with the 9 n region generally being characterized by lower densities in the axial region along axis variations in anomalous mass within each of the survey areas correlate with first order changes in the depth and cross sectional shape of the epr axial high we attribute these differences in axial morphology and the amplitude of the associated gravity anomalies to along strike changes in the size of the crustal magma chamber the width of the surrounding zone of cooling crustal rocks and densities in the uppermost mantle beneath the rise axis

gravity anomalies crustal thickness and the pattern of mantle flow at the fast spreading east pacific rise 9 10 n evidence for three dimensional upwelling gravity bathymetry and crustal structure data from the 9 to 10 n segment of the fast spreading northern east pacific rise are used to investigate density variations in the mantle in order to determine the pattern of mantle upwelling and melt distribution beneath the segment mantle bouguer gravity anomaly contours are nearly parallel to the ridge axis and there is only 3 4 mgal variation in axial mantle bouguer anomalies along the entire segment however inclusion of the gravity effects of variations in crustal thickness and structure results in a significant change in the pattern of gravity anomalies the subcrustal gravity anomalies show a very distinct gravity low centered over the segment axial depth minimum near 9 50 n axial subcrustal gravity anomalies increase by 10 mgal between 9 50 n and 9 23 n a gradient of 0 2 mgal km since the ridge axis has a uniform cross sectional shape throughout the entire segment with abundant evidence of magmatic activity along its entire length it is unlikely that there are significant variations in crustal thermal structure other than at the ridge tips we thus attribute the subcrustal gravity anomalies to density variations within the mantle the distinct gravity low centered over the depth minimum provides qualitative evidence that mantle upwelling is focused or enhanced at that location the effects of lithospheric cooling and subsidence away from the axis were removed from the bathymetry and free air gravity anomalies to isolate residual gravity and gravity anomalies associated with the axis the residual anomalies were modeled by considering the axial bathymetric high to be a flexural feature resulting from the upward buoyant load of a region of low density material beneath the axis after accounting for the isostatic effects of variations in crustal thickness the remaining mass deficiency necessary to support the axial high and satisfy the gravity anomalies is not evenly distributed along the axis but is 35 greater beneath the axial depth minimum at 9 50 n than between 9 17 and 9 27 n mantle upwelling in this segment thus appears focused or enhanced in the area of the depth minimum

controls on segmentation and morphology along the back arc eastern lau spreading center and valu fa ridge back arc spreading centers increasingly depart from mid ocean ridge mor characteristics with proximity to the arc volcanic front the close association of these departures with slab derived materials in erupted lavas suggests that subduction related chemical effects are their primary cause the eastern lau spreading center elsc and valu fa ridge vfr are type examples of this process together they constitute a first order spreading center in the lau back arc basin that progressively converges on the tofua arc volcanic front from north to south here we use ship multibeam and deep towed side scan sonar data to examine variations in axial morphology and volcanism at the second and third order segment scale along these ridges and develop a model for the processes that control them closest to the arc vfr and the southern segment of the elsc shoal toward second order segment ends in contrast to mors northward and beyond 70 km from the arc the axis becomes abruptly deeper and flatter and no longer shoals toward second order segment ends at vfr along axis topographic highs correlate with the location of arc volcanoes along slab flow lines these correlations are weaker along the southernmost elsc segment and absent along elsc segments farther north the observations show a modulation of back arc segmentation with arc proximity that rapidly diminishes with distance they support a model of the mantle wedge with a strongly hydrous domain within 70 km of the arc within which the arc and ridge interact and a much less hydrous domain farther from the arc without evident arc ridge interactions

tectonic implications of the gps velocity field in the northern adriatic region 1 continuous and episodic gps observations between 1991 and 2004 show that adria moves independently of both stable eurasia and nubia adria moves nne at 3 4 5 mm yr increasing from n to s relative to eurasia and may be fragmenting along the gargano dubrovnik seismic zone the observed 2 3 mm yr of n s adria eurasia convergence is taken up by contraction across a narrow 70 km zone in the eastern alps and concomitant extrusion of the alpine north pannonian unit the adria central dinarides boundary is a broader collisional zone with intense 1 1 5 mm yr shortening near shore and 2 mm yr spread across the dinarides the remaining 1 2 mm yr motion e of the alps and ne of the dinarides is absorbed by the inverted contracting pannonian basin leaving no significant deformation above 0 5 mm yr in the western and northern carpathians and european platform

gravity anomalies isostasy and mantle flow at the east pacific rise crest bathymetry and gravity data obtained during a detailed hydrosweep survey of the southern east pacific rise from 7 s to 9 s are used to investigate isostasy at the axis of a fast spreading mid ocean ridge in particular we examine the manner in which the bathymetric crestal high is supported and how this support varies along the axis within the 160 km long 7 12 s 8 38 s ridge segment the crestal high stands about 400 m above the adjacent ridge flanks and has a nearly constant minimum axial depth for a distance of 140 km the summit is broad and flat and an axial summit caldera is present for the entire length of the ridge segment however the width and cross sectional shape of the crestal high vary systematically along the axis it is broad with gentle slopes in the center of the segment but becomes progressively narrower and steeper toward the ends of the ridge segment the ridge crest is marked by a free air gravity anomaly high about 15 20 km wide with an amplitude of 10 15 mgal relative to the ridge flanks mantle bouguer anomalies vary systematically along the axis with minimum values found near the center of the segment the axial mantle bouguer anomalies thus do not reflect the axial depth but are correlated with changes in the cross sectional area of the crestal bathymetric high the effects of cooling and subsidence away from the axis were removed from the bathymetry and free air anomalies to isolate residual topographic and gravity anomalies associated with the ridge crest the residual crestal bathymetric high was modeled as a flexural feature resulting from the upward buoyant load of a region of low density material centered beneath the axis the lithosphere was treated as a broken plate either with a constant flexural rigidity or an effective elastic thickness te which grows at a rate proportional to the square root of distance from the axis the best fitting values of te for the constant rigidity case are in the range of 0 3 0 6 km for the growing plate model te increases at a rate of 0 2 0 3 km the gravity constrains the mass deficiency to extend to a depth of 20 30 km for both lithospheric models we interpret this low density material as a region of partial melt feeding magma to the ridge axis the best fitting density anomalies imply that a 4 9 melt fraction is present beneath the crestal high upwelling of melt to the axis is thus confined to a narrow zone within about 10 km of the axis the mass deficiency and thus the upwelling partial melt are not distributed evenly along the ridge axis but rather are concentrated in the central portion of the ridge segment it thus appears that differences between the along axis gravity and depth patterns observed at slow spreading and at fast spreading ridges are not the result of a change from three dimensional focused upwelling at slow spreading ridges to two dimensional sheetlike upwelling at fast spreading ridges rather the differences in axial gravity and depth between fast and slow spreading ridges reflect differences in the efficiency of the shallow along axis magma distribution

the spreading rate dependence of three dimensional mid ocean ridge gravity structure we analyze over 1300 km of high resolution along axis gravity profiles at ridges with half spreading rates ranging from 1 2 to 5 5 cm yr the results show consistently higher along axis gradients of mantle bouguer anomaly at the slow spreading mid atlantic ridge mar 0 3 1 2 mgal km than at the intermediate to fast spreading cocos nazca ridge and east pacific rise epr 0 1 0 2 mgal km the regional peak to trough amplitude of mantle bouguer anomaly is also greater along the mar 30 60 mgal than the cocos nazca ridge and the epr 10 20 mgal with increasing spreading rate the regional peak to trough amplitude of axial seafloor depth decreases from 1000 1700 m to 200 700 m 3 d numerical experiments suggest that mantle contributions to the gravity can be significant only near large offset transforms at the more commonly observed non transform offsets gravity anomalies will reflect crustal thickness variations the along axis gravity data thus indicate that the amplitude of along axis crustal thickness variation decreases with increasing spreading rate we propose that this spreading rate dependent crustal accretion style may originate in the mantle finite amplitude mantle upwelling is intrinsically plume like 3 d beneath a slow spreading ridge but more sheet like 2 d beneath a fast spreading ridge such a transition in mantle upwelling may occur if the relative importance of passive upwelling over buoyant upwelling increases with increasing spreading rate small amplitude 3 d upwellings may occur at a fast spreading ridge but their effects on crustal thickness variations will be significantly reduced by along axis melt flows along a persistent low viscosity crustal magma chamber in contrast the large crustal thickness variations due to 3 d mantle upwellings will be maintained at a slow spreading ridge because less along axis melt flows can occur in the colder and more rigid crust there

spreading process of the northern mariana trough rifting spreading transition at 22 n 1 we have conducted a geophysical survey of the northern mariana trough from 19 n to 24 n the trough evolves southward from incipient rifting to seafloor spreading within this region this study aims to clarify the location and time of the rifting to spreading transition which was controversial previously and processes of seafloor spreading after the transition the new data set includes swath bathymetry with side scan images and magnetic vector anomaly the mantle bouguer gravity anomaly mba was calculated using the free air gravity anomaly from satellite altimetry the rifting to spreading transition occurs at about 22 n which is proved by seafloor spreading fabric in the bathymetry clear magnetic lineations and the bull s eye pattern in mba four ridge segments separated by three nontransform discontinuities are recognized between 19 n and 22 n the northernmost segment has relatively abundant magma supply compared with the other segments which is estimated from a larger segment length shallower axial depths with no rift valley and lower mba the next segment to the south is on the other hand a magma starved segment with a prominent rift valley two anomalously deep grabens called the central grabens formed by amagmatic extension occur near the segment ends the succession of magma rich magma starved and normal segments with increasing distance from the volcanic arc is the same as the observation in the lau basin reported by martinez and taylor 2002 the magnetic anomaly revealed the detailed history of the spreading the seafloor spreading between 19 n and 20 n began prior to 5 ma and that between 20 n and 21 30 n began at about 4 ma spreading half rates in the western side of the spreading center were 2 to 3 cm year before 2 58 ma south of 21 30 n and during the matuyama chron north of 21 30 n but an average during the brunhes chron is 1 cm year or less orientations of the ridge axes which range from 20 to 0 at present have rotated about 20 clockwise since the start of the spreading these changes in rate and direction might be associated with changes in the motion of the philippine sea plate spreading has been asymmetric in the northern mariana trough the spreading rates of the western side of the spreading center have been significantly larger than the eastern counterpart in general the asymmetry may have been caused by an interaction of mantle upwelling systems under the volcanic front and the backarc spreading center and would be a characteristic of backarc spreading

coseismic fault zone deformation revealed with differential lidar examples from japanese mw 7 intraplate earthquakes abstract we use two recent japanese earthquakes to demonstrate the rich potential as well as some of the challenges of differencing repeat airborne light detection and ranging lidar topographic data to measure coseismic fault zone deformation we focus on densely vegetated sections of the 14 june 2008 iwate miyagi m w 6 9 and 11 april 2011 fukushima hamadori m w 7 1 earthquake ruptures each covered by 2 m resolution pre event and 1 m resolution post event bare earth digital terrain models dtms obtained from commercial lidar providers three dimensional displacements and rotations were extracted from these datasets using an adaptation of the iterative closest point icp algorithm these displacements remain coherent close to surface fault breaks as well as within dense forest despite intervals of 2 years iwate miyagi and 4 years fukushima hamadori encompassed by the lidar scenes differential lidar analysis is thus complementary to interferometric synthetic aperture radar insar and sub pixel correlation techniques which often break down under conditions of long time intervals dense vegetation or steep displacement gradients although the icp displacements are much noisier than overlapping insar line of sight displacements they still provide powerful constraints on near surface fault slip in the fukushima hamadori case near fault displacements and rotations are consistent with decreased primary fault slip at very shallow depths of a few tens of meters helping to account for the large along strike heterogeneity in surface offsets observed in the field this displacement field also captures long wavelength deformation resulting from the 11 march 2011 tohoku great earthquake

large scale ground deformation of etna observed by gps between 1994 and 2001 we have processed thirty global positioning system gps campaigns carried out at etna from 1994 to early 2001 between the last two main flank eruptions of the mt etna sicily italy this rest period allowed us to investigate the deep magma plumbing system of the mt etna the temporal dynamics of twenty three points observed three times or more were analyzed all the time series show a first order linear trend during the five years period it suggests that the volcano was continuously deformed by the action of a deep source while a discrete activity of the volcano was observed at the summit we have interpreted the residual deformation field as the result of an major eastward motion of the eastern flank of the volcano

scismotectonics of the northwest external dinarides abstract the region of the tectonic contact between the alps and the dinarides is studied comparing all the available geological geophysical and seismological data the peculiar crustal structures in particular the difference in thickness of the alps dinarides and pannonian basin can be correlated to the seismically active zones the highest seismicity is related to the adria microplate underthrusting the southern alps beneath the friulian piedmont arc this movement produces a composite lateral slip and an underthrust which is subparallel to the dinarides along the yugoslav coast the seismicity in western yugoslavia is more diffuse than in friuli although it is possible to pick out three narrow parallel bands with dextral shear subparallel to the periadriatic vardar fault system which separate the apulia from the pannonian area the interaction of this system with the sinistral strike slip faults of the western carpathians belt enhances the seismicity of the easternmost sector of the alps analogies and differences in the seismotectonic behaviour between central friuli and western yugoslavia are studied and a unique model with a vertical mechanical disengagement at the rear of the compressive fronts of the southern alps and external dinarides is proposed

evidence from gravity data for focused magmatic accretion along the mid atlantic ridge gravity data from the mid atlantic ridge between latitudes 27 50 n and 30 40 n show that the accretion of magma at the ridge is focused at discrete centres along the spreading axis large positive gravity anomalies equivalent to reductions of almost 50 in crustal thickness are observed over non transform discontinuities bounding spreading segments

holocene thermal maximum in the western arctic 0 180 w the spatio temporal pattern of peak holocene warmth holocene thermal maximum htm is traced over 140 sites across the western hemisphere of the arctic 0 180 w north of 60 n paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer than present conditions at 120 of these sites at the 16 terrestrial sites where quantitative estimates have been obtained local htm temperatures primarily summer estimates were on average 1 6 0 8 c higher than present approximate average of the 20th century but the warming was time transgressive across the western arctic as the precession driven summer insolation anomaly peaked 12 10 ka thousands of calendar years ago warming was concentrated in northwest north america while cool conditions lingered in the northeast alaska and northwest canada experienced the htm between ca 11 and 9 ka about 4000 yr prior to the htm in northeast canada the delayed warming in quebec and labrador was linked to the residual laurentide ice sheet which chilled the region through its impact on surface energy balance and ocean circulation the lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change the spatial asymmetry of warming during the htm resembles the pattern of warming observed in the arctic over the last several decades although the two warmings are described at different temporal scales and the htm was additionally affected by the residual laurentide ice the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing unlike the htm however future warming will not be counterbalanced by the cooling effect of a residual north american ice sheet

malaguana gadao ridge identification and implications of a magma chamber reflector in the southern mariana trough 1 six channel seismic reflection data reveal a magma chamber reflector beneath the malaguana gadao ridge the southernmost segment of the spreading center in the mariana trough for most of its length the spreading center in this active back arc basin is morphologically similar to slow spreading mid ocean ridges having a deep central graben flanked by a zone of abyssal hill fabric this southernmost segment however has a broad smooth cross section lacks a deep central graben and is thus similar in morphology to fast spreading ridges e g the east pacific rise we identify a magma chamber at 1 5 s two way travel time below the crest of the ridge observations from remotely operated vehicles along the ridge reveal not only fresh pillows lobate and sheet lava flows but also an abundance of volcaniclastic debris and intense hydrothermal activity these observations together with the fast spreading morphology of the ridge suggest that this segment has a considerably higher magma supply than is typical in the mariana trough we suggest that the volcanic arc or enhanced melting of a hydrated mantle is supplying volatile rich magma as evidenced by a highly negative coefficient of reflection 0 42 for this mcr and the presence of evolved highly vesicular lava and volcaniclastic materials the southeastern mariana back arc basin spreading ridge does not compare readily with mechanical models for global mid ocean ridge data sets because of marked asymmetry in both volcanism and deformation that may be the consequence of slab related geometry in this part of the convergent margin system

density structure of the mariana arc and its vicinity obtained from successive inversion of the gravity anomaly abstract free air anomalies measured by surface ships and those derived from geos 3 seasat 1 satellite altimetry were both used to determine the density structure in the upper mantle of the mariana arc and its vicinity compilation of the updated free air anomaly data was made by minimizing crossover errors in the ship measurements and adjusting regional discrepancies of altimetry derived free air anomalies to fit the ship measurements referring to the assumed density model for the flat basin of the western pacific a two dimensional density structure across the mariana arc was investigated on the basis of the residual gravity anomaly rga to which a successive inversion method was applied the structure estimated from the first rga shows that in the regional sense the lithosphere of the western philippine basin is 50 60 km thick and that of the parece vela basin is 20 40 km thick while the result also shows the existence of a locally anomalous structure from the west mariana ridge over to the east mariana ridge leaving the lithosphere determined from the first rga as it was the second rga which is regarded as being caused by an asthenospheric anomaly was derived and used to estimate the locally low density body the estimation shows that an abnormally low density body lies between the mariana trough and the east mariana ridge if the low density body is assumed to be confined from the moho to the asthenospheric surface at a depth of 80 km it can be concluded that the mean density of the body is 3 18 g cm3 and that it is 65 km thick and 500 km wide the location of the low density body is near the apparent volcanoes of the mariana arc

seismic attenuation tomography of the mariana subduction system implications for thermal structure volatile distribution and slow spreading dynamics 1 the anelastic structure of a subduction zone can place first order constraints on variations in temperature and volatile content we investigate seismic attenuation across the western pacific mariana subduction system using data from the 2003 2004 mariana subduction factory imaging experiment this 11 month experiment consisted of 20 broadband stations deployed on the arc islands and 58 semibroadband ocean bottom seismographs deployed across the fore arc island arc and back arc spreading center we compute amplitude spectra for p and s arrivals from local earthquakes and invert for the path averaged attenuation for each waveform along with the seismic moment and corner frequency for each earthquake additionally we investigate earthquake source parameter assumptions and frequency dependent exponents ranging from 0 to 0 6 tomographic inversion of nearly 3000 t estimates at 0 27 for 2 d qp 1 and qp qs structure shows a 75 km wide columnar shaped high attenuation anomaly with qp 43 60 beneath the spreading center that extends from the uppermost mantle to 100 km depth a weaker high attenuation region qp 56 70 occurs at depths of 50 100 km beneath the volcanic arc and the high attenuation regions are connected at depths of 75 125 km the subducting pacific plate is characterized by low attenuation at depths greater than 100 km but high attenuation is found in the plate between 50 and 100 km depth the fore arc shows high attenuation near the volcanic arc and beneath the serpentinite seamounts in the outer fore arc qs structure is less well resolved than qp because of a smaller data set but qp qs ratios are significantly less than 2 throughout the study region as temperatures estimated from qs 1 are unusually high we interpret the arc and wedge core anomalies as regions of high temperature with enhanced q 1 due to hydration and or melt the slab and fore arc anomalies as indicative of slab derived fluids and or large scale serpentinization and the columnar shaped high qp 1 anomaly directly beneath the back arc spreading center as indicative of a narrow region of dynamic upwelling and melt production beneath the slow spreading ridge axis

application of airborne lidar to mapping seismogenic faults in forested mountainous terrain southeastern alps slovenia results are presented of the first airborne lidar survey ever flown in europe for the purpose of mapping the surface expression of earthquake prone faults detailed topographic images derived from lidar data of the idrija and ravne strike slip faults in nw slovenia reveal geomorphological and structural features that shed light on the overall architecture and kinematic history of both fault systems the 1998 mw 5 6 and 2004 mw 5 2 ravne fault earthquakes and the historically devastating 1511 m 6 8 idrija earthquake indicate that both systems pose a serious seismic hazard in the region because both fault systems occur within forested terrain a tree removal algorithm was applied to the data the resulting images reveal surface scarps and tectonic landforms in unprecedented detail importantly two sites were discovered to be potentially suitable for fault trenching and palaeo seismological analysis this study highlights the potential contribution of lidar surveying in both low relief valley terrain and high relief mountainous terrain to a regional seismic hazard assessment programme geoscientists working in other tectonically active regions of the world where earthquake prone faults are obscured by forest cover would also benefit from lidar maps that have been processed to remove the canopy return and reveal the forest floor topography

submarine lava flow emplacement and faulting in the axial valley of two morphologically distinct spreading segments of the mariana back arc basin from wadatsumi side scan sonar images 1 high resolution deep tow side scan sonar data were collected over two distinct spreading segments in the central part of the mariana back arc basin these data allow mapping of small fissures and faults and the distinguishing of hummocky from smooth lava flows using these data we observe spatial variations in seafloor deformation and volcanic activity within each segment and also significant differences in the degree of tectonic deformation between the two segments one segment characterized by an hourglass shape suggestive of magmatic processes dominating over tectonic processes is in fact currently dominated by intense deformation rather than volcanism the other segment which exhibits morphology wide and deep linear axial valley typical of magma starved segments is subjected to very limited deformation and is covered by mostly unfaulted recent flows each segment also displays along axis variations in the degree of tectonic deformation and in lava flows freshness we observe a decrease of lava effusion rate from segment centers toward their ends we also investigated the apparent asymmetry of the mariana basin on the southern segment of the study area azimuths of tectonic structures are divided into two groups one segment parallel and one 15 oblique to strike of the segment these two trends of linear features developed synchronously with volcanic activity currently oblique structures seem to be the most active ones the tectonic structures that are parallel to the overall valley trend are distributed over the entire valley whereas the oblique structures are only located proximal to the eastern valley wall they are likely related to changes in the local stress field related to the obliquely trending eastern axial valley wall asymmetric character such as nonuniform spacing and throw of faults was not observed these observations suggest that the asymmetry of the basin is not due to asymmetric spreading but rather to eastward ridge jumps of several kilometers such small amplitude ridge jumps likely occurred frequently during basin development because the asymmetric character of the basin is strongly pronounced and no abandoned rift valley is recognizable within the entire basin

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

the 1998 bovec krn mountain slovenia earthquake sequence we study the 1998 bovec krn mountain slovenia earthquake sequence by combining hypocenters relocation strong motion inversion digital elevation modelling and field geology the main shock ms 5 7 a 12 km right lateral strike slip event on the dinaric fault system occurred on a sub vertical fault plane the rupture confined between 3 and 9 km depth with no evidence of surface faulting propagated bilaterally within two structural barriers the northwestern barrier is at the junction between dinaric and alpine structures where there is a sharp change in the geometry of faulting the southeastern barrier is within the dinaric system and its surface expression corresponds to the tolminka spring perched basin a 1 km restraining step over at this site the bovec krn earthquake fault overlaps with a 30 km strike slip fault segment that is free of aftershocks and could be undergoing an increase of stress this fault system represents the northern branch of the idrija right lateral fault

gravity anomalies and crustal thickness variations along the mid atlantic ridge between 33 n and 40 n multibeam bathymetry and gravity data have been obtained along an 800 km long section of the mid atlantic ridge from just south of the hayes fracture zone at 33 n to the northern edge of the azores platform near 40 n a three dimensional analysis of these gravity and topography data combined with results from earlier seismic refraction studies in this area reveal two different scales of crustal heterogeneity a systematic along axis segment scale 8 9 km near the middle of spreading segments and the thinnest crust 3 4 km near segment offsets the magnitude of this along axis variation in crustal thickness is proportional to the length of the spreading segment and the size of the adjacent ridge offset there also is a distinct asymmetry in crustal structure across the rift valley near large segment offsets with gravity highs inferred to be thinner crust beneath the inside corner highs adjacent to these offsets this segment scale crustal heterogeneity is similar to that reported from the kane to atlantis section of the mid atlantic ridge and from parts of the intermediate spreading southern mid atlantic ridge it is superimposed on a second longer wavelength variation in gravity and crustal thickness associated with the azores hot spot the most pronounced effect of the azores hot spot on the mid atlantic ridge occurs between 38 n and 40 n where the ridge axis rapidly shoals by more than 1000 m the crust thickens by over 2 km and the rift valley largely disappears the absence of a deep axial rift valley on the azores platform and near the midpoints of some ridge segments along the mid atlantic ridge to the south agrees well with the predictions of recent ridge crest thermal and rheological models that suggest a dependence of axial morphology on both crustal thickness and spreading rate the transition from a rift valley to an axial high morphology at these spreading rates 11 mm yr half rate occurs at a crustal thickness of about 9 1km

the temperature of europe during the holocene reconstructed from pollen data we present the first area average time series reconstructions of warmest month coldest month and mean annual surface air temperatures across europe during the last 12 000 years these series are based on quantitative pollen climate reconstructions from over 500 pollen sites assimilated using an innovative four dimensional gridding procedure this approach combines three dimensional spatial gridding with a fourth dimension represented by time allowing data from irregular time series to be focussed onto a regular time step we provide six regional reconstructed temperature time series as well as summary time series for the whole of europe the results suggest major spatial and seasonal differences in holocene temperature trends within a remarkably balanced regional and annual energy budget the traditional mid holocene thermal maximum is observed only over northern europe and principally during the summer this warming was balanced by a mid holocene cooling over southern europe whilst central europe occupied an intermediary position changes in annual mean temperatures for europe as a whole suggest an almost linear increase in thermal budget up to 7800 bp followed by stable conditions for the remainder of the holocene this early holocene warming and later equilibrium has been mainly modulated by increasing winter temperatures in the west which have continued to rise at a progressively decreasing rate up to the present day

the seismotectonic characteristics of slovenia slovenia with its neighbouring areas lies at the junction of the alps the dinarides and the pannonian basin these belong to the three plates europe adria and tisza on the slovenian territory itself converge the external dinarides nw se oriented right lateral strike slip faults the transdanubian range ne sw oriented left lateral strike slip faults and the southern alps e w oriented thrusts the direction of the principal stress 1 azimuth 6 dip 8 is determined under the assumption of uniform stress throughout the region dip of the least principal stress 3 of 5 is consistent with the regional strike slip regime listed structures form a pure shear structural mechanism on a regional scale

shear velocity structure of the mariana mantle wedge from rayleigh wave phase velocities 1 we examine the seismic structure of the mariana mantle wedge using data from a combined deployment of ocean bottom seismographs and land stations in 2003 2004 we measure rayleigh wave phase velocities and invert these results for the shear velocity structure and azimuthal anisotropy in the region in the back arc region low phase velocities indicate shear velocities as low as 3 9 0 1 km s at depths of about 60 km locations of the lowest seismic velocities at 18 0 n 18 5 n 16 0 n 16 5 n and 14 0 n 14 5 n correspond to the locations of gravity lows and probably indicate the presence of temperature and melt production maxima compared to elsewhere along the spreading center the shape of the low velocity anomaly also indicates that there is a degree of asymmetry to the thermal structure across the spreading center the fore arc exhibits low shear velocities vs 3 6 km s at depths shallower than 40 km these low uppermost mantle velocities are likely due to serpentinization of the fore arc azimuthal anisotropy results suggest an average peak to peak anisotropy of about 1 2 with a fast direction of nne fore arc anisotropy shows arc parallel fast directions at shallow depth in agreement with previous shear wave splitting observations and deeper arc perpendicular directions influenced by the slab back arc anisotropy is largely arc perpendicular consistent with splitting observations west of the spreading center

holocene sea level database for the atlantic coast of the united states we have constructed a database of holocene relative sea level rsl observations for the atlantic coast of the united states the database contains 492 index points which locate the position of rsl in time and space and 344 limiting dates which constrain the minimum or maximum limit of former sea level the majority of the index points in the database are from 6 ka bp to present with only 7 older than 6 ka bp spatially index points are distributed between maine and south carolina but there is an absence of data from georgia and the atlantic coast of florida the database is sub divided into 16 regions based on the distance from the former laurentide ice sheet and are classified depending upon their susceptibility to compaction the index points and limiting data demonstrate that rsl did not exceed present 0 m during the holocene except potentially in regions 1 and 2 eastern maine and southern maine rates of rsl change were highest during the early holocene and have decreased over time due to the diminishing response of the earth s mantle to glacial isostatic adjustment and reduction of ice equivalent meltwater input along the atlantic coast of the united states the linear rate of rsl rise prior to 4 ka bp ranged from 0 5 to 4 5 mm a 1 compared to 0 6 1 8 mm a 1 from 4 ka bp to ad 1900 the database suggests minimal 0 3 mm yr changes in these rates of rsl rise during the late holocene deglaciation of the laurentide ice sheet caused the spatial variability captured by the database the maximum rate of late holocene and ongoing rsl rise occurred in mid atlantic regions new jersey and inner delaware because of collapse of the peripheral forebulge

small scale convection under the back arc occurring in the low viscosity wedge abstract water released from subducting slabs through a dehydration reaction may lower the viscosity of the mantle significantly thus we may expect a low viscosity wedge lvw above the subducting slabs the lvw coupled with a large scale flow induced by the subducting slabs may allow the existence of roll like small scale convection whose axis is normal to the strike of the plate boundary such a roll structure may explain the origin of along arc variations of mantle temperature proposed recently in northeast japan we study this possibility using both 2d and 3d models with without pressure and temperature dependent viscosity 2d models without pressure and temperature dependence of viscosity show that with a reasonable geometry of the lvw and subduction speed small scale convection is likely to occur when the viscosity of the lvw is less than 10 19 pa s corresponding 3d model studies reveal that the wavelength of rolls depends on the depth of the lvw the inclusion of temperature dependent viscosity requires the existence of further low viscosity in the lvw since temperature dependence suppresses the instability of the cold thermal boundary layer pressure i e depth dependence coupled with temperature dependence of the viscosity promotes short wavelength instabilities the model which shows a relatively moderate viscosity decrease in the lvw most of the lvw viscosity is 10 18 10 19 pa s and a wavelength of roll 80 km has a rather small activation energy and volume 130 kj mol and 4 cm 3 mol of the viscosity this small activation energy and volume may be possible if we regard them as an effective viscosity of non linear rheology

holocene treeline history and climate change across northern eurasia radiocarbon dated macrofossils are used to document holocene treeline history across northern russia including siberia boreal forest development in this region commenced by 10 000 yr b p over most of russia forest advanced to or near the current arctic coastline between 9000 and 7000 yr b p and retreated to its present position by between 4000 and 3000 yr b p forest establishment and retreat was roughly synchronous across most of northern russia treeline advance on the kola peninsula however appears to have occurred later than in other regions during the period of maximum forest extension the mean july temperatures along the northern coastline of russia may have been 2 5 to 7 0 c warmer than modern the development of forest and expansion of treeline likely reflects a number of complimentary environmental conditions including heightened summer insolation the demise of eurasian ice sheets reduced sea ice cover greater continentality with eustatically lower sea level and extreme arctic penetration of warm north atlantic waters the late holocene retreat of eurasian treeline coincides with declining summer insolation cooling arctic waters and neoglaciation

mantle wedge control on back arc crustal accretion at mid ocean ridges plate separation leads to upward advection and pressure release partial melting of fertile mantle material the melt is then extracted to the spreading centre and the residual depleted mantle flows horizontally away in back arc basins the subducting slab is an important control on the pattern of mantle advection and melt extraction as well as on compositional and fluid gradients modelling studies predict significant mantle wedge effects on back arc spreading processes here we show that various spreading centres in the lau back arc basin exhibit enhanced diminished or normal magma supply which correlates with distance from the arc volcanic front but not with spreading rate to explain this correlation we propose that depleted upper mantle material generated by melt extraction in the mantle wedge is overturned and re introduced beneath the back arc basin by subduction induced corner flow the spreading centres experience enhanced melt delivery near the volcanic front diminished melting within the overturned depleted mantle farther from the corner and normal melting conditions in undepleted mantle farther away our model explains fundamental differences in crustal accretion variables between back arc and mid ocean settings