three dimensional splay fault geometry and implications for tsunami generation megasplay faults very long thrust faults that rise from the subduction plate boundary megathrust and intersect the sea floor at the landward edge of the accretionary prism are thought to play a role in tsunami genesis we imaged a megasplay thrust system along the nankai trough in three dimensions which allowed us to map the splay fault geometry and its lateral continuity the megasplay is continuous from the main plate interface fault upwards to the sea floor where it cuts older thrust slices of the frontal accretionary prism the thrust geometry and evidence of large scale slumping of surficial sediments show that the fault is active and that the activity has evolved toward the landward direction with time contrary to the usual seaward progression of accretionary thrusts the megasplay fault has progressively steepened substantially increasing the potential for vertical uplift of the sea floor with slip we conclude that slip on the megasplay fault most likely contributed to generating devastating historic tsunamis such as the 1944 moment magnitude 8 1 tonankai event and it is this geometry that makes this margin and others like it particularly prone to tsunami genesis

interpretation of porosity and lwd resistivity from the nankai accretionary wedge in light of clay physicochemical properties evidence for erosion and local overpressuring in this study we used porosity to assess the compaction state of the nankai accretionary wedge sediments and any implications for stress and pore pressure however hydrous minerals affect porosity measurements and accounting for them is essential toward defining the interstitial porosity truly representative of the compaction state the water content of sediments was measured in core samples and estimated from logging data using a resistivity model for shale we used the cation exchange capacity to correct the porosity data for the amount of water bound to clay minerals and to correct the porosity estimates for the surface conductivity of hydrous minerals the results indicate that several apparent porosity anomalies are significantly reduced by this correction implying that they are in part artifacts from hydrous minerals the correction also improves the fit of porosity estimated from logging while drilling lwd resistivity data to porosity measured on cores low overall porosities at the toe of the accretionary wedge and in the splay fault area are best explained by erosion and we estimated the quantity of sediments eroded within the splay fault area by comparing porosity effective stress relationships of the sediments to a reference curve additionally a comparison of lwd data with core data resistivity and p wave velocity obtained at site c0001 landward of the mega splay fault area suggested a contribution from the fracture porosity to in situ properties on the formation

interseismic stress accumulation at the locked zone of nankai trough seismogenic fault off kii peninsula abstract a primary source of stress variation prior to great subduction zone earthquakes is the tectonic loading due to plate convergence we have calculated the elastic stress around the locked zone accumulated during an interseismic period numerically using a 2d plane strain finite element model in the nankai trough off kii peninsula and examined its dependence on elastic properties and some boundary conditions for the modeling we used the geometry of subducting plate interface determined previously through seismic surveys and the physical properties that were obtained through iodp scientific drilling offshore kii peninsula to construct a physically realistic model a dislocation along the plate interface is calculated from a 5 m displacement imposed on one side of the subducting plate with the locked zone defined at a depth of 10 to 25 km along the plate interface calculated shear stress is maximized at the downdip edge of the locked zone decreases exponentially seaward and is almost zero near the updip edge maximum shear stress is primarily proportional to the young s modulus of the overlying section comparing the maximum shear stress with the average stress drop for subduction earthquakes 3 4 mpa the most appropriate young s modulus and poisson s ratio ranges are 50 70 gpa and 0 3 respectively which are in good agreement with previous estimations from observed vp vs the stress accumulated during one seismic cycle can be reasonably explained by a linear elastic model with an appropriately sized locked region we found that the envelope of simulated horizontal displacement on the surface agrees well with gps velocity data which also supports this inference disturbance near the updip edge is no larger than 0 1 mpa of stress or 0 1 radian of tilt which are difficult to detect with current borehole measurement techniques and likely complex borehole conditions

high angle reverse faulting associated with the 1946 nankaido earthquake abstract analysis of vertical crustal deformation data in the southwestern part of shikoku southwest japan suggests that the nankaido earthquake of 1946 m w 8 1 which is a principal interplate thrust earthquake was accompanied by subsidiary faulting on a splay fault adjacent to the coast of shikoku discarding crustal movement resulting from the main thrusting of the nankaido earthquake local leveling data are explained by slip on a simple rectangular thrust fault located just offshore of shikoku although it is difficult to constrain the fault location a possible result is a high angle thrust dipping landward at an angle of about 70 with a dislocation of about 1 5 m and source dimensions of 30 13 km along strike and dip respectively this result indicates that the fault may be one of the steeply dipping subsidiary faults branching from the main low angle thrust as was the case in the alaska earthquake of 1964 although several lines of evidence suggest that this faulting occurred as slow aseismic slip its discrimination from the main seismic event is extremely difficult this kind of high angle thrusting just offshore of the coast would play an important role for the formation of the marine terraces during the late quaternary period

garnet provenance studies juxtaposition of laurentian marginal terranes and timing of the grampian orogeny in scotland a study of the composition and zoning patterns of detrital garnets from ordovician greywackes from the northern belt of the southern uplands terrane of scotland reveals characteristics of the metamorphic sources very similar to the dalradian supergroup of the scottish grampian terrane the radiometric cooling and uplift ages of the dalradian metamorphic zones and the depositional ages of the southern uplands greywackes support the hypothesis for local provenance detrital metamorphic garnet identical to dalradian garnet has also been identified in the upper ordovican sandstones of the highland border complex these observations do not support proposals that the grampian midland valley and southern uplands terranes were exotic to each other in the late ordovician time these new results together with a review of published age dates clarify the late ordovician palaeogeography for this part of the laurentian margin the distances between the grampian midland valley and southern uplands terranes may have been similar to the present day it is concluded that large rivers flowed out of the uplifting mountainous grampian terrane and across the midland valley into a southern uplands trench during the late ordovician time the main orogeny i e mountain building in the grampian terrane was therefore post cambrian producing the first high mountains and resultant flysch in the caradoc

out of sequence thrust faults developed in the coseismic slip zone of the 1946 nankai earthquake mw 8 2 off shikoku southwest japan a multi channel seismic mcs reflection survey was conducted to study the subsurface structure of the coseismic slip zone of the 1946 nankai earthquake mw 8 2 off shikoku island in 1997 we could identify a splay fault system consisting of several sigmoid out of sequence thrust ost faults dipping landward with slope 10 25 on the poststack depth migrated mcs profiles most of the osts are apparently developed from the subducting oceanic basement to the seafloor in the forearc region cutting both underthrust sediments and the overriding accretionary prism in addition most of the osts are within the coseismic zone of the 1946 nankai earthquake and the interseismic locked zone the osts are considered to be related to large interplate earthquakes including the 1946 nankai earthquake these osts may be responsible for tsunami generation following deformation of forearc accretionary wedge

boltysh another end cretaceous impact the chixculub impact occurred at the cretaceous tertiary k t boundary and although several other late cretaceous and paleogene impact craters have at times been linked with the k t boundary isotope geochronology has demonstrated that all have significantly different ages the currently accepted age of the 24 km diameter boltysh crater a k ar whole rock age places it in the coniacian at 88 3 ma however comprehensive ar ar dating of a range of melt samples yields a mean age of 65 17 0 64 ma within errors of the k t boundary several of the fresh samples exhibit signs of excess argon but this seems to be concentrated in rapidly crystallized glass rich samples the ar ar age confirms an earlier fission track measurement and thus two dating techniques have yielded an age within errors of the k t boundary for this crater crucially although the ages of boltysh and chixculub are within errors they may not have formed synchronously craters of 24 km diameter occur much more commonly than impacts of chixculub dimensions but their proximity does raise the important question of how many impacts there might have been close to the k t boundary

paleocene eocene carbon isotope excursion in organic carbon and pedogenic carbonate direct comparison in a continental stratigraphic section the negative carbon isotope excursion at the paleocene eocene boundary is a chemo stratigraphic marker widely used for correlation of marine and continental stratigraphic sections it is linked to massive dissociation of sedimentary methane hydrates and helps to explain an important greenhouse thermal event paleocene eocene thermal maximum marine extinctions and mammalian faunal change on three continents we show that the carbon isotope excursion recorded in dispersed organic carbon doc from fine grained terrestrial sedimentary rocks at polecat bench wyoming is very similar to that described in two high resolution studies of pedogenic soil nodule carbonate from the same section all show a rapid onset an 40 m series of excursion values and a slower recovery however the carbon isotope excursion in soil nodule carbonate starts and ends 3 5 m lower stratigraphically than that in doc we hypothesize that enhanced diffusion of atmospheric co2 and subsurface diagenesis in an environment of good drainage and elevated temperature and p co2 may explain this offset the reliability of 13c in doc is attributed to mixing and averaging of isotopic signals from different organic compounds and tissues

late holocene tectonics and paleoseismicity southern cascadia subduction zone holocene deformation indicative of large subduction zone earthquakes has occurred on two large thrust fault systems in the humboldt bay region of northern california displaced stratigraphic markers record three offsets of 5 to 7 meters each on the little salmon fault during the past 1700 years smaller and less frequent holocene displacements have occurred in the mad river fault zone elsewhere as many as five episodes of sudden subsidence of marsh peats and fossil forests and uplift of marine terraces are recorded carbon 14 dates suggest that the faulting subsidence and uplift events were synchronous relations between magnitude and various fault offset parameters indicate that earthquakes accompanying displacements on the little salmon fault had magnitudes of at least 7 6 to 7 8 more likely this faulting accompanied rupture of the boundary between the gorda and north american plates and magnitudes were about 8 4 or greater

compressional velocity and porosity in sand clay mixtures laboratory measurements of porosity and compressional velocity were conducted on unconsolidated brine saturated clean ottawa sand pure kaolinite and their mixtures at various confining pressures a peak in p velocity versus clay content in unconsolidated sand clay mixtures at 40 percent clay by weight was found the peak in velocity is 20 30 percent higher than for either pure clay or clean sand a minimum in porosity versus clay content at 20 40 percent clay by weight is also observed such behavior is explained using a micro geometrical model for mixtures of sand and clay in which two classes of sediments are considered 1 sands and shaley sands in which clay is dispersed in the pore space of load bearing sand and thus reduces porosity and increases the elastic moduli of the pore filling material and 2 shales and sandy shales in which sand grains are dispersed in a clay matrix for these sediments the model reproduces the extrema in velocity and porosity and accounts for much of the scatter in

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

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

porosity of sediments in accretionary prisms and some implications for dewatering processes rapid dewatering largely through loss of porosity is one of the most striking changes affecting deformed sediments in accretionary prisms analysis of porosity from sample and seismic data confirms that porosity in accretionary prisms is significantly less than that in basinal strata of similar lithology more specifically the porosity depth gradient increases arcward across the prism until porosities less than 10 occur within a few kilometers of the surface in deeper parts of the prism dewatering and volume reduction occur not only during loss of porosity but also during dehydration and metamorphic reactions calculations involving volume change lead us to define a function which reflects total volume reduction the distribution of the relative intensity of dewatering within the prism can be calculated from the porosity contours and trajectories of sediment elements an initial attempt indicates that in the toe region the rate of dewatering is accelerated at depth relative to the basinal section and may be greatest near the base of the prism toward the rear of the prism the maximum rate of dewatering occurs at progressively shallower depths several lines of evidence suggest that in addition to gradual diffuse dewatering localized zones of strong dewatering are associated with zones of intense shear this model of shear dewatering based on critical state soil mechanics suggests that sediments adjacent to the basal decollement should be strongly dewatered

the late palaeocene early eocene and toarcian early jurassic carbon isotope excursions a comparison of their time scales associated environmental changes causes and consequences although the earth9s environment is constantly changing there have been a few unusual episodes over the last c 200 ma when change was extreme in terms of its rapidity severity long lasting consequences and unpredictability the geochemical and biotic records for two of these episodes the palaeocene eocene thermal maximum and the toarcian oceanic anoxic event early jurassic possess many significant similarities each event was associated with a major carbon isotope excursion significant levels of biotic extinctions severe global warming an enhanced hydrological cycle and evidence for widespread seawater anoxia both carbon isotope excursions can be subdivided into distinct stages with broadly similar characteristics and durations based on a detailed comparison the palaeocene eocene thermal maximum may have been an incipient oceanic anoxic event the geochemical and biotic changes during these two events are most readily explained by the abrupt large scale dissociation of methane hydrate that followed a period of more gradual environmental change linked to the emplacement of a large igneous province carbon release rates at those times were of the same order of magnitude as the current anthropogenic release rate of carbon to the atmosphere indicating that ancient events such as these may usefully serve as analogues for present day environmental change

on the mechanical role of smectite in subduction zones smectites a group of hydrated phyllosilicate minerals are often a main component of sediments entering a subduction zone they are common in hemipelagic sediments and consist of an authigenetic component that arises from the alteration of volcanic ash intercalated in the sediment and a detrital component smectite rich strata are structurally weak retain water and are highly porous a review of sediment lithology in subduction zones around the world suggests that decollement zones may preferentially form in smectite rich horizons one consequence of this observation is that the assignment of high frictional resistance to materials in a decollement may be unwarranted at deeper structural levels smectite is transformed to illite a mechanically stronger mineral estimates of the depth of this transition coincide with the depth at which earthquakes are first detected along plate interfaces i speculate that the smectite illite transition in subduction zones may be an important component of sediment consolidation processes that trigger interplate seismicity

two large meteorite impacts at the cretaceous paleogene boundary the end cretaceous mass extinction has been attributed by most to a single asteroid impact at chicxulub on the yucatan peninsula mexico the discovery of a second smaller crater with a similar age at boltysh in the ukraine has raised the possibility that a shower of asteroids or comets impacted earth close to the cretaceous paleogene k pg boundary here we present palynological and 13 c evidence from crater fi ll sediments in the boltysh impact crater our analyses demonstrate that a post impact fl ora formed on the ejecta layer was in turn devastated by the k pg event the sequence of flrecovery from the k pg event is directly comparable with that in middle north america we conclude that the boltysh crater predated chicxulub by 2 5 k y a time scale that constrains the likely origin of the bodies that formed the two known k pg craters

astronomical calibration of the paleocene time the first complete cyclic sedimentary successions for the early paleogene from drilling multiple holes have been retrieved during two odp expeditions leg 198 shatsky rise nw pacific ocean and leg 208 walvis ridge se atlantic ocean these new records allow us to construct a comprehensive astronomically calibrated stratigraphic framework with an unprecedented accuracy for both the atlantic and the pacific oceans covering the entire paleocene epoch based on the identification of the stable long eccentricity cycle 405 kyr high resolution x ray fluorescence xrf core scanner and non destructive core logging data from sites 1209 through 1211 leg 198 and sites 1262 1267 leg 208 are the basis for such a robust chronostratigraphy former investigated marine odp sites 1001 and 1051 and land based e g zumaia sections have been integrated as well the high fidelity chronology is the prerequisite for deciphering mechanisms in relation to prominent transient climatic events as well as completely new insights into greenhouse climate variability in the early paleogene we demonstrate that the paleocene epoch covers 24 long eccentricity cycles we also show that no definite absolute age datums for the k pg boundary or the paleocene eocene thermal maximum petm can be provided by now because of still existing uncertainties in orbital solutions and radiometric dating however we provide two options for tuning of the paleocene which are only offset by 405 kyr our orbitally calibrated integrated leg 208 magnetostratigraphy is used to revise the geomagnetic polarity time scale gpts for chron c29 to c25 we established a high resolution calcareous nannofossil biostratigraphy for the south atlantic which allows a much more detailed relative scaling of stages with biozones the re evaluation of the south atlantic spreading rate model features higher frequent oscillations in spreading rates for magnetochron c28r c27n and c26n

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

quantification of bound water content interstitial porosity and fracture porosity in the sediments entering the north sumatra subduction zone from cation exchange capacity and iodp expedition 362 resistivity data abstract in this study we investigate porosity evolution through the sedimentary input section of the north sumatra subduction zone by quantifying interstitial porosity bound water content and fracture porosity based on iodp expedition 362 data and post cruise chemical analyses during iodp expedition 362 total porosity of the sedimentary section entering the north sumatra subduction zone was measured this total porosity is derived from the total water content of core samples thus including pore water and water bound to hydrous minerals like smectite clay mineral composition varies over the sedimentary section and is mainly kaolinite illite in the nicobar fan units and smectite illite in the prefan pelagic unit below the prefan pelagic unit shows anomalously high total porosity values and is stratigraphically correlated to a high amplitude negative polarity hanp seismic reflector located landward this hanp reflector has been previously interpreted as a porous fluid rich layer where the decollement may develop along parts of the margin as a consequence of pore pressure buildup we estimate clay bound water content from cation exchange capacity cec which gives information about the smectite illite composition and soluble chloride content data interstitial porosity corresponds to onboard total porosity corrected from clay bound water and is more relevant in terms of sediment compaction state and fluid flow properties interstitial porosity versus vertical effective stress curve shows no evidence of undercompaction and suggests that the input section has been experiencing normal consolidation due to high sediment accumulation rate the porosity anomaly observed in the prefan pelagic unit results from the local occurrence of water bearing minerals like smectite rather than excess pore pressure which might however buildup more landward in the basin we also estimate fracture porosity using a resistivity model for shales used in previous works based on wireline resistivity log and show that fracture porosity yields 4 6 in damaged parts of the sedimentary section investigated

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

a complete high resolution paleocene benthic stable isotope record for the central pacific odp site 1209 1 we have compiled the first stratigraphically continuous high resolution benthic foraminiferal stable isotope record for the paleocene from a single site utilizing cores recovered at pacific odp site 1209 the long term trend in the benthic isotope record suggests a close coupling of volcanic co2 input and deep sea warming over the short term the record is characterized by slow excursions with a pronounced periodic beat related to the short 100 kyr and long 405 kyr eccentricity cycle the phase relationship between the benthic isotope record and eccentricity is similar to patterns documented for the oligocene and miocene confirming the role of orbital forcing as the pace maker for paleoclimatic variability on milankovitch time scales in addition the record documents an unusual transient warming of 2 c coeval with a 0 6 carbon isotope excursion and a decrease in carbonate content at 61 75 ma this event which bears some resemblance to eocene hyperthermals marks the onset of a long term decline in 13c the timing indicates it might be related to the initiation of volcanism along greenland margin

p and s wave velocity measurements of water rich sediments from the nankai trough japan acoustic velocities were measured during triaxial deformation tests of silty clay and clayey silt core samples from the nankai subduction zone integrated ocean drilling program expeditions 315 316 and 333 we provide a new data set continuously measured during pressure increase and subsequent axial deformation a new data processing method was developed using seismic time series analysis compressional wave velocities v p range between about 1450 and 2200 m s and shear wave velocities v s range between about 150 and 800 m s v p slightly increases with rising effective confining pressure and effective axial stress samples from the accretionary prism toe show the highest vp while fore arc slope sediments show lower vp samples from the incoming plate slightly richer in clay minerals have the lowest values for v p v s increases with higher effective confining pressures and effective axial stress irrespective of composition and tectonic setting shear and bulk moduli are between 0 2 and 1 3 gpa and 3 85 and 8 41 gpa respectively elastic moduli of samples from the accretionary prism toe and the footwall of the megasplay fault 1 50 and 3 98 gpa are higher than those from the hanging wall and incoming plate 0 59 and 0 88 gpa this allows differentiation between normal and overconsolidated sediments the data show that in a tectonosedimentary environment of only subtle compositional differences acoustic properties can be used to differentiate between stronger accretionary prism toe and weaker fore arc slope incoming plate sediments especially v p v s ratios may be instrumental in detecting zones of low effective stress and thus high pore fluid pressure

thermal constraints on the seismogenic portion of the southwestern japan subduction thrust for coastal cities an important factor in earthquake hazard from subduction zone earthquakes is the landward extent of the seismogenic portion of the subduction thrust fault in this study we test the hypothesis that the maximum downdip extent is defined by a critical temperature we have developed a transient thermal model for the nankai subduction zone of southwest japan to allow comparison of the thermally estimated downdip extent of the seismogenic zone with that from 1 seismicity and tsunami data for two great subduction earthquakes 2 the coseismic faulting extent of these events estimated from geodetic deformation data and 3 the interseismic locked zone determined from interseismic geodetic data the nankai margin has extensive heat flow and heat production data to control thermal models and thus crustal temperatures it has earthquake tsunami and geodetic data that constrain the coseismic rupture portion of the subduction thrust fault for past great earthquakes and the portion of the thrust fault that is locked and storing interseismic elastic strain on the nankaido margin off shikoku island the thermal model indicates that a temperature of 350 c taken to be the limit for seismic initiation from laboratory and field data is reached on the subduction thrust fault 150 km from the trench a transition zone into which rupture may extend with decreasing offset taken to be 450 c extends an additional 45 km downdip the thermal model results are in excellent agreement with the maximum downdip extent of coseismic displacement for the 1946 nankaido ms 8 2 earthquake off shikoku island and with the downdip extent of the present locked zone in the region of the 1944 tonankai ms 8 2 earthquake to the northeast the subduction angle is much steeper and the thermal models indicate a narrower downdip seismogenic extent the seismogenic locked zone from earthquake and geodetic data is also narrower thus our analysis of the southwest japan margin indicates that all three constraints on the downdip extent of the seismogenic zone thermal coseismic and interseismic geodetic data are in general agreement the study also supports the hypothesis that the seismogenic portion of subduction thrust faults is limited primarily by temperature the thermal control implies that subduction thrust faults with shallow dip have wider seismogenic zones compared to those with steep dip the subducting plate age and thus heat flow and the thickness of the insulating sediments on the incoming plate are also very important to the thermal regime and thus to the seismogenic width the relation of the maximum seismic rupture area to the interseismic locked zone is particularly important for earthquake hazard estimation on subduction margins such as cascadia where there have been no great historical events

laurentian crustal recycling in the ordovician grampian orogeny nd isotopic evidence from western ireland because magmatism associated with subduction is thought to be the principal source for continental crust generation assessing the relative contribution of pre existing subducted and assimilated continental material to arc magmatism in accreted arcs is important to understanding the origin of continental crust we present a detailed nd isotopic stratigraphy for volcanic and volcaniclastic formations from the south mayo trough an accreted oceanic arc exposed in the western irish caledonides these units span an arc continent collision event the grampian taconic orogeny in which an intra oceanic island arc was accreted onto the passive continental margin of laurentia starting at 475 ma arenig the stratigraphy corresponding to pre syn and post collisional volcanism reveals a progression of end t from strongly positive values consistent with melt derivation almost exclusively from oceanic mantle beneath the arc to strongly negative values indicating incorporation of continental material into the melt using end t values of meta sediments that represent the laurentian passive margin and accretionary prism we are able to quantify the relative proportions of continent derived melt at various stages of arc formation and accretion mass balance calculations show that mantle derived magmatism contributes substantially to melt production during all stages of arc continent collision never accounting for less than 21 of the total this implies that a significant addition of new rather than recycled continental crust can accompany arc continent collision and continental arc magmatism

transient ocean warming and shifts in carbon reservoirs during the early danian the palaeocene eocene thermal maximum petm at 55 ma marks the palaeocene eocene p e boundary and represents a discrete period of abrupt transient global warming there are few vegetation records from within the petm and such an absence of data prevents modelling of the vegetation response to climate warming outcrops exposing the sentinel butte member upper fort union formation and the golden valley formation bear den and lower camels butte members within the williston basin of western north dakota usa are known to span the p e boundary pollen and spore floras at the farmers butte locality stark county north dakota 46 92 n 102 11 w record changes in abundance of some reed fern and understorey plants across the sentinel butte bear den contact but no other composition changes occur until the arrival of eocene immigrants platycarya spp walnut pecan family and intratriporopollenites instructus linden sterculia cotton tree families at the top of the bear den member c 11 m above the change in co occurrence and relative abundance patterns of range through taxa the exact stratigraphic level at which these eocene marker taxa first occur is unclear owing to the heavily weathered nature of bear den strata below the alamo bluff lignite this pattern of stratigraphic change may be correlative to the well documented floral gap of petm records in wyoming though bulk 13corg ratios decrease by 2 4 across the alamo bluff lignite degradation of organic carbon within the upper bear den member partially masks full expression of the carbon isotope excursion associated with the petm hence strata around the alamo bluff lignite may represent a new terrestrial record of the petm in agreement with terrestrial petm records from other u s western interior localities palynological data indicate no floral extinction and little composition change across the palaeocene eocene boundary

tectonic signatures in centimeter scale velocity porosity relationships of costa rica convergent margin sediments 1 the costa rica convergent margin investigated during ocean drilling program leg 170 offers a unique opportunity to compare the tectonic effects of rapid subduction on incoming oceanic sediments to their laterally equivalent underthrust counterparts and to terrestrially derived wedge materials elevated pressure laboratory measurements of ultrasonic compressional and shear wave velocity and porosity are used to examine the importance of tectonic lithologic and diagenetic controls on physical and elastic properties of sediments in these three key tectonic domains depositional and stress path histories of the three domains for example can be distinguished by 1 trends of in situ velocity porosity and derived measurements correspondence and 2 the mechanical response of representative materials to isotropic consolidation a compressional wave velocity porosity model critical for the application of seismic imaging to margin wide physical property and mass balance estimates is developed from the laboratory measurements and shown to be consistent with the information derived from lwd bulk density and migrated seismic reflection data this consistency of the velocity porosity model over the large range of both frequency and length measurement scales is a key result supporting the assertion that core and borehole physical property measurements can be extrapolated to larger domains finally dewatering and overpressure effects critical factors in subduction zone and fault process dynamics and increasingly common multiphase converted wave imaging targets are discussed in terms of laboratory estimated in situ compressional and shear wave velocity relationships

the cretaceous paleogene boundary foraminifera sea grasses sea level change and sequence stratigraphy abstract the tsunami generated by the chicxulub impact eroded the uppermost cretaceous surface of the gulf coast region u s a forming a distinctive topography that was previously interpreted as a sequence boundary at more distal sites such as stevns klint denmark there appears to be no sequence boundary at the cretaceous paleogene boundary but there is one within the uppermost maastrichtian between the sigerslev and hojerup members and another in the lowermost paleocene top of zone p1a both of these surfaces are identified by distinctive phosphatized and incipient hardgrounds the changes in sea level involved in the generation of uppermost cretaceous sequences are thought to have been minimal as in the gulpen and maastricht formations of the maastricht area netherlands the presence of sea grasses and their associated foraminifera would indicate that the chalk sea floor remained within the range of water depth that would allow photosynthesis

correlation between isotope records in marine and continental carbon reservoirs near the palaeocene eocene boundary changes in the isotope content of the large marine carbon reservoir can force shifts in that of the smaller carbon pools in the atmosphere and on land the carbon isotope compositions of marine carbonate sediments from the late palaeocene vary considerably exhibiting a sudden decrease close to the palaeocene eocene boundary which coincides with deep sea benthic extinctions1 and with changes in ocean circulation here we report that these fluctuations in the marine carbon isotope record are closely tracked by the terrestrial records provided by palaeosol carbonates and mammalian tooth enamel in using palaeosol carbonates to reconstruct the co2 content of the ancient atmosphere2 isotope shifts of this sort will have to be taken into account the sharp decrease in 13c 12c ratios in the late palaeocene provides a datum for precise correlation of marine and continental records and suggests that abrupt climate warming at this time may have played an important role in the evolution of land mammals

porosity corrections for smectite rich sediments impact on studies of compaction fluid generation and tectonic history porosity is a fundamental parameter that must be correctly determined in order to relate physical property hydrologic and chemical flux studies to natural systems traditional porosity determinations generated from physical property or seismic data can greatly overestimate the true porosity of sediments in which hydrated minerals such as smectite are abundant to produce a true porosity distribution such data must be corrected to account for the h 2 o residing in smectite interlayers which can make up to 25 of the total hydrated mineral mass such h 2 o is easily removed from the mineral by oven drying and or exposure to low humidities standard physical property measurements can be corrected provided the weight percent smectite in the sediment is known and the interlayer h 2 o content of the mineral can be estimated we illustrate the significant consequences of this correction by comparing profiles of reported and corrected porosities for smectite rich barbados abyssal plain and accretionary wedge sediments from ocean drilling program leg 110 sites 671 and 672

crustal structure across the coseismic rupture zone of the 1944 tonankai earthquake the central nankai trough seismogenic zone 1 differences in the coseismic rupture process between the 1944 tonankai and the 1946 nankaido earthquakes have been studied by many fault models to understand what factors control coseismic rupture zones it is important to investigate differences in deep crustal structures of the rupture zones between the 1944 and 1946 earthquakes the previously published crustal structure of the rupture zone of the 1946 earthquake shows that the coseismic rupture extends to the neogene quaternary accretionary prism however little is known about the structure of the rupture zone of the 1944 earthquake to obtain a complete image of the seismogenic zone of the 1944 earthquake a wide angle seismic survey was performed across the presumed coseismic rupture zone of the 1944 earthquake from ocean to land our model for the crustal structure is based on ocean bottom seismographic data the crustal structure appears characteristic for subducting oceanic crust and a neogene quaternary accretionary prism bounded by an island arc crust the neogene quaternary accretionary prism reaches a maximum thickness of 7 km at 50 km distance landward from the deformation front the subducting oceanic crust can be traced down to 35 km the subduction angle becomes steeper landward reaching up to 11 beneath the island arc crust the depth of the top of subducting oceanic crust at the downdip limit of the rupture zone is 23 km while the updip limit is located beneath the island arc upper crust similar structures of the updip and downdip limits are also published for several other subduction zones

fluid pressure in the frontal thrust of the oregon accretionary prism experimental constraints seismic reflection profiles of many accretionary prisms including the oregon prism exhibit high amplitude reversed polarity reflections from the decollement and other thrusts it has been suggested that these reflectors image fault zones with enhanced fluid content due to dilation by very high fluid pressure we present measurements of velocity as a function of effective stress on samples of the oregon frontal thrust that show that velocity decreases by up to 15 as fluid pressure rises from hydrostatic to lithostatic conditions under constant confining stress in fault zone and wall rock alike synthetic seismic modeling shows that the frontal thrust reflector at this location is the result of a thin low velocity zone in the plane of the fault 100 300 m s slower than the walls combining models with experimental results we conclude that fluid pressure of 86 to 98 of lithostatic stress reduces velocity enough to generate the reflections

strong sediments at the deformation front and weak sediments at the rear of the nankai accretionary prism revealed by triaxial deformation experiments nineteen whole round core samples from the nankai accretionary prism iodp expeditions 315 316 and 333 from a depth range of 28 128 m below sea floor were experimentally deformed in a triaxial cell under consolidated and undrained conditions at confining pressures of 400 1000 kpa room temperature axial displacement rates of 0 01 9 0 mm min and up to axially compressive strains of 64 despite great similarities in composition and grain size distribution of the silty clay samples two distinct rheological groups are distinguished the first group shows deviatoric peak stress after only a few percent of compressional strain 10 or does not weaken at all this is characteristic of structurally strong material the strong samples tend to be overconsolidated and are all from the drillsites at the accretionary prism toe while the weak and normally consolidated samples come from the immediate hanging wall of a megasplay fault further upslope sediments from the incoming plate are also structurally weak the observed differences in mechanical behavior may hold a key for understanding strain localization and brittle faulting within the uniform silty and clayey sedimentary sequence of the nankai accretionary prism

critical porosity a key to relating physical properties to porosity in rocks discovering accurate relations between porosity and seismic wave velocities in porous rocks has been an important topic of rock physics for decades such relations if they actually exist are critical when seismic and or sonic data are to be used to infer porosity and porosity related properties e g permeability strength saturation in situ these inferences became especially important in recent years with the rapid development of seismic and sonic methods which are applied to the characterization of heterogeneous reservoirs and recovery monitoring

velocity porosity relationships for slope apron and accreted sediments in the nankai trough seismogenic zone experiment integrated ocean drilling program expedition 315 site c0001 in this study we focused on the porosity and compressional wave velocity of marine sediments to examine the physical properties of the slope apron and the accreted sediments this approach allows us to identify characteristic variations between sediments being deposited onto the active prism and those deposited on the oceanic plate and then carried into the prism during subduction for this purpose we conducted ultrasonic compressional wave velocity measurements on the obtained core samples with pore pressure control site c0001 in the nankai trough seismogenic zone experiment transect of the integrated ocean drilling program is located in the hanging wall of the midslope megasplay thrust fault in the nankai subduction zone offshore of the kii peninsula sw japan penetrating an unconformity at 200 m depth between slope apron sediments and the underlying accreted sediments we used samples from site c0001 compressional wave velocity from laboratory measurements ranges from 1 6 to 2 0 km s at hydrostatic pore pressure conditions estimated from sample depth the compressional wave velocity porosity relationship for the slope apron sediments shows a slope almost parallel to the slope for global empirical relationships in contrast the velocity porosity relationship for the accreted sediments shows a slightly steeper slope than that of the slope apron sediments at 0 55 of porosity this higher slope in the velocity porosity relationship is found to be characteristic of the accreted sediments textural analysis was also conducted to examine the relationship between microstructural texture and acoustic properties images from micro x ray ct indicated a homogeneous and well sorted distribution of small pores both in shallow and in deeper sections other mechanisms such as lithology clay fraction and abnormal fluid pressure were found to be insufficient to explain the higher velocity for accreted sediments the higher slope in velocity porosity relationship for accreted sediments can be explained by weak cementation critical porosity or differences in loading history

climatic oscillations stall vegetation recovery from k pg event devastation sedimentary rocks filling the boltysh meteorite crater preserve an expanded record of post cretaceous palaeogene k pg event vegetation destruction and subsequent floral recolonization a post destruction barren zone is succeeded by a fern spore spike recording the initial recovery vegetation the boltysh fern spore spike is divisible into two phases phase 1 is characterized by low abundances of fern spores whereas the overlying phase 2 has high fern spore abundances and contains common palm pollen comparison of the boltysh phase 2 fern spore spike with other palynological records shows strong similarities to the immediately post k pg boundary record of the western interior north america variation in the composition of the boltysh palynofloras has been used to define four moisture availability cycles between the k pg boundary and the dan c2 negative carbon isotope excursion a period of some 300 kyr early post k pg event vegetation community recovery followed a common seral successional pathway at rates seen in large igneous provinces although enhanced by high moisture availability continued succession to the first true swamp community was at a considerably slower tempo the post k pg event vegetation recovery was therefore retarded by lack of moisture availability extending the apparent period of recovery

deformation and fluid pressure variation during initiation and evolution of the plate boundary decollement zone in the nankai accretionary prism 1 the plate boundary decollement zone in the muroto region of the nankai accretionary prism records deformation and consolidation histories that have been affected by temporal changes in fluid pressure microstructural observations and chemical analysis demonstrate that the decollement zone initiated in an interval of porous clayey sediments characterized by cementation due to intergranular bonding of authigenic clays crosscutting relations of microstructures indicate that the decollement zone records two compactive deformations the early compactive deformation involved destruction of porous cemented structure probably caused by fluid pressure fluctuation the late compactive deformation was characterized by clay particle rotation and porosity collapse along the sets of slip surfaces resulting in zones of preferred orientation of clay particles these compactive deformations led to significantly higher bulk densities within the decollement zone compared to the compaction trend of the overlying prism sediments elevated fluid pressure following compactive deformations induced an overconsolidated state within the decollement zone with fluid filled dilatant fractures bulk density abruptly decreases at the top of the underthrust sediments but there is no microstructural evidence for cementation fluids in the dilated fractures and underconsolidated underthrust sediments are potential sources for the elevated fluid pressure in and below the decollement zone resulting in mechanical decoupling of the accretionary prism from underthrust sediments the fault fluid interactions in the muroto region may be applicable to other convergent plate margins where high temperature associated with the subduction of a spreading ridge or hot young oceanic crust enhances diagenesis and cementation

holocene paleoseismicity in the fold and thrust belt of the hikurangi subduction zone eastern north island new zealand abstract along the 500 km long eastern coastline of the north island new zealand there are at most seven distinct holocene marine terraces aged 7 ka b p or less the highest of the terraces is 27 m above present day mean sea level the coastal region is subdivided into fourteen distinct subregions based on radiocarbon ages of marine deposits overlying wave cut shore platforms and geographic distribution of similarly aged terraces holocene marine terraces are the result of uplift associated with large earthquakes co seismic deformation this conclusion is based on characteristic stepped terrace morphology clustering of ages of terrace deposits within subrogions and the occurrence of co seismic uplift in historic time differential uplift across structures and distinct age variations at subregion boundaries are also characteristic recurrence intervals of uplift in any one terrace sequence vary from 0 4 ka to 2 0 ka and individual amounts of uplift vary from 1 0 m to 4 0 m in the past 2 5 ka ages from all terraces within subrogions indicate at least 21 paleoseismic events affecting coastal areas of eastern north island in that period these events cluster in time and in separate parts of eastern north island several earthquakes occurred 0 3 0 6 1 0 1 5 2 1 and 2 3 ka b p our data strongly support the concept of segmentation of deformation along the subduction margin the likely cause of coastal uplift is movement on steep reverse faults local structures rather than the subduction thrust that propagate from or near the subduction thrust some 20 25 km below the region earthquakes of moment magnitude 7 3 8 0 are estimated to be associated with these fault movements

depth of seismic coupling along subduction zones underthrusting at subduction zones can cause large earthquakes at shallow depths but it is always accommodated by aseismic deformation below a certain depth the maximum depth of the seismically coupled zone or seismogenic zone is a transition from unstable to stable sliding along the plate interface we have determined the depth of this stability transition for the circurn pacific subduction zones of honshu kuriles kamchatka aleutians alaska mexico and chile these subduction zones have experienced great interplate earthquakes and the aftershock regions are well located depth estimates of interplate events that are located at the downdip edge of the aftershock regions are used to determine the maximum depth of seismic coupling for an average p wave velocity of 6 7 km s 1 above the plate interface we find that for most subduction zones the stability transition occurs at 40 5 km depth there are however several exceptions at the hokkaido trench junction where the japan trench and the kurile trench intersect seismic coupling is deep and extends down to 52 55 km deep coupling was also found in the coquimbo region in central chile the mexico subduction zone has shallow coupling the transition occurs at 20 30 km depth previous studies of micro earthquakes in honshu hokkaido the aleutians and alaska show that earthquakes within the upper plate extend no deeper than the downdip edge of the coupled zone that we find given our measurements of seismic coupling depth we then explore the mechanism that may determine coupling depth the concept of critical temperature has been used to explain the depth of seismic coupling in other tectonic environments thus we first test whether a critical temperature can explain our results temperatures at the plate interface are dependent on many variables but two that are poorly determined are shear stress and radiogenic heat generation shear stress has been constrained by inversion of heat flow data assuming a crustal radiogenic heat production rate of 3 1 exp z 8 5 wm 3 and a constant coefficient of friction we find two critical temperatures of about 400 c and 550 c the lower critical temperature may be characteristic of regions with a relatively thick continental crust and the higher temperature of regions with a relatively thin continental crust on the other hand one single critical temperature of about 250 c can explain the coupling depths if shear stresses are constant with depth

the paleocene eocene thermal maximum record in the organic matter of the claret and tendruy continental sections south central pyrenees lleida spain abstract the carbon isotope excursion cie associated with the paleocene eocene thermal maximum petm has been detected for the first time in the total organic carbon toc contained within the continental sediments of the tremp formation south central pyrenees lleida spain the 13 c toc magnitude of the cie is 4 3 in the claret section and 3 0 in the tendruy section with minimum values of 27 6 and 26 7 respectively previous studies have detected the cie in the south central pyrenees in both marine carbonates and within continental soil carbonate nodules these studies have located the onset of the cie either above or within the claret conglomerate interpreted as a megafan produced by a profound change in the precipitation regimen at the beginning of the petm our higher resolution 13 c toc study in the claret and tendruy sections places the onset of the cie below the base of the claret conglomerate and therefore suggests a 4 to 9 kyr time lag between the onset of the cie and an increase in intense seasonal precipitation rates furthermore this study suggests that the cie took place 30 55 kyr after the deposition of important late cernaysian tremp mammalian sites claret 4 tendruy v tendruy and palau which contain the youngest known occurrence of endemic paleocene mammalian taxa in europe before the mammalian dispersal event mde migration of new mammal groups such as perissodactyls artiodactyls primates marsupials carnivores creodonts and rodents the first immigrant mammals in europe are recorded at dormaal belgium above a hiatus the base of which has been dated to around the start of the cie our data indicate that the mde might have in fact occurred in europe within a time interval of about 67 kyr around the cie onset

lake sedimentological and ecological response to hyperthermals boltysh impact crater ukraine the boltysh meteorite impact crater ukraine formed at the cretaceous paleogene boundary at ca 65 2 ma a borehole drilled in the central part of the crater cored a 400 m thick high resolution lacustrine succession that covers the dan c2 hyperthermal event associated with a negative carbon isotope excursion continuous terrestrial records of past hyperthermals are of limited availability which makes this record a unique case study of the continental impact of rapid climate warming this study uses high resolution sedimentological core log data together with thin section x ray diffraction microprobe and palynological analyses to i reconstruct lake sedimentological and ecological development across the carbon isotope excursion and ii assess the environmental effect of hyperthermals on terrestrial ecosystems based on detailed facies analysis five gradual stages of lake formation are identified which show a strong relationship to carbon isotope shifts and associated climatic trends initially sediment supply into the boltysh lake was controlled by crater morphology during later lake stages sediment supply was increasingly controlled by changes in inflow evaporation ratios which affected seasonal stratification patterns and longer term lake levels an inferred increase in atmospheric pco2 related to the carbon isotope excursion together with increasing mean annual temperatures was probably responsible for periodic increases in biological activity of photosynthesising organisms and biomass production these fluctuations in facies and lake settings largely correspond to orbital paced moisture availability oscillations the gradual reduction in sediment supply commencing during early lake formation prior to carbon isotope excursion inception suggest that the dan c2 event did not initiate sedimentary changes but intensified sedimentary response to orbital controlled climate change this article is protected by copyright all rights reserved

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

in situ stress state from walkaround vsp anisotropy in the kumano basin southeast of the kii peninsula japan to reveal the stress state within the kumano basin which overlies the nankai accretionary prism we estimated seismic anisotropy from walkaround vertical seismic profiling vsp data recorded at site c0009 during integrated ocean drilling program iodp expedition 319 we obtained the following anisotropic parameters 1 p wave velocity anisotropy derived from azimuthal normal moveout nmo velocity analysis 2 p wave amplitude variation with azimuth and 3 axes of symmetry of s wave splitting azimuthal variations of p wave velocity by ellipsoidal fitting analysis showed that p wave velocity anisotropy within sediments of the kumano basin was 5 both the directions of fast p wave velocity and strong amplitude are aligned with the convergence vector of the philippine sea plate furthermore s wave splitting analysis indicated that s wave polarization axes were parallel to and normal to the direction of plate subduction these results indicate that the maximum horizontal stress at site c0009 in the kumano basin is in the direction of plate subduction the horizontal differential stress estimated from the p wave velocity anisotropy 2 7 5 5 mpa indicates that the maximum horizontal stress is similar in magnitude to or a little higher than the vertical stress

ground water radon anomaly before the kobe earthquake in japan radon concentration in ground water increased for several months before the 1995 southern hyogo prefecture kobe earthquake on 17 january 1995 from late october 1994 the beginning of the observation to the end of december 1994 radon concentration increased about fourfold on 8 january 9 days before the earthquake the radon concentration reached a peak of more than 10 times that at the beginning of the observation before starting to decrease these radon changes are likely to be precursory phenomena of the disastrous earthquake

updip limit of the seismogenic zone beneath the accretionary prism of southwest japan an effect of diagenetic to low grade metamorphic processes and increasing effective stress off southwest japan the seaward limit of coseismic displacement or updip limit of the seismogenic zone of the 1946 mw 8 3 thrust earthquake reaches to 4 km depth and 40 km landward of the trench this limit coincides with the estimated location of the 150 c isotherm and has been linked to changes in physical properties associated with the smectite to illite clay mineral transition here we show that this limit correlates with a suite of diagenetic to low grade metamorphic processes characterized by 1 declining fluid production and decreasing fluid pressure ratio and 2 active clay carbonate and zeolite cementation and the transition to pressure solution and quartz cementation these diagenetic to low grade metamorphic changes cause the onset of velocity weakening during thrust faulting an increase in effective stress and strengthening of the hanging wall which together combine to produce recordable earthquakes

the dan c2 hyperthermal event at gubbio italy global implications environmental effects and cause s abstract the dan c2 event is an early danian transient 100 kyr hyperthermal episode centered at 65 2 ma which records shifts in carbon reservoirs and ocean warming in the northwestern and southeastern sectors of the atlantic ocean here we present and discuss high resolution biochronostratigraphic and magnetic susceptibility data and geochemical records from the western tethyan contessa highway section gubbio italy which provide the first direct evidence of the dan c2 event beyond the atlantic ocean and point to the supra regional possibly global significance thereof at contessa highway the dan c2 event exhibits stressed ecological responses among calcareous nannoplankton and foraminifera which highlight marked environmental perturbation affecting the geobiosphere and resulting in enhanced eutrophication of the sea surface waters and carbonate dissolution as well as lowered oxygen content along the water column and at the sea bottom as for other early paleogene hyperthermal events the cause of the dan c2 event might likely to be found in changes potentially astronomically paced in the distribution of carbon within surface biosphere reservoirs however the role played by the concurrent third and last phase of deccan volcanism with its huge release of greenhouse gases into the atmosphere would be also taken into account in addition here we provide first evidence of a further short lived 38 kyr hyperthermal event not known up to now and that we term the lower c29n event

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

a high resolution nonmarine record of an early danian hyperthermal event boltysh crater ukraine carbon isotope and palynological analysis of the fine grained organic carbon rich lacustrine sediments that filled the cretaceous paleogene k pg boundary age boltysh impact crater ukraine preserve a uniquely complete and detailed record of a negative carbon isotope excursion in an expanded section of the early danian that we estimate lasted as long as 340 k y palynological assemblages recovered through the excursion reflect the increasing dominance of thermophylic normapolles species indicating an increasingly warm and dry climate while those recovered below and above the excursion reflect a cooler and wetter climate the record of a transient warming event hyperthermal in the early danian at boltysh has strong similarities with the dan c2 hyperthermal event recorded in marine sediments in tethys and the atlantic ocean and suggests that there were profound environmental changes occurring on a global scale shortly after the k pg boundary

the 2015 gorkha earthquake a large event illuminating the main himalayan thrust fault the 2015 gorkha earthquake sequence provides an outstanding opportunity to better characterize the geometry of the main himalayan thrust mht to overcome limitations due to unaccounted lateral heterogeneities we perform centroid moment tensor inversions in a 3 d earth model for the main shock and largest aftershocks in parallel we recompute s top and p to s receiver functions from the hi climb data set inverted centroid locations fall within a low velocity zone at 10 15 km depth and corresponding to the subhorizontal portion of the mht that ruptured during the gorkha earthquake north of the main shock hypocenter receiver functions indicate a north dipping feature that likely corresponds to the midcrustal ramp connecting the flat portion to the deep part of the mht our analysis of the main shock indicates that long period energy emanated updip of high frequency radiation sources previously inferred this frequency dependent rupture process might be explained by different factors such as fault geometry and the presence of fluids

a high resolution palaeoclimatic record for the last 27 500 years in tropical west africa from the carbon and nitrogen isotopic composition of lacustrine organic matter variations in the carbon and nitrogen isotopic composition of bulk organic matter in the sediments of lake bosumtwi ghana reflect climatically induced changes to the lake and the catchment flora cores spanning the last 27 5 kyr of sedimentation in the lake show large oscillations in 13corg pdb and 15norg air the late pleistocene record is particularly detailed showing changes of ca 20 in carbon and ca 10 in nitrogen isotopic compositions these variations are of complex origin although different in magnitude major isotopic excursions in the two records are generally in phase and reveal the occurrence of two major dry intervals at and immediately following the last glacial maximum the allerod younger dryas period also seems to have been marked by generally dry conditions in this part of tropical west africa nitrogen isotopic evidence suggests that during the period 9 2 3 2 kyr the lake had an extremely stable water column probably due to the absence of a windy or cool dry season or both regular circulation of the water column recommenced during the late holocene and has persisted until the present day

centennial to decadal vegetation community changes linked to orbital and solar forcing during the dan c2 hyperthermal event formed close to the k pg boundary the boltysh meteorite crater ukraine preserves 400 m of lacustrine sedimentary rocks that include a record of the early danian dan c2 hyperthermal event abundant pollen spores and algae recovered from these sediments have yielded a cyclic record of plant ecology change paced by c 21 kyr orbital precession cycles new higher resolution sampling across the inception of the dan c2 hyperthermal event has identified oscillations in vegetation community ecology at sub orbital periods of c 2 kyr c 200 years and c 11 years these are consistent with possible hallstatt devreis suess and schwabe solar cycles respectively rapid regime shift from savanna to a mesic forest ecosystem was paced by c 21 kyr precession with the shift probably occurring in c 2 kyr i e possible hallstatt oscillations between mesic and winterwet dominated plant communities increased in intensity suggestive of ecological flickering supplementary material detrended correspondence and changepoint analysis palynological frequency data for dca groups and core photographs are available at https doi org 10 6084 m9 figshare c 3803893

latest danian carbon isotope anomaly and associated environmental change in the southern tethys nile basin egypt abstract during the palaeocene and eocene epochs 65 5 33 9 ma the earth experienced the warmest conditions of the cenozoic this palaeogene greenhouse episode is characterized by several short lived negative carbon isotope 13 c excursions which are usually interpreted as transient warming events hyperthermals9 as indicated by rising temperatures of surface and bottom waters and accompanied carbonate dissolution in deep sea settings among these events the palaeocene eocene thermal maximum petm c 55 5 ma is globally the best documented and most prominent further negative 13 c anomalies have recently been identified in the eocene but the early to middle palaeocene has mostly been neglected here benthic foraminiferal 13 c records are presented from four upper danian lower selandian sections in the nile basin eastern egypt all records show a negative 13 c shift with an amplitude of up to 2 at the base of planktonic foraminiferal subzone p3b c 61 ma the supra regional nature of this event is emphasized by correlation with a well dated similar 13 c record from zumaia spain lithological changes the 13 c signature and biotic responses strongly resemble those of the petm in egypt which leads to the hypothesis that this latest danian event9 lde may represent another early palaeocene hyperthermal

seismically inferred dilatancy distribution northern barbados ridge decollement implications for fluid migration and fault strength a 5 x 25 km three dimensional seismic survey of the lower part of the northern barbados ridge accretionary prism creates a three dimensional image of a major active decollement fault the fault is usually a compound negative polarity reflection modeled as a low velocity high porosity zone less than 14 m thick this thickness is significantly less than that defined by drilling of a 40 m zone of deformation at ocean drilling program odp site 671b located within the surveyed area we infer that the seismically defined fault is a thin high porosity zone and is thus an undercompacted high fluid pressure dilatant section if these inferences are correct then map view variations in seismic reflection waveform and amplitude illustrate complex patterns of fault zone fluid content and fluid migration paths the amplitude map suggests kilometre wide channels of locally high porosity and thus focused fluid flow these paths are only subparallel to the expected minimum head as inferred from the shape of the overlying sediment wedge other factors must modify fluid concentrations and ultimately migration several areas of positive polarity fault reflections define square kilometre sized regions inferred to be lower porosity sections producing strong asperities in an otherwise weak fault one coincident with site 671b may explain the success of drilling through the fault here all other holes drilled in the area were within the negative polarity regions and were unsuccessful in penetrating through the entire fault zone possibly because of instability associated with high fluid pressures and a weak fault odp leg 156 planned for 1994 will test inferences related to fault permeability and fluid pressures

velocity porosity relationships for water saturated siliciclastic sediments seeking a global empirical relationship between compressional wave velocity and porosity for siliciclastic sediments we have brought together an extensive suite of both new and published log and core based data we undertook a detailed statistical analysis of ocean drilling program data from amazon fan to examine variables affecting compressional velocity in shallow unconsolidated sediments we identify three dominant variables porosity shale fraction and consolidation history and present two empirically determined boundary curves one for normally consolidated sediments and a second for highly consolidated environments e g accretionary prisms these two empirical relationships predict the compressional velocity of siliciclastic sedimentary rocks with water filled pores as a function of porosity and clay content for the full range of observed porosities velocities of siliciclastic sedimentary rocks decrease rapidly with both increasing porosity and increasing clay content at fractional porosities higher than about 0 4 fluid dominates the elastic properties and velocity exhibits a subtle dependence on porosity remarkably the amazon fan data show that clay content has no direct influence on velocity at high porosities both clay content and sorting do indirectly affect velocity through their control of porosity burial affects velocity not only by compaction related porosity decrease but also by pressure induced increase of intergrain coupling because of the sensitivity of velocity to consolidation history particularly at intermediate fractional porosities of about 0 30 0 40 no single velocity porosity relationship can apply to all high porosity sediments the two proposed relationships fit the majority of published and new data they are applicable however only for normally pressured in situ conditions and water filled pores

velocity porosity relationships in smectite rich sediments shikoku basin japan 1 at the nankai trough japan smectite rich sediments of the shikoku basin are both underthrust beneath and frontally accreted to the outer accretionary wedge to understand the changes that occur in the physical properties of sediments as they are underthrust or incorporated into the accretionary wedge it is necessary to characterize those physical properties outboard of the deformation front one key relationship to constrain is between the compressional wave velocity vp and porosity in order to estimate pore fluid pressure and determine the strength of fault rocks at depth here we investigate how the type of clay minerals and proportions of the different clays may affect the velocity porosity relationship with particular emphasis on the abundance of hydrous smectitic clays using data from iodp sites c0011 and c0012 in the shikoku basin we demonstrate that when the core based porosity is corrected for the abundance of smectite the resultant velocity porosity relationship does not fit previously established transforms therefore we propose a new empirical relationship for the smectite rich sediments of the shikoku basin and caution against the indiscriminate use of global and or pre existing models in smectite rich formations

high resolution carbon isotope stratigraphy and mammalian faunal change at the paleocene eocene boundary in the honeycombs area of the southern bighorn basin wyoming the paleocene eocene boundary is defined chemostratigraphically by the onset of a 100 kyr global carbon isotope excursion cie that is recognized in marine and continental strata in both carbonate and dispersed organic carbon the cie is important in continental sections as a proxy for environmental change during the paleocene eocene thermal maximum petm which clearly affected faunal succession in paleocene eocene mammals at polecat bench in the northern bighorn basin wyoming the cie is in the will wood formation where it spans four mammalian biozones from part of latest clarkforkian cf 3 through early wasatchian wa m meniscotherium wa 0 and part of wa 1 here we report a new high resolution study of the cie recorded in dispersed organic carbon of the basal willwood formation in the honeycombs area of the southern bighorn basin in the honeycombs area 58 isotope sample sites span a vertical section of 71 meters including the wa m locality halfway hill north with both meniscotherium and a heptodonlike perissodactyl and the richly fossiliferous wa 0 wash site castle gardens yielding a diverse mammalian fauna total organic carbon in the honeycombs section is in the range of 0 1 to 0 4 percent by weight and caco 3 is notably lacking except in the castle gardens interval where it reaches ca 3 percent pre and post excursion values of 13 c org pdb range from 26 2 to 24 1 permil the honeycombs cie is about 42 m thick and cie excursion values range from 28 8 to 26 2 permil the honeycombs area is important because the halfway hill north locality is the first to yield a perissodactyl from the wa m meniscotherium zone and the castle gardens wash site is the first to yield abundant evidence of wa 0 zone microvertebrates as at polecat bench the meniscotherium zone in the honeycombs area is in the lower part of the cie and castle gardens and other wa 0 sites are in the longer middle and upper parts starting near or after the maximum negative excursion the cie at polecat bench includes a series of 5 to 6 negative excursion landmarks that are spaced on average about 8 5 m apart these are tentatively interpreted as 21 kyr orbital precession cycles like those inferred for paleosol color negative excursion landmarks are present in the honeycombs cie as well but these are fewer and part of the honeycombs section may be condensed or missing full understanding of the paleocene eocene biotic transition will require investigation at even finer scales of temporal resolution and results reported here suggest that finer scale studies should be possible

response to the comment by w h schwarz et al on joint determination of 40k decay constants and 40ar 40k for the fish canyon sanidine standard and improved accuracy for 40ar 39ar geochronology by p r renne et al 2010

long term resilience decline in plant ecosystems across the danian dan c2 hyperthermal event boltysh crater ukraine mass balance calculations indicate that a massive amount of 13 c depleted carbon was released into the early danian atmosphere in volumes comparable with the younger paleocene eocene thermal maximum petm this danian hyperthermal event the dan c2 has been documented from the fill of the boltysh meteorite crater ukraine palynofloras recovered from the boltysh crater fill show a trend from mesic forest to savannah ecosystem dominance on a millennial scale across the hyperthermal inception with no abrupt compositional shift this longer term trend is overprinted by moisture availability oscillations reflecting orbital forcing forcing is not directly tracked by the oscillations which are composed of mesic forest and savannah palynofloras separated by rapid critical transitions the absence of an ecological collapse at the dan c2 indicates that plant ecosystems experienced dominant forcing from orbital cyclicity rather than a stochastic temperature rise

seismic modeling of the decollement zone at the base of the barbados ridge accretionary complex wide aperture seismic reflection profiling of the northern barbados ridge accretionary complex at 16 12 n has imaged the decollement horizon across more than 100 km of the accretionary complex revealing prominent changes in the amplitude of the decollement reflection synthetic seismograms from models of the variation of velocity and density with depth were compared with selected seismic traces between 2 5 km seaward of the toe of the accretionary complex and 20 km landward of the toe to determine the changes in velocity density properties along the decollement thrust zone modeling requires a thin low velocity layer to develop landward along the decollement beneath the complex while no such layer exists at the corresponding stratigraphic boundary in the undeformed sediments seaward of the complex two dimensional modeling that incorporated lateral variations in topography velocity and density was performed on a 7 km section of the decollement 20 km landward of the deformation front the best fitting model includes a 20 m thick low velocity layer at the decollement horizon with a relative velocity decrease in the layer of 0 2 km s changes in the reflection amplitude along this 7 km section could be produced by either a change in the velocity anomaly within the layer or a thinning of the decollement layer to less than 4 m the shape of the reflected wavelet from the decollement indicates that the principal cause of the amplitude variation is a change in the velocity contrast rather than a change in thickness the low velocity layer can be explained by a decollement shear zone that has high porosity maintained by elevated pore fluid pressure high fracture permeability within the decollement permits dewatering of sediment attached to the oceanic crust and thrust beneath the accretionary complex

nd isotope study of provenance patterns across the british sector of the iapetus suture the southern uplands greywacke succession scotland accumulated at the laurentian margin of the iapetus ocean it was sequentially incorporated into an imbricate accretionary thrust complex until closure of the ocean thereafter the thrust belt propagated across the suture zone as a foreland thrust belt directed towards the hinterland of avalonia a foreland basin migrating ahead of the thrust belt was the depositional site for the southernmost southern uplands units and the windermere supergroup english lake district a nd isotope study has shown that juvenile ophiolitic detritus was introduced into the oldest mid ordovician southern uplands greywackes before two distinct provenance areas evolved one supply ing juvenile andesitic detritus in addition to a quartzo feldspathic component the other proterozoic and exclusively quartzo feldspathic bimodal composition continued into the early silurian but was overlapped from late in the ordovician by greywackes with intermediate nd isotope composition this was not a sim ple mixing effect since the andesitic component is not represented and the necessary juvenile component comes from granodioritic and felsitic lithologies intermediate end values are then a consistent feature through the silurian both in the younger strata of the southern uplands and in the earliest foreland basin tur bidites of the windermere supergroup the transition suggests cessation of volcanicity and erosion of deeper levels of the provenance terrane s possibly linked to the evolution of the basin system from active margin accretion related to a foreland setting to the north of the southern uplands terrane beyond the southern upland fault a caradoc to wenlock turbidite sequence occupies inliers within the midland valley the older greywackes contain abundant juvenile ophiolite and plutonic detritus in addition to a quartzo feldspathic metamorphic component there are similarities with the most northerly part of the southern uplands from the late ordovician end values systematically decline so that early llandovery midland valley greywackes are exclusively quartzo feldspathic derived from an ancient source indistinguishable in isotopic terms from that periodically supplying the southern uplands in general the llandovery midland valley provenance was significantly more mature than that contemporaneously supplying the southern uplands thereafter the midland valley latest llandovery and early wenlock greywackes contain a higher proportion of a juvenile component and by the early wenlock greywackes from the midland valley southern uplands and lake district terranes are similar in terms of end a common provenance seems likely and suggests that by the mid silurian all three terrenes were in close proximity

detailed coseismic slip distribution of the 1944 tonankai earthquake estimated from tsunami waveforms coseismic slip distribution on the fault plane of the 1944 tonankai earthquake is estimated from inversion of tsunami waveforms three improvements from a previous study satake 1993 are made these are 1 smaller subfaults are used to resolve detailed slip distribution 2 the sub faults fit better to the plate interface geometry and 3 finer and more accurate bathymetry data is used the inversion result shows that a maximum slip of about 3 m occurred on the plate interface off shima peninsula the total seismic moment is estimated to be 2 0 1021 nm mw 8 2 the result confirms that the 1944 tonankai earthquake did not rupture the plate interface beneath the tokai region and supports the existence of the seismic gap in the tokai region suggested by ishibashi 1981 the slip of about 1 5 m on the plate interface beneath atsumi peninsula northeast of the large slip area is necessary to explain the observed tsunami waveforms although no seismic moment release was estimated from strong motion data by kikuchi et al 1999 this may suggest that the rupture beneath atsumi peninsula was slow

a nd isotope investigation of sediments related to crustal development in the british isles the times of original fractionation of the sm and nd component of clastic sediments from a mantle source crustal residence age have been estimated from sm nd model ages calculated relative to a depleted mantle evolution in this way the provenance and evolution of selected precambrian and phanerozoic sediments and metasediments from the british isles have been examined whereas some archaean and early proterozoic sediments have sm nd model ages that are close to their stratigraphic age the phanerozoic sediments analysed have model ages as much as 2 0 ga in excess of their stratigraphic age a more detailed study of lower palaeozoic sediments deposited on the northern margin of the iapetus ocean provides evidence for a marked change of provenance in the ordovician after the deposition of the dalradian supergroup a component with comparatively high143nd 144nd and sm nd ratio presumably basaltic is present in the sediments throughout the accretionary prism crustal residence age estimates average about 1 5 ga for both these lower palaeozoic sediments and modern pelagic clays and collectively fail to provide any evidence for significant continental growth during the phanerozoic