stuck in the mud earthquake nucleation and propagation through accretionary forearcs 1 subduction zone earthquakes can propagate to the surface causing large seafloor displacements resulting in tsunamis this requires the earthquake to rupture through clay rich sediments of the accretionary wedge which are largely aseismic as found previously the frictional properties of a range of wet clays at low slip velocity are velocity strengthening thus inhibiting earthquake nucleation however at high slip velocity the same materials weaken almost immediately resulting in a negligible critical slip weakening distance and fracture energy we interpret this behaviour as rapid thermal pressurization of the pore fluid within the clay gouge the lack of fracture energy can explain how a large rupture propagating from depth might not be arrested by clay rich velocity strengthening sediments as is commonly seen the results suggest that generally earthquakes may be difficult to nucleate on mature faults dominated by clay but the propagation of earthquakes through these zones is energetically very favourable

sahke seismic scatter imaging of subduction beneath wellington north island new zealand scattering reflectivity analysis of onshore seismic data seismic array hikurangi experiment images slab geometry and crustal structure at a geodetically locked subduction boundary a broad seismic scattering zone bsz up to 10 km thick above the subduction interface at depths of 16 30 km has seismic properties vp vp vs and q that imply high fluid pressures probably associated with underplated sediments the listric strike slip wairarapa fault and other splay faults that sole into the bsz imply long term weakness high rates of intraslab seismicity with low rates above the slab imply stress decoupling across the bsz association of high fluid pressures and long term weakness with geodetic locking is in contrast to similar observations at zones of slow slip at the northern hikurangi margin and suggest that either 1 pore fluid pressure or locking behavior may cycle over times longer than two decades or 2 local material properties play a significant role in determining if slow slip or locking occurs

magnetotelluric imaging of fluid processes at the subduction interface of the hikurangi margin new zealand 1 the subduction interface beneath the northern part of the hikurangi subduction margin on the east coast of new zealand s north island is exceptionally shallow and cool compared with other margins where slow slip has been observed here we use magnetotelluric data to show that a marked decrease in the conductivity of the fore arc sediments coincides with the onset of seismicity at 10 km depth below the sediments a dipping band of seismicity and intermediate conductivity at the subduction interface connects to a deeper more conductive zone above the down going plate this deeper conductive zone is interpreted to be under plated sediments these results and results from previous seismic tomography in the area suggest that the intermediate resistivity zone represents a region of upward fluid transport near the plate interface followed by fluid escape into the upper plate

methane flux and origin in the othrys ophiolite hyperalkaline springs greece abstract the occurrence and origin of methane ch4 generated by serpentinization of ultramafic rocks is of current timely interest in planetary geology astrobiology and energy resource exploration as it may contribute in particular to decipher the source of methane on mars the origin of life and the potential of abiotic hydrocarbon synthesis methane of dominant abiotic origin in serpentinized peridotites on continents ophiolites or igneous intrusions has been documented so far with complete carbon and hydrogen isotope composition in six countries in the philippines turkey oman new zealand japan and italy we report the discovery of two new sites in greece at archani and ekkara located in the othrys ophiolite massif portable sensors based on fourier transform infrared spectrometry ftir and tunable diode laser absorption spectroscopy tdlas allowed to realize that out of 21 ophiolitic springs methane is released only by four hyperalkaline ph from 10 7 to 11 3 and calcium hydroxide ca oh type waters all other 17 springs with ph

global cooling during the eocene oligocene climate transition about 34 million years ago earth s climate shifted from a relatively ice free world to one with glacial conditions on antarctica characterized by substantial ice sheets how earth s temperature changed during this climate transition remains poorly understood and evidence for northern hemisphere polar ice is controversial here we report proxy records of sea surface temperatures from multiple ocean localities and show that the high latitude temperature decrease was substantial and heterogeneous high latitude 45 degrees to 70 degrees in both hemispheres temperatures before the climate transition were 20 c and cooled an average of 5 c our results combined with ocean and ice sheet model simulations and benthic oxygen isotope records indicate that northern hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time

propagation of slow slip leading up to the 2011 mw 9 0 tohoku oki earthquake many large earthquakes are preceded by one or more foreshocks but it is unclear how these foreshocks relate to the nucleation process of the mainshock on the basis of an earthquake catalog created using a waveform correlation technique we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude mw 9 0 tohoku oki earthquake in japan the time history of quasi static slip along the plate interface based on small repeating earthquakes that were part of the migrating seismicity suggests that two sequences involved slow slip transients propagating toward the initial rupture point the second sequence which involved large slip rates may have caused substantial stress loading prompting the unstable dynamic rupture of the mainshock

mapping fluids to subduction megathrust locking and slip behavior in subduction zones high fluid content and pore pressure are thought to promote aseismic creep whereas well drained conditions are thought to promote locking and failure in earthquakes however observations directly linking fluid content and seismic coupling remain elusive heise et al 2017 use a magnetotelluric survey to image the electrical resistivity structure of the northern hikurangi subduction thrust to 30 km depth as an indicator of interconnected fluid content the authors document a clear correlation between high resistivity and a distinct geodetically locked patch and between conductive areas and weak coupling their study together with other recent geophysical investigations provides new evidence for the role of fluids in governing subduction thrust locking

subducting an old subduction zone sideways provides insights into what controls plate coupling abstract the hikurangi plateau has had two episodes of subduction beneath new zealand firstly at ca 100 ma during north south convergence with gondwana and currently during east west convergence between the pacific and australian plates as a result of this ninety degree change in convergence direction an old subduction zone is now being subducted sideways and the tectonic history of the subducted plate varies dramatically along the strike of the hikurangi margin here we identify the location of the underplated hikurangi plateau along the shallow part of the hikurangi margin using results from both relocated seismicity and seismic tomography next we decipher the tectonic history of the plateau along strike particularly in terms of the hydration state of the plateau and the nature of any sedimentary rock units capping the plateau we then use this information to understand plate coupling at two scales on the large scale the southward transition from typical subduction in the north island to continental collision in the south island and at a smaller scale the strong lateral change from a high deficit in slip rate at the plate interface in the southern north island to a low deficit in slip rate in the northeastern north island we find that the southward transition from subduction to continental collision is controlled by the plateau being more dehydrated to the south as a result of being more deeply subducted at the gondwana margin the southward transition from localized slip at the plate interface to distributed upper plate deformation with no active plate interface occurs in cook strait and is relatively sharp the high deficit in slip rate at the plate interface in the southern north island is likely due to a relatively smooth plate interface from sedimentary rocks capping the hikurangi plateau an impermeable terrane in the overlying plate and the hydrated plateau acting in concert to produce an interseismically sealed plate interface further northeast where the slip rate deficit at the plate interface is low the plate interface has a rough topography including seamounts there is no impermeable terrane in the overlying plate and fluid from the dehydrating plateau migrates across the plate interface

the polonez cove formation of king george island antarctica stratigraphy facies and implications for mid cenozoic cryosphere development the middle to late oligocene polonez cove formation exposed on south eastern king george island south shetland islands provides rare evidence of mid cenozoic west antarctic cryosphere evolution a revised lithostratigraphy and facies analysis and a review of the palaeoenvironmental significance of the formation are presented here the diamictite dominated basal member of the formation krakowiak glacier member records the presence and retreat of marine based ice on a shallow continental shelf five overlying members are recognized these consist of basaltic sourced sedimentary rocks and lavas and represent a variety of shoreface and shallow continental shelf environments in an active volcanic setting these units contain diverse reworked and ice rafted exotic clasts that become sparse towards the top of the formation suggesting a continuing but waning glacial influence new 40ar 39ar dates from interbedded lava flows indicate a late oligocene age 25 6 27 2 ma for the polonez cove formation but are slightly younger than skeletal carbonate sr isotope ages obtained previously 28 5 29 8 ma there is evidence for wet based subice conditions at the base of the polonez cove formation but no sedimentary facies to suggest substantial meltwater this may reflect a subpolar setting or may result from lack of preservation or a high energy depositional environment a northern antarctic peninsula south shetland islands provenance is probable for most non basaltic clasts but certain lithologies with possible origins in the transantarctic and ellsworth mountains also occur sparsely throughout the formation there is evidence to suggest that the presence of such far travelled clasts within subglacially deposited facies at the base of the formation reflects the advance of a local ice cap across marine sediments containing the clasts as ice rafted material the presence of these clasts suggests that extensive marine based ice drained into the southern weddell sea region and that a strong weddell sea surface current operated both before and during deposition of the polonez cove formation

complex evolution of transient slip derived from precise tremor locations in western shikoku japan transient slip events which occur more slowly than traditional earthquakes are increasingly being recognized as important components of strain release on faults and may substantially impact the earthquake cycle surface based geodetic instruments provide estimates of the overall slip distribution in larger transients but are unable to capture the detailed evolution of such slip either in time or in space accompanying some of these slip transients is a relatively weak extended duration seismic signal known as nonvolcanic tremor which has recently been shown to be generated by a sequence of shear failures occurring as part of the slip event by precisely locating the tremor we can track some features of slip evolution with unprecedented resolution here we analyze two weeklong episodes of tremor and slow slip in western shikoku japan we find that these slip transients do not evolve in a smooth and steady fashion but contain numerous subevents of smaller size and shorter duration in addition to along strike migration rates of 10 km d observed previously much faster migration also occurs usually in the slab dip direction at rates of 25 150 km h over distances of up to 20 km we observe such migration episodes in both the updip and downdip directions these episodes may be most common on certain portions of the plate boundary that generate strong tremor in intermittent bursts the surrounding regions of the fault may slip more continuously driving these stronger patches to repeated failures tremor activity has a strong tidal periodicity possibly reflecting the modulation of slow slip velocity by tidal stresses

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

the origin of rodingites from cassiar british columbia and their use to estimate t and p h2o during serpentinization abstract the cassiar serpentinite located in north central british columbia is a low grade alpine type serpentinite within the sylvester allochthon two stages of rodingitization have occurred at cassiar and these correlate with two stages of serpentinization that have occurred in the ultramafic rock the first stage is characterised by an increase in ca activity and decreases in mg and sio 2 activities in the rodingite culminating in the crystallization of grossular in the rodingite and by the formation of lizardite in the serpentinite at a later time a second event occurred characterised by a decrease in ca activity and increases in mg and sio 2 activities both in the rodingite and the serpentinite this was marked by the crystallization of diopside prehnite and lizardite in the rodingite and by the recrystallization of lizardite to chrysotile and antigorite in the serpentinite the serpentine recrystallization and the development of the second stage rodingite minerals indicate that the changes in rodingite and serpentine mineral assemblages were driven by similar changes in the bulk rock compositions this suggests that the second stage event in both rodingite and serpentinite was caused by an externally derived fluid measurements on fluid inclusions in the rodingite minerals clinozoisite grossular and diopside of the second event indicate that the externally derived fluid was co 2 poor but relatively saline 8 1 5 equiv wt nacl by combining the pressure dependant temperature measurements from fluid inclusions with the pressure independant temperature measurements on 18 o in coexisting serpentine magnetite pairs the pressure of formation can be estimated the second event of serpentine recrystallization and rodingitization was an isothermal process at 300 c 36 c p h 2 o

rates and mechanics of rapid frontal accretion along the very obliquely convergent southern hikurangi margin new zealand analysis of seismic reflection profiles swath bathymetry side scan sonar imagery and sediment samples reveal the three dimensional structure morphology and stratigraphic evolution of the central to southern hikurangi margin accretionary wedge which is developing in response to thick trench fill sediment and oblique convergence between the australian and pacific plates a seismic stratigraphy of the trench fill turbidites and frontal part of the wedge is constrained by seismic correlations to an already established stratigraphic succession nearby by coccolith and foraminifera biostratigraphy of three core and dredge samples and by estimates of stratigraphic thicknesses and rates of accumulation of compacted sediment structural and stratigraphic analyses of the frontal part of the wedge yield quantitative data on the timing of inception of thrust faults and folds on the growth and mechanics of frontal accretion under variable convergence obliquity and on the amounts and rates of horizontal shortening the data place constraints on the partitioning of geological strain across the entire southern hikurangi margin the principal deformation front at the toe of the wedge is discontinuous and represented by right stepping thrust faulted and folded ridges up to 1 km high which develop initially from discontinuous protothrusts in the central part of the margin near 41 s where the convergence obliquity is 50 orthogonal convergence rate is slow 27 mm yr and about 75 of the total 4 km of sediment on the pacific plate is accreted frontally the seismically resolvable structures within 30 km of the deformation front accommodate about 6 km of horizontal shortening at least 80 of this shortening has occurred within the last 0 4 0 1 m y at an average rate of 12 3 mm yr this rate indicates that the frontal 30 km of the wedge accounts for about 33 55 of the predicted orthogonal contraction across the entire plate boundary zone despite plate convergence obliquity of 50 rapid frontal accretion has occurred during the late quaternary with the principal deformation front migrating seaward up to 50 km within the last 0 5 m y i e at a rate of 100 km m y the structural response to this accretion rate has been a reduction in wedge taper and consequently internal deformation behind the present deformation front near the southwestern termination of the wedge where there is an along the margin transition to continental transpressional tectonics the convergence obliquity increases to 56 and the orthogonal convergence rate decreases to 22 mm yr the wedge narrows to 13 km and is characterized simply by two frontal backthrusts and landward verging folds these structures have accommodated not more than 0 5 km of horizontal shortening at a rate of 1 mm yr which represents 5 of the predicted orthogonal shortening across the entire plate boundary in southern north island the landward vergent structural domain may represent a transition zone from rapid frontal accretion associated with low basal friction and high pore pressure ratio in the central part of the margin to the northern south island region where the upper and lower plates are locked or at least very strongly coupled

tracking repeated subduction of the hikurangi plateau beneath new zealand abstract the hikurangi plateau has been subducted beneath new zealand twice firstly at ca 100 ma during n s convergence with gondwana and currently during e w convergence between the pacific and australian plates here we use a nationwide 3 d seismic velocity model derived from seismic tomography studies and seismicity relocated with this model to determine the location of the subducted western and southern edges of the plateau in the hikurangi subduction zone in the north island and northern south island we identify the western edge in the 37 140 km depth range based on the distribution of seismic velocities in the top of the subducted pacific plate changes in the thickness of the dipping seismic zone and steepening of the subducted plate downdip of the buoyant plateau in the central south island where the hikurangi plateau is subducting for a second time the plateau dips less steeply its southern edge is well defined by the collision of the delaminated lower crust of the plateau with the northern fiordland subduction zone where it bends the younger subducted australian plate to vertical the hikurangi plateau was originally rifted from the ontong java plateau and the subducted portions of the hikurangi plateau identified here fill a gap in reconstructions of this large igneous province

three dimensional velocity structure of the northern hikurangi margin raukumara new zealand implications for the growth of continental crust by subduction erosion and tectonic underplating traveltimes between shots from nine marine seismic reflection lines and nine onshore recorders were used to construct a 3 d p wave velocity model of the northern hikurangi subduction margin new zealand from north to south between raukumara basin and raukumara peninsula the moho of the overriding plate increases in depth from 17 to similar to 35 km low seismic p wave velocities of 3 5 5 0 km s are localized within a similar to 10 km thick prism in the lower crust of the overriding plate immediately updip of the intersection between the subduction thrust and moho and beneath the topographic crest of east cape ridge and the raukumara range southward this region of low seismic velocities and surface uplift increases in distance from the trench as the thickness of the crust in the overriding plate increases we interpret this low velocity volume to be underplated sedimentary rocks and crustal materials that were tectonically eroded by subduction beneath the trench slope the buoyancy and low strength of these subducted materials are proposed to assist the escape from a subduction channel near the base of the crust and drive local rock uplift in the middle crust our observations of very low velocity suggest high fluid filled porosities of 12 18 and the implied buoyancy anomaly may enhance underplating at greater depths the process is driven by the contrast between upper crustal quartz feldspar mineralogy and the denser diabase or olivine rich lithologies of the lower crust and mantle we estimate a rate of lower crustal underplating at the northern hikurangi margin of 20 7 km 3 ma 1 km 1 since 22 ma we suggest that underplating provides an efficient means of accreting subducted sediment and tectonically eroded material to the lower crust and that the flux of forearc crustal rocks into the mantle at subduction zones may be systematically overestimated

non volcanic tremor associated with the march 2010 gisborne slow slip event at the hikurangi subduction margin new zealand 1 non volcanic tremor accompanies slow slip events at most circum pacific subduction zones previously the hikurangi subduction margin new zealand and the boso peninsula of japan have been noted as exceptions where slow slip which occurs at shallow depth compared to other subduction zones does not generate seismic tremor the lack of tremor observations raises questions whether tremor and slow slip are manifestations of the same process and whether different temperature and pressure conditions influence the physical mechanism of tremor production analysis of seismic data during the march 2010 gisborne slow slip event new zealand reveals that this slow slip event at the northern hikurangi margin is accompanied by tremor with distinctive characteristics compared to local microearthquakes both the gisborne area of new zealand and the boso peninsula of japan are underlain by thick accumulations of sedimentary rocks that likely inhibit the observation of low amplitude tremor due to high attenuation discovery of tremor in new zealand suggests that tremor may always accompany slow slip and that its apparent absence at the boso peninsula the hikurangi margin prior to this study and any future regions discovered to experience slow slip without concurrent tremor may be the effect of highly attenuating sediments

a three dimensional image of shallow subduction crustal structure of the raukumara peninsula new zealand summary earthquake arrival time data from a 36 station deployment of portable seismographs on the raukumara peninsula have been used to determine the 3 d vp and vp vs structure of this region of shallow subduction a series of inversions have been performed starting with an inversion for 1 d structure then 2 d and finally 3 d this procedure ensures a smooth regional model in places of low resolution the subducted plate is imaged as a northwest dipping feature with vp consistently greater than 8 5 km s 1 in the uppermost mantle of the plate structure in the overlying plate changes significantly along strike in the northeast there is an extensive low velocity zone in the lower crust underlying the most rapidly rising part of the raukumara range it is bounded on its arcward side by an upwarp of high velocity a viable explanation for the low velocity zone is that it represents an accumulation of underplated subducted sediment while serpentinization of the uppermost mantle may be responsible for the adjacent high velocity region the low velocity zone decreases and the adjacent high velocity region is less extensive in the southwest this change is interpreted to be related to a change in the thickness of the crust of the overlying plate in the northeast the crust is thinner and subducted sediment ponds against relatively strong uppermost mantle while in the southwest the crust is thicker and the relatively weak lower crust allows sediment subduction to greater depths a narrow zone of high vp vs parallels the shallow part of the plate interface this suggests elevated fluid pressures with the distribution of earthquakes about this zone further suggesting that these pressures may be close to lithostatic the plate interface at 20 km depth beneath the raukumara peninsula may thus be a closed system for fluid flow similar to that

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

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

bathymetric distribution of fossil foraminifera within marine sediment cores from the eastern part of lutzow holm bay east antarctica and its paleoceanographic implications abstract faunal analysis of fossil foraminifera from marine gravity and piston cores collected by the japanese antarctic research expeditions 1981 and 1992 is used to estimate the impact of the latest quaternary paleoceanography on coastal environments of the eastern part of lutzow holm bay east antarctica accelerator mass spectrometry ams carbon 14 ages produced from sedimentary organic carbon were less than 16 ka non corrected detailed correlation among submarine cores and holocene elevated marine deposits exposed on the eastern shore of the embayment is difficult due to the indefinite reservoir correction value for marine organic matter and to upward increasing abnormal ages for some cores a local carbonate dissolution level can be delineated around the present depth of 300 400 m or shallower in the eastern part of lutzow holm bay during the holocene based on distributional trends of arenaceous calcareous benthic and planktonic foraminifera recognized within a depth less than 600 m downcore recovery of calcareous foraminifera containing bulimina aculeata from two cores obtained in a drowned glacial trough deeper than 600 m situated far beyond the dissolution depth of caco3 indicates the incursion of warm high nutrient and caco3 saturated circumpolar deep water cdw from the offshore area along the trough toward the southeastern coast of lutzow holm bay during the holocene the intrusion of cdw impacted on the marine environments of the southeastern coast thereby contributing to peripheral retreat of the ice sheet as well as increasing calcareous benthic foraminiferal productivity along the southeastern coast of lutzow holm bay

benthic foraminiferal distributions in chilean fjords 47 s to 54 s abstract surface sediment samples collected from the fjord region of southern chile 47 to 54 south were analyzed for benthic foraminifera a total of 175 species were identified including agglutinated and calcareous benthic taxa hierarchical cluster analysis of the foraminiferal data resulted in the recognition of three distinct biofacies inner fjord intermediate fjord and channel and oceanic biofacies geographically controlled by relative position between the pacific ocean and fjord heads similarity percentage simper analysis identified key taxa in the definition of the biofacies that include globocassidulina rossensis cassidulina laevigata and bulimina notovata principal components analysis resulted in two principal components representing sediment size and bottom water temperature and salinity regional distributions are strongly controlled by the oceanographic conditions influenced from the pacific in the west and the glacial freshwater input from the east localized distributions of foraminifera are controlled by conditions influenced by the physiography of the individual fjords and channels the distribution of chilean fjord foraminifera and their environmental associations are consistent with results from other temperate to high latitude fjord foraminiferal studies

plate interface properties in the northeast hikurangi subduction zone new zealand from converted seismic waves arrival time inversion of local earthquakes in the northeast hikurangi subduction zone has indicated high vp vs at the plate interface but the thickness of the anomalous zone is poorly constrained by the p and s travel times we investigate this plate interface zone further by modeling s to p converted phases using synthetic seismograms for upgoing rays of earthquakes in the subducting plate mantle the modeling indicates a low velocity layer at the plate interface which is generally 1 2 km thick and has vp of 5 0 5 35 km s and vp vs of 2 this is consistent with a subducting sediment channel with near lithostatic fluid the low rigidity indicates a weak zone which will have a strong influence on the distribution of deformation the modeling approach shows promise in defining rheological parameters at the plate interface and mapping their variation across the seismogenic zone of the subduction thrust

holocene foraminiferal assemblages from firth of tay antarctic peninsula paleoclimate implications abstract the 77 m sediment core from firth of tay provides complete record of glacial retreat and holocene climate change on the weddell sea side of the antarctic peninsula that began 9400 yr bp benthic foraminiferal data indicate significant environmental changes as recorded at 600 m water depth at the drill site three foraminiferal assemblages fas globocassidulina spp fursenkoina fusiformis fa miliammina arenacea fa and paratrochammina bartrami portatrochammina antarctica fa reflect increasingly glacier distal conditions they started with most glacier proximal conditions that lasted until 8800 yr bp which is indicated by cribroelphidium cf webbi and continued with elevated input of coarse glacial sediment until 7750 yr bp the mid holocene climatic optimum between 7750 and 6000 yr bp appears to be the time of highest primary production which led to higher corrosiveness of bottom waters and biased species composition of the m arenacea fa it was terminated by minor cooling the neoglacial that took place after 3500 yr bp is marked by an increase in p bartrami and p antarctica the major constituents of the p bartrami p antarctica fa this fa became periodically dominant after 900 yr bp indicating increasingly glacier distal conditions due to cooling coinciding with increasing aridity rising altitude of the glacial equilibrium line and less glacial influence on marine biota episodic high abundances of a fourth foraminiferal assemblage globocassidulina biora fa that occurs practically throughout the core is difficult to interpret explicitly although there are some concerns if g biora fa represents in situ fauna it appears to be an opportunistic fauna that dominated during periods of more glacial sediment input and sediment remobilization leading to better carbonate preservation

shallow water benthic foraminifera from the polonez cove formation lower oligocene of king george island west antarctica abstract we present the first description of benthic foraminifera from the lower oligocene of the antarctic peninsula sector south shetlands of west antarctica the single assemblage was collected at several sites and has no modern antarctic analogue it is dominated by robust calcareous species and represents a fan delta front system the assemblage includes a group of the most morphologically conservative antarctic foraminifera known from other cenozoic neritic sites around antarctica indicating their presence since at least the eocene despite including some characteristic taxa e g ammoelphidiella sp it is difficult to correlate this assemblage with any particular interval of the ross sea record mainly because of a strong taxonomic imprint of a shallow water environment

persistent tremor within the northern costa rica seismogenic zone 1 we identify tremor using a spectral detection method and characterize its occurrence over a period of four years 2006 2009 in the vicinity of the nicoya peninsula costa rica although a few major tremor events accompanied by geodetic slow slip occur much of the tremor record consists of minor episodes with short duration and no detectable geodetic slip its persistent occurrence suggests that some portion of the interface is experiencing slow slip nearly continuously driving small patches to fail in accelerated slip locations indicate that much of the tremor occurs at shallow depth in freely slipping regions of the seismogenic zone this result is significant in that locations of slow slip and tremor at other subduction zones are largely limited to the downdip frictional transition tremor locations may help to refine the heterogeneous distribution of locked and freely slipping patches within the costa rica seismogenic zone

high pore fluid pressure may cause silent slip in the nankai trough silent slip events have been detected at several subduction zones but the cause of these events is unknown using seismic imaging we detected a cause of the tokai silent slip which occurred at a presumed fault zone of a great earthquake the seismic image that we obtained shows a zone of high pore fluid pressure in the subducted oceanic crust located down dip of a subducted ridge we propose that these structures effectively extend a region of conditionally stable slips and consequently generate the silent slip

sedimentary underplating at the cascadia mantle wedge corner revealed by seismic imaging earth s largest earthquakes occur at the boundary between subducting oceanic crust and the overriding plate yet the position of the plate boundaries remains uncertain analysis of zones of low seismic wave velocities beneath the northern cascadia subduction zone implies that the plate boundary here may be deeper than previously thought

diverse slow slip behavior at the hikurangi subduction margin new zealand 1 the installation of a continuous gps cgps network in new zealand since 2002 has enabled the discovery of 15 slow slip events at the hikurangi subduction margin our analysis and interpretation of the cgps data reveal a marked diversity in characteristics of slow slip events sses in the north island with durations varying from 6 days to 1 5 years equivalent moment release between mw 6 3 7 2 and recurrence intervals of repeating sses on the order of 2 years to more than 5 years the duration and magnitude characteristics of hikurangi sses appear to be related to the depth where they occur the deepest longest duration and largest sses occur at the southern hikurangi margin near the downdip limit of deep down to 40 km depth strong interseismic coupling the shallowest shortest duration smallest and most frequent sses occur at the northern and central hikurangi margin near the downdip limit of unusually shallow 10 15 km depth interseismic coupling the direction of slip on the interface in the hikurangi sses is consistent with slip partitioning at the hikurangi subduction margin we also show that moment accumulation rates on the interface for the time periods between sses are 40 higher than for the period of more than a decade averaging through the sses indicating that sses compose a major portion of the overall moment release budget of the hikurangi subduction interface

small earthquakes provide insight into plate coupling and fluid distribution in the hikurangi subduction zone new zealand abstract to better understand the nature of interplate coupling in the southern north island of new zealand we compare the distribution of relocated small earthquakes with interseismic geodetic locking of the plate interface from gps and structure within the overlying plate from tomographic inversions relocated seismicity shows a good correlation with both the distribution of strong geodetic locking and geological terranes in the overlying plate it appears that the strong permian triassic rakaia geological terrane controls coupling at the plate interface this relatively impermeable terrane also modulates the small earthquake distribution within the underlying slab promoting clustered seismicity in the slab crust and suppressing lower plane seismicity in the mantle the seismicity and structural data suggest a model where plate coupling is controlled by the ability of fluid to cross the plate interface when an impermeable terrane in the overlying plate prevents such fluid flow plate coupling appears to be strong

oligocene and pliocene interglacial events in the antarctic peninsula dated using strontium isotope stratigraphy strontium isotope stratigraphy is used to date two interglacial marine deposits in the antarctic peninsula region on king george island interglacial pectinid rich sediments in the low head member of the polonez cove formation give a strontium isotope stratigraphy age of 29 0 0 7 0 6 to 29 8 0 8 0 7 ma mid oligocene which in conjunction with previous k ar dating of volcanic rocks indicates a glacial episode in the antarctic peninsula between middle eocene 42 0 1 0 ma and mid oligocene time in addition an inter glacial deposit pecten conglomerate from tectonically elevated exposures on cockburn island is dated as pliocene 3 5 5 3 ma published data suggest these latter sediments were deposited under shallow marine conditions which were warmer than those of present day antarctica

aqueous fluids derived from a subducting slab observed high 3he emanation and conductive anomaly in a non volcanic region kii peninsula southwest japan abstract it has long been recognized that the kii peninsula in the southwest japan arc is peculiar in a non volcanic region indicated by the presence of high temperature hot springs high terrestrial heat flow and high 3 he content in hot spring gases geophysical and geochemical studies were carried out to understand the geotectonic environment in the southern part of the kii peninsula most of the measured 3 he 4 he ratios are similar or higher than air indicating wide spread incorporation of mantle derived helium into meteoric water a region with rather high 3 he 4 he ratios 4 r a on the west side of the omine mountains coincides with the occurrence of high temperature hot springs a deep crustal resistivity structure across the omine mountains was imaged by wide band magnetotelluric soundings a 2 d inversion with n s strike using both tm and te modes reveals two conductors one in the upper 3 7 km depth and the other in lower crust 25 35 km depth to the west of the omine mountains the distribution of microearthquakes and low frequency tremors and the existence of seismic reflectors indicate that the large conductor in the lower crust is related to aqueous fluids derived from the philippine sea plate the upper crustal conductive zone may also reflect the aqueous fluids trapped in the upper crust which are presumably derived from the subducting slab considering the occurrence of seismic events in the subducting slab beneath the southern kii peninsula the aqueous fluids generated by dehydration of the slab mantle could plausibly include morb type helium derived from the residual lithospheric mantle therefore the high temperature hot springs and high 3 he emanations in hot spring gases and other geotectonic events in the southern kii peninsula may be due to heat flux and mantle derived helium discharged from aqueous fluid in the upper crust

fluid budgets along the northern hikurangi subduction margin new zealand the effect of a subducting seamount on fluid pressure we estimate fluid sources around a subducted seamount along the northern hikurangi subduction margin of new zealand using thermomechanical numerical modelling informed by wedge structure and porosities from multichannel seismic data calculated fluid sources are input into an independent fluid flow model to explore the key controls on overpressure generation to depths of 12 km in the thermomechanical models sediment transport through and beneath the wedge is calculated assuming a pressure sensitive frictional rheology the change in porosity pressure and temperature with calculated rock advection is used to compute fluid release from compaction and dehydration our calculations yield more precise information about source locations in time and space than previous averaged estimates for the hikurangi margin the volume of fluid release in the wedge is smaller than previously estimated from margin averaged calculations 14 m3 yr 1 m 1 and is exceeded by fluid release from underlying subducting sediment 16 m3 yr 1 m 1 clay dehydration contributes only a small quantity of fluid by volume 2 m3 yr 1 m 1 from subducted sediment but the integrated effect is still significant landward of the seamount fluid source terms are used to estimate fluid pressures around a subducting seamount in the fluid flow models using subducted sediment permeability derived from porosity and testing two end members for decollement permeability models in which the decollement acts as a fluid conduit predict only moderate fluid overpressure in the wedge and subducting sediment however if the subduction interface becomes impermeable with depth significant fluid overpressure develops in subducting sediment landward of the seamount the location of predicted fluid overpressure and associated dehydration reactions is consistent with the idea that short duration shallow slow slip events sses landward of the seamount are caused by anomalous fluid pressures alternatively it may result from frictional effects of changing clay content along the subduction interface

late oligocene early miocene glacial record of the ross sea antarctica evidence from dsdp site 270 foraminifera from deep sea drilling project site 270 ross sea antarctica are used to trace an early phase of glaciation during the late oligocene early miocene the central ross sea underwent significant bathymetric and oceanographic evolution with the inception of glaciomarine sedimentation resulting in the sequential development of four contrasting foraminiferal populations assemblage zones gradual climatic change in the ross sector during latest paleogene early neogene time culminated in major ice build up by the late early miocene conclusions derived from our microfaunal studies reaffirm climatic and oceanographic trends interpreted from oxygen isotope data for sub antarctic deep sea sites north of the ross sea intensification of glaciation within the ross sea area may be responsible for the increase in production of antarctic bottom water and associated development of widespread early neogene deep sea hiatuses reported from lower latitude regions

stable creeping fault segments can become destructive as a result of dynamic weakening faults in earth s crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast seismic wave producing rupture events perceived as earthquakes these types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment one with stable rate strengthening friction and the other with rate weakening friction that leads to stick slip the 2011 tohoku oki earthquake with moment magnitude m w 9 0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping here we propose a model in which stable rate strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids allowing unstable slip to occur in segments that can creep between events the model parameters are based on laboratory measurements on samples from the fault of the m w 7 6 1999 chi chi earthquake the long term slip behaviour of the model which we examine using a unique numerical approach that includes all wave effects reproduces and explains a number of both long term and coseismic observations some of them seemingly contradictory about the faults at which the tohoku oki and chi chi earthquakes occurred including there being more high frequency radiation from areas of lower slip the largest seismic slip in the tohoku oki earthquake having occurred in a potentially creeping segment the overall pattern of previous events in the area and the complexity of the tohoku oki rupture the implication that earthquake rupture may break through large portions of creeping segments which are at present considered to be barriers requires a re evaluation of seismic hazard in many areas

the hydrothermal plumbing of a serpentinite hosted detachment evidence from the west iberia non volcanic rifted continental margin this study documents the critical role of structurally induced fluid flow during the evolution of the footwall succession to a major low angle normal detachment fault drilled by the ocean drilling program leg 173 site 1068 beneath the southern iberia abyssal plain the fault zone comprises carbonate altered rodingitized and albitized metabasite rich sedimentary breccias and serpentinized mantle peridotites the brittle infrastructure of the detachment consists of mineralized high dilation breccias and meshes of mineralized extensional and shear veins that root into chlorite and serpentine cataclasite and gouge the fault rocks are underlain by cohesive serpentinite that shows kernel textures indicative of volume expansion accompanying serpentinization of peridotite the texture is disrupted and offset by small scale fractures and faults the distribution of serpentine polytypes carbonates fe ni alloys sulfides oxides and other silicate phases varies across the fault zone in patterns consistent with mineralization and replacement from solutions derived from two end member components seawater and ch4 bearing calcium hydroxide enriched hydrothermal solutions the latter form when heated seawater reacts with peridotite to form serpentinite at low water to rock ratios serpentine mineral chemistries indicate that fracture controlled serpentinite recrystallization and replacement occurred at various fo2 asio2 and ca2 conditions in places this also involved mild prograde thermal events the serpentinite also hosts tochilinite valleriite group minerals and aragonite both are interpreted as indicators of sea water incursions into the upper reaches of the detachment to account for the evidence of coeval hydrothermal mineralization and displacements across the detachment we relate hydrothermal discharge to the buffering of high pore fluid pressures by fault slip localized sources of high fluid pressures at depth are attributed to serpentinization of peridotite around the fault that promotes changes to solution mass density exothermic reactions and swelling pressures sealing of the fault between the serpentinization front and the top of the detachment results from hydrothermal mineralization alteration and serpentine gouges hydrothermal discharges from the detachment accompanying shear failure allow for variable mixing between the hydrothermal solutions and seawater and post slip convective draw down of seawater into the detachment it is suggested that the latter may have been limited in duration by ongoing mineralization leading to the restoration of the fault seal concomitant serpentinization around the detachment at depth provides scope for cyclic hydrothermal discharges and fault slip

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

fluid inclusions in jadeitite and jadeite rich rock from serpentinite melanges in northern hispaniola trapped ambient fluids in a cold subduction channel abstract freezing point depression was measured in aqueous fluid inclusions to determine salinities in six samples of jadeitite and jadeite rich rock from the jagua clara serpentinite melange of the rio san juan complex dominican republic the melange represents a fossil subduction zone channel from a cold mature subduction zone with a geothermal gradient of 6 c km one hundred and twenty five determinations of salinity in primary inclusions hosted in jadeite quartz apatite and lawsonite range between extremes of 1 2 and 8 7 but yield a well defined mean of 4 5 1 1 wt 1 s d nacl equiv slightly higher than mean seawater 3 5 wt in one sample eight additional fluid inclusions in quartz aligned along grain boundaries yield slightly lower values of 2 7 1 3 wt nacl equiv homogenization temperatures were also measured for 47 fluid inclusions in two samples but primary entrapment densities are not preserved it is significant that the suite includes two types of samples those precipitated directly from an aqueous fluid as well as examples of metasomatic replacement of a pre existing magmatic rock nevertheless the results indicate identical salinity for both types and suggest a much stronger genetic link between the two types of jadeitite and jadeite rich rock than has previously been assumed based on the results of conductivity measurements in modern subduction zones we envision a pervasive fluid in the subduction channel that evolved from salinity levels lower than those in sea water up to the measured values due to on going but largely completed serpentinization in the subduction channel the present data represent a reference marker for the subduction channel of the rio san juan intra oceanic subduction zone at 30 50 km depth and after 50 60 myr of operation

interseismic locking on the hikurangi subduction zone uncertainties from slow slip events interseismic locking on the hikurangi subduction zone in new zealand is examined in light of alternative assumed locking distributions and the impact of transients slow slip and volcanic sources on temporal and spatial resolution the modern pattern of locking in the north is poorly resolved and based on simulations of possible transient behavior may be an ephemeral feature of the subduction cycle while there appears to be some contemporary locking in the northern half of the hikurangi subduction zone hsz its location is model dependent and hence its relationship to structure slow slip or any transition zone there is unclear simulations of site velocities using the 14 year history of transient events reveal that in the timescale of the interseismic period the northern half of the hsz could be either locked or unlocked and this may not be resolvable for decades in the southern half there is strong contemporary locking in the 15 to 40 km depth range but again the slow slip history leads to uncertainty in the long term pattern slow slip events not only reduce the long term locking by aseismic slip but also greatly hinder our ability to see it it is within the range of possible models that the slip deficit rate at the hsz is more uniform along strike and the modern appearance is controlled by the particular pattern of transients over the past 10 to 20 years when the gps data were collected similarly uncertainties in surface velocities will be large at any subduction zone with large transients

electrical resistivity cross section across the garhwal himalaya proxy to fluid seismicity linkage abstract magnetotelluric mt measurements along a profile cutting across the garhwal himalaya of india are inverted to obtain 2 d electrical resistivity structures of the himalayan wedge and of the underthrusting indian plate the imaged resistivity cross section is dominated by a low angle north east dipping intra crustal high conducting layer ic hcl with an average thickness of 5 km at transition from the lesser himalaya to the higher himalaya the ic hcl is marked by a ramp structure across which its top jumps from a depth of 8 km to 13 km high conductivity of the layer is caused by pounding of upward propagating metamorphic fluids trapped by tectonically induced neutral buoyancy in compression regime of the himalaya the mechanical weakening effects of the fluids counteract the fault normal stresses thereby facilitating thrust type earthquakes on a plane imaged as the top of the ic hcl it is suggested that in the himalaya collision belt like the active subduction zone the active seismic plane forming seat of large and great earthquakes is located a few kilometers above the top of the down going plate in this tectonic setting the high conductance ramp symbolizes a block of low shear strength and high strain which under the deviatoric stresses release accentuated stresses into the brittle crust thereby generating small but more frequent earthquakes in the narrow himalayan seismic belt in response to either the co seismic pumping or the stress transfer during inter seismic period the upward infiltration of fluid fluxes into the over pressurized zones sufficiently reduces the shear strength of local thrusts and shear zones turning these into locales of concentrated seismicity

slow slip events and seismic tremor at circum pacific subduction zones 1 it has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements however only recently has a fuller spectrum of strain release processes including normal slow and silent earthquakes or slow slip events and continuous and episodic slip been observed and generated by numerical simulations of the earthquake cycle despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive the concurrence of seismic tremor with slow slip episodes in cascadia and southwestern japan provides insight into the process of slow slip a perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface alternatively evidence is accumulating to support the notion that tremor results from shear failure during slow slip global observations of the location spatial extent magnitude duration slip rate and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation most slow slip events occur just downdip of the seismogenic zone consistent with rate and state dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation at a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault bringing it closer to or farther from earthquake failure respectively this paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide with a focus on circum pacific subduction zones trends in global observations of slow slip events suggest that 1 slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it 2 different frictional properties likely control fast versus slow slip 3 the depth range of slow slip may be related to the thermal properties of the plate interface and 4 the equivalent seismic moment of slow slip events is proportional to their duration mo different from the mo 3 scaling observed for earthquakes

metamorphism denudation and sea level in the archean and cooling of the earth abstract over long enough time scales an antagonistic balance acting between tectonics uplift and rifting and the sedimentary cycle erosion and deposition probably keeps continental surfaces close to sea level we argue that this balance constitutes the primary mechanism for keeping long term continental freeboard constant by regulating the continental thickness an important implication is that the long term uplift or down warp history of ancient continental segments provides direct information on secular changes in the isostasy of the adjacent ocean basins through time the amount of uplift can be estimated from the regional metamorphic grade the burial pressures at present exposure of ten undisturbed archean granite greenstone segments are estimated to be 1 5 0 5 kb from this we infer a maximum long term uplift and erosion of 5 2 km for stable continent since 3 0 ga implying a mean continental thickness of 46 km at the time of crustal stabilization for a constant mean ocean depth isostasy requires a palaeo oceanic crust 14 2 km thick in the middle archean alternatively if little continent existed then the oceans would have been shallower and the palaeo oceanic crust 21 2 km thick assuming plate spreading did occur in the archean potential temperatures in the shallow mantle at 3 ga were 90 30 c or 170 20 c for no continent hotter than those prevailing today these temperatures translate into time averaged cooling rates for the shallow mantle of 57 c ga 1 and are comparable to estimates of the present day cooling rate for the whole earth the low burial pressures are a strong argument against the existence of catastrophic mantle flush events in the geological past which have been predicted by some mantle convection models taken together these constraints suggest a plume related geological setting i e oceanic plateau like flood basalt for the initial stage of greenstone belt evolution

changes in electrical resistivity track changes in tectonic plate coupling 1 interplate coupling on the hikurangi subduction margin along the east coast of new zealand s north island changes north to south from almost uncoupled to locked clay rich sediments and aqueous fluids at the subduction interface have been invoked as key factors in the frictional processes that control interplate coupling here we use magnetotelluric data to show that the subduction interface in the weakly coupled region is electrically conductive but is resistive in the locked region these results indicate the presence of a layer of fluid and clay rich sediments in the weakly coupled region and support the idea that the presence of fluid and hydrated clays at the interface is a major factor controlling plate coupling

spatial temporal patterns of seismic tremors in northern cascadia 1 we study in detail the two consecutive episodic tremor and slip ets events that occurred in the northern cascadia subduction zone during 2003 and 2004 for both sequences the newly developed source scanning algorithm ssa is applied to seismic waveform data from a dense regional seismograph array to determine the precise locations and origin times of seismic tremors in map view the majority of the tremors occurred in a limited band bounded approximately by the surface projections of the 30 km and 50 km depth contours of the plate interface the horizontal migration of tremor occurrence is from southeast to northwest with an average speed of 5 km d in cross section tremors in both sequences span a depth range of over 40 km across the interface with the majority occurring in the overriding continental crust in particular 50 55 of them are located within 2 5 km from the strong seismic reflector bands above the plate interface the lack of vertical migration implies that a slow diffusion process in the vertical direction cannot be responsible for tremor occurrences the source spectra of tremors clearly lack high frequency content 5 hz relative to local earthquakes we propose two possible models to explain the relationship between slip and tremors the first one regards ets tremors as the manifestation of hydroseismogenic processes in response to the temporal strain variation associated with the episodic slip along the lower portion of the plate interface downdip from the locked zone in the second model tremors and slip are associated with the same process along the same structure in a distributed deformation zone across the plate interface neither model can be dismissed conclusively at this stage

rich shallow water benthic ecosystem in late miocene east antarctica fisher bench fm prince charles mountains abstract a single shell of a pectenoid bivalve was found in the lower part of the fisher bench formation fisher massif prince charles mountains in contrast to glacigenic sediments that form extensive outcrops in this area and are almost barren of foraminifera small pieces of muddy sand attached to this shell contained a rich assemblage of calcareous and siliceous microfossils the diatom assemblage associated with this shell was dominated by marine benthic forms with abundant saeptifera associated with subordinate marine neritic taxa and chaetoceros resting spores benthic foraminifera are very abundant but of low diversity strongly dominated by rosalina globularis with uniform chambers it is the first miocene foraminiferal assemblage reported from east antarctica excluding the ross sea area these new results confirm the early late miocene age of the shell that was dated by sr isotope values in an earlier study and suggest an initial phase of deposition in a shallow water possibly no 10 m marine cold and possibly oligotrophic environment after initial burial in microfossil bearing sediment that was weakly lithified the shell was eroded and transported to be incorporated in fossil poor glacigenic sediments since transport from a nearby location could have been facilitated by glacial and or down slope movements in this fjordal setting the shell is considered para autochthonous based on the antarctic foraminiferal fossil records it appears that through most of the cenozoic those parts of the antarctic continental shelf that were deeper than a few tens of meters with the exception of the ross sea area were mostly unfavorable for development and or preservation of calcareous microfossils

stabilizing effect of high pore fluid pressure on slip behaviors of gouge bearing faults this work is supported by the department of energy office of science the office of basic energy sciences chemical sciences geosciences biosciences division under award no de fg 0207er15916 and by the national science foundation under grant no ear 1761912

simultaneous long term and short term slow slip events at the hikurangi subduction margin new zealand implications for processes that control slow slip event occurrence duration and migration 1 we document a sequence of simultaneous short term and long term slow slip events sses at the hikurangi subduction zone during the 2010 2011 period the sequence of short term events each 2 3 weeks in duration ruptured much of the shallow plate interface 15 km at central and northern hikurangi over a 6 month period was accompanied by microseismicity and involved patchy irregular migration of sse slip we suggest that the patchy migration of the short term sse is due to large scale 100 3500 km heterogeneities on the plate interface related to seamount subduction and sediment subduction and or underplating this is in contrast to a 2010 2011 long term sse at the central hikurangi margin which evolved steadily over 1 5 years and ruptured much of the plate interface between 20 and 70 km depth we suggest that the occurrence of long term versus short term sses at hikurangi is related to differences in effective normal stresses and relative heterogeneity of the subduction interface the long term sse sequence began 1 year before the short term sequence coulomb stress change models suggest that the long term sse may have triggered initiation of the subsequent short term sse sequence initiation of the short term sequence occurred in a region just updip of or within an interseismically locked portion of the plate interface and may be located within the updip transition from seismic to aseismic behavior alternatively it could be characteristic of a region undergoing partial interseismic coupling this is in contrast to sses observed elsewhere in the world that typically occur within the downdip transition from seismic to aseismic behavior

spontaneous and triggered aseismic deformation transients in a subduction fault model 1 aseismic deformation transients can emerge as a natural outcome of the rate and state friction processes revealed in laboratory fault sliding experiments when that constitutive formulation is applied to model subduction earthquake sequences transients can arise spontaneously for certain effective stress variations with depth we show that if interstitial fluids are present and pore pressure is near lithostatic around and downdip from the frictional stability transition transients with recurrence intervals of 1 year are predicted on the basis of laboratory friction parameters and their temperature hence depth variations the recurrence interval decreases with and reaches 14 months when is 2 3 mpa dimensional analysis and numerical studies show that the fault response primarily depends on a parameter w h here the high pore pressure zone extends distance w updip from the stability transition and h is the stable patch size for steady sliding evidence that such fluid conditions may actually be present is independently provided by the occurrence of nonvolcanic tremors as apparent responses to extremely small stress changes and by petrological constraints on expected regions of dehydration for the shallow dipping subduction zones where transients are observed transient sequences can also be triggered by a modest one time step like interseismic stress perturbation on the subduction fault due to nearby earthquakes or to pore pressure changes e g during episodes of metamorphic fluid release properties of triggered transients and future thrust earthquakes depend on the interseismic time when the perturbation is introduced its relative location along the subduction fault and its magnitude

antarctic peninsular cryosphere early oligocene c 30 ma initiation and a revised glacial chronology strontium isotope stratigraphy provides a chronology for cenozoic cryogenic strata in the northern antarctic peninsula and allows an assessment of diachronism in onset of glacial conditions between east and west antarctica the earliest observed event on the antarctic peninsula was late early oligocene 29 8 0 6 ma at least c 4 ma later than in east antarctica with a second in the early early miocene 22 6 0 4 ma both glacials and intervening interglacial were continent wide phenomena two late neogene glaciations are distinguished early late miocene 9 9 0 97 ma hobbs glacier jones mountains and latest miocene alexander island a further late neogene glacial deposit weddell formation can be constrained only as c 10 ma

slow slip and frictional transition at low temperature at the hikurangi subduction zone temperature changes with depth do not appear to be a primary control for either slow slip or fault locking processes at the hikurangi margin north island new zealand both slow slip events and the geodetically observed transition from fault locking to free slip at depth occur at temperatures as low as 100 c shallow portions of faults exhibit brittle stick slip behaviour that gives way to more stable sliding with increasing depth limiting the depths to which earthquake inducing slip can occur the increase of temperature with depth is often assumed to transform friction in the fault from velocity weakening unstable to velocity strengthening stable and to change conditions from brittle to ductile1 2 3 4 5 a temperature of 350 c has been suggested to mark the base of the frictionally unstable portion of the fault which becomes free slipping at depth where temperatures rise above 450 c refs 2 4 6 here we show that both slow slip events and the geodetically observed transition from fault locking to free slip at the hikurangi subduction zone east of the north island new zealand occur at temperatures as low as 100 c suggesting that temperature is not a primary control on either slow slip or fault locking processes at the hikurangi margin although globally shallow slow slip events are rare five out of seven events observed so far at the hikurangi margin are less than 15 km deep

fluid and deformation regime of an advancing subduction system at marlborough new zealand newly forming subduction zones on earth can provide insights into the evolution of major fault zone geometries from shallow levels to deep in the lithosphere and into the role of fluids in element transport and in promoting rock failure by several modes the transpressional subduction regime of new zealand which is advancing laterally to the southwest below the marlborough strike slip fault system of the northern south island is an ideal setting in which to investigate these processes here we acquired a dense high quality transect of magnetotelluric soundings across the system yielding an electrical resistivity cross section to depths beyond 100 km our data imply three distinct processes connecting fluid generation along the upper mantle plate interface to rock deformation in the crust as the subduction zone develops massive fluid release just inland of the trench induces fault fracture meshes through the crust above that undoubtedly weaken it as regional shear initiates narrow strike slip faults in the shallow brittle regime of interior marlborough diffuse in width upon entering the deeper ductile domain aided by fluids and do not project as narrow deformation zones deep subduction generated fluids rise from 100 km or more and invade upper crustal seismogenic zones that have exhibited historic great earthquakes on high angle thrusts that are poorly oriented for failure under dry conditions the fluid deformation connections described in our work emphasize the need to include metamorphic and fluid transport processes in geodynamic models

national seismic hazard model for new zealand 2010 update a team of earthquake geologists seismologists and engineering seis mologists has collectively produced an update of the national probabilistic seismic hazard psh model for new zealand national seismic hazard model or nshm the new nshm supersedes the earlier nshm published in 2002 and used as the hazard basis for the new zealand loadings standard and numerous other end user applica tions the new nshm incorporates a fault source model that has been updated with over 200 new onshore and offshore fault sources and utilizes new new zealand based and international scaling relationships for the parameterization of the faults the dis tributed seismicity model has also been updated to include post 1997 seismicity data a new seismicity regionalization and improved methodology for calculation of the seismicity parameters probabilistic seismic hazard maps produced from the new nshm show a similar pattern of hazard to the earlier model at the national scale but there are some significant reductions and increases in hazard at the regional scale the national scale differences between the new and earlier nshm appear less than those seen between much earlier national models indicating that some degree of consis tency has been achieved in the national scale pattern of hazard estimates at least for return periods of 475 years and greater online material table of fault source parameters for the 2010 national seismic hazard model

seismotectonics and seismogenesis of mw7 8 gorkha earthquake and its aftershocks abstract the april 25 2015 mw7 8 gorkha earthquake in central nepal was followed by intense aftershock activity including mw6 7 shock on april 26 2015 and mw7 3 shock on may 12 2015 synthesis of the focal mechanisms space time distribution of seismic activity in relation to previously imaged crustal velocity and resistivity structures reveals focusing of the mw7 8 gorkha earthquake near the upper surface of the thin fluid filled low velocity and high conducting layer immediately above the plane of the detachment on the geophysical sections the detachment is identified as a sharp positive velocity interface modulation of frictional coupling and mechanical weakening by high pore pressure fluids counteract the arc normal stresses creating conditions for failure and nucleation of the gorkha earthquakes on a plane sub parallel with the detachment spatio temporal patterns in aftershock activity indicate rapid alteration of main shock induced stress fields triggering a strong aftershock of mw6 7 large stress drop and increased energy released by the mw6 7 event facilitates upward injection of high pore pressure fluid fluxes into the hidden out of sequence thrust it is suggested that decrease in shear strength along the hidden thrust plane due to the diffusion of high pore pressure fluids created conditions favourable to trigger mw7 3 aftershock

electrical resistivity imaging of the inter plate coupling transition at the hikurangi subduction margin new zealand abstract inter plate coupling on the hikurangi subduction margin along the east coast of new zealand s north island changes from weakly coupled in the north to locked in the south 3 d inverse modeling of magnetotelluric mt data across the coupling transition shows that the electrical resistivity structure is correlated with the areal strain rate which provides a measure of plate coupling the correlation between strain rate and resistivity is seen parallel to the strike and dip directions of the subduction in the region where the strain is extensional the upper plate is more conductive than in the south where contraction is occurring and the plates are locked the increased mid crustal resistivity in the south can be interpreted to be a consequence of reduced fluid interconnectivity due to contraction or reduced fluid content due to decreased upward transport from sources beneath the subduction interface the increased mid crustal conductivity in the extensional area is interpreted to be a consequence of fluid released by subducted sediment that are also the cause of the extension seismicity in the upper 5 km of the subducting plate shows similar changes with a greater concentration of near interface seismicity beneath the conductive extensional region we interpret the concentration of seismicity below the subduction interface in the extensional region to show fluid sourced from dehydration reactions within the subducting plate or from the de watering of subducted sediments rising into the upper plate and decreasing the resistivity of the middle crust decreased near interface seismicity beneath the contractional region can be interpreted to be a consequence of decreased upper plate permeability preventing upward fluid escape or reduced lower plate fluid availability

serpentinites of the zermatt saas ophiolite complex and their texture evolution the zermatt saas serpentinite complex is an integral member of the penninic ophiolites of the central alps and represents the mantle part of the oceanic lithosphere of the tethys metamorphic textures of the serpentinite preserve the complex mineralogical evolution from primary abyssal peridotite through ocean floor hydration subduction related high pressure overprint meso alpine greenschist facies metamorphism and late stage hydrothermal alteration the early ocean floor hydration of the spinel harzburgites is still visible in relic pseudomorphic bastite and locally preserved mesh textures the primary serpentine minerals were completely replaced by antigorite the stable assemblage in subduction related mylonitic serpentinites is antigorite olivine magnetite diopside the mid tertiary greenschist facies overprint is characterized by minor antigorite recrystallization textural and mineral composition data of this study prove that the hydrated mineral assemblages remained stable during high pressure metamorphism of up to 2 5 gpa and 650 c the zermatt saas serpentinites thus provide a well documented example for the lack of dehydration of a mantle fragment during subduction to 75 km depth

progressive cenozoic cooling and the demise of antarctica s last refugium the antarctic peninsula is considered to be the last region of antarctica to have been fully glaciated as a result of cenozoic climatic cooling as such it was likely the last refugium for plants and animals that had inhabited the continent since it separated from the gondwana supercontinent drill cores and seismic data acquired during two cruises shaldril i and ii in the northernmost peninsula region yield a record that when combined with existing data indicates progressive cooling and associated changes in terrestrial vegetation over the course of the past 37 million years mountain glaciation began in the latest eocene approximately 37 34 ma contemporaneous with glaciation elsewhere on the continent and a reduction in atmospheric co2 concentrations this climate cooling was accompanied by a decrease in diversity of the angiosperm dominated vegetation that inhabited the northern peninsula during the eocene a mosaic of southern beech and conifer dominated woodlands and tundra continued to occupy the region during the oligocene approximately 34 23 ma by the middle miocene approximately 16 11 6 ma localized pockets of limited tundra still existed at least until 12 8 ma the transition from temperate alpine glaciation to a dynamic polythermal ice sheet took place during the middle miocene the northernmost peninsula was overridden by an ice sheet in the early pliocene approximately 5 3 3 6 ma the long cooling history of the peninsula is consistent with the extended timescales of tectonic evolution of the antarctic margin involving the opening of ocean passageways and associated establishment of circumpolar circulation

foraminiferal biostratigraphy and palaeoecology in upper oligocene lower miocene glacial marine sequences 9 10 and 11 crp 2 2a drill hole victoria land basin antarctica abstract three cape roberts project drillholes crp 1 2 2a and 3 penetrated in aggregate a 1500 m succession of glacial marine oligocene lower miocene strata on the margins of victoria land basin the upper 1000 m of which consists of a stack of more than 50 unconformity bounded stratigraphic sequences the benthic foraminiferal biostratigraphy ecology and lithofacies relationships of three contiguous sequences sequences 9 10 and 11 130 27 306 65 mbsf from crp 2 2a were first determined and then tested against motif a a sedimentation model developed for the drillhole succession these sequences apparently represent relatively complete glacial deglacial cycles which span an interval of 450 kyr straddling the oligocene miocene boundary 24 ma sedimentological and paleontological data suggest shoreface inner shelf to outer shelf basin margin settings with deposition under the influence of near shore traction currents subglacial ice contact ice rafting meltwater and turbidity associated with ice margin advance and retreat along with sea level variations in the order of 50 m stratigraphic distribution data for benthic foraminifera are at an average sampling interval of 1 m 1000 to 3000 years which offers stratigraphic resolution at less than orbital cycle frequencies in all major lithofacies within the three sequences taxa recovered represent a restricted immigrant group that repeatedly penetrated the shallow coastal waters during deglacial phases of each cycle and originated in the much more diverse assemblages of west antarctic rift system basins both eurytopic and stenotopic taxa are recognized the former occur in all lithofacies and appear tolerant to a wide range of environmental parameters at and near the seafloor representative genera include trochammina cassidulinoides fursenkoina eponides epistominella cibicides nonionella melonis pullenia elphidium ammoelphidiella and cribroelphidium stenotopic taxa are less common occur mainly in fine grained lithofacies represent maximum oceanicity and coincide with maximum retreat of coastal glaciers and sea level highstands representative genera include quinqueloculina pyrgo triloculina lenticulina marginulina vaginulinopsis nodosaria pseudonodosaria pyrulinoides oolina fissurina parafissurina rosalina anomalinoides and hanzawaia planktic foraminifera are absent our foraminiferal data provide strong support for the motif a model and allow interpretation of intra model facies and events motif a is an idealized glacial stratigraphic sequence construct derived from analysis of the entire upper oligocene lower miocene sequence stack in this model lowstand system tract lst diamictites form the base of the sequence diamictites with microfaunas are considered glaciomarine those without are more likely ice proximal or subglacial fine grained sandstone muddy sandstone and mudstone of mid sequence aggradational transgressive system tract tst and highstand system tract hst strata reflect high stands of sea level inshore penetration of open marine waters and peak recession of ice margins and normally contain the most diverse and abundant microfaunas up to 17 spp sample sediments of the overlying regressive system tract rst display low and upwardly declining foraminiferal diversity in response to glacier ice advance sediment progradation across the basin margin and falling sea level the time variable glacial surface of erosion gse or sequence boundary terminates the regressive system tract rst and demarcates the base of the succeeding stratigraphic sequence

mapping subduction interface coupling using magnetotellurics hikurangi margin new zealand the observation of slow slip seismic tremor and low frequency earthquakes at subduction margins has provided new insight into the mechanisms by which stress accumulates between large subduction megathrust earthquakes however the relationship between the physical properties of the subduction interface and the nature of the controls on interplate seismic coupling is not fully understood using magnetotelluric data we show in situ that an electrically resistive patch on the hikurangi subduction interface corresponds with an area of increased coupling inferred from geodetic data this resistive patch must reflect a decrease in the fluid or sediment content of the interface shear zone together the magnetotelluric and geodetic data suggest that the frictional coupling of this part on the hikurangi margin may be controlled by the interface fluid and sediment content the resistive patch marking a fluid and sediment starved area with an increased density of small seismogenic asperities and therefore a greater likelihood of subduction earthquake nucleation

episodic slow slip events in the japan subduction zone before the 2011 tohoku oki earthquake abstract we describe two transient slow slip events that occurred before the 2011 tohoku oki earthquake the first transient crustal deformation which occurred over a period of a week in november 2008 was recorded simultaneously using ocean bottom pressure gauges and an on shore volumetric strainmeter this deformation has been interpreted as being an m6 8 episodic slow slip event the second had a duration exceeding 1 month and was observed in february 2011 just before the 2011 tohoku oki earthquake the moment magnitude of this event reached 7 0 the two events preceded interplate earthquakes of magnitudes m6 1 december 2008 and m7 3 march 9 2011 respectively the latter is the largest foreshock of the 2011 tohoku oki earthquake our findings indicate that these slow slip events induced increases in shear stress which in turn triggered the interplate earthquakes the slow slip event source area on the fault is also located within the downdip portion of the huge coseismic slip area of the 2011 earthquake this demonstrates episodic slow slip and seismic behavior occurring on the same portions of the megathrust fault suggesting that the faults undergo slip in slow slip events can also rupture seismically

links between sediment consolidation and cascadia megathrust slip behaviour at sediment rich subduction zones megathrust slip behaviour and forearc deformation are tightly linked to the physical properties and in situ stresses within underthrust and accreted sediments yet the role of sediment consolidation at the onset of subduction in controlling the downdip evolution and along strike variation in megathrust fault properties and accretionary wedge structure is poorly known here we use controlled source seismic data combined with ocean drilling data to constrain the sediment consolidation and in situ stress state near the deformation front of the cascadia subduction zone offshore washington where the megathrust is inferred to be strongly locked we find over consolidated sediments near the deformation front that are incorporated into a strong outer wedge with little sediment subducted these conditions are favourable for strain accumulation on the megathrust and potential earthquake rupture close to the trench in contrast offshore central oregon a thick under consolidated sediment sequence is subducting and is probably associated with elevated pore fluid pressures on the megathrust in a region where reduced locking is inferred our results suggest that the consolidation state of the sediments near the deformation front is a key factor contributing to megathrust slip behaviour and its along strike variation and it may also have a significant role in the deformation style of the accretionary wedge consolidated sediments in the cascadia subduction zone may create conditions favourable for megathrust earthquake ruptures over long distances and close to the trench according to analyses of seismic velocity of sediments from the region less consolidated sediments instead may promote aseismic slip of the plate boundary