the anarak jandaq and posht e badam metamorphic complexes in central iran new geological data relationships and tectonic implications abstract the anarak jandaq and posht e badam metamorphic complexes occupy the nw part of the central east iranian microcontinent and are juxtaposed with the great kavir block and sanandaj sirjan zone our recent findings redefine the origin of these complexes so far attributed to the precambrian early paleozoic orogenic episodes and now directly related to the tectonic evolution of the paleo tethys ocean this tectonic evolution was initiated by late ordovician early devonian rifting events and terminated in the triassic by the eocimmerian collision event due to the docking of the cimmerian blocks with the asiatic turan block the variscan accretionary complex is a new name we proposed for the most widely distributed metamorphic rocks connected to the anarak and jandaq complexes this accretionary complex exposed from sw of jandaq to the anarak and kabudan areas is a thick and fine grain siliciclastic sequence accompanied by marginal sea ophiolitic remnants including gabbro basalts with a supra subduction geochemical signature new 40ar 39ar ages are obtained as 333 320 ma for the metamorphism of this sequence under greenschist to amphibolite facies moreover the limy intercalations in the volcano sedimentary part of this complex in godar e siah yielded upper devonian tournaisian conodonts the northeastern part of this complex in the jandaq area was intruded by 215 15 ma arc to collisional granite and pegmatites dated by id tims and its metamorphic rocks are characterized by some 40ar 39ar radiometric ages of 163 156 ma the variscan accretionary complex was northwardly accreted to the airekan granitic terrane dated at 549 15 ma later from the late carboniferous to triassic huge amounts of oceanic material were accreted to its southern side and penetrated by several seamounts such as the anarak and kabudan this new period of accretion is supported by the 280 230 ma 40ar 39ar ages for the anarak mild high pressure metamorphic rocks and a 262 ma u pb age for the trondhjemite rhyolite association of that area the triassic bayazeh flysch filled the foreland basin during the final closure of the paleo tethys ocean and was partly deposited and or thrusted onto the cimmerian yazd block the paleo tethys magmatic arc products have been well preserved in the late devonian carboniferous godar e siah intra arc deposits and the triassic nakhlak fore arc succession on the passive margin of the cimmerian block in the yazd region the nearly continuous upper paleozoic platform type deposition was totally interrupted during the middle to late triassic local erosion down to lower paleozoic levels may be related to flexural bulge erosion the platform was finally unconformably covered by liassic continental molassic deposits of the shemshak one of the extensional periods related to neo tethyan back arc rifting in late cretaceous time finally separated parts of the eocimmerian collisional domain from the eurasian turan domain the opening and closing of this new ocean characterized by the nain and sabzevar ophiolitic melanges finally transported the anarak jandaq composite terrane to central iran accompanied by large scale rotation of the central east iranian microcontinent ceim due to many similarities between the posht e badam metamorphic complex and the anarak jandaq composite terrane the former could be part of the latter if it was transported further south during tertiary time

predicting stress induced velocity anisotropy in rocks a simple transformation using measured isotropic vp and vs versus hydrostatic pressure is presented for predicting stress induced seismic velocity anisotropy in rocks the compliant crack like portions of the pore space are characterized by generalized compressional and shear compliances that are estimated from the isotropic vp and vs the physical assumption that the compliant porosity is crack like means that the pressure dependence of the generalized compliances is governed primarily by normal tractions resolved across cracks and defects this allows the measured pressure dependence to be mapped from the hydrostatic stress state to any applied nonhydrostatic stress predicted p and s wave velocities agree reasonably well with uniaxial stress data for barre granite and massillon sandstone while it is mechanically similar to methods based on idealized ellipsoidal cracks the approach is relatively independent of any assumed crack geometry and is not limited to small crack densities

evaluation of anisotropy by shear wave splitting the polarizations of three component shear wavetrains carry unique information about the internal structure of the rock through which they pass specifically commonly observed shear wave splitting may contain information about the orientation of crack distributions this information cannot usually be recovered from shear waves recorded at the free surface because of interference with the interaction of the shear wave with the surface even for nearly vertical incidence however shear wave splitting in synthetic three component vertical seismic profiles in some cases may be interpreted directly in terms of the direction of strike of vertical cracks because the human eye is not skilled at identifying the phase relationships between three component seismograms played out conventionally as parallel time series the polarizations are displayed in orthogonal sections of the particle displacements to facilitate recognition and evaluation of the shear wave splitting estimating the orientations of cracks an

detection of stress induced velocity anisotropy in unconsolidated sands velocity anisotropy in rocks and soft sediments can indicate stress anisotropy and can be more sensitive to stress in soft sediments than in rocks most of the experimental studies on velocity anisotropy in soft sediments have been focused in the s wave response however s waves are highly attenuated in soft sediments under field conditions p waves are less attenuated and frequently acquired using in situ geophysical methods hence detecting stress anisotropy with p waves in soft sediments would be of great value

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

variation of physical properties beneath a fault observed by a two ship seismic survey off southwest japan 1 we conducted a two ship seismic reflection survey at kumano nada off the southwest japan arc in 2002 in order to clarify physical properties along a splay fault that branches from the plate boundary of the nankai trough subduction zone during the survey seismic reflection data were collected out to maximum offset of 20 km using multiple passes of a shooting and a receiving vessel separated by a different constant offset on each pass we conducted analyses on reflection polarity and amplitude variation with offset avo effects to examine physical properties of layers immediately beneath the splay fault reflections from the splay fault showed varying polarities along the fault in the present study we assumed that the poisson s ratio of the layer above the fault was 0 30 0 40 where polarity is reversed the poisson s ratio of the layer immediately below the fault was estimated to be 0 33 0 445 11 increase on average where polarity was normal the ratio was estimated to be 0 263 0 365 11 decrease on average if the reverse polarity indicates the existence of fluid as many authors suggest the polarity analysis demonstrates inhomogeneous distribution of fluid in the splay fault shear zone the results of avo analysis also support the possibility of the spatial variation of fluid distribution under some assumptions because the poisson s ratio changes with content of fluid in rocks the variation in reflection polarity and corresponding avo effects may signify the possibility of localized fluid migration in the splay fault shear zone

s wave splitting in the aftershock region of the 1995 hyogo ken nanbu earthquake the 1995 hyogo ken nanbu earthquake kobe earthquake m7 2 occurred on january 17 1995 a temporary aftershock observation was carried out by the geophysical research group organized by universities for prediction seismology in 1995 from october 1995 to january 1996 a dense seismic network was deployed in and around the aftershock region and some seismic stations were set directly on the active fault traces we analyze the s wave splitting in and around the aftershock region of the hyogo ken nanbu earthquake we detect a spatial variation of s wave splitting which can be related to crack orientations in an area where a large earthquake has occurred at stations more than 1 km away from the hyogo ken nanbu earthquake fault zone the leading shear wave polarization directions lspd are found to be parallel to the axis of the regional maximum horizontal compressional stress e w suggesting that cracks caused by regional tectonic stress exist in the area however at stations within 500 m of the earthquake fault zones the lspds are parallel to the fault strikes n45 50 e this suggests that new fractures were produced parallel to the faults by shear faulting of the hyogo ken nanbu earthquake and resulted in s wave splitting along the earthquake fault zone nevertheless shear fault origin anisotropy was not evident at stations on the active faults which ruptured in 1596 this implies that healing processes have already closed the fractures produced by shear faulting in 1596 therefore we can expect that s wave splitting can be a useful tool for monitoring healing processes of active faults

evolution of the nankai trough decollement from the trench into the seismogenic zone inferences from three dimensional seismic reflection imaging we mapped the amplitude of the nankai trough subduction thrust seismic reflection from the trench into the seismogenic zone with three dimensional seismic reflection data the decollement thrust forms within the lithologically homogeneous lower shikoku basin facies along an initially nonreflective interface the reflection develops from a porosity contrast between accreted and underthrust sedimentary material because of accretionary wedge consolidation and rapid loading and delayed consolidation of the underthrust section a decollement amplitude map shows a significant decline from high amplitudes at the trench to barely detectable levels 25 30 km landward three other observations coincide with the amplitude decline 1 the decollement initially steps down to deeper stratigraphic levels 2 the wedge taper increases dramatically and 3 the thrust becomes seismogenic the amplitude decline and the coincident decollement and accretionary wedge tectonic and seismogenic behavior are attributed to the loss of fluids and potentially loss of excess fluid pressures downdip along the subduction thrust

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

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

metallogeny and temporal spatial distribution of manganese mineralizations in iran implications for future exploration abstract there are a lot of manganese mn deposits and numerous mineral occurrences of this type of mineralization in iran the major tectonic structural zones of iran that host manganese deposits are 1 urumieh dokhtar magmatic assemblage udma 2 the central iran ci 3 the sabzevar zone sz 4 the alborz magmatic belt amb and 5 the cretaceous ophiolites these manganese deposits were formed during discrete time periods 1 late neoproterozoic early cambrian narigan and halab deposits in the ci 2 jurassic halalan deposit in the sz 3 cretaceous mn mineralizations in the late cretaceous volcano sedimentary sequence of southwest sabzevar basin in the sz nasirabad abadeh tashk alashtar sorkhvand esfandagheh benvid gugher kamar talar sardasht and safou manganese deposits in the southeast of birjand dehoo and north of sabzevar deposits which occur in the upper cretaceous ophiolites and 4 eocene miocene e g venarch jalal shahrestanak boznein garab menamin robat karim qaleh mohammad khan rabiei zarashlou narkan sarikand jokandy gharaeh tavaragh and barout aghaji deposits in the udma and amb magmatic arcs intra arc rifts and back arc basins are the principal plate tectonic settings for iranian manganese deposits all of the manganese deposits of the udma and amb formed within tertiary arc and back arcs respectively that developed during subduction of the neo tethyan crust beneath the iranian plate intra oceanic or continental back arc spreading settings are recognized in the neo tethys domain in iran and these host several manganese deposits in the sz and ophiolites the trace element content of all studied manganese deposits is generally low in concentrations and tends to enrichment in the assemblage of v cu pb zn and as with geochemical characteristics similar to hydrothermal deposits rare earth element ree patterns of the iranian manganese deposits support a hydrothermal origin the main time period of formation of manganese mineralization in iran was from cretaceous to miocene the udma and sz are the most favourable metallogenic provinces in iran for manganese exploration because these zones host the most and the largest manganese deposits including venarch and shahrestanak deposits in the udma and manganese mineralizations in the late cretaceous volcano sedimentary sequence of the southwest sabzevar in the sz

slow and delayed deformation and uplift of the outermost subduction prism following ets and seismogenic slip events beneath nicoya peninsula costa rica abstract two odp cork ocean drilling program circulation obviation retrofit kit borehole hydrologic observatory sites deployed in 2002 at the toe of the subduction prism off nicoya peninsula costa rica were visited in december 2013 the five years of seafloor and formation fluid pressure data collected since the previous visit include clear signals associated with an episodic tremor and slip ets event off the coast of nicoya peninsula in 2009 and a mw 7 6 subduction thrust earthquake beneath the peninsula in 2012 formation pressure anomalies associated with the ets event are similar to ones observed following ets events observed previously here as well as ones following very low frequency earthquake swarms within the nankai accretionary prism off southwestern japan positive and negative impulsive transients in the hanging wall and foot wall of the subduction thrust respectively suggest contractional and dilatational strain generated by local slip propagating up the thrust fault beneath the outermost prism in the case of the 2009 event the transients occurred roughly two weeks after the initiation of slip observed at gps sites along the adjacent coast at the same time a decrease in seafloor pressure at the prism site relative to the subducting plate was observed indicating concurrent uplift of the prism of 1 2 cm other events at the prism toe following ets events closer to the coast are seen in 2006 2007 2008 2010 and 2011 the time between the initiation of ets slip constrained by gps and the onset of the prism toe transients suggest up dip rupture propagation along the seaward part of the subduction thrust at rates of a few km day in the case of the 2009 event the slip at the prism toe c 11 cm estimated from the 1 2 cm uplift and the local dip on the decollement 6 is roughly a factor of 5 greater than the slip further landward estimated from gps data by dixon et al in press in other cases slip at the toe is less or unresolvable similar uplift and formation fluid pressure transients occurred two days after the 2012 nicoya thrust earthquake then episodically unrelated to aftershocks every 1 3 weeks over the next few months slip rates at the prism toe estimated from the magnitude and duration of these and ets related uplift events are roughly 5 cm day such rates are much too slow for tsunamigenesis or seismogenesis total slip of the outermost prism after the 2012 earthquake determined from the uplift accumulated until the end of the observation period and the estimated local fault dip is roughly 75 cm a significant fraction of the seismogenic slip of the mw 7 6 earthquake itself a maximum of over 3 m negative steps in formation pressure are observed at both the prism and subducting plate sites simultaneous with the 2012 thrust earthquake the sign of these steps is inconsistent with the contractional deformation predicted by an elastic fault dislocation model with slip limited to the seismogenic zone highly compliant low shear modulus sediment below the decollement or very low stress deformation along splay faults may be responsible for the co seismic dilatation observed in the outermost prism and incoming plate

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

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

the action of water films at a scales in the earth implications for the nankai subduction system abstract water properties change with confinement within nanofilms trapped between natural charged clay particles we investigated nanofilm characteristics through high stress laboratory compression tests in combination with analyses of expelled pore fluids we utilized sediments obtained from deep drilling of the nankai subduction zone at site c0002 of the integrated ocean drilling program iodp we show that below 1 2 km there should be widespread ultrafiltration of migrating fluids experiments to 100 mpa normal compression collapse pores below a few ion monofilm thicknesses a reduction towards a single condensing dehydrating ion monofilm occurs as stresses rise 100 200 mpa and clay separations are reduced to

initiation of plate boundary slip in the nankai trough off the muroto peninsula southwest japan 1 to investigate variations in physical properties accompanying the development of the decollement we used a neural network analysis of seismic attributes derived from 3d seismic reflection data gathered in the nankai trough convergent margin off the muroto peninsula of southwest japan this analysis resulted in a detailed map of the geological features along the decollement and revealed a drastic change in physical properties at the sole of the proto thrust ocean drilling program odp data suggest that the decollement physical property change coincides with the initiation of slip furthermore changes in the structure of the accretionary prism and reorganization of the decollement geometry also attend the initiation of plate boundary slip

3d geometry of a plate boundary fault related to the 2016 off mie earthquake in the nankai subduction zone japan abstract we used recent seismic data and advanced techniques to investigate 3d fault geometry over the transition from the partially coupled to the fully coupled plate interface inboard of the nankai trough off the kii peninsula japan we found that a gently dipping plate boundary decollement with a thick underthrust layer extends beneath the entire kumano forearc basin the 1 april 2016 off mie earthquake mw6 0 and its aftershocks occurred where the plate boundary decollement steps down close to the oceanic crust surface this location also lies beneath the trenchward edge of an older accretionary prism 14 ma developed along the coast of the kii peninsula the strike of the 2016 rupture plane was similar to that of a formerly active splay fault system in the accretionary prism thus the fault planes of the 2016 earthquake and its aftershocks were influenced by the geometry of the plate interface as well as splay faulting the 2016 earthquake occurred within the rupture area of large interplate earthquakes such as the 1944 tonankai earthquake mw8 1 although the 2016 rupture area was much smaller than that of the 1944 event whereas the hypocenter of the 2016 earthquake was around the underplating sequence beneath the younger accretionary prism 6 ma the 1944 great earthquake hypocenter was close to oceanic crust surface beneath the older accretionary prism the variation of fault geometry and lithology may influence the degree of coupling along the plate interface and such coupling variation could hinder slip propagation toward the deeper plate interface in the 2016 event

a fast robust method for detecting and characterizing azimuthal anisotropy with marine ps converted waves and its application to the west svalbard continental slope summary a method for using ps converted waves to detect and characterize azimuthal seismic anisotropy is developed and applied to four component ocean bottom seismometer data acquired near the base of the continental slope west of svalbard the method determines the distribution of coherent signal vibrating perpendicular to the sagittal plane the transverse direction and employs an optimized rotation technique to separate the effects of anisotropy from other contributions to the seismic amplitude the magnitude of the ps wave transverse amplitude when normalized by its radial counterpart is shown to correspond to the degree of ellipticity of particle motions and is used to constrain the anisotropic symmetry class in the near surface sediments results indicate the presence of orthorhombic or horizontal transversely isotropic symmetry that is consistent with the presence of near vertical aligned cracks from its orientation the observed anisotropy is associated with 1 gravitational downslope stresses in the sediment sequence which dips by approximately two degrees to the sw and 2 tectonic stresses associated with the segmented spreading centres of the northern knipovich ridge which spread in the nw se direction aligned cracks are likely to influence the local distribution of gas hydrate and free gas in these sediments an investigation of the effect of seismic noise on optimized rotation shows that the vectorial combination of independent geophone records has variable sensitivity to source related noise this sensitivity peaks where the sagittal azimuth bisects the deployment orientation of the geophones on the seabed a method to reduce the sensitivity to directional noise is developed and shown to improve the transverse amplitude plots this approach to noise reduction may be used to improve the quality of seismic images derived from multicomponent data

cenozoic evolution of neotethys and implications for the causes of plate motions africa north america eurasia plate circuit rotations combined with red sea rotations and new estimates of crustal shortening in iran define the cenozoic history of the neotethyan ocean between arabia and eurasia the new constraints indicate that arabia eurasia convergence has been fairly constant at 2 to 3 cm yr since 56 ma with slowing of africa eurasia motion to 1 cm yr near 25 ma coeval with the opening of the red sea ocean closure occurred no later than 10 ma and could have occurred prior to this time only if a large amount of continental lithosphere was subducted suggesting that slowing of africa significantly predated the arabia eurasia collision these kinematics imply that africa s disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern eurasia slowed its motion the slow steady rate of northward subduction since 56 ma contrasts with strongly variable rates of magma production in the urumieh dokhtar arc implying magma production rate in continental arcs is not linked to subduction rate

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

geochemistry and origin of mn deposits in the waziristan ophiolite complex north waziristan pakistan the waziristan ophiolite complex is located along the western margin of the indian plate in northwestern pakistan the mn deposits in the saidgi and shuidar areas are part of this ophiolite complex these deposits both banded and massive in nature are hosted by metachert and are generally overlying metavolcanics braunite and cryptocrystalline quartz are the main constituents of the manganese ores in both areas hematite occurs in the shuidar deposits as a minor phase metacherts are microcrystalline aggregates of microcrystalline quartz chalcedony and lesser hematite chemically the studied mn deposits and associated metacherts are very similar to those formed by submarine hydrothermal effusive processes the deposits originated along sea floor spreading centers mid ocean ridges within the neo tethys ocean and were later obducted as part of the waziristan ophiolite complex

hypocenters in the nankai trough determined by using data from both ocean bottom and land seismic networks and a 3d velocity structure model implications for seismotectonic activity abstract we investigated the hypocenter distribution along the nankai trough off the kii peninsula japan by using data from both ocean bottom and land based seismic networks because seismic velocity structures differ greatly below land and ocean we used a 3d velocity model based on a structural model of the philippine sea plate phs which provides much more accurate estimations of source locations than 1d velocity models derived from either onshore or ocean bottom seismic data alone especially for sources between the coast and the trough axis we identified intensive seismic activity below the axis of the nankai trough which we interpreted to be aftershocks of the 2004 off the kii peninsula earthquakes m jma 7 1 7 4 and 6 5 but found much less seismic activity along the subducting phs the earthquake sources below the trough axis lie on dipping planes within the phs from which we inferred that a fracture zone is developing within the phs our estimated focal mechanisms for these earthquakes showed that their p axes were oriented north south to northeast southwest similar to those of the 2004 events which were rotated clockwise by 45 90 from the northwest southeast direction of convergence between the phs and the eurasian plates we consider that the fracture zone represents a boundary between the phs and the izu microplate which are converging in a north south direction and that the 2004 earthquakes and subsequent seismic activity were caused by the collision of these plates

azimuthal anisotropy of rayleigh waves in the crust in southern tohoku area japan to reveal seismic anisotropy within the crust in the southern tohoku area japan we analyze the azimuthal anisotropy of rayleigh waves in the frequency range of 40 65 mhz rayleigh wave anisotropy is estimated by array analysis of 102 teleseismic events that occurred between 2007 and 2014 the frequency variation of the estimated azimuthal anisotropy indicates depth variation of the seismic anisotropy within the crust 1 north south fast velocity direction around the upper crust and 2 trench normal fast velocity direction in the deeper crust we also conduct a time lapse analysis of rayleigh wave anisotropy to demonstrate the stability of the estimated anisotropy in time and to estimate possible changes in seismic anisotropy associated with the 2011 tohoku oki earthquake we demonstrate that the azimuthal location of teleseismic events influences the accuracy of time lapse analysis moreover a decrease of azimuthal anisotropic ratio in time lapse results might be related to changes in the velocity structure associated with release of crustal stress during the tohoku oki earthquake

in situ stress magnitudes at the toe of the nankai trough accretionary prism offshore shikoku island japan quantifying the orientation and magnitude of tectonic stresses is essential toward understanding deformation and faulting in subduction zones however constraints on in situ horizontal stress magnitudes shmin and shmax are rare we estimate shmin and shmax at ocean drilling program site 808 at the toe of the nankai accretionary prism offshore japan using coupled constraints from 1 the width of wellbore breakouts together with estimates of rock strength and a model describing stress redistribution at the borehole wall and 2 limits on regional differential stress defined by failure on preexisting faults our analysis extends from 175 to 915 m below seafloor mbsf and spans the active frontal thrust for an upper bound on rock unconfined compressive strength ucs and assuming hydrostatic formation pore pressure shmin and shmax referenced to the seafloor increase from 6 5 mpa at 175 mbsf to 17 4 mpa at 915 mbsf with the stress state gradually transitioning from a thrust or strike slip faulting regime above 800 mbsf to a normal faulting regime below for cases with higher formation pore pressure horizontal stresses are slightly lower but follow a similar pattern we show that estimated shmin and shmax are strongly dependent on ucs breakout width and friction coefficient all of which are characterized by uncertainty our results suggest that the prism is near thrust failure in the upper 300 mbsf but far from failure below this may be reconciled with active thrusting if thrust faults are locally weaker than the surrounding rock or if shmax fluctuates during the seismic cycle

manganese deposits in turkey distribution types and tectonic setting abstract manganese deposits in turkey are divided into four main groups on the basis of their age host rocks and processes of formation the first is hydrothermal hydrogenetic and rarely diagenetic type manganese deposits which are chiefly associated with radiolarian chert series these deposits occur as lenses and small ore beds within ophiolitic melanges zones of paleo tethyan karakaya and neo tethyan north anatolian and south anatolian suture belts the second is black shale hosted manganese deposits that is found in black shale calcareous shale and calciturbiditic limestone horizons of the passive margin sediments of late cretaceous age in the western taurides these deposits generally are metamorphosed to greenschist facies and include mn carbonate silicate and oxide minerals the third is volcanic arc hosted ores along the black sea margin which occur in different types of metasomatic hydrothermal and stratabound settings rock associations include upper cretaceous dacitic tuff reddish limestone marl and hemipelagic claystone the fourth is oligocene hosted ores in the thrace basin these deposits are similar to those of the paratethyan oligocene belt which occur on the eastern and northern margin of black sea and includes the chiatura georgia nikopol ukraine and varna bulgaria respectively the oligocene mn deposits of the thrace basin were formed by diagenetic replacement processes during a marine regression

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

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

intraoceanic thrusts in the nankai trough off the kii peninsula implications for intraplate earthquakes 1 we identified intraoceanic thrusts developed as imbricate structures within the subducting philippine sea plate off the kii peninsula in central japan manifesting as strong amplitude reflections observed in an industry standard three dimensional 3d seismic reflection data set these imbricate intraoceanic thrusts cut through the oceanic crust as a discontinuous thrust plane striking approximately parallel to the trench in our survey area large intraplate earthquakes with moment magnitudes mw over 7 occurred on 5 september 2004 causing strong ground motions on the islands of japan and tsunami waves the locations of the intraoceanic thrusts recognized in the seismic data are distributed around the estimated hypocenters of the mainshocks and aftershocks of the 2004 earthquakes furthermore their geometry extracted from the 3d seismic data could explain the kind of complex rupture pattern observed during the 2004 events therefore we propose that the intraoceanic thrusts are seismogenically active

propagation mechanism of long period ground motions for offshore earthquakes along the nankai trough effects of the accretionary wedge a thick accretionary wedge with low seismic velocity overlying a subducting plate is an important factor affecting the amplitudes and durations of long period ground motions for great offshore earthquakes we performed a series of 3d long period ground motion simulations to obtain a better understanding of the effects of the accretionary wedge along the nankai trough japan the simulation results demonstrate that the accretionary wedge has the effect of decreasing the peak amplitude and velocity response but amplifying and elongating later phases of long period ground motions in the land area these effects depend significantly on the focal depth and are pronounced for shallow seismic sources the amplified and elongated later phases originate mainly from prominent basin induced surface waves excited near the trough axis we also identified hard sediments with intermediate s wave velocity in the accretionary wedge as a key layer that enhances the propagation of long period ground motions from offshore to onshore in the case of the nankai trough the hard sediments allow long period ground motions developed inside the accretionary wedge to be efficiently transmitted outward in the longer period than 10 s comparisons between the observed and simulated records suggest that for more accurate predictions of long period ground motions velocity structure models of not only the accretionary wedge but also the surrounding upper crust should be validated and revised using seafloor observations

s wave splitting in the offshore south island new zealand insights into plate boundary deformation local and regional s wave splitting in the offshore south island of the new zealand plate boundary zone provides constraints on the spatial and depth extent of the anisotropic structure with an enhanced resolution relative to land based and sks studies the combined analysis of offshore and land measurements using splitting tomography suggests plate boundary shear dominates in the central and northern south island the width of this shear zone in the central south island is about 200 km but is complicated by stress controlled anisotropy at shallow levels in northern south island a broader 200 km zone of plate boundary parallel anisotropy is associated with the transitional faulting between the alpine fault and hikurangi subduction and the hikurangi subduction zone itself these results suggest s phases of deep events 90 km in the central south island are sensitive to plate boundary derived ne sw aligned anisotropic media in the upper lithosphere supporting a thin viscous sheet deformation model

seismic structure of western end of the nankai trough seismogenic zone 1 in 1998 a seismic experiment along a 320 km long profile using an air gun array and ocean bottom seismographs obss was collected in the on shore offshore forearc region of the western nankai trough seismogenic zone southwestern japan this area is outside the coseismic rupture area of the 1946 nankaido earthquake ms 8 2 the main objectives of this paper are to clarify the p wave and the poisson s ratio profile around the forearc region of southwestern japan and estimate differences between this area and the nankaido coseismic rupture area the p wave velocity model estimated by two dimensional 2 d ray tracing and travel time inversion indicates three units with distinctive velocity patterns the lens shaped unit has a maximum thickness of 5 km and velocity of 3 4 4 0 km s the underlying unit has velocity of 5 4 5 6 km s and its p wave velocity increases on land vp 6 2 6 4 km s the relative homogeneous unit with p wave velocity of 6 6 6 9 km s exists just beneath secondary unit with p velocity of 5 4 5 6 km s the angle of subduction is 7 we also obtained a poisson s ratio of the crustal structure of the forearc region the poisson s ratio of the southern part of secondary unit is larger than that of the northern part we conclude that these data indicate clay rich metamorphic rocks plus oceanic basaltic rocks rather than high porosity materials comprise the majority of the layer we suggest that the region of high poisson s ratio probably corresponds to underplating and the metamorphism of the clay rich sediments and possibly the oceanic basalt just below the decollement

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

environments and processes of manganese deposition concentration of manganese in solution and its deposition takes place by redox controlled processes in a variety of modern and ancient geologic and geochemical environments modern mn deposition occurs predominantly in deep sea areas rather than shallow water domains although deep sea sedimentary deposits dominate hydrothermal contribution of mn to the ocean system may be substantial mn deposition from hydrothermal solutions at or near sea floor spreading centers and less commonly in island arc areas is known in addition near and far field dispersion of mn from vent sites is also substantial such distributions are controlled by the flow rate and egress temperature of the solution and the residence time of mn in seawater thus even in sedimentary deposit domains at least partial derivation of mn from a hydrothermal source is possible sedimentary fe mn crusts on older volcanic substrates on seamounts form by hydrogenous deposition of metal concentrated from terrigenous sources in the mid water column oxygen minimum zones thus the presence or absence of volcanic rocks is not a clear indication of whether sedimentary mn deposits particularly in the ancient geologic record are the result of a totally terrigenous or a totally volcanogenic source abyssal fe mn nodules are considered to form from a basin water hydrogenous and or pore water early diagenetic supply of metals but in most cases the extent of supply from either of the sources is unknown the metal incorporation mechanisms of free moving nodules is little understood and it is possible that in most cases both sources contribute to the nodule composition therefore no nodule should be considered as totally hydrogenous or totally early diagenetic based only on its bulk composition the determined growth rate giving only an average value cannot by itself reveal the growth history of the nodules biological participation directly or indirectly controls mn deposition the stratified black sea demonstrates the concentration of mn in solution in an anoxic zone its advection toward the redox interface and its precipitation in an oxygenated condition similar stratified basins are contemplated for ancient mn deposition in shallow water basin margin areas geologic and geochemical signatures indicate that during sea level highstands stratified basins formed in which mn was concentrated in solution in the anoxic part corresponding transgression led to the impingement of the redox interface on the continental shelf and precipitation of mn oxides could take place across the interface during transgression regression cycles offshore in anoxic or dysaerobic conditions mn carbonate could form by early diagenetic reaction of mn super 2 with co 2 or hco 3 super produced by organic carbon oxidation critical mn deposits occurring in transgressive glaciogenic and black shale bearing ancient sequences support this paleoenvironmental model for mn deposition

cretaceous tertiary convergence and continental collision sanandaj sirjan zone western iran abstract the sanandaj sirjan zone contains the metamorphic core of the zagros continental collision zone in western iran the zone has been subdivided into the following from southwest to northeast an outer belt of imbricate thrust slices radiolarite bisotun ophiolite and marginal sub zones which consist of mesozoic deep marine sediments shallow marine carbonates oceanic crust and volcanic arc respectively and an inner complexly deformed sub zone late palaeozoic mesozoic passive margin succession rifting and sea floor spreading of tethys occurred in the permian to triassic but in the sanandaj sirjan zone extension related successions are mainly of late triassic age subduction of tethyan sea floor in the late jurassic to cretaceous produced deformation metamorphism and unconformities in the marginal and complexly deformed sub zones deformation climaxed in the late cretaceous when a major southwest vergent fold belt formed associated with greenschist facies metamorphism and post dated by abundant palaeogene granitic plutons in the southwest of the zone a late cretaceous island arc passive margin collision occurred with ophiolite emplacement onto the northern arabian margin similar to that in oman final closure of tethys was not completed until the miocene when central iran collided with the northeast arabian margin

insights from the talysh of azerbaijan into the paleogene evolution of the south caspian region the age and mode of formation of the south caspian basin are disputed an 10 km thick predominantly middle eocene clastic and volcanic succession is exposed in the talysh mountains of azerbaijan at its western margin here high k alkali basalts pass laterally to the east and southeast into volcanogenic sandstone dominated turbidity current and debris flow deposits these southeasterly directed depositional systems accumulated in water depths generally greater than 200 m and fed directly into the western south caspian basin new ar ar ages cluster around 39 ma with an upper 1400 m thick volcanic interval being deposited in 2 2 0 2 m y we interpret that this rapid deposition and magmatism records a major back arc extensional transtensional event in the talysh north of the north dipping neotethyan subduction zone this event is recognized across much of southwest asia and may indicate a period of significant basin formation within the adjacent south caspian basin a transition into upper eocene lower oligocene strata dominated by fine grained turbidity current and hemipelagic sediments with slope instability features is interpreted to mark the end of rifting and volcanism in the talysh and the start of the arabia eurasia collision overlying oligocene coarse clastic rocks are interpreted as the erosional products of localized topography created by the further propagation of compressional deformation into the talysh region

spectral characterization and aster based lithological mapping of an ophiolite complex a case study from neyriz ophiolite sw iran abstract the neyriz ophiolite occurs along the zagros suture zone in sw iran and is part of a 3000 km obduction belt thrusting over the edge of the arabian continent during the late cretaceous this complex typically consists of altered dunites and peridotites layered and massive gabbros sheeted dykes and pillow lavas and a thick sequence of radiolarites reflectance and emittance spectra of neyriz ophiolite rock samples were measured in the laboratory and their spectra were used as endmembers in a spectral feature fitting sff algorithm laboratory spectral reflectance measurements of field samples showed that in the visible through shortwave infrared vnir swir wavelength region the ultramafic and gabbroic rocks are characterized by ferrous iron and fe mg oh spectral features and the pillow lavas and radiolarites are characterized by spectral features of ferric iron and al oh the laboratory spectral emittance spectra also revealed a wide wavelength range of si o spectral features for the ophiolite rock units after continuum removal of the spectra the sff classification method was applied to the vnir swir 9 band stack and to the 11 band data set of swir and tir data sets of the advanced spaceborne thermal emission and reflection radiometer aster sensor using field spectra as training sets for evaluating the potential of these data sets in discriminating ophiolite rock units output results were compared with the geological map of the area and field observations and were assessed by the use of confusion matrices the assessment showed in terms of kappa coefficient that the sff classification method with continuum removal applied to the swir data achieved excellent results which were distinctively better than those obtained using vnir swir data and tir data alone

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

the timing of calc alkaline magmatism in parts of the alpine himalayan collision zone and its relevance to the interpretation of caledonian magmatism discussion of the timing of calc alkaline caledonian magmatism in scotland has centred on its tectonic setting the view that active subduction was responsible for the formation of 415 400 ma magmatism is in conflict with the palaeogeographical and stratigraphical evidence in order to shed light on the problem magmatism in the continent continent collision zone of modern times turkey iran and tibet is surveyed the conclusion is reached that the final stage of calc alkaline magmatism displays a time lapse and possible space shift after two continents have collided from the evidence of magmatism the timing of the major collision events in the himalayas is thought to be diachronous ranging from around or no later than 38 30 ma for the central part to later than 30 ma for the eastern part this view is supported by the available palaeogeographical and stratigraphical evidence evidence from this survey enables the scottish data to be seen in a new context by comparing modern collision zones with old ones such as those in scotland and the appalachians it is also concluded that collision related magmatism is not volumetrically trivial and is diverse in composition

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

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

layer stripping of shear wave splitting in marine ps waves summary the properties of split s waves can be used to infer 1 the state of stress and strain in the earth 2 the directional dependence of hydraulic conductivity and 3 small changes in pore fluid pressure in the rock mass that occur in response to dynamic processes such as the earthquake cycle measurements of split s waves are particularly useful in shallow 1000 m subseabed marine sediments where s wave splitting from an azimuthal elastic anisotropy is typically produced by the presence of near vertical aligned cracks here we present a method of measuring small amounts of s wave splitting in marine p to s mode converted waves and illustrate the technique with data from an ocean bottom seismometer obs deployed on the west svalbard continental slope the analysis applies a modified version of the alford rotation and layer stripping technique developed for zero offset s wave sources and treats ps waves that undergo mode conversion at reflectors that are close to the seabed in comparison with the overlying water depth when the seismic record contains coherent signal on both the in plane and out of plane components the layer stripping technique is capable of decoupling the swave splitting from the effects of p wave velocity anisotropy and reflector dip that influence the downgoing p wave part of the ray path the amount of s wave splitting in the data is small however and we find that this causes a greater practical problem for the analysis than the known theoretical limitations of the layer stripping theory such as use of a finite offset source for the analysis of the example data we develop a number of procedures that are necessary to mitigate the low signal to noise levels these include using a wide range of shot receiver azimuths to generate data redundancy methods of identifying and rejecting poor measurements and a predictive layer stripping approach that minimizes the propagation of errors through the analysis that arise from scatter in the layer by layer results with the ps waves of the example data which have a dominant period about 30 ms we find the technique is capable of measuring s wave splitting to a precision of about 0 5 ms for 4 or 5 layers the number of layers successfully treated would increase if the amount of s wave splitting were larger than in these data for which the total cumulative s wave splitting was about 10 ms over a 450 m depth interval the orientation of the fast split s wave was measured with a precision of about 15 our results give an s wave velocity anisotropy of 1 2 per cent in the shallowest 25 30 m subseabed that implies the presence of a differential horizontal stress at or very close to the seabed the s wave splitting accumulated throughout the investigated section at a rate that was consistent with predictions made for a single set of parallel fluid filled cracks with crack density about 0 015 the fast s wave was found to be oriented at 75 15 for the uppermost 150 m before drifting clockwise to an azimuth of 190 210 the clockwise drift in the fast s wave polarization direction implies a transfer of dominance between one set of cracks in the near surface probably related to the slope of the seabed and a different set in deeper sediments of tectonic origin a zone of azimuthal isotropy where the mechanisms that produce the elastic anisotropy may cancel each other out occupies the interval between the two almost orthogonal sets of cracks from interpretation

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

estimation of net to gross from p and s impedance in deepwater turbidites the limitations of using low frequency 3 d seismic data for detailed reservoir characterization are well recognized nonetheless these data are very well suited for quantitative estimates of the net to gross n g which is a reservoir scale property critical in deepwater turbidite reservoir characterization and development projects the acoustic impedance inversion of 3 d seismic has been routinely used with varying success to estimate n g in many clastic reservoirs indeed when the shale baseline impedance can be estimated the departure from this trend can be argued to represent a certain measure of the hydrocarbon saturated sand volume on the reservoir scale we take this technique a step further by using both acoustic and shear impedance ai and si and applying them to horn mountain deepwater reservoirs gulf of mexico gom where six appraisal wells were available for calibration

trench parallel fluid flow in subduction zones resulting from temperature differences differences in the thermal state of subducting crust along the trench of a subduction zone cause differences in subduction zone temperature that persist to tens of kilometers down dip of the trench the resulting differences in fluid viscosity permeability and hydraulic conductivity can lead to trench parallel variations in fluid pressure on the plate boundary fault temperature differences in locations with low decollement temperature 75 c at the trench result in large differences in fluid viscosity and fluid flow from the cold to the hot side of the system margins characterized by high decollement temperature at the trench are probably dominated by temperature controlled differences in intrinsic permeability resulting in fluid flow from the hot to the cold side of the system margins with large trench parallel temperature differences support considerable trench parallel fluid flow and the effect is accentuated for cases where compaction driven dewatering is concentrated near the trench type locations for along strike hydrologic differences include margins with subducting crust with differences in plate age along the trench or patchy hydrothermal circulation in such cases the three dimensional pattern of subduction zone fluid flow should be considered when inferring the location of the source of fluids sampled from boreholes or seeps additionally trench parallel differences in fluid pressure control effective stress on the plate boundary fault reduced effective stress on the plate boundary on the low hydraulic conductivity side of a subduction zone reduces the effective friction coefficient which both reduces frictional heating and may delay the onset of frictional instability

zircon u pb age constraints from iran on the magmatic evolution related to neotethyan subduction and zagros orogeny abstract this study reports zircon la icpms u pb ages of 50 igneous rock samples from the urumieh dokhtar magmatic arc udma and sanandaj sirjan structural zone ssz in iran these results together with literatures and our unpublished age data better delineate the magmatic evolution related to the neotethyan subduction and subsequent zagros orogeny that resulted from the arabia eurasia collision subduction related magmatism was active during jurassic time as evidenced by the presence of widespread i type granitoids from the middle to late jurassic 176 144 ma in the ssz after a protracted magmatic quiescence in the early cretaceous igneous activity renewed inland in the udma from which we identify late cretaceous granitoids 81 72 ma in jiroft and bazman areas the southeastern segment of the udma the udma volcanism was most active and widespread during the eocene and oligocene 55 25 ma much longer lasting than previously thought as just an eocene pulse such a prolonged igneous flare up event in the udma can be correlated to armenia where coeval calc alkaline rocks are common the udma magmatism ceased progressively from northwest to southeast with magmatic activities ending the early miocene ca 22 ma in meghri the middle miocene ca 16 ma in kashan and the late miocene ca 10 6 ma in anar respectively the southeastward magmatic cessation is consistent with the notion of oblique and diachronous collision between arabia and eurasia post collisional volcanism started ca 11 ma in saray east off the urumieh lake which along with later eruptions in sahand 6 5 4 2 ma and sabalan 0 4 ma volcanoes forms a compositionally unique component of the vast volcanic field covering much of the lesser caucasus nw iran and eastern anatolia regions

texture development in naturally compacted and experimentally deformed silty clay sediments from the nankai trench and forearc japan the petrophysical properties of fine grained marine sediments to a large extent depend on the microstructure and crystallographic preferred orientations cpos in this contribution we show that rietveld based synchrotron texture analysis is a new and valuable tool to quantify textures of water saturated fine grained phyllosilicate rich sediments and assess the effects of compaction and tectonic deformation we studied the cpo of compositionally almost homogeneous silty clay drillcore samples from the nankai accretionary prism slope and the incoming philippine sea plate offshore sw japan basal planes of phyllosilicates show bedding parallel alignment increasing with drillhole depth thus reflecting progressive burial and compaction in some samples calcite and albite display a cpo due to crystallographically controlled non isometric grain shapes or nannofossil tests consolidated undrained experimental deformation of a suite of thirteen samples from the prism slope shows that the cpos of phyllosilicate and calcite basal planes develop normal to the experimental shortening axis there is at least a qualitative relation between cpo intensity and strain magnitude scanning electron micrographs show concurrent evolution of preferred orientations of micropores and detrital illite flakes normal to axial shortening this indicates that the microfabrics are sensitive strain gauges and contribute to anisotropic physical properties along with the cpo

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

seismic anisotropy of shales the seismic properties and preferred clay mineral orientation of a suite of shales are investigated using laboratory velocity measurements as a function of confining pressure x ray diffraction techniques and electron microprobe backscatter bse imaging the velocity measurements indicate that these shales are transversely isotropic with the main symmetry axis perpendicular to bedding anisotropy at elevated pressures caused mainly by preferred orientation of clays illite parallel to bedding ranges from 20 vp and 19 vs for a sample of new albany shale to 30 vp and 35 vs for a sample of chattanooga shale the degree of clay mineral alignment in the shales is constrained by orientation indices produced using simple x ray diffraction techniques a strong positive correlation is found between the degree of preferred orientation as expressed in the orientation indices and seismic anisotropy bse images of the shale fabrics confirm in a qualitative manner the results of the x ray study to investigate wave propagation in the shales elastic constants of each sample are calculated and used to produce phase and group wave velocity surfaces which describe variation in velocity as a function of angle to the bedding normal the calculated velocity surfaces constrained by independent velocity measurements display a lack of shear wave splitting at near normal incidence in even the most anisotropic shales for the highly anisotropic chattanooga shales group velocity surfaces differ significantly from corresponding phase velocity surfaces

distribution of stress state in the nankai subduction zone southwest japan and a comparison with japan trench to better understand the distribution of three dimensional stress states in the nankai subduction zone southwest japan we review various stress related investigations carried out in the first and second stage expeditions of the nankai trough seismogenic zone experiment nantroseize by the integrated ocean drilling program iodp and compile the stress data overall the maximum principal stress 1 in the shallower levels 1 km below seafloor or in underlying accretionary prism with 1 becoming horizontal is also suggested at all deeper drilling sites we also make a comparison of the stress state in the hanging wall of the frontal plate interface between site c0006 in the nankai and site c0019 in the japan trench subduction zone drilled after the 2011 mw 9 0 tohoku oki earthquake in the japan trench a comparison between stress state before and after the 2011 mega earthquake shows that the stress changed from compression before the earthquake to extension after the earthquake as a result of the comparison between the nankai trough and japan trench a similar current stress state with trench parallel extension was recognized at both c0006 and c0019 sites hypothetically this may indicate that in nankai trough it is still in an early stage of the interseismic cycle of a great earthquake which occurs on the decollement and propagates to the toe around site c0006

the petrogenesis and tectonic setting of lavas from the baft ophiolitic melange southwest of kerman iran a late cretaceous ophiolite complex in the baft area southwest of kerman iran is characteristic of the central iranian ophiolitic melange belt which wraps around the lut block despite the extensive tectonic disruption of the baft complex most ophiolitic lithologies are present and many original igneous contacts are preserved a lack of cumulate gabbros within the sequence suggests that a large and continuous magma chamber did not exist beneath the baft spreading axis geochemical data confirm the presence of two distinct compositional groups in the mafic lavas 1 tholeiitic basalt and 2 transitional tholeiitic basalt the tholeiitic lavas are similar to typical mid ocean ridge basalt compositions whereas the transitional tholeiites are similar to intraplate basalts the available data suggest that the baft ophiolite complex formed in a small ocean basin possibly at or near a ridge transform intersection emplacement may have occurred as a result of conversion of the transform fault to a subduc

fracture alignments in marine sediments off vancouver island from ps splitting analysis alignments of fractures and cracks in marine sediments may be controlled by various mechanisms such as horizontal compaction and extension and basement faulting the orientation of these alignments can be estimated through analyses of s wave splitting if sensors in ocean bottom observations are deployed through free fall sensor orientation needs to be determined in order for the recorded data to be used for such analyses here we estimate the sensor orientation from the linear particle motions of p to s ps phases converted at the sediment basement interface and also from t waves that are excited by earthquakes and propagate in the seawater we examine waveforms of local earthquakes recorded by 32 ocean bottom seismometers obss that were deployed through free fall for three months in 2010 off vancouver island where the strike slip nootka fault zone nfz intersects the deformation front of the cascadia subduction zone because the particle motion of the ps wave was corrected by estimating splitting parameters the fast polarization direction which reflects s wave anisotropic structure within the sediment can also be evaluated consequently we could estimate the fast polarization direction at obss deployed near the nfz and west of the deformation front the obtained fast directions appeared to correspond to alignments of shear fractures in the marine sediments associated with the left lateral motion of the fault in the basement along the nfz margin normal cracks due to horizontal compression west of and slightly away from the deformation front and frontal thrust faults within the accretionary prism near the deformation front

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

on acoustic waveform tomography of wide angle obs data strategies for pre conditioning and inversion we successfully apply the acoustic laplace fourier waveform tomography method to delineate p wave velocity structures of the mega splay fault system in the central part of the seismogenic nankai subduction zone offshore japan using densely sampled wide angle ocean bottom seismograph obs data originally acquired in 2004 our success is due to new and carefully designed data preconditioning and inversion strategies to mitigate i the well known non linearity of waveform inversion ii the challenges arising from crustal scale survey designs e g undersampling of the obss and iii modelling errors due to the use of the acoustic assumption we identify a sixfold set of key components that together lead to the success of the high resolution waveform tomography image i availability of low frequency components starting at 2 25 hz reducing the non linearity and access to large offset data up to 55 km increasing the depth of illumination and the recovery of low wavenumber components ii a highly accurate traveltime tomography result with an rms error of approximately 60 ms that further mitigates the non linearity iii a hierarchical inversion approach in which phase spectra are inverted first to reduce artefacts from the acoustic assumption and amplitude information is only incorporated in the final stages iv a laplace fourier domain approach that facilitates a multiscale approach to mitigate non linearity by restricting the inversion to the low frequency components and early arrivals first and sequentially including higher frequencies and later arrivals v a pre conditioning strategy for eliminating undesirable high wavenumber components from the the gradient vi a strategy for source estimation that reduce the influence of the instrumental design in the obs case study used for illustration purposes laplace fourier waveform tomography retrieves velocity anomalies as small as 700 m horizontally and 350 m vertically above the top of the philippine sea plate the resulting velocity structures include low velocity zones and thrust structures which have not been previously identified clearly the velocity models are validated by scrutiny of synthetic and observed waveforms by evaluating the coherency of source estimates and by comparison with 3 d pre stack migrated presdm images chequerboard tests and point scatter tests demonstrate both the reliability and the limitations of the acoustic implementation

vibracoring a new method for coring deep lakes abstract a major limitation facing lacustrine researchers is an inability to take long 6 to 18 m continuous sediment cores in water depths greater than several metres at a low cost these problems have limited the advancement of palaeolimnology and quaternary stratigraphy working from a frozen lake surface new developments make it possible to take 18 m long vibracores in water depths of at least 55 m high frequency low amplitude vibrations are transferred down a series of 6 m long 7 6 cm diameter core tubes 3 inch aluminum irrigation pipe rigidly coupled end to end vibrations liquify sediment adjacent to the core tube walls thus allowing penetration of the sediment a core catcher prevents sediment from extruding out of the tube end during extraction this cost effective and labour efficient two persons coring system has been achieved by developing rigid core tube couplers a hand powered drum cable hoist and a set of operation procedures the hoist cable end is attached to a clamp 1 m above the core catcher and at each coupler along the pipe string at 6 m intervals lifting or lowering using a drum cable hoist allows for quick coupling and decoupling of core tubes although vibracoring is an improvement over other systems it still has portability limitations because of the bulk and weight of the equipment and large amount of pipe required for deep coring three sleds are required to transport equipment from the nearest vehicle access to the coring sites

quantitative estimation of fluid pressure ratio of shear vein in an on land accretionary complex the yokonami melange the cretaceous shimanto belt kochi southwest japan abstract the fluid pressure ratio and effective friction coefficient of shear veins in an exhumed accretionary complex in the cretaceous shimanto belt southwest japan were constrained by fluid inclusion and stress inversion analyses the shear veins are considered to be developed along the decollement temperature and pressure conditions for shear veins were found to be in the range of 175 225 c and 143 215 mpa respectively fluid pressure ranged between the lines of 70 100 lithostatic pressure when the geothermal gradient was assumed on the basis of the slab age at the trench the effective friction coefficient of shear veins was estimated to be 0 1 0 2 by stress inversion analysis which corresponds to a fluid pressure ratio of 0 67 0 83 both pressure temperature and friction coefficient results indicate that the fluid pressure ratio is higher than about 0 7 in this paper we propose the procedure to constrain paleo fluid pressure ratio from natural materials wedge states were examined using the weak decollement friction coefficient with shallow and steep taper angles indicating that the wedge state is stable or compressively critical and is controlled by the fluid pressure ratio within the wedge

petrogenesis of post collisional a type granitoids from the urumieh dokhtar magmatic assemblage southwestern kerman iran constraints on the arabian eurasian continental collision abstract three plutons deh siahan bande bagh and baghe khoshk sharghi collectively referred to as the dbb hereafter in southwestern kerman in the southeastern part of the urumieh dokhtar magmatic assemblage udma of the zagros orogenic belt differ from the typical calc alkaline metaluminous i type intrusions of the region the dbb intrusions have a distinct lithological assemblage varying from diorite through monzogranite and monzonite to alkali feldspar syenite and alkali granite the dbb granitoids are metaluminous to slightly peraluminous alkaline to shoshonitic in composition and have high total alkali contents with k2o na2o high feot mgo values and low cao and mgo contents they are enriched in some liles such as rb and th and hfses such as zr y and rees except eu and depleted in sr and ba relative to primordial mantle and have low concentrations of transitional metals these features along with various geochemical discriminant diagrams suggest that the dbb granitoids are post collisional a type granitoids which had not been recognized previously in the udma the chondrite normalized ree patterns of the dbb granitoids show slightly enriched light rees la sm n 2 26 4 13 negative eu anomalies eu eu n 0 19 0 74 and flat heavy ree patterns gd yb n 0 80 1 87 the negative eu anomaly indicates an important role for plagioclase and or k feldspar during fractional crystallization whole rock rb sr isotope analysis yields an isochron age of 33 1 ma with an initial 87sr 86sr value of 0 7049 0 0001 whole rock sm nd isotope analysis gives endt values from 2 56 to 3 62 at 33 ma the positive endt and low isr values of the dbb granitoids together with their tdm of 0 6 0 7 ga suggest their formation from partial melting of a lithospheric mantle source modified by fluids or melts from earlier subduction processes melting of lithospheric mantle occurred via a dehydration melting process at pressures below the garnet stability field as a consequence of lithospheric mantle delamination or break off of a subducted slab and melting of the lithospheric mantle by upwelling of hot asthenosphere on the basis of rb sr age dating and the post collisional geochemical signatures of the dbb granitoids along with extensive pre collisional volcanic eruptions in middle eocene we suggest late eocene for the time of collision between the arabian and central iranian plates this also implies that the calc alkaline i type intrusions in the southwestern kerman and in other parts of the udma may have formed in a post collisional context

seismic velocity anisotropy of phyllosilicate rich rocks characteristics inferred from experimental and crack model studies of biotite rich schist summary seismic velocity anisotropy of biotite schist 30 per cent mode biotite was measured under confining pressures up to 150 mpa the rock shows weak orthotropy which was altered from transverse isotropy ti generated by biotite preferred orientation the orthotropy was caused by microfolding in the rock the velocity increase under confining pressure indicates that most crack planes are aligned parallel to the cleavage planes silicate sheet of the oriented biotite minerals the anisotropy of the rock is basically ti due to both the aligned biotite minerals and cracks which have a common symmetry axis we found that other sheet silicate rich rocks have a similar anisotropy with the biotite schist in which the ti type anisotropy is characterized by the slow p and s wave velocities along the symmetry axis this is caused by the preferred orientation of sheet silicate minerals and the extremely slow p and s wave velocities along the axis perpendicular to the silicate sheet compared to the directions along the silicate sheet when rock contains a large percentage of highly oriented sheet silicates the fast and slow shear waves exchange their polarities at some off symmetry axis directions indicating that the qswave quasi s wave velocity exceeds the sh wave velocity the phase velocity distribution of qs wave shows an asymmetry with respect to the angle from the symmetry axis which is characterized by a bulge in this distribution located near the symmetric axis this is inherent to most sheet silicate minerals when crack density of aligned cracks increases the p wave velocity along the symmetry axis decreases considerably the qs wave phase velocity in the off axis directions also decreases in accordance with the decrease of the p velocity along the symmetry axis the asymmetry of the qs wave phase velocity distribution increases as the p wave velocity decreases along the symmetry axis this relationship can be well understood by means of berryman s extended thomsen approach

distribution and mineral assemblages of bedded manganese deposits in shikoku southwest japan implications for accretion tectonics abstract numerous bedded manganese and manganese iron ore deposits occur in shikoku southwest japan the mineralogy wall rock characteristics and fossil age data of the deposits are synthesized in this paper their mineral assemblages correlate well with the progressive metamorphic grade of the accretionary complexes in shikoku based on the plate tectonic framework of subduction accretion process the deposits are considered to have formed by metamorphism of mn fe nodule bearing siliceous sediments on the ocean floor

a cause of rupture segmentation and synchronization in the nankai trough revealed by seismic imaging and numerical simulation 1 a giant earthquake occasionally occurs in a subduction zone owing to a simultaneous rupture in adjacent segments which have been previously ruptured by large earthquakes however it is still unknown if a giant earthquake coincidentally occurs or if there is a causal factor to control its generation in this study we show a cause and a growth process of a giant earthquake which may occur along southwestern japan on the basis of seismic images obtained from wide angle seismic data and a numerical simulation incorporating the structural images the wide angle seismic data were acquired along three trough parallel profiles crossing the rupture segmentation boundary between the 1944 tonankai moment magnitude mw 8 1 and the 1946 nankai mw 8 4 earthquakes the seismic imaging detected a high seismic velocity body forming a strongly coupled patch at the segmentation boundary the numerical simulation explained the historic rupture patterns and shows the occurrence of a giant earthquake along the entire nankai trough a distance of over 600 km long mw 8 7 the growth process revealed from the simulated slip history in and around the strongly coupled patch is 1 prior to the giant earthquake a small slow event or earthquake occurs near the segmentation boundary 2 this accelerates a very slow slip slower than the plate convergent rate at the strong patch which reduces a degree of coupling and 3 then a rupture easily propagates through the strong patch when the next earthquake is nucleated near the segmentation boundary consequently growing into a giant earthquake

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

geochemistry and depositional environment of mn oxide deposits in the tokoro belt northeastern hokkaido japan numerous early cretaceous mn oxide and mn fe deposits are distributed in the tokoro belt northeastern hokkaido japan the mn oxide deposits usually occur in the southwestern part of the belt and within bedded cherts whereas the mn fe deposits are restricted to the northeastern part of the belt and occur between bedded cherts and underlying basaltic pillow lava the mn oxide ores are characterized by low fe mn ratios and the trace element concentrations and rare earth element ree patterns are similar to those of the submarine hydrothermal mn deposits distribution patterns of trace elements co ni cu and zn and ree in the mn oxide ores determine two types of deposits hydrogenous deposits which have relatively high concentrations and submarine hydrothermal deposits which have low concentrations these compositional trends and geologic evidences of the tokoro mn deposits suggest that the fe phases precipitated first closer to their source whereas the mn phases deposited later at a distance from their source some hydrogenous effects on the mn oxide deposits are due to the adsorption of trace elements from seawater trace element concentrations of tokoro mn oxide deposits show that they formed within 40 km from their source

u pb zircon ages field geology and geochemistry of the kermanshah ophiolite iran from continental rifting at 79ma to oceanic core complex at ca 36ma in the southern neo tethys abstract the geodynamic evolution of the zagros mountains of iran remains obscure in particular the time of formation of the zagros ophiolites and the closure of the neo tethys ocean are highly controversial here we present new precise zircon u pb ages that show that the younger part sahneh kamyaran of the kermanshah ophiolite formed at 35 7 0 5 ma and the older part harsin at 79 3 0 9 ma field relations and geochemical evidence show that the younger sahneh kamyaran part is probably a fossil oceanic core complex and the older sahneh part is probably a continental oceanic transition complex both the sahneh kamyaran and sahneh parts were later emplaced into an accretionary complex we conclude and infer that the final closure time of the southern neo tethys ocean was after the late eocene our data and tectonic model have crucial implications for the geodynamic evolution of the zagros region

stress forecasting not predicting earthquakes a paradigm shift after 120 years of unsuccessful endeavor a paradigm shift is required before earthquakes can be predicted the most sensitive diagnostic of low level changes of stress in in situ rock variations in microcrack geometry can be monitored by analyzing shear wave splitting the suggested paradigm shift is that instead of investigating the source zone we monitor stress accumulation before earthquakes at possibly substantial distances from the source characteristic temporal variations of shear wave time delays have been observed in retrospect before 14 earthquakes worldwide on one occasion when changes were recognized early enough the time magnitude and fault break of an m 5 earthquake in southwest iceland were successfully stress forecast in a narrow time magnitude window such stress accumulation can be theoretically modeled and is believed to be at least partially understood when sufficient shear wave source earthquakes are available increasing time delays also show an abrupt decrease shortly before the impending earthquake occurs this is not fully understood but is thought to be caused by stress relaxation as microcracks coalesce onto the eventual fault break the new result confirming these ideas and justifying the paradigm shift is that logarithms of the durations of both increases and decreases in time delays are found to be proportional self similar to the magnitudes of impending earthquakes

evidence from shear wave splitting for the restriction of seismic anisotropy to the upper crust the existence of anistropy in the propagation speed of seismic waves through the earth s crust has been attributed to the non random alignment of microcracks in the crust1 for sparsely distributed parallel vertical cracks perturbation theory predicts the splitting of a shear wave into two orthogonally polarized waves2 4 here we present extremely clear evidence for shear wave splitting in three component seismograms from crustal and sub crustal microearthquakes recorded in the shikoku district of japan quantitative analysis of travel time differences between split shear waves leads to the conclusion that the observed anisotropy is limited to the upper crust shallower than 10 15 km this model is consistent with recent results from reflection seismology5 and implies that microcrack density or orientation changes from the upper to the lower crust

plate tectonic evolution of the southern margin of eurasia in the mesozoic and cenozoic abstract thirteen time interval maps were constructed which depict the triassic to neogene plate tectonic configuration paleogeography and general lithofacies of the southern margin of eurasia the aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework the hercynian orogeny was completed by the collision of gondwana and laurussia whereas the tethys ocean formed the embayment between the eurasian and gondwanian branches of pangea during late triassic early jurassic times several microplates were sutured to the eurasian margin closing the paleotethys ocean a jurassic cretaceous north dipping subduction boundary was developed along this new continental margin south of the pontides transcaucasus and iranian plates the subduction zone trench pulling effect caused rifting creating the back arc basin of the greater caucasus proto south caspian sea which achieved its maximum width during the late cretaceous in the western tethys separation of eurasia from gondwana resulted in the formation of the ligurian penninic pieniny magura ocean alpine tethys as an extension of middle atlantic system and a part of the pangean breakup tectonic system during late jurassic early cretaceous times the outer carpathian rift developed the opening of the western black sea occurred by rifting and drifting of the western central pontides away from the moesian and scythian platforms of eurasia during the early cretaceous cenomanian the latest cretaceous paleogene was the time of the closure of the ligurian pieniny ocean adria alcapa terranes continued their northward movement during eocene early miocene times their oblique collision with the north european plate led to the development of the accretionary wedge of the outer carpathians and its foreland basin the formation of the west carpathian thrusts was completed by the miocene the thrust front was still propagating eastwards in the eastern carpathians during the late cretaceous the lesser caucasus sanandaj sirjan and makran plates were sutured to the iranian afghanistan plates in the caucasus caspian sea area a north dipping subduction zone jumped during paleogene to the scythian turan platform the shatski terrane moved northward closing the greater caucasus basin and opening the eastern black sea the south caspian underwent reorganization during oligocene neogene times the southwestern part of the south caspian basin was reopened while the northwestern part was gradually reduced in size the collision of india and the lut plate with eurasia caused the deformation of central asia and created a system of nw se wrench faults the remnants of jurassic cretaceous back arc systems oceanic and attenuated crust as well as tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems

eocene k rich adakitic rocks in the central iran implications for evaluating its cu au mo metallogenic potential abstract the kal e kafi intrusive complex is located in the central iran magmatic zone and includes a series of granitoid rocks ranging in composition from gabbro to granite these granitoids show some affinities with adakites e g high sr y and la yb ratios coupled with low yb and y enrichment in lree and lile with no eu anomalies similar to products from all of which are compatible with derivation from slab melting however relatively their low end t values 0 21 to 2 35 and higher 87 sr 86 sr i 0 7041 0 7044 are inconsistent with an origin by slab melting with these rocks also showing shoshonitic affinities with high k 2 o na 2 o ratios geochemical characteristics indicate that the kal e kafi intrusive complex was probably derived by the partial melting of delaminated lower crust at pressures equivalent to crustal thicknesses of 40 km generated near the boundary between garnet bearing amphibolite or amphibole bearing eclogite melting moreover the kal e kafi adakitic magmas must have interacted with the surrounding metasomatized mantle peridotite during their ascent which elevated not only their mgo cr and ni contents but also the oxygen fugacity o 2 of the magma the high o 2 could have induced oxidation of metallic sulfides in the mantle resulting in the mobilization of chalcophile elements which are required to produce porphyry cu au and mo mineralization

overpressure detection from compressional and shear wave data by analyzing experimental data we show that in many room dry rocks the poisson s ratio pr decreases with decreasing differential pressure confining minus pore pressure this means that in gas saturated rocks pr decreases with increasing pore pressure we confirm the generality of the observed effect by theoretically reproducing it via effective medium modeling this effect can be used as a new tool for overpressure detection from surface seismic cross well sonic logs and measurements ahead of the drill bit

structure of the nankai trough accretionary zone from multichannel seismic reflection data new multichannel seismic reflection data collected over the nankai trough image the accretionary complex in two areas the international program of ocean drilling leg 87 transect area western area and the region of upcoming ocean drilling program leg 131 eastern area the incoming shikoku basin sedimentary section consists of hemipelagic clays and thin terrigenous turbidites the basin section is overlain by a trench wedge that is 12 16 km wide and 350 750 m thick at the thrust front accretionary deformation begins in a protothrust zone that is characterized by thickening and seaward tilting of the trench wedge the zone in the western area is 4 5 km wide and is characterized by kink folds the zone in the eastern area is only 2 5 km wide and does not exhibit such folds the frontal thrusts in each area are imaged as fault plane reflections and ramp upward from within the basin hemipelagic section the overthrusting sediments form fault bend folds over these ramps thrust spacing at the toe of the slope is 1 5 2 5 km the second thrust cuts up from an inferred decollement within the shikoku basin sedimentary section in the eastern area a reflection marking the top of the basin pelagic sediment section changes from normal to reversed polarity about 6 3 km seaward of the thrust front and underlies the entire protothrust zone this reflector continues with reversed polarity under the accretionary complex and is at the level of the basal decollement the underlying basin pelagic section is apparently thrust undisturbed beneath the accretionary prism the reversal of polarity indicates a change in reflection coefficient that is due to a combination of decreasing seismic velocity and density across the interface this decrease in velocity and density may indicate that the decollement is a zone of high porosity due to fluid expulsion from deeper within the accretionary prism the reflections from the first and second thrusts are also reversed polarity possibly indicating that they also are pathways of fluid expulsion the critical wedge taper of the western area is greater than that of the eastern area an observation that is consistent with the existence of an overpressured decollement in the eastern area

deformable backstop as seaward end of coseismic slip in the nankai trough seismogenic zone abstract wide angle seismic surveys performed in the last decade have clarified the 3 d crustal structure along the nankai trough the geometry and velocity structure of the southwestern japan subduction zone are now well constrained comparing these observations with the rupture distribution of historic great thrust earthquakes it appears that the coseismic rupture occurred along plate boundaries deeper than the wedge backstop boundary the boundary between the neogene quaternary accretionary wedge and the crust forming the backstop from the view of spatial relationship both rupture distributions of the last two large events and the crust forming the backstop are considerably retreated from the trough axis in the west and east off the kii peninsula in both areas seamount or ridge subduction is apparent in seismic results geomorphological data and geomagnetic data the landward indentation of the deformable backstop which corresponds to the crustal block of old accreted sediments may be formed by seamount subduction according to published results of sandbox modeling in particular the subducted seamount may be a structural factor affecting the recession of the crustal block forming the backstop

s wave velocities and anisotropy in sediments entering the nankai subduction zone offshore japan summary p and mode converted s waves from airgun shots recorded along a line of ocean bottom seismometers were used to construct a 2 d velocity section across the nankai trough and the toe of the accretionary complex offshore southeast japan the site was chosen because of plans to drill into the seismogenic zone of the main subduction thrust which has a history of m 8 earthquakes the section is constrained by well log data from three ocean drilling program boreholes s wave velocities of the sediments over the entire section down to 1 1 km below seafloor range from 107 to 915 m s 1 shear wave splitting indicates anisotropy in all the sediments except possibly the distal trench fill if interpreted conventionally as being due to vertical stress aligned cracks the anisotropy in both the trench and the toe of the accretionary wedge is consistent with crack orientation nw se parallel to the direction of maximum tectonic compression crack density is 0 01 0 03 consistent with closeness to fracture criticality

constraints on arabian plate motion and extensional history of the red sea analysis of the geologic and geophysical data from the western and northern margin of the arabian plate combined with data from the red sea gulf of aden leads to an interpretation of arabian plate motion that supports an episodic extensional history in the red sea and gulf of aden phase 1 extension began in medial to late eocene and was caused by the nw propagation of the reoriented central indian ridge spreading center it stretched and thinned continental crust along numerous wrench and normal faults that reactivated preexisting structures first phase extension stopped when the arabian plate terminally sutured to eurasia in the medial miocene and halted northward movement of arabia relative to africa the combined african arabian plates moved north more slowly constricting and thickening continental crust in the bitlis zagros sutures while the red sea remained technically quiescent and accumulated salt by the early pliocene continued northward movement was accommodated by lateral extrusion of large continental wedges north of the bitlis zagros sutures this allowed arabia to move northward faster than africa and reopen the red sea where phase 2 extension was expressed by seafloor spreading extension within the red sea gulf of aden rift system has been controlled by the interactions and effects of two factors 1 convergent processes between the north margin of the arabian plate and the eurasian plate to the north and 2 northwest propagation of extension associated with the medial eocene reorganization of the central indian spreading center

present day principal horizontal stress orientations in the kumano forearc basin of the southwest japan subduction zone determined from iodp nantroseize drilling site c0009 a 1 6 km riser borehole was drilled at site c0009 of the nantroseize in the center of the kumano forearc basin as a landward extension of previous drilling in the southwest japan nankai subduction zone we determined principal horizontal stress orientations from analyses of borehole breakouts and drilling induced tensile fractures by using wireline logging formation microresistivity images and caliper data the maximum horizontal stress orientation at c0009 is approximately parallel to the convergence vector between the philippine sea plate and japan showing a slight difference with the stress orientation which is perpendicular to the plate boundary at previous nantroseize sites c0001 c0004 and c0006 but orthogonal to the stress orientation at site c0002 which is also in the kumano forearc basin these data show that horizontal stress orientations are not uniform in the forearc basin within the surveyed depth range and suggest that oblique plate motion is being partitioned into strike slip and thrusting in addition the stress orientations at site c0009 rotate clockwise from basin sediments into the underlying accretionary prism

detailed structural image around splay fault branching in the nankai subduction seismogenic zone results from a high density ocean bottom seismic survey 1 to investigate megathrust earthquake and tsunami generation in a subduction seismogenic zone it is important to know the detailed structure around the plate boundary and active splay fault system the nankai trough southwestern japan is among the best studied subduction zones with splay faults in the world this paper presents a detailed structural image around the splay fault in the coseismic rupture zone of the 1944 tonankai earthquake in the central nankai trough based on results from a wide angle high density ocean bottom seismograph obs survey our seismic image clearly shows for the first time the subduction structure along with the splay fault reflections imaged on a previously obtained seismic reflection profile the correspondence between the splay fault reflections imaged on the seismic reflection profile and our reflectivity image was confirmed by converting the time migrated section to a depth section by using a velocity model estimated from the wide angle obs data in this study the high resolution seismic image obtained by the high density obs survey demonstrates a zone of low velocity gradient just above and along the splay fault we focused specifically on the detailed structure around the splay fault a simple amplitude analysis of the wide angle reflections showed that it is likely that a thin low velocity layer with velocities 0 5 1 5 km s slower than those in the surrounding rock exists above the splay fault the presence of this layer suggests elevated fluid pressure in the fault zone which cut through the relatively homogeneous rock of the accretionary prism and generated past megathrust earthquakes

characterization of hydrate and gas reservoirs in plate convergent margin by applying rock physics to high resolution seismic velocity model abstract gas hydrates are widely distributed in the kumano forearc basin which is located above accretionary prism in the nankai margin off the kii peninsula japan bottom simulating reflector bsr at the base of gas hydrate stability zone has been imaged as a strong acoustic impedance contrast on the reflection seismic profiles in order to better define the accumulations of gas hydrates and free gases we performed a high resolution seismic velocity analysis to 3d seismic data using a method of conventional semblance spectra via automatic velocity picking algorithm the results revealed that gas hydrate bearing sediments above the bsr and free gas bearing sediments below the bsr are characterized by p wave velocities of 1900 2500 m s and 1000 1800 m s respectively then the velocity model was converted into gas hydrate and free gas saturation using rock physics approaches the results indicated that saturation of gas hydrates ranges from 0 to 45 in the pore space and highly concentrated around the outer ridge where faults are densely developed additionally concentrations of free gas ranging from 0 to 20 in the pore space are widely distributed below bsrs and are considerably high above ridge structure generated by displacement of large fault splayed from the deep plate boundary decollement based on these results we suggest that the gas hydrates concentrated due to the free gas influx which migrated upward through the steeply dipping strata and faults or fractures cutting through the basin the accumulations of gas and or hydrates are further controlled by fault movements in the accretionary prism beneath the forearc basin therefore these factors generated by intensive tectonic movements in the plate subduction zone control the distribution and saturation pattern of gas hydrate and free gas formations

vp vs ratio and shear wave splitting in the nankai trough seismogenic zone insights into effective stress pore pressure and sediment consolidation to estimate variation of stress state and sediment consolidation in the nankai plate subduction zone off southwest japan we measured the p wave to s wave velocity ratio vp vs and s wave splitting along the seismic line extending from the trench to the seismogenic zone for this purpose we used active source seismic data recorded by multicomponent ocean bottom seismometers obs because it is difficult to identify the ps converted reflection waveforms for each of the geological boundaries in this deep offshore region we focused on the more easily identified pps refracted waveforms that register the conversion of the up going p waves to s waves at the igneous crust surface we estimated the average vp vs ratio within the sedimentary section by using the time lag between the p refracted waves and pps converted waves this vp vs ratio changes abruptly at the trough axis i e the deformation front of the accretionary prism arguably because of compaction associated with the accretion process we observ

method for estimating ductile horizontal strain from magnetic fabrics in poorly consolidated clay rich sediments abstract we propose a simple method based on the normalized eigenvalues of the tensor of anisotropy of magnetic susceptibility ams to estimate horizontal ductile strain in detrital clay rich sedimentary rocks subjected to layer parallel shortening lps this method is mainly based on two assumptions 1 the magnetic carriers are contacting clay mineral platelets and 2 the platelets respond to lps by crenulation and formation of a zone axis of unchanged magnetic susceptibility perpendicular to the plane of deformation we further simplify the problem by considering as the exact distribution of particles orientations is unknown that the ams tensor arises from a single equivalent clay platelet of which the angle with the bedding plane directly reflects the amount of horizontal strain the proposed method is applied to data from samples retrieved during integrated ocean drilling program iodp expeditions 315 and 316 of the nankai trough seismogenic zone experiment nantroseize complex drilling project sample wise finite strain values assist ams data interpretation which is traditionally based on the ams ellipsoid shape parameter and allow comparison with strain estimates obtained by other means in the nankai accretionary prism ams derived strain values range from 0 to 25 and suggest substantial mechanical compartmentalization with inter unit strain contrasts larger than 5 percentage points including the penetrated shallow portion of a megasplay fault at a local scale ams strain also appears to be affected by thrusting what can be interpreted as a record of a ductile strain component away for the brittle zone or as an interseismic ductile strain within otherwise brecciated material

pressure and porosity influences on vp vs ratio in unconsolidated sands elevated pore pressures commonly encountered in the shallow unconsolidated section of the sedimentary column present a significant hazard during the drilling and completion of offshore wells the porosity of the ocean floor sediments is high and a cover of low permeability clay can prevent the underlying sediments from draining even at very shallow depths below the seafloor as further deposition loads the sediment the entrapped fluids impede normal compaction by becoming pressurized the lowered effective stress that results from the higher pore fluid pressure produces a proportional drop in the strength of non cohesive sediments resulting in very weak shallow sands this weakness can result in washouts or fracturing in the shallow strata potentially leading to the loss of the well and of neighboring wells