deep seismic structure of the seismogenic plate boundary in the off sanriku region northeastern japan we determined the deep seismic structure of the seismogenic plate boundary zone of off sanriku the northern part of the japan trench inner slope area travel time data from aftershocks of the 1994 far off sanriku earthquake m 7 5 recorded both by ocean bottom seismographs and the local land seismic network enable us to image the three dimensional seismic velocity structure of the region along the plate boundary there exists a p wave low velocity layer of ca 7 km s 1 and with thickness 10 km as the topmost layer of the subducting pacific plate the present analysis indicates that this layer interpreted as the subducting oceanic crust continues without any velocity variations at least down to ca 40 km depth in the overriding plate we found a zone of considerable high p wave velocity ca 8 km s 1 between the pacific coastal line of the northeastern japan arc at the longitude of 142 5 e this manifests that the trenchward toe of the mantle wedge has significantly higher velocity than that beneath the land area of the arc the landward limit of the high p wave velocity toe corresponds to the down dip limit of the seismogenic plate boundary further to the east the p wave velocity is ca 6 km s 1 the structure image obtained indicates that the nature of the overriding plate is significantly different along the plate boundary in the eastern half of the seismogenic zone the island arc crust and subducting oceanic crust are in contact with each other whereas the high velocity mantle wedge makes up the hanging wall of the deeper part of the seismogenic zone

effects of lateral friction on the structural evolution of fold and thrust belts insights from sandbox experiments with implications for the origin of landward vergent thrust wedges in cascadia various factors are inferred to influence the structural evolution of fold and thrust belts or thrust wedges but the effects of lateral friction such as that exerted by the opposite block of a strike slip fault in nature or by sidewalls in analogue models have rarely been given sufficient attention and hence are still far from being fully understood up to now seaward vergent and dually vergent thrust wedges have been satisfactorily explained by the classic coulomb wedge theory and can be well reproduced in analogue and numerical models in contrast landward vergent thrust wedges which are uncommon in nature e g those occurring in the cascadia subduction zone have not yet been adequately explained by the classic coulomb wedge theory and can only be reproduced in a few analogue models under particular conditions in order to look closer at the effects of lateral friction on the structural evolution of fold and thrust belts and to explore the origin of landward vergent thrust wedges we conducted a series of sandbox models under different conditions of lateral friction and various ratios of initial average lateral frictional stress to basal shear stress s d results of our models revealed that in the presence of a weak or ductile basal decollement the direction of lateral friction can dictate not only the deformation propagation direction and the surface slope direction but also the structural vergence of fold and thrust belts fold and thrust belts normally show a structural vergence in the same direction as the direction of lateral friction but a deformation propagation direction and surface slope direction opposite to the direction of lateral friction according to the results of models and the relationships between structural vergence and lateral friction direction occurring both in cascadia and the analogue models we propose that an extremely high s d ratio due to an extremely weak basal decollement and landward directed lateral friction exerted by the opposite blocks of basement involved strike slip faults are probably the two key factors responsible for the origin of landward vergent thrust wedges in cascadia this work illustrates that effects of lateral friction should be properly taken into account both in the kinematic analysis and designs of models to simulate fold and thrust belts in the presence of weak or ductile basal decollements

northward propagation of the subseasonal variability over the eastern pacific warm pool 1 previous studies suggest that easterly vertical shear of summer mean flow could be a key factor in the northward propagation of the subseasonal variability ssv over the asian monsoon region e g jiang et al 2004 analysis indicates that this same mechanism may also be dictating propagation features over the eastern pacific epac consistent with the presence of local easterly vertical wind shear northward propagation of the ssv is also evident over the epac with a phase speed of about 0 6 deg day 1 moreover similar to its counterpart in the indian ocean the northward propagating ssv over this region is also characterized by positive anomalies of equivalent barotropic vorticity and lower tropospheric specific humidity and planetary boundary layer pbl convergence to the north of the convection center thus the present study provides another independent example of the essential role that easterly vertical wind shear may be playing in regulating the meridional migration of the ssv

a possible new mechanism for northward propagation of boreal summer intraseasonal oscillations based on trmm and merra reanalysis boreal summer intraseasonal oscillations bsisos manifest in the active and break spells and act as the primary building block of the indian summer monsoon although recent research has evolved a basic framework for understanding the scale selection and northward propagation of the bsiso the role of different hydrometeors in modulating these processes remains poorly explored in this study trmm 2a12 retrievals and modern era retrospective analysis for research and applications reanalysis data are examined to establish relationship between cloud hydrometeors and other atmospheric dynamical parameters with the northward propagation of the bsisos the study reveals that the cloud liquid water leads the deep convection during the northward propagation of bsisos in the lower troposphere while the cloud ice slightly lags the convection this distribution indicates the occurrence of a possible mechanism of the lower level moistening through the large scale moisture advection in lower atmosphere and boundary layer pbl convergence followed by triggering of the deep convection the analyses of moisture advection and the dynamical fields with respect to the convection center show that low level moistening is a manifestation of the barotropic vorticity and pbl convergence of moisture anomaly north of the convection center a new internal dynamical thermodynamical mechanism is unraveled to understand the reason behind the middle tropospheric heating maximum and its role on the northward propagation it is shown that the enhanced moisture perturbation in lower levels together with the heat transport by the sub grid scale eddies within the pbl induces lower level instability required to precondition the lower atmosphere for triggering the deep convection vigorous upward motion inside the deep convection uplifts the liquid hydrometeors to upper levels and the formation of precipitable ice leads to the heating maxima in the middle troposphere to check the robustness of the proposed hypothesis similar analysis is performed for the weak northward propagating bsiso cases

geodynamic models of crustal scale episodic tectonic accretion and underplating in subduction zones we investigate the dynamics of crustal scale episodic accretion at convergent margins using a finite element model of subduction the numerical model incorporates effects from flexure subduction loading and large scale variations in material properties the model is used to assess the influence of these parameters on the discrete transfer of units from the lower to the upper plate during subduction the primary controls investigated are spatial variations in density material strength and thickness of material layers these controls correspond to natural examples where episodic accretion results from the thermal structure of subducting lithosphere giving rise to areas of thermally activated ductile creep attempted subduction of small crustal blocks density frictional and or ductile strength variations interaction between well attached basement blocks and overlying detachable sediments and spatial changes in thickness of sediment and crust in the experiments accretion of small continental terranes within a model subduction zone can cause crustal scale fold nappes and shear zones to develop with accompanying tectonic underplating and or frontal accretion the model results may provide insight into real cases of episodic accretion for example the emplacement of the upper penninic nappe stack of the central alps

history of metamorphic fluids along outcrop scale faults in a paleogene accretionary prism sw japan implications for prism scale hydrology 1 synkinematic quartz crystals collected from late stage syn to post cleavage faults in the paleogene shimanto accretionary complex contain fluids that provide constraints on fluid flow within the accretionary wedge in particular the trapped fluids provide a glimpse of intraprism flow during a phase of widespread prism thickening carbonic ch4 co2 rich and aqueous h2o rich inclusions occur intermixed within single crystals that nucleated primarily in releasing stepovers along faults that deform well indurated and or cleaved wallrock invariably the carbonic inclusions contain an aqueous liquid as a perimeter phase and the aqueous inclusions contain a carbonic vapor phase suggesting coeval trapping of unmixed phases from a miscible parent fluid these observations are interpreted to reflect crystal growth following deformation driven dilitation and consequent unmixing of the parent fluid at one location cape oyama the occurrence of ch4 and h2o in the absence of co2 enables explicit constraints to be placed on pressure and temperature conditions during crystal growth these conditions suggest geothermal gradients of 50 c km during late stage faulting our results suggest local intraprism flow that was driven by deformation the scale of flow that is suggested is quite restricted and this leads us to hypothesize that the paleogene shimanto accretionary prism acted largely as a barrier to fluid flow during late stage deformation as a consequence the paleogene rocks probably served to focus fluid escape elsewhere most likely trenchward and arcward the combination of the elevated geothermal gradient which would have contributed to increasing the relative strength of this package of rocks and the lack of fluid pathways within it would have favored the development of new out of sequence thrust faults outboard of the paleogene prism or the reactivation of older more landward structures

high resolution simulation of the boreal summer intraseasonal oscillation in met office unified model the present study investigates the fidelity and resolution sensitivity of met office unified model global atmosphere 3 0 in simulating the intra seasonal oscillation iso of the east asia and western north pacific summer monsoon two sets of model simulations at horizontal resolutions of n216 60km and n96 130km forced by observed daily high resolution sea surface temperature are examined and compared with the observations diagnostic results show that the model can well reproduce the gross spatio temporal features of observed summer iso over the east asia and western north pacific in terms of period dominant reof mode variance northward propagation cycle evolution and vertical structure the intra seasonal change in intensity and position of western north pacific subtropical high and upper troposphere westerly jet associated with the northward propagating isos are also reasonably captured in the model moreover increasing horizontal resolution improves most aspects of the iso simulation especially the intensity and northward propagation of the iso related convection and circulation systems further analysis indicates that the improvement as resolution increases is related to the weakening in background state of east asian summer monsoon which is due to the realistic simulation of land sea thermal contrast at higher resolution model this study suggests that enhanced model resolution can have some beneficial impacts on the iso simulation

quasi periodic oscillations in a symmetric general circulation model abstract long lime integrations with a symmetric version of the clas climate model with hydrology have shown that the hadley circulation has well defined strong and weak episodes this oscillation of the hadley circulation seems to occur in two dominant range of periodicities one with periods between 10 and 15 days and another with periods between 20 and 40 days this quasi periodic behavior of the hadley circulation is seen only when the moist convective heating is determined by dynamics if the latent beating in the atmosphere is prescribed and kept artificially fixed this oscillation of the hadley circulation disappears thus this oscillation of the hadley circulation appears as a result of interactions between moist convective and dynamical processes a wave phenomenon is seen in the lower atmosphere that propagates toward the position of maximum radiative beating this wave perturbation has a length scale of about 15 20 degrees latitude in the north south direction this phenomenon has large ampli

landward vergence and oblique structural trends in the oregon margin accretionary prism implications and effect on fluid flow abstract the central oregon margin spans a regional transition in accretionary structures from seaward verging in the south to landward verging in the north new multichannel seismic mcs data image both landward and seaward vergent provinces along the central and northern oregon margin landward vergence is characterized by a deep decollement with deformation distributed across a broad lower continental slope in a coherent structural style in the landward vergent area virtually all 4 km of incoming trench sediments overthrust the preceding thrust sheet forming fault bend folds and a distinctive ridge trough morphology this style of landward vergence is not explained by existing models in contrast seaward vergence correlates with a shallower decollement approximately 1 4 km above the oceanic crust and a more intense style of deformation within a narrower slope initial thickening of the trench sediments occurs across a well developed protothrust zone the frontal thrust forms a ramp anticline that is cut by a prominent backthrust previously observed seafloor vent sites in both regions correlate with thrusts that exhibit high amplitude reversed polarity reflections suggestive of enhanced porosity along the faults potential fluid sources and migration paths are strongly influenced by changes in the level of the decollement and vergence along the margin abrupt changes in structural style occur both along strike and updip and are bounded by two sets of oblique slip faults three nw striking left lateral faults are imaged in both mcs and seabeam data plunging anticlines developed along the nw striking faults are venting fluids and were previously interpreted as mud volcanoes the deformation front is locally disrupted where these faults intersect the prism but they appear to have limited influence on the structural evolution of the prism in contrast the ne striking right lateral faults are confined to the deforming sediments of the upper plate these faults interact with the thrusts within the prism forming a rhomboidal pattern of three dimensional deformation

seasonality of the structure and propagation characteristics of the mjo the seasonality of the madden julian oscillation mjo is documented in observational data and a nonlinear shallow water model is used to help interpret some of the contrasts in mjo structure between the boreal winter season november march ndjfm and the asian summer monsoon period june september jjas at upper tropospheric levels the flanking rossby waves remain centered around 28 degrees n s year round but they tend to be stronger in the winter hemisphere where the climatological mean jet stream is stronger rendering the subtropical circulation more sensitive to forcing by a near equatorial heat source amplitudes of the mjo related deep convection and lower tropospheric zonal wind are stronger in the summer hemisphere where the column integrated water vapor is larger during ndjfm the equatorial asymmetry is subtle as in the annual mean moisture convergence into swallowtail shaped regions of enhanced deep convection is an integral part of the equatorial rossby wave signature and the eastward propagation is due to moistening of the air to the east of the enhanced convection by poleward moisture advection during the asian summer monsoon in jjas the convection assumes the form of northward propagating west northwest east southeast oriented rainbands embedded within cyclonic shear lines these features are maintained by frictional convergence of moisture and their northward propagation is mainly due to the presence of features in the climatological mean fields that is the west east moisture gradient over india and the arabian sea and the southwesterly low level monsoon flow over the northwest pacific

shortening of analogue models with contractive substrata insights into the origin of purely landward vergent thrusting wedge along the cascadia subduction zone and the deformation evolution of himalayan tibetan orogen abstract origin of certain uncommon fold and thrust belts such as the purely landward vergent rearward vergent thrusting wedge along the cascadia subduction zone and the wide flat toped himalayan tibetan orogen were proposed to be closely related to their ductile substrata results of a series of sandbox models with contractive substrata of various contracting velocities and different contracting directions designed to study the influences of horizontal contraction of ductile substrata on deformation evolution and structural style of fold and thrust belts show that purely rearward vergent thrusting wedges can be reproduced under the condition of syn directionally horizontal contraction of the ductile substrata without other requirements of forward dipping backstops landward dipping detachments and strong wedges relative to weak bases therefore syn directionally horizontal contraction of the ductile substrata can be considered an important cause for the formation of purely landward vergent thrusting wedge along the cascadia subduction zone our modeling results together with the results of some other previous physical and numerical models reinforce the opinion that the deformation evolution of the himalayan tibetan orogen were likely governed by its weak lower crust and suggest that the north and south edges of the himalayan tibetan orogen may have undergone almost synchronous cenozoic deformation evolution owing to the existence of weak lower crust it is also proposed that 1 development of thrusts in the himalayan tibetan orogen may not necessarily occur in a frontward sequence 2 much later uplift deduced from cenozoic sedimentary records in the basins along the northeastern margin of the himalayan tibetan orogen does not necessarily imply much later initiation of uplift and deformation at the northeastern margin of the orogen

forearc structure and morphology along the sumatra andaman subduction zone the sunda subduction margin the location of recent magnitude 8 9 megathrust earthquakes is characterized by major changes in prism and forearc morphology and structure along its 5000 km length on the sumatra andaman section measurements of prism width and surface slope indicate along strike segments inclu1ding abrupt changes of prism morphology 1 a narrow and steep prism between burma and the andamans 2 broad with an averaged gentle slope in the andamans nicobars and north sumatra 3 steep and narrow in central sumatra and 4 wider and less steep offshore south sumatra decreasing in width to west java prism width varies from 90 to 180 km and average surface slope from 1 to 3 with a strong inverse correlation between width and slope also observed globally the prism deviates from typical taper geometry in parts of the margin notably offshore north sumatra where it is characterized by a steep toe and broad plateau along strike changes in morphology are strongly linked to input sediment thickness sections of the prism toe represent key global examples of unusual landward vergent thrusting these sections correspond to a thick sediment input and to a wide prism with shallow surface slope a low basal shear stress or backstop mechanism may drive this style of faulting prism morphology and structure appear to be driven predominantly by input sediment thickness linked to oceanic basement topography with sediment properties plate smoothness and orthogonal subduction rate and obliquity also contributing and no clear role of plate age or dip

what 2 d multichannel seismic and multibeam bathymetric data tell us about the north sumatra wedge structure and coseismic response recent large earthquakes have prompted studies to reevaluate seismicity and rupture propagation behavior along the world s major subduction margins our study area covers the entire fore arc from northwest of northern sumatra to west of simeulue island the southern portion of the 2004 tsunamigenic earthquake rupture zone the accretionary prism width is up to 180 km water depths between 4 5 km near the sunda trench and 1 km on fore arc high the wedge consists of a steep outer slope 5 12 a plateau 100 120 km wide with anticlinal folds spaced 2 15 km apart and a steep inner slope adjacent to the aceh basin analysis of seismic profiles and bathymetry reveal three main structural zones consistent along strike from the trench landward 1 predominantly landward vergent folds 2 mixed vergent folds and 3 predominantly seaward vergent folds this paper uses those zones to propose a geometry of an underlying rigid backstop this backstop is seaward dipping and extends from under the aceh basin to beneath the mixed vergence zone a dynamic backstop possibly exists seaward of the rigid backstop and is responsible for the steep slope of the outer prism indurated accreted sediments form the landward vergence zone along with the possible dynamic backstop beneath the outer wedge and the rigid backstop in the inner wedge all behave as a solid block coseismically this block allows great earthquake rupture to propagate farther seaward toward the sunda trench with resultant hazardous tsunamigenic potential

a unified moisture mode framework for seasonality of the madden julian oscillation abstractthe madden julian oscillation mjo exhibits pronounced seasonality while it is largely characterized by equatorially eastward propagation during the boreal winter mjo convection undergoes marked poleward movement over the asian monsoon region during summer producing a significant modulation of monsoon rainfall in classical mjo theories that seek to interpret the distinct seasonality in mjo propagation features the role of equatorial wave dynamics has been emphasized for its eastward propagation whereas coupling between mjo convection and the mean monsoon flow is considered essential for its northward propagation in this study a unified physical framework based on the moisture mode theory is offered to explain the seasonality in mjo propagation moistening and drying caused by horizontal advection of the lower tropospheric mean moisture by mjo winds which was recently found to be critical for the eastward propagation of the winter mjo is also shown to play a dominant role in operating t

effects of monsoon trough intraseasonal oscillation on tropical cyclogenesis over the western north pacific abstractthe effects of intraseasonal oscillation iso of the western north pacific wnp monsoon trough on tropical cyclone tc formation were investigated using the advanced research weather research and forecasting arw model a weak vortex was specified initially and inserted into the background fields containing climatological mean anomalies associated with active and inactive phases of monsoon trough isos the diagnosis of simulations showed that monsoon trough iso can modulate tc development through both dynamic and thermodynamic processes the dynamic impact is attributed to the lower midtropospheric large scale vorticity associated with monsoon trough iso interactions between cyclonic vorticity in the lower middle troposphere during the active iso phase and a vortex lead to the generation of vortex scale outflow at the midlevel which promotes the upward penetration of friction induced ascending motion and thus upward moisture transport in addition the low level convergence associated with ac

characteristics and mechanisms of the subseasonal eastward extension of the south asian high abstractthis study investigates the features of eastward extension of the south asian high sah and its connection with diabatic heating and rainfall over eastern asia on subseasonal time scales the causes of sah s eastward extension are examined by potential vorticity pv diagnosis with emphasis on the joint role of diabatic heating feedback and midlatitude wave train the sah s eastward extension features eastward propagation of a wave train across eurasia among the wave train the migration of weak high from the western flank of the tibetan plateau tp to the east of tp contributes to the sah s eastward extension at the early stage when the sah approaches its easternmost position a strong negative pv positive geopotential height center prevails to the east of the tp at 200 hpa the associated anomalies in diabatic heating and rainfall include the anomalous heating and above normal rainfall over the south china sea scs and subtropical western pacific occurring 12 days before the sah s eastern

experimental modelling of orogenic wedges a review abstract experimental modelling applied to the study of orogenic wedge dynamics has been a subject of fruitful research for more than 30 years although the technique dates back as far as the early xix th century on one hand several first order parameters controlling the structural evolution of mountain belts have been intensively investigated using the classic tectonic sandbox models the main parameters are the properties of the basal decollement the deforming material the backstop and fluxes kinematics and surface processes on the other hand the morphological evolution of a mountain relief subjected to changing tectonic or climatic forcing has been addressed using another kind of approach called geomorphic models nowadays the literature is extremely rich particularly for the sandbox technique so that it becomes difficult to have an exhaustive view of the effects of the above parameters on mountain evolution in this article we propose a detailed review of the main results obtained using both tectonic and geomorphic approaches our goal is to provide an almost complete state of the art in the experimental study of relief dynamics to guide present and future researchers in their understanding of mountain belt evolution

effects of air sea coupling on the boreal summer intraseasonal oscillations over the tropical indian ocean the effects of air sea coupling over the tropical indian ocean tio on the eastward and northward propagating boreal summer intraseasonal oscillation bsiso are investigated by comparing a fully coupled ctl and a partially decoupled indian ocean pdio experiment using sintex f coupled gcm air sea coupling over the tio significantly enhances the intensity of both the eastward and northward propagations of the bsiso the maximum spectrum differences of the northward eastward propagating bsiso between the ctl and pdio reach 30 25 of their respective climatological values the enhanced eastward northward propagation is related to the zonal meridional asymmetry of sea surface temperature anomaly ssta a positive ssta appears to the east north of the bsiso convection which may positively feed back to the bsiso convection in addition air sea coupling may enhance the northward propagation through the changes of the mean vertical wind shear and low level specific humidity the interannual variations of the tio regulate the air sea interaction effect air sea coupling enhances reduces the eastward propagating spectrum during the negative indian ocean dipole iod mode positive indian ocean basin iob mode and normal years during positive iod and negative iob years such phase dependence is attributed to the role of the background mean westerly in affecting the wind evaporation sst feedback a climatological weak westerly in the equatorial indian ocean can be readily reversed by anomalous zonal sst gradients during the positive iod and negative iob events although the ssta is always positive to the northeast of the bsiso convection for all interannual modes air sea coupling reduces the zonal asymmetry of the low level specific humidity and thus the eastward propagation spectrum during the positive iod and negative iob modes while strengthening them during the other modes air sea coupling enhances the northward propagation under all interannual modes due to the persistent westerly monsoon flow over the northern indian ocean

influence of the pacific japan pattern on indian summer monsoon rainfall abstractthis study discusses the impact of the pacific japan pj pattern on indian summer monsoon ism rainfall and its possible physical linkages through coupled and uncoupled pathways empirical orthogonal function analysis of 850 hpa relative vorticity over the western north pacific wnp is used to extract the pj pattern as the leading mode of circulation variability the partial correlation analysis of the leading principal component reveals that the positive pj pattern which features anticyclonic and cyclonic low level circulation anomalies over the tropical wnp and around japan respectively enhances the rainfall over the southern and northern parts of india the northwestward propagating rossby waves in response to intensified convection over the maritime continent reinforced by low level convergence in the southern flank of westward extended tropical wnp anticyclone increase rainfall over southern peninsular india meanwhile the anomalous moisture transport from the warm bay of bengal due t

effects of the south asian monsoon intraseasonal modes on genesis of low pressure systems over bangladesh abstractthe quasi biweekly oscillation qbw is a dominant intraseasonal mode in summer rainfall over bangladesh active phases of the qbw are often accompanied by low pressure systems lpss such as vortex type lows this study investigated the effects of two intraseasonal modes the qbw and the boreal summer intraseasonal oscillation bsiso on the genesis of lpss over bangladesh during 29 summer monsoon seasons daily lag composites of convection and low level atmospheric circulation were constructed for active phase cases with lpss lps case and without lpss non lps case based on rainfall in the qbw over bangladesh in the qbw mode a westward propagation of an anticyclonic anomaly from the western pacific to the bay of bengal bob is common in both cases however the anticyclonic center in the lps case is located slightly to the east of that in the non lps case which results in stronger cyclonic vorticity over and around bangladesh in contrast the bsiso mode shows an opposite phase between t

mechanisms of meridional propagating high frequency intraseasonal oscillation associated with a persistent rainfall over south china abstractthe present study divides the intraseasonal variations into high frequency intraseasonal oscillation hf iso with a 5 20 day period and low frequency iso lf iso with a 30 60 day period here defined hf iso is heavily different from some previous work because over south china persistent rainfall pr is not only related to the quasi biweekly oscillation 10 20 day period but also connected with the quasi weekly oscillation 5 10 day period associated with a pr over south china during the first half of june 2016 pr1606 the propagating components of the convections are largely attributed to the hf isos moreover both southward and northward propagating hf isos are found in this case over southern china the moisture advection dominated by anomalous flow and mean water vapor plays an important role in the southward propagation of the hf iso and the cloud radiation effect may be also at least partially responsible for the southward shift of the associated convective zone neverthele

influences of northward propagating 25 90 day and quasi biweekly oscillations on eastern china summer rainfall the present study reveals that rainfall anomalies associated with the 25 90 day quasi biweekly tropical convective activity propagates northward northwestward into northern china the yangtze river enhanced rainfall over southern china results directly from enhanced convection propagating northward from the south china sea scs western north pacific wnp strengthened northward water vapor transport and intensified upper level divergence the anomalous anticyclone over scs wnp which is induced by local lower sea surface temperature provides a favorable condition for transporting more moisture to southern china stronger subtropical westerly jet and south asia high strengthen upper level divergence the northward propagating 25 90 day oscillation over eastern china reaches farther north than the quasi biweekly oscillation qbwo the intensity of qbwo in summer rainfall has significantly strengthened over southern china after 1993 but not for the 25 90 day oscillation this is mainly contributed by an interdecadal increase in rainfall over southern china and the yangtze river basin in the wet phases of qbwo the interdecadal enhancement of rainfall associated with the qbwo is attributed to three factors one is lower tropospheric convergence caused by anomalous anticyclone over the wnp and anomalous cyclone over korean peninsula and japan the second is upper tropospheric divergence resulting from strengthening of subtropical westerly jet and the south asia high the last is enhanced ascent over south china through meridional vertical circulation

growth of the south pyrenean orogenic wedge a six step reconstruction of the south pyrenean foreland fold and thrust belt in spain delineates the topographic slope basal dtcollement angie internal deformation and thrust front advance from the early eocene until the end of contractional deformation in the late oligocene style of thrust front advance dip of the basal dtcollement slope of the upper surface and internal deformation are decoupled and not simply related internal deformation increased decreased and maintained surface slope angle at different stages from the onset to the cessation of deformation the basal dtcollement angle decreased overall suggesting translation of the thrust belt onto stronger crust with time taper angle of the pyrenean thrust wedge was fundamentally controlled by the flexural rigidity of the lower plate the relative rate of creation of structural relief in the rear versus the front of the wedge the extent of deposition of eroded material within the deforming wedge and the taper of the pretectonic stratigraphic wedge

convectively coupled kelvin waves in cmip5 coupled climate models this study provided a quantitative evaluation of convectively coupled kelvin waves cckws over the indian ocean and the pacific ocean simulated by 20 coupled climate models that participated in coupled model intercomparison project phase 5 the two leading empirical orthogonal function eof modes of filtered daily precipitation anomalies are used to represent the eastward propagating cckws in both observations and simulations the eigenvectors and eigenvalues of the eof modes represent the spatial patterns and intensity of cckws respectively and the lead lag relationship between the two eof principle components describe the phase propagation of cckws a non dimensional metric was designed in consideration of all the three factors i e pattern amplitude and phase propagation for evaluation the relative rankings of the models based on the skill scores calculated by the metric are conducted for the indian ocean and the pacific ocean respectively two models noresm1 m and mpi esm lr are ranked among the best 20 for both the regions three models inmcm4 mri cgcm3 and hadgem2 es are ranked among the worst 20 for both the regions while the observed cckw amplitude is greater north of the equator in the pacific some models overestimate the cckw ampliutde in the southern hemisphere this bias is related to the mean state precipitation bias along the south pacific convergence zone

air sea interactions of relevance to the itcz analysis of coupled instabilities and experiments in a hybrid coupled gcm the eastern pacific and atlantic have a curious climatic asymmetry relative to the equator whereas the intertropical convergence zone itcz characterized by persistent and heavy rainfall and the warmest surface waters reside north of the equator a cold tongue in sea surface temperature sst occurs at and south of the equator even though the time mean solar radiation is approximately symmetric about the equator in this paper the author investigates the relative role of three types of coupled ocean atmosphere interaction processes the meridional wind sst feedback the evaporation wind feedback and the low level stratus cloud sst feedback in determining the climatic asymmetry relative to the equator this study has two components first a simple analytical model is constructed in which the aforementioned three positive feedback mechanisms are all included in a unified dynamic framework the author s stability analysis indicates that in a reasonable parameter regime the growth rates associated with the three coupled instabilities are of the same order of magnitude suggesting that they are all important in contributing to the climatic asymmetry because of the dependence of the three feedback mechanisms on the existence of a shallow oceanic mixed layer that in turn is a result of equatorial easterlies the existence of the equatorial easterlies is essential for the amplification of the climatic asymmetry next a hybrid coupled general circulation model is used in which a realistic continental and coastal geometry is presented the model starts from an ideal symmetric condition forced only by the annual mean insolation at the top of the atmosphere which is approximately symmetric about the equator in the presence of the three air sea interaction mechanisms the coupled model is capable of reproducing a realistic asymmetric time mean state in the eastern pacific and atlantic the fundamental cause of the asymmetry in the eastern pacific is the tilt of the western coast of the americas which perturbs sst in the vicinity of the coastal region through a so called coastal wind upwelling mechanism the asymmetry in the atlantic on the other hand results from the land ocean thermal contrast between the bulge of northwestern africa and the ocean to the south the ocean atmosphere interactions act as an amplifier to amplify the asymmetry set up by the continental or coastal asymmetry numerical experiments presented here demonstrate the importance of the geographic asymmetries and the ocean atmosphere interactions in determining the preferred climatic position for the itcz

causes of intraseasonal diabatic heating variability over and near the tibetan plateau in boreal summer the structure and evolution features of the first two leading modes of the intraseasonal diabatic heating variability over the tibetan plateau tp during northern summer are investigated using reanalysis and observational data both of the leading modes present a dominant 10 30 day intraseasonal oscillation iso the first mode is characterized by a perturbation center over the southern tp stp which remains quasi stationary and is closely related to the low latitude iso the associated low latitude iso is originated from the tropical western pacific wp and propagates westward northwestward toward northwestern india along the mean monsoon trough the westward propagation near the south china sea is mainly attributed to anomalous meridional vorticity advection and the advection of the planetary vorticity by iso flow the stationary feature of the perturbation over the stp is ascribed to the topographical features around the stp the intraseasonal heating variability over the stp is attributed to the alternation of anticyclonic and cyclonic flow associated with the westward propagating iso perturbation originated from the tropical wp the second leading mode is characterized by an east west asymmetric structure over the tp the intraseasonal diabatic heating anomaly propagates clockwise from the northwestern to eastern tp while a heating anomaly with an opposite sign propagates from the southeastern to western tp the mid latitude rossby wave trains play an essential role in forming the dipole structure the wave trains propagate southeastward before reaching the tp and then eastward as they cross the tp the source of anomalous water vapor over the tp is originated from lower latitudes the upper and lower level wave trains are well coupled over the tp exhibiting a baroclinic structure

coupled model simulations of boreal summer intraseasonal 30 50 day variability part 1 systematic errors and caution on use of metrics boreal summer intraseasonal 30 50 day variability bsisv over the asian monsoon region is more complex than its boreal winter counterpart the madden julian oscillation mjo since it also exhibits northward and northwestward propagating convective components near india and over the west pacific here we analyze the bsisv in the cmip3 and two cmip2 coupled ocean atmosphere models though most models exhibit eastward propagation of convective anomalies over the indian ocean difficulty remains in simulating the life cycle of the bsisv as few represent its eastward extension into the western central pacific as such few models produce statistically significant anomalies that comprise the northwest to southeast tilted convection which results from the forced rossby waves that are excited by the near equatorial convective anomalies our results indicate that it is a necessary but not sufficient condition that the locations the time mean monsoon heat sources and the easterly wind shear be simulated correctly in order for the life cycle of the bsisv to be represented realistically extreme caution is needed when using metrics such as the pattern correlation for assessing the fidelity of model performance as models with the most physically realistic bsisv do not necessarily exhibit the highest pattern correlations with observations furthermore diagnostic latitude time plots to evaluate the northward propagation of convection from the equator to india and the bay of bengal also need to be used with caution here incorrectly representing extratropical tropical interactions can give rise to apparent northward propagation when none exists in association with the eastward propagating equatorial convection despite these cautions the use of multiple cross checking diagnostics enables the fidelity of the simulation of the bsisv to be meaningfully assessed

control of folding by gravity and matrix thickness implications for large scale folding 1 we show that folding of a non newtonian layer resting on a homogeneous newtonian matrix with finite thickness under influence of gravity can occur by three modes 1 matrix controlled folding dependent on the effective viscosity contrast between layer and matrix 2 gravity controlled folding dependent on the argand number the ratio of the stress caused by gravity to the stress caused by shortening and 3 detachment folding dependent on the ratio of matrix thickness to layer thickness we construct a phase diagram that defines the transitions between each of the three folding modes our priority is transparency of the analytical derivations e g thin plate versus thick plate approximations which permits complete classification of the folding modes involving a minimum number of dimensionless parameters accuracy and sensitivity of the analytical results to model assumptions are investigated in particular depth dependence of matrix rheology is only important for folding over a narrow range of material parameters in contrast strong depth dependence of the viscosity of the folding layer limits applicability of ductile rheology and leads to a viscoelastic transition our theory is applied to estimate the effective thickness of the folded central asian upper crust using the ratio of topographic wavelength to moho depth phase diagrams based on geometrical parameters show that gravity does not significantly control folding in the jura and the zagros mountains but does control folding in central asia applicability conditions of viscous and thin sheet models for large scale lithospheric deformation derived in terms of the argand number have implications for the plate like style of planetary tectonics

cloud regime evolution in the indian monsoon intraseasonal oscillation connection to large scale dynamical conditions and the atmospheric water budget we examine the intraseasonal oscillation iso of the indian summer monsoon to establish the connections of cloud regimes to large scale dynamical states defined by dynamical convergence and moisture advection over the indian subcontinent the developing phase toward iso peaks rainfall maximum is associated with positive anomalies of moisture advection leading in 4 6 days to positive anomalies of dynamical convergence triggering abrupt transitions from shallow cumulus to deep convections in 1 2 days the decaying phase toward iso troughs rainfall minima is associated with negative anomalies of moisture advection and decreasing dynamical convergence accompanying opposite transitions in cloud regimes due to northward propagation of anomalies processes over the indian ocean are similar but lead those over the subcontinent by 10 days during the transitions cirrus clouds always accompany but lag deep convective clouds by 10 days over the equatorial indian ocean cirrus clouds are modulated by equatorial waves

fault kinematics and past plate motions at a convergent plate boundary tertiary shimanto belt southwest japan early and late stage outcrop scale faults have been documented in paleogene strata of the muroto peninsula of southwest japan the former were active early in the consolidation history of the sediment and are crosscut by the latter which were active after regional scale imbrication folding and penetrative deformation i e regional spaced pressure solution cleavage orientation distributions of striae and kinematic axes indicate that the two generations of faults reflect distinct kinematic regimes the orientations and crosscutting relations indicate a counterclockwise viewed downward rotation of the principal shortening direction between early and late stage faulting existing fossil and radiometric age data suggest this transition occurred during eocene oligocene time the fault kinematic data are interpreted to reflect a change in relative plate motions between eurasia and an oceanic plate subducting beneath eurasia in paleogene time these results coupled with existing paleothermal and paleopressure data are consistent with the presence of a spreading ridge in the western pacific basin during this time

structures and mechanisms of the northward propagating boreal summer intraseasonal oscillation abstract the spatial and temporal structures of the northward propagating boreal summer intraseasonal oscillation bsiso are revealed based on the analysis of both the echam4 model simulation and the ncep ncar reanalysis the bsiso structure and evolution characteristics simulated by the model bear many similarities to those derived from the ncep ncar reanalysis the most notable features are the remarkable meridional asymmetries relative to the bsiso convection in the vorticity and specific humidity fields a positive vorticity perturbation with an equivalent barotropic structure appears a few latitude degrees north of the convection center the maximum specific humidity also shows a clear northward shift in the lower troposphere two internal atmospheric dynamics mechanisms are proposed to understand the cause of the northward propagation of the bsiso the first is the vertical shear mechanism the key process associated with this mechanism is the generation of barotropic vorticity due to the couplin

mechanical role of backstops in the growth of forearcs we use numerical and laboratory modeling to analyze the mechanical role of backstops in the overriding plate at subduction zones a backstop is defined as a region within a forearc that has significantly greater shear strength than the sediment lying farther trenchward it can be thought of as the bulldozer behind an accretionary wedge we calculate the stress and displacement fields within forearcs for various backstop models using the finite element method and we simulate deformation over a backstop using a small scale laboratory model in this way we model the effects of the mechanical properties and geometry of a backstop on forearc structures we find that the growth of an outer arc high the development of an inner deformation belt with landward vergence and the seemingly paradoxical presence of an undeformed forearc basin within an otherwise highly deformed forearc can be explained by assuming the existence of a geometrically simple backstop with geologically reasonable contrasts in mechanical properties compared to the sediments just trenchward of it the structures produced in our numerical models are quite insensitive to the rheology boundary conditions and exact mesh geometry employed the general types of structures observed in the laboratory models depend only weakly upon the strength and the geometry of the backstop these results suggest that a detailed picture of an underlying backstop cannot be determined from surface information alone backstops in which the contact with the accretionary wedge dips arcward rather than trenchward however should produce only slightly different forearc structures with less development of both the outer arc high and the landward vergent inner deformation belt although natural forearcs are far more complex than our simple models they exhibit many of the same features indicating that relatively simple backstop mechanics may be a very important factor in the overall growth of forearcs

effect of overburden thickness on thrust belt geometry and development laboratory sand models simulating development of thrust belts indicate that 1 distance between the backstop and the first formed thrust is a linear function of initial sand layer thickness 2 spacing between the first two thrusts is most likely a nonlinear function of initial sand layer thickness 3 initial dip of successive ramps decreases progressively toward the foreland because of variations in principal stress directions with depth and or changes of mechanical properties of sand with increasing overburden 4 faults to the hinterland steepen and become less active as hinterland thrust sheets undergo penetrative shear during sand wedge growth and 5 new ramp initiation occurs to the hinterland of the basal detachment tip line these observations can be interpreted both in context of area balance considerations and soil mechanics theory if initial sand layer thicknesses in our models represent syntectonic overburden in natural thrust belts i e distance between the ground surface and the detachment then our results suggest that locations of some thrust belt salients are controlled by along strike variations in stratigraphic thicknesses and that initial thrust spacing decreases progressively to the foreland if the thrust belt involves a foreland tapering basin furthermore our sand model observations suggest that the concept of a fixed rigid backstop in the hinterland of thrust belts may be misleading as a consequence of thickening the hinterland portion of the thrust belt becomes stabilized and effectively becomes the backstop itself

the evolution of planetary scale 200 mb divergent flow during the fgge year a descriptive study of the large scale horizontally divergent wind field during the fgge year is presented using empirical orthogonal functions eofs of the 200 mb velocity potential the mean flow and annual cycle are shown to be realistically related to climatological features these and large scale patterns represented by the eofs are consistent with very similar patterns of opposite sign seen at 850 mb the main result of this work is the clear description of an eastward propagating wave in the 200 mb divergences with zonal wavenumber 1 and period 30 50 days this mode has been deduced in other studies and related to variability in the asian summer monsoon these results show it to exist throughout the fgge year and imply that a relationship exists between the planetary scale eastward propagating mode and smaller scale divergence bands apparently propagating northward over the monsoon region

petrology and provenance of the cretaceous kodiak formation alaska petrographic analysis of 30 sandstone samples from the cretaceous kodiak formation indicates that they consist mainly of intermediate to basic volcanic and plutonic detritus derived from a source area east of kodiak island this source area had extensive volcanic cover with rare exposure and weathering of cogenetic plutons the petrology of the kodiak formation is similar to that of related rocks in the alaskan peninsula and is indicative of the longevity of the volcano plutonic source area

earthquakes along the ryukyu kyushu arc strain segmentation lateral compression and the thermomechanical state of the plate interface we systematically determined the focal depths and mechanisms of 49 large to moderate sized earthquakes mb 5 4 that occurred along the ryukyu kyushu arc since 1963 by inverting the waveforms and amplitudes of p and sh wave trains at teleseismic distances the results are sufficiently precise to delineate seismogenic structures near the plate interface in detail revealing features not predicted by plate kinematics in contrast to previous studies of this arc and those along other subduction zones shallow seismicity along the plate interface is systematic showing two distinct layers of activities the second layer of seismicity is delineated by a few earthquakes that occurred at depths between 50 and 65 km some 10 20 km directly beneath the seismogenic portion of the interplate thrust zone these earthquakes indicate lateral compressional strain within the subducted slab as their p axes are subparallel to the local strike of the arc not perpendicular to the arc as one would expect from the direction of plate convergence the occurrence of these events cannot be accounted for by membrane stress due to the geometry of the subducted slab to our knowledge similar earthquakes occurred only beneath the northern indoburman ranges and along the banda arc where subducted slabs as part of the indian plate are being dragged northward with their northern edges bumping into east west trending collision zones nearby by drawing an analogy between the tectonic settings of these three regions we interpret events beneath the plate interface along the ryukyu kyushu arc as a consequence of ongoing collision between the philippine sea plate and eurasia near taiwan the interplate thrust zone is largely aseismic down to a depth of approximately 30 km a large number of earthquakes showing low angle thrust faulting commence at this depth and are accompanied by two events that show antithetic thrust faulting at a slightly shallower depth of 20 25 km these observations suggest that the strength of the plate interface increases significantly below the depth of proximately 25 5 km based upon available heat flow measurements between the trench axis and the volcanic arc we estimated the temperature field and magnitude of shear traction along the interplate thrust zone the deepest interplate earthquakes 40 50 km correspond to temperatures of approximately 730 980 c comparable to the limiting temperature of intraplate mantle earthquakes 800 c and that of intermediate and deep focus earthquakes at wadati benioff zones potential temperature 900 k therefore the cessation of seismicity in general is probably controlled by similar temperature conditions regardless of the tectonic settings of source regions the magnitude of shear traction along the seismogenic portion 40 50 km depth of the interplate thrust zone seems to be of the order of 100 mpa which in turn implies a low average coefficient of friction of only 0 10 0 05 considerably less than those observed for laboratory specimens the inception of intermediate focus earthquakes within the subducted slab is at a depth of about 100 km whereas shallow earthquakes show no apparent variations along the entire arc intermediate depth earthquakes indicate downdip extension along the northern end of the arc near kyushu but abruptly change to downdip compression along the rest of the arc all available evidence indicates that this is a spatial pattern unrelated to earthquake cycles at the moment tectonic interpretation of such a distinct strain segmentation along the arc is enigmatic without the presence of clear discontinuities in the age of the subducted slab the sudden switch in the strain field of the slab is difficult to explain by the continuously varying rate of subduction along the arc in any case this pattern of strain segmentation requires the presence of a major accommodation structure such as a tear fault in the subducted slab near the tokara channel appendix is available with entire article on microfiche order from american geophysical union 2000 florida ave n w washington dc 20009 document b91 004 2 50 payment must accompany order

episodic accretion and strain partitioning in a model sand wedge we model led thrust wedge accretion and deformation partitioning in a passively layered sand detached and shortened above a smooth rigid decollement the thrust wedge accretes in piggyback style during forward advance of a rear wall the passively layered sand accommodates the shortening penetratively by kinking ramp folding and by imbrication in single layers the style of compression changes with time and or stratigraphic position within the sand prism initial penetrative layer shortening above a slipped zone of decollement is succeeded by formation of monoclinal or conjugate shear bands at temporary terminations of decollement the shear bands subsequently narrow down and lock as thrust ramps the model sand wedge accrets episodically rather than steadily episodicity is controlled by the stick slip mode of decollement propagation and by volume loss and compaction of the wedge material in response to convergence this results in formation of a wedge with a convex upwards cross sectional topography

identification of the static backstop and its influence on the evolution of the accretionary prism in the nankai trough abstract to reveal the origin of a backstop and its influence on the evolution of the accretionary prism we analyzed reflection seismic data acquired in the nankai trough off the kii peninsula the deformation features of the forearc basin sequence show that the landward accretionary prism close to the coast was not deformed after the development of the forearc basin about 2 4 ma the surface of the landward prism can be identified as strong amplitude reflector indicating that the landward prism has higher seismic velocity therefore the landward accretionary prism inferred to be of higher strength constitutes a static backstop based on seismic and geologic observations we interpret that the backstop was generated due to the large age differences of accreted material resulting from an inferred hiatus in subduction between 13 and 6 ma the time dependent processes such as the igneous activity in middle miocene further contribute to the development of the backstop a ridge structure beneath the forearc basin located trenchward of this backstop and running roughly parallel to it appears to reflect activity on an ancient splay fault the strike of the ancient splay fault runs parallel to the backstop identified in this study and oblique to the current trench this geometry suggests that location and mechanical behavior of this splay fault system is influenced by the backstop and its distribution could be related to the coseismic rupture area

non coulomb wedges wrong way thrusting and natural hazards in cascadia landward vergence in accretionary wedges is an uncommon phenomenon not readily explained by classical mohr coulomb critical wedge theory predominantly landward vergent thrust faults are observed along the cascadia convergent margin from 45 n to 48 n we present depth migrated multichannel seismic images of the internal structure of the accretionary wedge offshore washington collected during the orwell project in 1996 these reveal a high p wave velocity 4 km s basal layer that thickens landward and serves as a decollement for a series of overlying landward vergent thrust faults analog modeling using a ductile basal layer consisting of silicone putty produces an array of trenchward propagating landward vergent thrusts and offers a plausible mechanical model for the evolution of these structures the rheological properties of a basal calcareous mudstone layer offshore cascadia are discussed in relation to the mechanics of landward vergence and to rapid loading due to the prograding nitinat and astoria deep sea fans a viscoelastic layer beneath the accretionary wedge is considered to be capable of rupturing during great interplate earthquakes and thus represents an increased risk for both the maximum size of such an event and for the generation of tsunamis

subseasonal intensity variation of the south asian high in relationship to diabatic heating observation and cmip5 models this study investigates the subseasonal intensity variation of south asian high sah and the dynamic linkage with precipitation induced diabatic heating during the summer of 1979 2005 based on the observation and 18 models from the coupled model intercomparison project cmip5 the sah s intensity variation with a period of approximately 10 36 days is identified both in the observation and 18 models by performing an empirical orthogonal function eof analysis on the standardized subseasonal anomalies in geopotential height at 100 hpa over the sah s main body region with the observed strengthening of the sah an enhanced rainfall belt between 70 120 e migrates northward from the equatorial region the northward propagating rainfall belt occupies almost the whole indian subcontinent indochina peninsula and subtropical east asian regions between 20 40 n when the sah reaches the strongest the relative vorticity diagnosis reveals the dynamical linkage between the subseasonal sah s intensity variation and the precipitation anomalies over the asian monsoon region 1 the observed northward propagating rainfall band forms a horizontal gradient of diabatic heating favoring an enhancement of the sah over its southern part 2 when the rainfall band approaches the regions of south and east asia between 20 40 n the increased vertical gradient of diabatic heating in the upper level contributes significantly to the intensification of the sah 3 the horizontal advection process favors the westward expansion of the sah the observation to model comparisons indicate that the model s capacity to reproduce the sah s intensity variation is highly associated with simulations of the anomalous rainfall band and its northward propagation a realistic reproduction of precipitation anomalies is fundamental to simulating the dynamical processes related to diabatic heating and thus the simulation of the sah s subseasonal intensity variation

loci and maximum size of thrust earthquakes and the mechanics of the shallow region of subduction zones earthquakes do not extend updip along the plate interface at most subduction zones all of the way to the plate boundary at the trench axis or deformation front rather the shallowest part of that interface moves mainly through stable aseismic slip that part of the plate boundary referred to here as the aseismic zone occurs along the base of an accreted wedge of young sediments the probable primary cause for the existence of this aseismic zone is the stable slip properties of the unconsolidated and semiconsolidated sediments in that zone subducted sediment is progressively dewatered and underplated to the base of the overriding plate through this process more consolidated rocks eventually come into contact at depth across both sides of the plate boundary from the point where sufficiently hard rock is found across the plate interface that interface will change its slip behavior to unstable stick slip sliding which is characteristic of consolidated material under most conditions this type of motion is accommodated seismically as episodic slip in large earthquakes the location of this transition to seismic behavior referred to as the seismic front marks the deep end of the aseismic zone and the top of the seismogenic zone i e that part of the plate interface that moves primarily in thrust earthquakes several convergent plate margins are discussed to illustrate the seismic front and the aseismic zone we find that the seismic front defined by smaller earthquakes that occur during the interval between large events is nearly the same as that for large events as inferred from the locations of their aftershocks the location of the seismic front is important for making estimates of the maximum possible size of thrust earthquakes along the plate boundary because it delimits the trenchward limit of the potential rupture area of these events the size of large thrust earthquakes is proportional to rupture area and to at least the cube of the downdip width w of that area thus by defining the location of the seismic front for convergent margins it is possible to make better estimates of w and hence to deduce the maximum size of future interplate earthquakes the average repeat time of such events is also related to w and so better estimates of average repeat time are possible from improved knowledge of w the hypothesis that the location of the seismic front is related to the maximum depth of subduction of unconsolidated sediment has implications for forearc mechanics we use a mechanical analysis laboratory modeling and multichannel seismic information to develop a simple model explaining the growth of forearcs the outer arc high or trench slope break that occurs arcward of most accretionary wedges represents an abrupt change in the critical taper of the accretionary wedge we argue that that change is caused by a large arcward increase in the strength of the material within the overriding plate that stronger material is called the backstop our laboratory modeling experiments indicate that a backstop with a trenchward dipping upper surface results in the development of an overlying structure that includes all of the primary morphologic features observed in modern forearcs in our modeling an accretionary wedge develops trenchward of the backstop an outer arc high develops above the trenchward toe of the backstop and farther arcward a passive forearc basin forms above the stronger material of the backstop this model is consistent with the observation that earthquakes do not extend updip along the plate interface all the way to the trench axis we hypothesize that plate motion is accommodated seismically along the base of the consolidated backstop and mostly or entirely aseismically trenchward of the toe of the backstop along the base of the accretionary wedge at several margins the seismic front is approximately coincident with the outer arc high supporting this interpretation

linkage between interannual variation of the east asian intraseasonal oscillation and mei yu onset abstractthe mei yu onset over the middle to lower reaches of the yangtze river valley mlyrv varies considerably from early june to mid july which leads to large interannual changes in rainy seas

poleward propagating intraseasonal monsoon disturbances in an intermediate complexity axisymmetric model abstract a model of intermediate complexity based on quasi equilibrium theory a version of the quasi equilibrium tropical circulation model with a prognostic atmospheric boundary layer as well as two free tropospheric modes in momentum and one each in moisture and temperature is used in a zonally symmetric aquaplanet configuration to simulate aspects of the south asian monsoon and its variability key qualitative features of both the mean state and the 30 60 day mode of the intraseasonal variability are simulated satisfactorily the model has two limit cycles of similar period and structure that can account for this mode both feature northward propagation of the tropical convergence zone from 5 s to 25 n with a period of about 50 days the dynamics of the oscillations are investigated the system reaches a hopf bifurcation when the asymmetry of the sea surface temperature sst forcing is increased beyond the bifurcation the mean flow is linearly unstable and the one linearly unstable mode is simila

extremely late onset of the 2018 south china sea summer monsoon following a la nina event effects of triple sst anomaly mode in the north atlantic and a weaker mongolian cyclone

multi scale interactions of equatorial waves associated with tropical cyclogenesis over the western north pacific the tropical cyclone tc centric approach developed in previous studies tends to overemphasize the direct impact of tropical waves and underestimates their large scale modulation of western north pacific wnp tropical cyclogenesis tcg to overcome these limitations this study proposes a new approach based on empirical orthogonal function analyses to re examine associations of multiple waves including the madden julian oscillation mjo quasi biweekly oscillation qbwo convective equatorial rossby er waves and synoptic scale waves ssws with wnp tcg events there is a close association between wnp tcg events total of 273 tcs in this study and ssws 64 mjo 68 qbwo 64 and er 65 waves these suggest that ssw is critical for many tcg events and all of these intra seasonal waves significantly modulate tcg events a majority of tcs 79 were found to be related to more than one wave type indicating an important role for a combination of dynamic and thermodynamic conditions associated with multiple waves in tcg events further analyses show that ssw activity is strongly modulated by the mjo and er waves while the qbwo has no significant impact on ssws during convectively active mjo and er phases stronger ssw trains with more distinct southeast northwestward aligned structures can be found compared to convectively inactive phases similar intra seasonal modulation of the transition from the mixed rossby gravity waves from the equatorial central pacific to the ssw trains over the wnp by the three waves is noted with such transitions largely favored during convectively active mjo and er phases

the boreal summer intraseasonal oscillation relationship between northward and eastward movement of convection the summertime intraseasonal oscillation iso is an important component of the south asian monsoon lagged regressions of intraseasonally filtered 25 80 days outgoing longwave radiation olr reveal that centers of convection move both northward and eastward from the central equatorial indian ocean subsequent to the initiation of an iso eastward movement of convection is also seen at indian subcontinent latitudes 10 8 208n based on the regression results the summertime iso convection signal appears as a band tilting northwestward with latitude and stretching from the equator to about 208n viewed along any meridian convection appears to propagate northward while equatorial convection propagates to the east to examine the robustness of the connection between eastward and northward movement individual isos are categorized and composited relative to the strength of the large scale eastward component of convection in the central equatorial indian ocean it is found that the majority of isos that exhibit northward movement onto the indian subcontinent 42 out of 54 isos or 78 also exhibit eastward movement into the western pacific ocean it is also found that when convection in the central indian ocean is not followed within 10 20 days by convection in the western pacific ocean 12 out of 54 isos or 22 the independent northward movement of convection in the indian ocean region is somewhat stunted the link between the eastward and northward movement of convection is consistent with an interpretation of the summertime iso in terms of propagating equatorial modes the northward moving portion of convection is forced by surface frictional convergence into the low pressure center of the rossby cell that is excited by equatorial iso convection a similar convergence pattern is seen for the northern winter iso but it does not generate poleward movement due to relatively cool ssts underlying the surface convergence

continental margin tectonics forearc processes recent studies of convergent plate margins and the structural development of forearc terranes are summarized in a critical review of u s research from the period 1987 1990 topics addressed include the geometry of accretionary prisms coulomb wedge taper and vertical motion in response to tectonic processes offscraping vs underplating or subduction the response to oblique convergence fluids in forearc settings the thermal framework and the effects of fluid advection and serpentinite seamounts also included is a comprehensive bibliography for the period

mechanisms of monsoon low frequency variability surface hydrological effects abstract observations indicate that monsoon systems are characterized by orderly large scale and low frequency variations with a time scale of two weeks and sometimes longer regions of ascending motion are observed to form to the north of the equator and propagate slowly northward across southeast asia the propagation appears to be associated with the active break sequence of the summer monsoon which acts as a modulator on the activity of the synoptic scale disturbances a zonally symmetric non linear two layer model containing an interactive ocean and a continent poleward of 18 n is used to investigate the mechanisms which produce the observed low frequency variability only when a full hydrology cycle is considered does the model product variations which resemble the observed structures mechanisms are traced to include the interaction of the components of the total heating function the sensible heat input in the boundary layer although considerably smaller than the other heating components de

basement slivers within the new britain accretionary wedge implications for the emplacement of some ophiolitic slivers using multichannel seismic data from the western solomon sea we have imaged several 2 5 to 3 km thick oceanic basement slivers within the new britain accretionary wedge which may serve as a modern analogue for the detachment of some ophiolitic slivers the most recently accreted basement sliver is located just over 5 km from the thrust front an approximate area balance indicates the subjacent section of the downgoing plate from which this sliver originated is between 11 km and 15 km arcward of its present position though we have not imaged the basement ramp sedimentary strata beneath the basement sliver pinch out between 9 and 12 km from its seaward edge suggesting that detachment occurred in that vicinity normal faults reactivated in response to the flexural bending of the downgoing oceanic plate are a prominent feature of this region significantly almost all basement normal faults near the recently accreted basement sliver including those imaged beneath the toe of the wedge dip arcward based on these data we suggest that small 1 3 km thick basement slivers are decoupled along favorably oriented preexisting zones of weakness formed by normal fault detachments within the oceanic basement

heat flow and thermal structure of the washington oregon accretionary prism a study of the lower slope heat flow measurements across the washington oregon convergent margin show several characteristic features a well defined peak at the foot of the overthrust a gradual decrease landward across the lower slope reaching a minimum at the ridge and a gradual rise further landward constrained by geological and seismic evidence on the rate of stacking and the dimension of stacked thrust sheets and by drilling results on sediment properties we use a two dimensional time dependent finite element procedure to model the stacking of overthrust slices of sediments and to calculate the thermal structure beneath the lower slope of the accretionary prism the calculated heat flow profile is in good agreement with the measurements advective heat transfer due to stacking of overthrust sheets and topographic changes are shown to play a dominant role in controlling the surface heat flow and the thermal state of the accretionary prism

mechanism for northward propagation of boreal summer intraseasonal oscillation convective momentum transport 1 this study demonstrates that the momentum transport by cumulus convection plays a significant role in the organization and northward propagation of intraseasonal iso convection anomalies over the indian and western pacific regions during boreal summer a version of seoul national university s atmosphere ocean coupled general circulation model simulates northward propagation when convective momentum transport cmt is implemented the northward propagation disappears when cmt is disabled an axially symmetric shallowwatermodel withaparameterized cmtis used to understand the role of cmt in the northward propagation of iso the basic mechanism of northward propagation is the lower level convergence to the north of convection which is induced by the secondary meridional circulation associated with large momentum mixing by convection in the region of large mean vertical shear a large meanverticalshearexistsinsouthasianregionduringboreal summer citation kang i s d kim and j s kug 2010 mechanism for northward propagation of boreal summer intraseasonal oscillation convective momentum transport geophys res lett 37 l24804 doi 10 1029 2010gl045072

evidence for fluid circulation overpressure and tectonic style along the southern chilean margin the southern chilean convergent margin between 50 and 57 s is shaped by the interaction of the three main plates antarctic south america and scotia north of 53 s the convergence between antarctic and south america plates is close to orthogonal to the continental margin strike here the deformational style of the accretionary prism is mainly characterized by seaward verging thrusts and locally by normal faults and fractures a very limited lateral extension of prism a very shallow dip 6 decollement and subduction of a thick and relatively undeformed trench sedimentary sequence south of 53 s convergence is oblique to the margin locally the trench sediments are proto deformed by double vergence thrusting and the front of the prism grows through landward verging thrusting the decollement is sub horizontal and deep involving most of the sediment over the oceanic crust in the accretionary process building a comparatively wide and thicker prism a bottom simulating reflector is present across the whole prism to the abyssal plan suggesting the presence of gas in the sediments the analysis of p and s wave velocity reflectivity sections derived by amplitude versus offset technique avo detailed velocity information and the velocity derived sediment porosity have been integrated with the structural analysis of the accretionary prism of two selected pre stack depth migrated seismic lines aiming to explain the relation between fluid circulation and tectonics accretion along double vergence thrust faults may be associated with the presence of overpressured fluid which decreases the effective shear stress coefficient along the main decollement and within the sediments and modify the rheolgical properties of rocks the presence of an adequate drainage network represented by interconnected faults and fractures affecting the entire sedimentary sequence can favour the escape of pore fluid toward the sea bottom while less permeable and not faulted sediments can favour fluid accumulations gravitational and tectonic dewatering and stratigraphy could control the consolidation and the pore overpressure of sediments involved in subduction along the trench the results of our analysis suggest the existence of a feedback between tectonic style and fluid circulation

the 30 50 day mode at 850 mb during monex abstract the analyzed wind field at 850 mb during the summer monsoon experiment monex is subjected to a time series analysis to confirm the existence of a peak in the time range of 30 50 days having established that this study presents a mapping of the motion field for this time scale in this short paper we illustrate the steady meridional propagation of a train of troughs and ridges that seem to form near the equator and dissipate near the himalayas the meridional scale of this mode is around 300 km and its meridional speed of propagation is 0 75 latitude per day the amplitude of the wind for this mode is around 3 6 m s 1 the salient contributions here are the mapping and the demonstration of a very regular behavior of this mode its existence is here noted from a period well before the onset of monsoon i e from early may to late july three major storms during monex were noted to form within the trough line of this system and the period of major cessation of rains over the indian subconti

deepwater fold and thrust belt classification tectonics structure and hydrocarbon prospectivity a review abstract deepwater fold and thrust belts dwftbs are classified into near field stress driven type 1 systems confined to the sedimentary section and type 2 systems deformed by either far field stresses alone or mixed near and far field stresses dwftbs can occur at all stages of the wilson cycle up to early stage continent continent collision type 1 systems have either weak shale or salt detachments they occur predominantly on passive margins but can also be found in convergent related areas such as the mediterranean and n borneo examples include the niger and nile deltas the west coast of africa and the gulf of mexico type 2 systems are subdivided on a tectonic setting basis into continent convergence zones and active margin dwftbs continent convergence zones cover dwftbs developed during continent arc or continent continent collision and those in a deepwater intracontinental setting e g w sulawesi makassar straits active margins include accretionary prisms and transform margins the greatest variability in dwftb structural style occurs between salt and shale detachments and not between tectonic settings changes in fold amplitude and wavelength appear to be more related to thickness of the sedimentary section than to dwftb type in comparison with shale salt detachment dwftbs display a lower critical wedge taper more detachment folds long and episodic duration of deformation and more variation in vergence structures unique to salt include canopies and nappes accretionary prisms also standout from other dwftbs due to their relatively long continuous duration rapid offshore propagation of the thrust front and large amount of shortening in terms of petroleum systems many similar issues affect all dwftbs these include the oceanward decrease in heat flow offshore increase in age of mature source rock and causes of trap failure e g leaky oblique and frontal thrust faults breach of top seal by fluid pipes one major difference between type 1 and type 2 systems is reservoir rock high quality continent derived quartz rich sandstones are generally prevalent in type 1 systems more diagenetically reactive minerals derived from igneous and ophiolitic sources are commonly present in type 2 systems or many are simply poor in well developed turbidite sandstone units however some type 2 systems particularly those adjacent to active orogenic belts are partially sourced by high quality continent derived sandstones e g nw borneo s caspian sea columbus basin in some cases very high rates of deposition in accretionary prisms adjacent to orogenic belts coupled with uplift due to collision results in accretionary prism related fold belts that pass laterally from sub aerial to deepwater conditions e g s caspian sea indo burma ranges the six major hydrocarbon producing regions of dwftbs worldwide gulf of mexico niger delta nw borneo brazil west africa s caspian sea stand out as differing from most other dwftbs in certain fundamental ways particularly the very large volume of sediment deposited in the basins and or the great thickness and extent of salt or overpressured shale sdetachments

landward vergence in accretionary prisms the role of the backstop and thermal history the accretionary histories recorded along the convergent margins in southwest alaska and southwest japan are punctuated by two anomalous events near trench magmatism closely associated in time and space with landward structural vergence in both areas the near trench magmatism is believed to be related to the subduction of an active spreading center it is postulated that these anomalous thermal events caused the backstop i e mechanical boundary within the prism to be reoriented to a seaward instead of a landward dip this seaward dipping backstop resulted in the development of landward verging structures for the only time in the almost 100 m y history of these two margins a modern analog may be the washington convergent margin these examples illustrate the potential importance of thermal history and the dip of the backstop in controlling the style of accretion in submarine wedges

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

ocean atmosphere coupling in the monsoon intraseasonal oscillation a simple model study a simple coupled model is used in a zonally symmetric aquaplanet configuration to investigate the effect of ocean atmosphere coupling on the asian monsoon intraseasonal oscillation the model consists of a linear atmospheric model of intermediate complexity based on quasi equilibrium theory coupled to a simple linear model of the upper ocean this model has one unstable eigenmode with a period in the 30 60 day range and a structure similar to the observed northward propagating intraseasonal oscillation in the bay of bengal west pacific sector the ocean atmosphere coupling is shown to have little impact on either the growth rate or latitudinal structure of the atmospheric oscillation but it reduces the oscillation s period by a quarter at latitudes corresponding to the north of the indian ocean the sea surface temperature sst anomalies lead the precipitation anomalies by a quarter of a period similarly to what has been observed in the bay of bengal the mixed layer depth is in phase opposition to the sst a monsoon break corresponds to both a warming and a shoaling of the mixed layer this behavior results from the similarity between the patterns of the predominant processes wind induced surface heat flux and wind stirring the instability of the seasonal monsoon flow is sensitive to the seasonal mixed layer depth the oscillation is damped when the oceanic mixed layer is thin about 10 m deep or thinner as in previous experiments with several models aimed at addressing the boreal winter madden julian oscillation this suggests that the weak thermal inertia of land might explain the minima of intraseasonal variance observed over the asian continent

a model for the boreal summer intraseasonal oscillation abstract the tropical intraseasonal oscillation iso exhibits pronounced seasonality the boreal summer iso is more complex than its winter counterpart due to the coexistence of equatorial eastward off equatorial westward and northward propagating low frequency modes and their interactions based on observational evidence and results obtained from numerical experiments a mechanism is proposed for the boreal summer iso in which the northern hemisphere summer monsoon nhsm circulation and moist static energy distribution play essential roles with a climatological july mean basic state the life cycle of model low frequency waves consists of four processes an equatorial eastward propagation of a coupled kelvin rossby wave packet an emanation of moist rossby waves in the western pacific a westward propagation and amplification of the rossby waves in south asian monsoon regions and a reinitiation of the equatorial disturbances over the central indian ocean the life cycle spans about one month and p

intraseasonal teleconnection between the summer eurasian wave train and the indian monsoon this study investigated the most recurrent coupled pattern of intraseasonal variability between midlatitude circulation and the indian summer monsoon ism the leading singular vector decomposition svd pattern reveals a significant coupled intraseasonal variation between a rossby wave train across the eurasian continent and the summer monsoon convection in northwestern india and pakistan hereafter referred to as nism the wave train associated with an active phase of nism rainfall displays two high pressure anomalies one located over central asia and the other over northeastern asia they are accompanied by increased rainfall over the western siberia plain and northern china and decreased rainfall over the eastern mediterranean sea and southern japan the circulation of the wave train shows a barotropic structure everywhere except the anomalous central asian high located to the northwest of india where a heat induced baroclinic circulation structure dominates the time lagged svd analysis shows that the midlatitude wave train originates from the northeastern atlantic and traverses europe to central asia the wave train enhances the upper level high pressure and reinforces the convection over the nism region meanwhile it propagates farther toward east asia along the waveguide provided by the westerly jet after an outbreak of nism convection the anomalous central asian high retreats westward composite analysis suggests a coupling between the central asian high and the convective fluctuation in the nism the significance of the midlatitude ism interaction is also revealed by the close resemblance between the individual empirical orthogonal functions and the coupled svd modes of the midlatitude circulation and the ism it is hypothesized that the eastward and southward propagation of the wave train originating from the northeastern atlantic contributes to the intraseasonal variability in the nism by changing the intensity of the monsoonal easterly vertical shear and its associated moist dynamic instability on the other hand the rainfall variations over the nism reinforce the variations of the central asian high through the monsoon desert mechanism thus reenergizing the downstream propagation of the wave train the coupling between the eurasian wave train and nism may be instrumental for understanding their interaction and can provide a way to predict the intraseasonal variations of the indian summer monsoon and east asian summer monsoon

the influence of sea surface temperature on the tropical intraseasonal oscillation a numerical study abstract the development and movement of the tropical intraseasonal system tis exhibit remarkable annual variations it was hypothesized that spatial and temporal variation in sea surface temperature sst is one of the primary climatic factors that are responsible for the annual variation of tiss this paper examines possible influences of sst on the tis through numerical experiments with a 2 5 layer atmospheric model on an equatorial plane in which sst affects atmospheric heating via control of the horizontal distribution of moist static energy and the degree of convective instability the gradient of the antisymmetric with respect to the equator component of sst causes a southward propagation of the model tis toward northern australia in boreal winter and a northward propagation over the indian and western pacific oceans in boreal summer the phase speed of the meridional propagation increases with the magnitude of antisymmetric sst gradients the poleward propagation of the equatorial disturba

role of north indian ocean air sea interaction in summer monsoon intraseasonal oscillation abstractair sea coupling processes over the north indian ocean associated with the indian summer monsoon intraseasonal oscillation miso are investigated observations show that miso convection an

upward delamination of cascadia basin sediment infill with landward frontal accretion thrusting caused by rapid glacial age material flux the cascadia convergent margin is a first order research target to study the impact of rapid sedimentation processes on the mechanics of frontal subduction zone accretion the near trench part of the accretionary prism offshore washington is affected by strongly increased glacial age sedimentation and fan formation that led to an outstanding quaternary growth rate with landward vergent thrust faulting that is rarely observed elsewhere in accretionary wedges multichannel seismic reflection data acquired on the orwell project allows us to study the structure and dynamics of the atypical frontal accretion processes we performed a kinematical and mechanical analysis of the frontal accretion structures and developed a dynamic coulomb wedge model for the landward verging backthrust formation backthrusting results from heterogeneous diffuse strain accumulation in the mechanically heterogeneous cascadia basin sediment succession entering the subduction zone and strain partitioning along a midlevel detachment that is activated by gravitational loading caused by rapid glacial age sedimentation these complex deformation processes cause the passive upward delamination of the upper turbidite beds from the basal pelagic carbonate section similar to triangle zone formation and passive backthrust wedging in foreland thrust belts caused by rapid burial beneath syntectonic sediment deposits the deformation mechanism at the tectonic front of the cascadia margin is an immediate response to the strongly increased late pleistocene sediment flux rather than to atypical physical boundary conditions as generally thought

synchronous and velocity partitioned thrusting and thrust polarity reversal in experimentally produced doubly vergent thrust wedges implications for natural orogens a sandbox analog modeling research program was used to study the detailed evolution of doubly vergent thrust wedges high resolution multilayers of thin alternating sand and mica layers were used in contractional coulomb wedge experiments to simulate deformation of anisotropic brittle upper crustal strata in doubly vergent orogens experiments incorporating syntectonic sedimentation in foreland basins and in piggyback basins were also carried out our laboratory models evolved in two main stages 1 initial high velocity thrusting in the retrowedge and high frequency together with low displacement folding and thrusting in the prowedge and 2 low frequency high displacement synchronous thrusting in the prowedge and low velocity thrusting in the retrowedge transition from stage i to stage ii occurred when the growing wedges reached the critical height at which they behaved as a backstop for further prowedge accretion addition of syntectonic sediments increased the persistence of stage i and triggered out of sequence thrusting in the axial zone of the experimental orogens thrust motion was stick slip retrovergent thrusting occurred along a long lived ramp whose lower tip was located at the subduction slot provergent kink bands nucleated at the subduction slot in stage i in contrast during the second stage of wedge evolution kink bands nucleated in a piggyback fashion in the foreland far from the subduction slot and then evolved into high displacement faults that remained active up until the end of the experiments at progressively decreasing rates of thrusting the axial zones of the model wedges were characterized by fast uplift rates during stage i due to backward translation of the belt along the retrovergent long lived ramp and due to the localization of deformation close to the subduction slot outward migration of the deformation front in the prowedge region during stage ii caused the progressive decrease in the rate of the wedge uplift until it eventually stopped analytical models to quantify the coulomb behavior in the wedges validated the reversal of thrust polarity with increasing shortening triggered by the buildup of the topographic load during deformation this thrust polarity reversal highlights problems with the classic concept of back thrusting as a reflection of a significant change in the deformation regime our results compare well with the kinematic evolution of natural accretionary prisms and of thrust and fold belts such as the lesser antilles arc system the mediterranean ridge and the pyrenees