first evidence of juvenile ceratopsians reptilia ornithischia from the frenchman formation late maastrichtian of saskatchewan the first occurrence from the frenchman formation late maastrichtian of juvenile ceratopsians chasmosaurinae is reported here based on two postorbital horn cores the sutures confirm that the frontal attaches along the medial side of the postorbital much like that in centrosaurinae and cannot be used as a tool for distinguishing the two ceratopsid subfamilies

subduction of the daiichi kashima seamount in the japan trench lallemand s culotta r and von huene r 1989 subduction of the daiichi kashimi seamount in the japan trench in j p cadet and s uyeda editors subduction zones the kaiko project tectonophysics 160 231 247 in 1984 1985 the kaiko consortium collected seabeam single channel seismic and submersible sampling data in the vicinity of the daiichi kashima seamount and the southern japan trench we performed a prestack migration of a shell multichannel seismic profile that crosses this area and examined it in the light of this unusually diverse kaiko dataset unlike the frontal structure of the northern japan trench where mass wasting appears to be the dominant tectonic process the margin in front of the daiiclr kashima shows indentation imbrication uplift and erosion emplacement of the front one third of the seamount beneath the margin front occurs without accretion we conclude that the daiichi kashima seamount exemplifies an intermediate stage between the initial collision and subduction of a seamount at a continental margin

the effect of subauroral polarization streams on ionosphere and thermosphere during the 2015 st patrick s day storm global ionosphere thermosphere model simulations

a proposed production model of rapid subauroral ion drifts and their relationship to substorm evolution multisatellite data are used to examine the temporal relationship between subauroral ion drifts said and the phases of an auroral substorm utilizing images of auroral luminosities taken by the dynamics explorer 1 de 1 spacecraft and observations of particle injection at geosynchronous orbit we identify the time of expansive phase onset and estimate the time at which recovery begins noting the times at which said are observed simultaneously by the de 2 spacecraft we find that said typically occur well after substorm onset more than 30 min during the substorm recovery phase substantial westward ion drifts and field aligned currents are observed well equatorward of the auroral oval during the expansion phase of a substorm but the drifts lack the narrow spike signature associated with said prior to substorm onset and after substorm recovery field aligned currents are absent equatorward of the auroral oval and the ionosphere is very nearly corotating a phenomenological model of said production is proposed that qualitatively agrees with the observed ionospheric signatures and substorm temporal relationship in this model substorm generated subauroral field aligned currents close via pedersen currents with the outward flowing region 1 currents at higher latitudes these pedersen currents flow in the region of low conductivity equatorward of the auroral oval and are associated with relatively large poleward directed electric fields the frictional heating of the ions caused by collisions with the corotating neutral atmosphere substantially increases the rate of ion atom interchange between o and n2 subsequent fast recombination of no with electrons further reduces the subauroral f region conductivities with a corresponding increase in the electric field and the frictional heating this heating leads to thermal expansion substantial field aligned plasma flow and very large depletions in the f peak concentration thus additionally reducing the height integrated pedersen conductivity

seismic structure of the northeastern japan convergent margin a synthesis many studies recently made on the basis of seismic observations have revealed a detailed structure of the crust and the upper mantle beneath the northeastern japan arc and its relationship to seismic and volcanic activity spatial distributions of the depths to the conrad and the moho discontinuities estimated from shallow earthquake data and seismic explosion data show that both discontinuities are deep in the middle of the land area and shallow toward the coastlines of the japan sea and the pacific ocean the pn velocity has a lateral variation it is as low as 7 5 km s beneath the land area while that beneath the japan sea and the pacific ocean is 8 0 8 2 km s it changes abruptly at the transition zones which are located along the coastlines precise structure and location of the subducted pacific plate beneath the land area is inferred from converted or reflected seismic waves at the top or bottom of the plate the pacific plate is composed of a thin 5 km low velocity upper layer and a thick high velocity lower layer its total thickness being 80 90 km the upper plane seismicity of the double seismic zone is confined to the thin low velocity upper layer which probably corresponds to the subducted former oceanic crust the lower plane seismicity lies at the middle of the high velocity lower layer and the lower half of the plate below it is incapable of generating earthquakes the shallower portion of the upper surface of the plate beneath the pacific ocean along which major seismicity with low angle thrust faultings is actually occurring is also located by seismic observations on land and in the sea the pacific plate subducts at an extremely low angle of 5 for the first 25 km depth and then the dip steepens rather abruptly to 30 normal fault type events at the top of the plate have not been detected in the portion where the downward bending is the largest but have been ditected near the trench axis where it is rather small tomographic inversions for seismic velocity structure clearly delineate the inclined high velocity pacific plate with a thickness of 80 90 km and low velocity zones in the crust and the mantle wedge beneath active volcanoes seismic attenuation tomography also shows similar zones of low q value beneath active volcanoes although its spatial resolution is much lower the low velocity zones with 2 6 velocity lows are continuously distributed from the upper crust just beneath active volcanoes to a depth of 100 150 km in the mantle wedge and are approximately parallel to the dip of the underlying pacific plate these low velocity zones probably reflect the pathway of magma ascent from a depth in the mantle wedge to the earth s surface corresponding to a portion of the subduction induced secondary mantle wedge flow

crustal structure and seismicity beneath the forearc off northeastern japan marine seismological and other data in the japan trench area north of 38 5 n were used to infer the relation of subducting plate structure seismicity and focal mechanisms especially at the aseismic to seismogenic zone along the interface between the two interacting plates previous crustal models from ocean bottom seismographic refraction obs surveys were improved by taking into account the relative seismic amplitude characteristics and constraining the shallow structure using multichannel seismic data a wave speed discontinuity in these models is interpreted to be the contact zone of the crust of the overriding plate and the subducting pacific plate crust its dip angle increases to about 7 110 km landward of the trench axis a large increase beneath the deep sea terrace is required to reach the well defined angle of 25 beneath the tohoku east coast a large wave speed gradient within layer 2 commonly observed under normal oceans seems to vanish beneath the inner trench slope at about 10 km depth within the overriding plate apparently brittle material with a p wave speed of 6 km s can be found as near as 35 km from the trench axis the upper limit of the seismogenic zone of interplate low angle thrust events is about 15 km depth from obs seismicity and large event analyses both the strength of the crust of the overriding plate and the characteristics of subducting sediments must be investigated to define the seismic coupling of interacting plates

ionospheric disturbances observed by dmsp at middle to low latitudes during the magnetic storm of june 4 6 1991 this paper extends a recent study of electric field penetration into the inner magnetosphere observed by the combined release and radiation effects crres satellite and the defense meteorological satellite program dmsp satellite f8 during the magnetic storm of june 4 6 1991 to consider its ionospheric consequences effects include the development of 1 km s subauroral ion drift said structures the formation of midlatitude density troughs and the vertical transport of equatorial plasma bubbles nearly simultaneous auroral electron and plasma drift measurements were acquired by three dmsp satellites with f8 and f9 in one hemisphere and flo in the other moderate to strong said structures were consistently detected for 10 hours during the early main phase of the storm weak saids were encountered during 8 hours of the early recovery phase dmsp data show that saids with similar characteristics developed at magnetically conjugate locations and extended for at least 3 hours in local time simultaneous measurements show that the saids spanned temporally grooving but latitudinally narrow plasma density troughs these observations suggest that the magnetospheric sources of saids act more like voltage than current generators energetic electron fluxes electric fields and plasma waves measured by crres indicate that during this storm the ring current shielding charges and said sources were located in regions of high plasma density characteristic of the plasmasphere the sequence in which dmsp detected equatorial plasma density irregularities is consistent with model predictions that stormtime electrodynamics at low latitudes operate on distinctive fast and slow timescales fejer and schcrliess 1997

tectonics and hydrogeology of accretionary prisms role of the decollement zone abstract at convergent margins the decollement zone comprises the plate boundary and is marked by profound structural disharmony by changes in stress orientation and by a discontinuity in plate velocity the decollement zone initiates in a weak sediment layer typically a low permeability hemipelagic mud lying below a more rapidly deposited stronger more permeable trench turbidite sequence at the deformation front trench turbidites tend to be offscraped whereas the finer grained hemipelagic and pelagic sediments are more likely to be underthrust offscraped materials may undergo only limited burial whereas underthrust deposits can be deeply buried undergo high pressure metamorphism and are more likely to be preserved in the stratigraphic record burial rates associated with underthrusting are high exceeding 20 km my with high rates of underthrusting sediment descending below the decollement zone is probably buried faster than it can dewater resulting in emplacement of relatively high porosity deposits at depth fluids flowing from modern decollement zones have migrated substantial distances laterally and tapped deep sources the episodicity of flow suggests pumping of fluid by cycles of dilation and flow to the decollement zone followed by failure and fluid expansion along the decollement zone possible pressure gradients below the decollement zone allow flow upward into it while maintaining minimum effective stress along it the thickness of sediment underthrust beneath the decollement zone determines whether these deposits are emplaced by diffusive underplating with stratal disruption and efficient dewatering or by coherent underplating with the formation of macroscopic duplexes and transfer of fluid to the base of the accretionary prism deformation mechanisms affecting accreted sediment depend on depth of entrainment into the decollement zone and duration of residence

a quantitative study of ionospheric density gradients at midlatitudes the subauroral ionosphere at the magnetic latitudes which characterize the northeastern united states is subject to severe f region ionospheric density structuring due to the space weather effects of magnetospheric disturbance electric fields communications and navigation systems relying on transionospheric propagation must be able to compensate for the effects of the sharp changes 10x in total electron content tec associated with the ionospheric trough and storm time disturbance effects at midlatitudes the millstone hill incoherent scatter radar database has been used to investigate the spatial extent and temporal evolution of tec and density altitude latitude structure at middle and subauroral latitudes as a function of solar cycle local time and level of geomagnetic activity more than 11 000 radar elevation scans covering 20 of latitude and altitudes between 150 and 750 km have been used to identify the characteristics of the density gradient near the equatorward edge of the ionospheric trough in a variety of circumstances spanning 20 years and two solar cycles pronounced density gradients can be identified in 35 of the millstone hill scans and we present a statistical characterization of average magnitude and location for these steepest tec gradients in some cases especially near noon the equatorward edge of the trough lies poleward of our observational field of view and gradients associated with phenomena other than the trough contribute to our statistics on most days the trough appears in the radar scans between 1600 and 2000 magnetic local time mlt larger tec gradients occur at solar maximum and when the background tec is higher the steepest gradients occur in an environment of high tec at solar maximum and adjacent to regions of storm enhanced density sed when the processes which generate the trough are strongest high kp high gradient values occur in the sunlit sector with maximum values of tec gradient 10 tec deg latitude with 1 tec unit 10 16 el m 2 found in the postnoon ionosphere mean solar maximum tec gradient at 1600 mlt is 3 4 tec deg for kp 100 over new england and tec gradients of 50 tec deg

velocity analysis by iterative profile migration in conventional seismic processing velocity analysis is performed by using the normal moveout nmo equation which is based on the assumption of flat horizontal reflectors imaging by migration either before or after stack is done normally in a subsequent step using these velocities in this paper velocity analysis and imaging are combined in one step and migration itself is used as a velocity indicator because unlike nmo migration can be formulated for any velocity function migration based velocity analysis methods are capable of handling arbitrary structures i e those with lateral velocity variations in the proposed scheme each shot gather profile is migrated with an initial depth velocity model profile migration is implemented in the x domain but the actual implementation of profile migration is not critical as long as it is not done in a spatial wavenumber domain which would preclude handling of lateral velocity variations after migration with an initial velocity model the

satellite measurements through the center of a substorm surge measurements have been made of electric and magnetic fields plasma drifts and electron precipitation within a surge at the westward leading edge of the auroral bulge at the peak of the substorm expansion phase the trajectory of the de 2 satellite over the auroral emissions is determined from nearly simultaneous observations with the imager on the de 1 satellite at a higher altitude the electric field and plasma drift measurements have enabled us to deduce the basic configuration of the ionospheric electric potential or plasma convection around the surge the electric potential shows that the bulge is associated with a protrusion of the dawn convection cell into the dusk cell poleward of the harang discontinuity this protrusion contains a westward electric field that strongly enhances the westward electrojet current by the creation of a cowling channel this westward electric field and the associated cowling current appear to terminate within the surge which contains an intense upward field aligned current the magnetic field measurements show that the region containing this field aligned current is shaped more like a cylinder rather than a long sheet the total current is found to exceed one half million amperes

electrodynamic parameters in the nighttime sector during auroral substorms the characteristics of the large scale electrodynamic parameters field aligned currents facs electric fields and electron precipitation which are associated with auroral substorm events in the nighttime sector have been obtained through a unique analysis which places the ionospheric measurements of these parameters into the context of a generic substorm determined from global auroral images a generic bulge type auroral emission region has been deduced from auroral images taken by the dynamics explorer 1 de 1 satellite during a number of isolated substorms and the form has been divided into six sectors based on the peculiar emission characteristics in each sector west of bulge surge horn surge middle surge eastern bulge and east of bulge by comparing the location of passes of the dynamics explorer 2 de 2 satellite to the simultaneously obtained auroral images each pass is placed onto the generic aurora the organization of de 2 data in this way has systematically clarified peculiar characteristics in the electrodynamic parameters an upward net current mainly appears in the surge with little net current in the surge horn and the west of bulge the downward net current is distributed over wide longitudinal regions from the eastern bulge to the east of bulge near the poleward boundary of the expanding auroral bulge a pair of oppositely directed fac sheets is observed with the downward fac on the poleward side this downward fac and most of the upward fac in the surge and the middle surge are associated with narrow intense antisunward convection corresponding to an equatorward directed spikelike electric field this pair of currents decreases in amplitude and latitudinal width toward dusk in the surge and the west of bulge and the region 1 and 2 facs become embedded in the sunward convection region the upward fac region associated with the spikelike field on the poleward edge of the bulge coincides well with intense electron precipitation and aurora appearing in this western and poleward portion of the bulge the convection reversal is sharp in the west of bulge and surge horn sectors and near the high latitude boundary of the upward region 1 fac in the surge the convection reversal is near the low latitude boundary of the upward region 1 with a near stagnation region often extending over a large interval of latitude in the eastern bulge and east of bulge sectors the region 1 and 2 facs are located in the sunward convection region while a spikelike electric field occasionally appears poleward of the aurora but usually not associated with a pair of fac sheets in the eastern bulge magnetic field data show complicated fac distributions which correspond to current segments and filamentary currents

observed change in plate coupling close to the rupture initiation area before the occurrence of the 2011 tohoku earthquake implications from an earthquake cycle model changes in plate coupling off the coast of fukushima have been detected by gps since 2000 these changes occurred close to the rupture initiation area of the mw9 0 2011 tohoku earthquake and possibly initiated the earthquake we investigated these changes with quasi dynamic earthquake cycle simulations using a hierarchical asperity model we modeled the entire rupture region as rate weakening but conditionally stable while areas with huge slips and mw7 asperities were modeled as strong and ordinary rate weakening unstable friction respectively the following observed characteristics were reproduced long recurrence time large rupture region including a localized huge coseismic slip area and source area of recurring mw7 earthquakes and a mw7 foreshock triggering the tohoku earthquake off fukushima repeated aseismic slips propagating northward appeared in the last half of the cycle and possibly caused the decrease in plate coupling however it is not necessarily related to the immediate occurrence of the giant earthquake

simultaneous measurement of duskside subauroral irregularities from the cutlass finland radar and eiscat uhf system 1 dusk scatter event duse first reported by ruohoniemi et al 1988 is one of the most reproducible features among the superdarn radar backscatter within the subauroral ionosphere hosokawa et al 2001 analyzed the scattering occurrence percentage of the northern hemisphere superdarn radars in a statistical fashion and pointed out that the region where the duse appears has a close relationship with the duskside end of the midlatitude trough in longitudinal direction they proposed a model explaining the generation of the duse which employs a sunward density gradient at the duskside edge of the trough and an ambient poleward electric field in order to confirm the model proposed by hosokawa et al 2001 we have investigated two duse events which had been observed by the cutlass finland radar and the eiscat uhf system simultaneously consequently when the cutlass finland radar observed the duse a sunward directed density gradient was observed by the eiscat in the vicinity of the duse after the passage of the duse the eiscat observed an ion temperature enhancement which suggested that the eiscat entered the trough through its duskside edge these observational facts suggest that the geometry of the parameters around the duse is quite consistent with the model proposed by hosokawa et al 2001 in addition the eiscat observed an enhancement of the poleward electric field around the duse and a signature of the substorm was identified by the ground magnetometer on the nightside we suggest generation mechanisms of the trough responsible for the duse during substorm conditions in terms of the role of the enhanced subauroral electric field and discuss a relationship between the duse and the other substorm related phenomena

detailed plate boundary structure off northeast japan coast in 1997 a seismic experiment using an airgun array and ocean bottom seismographs obss was performed in the forearc region of the northeast japan nej arc the objectives of this experiment were to clarify whole of the velocity structure around the forearc region of nej arc including a detailed plate boundary structure and the heterogeneous structure in this paper we estimated the heterogeneous velocity structure around the forearc region of northeast japan by applying 2 d ray tracing and travel time inversion to the airgun obs data the depth where the island arc moho comes into contact with the subducting oceanic crust is about 20 km we suggest the existence of an oceanic layerl overlying the oceanic crust subducting down to at least near 18 km by comparing observed waveforms with these calculated using the reflectivity method

structured subauroral polarization streams and related auroral undulations occurring on the storm day of 21 january 2005 we investigate structured subauroral polarization streams saps and their impacts on the midlatitude trough and auroral regions during the 21 22 january 2005 geomagnetic storm this was a storm with two sudden commencements occurring under varying interplanetary magnetic field imf conditions and three main phases two of them unfolding during northward imf its onset at 1700 ut allowed us to investigate saps wave structures ws and their impacts during the local evening hours under both southward and northward imf conditions in the american sector results suggest that during southward imf saps ws might be related with standing toroidal alfven waves and structured most intensively the stagnation trough during northward imf the trough was created by saps electric e field effects only and became less structured by saps ws that were of alfvenic origin auroral wave structures and undulations occurred in the structured and unstructured oval regions respectively and triggered the subauroral region s response to produce saps ws spectrogram images only one shown confirmed ring current injections implying magnetotail reconnections during the four saps ws events investigated periodic tail connections are also evidenced by the periodic increases seen in both the solar wind magnetosphere coupling function e and the energy input efficiency finally we conclude for the time period investigated that 1 the nature of saps ws was informative of imf orientation 2 plasma stagnation enhanced saps e field and saps ws development and 3 more efficient energy input into the magnetosphere contributed to the better development of auroral undulations and saps ws

substorm triggering by new plasma intrusion incoherent scatter radar observations received 4 december 2009 revised 16 march 2010 accepted 30 march 2010 published 27 july 2010 1 in the companion paper we identified a repeatable sequence of events leading to substorm onset in themis all sky imager observations enhanced flows bring new plasma into the plasma sheet the new plasma then moves earthward as a flow channel bringing it to the near earth plasma sheet and where it produces onset instability new plasma entering the dusk dawn convection cell drifts equatorward and eastward and then around the harang reversal leading to pre midnight near and post midnight onset here we present evidence supporting this sequence using incoherent scatter radar isr ionospheric observations using the sondrestrom isr we find that enhanced flows of new plasma commonly enter the plasma sheet from the polar cap 8 min prior to onset these flows are related to poleward boundary intensification signatures consistent with the inferences from the imagers using the poker flat isr pfisr we find that shortly before onset enhanced westward flows reach the subauroral polarization streams saps region equatorward of the harang reversal dusk cell onsets or enhanced eastward flows enter the onset region from the poleward direction dawn cell onset pfisr proton precipitation signatures are consistent with the possibility that the enhanced flows consist of reduced entropy plasma sheet plasma and that onset occurs poleward of much of the enhanced saps flow dusk cell onsets or equatorward of the enhanced eastward flows dawn cell onsets consistency with reduced entropy plasma is seen only within the enhanced flows leading us to suggest that intrusion of low entropy plasma may alter the radial gradient of entropy toward onset instability

a statistical study of the subauroral polarization stream over north american sector using the millstone hill incoherent scatter radar 1979 2019 measurements this work conducts a statistical study of the subauroral polarization stream saps feature in the north american sector using millstone hill incoherent scatter radar measurements from 1979 to 2019

coulomb theory applied to accretionary and nonaccretionary wedges possible causes for tectonic erosion and or frontal accretion based on observations from both modem convergent margins and sandbox modeling we examine the possible conditions favoring frontal accretion and or frontal and basal tectonic erosion mean characteristic parameters t t and are used to discuss the mechanical stability of 28 transects across the frontal part of convergent margins where the coulomb theory is applicable natural observations reveal that typical accretionary wedges are characterized by low tapers with smooth surface slope and subducting plate low convergence rates and thick trench sediment while nonaccretionary wedges display large tapers with irregular surface slopes and rough subducting plate high convergence rates and almost no trench fill sandbox experiments were performed to illustrate the effects of seamounts ridges in the subduction zone on the deformation of an accretionary wedge these experiments show that a wedge of sand is first trapped and pushed in front of the seamount which acts as a moving bulldozer this is followed by a tunnelling effect of the subducting seamount through the frontal wedge material which results in considerable sand reworking at an advanced subduction stage the d6collement jumps back from a high level in the wedge to its former basal position we conclude that a high trench sedimentation rate relative to the convergence rate leads to frontal accretion in contrast several conditions may favor tectonic erosion of the upper plate first oceanic features such as grabens seamounts or ridges may trap upper plate material during their subduction process second destabilization of the upper plate material by internal fluid overpressuring causing hydrofracturing is probably another important mechanism

subauroral electric fields and magnetospheric convection during the april 2002 geomagnetic storms 1 we analyze the ionospheric electric fields during the geomagnetic storms of april 2002 using data from the dmsp satellites the subauroral potential drop sa in the evening sector exceeded 60 kv at times and was often a substantial fraction of total cross polar cap potential drop pc at storm commencement the subauroral electric field penetration moved rapidly equatorward reaching the lowest magnetic latitude well before the end of the storms main phases pc and sa were correlated well with ae with no time delay however the correlations of pc and sa with dst occurred with significant time delays about an hour for pc and longer for sa the largest values of pc were seen near the end of the storm main phases while the largest values of sa were seen well into the recovery phases the results of this study have important implications on models attempting to describe the dynamics of the plasmasphere the inner magnetosphere and the ring current

first observations of the temporal spatial variation of the sub auroral polarization stream from the superdarn wallops hf radar 1 in this letter we present the first two dimensional observations of sub auroral ion drift said variability within the sub auroral polarization stream saps using a new mid latitude superdarn radar located at wallops island va the radar data are complemented with observations from the dmsp f15 timed and noaa 18 spacecraft to confirm that a backscatter feature observed at the equatorward edge of the auroral oval is a manifestation of saps said during a several hour long period on august 6 2005 the velocity data indicate that significant changes in the saps flow occurred on time scales of a few minutes the wallops hf radar observations demonstrate that the saps phenomenon is a source of small scale irregularities extending over many hours of mlt and that the electric fields associated with said in particular are highly variable

formation of density troughs embedded in the outer plasmasphere by subauroral ion drift events a dynamic global core plasma model dgcpm is used to investigate the effects of subauroral ion drift said events on the formation of trough density profiles in the outer plasmasphere during periods of high magnetic activity the dgcpm includes the influences of convection on the changing flux tube volumes as well as daytime refilling and nighttime draining of plasma to calculate the plasma tube contents and equatorial plasma density distribution versus time throughout the magnetosphere saids are regions of latitudinally narrow westward flow of plasma equatorward of the auroral zone we present dgcpm results for various presumed said locations and durations relative to enhanced substorm convection onset and decay to parametrically elicit the formation of plasmaspheric density trough structures resulting from said effects it is found that imposing a said event in the dusk evening sector for 30 min leads to the formation of a narrow less than 1 re near the equatorial plane embedded plasma density trough in the dusk bulge region the modeled plasmasphere density profiles with troughs generally resemble plasmasphere density profiles observed from de 1 measurements

coulomb wedge model applied to the subduction of seamounts in the japan trench results from the french japanese kaiko exploration program of the japan trench and complementary data are used to propose a model of subduction of seamounts examples in two seamount chains one at the junction between the japan and kuril trenches and the other in the southern part of the japan trench off inubo cape illustrate the stages of subduction the japan trench margin evolved as a homogeneous wedge of deformable noncohesive coulomb material during seamount subduction this is illustrated by the subduction of the daiichi kashima seamount in the southern japan trench our model predicts that the first consequence of seamount subduction is a compressive thickening of the toe of the wedge above the advancing flank of the seamount because of the oversteepening of the rigid base of the wedge this agrees with our observations in the daiichi kashima area this thickening shifts landward across the wedge with the advancing flank of the seamount erosion dominates the wedge above the trailing flank of the seamount because of the corresponding understeepening of the rigid base of the wedge a reentrant of the toe of the wedge is thus created it is largest when the oceanic flank of the seamount coincides with the base of the landward slope at this time the trench axis will probably have an abnormally large amount of sediments as illustrated at the junction between the japan and kuril trenches after the subduction of the seamount the edge of the wedge should progressively move back to its initial location frontal accretion is absent or very limited

coordinated stable auroral red arc observations relationship to plasma convection during the march 20 22 1990 magnetic storm millstone hill radar and dmsp satellite observations detailed the conditions surrounding the occurrence of a sar arc which was observed continuously through an 8 hour interval from dusk till past midnight in the north american sector all sky imaging with a 630 0 nm imager continually monitored the two dimensional position and magnitude of the sar arc emission while radar scans and satellite overflights measured magneto spheric inputs and ionospheric response the arc was colocated with a deep narrow plasma trough and a region of enhanced westward plasma convection of similar width simate3 immediately equa torward of the low latitude extent of plasma sheet particle precipitation a region of low energy ion precipitation was observed at the equatorward edge of the sar arc during a period of spatial tem poral coincident satellite radar observations near the millstone hill longitude the width of the sar arc and related phenomena was of the order of 2 o and the 200 r emission was associated with an electron temperature of 3500ok and a 10x reduction of plasma density at an altitude of 450 kin the best fit model for the emission intensities of both the sar arc and the background airglow suggests that either the electron temperature at the center of the sar arc was somewhat higher than observed by the radar 4000ok or the neutral densities 0 2 and o were increased by factors of 2 and 4 respectively with respect to the msis values the ionospheric trough and a colocated region of enhancext sunward convection 500 1700 m s 1 were observed in conjugate hemispheres through out the local time range 18 02 mlt the convection feature seen in association with the sar arc had many of the characteristics of a subauroral ion drifts said event we report here the first long duration observations of a colocated said sar arc event a narrow ionospheric trough developed during the interval when the said velocity was 1000 m s and was accompanied by a weak 100 r 630 0 nm emission as the velocity fell to 700 m s 1 the density in the trough recovered some what and the arc intensity rose to 300 r above background this brighter period of the sar arc occurred within a fossil trough said we conclude that there is a close spatial and temporal associ ation among these three types of subauroral low altitude phenomena the sar arc the said even and the fossil convection related trough and that this is indicative of the interrelationship of the

a substorm onset signature at the auroral zone as observed with superdarn and equatorial magnetometers ionospheric convection enhancement with high westward velocities exceeding 1500 m s 1 was observed in association with the particle injection event by superdarn in the dusk sector of the auroral zone such a convection enhancement could be attributable to the enhanced sunward plasma flows in the dusk sector of the magnetosphere at the dip equator a ground pi2 onset was found to occur in association with these convection transients the onset of the pi2 lagged behind the convection enhancement by 4 11 min it is argued that the convection transient could be the earliest indicator of the substorm onset among energetic particle injection low latitude pi2 onset and perhaps the auroral breakup

tectonic features of the japan trench convergent margin off sanriku northeastern japan revealed by multichannel seismic reflection data near the japan trench convergent plate margin the seaward edge of the continental plate is deformed by subduction of the oceanic plate we report the results of a multichannel seismic survey in the northern japan trench in which this deformed zone is demarcated from the rigid continental framework by a pronounced landward dipping reflector the oceanic plate also undergoes deformation as the two plates interact in the subduction processes resulting in a progressive deformation or destruction of a horst structure along the top of the subducting oceanic crust this may eventually lead to the formation of a smooth plate boundary at the greater depth more than 45 km landward from the trench axis a smooth reflector suggesting a stable slip plane is visible along and above the oceanic crust our data indicate that the deformed zone pinches out landward 60 km from the axis at 13 km depth and the slip plane becomes less obvious there seismicity of interplate earthquakes rapidly increases landward from this location leading us to speculate that this is where coupling at the plate boundary becomes strong enough for earthquakes to occur we conclude that the updip limit of the seismogenic zone of interplate earthquakes in the study area is characterized by the tectonic feature of a pinchout of the deformed sediments which overlie the subducting oceanic crust

tectonic erosion at the front of the japan trench convergent margin abstract the imaging of a multichannel seismic record was improved by reprocessing using pre stack techniques the reprocessed record shows structures that indicate tectonic erosion and gravity collapse at the front of the japan trench margin much of the lower slope appears to be underlain by a detached coherent block of continental crust the lower slope has failed by mass wasting and the resulting apron of slump debris at the base of the slope has become involved in thrust faulting at the front of the subduction zone slumping continues as long as debris is removed from the front of the margin by subduction and the apron cannot build up sufficiently to stabilize the failing lower slope truncated beds at the base of the upper plate indicate subcrustal erosion as well this probably being the main cause of massive subsidence of the margin subsidence was the cause of oversteepening destabilization and subsequent gravity collapse of the leading edge of the upper plate

hemispheric asymmetry of subauroral ion drifts statistical results a large database of more than 18 000 subauroral ion drift said events from dmsp observations from 1987 to 2012 is used to systematically investigate the features of said said occurs mostly at 62 60 magnetic latitude mlat and 22 15 22 45 magnetic local time mlt for geomagnetically quiet conditions and at 58 56 mlat and 22 15 22 45 mlt for geomagnetically disturbed conditions in the north hemisphere nh south hemisphere sh respectively significant north south asymmetries in said occurrence shape and geomagnetic activity variations are found in this statistical study the latitudinal width of a said is larger in the nh than in the sh an interesting finding of this work is that the said occurrence probability peaks have an 180 difference in longitude between the two hemispheres in the geographic coordinates for both geomagnetically quiet and disturbed conditions the said width peaks in almost the same geomagnetic meridian zone with a geomagnetic longitude of 80 120 in both hemispheres significant hemispheric asymmetries and spike signatures with sharp dips are found in all the latitudinal profiles of the horizontal velocities of saids the said is highly correlated to geomagnetic activity indicating that the location and evolution of the said might be influenced by global geomagnetic activity auroral dynamics and the dynamics of ring currents

the 2011 tohoku oki earthquake displacement reaching the trench axis we detected and measured coseismic displacement caused by the 11 march 2011 tohoku oki earthquake moment magnitude mw 9 0 by using multibeam bathymetric surveys the difference between bathymetric data acquired before and after the earthquake revealed that the displacement extended out to the axis of the japan trench suggesting that the fault rupture reached the trench axis the sea floor on the outermost landward area moved about 50 meters horizontally east southeast and 10 meters upward the large horizontal displacement lifted the sea floor by up to 16 meters on the landward slope in addition to the vertical displacement

influence of auroral streamers on rapid evolution of ionospheric saps flows subauroral polarization streams saps often show large rapid enhancements above their slowly varying component we present simultaneous observations from ground based all sky imagers and flows from the super dual auroral radar network radars to investigate the relationship between auroral phenomena and flow enhancement we first identified auroral streamers approaching the equatorward boundary of the auroral oval to examine how often the subauroral flow increased we also performed the reverse query starting with subauroral flow enhancements and then evaluated the auroral conditions in the forward study 98 of the streamers approaching the equatorward boundary were associated with saps flow enhancements reaching 700 m s and typically hundreds of m s above background speeds the reverse study reveals that flow enhancements associated with streamers 60 and enhanced larger scale convection 37 contribute to saps flow enhancements the strong correlation of auroral streamers with rapid evolution approximately minutes of saps flows suggests that transient fast earthward plasma sheet flows can often lead to westward saps flow enhancements in the subauroral region and that such enhancements are far more common than only during substorms because of the much more frequent occurrences of streamers under various geomagnetic conditions we also found a strong correlation between flow duration and streamer duration and a weak correlation between saps flow velocity and streamer intensity this result suggests that intense flow bursts in the plasma sheet which correlate with intense streamers are associated with intense saps ionospheric flows perhaps by enhancing the ring current pressure and localized pressure gradients when they are able to penetrate close enough to earth

a summary of cenozoic tectonic history along the ipod japan trench transect along the international program of ocean drilling ipod japan trench transect a mid cenozoic period of tectonism without arc volcanism separated an earlier cretaceous to paleogene and a later neogene period of plate convergence and subduction the cretaceous to early paleogene period of convergence is evidenced by andesitic volcanism associated with a large syncline probably a forearc basin the seaward flank of the basin is a tectonically thickened sediment sequence inferred to be an accretionary complex the arc the syncline and the thickened sediment sequence resemble an arc trench system of the size and structure of the great valley forearc basin and franciscan accretionary complex of california and they were probably continuations of the yezo geosyncline and associated sequences exposed to the north on hokkaido the arc trench system is contemporaneous with the adjacent shimanto arc trench system southwest of tokyo bay in the early paleogene volcanism ceased and part of the thickened sediment sequence of the cretaceous paleogene margin was emergent as a 160 km wide landmass which is recognized in seismic records as a later paleogene sediment source at the end of the paleogene this landmass began to subside and volcanism began again but it was located first briefly on the east and then on the west of the cretaceous arc along the present arc of northern honshu the land mass erosion surface is clearly visible as an angular unconformity in multichannel seismic reflection records the sequence of neogene sediment explosive volcanism and benthic foraminiferal assemblages recording subsidence from subareal conditions to the present bathyal depths have been studied in deep sea drilling project dsdp cores cretaceous subduction appears to have resulted in a very extensive accretionary complex whereas the neogene subduction period appears to have been marked by little net accretion in the forearc area but massive subsidence and some erosion of the front of the convergent margin

average characteristics and activity dependence of the subauroral polarization stream 1 data from the millstone hill incoherent scatter radar taken over two solar cycles 1979 2000 are examined to determine the average characteristics of the disturbance convection electric field in the midlatitude ionosphere radar azimuth scans provide a regular database of ionospheric plasma convection observations spanning auroral and subauroral latitudes and these scans have been examined for all local times and activity conditions we examine the occurrence and characteristics of a persistent secondary westward convection peak which lies equatorward of the auroral two cell convection individual scans and average patterns of plasma flow identify and characterize this latitudinally broad and persistent subauroral polarization stream saps which spans the nightside from dusk to the early morning sector for all kp greater than 4 premidnight the saps westward convection lies equatorward of l 4 60 invariant latitude spans 3 5 of latitude and has an average peak amplitude of 900 m s in the predawn sector saps is seen as a region of antisunward convection equatorward of l 3 55 spanning 3 of latitude with an average peak amplitude of 400 m s

outer slope faulting associated with the western kuril and japan trenches summary elongated fault escarpments on the outer slopes of the western kuril and japan trenches have been investigated through detailed swath bathymetric mapping numerous horsts and grabens formed by these escarpments were identified distinct n70 e linear alignment of the escarpments parallel to the magnetic anomaly lineations was revealed on the outer slope of the western kuril trench in the japan trench north of 39 00aen most of the escarpments are parallel to the trench axis and oblique to the magnetic lineations a zig zag pattern of faulting exists south of 39 00aen each topographic profile was decomposed by computer analysis into two curves representing 1 the smoothed long wavelength slope of the subducting ocean crust surface and 2 the short wavelength 10 km roughness of plateaus and valleys edged by outwardand inward facing fault escarpments throughout the surveyed areas escarpment heights increase from the crest of the trench outer swell down to a depth of about 6000 m on the slope of the outer trench wall but with no distinct increase below that depth no significant diverence is recognized in fault throws towards and away from the trench it can be concluded that these elongated escarpments originate from normal faults on the upper layer of the oceanic crust under extensional stress in a direction perpendicular to the trench axis which is caused by downward bending of the subducting lithosphere the relationship of escarpment height to escarpment length is similar to that obtained from normal fault escarpments in the east pacific rise crest the maximum length and height of escarpments are small in the kuril trench compared with those in the japan trench implying a diverence in mechanical strength depending on the fault orientation the crust is weakest along the inherited spreading fabric second weakest probably along the non transform ovset direction and strongest in directions very oblique to these orientations seamounts appear to be more rigid than normal ocean crust with no particular weak orientations resulting in fewer but larger faults along the axis of plate bending as most clearly represented in the subducting daiichi kashima seamount

observations of shear coupled pl waves from shallow earthquakes in the sumatra and java subduction zones summary s phases generated by shallow earthquakes in the sumatra subduction zone and recorded at the geoscope station paf on the kerguelen isles in the southern indian ocean are often followed by a long and particularly large wave train on the longitudinal component the wave train has a dominant period of 25 30 s and lasts usually for more than 100 s it shows slight normal dispersion and has a prograde elliptical motion in the vertical propagation plane these characteristics suggest that the observed waves are shear coupled pl spl waves similar wave trains are not observed for events at comparable distances in other source regions a computational scheme based on the reflectivity method and allowing for different crust and upper mantle structures beneath source and receiver has been used to model the spl waveforms for six of the events located beneath the accretionary domain and outer high of the sumatra subduction zone for the source area a model representing the structure seaward of the trench has been used comprising a 5 5 km water layer and 600 m of sediments by placing the sources in the sedimentary layer the spl wave train on the longitudinal component is reproduced quite well these findings suggest that wave energy is guided into the water and sedimentary layers seaward of the trench where p and s wave reverberations are generated and leak as sv waves into the mantle the guidance can be explained by trapping of wave energy within the wedge shaped accretionary domain and outer high or in oceanic sediments which are subducted with the oceanic plate

correlation of the subauroral polarization streams saps with the dst index during severe magnetic storms 1 the subauroral polarization stream saps is the enhanced poleward electric field westward plasma flow in the region equatorward of the auroral electron precipitation boundary in the dusk midnight sector an important characteristic of saps is its great intensification during magnetic storms however the relationship of saps characteristics to the strength of magnetic storms is not well known using defense meteorological satellite program dmsp satellite measurements we have examined the location magnetic latitude of the saps channel during four severe magnetic storms with minimum dst values between 271 and 422 nt we find that the latitude of the saps channel varies directly with the magnitude of dst for example in one storm case saps moved from 60 magnetic latitude at the storm sudden commencement with dst of near zero to 38 at the end of the storm main phase with dst of 422 nt we have identified more than 300 locations of saps and corresponding dst values during the four storms the most important finding is that the saps latitude is linearly correlated with dst and an empirical formula is derived if the saps channel is mapped along the magnetic field lines to the magnetospheric equatorial plane the mapped saps location corresponds to the inner edge of the ion plasma sheet and is close to the peak of the ring current the result of this paper suggests a promising method of using ionospheric satellite and radar measurements of saps to monitor the evolution of the plasma sheet inner boundary and ring current during magnetic storms

the convection electric field in auroral substorms dynamics explorer 2 de 2 electric field and ion drift data are used in a statistical study of the ionospheric convection electric field in bulge type auroral substorms thirty one individual de 2 substorm crossings were carefully selected and organized by the use of global auroral images obtained by de 1 the selected passes which occurred during substorm expansion phase maximum or early recovery phase cover the entire nighttime substorm the organization of the data used the method developed by fujii et al 1994 which divided the data into six local time sectors covering the nighttime substorm region following the procedures employed in the paper by gjerloev and hoffman 2000b the latitudinal width and location of each auroral oval crossing was then adjusted to fit the sector average in addition to the detailed study of the characteristics of the field within each sector this database enabled us to compile a model of the ionospheric convection electric field the characteristics of the premidnight convection reversal show a pronounced local time dependency far west of the surge it is a fairly well defined point reversal or convection shear approaching the surge and within the surge it is a region of weak electric fields increasing in width toward midnight that separates regions of equatorward and poleward electric fields therefore we adopt the term harang region rather than the harang discontinuity for the premidnight convection reversal a relatively narrow convection channel is coincident with the highest conductances located just poleward of the harang region this channel drives the substorm current wedge component of the westward electrojet in the surge and middle surge sectors it is present in all premidnight passes and consequently is an integral part of the three dimensional substorm current wedge system

along arc structural variation of the plate boundary at the japan trench margin implication of interplate coupling 1 at the japan trench convergent margin many large interplate earthquakes of greater than m7 5 frequently occur their epicenters have uneven distribution mostly located in the northern area to investigate the relationship between this distribution and tectonic structures we have conducted multichannel seismic surveys since 1996 our data show two kinds of interplate sedimentary units a wedge shaped unit and a channel like unit both units have a lower p wave velocity than the basal part of the overriding island arc crust the wedge shaped unit having a velocity of 2 3 km s is widely distributed over the forearc region in the northern area its thickness decreases with depth becoming several hundred meters at a depth of 12 km the channel like unit having a velocity of 3 4 km s is observed in the southern area extending in the downdip direction its thickness reaches 2 km at a depth of 12 km if the low velocity of these units results from the existence of fluid as many authors assume the units being thick implies higher fluid content assuming constant porosity considering that fluid reduces basal friction and with an assumption that fluid available at a specific interface is proportional to the total fluid content in the sediment the thickness variation of the units would cause different degrees of coupling at the plate boundary along the arc this may provide one explanation for the regional disparity in the interplate earthquake occurrence in the margin furthermore we attempt to call attention to the possibility that the channel like sediment works as a shear stress releaser

subducting seamounts and deformation of overriding forearc wedges around japan abstract two subducting seamounts under inner trench slopes have been identified around japan on the basis of magnetic anomalies morphology and geological structure the first one is located under the foot of the inner trench slope at the junction between the japan trench and the kuril trench another one occurs beneath the slope slightly seaward of the tosabae the basement high at the trench slope break along the nankai trough off shikoku the magnetic anomalies of seamount origin are accompanied by the characteristic morphology of a forearc wedge i e a swell landward and a depression seaward the seamounts beneath the inner trench slopes have preserved magnetization showing reasonably consistent directions which suggests that the subducting seamounts have kept roughly their original shapes the morphology of the forearc wedge can be explained by a subducting seamount on the oceanic crust pushing the forearc material forward and upward deformation of the forearc wedge by the subducting seamount extends to the forearc basin the seamounts are stronger and less deformable than the inner slope material and are not offscraped onto inner trench slopes two other examples of deformed inner trench slopes around japan which can be explained by subduction of topographic highs are presented one example is a depression on the foot of the inner trench slope northeast of the junction between the kyushu palau ridge and the nankai trough another one is an area of complex morphology of the inner trench slope along the japan trench around the daiichi kashima seamount

dynamic subauroral ionospheric electric fields observed by the falkland islands radar during the course of a geomagnetic storm ion drift said located between 53 and 58 magnetic south and lasting 6 5 hours was observed by the falkland islands radar in the pre midnight sector coincident flow data from the dmsp satellites and the magnetically near conjugate northern hemisphere blackstone hf radar reveal that the said was embedded within the broader subauroral polarization streams saps dmsp particle data indicate that the said location closely followed the equatorward edge of the auroral electron precipitation boundary while remaining generally poleward of the equatorward boundary of the ion precipitation the latitude of the said varied throughout the interval on similar timescales to variations in the interplanetary magnetic field and auroral activity while variations in its velocity were more closely related to ring current dynamics these results are consistent with said electric fields being generated by localized charge separation in the partial ring current but suggest that their location is more strongly governed by solar wind driving and associated large scale magnetospheric dynamics

large plasma density enhancements occurring in the northern polar region during the 6 april 2000 superstorm we focus on the ionospheric response of northern high latitude region to the 6 april 2000 superstorm and aim to investigate how the storm enhanced density sed plume plasma became distributed in the regions of auroral zone and polar cap plus to study the resultant ionospheric features and their development multi instrument observational results combined with model generated two cell convection maps permitted identifying the high density plasma s origin and the underlying plasma transportation processes results show the plasma density feature of polar cap enhancement pce 600 103 i cm3 appearing for 7 h during the main phase and characterized by increases reaching up to 6 times of the quiet time values meanwhile strong westward convections 17 500 m s created low plasma densities in a wider region of the dusk cell oppositely small 750 m s but rigorous westward drifts drove the sed plume plasma through the auroral zone wherein plasma densities doubled as the sed plume plasma traveled along the convection streamlines and entered the polar cap a continuous enhancement of the tongue of ionization toi developed under steady convection conditions however convection changes caused slow convections and flow stagnations and thus segmented the toi feature by locally depleting the plasma in the affected regions of the auroral zone and polar cap from the strong correspondence of polar cap potential drop and subauroral polarization stream saps we conclude that the saps e field strength remained strong and under its prolonged influence the sed plume provided a continuous supply of downward flowing high density plasma for the development and maintenance of pces

triple seismic zone and the regional variation of seismicity along the northern honshu arc the regional variation of seismicity along the northern honshu arc japan is studied using accurate focal depths and focal mechanism types we use focal depths determined from pp p time intervals reported in the isc bulletins for submarine earthquakes depths are corrected by considering the pp phase reported in the bulletins as the pwp phase the reflection from the ocean surface out of more than 600 well located earthquakes selected from the isc bulletins we determine the types of the focal mechanisms of 184 events using p wave first motion data based on historical seismicity of great and large earthquakes we divide the zone of thrust type earthquakes at the plate interface into two regions the shallow thrust zone 0 40kin where great earthquakes ms 8 0 occur and the deep thrust zone 40 60km where large earthquakes ms 7 4 occur the activity of great or large earthquakes shows a variation along the are in some regions both the shallow and deep thrust zones are active and in other regions only one of the thrust zones is active the seismicity of recent moderate size earthquakes mb 4 combined with the focal mechanism type shows a variation along the are which reflects the variation of the activity of great or large earthquakes where large earthquakes do not occur in the deep thrust zone neither thrust type nor down dip compression tension type events occur in and beneath the deep thrust zone where large earthquakes do occur in the deep thrust zone we find a number of thrust type earthquakes further in the latter case in some regions the down dip compression and tension type events of the double seismic zones extend seaward just beneath the deep thrust zone and form a triple planed structure of seismicity the triple seismic zone this study confirms the hypothesis of previous workers seno and pongsawat 1981 on the causal relation between the strong seismic coupling of two converging plates at the deep thrust zone and extension of the double seismic zone i e the presence or absence of activity within the slab beneath the deep seismic zone occurs when the deep thrust zone has a strong or weak coupling respectively here the weak coupling could be interpreted as either aseismic slip or as low stress buildup since the last large event occurred at the deep thrust zone triple seismic zones are found offshore of miyagi prefecture where the deep thrust zone has been broken recently in 1978 and offshore of fukushima prefecture we expect a future large earthquake at the deep thrust zone offshore of fukushima prefecture because the presence of the triple seismic zone suggests stress has been accumulating and 40 years have passed since the deep thrust zone was ruptured in 1938

tectonic structure across the accretionary and erosional parts of the japan trench margin structure sections across the japan trench from prestack depth migrated seismic data define the accretionary prism a wedge shaped seaward end of the continental framework and a tectonized middle slope between them the 10 km wide accretionary prism is underthrust by sediment remaining with the subducted oceanic crust structure beneath the steep middle slope more nearly resembles the adjacent continental margin than the accreted mass this deformed middle slope domain forms a buffer between the compliant accretionary wedge and a more rigid older continental framework along the plate boundary subducted strata thicken beneath the middle and upper slopes and where last imaged are four times the input thickness beneath the accretionary prism this interplate stratified layer appears to control interplate friction because the layer is imaged 45 km landward from the trench axis to 12 km depth and in that expanse few upper plate earthquakes are recorded erosion of the base of the upper plate beneath the middle continental slope is indicated by margin subsidence and material flux this erosion is concurrent with accretion at the front of the margin

time evolution of the subauroral electric fields a case study during a sequence of two substorms 1 the temporal evolution of the subauroral polarization stream saps is investigated using the doppler velocity observations by the unwin hf radar in conjunction with the simultaneously observed auroral luminosity and plasma convection reversal regions the event under study of 14 december 2004 1000 1600 ut occurred during geomagnetically quiet conditions when a sequence of two substorms separated by 2 hours was observed by the image satellite it is shown that the saps appeared shortly after the first substorm onset and continued to dominate the westward plasma convection at subauroral magnetic latitudes 59 63 s for 6 hours an unexpected exception occurred near the second substorm onset time when a narrow channel of weaker saps westward convection became embedded in the slow eastward drifting plasma for a short 25 min period which was attributed to the equatorward expansion of the dawn convection cell during the growth and expansion phases of the second substorm another remarkable plasma convection feature was observed in the same 25 min period 5 poleward of saps this was a narrow mirror channel of the eastward drifting plasma parallel to the main saps channel it is argued that the latter feature may also be caused by the equatorward expanding dawn convection cell whose streamlines become compressed by and aligned with the saps poleward edge a possible relationship between the saps intensity and its position relative to the auroral oval is also investigated the results suggest that the magnetosphere ionosphere feedback processes within saps become more effective as the equatorward edge of the eastward convection region retreats poleward with the saps position much less affected by the auroral dynamics

nightside ionospheric electrodynamics associated with substorms pfisr and themis asi observations 1 observations from the newly available poker flat incoherent scatter radar have been used to study the ionospheric electrodynamics during the substorm expansion phase substorm events selected have been divided into three categories based on onset location relative to the radar and repeatable features have been identified west of onset westward flows increased in response to the passage of the westward traveling surge wts poleward of them the enhanced flows occurred within the sub auroral polarization streams region of downward region 2 currents which extend equatorward from near the equatorward boundary of electron precipitation strong e region ionization increase associated with the wts occurred poleward of the enhanced westward flows suggesting that poleward pedersen currents fed by the downward region 2 field aligned current fac further equatorward contribute at least partially to closure of the upward fac of the wts an enhanced eastward flow channel developed east of onset e region ionization decreased poleward of this flow peak implying formation of downward fac and further increased equatorward of the flow peak suggesting strengthening of preexisting region 2 upward fac these observations indicate that the downward fac formed at onset at least partially closes via the upward region 2 currents the enhanced eastward flows decreased after passage of the auroral bulge and the reduced e region ionization increased again when onset occurred within the radar fov the thin breakup arc of onset occurred at the center of the harang reversal while if the optical onset was poleward of the radar fov the harang reversal was observed after the onset a 2 d picture of the evolution of ionospheric electrodynamics was generated by synthesizing observations from the three categories which provides a schematic description of the relationship between region 2 and substorm expansion electrodynamics

formation of polar ionospheric tongue of ionization during minor geomagnetic disturbed conditions previous investigations of ionospheric storm enhanced density sed and tongue of ionization toi focused mostly on the behavior of toi during intense geomagnetic storms little attention has been paid to the spatial and temporal variations of toi during weak to moderate geomagnetic disturbed conditions in this paper we investigate the source and development of toi during a moderate geomagnetic storm on 14 october 2012 multi instrumental observations including gps total electron content tec defense meteorological satellite program dmsp in situ measured total ion concentration and ion drift velocity superdarn measured polar ion convection patterns and electron density profiles from the poker flat incoherent scatter radar pfisr have been utilized in the current analysis gps tec maps show salient toi structures persisting for about 5 h over high latitudes of north america on 14 october 2012 in the later recovery phase of the storm when the magnitudes of imf by and bz were less than 5 nt the pfisr electron density profiles indicate that the extra ionization for tec enhancements mainly occurred in the topside ionosphere with no obvious changes in the bottomside ionosphere and vertical plasma drifts additionally there were no signatures of penetration electric fields in the equatorial electrojet data and upward ion drifts at high latitudes at the same time strong subauroral polarization streams with ion drift speeds exceeding 2 5 km s carried sunward fluxes and migrated toward lower latitudes for about 5 based on the dmsp cross track drift measurements based on those measurements we postulate that the combined effects of initial build up of ionization at midlatitudes through daytime production of ionization and equatorward or less poleward than normal daytime neutral wind reducing downward diffusion along the inclined filed lines and an expanded polar ion convection pattern and its associated horizontal plasma transport are important in the formation of the toi

subduction of a late cretaceous seamount of the louisville ridge at the tonga trench a model of normal and accelerated tectonic erosion the hotspot generated louisville ridge is a 4000 km chain of seamounts typically 2 2 5 km high and 10 40 km in diameter and an underlying crustal swell 1 5 km high and 100 km wide trending nnw across the southwestern pacific the northwest end of the ridge collides with the north trending tonga trench 26 s which just north of that point is exceptionally deep 10 8 km and lacks both a turbidite wedge and a bordering accretionary complex the collision zone is moving rapidly southward multichannel seismic reflection data in the collision zone show a west dipping subsurface platform 2 3 km beneath the lower western trench slope which is interpreted as the flat summit of a subducted guyot motuku of the louisville chain projected eastward the summit plain passes 1 2 km above the trench floor dredging of the nearby inner trench wall recovered uppermost cretaceous maestrichtian oceanic pelagic sediments interpreted to be fragments of the sedimentary mantle of a subducted louisville seamount the principal effects of hotspot ridge collision with a sediment starved trench are 1 the impacting seamounts are subducted rather than accreted and 2 although some seamount rocks are temporarily accreted the inner trench wall is tectonically eroded arcward at rates possibly as high as 50 km m y accelerated tectonic erosion is related to 1 fracturing shearing and general weakening of arc substrate rocks as they are lifted by the swell penetrated by impacting seamounts and left to collapse as the ridge moves away 2 a more effective removal of weakened rock in underthrusting grabens which are larger in the crustal swell 3 a possible elevation of the subduction decollement to account for the removal of as much as 30 000 km of material from a 400 km sector of the trench in 1 million years and 4 a reduction in supply of arc derived debris resulting from the gap in arc volcanism accompanying subduction of the ridge normal tectonic erosion in the tonga trench is apparently minor and we conclude that the bulk of the 37 000 km of material which fills subducting grabens each million years is arc derived volcanic and pelagic sediment