high frequency radar observations of atmospheric gravity waves in the high latitude ionosphere the johns hopkins university high frequency coherent scatter radar at goose bay labrador often observes the effects of propagating atmospheric gravity waves particularly in ground backscatter returns to date these waves have been identified in late fall and early winter on propagation paths directed over the davis strait between northeastern canada and greenland the waves appear as spatially localized enhancements in the backscattered power and as quasiperiodic fluctuations in the backscattered powers doppler velocities and reflection heights they are generally observed during daylight hours and are usually accompanied by backscatter from higher latitude ionospheric irregularities that appear to be located near the ionospheric convection reversal boundary the lowest frequencies associated with the gravity waves lie in the range 0 4 to 0 6 mhz and the wavelengths lie in the range 300 to 600 km the waves generally propagate equatorward at an angle of 150 to 180 east of geographic north during intervals with an expanded polar cap northward propagating gravity waves are sometimes observed measurements of the parameters of the waves and the ranges to the sources suggest that the waves are excited at a height of 100 to 150 km near the convection reversal boundary and the polar cusp and that the bulk of the observed perturbations are due to earth reflected waves

hatton bank northwest u k continental margin structure summary the continent ocean transition near hatton bank was studied using a dense grid of single ship and two ship multichannel seismic mcs profiles extensive oceanward dipping reflectors in a sequence of igneous rocks are developed in the upper crust across the entire margin at the landward shallowest end the dipping reflectors overlie continental crust while at the seaward end they are formed above oceanic crust beneath the central and lower part of the margin is a mid crustal layer approximately 5 km thick that could be either stretched and thinned continental crust or maybe newly formed igneous crust generated at the same time as the dipping reflector sequence beneath this mid crustal layer and above a well defined seismic moho which rises from 27 km continental end to 15 km oceanic end across the margin the present lower crust comprises a 10 15 km thick lens of material with a seismic velocity of 7 3 to 7 4 kds we interpret the present lower crustal lens as underplated igneous rocks left after extraction of the extruded basaltic lavas a considerable quantity of new material has been added to the crust under the rifted margin the present moho is a new boundary formed during creation of the margin and cannot therefore be used to determine the amount of thinning

evidence for reflectors in the lower continental crust before rifting in the valencia trough the past decade has seen a rapid advance in our understanding of the deep structure of the continental crust especially in europe1 3 australia4 and north america5 where seismic profiling has revealed a highly reflective layer in the lower crust on many profiles the reflective layer is associated with regions of extension6 7 suggesting that the reflectors originate by some form of ductile flow or magmatic intrusion during rifting8 9 to test this hypothesis we have examined geophysical and geological data from the valencia trough a rift basin10 12 of late oligocene early miocene age from a comparison of profiles in different parts of the trough and independent constraints on the initial crustal thickness we argue that the reflective layer in this basin was probably already in the crust before rifting and that a mid tertiary extensional event is not required to explain it

pliocene uplift of the eastern iberian margin inferences from quantitative modelling of the valencia trough we present the results of quantitative modelling of subsidence in the valencia trough and associated uplift in the catalan coastal ranges and the balearic islands basement subsidence moho depth and gravity anomalies are calculated for different effective elastic thicknesses eet and durations of rifting along two profiles constrained by recently collected multichannel seismic and gravity data the tectonic evolution of the catalan coastal ranges cannot be explained with traditional two layer lithospheric stretching models for the valencia trough but is consistent with a thermomechanical model invoking lithospheric necking combined with a late stage uplift event the modelling of the topography of the balearic islands suggests an interaction of extension in the valencia trough with extension in the south balearic basin our study supports a rifting model with low values for the flexural rigidity an intermediate level of necking and one finite duration stretching event propagating from the northeast towards the southwestern part of the valencia trough the modelling provides constraints on the magnitude of a large scale pliocene uplift of the eastern margin of the iberian peninsula

multiple post caledonian exhumation episodes across nw scotland revealed by apatite fission track analysis abstract the post caledonian exhumation history of nw scotland is a controversial issue with some studies advocating largely continual emergence whereas others suggest dominantly early palaeogene plume driven exhumation apatite fission track analysis afta data for samples of precambrian basement and permian cretaceous sediments from onshore and offshore reveal multiple phases of post caledonian cooling triassic beginning 245 225 ma cretaceous 140 130 ma 110 90 ma and cenozoic 65 60 ma 40 25 ma 15 10 ma all of which are interpreted at least in part as recording exhumation basement and sedimentary cover rocks display similar thermal histories emphasizing the regional nature of these episodes and implying that sedimentary outliers represent the remnants of previously more extensive sequences significant thicknesses of jurassic rocks may once have covered nw scotland palaeocene palaeothermal effects are most pronounced in the vicinity of igneous centres probably reflecting combined effects of heating by elevated heat flow deeper burial and hydrothermal activity most of the region underwent kilometre scale neogene exhumation contrary to the common assumption of monotonic cooling and denudation histories integration of geological evidence with afta data defines an episodic thermal history involving repeated cycles of burial and exhumation we suggest that onshore passive margins and continental interiors may also best be characterized by similar histories

superdarn observations of daytime mstids in the auroral and mid latitudes possibility of long distance propagation 1 the propagation parameters of daytime medium scale traveling ionospheric disturbances mstids are investigated for the first time using near simultaneous superdarn radar data obtained at auroral and middle latitudes the observations suggest that mstids can propagate from auroral to mid latitudes with persistent propagation parameters if the dominant propagation direction is approximately equatorward however statistical analysis implies that a portion of mstids with higher horizontal phase velocity are unable to reach the mid latitude due to enhanced dissipation and the reduction of the ion drag effect

identification of high latitude acoustic gravity wave sources using the goose bay hf radar observations of medium scale acoustic gravity waves using the goose bay hf radar are presented data were examined for the period of november and december 1991 and days that showed evidence of traveling ionospheric disturbances tids were selected for analysis tids were identified in the hf radar data by quasi periodic enhancements of the power in the ground scattered portion of the radar signal various parameters were determined from the data including the wave frequency the wavelength the propagation direction and the phase velocity it was found that multiple wave packets from multiple directions are often present simultaneously source times and locations were identified from data from 2 days december 5 and 6 1991 and these were compared with data from the greenland magnetometer chain the source times and locations were found to correspond to sudden magnetometer deflections indicating the correlation of gravity wave sources with the occurrence of ionospheric electrojet current surges finally the source times and locations were examined in local time and magnetic latitude and it was found that the sources were clustered in two locations near the magnetospheric cusp and near 1600 mlt at about 75 magnetic latitude

a wide angle seismic reconnaissance survey of the crust and upper mantle in the celtiberian chain of eastern spain abstract data from seismic refraction profiles to investigate the crust and upper mantle in the celtiberian chain are presented and discussed a rather heterogeneous deep crustal structure with lateral variations can be inferred from the available data in the central part of the chain crustal depths of about 32 km are coincident with those in the iberian meseta whereas close to the mediterranean shore the moho is located at about 20 km depth the varying thickness of the crust can be interpreted in terms of different tectonic regimes the shallowing towards the mediterranean is associated with the neogene rifting process which has its main expression in the gulf of valencia but whose effects seem to reach well towards the interior of iberia the upper mantle has a structure typical for the hercynian domain in europe a seismic phase reflected from about 80 km is the most important feature this may be interpreted as a mantle discontinuity with a positive velocity jump or alternatively as an indication for the bottom of the lithosphere

medium scale traveling ionospheric disturbances observed with the superdarn hokkaido radar all sky imager and gps network and their relation to concurrent sporadic e irregularities 1 we present midlatitude medium scale traveling ionospheric disturbances mstids observed with a super dual auroral radar network superdarn hf radar at around 10 mhz in hokkaido japan in combination with a 630 nm all sky imager and a gps network geonet that provides total electron content tec data mstids propagating southward from high latitudes are detected at first with the hf radar and then with the imager and geonet we analyze two mstid events one in winter event 1 and the other in summer event 2 to find that mstids appear simultaneously at least at 55 25 n it is shown that nighttime mstids propagate toward the southwest over a horizontal distance of about 4000 km and daytime mstids do so toward the southeast daytime radar echoes are due to ground sea surface gs scatter while nighttime echoes in event 1 return from 15 m scale f region field aligned irregularities fais and those in event 2 are due to gs scatter doppler velocities of the nighttime f region fai echoes in event 1 are negative motion away from the radar within strong echo regions and are positive motion toward the radar within weak echo regions this fact suggests that the strong weak echoes return from suppressed enhanced airglow tec areas in line with previous observations over central japan the nighttime mstids in events 1 and 2 are often accompanied by concurrent coherent echoes from fais in sporadic e es layers the es echo areas in event 2 rather coincide with suppressed airglow tec areas in the f region that are connected with the echo areas along the geomagnetic field indicating the existence of e and f region coupling at night

total tectonic subsidence a parameter for distinguishing crust type at the u s atlantic continental margin total tectonic subsidence tts is the difference between the prerifting continental crust elevation and the present sediment unloaded basement depth in a sedimentary basin tts is calculated using observations of bathymetry and basement depth and assumptions about sediment density and the loading response of the lithosphere i use the extensional model for sedimentary basin formation to interpret the tts of a passive continental margin that model predicts that the tts on an old margin should define the major crust type boundaries and indicate the lateral distribution of extension within the extended continental crust tts analysis of the u s atlantic continental margin indicates that the boundary between extended continental and oceanic crusts lies along the east coast magnetic anomaly ecma to the north of the blake spur fracture zone bsfz and along the blake escarpment to the south there is no tts anomaly associated with the blake spur magnetic anomaly which seems to be underlain by normal oceanic crust the ecma appears to be associated with a tts minimum but i attribute that to artificially shallow estimates of depth to magnetic basement under the ecma tts estimates of extended continental crust thickness agree well with gravity models except where the problem with magnetic basement depth estimates interferes the amount of crust extension prior to seafloor spreading varies along the strike of the margin the most abrupt change is at the bsfz across the bsfz the amount of extension varies by 160 km but the volume of continental material does not vary the extension variation may be caused by lateral changes in the gross rheology of the continental lithosphere in the case of the bsfz it would be the suture of more ductile pre late paleozoic african craton with more brittle north american craton that could cause the abrupt change

large scale traveling ionospheric disturbance observed by superdarn hokkaido hf radar and gps networks on 15 december 2006 1 on 15 december 2006 during the main phase of a relatively large storm doppler velocity data from the super dual aural radar network superdarn hokkaido radar together with total electron content tec data from the gps earth observation network geonet recorded daytime large scale traveling ionospheric disturbances lstids we studied two disturbances propagating southward and one disturbance propagating northward between 0000 and 0600 ut on 15 december 2006 the former disturbances were lstids typical of those reported in many previous studies whereas the latter was confirmed as an lstid propagating from the southern into the northern hemisphere reported in a few past studies from comparisons of superdarn hokkaido radar doppler velocity and geonet tec we found a positive correlation between downward ionospheric motion and increasing tec this relationship is consistent with results of model calculation this is the first observation of lstids ranging from high to low latitude combining simultaneous superdarn hf radar and gps network observations

observations of 50 and 12 mhz auroral coherent echoes at the antarctic syowa station data on 50 and 12 mhz e region coherent echoes from approximately the same directions and in a broad range of azimuths are available for 1995 1997 radar observations at the antarctic syowa station one event of such observations is considered to compare power and doppler velocity of echoes at these significantly different frequencies for the considered event doppler velocities of more than 600 ms 1 as recorded at both radar frequencies were observed we show that even though the 50 mhz echoes exhibit strong flow angle variation of the power the 12 mhz echoes do not apparent aspect angle power attenuation is found to be 10 and 2 5 dbdeg 1 at 50 and 12 mhz respectively measured doppler velocities along specific radar directions are found to be comparable in spite of the significant difference in radar frequencies with the velocity ratio v50mhz v12mhz being in between 1 6 and 0 9 for high velocities of more than 400 ms 1 the velocity ratio varies with slant range and azimuth of observations ionospheric propagation effects for radio waves and plasma physical effects for irregularities are considered in an attempt to explain several observed features for example the echo power and velocity ratio variations with slant range

crustal structure of the goban spur continental margin northeast atlantic from deep seismic reflection profiling deep reflection data across the uk continental margin are used to test theories concerning the origin of a pervasive reflective fabric in the lower continental crust seen on many deep reflection profiles worldwide the origin of the reflections is at present little understood but clearly represents an important crustal process the western approaches margin wam line was designed to determine the behaviour of the lower crustal reflections in crust which has undergone significant extension the wam profile across the continental shelf is characterized by bright continuous lower crustal reflections some of which reach 30 km in length and have minimum reflection coefficients of 0 1 deep water multiples in the area of the continental slope partially obscure reflections from the lower crust but detailed analyses show that reflectors are present in the lower crust on the continental slope adjacent to the continent ocean boundary the lower crust on the wam profile is well imaged and free of noise and multiples this very thin crust exhibits the same reflectivity pattern as is observed on the continental shelf i e the upper half of the crust is blank and the lower half contains sub horizontal reflections the lower crustal reflections adjacent to the continent ocean boundary are less continuous than the reflections seen on the shelf and are interpreted as being the remnants after extension of the lower crustal reflectors observed on the continental shelf the lower crustal reflectors are thus interpreted to pre date the extensional episode that led to the opening of the atlantic the preservation of thinned sections of both transparent upper crust and reflective lower crust adjacent to the continent ocean boundary suggests that extension by pure shear was the mechanism by which the crust was thinned in the goban spur area

is lower crustal layering related to extension summary the western approaches margin wam profile was shot to test the hypothesis that the reflectivity observed in the lower crust is related to extensional processes the preliminary results of the experiment show that the reflectivity in the lower crust appears to become weaker on the continental shelf near the slope break detailed examination of the data however show a significant increase in noise in the region where the layering appears to fade the noise may be of sufficient amplitude to obscure any coherent lower crustal events present therefore the only conclusion that can presently be drawn from the dataset is that the layering does not become more pronounced in the region of maximum extension

an empirical model of the earth s horizontal wind fields hwm07 1 the new horizontal wind model hwm07 provides a statistical representation of the horizontal wind fields of the earth s atmosphere from the ground to the exosphere 0 500 km it represents over 50 years of satellite rocket and ground based wind measurements via a compact fortran 90 subroutine the computer model is a function of geographic location altitude day of the year solar local time and geomagnetic activity it includes representations of the zonal mean circulation stationary planetary waves migrating tides and the seasonal modulation thereof hwm07 is composed of two components a quiet time component for the background state described in this paper and a geomagnetic storm time component dwm07 described in a companion paper

mhd nature of night time mstids excited by the solar terminator 1 we have obtained first experimental evidence in favour of the magnetohydrodynamic mhd nature of night time medium scale travelling ionospheric disturbances mstids we used total electron content tec measurement data from the dense gps networks in california and in japan for 2008 2009 it was found that the spectral mstid characteristics are determined by the solar terminator st dynamics in summer mstids are detected 1 5 3 hours before the evening st at 100 km above the point of observations but at the moment of the evening st passage through the magnetoconjugate point at the equinox mstids are registered at once after st appearance in winter mstids are observed 1 5 3 hours after the evening st occurrence at the point of observations but at the moment of the evening st passage in the magnetoconjugate point the mstid occurring synchronously with the st passage through the magnetoconjugate area suggest that the st excited mstids are of mhd nature

subsidence history crustal structure and thermal evolution of the valencia trough a young extensional basin in the western mediterranean the valencia trough is an extensional basin that began rifting during the late oligoceneearly miocene yet it is located within a region of compression between the european and african plates seismic reflection seismic refraction well gravity and geoid data have been used to determine the relative importance of extensional and compressional processes in controlling the structure and evolution of the trough although the trough appears symmetric on bathymetric maps seismic and gravity and geoid data indicate a fundamental asymmetry in its deep crustal and upper mantle structure two dimensional flexural backstripping techniques have been used to estimate the total amount of crustal stretching along a transect of the trough between the catalan coastal ranges and mallorca there is good agreement between the predicted depth to the mono based on a stretching model and the seismically constrained depth beneath the catalan margin but poor agreement beneath mallorca the seismic moho beneath mallorca can be explained by a model in which the crust was modified by the flexural effects of thrust fold loading geoid data suggest that the differences in the crustal structure between the two margins extend into the upper mantle the catalan margin is characterized by a thermal and mechanical boundary which marks the transition between cold unstretched lithosphere and hot thin lithosphere while mallorca is located above a broad region of lithospheric thinning the subsidence history and amount of crustal thinning in the catalan margin resemble that of typical atlantic type nonvolcanic margin however a narrow transition zone 60 km the lack of any evidence for a conjugate margin and the absence of oceanic crust suggest fundamental differences in the way that extensional processes may occur in convergent plate settings

identification of the temperature gradient instability as the source of decameter scale ionospheric irregularities on plasmapause field lines 1 recent observations with the new mid latitude superdarn hf radar located at wallops island virginia have identified a class of ionospheric irregularities that is prevalent in the nightside sub auroral ionosphere under low to moderate kp conditions these irregularities can be observed for many hours and generally exhibit very low doppler velocities a recent collaborative experiment using the wallops radar and the millstone hill incoherent scatter radar has determined that these irregularities are located at the ionospheric footprint of the plasmapause and in a region of opposed electron density and electron temperature gradients we conclude that the irregularities are produced by the temperature gradient instability tgi or by turbulent cascade from primary irregularity structures produced from this instability this is the first experimental confirmation that the tgi is effective in producing decameter scale ionospheric irregularities

constraints on melt distribution from seismology a case study in ethiopia low seismic velocities and or strong seismic anisotropy are often interpreted as being caused by partial melt to better understand this we used numerical modelling varying the shape and amount of melt to show how seismic phases are affected by melt we observed that seismic waves are more sensitive to the shape than to the amount of melt rayleigh wave velocities were almost always reduced in the presence of melt while pn wide angle p wave refraction and love wave velocities showed low velocity anomalies for vertically aligned melt but little anomaly for horizontally aligned melt these data can therefore be used to determine the alignment of melt shear wave splitting receiver functions showed strong anisotropy and can be used to constrain the strike of vertically aligned partial melt we showed that melt in the mantle beneath ethiopia is probably stored in low aspect ratio disc like inclusions suggesting that the melt is not in textural equilibrium we estimated that 2 7 of the vertically aligned melt is stored beneath the main ethiopian rift 6 of the horizontally and vertically aligned melt is stored beneath the red sea rift and 1 6 of the horizontally aligned melt is stored beneath the danakil microplate this supports the idea of strong shear derived segregation of melt in the narrow main ethiopian rift compared with that observed beneath afar

crustal structure and the mechanical properties of extended continental lithosphere in the valencia trough western mediterranean seismic refraction and reflection gravity and well data have been used to constrain the structure and evolution of the valencia trough a young extensional basin in the western mediterranean seismic refraction data reveal the present day crustal structure while backstripping of seismic reflection and well data reveal the structure at the time of rifting by comparing the seismically constrained crustal structure to that inferred from backstripping we have been able to evaluate whether the moho is in the expected position given the tectonic subsidence uplift and sediment loading history of the trough the best overall fit between the predicted and seismically constrained crustal structure in the trough is for a model in which the extended continental crust and lithosphere has acquired little or no strength following rifting a low strength is in accord with the observed free air gravity anomaly as well as results from other types of rift basins such as the north sea and the continental margin off the east coast of the usa there are discrepancies between the observed and predicted moho depths beneath the flanks of the valencia trough but they are attributed to either the removal of crustal material during or following rifting iberian peninsula or to orogenic loading of previously extended continental crust mallorca the largest discrepancy up to 10 km correlates with the ebro delta which has prograded into the trough by more than 60 km since the pliocene the discrepancy cannot be explained by the same large scale processes that modified the moho beneath the trough flanks and requires that the lithosphere beneath the ebro delta region is associated with a high 60 t c

statistical study of midlatitude e region echoes observed by the hokkaido superdarn hf radar statistical characteristics of short range coherent echoes observed by the hokkaido super dual auroral radar network superdarn high frequency hf radar geographic geomagnetic latitude 43 5 n 37 3 n at midlatitudes are investigated we show that the echo occurrence is increased during nighttime and especially strongly during winter and summer during summer the occurrence rates are still large during morning prenoon hours for these periods strong sporadic e layers are observed by the wakkanai ionosonde geographic geomagnetic latitude 45 2 n 39 1 n located in the vicinity of the radar field of view echo occurrence rate does not increase with the planetary magnetic activity characterized by the kp and dst magnetic indices and seasonally anticorrelates with variations of the ap index with respect to the magnetic l shells echoes are seen more frequently in beams oriented almost perpendicular to l shells during summer in beams at intermediate angles during equinoxes and winter and sometimes in beams at the smallest available angles 45 during winter midlatitude echoes are of about the same power as at high latitudes but narrower by a factor of 5 power and spectral width of nighttime echoes increases with doppler velocity consistent with high latitude observations the doppler velocity shows a clear semidiurnal variation the local time of these maxima changes with season it is hypothesised that many hokkaido echoes are received at high magnetic aspect angles of several degrees and they are coming from the lower part of the e region where the irregularity phase velocity is affected by both e b plasma drifts and neutral winds

high resolution mapping of tec perturbations with the gsi gps network over japan two dimensional total electron content tec perturbations over japan are mapped with the geographical survey institute gsi gps network geonet gps earth observation network its spatial resolution is 0 15 latitude 0 15 longitude and temporal resolution is 30 seconds two dimensional tec observations with these high resolutions revealed spatial structures and temporal evolutions of traveling ionospheric disturbances tids in the nighttime mid latitude ionosphere on july 03 1997 a preliminary result of the tec perturbation mapping indicates that it would be a strong tool to investigate the ionospheric structures in detail coordinated observations with other ionospheric observation techniques such as incoherent scatter is radars airglow imagers and ionosondes are needed to clarify the vertical structure of the ionosphere

comparative investigations of continental reflectivity abstract based on observations of reflectivity and lengths of reflecting boundaries in various geological units a consistent picture for explaining the different reflectivity patterns is derived whereas in the upper brittle part of old crusts reflectivity concentrates on fault zones of former or present compressional zones it is absent in warm extensional areas where in addition granitic plutons may disturb any upper crustal layering the lower crust of these young and warm areas with its reflecting lamellae is dominated by strain and shear processes i e by an ordering process in a low viscosity environment any change of sialic or low grade to more mafic or high grade layers at mid crustal levels conrad discontinuity is not related to the beginning of the lamellae but may be responsible for a finger type appearance of lower crustal reflectivity

some unsolved birps problems summary birps has 8000 km of records around britain that are relevant to the rheology of continents and to faulting of the lithosphere problems include the need to measure seismic velocities with better resolution and to eliminate multiples in deep water the question are blank bits of records due to noise increase or to geology and the need to know the physics of the origin of deep reflections in order to answer geologists questions

coincident seismic reflection refraction studies of the continental lithosphere a global review summary vertical incidence reflection profiling has identified several characteristic features of the continental iithosphere including a generally transparent upper crust a reflective lower crust reflections from the crust mantle boundary and a commonly transparent upper mantle the underlying physical causes of these characteristic features remain poorly understood this review summarizes additional information brought to bear on the physical properties of these characteristic crustal structures through the use of coincident wide angle refraction profiling

evidence for shear zones in the lower crust offshore britain lower crustal reflections seen on british institutions reflection profiling syndicate birps deep seismic reflection data recorded offshore the united kingdom are commonly short convex up and crosscutting consequently the lower crust should not be described as layered as much of the reflecting structure is not fully resolved and may be quite complex moreover the lower crustal reflective zone lcrz is not a uniformly reflective layer but contains reflective bands that wrap around nonreflective transparent zones because transparent zones probably correspond to a lack of a reflecting fabric understanding why these features are unreflective may help constrain the cause of the reflectivity of the lower crust although transparent zones may have a variety of explanations e g large shear pods or frozen magma bodies the geometry of reflective bands and transparent zones is perhaps best explained by the geometry of shear zones and low strain lozenges predicted both by combining theoretical lithospheric strength profiles with slip line field theory and by drawing analogies with structures developed in highly tectonised high grade metamorphic terrains this interpretation implies that lower crustal reflections may be from shear zones and also has implications for the way the lower crust deforms in particular extension may be accommodated by the relative movement of low strain lozenges along intervening zones of simple shear the lower crust may be stretched during extension but it must also transfer deformation between the upper crust and the mantle the observation on birps data of mantle reflections interpreted as mantle shear zones implies that deformation in the mantle is localised however the manue reflections are never colinear with faults in the upper crust requiring at least locally a component of sub horizontal bulk strain within the lower crust which may greatly increase the amount of shearing therein and hence perhaps may increase the reflectivity of the lcrz

effects of finite rifting times on the development of sedimentary basins abstract most thermo mechanical models for the development of sedimentary basins have assumed that the rifting responsible for the formation of the basin occurred instantaneously and have examined the post rift development of the basin this assumption greatly simplifies the mathematical treatment but is not in accord with what is found in nature where 10 to 50 m y rifting events commonly accompany the formation of sedimentary basins and continental margins the effects of a finite rifting time on the development of sedimentary basins are examined using an analytic technique which allows an arbitrary rifting history in both time and space and which considers the effects of both vertical and horizontal heat transfer this technique allows the thermal structure of the lithosphere to be calculated throughout the rifting event and thus permits the subsidence history and surface heat flow of the developing basin to be traced the effect of a finite duration extension event is that heat is lost during rifting increasing the syn rift subsidence at the expense of the post rift lateral heat flow which was not included in previous studies of the effect of finite rifting times has a significant effect on the subsidence history distribution of sediments and thermal history in particular the post rift subsidence is decreased by more than 25 for a 20 m y rifting event and by more than 10 15 for a rifting event as short as 10 m y this will significantly decrease the subsidence rates in the post rift stage and implies that inferences concerning the structure development and thermal history of the basin derived from using curves to interpret backstripped subsidence can be greatly in error variations in syn rift sediment accumulation and lithospheric thermal structure at the end of rifting resulting from different rifting histories can interact with other factors such as the flexural response of the lithosphere to sediment loading to affect the final width of the basin the total amount of sediments that accumulate and the basin stratigraphy

goose bay radar observations of earth reflected atmospheric gravity waves in the high latitude ionosphere in the late fall and early winter the johns hopkins university hf radar at goose bay labrador observes the effects of atmospheric gravity waves on radar transmissions that are obliquely reflected from the ionosphere and subsequently backscattered from the earth s surface the waves exist under a wide variety of geomagnetic conditions however they are particularly noticeable under quiet conditions o le kp le 1 the clearest signatures of the waves are spatially localized enhancements in the backscattered power and quasi periodic fluctuations in the backscatter powers doppler velocities and reflection heights the waves are generally observed during daylight hours and propagate equatorward from regions of high latitude ionospheric backscatter that are located near the ionospheric convection reversal boundary the gravity waves appear to be generated just equatorward of the dayside flow reversal boundary in the vicinity of the auroral electrojet at altitudes of 115 to 135 km and propagate approximately perpendicular to the boundary along azimuths ranging from 156 degree to 180 degree the waves propagate obliquely downward through the lower atmosphere until they are reflected by the earth s surface back into the upper atmosphere the frequencies associated with these gravity waves cover the range of 0 3 to 0 6 mhz with wavelengths of 300more to 500 km and with average phase velocities of 110 to 180 m s the maximum phase speeds are 270 to 300 m s which is slightly less than the speed of sound in the lower atmosphere poleward propagating gravity waves are sometimes observed under disturbed conditions when the polar cap and convection reversal boundary have expanded equatorward less

height comparison of midlatitude e region field aligned irregularities and sporadic e layer we present for the first time detailed comparison of heights of mu radar field aligned echoes and sporadic e es layer by applying an fm cw sounding technique for observing es virtual height with high spatial 750 m and time one minute resolutions the production of typical discrete quasi periodic qp radar echoes appearing after sunset is closely related to the oscillation of es height supporting a theory of the qp echo generation no es height oscillations however were observed for the qp echoes appearing around midnight continuous radar echoes appearing after sunrise are located at 90 100 km heights that are lower than the es heights 100 km suggesting that a new mechanism other than the gradient drift plasma instability is necessary for producing these morning continuous echoes

imaging coherent scatter radar incoherent scatter radar and optical observations of quasiperiodic structures associated with sporadic e layers 1 during june and july 2002 a 30 mhz imaging coherent scatter radar was installed and operated on the island of st croix to view the e region ionosphere above arecibo puerto rico during the observing period 10 events with discernible quasiperiodic echo structure were observed with the coherent scatter radar in six of those events simultaneous measurements were made with the arecibo 430 mhz incoherent scatter radar the imaging coherent scatter radar allows us to locate and track the echo structures within the volume illuminated by the transmitter which shows structures that are generally aligned along wavefronts a slight preference for motion of the structures toward the southwest is evident throughout the period but the propagation directions and speeds vary greatly the incoherent scatter radar measurements show a close correspondence between the occurrence of the coherent echoes and the location of the enhanced electron density structures in particular the coherent echoes occur when the electron density layers show uplifts

deep crustal reflection results from the central eromanga basin australia abstract from 1980 to 1982 deep seismic reflection profiles were recorded across the central eromanga basin in eastern australia to study the regional structure stratigraphy and geological history of the eromanga basin and infra basins the reflection data were recorded to 20 s to obtain additional information on the nature and structure of the crust below the sediments and their relationship to the development of the basins the seismic sections show good quality reflections from the deep crust as well as from the sedimentary layers based on the character strength coherence continuity and spatial distribution of the reflections the sections can be divided into four zones the tope zone between 0 and 2 5 s shows fairly uniform coherent and continuous events which correlate with the mesozoic and late palaeozoic sediments the zone from 2 5 to 8 s 4 to 22 km does not show any primary reflections and is interpreted as the highly deformed metasedimentary and metavolcanic rocks of the early palaeozoic thomson orogen underlying the sediments without any recognisable reflection or diffraction patterns in this zone it is difficult to say whether the faulting and folding observed in the sediments extend into the upper crustal basement the deeper zone of numerous reflection segments between 8 and 12 5 s 22 to 36 km is interpreted as thin laminae of alternating low and high velocity intermediate and basic rocks and correlates with the lower crust bounded by refraction velocity discontinuities the lowest zone of no reflections below 12 5 s corresponds with the upper mantle the reflection character and thickness as well as the refraction velocity structure of the crust under the central eromanga basin area are significantly different from those of the precambrian crust under the georgina basin to the northwest it is proposed that the crust under the eromanga basin is extensionally attenuated crust which had been intruded by sills of basaltic melt from the underlying asthenosphere

spatial relationship of nighttime medium scale traveling ionospheric disturbances and f region field aligned irregularities observed with two spaced all sky airglow imagers and the middle and upper atmosphere radar 1 we report simultaneous observations of medium scale traveling ionospheric disturbances mstids and field aligned irregularities fais in the f region using two all sky airglow imagers and the middle and upper atmosphere mu radar mstids propagating southwestward were observed simultaneously in 630 nm airglow images over sakata 39 0 n 139 9 e and shigaraki 34 9 n 136 1 e japan on the night of 16 june 2004 by using all sky images over both sites we estimated the altitude of the airglow layer to be 260 km by the triangulation method during the mstid event fais in the f region were observed by making multibeam measurements with the mu radar at shigaraki in order to investigate the spatial relationship between the mstids and fais the fais were mapped onto the 630 nm airglow layer altitude 260 km along the geomagnetic field lines we found that fais with an intense weak signal to noise ratio coincided with the airglow depletion enhancement caused by the mstids fai velocity obtained from a combination of the doppler velocities on the three radar beams oscillated in the northwest southeast direction with an amplitude of approximately 82 m s the fai velocity was northwestward southeastward at the airglow depletion enhancement the directions of the fai velocity were consistent with those of the e b drifts caused by the polarized electric fields associated with the mstids the northeastward polarized electric field at the airglow depletion region strengthened the background eastward effective electric field and drove the gradient drift instability generating fais this might be the reason why the fais preferred to occur at the airglow depletion region

hokkaido hf radar signatures of periodically reoccurring nighttime medium scale traveling ionospheric disturbances detected at short ranges the super dual auroral radar network hokkaido hf radar often detects periodically reoccurring e region echoing regions propagating toward or away from it in this work we consider 117 of such events identified for 2008 2012 these are shown to occur at nighttime preferentially during summer although significant number for events was found for winter statistics for the local time of occurrence magnitude of the speed and polarity of progressions and temporal and spatial periodicities are presented we show that the power of echoes is linearly related to their doppler velocity which makes it possible to identify the events on both power and doppler velocity plots other peculiar characteristics of echoes are discussed the onset of events is associated with gravity waves propagation through the radar field of view

long listening multichannel seismic profiles in the valencia trough valsis 2 and the gulf of lions ecors a comparison abstract the long listening multichannel seismic mcs profiles recorded during the valsis and ecors experiments were analysed in order to understand the rifting processes of a young passive margin the seismic lines were interpreted within a geological framework which is considerably improved by the results from industrial wells the disturbed upper crust off catalonia is tentatively connected with a variscan front the origin of lamellae in the lower crust beneath the valencia shelf is discussed a variscan origin is rejected and a relation to a jurassic extensional event is proposed a companion basin to the onshore maestrazgo basin is located off shore of valencia and these two basins are probably connected by the left lateral strike slip castellon fault this fault is parallel to the north pyrenean fault which is the trace of the rotation of spain relative to europe the castellon fault may be connected with the asturian fault which is located on the atlantic side of spain a contour map down to the moho has revealed some new deep features and the results are compared with the previous refraction results the sedimentary column of the deep north balearic provencal basin is much thicker than that of the eastern part of the valencia trough and this diversity in the sedimentary infilling is probably related to a difference in the subsidence processes a comparison of the valencia trough to the gulf of lions shows that the thinning of the continental crust looks similar in both regions but the crust is thinner beneath the valencia continental shelf than that below the gulf of lions in both regions the moho rises possibly at the expense of the continental crust by a process as yet unexplained petrological or and thermal variation

observation of three dimensional structures of quasi periodic echoes associated with mid latitude sporadic e layers by mu radar ultra multi channel system 1 quasi periodic qp backscatter observed by vhf radars associated with the mid latitude sporadic e es layers is characterized by distinct striations on range time intensity rti plots two competing models claim to explain the structure of unstable regions that scatter the radar waves horizontally drifting patches at an almost constant altitude and unstable regions elongated in altitude along the geomagnetic field line we have conducted interferometric imaging observations of qp radar echoes to investigate spatial structures of qp echoes precisely kyoto university s newly developed ultra multi channel receiving system of middle and upper atmosphere mu radar was used we used 19 independent channels for the radar imaging and determined the three dimensional structure and the motion of the qp echoes during the observation from 30 may to 02 june 2005 well defined qp echoes were observed on the nights of 31 may 01 june and 02 june 2005 some of qp echoes were found at altitudes higher than 120 km and appeared to descend in altitude as they approached the radar this result suggests that backscatter regions are developed along the geomagnetic field line from es layer altitudes to as high as 130 km and that the fluctuations in plasma density and electric field observed by pfaff et al 2005 using in situ measurements form a part of qp echoes

deep crustal configuration of the valencia trough and its iberian and balearic borders from extensive refraction and wide angle reflection seismic profiling abstract new constraints on the crustal structure of the valencia trough and its iberian and balearic borders have been obtained from a seismic experiment carried out in autumn 1989 a total of 290 sea shots were fired along three refraction wide angle reflection profiles recorded by 10 ocean bottom seismometers obss in the valencia trough and 110 land stations distributed on both flanks the huge amount of recorded data in each profile has been integrated and jointly interpreted to obtain a single 2 d velocity depth model along each line the geometry and deep crustal structure of the basin are fairly well defined in terms of laterally inhomogeneous layered media the sedimentary cover shows a layer of consolidated sediments overlain by neogene and quaternary sediments with a velocity of 5 1 km s interpreted as mesozoic carbonates at the northwestern side of the valencia trough a fairly homogeneous crystalline basement is found on all profiles at a mean depth of 4 km below sea level with a velocity of 6 0 6 1 km s the observed critical distances and arrival times of the moho reflected waves are firm evidence supporting a thinning of the crust towards the centre of the basin the moho rises up to 13 km in the axis of the trough in the nw se and e w profiles and up to 15 km in the ne sw profile moreover the analysis of the well defined pmp phase shows differences between the deep structure of the flanks and the trough respectively a sharp velocity contrast at the moho from a fairly uniform lower crust of 6 4 km s velocity is proposed in both flanks in contrast to a high velocity gradient within the lower crust interpreted near the axis of the trough an anomalous upper mantle velocity of 7 8 km s fits the data throughout the valencia trough and mallorca with slightly higher values of 7 9 km s required towards the continent these velocity values do not favour an interpretation in terms of underplating the geometry of the moho discontinuity shows a gradual deepening towards the iberian peninsula in contrast to a more abrupt slope towards mallorca depth values of 30 32 km typical of a continental crust are inferred about 40 km inland on the iberian peninsula in agreement with the crustal thicknesses already reported for the iberian range and the ebro basin the present crustal thinning resulting from rift episodes in the valencia trough and the iberian border is thus confirmed and constrained from our seismic results of the deep crust and upper mantle

azimuth time intensity striations of quasiperiodic radar echoes from the midlatitude e region ionosphere the valensole high frequency hf radar in the south of france is an ionospheric doppler sounder which can perform e region coherent backscatter measurements over an azimuthal sector of 86 from 26 e to 58 w with 2 angular resolution this large azimuthal coverage is taken advantage of in order to study quasiperiodic qp echoes in the zonal direction using azimuth time intensity ati analysis ati plots show sequential sloping striations of scatter reminiscent of those detected routinely in the range time intensity rti plots of midlatitude radars which view the medium at a fixed azimuth about the meridian it was found that ati striation periods range from a few minutes to less than 30 min whereas the striation slopes are systematically negative motions westward prior to local midnight and turn positive motions eastward in the post midnight hours the zonal rates dx dt computed from the striation slopes take values between 30 and 160 m s these are due to real motions of unstable plasma structures most likely sporadic e patches that drift along with the neutral wind that have zonal scale lengths of several tens of kilometers the present observations imply that the mechanism responsible for qp echoes is independent of azimuth and can basically operate effectively in any direction in the horizontal plane

deep structure of the aquitaine shelf constraints from expanding spread profiles on the ecors bay of biscay transect abstract this paper describes the analysis and interpretation of six expanding spread profiles esp which were shot approximately perpendicular to a 300 km long vertical reflection profile along the eastern continental margin of the bay of biscay aquitaine shelf by the french ecors program in association with hispanoil this transect crosses various tectonic features of different ages the armorican shelf the parentis basin and the cantabria shelf velocity depth models have been derived from the esps by the combination of two complementary methods using time distance and intercept slowness domains they provide important constraints for the analysis of the vertical reflection data the velocities allow definition of crustal layering with a 5 8 6 2 km s 1 upper crust and a 6 5 7 1 km s 1 lower crust this layering matches the change of reflectivity observed on cdp data with a relatively transparent upper crust and upper mantle in opposition to a highly layered lower crust important variations of the thickness of these two layers are revealed by this study the most important one occurs beneath the parentis basin with a 15 km shallowing of the upper mantle the velocity distribution suggesting that major crustal thinning has taken place at the cost of a large part of the lower crust

climatology of medium scale traveling ionospheric disturbances observed by a gps network in central china 1 the 15 month climatology of medium scale traveling ionospheric disturbances mstids during a solar minimum period has been constructed from observations of a dense gps receiver array in central china in total 793 mstid events are identified with peaks in occurrence at 1500 lt and 0100 lt the occurrence of mstids decreases following an increase in geomagnetic activity with 46 of the mstids occurring in the daytime daytime mstids are characterized by a major occurrence maximum around the winter solstice and by an equatorward propagation direction the period phase velocity azimuth and amplitude of daytime mstids are 20 60 min 100 400 m s 130 270 and 0 8 1 5 respectively the remaining 54 of the mstids occurred at night and were characterized by a peak in occurrence at the summer solstice and by a southwestward propagation direction the period phase velocity azimuth and amplitude of nighttime mstids are 20 70 min 50 230 m s 170 300 and 2 7 respectively the propagation directions and the seasonal behaviors support the view that daytime mstids are an ionospheric manifestation of atmospheric gravity waves from the lower atmosphere while a possible excitation mechanism of nighttime mstids is the electrodynamics process caused by plasma instability in the f layer

moho and lower crustal reflectivity beneath a young rift basin results from a two ship wide aperture seismic reflection experiment in the valencia trough western mediterranean summary we present new images of the lower crust and moho beneath the valencia trough a young rift basin in the western mediterranean these images were obtained from a two ship wide aperture reflection experiment and show several features not distinguishable on previously available conventional single ship reflection profiles the moho which was previously only seen intermittently can now be confidently traced throughout the basin we have constructed a present day depth to moho map and estimated the degree of crustal thinning for the whole basin crustal thinning is at a maximum in the centre of the basin where values reach 3 15 0 25 at the margins of the basin the value decreases to 1 5 0 1 the reflective character of the lower crust and moho is different beneath different parts of the basin we have been able to correlate these differences with the amount of stretching we therefore interpret the variations of the observed lower crustal reflectivity as having been caused by the most recent neogene stretching event that opened the valencia trough along the iberian margin there is well developed lower crustal reflectivity consisting of 1 2s two way time twt of 1 4 km long near horizontal reflectors underlain by a more continuous although not significantly stronger reflector interpreted to be the reflection moho offshore this lower crustal reflective unit thins rapidly such that it is undetectable 40 50 km from the coastline where the crust has been stretched by a factor of 1 7 0 1 as the lower crustal reflectivity becomes undetectable the reflection moho becomes a robust continuous event where exceeds 2 4 0 2 however the moho is a weak event and difficult to trace we infer that either the extension itself or associated melting significantly weakened or even destroyed the lower crustal reflectivity in the centre of the basin and enhanced the moho where extension was moderate the balearic margin is somewhat anomalous in that there appears to have been flexural loading of the crust due to thrusting and folding that occurred at the same time as extension in the valencia trough the lower crust shows evidence of weak but locally variable lower crustal reflectivity it is possible that the lower crustal reflectivity was preserved simply because the moho was flexed downward and so decompression and hence melting of the upper mantle was restricted this suggests that the melting itself rather than the extension is the primary mechanism of lower crustal modification

the valencia trough western mediterranean an overview abstract the valencia trough located between the spanish mainland and the balearic islands corresponds to a late oligocene to recent sedimentary basin that is characterized by a highly attenuated continental crust its northwestern part evolved in response to a late oligocene to early miocene rifting phase that was followed by a period of post rift subsidence and a late miocene pleistocene phase of renewed crustal extension and magmatism its southeastern part is characterized by late oligocene to mid miocene compressional deformation and subsequent extension in the axial parts of the basin the crust has been thinned by a factor of 3 whereby the lower crust is either absent or very thin upper crustal extension appears to be considerably smaller than indicated by the crustal configuration of the basin a major problem in understanding the evolution of the valencia trough is the lack of knowledge about the physical state and structure of the lithosphere before late oligocene extension evolution of the northwestern part of the basin appears to be linked with the development of the oceanic provencal basin middle miocene compressional deformation of the balearic fold belt forming the southeastern margin of the valencia trough appears to have interfered with the tensional evolution of the latter which only resumed after crustal shortening in the balearic domain had given way to extensional tectonics during the late miocene

lower crustal heterogeneity beneath britain from deep seismic reflection data 450 km of deep seismic reflection data have been acquired over the uk landmass a qualitative assessment of lower crustal reflectivity based on the amplitude and continuity of deep crustal events has been made in the cratonic area of central england the lower crust is generally poorly reflective while in the foldbelt terrains of southern eastern and northern england it is more strongly reflective beneath the variscides of southern england an important distinction can be made between poorly reflective foreland type lower crust lying beneath the variscan front thrust and strongly reflective orogenic lower crust farther south a brief review is given of hypotheses for the origin of lower crustal reflectivity and the relationship of the latter to crustal tectonic regime both in the uk and elsewhere it is concluded that the types of lower crustal heterogeneity required to produce the observed reflections are more easily generated in orogenic provinces fold thrust metamorphic belts than in areas which have undergone only low to moderate crustal extension beneath typical sedimentary basins the generation of granites by partial melting within the lower crust and processes of metamorphic differentiation and recrystallization which accompany orogenic activity are likely to play a significant role in the development of such heterogeneities in addition post orogenic processes of magmatic underplating and low viscosity ordering may also have played a part

statistical study of nighttime medium scale traveling ionospheric disturbances using midlatitude airglow images 1 we have investigated statistical characteristics of the nighttime medium scale traveling ionospheric disturbances mstids observed in 630 nm airglow images at two stations rikubetsu 43 5 n 34 8 mlat and shigaraki 34 9 n 25 4 mlat in japan for 1998 2000 near the solar maximum period most of the observed mstids propagate southwestward in the images the typical wavelength velocity period and amplitude are 100 300 km 50 100 m s 0 5 1 5 h and 5 15 respectively seasonal variations in these parameters are not clear the occurrence rate has a major peak 50 60 in summer that appears 2 months earlier at lower latitudes and a minor peak in winter similar occurrence characteristics are obtained from midlatitude spread f signatures using multipoint ionosonde data in japan though the coincidence of the spread f and the mstids in airglow images is only 10 15

mid latitude e region field aligned irregularities observed with the mu radar fine structures e region field aligned irregularities were observed on june 24 25 1989 with the mu radar at shigaraki japan 34 9 n 136 1 e geomagnetic latitude 25 0 n the 3 2 m scale irregularities were observed with the mu radar in five main beam directions each of which was nearly perpendicular to the geomagnetic field at 100 km altitude doppler spectra were obtained every 20 s with a range resolution of 600 m field perpendicular echoes appeared from 2130 to 2330 lt and from 0400 to 1100 lt times that correspond to postsunset and postsunrise period in the e region a preliminary examination of the doppler spectra indicates spectral widths of 50 120 m s 1 and the mean doppler velocities are well below the ion acoustic speed these spectral characteristics are consistent with those obtained in the equatorial and auroral electrojets and have been attributed to the gradient drift instability the echoes observed during the postsunset and postsunrise periods showed quite different morphologies in the time height distribution for this reason they are classified into two types continuous and quasi periodic the appearance of the continuous echoes was mainly continuous in time and situated between 90 and 100 km altitude during the postsunrise period the appearance of the quasi periodic echoes was intermittent with periods of 5 10 min and situated above 100 km altitude during the postsunset period the quasi periodic echoes showed phase propagation toward the radar while the averaged mean doppler velocity was away from the radar by measuring the time delays in echo regions from five directions an apparent westward motion approximately 120 m s 1 of the irregularity regions was estimated

the ecors deep reflection seismic survey across the pyrenees the pyrenees are an alpine age mountain belt located on the boundary between the iberian and european plates using the same geological and geophysical data earth scientists studying the structure of the pyrenees during the past ten years have not reached a consensus here we report the first results from a nearly continuous 255 km long reflection seismic survey across the pyrenean chain this first deep reflection profile of an entire erogenic belt will help to constrain possible models for the structure and formation of the pyrenean chain

velocity analysis for wide aperture seismic data common midpoint data are now being collected with ever increasing source receiver offsets for wide aperture seismic data classical methods of interpretation fail since velocity analyses and signal to noise enhancement methods based on hyperbolic traveltime curves are no longer appropriate therefore the goals of increased velocity resolution and signal enhancement which motivate the increase in offset are not achieved approximate methods involving higher order traveltime curves or extrapolations have been developed for velocity analysis but these are ineffective in the presence of refracted arrivals and lack a physical basis these problems can be minimized by transforming the observational data to the domain of intercept or vertical delay time and horizontal ray parameter p in this domain headwave refractions are collapsed into points and both near vertical and wide angle reflections can be analyzed simultaneously to derive velocity depth information even in the presence of velocity gradients or low velocity zones