long base line measurements of short period mesospheric gravity waves during the seek campaign simultaneous observations of short period 1 hour mesospheric gravity waves were made over an extended base line 660 km from two sites in japan at shigaraki and yamagawa during the seek sporadic e experiment over kyushu campaign 9 23 august 1996 coincident image data obtained on four nights provided a rare opportunity to investigate the horizontal spatial extent and propagation characteristics of the waves in detail surprisingly out of a total of 12 events observed from shigaraki and 10 from yamagawa at most only three exhibited similar propagation characteristics at each site the majority of the wave displays 70 75 had quite dissimilar characteristics suggesting a preponderance for localized wave motions of limited lifetimes and geographical extent a marked preference for wave progression towards the n ne indicates that the gravity waves imaged in the near infrared oh and oi 557 7 nm nightglow emissions were probably not directly associated with the observed e region irregularities

flow to horizontal drains in isotropic unconfined aquifers the laplace transform solution for the problem of flow to horizontal drains in an anisotropic unconfined aquifer is derived the solution for the constant flux horizontal well by zhan and zlotnik zhan h zlotnik v a 2002 groundwater flow to a horizontal and slanted well in an unconfined aquifer water resour res 38 7 13 1 13 11 is modified to obtain the solution for a constant head horizontal drain the laplace transform solution is converted to the real time domain and type curves for the drawdown around and the discharge to a horizontal drain are computed the solution is verified by a numerical simulation the type curves and derivative type curves of the drains are compared with type curves for horizontal wells the sensitivity of type curves on piezometer location specific storage horizontal drain elevation aquifer delay index and drain length is tested these type curves can be used for interpretation of drainage data

a shear instability seeding mechanism for quasiperiodic radar echoes the quasiperiodic echoes with periods in the range of 1 10 minutes originally discovered at the middle and upper atmosphere mu radar in japan in the early 1990s are now known to be a common feature of midlatitude sporadic e a possible role of shear instabilities and the associated kelvin helmholtz structure in seeding the plasma instabilities that produce the radar echoes is suggested in this paper the proposed mechanism has the advantage that the seed structure is generated in situ as part of the same neutral wind structure that serves to initiate the generation of the sporadic e layer in addition the range of observed periods can easily be explained since the kelvin helmholtz structure is embedded in the shear flow and moves with the mean flow in the shear layer the period observed in the ground based frame is simply a product of the horizontal wavelength and the mean flow velocity at the center of the disturbance finally a typical feature of the radar observations has been that the quasiperiodic structure often ebbs and wanes in intensity over a period of 30 to perhaps 60 min recent simulations of unstable neutral shears show that the timescale for the build up and eventual restabilization of the shear flow is 30 40 min comparable to the timescale found in the observations

rheological evolution of the ocean crust a microstructural view rheological studies of the oceanic lithosphere have used direct observations of rocks and inferences based on thermal mechanical and experimental models modeling studies help to constrain an average crust and mantle rheology and the deep seated processes that control regional scale strength and stress field variations the smoothing of fine scale variations in such models can obscure many of the geological processes that influence strain localization and deformation partitioning in the ocean crust examination of deformation mechanisms and histories in ocean crust rocks provides a complementary approach to modeling examples of structures and deformation histories in diabases from deep sea drilling project ocean drilling program site 504b the hayes and atlantis fracture zones mid atlantic ridge and the troodos ophiolite cyprus are presented in conjunction with a synthesis of microstructural studies of the ocean crust over the last 25 years a survey of brittle quasi plastic and synmagmatic viscous deformation is used to demonstrate the influence of primary compositional and textural characteristics and variable magmatic and hydrothermal histories on deformation mechanisms and strain localization in the ocean crust geological evidence indicates that hydrothermal fluids strongly influence the nature of deformation and that effective stresses may be low due to fluid overpressures melt distribution will strongly influence strain localization at the base of the crust and synkinematic hydration during crystal plastic deformation plays a key role in the relative strengths of polyphase oceanic lithologies a schematic distribution of failure mechanisms in the ocean crust is used to discuss the controls on variations in lateral and vertical strength profiles and their possible relation to spreading rates although microstructural studies of ocean crust are still in their infancy they provide valuable constraints for rheological models and further insights to explain the distribution of seismicity at spreading centers and acoustic signatures

the importance of carbonate content in the acoustic stratigraphy of panama basin dsdp cores from areas of low site 505 and high heat flow site 504 b near the costa rica rift together with seismic profiles from the panama basin have been studied to determine the relationship between 1 carbonate content and physical and acoustic properties and 2 carbonate content carbonate diagenesis and acoustic stratigraphy except for ash and chert layers bulk density correlates strongly and linearly with carbonate content velocity is uniform downcore and only small variations at a small scale are measured thus an abrupt change in carbonate content will cause abrupt changes in acoustic impedance and should cause reflectors that can be detected acoustically a comparison of seismic profiler reflection records with physical properties carbonate content and reflection coefficients indicates that the main reflectors can be identified with ash layers diagenetic boundaries and carbonate content variations diagenesis of carbonate sediments is present at site 504 b in a 260 m thick ooze chalk limestone chert sequence these diagenetic sequences occur in areas of higher heat flow 200 mw m 2 seismic profiler records can be used to map the extent and depth of these diagenetic boundaries

radar studies of long wavelength waves associated with mid latitude sporadic e layers the cornell university portable radar interferometer cupri a 50 mhz doppler radar system was operated during may and august september 1983 on the island of st croix 17 7 n 64 8 w to study the plasma instabilities associated with nighttime sporadic e layers two events on may 7 and august 22 show evidence of large amplitude waves with apparent horizontal wavelengths of 10 12 km and periods of 2 6 min these apparent wavelengths are upper limits for the true wavelengths the cupri beam was directed over arecibo puerto rico and on may 7 concurrent electron density profiles within the cupri scattering volume were measured by the arecibo observatory s 430 mhz radar during the stronger event of august 22 radar echoes were received from several altitudes up to 130 km large mean doppler velocities at times exceeding 250 m s were observed during this event and the power spectra closely resemble those obtained at the magnetic equator during type 1 conditions we believe 1 that the mid latitude large scale waves are generated by the same gradient drift instability mechanism responsible for equatorial large scale waves and 2 that the type 1 3 m waves can be generated at mid latitudes with drift velocities well below the sound speed because of the very sharp plasma density gradients associated with metallic ion sporadic e layers

spatial occurrence of decameter midlatitude e region backscatter this paper provides a statistical analysis of the spatial occurrence of midlatitude e region decameter backscatter measurements were made using the valensole hf high frequency radar located in southern france during the summer of 1995 when it operated simultaneously at four frequencies on the basis of the premise that e region scattering is fully magnetic aspect sensitive the spatial occurrence statistics show that the aspect sensitive region moves toward the radar southward with respect to line of sight propagation calculations with the lower frequency echoes being closer toward the radar than the higher frequency ones are in agreement with refraction theory predictions ray tracing inside nighttime midlatitude electron density profiles augmented with dense sporadic e s layers was used to calculate the expected echoing region and good agreement with the observed region was found another finding is the angular distribution of backscatter inside the wide azimuthal sector covered by the radar scan the spatial distribution of echo occurrence has its maximum at small azimuths at and about the geomagnetic north suggesting that statistically the meridional direction is strongly preferred for backscatter under the postulation that these are secondary decameter waves we concluded that the observed angular anisotropy in spatial occurrence is at odds with the concept of strong isotropic plasma turbulence sudan 1983 but in general agreement with the two step gradient drift instability theory of secondary wave generation proposed by sudan et al 1973

heat flow variations correlated with buried basement topography on the juan de fuca ridge flank systematic heat flow variations are commonly observed on sedimented flanks of mid ocean ridges these variations have been attributed to the convective circulation of pore fluids within the oceanic crust and have been used to estimate the scale and pattern of this circulation here we report similar systematic variations observed in a detailed heat flow and seismic reflection survey over sediment covered 3 myr old sea floor on the eastern flank of the juan de fuca ridge we find that heat flow peaks are located above buried basement ridges and adjacent to two minor basement outcrops heat flow lows are found where thick sediments fill basement valleys the simple inverse relationship between heat flow and sediment thickness defined by the data indicates that hydrothermal circulation sealed within the permeable portion of the oceanic crust is vigorous enough to maintain approximately isothermal 10 k conditions at the sediment crust interface as no systematic variations in estimated basement temperatures are observed it seems that at this location the heat flow variations result only from sediment thickness variations and do not reflect a particular convective pattern

an interpretation of magnetic signatures of subduction zones detected by magsat abstract the magnetic anomalies detected by magsat over subduction zones are related to the thermal state and the location with respect to the geomagnetic poles of the subducting oceanic lithosphere it is shown that an old about 100 m y subducting lithosphere produces about twice as strong a magnetic anomaly as that associated with a young about 40 m y one also a given subducting oceanic lithosphere produces a stronger magnetic anomaly at high geomagnetic latitudes than near the geomagnetic equator based on the thermal evolution models of the oceanic lithosphere and assuming a mean magnetic susceptibility of 13 10 3 si the pacific plate subducting along the kuril trench produces a magnetic anomaly similar to the observed one the nazca plate subducting along the peru chile trench produces a magnetic anomaly of less than 0 5 nt no distinct anomaly observed by magsat over this region

off axis hydrothermal circulation parametric tests of a refined model of processes at deep sea drilling project ocean drilling program site 504 we have developed a refined model of coupled heat and fluid flow to numerically simulate off axis hydrothermal circulation through the upper oceanic crust the new representation includes mesh elements with curved sides and noncentered nodes these curvilinear elements allow improved simulation of topography at the seafloor and within underlying sediment and basaltic layers curvilinear simulations of circulation at deep sea drilling project ocean drilling program site 504 confirm the broad conclusions derived from the rectilinear simulations of fisher et al 1990 but also suggest that permeability within the upper few hundred meters of crust around hole 504b must be concentrated within several narrow zones this interpretation is consistent with core observations and wireline logs from hole 504b within these highly permeable zones absolute permeability may be several orders of magnitude higher than the bulk permeability measured for the upper crust as a whole a series of detailed parametric simulations was conducted to determine the quantitative importance of basal heat flow seafloor bathymetry basement relief and differential sediment thickness in modifying the geometry and intensity of off axis hydrothermal circulation these studies reveal that basement relief and differential sediment thickness are more important than seafloor bathymetry in enhancing off axis convection within the seafloor observed natural correlations between seafloor bathymetry and heat flow may exist because bathymetry is a proxy for the other two important parameters basement relief and differential sediment thickness off axis convection at geochemically significant velocities is possible even with heat input appropriate for some of the oldest oceanic crust a thick sediment layer over older crust may cause enough conductive refraction at the seafloor to mask the variations in seafloor heat flow often associated with off axis hydrothermal convection

a new method for the determination of in situ hydraulic properties by pressure pulse tests and application to the higashi hachimantai geothermal field a new method is proposed to evaluate in situ hydraulic properties of formations using the so called pressure pulse test over short test intervals the analysis utilizes the continuous distribution of instantaneous ring sources of fluid over the well bore surface in order to reduce the problem to a set of singular integral equations for a homogeneous and isotropic porous medium when the ratio of the test interval length to well bore diameter is small or the specific storage is small the flow parallel to the well bore axis becomes significant and the shape of the type curves obtained from the present analysis is different from that of the conventional type curves use of the conventional type curves should be restricted to intervals that are more than 20 times longer than the well bore diameter finally the present method is applied to evaluate the in situ hydraulic properties of the higashi hachimantai geothermal model field of hot dry rock tohoku university

in situ electrical resistivity and bulk porosity of the oceanic crust costa rica rift in situ electrical resistivity was measured in dsdp hole 504b to a depth of 1 013 m into oceanic basement apparent resistivities are about 10 m in about 600 m of pillow lavas sharply increasing to nearly 1 000 m in the underlying dykes bulk porosities calculated from resistivities show a distinct layering apparently corresponding to geophysical layers 2a 2b and 2c

quasi periodic radar echoes from midlatitude sporadic e and role of the 5 day planetary wave using measurements of magnetic aspect sensitive radar echoes from midlatitude sporadic e collected over a two month period from tanegashima japan we show that while their occurrence duration from night to night did not exhibit any systematic variation that of the so called quasi periodic qp echoes varied sinusoidally with a period of 5 days we have interpreted this behavior in terms of effects produced by a planetary wave and identified its presence through neutral wind measurements made with a partial reflection drift radar located nearby at yamagawa we propose that the occurrence of qp echoes is affected both by a contribution of the wind to the dynamo electric field and by the direction of the neutral wind we argue that because the wind vector of the planetary wave is elliptically polarized at midlatitudes a preferred wind direction conducive to the generation of qp echoes occurs once every 5 days on the other hand this wave is linearly polarized and directed zonally over the geographic equator the fact that qp echoes are most fully developed at midlatitudes and less so at lower latitudes suggests that zonal flow is not particularly favorable for qp echo production

crustal processes at spreading centers recent discoveries and research on mid ocean ridges mor s in the last four years have greatly increased our knowledge of this fundamental type of plate boundary the last iugg review of mor research was in 1975 aumento et al 1975 and its omission as a topic in 1978 may have reflected a feeling that spreading centers were reasonably well understood since that time however there has been a surfeit of important new observations and exciting research and there is now a turmoil of innovative ideas about the processes which create and leave their imprint on two thirds of the earth s crust new seismic measurements have been made and interpreted as evidence for the existence of shallow axial magma chambers amc beneath intermediate total opening rate 5 9 cm yr and fast 9 18 cm yr spreading centers fig 1 yet there is controversy as to whether they are steady state whether they persist beneath slow ridges as well in the steady state what the dimensions and shape of the chamber are its relation to oceanic crustal stratigraphy and its relation to observations in ophiolites black smoker hydrothermal vents have been discovered in the pacific spewing forth 350 c fluids blackened by polymetallic sulfide precipitates this discovery is embroiled in debate as to how long the vents last whether they occur at slow spreading rates as well whether the enormous heat flux of the vents freeze the magma chamber even at fast spreading rates their influence on geochemical balances in the ocean and the value of the sulfide deposits commercially it has been found that our initial view of mor s as two dimensional linear structures has served us well as an initial working model but must be significantly modified to account for variations in tectonic volcanic and hydrothermal activity along strike as well as for episodicity of these processes deep sea drilling project dsdp samples have raised fundamental questions about formation of the magnetic source layer hydrothermal circulation and fault mechanisms along the mor spreading centers which penetrate existing lithosphere along strike as propagating rifts have modified our views of how plate boundaries reorient themselves and how v shaped magnetic and topographic trends are formed we have also found that transform faults may modify spreading center processes for some distance away from their intersections with mor s and that rigid plate transform faults may fail to develop at fast spreading centers under certain conditions resulting in en echelon overlapping of spreading centers this review will focus on these developments and several others only example references to these topics will be given in the text and many important topics will not be discussed directly e g petrology and geochemistry mantle convection research on lithosphere older than 1 m y however i have tried to compile and have included an extensive bibliography for u s research on a broader range of mor topics for mid 1978 to mid 1982 which is the main purpose of this report pre 1978 references are occasionally included where appropriate abstracts are not included

anomalous fluid emission of a deep borehole in a seismically active area of northern apennines italy abstract the miano borehole 1047 m deep is located close to the river parma in the northern apennines italy a measuring station has been installed to observe the discharge of fluids continuously since november 2004 the upwelling fluid of this artesian well is a mixture of thermal water and ch4 as main components in non seismogenic areas a relatively constant fluid emission would be expected perhaps overlaid with long term variations from that kind of deep reservoir over time however the continuous record of the fluid emission in particular the water discharge the gas flow rate and the water temperature show periods of stable values interrupted by anomalous periods of fluctuations in the recorded parameters the anomalous variations of these parameters are of low amplitude in comparison to the total values but significant in their long term trend meteorological effects due to rain and barometric pressure were not detected in recorded data probably due to reservoir depth and relatively high reservoir overpressure influences due to the ambient temperature after the discharge were evaluated by statistical analysis our results suggest that recorded changes in fluid emission parameters can be interpreted as a mixing process of different fluid components at depth by variations in pore pressure as a result of seismogenic stress variation local seismicity was analyzed in comparison to the fluid physico chemical data the analysis supports the idea that an influence on fluid transport conditions due to geodynamic processes exists water temperature data show frequent anomalies probably connected with possible precursory phenomena of local seismic events

evolution of heat flow hydrothermal circulation and permeability on the young southern flank of the costa rica rift we analyze 67 new conductive heat flow measurements on the southern flank of the costa rica rift crr heat flow measurements cover five sites ranging in oceanic crustal age between approximately 1 6 and 5 7 ma and are co located with a high resolution multi channel seismic line that extends from slightly north of the first heat flow site 1 6 ma to beyond odp hole 504b in 6 9 ma crust for the five heat flow sites the mean observed conductive heat flow is 85 mwm 2 this value is approximately 30 per cent of the mean lithospheric heat flux expected from a half space conductive cooling model indicating that hydrothermal processes account for about 70 per cent of the heat loss the advective heat loss fraction varies from site to site and is explained by a combination of outcrop to outcrop circulation through exposed basement outcrops and discharge through faults super critical convection in layer 2a extrusives occurs between 1 6 and 3 5 ma and flow through a thinly sedimented basement high occurs at 4 6 ma advective heat loss diminishes rapidly between 4 5 and 5 7 ma which contrasts with plate cooling reference models that predict a significant deficit in conductive heat flow up to ages 65 10 ma at 5 7 ma the crr topography is buried under sediment with an average thickness 150 m and hydrothermal circulation in the basement becomes sub critical or perhaps marginally critical the absence of significant advective heat loss at 5 7 ma at the crr is thus a function of both burial of basement exposure under the sediment load and a reduction in basement permeability that possibly occurs as result of mineral precipitation and original permeability at the time of formation permeability is a non monotonic function of age along the southern flank of the crr in general agreement with seismic velocity tomography interpretations that reflect variations in the degree of ridge axis magma supply and tectonic extension hydrothermal circulation in the young oceanic crust at southern flank of crr is affected by the interplay and complex interconnectedness of variations in permeability sediment thickness topographical structure and tectonic and magmatic activities with age

groundwater flow to a horizontal or slanted well in an unconfined aquifer 1 new semianalytical solutions for evaluation of the drawdown near horizontal and slanted wells with finite length screens in unconfined aquifers are presented these fully three dimensional solutions consider instantaneous drainage or delayed yield and aquifer anisotropy as a basis solution for the drawdown created by a point source in a uniform anisotropic unconfined aquifer is derived in laplace domain using superposition the point source solution is extended to the cases of the horizontal and slanted wells the previous solutions for vertical wells can be described as a special case of the new solutions numerical laplace inversion allows effective evaluation of the drawdown in real time examples illustrate the effects of well geometry and the aquifer parameters on drawdown results can be used to generate type curves from observations in piezometers and partially or fully penetrating observation wells the proposed solutions and software are useful for the parameter identification design of remediation systems drainage and mine dewatering

e region observations over chung li during the seek campaign during the sporadic e experiment over kyushu seek campaign e region field aligned irregularities fai were observed with the chung li vhf radar operated on 52 mhz in taiwan between august 15 22 1996 the characteristics of the quasi periodical echoes from the e region about 80 km north of the chung li radar are studied during the same period ionogram records were taken with the digisonde located at the chung li radar site strong sporadic e layers were detected with the digisonde when the fai observed with the vhf radar were also very intense the variations of sporadic e layer critical frequency and of the field aligned irregularities were studied the latter were estimated to be located at altitudes 95 115 km occurring in layers of 5 15 km thickness moving downwards at a rate of about 2 5 km h there seemed to be a change over of the fai echoes from lower to upper e region every night approximately at 23 hour lt the distinction between post sunrise and post sunset fai echoes observed earlier by mu radar was not clearly seen in chung li a preliminary examination of the morphology of the fine structures within the layers indicates quasi periodic features with 5 10 minutes period many of these periodic fine structures were observed at the chung li vhf radar to have opposite slopes than those detected earlier with the mu radar in japan which is located 1500 km north of the chung li vhf radar

daytime e region field aligned irregularities observed during a solar eclipse the driving mechanism of the midlatitude field aligned irregularities fais has been in dispute for many years the experimental observations were carried out during the solar eclipse of 22 july 2009 in wuhan china to study the possibility of the wave driven irregularities a high frequency coherent scatter radar was used to detect the e region irregularities an ionosonde was applied to record the trace of gravity waves in ionosphere the e region fais occurred at the end of the solar eclipse with fluctuant doppler at the same time the oscillations on the fes maximum reflecting frequency of es curve and in the doppler velocity of the echoes from the es layer were also recorded the data analysis and comparison show that the gravity waves and the fais occurred at the same time with the in phase variations in amplitude and phase thus the solar eclipse and the gravity waves may play important roles in the occurrence of the irregularities a schematic diagram of one period gravity wave is used to explain the possible gravity wave driven mechanism and the doppler fluctuation in the irregularities the daytime fai in midlatitude is a rare phenomenon even in the condition of solar eclipse there are only four cases of the e region fais observed during a solar eclipse including our observations the unique feature of our observations is the synchronized oscillations in the irregularities and in the es layer which will help address the outstanding question of the source of the midlatitude e region fais

heat flow on the western flank of the east pacific rise at 21 n we report 48 new heat flow measurements on the western flank of the east pacific rise at 21 n the stations were taken in 1 to 30 m of sediment on 0 4 to 1 4 m y old crust the low average measured value of 173 mw 2 including 12 tilted minimum values is about 1 3 the mean heat flow predicted for crust of this age range by cooling plate theory this may be partly due to a bias of measurement locations in sediment ponds nevertheless 4 km running averages of measured heat flows projected normally to the axis display an oscillatory trend suggestive of cellular hydrothermal circulation in the basement we sampled no more than one cycle of the apparent heat flow modulation which is of 15 km wavelength and 200 mw m2 amplitude this variation appears to be uncorrelated with the topographic variation of 10 km wavelength assuming that the porosity sensitive electromagnetic results of young and cox 1981 reflect a permeability distribution that restricts the depth of circulation to 1 4 km average temperatures of circulation may be 50 60 c deeper higher temperature circulation is allowable if a more uniform permeability depth distribution holds

highly permeable and layered jurassic oceanic crust in the western pacific bulk permeability was determined from drillstring packer measurements in odp hole 801c in jurassic oceanic crust in the western pacific the values average 8 10 14 m2 over 93 m of open hole or 4 10 13 m2 if the permeable interval is confined to an 18 m thick hydrothermal zone within oceanic basement these values are about 1 10 times higher than those reported for the upper sections of holes 395a 504b and 735b in 3 7 5 9 and 11 ma old oceanic crust respectively the discovery that 160 ma old oceanic crust contains a zone with extremely high permeability is not predicted by any model of ocean crustal evolution the high permeability interval appears to be associated with the burial by off ridge volcanism of a zone of hydrothermal precipitates and altered basalts the generality of this result may depend on the generality of off ridge volcanism necessary to create and preserve such zones of high permeability within the ocean crustal section although the crustal and permeability structures detected at hole 801c may not fit easily into currently accepted models of crustal accretion and aging the generality of off ridge volcanism suggests that these structures could actually be typical of large portions of the world s oceanic crust

the galapagos spreading center at 86 w a detailed geothermal field study appendix is available with entire article on microfiche orderfrom american geophysical union 2000 florida avenue n w washington d c 20009 document j80 013 01 00 payment mustaccompany order we report here measurements of the heat flow field of the galapagos spreading center on crust of age less than 1 0 m y the 443 measurements in an area of about 570 km2 reveal the general planform of the geothermal flux and permit the first truly areal estimate of the near axis conductive heat flux the intrusion process and associated hydrothermal circulation dominate the surface heat flow pattern with circulation apparently continuing beyond the limits of our survey the areal average of the conductive heat flux is 7 1 0 8 hfu 295 33 mw m2 about one third the heat flux predicted by plate models the remaining heat is apparently removed by venting of hydrothermal waters at the spreading axis and through basalt outcrops and hydrothermal mounds off axis the pattern of surface heat flux is lineated parallel to the axis and the strongly lineated topography sharp lateral gradients in the heat flow greater than 10 hfu km near escarpments and commonly expressed as high heat flow at the tops of the scarps and lower heat flow in the valleys may indicate a local concentration of the circulation by surface fault systems and or variable sediment thickness

constraints upon water advection in sediments of the mariana trough thermal gradient measurements consolidation tests and pore water compositions from the mariana trough imply that water is moving through the sediments in areas with less than about 100 m of sediment cover the maximum advection rates implied by the thermal measurements and consolidation tests may be as high as 10 5 cm s 1 but are most commonly in the range of 1 to 5 10 6 cm s 1 theoretical calculations of the effect of the highest advection rates upon carbonate dissolution indicate that dissolution may be impeded or enhanced depending upon the direction of flow by a factor of 2 to 5 times the rate for diffusion alone the average percentage of carbonate is consistently higher in two cores from the area with no advection or upward advection than the average percentage of carbonate in three cores from the area with downward advection this increase in average amount of carbonate in cores with upward moving water or no movement cannot be attributed solely to differences in water depth or in amount of terrigenous dilution if the sediment column acts as a passive boundary layer then the water velocities necessary to affect chemical gradients of silica are in the range 10 9 to 10 10 cm s l however if dissolution of silica occurs within the sediment column then the advection velocities needed to affect chemical gradients are at least 3 10 8 cm s l and may be as high as 3 10 6 cm s l this order of magnitude increase in advection velocities when chemical reactions occur within the sediments is probably applicable to other cations in addition to silica if so then the advection velocities needed to affect heat flow 10 8 cm s 1 and pore water chemical gradients are much nearer in magnitude than previously assumed

gas geochemistry as a tool to investigate the earth s degassing through volcanic and seismic areas the soul of the 8th international conference on gas geochemistry

possible evidence of gravity wave coupling into the mid latitude f region ionosphere during the seek campaign on five of eight observation nights during the 1996 seek sporadic e experiment over kyushu campaign japan unusual wave like structures were imaged in the 630 nm thermospheric nightglow emis sion four of these events were observed to travel to wards the southwest providing new evidence in support of recent theories describing the coupling of medium scale gravity waves into the mid latitude f region iono sphere available ionosonde data and the visual charac teristics of the wave structures indicate no association

turbulent upwelling of the mid latitude ionosphere 1 observational results by the mu radar in this paper we present the detailed results of a series of experiments designed to study the coherent backscatter of 50 mhz radar waves from the mid latitude f region data were obtained with the active phased array mu radar in japan and include some auxiliary e region coherent echoes as well as in other turbulent ionospheric phenomena the intense nonthermal scatter comes from irregularities oriented parallel to b the strongest echoes correspond to irregularities at least 20 db stronger than thermal backscatter at the same frequency from typical f region densities at the same range simultaneous observations with ionosondes show that these echoes occur during strong mid latitude spread f as defined by ionosondes the latter phenomenon is certainly much more widespread than the turbulent upwelling events described here but we believe that in some sense these correspond to the most violent mid latitude spread f the strongest echoes occur in large patches which display away doppler shifts corresponding to irregularity motion upward and northward from the radar at the edges of these patches there is often a brief period of toward doppler before the echoing region ceases on rare occasions comparable patches of strong away and toward doppler are detected although in such cases the doppler width of the toward echoes is much narrower than that of the away echoes the away patches often are characterized by mean velocities well over 250 m s and doppler widths full width at half maximum of 50 m s the multiple beam capability at mu allowed us to track the patches in the zonal direction on two days the patches moved east to west in both cases at velocities of 125 m s and 185 m s respectively there is a distinct tendency for the bottom contour of the scattering region to be modulated at the same period as the patch occurrence frequency as well as at higher frequencies this higher frequency component may correspond to substructures in the large patches and to the e region coherent scatter patches which were detected simultaneously in several multiple beam experiments in the companion paper kelley and fukao this issue we explore a number of possible explanations for this phenomenon in more detail

the heights of sporadic e layer simultaneously observed by the vhf radar and ionosondes in chung li ionosondes and vhf radars have been employed to simultaneously observe the sporadic e es layer in previous studies an absence of correlation was found between the height of field aligned irregularities fai observed by the radars and the virtual height of the es layer h es by their colocated ionosondes a careful study shows that the low correlation results from the beam broadening effect of the ionosonde in this paper the investigation shows a better correlation between the heights of the fai bottom side hfaib observed by the vhf radar and the h es by ionosondes in chung li it is found that the h es is greater than the hfaib by about 5 10 km meanwhile we demonstrate that h es observed by two nearby ionosondes and or radars can be employed to evaluate the velocity of waves in the es layer

geochemical applications of noble gases abstract noble gases are unique tracers due to their rarity on earth and their inertness several of their isotopes are produced by nuclear reactions whereas others were trapped when the earth formed they have been widely used for understanding the evolution and structure of the earth dating geological events processes characterizing magma genesis and volcanism in different tectonic environments tracing mantle crust interaction even in non volcanic areas and for monitoring earthquake and volcanic activities some of these topics were presented at the 9th international conferences on gas geochemistry that was held in 2007 in taipei taiwan this special volume includes twelve papers which cover a wide range of applications of noble gases geochemistry such as tracing the thermal evolution of the early earth understanding the mantle source of continental basalts establishing the spatial variations of gas compositions in hot springs and fumaroles from volcanic and forearc areas as well as in key non volcanic areas such as faults and seismic zones and tracing the origin and evolution of ore forming fluids of uranium deposits reproducing the noble gas behavior during faulting and finally using argon as a tracer of large scale geologic processes

lower e region field aligned irregularities studied using the equatorial atmosphere radar and meteor radar in indonesia 1 this paper presents the first observations of lower e region echoes made with the equatorial atmosphere radar ear located in west sumatra indonesia 0 2 s 100 32 e dip latitude 10 36 s the lower e region echoes observed over west sumatra display descending layer structures with occasional descent to altitude as low as 85 km the descending characteristics resemble the characteristics of tidal winds simultaneous observations of wind measured using a meteor radar show tidal wind fields with westward and northward winds above and eastward and southward winds below the velocities of the field aligned irregularities fai observed by the ear are found to agree quite well with the winds measured by the meteor radar this suggests that in the collision dominated lower e region the fai velocities represent essentially the neutral winds the observations of low altitude fai are found to be consistent with the gradient drift instability except those occurring below 90 km which deserves further investigation

permeability underpressures and convection in the oceanic crust near the costa rica rift eastern equatorial pacific in situ permeability and pore pressures were measured 200 m deep beneath the top of the oceanic crust at dsdp site 504b these measurements have relevance for the transition from convective to conductive heat flow on the south flank of the costa rica rift conventional slug and constant rate injection tests were made below a hydraulic packer set at various depths in the hole the packer was first set in a massive flow unit 37 m below the sediment basement interface the bulk permeability of the 172 5 m of pillow basalts and basaltic flows below the packer was found to be about 40 millidarcys 4 10 10 cm2 measurements over 3 and 15 m intervals at the bottom of the hole in an altered pillow zone indicated a bulk permeability of 2 4 millidarcys these values are thought to be accurate to 30 formation pore pressures were found to be approximately 8 bars 2 below hydrostatic interpretation of the data with respect to simple numerical convection models suggests that the transition from convective to conductive heat flow is controlled by the cessation of convective heat transport through the sedimentary layer rather than the cessation of convection in the sediment furthermore the agreement between observed and modeled underpressures implies that hole 504b penetrated an active ocean crustal convection system the thick sedimentary layer layers of basal chert and massive flow basalts above the layer 2a pillow flows apparently form an impermeable lid effectively isolating the convection system from the ocean

comparison of e region electric fields observed with a sounding rocket and a doppler radar in the seek campaign this paper describes results from simultaneous measurements of mid latitude irregularities by a sounding rocket and a doppler radar the experiment was conducted on august 26 1996 as part of the seek sporadic e experiment over kyushu campaign in japan electric field observed with a double probe sensor on the rocket showed very large fluctuations of 10 mv m where irregularity echoes were quite intense doppler velocities observed with the radar agreed well with the electric fields we estimated growth rates of the gradient drift instability which showed positive values around the major sporadic e layer it was found that within intense irregularity region with quasi periodic structures there were large polarization electric fields that was likely to be associated with spatial structure of the sporadic e layer

propagation directions of gravity wave patterns observed in oh ccd images during the seek campaign oh airglow about 87 km altitude was observed with a ccd imager at shigaraki 34 9 n 136 1 e in august 1996 during the seek campaign period from nine night observations the characteristics of the gravity wave modulation of the oh airglow layer were extracted and analyzed the distributions of the horizontal wavelength observed wave period and horizontal phase speed were 10 30 km 5 30 min and 20 60 m s respectively the horizontal propagation direction was mainly north eastward this preferential direction is similar to previous mu radar observations of mesospheric gravity waves 68 80km in summer months but different from the propagation direction of gravity waves expected from fai theories and observations in the e region

mechanisms for the origin of mid ocean ridge axial topography implications for the thermal and mechanical structure of accreting plate boundaries to better understand the implications of ridge axis morphology for the thermal and mechanical structure of accreting plate boundaries we examine mechanisms for the creation of stress supported axial topography and its dependence on parameters such as spreading rate asthenosphere viscosity and plate thickness near the ridge axis three basic mechanisms are considered 1 asthenospheric upwelling in a narrow steady state conduit beneath a ridge axis 2 mantle flow stresses due to plate spreading extending ridge axis lithosphere or melt segregation and associated mantle compaction and 3 topography supported by moments due to horizontal extensional stresses in a thickening lithosphere if mid ocean ridge topography is due to asthenosphere rising in a narrow conduit at the ridge axis then the conduit structure cannot be thermally controlled as the associated thermal structure has relatively broad flat isotherms instead of a conduitlike shape mantle flow associated with plate spreading alone induces no stress supported topography thus the intuitive notion that diverging flow at the ridge axis due solely to plate spreading produces the axial valley is incorrect vertical mantle flow at the base of a stretching accreting lithosphere and mantle flow associated with melt segregation can however lead to stress supported axial topography however for these mantle flow related processes to produce significant amounts of axial relief the mantle viscosity beneath the ridge axis must be on the order of 1020 pa s 1021 p poise significantly higher than generally accepted values of 1018 pa s 1019 p horizontal extensional stresses in a strong brittle lithosphere that thickens with distance from the ridge axis can produce axial topography of the form and amplitude observed on slow spreading ridges a continuum idealization of deformation due to faulting is used to examine this mechanism this model predicts the axial valley width is controlled by the plate thickness near the ridge axis an 8 km thick plate near the ridge axis would produce the 30 km wide axial valley observed at slow spreading ridges an increased lithosphere thickness of only several kilometers over the half width of the axial valley can produce kilometer scale relief to examine whether a plate 8 10 km thick at the ridge axis that thickens by several kilometers within 15 km of the axis is plausible at a slow spreading ridge thermal models that include both the heat of magmatic crustal accretion on the ridge axis and upwelling mantle flow beneath the axis are formulated hydrothermal cooling that increases the effective conductivity by about a factor of 10 is required for an 8 km thick plate to exist at a slow spreading ridge axis however even with this enhanced hydrothermal cooling the plate thickness at a fast spreading ridge axis and the resulting horizontal force in the plate are too small to result in appreciable topography while mid ocean ridge axial topography is strongly influenced by spreading rate other factors also shape axial structure for example the anomalously shallow slow spreading reykjanes ridge has an axial structure more like that of a fast spreading ridge and the anomalously deep intermediate spreading australian antarctic discordance has a median valley axial structure typical of a slower spreading ridge in addition within a given spreading segment there is often a systematic deepening of the ridge axis toward transform offsets these non spreading rate dependent axial topographic variations may be produced by variations in magmatic heat input associated with crustal emplacement which shapes the thermal structure and lithosphere thickness near the ridge axis

a statistical analysis of sporadic e layer occurrence in the midlatitude china region a statistical analysis of sporadic e layer recorded from september 2011 to september 2015 at four chinese ionospheric sounding stations of mohe 122 37 e 53 50 n beijing 116 25 e 40 25 n wuhan 114 61 e 30 53 n and hainan 109 13 e 19 52 n are presented to investigate the characteristics of sporadic e layer at the middle latitudes over china the occurrence of the sporadic e layer in mid latitude china region shows strong dependence on local time and season consistent with previous studies the occurrence of the mid latitude sporadic e layer is prominent at local daytime in summer season the results also reveal that the post sunset sporadic e layer is statistically pronounced in mid latitude china region possibly related to the nighttime mid latitude e region irregularities the mid latitude sporadic e layer is modulated by atmospheric tidal waves and planetary waves at different latitudes the occurrence of the mid latitude sporadic e layer also tends to increase with the level of geomagnetic activity on basis of both the statistical analysis and case study

morphology and seasonal characteristics of low latitude e region quasiperiodic echoes studied using large database of gadanki radar observations 1 in this paper we study the morphology seasonal features and statistics of low latitude quasiperiodic qp echoes using an unprecedented data set of 147 nights of observations spanning over all seasons made using the gadanki radar the qp echoes have periods 2 20 min and occur on more than 50 nights they are often found embedded in descending echoing layers whose characteristics resemble to those of tidal winds their occurrence shows strong seasonal dependence with 48 of the time in summer 26 32 in equinox and 14 in winter the qp echoes have a tendency to appear first during 21 00 lt which could last for 2 8 h leading to their maximum occurrence rate during postmidnight hours height time occurrences of radar echoes and qp structures both show common descending behavior which agree extremely well with the observed descending behavior of the es layers we also find that the seasonal variations of qp echo occurrence are in very close agreement with that of the es activity tidal activity in the same height region and also gravity wave activity in the mesosphere interestingly the occurrence statistics are much more than their midlatitude counterpart and time of first appearance time of maximum occurrence and duration of qp echoes all strongly contrast the midlatitude features these observations have been discussed in detail in the light of current understanding of qp echoes

e region radar echoes from low latitude field aligned irregularities due to gravity waves and tides a case study using radar lidar and radiosonde observations and simulations on the night of 5 february 2011 the height time plot of echo from e region field aligned irregularities fai received by the indian mesosphere stratosphere troposphere radar at gadanki 13 5 n 79 2 e shows a slow descending layered structures separated by nearly 8 km in the height region 80 100 km and vertically elongated structures with quasiperiodic variations at higher heights the stratospheric thermal structure also shows similar slowly descending structures with nearly 8 km separation hodograph of 7 9 km band pass filtered radiosonde zonal and meridional winds over gadanki form clearly an ellipse and the dominant period obtained from the ratio of major to minor axes of the ellipse is nearly 24 h indicating the presence of a nonmigrating diurnal tide with vertical wavelength of 8 km the two dimensional spectrum of temperature perturbations which are assumed to be due to gravity waves shows dominant periods near 1 h and 1 5 h the spectrum of fai echo also shows similar dominant periods altitude time cross section of vertical ion velocity is computed using winds composed of observed gravity wave and tidal parameters as the diurnal tide over tirunelveli 8 7 n 77 8 e shows weaker amplitudes above 90 km the removal of tidal contribution clearly reveals the observed fai echo structure of vertically slanting plasma blob structures at higher heights and slowly descending continuous structures separated by 8 km at lower heights the present study clearly demonstrates the role of tides and gravity waves in the formation of descending echo structures and quasiperiodic echoes respectively

densities and porosities in the oceanic crust and their variations with depth and age we have used drilling and downhole logging results from deep sea drilling project holes 395a and 418a measured properties of core samples from the seafloor and from ophiolites and seismic velocity structure models of the oceanic crust to constrain empirical statistical relationships between in situ densities porosities and seismic velocities and to estimate densities and porosities in the oceanic crust with the following principal results our review of drilling results and studies of ophiolites suggests that the velocity structure of the oceanic crust is more closely related to changes in porosity and alteration or metamorphic grade than to its igneous structure the transition from layer 2a 3 7 0 4 km s 1 to 2b 5 2 0 4 km s 1 occurs within the extrusive pile the top of layer 2c 6 2 0 2 km s 1 is associated with the top of the sheeted dike complex and with the first appearance of greenschist facies alteration products ophiolite studies have shown that the top of layer 3 occurs within the sheeted dikes where the metamorphic grade of alteration products increases from greenschist to amphibolite facies a comparison of reprocessed and corrected downhole logs from holes 395a and 418a indicates that in situ densities and fractional porosities differ by 0 2 mg m 3 and 0 07 respectively these differences are consistent with prevailing views of the progressive alteration of the upper oceanic crust statistical relationships between in situ density porosity and slowness are highly linear and indicate that the density slowness relation estimated from laboratory samples pb 3 81 0 02 6 0 0 1 s applies to in situ properties as well we obtained a similar empirical relationship for porosities from the hole 418a log data f 0 35 0 03 2 37 0 15 s r2 0 84 s e 0 015 applying these empirical models to seismic velocity structure models yields the following crustal densities and porosities layer 2 2 62 2 69 mg m 3 0 10 0 12 and layer 3 2 92 2 97 mg m 3 the estimated average density of the oceanic crust is 2 86 0 03 mg m 3 densities and porosities estimated from a seismic crustal structure model for old atlantic crust agree very well with the logging data from hole 418a suggesting that in situ densities and porosities can be estimated from seismic velocities high density and porosity gradients are characteristic of the upper oceanic crust increasing densities reflect both a progressive decrease of porosity and increasing grain density with depth based on the seismic properties of layer 2a we estimate that the layer thins at an approximate rate 20 to 45 m m y 1 while the velocity increases by 0 040 km s 1 m y 1 the corresponding rates of change of density and porosity are 0 016 0 009 mg m 3 m y 1 and 0 005 0 003 m y 1 respectively

physical properties of upper oceanic crust ocean drilling program hole 801c and the waning of hydrothermal circulation 1 the hydrologic evolution of oceanic crust from vigorous hydrothermal circulation in young permeable volcanic crust to reduced circulation in old cooler crust causes a corresponding evolution of geophysical properties ocean drilling program odp hole 801c which obtained the world s oldest section of in situ normal oceanic crust provides the opportunity to examine relationships among hydrologic properties porosity permeability fluid flow crustal alteration and geophysical properties at both core plug and downhole log scales within these upper crustal basalts fluid flux in zones with high porosity and associated high permeability fosters alteration particularly hydration consequently porosity is correlated with both permeability and a variety of hydration indicators porosity dependent alteration is also seen at the log scale potassium enrichment is strongly proportional to porosity we extend the crustal alteration patterns observed at hole 801c to a global examination of how physical properties of upper oceanic crust change as a function of age based on global data sets of deep sea drilling project and odp core physical properties and downhole logs increasing crustal age entails macroporosity reduction and large scale velocity increase despite intergranular velocity decrease with little microporosity change the changes in macroporosity and velocity are significant for pillows but minor for flows matrix densities provide the strongest demonstration of systematic age dependent alteration on the basis of observed decreases in matrix density that are proportional to the logarithm of age approximately half of all intergranular scale crustal alteration occurs after the first 10 15 myr apparently crustal alteration continues at a decreasing rate throughout the lifetime of oceanic crust

oceanic ridge crest processes oceanic ridge crest processes constitute a vigorous frontier of multidisciplinary research with global ramifications in the earth atmospheric and biologic sciences this deep ocean frontier is gradually opening in response to investigations which are elucidating the role of these processes in the lithosphere hydrosphere atmosphere and biosphere and the application of advanced instrumental and interpretive techniques which are increasing the quality and quantity of data these techniques include crustal drilling with borehole logging deep sea drilling project reports high resolution bathymetry sea beam etc side scan sonar seamarc i and ii gloria etc imagery with video and photography multichannel seismics determination of water column properties ctd with rosette sampler etc and submersible applications

geothermal regimes of the costa rica rift east pacific investigated by drilling dsdp ipod legs 68 69 and 70 drilling durin deep sea drilling project legs 68 69 and 70 on the southern limb of the costa rica rift was used to study geothermal processes in the ocean crust two areas were drilled one was a geothermally hot site on 6 2 m y old crust where topography is smooth heat flow is close to that predicted by conductive cooling of the lithosphere 200 mwm 2 and hydrothermal circulation may be sealed within the crust the other was on 3 9 m y old crust where rough topography is associated with low heat flow 15 to 50 mwm 2 and possible open convection of sea water at both sites about 250 m of siliceous calcareous sediments overlies igneous basement in the hot area it blankets the topography whereas in the cold area basement outcrops still occur operations included numerous down hole experiments in both areas and hydraulic piston coring of a 230 m sediment section in the hot area diagenesis of the sediments appears closely related to temperature at the hot site chert was found near basement and the chemistry of pore fluids sampled from both sediments and basement is strongly influenced by reactions within the basement strong lateral gradients in the composition of pore fluids occur in the sediments at the cold site no chert was found and bacterial processes within the sediment dominated the chemistry of the pore fluids basaltic basement in both areas consists mainly of pillow lavas and thin flows with occasional more massive units the basalt is relatively magnesian the degree of alteration is very small in the cold area but much more extensive in the hot area ease of drilling also shows a strong contrast basement penetration reached 562 m in the hot area and was halted because of lack of time at the cold site 43 m of basement was cored only with difficulty the most intensive in hole experiments were conducted in the hot area successful runs with the borehole televiewer allowed basement lithology to be determined and showed the presence of more and less fractured zones pulse tests using a single borehole packer gave values of basement permeability of about 2 to 40 millidarcies numerous temperature logs established a broadly conductive in situ temperature gradient with temperatures reaching 120 c at 562 m into the basement however anomalously low temperatures in the upper part of the hole which persisted after drilling disturbance had decayed away showed that cold ocean water was flowing down the hole and into the basement at about 90 m below the base of the sediments at rates of about 80 to 100 m hr the packer records indicate a pressure at this depth of 10 bars below hydrostatic costa rica rift united scientific team made up of shipboard participants on legs 68 501 69 and 70 who were in reverse alphabetical order

correlated sediment thickness temperature gradient and excess pore pressure in a marine fault block basin measurements of temperature gradient and excess pore pressure in the surficial sediment of a fault block basin in the guatemala basin correlate with sediment thickness the temperature gradient is smaller and the excess pore pressure gradient is more negative in areas of thinner sediment this correlation is explained by postulating downward pore water advection within the sediments with flow velocities on the order of 10 9 to 10 8 m s in the thinnest sediments and much less flow in the thickest sediments sediment physical properties and pore water chemistry also support this interpretation since the conductive heat flow of the basin as a whole is less than one third that predicted by sea floor spreading models the oceanic basement may be the site of a vigorous hydrothermal circulation system the pore water advection in the sediments may be driven by this larger scale circulation

numerical simulations of hydrothermal circulation resulting from basalt intrusions in a buried spreading center a two dimensional one by two kilometer section through the seafloor was simulated with a numerical model to investigate coupled fluid and heat flow resulting from basalt intrusions in a buried spreading center boundary and initial conditions and physical properties of both sediments and basalt were constrained by field surveys and drilling in the guaymas basin central gulf of california parametric variations in these studies included sediment and basalt permeability anisotropy in sediment permeability and the size of heat sources faults were introduced through new intrusions both before and after cooling background heat input caused fluid convection at velocities 3 cm a 1 through shallow sediments eighty to ninety percent of the heat introduced at the base of the simulations exited through the upper horizontal surface even when the vertical boundaries were made permeable to fluid flow the simulated injection of a 25 50 m thick basalt intrusion at a depth of 250 m resulted in about 10 yr of pore fluid expulsion through the sea floor in all cases leaving the sediments above the intrusions strongly underpressured a longer period of fluid recharge followed sometimes accompanied by reductions in total seafloor heat output of 10 in comparison to pre intrusion values additional discharge recharge events were dispersed chaotically through the duration of the cooling period these cycles in heat and fluid flow resulted from the response of the simulated system to a thermodynamic shock the sudden emplacement of a large heat source and not from mechanical displacement of sediments and pore fluids which was not simulated water rock mass ratios calculated from numerical simulations are in good agreement with geochemical estimates from materials recovered from the guaymas basin assuming a bulk basalt permeability value of at least 10 17 m2 10 2 md the addition of faults through intrusions and sediments in these simulations did not facilitate continuous rapid venting increased heat input at the base of the faults resulted in temporarily greater fluid discharge but the flow could not be sustained because the modeled system could not recharge cold fluid quickly enough to remove sufficient heat through the vents

a model of hydrothermal circulation in fault zones at mid ocean ridge crests summary a model of hydrothermal circulation close to mid ocean ridge crests has been developed the flow is modelled as a transient open loop thermosyphon restricted to a single fracture parallel to the spreading centre circulation is to a depth of 500 1000m and heat exchange occurs at the fault walls conduction is the sole heat transfer mechanism within the rock the aim is to model the conditions under which deposition of ore deposits such as those in the cyprus ophiolites could occur hot springs with the characteristics of the black smokers at 21 n on the east pacific rise are obtained from the model but only when the vents are at the unrealistically large spacing of lokm apart and then water at over 350 c is vented for a maximum of only 175 yr the model demonstrates that heat transfer through the rock by conduction alone is too slow to maintain the power output of a group of black smokers the skin depth of the temperature field limits the total heat available to the system but even without this constraint insufficient high grade heat would be available from the volume of rock within the likely field of influence of a vent it would take about 2500yr to accumulate a 3 million ton ore deposit from 1 vent or 250yr from a group of 10 vents the rate of heat extraction and the duration of the vents must both be at least an order of magnitude greater than those obtained from this model thus requiring a much greater source of heat than in the rocks alone the only source likely to be great enough is the magma chamber itself

simultaneous middle and upper atmosphere radar and ionospheric sounder observations of midlatitude e region irregularities and sporadic e layer 1 we made middle and upper atmosphere mu radar observations of midlatitude e region field aligned irregularities fais in the summer of 1999 and 2000 sporadic e es layer was monitored with a routine ionosonde and its altitude was measured with an fm cw sounder fcs in this paper we draw attention to two findings first we show that quasiperiodic qp radar echoes appearing before 0200 lt are more enhanced with increasing foes fbes which means that the fai generation is closely related to localized density gradients within es and extend from 100 to 130 km in altitude while es altitudes determined from the fcs soundings are between 100 and 110 km the latter fact suggests that existing models for the qp echo generation which require a deep modulation of es altitude are not applicable to our observational results we propose a new working model for generating qp echoes in which polarization electric fields originated from high density plasma clouds within es are mapped upward along the geomagnetic field to produce relatively weak irregularities above the es layer second we show new findings obtained from the current observations namely two types of qp echoes that occur below 100 km in the morning one is the morning qp mqp echoes with periods of 4 8 min and the other is the qp echoes with periods of 1 min the latter type can be categorized as low altitude qp echoes that were found from previous nighttime mu radar observations until now the mu radar qp echoes have been believed to occur above 100 km for the period from sunset to midnight although we do not know the generation mechanisms of the low altitude mqp echoes we suppose that these echoes might be caused by a weak es that exists below 100 km

semidiurnal behavior of quasi periodic echoes in the mid latitude es region observed with the chung li vhf radar the range rate of the so called quasi periodic qp echoes from nighttime mid latitude sporadic e regions observed with the chung li vhf radar during the seek sporadic e experiment over kyushu campaign displayed semidiurnal characteristics the time periods before 2200 lt and after 0400 lt were dominated by the negative range rate qp nqp echoes in contrast a preponderance of positive range rate qp pqp echoes occurred between 2200 and 0400 lt the slopes of nqp echoes found during the evening period steepened with time and became positive around 2200 lt similar behavior was also found prior to 0400 lt when pqp echoes were replaced by nqp echoes during the seek campaign the sign of the range rate changed around 2200 and 0400 lt on the six consecutive nights semidiurnal neutral wind variations are proposed to explain the slope sign reversals in the observations these results together with previous findings suggest that semidiurnal tides and long period waves with 30 minute periodicity may be playing a role in addition to atmospheric gravity waves in the formation of qp echoes

horizontal velocities and propagation directions of gravity waves in the ionosphere over the czech republic 1 using a five point continuous doppler sounding system operating at 3 59 mhz developed at the institute of atmospheric physics as cr iap we investigate propagation directions and velocities of gravity waves gws at altitudes from 150 to 250 km over the western part of the czech republic the velocities and directions are computed from the time delays between the observations of corresponding gws at different reflection points that correspond to various sounding paths we focused on the gws that produce an s shaped trace in doppler shift spectrograms and are observed close to sunrise and sunset we have selected about 100 of such events our results show that the analyzed gws propagate with typical horizontal velocities from 100 to 200 m s the north south component of gw velocities depends on the season it is directed northward in the summer and southward in the winter at the same time the north south component of the neutral winds calculated by the horizontal wind model hwm07 has the opposite sign typical observed periods of the analyzed waves range from 10 to 30 min

evaluation of ocean crustal sites 1256 and 504 for long term co2 sequestration 1 geologic storage of co2 in ocean basalt reservoirs is a potentially long term solution to offset anthropogenic greenhouse gas emissions prior drilling at deep sea drilling project dsdp ocean drilling program odp integrated ocean drilling program iodp sites 1256 and 504 provides evidence that the extrusive ocean crust has sufficient porosity and permeability to enable storage of large volumes of co2 six intervals are identified as potential reservoirs in the shallow crust at sites 1256 and 504 with new and reprocessed estimates of porosity from electrical resistivity logs ranging from 6 to 14 and permeability from 10 14 to 10 15 m2 calculations using specific reservoir thickness and porosity estimates suggest that even the smallest reservoir could provide storage capacity for decades of global anthropogenic carbon emissions in situ hydrologic experiments and pilot injection studies are needed to confirm high permeability and porosity estimates at sites 1256 and 504 as well as the potential for co2 injection and retention in these basalt reservoirs

pore pressure and oceanic crustal seismic structure summary marine refraction studies during the past decade have found considerable lateral variability in the seismic properties of the upper basaltic regions of the oceanic crust in many localities compressional and shear wave velocities are quite low at the top of the basalt section and velocities increase rapidly with depth it is concluded that pore pressure may be at least in part responsible for the low upper crustal velocities and contribute significantly to the lateral variability this is supported by compressional and shear wave velocity measurements as functions of confining pressure and pore pressure for basalt from the juan de fuca ridge and dolerite from the samail ophiolite oman within the oceanic crust regions of overpressure and underpressure will possess anomalous velocities the magnitude of which will depend upon the porosity and the deviation of the pore pressure from hydrostatic the influence of pore pressure on velocities is expected to diminish with depth and is unlikely to be significant at lower crustal depths where porosity is extremely low of significance poisson s ratio is shown to be dependent on pore pressure as well as confining pressure at constant confining pressure poisson s ratio increases with increasing pore pressure thus overpressured regions within the upper oceanic crust are likely to have relatively high poisson s ratios as well as low compressional and shear wave velocities

characterization of a subsurface artificial fracture by the triaxial shear shadow method summary we have successfully measured the 3 d configuration and reopening behaviour of a single fracture in the hot dry rock model field at higashi hachimantai japan by the triaxial shear shadow method the crack was created by hydraulic fracturing in intact welded tuff at a depth of 370 m we have carried out crosshole seismic measurements using a downhole air gun and a triaxial seismic detector extinction at a specific polarization direction was determined by a triaxial hodogram analysis of detected signals and the orientation and distribution of the fracture were evaluated the results are in good agreement with data obtained by independent experiments in the field the reopening behaviour of the fracture has also been observed through the delay of the transmitted p wave in an experiment during a pressurization of the fracture the mechanism can be explained by a model considering the pressure transmission into the rock from the fracture surface and the reopening of the microcrack in the vicinity of the fracture

the seek sporadic e experiment over kyushu campaign the seek sporadic e experiment over kyushu campaign was conducted in late august 1996 from the southern region of kyushu japan to investigate the mechanism for the generation of quasi periodic qp radar backscatter from field aligned irregularities imbedded in nighttime sporadic e es layers seek was designed to determine in situ small scale electrodynamical properties using two sounding rockets and large scale dynamics and electrodynamics using ground based sensors which included a transportable radar and other radio and optical instruments deployed in the vicinity of the rocket range it was observed by this campaign that es layers existed in a convergent wind shear region where large electric fields were induced and when active atmospheric gravity waves existed in the mesosphere however there was little evidence which positively supported the hypothesis that es layers were deeply modulated in altitude

a mini slug test method for determination of a local hydraulic conductivity of an unconfined sandy aquifer abstract a new and efficient mini slug test method for the determination of local hydraulic conductivities in unconfined sandy aquifers is developed the slug test is performed in a small diameter 1 inch driven well with a 0 25 m screen just above the drive point the screened drive point can be driven from level to level and thereby establish vertical profiles of the hydraulic conductivity the head data from the test well are recorded with a 10 mm pressure transducer and the initial head difference required is established by a small vacuum pump the method described has provided 274 spatially distributed measurements of a local hydraulic conductivity at a tracer test site at vejen denmark the mini slug test results calculated by a modified dax slug test analysing method applying the elastic storativity in the dax equations instead of the specific yield are in good accordance with the results from two natural gradient tracer experiments performed at the test site the original dax the bouwer and rice and the chirlin analysing methods all led to an underestimation of the effective hydraulic conductivity by a factor of more than 2 when compared with the tracer tests in contrast the spherical flow model of karasaki et al overestimated the results of the tracer tests by approximately a factor 1 4 the dax and the cooper et al methods assuming only radial flow to the partially screened well yielded a better approximation of the horizontal hydraulic conductivity than the chirlin method which also considers axial flow this fact is suggested to be a result of aquifer anisotropy as a significant higher horizontal than vertical hydraulic conductivity may suppress the significance of the axial flow component

frictional stability permeability relationships for fractures in shales there is wide concern that fluid injection in the subsurface such as for the stimulation of shale reservoirs or for geological co2 sequestration gcs has the potential to induce seismicity that may change reservoir permeability due to fault slip however the impact of induced seismicity on fracture permeability evolution remains unclear due to the spectrum of modes of fault reactivation e g stable versus unstable as seismicity is controlled by the frictional response of fractures we explore friction stability permeability relationships through the concurrent measurement of frictional and hydraulic properties of artificial fractures in green river shale grs and opalinus shale ops we observe that carbonate rich grs shows higher frictional strength but weak neutral frictional stability the grs fracture permeability declines during shearing while an increased sliding velocity reduces the rate of permeability decline by comparison the phyllosilicate rich ops has lower friction and strong stability while the fracture permeability is reduced due to the swelling behavior that dominates over the shearing induced permeability reduction hence we conclude that the friction stability permeability relationship of a fracture is largely controlled by mineral composition and that shale mineral compositions with strong frictional stability may be particularly subject to permanent permeability reduction during fluid infiltration

evidence for excess pore pressures in southwest indian ocean sediments brown clay cores from the madagascar and crozet basins show the following evidence of excess pore pressures large amounts of flow in increasing average sedimentation rate with age and nonlinear temperature gradients additionally many hilltops in these basins have no visible sediment cover the bare hilltops may result from periodic slumping caused by excess pore pressures calculated excess pore pressures which equal or exceed the overburden pressure were inferred from water fluxes predicted by nonlinear temperature gradients and laboratory permeability measurements by using darcy s law since pore pressures which exceed the overburden pressure are unreasonable we attribute this discrepancy to laboratory measures which underestimate the in situ permeability the widespread presence of overpressured sediments in areas of irregular topography provides a process for resuspension of clay sized particles this mechanism does not require high current velocities for the erosion of clay and therefore can be applied to many areas where no strong currents are evident carbonate rich sediments from the madagascar ridge the mozambique ridge and the agulhas plateau had almost no flow in and occurred in areas where all topography was thickly draped with sediment since the age and tectonic location of the ridges and plateaus preclude water circulation in the basement wemore attribute these differences between the brown clay and the carbonate rich material to an absence of significant excess pore pressures in the plateau and ridge sediments less

utilization of observations of well bore failure to constrain the orientation and magnitude of crustal stresses application to continental deep sea drilling project and ocean drilling program boreholes

thermoremanent magnetization of the oceanic lithosphere inferred from a thermal evolution model implications for the source of marine magnetic anomalies abstract thermoremanent magnetization models of the oceanic crust and the uppermost part of the oceanic mantle are derived on the basis of a typical thermal evolution model of the oceanic lithosphere using different magnetic blocking temperature ranges the magnetization of the basaltic layer 2a has a similar pattern but with a lower intensity to that of the standard sea floor spreading magnetic model however the magnetization patterns of the lower crust and upper mantle are skewed so that in a given polarity period the total magnetization of a lithospheric column which is created early in the period is greater than that of a column which is created later in the period magnetic anomalies of the magnetization models are calculated at sea level and at magsat elevation for slow moderate and fast sea floor spreading velocities although the magnetization models are derived based on purely physical reasoning without using any a priori information about the observed marine and magsat magnetic anomalies they do yield magnetic anomalies which are similar to the observed anomalies the models explain several features of the marine and magsat anomalies the anomalous skewness of marine magnetic anomalies is explained in terms of the magnetization of the oceanic lower crust the magnetization of the oceanic upper mantle may account for the anomalous skewness observed over the cretaceous quiet zones in the atlantic ocean the skewness of the magnetic anomalies calculated at sea level decreases with the increase in the sea floor spreading velocity

quasi periodic echoes observed with the chung li vhf radar during the seek campaign the 52 mhz chung li vhf radar located in taiwan was operated during the seek sporadic e experiment over kyushu campaign to investigate the so called quasi periodic qp echoes that occur from nighttime sporadic e es layers highlights of this study are presented in this paper using measurements made on august 17 1996 to illustrate the echo characteristics qp echoes displaying 5 to 10 minute periods were observed throughout this night a new finding is the occurrence of qp echoes whose striations were almost vertically oriented when plotted using a height time intensity hti format this observation provides the first unambiguous evidence for the existence of steep spatial tilts in es layers that are responsible for qp echoes other characteristics from three periods during this night are described including striations with positively sloped striations these characteristics are discussed in light of existing models for qp echoes

equatorial quasiperiodic echoes from field aligned irregularities observed over jicamarca this is a report of so far undescribed equatorial quasiperiodic eqp echoes from field aligned irregularities from the e and lower f region these echoes were observed on october 20 1993 at the jicamarca radio observatory in conjunction with a spectacular spread f event we have identified two regions where striated eqp echoes are clearly observed the time periods are between 1 and 5 min in the first region 120 140 km the slope of the striations is negative apparent downward propagation while in the second 160 200 km the slope is positive moreover in the first region the time periods striation spacings are smaller and the altitude rates of change are higher than those observed in the second region although these equatorial echoes appear somewhat similar to those seen at midlatitudes we believe that the two phenomena are different we have no explanation as yet for these eqp observations our purpose in presenting these data is primarily to describe their properties in more detail than has been done in the past

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

topographic relief and sediment thickness their effects on the thermal evolution of the oceanic crust we compiled a suite of 490 heat flow measurements from the pacific ocean in areas with less than 85 m of sediment heat flow patterns at different basement ages vary with topographic relief areas with reliefs 300 meters are conductively blanketed at 70 90 m y and convect out to 90 110 m y

the seek chemical release experiment observed neutral wind profile in a region of sporadic e wind measurements made with the chemical release technique during a sporadic e layer event are presented the data were obtained as part of the sporadic e experiment over kyushu seek sounding rocket campaign the winds show a strong maximum in the lower e region approaching 150 m s 1 near 105 km altitude and a large shear below the maximum the large shear was within a few kilometers altitude of the peak in the electron densities measured on the downleg of the rocket trajectory calculations of the richardson numbers for the wind profile show that the altitude range near the layer was highly unstable