224ra 228ra and226ra in winyah bay and delaware bay the first224ra t1 2 3 64days measurements from mixing zones of estuarine systems are presented for the pee dee river winyah bay and delaware bay estuaries high resolution gamma ray spectrometry was used to determine224ra 228ra t1 2 5 7years and226ra t1 2 1622years activity ratios desorption and diffusion from suspended and bottom sediments contributes to the non conservative increases of the three isotopes in each systems in delaware bay224ra concentrations were nearly constant over the 2 5 to 15 salinity range where two turbidity maximum zones are located 228th scavenging onto the suspended particles in the turbid zones may supply a regenerative source of224ra in this system samples collected on the ebb and flood tide from a salt marsh along delaware bay have a 5 fold increase in224ra from flood to ebb and 3 and 2 fold increases for228ra and226ra respectively indicating salt marshes are another source of radium to estuarine waters

chemistry of uranium thorium and radium isotopes in the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal abstract the most comprehensive data set on uranium thorium and radium isotopes in the ganga brahmaputra one of the major river systems of the world is reported here the dissolved 238u concentration in these river waters ranges between 0 44 and 8 32 1 and it exhibits a positive correlation with major cations na k mg ca the 238 u cations ratio in waters is very similar to that measured in the suspended sediments indicating congruent weathering of uranium and major cations the regional variations observed in the 234 u 238 u activity ratio are consistent with the lithology of the drainage basins the lowland tributaries chambal betwa ken and son draining through the igneous and metamorphic rocks of the deccan traps and the vindhyan bundelkhand plateau have 234 u 238 u ratio in the range 1 16 to 1 84 this range is significantly higher than the near equilibrium ratio 1 05 observed in the highland rivers which drain through sedimentary terrains the dissolved 226ra concentration ranges between 0 03 and 0 22 dpm 1 the striking feature of the radium isotopes data is the distinct difference in the 228ra and 226ra abundances between the highland and lowland rivers the lowland waters are enriched in 228ra while the highland waters contain more 226ra this difference mainly results from the differences in their weathering regimes the discharge weighted mean concentration of dissolved 238u in the ganga at patna and in the brahmaputra at goalpara are 1 81 and 0 63 1 respectively the ganga brahmaputra river system constitutes the major source of dissolved uranium to the bay of bengal these rivers transport annually about 1000 tons of uranium to their estuaries about 10 of the estimated global supply of dissolved uranium to the oceans via rivers the transport of uranium by these rivers far exceeds that of the amazon although their water discharge is only about 20 of that of the amazon the high intensity of weathering of uranium in the ganga brahmapura river system can also be deduced from the 232 th 238 u and 230 th 238 u activity ratios measured in the suspended sediments 230th is enriched by about 19 in the suspended sediments relative to its parent 238u the flux of excess 230th supplied to the bay of bengal via these river sediments is 980 1012 dpm a about six times more than its in situ production from seawater in the entire bay of bengal

transport of u and th series nuclides in a baltic shield watershed and the baltic sea the transport of th ra and 210 pb from a continental source region and through an estuarine environment was investigated unlike previous studies here both short and long lived nuclide data were obtained for river inputs river water and estuarine waters the mire rich kalix river drainage basin was chosen as a typical northern shield area because this river may represent typical waters flowing into the arctic and northern seas groundwaters from bedrock and glacial tills have comparable th isotope concentrations and do not exhibit significant th isotopic shifts relative to host rocks the extensive peat deposits of the basin receive groundwater discharges and concentrate th and u but not ba and ra which cause high 230 th 232 th ratios in mire waters however mire outflows do not have a significant impact on th and ra isotopic compositions of the river overall weathering characteristics for the basin are obtained from the river data the 230 th 232 th 228 ra 226 ra and 226 ra ba river ratios are comparable to those of source rocks consistent with similar release rates of these nuclides from u th and ba bearing minerals river ratios of 230 th 238 u ar and 226 ra 238 u ar are 1 so that th and possibly ra are accumulating in the weathering regions and the weathering profile is still evolving low 228 ra 232 th ar and 226 ra 230 th ar ratios indicate that th is preferentially retained over ra river 234 th 238 u ar ratios are greater than 230 th 238 u ar ratios and suggest that in systems where river inputs are well characterized these ratios can be used to calculate th transit times through the watershed filtration data indicate that although a dominant fraction of the th is transported in the river on particles the rest is almost entirely carried by colloids the kalix river discharges into the baltic sea model calculations for the transport of th and ra isotopes in the baltic sea show that the high ratios of 234 th 238 u ar found here reflect long th residence times relative to particle scavenging of 50 d the water column 232 th budget is dominated by eolian inputs the 226 ra concentrations may be higher than those of water inflows with 60 derived from underlying sediments a greater fraction of 228 ra is derived from sediments to balance the decay of 228 ra within the water column during the 35 yr residence time of water in the baltic the baltic 228 ra 226 ra ar ratios which are relatively constant over a range of salinities are fortuitously similar to those of the river inflows

radium isotopes in the chesapeake bay 228ra and 226ra are enriched in waters of chesapeake bay through fluxes from the bottom sediments and desorption from particles entering the estuary the activity ratio of 228ra 226ra increases from 1 5 in the susquehanna river to 3 4 in waters of 15 20 salinity apparently much of the 228ra is supplied by diffusion from sediments within the bay while desorption from particles entering the bay is more important for 226ra because of the multiple inputs and long residence time of water in the bay no curvature is obvious in a plot of radium isotope concentration vs salinity

frictional coefficient on faults in a seismogenic region inferred from earthquake mechanism solutions the coefficient of friction associated with faults in a seismogenic region is inferred from numerous focal mechanism solutions earthquake slip can occur on a favorably oriented fault plane when preexisting fault planes are oriented in various directions the fault plane is thought to be selected when the coulomb failure stress given by f n p s0 has a maximum value along a slip direction on the plane here is the shear stress is the coefficient of friction n is the normal stress p is the pore pressure and s0 is the cohesion consequently the geometry of the plane and the slip direction include information concerning the coefficient of friction for the faults in the present paper the coefficient of friction is inferred from the distribution of p axis orientations assuming hydrostatic pore pressure the method is very simple and has the advantage that the results obtained do not depend on pore pressure when pore pressure is not proportional to the normal stress observed distributions of p axis azimuths and plunges display a very narrow peak having a width of about 20 the coefficient of friction on the faults can then be estimated from the width to be less than or equal to 0 2 when the stress is balanced by friction the shear stress can be calculated here the shear stress in megapascals has a value of 4 0z where z is the depth in kilometers under the assumption of hydrostatic pore pressure and a coefficient of friction of 0 2 the value obtained for the coefficient of friction is very small compared with those derived from laboratory frictional experiments it is thought that this small value of is attributed to the friction itself when pore pressure is not proportional to the normal stress

advances in marine chemistry 1979 1982 these four years saw advances in many areas further developments in sampling and analytical techniques have opened new avenues of exploration for trace elements and particulate matter the impact of the geosecs expedition was further felt in the field of marine chemistry as the results were still being published a major field effort occurred as a follow on to the geosecs work tto and intensive sampling was performed in the newly discovered submarine hydrothermal vent fields an important and unresolved controversy has arisen regarding the ability to measure preformed co2 in the seawater system in many respects the field of marine chemistry appears to be gaining a momentum spurred by both improvements in analytic techniques and an increasing social and economic relevance

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

roughness at the base of the seismogenic zone contributing factors the cutout depth of microseismic activity in continental fault zones appears to correspond to the onset of greenschist metamorphic conditions at about 300 c it can generally be modeled as the transition from frictional to quasi plastic behavior in quartzofeldspathic crust shear resistance increases with depth through the frictional regime to peak at the transition beneath which it falls off exponentially with increasing temperature larger earthquake ruptures ml 5 5 nucleate around this transition depth where the highest concentrations of strain energy may accumulate varying depth and amplitude of the peak shear resistance along strike induce fluctuations in strain energy concentration at the base of the seismogenic zone factors affecting the depth of the transition include crustal composition geometry and mode of faulting fluid pressure levels in the frictional regime and water content in the quasi plastic regime quasi plastic strain rate and geothermal gradient evaluation of their relative importance is complicated because several are interdependent however compositional change may cause abrupt irregularities in seismogenic depth and peak shear resistance while regional variations in heat flow look to be particularly effective in creating long wavelength heterogeneities in strain energy concentration affecting faulting style

stress fields in and around metropolitan osaka japan deduced from microearthquake focal mechanisms abstract present day stress fields in and around metropolitan osaka japan have been investigated based on 238 microearthquake focal mechanism solutions from approximately the past 10 years the successful retrieval of the focal mechanisms in the noisy urban area owed much to the clean seismic data recorded at four borehole observatories deeper than 500 m depth in osaka prefecture in which p wave onset polarity of the microearthquake could be clearly identified we found many microearthquakes with a pure reverse faulting mechanism which is consistent with the faulting style of major active faults within the area 42 km long east dipping uemachi and 38 km long east dipping ikoma fault zones however a considerable number of microearthquakes with strike slip components were also found to occur most of the p axes are oriented in the ese wnw to ene wsw directions sub horizontally conforming to the general tectonic trend of the area the analysis of a stress tensor inversion delineated small but noticeable differences in stress regime on a scale of at least 10 km where strike slip faulting prevails throughout the region but the middle and southern sections of the uemachi fault zone contain some reverse faulting components based on the estimated stress fields together with assumptions regarding the deep geometry of the uemachi fault zone we assessed the reactivation potential of the fault zone through slip tendency analysis the results indicate higher potential in the middle and southern sections of the fault zone which is related to the locally increased reverse component detected there

scavenging of thorium isotopes in the canada basin of the arctic ocean abstract investigations on the distribution of thorium isotopes in the water column have been utilized as powerful tracers to investigate the geochemical pathways of particle reactive material in the ocean we measured th 228 th 230 th 232 th and 234 th isotopes in samples collected along a horizontal profile from barrow ak to the canada basin as well as two vertical profiles in the canada basin the suspended particle concentrations were also measured to investigate the role of suspended particulate matter spm in th scavenging the spm inventory is more than an order of magnitude higher than that reported for the alpha ridge ice station indicating that the spm inventories vary over an order of magnitude in the deep arctic basins the conditional partition coefficient of th isotopes between suspended particulate matter and dissolved phase generally appears to be higher than those in non polar regions and this is attributed to more reactive suspended particulate matter the residence times of total 230 th are significantly lower than those calculated for the alpha ridge station while higher than those found in the eurasian basin and beaufort sea in the canadian basin the calculated residence time in all the deep basins of the arctic ocean varied between 13 1 and 45 1 years a reversible scavenging model applied to the distribution of th isotopes 230 th 228 th in the deep waters and 234 th 228 th in the upper 100 m indicates that the forward removal rate constant is higher than the value reported for the alpha ridge while the reverse rate constant is comparable to the alpha ridge station suggesting faster removal onto particulate matter and slower desorption of th from the particulate matter

joint focal mechanism determination with source region station corrections using short period body wave amplitude data abstract we have developed a method that simultaneously determines focal mechanism solutions of many small earthquakes and source region station corrections for short period body wave amplitudes by inverting amplitude data of p sh and sv waves together with p wave polarity data the observed seismic waveform includes the effects of site amplification and attenuation along its ray path in addition to the radiation pattern of earthquake source the amplitude of seismograms at frequencies higher than a few hertz is extremely sensitive to heterogeneous structure near the ground surface consequently we need to know in detail the effects of site amplification and attenuation in order to estimate focal mechanisms by using short period waveforms however at present we do not know the detailed crustal structure with a resolution necessary for this estimation in the present study we assume that p and s wave attenuation factors along ray paths from hypocenters to each station can be expressed as a function of hypocentral distance backazimuth and incident angle based on this assumption we determined focal mechanism solutions of many earthquakes and the coefficients in the function for each station simultaneously by using p sh and sv wave amplitudes and p wave polarities we applied the present method to 170 aftershocks of the 1996 onikobe earthquake m 5 9 which occurred in the central part of northeastern japan we obtained focal mechanism solutions of many microearthquakes whose mechanism solutions could not be determined by using p wave polarity data alone p axes of almost all the obtained focal mechanism solutions are horizontal and oriented in the east west direction t axes are on average near vertical at the shallowest depth as the depth approaches 5 km the t axes become horizontal and then gradually become near vertical again

earthquake source nucleation a physical model for short term precursors abstract ohnaka m 1992 earthquake source nucleation a physical model for short term precursors in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 149 178 this paper deals with a quasistatic leading to a quasidynamic at a later time nucleation process that precedes the earthquake dynamic rupture and models of the earthquake source nucleation are put forward based on physical principles a quasistatic to quasidynamic rupture nucleation process is an intrinsic part of the ensuing earthquake dynamic rupture in other words the nucleation process itself is an short term or immediate precursor that occurs in a localized zone during the earthquake nucleation premonitory slip proceeds in the localized nucleation zone and shear stress also decreases gradually in the zone since slip weakening occurs during the nucleation immediate foreshock activity is a part of the nucleation process leading to the mainshock dynamic rupture therefore hypocentral locations of foreshocks are necessarily restricted to lie near the mainshock hypocentre onset of the mainshock rupture whether or not foreshocks occur during the mainshock nucleation depends on how the rupture growth resistance varies on a local to small scale since patches of greater rupture growth resistance are considered to prevail on a local to small scale in the fault zone carrying immediate foreshocks would be one of the major characteristics of earthquakes that nucleate within the brittle seismogenic layer when a mainshock earthquake nucleates within the brittle seismogenic layer and its hypocentre is located near the base of the seismogenic layer immediate foreshocks for this mainshock are necessarily restricted to lie within a localized region shallower than hypocentral depth of the mainshock by contrast the nucleation process below the base of the seismogenic layer is aseismic in nature so that carrying no conspicuous foreshocks would be a common characteristic of interplate earthquakes that nucleate below the base of the brittle seismogenic layer the breakdown strength p the breakdown stress drop b and the critical slip displacement dc are indicative of the rupture growth resistance to estimate depth variations of these parameters the effects of the normal stress n and temperature t on those parameters are examined using available data so far published the combined effects of n and t on p in the brittle to semibrittle regime are found to be represented empirically by p n t po n 1 cosh 50 t 40 sinh 50 t exp 2000 t where po n 135 7 0 750 n and t is measured in k and n in mpa it is found that dc increases sharply with t but is insensitive to n above 300 c while dc depends on n but is insensitive to t below 300 c on the basis of these results variations in p dc and b at mid crustal depths are estimated for quartzo feldspathic rocks for a given geothermal gradient

226ra in the black sea and sea of marmara water column distributions of226ra were determined at stations in the sea of marmara and the black sea as part of the 1988 joint u s turkish black sea expedition black sea surface water226ra concentrations were a factor of three to four lower than measurements made 20 years earlier the most likely cause is increased removal of226ra and ba 35 due to increased surface biological activity a secondary effect is decreased fluvial discharge and related dimunition of inputs by desorption from fluvial suspended sediments the amount of226ra missing from the surface waters of the black sea over this period is accounted for in the high porosity surficial fluff sediment layer throughout the black sea depth profiles of226ra exhibited pronounced maxima of approximately 25 dpm 100 l at about 16 2 16 3 in the vicinity of a bacterial maximum but slightly shallower than the total dissolved mn and fe maxima 16 4 16 5 reported by lewis and landing 38 while the226ra maximum may in part be linked to the cycling of mn and fe oxyhydroxides near theo2h2s interface its distribution appears to be more plausibly explained as a result of the microbial breakdown of particulate organic matter and the subsequent release and partial dissolution of associated barite in this region a simple steady state two model has been used to obtain a semiquantitative understanding of the behavior of226ra in the black sea by incorporating reasonable estimates for the input and removal of226ra in the black sea an excellent agreement between predicted and observed 1988 226ra concentrations was achieved the model suggests that the dominant variables controlling the distribution of226ra in the black sea are riverine input and cycling with ba

the brittle plastic transition and the depth of seismic faulting a simple rheological model of shearing of the lithosphere that has gained wide acceptance is a two layer model with an upper brittle zone in which deformation takes place by frictional sliding on discrete fault surfaces and a lower plastic zone in which deformation takes place by bulk plastic flow the two are separated by an abrupt brittle plastic transition which is assumed to be indicated by the lower limit of seismicity experimental studies however as well as the deformation structures of mylonites indicate that a broad transitional field of semi brittle behavior lies between these extremes this is a field of mixed mode deformation with a strength that can be expected to be considerably higher than that predicted from the extrapolation of high temperature flow laws for quartzofeldspathic rocks the semi brittle field lies between t1 the onset of quartz plasticity at about 300 c and t2 feldspar plasticity at about 450 c a model is presented in which the transition t1 does not correspond to a transition to bulk flow but to a change from unstable velocity weakening friction to stable velocity strengthening friction t1 thus marks the depth limit of earthquake nucleation but large earthquakes can propagate to a greater depth t3 t3 t2 which corresponds to the lower limit of dynamic frictional behavior in the semi brittle field and approximately to the peak in strength the zone between t1 and t3 is one of alternating behavior with flow occurring m the interseismic period and with co seismic dynamic slip occurring during large earthquakes this zone is characterized by mylonites interlaced by pseudotachylytes and other signs of dynamic faulting the transition t1 is also marked by a change in the generation mechanism of fault rocks from abrasive wear above which produces cataclastites to adhesive wear below which is proposed as an important generation mechanism of mylonites in the upper part of the semi brittle field

226ra contents and 228ra226ra activity ratios of the fenland rivers and the wash eastern england spatial and seasonal trends measurements of 226ra and 228ra in the fenland rivers and the wash show that physical and hydrological factors play an important role in controlling the transport and fate of radium isotopes in the surficial environment higher 226ra contents and lower 228ra226ra activity ratios are found in waters from catchments with a greater proportion of carbonate rich source materuals this relationship is more obvious during periods of high runoff and river discharge when enhanced surficial weathering and regolith saturation takes place in the nearshore zone 226ra content is relatively uniform whilst 228ra226ra activity ratio is controlled by ionic concentrations cl so4 and co3 and the acquisition of marine characteristics the observed 228ra226ra activity ratio trend can be attributed to a combination of conservative mixing and radium desorption from suspended sediments whilst more uniform 226ra contents may reflec bottom sediment diffusion of excess 226ra over a greater area the relative importance of these two processes is controlled by differential input from the freshwater and saline end members of the estuary

practical aspects of avo modeling avo amplitude variation with offset modeling contributes significantly in seismic data acquisition design and prestack seismic data processing and interpretation it has become a common practice in prestack seismic analysis it is also used for verifying and developing avo theories conducting avo modeling is by nature an exercise of multidiscipline integration it thus enhances reservoir characterization and reduces the risk in hydrocarbon exploration

source and distribution of dissolved radium in the bega river estuary southeastern australia abstract measurements of the activities of the four naturally occurring radium isotopes in the surface water and porewater of an estuary have yielded information on the release of radium from sediments and on the extent of surface water porewater interaction in the estuary under low flow conditions the non conservative behaviour of dissolved radium in the estuary is almost entirely due to the flux of radium from estuarine bed sediments radium accumulates in bottom sediment porewater and is then mixed with estuarine surface water probably as a result of tidal action it is shown experimentally that the enrichment of the short lived isotopes 224ra and 223ra relative to 226ra in estuarine porewater can be explained by the repeated leaching of radium from bottom sediments by saline water and the rapid regeneration of the short lived isotope activity from their sediment bound parent nuclides the leaching of radium from bottom sediments is apparently occurring on a time scale which is long weeks months compared with the 224ra and 223ra half lives indicating that the amount of ion exchangeable radium adsorbed to the sediments is large compared with the amount dissolved in porewater by applying a simple 2 d steady state multi box model 224ra and 223ra surface water and porewater concentrations have been used to estimate the daily flux of porewater crossing the sediment water interface in the bega estuary this flux is found to be about 15 of the estuary volume

temporal changes in coda q 1 and b value due to the static stress change associated with the 1995 hyogo ken nanbu earthquake the seismicity in the tamba region northeast of the hyogo ken nanbu earthquake in japan january 17 1995 mjma 7 2 increased significantly following this earthquake this increase suggests that the static stress change due to a large earthquake causes a change in the crustal condition or dynamics in order to reveal the changes quantitatively we investigate the temporal variation in coda q l and b value in the tamba region we analyze the waveform data of many shallow microearthquakes m 1 5 3 0 in the region recorded in a period from 1987 to 1996 coda q 1 is estimated in 10 frequency bands in a range of 1 5 24 hz based on the single isotropic scattering model at frequencies between 1 5 and 4 0 hz the temporal variation in coda q 1 shows significant correlation with the occurrence of the hyogo ken nanbu earthquake coda q l increases after the event a variation in b value whose sign is opposite to that of coda q 1 is recognized the fracture dimensions of microearthquakes that contribute to the variation in b value are estimated to be 400 m this scale length is consistent with the characteristic scale length of scatterer 300 600 m which contributes effectively to a temporal variation in coda q 1 the crustal activity in the tamba region is possibly controlled by the heterogeneity with dominant scale of 102 m the stress sensitivity of the coda q 1 change is estimated to be 10 mpa 1 this value is an order of magnitude larger than the stress sensitivity of seismic velocity reported before

depth dependent change in the focal mechanism of shallow earthquakes implications for brittle plastic transition in a seismogenic region an analysis is conducted of the focal mechanism solutions of 2150 shallow earthquakes that have occurred in the central part in the kinki district japan it is found that in regions shallower than the characteristic depth the depth at which the frequency depth distribution of earthquakes is maximum t axis plunges are widely distributed in the horizontal and vertical directions furthermore the distribution of the plunges does not change with depth in the region in regions deeper than the characteristic depth the plunges are concentrated horizontally that is both strike slip and reverse fault events are found in regions shallower than the characteristic depth while strike slip events dominate in the deeper region it is inferred from the above results that the minimum horizontal stress has almost the same magnitude as the vertical stress in regions shallower than the characteristic depth while in the deeper regions the minimum horizontal stress is less than the vertical stress this conclusion implies that the minimum horizontal stress increases proportional to the depth in regions shallower than the characteristic depth but does not increase in proportion to depth in the deeper regions it was also concluded that the brittle semibrittle transition could possibly occur at the characteristic depth

local stress concentration in the seismic belt along the japan sea coast inferred from precise focal mechanisms implications for the stress accumulation process on intraplate earthquake faults 1 spatial changes in the azimuth of the maximum principal stress 1 axis are found in the intraplate region of southwest japan it is inferred from stress inversions of numerous precise focal mechanisms that the azimuths of the 1 axis in the seismic belt along the japan sea coast are oriented in n110 e n130 e directions while in the surrounding region they are aligned in almost the ew direction n90 e n100 e maximum horizontal compressional stresses in an ew direction are widely observed in the shallow crust in the inland plate along the nankai trough however the maximum horizontal stress in a wnw ese direction is seen only in the seismic belt this spatial change in the stress field in and around the seismic belt is explained by the deformation of an aseismic fault or a ductile fault zone in the lower crust beneath the seismic belt

lateral stretching of the philippine sea plate subducting along the nankai suruga trough focal mechanisms are investigated for shallow earthquakes h 60 km of central japan by using telemetered seismic data of microearthquakes shallow earthquakes in central and southwestern japan can be distinguished into three groups upper crustal earthquakes subcrustal earthquakes and interplate thrust earthquakes the first and the second ones being subjects of the present study most of the upper crustal earthquakes are of strike slip type or reverse faulting with e w to se nw compression whereas the subcrustal earthquakes are characterized by strike slip or normal faulting with e w to ne sw extension the subcrustal seismic zone subparallel to the nankai trough becomes progressively deeper landward to the north and progressively shallower to the east so that it emerges into a very shallow seismic activity in the izu peninsula which has been interpreted as a microcontinent of the philippine sea plate colliding against the eurasian plate on the basis of hypocentral distribution three dimensional seismic velocity structure and focal mechanisms subcrustal earthquakes are considered to occur within the subducting philippine sea plate that extends down to a depth of at least 60 km on the basis of this and other focal mechanism studies stress trajectories are drawn for the subducting philippine sea plate and for the overriding eurasian plate the overriding plate is on the whole under the e w compression which coincides with the moving direction of the pacific plate relative to the eurasian plate the subducting plate on the other hand is under lateral extension along its strike we interpret that the latter is a stress regime unique to an incipient subduction zone where the subducting plate at subcrustal depths is forced to warp downward being constrained laterally at the arc arc junctions and thereby comes under lateral stretching the lateral constraints arise either from apparent increase in flexural strength of the plate at the arc arc junction or from buoyancy of a microcontinent that resists subduction

non steady state 210pb flux and the use of 228ra 226ra as a geochronometer on the amazon continental shelf the recovery of quasi cyclic 210pb profiles from the foreset region of the amazon subaqueous delta has raised questions concerning the non steady state flux of 210pb to this region of the shelf radioisotopic profiles 210pb 234th 228ra 226ra 137cs from seven kasten cores along with the analysis of grain size organic carbon and clay sized mineralogy are used to investigate the time scale and the controlling mechanisms of the 210pb cyclicity a common assumption used in 210pb geochronology is that the initial specific activity is constant with time an assumption that is invalid in this region variations of particle affinity for 210pb have been shown to affect the initial specific activity reaching the seabed in various other studies however investigations of grain size organic carbon and mineralogy have revealed no relationship with the fluctuating 210pb activity in this area a new geochronometer 228ra 226ra is used to determine sediment accumulation rates over a 30 year time scale which range from 10 to 60 cm yr in the study area spectral analysis of the 210pb cyclicity has revealed that the major component of 210pb cyclicity has a frequency of approximately 2 3 years in addition components of the 210pb cyclicity occur on annual and semi annual frequencies the controlling mechanism for the 210pb cyclicity on these time scales appears to be the seaward transport and accumulation of low activity fluid muds from the topset region

226ra and 228ra in the mixing zones of the pee dee river winyah bay yangtze river and delaware bay estuaries 226ra and 228ra have non conservative excess concentrations in the mixing zones of the pee dee river winyah bay estuary the yangtze river estuary and the delaware bay estuary laboratory experiments using pee dee river sediment indicate desorption of 226ra to increase with increasing salinities up to 20 in winyah bay desorption from river borne sediments could contribute almost all of the increases for both isotopes desorption adds only a portion of the excess 228ra measured in the yangtse river and adjacent shelf waters and delaware bay in the yangtze river the mixing zone extends over a considerable portion of the continental shelf where 228ra is added to the water column by diffusion from bottom sediments while 226ra concentrations decrease from dilution diffusion of 228ra from bottom sediments in delaware bay primarily occurs in the upper part of the bay 22 water where fine grained sediments predominate a diffusive flux for 228ra of 0 33 dpm cm 2 year was determined for delaware bay

residence times of surface water and particle reactive 210pb and 210po in the east china and yellow seas 228ra 226ra 210pb and 210po were measured in the surface waters of the east china and yellow seas using mass balance equations for the ra isotopes we estimated the total flux of diffusion from sediments and desorption from suspended particles to be 0 1 dpm 226ra cm 2 a 1 and 1 dpm 228ra cm 2 a 1 and residence times to be 2 3 years for the waters on the east china sea shelf and 5 6 years for yellow sea waters box model calculations yielded generally congruent scavenging residence times for 210pb and 210po in the waters of 2 months on the shelf and 7 months in the kuroshio current these suggest that reactive heavy metals and pollutants discharged through rivers from the continent to the east asian continental shelf are largely deposited on the bottom sediments prior to transport to the pelagic ocean by lateral mixing

quantifying saline groundwater flow into a freshwater lake using the ra isotope quartet a case study from the sea of galilee lake kinneret israel we investigated the ra isotope quartet in order to quantify the discharge of saline groundwater into a freshwater lake the activities of 226ra 228ra 223ra and 224ra were measured in the sea of galilee israel surrounding saline springs and the jordan river coupled with u th and 226ra measurements in sediment cores and laboratory ra adsorption experiments under different salinity conditions the 226 ra activity 0 007 0 008 bq l 21 and 226 ra cl ratio in the lake were significantly lower than those of the inflowing saline springs indicating that 75 86 of the incoming 226 ra is removed from the lake water this missing ra is likely adsorbed onto suspended particles given the observed differential depletion of ra isotopes we present a model consisting of adsorption desorption recoil and decay of the short lived 224 ra and 223 ra isotopes we predict a removal time of 2 weeks for ra inferring the apparent residence time of suspended matter in the lake a mass balance calculation of the different 226ra inventories reveals a saline groundwater flux of 44 61 3 109 ly r 21 for fuliyatype water the residence time of dissolved 226ra in the lake is estimated as 3 4 yr the 228ra 226ra ratio of the lake water and a mass balance calculation show that 228ra arrives from regeneration though bottom sediments in addition to groundwater flux mass balance calculations of the expected saline fluxes before the diversion of saline inflows to the lake early 1960s provide 226ra activity estimates in the lake 0 018 0 020 bq l21 that are similar to the value 0 018 6 0 0001 bq l21 measured in the lake in 1962

u th ra fractionation during weathering and river transport the potential of radioactive disequilibria as tracers and chronometers of weathering processes has been recognised since the 1960 s e g rosholt et al 1966 hansen and stout 1968 this interest results from the dual property of the nuclides of the u and th radioactive series 1 to be fractionated during water rock interactions and 2 to have radioactive periods of the same order of magnitude as the time constants of many weathering processes and chemical transfers to ground and river waters therefore the study of radioactive disequilibria in surface environments should help to bring information about the nature the intensity but also the time scale of the water rock interactions produced during weathering and related chemical transfers these different properties have justified many of the studies on u th series in weathering profiles and river waters rosholt 1982 scott 1982 and osmond and ivanovich 1992 gave a synthesis of the studies of u series in weathering and surface hydrology up to the 1980 s and the 1990 s respectively here we present the main directions taken in these domains over the last decade they were partly stimulated by the analytical developments made in the measurement of the medium half life nuclides of 238u series i e 234u 230th 226ra in the mid 1980 s namely the use of thermal ionisation mass spectrometry tims e g chen et al 1986 edwards et al 1987 cohen et al 1991 chabaux 1993 chabaux et al 1994 and more recently the use of mc icp ms turner et al 2001 robinson et al 2002 for u and th isotope analysis details of these developments are given in this volume goldstein and stirling 2003 compared to the radioactive counting methods previously used the new techniques permit 1 a reduction by one order of magnitude or more of the size of the sample required for

radium isotopes in coastal waters on the amazon shelf abstract radium isotope distributions on the continental shelf adjacent to the amazon river are a complex function of salinity the river and seawater endmembers for each radium isotope are low data from intermediate salinities plot as a highly scattered region above the conservative mixing line connecting the river and ocean endmembers spatial and temporal variability in sediment mixing and water residence times cause the scatter in the radium isotope data we have used the distributions of 226 ra 228 ra and 224 ra collected during four cruises representing different conditions on the shelf to construct inventories of radium due to nonconservative additions from sediments using estimates of water residence times we calculate fluxes of these radium isotopes from the amazon system the amount of fresh river sediment entering the system each year is adequate to support the nonconservative flux of 226 ra from the shelf sediments however the ultimate release of 226 ra from the sediments requires weeks to months to support the nonconservative flux of 228 ra from this system sediments of the 1 2 m thick surface mixed layer must be resuspended every two years the resulting flux supports 15 of the 228 ra entering the surface atlantic ocean release of 224 ra from suspended sediments primarily fluid mud is more than adequate to support the inventory of 224 ra on the amazon shelf comparing the amasseds low discharge cruise november 1991 to a low discharge sampling in december 1982 revealed no significant changes in the 226 ra and 228 ra distributions

radium isotopes in the orinoco estuary and eastern caribbean sea radium isotopes provide a means of identifying the source of freshened waters in the ocean and determining the time elapsed since these waters were in the estuary we present evidence that during april waters from the amazon mixing zone pass within 50 km of the mouth of the orinoco river these amazon waters are characterized by a lower 228ra 226ra activity ratio ar than are waters from the orinoco at similar salinities during autumn the increased discharge of the orinoco displaces the freshened amazon waters seaward yet the two can be distinguished clearly within the caribbean sea waters of orinoco origin carry a characteristic radium signature including excess activities of 224ra this isotope may be used to estimate the time elapsed since the waters were removed from contact with sediments current speeds based on 224ra dating ranged from 15 to 33 cm s during april the radium isotopes also provide an assessment of sediment mixing in the estuary during low discharge april considerable mixing of older sediment by physical or biological processes or dredging maintained high activities of 228ra in the estuary and produced the highest 228ra 226ra ar s yet measured in any estuary during high discharge september a large fraction of the 228ra was derived from desorption from fresh sediment rather than mixing of older sediments activities of 224ra were high in the estuary during both high and low discharge indicating that considerable mixing of recently introduced sediment must occur during each period the high 224ra 228ra ar s measured in september imply that the same sediments were being resuspended during high discharge and that there was little exposure of older sediments which had been stored in the estuary for months to years during april 224ra and 228ra activities in the water were about equal indicating that most of the sediment being resuspended had been stored in the estuary long enough to reestablish radioactive equilibrium in the 232th decay series i e 20 years

tracing the flow rate and mixing ratio of the changjiang diluted water in the northwestern pacific marginal seas using radium isotopes we measured ra isotopes 223ra and 228ra in surface seawater of the northwestern pacific marginal seas to trace the flow rate and mixing of the changjiang diluted water cdw in the summer of 2012 based on the horizontal distribution of 223ra activities the arrival time of cdw from the river mouth to 450 km offshore northeast was estimated to be 20 35 days which is similar to that determined in previous studies moreover we successfully calculated the relative contribution of cdw at each sampling station using a salinity and 228ra diagram using this unique method we found that the relative contribution of cdw was more than 30 in most surface seawaters of the northern east china sea the yellow sea and the southern sea off korea our results suggest that cdw is of high significance in the biogeochemistry of surface seawater of these northwestern pacific marginal seas during the summer monsoon period

an excess 226ra chronology for deep sea sediments from saanich inlet british columbia abstract to further explore the efficacy of 226 ra excess dating for deep sea sediments previously dated varve sediments from saanich inlet were investigated ages obtained using 226 ra excess are comparable to the varve ages in the upper 20 25 m of the sedimentary record but radiometric ages for those sediments older than c 4000 yr bp are significant underestimates this results from major changes in sedimentation within saanich inlet around 4000 yr bp linked to rising sea levels with younger sediments characterised by a higher biogenic contribution resulting from the establishment of an anoxic fjord environment the older sediments were deposited in a shallow water inlet characterised by variable ra mass balance and non radiogenic losses therefore while 226 ra excess can produce reliable dates its application may be limited where the relative significance of authigenic and allogenic input and bottom water anoxia has been variable and where closed system behaviour is compromised

224ra in continental shelf waters abstract measurements of 224 ra off the coasts of south carolina and georgia reveal that significant activities occur up to 70 km offshore although some of this activity may be transported from estuarine salt marsh and nearshore source regions high near bottom activities in stratified waters suggest that additional 224 ra is being supplied by the decay of 228 th in mid shelf sediments this 228 th is probably derived from the decay of 228 ra in the water column 224 ra is potentially a powerfull tracer of water mixing on the shelf however a good understanding of its input functions is required before this potential may be realized

radium isotopes and their environmental implications in the changjiang river system abstract radium ra isotopes are widely used to trace water motion and nutrient transport in coastal oceans to enhance our understanding of ra behavior from river to ocean this study examines 226 ra and 228 ra activity concentrations in the water column suspended particulate matter and river bed surface sediments along the middle and lower changjiang river cjr basin based on two cruises in 2006 and 2008 the results show that the ra activity concentrations in the cjr basin are comparable with other rivers in the world higher ra activity concentrations and lower 228 ra 226 ra activity ratios are detected in the tributaries i e in the dongting and poyang lakes than in the mainstream the comparison of pre three gorges dam tgd data taken in 1984 and post tgd data this work illuminates the effect that a major dam has on radium transport within the river and into the estuary we estimate a riverine 226 ra flux of 1 04 0 08 tbq yr 1 extended ra datasets collected in the estuary and the east china sea show that the dissolved and sedimentary ra activity concentrations are higher in the estuary but lower in the sea whereas the particulate ra activity concentrations are larger in the river this finding indicates significant ra desorption from particulate to dissolved phase in the brackish estuary where riverborne materials are filtered and trapped overall these results help to elucidate ra transport from river to ocean and assist further application of ra isotopes in land ocean interaction studies such as submarine groundwater discharge mixing and diffusion processes and determination of water mass and or current structures in the estuarine and coastal zones

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

distribution and flux of 226ra and 228ra in the amazon river estuary measurements of sup 226 ra and sup 228 ra in the amazon river estuary show that desorption from riverborne suspended particulate matter in the estuary increases the riverine flux of both isotopes to the ocean by a factor of approximately 5 over the flux attributable to radium dissolved in the river water alone the total amazon flux supplies approximately 0 20 of the sup 226 ra and approximately 2 6 of the sup 228 ra standing crops in the near surface atlantic 0 200 m diffusive flux from estuarine and shelf sediments and desorption from resuspended sediments in the region of the estuary approximately double the estuarine sup 226 ra concentration and quadruple the estuarine sup 228 ra concentration above that caused by the dissolved and desorbed river components alone

natural radionuclides in waters of the new york bight the half removal time of228th from the surface waters by settling particles tc does not change much with season except in the winter when regenerated228th as well as210pb and210po were transported back to the surface water from the bottom water and or near shore sediments the removal of228th and210pb from the surface waters of new york bight by phytoplankton zooplankton fecal pellet route is not important in the shelf but is important in the slope areas the removal of210po is almost entirely associated with the phytoplankton zooplankton fecal pellet pathway throughout the new york bight

radium and barium in the amazon river system data for sup 226 ra and sup 228 ra in the amazon river system show that the activity of each radium isotope is strongly correlated with barium concentrations two trends are apparent one for rivers which drain shield areas and another for all other rivers these data suggest that there has been extensive fractionation of u th and ba during weathering in the amazon basin the sup 226 ra data fit a flux model for the major ions indicating that sup 226 ra behaves conservatively along the main channel of the amazon river

vp vs relationship and amplitude variation with offset modelling of glauconitic greensand the relationship between vp and vs may be used to predict vs where only vp is known vp vs is also used to identify pore fluids from seismic data and amplitude variation with offset analysis theoretical physical as well as statistical empirical vp vs relationships have been proposed for reservoir characterization when shear wave data are not available in published work the focus is primarily on the vp vs relationship of quartzitic sandstone in order to broaden the picture we present vp vs relationships of greensand composed of quartz and glauconite by using data from the paleocene greensand nini oil field in the north sea a vp vs relationship derived from modelling is compared with empirical vp vs regressions from laboratory data as well as from log data the accuracy of vs prediction is quantified in terms of root mean square error we find that the vp vs relationship derived from modelling works well for greensand shear wave velocity prediction we model the seismic response of glauconitic greensand by using laboratory data from the nini field our studies here reveal that brine saturated glauconitic greensand can have a similar seismic response to that from oil saturated quartzitic sandstone and that oil saturated strongly cemented greensand can have a similar amplitude variation with offset response to that from brine saturated weakly cemented greensand

modelling the effect of salinity on radium desorption from sediments abstract the desorption of the four naturally occurring radium isotopes 223 ra 224 ra 226 ra and 228 ra from estuarine sediments is investigated these isotopes are created within sediments by the radioactive decay of insoluble thorium parents due to competition from other ions for the occupation of adsorption sites on the sediment grains radium desorption is a function of salinity a model is developed to describe radium desorption as it is affected by salinity grain size and sediment concentration it is shown that to model the desorption of radium for a particular sediment requires the estimation of two independent parameters one of these parameters is the concentration of radium available for exchange on the sediment the other depends on major ion and radium exchange coefficients desorption experiments performed on sediments from the bed of the bega river australia are used to validate the model and to evaluate the parameters needed for model application

processes controlling the regional distribution of210pb 226ra and anthropogenic zinc in estuarine sediments the concentration of226ra in bottom sediments in chesapeake bay is lower than in incoming sediments and decreases systematically in the seaward direction reflecting both a seaward increase in sediment grain size and a displacement of ra from sediments as salinity increases the amount of226ra lost from sediments approximately balances that gained by the water in the seaward 150 km of this estuary where atmospheric deposition is the dominant210pbex source the210pbexorg c ratio is virtually constant in surface samples because the production of carbon is apparently regulated so as to be roughly constant per unit area from independent productivity estimates about 10 of the carbon is found to survive remineralization in the estuary long enough to be incorporated into surface sediments zinc is enriched in surface sediments of the northern two thirds of the bay by a factor of 2 3 over shales theznexorg c ratio decreases systematically southward unlike the210pborg c ratio this reflects a regional decline southward in deposition of anthropogenic zn from the atmosphere a negative210pb anomaly is the most distinctive indicator of sediments deposited by a major flood in 1972 and testifies to the importance of such events in estuarine sedimentation

fluxes of 226ra and barium in the pacific ocean the importance of boundary processes abstract the 226 ra ba ratio in particles collected in sediment traps decreases with depth fluxes of ba and al increase with depth these observations cannot be explained by simple vertical processes instead they require a component to the deep flux which originates at the ocean margins we suggest that the deep traps are enriched in ba through the advection of barite originally precipitated in biologically productive regions of the ocean margin this source is less important for 226 ra because some is lost by radioactive decay between the precipitation of barite on the margin and outward transport the boundary flux is an important source of material to the deep sea from 226 ra fluxes in the upper 1000 m of the water column we estimate that the residence time of 226 ra in the upper ocean is 400 years the removal of 226 ra in the particle flux is approximately balanced by the upwelling of waters enriched in 226 ra

rapid mineral surface weathering beneath the greenland ice sheet shown by radium and uranium isotopes abstract glaciated watersheds are regions of intense physical and chemical weathering in order to gain new insight on subglacial weathering processes we measured uranium and radium isotopes from a proglacial river draining the greenland ice sheet gris time series samples were collected from the spring to mid summer a time period during which subglacial drainage pathways are thought to transition from slow inefficient distributed to fast efficient channelized systems the 228ra 226ra activity ratio of the dissolved load varied from 5 2 0 9 16 9 3 6 which was significantly higher than the 228ra 226ra ratio of a suspended sediment load sample of 2 1 0 07 and crustal values of 1 the high 228ra 226ra in the dissolved load relative to the source rock material is indicative of mineral surface weathering induced by rapid and continuous flushing of the subglacial drainage network during the course of the melt season and those prior the 234u 238u ratio 234u varied between 33 and 106 with a discharge weighted mean of 67 the seasonal evolution of 234u did not correlate to geochemical indicators of subglacial meltwater storage time an experiment designed to measure changes in 234u with increasing meltwater storage times found that 234u in the dissolved phase decreased rapidly with increasing storage time similarly samples collected along a transect moving downstream from the ice sheet terminus had decreasing 234u values from 63 to 15 further indicating that with increased weathering the 234u of meltwater decreases coupled with the relatively low 234u and high 228ra 226ra u appears to be impacted by rapid chemical weathering of subglacial and suspended sediments the leverett river discharge weighted u concentration was 0 13 nm if this system is considered representative of the broader gris then the total dissolved u flux from the gris would be on the order of 6 4 104 mol y using a similar set of assumptions the dissolved 228ra and 226ra flux from the gris was 1 1 1014 dpm y and 5 5 1013 dpm y respectively these estimates suggest that the 226ra flux to the ocean from the gris is globally significant and that the 228ra flux in particular is larger than most river inputs

depth dependent earthquake focal mechanism orientation evidence for a weak zone in the lower crust the traction free boundary condition across the earth s surface provides an opportunity for studying the relationship between stress orientation and earthquake focal mechanisms because it requires alignment of principal stress axes with vertical and horizontal orientations a survey of earthquake focal mechanisms in northern california shows that their principal axes are also closely aligned with the vertical and the horizontal in the upper few kilometers of earth s crust thus the signature of the free surface boundary condition on stress appears in focal mechanism orientations as well the focal mechanism alignment can also be characterized by the relative magnitude of the off diagonal elements mxz and myz of the seismic moment tensor we find significant and systematic depth variations in the horizontal moment tensor element ms which relates to the shear traction acting on a horizontal plane for the special case of perfect alignment between principal stress and focal mechanism axes values of ms near earth s surface are small but increase with depth to a maximum between 5 and 8 km at greater depths there is a gradual decrease which suggests decreasing horizontal shear traction toward the base of the seismogenic zone we interpret this tendency of axes to become oriented near the base of the seismogenic zone and its expression in ms as the signature of a weak zone in the lower crust if correct this observation would have important implications for the mechanics of lithospheric deformation

tracing the amazon component of surface atlantic water using 228ra salinity and silica high 228ra 226ra activity ratios characteristic of waters in the amazon estuary provide a sensitive indicator of the presence of these waters in the atlantic ocean a conservative mixing model utilizing the 228ra 226ra activity ratio ar tied to absolute measurements in the estuary allows us to estimate that 20 34 of the surface water east of the antilles during june 5 9 from the same area during december and 15 20 of the eastern caribbean surface water during december are derived from the amazon estuary differences in 228ra input occur in response to variable stratification of water near the river mouth during high discharge intense vertical mixing enriches the water in the estuary in 22sra a large fraction of this water moves to the north and east of the antilles where its relatively high 22sra 226ra ar distinguishes it over 1500 km from its source during low discharge northern hemisphere fall a significant fraction of river water passes northwest of the zone of intense mixing into a vertically stratified region where 228ra gain is lower this water is transported by the guiana current along the coast of south america and into the caribbean

distinguishing seawater from geologic brine in saline coastal groundwater using radium 226 an example from the sabkha of the uae article sabkhat salt flats are common geographic featuresof low lyingmarinecoastalareas thatdevelopunder hyper aridclimaticconditions theyare characterizedby thepresenceof highlyconcentratedsalinesolutions and evap oritic minerals and have been cited in the geologic literature as present day representations of hyper arid regional paleohydrogeology paleoclimatology coastal processes and sedimentation in the geologic record it is therefore important that a correct understanding of the origin and development of these features be achieved knowledge of the source of solutes is an important first step in understanding these features historically two theories have been advanced as to the main source of solutes in sabkha brines an early concept entailing seawa ter as the obvious source and a more recent and dynamic theory involving ascending geologic brine forced upward into the base of the sabkha by a regional hydraulic gradient in the underlying formations ra 226 coulduniquely distinguish betweenthese sourcesunder certain circumstances asitistypically present atelevat ed activity of hundreds to thousands of bq m 3 becquerels per cubic meter in subsurface formation brines at exceedingly low activities in open ocean and coastal water and not significantly supplied to water from recently formed marine sedimentary framework material the coastal marine sabkha of the emirate of abu dhabi was used to test this hypothesis the distribution of ra 226 in 70 samples of sabkha brine mean 700 bq m 3 7 sam ples of underlying deeper formation brine mean 3416 bq m 3

ground water geochemistry of 228ra 226ra and 222rn abstract 228ra 226ra and 222rn activities were determined on over 150 ground water samples collected from drilled public water supply wells throughout south carolina a wide range of aquifer lithologies were sampled including the crystalline rocks of the piedmont and sedimentary deposits of the coastal plain a significant linear relationship between log 228ra and log 226ra n 182 r 0 83 was indistinguishable between piedmont and coastal plain ground water median 228 ra 226 ra activity ratios for the piedmont 1 2 and coastal plain 1 3 ground water are close to estimated average crustal 232 th 238 u activity ratios of 1 2 to 1 5 corresponding to th u weight ratios of 3 5 to 4 5 a linear correlation was also found between log 222rn and log 226ra for piedmont n 68 r 0 62 and coastal plain n 89 r 0 64 ground water however the median 222 rn 226 ra activity ratio for piedmont ground water 6100 was much higher than for coastal plain ground water 230 higher excess 222rn activities may be due to greater retention of 226ra by the chemically active piedmont aquifers compared to the more inert sand aquifers sampled in the coastal plain the relationship between log 228ra and log 226ra was used to predict total ra 228 ra 226 ra distributions in appalachian and atlantic and gulf coastal plain ground water predictions estimate that 2 4 of appalachian and 5 3 of atlantic and gulf coastal plain ground water supplies contain total ra activities in excess of the 5 pci l limit established by the u s environmental protection agency these predictions also indicate that 40 50 of these ground water wells may be overlooked using the presently suggested screening activity of 3 0 pci l of 226ra for 228ra analysis

quantitative seismic pre stack analysis of potential gas hydrate resources in the makran accretionary prism offshore iran abstract gas hydrates are classified as a major unconventional resource and assumed to be a future potential energy source high pressures low temperature stability conditions of the hydrates restrict their occurrence to the permafrost and deep sea regions from the continental slop to the abyssal in these regions where the well information is most often absent or sparse the amplitude variation with angle ava is a common method of hydrate free gas assessment in this method various linear reflection coefficient equations are fitted to a series of data points to compute some pre stack attributes these attributes have the advantage of being an interface property rather than a layer property which makes them an easy to use characterization tool in lack of well data in recent years rock physics templates nomograms have been presented to estimate the hydrate free gas saturations solely based on these interface properties ava inversion approach was applied to the seismic data in the makran accretionary prism offshore iran to estimate the bottom simulating reflector bsr vicinity hydrate and gas saturations this inversion process included four pre stack attributes of the intercept gradient normal incidence ni and poisson reflectivity pr and was limited to the bsr estimated bsr vicinity saturations were ranged from 7 8 5 for hydrate and 5 6 5 for free gas at three representative locations accuracy of each attribute was analyzed by a synthetic modeling in this modeling the effective medium theory emt was considered to calculate the physical properties of hydrate and gas bearing sediments lithological properties and the acquisition geometry were set to the corresponding values of the field data results of the synthetic ava inversion showed that if the hydrate saturation does not exceed 30 the error of the estimation for pre stack attributes would be in acceptable range the expected estimation errors for actual attributes were derived from this synthetic modeling

radium 228 in the south atlantic bight radium 228 in surface ocean waters is derived from sedimentary fluxes generated in estuaries salt marshes and fine grained sediments of the inner shelf thus the sup 228 ra activity of shelf waters is a measure of their interaction with these sediments mixing of the sup 228 ra signal offshore follows known circulation patterns and examination of the sup 228 ra field as determined by the sup 228 ra sup 226 ra activity ratio ar reveals details of these patterns during february sinking of chilled shelf waters carries high ar water to depths of 80 130 m just below the shelf break in april upwelling from 500 700 m depth brings low ar water to the shelf break where it replaces the high ar waters present 2 months earlier during august low ar waters at the shelf break could be traced to the surface where they separated higher ar waters both inshore and offshore of the shelf break because of such short term variability one dimensional steady state models which balance sup 228 ra decay with mixing do not provide a true measure of horizontal mixing rates fluxes necessary to support the sup 228 ra standing crop in the south atlantic bight are of the order of 2 5 x 10 sup 14 dpm yr thesemore are similar to estimates from the new york bight but 25 times lower than the apparent flux from the amazon system copyrightamerican geophysical union 1987 less

behavior of 226ra in the mississippi river mixing zone the behavior of 226ra in the mississippi river mixing zone is strongly nonconservative and includes desorption similar to that reported for the hudson pee dee and amazon rivers however dissolved and desorbed 226ra concentrations in the mississippi are 2 to 5 times greater than in the other rivers at the same salinity radium concentrations vary inversely with the water discharge rate the 226ra desorption maximum occurs at a salinity of 5 0 much lower than the 18 to 28 salinity values for the maxima of the other three rivers high concentrations of dissolved 226ra up to 82 dpm per 100 l and the low salinity values for the desorption maximum in the mississippi river result from three major factors suspended sediments include a large fraction of montmorillonite which gives the sediment a high cation exchange capacity 0 54 meq g the average suspended sediment load is large about 510 mg l and contains 1 9 dpm g desorbable 226ra the dissolved 226ra river water end member 9 6 dpm per 100 l is higher than in surface seawater the annual contribution of 226ra to the ocean from the mississippi river is 3 7 1014 dpm yr based on data from three cruises evidence of flux of 226ra from estuarine and shelf sediments is common in vertical profile sampling of the deltaic waters but is not reflected in calculations made with an apparent river water ra value extrapolated to zero salinity

determining groundwater ra end member values for the estimation of the magnitude of submarine groundwater discharge using ra isotope tracers radium isotopes 228ra and 226ra are excellent tracers of submarine groundwater discharge sgd to estimate sgd magnitudes information on the end member values of ra concentrations in groundwater is critical however the distribution characteristics of ra in coastal aquifers are poorly understood in this study we show that ra concentrations in coastal groundwater are primarily dependent on salinity based on the data n 500 obtained from global coastal aquifers although previous end member calculations averaged all ra concentrations without considering salinity if we assume that sgd is composed mainly of seawater infiltrating the aquifer previous estimates of sgd for the atlantic ocean and the global ocean were overestimated twofold to threefold this may be similar for other applications using different ra isotopes our study highlights that the end members of ra isotopes in groundwater should be carefully considered when estimating sgd using ra isotope mass balances in the ocean

the effect of interpolation on imaging and avo a viking case study the use of prestack interpolation prior to prestack migration to improve avo analysis on image gathers is demonstrated on an exploration play the interpolation achieves this improvement by reducing migration artifacts avo analysis attempts to estimate fundamental information from surface seismic data and likely will be used more frequently if the estimates can be more accurately produced land 3d seismic typically has poor and irregular sampling this poor sampling creates migration noise which is a material cause of inaccurate avo estimates prestack 5d interpolation is applied prior to prestack migration and avo analysis on the imaged gathers to address this noise problem the interpolation algorithm includes offset and azimuth dimensions that preserve avo information this method is evaluated bycomparing the results to those of alternate approaches such as superbinning that suppress this kind of noise in avo analysis the evaluation is determined by comparing our ability to predict the reservoir q

radium isotopes in the lower mississippi river radium isotopes have been measured in mississippi river water at several locations between st francisville and venice louisiana measured activities averaged 11 1 dpm 100 l disintegrations per minute per 100 l for dissolved 226ra with a 228ra 226ra activity ratio of 1 04 and a 224ra 228ra activity ratio of 1 06 for the section of river above a phosphogypsum waste discharge input down river from this site the dissolved 226ra activity averaged 22 4 dpm 100 l with a 228ra 226ra activity ratio of 0 55 and a 224ra 228ra activity ratio of 0 87 chemical and isotopic reequilibration of the radium in the waste with that in the river water and suspended sediments occurs very rapidly fluxes of 226ra are calculated to be 2 44 1014 dpm yr disintegrations per minute per year for the main stem of the mississippi during phosphogypsum disposal compared to 0 98 1014 dpm yr when no phosphogypsum disposal is occurring 28ra flux is calculated to be 1 06 1014 dpm yr during disposal and 1 01 1014 dpm yr in the absence of disposal the radium flux is estimated to be 45 in the dissolved state and 55 in the adsorbed state

cenozoic deformation history of the area around yangnam yangbuk se korea and its tectonic significance abstract detailed mapping and structural analysis were carried out to establish the cenozoic deformation history of the yangnam yangbuk area se korea all structural elements were analyzed to establish the chronological sequence based on the classification of the fracture systems and the ages of the rocks two detailed grid maps represent the deformation history based on the cross cutting relationship between deformation fabrics we established the cenozoic deformation history in the studied area by synthesizing the analysis of structural elements in rocks of different ages and observing cross cutting relationships on grid maps results using these two approaches with two independent data sets are consistent the deformation history is comparable to that proposed from previous studies restoration of the structural elements suggests tilting and rotation in this area there is clear evidence of tectonic inversion which was observed in a previous trench study of the eupchon fault this implies that normal faults related to the right lateral yangsan fault associated with opening of the east sea japan sea may have been reactivated as thrust faults in the quaternary period

comparison of the aftershock distribution and the fault plane size of the m 4 9 kameoka earthquake on may 28 1987 japan abstract it has been pointed out in several investigations that an aftershock gap exists in the neighborhood of the main shock where the main shock slip is large for large earthquakes since the source process of small earthquakes is thought to be less complex than that of large earthquakes it is expected that by comparing the size of the fault plane and the pattern of aftershock distribution for small earthquakes the physical meaning for large earthquakes may be clarified the 28 may 1987 kameoka earthquake with m 4 9 occurred in the midst of a telemetered seismic network and the data therefore were recorded with high accuracy the aftershocks were relocated by means of the master event technique with the aftershock gap found in the neighborhood of the hypocenter of the main shock p wave forms radiated by the kameoka earthquake were observed with low gain velocity seismographs having a natural period of 10 s without saturation the fault plane size was estimated by comparing observed seismograms having small hypocentral distances with synthetic seismograms obtained by forward modeling it was shown that the gap of aftershocks was comparable to the fault plane size of the small earthquake such as the m 4 9 kameoka earthquake

mean residence time of the shelf water in the east china and the yellow seas determined by 228ra 226ra measurements increasing attention of oceanographers has recently been paied on east asian marginal seas regarding their role on the global environment yet geochemical investigations have been few to date we here report new data on the distribution of 228ra and 226ra in the surface water of the east china and the yellow seas in an effort to constrain the time necessary for the coastal and shelf waters to exchange with offshore waters such information is needed in evaluating the exchange of heat and water across the air sea interface that affects the local climate and the fate of pollutants nutrients and weathering products supplied from the continent based on the ra isotope signals we have estimated that the shelf water component contributes 20 of the tsushima current water passing through the tsushima strait and the mean residence time for the shelf water to mix with the kuroshio surface water is 2 3 years as many of materials derived from the continent such as heavy metals and the nutrients have their mean residence times less than a few months in the nearshore and shelf waters they must largely deposit on the shelf sediments prior to the transport from the shelf to the open sea by mixing

geothermal springs of the west florida continental shelf evidence for dolomitization and radionuclide enrichment abstract on the sea bed of the west florida continental shelf about 45 km ssw of ft myers florida an 85 km 2 area has been discovered in which six thermal springs discharge warm chemically altered seawater from vents and seepage zones the spring water apparently originates in the subsurface ocean around the florida platform and penetrates the highly porous strata of the platform about 500 1000 meters below sea level it percolates toward the interior of the platform and is geothermally heated to about 40 c en route then it rises along more vertical flow channels and is discharged in warm submarine springs beneath the platform several chemical processes alter the percolating seawater one process seems to be a secondary dolomitization of the limestone of the platform because in the discharging seawater magnesium is lower by 2 7 mmole kg and calcium higher by 3 6 mmole kg than in normal seawater with the same chlorinity other reactions within the sediments of the platform enrich the spring effluents 1000 fold in 226 ra 10 000 fold in 222 rn and 90 fold in 228 ra compared to the seawater surrounding the platform thus the springs may be important sources of radionuclides for the gulf of mexico the percolating seawater also loses all of its oxygen and nitrate to reduction processes loses most of its phosphate and 40 of its 238 u and roughly quadruples its silica content coastal carbonate platforms are fairly common geological features thus processes like those beneath the west florida shelf may function on a world wide basis to play an important role in the diagenesis of carbonate sediments

evidence for rapid fault healing derived from temporal changes in s wave splitting 1 tadokoro et al 1999 had made an s wave splitting analysis on the nojima fault zone that ruptured during the 1995 hyogo ken nanbu earthquake for a period 9 12 months after the mainshock the direction of faster shear wave polarization had been parallel to the fault strike suggesting fractures of shear fault origin in this study we made an additional s wave splitting analysis for a period 33 45 months after the mainshock and detected the rotation of that is the direction was parallel to the regional maximum horizontal compressional stress which is oblique to the fault strike this temporal change suggests that all the fractures of shear fault origin had completely healed and cracks of tectonic stress origin recovered between the two periods this is strong evidence for rapid fault healing which completed within 33 months after the mainshock