teleseismic observations of aftershocks immediately following an underground explosion summary underground explosions often trigger a series of earthquakes aftershocks at least one magnitude unit less than the magnitude of the explosion in the first one or two hours following an explosion the rate of occurrence of the aftershocks can be so high that the signals from separate shocks overlap few if any of the p waves from these aftershocks have been observed at teleseismic distances here however evidence is presented that the aftershock sequence triggered by at least one explosion the nevada test site explosion greeley commenced a second or two after the firing of the explosion and that the radiation from some of the first of these aftershocks was detected at teleseismic distances the radiation being present in the coda of the p signal from the explosion the evidence for the presence of the aftershocks is that for the greeley explosion the coda of the p signal contains a much higher proportion of high frequency energy than the initial p pulse and yet the absence of high frequency energy in the p pulse seems to be a source effect and not the result of losses on the transmission path so as the explosion source radiated little high frequency energy it is proposed that the highfrequency energy in the coda is from aftershocks which have p wave spectra with corners well above the corner frequency of that of the explosion the body wavemagnitude of the largest of the aftershocks is estimated to be about one unit less than that of the explosion the low magnitude of the aftershocks does not however appear to rule out the possibility that the radiation from the aftershocks can account for all the radiation from the explosion source that is usually attributed to a double couple type of source occurring simultaneously with or immediately following the explosion

the equilibrium alluvial river under variable flow and its channel forming discharge when the water discharge sediment supply and base level vary around stable values an alluvial river evolves toward a mean equilibrium or graded state with small fluctuations around this mean state i e a dynamic or statistical equilibrium state here we present analytical relations describing the mean equilibrium geometry of an alluvial river under variable flow by linking channel slope width and bed surface texture the solution holds in river normal flow zones or outside both the hydrograph boundary layer and the backwater zone and accounts for grain size selective transport and particle abrasion we consider the variable flow rate as a series of continuously changing yet steady water discharges here termed an alternating steady discharge the analysis also provides a solution to the channel forming water discharge which is here defined as the steady water discharge that given the mean sediment supply provides the same equilibrium channel slope as the natural long term hydrograph the channel forming water discharge for the gravel load is larger than the one associated with the sand load the analysis illustrates how the load is distributed over the range of water discharge in the river normal flow zone which we term the normal flow load distribution the fact that the distribution of the imposed sediment supply spatially adapts to this normal flow load distribution is the origin of the hydrograph boundary layer the results quantify the findings by wolman and miller 1960 regarding the relevance of both magnitude and frequency of the flow rate with respect to channel geometry

a model for garnet and plagioclase growth in pelitic schists implications for thermobarometry and p t path determinations numerical models of the progressive evolution of pelitic schists in the ncmnkfmash system with the assemblage garnet biotite chlorite staurolite plagioclase muscovite quartz h2o are presented with the goal of predicting compositional changes in garnet and plagioclase along different p t paths the numerical models support several conclusions that should prove useful for interpreting the p t paths of natural parageneses i garnet may grow along p t vectors ranging from heating with decompression to cooling with compression p t paths deduced from garnet zoning that are inconsistent with these growth vectors are self contradictory ii there is a systematic relation between garnet and plagioclase composition and growth such that for most p t paths garnet growth requires plagioclase consumption furthermore mass balance in a closed system requires that as plagioclase is consumed the remaining plagioclase becomes increasingly albitic inclusions of plagioclase in the core of garnet should be more anorthitic than those near the rim and zoned matrix plagioclase should have rims that are more albitic than the cores complex plagioclase textures may arise from the local variability of growth and precipitation kinetics iii a decrease of fe fe mg in a garnet zoning profile is a reliable indicator of increasing temperature for the assemblage modelled however there is no single reliable p monitor and inferences about p can only be made by considering plagioclase and garnet together iv consumption of garnet during the production of staurolite removes material from the outer shell of a garnet and may make recovery of peak metamorphic compositions and p t conditions impossible low peak temperatures typically recorded by staurolite bearing assemblages may reflect this phenomenon v diffusional homogenization of garnet affects the computed p t path and results in a clockwise rotation of the computed p t vector relative to the true p t path

mathematical modeling of graded river profiles numerical modeling of the longitudinal profiles of rivers at grade is accomplished using the basic equations of open channel flow sediment transport equations and empirical relations for downstream variation in flow discharge sediment discharge sediment caliber and channel width only in some cases are the computed stream profiles fit exactly by any one of the commonly supported mathematical function analogs to graded profile form exponential logarithmic or power function but in most cases any of these functions can provide a fit with a degree of error smaller than would be noted in treating field data profiles dominated by spatial change in fluid and sediment discharge are distinctly power functions while profiles dominated by sediment size reduction are not necessarily exponential in form other important controls on profile shape are the degree of downstream width change in response to increasing discharge and the general range of sediment size a dynamic model of a river s approach to grade

the quasi equilibrium longitudinal profile in backwater reaches of the engineered alluvial river a space marching method an engineered alluvial river i e a fixed width channel has constrained planform but is free to adjust channel slope and bed surface texture these features are subject to controls the hydrograph sediment flux and downstream base level if the controls are sustained or change slowly relative to the timescale of channel response the channel ultimately achieves an equilibrium or quasi equilibrium state for brevity we use the term quasi equilibrium as a shorthand for both states this quasi equilibrium state is characterized by quasi static and dynamic components which define the characteristic timescale at which the dynamics of bed level average out although analytical models of quasi equilibrium channel geometry in quasi normal flow segments exist rapid methods for determining the quasi equilibrium geometry in backwater dominated segments are still lacking we show that irrespective of its dynamics the bed slope of a backwater or quasi normal flow segment can be approximated as quasi static i e the static slope approximation this approximation enables us to derive a rapid numerical space marching solution of the quasi static component for quasi equilibrium channel geometry in both backwater and quasi normal flow segments a space marching method means that the solution is found by stepping through space without the necessity of computing the transient phase an additional numerical time stepping model describes the dynamic component of the quasi equilibrium channel geometry tests of the two models against a backwater exner model confirm their validity our analysis validates previous studies in showing that the flow duration curve determines the quasi static equilibrium profile whereas the flow rate sequence governs the dynamic fluctuations

magnitude bias in the great basin and its implications for explosion magnitude versus yield estimates comparison of teleseismic p wave delays in the vicinity of the central nevada test site in hot creek valley nevada with p delay data over a wider region in the great basin shows that upper mantle speeds under hot creek valley stations are higher than the average for the great basin as a whole but lower than those beneath pahute mesa these observations indicate that the caldera complex in hot creek valley may have a high speed root similar to that proposed to exist beneath the silent canyon caldera at pahute mesa however the hot creek valley anomaly is not as strong as the pahute mesa anomaly these high speed upper mantle structures cause defocusing for outgoing rays resulting in a shadow zone at the distance range corresponding to many european stations the shadow zone caused by the pahute mesa structure is much more pronounced and consequently magnitudes of pahute mesa explosions can be underestimated relative to the magnitude of hot creek valley explosions of similar yield when magnitude versus yield relationships developed using pahute mesa data are applied to other areas such as hot creek valley they can result in a biased estimate of yield

comparative analysis of teleseismic p coda and lg waves from underground nuclear explosions in eurasia this study has investigated the characteristics of p coda and lg waves recorded at the norsar and graefenberg arrays from presumed nuclear explosions in western russia lg waves were found to be more energetic relative to the preceding coda in the mid band frequency range 0 2 to 1 0 hz recorded on the broadband graefenberg instruments than in the high frequency band 0 6 to 3 0 hz at either array comparison of the log rms coda envelopes at the two arrays revealed that the early high frequency p coda at norsar is stronger relative to lg than at graefenberg also the amplitudes of p waves and early p coda waves within 55 sec after p recorded at the centers of the norsar subarrays are positively correlated indicating the effect of focusing defocusing on the p and coda waves however for subarrays which cluster spatially there is an inverse correlation which seems to be due to scattering attenuation suggesting that much of the early p coda is generated by local p wave scattering beneath the norsar array also the norsar coda envelopes flatten between about 219 and 352 sec after p whereas the graefenberg coda decays monitonically from the p wave out to the sn and lg arrival times the standard deviation across the norsar array of the log rms amplitudes of lg and s coda phases are higher by about 0 05 to 0 06 magnitude units than those of p coda phases these differences are probably related to differential site and propagation path effects on p s and lg waves in the p coda the flattening of the norsar coda envelopes appears to be a burst of energy not associated with any known regional phases the burst may be caused by forward scattering of lg to p waves along the path between the source and norsar based on a regional travel time curve for western russia the start and end time of the coda flattening is consistent with lg to p scattering in the distance range of 23 to 29 from norsar which brackets the ural mountains the lg propagation path from the source region to graefenberg does not appear to traverse the ural mountains which may explain why the coda flattening is not observed at graefenberg

mesoproterozoic metamorphism and 40 ar 39 ar thermal history of the 1 4 ga priest pluton manzano mountains new mexico paleoproterozoic supracrustal rocks in the aureole of the 1 43 pm 0 01 ga priest pluton provide evidence for a polyphase proterozoic metamorphic history in central new mexico this history involved pre syn and post emplacement metamorphic mineral growth the 1 2 km wide priest pluton contact aureole is characterized by two isograds first appearance of sillimanite and staurolite respectively garnet biotite temperatures combined with assemblage data sillimanite k feldspar indicate an increase from 525 to 650 c toward the pluton at pressures of 4 kb suggesting emplacement depths of 12 km an 40 ar 39 ar age of 1 44 pm 0 005 ga for hornblende in the aureole suggests rapid cooling through 500 c following pluton emplacement the well defined thermal aureole can be used to help constrain both pre and post emplacement metamorphisms pre pluton metamorphism is recorded by amphibolite facies inclusions inside contact metamorphic porphyroblasts included minerals are interpreted

analysis of near source contributions to early p wave coda for underground explosions iii inversion for isotropic scatterers a systematic array processing analysis is applied to 916 teleseismic shortperiod p wave signals from 25 underground explosions at pahute mesa in order to establish whether coherent arrivals scattered from near source velocity heterogeneity can be identified the signal coherence is measured using semblance which can be statistically evaluated using the noncentral f distribution if the noise properties are suitable the effects of unsuitable correlated noise due to common path and receiver contributions are suppressed by applying station weighting functions obtained by stacking all observations at a given receiver similar corrections for individual events are applied to reduce biases due to variations in surface reflection times and spall effects the characteristics of the spatial and phase velocity resolution of the semblance analysis are established by a series of synthetic calculations including cases with random arrivals in the p wave coda the procedure is applied to the actual data under the assumption that any scattering structures present radiate isotropically although this constraint could be relaxed given independent knowledge of a particular scatterer s nature the pahute mesa data show some evidence for enhanced scattering contributions to the first 15 sec of the p wave signals from the western edge of the silent canyon caldera the overall confidence level in this interpretation is fairly low because simulations with random scattering in the p coda successfully match many features observed in the stacked data

observations of teleseismic p wave coda for underground explosions the earlyp wave coda 5 15 sec after the first arrival of underground explosions at the nevada test site is studied in the time domain using 2082 teleseismic short period recordings with the intent of identifying near source contributions to the signals in the frequency range 0 2 2 0 hz smaller magnitude events tend to have relatively high coda levels in the 0 4 0 8 hz frequency band for both yucca flat and pahute mesa explosions coda complexity in this low frequency passband is negatively correlated with burial depth for pahute mesa events but is only weakly correlated with depth for yucca flat events enhanced excitation of relatively long period scattered waves for smaller less deeply buried events is required to explain this behavior coda complexity in the 0 8 1 1 hz band is positively correlated with magnitude and depth for pahute mesa events but has no such dependence for yucca flat events this may result from systematic variations between the spectra of direct signals and coda arrivals caused bypp interference for the largest events all of which were detonated at pahute mesa another possible explanation is a frequency dependent propagation effect on the direct signals of the larger events most of which were located in the center of the mesa overlying strong lateral velocity gradients in the crust and upper mantle event average complexity varies spatially for both test sites particularly in the 0 8 1 1 hz band providing evidence for frequency dependent focussing or scattering by near source structure both the direct arrivals and the early coda have strong azimuthal amplitude patterns that are produced by defocussing by mantle heterogeneity the direct arrivals have stronger coherent azimuthal patterns than the early coda for pahute mesa events indicating more pronounced deep crustal and shallow mantle defocussing for the direct signals however for yucca flat events the direct arrivals have less coherent azimuthal patterns than the coda suggesting that a highly variable component of near source scattering preferentially affecting the downgoing energy is superimposed on a pattern produced by mantle heterogeneity that affects the entire signal this complicated behavior of the direct arrivals may be the result of triplications and caustics produced by the complex basement structure known to underlie the yucca flat test site the presence of strong azimuthal patterns in the early coda indicates that source strength estimates based on early coda are subject to biases similar to those affecting estimates based on direct arrivals

bankfull discharge recurrence interval in gravel bed rivers bankfull discharge was identified in some 30 gravel bed rivers representing in total c 40 gauging stations the catchment sizes vary from 4 km 2 to nearly 2700 km 2 bankfull discharge value increases with basin size in the case of gravel bed rivers developed on an impermeable substratum the following equation emerges q b 0 087 a 1 044 bankfull discharge recurrence interval was determined by fitting maximum annual floods t a into gumbel s distribution and then using the partial duration series t p in this same distribution recurrence interval is below 0 7 years t p for small pebble bed rivers developed on an impermeable substratum it reaches 1 1 to 1 5 years when the catchment size of these rivers exceeds 250 km 2 rivers incised in the soft schists of the famenne show larger channel capacity at bankfull stage a small width depth ratio and thus higher recurrence intervals 1 4 5 3 years with t a and 1 4 4 years with t p baseflow dominated gravel bed streams and sandy or silty rivers experience less frequent bankfull discharges with a recurrence interval higher than 2 or even 3 years t p 1997 by john wiley sons ltd

tectonic setting of the sandia pluton an orogenic 1 4 ga granite in new mexico structural studies of the circa 1 42 ga sandia pluton and its aureole document significant deformation synchronous with pluton emplacement and call into question the anorogenic label associated with this and other 1 4 ga granites in the southwestern united states the se margin of the pluton is a 1 to 2 km wide nw dipping ductile shear zone field and microstructural observations melt filled shear bands high temperature dynamic recrystallization of k feldspar megacrysts and crosscutting pegmatite dikes indicate that top to the nw normal movement in the shear zone took place in the presence of melt subparallel magmatic fabrics north of and structurally above the shear zone contain kinematic indicators consistent with top to the nw shear sense suggesting that over large regions of the pluton magmatic flow mimicked solid state strain in the northern aureole contact metamorphic aluminosilicate porphyroblasts grew during the formation of a ne striking crenulation cleavage s3 and related folds of late stage pegmatite dikes these features document the synchroneity of magma emplacement shortening and metamorphism and indicate that the sandia pluton is syntectonic not anorogenic we interpret the kinematic consistency of structural elements from the base of the pluton the interior of the pluton and the northern aureole to reflect a regional larger than the pluton strain field and suggest that the orogeny recorded in and around the sandia pluton involved a three dimensional strain field with subhorizontal extension n s and contraction e w directions n s extension is documented by the orientation of mineral lineations and movement directions in the basal shear zone and in high strain zones in the northern aureole and by the orientations of tabular pegmatite and aplite dikes in the pluton and aureole east to se shortening is documented in the northern aureole by orientations of folded pegmatite dikes and associated s3 crenulation cleavage and east to se shortening or least extension directions in the pluton proper are documented by the intersections of orthogonal dikes thus emplacement of the sandia pluton is interpreted to record a snapshot of regional strains inboard of an active plate margin rather than local strains generated by emplacement

effects of lateral velocity heterogeneity under the nevada test site on short period p wave amplitudes and travel times short period teleseismicp waves from the nevada test site nts show systematic variations in amplitudes and travel times with low amplitudes corresponding to fast travel times suggesting elastic focussing defocussing effects also the azimuthal amplitude and travel time patterns for events at the pahute mesa subsite are systematically different from those at the yucca flat subsite indicating the presence of a near source component in both the amplitude and travel time variations this component is isolated by removing the mean station pattern for all of nts from the observations a very near source component in the pahute mesa observations is also isolated by removing subsite station means from the measurements whereas the yucca flat observations exhibited no coherent very near source component these anomalies are back projected through laterally homogeneous structure to form thin lens models at various depths travel time delays are predicted from the amplitude variations using the equation for wavefront curvature the long wavelength components of the predicted and observed time delays correlate well at depths of 25 km for the very near source component under pahute mesa and 160 km for the regional component under nts the time delay surfaces predicted by the amplitudes at these depths are mapped into warped velocity discontinuities suitable for the calculation of synthetic seismograms using the kirchhoff helmholtz integral formulation both the intersite near source and intrasite very near source differences in amplitudes are qualitatively predicted very well although the range of variation is somewhat underpredicted this deficiency is likely due to the destructive interference of anomalies inherent in back projection to a single layer

proterozoic tectonic assembly of new mexico proterozoic rocks in northern and central new mexico originated in at least six tectonostratigraphic terranes which can be distinguished by differences in lithology age and or metamorphic grade boundaries between some terranes have the geometry of bedding parallel north verging ductile thrusts these were active during metamorphism but prior to the thermal peak one terrane boundary is a south verging ductile shear zone that has placed medium grade on top of high grade metamorphic rocks it was active at and after the peak of metamorphism and may be extensional in origin we interpret that terrane assembly occurred by ductile deformation in the middle levels of the continental crust we do not know the original geographic relations among terranes but the possibility exists of significant horizontal translation

growth stabilization and reactivation of proterozoic lithosphere in the southwestern united states growth of proterozoic continental lithosphere in the southwestern united states involved assembly of tectonostratigraphic terranes during several pulses of convergent tectonism ca 1 74 1 70 and 1 65 1 60 ga prograde metamorphism accompanied orogenic assembly and peak metamorphic conditions outlasted deformation regions now characterized by the highest metamorphic grades underwent slow isobaric cooling and were not uplifted until more than 200 m y after assembly regions of low metamorphic grade were not uplifted substantially after assembly we suggest that 1 relatively thin lithospheric fragments were assembled into isostatically stable normal thickness continental lithosphere 2 assembly did not erase lithospheric scale heterogeneities 3 the present juxtaposition of different crustal levels reflects differential uplift related to 1 4 1 1 ga tectonomagmatic activity and 4 the boundaries between different lithospheric blocks were repeatedly reactivated from precambrian through tertiary time

scattering and attenuation abstract an extensive existence of strong small scale heterogeneity in the earth is suggested by the great variability of direct waves and remarkable stability of scattered waves both in the case of teleseismic p coda and in the case of local earthquake s coda quantitative studies of small scoale heterogeneities have been made by the following three methods a lower bound of heterogeneity in the lithosphere has been estimated by the deterministic or stochastic modeling of travel time and amplitude fluctuation of teleseismic p waves across a large aperture seismic array an upper bound of heterogeneity has been estimated by modeling the attenuation of s waves as a scattering loss due to heterogeneity these two approaches suggest the existence of heterogeneity with rms velocity fluctuations from 3 to 10 per cent the third method is based on the estimation of heterogeneity from the amplitude of coda waves we found a significant discrepancy between the result obtained by the third method and those from the first two and attribute the discrepancy to the assumption of a single scattering model adopted in the coda generation theory the need for including multiple scattering as well as for considering vector elastic waves rather than scalar waves is emphasized

determining the extent and nature of mazatzal related overprinting of the penokean orogenic belt in the southern lake superior region north central usa abstract twenty one hornblende and mica 40ar 39ar dates from central and northwest wisconsin usa provide important information on the timing spatial extent and intensity of mazatzal age metamorphism and deformation which overprinted the paleoproterozoic 1870 1820 ma penokean orogenic belt in the southern lake superior region 1760 1750 ma mica plateau ages from bedrock beneath undeformed 1750 1630 ma quartzites are interpreted as the time of lower temperature 300 350 c cooling and crustal stabilization after the penokean orogeny six mica ages from bedrock underlying deformed paleoproterozoic quartzites cluster around 1600 ma 1576 1614 ma the complete absence of 1760 1750 ma mica ages beneath regions of deformed quartzites suggests widespread heating to temperatures above 300 350 c during mazatzal related deformation and metamorphism the 1600 ma mica ages are interpreted to date the cooling phase of this metamorphism two anomalously young biotite dates are interpreted to indicate partial resetting associated with mesoproterozoic rifting at 1100 ma ten hornblende 40ar 39ar dates obtained in this study address the higher temperature overprinting effects in the southern lake superior region one latest archean age of 2503 18 ma and two ages of 1853 and 1830 ma are interpreted as remnant evidence of archean and penokean age amphibolite metamorphic events respectively the majority of hornblende ages are younger than the penokean orogeny scattering between 1796 and 1638 ma microtextural analysis indicates that similar microstructures exist in samples yielding highly discordant hornblende ages this suggests that shearing and recrystallization did not play an important role in the retention or loss of argon the 1638 ma hornblende age is concordant with the mazatzal orogeny to the south and is interpreted as representing complete thermal or fluid related resetting associated with that event six other post penokean ages scatter over a 70 million year interval 1796 1723 ma and probably reflect variable retention of radiogenic argon they are interpreted to indicate variable degrees of partial intermediate temperature 350 500 c resetting of hornblende argon systematics at 1650 1630 ma collectively these data suggest that the effects of the mazatzal orogeny in the southern lake superior region involved 350 500 c metamorphism and penetrative deformation

a study of p waves from nevada test site explosions near source information from teleseismic observations spectral analyses of short period p arrivals on teleseismic recordings of nuclear explosions at yucca flats and pahute mesa regions of the nevada test site seem to provide explosion source medium information the spectral ratio p p coda on short period vertical component records at norsar shows significant correlation with explosion medium velocity for a given yield spectrum of the initial p waves from an explosion within a high velocity medium is richer in high frequencies as compared to that for p waves from an explosion within a low velocity medium the spectra of p codas on the other hand are considerably less sensitive to the near source velocity differences from one shot to another so that the spectral ratio p p coda is diagnostic of the shot medium velocity relative insensitivity of the p coda spectra and amplitudes to the overburden velocity is perhaps due to several factors including an effective source function controlled by average properties of rock within a fairly large nonlinear region around the shot point the study provides valuable insight into effects of the shot medium on the spectra and amplitudes of compressional arrivals and offers the exciting possibility of extracting near source information from teleseismic observations

k ar and 40ar 39ar whole rock ages of slate phyllite from allochthonous basement and cover in the tectonic windows of finnmark norway evaluating the extent and timing of caledonian tectonothermal activity slate phyllite samples collected within allochthonous basement rocks raipas super group exposed in the komagfjord and alfa kvaenangen tectonic windows in finnmark northern norway display variably discordant 40 ar 39 ar age spectra in which apparent ages systematically increase from ca 400 425 ma recorded at low experimental temperatures to dates as old as ca 1750 1800 ma in some high temperature increments the apparent age variations are not matched by fluctuations in apparent k ca ratios and are therefore interpreted to reflect intracrystalline gradients in the concentration of 40 ar within constituent fine grained white mica the gradients are suggested to have developed as a result of a variable caledonian thermal rejuvenation of white mica argon systems which had initially cooled through argon retention temperatures at ca 1700 1800 ma following the sveco karelian orogeny the extent of whole rock spectra discordancy is related to the proximity of the basal thrust of the structurally overlying kalak nappe complex whole rock sample suites were also collected structurally downward 0 6 20 m from the kalak thrust within penetratively cleaved allochthonous cover sequences lomvatn formation exposed along the northern edge of the komagfjord window these display discordant 40 ar 39 ar age spectra with most intermediate temperature gas fractions recording mutually similar apparent 40 ar 39 ar ages of 410 430 m y observed variations in k ar and 40 ar 39 ar ages suggest that a late caledonian tectonothermal event ca 420 425 ma variably affected the allochthonous basement and cover units exposed in the two finnmark windows this thermal overprint is interpreted to have developed during emplacement of the structurally overlying kalak nappe complex while it was maintained at post scandian metamorphic temperatures in excess of at least 350 c although the effects of a late cambrian early ordovician orogenic event have been described from portions of the kalak nappe complex no clear record of correlative tectonothermal activity has been documented within structurally underlying tectonic units it is therefore likely that most of the paleozoic metamorphism and deformation observed along the eastern margin of the caledonide orogen in northern scandinavia developed during eastward transport of previously assembled composite scandian nappes into their present structural position on the baltoscandian platform between ca 400 and 425 ma

the graded alluvial river profile concavity and downstream fining there has been quite some debate on the relative importance of particle abrasion and grain size selective transport regarding the river profile form and the associated grain size trends in a graded alluvial stream here we present new theoretical equations for the graded alluvial river profile that account for the effects of particle abrasion and grain size selective transport in the absence of subsidence uplift and sea level change under graded conditions we find that abrasion results in a mild profile concavity and downstream fining whereas under aggradational conditions grain size selective transport can lead to large spatial changes in channel slope and bed surface mean grain size

polyphase late paleozoic tectonothermal evolution of the southwestern meguma terrane nova scotia evidence from 40ar 39ar mineral ages 40ar 39ar incremental release ages of hornblende muscovite and biotite from a variety of granitic stocks and host metamorphic rocks suggest a complex late paleozoic tectonothermal evolution for the southwestern meguma terrane regional d1 folding with cleavage formation under greenschist lower amphibolite facies m1 metamorphic conditions occurred at ca 400 410 ma and was followed by emplacement of a series of granitic stocks ranging in age between ca 375 and 315 ma these were emplaced at relatively shallow crustal levels and developed contact metamorphic aureoles of variable grade these are locally superposed on m1 regional metamorphic assemblages and result in a complex isograd pattern 40ar 39ar mineral ages suggest episodes of contact metamorphism occurred at 1 360 375 ma possibly related to emplacement of the south mountain batholith or temporal equivalents 2 350 356 ma around the port mouton pluton and northeastern shelburne pluton 3 ca 315 325 ma near the wedgeport pluton and in

inversion of p coda for isotropic scatterers at the yucca flat test site although many studies have addressed the statistical properties of p coda there have been few attempts to analyze coda in a deterministic framework in this analysis 1050 teleseismic p wave seismograms from 32 yucca flat explosions are inverted for the locations of any isotropic point scatterers in the source region that contribute coherent arrivals to the coda a rectangular grid of potential scattering locations is constructed around the source array and the semiblance a measure of waveform ensemble coherence for each point is computed by slant stacking the full set of seismograms at various move out velocities the potential resolution or sensitivity of the method for this data set is tested by constructing a corresponding suite of synthetic seismograms with direct arrivals plus arrivals from various point scatters and calculating the semiblance at each point on the grid the particular source station geometry produces better sensitivity near the array sensitivity is enhanced parallel to the trend of the elongated source array and diminished in the orthogonal direction stacking the data for a velocity of 2 5 km sec yields relatively high semiblance values in the central portion of the test site as well as about 10 km to the ene and moderately high semiblance valuesmore about 10 km to the wnw less

estimating explosion yield by analytical waveform comparison summary the yields of 28 underground nuclear explosions at nts 25 on pahute mesa are estimated by applying a relative waveform analysis called intercorrelation to 1256 teleseismic short period p waves recorded at 74 wwssn and csn stations corrections for the effects of pp interference and yield scaling of the explosion source functions are determined and applied to the waveforms enabling analytical comparison of signals from events with different yields and burial depths the procedure accounts for common receiver and propagation effects relative explosion source strengths in the 0 5 2 0 hz frequency band are determined with results of near field modelling of strong ground motions establishing the absolute source spectral levels four events with detailed near field models are used as master events in the intercorrelation process and it is demonstrated that the relative source strengths are better resolved than the absolute values events with announced yields are used to determine empirical relations between yield and source strength which in turn predict the yields of the other events these yield estimates are shown to be comparable with those obtained by standard mb and relative amplitude analysis the analytical waveform comparisons also provide estimates of the pp parameters for each event and criteria for identifying anomalous events such as pipkin and muenster for which the waveforms differ from those of other events in the test site possible mechanisms affecting the anomalous events are considered pahute mesa is shown to be a distinct subsite within nts with different teleseismic amplitude and waveform variations than observed at other subsites

focusing and defocusing of teleseismic p waves by known three dimensional structure beneath pahute mesa nevada test site the focusing and defocusing of teleseismic p waves predicted by a known three dimensional structure beneath the nevada test site is calculated by dynamic raytracing and superposition of gaussian beams the 20 to 100 km scale lengths of this model having velocity fluctuations of several per cent account for a factor of 3 fluctuation in the azimuthal pattern of p amplitudes since similar sized scale lengths and intensities of velocity fluctuation are commonly resolved in three dimensional inversions of mantle structure in other regions focusing and defocusing of teleseismic p waves is likely to be a ubiquitous feature of every test site hence network averages of mb that weight azimuthal windows in which p energy is either focused or defocused will tend to either over or underestimate the yields of underground tests the results obtained with a known nevada test site structure suggest that structural inversions having similar structural resolution may be capable of reducing 25 per cent of the variance in amplitudes due to the focusing and defocusing of upper mantle structure near the source assuming that scattering processes are concentrated in the crust and upper most mantle beneath the source and receiver the integrated energy in the p coda should be more stable than direct p because it tends to homogenize the effect of focusing defocusing structure near the source for scattering into direct p near the source for direct p scattering near the receiver however even the late coda is not capable of completely removing the effects of focusing defocusing near the source

unravelling the conundrum of river response to rising sea level from laboratory to field part ii the fly strickland river system papua new guinea the most recent deglaciation resulted in a global sea level rise of some 120 m over ca 12 000 years a moving boundary numerical model is developed to predict the response of rivers to this rise the model was motivated by experiments at small scale which have identified two modes describing the transgression of a river mouth i autoretreat without abandonment of the river delta no sediment starvation at the topset foreset break and ii sediment starved autoretreat with abandonment of the delta in the latter case transgression is far more rapid and its effects are felt much further upstream of the river mouth a moving boundary numerical model that captures these features in experimental deltas is adapted to describe the response of the fly strickland river system papua new guinea in the absence of better information the model is applied to the case of sea level rise without local climate change in new guinea the model suggests that i sea level rise has forced the river mouth to transgress over 700 km since the last glacial maximum ii sediment starved autoretreat has forced enough bed aggradation to block a tributary with a low sediment load and create the present day lake murray iii the resulting aggradation was sufficient to move the gravel sand transition on the strickland river upstream iv the present day fly estuary may be in part a relict river valley drowned by sea level rise and partially filled by tidal effects and v the fly river is presently reforming its bankfull geometry and prograding into the fly estuary a parametric study with the model indicates that sediment concentration during floods plays a key role in determining whether or not and to what extent transgression is expressed in terms of sediment starved autoretreat a sufficiently high sediment concentration can prevent sediment starved autoretreat during the entire sea level cycle this observation may explain why some present day river mouths are expressed in terms of deltas protruding into the sea and others are wholly contained within embayments or estuaries in which water has invaded landward

tectonic evolution of proterozoic rocks in the cimarron mountains northern new mexico usa abstract portions of three proterozoic tectonostratigraphic sequences are exposed in the cimarron mountains of new mexico the cimarron river tectonic unit has affinities to a convergent margin plutonic volcanic complex igneous hornblende from a quartz diorite stock records an emplacement pressure of 2 2 6 kbar rocks within this unit were subsequently deformed during a greenschist facies regional metamorphism at 4 5 kbar and 330 50 c the tolby meadow tectonic unit consists of quartzite and schist mineral assemblages are indicative of regional metamorphism at pressures near 4 kbar and temperatures of 520 20 c a low angle ductile shear zone separates this succession from gneisses of the structurally underlying eagle nest tectonic unit gneissic granite yields hornblende pressures of 6 8 kbar pelitic gneiss records regional metamorphic conditions of 6 7 kbar and 705 15 c overprinted by retrogression at 4 kbar and 530 10 c comparison of metamorphic and retrograde conditions indicates a p t path dominated by decompression and cooling the low angle ductile shear zone represents an extensional structure which was active during metamorphism this extension juxtaposed the tolby meadow and eagle nest units at 4 kbar and 520 c both units were later overprinted by folding and low grade metamorphism and then were emplaced against the cimarron river tectonic unit by right slip movement along the steeply dipping fowler pass shear zone an argon isotope correlation age obtained from igneous hornblende dates plutonism in the cimarron river unit at 1678 ma muscovite associated with the greenschist facies metamorphic overprint yields a 40 ar 39 ar plateau age of 1350 ma by contrast rocks within the tolby meadow and eagle nest units yield significantly younger argon cooling ages hornblende isotope correlation ages of 1394 1398 ma are interpreted to date cooling during middle proterozoic extension muscovite plateau ages of 1267 1257 ma appear to date cooling from the low grade metamorphic overprint the latest ductile movement along the fowler pass shear zone post dated these cooling ages argon released from muscovites of the eagle nest tolby meadow composite unit at low experimental temperatures yields apparent ages of c 1100 ma similar ages are not obtained north east of the fowler pass shear zone suggesting movement more recently than 1100 ma

f k analysis of noress array and single station data to identify sources of near receiver and near source scattering abstract f k analyses of short period recordings of both u s and soviet underground nuclear explosions at the eskdalemuir eka scotland array indicate arrivals from a local source about 15 km due northwest of the array use of residual seismograms derived by subtracting the beamed record from each array channel confirmed the presence of the same scatterer the secondary seismic source appears to be short period surface waves due to the scattering of incident p waves at a nearby deep valley known as moffat water in agreement with key s 1967 earlier results similar analyses of the noress norway array data from u s and soviet nuclear shots also indicate secondary arrivals suggesting a local near surface scatterer about 25 30 km south west of the array in the region of lake mjosa thus short aperture array data can be useful in identifying and locating sources of near receiver scattering f k analyses of short period recordings of both explosion and earthquake sources at the high frequency noress array indicate secondary arrivals from a near receiver source about 25 30 km southwest of the array f k power difference plots obtained by subtracting after normalization the f k power versus slowness estimates for the initial p window from those for the later windows provided nearly identical results the secondary seismic source appears to be short period surface waves rg generated by the scattering of incident p waves in the region of lake mjosa 27 km sw of noress where there is about 1 km of relief from the bottom of the lake to the top of an adjacent hill

long term modelling of fluvial systems at the watershed scale examples from three case studies abstract to date many numerical approaches are available in studying water flow and sediment dynamics along rivers from the reach to the watershed scale based on various simplifications the aim of the present research is to demonstrate how the so called morphodynamic quasi equilibrium hypothesis is effective in modelling riverine landscape morphodynamics evolution at the watershed scale focussing on the long term changes of longitudinal profile and bed grainsize composition of large alluvial rivers a lumped 0 d two reach two grainsize model based on the local uniform flow hypothesis and originally developed for reproducing fluvial changes at the historical time scale has been applied to three large watercourses to reproduce their long term evolution performing a sensitivity analysis based on the present conditions three morphometric parameters were analysed aiming to describe the evolution of the longitudinal profile concavity and aggrading and the grainsize composition of the river bed fining though the 0 d approach does not allow for a spatial distribution of the input parameters namely the liquid and solid discharge the modelling outcomes show reasonably good qualitative trends at the scale of analysis centuries to millennia and for the chosen large sedimentary systems thousands of kilometres long which show high inertia to geomorphological changes likely owing to their longitudinal scale the model can be helpful in detecting where the present conditions reflect a big disturbance to the natural trend this initial detection method can provide additional insights in evaluating the capability of actual rivers to respond to the present external forcing eventually reaching a quasi stable configuration

downstream variation in stream power abstract stream power has a significant influence on many form and process attributes of the fluvial system using a similar approach to that suggested by d m lawler in 1992 and 1995 a model is developed to explore how stream power might vary in the downstream direction based on the assumption that the longitudinal profile of the river has an exponential form no particular discharge is necessarily specified but near bankfull flows are regarded as significant morphologically and one such discharge is the focus here total stream power per unit channel length qs is predicted to peak at an intermediate location the position of which depends on the ratio b where b and are the downstream rates of change of discharge and slope respectively if b is a relatively conservative quantity then the form of the longitudinal profile and in particular its degree of concavity will have the major influence on the position of maximum stream power specific stream power w is even more sensitive to and is expected to peak closer to the headwaters about half way between source and the location of the stream power maximum although this will depend on how channel width w varies with distance from source the model is tested along three connected streams of different size in the catchment of the river trent taking advantage of a relationship between mean annual flood and link magnitude which enables this near bankfull discharge to be estimated at any point within the network the model is verified in so far as stream power does attain a mid basin maximum but the observed and predicted locations of the maxima do not always correspond largely because of the distinctive variation in discharge and especially slope along individual pathways for example maximum power lies far downstream along the trent because of the large increase in mid basin discharge associated with a series of large closely spaced tributaries the importance of slope is borne out by the near headwater locations for specific power maxima which tend to be further upstream than predicted along all three rivers as a result of the steepness of upper reaches the variety of geomorphic settings produces deviations from expectation which has implications for the movement and storage of material in the fluvial system

analysis of near source contributions to early p wave coda for underground explosions i waveform complexity a data set of more than 1600 teleseismic short period p waves from 46 nuclear explosions is analyzed to establish near source contributions to the first 15 sec of the p signals the near source components are isolated by event to event comparisons of first cycle magnitudes rms amplitudes in the first 5 and next 10 sec of the wave forms and energy temporal centroid measurements events from the nevada amchitka and novaya zemlya test sites are analyzed separately to characterize overall source region variations event averaged waveform complexity variations between explosions within a given site are tested for dependence on source strength burial depth location within the site and tectonic release azimuthal patterns of the individual event complexity anomalies are used to discriminate between possible near source influences for events at pahute mesa a strong azimuthal amplitude pattern in both the direct p waves and the p coda for all of the events is produced principally by deep mantle variations defocusing by a high velocity anomaly in the crust and uppermost mantle beneath the site has a stronger effect on the direct p signals than on the early p coda resulting in a systematic spatially varying relative pattern

sediment supply and the development of the coarse surface layer in gravel bedded rivers the bed surface of most gravel rivers is considerably coarser than the sub surface or the gravel load transported over it a phenomenon affecting river dynamics morphology and ecology the coarse surface layer often called an armour or pavement has been attributed to an inherent tendency for small grains to settle between larger ones during active transport of all sizes1 2 and to selective erosion or trapping of finer particles when the coarse grains are relatively immobile3 4 where bedload supply is cut off below dams selective erosion causes coarsening5 6 using a simple quantitative model we propose that surface coarsening develops in gravel bedded rivers when local bedload supply from upstream is less than the ability of the flow to transport that load we present laboratory results which support this hypothesis and show that supply reduction causes changes in bedforms and progressive confinement of active bedload transport to a narrow band of finer bed surface bordered by a coarse less active bed it may therefore be possible to relate the degree of river bed surface coarsening to sediment supply resulting from land use

40ar 39ar ages of detrital muscovite and whole rock slate phyllite narragansett basin ri ma usa implications for rejuvenation during very low grade metamorphism late pennsylvanian sedimentary rocks in the narragansett basin were metamorphosed lower anchizone to sillimanite grade during late paleozoic regional metamorphism at ca 275 280 ma twenty five variably sized concentrates of detrital muscovite were prepared from samples collected within contrasting low grade areas diagenesis lower greenschist facies microprobe analyses suggest that the constituent detrital grains are not chemically internally zoned however some grains within several concentrates display very narrow 25 m compositionally distinct low grade epitaxial peripheral overgrowths detrital muscovite concentrates from the lower anchizone are characterized by internally concordant 40ar 39ar age spectra which define plateau ages of ca 350 360 ma these are interpreted to date post devonian acadian cooling within proximal source areas concentrates from lower grade sectors of the middle anchizone display slightly discordant spectra in which apparent ages systematically increase from ca 250 275 ma to define intermediate and high temperature plateaus of ca 360 400 ma detrital muscovite within samples from higher grade sectors of the middle anchizone and the upper anchizone are characterized by systematic low age discordance throughout both low and intermediate temperature increments high temperature ages only range up to ca 330 ma six size fractions of detrital muscovite from a sample collected within the lower greenschist facies have similarly discordant spectra in which apparent ages increase slightly throughout the analyses from ca 250 ma to 275 ma the detrital muscovite results are interpreted to reflect variable affects of late paleozoic regional metamorphism however it is uncertain to what extent the systematic low age spectra discordance reflects intracrystalline gradients in the concentration of 40ar and or experimental evolution of gas from relatively non retentive epitaxial overgrowths however low age discordance occurs regardless of the extent of epitaxial overgrowth intermediate temperature increments evolved during 40ar 39ar whole rock analyses of five slate phyllite samples are characterized by internally consistent apparent k ca ratios these are attributed to gas evolved from constituent very fine grained white mica samples from lower grade portions of the middle anchizone are characterized by intermediate temperature apparent ages which systematically increase from ca 275 300 ma to ca 360 375 ma before evolution of a high temperature contribution from detrital plagioclase feldspar this age variation may reflect partial late paleozoic rejuvenation of very fine grained detrital material with a source age similar to that for the detrital muscovites slate phyllite samples from upper sectors of the middle anchizone and from the upper anchizone were completely rejuvenated during late paleozoic metamorphism and record intermediate and high temperature plateau ages of ca 270 290 ma these data document that metamorphic conditions of the lower to middle biotite zone ca 325 350 c are required to completely rejuvenate intracrystalline argon systems of detrital muscovite therefore the 40ar 39ar dating method may be useful in determination of detrital muscovite provenance and in resolution of the metamorphic evolution of low grade terranes

evidence for normal and inhomogeneous lowermost mantle and core mantle boundary structure under the arctic and northern canada summary seismic p waves from a total of about 200 nuclear explosions in the usa the former ussr and china observed at 10 arrays and four networks in europe canada and the usa are used to analyse the structure at the base of the mantle and the core mantle boundary cmb the simple waveforms and well controlled source parameters of nuclear explosions allow one to use the events as source arrays in addition to the usual receiver array configuration a new array technique double beamforming kruger et al 1993 integrating both concepts is applied which increases the slowness resolution considerably a total of 56 source receiver combinations i e reflection points in the lower mantle or on the cmb could be analysed in five regions anomalous arrivals pdp with slowness and arrival times between those of p and pcp are observed one of these five areas svalbard region shows short period pcp p amplitude ratios which are about three times higher than those predicted by standard earth models in the severnaya zemlya region where pdp and pcp precursors were observed previously kruger et al 1993 pcp shows azimuth deviations of up to 10 for some other regions deviations of the pcp waveform from the direct p waveform are also observed these anomalous phases and the pcp waveform distortions cannot be explained with standard 1 d earth models they are probably produced by inhomogeneities in the lowermost mantle the observed variations in the waveforms are strong indications of a laterally heterogeneous structure in two depth ranges the first is the cmb and its immediate vicinity of a few tens of kilometres the second region is the depth range between about 200 and 300 km above the cmb maps of the north pole region giving the distributions of inhomogeneities in the lower mantle and on the cmb are presented these maps show evidence of strong heterogeneity of the d boundary layer and possibly also of the cmb in the same area

on the equilibrium profile of river beds 1 despite the wide spectrum of perturbations of flow and sediment transport experienced by rivers as a result of hydrologic variations the paradigm of morphodynamic equilibrium has long been present in the geomorphological literature where it is traditionally associated with the semiempirical notion of formative discharge whereby the unsteady forcing is taken as morphologically equivalent to some effective steady forcing here we investigate the mechanisms responsible for maintaining a quasi equilibrium bed profile of a river reach sufficiently short to have no significant tributary inputs more importantly we assume the channel banks to be fixed hence the case we have in mind is that of rivers protected by levees which cannot respond to hydrologic forcing by changing their width like natural rivers employing a 1 d model of river morphodynamics we first determine the equilibrium profile of the river reach for given steady forcing conditions and discuss the capability of this approach for interpreting bed profiles observed in the field by applying it to the terminal reach of the magra river italy field observations turn out to be reasonably well fitted by the equilibrium profile associated with a steady effective discharge which however differs from the typical formative discharge mean annual flood for natural channels with erodible banks finally we clarify how fluctuations of the hydrodynamic forcing associated with the recorded historical sequence of hydrologic events of variable intensities have acted to maintain the river equilibrium

numerical analytical interfacing in two dimensions with applications to modeling nts seismograms a new method for interfacing numerical and integral techniques allows greater flexibility in seismic modeling specifically numerical calculations in laterally varying structure are interfaced with analytic methods that enable propagation to great distances such modeling is important for studying situations containing localized complex regions not easily handled by analytic means the calculations involved are entirely two dimensional but the use of an appropriate source in combination with a filter applied to the resulting seismograms produces synthetic seismograms which are point source responses in three dimensions the integral technique is called two dimensional kirchhoff because its form is similar to the classical three dimensional kirchhoff data from yucca flat at the nevada test site are modeled as a demonstration of the usefulness of the new method in this application both local and teleseismic records are modeled simultaneously from the same model with the same finite difference run this application indicates the importance of locally scattered rayleigh waves in the production of teleseismic body wave complexity and coda

response of coastal plain rivers to falling relative sea level allogenic controls on the aggradational phase this study combines mathematical modelling and supporting flume experiments to address the problem of how coastal plain rivers respond to a steady fall in relative sea level the theoretical component of the study focuses on the development of a moving boundary model of fluviodeltaic progradation that treats rigorously the dynamics of the shoreline and alluvial basement transition the upstream limit of the alluvial river system dimensional analysis and numerical solutions to the model governing equations together suggest that at first order coastal plain rivers will remain aggradational on a timescale that varies with allogenic sediment and water supply and the fall rate of relative sea level in natural fluviodeltaic systems this intrinsic timescale is likely to vary by several orders of magnitude suggesting that the aggradational phase of river response can be geologically long lived at second order the duration of alluvial aggradation is controlled by two dimensionless numbers that embody system geometry and the kinematics of alluvial sediment transport model predictions were tested in a series of carefully scaled flume experiments the level of agreement between predicted and measured trajectories for the shoreline and alluvial basement transition strongly suggests that the moving boundary theory developed here successfully captures the response of small scale fluviodeltaic systems to falling sea level the results of this study have several sequence stratigraphic implications a fall in relative sea level at the shoreline is not a sufficient condition for river incision the onset of alluvial degradation and sequence boundary formation need not coincide with a maximum in the rate of sea level fall and the onset of sequence boundary formation is sensitive to allogenic sediment supply

analysis of near source contributions to early p wave coda for underground explosions ii frequency dependence an analysis of dispersion in more than 1600 teleseismic short period p waves from 46 underground explosions has established that near source effects are responsible for systematic frequency dependent variations observed in the first 15 sec of the p signals explosions from the nevada amchitka and novaya zemlya test sites exhibit a common magnitude dependence of the dispersive behavior with smaller events having relatively enriched low frequency 0 4 to 0 8 hz energy in the coda for the nevada and amchitka sites the larger events have relatively enhanced high frequency 0 8 to 1 1 hz energy in the coda as well which may actually be a consequence of diminished high frequency content of the direct arrivals the dispersive behavior also correlates well with known source depths for the nevada test site and amchitka events and with estimated pp delay times for the novaya zemlya events indicating that burial depth and or explosion size are important factors pahute mesa tests show a secondary dependence on position in the site with centrally located events having stronger dispersion as well as more pronounced slowly varying azimuthal patterns in the frequency dependence stations at azimuths to the north northeast from the mesa have particularly strong dispersion for centrally located events the spatial and azimuthal variations for pahute mesa events do not appear to be the result of aftershock radiation as suggested by douglas 1984 but instead are associated with frequency dependent defocusing and scattering from a high velocity structure beneath the test site some of the dispersion from novaya zemlya events appears to result from deep path properties however the strong magnitude depth dependence for all of the test sites indicates that very near source conditions have the strongest influence on the frequency dependence a likely explanation for the dispersive behavior is a combination of relatively enhanced surface wave excitation and scattering for shallower events and frequencydependent defocusing for sites overlying anomalous high velocity structures as is the case for both pahute mesa and amchitka

transient scour and fill the case of the pilcomayo river abstract transient scour and fill refers to the general scour and fill in a riverbed due to flood passage it was given much attention in times of leopold and maddock 1953 and colby 1964 from records of outstanding case studies field data from a station in a contracted long reach of the large sand bed pilcomayo river 1192 newly typed in forms are presented with sediment concentration in the database up to 60 kg m 3 mostly wash load water surface rises and falls during a flood event whereas streambed evolves in reverse it renders the analogy to an accordion streambed scouring accounts for 36 of the change in flow area during floods and data reveal scouring up to 4 m from the streambed elevation when flood starts velocity data display large hysteresis loops inexplicable by unsteady flow only once streambed starts to fall river bed scour is self sustaining water depth gradient appears to be a crucial variable in a novel equation for transient scour and fill derived from exner equation it turns out that flow non uniformity is relevant to explain transient scour and fill in contrast to flow unsteadiness which is not quasi steady gradually varied flow equation solved along the contracted reach is the base for a model that captures well the recorded bed evolution the model explains most of the transient scour and fill by the downstream expansion but the non uniform flow and the bed material suspended load also play a role the model fails on the days of highest sediment concentrations

late proterozoic grenville deformation in central new mexico determined from single crystal muscovite 40ar 39ar age spectra abstract 40 ar 39 ar age spectrum analyses on deformed and undeformed single crystal muscovites from the manzano mountains in central new mexico provide insights on the argon systematics of deformed muscovite the post 1 4 ga cooling history of the region and the timing of low temperature deformation microstructures in narrow east side up shear zones in and around the 1427 ma priest pluton indicate post pluton greenschist facies 350 c deformation single crystal 40 ar 39 ar analysis of three samples containing undeformed muscovite yield plateau spectra with ages of 1390 3 1395 2 and 1401 3 ma suggests that by this time the pluton had cooled below 350 400 c single crystal muscovites from within the shear zones have markedly different age spectra and reveal well defined age gradients from 1 1 to 1 4 ga the age gradients are interpreted as resulting from deformation induced argon loss or reduction of the effective radius for argon diffusion thereby decreasing the closure temperature of the originally pristine magmatic muscovites these data and previously published results suggest a long period of crustal stability ca 1 4 to 1 1 ga in which average cooling rates were probably about 1 c ma the 1 1 ga ages in the deformed muscovite age spectra are interpreted as indicating that grenvillian tectonism to the southeast affected central new mexico it can not be unambiguously determined if the consequences of the grenville orogeny in new mexico was uplift and erosion cooling a discrete thermal pulse reheating or if the shear zones record grenville age contractual deformation

near source contributions to teleseismic p waves and p wave coda for underground explosions characterization of near source crustal properties for underground nuclear explosions using distant seismic observations can potentially improve nuclear test monitoring capabilities previous analyses of the relative spectral content of direct p waves and p wave coda have suggested that important physical parameters such as source overburden velocity and shot point velocity can be inferred from teleseismic signals such observations have the potential to both improve yield estimation by indicating coupling conditions and to shed light on the basic mechanisms of coda excitation reliable isolation of any near source influences requires thorough suppression of propagation and near receiver effects on the signals which are shown herein to be significant for comparisons of p and p coda a spectral factoring procedure is used to determine eventaveraged source spectra from which propagation and receiver terms have been removed for both direct p signals and early p coda a large short period waveform data set 2457 signals for 71 events at the nevada and novaya zemlya test sites is analyzed with the event averaging procedure spectral ratios and slopes of spectral ratios for the event averaged p and p coda source terms are examined for dependence on event magnitude burial depth overburden velocity and other known source characteristics the slopes of p i p coda ratios over the frequency band 0 3 to 2 5 hz for nts events show only weak dependence on near source properties for the event averaged spectra while individual stations sometimes show strong systematic trends as discovered by gupta and blandford 1987 the tendency is for larger deeper events with higher average overburden velocities to have relative enrichment of high frequency p wave energy compared to the coda single frequency pip coda spectral amplitude ratios increase with increasing magnitude depth and overburden velocity for frequencies less than 0 5 hz with these trends being reversed near 0 8 hz for novaya zemlya the slope of p p coda shows a strong variation with magnitude but p waves from larger events have relatively depleted high frequency content differences in magnitude depth scaling may contribute to this difference between test sites single frequency pip coda spectral ratios at frequencies less than 1 0 hz increase with magnitude for novaya zemlya similarly to the nts events possibly as a result of enhanced coda excitation for shallower events combined with low frequency pp interference these variations are not yet quantitatively understood but may ultimately provide empirical procedures for characterizing the near source environment of isolated events or additional test site explosions

unravelling the conundrum of river response to rising sea level from laboratory to field part i laboratory experiments the most recent deglaciation resulted in a global sea level rise of some 120 m over approximately 12 000 years in this part i of two parts a moving boundary numerical model is developed to predict the response of rivers to this rise the model was motivated by experiments at small scale which have identified two modes describing the transgression of a river mouth autoretreat without abandonment of the river delta no sediment starvation at the topset foreset break and sediment starved autoretreat with abandonment of the delta in the latter case transgression is far more rapid and its effects are felt much further upstream of the river mouth the moving boundary numerical model is checked against experiments the generally favourable results of the check motivate adaptation of the model to describe the response of the much larger fly strickland river system papua new guinea to holocene sea level rise this is done in the companion paper part ii

a unified framework for stability of channel bifurcations in gravel and sand fluvial systems bifurcating rivers shape natural landscapes by distributing water and sediments on fluvial plains and in deltas symmetrical bifurcations were often found to be unstable so that one branch downstream of the bifurcation enlarged while the other dwindled a unified theory able to predict bifurcation stability in both gravel bed and sand bed rivers is still lacking here we develop a new theory for the stability of bifurcations for the entire range of gravel bed to sand bed rivers the theory indicates opposite behavior of gravel bed and sand bed rivers we predict that symmetrical bifurcations are inherently stable for intermediate shields stresses but are inherently unstable for the low and high shields stresses found in the majority of rivers on earth in the latter conditions asymmetrical bifurcations are stable these predictions are corroborated by observations and have ramifications for many environmental problems in fluviodeltaic settings

causes of concavity in longitudinal profiles of rivers a smooth concave configuration represents the most common quasi equilibrium profile of alluvial rivers in the present paper a generalized unified set of models for the longitudinal profile of rivers is presented various independent effects that drive concavity in longitudinal rivers are considered and classified the driving mechanisms considered here are 1 horizontal wavelike progradation of the river profile 2 abrasion of bed particles 3 aggradation of the river profile balancing subsidence at a constant speed and 4 the effect of tributaries adding sediment and water to the main stem of the river for simplicity it is assumed that the long term supply of water and sediment is constant hence a single discharge that is bank full discharge is used as an approximate characterization of the hydrologic regime for each point along the river sediment sorting has been studied elsewhere and is excluded from this analysis the river is assumed to have uniform bed material although the mean size may vary downstream it is concluded that the quasi equilibrium longitudinal profile created by each of the first three driving mechanisms mentioned above is concave the degree of concavity varies however depending on a set of physical conditions that can be identified by a set of dimensionless numbers a comparison of these numbers reveals the relative importance of the driving mechanisms for concavity a condition for concavity driven by the fourth mechanism that is tributary input is delineated