theoretical investigation of the oceanic inverted barometer response dynamic tidal theory is generalized in order to predict the oceanic response to atmospheric pressure variations the oceans are found to exhibit distinct dynamic behavior when forced at periods less than 1 week depending on the harmonic type of forcing the amplitude of the response can differ by 20 or more from the static response even at roughly 2 months the traditional inverted barometer may not be sufficiently accurate for applications in which detection of long term sea level trends or vertical crustal motion is the goal for forcing at periods of order 1 year the oceanic response differs by at most a few percent from the static not the inverted barometer response thus calculations of meteorological excitation of the annual and chandler wobbles can employ the static approximation without reservation

the estimation of green s function from local earthquake recordings and the modelling of the site response abstract a method is presented for the modelling of the site response from the deconvolution of local earthquake recordings the green s function for the propagation medium is obtained by using the assumption of minimum phase propagation for a stratified absorptive earth model as deconvolution criterion the application of this technique to theoretical data shows that local synthetic seismograms can be deconvolved with high accuracy the site response for an actual site bhb in the swabian jura southwest germany has been estimated by integrating over a number of green s functions obtained for different incidence angles thus enhancing the effects of the superficial layers and reducing the effects of the deeper structure the comparison between accelerograms modelled with the obtained average site response and an observed accelerogram yields a good fit in peak and rms acceleration and strong motion duration

revised predictions of long period ocean tidal effects on earth s rotation rate the rotational response of earth to long period tidal forces embodied in a zonal response function can be expected to vary with frequency because of variable contributions by the oceans mantle and core the zonal response function has been estimated from 9 years of international radio interferometric surveying iris universal time ut1 data and compared with theoretical predictions using a spherical harmonic tide model to compute the oceans dynamic response at semiannual monthly fortnightly and 9 day lunisolar tidal frequencies different amounts of mantle anelasticity have been considered for both the oceanic and solid earth responses predictions have been made assuming axial core mantle coupling which is either complete or absent additionally an extensive recalibration of the ocean model s frictional parameters was performed using constraints derived in part from space92 polar motion data zonal response function predictions have also been made employing this recalibrated ocean tide model our results indicate that any amount of core coupling can be ruled out at a fortnightly period and probably at a 9 day period but not at a monthly period our results also suggest that the mantle responds purely elastically at a 9 day period but may behave increasingly anelastically at longer periods a simple dispersive rule is postulated for periods ranging up to the 14 month chandler wobble period

auto correlation analysis of coda waves from local earthquakes for detecting temporal changes in shallow subsurface structures the 2011 tohoku oki japan earthquake for monitoring temporal changes in subsurface structures i propose to use auto correlation functions of coda waves from local earthquakes recorded at surface receivers which probably contain more body waves than surface waves use of coda waves requires earthquakes resulting in decreased time resolution for monitoring nonetheless it may be possible to monitor subsurface structures in sufficient time resolutions in regions with high seismicity in studying the 2011 tohoku oki japan earthquake mw 9 0 for which velocity changes have been previously reported i try to validate the method kik net stations in northern honshu are used in this analysis for each moderate earthquake normalized auto correlation functions of surface records are stacked with respect to time windows in the s wave coda aligning the stacked normalized auto correlation functions with time i search for changes in phases arrival times the phases at lag times of 1 s are studied because changes at shallow depths are focused temporal variations in the arrival times are measured at the stations based on the stretching method clear phase delays are found to be associated with the mainshock and to gradually recover with time the amounts of the phase delays are 10 on average with the maximum of about 50 at some stations the deconvolution analysis using surface and subsurface records at the same stations is conducted for validation the results show the phase delays from the deconvolution analysis are slightly smaller than those from the auto correlation analysis which implies that the phases on the auto correlations are caused by larger velocity changes at shallower depths the auto correlation analysis seems to have an accuracy of about several percent which is much larger than methods using earthquake doublets and borehole array data so this analysis might be applicable in detecting larger changes in spite of these disadvantages this analysis is still attractive because it can be applied to many records on the surface in regions where no boreholes are available

an analysis of tidal variations in the length of day observations of the length of day lod corrected for the effects of variations in the angular momentum due to changes in wind velocity and atmospheric pressure ocean tide heights and currents and solid earth zonal tides were analyzed the apparent effect of atmospheric angular momentum aam on the astronomically determined lod is found to be much less at the highest frequencies than at lower frequencies for periods shorter than ten days there appears to be essentially no correlation between aam and lod the international earth rotation service iers standards 1992 model for the effects of zonal tides on the earth s rotation which includes ocean tidal effects adequately accounts for the observations of the variations in the length of day with periods between five and 180 days at the present level of accuracy a currently unexplained semi annual variation in the length of day remains but this may be due to the unmodeled effects of stratospheric winds the power spectrum of the remaining variations with periods less than twenty days is essentially that of a white noise process the amplitudes of the remaining unexplained variations in length of day are less than thirty microseconds this paper has been accepted by geophysical journal international for publication

a comparative study of island seafloor and subseafloor ambient noise levels abstract a study of seafloor and island stations shows that for the frequency band 0 1 to 10 hz the seismic noise levels on islands are comparable to the levels on the seafloor the microseism peak at the seafloor appears to be comparable to the highest levels observed on small islands for this band seafloor stations are realistic alternatives when island sites are not available seven year averages of the ambient noise levels recorded by seismic research observatory sro stations on three islands guam gumo taiwan tato and new zealand9s north island snzo are compared with those recorded by the international deployment of accelerometers ida station on easter island and on and beneath the ocean floor by ocean bottom seismometers obss and the marine seismic system mss deployed in a south pacific dsdp drill hole at 23 8 s 165 5 w adair et al 1986 from 0 3 to 2 hz the sro displacement power levels fall in the range historically observed by the scripps9 obss decreasing at 70 db decade from 1 by 10 6 nm 2 hz at 0 3 hz to 1 nm 2 hz at 2 hz and are 10 to 15 db above mss levels above 2 hz it appears that the same ratios hold the sro power levels decrease at 70 db decade to 1 by 10 3 nm 2 hz at a frequency of 10 hz although this correlation is based on very limited high gain short period data at frequencies below 0 3 hz the sro noise levels peak and decrease to approximately 2 by 10 3 nm 2 hz at 40 mhz the noise levels recorded at easter island are somewhat higher decreasing at 70 db decade from 1 by 10 7 nm 2 hz at 0 2 hz to 1 nm 2 hz at 10 hz and to 1 by 10 5 nm 2 hz at 50 mhz at the microseism peak near 0 2 hz the mss levels are from 15 to 20 db higher than observed by the sro stations and equivalent to those recorded at easter island there appears to be little dependence of the variance in noise level estimates on frequency the upper 95 per cent confidence limit generally lies 10 db above the average noise levels for all island stations all island noise level curves are dominated by the broad double frequency microseism peak centered between 0 15 to 0 2 hz the single frequency peak ranges from absent easter island to discernable guam and new zealand to obvious at taiwan the center frequency of this peak ranges from 0 07 hz at guam and new zealand to 0 1 hz at taiwan we speculate that the increased amplitude and frequency of the single frequency microseism peak is due to the interaction between the shallow continental shelf and surface gravity waves and or the presence of taiwan in a region of limited fetch

elastic wave velocities within oceanic layer 2 from sonic full waveform logs in deep sea drilling project holes 395a 418a and 504b multichannel full waveform acoustic logs were recorded in deep sea drilling project dsdp hole 418a during ocean drilling program odp leg 102 dsdp hole 395a during odp leg 109 and dsdp hole 504b during odp leg 111 to provide nearly continuous measurements of elastic wave velocities as a function of depth within oceanic layer 2 for different spreading rates and crustal ages the velocities depend primarily on the morphology of the basalt massive units have vp above 5 km s vs above 2 8 km s and vp vs below 1 9 their velocities increase with depth as expected from crack closure due to confining stress and are lower where fractures are present vp and vs within pillows are quite variable but in general are lower than in massive units and vp vs is higher velocities within breccias are similar to or lower than those of pillows within a given morphology the elastic properties do not depend on spreading rate within pillows velocity variations depend primarily on the degree of alteration infilling and the mineralogy of the infilling material and secondarily on conditions at emplacement coherent shear arrivals are sometimes not found within shallow pillows and in extreme cases the compressional arrival is also incoherent because of scattering resulting from the similarity between the sonic wavelength and the pillow size this sampling bias in the sonic log is the most likely cause of somewhat higher average sonic than seismic velocities measured within extrusive basalts at shallow depths other causes include the fact that laterally finite massive units may be oversampled by borehole measurements and that voids between pillows and fractures whose size is within an order of magnitude of the sonic wavelength have less effect on sonic than on seismic velocities the crustal section can be separated only roughly into seismic layers on the basis of the sonic velocities changes in velocity with depth within the extrusive section at a single site giving rise to previously defined seismic layers 2a and 2b are due to a change with depth in the properties of the pillows associated with differences in the amount and type of infilling materials rather than to a change with depth in the relative proportion of pillows and massive units because alteration occurs early and its history is different at different depths depth dependent variations in pillow properties are 1 established at young age and 2 persist even in old crust within the intrusive section of dsdp hole 504b velocities are similar to or higher than those measured in saturated minicores at atmospheric pressure and seismic and sonic velocities are approximately equal suggesting that little large scale porosity is present

new aspects of the equilibrium pole tide summary we have developed a new spherical harmonic algorithm for the calculation of the loading and self gravitating equilibrium pole tide based on a suggestion of dahlen this approach minimizes the distortions in tide height caused by an incomplete representation of the ocean function with slight modification our approach easily could be used to compute self gravitating and loading luni solar tides as well using our algorithm we have compared the static pole tide with tide observations at a variety of locations around the world we find statistically significant evidence for pole tide enhancements in mid ocean as well as the shallow seas we have also re investigated the effect of the static tide on the chandler wobble period the difference between the wobble period of an oceanless elastic earth with a fluid core smith dahlen and the period of an earth minus static oceans yields a 7 4 day discrepancy we conclude from tide observations that much of the discrepancy can probably be accounted for by non equilibrium pole tide behaviour in the deep oceans

modelling the pole tide and its effect on the earth s rotation summary the pole tide is the response of the ocean to incremental centrifugal forces associated with the chandler wobble the tide has a potentially important effect on the period and damping of the wobble but it is at present not well constrained by observations here we construct both analytical and numerical models for the pole tide the analytical models consider the tide first in a global ocean and then in an enclosed basin on a beta plane the results are found to approach equilibrium linearly with decreasing frequency and inversely with increasing basin depth the numerical models solve laplace s tidal equations over the world s oceans using realistic continental boundaries and bottom topography the results indicate that the effects of the non equilibrium portion of the deep ocean tide on the chandler wobble period and damping are negligible

seismic imaging of the site response using microearthquake recordings part i method abstract microearthquake signals from widely distributed geographical regions have been noticed repeatedly to be strongly affected by local site effects the corresponding seismograms contain important information on the individual propagation path a single station inversion method is presented which allows the imaging of the subsurface impedance structure from locally recorded sh waves records the technique is based on the kunetz claerbout equation which in its original form states the relationship between the transmission response and the reflection response for p waves in a horizontally layered medium and vertical incidence claerbout 1968 by adapting claerbout9s formulation to the transmission problem for sh waves under oblique incidence microearthquake recordings can be used to calculate corresponding pseudo reflection seismograms which in turn can be inverted for the impedance structure by exploiting levinson recursion limitations in the high frequency content of the signals due to the combined effects of absorption recording system and bandlimited source signals as well as the influence of noise drastically reduce the resolutional power of the inversion procedure a number of different deconvolution techniques have been tested with synthetic seismograms for the applicability to reduce these effects good results have been obtained with the blind deconvolution technique of scherbaum and stoll 1985 utilizing the minimum phase property of the green9s function from the analysis of synthetic data it can be expected that for realistic source receiver situations and short period recording systems the main reflectors down to a depth of several hundreds of meters could be resolved

dynamics of the long period tides abstract the long period tides are a tool for understanding oceanic motions at low frequencies and large scales here we review observations and theory of the fortnightly monthly and pole tide constitutents observations have been plagued by low signal to noise ratios and theory by the complex lateral geometry and great sensitivity to bottom slopes a new spectral element model is used to compute the oceanic response to tidal forcing at 2 week and monthly periods the general response is that of a heavily damped q 5 system with both the energy input from the moon and the dissipation strongly localized in space the high dissipation result is probably generally applicable to all low frequency barotropic oceanic motions over much of the ocean the response has both the character of a large scale and a superposed rossby wave like character thus vindicating two apparently conflicting earlier interpretations to the extent that free waves are excited they are consistent with their being dominated by rossby and topographic rossby wave components although gravity modes are also necessarily excited to some degree in general a modal representation is not very helpful the most active regions are the southern ocean and the western and northern north atlantic these results are stable to changes in geometry topography and tide period on a global average basis the dynamical response of mm is closer to equilibrium than is mf

strong motion prediction using mathematical modeling techniques abstract the parkfield california earthquake of 1966 produced the first recording of ground motion in the immediate vicinity of an earthquake fault the simplicity of displacement pulse observed at station 2 aroused great interest among seismologists working in the area of earthquake source mechanism since then numerous theoretical works on simulating strong motion have been carried out starting with the use of a simple kinematic model assuming a uniform slip over a fault plane the assumption of uniform slip had to be modified to explain the strong motion observed during the parkfield earthquake of 1966 the borrego mountain earthquake of 1968 the san fernando earthquake of 1971 the imperial valley earthquake of 1979 the el asnam earthquake of 1980 and others through these studies the simulation technique has been advanced to include a more realistic medium in the beginning most methods used green9s function for an unbounded homogeneous medium then the free surface effect the effect of a sedimentary layer as well as laterally heterogeneous basin structure have been included in the simulation the above simulation studies were however restricted to relatively low frequency waves represented in a displacement or velocity seismogram in order to predict an acceleration seismogram dominated by high frequency waves hybrid models have been proposed in which gross features of rupture propagation are specified deterministically but the details of the process are described by a stochastic model specified by a small number of parameters the application of these models to several california earthquakes revealed encouraging results that some of the key parameters of the model are stable among earthquakes mathematical modeling techniques will play an important role in the prediction of strong motion for a great earthquake in california as well as for major earthquakes outside california based on the records of moderate earthquakes already acquired in california

experiments in tidal mass conservation summary a common feature of theoretical ocean tide models is their failure to conserve mass over the oceans this failure distorts the tidal solution and imparts ambiguity to the calculation of tidal effects on gravity crustal loading and earth rotation for example predicted effects of long period tides on rotation could be uncertain by up to 50 per cent in magnitude and 100 per cent in phase using the spherical harmonic tide theory developed by dickman 1989 the influence of various global conservation constraints on the tidal solution is explored an ocean wide mass conservation constraint implemented using lagrange multipliers produces a realistic and significantly more accurate and unambiguous tidal solution

source parameters and scaling laws of the 1978 swabian jura southwest germany aftershocks the 3 september 1978 swabian jura southwest germany earthquake mwa 5 7 was followed by a large number of aftershocks which have been recorded with a local network of five portable seismic stations the seismic moments fault radii and the static stress drops have been determined from the sh displacement spectra using the brune 1970 source model the data set is consistent with the gutenberg richter energy magnitude relation below a wood anderson magnitude of about 4 the corner frequencies increase only slowly with decreasing magnitudes no corner frequency higher than 15 hz has been observed in the magnitude range down to 0 8 correspondingly the high frequency decay slopes show a strong increase when the corner frequencies are approaching the maximum frequency this prevents the use of slope data for q determinations in terms of the madariaga 1977 crack model the data show a strong influence of source complexities on the smaller events

constraints on q at long periods from earth s rotation in this work we assess constant q and frequency dependent q models of mantle anelasticity our assessment uses the degree 2 love numbers we had inferred previously from a comparison of observed and predicted changes in the length of day at monthly fortnightly and nine day lunar tidal periods the comparison accounted for variable contributions to the tidal signals by dynamic oceans and allowed for axial core mantle coupling that was either complete or absent the love number derived from an earlier analysis of the period of the chandler wobble is also employed we find that the similarity of the degree 2 love number inferred at a nine day period to that at seismic frequencies combined with the significant amount of relaxation at the chandler period together imply that q models operating within the seismic band cannot extend all the way to long tidal periods our analysis of q also allows us to refine estimates of the love number at fortnightly and monthly periods

strong motion seismology although this is the first review on this topic to appear in a quadrennial report the roots of strong motion seismology extend back to at least 1932 when far sighted engineers in the seismological field survey of the u s coast and geodetic survey installed rugged fieldworthy instruments designed to make on scale recordings of large earthquakes carder 1964 these instruments are called accelerographs for their output closely mimics ground acceleration hudson 1979 the original instruments and their offspring have provided a wealth of information about ground motions of direct use to engineers due in large part to the continued devotion of the seismological field survey now part of the branch of engineering seismology and geology at the u s geological survey the number of recordings has increased substantially particularly in the last two decades and multiple recordings of a few california earthquakes have provided the data necessary to begin to unravel the complexities of the ground motions and to predict these motions on an empirical basis although seismologists used accelerograph records in studies of earthquake energy and ground motion attenuation as long ago as 1942 gutenberg and richter 1942 1956 widespread seismological use of the records began with aki s 1968 analysis of the 1966 parkfield earthquake

crustal structure flexure and subsidence history of the hawaiian islands seismic reflection profile data have been used to estimate the long term 106 years mechanical properties of the oceanic lithosphere underlying the hawaiian islands the data show prominent reflectors associated with the top of the oceanic crust reflector 2 the m discontinuity and the base of the crust reflector 3 the two way travel time to the reflectors has been depth converted using velocity depth functions derived from seismic refraction expanding spread profile data and compared to calculated depths based on simple three dimensional elastic plate models a good fit to the reflector depths was obtained for a model with an effective elastic thickness of the lithosphere te of 40 km the main discrepancies with the refraction data occur beneath oahu and molokai where the predicted depth of the base of the flexed crust is too shallow and beneath the southeast flank of hawaii where it is too deep we attribute the thickened crust beneath oahu to ponding of magma at the base of the crust following the last phases of tholeiitic shield building and the thinned crust beneath the flanks of hawaii to crustal melting beneath the youngest part of the chain the effective te of 40 km is higher than expected for 80 m y oceanic lithosphere possibly due to the effects of subsurface loads that act at or near the base of the flexed crust according to free air gravity anomaly and bathymetry data te does not change significantly along the island chain retaining a similar value for hawaii as it does for oahu we have used this result to estimate the pattern of subsidence and uplift that would be expected along the hawaiian islands because of flexural loading of hawaii the observed depth of the haleakala wave cut terrace northeast of maui can be generally explained by the flexure model the main discrepancies between observed and the predicted depths occur northwest of hawaii where they suggest a somewhat higher value of te possibly due to incomplete adjustment of the lithosphere we suggest that the addition of loads to the end of a volcanic chain generated as a plate moves over a mantle hotspot is accommodated by progressive flexing downstream causing subsidence of preexisting volcanos that lie in the flexural moat and uplift of islands on the flanking bulge the progressive flexure model predicts a characteristic pattern of offlap and onlap in the regions flanking the hawaiian islands that is generally similar to stratigraphic relationships observed along previously published seismic profiles of the moat a progressive flexure model may also apply to the case of a continental plate moving over a mantle hotspot and could explain the observations of 1 a clinoform pattern of stratigraphy in some flood basalt provinces and 2 a seaward dipping reflector sequence at some passive continental margins

levinson inversion of earthquake geometry sh transmission seismograms in the presence of noise the kunetz claerbout equation for the acoustic transmission problem in a layered medium in its original form establishes the relation between the transmission and the reflec tion response for p waves in an horizontally layered medium and with vertical incidence it states that the reflection seismogram due to an impulsive source at the surface is one side of the autocorrelation of the seismogram due to an impulsive source at depth and a surface receiver by adapting claerbout s formulation to the transmission of sh waves the kunetz claerbout equation also holds for reflection and transmission coefficients dependent on the incident angle thus earthquake geometry sh transmission seismograms can be used to caculate corresponding pseudoreflection seismograms which in turn can be inverted for the impedance structure using the levinson algorithm if the average incidence angle is known a geometrical correction on the resulting impedance model can improve the resolution of layer thicknesses in contrast to the inversion of reflection seismograms the levinson algorithm is shown to yield stable results for the inversion of transmission seismograms even in the presence of additive noise this noise stabilization is inherent to the kunetz claerbout equation results of inverted sh wave microearthquake seismograms from the swabian jura sw germany seismic zone obtained at recording site hausen im tal have been compared with sonic log data from nearby exploration drilling at trochtelfingen the agreement of the main structural elements is fair to a depth of several hundred metres

the rotation of the earth earth rotation studies are reviewed for the 1987 1990 time period it is noted that the emphasis in these studies has shifted from improvements in the observational techniques to interpreting and gaining greater understanding of the variations of the earth rotations there have been progressive improvements in the accuracy and the temporal resolution of earth rotation measurements

a complete spherical harmonic approach to luni solar tides summary in this work a spherical harmonic theory of ocean tides is presented the theory is based on laplace tide equations modified to include turbulence with constant eddy viscosity linearized bottom friction and oceanic loading and self gravitation variable bathymetry is also treated in harmonic terms and no flow boundary conditions are applied at continental coastlines the tide and boundary constraint equations are reduced to matrix form and solved by a weighted least squares procedure five zonal luni solar tides ranging in period from 14 days to 18 6 yr are investigated using the theory such tides have typically been difficult to compute using traditional numerical approaches the polar motion and changes in the length of day induced by these long period tides are calculated tidal solutions are compared extensively with results from other tidal theories and from recent satellite and sea level observations the greatest limitation to accurate prediction of zonal tides for any theory appears to be the marginal failure of all tide theories to conserve mass globally the use of additional mass constraints may be warranted

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

determination of oceanic dynamic barometer corrections to atmospheric excitation of earth rotation the excitation of earth s rotation by atmospheric pressure fluctuations on timescales from days to years is modified by the oceanic response to the pressure load that response has often been approximated as a static inverted barometer ib change in sea level but evidence from theory and both tide gauge and altimetric data suggests that the ib poorly models the sea level response at short periods static models also fail to account for the currents induced by the pressure loading the actual dynamic response of the oceans to barometric loads depends on frequency and on the spatial structure of the loading this work presents a green s function approach to determining the rotational effects of that oceanic response the green s functions characterize the rotational effects of the oceanic response to pressure loads described spatially by individual spherical harmonics for each harmonic of forcing they were computed at nine periods ranging from 4 days to 18 years and interpolated at intermediate periods computations were based on solutions to the author s dynamic spherical harmonic ocean tide model the effects on rotation of the dynamic barometer oceanic response are obtained by a convolution type combination of the green s functions with actual atmospheric pressure data results for data spanning the past decade will be illustrated using harmonically decomposed national center for environmental prediction ncep and european centre for medium range weather forecasts ecmwf pressure fields

effect of alteration formation absorption and standoff on the response of the thermal neutron porosity log in gabbros and basalts examples from deep sea drilling project ocean drilling program sites this study focuses on the effects of hydrous alteration minerals formation absorption and standoff on the response of the thermal neutron porosity log in the basaltic and gabbroic rocks logged at sites 395 418 504 642 and 735 during the ocean drilling program the concentration of hydrogen present in the rocks in the form of free water pore space and bound water hydrous minerals is the primary factor controlling the neutron elastic scattering process while the presence of other elements such as chlorine gadolinium boron lithium and samarium in the fluids and in the rock matrix can largely affect the thermal diffusion phase these neutron absorbers cause an increase of the capture cross section and in turn of the apparent thermal porosity further perturbations occur when the recording conditions depart from those under which the tool has been calibrated a large and irregular hole diameter and a lack of eccentralization both produce erroneous porosity readings the effect of hydrous alteration minerals on the thermal neutron porosity log has been estimated from 922 core oxide measurements using an analysis program that calculates the slowing down length and converts it into apparent porosity the results show that the computed apparent porosity ranges from less than 1 in fresh basalts and gabbros to about 30 in highly altered units depending on the alteration mineral assemblage natural gamma ray capture cross section or hydrogen logs have been used to continuously predict the effect of bound hydrogen at each site corrected porosities generally show excellent agreement with core data for massive units whereas they are higher for pillow basalts and fractured zones the discrepancy is interpreted as the result of 1 difference in the volume of rock investigated core specimens do not sample large vugs and fractures and 2 frequent variations in the hole size and lack of tool contact with the borehole wall standoff not completely accounted for in the corrections high capture cross section values measured on selected basalt samples seem to be associated with more altered basalts suggesting a larger concentration of strong neutron absorbers in secondary minerals the concentrations of elements with large capture cross section measured at three of the five sites studied yield a maximum increase of 1 in the apparent neutron porosity this is too low to explain the porosity values some greater than 7 observed in some of the fresh and unfractured massive units a 1 to 2 inch standoff due to the lack of eccentralization of the tool string used in the ocean drilling program is considered the most probable cause of such discrepancy this interpretation is confirmed by the neutron porosity values recorded at site 735 where the nuclear string was for the first time fully eccentralized and only a correction for borehole size and the presence of hydrous minerals has been applied

inversion of earth s changing shape to weigh sea level in static equilibrium with surface mass redistribution 1 we develop a spectral inversion method for mass redistribution on the earth s surface given geodetic measurements of the solid earth s geometrical shape using the elastic load love numbers first spectral coefficients are geodetically estimated to some degree spatial inversion then finds the continental surface mass distribution that would force geographic variations in relative sea level such that it is self consistent with an equipotential top surface and the deformed ocean bottom surface and such that the total ocean plus continental mass load has the same estimated spectral coefficients applying this theory we calculate the contribution of seasonal interhemispheric degree 1 mass transfer to variation in global mean sea level and nonsteric static ocean topography using published gps results for seasonal degree 1 surface loading from the global igs network our inversion yields ocean continent mass exchange with annual amplitude 2 92 0 14 1015 kg and maximum ocean mass on 25 august 3 days after correction for the annual variation in global mean vertical deformation of the ocean floor 0 4 mm amplitude we find geocentric sea level has an amplitude of 7 6 0 4 mm consistent with topex poseidon results minus steric effects the seasonal variation in sea level at a point strongly depends on location ranging from 3 to 19 mm the largest being around antarctica in mid august seasonal gradients in static topography have amplitudes of up to 10 mm over 5000 km which may be misinterpreted as dynamic topography peak continental loads occur at high latitudes in late winter at the water equivalent level of 100 200 mm

the self consistent dynamic pole tide in non global oceans summary fluid dynamic theories of the pole tide are in conflict with pole tide observations the former predict that the oceanic response to the chandler wobble should be nearly static while the latter reveal the tide to possess significant non equilibrium characteristics resolution of the conflict would determine whether mantle anelasticity or non equilibrium oceans is responsible for a measurable contribution to the chandler period it is possible that resolution might be achieved through a more exact mathematical investigation of pole tide fluid dynamics than theories have carried out to date the theories have also neglected to consider a unique property of the pole tide its ability to lengthen the period of its own forcing function this property implies that the pole tide characteristics and effects on wobble cannot be correctly determined unless the tide and wobble equations are jointly solved this work constitutes a first attempt to determine accurately and self consistently the nature of the pole tide and its effects on the chandler wobble the laplace tidal equations modified by the addition of bottom friction but with no simplifying approximations are employed together with the liouville equations to elucidate pole tide characteristics this work is a first attempt because the earth model chosen is a crude one consisting of global oceans of uniform depth overlying a rigid mantle with a fluid core results for this model suggest that departures of the pole tide from equilibrium may indeed be minimal the relevance of these results to the actual pole tide however must await the application of our self consistent and more exact dynamical theory to the situation of realistic oceans

physical properties of 110 ma oceanic crust at site osn 1 implications for emplacement of a borehole seismometer an extensive suite of downhole geophysical logs was acquired through a 70 m thick section of basalt drilled by the ocean drilling program odp into 110 ma oceanic crust 225 km sw of hawaii these data include standard sonic electrical and nuclear logs as well as electrical and acoustic images of the wellbore and enable a vertically continuous characterization of the physical properties of shallow old oceanic crust fracture porosity and alteration increase with depth in this hole and consid ered together with results obtained elsewhere in both young and old 5 to 110 ma crust suggest that physical proper ties gradients in the uppermost few hundred meters of oceanic basement are controlled by crustal morphology and alteration and are ubiquitously variable as this hole was drilled primarily for pilot experiments at the first site of the ocean seismic network evaluation of the log data demon strates the importance of careful in situ data collection in order to emplace a broadband monitoring device below the seafloor for long term seismic measurements

another look at north sea pole tide dynamics summary in this research note we re evaluate the mechanism proposed by wunsch to explain pole tide observations in the north sea that mechanism included bottom topography and bottom friction with a constant drag coefficient and the sea shallowing to the south the dynamics yielded an eastward intensification of the tide height reminiscent of observations errors subsequently brought to light have left the proposal with uncertain status we have found that a general solution to the tide equations is possible without approximation after slight modification of wunsch s model the unknown coefficients of the solution are determined through a boundary condition at the open edge of the sea which corresponds to forcing by a non equilibrium pole tide in the adjacent atlantic however although the boundary condition is physically plausible as a constraint for these tide equations it allows multiple determination of the coefficients in every case dissipation by the tidal currents greatly exceeds the total dissipation of chandler wobble energy the extreme dissipation and the solution non uniqueness both reflect the inability of the solution to satisfy the open boundary condition and imply that the original tidal equations themselves provide an inadequate description of north sea dynamics the nature of the difficulties suggests an analogy with stokes paradox and implies that resolution of the problem may be achieved by inclusion of inertial terms in the tidal equations

some results of heterogeneous data inversions for oceanic tides many different instruments directly or indirectly observe the oceanic tidal movements among them we consider here the coastal tide gauge and deep sea pressure recorder which provide at least the principal spectral constituents of the tidal height the gravimeter which indirectly observes the oceanic tides through the gravitational effect generated by the deformation of the solid earth under the ocean tidal mass load and the satellite altimeter which samples the tides in the time domain and over the nearly whole ocean our present paper deals with an empirical method for the recovery of the oceanic tides by inversion of heterogeneous data sets the aim is to take advantage of the different kinds of information coming from the measurement instruments in order to complete more accurate empirical solutions first tide gauge and gravity loading data are separately and jointly inverted to provide global charts of the major semidiurnal m2 wave the results prove that the tide gauge data have a major contribution in the tidal mapping but also suggest that the gravity loading data distort the information this is certainly due to unmodelled geophysical phenomena and instrumental errors second tide gauge and satellite altimeter data are considered in a separate and a joint inversion computation to provide tidal estimations along a predefined geographical line in the north atlantic the results are accurate enough to make provision for the boundary conditions of an hydrodynamical tidal model as an intrinsic advantage of the inversion method a posteriori standard deviations and error covariances for all the solutions displayed are provided and analyzed

long period tides observed with a superconducting gravimeter at syowa station antarctica and their implication to global ocean tide modeling abstract the long period tides mf and mm waves were analyzed with the 2 years data obtained with a superconducting gravimeter sg installed at syowa station 69 0 s 39 6 e antarctica the observed amplitudes phase lags and amplitude factors factors were 11 642 0 035 gal 0 12 0 17 and 1 1218 0 0034 for the mf wave and 6 143 0 058 gal 0 33 0 54 and 1 1205 0 0106 for the mm wave respectively 1 gal 10 8 m s 2 the ocean tide effects effects of the attraction and loading due to the ocean mass at the observation site were estimated using the five global ocean tide models equilibrium ocean tide model schwiderski model schwiderski e w 1980 on charting global ocean tides rev geophys space phys 18 243 268 dickman model dickman s r 1989 a complete spherical harmonic approach to luni solar tides geophys j int 99 457 468 csr model eanes r j 1995 private communication and desai and wahr model desai s h wahr j m 1995 empirical ocean tide models estimated from topex poseidon altimetry j geophys res 100 25205 25228 the averages of the five estimates are 0 433 gal and 0 244 gal in amplitude and 192 9 and 179 5 in phase for the mf and mm waves respectively the five estimates differ by a maximum of 0 104 gal in amplitude and 18 8 in phase for the mf wave and by 0 033 gal and 6 4 for the mm wave the estimated mm phases are nearly 180 for the five models and the variation of their values among the models is relatively small compared with that of the mf phases these indicate that the mm wave is much closer to an equilibrium tide than the mf wave due to the variation of the ocean tide corrections the corrected factors were scattered within the ranges of 1 158 to 1 169 for the mf wave and of 1 163 to 1 169 for the mm wave however it is noted that the mean factors of the five ocean models i e 1 162 0 023 for the mf wave and 1 165 0 014 for the mm wave prefer slightly larger value rather than those estimated from the theory of the elastic tide

the variation with frequency of the long period tides the oceanic response to long period tidal forcing in closed basins approaches equilibrium for periods much longer than a month for moderate values of dissipation at a given frequency the response is closest to equilibrium near the eastern wall of the basin global calculations of the mf and mm tides made using a 2 2 grid are presented changes in the length of day have also been computed for these tides

measurements of attenuation from vertical seismic profiles values of attenuation have been extracted from five detailed velocity surveys significant amounts of attenuation are observed in all five wells measured values of attenuation vary by a factor of 10 ranging from less than 0 1 to 0 9 db wavelength correlation of attenuation with lithology is good considering the resolution limits of the surveys one of the surveys was performed in west texas and the other four were carried out in the gulf coast area the total number of recording depths in each survey varied from 31 to 208 with downhole recordings taken every 10 or 20 ft over key stratigraphic zones in all five surveys a monitor geophone was placed near the well to check for source consistency our procedure for measuring attenuation involved constructing the spectral ratio between each downhole pulse and one particular reference pulse a value of cumulative attenuation ca was then extracted from each spectral ratio and plotted as a function of geophone depth this method allowed us to use many m

simulation of ground accelerations for the may 1980 mammoth lakes california earthquakes abstract strong motion accelerograms from the may 1980 mammoth lakes earthquake sequence are used to support the technique of estimating near source ground motion by the summation of existing records an sma 1 record recovered 3 km from the epicenter of the first magnitude m l 6 earthquake in the mammoth lakes sequence 25 may 16 33 44 utc is simulated by the summation of records from later events the source time history on which this summation is based comes from a study of the teleseismic p waves the summation method has several distinct advantages it is easy to apply inexpensive costly wave propagation codes are not needed and source to receiver propagation effects are automatically included the method however requires a good data base from which to perform the summation

pseudoreflection profiling method an efficient complement to cdp method1 a method for pseudoreflection profiling prp is presented by using transmission seismograms this method produces time sections similar to those obtained using the common depth point cdp method pseudoreflection profiles are obtained using the following procedure equivalent transmission responses at sites on soft deposits are derived by wiener filter estimation using seismograms acquired on the sites and on the basement rock these responses are substituted into the claerbout kunetz equation to obtain the pseudoreflection profiles a 3d subsurface model is produced when the prp method is applied to explosion seismograms the time sections thus obtained are consistent with those obtained using the cdp method in a neighbouring area the maximum station interval for obtaining coherent profiles with this method is estimated to be one quarter of the wavelength of the transmitted waves this technique should be used in combination with another method such as the cdp method because it has two weak points the velocity structure cannot be obtained directly and undesirable waves cannot be eliminated through processing