bluuebunny/crossref_metadata_2025_split huggingface dataset:
Generation of Langmuir waves by nonlinear wave‐wave interaction in the ionosphere
Authors: Cerisier J. C. , Lavergnat J. , Rihouey J. J. , Pellat R. 
Published: February 2008

The nonlinear interaction between two parallel high‐frequency electromagnetic waves can generate either an electron plasma wave or an extraordinary wave, depending upon the angle of propagation with the external magnetic field (either θ ≃0 or θ≠0). When propagating in the inhomogeneous ionosphere the extraordinary mode couples to the plasma wave and the results obtained in both cases turn out to be identical.The plasma wave can be detected from the ground through the enhancement of the amplitude of the plasma lines associated with the scattered spectrum of a third electromagnetic probing wave.The amplitude of the electrostatic plasma wave, and of the scattered plasma lines, are calculated. The rendezvous conditions (in time and in space) between the plasma wave pulse and the probing pulse are evaluated and discussed for the Eiscat sounder.
Height and latitude structure of electric fields and currents due to local east‐west winds in the equatorial electrojet
Authors: Reddy C. A. , Devasia C. V. 
Published: February 2008

Using the equivalent electrical circuit method for the theoretical treatment of the local wind effects on the equatorial electrojet, the height structures of electric fields and currents that are generated by height‐varying east‐west winds in the electrojet region have been calculated for theoretical model wind sturctures and for a variety of experimentally observed wind structures. The results bring out clearly the nature and extent of the local wind effects on the height and latitude structures of the equatorial electrojet.The more important conclusions of the present study are: (a) The vertical wind shears associated with tidal winds and gravity waves can generate significantly large electric fields and east‐west currents in the equatorial electrojet (EEJ). (b) The wind‐generated electric fields and currents are characterized by large height gradients, latitudinal gradients, and reversals of direction. (c) At the magnetic equator, wind‐generated electric fields and currents are often small (10%–30%) in comparison with the eastward electric‐field‐generated polarization field and east‐west currents around noon hours. (d) At geomagnetic latitudes of 3° and beyond the wind‐generated currents and electric fields often exceed those caused by the eastward electric field. (e) Beyond 2° the neutral winds can drastically alter the intensity and latitudinal structure of the EEJ, depending upon the magnitude and height location of the wind shear. (f) The observed variabilities in the ‘width’ and latitude structure of the EEJ can arise from the effects of such east‐west winds that have been observed experimentally.
Temporal variation of the activity of intermediate and deep focus earthquakes
Authors: Abe Katsuyuki , Kanamori Hiroo 
Published: February 2008

The appendix is available with entire article on microfiche. Order from American Geophysical Union, 1909 K Street, N.W., Washington, D.C. 20006. Document J79‐003; $1.00. Payment must accompany order.The temporal variation of the activity of intermediate and deep focus earthquakes for the period from 1904 to 1974 is investigated on the basis of a uniform body‐wave magnitude scale. The mb scale has been traditionally used for intermediate and deep focus earthquakes. However, the period of seismic waves and the Q function used for the magnitude determination have changed as a function of time, so that uniform evaluation of the activity is difficult. In this study, we used a body‐wave magnitude mB determined from the maximum amplitude of body waves recorded by broad‐band or long‐period instruments to investigate the temporal variation. For the period from 1904 to 1952, mb values were calculated from the unpublished material of Gutenberg and Richter. For 1953 to 1958, mB values were calculated from the amplitude and the period data in Gutenberg's unpublished file. For the period from 1959 to 1974, seismological bulletins from various stations were used to determine mB. Consistency between the values of mB calculated from these different sources was carefully checked. The temporal variation of the number of intermediate‐deep events with mB ≥ 7 is remarkably similar to that of shallow earthquakes with Ms ≥ 7. The temporal variation of the energy release in intermediate‐deep earthquakes shows a maximum around 1910. The sum of the energy release curve of intermediate‐deep and shallow earthquakes shows a good correlation with the amplitude of the Chandler wobble. The energy release becomes maximum at the depth of 350 and 600 km.
Reevaluation of the turn‐of‐the‐century seismicity peak
Authors: Kanamori Hiroo , Abe Katsuyuki 
Published: February 2008

According to currently available seismicity catalogues, seismicity (for example, the number of events with Ms ≥ 8) around the turn of the century, from 1897 to 1906, was significantly higher than in recent years. However, the magnitudes of the earthquakes which occurred during this period were determined by Gutenberg, who used the records obtained by the undamped Milne seismograph with the assumption that the effective magnification is 5. Because of saturation of the Milne seismogram for very large events used by Gutenberg for calibration, the gain (=5) used by Gutenberg could have been underestimated, and therefore the magnitude overestimated. Because of the lack of damping, the magnification of this instrument needs to be calibrated carefully. In order to calibrate the instrument response, a Milne seismograph was constructed and has been in operation side by side with damped seismographs at Pasadena. Eleven events have been recorded since February 1977. On the basis of (1) comparison of the amplitudes measured on the Milne seismograms with those of the standard seismograms, (2) numerical experiments simulating the response of the Milne seismographs to surface waves, and (3) examination of Gutenberg's original materials used for the calibration, we conclude that the average effective gain is as large as 20 for very large earthquakes, resulting in systematic reduction of the magnitude of up to 0.6. This reduction is large enough to suggest that the turn‐of‐the‐century seismicity peak is of marginal significance.Tables are available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document J79‐006; $01.00. Payment must accompany order.
Distance corrections for single‐ and dual‐color lasers by ray tracing
Authors: Berg Eduard , Carter Jerry A. 
Published: February 2008

The appendix is available with entire article on microfiche. Order from the American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document J80‐007; $1.00. Payment must accompany order.The physical arc length difference between the red and blue beam of a dual‐color laser generates an error term in determining Δn (and thus n, the refractive index, and D, the line length). Numerical ray trace examples and theoretical approximations show the resulting relative error ΔD/D to increase as D2. The error reaches 1 part in 108 (107) at D of 12 (40) km, respectively, through an atmospheric structure of a line with Δh ≅ 2000 m. Error reduction by a factor of nearly 10 is possible by using the pressure, temperature, and humidity of both endpoints to calculate n or, to a lesser degree, by assuming a standard coefficient of refraction k. Two lines, approximately 30 km each, with Δh of 2000 and 3000 m, were sampled by helicopter on the island of Maui through an inversion layer. The two ray trace lengths were compared to standard reductions. Hypothetical shorter and longer lines through the same atmospheric structures and elevation difference Δh are also reduced by both methods. Length differences from the two methods appear at 10−7 level for lines longer than 60 km and depend on the sharpness of the temperature inversion. The dual zenith angle method of determining Δh would yield errors of the order of 60 cm for the real line.
Preseismic and coseismic deformation associated with the Coyote Lake, California, earthquake
Authors: King N. E. , Savage J. C. , Lisowski M. , Prescott W. H. 
Published: February 2008

Supplement is available with entire article on microfiche. Orderfrom American Geophysical Union, 2000 Florida Avenue, N.W.,Washington, D.C. 20006. Document J79‐008; $01.00. Payment mustaccompany order.The Coyote Lake earthquake (ML = 5.9; August 6, 1979; epicenter about 100 km southeast of San Francisco) occurred on the Calaveras fault within a geodetic network that had been surveyed annually since 1972 to monitor strain accumulation. The rupture surface as defined by aftershocks is a vertical rectangle 20 km in length extending from a depth of 4 km to about 12 km. The observed deformation of the geodetic network constrains the average slip to be about 0.33 ± 0.05 m right lateral. Although the geodetic data furnished an exceptionally detailed picture of the preearthquake deformation, no significant premonitory anomaly associated with the Coyote Lake earthquake can be identified.
The Galapagos Spreading Center at 86°W: A detailed geothermal field study
Authors: Green Kenneth E. , Von Herzen Richard P. , Williams David L. 
Published: February 2008

Appendix is available with entire article on microfiche. Orderfrom American Geophysical Union, 2000 Florida Avenue, N.W.,Washington, D.C. 20009. Document J80‐013; $01.00. Payment mustaccompany order.We report here measurements of the heat flow field of the Galapagos Spreading Center on crust of age less than 1.0 m.y. The 443 measurements in an area of about 570 km2 reveal the general planform of the geothermal flux and permit the first truly areal estimate of the near‐axis conductive heat flux. The intrusion process and associated hydrothermal circulation dominate the surface heat flow pattern, with circulation apparently continuing beyond the limits of our survey. The areal average of the conductive heat flux is 7.1 ± 0.8 HFU (295 ± 33 mW/m2), about one‐third the heat flux predicted by plate models. The remaining heat is apparently removed by venting of hydrothermal waters at the spreading axis and through basalt outcrops and hydrothermal mounds off axis. The pattern of surface heat flux is lineated parallel to the axis and the strongly lineated topography. Sharp lateral gradients in the heat flow, greater than 10 HFU/km near escarpments and commonly expressed as high heat flow at the tops of the scarps and lower heat flow in the valleys, may indicate a local concentration of the circulation by surface fault systems and/or variable sediment thickness.
Constraints on the seismic wave velocity structure beneath the Tibetan Plateau and their tectonic implications
Authors: Chen Wang‐Ping , Molnar Peter 
Published: February 2008

We combine observations of group and phase velocity dispersion of Rayleigh waves, of the waveform of a long‐period PL phase, of Pn and Sn velocities from unreversed refraction profiles using earthquakes, and of teleseismic S‐P travel time residuals to place bounds on the seismic wave velocity structure of the crust and upper mantle under Tibet. From surface wave measurements alone, the Tibetan crustal thickness can be from 55 to 85 km, with corresponding uppermost mantle shear wave velocities of about 4.4 to 4.9 km/s, respectively. The Pn and Sn velocities were determined to be 8.12±0.06 and 4.8±0.1 km/s, respectively, using travel time data at Lhasa from earthquakes in and on the margins of Tibet. Combining these results, the crustal thickness is most likely to be between 65–80 km with an average shear wave velocity in the upper crust less than 3.5 km/s. A synthesis of one PL waveform does not provide an additional constraint on the velocity structure but is compatible with the range of models given above. In contrast to observations obtained for eight earthquakes in the Himalaya, measurements of both teleseismic S and P wave arrival times for nine earthquakes within Tibet show unusually large intervals between P and S compared with the Jeffreys‐Bullen Tables. Thus the Pn and Sn velocities apparently do not reflect high velocities in the mantle to a great depth beneath Tibet. From the dependence of the seismic velocities of olivine on pressure and temperature and from the similarity of the measured Pn and Sn velocities beneath Tibet and beneath shields and platforms, the velocities at the Moho beneath Tibet are compatible with the temperature being 250°–300° higher than beneath shields and platforms, i.e., 750°C if the temperature beneath the platforms is close to 500°C. Such a temperature could reach or exceed the solidus of the lower crust. Simple one‐dimensional heat conduction calculations suggest that the volcanic activity could be explained by the recovery of the geotherm maintained by a mantle heat flux of about 0.9 HFU at the base of the crust. If the distribution of radioactive heat production elements were not concentrated at the top of the crust, radioactive heating could also contribute significantly to the recovery of the geotherm and thus lower the required mantle heat flow. Thus the idea of a thickened crust in response to horizontal shortening is compatible both with these data and with these calculations.Appendices are available with entire article on microfiche. Order from the American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document J81‐004; $1.00. Payment must accompany order.
Velocity‐density properties of the lithosphere from three‐dimensional modeling at the Geysers‐Clear Lake Region, California
Authors: Oppenheimer David H. , Herkenhoff Ken E. 
Published: February 2008

The analysis of travel time delays from 94 teleseisms recorded at The Geysers‐Clear Lake, California, region reveals a broad area of delay centered at Mount Hannah and encompassing The Geysers geothermal field. A three‐dimensional velocity inversion of the delays indicates that the source of the delays is a low‐velocity body largely within the top 30 km of the lithosphere. Velocity decreases of as much as 20% are observed in the top 15 km near Mount Hannah and diminish with depth. No significant velocity fluctuations are observed below 60 km. The block model of velocity perturbations resulting from the teleseismic residual inversion is used to predict the observed Bouguer gravity field by solving for the relation between velocity and density perturbation. Comparison between the predicted gravity and observed gravity indicates that the same body responsible for the teleseismic delays accounts for the long‐wave‐length 30‐mGal Bouguer gravity minima at Mount Hannah. The results of the velocity‐density modeling suggest that the material beneath Mount Hannah and The Geysers may be partially molten and somewhat more silicic than the surrounding medium.Supplemental table is available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document J81‐006; $1.00. Payment must accompany order.
Seasonal carbon dioxide exchange between the regolith and atmosphere of Mars: Experimental and theoretical studies
Authors: Fanale Fraser P. , Banerdt W. Bruce , Saunders R. Steven , Johansen L. A. , Salvail James R. 
Published: February 2008

Measurements of the rate of penetration of a CO2 ‘pressure wave’ through basalt‐clay soils have been conducted under conditions of PCO2 (∼6 mbar), ΔPCO2 (∼2 mbar), soil density (ρ ∼ 1.3), and T (−40° to −70°C) which simulate the penetration of the cap‐induced seasonal CO2	pressure wave through the topmost regolith on Mars. Results suggest that existing theoretical models for diffusion of a gas through a porous, highly adsorbing medium may be reliably used to assess the importance of Martian seasonal regolith‐atmosphere CO2 exchange. Results also suggest that although Mars topsoils with a substantial component of fine‐grained weathering products could harbor, within a few meters of the surface, a substantial fraction of the atmospheric CO2 inventory, seasonal cap‐atmosphere CO2 exchange is still much more important than seasonal regolith‐atmosphere exchange. This is so because the high adsorptive capacity of such soils greatly slows CO2 diffusion through them owing to the typically high ratio of mean residence time for CO2 in the (static) adsorbed phase to that in the pore gas at T
−40°C. At such temperatures, typical of the Martian regolith, the CO2 diffusivity of such soils may be ∼1 × 10−2 cm2 s−1—only somewhat higher than the thermal diffusivity and not high enough to allow seasonal isothermal regolith buffering of the cap‐induced CO2 pressure wave to be effective. On the other hand, even the adsorption‐slowed diffusivities are still high enough to allow thermally driven regolith atmosphere exchange to be effective on a time scale of the obliquity cycle (∼105 yr). We also examined the maximum effect of thermally driven exchange between the topmost seasonally thermally affected regolith and the atmosphere. While of somewhat greater potential importance than the isothermal exchange, the thermally driven exchange would be recognizable only if the pressure wave from CO2 thus exchanged at high latitudes did not propagate though the atmosphere at a faster rate than that at which the exchange itself occurred—an unreasonable assumption. Our results are insensitive to soil geometry and temperature and suggest that both isothermal and thermally driven regolith‐atmosphere seasonal CO2 exchange effects are likely to be greatly dominated by cap‐atmosphere exchange. In principle, it is conceivable that a more profound understanding of the cap‐atmosphere‐regolith interaction could eventually allow us to use the externally imposed pressure waves as a natural experiment to set limits on global or regional soil properties. However, the regolith effects, while quite possibly dominant for H2O, are seemingly too weak and too complex for CO2 to allow this to be accomplished.
Seismicity and aseismic slip along the Eltanin Fracture Zone
Authors: Stewart Lisa M. , Okal Emile A. 
Published: February 2008

Table Al is available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue N.W., Washington, DC 20009. Document B83‐006; $2.50. Payment must accompany order.The seismic history of the Eltanin Fracture Zone on the Pacific‐Antarctic Ridge for the years 1920–1981 shows that the seismic slip accumulated during this recording interval accounts for only a small fraction (less than 10%) of the amount of slip predicted by kinematic models of plate motion. We propose that the remainder of the plate motion along the transform faults making up the Eltanin system occurs as aseismic creep. This property singles out the Eltanin among transform systems, where previous studies have found good agreement between seismic slip and predicted rates of motion. The absence of record of any gigantic earthquakes and the geometry of the fault area reduce the likelihood of the Eltanin rupturing along its entire length. We interpret the Eltanin Fracture Zone in the light of an “asperity” model, involving small, well‐separated asperities. Its segmented nature and creeplike behavior may be due to the presence of excess magma and, possibly, local upwelling, which could also be involved in the mechanism of generation of the Louisville Ridge.
The May 18, 1980, eruption of Mount St. Helens: 3. Stability and chemistry of amphibole in the magma chamber
Authors: Rutherford Malcolm J. , Devine Joseph D. 
Published: February 2008

Additional experiments have been done with the May 18, 1980, Mount St. Helens dacite and a more mafic, October 1980 sample to resolve questions concerning amphibole stability and dissolved volatiles in the magma chamber prior to the May 18 eruption. The experiments were done at 920°C, at fluid pressures of 220 or 320 MPa, and, in contrast to previous work, at an ƒO2 between the NNO and MnO‐Mn3O4 oxygen buffers. Fe‐Ti oxides are present in the melt under these conditions, and amphibole is stable when XH2O in the fluid is greater than 0.67. The An content of plagioclase in equilibrium with melt decreases with decreasing XH2O in the fluid and, in the amphibole‐bearing experiments, reaches the natural plagioclase rim compositions (An49) at an XH2O of 0.67. Under these H2O‐undersaturated conditions the experimentally produced amphibole, low‐Ca pyrpxene, and Ca‐rich pyroxene are compositionally equivalent to phenocrysts in the May 18 white pumice. The melts (glasses) in amphibole‐bearing experiments range from the average plagioclase melt inclusion composition [Rutherford et al., 1985] to slightly less evolved compositions as XH2O approaches 1.0.Melt inclusions in natural amphiboles were analyzed, and the compositions were plotted on SiO2 variation diagrams along with experimental glass analyses. The amphibole melt inclusions define a liquid line of descent for the magina which extends from relatively primitive compositions (68 wt % SiO2, anhydrous basis) to the more evolved average plagioclase melt inclusion composition (73 wt % SiO2). The volatile content of the amphibole melt inclusions (difference method) reaches 5.0±0.5 wt %, which compares favorably with the volatile content of the amphibole‐bearing experimental melts produced at XH2O = 0.67.
Introduction: The practice of physical oceanography
Authors: Jennings Feenan D. , Nowlin Worth D. 
Published: February 2008

The papers appearing in this special issue of JGR‐Oceans were among approximately 30 presentations made in April 1983 at a symposium honoring Robert O. Reid of Texas A&M University. The authors are his former students and colleagues.The 2‐day symposium, called the Practice of Physical Oceanography, was convened by Reid's former students to honor him for his “exceptional guidance of graduate students” in his more than 30 years at Texas A&M University. The symposium was planned and organized by Feenan D. Jennings, Executive Director, Office of University Research Services, Texas A&M University; A. D. Kirwan, Jr., University of South Florida,; and William J. Merrell, Jr., and Worth D. Nowlin, Jr., Department of Oceanography, Texas A&M University.
Barium, equatorial high productivity, and the northward wandering of the Indian continent
Authors: Schmitz Birger 
Published: February 2008

High concentrations of biologically precipitated barite characterize the deep‐sea sediments underlying the equatorial high‐productivity belt of the Indian Ocean. By studying the barium distribution in five Deep Sea Drilling Project cores (213–217), drilled in the eastern Indian Ocean north of and below the present high‐productivity zone, it is possible to determine the times when the different coring sites passed beneath the zone. From this information, net northward spreading rates of the Indian plate can be deduced. The results suggest that northward movement was very rapid during the early and middle Paleogene, slow during the mid‐Cenozoic, and then rapid again from the Late Miocene onwards. The Late Miocene revitalization of active seafloor spreading south of the Indian continent coincides with the main phase of the Himalayan uplift.Supplemental tables are availablewith entire article on microfiche. Orderfrom American Geophysical Union, 2000Florida Avenue, N. W., Washington, D. C.,20009. Document P86‐002; $2.00. Paymentmust accompany order.