bluuebunny/crossref_metadata_2025 huggingface dataset:
Spreading rates and heat flow
Authors: Harrison C. G. A.
Published: February 2008

It has been proposed that the cause of the Cretaceous transgression may be found in the volume of ridge crest material. High spreading rates produce a greater volume of material, which displaces sea water and causes flooding of the continents. A direct corollary of this is that the average oceanic heat flow during these times of high sea level must be greater, since heat flow is closely connected to oceanic age and thus crustal elevation. Calculations show that at 85 m.y.b.p. the average oceanic heat flow was 1.35 times its present value. Variations of average oceanic heat flow must be taken into account in any model of mantle convection.
Limit on rotational energy available to excite Jovian aurora
Authors: Eviatar Aharon , Siscoe George L.
Published: February 2008

There is a fundamental relationship between the power that is extracted from Jupiter's rotation to drive magnetospheric processes and the rate at which mass is injected into the Io plasma torus. Half of this power is consumed by bulk motion of the plasma and the other half represents an upper limit on the energy from rotation available for dissipation and in particular to excite the Jovian aurora. Since the rotation of the planet is the only plausible source of energy, the power inferred from the observed auroral intensities requires a plasma injection rate of 2.6 × 1029 AMU/sec or greater. This in turn leads to a residence time of a torus particle of 48 d. or less. These results raise doubts about the applicability of equilibrium thermodynamics to the determination of plasma parameters in the Io torus.
Viscoelastic membrane tectonics
Authors: Dickman S. R. , Williams David R.
Published: February 2008

The theory of membrane tectonics proposed by Turcotte and Oxburgh [1973] to explain intraplate tensional features and earthquakes, and developed by Turcotte [1974] for an elastic lithospheric membrane, is extended to the case of a viscoelastic lithosphere. Such an extension may be expected to seriously modify the theory since, for all lithospheric viscosities except the very highest, the time scale for viscous relaxation is comparable to the time scale for changes in plate curvature. It is found that for most viscosities considered, the membrane stresses generated by changes in plate curvature do not exceed ∼10² bars. We conclude that either the effective viscosity of the lithosphere is much higher than indicated by most studies, or membrane tectonic stresses play a secondary role in the generation of intraplate features and earthquakes.
Meteorological effects on the seasonal variations of the rotation of Mars
Authors: Cazenave Anny , Balmino Georges
Published: February 2008

We have investigated the meteorologically induced seasonal variations in the rotation rate of Mars. As on Earth, meteorological effects are expected to produce fluctuations in the rotation of Mars but unlike on Earth, where zonal winds are the major contributors, on Mars seasonal variations are mainly the result of exchange of CO2 between atmosphere and polar caps through a variation of the polar moment of inertia.

From Viking pressure data and zonal winds models by Haberle et al. [1979] we predict an annual and a semi‐annual cycles in the relative rotation rate of Mars of amplitude ∼ 0.2 × 10−8 and 0.1 × 10−8 respectively. On the length of the martian day these seasonal changes are 0.17 ms and 0.09 ms respectively. Between the fall equinox and winter solstice (northern hemisphere), the maximum change in the martian l.o.d. amounts to 0.44 ms.
Plate tectonics on Venus
Authors: Anderson Don L.
Published: February 2008

The high surface temperature of Venus implies a permanently buoyant lithosphere and a thick basaltic crust. Terrestrial style tectonics with deep subduction and crustal recycling is not possible. Overthickened basaltic crust partially melts instead of converting to eclogite. Because mantle magmas do not have convenient access to the surface the 40Ar abundance in the atmosphere should be low. Venus may provide an analog to Archean tectonics on the Earth.
Radium‐226 and radon‐222 in southern California groundwaters: Spatial variations and correlations
Authors: Chung Yu‐Chia
Published: February 2008

As part of the radon and helium monitoring program for earthquake prediction studies in Southern California, concentrations of radium‐226 in groundwaters have been measured along the major fault zones including the Palmdale area. Radium was measured in order to obtain information on its spatial variation as well as baseline levels. Several measurements were made at selected sites to examine their temporal variations. Radium concentrations are used to define the portion of radium supported radon in the observed groundwater radon. Radium levels vary spatially by 4 orders of magnitude (0.015 to 146 dpm/kg), but temporally by a factor of 2 or less. Similar spatial and temporal variations are observed in groundwater radon (60 to 46,700 dpm/kg). The radon/radium activity ratio ranges from 10 to 105. These values indicate that radon is in large excess over radium in groundwaters because of radon diffusion from the ambient rocks. The spatial variations of radon, radium and the activity ratio are probably due to different chemical and physical properties of the rocks through which groundwaters flow.

The dependence of groundwater radium concentrations on the water temperature and conductivity is explored. It appears that radium increases in general with conductivity but not necessarily with temperature. Radium is probably leached more readily into the groundwater when the water is more conductive with more dissolved chemical constituents.
Radon and hydrologic anomalies on the Rough Creek Fault: Possible precursors to the M5.1 Eastern Kentucky Earthquake, 1980
Authors: Steele S. R.
Published: February 2008

Soil radon emanation increased sharply on the Rough Creek fault near the Illinois‐Kentucky border in April, 1980, 3 1/2 months before a M5.1 earthquake in eastern Kentucky, July 27, 1980. The spikelike anomaly was similar to a radon anomaly in the New Madrid seismic zone in 1979 that preceded by 2 months a M3.9 tremor at the site of that anomaly. Weekly radon monitoring was initiated on the Rough Creek fault after abrupt cessation of spring flow on the fault occurred at a site that had experienced similar flow cessation 1 month prior to a M5.3 earthquake in southeastern Illinois in 1968. Although the recent Kentucky epicenter was 380 km east of the site of the detected radon anomaly, factors relating to regional structures, recent seismicity, additional radon data, and the stress regime suggest that the hydrologic and radon anomalies may have been precursors to an eastward progression of strain that culminated in the eastern Kentucky tremor.
Dislocation model for radon response to distant earthquakes
Authors: Fleischer Robert L.
Published: February 2008

If radon changes associated with earthquakes are caused by changes in strain within the earth, reports of radon signals that are measured at considerable distances from the hypocenters of earthquakes can be understood. A simple dislocation model leads to estimates of distances that increase to hundreds of kilometers at earthquake magnitudes of 5 and above. The essential components of the theory are that the strain from a dislocation loop varies at large distances x as x−3, while the strains increase with the magnitude of the earthquake represented. A threshold sensitivity is inferred from radon measurements associated with earthquakes near Blue Mountain Lake, New York. The usefulness of a global 222Rn‐monitoring network is inferred.
Observations of large scale steady magnetic fields in the nightside Venus ionosphere and near wake
Authors: Luhmann J. G. , Elphic R. C. , Russell C. T. , Slavin J. A. , Mihalov J. D.
Published: February 2008

Pioneer Orbiter Magnetometer observations during the few minutes surrounding nightside periapsis traversals generally show a weak average field of magnitude <10 gammas between ∼200 km and the periapsis altitude of ∼150 km except when either 1) the local solar wind dynamic pressure is high or 2) the spacecraft is in a ∼70° wide solar zenith angle range, which includes the midnight meridian and is centered west of it at ∼1 hr local time. Both the direction and magnitude of the low altitude weak field vary irregularly along the orbit on apparent spatial scales of 1‐1000 km, the peak value of the field magnitude remaining under ∼20 gammas. When the local solar wind dynamic pressure exceeds ∼5 × 10−8dynes cm−2average low altitude fields of up to ∼40 gammas with a primarily horizontal orientation are observed in the regions adjacent to the terminator. In contrast, within ∼35° of the antisolar point where the average magnetic field is typically higher (∼10‐20 gammas), the field magnitude does not exhibit a similar correlation with incident solar wind dynamic pressure. Moreover, it is found that the radial component may exceed 60% of the total field magnitude. Closer inspection of the data near the antisolar point indicates that the radial fields are frequently related to the observation at higher altitudes of extended regions of radial field that reverse direction along the orbit. These results are consistent with the interpretation that a magnetotail‐like feature is sometimes present down to ionospheric altitudes on the nightside of Venus.
Water diffusion in quartz at high pressure: Tectonic implications
Authors: Blacic J. D.
Published: February 2008

An indirect method based on the effect of water on plastic deformation mechanisms in quartz is used to estimate water diffusion penetration depths at high pressure. Diffusivities calculated by this method are orders of magnitude greater than those determined at low pressure, and high‐pressure activation energy for water diffusion is three to five times greater than low‐pressure values. This implies very temperature‐sensitive hydrolytic weakening at deep crustal and upper mantle depths, potentially leading to a sharp mechanical decoupling of the lithosphere.
Direct measurement of lower atmospheric vertical potential differences
Authors: Holzworth R. H. , Dazey M. H. , Schnauss E. R. , Youngbluth O.
Published: February 2008

A high impedance system has been developed to make direct measurements of the atmospheric potential difference up to several thousand feet. A tethered balloon flown from Wallops Island, Virginia was used to loft a high voltage, insulated wire and a conducting collector in a test flight to 550 meters for two days of experiments in October 1980. The balloon was equipped with a payload to measure exact altitude, wind speed and direction, and other meteorological parameters. Electric potentials of 170,000 volts at 550 meters were measured. The collected currents which could be drawn through the wire by grounding the lower end were in the 10 microamp range indicating a system impedance of about 1010 ohms. This paper will describe the apparatus and details of these measurements.
The auroral plasma cavity
Authors: Calvert W.
Published: February 2008

A region of diminished plasma density has been found to occur at the source of auroral kilometric radiation (AKR). The density within this auroral plasma cavity, determined from limited Hawkeye wave data, was less than 1 cm−3 from 1.8 RE to 3 RE geocentric, at 70° ± 3° invariant magnetic latitude. The altitude variation of the magnetic field produces a minimum in the ratio of plasma frequency to cyclotron frequency within the cavity which accounts for the observed spectrum of AKR.
Peroxyacetyl nitrate (PAN) in the unpolluted atmosphere: An important reservoir for nitrogen oxides
Authors: Singh Hanwant B. , Hanst Philip L.
Published: February 2008

Based on the measured atmospheric distributions of ethane and propane (at midlatitudes in the northern hemisphere) and a simplified mechanism for their oxidation, it is predicted that acetaldehyde, acetone, and PAN [CH3C(O)OONO2] are ubiquitous components of the troposphere and the lower stratosphere. Average acetaldehyde concentrations (from ethane oxidation) of 22 parts per trillion (ppt), 3 ppt, and 7 ppt; average acetone concentrations (from propane oxidation) of 111 ppt, 15 ppt, and 3 ppt and average PAN concentrations of 17 to 34 ppt, 90 to 360 ppt, and 40 to 85 ppt are estimated for the lower troposphere (∼ 2 km), upper troposphere (∼ 9 km), and the lower stratosphere (∼ 15 km), respectively. These calculations suggest that in the troposphere, nitrogen oxides (NOx) contained in their organic form may be as much or more abundant as their inorganic form. This organic form of reactive nitrogen is in chemical equilibrium [CH3C(O)OONO2 ⇄ CH3C(O)OO + NOs] with inorganic NO2 and acts as reservoir of inorganic NOx. Measurement methods for PAN are currently available to verify these predicted results.
Anisotropic gradients in the upper mantle
Authors: Garmany Jan
Published: February 2008

Pn amplitudes in some widely spaced sets of orthogonal marine refraction lines on young oceanic crust are greater in the fast direction than in the slow direction. This is inconsistent with the predicted amplitude behavior for simple head waves, but can be explained by an increase in anisotropy with depth. It appears that these gradients are due to increasing olivine crystal orientation, although changes in the relative abundance of two anisotropic minerals without variable tectonization could also account for the observations. Depth variation of tectonization most probably indicates very high temperature gradients at the Moho. This would imply a substantial amount of convective heat transport in the whole oceanic crust near mid‐ocean rises.
Spectroscopic identification of CHCℓF2 (F‐22) in the lower stratosphere
Authors: Goldman A. , Murcray F. J. , Blatherwick R. D. , Bonomo F. S. , Murcray F. H. , Murcray D. G.
Published: February 2008

Infrared atmospheric spectra were obtained at ∼0.02 cm−1 resolution during a balloon flight made on 3/23/81. These spectra show an absorption feature near 829 cm−1 which we identify as due to CHCℓF2 (Fluorocarbon 22). A preliminary estimate from the sunset spectra shows approximately 100 pptv F‐22 near 15 km.
A satellite investigation of energy flux and inferred potential drop in auroral electron energy spectra
Authors: Menietti J. D. , Burch J. L.
Published: February 2008

A predicted relationship between auroral electron energy flux (ε) and the inferred accelerating potential drop (V) for accelerated Maxwellian distributions has been derived by R. Lundin and I. Sandahl. This relationship (ε∞V²) has been favorably tested with sounding rocket data by Lundin and Sandahl for the limiting case of eV/Ec»1 (where Ec is the characteristic energy of the accelerated Maxwellian distribution) and by L. Lyons for a single inverted‐V observed by the Injun 5 satellite. The study reported in this paper has utilized data from Atmosphere Explorer D to extend these studies over the range .2<eV/Ec<5 and for a wide range of latitudes and local times on both the nightside and the dayside. Our results show good agreement with the full accelerated Maxwellian model. We have further derived an analytical approximation to the electron energy flux which much better describes the data over the range .2<eV/Ec<3 than does the ε∞V² approximation. In addition, analyses of individual energy spectra at small and large pitch angles through well‐defined inverted‐V structures suggest that the altitude of the inferred potential drop maximizes near the center of the inverted‐V's.
Retrospective studies of unusual animal behavior as an earthquake predictor
Authors: Lott Dale F. , Hart Benjamin L. , Howell Mary W.
Published: February 2008

We systematically applied a retrospective interview approach to the study of unusual animal behavior prior to seven earthquakes in North, Central and South America. Data taken at some distance from two of the earthquakes provided a baseline rate of unusual animal behavior. In comparison to this baseline one earthquake was preceded by a significant increase in unusual animal behavior and four were not.
Ultrasonic studies on a basalt melt
Authors: Rai C. S. , Manghnani M. H. , Katahara K. W.
Published: February 2008

Compressional wave attenuation, Qp−1, and velocity, Vp, for an alkalic olivine basalt have been measured from 1250° to 1450°C and from 5 to 10 MHz by an ultrasonic interferometric technique. Vp shows no significant frequency or temperature dependence, and Qp−1 increases with increasing frequency and decreasing temperature. For the conditions of this study, the melt can be modeled as a viscoelastic material with a single thermally activated structural relaxation mechanism having an activation energy of 2.2 eV and a relaxation time on the order of 1 ns. The data presented here fall in the region of the relaxation spectrum where the frequency, f, is much smaller than the relaxation frequency, and the absorption coefficient is proportional to f². Analysis of the data suggests that (1) compressional wave losses will be negligible in a basalt melt at seismic frequencies, and (2) the volume viscosity of basalt melt is comparable in magnitude to shear viscosity.
Evidence for the acceleration of ionospheric O+ in the magnetosheath of Venus
Authors: Mihalov John D. , Barnes Aaron
Published: February 2008

Energetic ions (E/q ≃ 4 kV) in the magnetosheath near Venus, in the vicinity of the planet's terminator plane, have been detected by the plasma analyzer of the Pioneer‐Venus Orbiter. These ions have energy per unit charge consistent with O+, the most abundant ionospheric ion, moving at a speed somewhat slower than or comparable to the local magnetosheath speed. These ions are slowest and most intense at low altitudes. We interpret these observations as indicating that O+ is picked up by the magnetosheath plasma and accelerated up to the ambient proton flow speed within one Venus radius of the surface of the planet, and subsequently convected away through the wake of the planet.
Effects of diagenesis and clays on compressional velocities in rocks
Authors: Tosaya Carol , Nur Amos
Published: February 2008

Experimental results at ultrasonic frequencies in brine‐ or water‐saturated samples cut perpendicular to bedding demonstrate that compressional velocities vary linearly with porosity and volume‐fraction clay in detrital silicate rocks characterized by pores with low aspect ratios. P‐wave velocity is more sensitive to porosity than clay content, obeying the empirically derived expression Vp = −2.4C − 8.6ϕ + 5.8 at 800 bars confining pressure and 400 bars pore pressure, where the units of Vp are kilometers per second, ϕ is the volume fraction pores, and C is the volume fraction clay. Deviations from this equation are less than ± 2% with the exception of the high pore aspect ratio St. Peter sandstone, which has a compressional velocity that is 17% higher than the predicted value. The equation is insensitive to the chemical compostion of the dominant clay mineral and apparently insensitive to the location of the clay grains with respect to the mineral framework, e.g., in free pore space or in contact zones between mineral grains of lower compressibilities.
Oceanic penetration of excess CO2 in a cross section between Alaska and Hawaii
Authors: Chen Chen‐Tung A.
Published: February 2008

Results from the recent "CO2 Dynamics" cruise in the northeast North Pacific Ocean (June‐July, 1981) are presented. The shipboard CO2 data indicate that the excess CO2 has penetrated to the deepest depth (1000 ± 300 m( near the Subtropical Front but to a shallower depth outside of the Frontal Zone. In general, the depth of penetration is several hundred meters shallower than in the northwest Pacific.
MAGSAT scalar anomaly distribution: The global perspective
Authors: Frey Herbert
Published: February 2008

MAGSAT scalar anomalies are compared on a global basis with known geologic and tectonic structures. For many anomalies good geographic coincidences are found with some shields, cratons and platforms, sedimentary basins, deep oceanic abyssal plains, submarine plateaus and some subduction zones.
Crustal xenolith magnetic properties and long wavelength anomaly source requirements
Authors: Wasilewski Peter , Mayhew M. A.
Published: February 2008

Granulite xenoliths, probable components of the lower continental crust, are a primary source of information about the magnetization of the lower crust. Magnetization values for lower crustal xenoliths from three tectonic settings (converging plate margin, rift valley, and continental intraplate region) demonstrate that metabasic rocks in the granulite facies have magnetization values consistent with magnetizations inferred for modeled sources of long wavelength anomalies. Measured Curie points for granulite xenoliths are near 560‐570°C except for those from rift zones and other regions where anhydrous, probably reducing lower crustal conditions exist in a steep geothermal gradient. In samples from the reducing environments Curie points <300°C are measured. The lower crust could be the most magnetic crustal layer. Satellite magnetic anomalies may serve to delineate magnetization provinces which may be related to the tectonic and chemical evolution of continents.
Eccentric dipole coordinates for MAGSAT data presentation and analysis of external current effects
Authors: Wallis D. D. , Burrows J. R. , Hughes T. J. , Wilson M. D.
Published: February 2008

Magsat data provide an unequalled opportunity to study the magnetic field produced by currents external to the earth. Analyses of Magsat’s measurements are facilitated by an appropriately chosen magnetic coordinate system but existing coordinate systems are inappropriate. An eccentric dipole system based on Magsat measurements is presented which is useful both for positional information and data display. These two aspects must be carefully matched or unacceptable biases will be introduced. The proposed system facilitates intercomparison of Magsat measurements and numerical modelling results. Additionally the system permits a partial separation of magnetic field aligned currents, further facilitating external current analyses.
Transverse and parallel geomagnetic perturbations over the polar regions observed by MAGSAT
Authors: Iijima Takesi , Fukushima Naoshi , Fujii Ryoichi
Published: February 2008

MAGSAT data revealed the following characteristics of geomagnetic perturbations at high latitudes: Parallel (ΔB∥) and transverse (Δ
, especially geomagnetic east‐west component) magnetic perturbations represent respectively scalar potential field (due primarily to electric currents within the ionosphere) and vector potential field (attributable to field‐aligned currents and associated ionospheric currents). The spatial gradient of ΔB∥ is shown to be very useful to infer the ionospheric current distribution. The ratio of ΔB∥ and ΔB⊥ depends on the height of satellite measurement and also on the electric conductivity of the ionosphere.
Mechanism of induced seismicity at the Geysers Geothermal Reservoir, California
Authors: Allis R. G.
Published: February 2008

The Geysers reservoir is situated in a 60–80 km‐wide right‐lateral shear zone associated with the North American‐Pacific plate boundary. A small fraction of the shear may be occurring as permanent aseismic creep, which is being converted to stick‐slip movement in The Geysers reservoir due to steam production. Two mechanisms could be responsible for the induced seismicity: a large (>100 bars) increase in effective rock pressure; and an increase in the coefficient of friction. The first mechanism requires that the initial state of the reservoir be predominantly liquid‐dominated. The second mechanism is a consequence of dehydration of the reservoir causing both the ‘hardening’ of clay and fault gouge, and the precipitation of silica.
Associated lightning discharges
Authors: Mazur Vladislav
Published: February 2008

From observation of lightning activity in severe storms with VHF radar the echoes from lightning discharges following one another within a time interval typical for a multistroke cloud‐to‐ground flash and spaced in range by several km are designated "associated discharges". The hypothesis of association between lightning flashes is tested against an alternative hypothesis of independence between them by using methods of statistical analysis for series of events. The hypothesis of independence is rejected at a level of significance of 5%. The probability for lightning flashes in multicell storms to be associated increases when time intervals between flashes are very short (<100 ms for the investigated storm).
Free carbon & electrical conductivity in the Earth's mantle
Authors: Duba A. G. , Shankland T. J.
Published: February 2008

Laboratory measurements indicate that solid carbon, either amorphous or as graphite, enhances the electrical conductivity of rocks. Carbon in quantities of only a few ppm, providing it forms an interconnected phase, could give rise to electrical conductivities of the order seen in the high conductivity layers in the earth's mantle. This possibility is consistent with carbon petrology in mantle rocks and puts the formation and migration of abiogenic carbon compounds into a broader context.
Paleomagnetic test of the Emperor Fracture Zone Hypothesis
Authors: Gordon Richard G.
Published: February 2008

Late Cretaceous paleomagnetic data from the Pacific plate were used to test Farrar and Dixon’s [1981] hypothesis that ∼1700 km of strike‐slip accumulated during the early Tertiary along the Emperor fracture zone system, an 8000 km long NW‐SE trending feature, which consists mainly of the Emperor trough, the Gardner seamounts, and the Line Islands. The data strongly disagree with this hypothesis; instead the data are consistent with no motion having occurred between seafloor east of the Emperor fracture zone and seafloor west of the Emperor fracture zone.
Sunspot time series: Spectrum from square law modulation of the Hale cycle
Authors: Sonett C. P.
Published: February 2008

The spectrum of the sunspot index can be qualitatively accounted for by a very simple time series model which the Hale 22 year cycle dominates; the series is amplitude modulated at the 90 year Gleissberg period with an index of 25%. The square of the modulated Hale cycle reproduces all of the spectral lines of the Zurich sunspot index spectrum, provided that a small offset is included in the Hale carrier. Without this, evidence of the 22 year periodicity disappears. The squaring explains the dominance of the 11 year cycle which is an artifact of the modulation as is the 45 year line. The offset suggests a small relict magnetic field in the Sun's core. Lastly Gilliland [1981] finds a radial eigenmode in the Sun with period of 76 ± 8 years suggestive of a physical basis for the Gleissberg modulation.
Detailed observations of the source of terrestrial narrowband electromagnetic radiation
Authors: Kurth W. S.
Published: February 2008

We present detailed observations of a region near the terrestrial plasmapause where narrowband electromagnetic radiation (previously called escaping nonthermal continuum radiation) is being generated. These observations show a direct correspondence between the narrowband radio emissions and electron cyclotron harmonic waves near the upper hybrid resonance frequency. In addition, electromagnetic radiation propagating in the Z‐mode is observed in the source region which provides an extremely accurate determination of the electron plasma frequency and, hence, density profile of the source region. The data strongly suggest the electrostatic waves and not Cerenkov radiation are the source of the banded radio emissions and define the coupling which must be described by any viable theory.
Current‐driven double layers and the auroral plasma
Authors: Singh Nagendra , Schunk R. W.
Published: February 2008

Simulation results on current‐driven double layers are presented. The role of the Buneman instability in the formation of double layers is clearly identified. The recurring formation and motion of double layers produce a temporal variation of the electric fields similar to that observed in the auroral plasma by the S3‐3 satellite.
Radiocarbon in the Weddell Sea as observed in a deep‐sea coral and in Krill
Authors: Michel Robert L. , Druffel Ellen M.
Published: February 2008

Radiocarbon measurements were performed on krill and coral samples collected from the Weddell Sea during IWSOE ′80. These are the first radiocarbon measurements available from this area since 1973. These data reveal carbon‐14 levels for Weddell surface water and southern Weddell Shelf water. These data indicate that the radiocarbon levels in surface waters in 1980 were the same or slightly lower than those present in 1973. In addition, an unusually low Δ14C value for shelf water (from coral) at 500 m is evidence that Warm Deep Water (WDW) may penetrate much further and more frequently onto the shelf region than had previously been expected.
Shock compression of diamond crystal
Authors: Kondo Ken‐ichi , Ahrens Thomas J.
Published: February 2008

Two shock wave experiments employing inclined mirrors have been carried out to determine the Hugoniot elastic limit (HEL), final shock state at 191 and 217 GPa, and the post‐shock state of diamond crystal, which is shock‐compressed along the intermediate direction between the <111> and <110> crystallographic axes. The HEL wave has a velocity of 19.9 ± 0.3 mm/µsec and an amplitude of 63 ± 28 GPa. An alternate interpretation of the inclined wedge mirror streak record suggests a ramp precursor wave and then another HEL value. The maximum post‐shock density achieved upon release from the ∼200 GPa shock state is ∼3.95 Mg/m³, which compares to the initial density 3.52 Mg/m³. This result suggests an elastic unloading effect or shock‐induced transition to a denser (possibly metallic) phase.
A seismic gap along an accreting plate boundary : Example of the Djibouti Ridge, Afar, East Africa
Authors: Ruegg Jean‐Claude , Lépine Jean‐Claude
Published: February 2008

A segment of the Gulf of Tadjoura (Djibouti, East‐Africa) accreting plate boundary, shows a period of quiescence in the seismic activity since 1974. This segment corresponds to the extension area of the aftershock activity that has occured after a cluster of magnitude 5.5 earthquakes in April 1973. From this example we propose that the seismic gap concept can be extended to moderate earthquakes occuring at extensional plate boundaries. The magnitude of the largest earthquakes at the spreading axis is limited by the size of the rupture length and by the strength of the brittle lithosphere. In the case of the Djibouti ridge recurrence time of 10‐20 years are found for earthquakes of about M =6.
An alternative interpretation of ion ring distributions observed by the S3‐3 satellite
Authors: Gorney D. J.
Published: February 2008

Recently, theoretical interest has grown in possible plasma wave instabilities arising from free energy in auroral ion distributions, and a number of ion‐mode instabilities have been identified. These instabilities typically rely on positive slopes in the ion's velocity distribution parallel (∂f/∂v∥ > O) or perpendicular (∂f/∂v⊥ > O) to the magnetic field. Upflowing ion beams generated by electrical potential drops along auroral field lines are obvious candidates for the parallel (beam) instability, while ion conics have been treated in the limit of the flute mode instability, assuming that a positive perpendicular gradient exists. However, ion conics are not responsible for the condition ∂f/∂v⊥ > O. Downflowing ion beam distributions can have ∂f/∂v⊥ > O and therefore might lead to flute mode instability. Examples of both conics and downflowing beams are presented showing that only the downflowing component leads to significant ∂f/∂v⊥ > O, while ion conics generally have ∂f/∂v⊥ < O and are themselves stable to the flute mode.
New observations of plasma vortices and insights into their interpretation
Authors: Hones E. W. , Birn J. , Bame S. J. , Russell C. T.
Published: February 2008

Two‐ and three‐dimensional plasma measurements and three‐dimensional magnetic field measurements made with the ISEE 1 and 2 satellites during sixteen plasma vortex occurrences in the magnetotail plasma sheet are used to develop a fuller description of the vortex phenomenon than has existed heretofore. We studied in particular the phase and energy propagation properties of the vortex waves. The rotation period of the vortices (T ≈ 10 ± 5 minutes) is apparently independent of location, while the wavelength (λ ≳ several Re) increases with increasing distance down the tail, pointing to a global mode of propagation in which effects of inhomogeneous equilibrium are important. The flow rotation can be explained by propagation of surface waves or resonant waves in a uniform medium. Other observed features, however, require a nonuniform model: Nonuniform propagation properties and differences of the phase propagation speed calculated from different components of velocity or magnetic field.
Shallow shear wave velocity and Q structures at the El Centro strong motion accelerograph array
Authors: Barker Terrance G. , Stevens Jeffry L.
Published: February 2008

At three sites in the U.S. Geological Survey El Centro Strong Motion Accelerograph Array (EO5, EO6 and EO7), we have used the dispersive and attenuative properties of artificially generated Rayleigh waves to infer the depth dependence of shear wave velocity (β) and quality factor (Q) and a site dependent equivalent elastic source spectrum. This approach provides an inexpensive means for determining two important quantities (β and Q) required to estimate the response of sites to earthquakes. We find that the shear velocities and the gradients in shear velocities down to depths of 100 meters at station EO6 (in the wedge between the Imperial and Brawley faults) are nearly twice those at either station EO5 and EO7 (east and west, respectively, of the wedge). Also, the seismogram character, surface wave dispersion and shear wave velocity structure at stations EO5 and EO7 are similar to each other while they are different from EO6. These results show significant structural differences between the wedge beneath EO6 and surrounding areas. The anomalously high accelerations recorded at EO6 during the 1979 Imperial Valley earthquake may be related to these differences.
Long‐period Love numbers and their frequency dependence due to dispersion effects
Authors: Lambeck Kurt , Nakiboglu S. M.
Published: February 2008

In a dispersive medium the Love numbers are frequency dependent. These effects are small over the range of frequencies usually encountered (from about 12 hours to 430 days) in tidal and rotational studies. Models of dispersion predict that at periods of 18.6 years the effect may become quite significant. A preliminary analysis of the long period tidal perturbations in the motion of the LAGEOS satellite indicates that k2 ≃ 0.36 compared with an elastic value of 0.30. This value is in agreement with a mantle shear Q that is proportional to (frequency)β with β of the order 0.3 to 0.4.
Satellite limb‐scanning thermal infrared observations of the El Chichon stratospheric aerosol: First results
Authors: Thomas G. E. , Jakosky B. M. , West R. A. , Sanders R. W.
Published: February 2008

The Infrared Radiometer experiment on the Solar Mesosphere Explorer satellite has been continuously measuring the 6.8‐µm thermal emission from the stratospheric aerosol from the El Chichon volcano since the time of eruption in early April, 1982. Inversion results for the zonally‐averaged infrared extinction coefficient in height, latitude, and time show that the aerosol increased in mass to a maximum of 8 Tg(8×1012gm) about 15 weeks after the April 4 eruption. It descended in height with an average speed consistent with the gravitational settling time of particles with a diameter of about 1.4 µm.
Detection of 18.6 year nodal induced drought in the Patagonian Andes
Authors: Currie Robert G.
Published: February 2008

Analysis of tree‐ring chronologies from the Patagonian Andes yields evidence for the 18.6 yr lunar nodal term in drought/flood. The mean discrepancy between epochs of drought/flood and the nodal tide since AD 1600 is 0.7 ± 2.2 yr, but the polarity of the signal is apparently bimodal. From nodal epoch 1750.0 through 1898.9 drought and tide were in phase, whereas prior to 1750.0 and subsequent to 1898.9 drought and tide were out of phase. There is evidence also for the solar cycle drought signal in the data.
Fast collisionless tearing in an anisotropic neutral sheet
Authors: Chen J. , Palmadesso P. J. , Fedder J. A. , Lyon J. G.
Published: February 2008

The collisionless tearing mode in a neutral sheet is studied in the presence of ion temperature anisotropy using Vlasov description for both ions and electrons. It is found that the growth rate of the instability is significantly enhanced if Ti⊥/Ti∥ > 1 where the symbols ⊥ and ∥ refer to the directions perpendicular and parallel to the equilibrium magnetic field. For typical magnetotail parameters with modest temperature anisotropy, it is shown that the linear e‐folding time is reduced to a small fraction of the time delays believed to precede the onset of reconnection. This enhancement of the growth rate is due to the Lorentz force acting on the ions that cross the neutral plane, traversing beyond the conventional electron tearing layer.
Geological and seismic evidence of a new branch of the Agua Blanca Fault
Authors: González J. Javier , Suárez Francisco
Published: February 2008

The Agua Blanca fault is a major, trans‐peninsular, right‐lateral fault located in northern Baja California. Its WNW‐ESE orientation is markedly different from the general trend of the San Andreas‐Gulf of California fault system. From a geological point of view, the Agua Blanca fault is considered active, but there has been little significant seismic activity directly associated with it. On October 9, 1981, the onset of an earthquake swarm was detected at the Ensenada seismic station (ENX), with a S‐P time average of 2 sec. Shortly after this, an array of up to seven portable seismic stations was installed by CICESE around Todos Santos Bay. More than 180 events were recorded during the following 10 days, after which the local seismicity decreased. A second swarm consisting of 100 microearthquakes was detected between November 28 and December 5, 1981. The epicentral locations of those events recorded at four or more local stations all lie inside Todos Santos Bay. The composite fault plane solution for both swarms indicates a right‐lateral strike‐slip vertical fault with a strike of N52°W. Geological observations allow us to conclude that the seismic activity reported here is associated with the Agua Blanca fault zone.
On bistable phasing of 18.6 year nodal induced flood in India
Authors: Currie Robert G.
Published: February 2008

In agreement with Campbell (1983), Flood Area Indices (FAI) for India are interpreted as being modulated by tidal forcing at the 18.6 yr lunar nodal period. There is evidence maximum flood was approximately out of phase with nodal epoch 1898.9 whereas at epochs 1917.5, 1936,1, 1954.7, and 1973.3 maximum flood was approximately in phase. This interpretation implies that India should be experiencing widespread dryness in an interval ±2 to 3 years centered at mid‐epoch 1982.6.
Lightning flash density versus altitude and storm structure from observations with UHF‐ and S‐band radars
Authors: Mazur Vladislav , Gerlach John C. , Rust W. David
Published: February 2008

The UHF‐ (70.5 cm wavelength) and S‐band (10 cm wavelength) radars at NASA Goddard Space Flight Center/Wallops Flight Facility in Virginia have been used to relate lightning activity to altitude and to the reflectivity structure of a thunderstorm. Two centers of lightning flash density were found, one between 6 and 8 km altitude and another between 11 and 15 km. Our observations show a tendency for lightning to be within the high reflectivity region and ahead of it in the less intense precipitation at the leading edge of the storm.
Model for the domain state of Ti‐rich titanomagnetites
Authors: Appel E. , Soffel H. C.
Published: February 2008

Domain structure observations on synthetic and natural Ti‐rich titanomagnetites (≈TM60), some of which were made under external uniaxial pressure, lead to a new model for the domain state of such materials. Instead of a classical domain configuration, we observed in most cases a more complicated micromagnetic structure with multidomain particles consisting of a conglomerate of quasi‐single domain, multi‐domain and spin cluster zones due to an inhomogeneous anisotropy field caused by internal stress. Pseudo‐single domain properties such as stable TRM can be explained by spin rotation processes as in single domain particles.
Earthquake triggering during preparation for great earthquakes
Authors: Habermann R. E. , Wyss M.
Published: February 2008

Seismic quiescence has been proposed as a precursor to many large earthquakes. In this paper we present two cases in which precursory quiescence is interrupted several years prior to great earthquakes by triggered events in the upcoming rupture areas. This triggering results in complex precursory patterns which include seismic quiescence and triggered events. Prior to the Kermadec earthquake of 1976 (Ms = 8.0) events in the rupture zone were triggered by a quake on the outer rise and one near the future mainshock epicenter. Events were triggered by an earthquake on an adjacent segment of the plate interface and by one near the epicenter of the New Hebrides earthquake of 1980 (Ms = 8.0). We propose that two preconditions must be fulfilled for triggering to occur. First the stress in the region must be close to the failure stress and second nearby events must occur which are large enough to affect the stress field but not large enough to cause an immediate mainshock.
Airborne observations of Arctic aerosols. III: Origins and effects of airmasses
Authors: Radke Lawrence F. , Hobbs Peter V. , Bailey Ian H.
Published: February 2008

Multiple layers of haze encountered in the troposphere over the Beaufort and Chukchi Seas during April 1983 occurred in airmasses that originated in eastern USSR, eastern North America and Asia. This, together with observations on the composition and nature of the hazes, indicate that they were primarily anthropogenic in origin. Giant particles (>2 µm in diameter), on the other hand, which were distributed roughly uniformly with height in the troposphere, appeared to have both anthropogenic and natural origins. Relationships between the haze layers and adjacent regions of clean air are discussed.
Mesoscale wetfall chemistry around Philadelphia during frontal storms
Authors: Patrinos A. A. N. , Brown R. M.
Published: February 2008

Preliminary results from a mesoscale "acid rain" study are presented. The study concentrates on precipitation‐event sampling at a network of ∼40 stations located between 20 km and 60 km from the city of Philadelphia, Pennsylvania, with the goal of establishing the contribution of local emissions to the total ionic wet deposition load and of determining the spatial variability of this deposition on the suburban‐rural scale. Two storms associated with weak warm fronts and displaying similar meteorological features were sampled successfully. For the first, urban emissions appear to have significantly affected the deposition of several inorganic ionic species, most notably NO3−; no effect was evident for the second storm. A possible explanation of the apparent contrast is given in terms of the weekday‐weekend emissions variability. A sampling density of approximately one collector per 200 to 300 km² appears adequate for both storms.
A plausible model for the synchroneity or the phase shift between climatic transitions
Authors: Nicolis C.
Published: February 2008

A class of climate models describing the dynamics of the sea ice‐ocean surface temperature interactions is considered. The coupling mechanism between different spatial regions is analyzed, and the possibility of inhomogeneous phase shifted states is established. It is concluded that many major climatic transitions should occur in an asynchronous fashion. A new examination of the climatic record seems therefore to be necessary, in the light of this possibility.
Mineralogy and composition of the upper mantle
Authors: Anderson Don L. , Bass Jay D.
Published: February 2008

Seismic velocities are calculated for two petrological models of the upper mantle, an olivine‐rich assemblage, pyrolite, and a garnet‐clinopyroxene rich, olivine bearing, assemblage, piclogite. These are compared with recent seismic profiles for various tectonic provinces. The shield data is most consistent with a cold olivine and orthopyroxene‐rich LID (the seismic lithosphere) extending to 150 km followed by a high temperature gradient and/or a change in mineralogy that serves to decrease the velocity. From 200 to 400 km the velocities follow a 1400°C adiabat. The rise‐tectonic mantle is much slower, presumably hotter and is likely to be above the solidus to depths of at least 300 km. The high Vp/Vs ratio of the lower oceanic lithosphere in the western Pacific is most consistent with eclogite.
Seasonal variations of ozone in the upper mesosphere and gravity waves
Authors: Thomas Ronald J. , Barth Charles A. , Solomon Susan
Published: February 2008

Ozone densities in the upper mesosphere have been measured as a function of time and latitude over a two‐year period (1982‐1983) by the Solar Mesosphere Explorer (SME) satellite. Large seasonal changes occur, particularly near 80 km where ozone densities at the equinoxes are about 2‐3 times those observed at the solstices. The structure of the ozone secondary maximum also fluctuates substantially during the year, with extremes near equinox and solstice. Further, the variations are highly repeatable from year to year and from hemisphere to hemisphere. We propose that the seasonal variability in ozone is produced by the variation of gravity‐wave‐induced transport in the mesosphere which, in turn, results from the seasonal modulation of the propagation and breaking of small‐scale gravity waves.
Thermocline displacement across the Atlantic North Equatorial Countercurrent during 1983
Authors: Katz Eli Joel , Garzoli Silvia L.
Published: February 2008

Two time series of thermocline displacement across the North Equatorial Countercurrent are derived from pairs of Inverted Echo Sounders which straddle the countercurrent along the 28°W and 38°30′W meridians. The observations reported are from February to September 1983. From mid‐May to the end of the record the thermocline deepens to the south and shallows to the north of the countercurrent, suggesting a continual strengthening of the countercurrent. The rate of increase of the thermocline slope at the western meridian is about twice that at 28°W, as expected from historical data. An Empirical Orthogonal Functions (EOF) analysis of the four sounders finds the dominant mode accounting for 64% of the variance. This is compared to an EOF analysis of model results by Philander and Pacanowski where the forcing is provided by the historical average wind field. With the model, the dominant mode is almost the entire response (92% of the variance). The time dependence of the observed mode tracks that derived from the model during the overlapping seasons.
modes of variability of the 1983 thermocline signal
Authors: Garzoli Silvia L.
Published: February 2008

Acoustic travel time series from an array of nine inverted echo sounders deployed along the equator and in the North Equatorial Countercurrent (NECC) are decomposed into Empirical Orthogonal Functions (EOF) to analyze the dominant frequencies of oscillations in the thermocline field. At low frequencies the first EOF mode describes the seasonal signal, shows the reversal of the NECC and separates the behavior of the Gulf of Guinea from the rest of the basin. The second EOF mode shows rapid changes in the depth of the thermocline in short periods of time on the equator at 10°W and at 3°N 38° 30′W. Comparison with a simulation model by Philander and Pacanowski shows that the theoretical time series behave in a similar way at these two locations. At high frequencies the modes show oscillations in the inertia‐gravity wave band.