bluuebunny/crossref_metadata_2025 huggingface dataset:
Mantle flow pressure and the angle of subduction: Non‐Newtonian corner flows
Authors: Tovish Aaron , Schubert Gerald , Luyendyk Bruce P.
Published: February 2008

Corner flows of Newtonian and non‐Newtonian fluids are used to model the flow in a subduction zone which is viscously driven by the motions of the converging plates and the descending slab. The pressures induced by the flow tend to lift the slab up beneath the overriding plate thereby offsetting the tendency of gravity to align the slab with the vertical. The low angles of subduction observed in Peru and Central Chile may be the result of strong dynamic pressures forcing the slab up against the overriding plate. Viscous coupling between the overriding plate and the downgoing slab is essential if the nonvertical dips of slabs are a consequence of the balance between gravitational and pressure torques. For a Newtonian mantle, shear stresses and pressures on the top of the slab are comparable. If the mantle is non‐Newtonian, however, the pressures greatly exceed the shear stresses, for most acute dip angles. Thus frictional forces on the top and bottom surfaces of slabs are less important in resisting slab descent into a non‐Newtonian mantle than they are in resisting penetration into a Newtonian mantle.
A reevaluation of the Grüneisen parameter for the Earth's core
Authors: Jamieson John C. , Demarest Harold H. , Schiferl David
Published: February 2008

We have reexamined the adiabatic and melting gradients in the core and the relationship between them. We consider possible contributions to CV and γ in the core from vibrational, electronic, and magnetic (ferromagnetic and Schottky anomaly) terms. Both vibrational and electronic terms are important in the core. Magnetic terms are probably not important, but any contribution they make will tend to make γ larger. Considering these contributions we find that 1.2 < γ < 2.0 in the core. This evaluation of γ is consistent with the idea of adiabatic circulation in the core and a reasonable extrapolation of the melting gradient of iron, using, for example, the Lindemann‐Gilvarry melting model. The Kraut‐Kennedy melting model predicts a comparatively small melting point gradient under core conditions, prohibiting convection unless γ < 1.0. We find that the “core paradox” of Higgins and Kennedy has been somewhat exaggerated owing to numerical errors in calculating the adiabat.
Some thermal consequences of a gravitationally powered dynamo
Authors: Loper David E.
Published: February 2008

It is argued that the most plausible source of power for the geodynamo is gravitational energy released by the growth of the solid inner core, and the essential features of this mechanism are outlined. The thermal regimes of the outer core which are possible if the dynamo is gravitationally powered are studied, and a number of interesting possibilities are found. First, if the liquidus gradient TL′ is less than the conduction gradient TC′, a slurry must occur in the fluid at the bottom of the outer core. Second, it is shown that compositionally driven convection can occur even if the actual temperature gradient T′ is less than the adiabat TA′. This allows the possibility that heat may be transferred radially inward by the motions. Hence there is no direct relation between the rate that heat is conducted outward in the core and the rate of heat transfer to the mantle. Third, it is found that Higgins and Kennedy's hypothesis does not preclude convective overturning driven by compositional buoyancy provided the thermal conductivity of the outer core is sufficiently large. Fourth, a slurry in the bulk of the outer core is stabilizing and incompatible with a convectively driven dynamo of any kind. It is argued that the gravitationally powered dynamo is possible only if the composition of the core is more metallic than the eutectic. The thermal evolution of the earth is considered, and it is found that if TA′ < TC′, the heat transfer problems for the core and mantle decouple with conditions in the core leading to a prescribed temperature at the base of the mantle and the mantle then prescribing the heat flux which must emanate from the core. It is shown that if T′ = TL′, a large flux of heat may flow from the core with virtually no change in temperature.
Geodimeter measurements of strain during the Southern California Uplift
Authors: Savage J. C. , Prescott W. H.
Published: February 2008

A review of geodimeter measurements made along the ‘big‐bend’ section of the San Andreas fault in southern California indicates no significant increment in strain during the period of major uplift (late 1959 to mid‐1963). Specifically, no evidence of an increment in compressional strain normal to the San Andreas fault at the time of the uplift was found. Geodolite measurements at four networks along the big bend independently indicate that the strain rate during the 1974–1977 episode of subsidence was essentially a uniaxial north‐south compression at the rate of about ⅓ μstrain/yr. Whether the 1974–1977 rate is significantly different from earlier rates determined by triangulation is not clear owing to a rather large variability in the earlier determinations.
Geodesy and astrometry by transatlantic long base line interferometry
Authors: Cannon W. H. , Langley R. B. , Petrachenko W. T. , Kouba J.
Published: February 2008

We report geodetic and astrometric results from the analysis of fringe frequency observations from a series of three long base line interferometry (LBI) experiments carried out in 1973 between the 46‐m antenna of the Algonquin Radio Observatory, Lake Traverse, Canada, and the 2‐m antenna at Chilbolton Field Station, Chilbolton, England. The rms deviation from the mean of the estimates of the length and orientation of the 5251‐km equatorial component of the base line from all three experiments is 1.05‐m and 0.015″, respectively. The experiments also yielded positions of five extragalactic radio sources. The reported positions, each of which is from only a single experiment, have uncertainties of about 0.2″ in declination (except for low declination sources) and about 0.01 s in right ascension. The LBI determination of the length and orientation of the equatorial component of the base line is compared to the corresponding values derived from Naval Weapons Laboratory 9D (NWL‐9D) coordinates for the antennae. The two length measurements agree in scale within quoted experimental errors, however, the NWL‐9D coordinate frame is found to be rotated 0.867″±0.1″ to the east relative to the average terrestrial frame of the Bureau International de l'Heure (BIH), (LBI coordinate frame). This is in good agreement with the expected misalignment of 0.65″±0.2″. The differences in the rates of the clocks used at each end of the base line were also determined and compared to Loran‐C observations.
Mono Lake geomagnetic excursion
Authors: Liddicoat Joseph C. , Coe Robert S.
Published: February 2008

Extensive sampling has revealed a new feature of the Mono Lake geomagnetic excursion. The previously known eastward swing in declination and steepening of inclination are preceded by an even greater swing to westerly declination and shallow inclination. The duration of the entire excursion is estimated to be about 1000 years. Excellent agreement of paleomagnetic directions between four sites shows the excursion is a real expression of the geomagnetic field. Interpretation of natural remanent magnetization/anhysteretic remanent magnetization (NRM/ARM) ratios for one site indicates the field intensity may have fallen well below and then increased well above the dipole field intensity, suggesting the excursion is a manifestation of the nondipole field. The source can be modeled by a radial eccentric dipole at high northern latitudes and pointing outward during the first part of the excursion, and near the equator and pointing inward during the latter part. Movement of the source appears localized, displaying a complex pattern of eastward, westward, and even northward drift. The average moment of the hypothetical eccentric dipole during the excursion is comparable with the largest calculated for the 1945 field, and the maximum moment is almost twice as great.
Erosion, uplift, exponential heat source distribution, and transient heat flux
Authors: Lee Tien‐Chang
Published: February 2008

The linear relation observed between heat flux and radiogenic heat production of near‐surface rocks in many individual geological provinces of the world can be explained in terms of various source distributions. If this relation survives through differential erosion in space, a unique solution exists under the condition of steady state heat conduction such that heat production decreases exponentially with depth. During an episode of differential erosion in a region with an exponential source distribution, an analytical solution shows that the transient heat flux is no longer linearly related to the heat production of the exposed rocks. Depending upon the rate and duration of erosion as well as the variation of temperature at the ground surface, the transient heat flux may increase, while the near‐surface rocks which contain exponentially higher amounts of heat generating elements are stripped away. After the termination of erosion, it takes ∼20% of the duration of erosional episode, as shown by a finite element analysis, for the transient heat flux to reach its steady state value. In a tectonically active area, a linear relation may not be observable owing to transient effect of erosion and other perturbing factors.
Modeling of rock friction: 2. Simulation of preseismic slip
Authors: Dieterich James H.
Published: February 2008

The constitutive relations developed in the companion paper are used to model detailed observations of preseismic slip and the onset of unstable slip in biaxial laboratory experiments. The simulations employ a deterministic plane strain finite element model to represent the interactions both within the sliding blocks and between the blocks and the loading apparatus. Both experiments and simulations show that preseismic slip is controlled by initial inhomogeneity of shear stress along the sliding surface relative to the frictional strength. As a consequence of the inhomogeneity, stable slip begins at a point on the surface and the area of slip slowly expands as the external loading increases. A previously proposed correlation between accelerating rates of stable slip and growth of the area of slip is supported by the simulations. In the simulations and in the experiments, unstable slip occurs shortly after a propagating slip event traverses the sliding surface and breaks out at the ends of the sample. In the model the breakout of stable slip causes a sudden acceleration of slip rates. Because of velocity dependency of the constitutive relationship for friction, the rapid acceleration of slip causes a decrease in frictional strength. Instability occurs when the frictional strength decreases with displacement at a rate that exceeds the intrinsic unloading characteristics of the sample and test machine. A simple slider‐spring model that does not consider preseismic slip appears to approximate the transition adequately from stable sliding to unstable slip as a function of normal stress, machine stiffness, and surface roughness for small samples. However, for large samples and for natural faults the simulations suggest that the simple model may be inaccurate because it does not take into account potentially large preseismic displacements that will alter the friction parameters prior to instability.
Thermal infrared properties of the Martian atmosphere: 1. Global behavior at 7, 9, 11, and 20 μm
Authors: Martin Terry Z. , Peterfreund Alan R. , Miner Ellis D. , Kieffer Hugh H. , Hunt Garry E.
Published: February 2008

Infrared observations of Mars by the Viking infrared thermal mapper (IRTM) are presented for both conditions of a relatively clear and a dust‐laden atmosphere. The 7‐, 9‐, 11‐, and 20‐μm bands of the IRTM respond differently to radiation emitted through and by a dusty atmosphere, permitting characterization of the global atmospheric state, monitoring of secular changes, and derivation of optical depth information. Surface temperature behavior is found to be greatly modified by the diminution of insolation and thermal blanketing resulting from global dust storms. Brightness temperature at 7 μm (T7) is employed to estimate surface temperatures in the presence of dust absorption. The difference T7‐T9 is strongly indicative of airborne dust when thermal contrast exists between the surface and atmosphere. The diurnal behavior of T7‐T9 reveals changes in that contrast; the sign of the differential reverses as the surface, warmer than the atmosphere in daytime, becomes cooler than the atmosphere at night. IRTM observations of local areas at varying emission angle yield optical depths indicative of global trends. Two global dust storms in 1977 produced large optical depth changes; at 9 μm the optical depth became as large as 2.0.
Thermal infrared properties of the Martian atmosphere: 4. Predictions of the presence of dust and ice clouds from Viking IRTM spectral measurements
Authors: Hunt Garry E.
Published: February 2008

In this paper we investigate the response of the Martian atmosphere at the wavelengths measured by the Viking infrared thermal mapper instrument (IRTM) to the presence of varying amounts of dust and water ice clouds. A detailed radiative transfer study is represented to show that these IRTM measurements at channels centered at 7, 9, 11, and 20 μm may be used to differentiate between the presence of dust and water ice clouds in the Martian atmosphere. They show further that these measurements may also be used to provide some information on the structure of the lower atmosphere. The use of the IRTM measurements in the manner we describe can provide information associated with the thermal characteristics of Martian dust storms.
The seasonal variation of atmospheric pressure on Mars as affected by the south polar cap
Authors: Hess Seymour L. , Henry Robert M. , Tillman James E.
Published: February 2008

The daily mean pressures at two locations on Mars, observed over 57% of a martian year, reveal a semiannual oscillation with a peak‐to‐peak difference that is 26% of the mean pressure. This intrinsically martian phenomenon is caused by exchange of CO2 between the atmosphere and the winter polar caps. The results are quantitatively in agreement with the simple model of Leighton and Murray (1966), indicating that radiation and conduction are the dominant processes, while atmospheric heat transport is a minor effect. There is no evidence to support a significant role of adsorption on the regolith, on an annual time scale. Evidence is presented that the difference in pressure at the two landers varies with season and that the seasonal variation is not completely removed by hydrostatic correction for the difference in elevation. The mass of CO2 sublimed from the south polar cap is estimated to be ≥7.9×1012 metric tons, corresponding to a mean thickness of solid CO2 over the maximum extent of that cap of ≥23 cm. Estimates are formed of the meridonal wind speed conveying gas out of the dissipating cap and the associated zonal geostrophic wind, both averaged over longitude. The results are
ms−1 and Ug ≃ 14 ms−1, respectively.
Static stability and thermal wind in an atmosphere of variable composition: Applications to Mars
Authors: Hess Seymour L.
Published: February 2008

Radiometric measurements of the temperature of the south polar cap of Mars in winter have yielded values significantly below the expected 148 K. One proposed explanation for this result is a substantial reduction in the CO2 content of the atmosphere and a lowering of the mean molecular weight near the surface. We explore the meteorological consequences of this explanation by deriving a criterion for vertical static stability and a thermal wind law for an atmosphere of variable composition. The atmosphere proves to be statically unstable unless the anomaly in the CO2 mixing ratio extends to heights of tens of kilometers. The effect of varying molecular weight exceeds the effect of temperature gradient, in the thermal wind law, producing shears with height of reversed sign. The shears are baroclinically unstable, and this instability would eradicate the latitudinal gradient of molecular weight. This inconsistency can be resolved by invoking a reasonable elevation of the central polar cap and by imposing an adequate zonal wind. We conclude that if the explanation requiring a change in atmospheric composition is correct, it must be accompanied by other special circumstances to make it meteorologically consistent. No attempt is made to estimate the possible occurrence of barotropic instability.
A convective heat transfer model for lithospheric thinning and crustal uplift
Authors: Withjack Martha
Published: February 2008

Lithospheric thickness and crustal uplift dimensions are calculated numerically as functions of time after the onset of a convective transfer of heat into the lithosphere by magma intrusion. The numerical models show that the rate of lithospheric thinning depends on the rate or magma entry into the lithosphere and the initial temperature regime of the lithosphere. The width and height of uplift for continental regions depends on (1) the apparent flexural rigidity of the lithosphere, (2) the diameter of the hot spot beneath the lithosphere, (3) the density contrast between the new asthenosphere and the original lithosphere, (4) erosion rates, and (5) the rate of magma entry into the lithosphere. For oceanic lithosphere the amount of uplift depends on points 1, 2, and 3 above, on the eruption depth, and on the size of the volcanic load (if any). With reasonable values for these parameters the model produces crustal uplift rates and lithospheric deflections similar to those observed for continental rifts and Hawaii. The model suggests that a fractured lithosphere beneath Hawaii is not necessary. Volcanic loading combined with the uplift produced by lithospheric thinning can produce an arch with an amplitude comparable to that of the Hawaiian arch. The model applied to moving plates suggests that the lithosphere/asthenosphere boundary is asymmetrically distorted in the direction of plate movement.
Some characteristics of foreshocks and their possible relationship to earthquake prediction and premonitory slip on faults
Authors: Jones Lucile M. , Molnar Peter
Published: February 2008

Foreshocks occur before a large fraction of the world's major (M ≥ 7.0) earthquakes. Teleseismically located events before major earthquakes from 1914 to 1973 were considered together to examine possible average temporal and spatial patterns of foreshock occurrence. Several days before the main shocks and apparently near the epicenters of them (Δ ≲ 30 km) the activity begins to increase, culminating in a final rapid acceleration of activity in the last day. The acceleration continues up to the time of the main shocks, except for a possible temporary decrease about 6 hours before them. The seismicity increases approximately as the inverse of time before main shock. This relationship is essentially unrelated to the magnitude of the main shock. The magnitude of the largest foreshock is also unrelated to the magnitude of the main shock. In addition, pairs of major events are common. Ten percent of the world's major events are preceded by other major events within 100 km and 3 months. For foreshocks within each of three sequences studied, the ratio of the amplitudes of the P and S waves were approximately the same, suggesting that the faulting mechanisms are the same for events in each sequence. By assuming an inhomogeneous fault plane on which asperities fail by static fatigue, we derived an equation for accelerating premonitory slip as a function of time, which agrees with the observed time dependence of foreshocks.
Results of Geos 3/ATS 6 Satellite‐to‐Satellite Tracking Orbit Determination Experiment
Authors: Argentiero P. , Schmid P. E. , Vonbun F. O.
Published: February 2008

The purpose of the Geos 3/ATS 6 satellite‐to‐satellite tracking experiment was to develop, test, and evaluate methods of deriving orbit estimates from satellite‐to‐satellite tracking data. The results of the experiments are presented in the form of conventional orbit overlap tests, and a comparison of a Geos 3 orbit estimate obtained from satellite‐to‐satellite (SST) tracking data with an orbit estimate derived from C‐band data. The method recommended for estimating orbits from SST data is a Bayesian least squares procedure utilizing independent ranging to the relay satellite.
A Geos 3 Orbit Determination Experiment
Authors: Pisacane V. L. , Eisner A. , Yionoulis S. M. , McConahy R. J. , Black H. D. , Pryor L. L.
Published: February 2008

The purpose of this experiment was to investigate the value of altimetry data in high‐precision satellite orbit determination. To accomplish this, software was developed to process laser, C‐band, doppler and altimeter data singly or jointly. Initially, orbit determination studies were undertaken using synthetic data to validate the software. As data became available, preliminary experiments were carried out. When all the data became available, an intensive study was made covering a 4‐day span in 1976. The results showed that even with sparse altimeter data it was possible to accurately determine the semimajor axis and eccentricity with altimeter data only. When altimeter data was supplemented with (as few as) two C‐band passes, high‐precision ephemerides were obtained. Using two laser passes to supplement the altimetry data did not achieve that same high precision. This is probably because the geographic location (mid‐Atlantic) of the highly accurate laser data were such that they did not ideally complement the available (south Atlantic and Indian Ocean) altimeter data.
An analysis of isostasy in the world's oceans: 2. Midocean ridge crests
Authors: Cochran J. R.
Published: February 2008

Cross‐spectral techniques are used to analyze the relationship between gravity and bathymetry at the Mid‐Atlantic Ridge and the East Pacific Rise crests. The resulting transfer functions were used to study the nature of the isostatic mechanism operative at these ridge crests. The most satisfactory results were obtained for models in which the oceanic lithosphere is treated as a thin elastic plate overlying a weak fluid. The best fitting elastic thickness to explain gravity and bathymetry at the fast spreading (v > 5 cm/ yr) East Pacific Rise is in the range of 2–6 km and at the relatively slow spreading (v < 2 cm/yr) Mid‐Atlantic Ridge is in the range 7–13 km. These estimates are significantly smaller than the elastic thickness of 20–30 km obtained from surface loads formed on old (>80 m.y.) parts of the oceanic lithosphere. This difference is consistent with the fact that ridge topography is formed near the ridge axis, where isotherms are shallower and the lithosphere is thus weaker than in older regions. The difference between the elastic thickness of the East Pacific Rise and Mid‐Atlantic Ridge is significant and may represent differing temperature structures at these ridges. Simple models in which it is assumed that the elastic thickness represents the depth to the 450°C isotherm show that these variations can be explained by differences in the spreading rate at these ridges. Thus the lower effective thickness at the East Pacific Rise can be attributed to higher average temperatures at shallow depths in a region surrounding the ridge crest. This is due to the faster spreading rate which results in isotherms having a shallower dip away from the axis than at the slower spreading Mid‐Atlantic Ridge. This model cannot, however, explain gravity and bathymetry data over the Rekyjanes Ridge. The best fitting elastic thickness for this slow spreading ridge is similar to the thickness determined for the East Pacific Rise, suggesting an anomalous thermal regime at this ridge crest.
Sound velocities and anisotropy of kaersutite
Authors: Shaw George H.
Published: February 2008

Compressional and shear wave velocities have been measured in a single crystal kaersutite from an alkali basalt. The kaersutite is highly anisotropic (24% for compressional velocity and 22% for shear velocity) and has a rather low value of Poisson's ratio (0.17). Comparison with velocities measured in hornblendes indicates that kaersutite may have unusually high shear velocities. If kaersutite is present in significant amounts in the upper mantle, its large anisotropy may be important in modeling the seismic structure.
Crack growth and the thermoelastic behavior of rocks
Authors: Bruner William M.
Published: February 2008

The effect of cracks on the elastic moduli of rocks has received considerable attention in recent years; the role of crack growth in the brittle creep and dilatant deformation of rocks has also been extensively studied. However, less attention has been paid to the effects of cracks on other thermoelastic constants of rocks, such as their thermal expansion coefficients, and to the deformation resulting from the growth of cracks in rocks containing internal stresses. These effects have been studied experimentally and discussed in qualitative terms, but quantitative theories relating thermoelastic behavior to the presence or growth of cracks are lacking. A thermodynamic approach can be used to calculate changes in stress, pore volume, and thermoelastic properties for a sample of brittle rock containing open, growing cracks and subjected to changing temperature, pore pressure, and macroscopic strain. The analysis is based upon the relation between the flow of energy to an advancing crack edge and the crack tip stress intensity factors. The effect of cracks on the thermal expansion of aggregates is illustrated by applying the results of this analysis to a simple model of a monomineralic aggregate of uniaxial grains. Changes in the temperature of the aggregate from an initial stress‐free and crack‐free state lead to grain‐scale thermal stresses, which cause the growth of cracks. The resulting change in the linear thermal expansion of the material has the same sign as the temperature change; the magnitude of the change can be a significant fraction of the difference in linear thermal expansion between the a and c directions for the individual grains. These results, though not directly applicable to real rocks, indicate the importance of such effects in rocks and suggest the potential value of the thermal expansion properties of rocks as indicators of their history. Similar calculations show that the relaxation of internal stresses in rocks by crack growth can lead to strains comparable to those resulting from stress changes of tens to hundreds of bars, although the strain resulting from the growth of a single crack will not usually be resolvable. The common belief that the growth of cracks in internal stress fields cannot lead to a shortening or volume reduction may be incorrect in some cases, because of the grain‐scale elastic inhomogeneity and interactions between cracks and pores which are present in most rocks.
Theory and experiment for passive microwave remote sensing of snowpacks
Authors: Kong J. A. , Shin R. , Shiue J. C. , Tsang L.
Published: February 2008

Both the theory and experiment for the passive remote sensing of snow with microwave radiometers have been studied. We account for volume scattering effects of snow by incorporating Mie scattering theory into a radiative transfer model. The theory is applied to the interpretation of experimental data obtained from various snow measurements. The spectral and angular dependences of the brightness temperatures are illustrated and show good agreements between the theory and experiment. The brightness temperatures as a function of snow depths are also interpreted and discussed. It is observed that as the snow depth increases, the brightness temperature increases when the subsurface is an aluminum plate due to the fact that the plate is cold and snow absorption induces brightening effect and the brightness temperature decreases when the subsurface is soil due to the fact that snow scattering induces darkening effects.
Comment on ‘Isotopic anomalies of noble gases in meteorites and their origins: 2. Separated minerals from Allende’ by Roy S. Lewis, Jacques Gros, and Edward Anders
Authors: Manuel O. K.
Published: February 2008

Correlations between elemental and isotopic ratios of noble gases in mineral separates of Allende are not consistent with the reported identification of a noble gas component trapped in ‘Q’ with 136Xe/132Xe = 0.310 and 20Ne/132/Xe = 10 ± 4. If Q trapped a noble gas component with 136Xe/132Xe = 0.310, then the correlations indicate that there was no Ne in this gas component. If Q trapped a noble gas component with 20Ne/132Xe = 10 ± 4, then the correlations indicate that Q contains no fission Xe.
Theory of electrokinetic‐magnetic anomalies in a faulted half‐space
Authors: Fitterman David V.
Published: February 2008

Fluid motion in the vicinity of a vertical fault separating regions of different streaming potential coefficient can produce an external magnetic field of observable magnitude. If tectonic stress changes along the fault produce fluid motion, the magnetic field changes would be indicative of stress changes, and might precede severe fault motion. The largest component of the magnetic field is oriented parallel to the strike of the fault. Magnetic field changes produced by this mechanism will have electric fields associated with them with similar time variation; this is in contrast to magnetic field changes produced by changes in susceptibility or remanent magnetization, which have no associated electric field. Experiments aimed at the detection of tectonomagnetic effects should include electric field sensors to help in determining the source of any observed variations. The hypothesis of Mizutani and Ishido (1976) that the magnetic field changes associated with the Matsushiro earthquake swarms were produced by electrokinetic currents seems reasonable.
A crystal defect theory approach to faulting in geological structures
Authors: Chou Tsu‐Wei , Malasky Henry J.
Published: February 2008

Crystal defect theory is employed to predict residual displacement fields resulting from faulting in a semi‐infinite, isotropic elastic medium. The description of faulting structures should consider not only translational but also rotational movements. The concept of rotational defects, also known as disclinations in crystal physics, can be employed to treat the problem of rotational fault movements. The combination of dislocation and disclination theories completes the physical concept necessary to describe fault movements in general. Four examples of rotational faults have been identified in geological literature. Furthermore, a model for fault surfaces involving circular and semicircular disclinations and dislocations is proposed. The model permits any fault orientation and location relative to the ground or free surface. The characteristics of translational and rotational faults are illustrated by the contour maps of displacements at the free surface for vertical strike slip and rotational faults. Comparisons between this model and existing analyses and field observations are favorable. It is proposed that this model can assist in defining the geometry of fault planes.
Initial phase analysis of R waves from great earthquakes
Authors: Furumoto Muneyoshi
Published: February 2008

Phase equalization was carried out for R waves in order to obtain information on source mechanisms of four earthquakes, the Kurile earthquake of 1963, its largest aftershock, the Rat Island earthquake of 1965, and the Tokachi‐oki earthquake of 1968. The initial phase was computed using the corresponding complete great‐circle phase velocity, so that influences of the lateral heterogeneity of the earth's structure were considerably reduced. The fault length of the Kurile earthquake was determined from the initial phase radiation pattern on the basis of a simple propagating fault model. There is no trade‐off in this method between the fault length and the rupture velocity. Such a trade‐off is inherent to the conventional directivity method. A fault length of 250 km was obtained, which was found to be nearly equal to the length of the aftershock area. We have introduced a dynamic fault parameter ‘source time’ that can be determined from the phase measurement using the complete great‐circle phase velocity rather than the average phase velocity of the individual multiple R waves. This quantity corresponds to the rise time of the source time function of an equivalent point source. Source times of 97, 62, 174, and 115 s were obtained for the above four earthquakes.
The extended mission of Viking
Authors: Snyder Conway W.
Published: February 2008

The primary mission of the Viking project, with two orbiters and two landers at Mars, was completed in November 1976, but operations have since been extended in a series of stages, and they are still continuing as of November 1979. The lander investigations that searched for evidence of living organisms and organic chemicals in the surface material and determined the chemical composition of the atmosphere were completed early in 1977. Since then a major emphasis has been on the study of the weather on Mars, with instruments on all four spacecraft contributing. The acquisition of samples for the inorganic analysis of surface material, the manipulation of the sampling tool to investigate the physical and magnetic properties of the surface, and the seismic measurements were terminated a year later, but other investigations were continued. Orbiters and landers have acquired large quantities of photographs of the surface and of atmospheric phenomena. Viking Orbiter 2 ceased to operate in July 1978; Viking Orbiter 1 was shut down temporarily in February 1979 but resumed operations in July for an additional 3 months or more. Both landers have been programmed to continue for another decade, but only Viking Lander 1 will yield scientific data. This paper discusses the operation and chronology of the Viking mission. The scientific results are discussed in a companion paper.
Plains and channels in the Lunae Planum—Chryse Planitia Region of Mars
Authors: Theilig Eilene , Greeley Ronald
Published: February 2008

The Lunae Planum‐Chryse Planitia region provides the opportunity to study a sequence of channeling events and to determine their temporal and genetic relationships to plains units in the northern hemisphere of Mars. Two sets of small channels and four major channel systems can be divided into four periods of channeling by superposition and contact relationships to the plains. All of the channels are considered to have formed by water erosion. The first two channeling events occurred early in the history of this area and formed small, narrow channels within the old rugged terrain. These channel events were separated by deposition of a mantle unit. The small channels probably formed by runoff of surface water or by a sapping process. These channels preceded the emplacement of vast volcanic plains in both Lunae Planum and Chryse Planitia. Channels postdating the plains are Vedra, Maumee, Bahram, and Maja valles; the first three of these deposited a sedimentary unit on the western slope of Chryse Planitia that was eroded by Maja Vallis. These large‐scale channels were probably formed predominantly by catastrophic floods and may represent two periods of water release from Juventae Chasma. The origin of Bahram Vallis remains uncertain.
Martian fluidized crater morphology: Variations with crater size, latitude, altitude, and target material
Authors: Mouginis‐Mark Peter
Published: February 2008

On the basis of morphology of the exterior deposits of 1558 fresh Martian impact craters, 6 crater types are defined, and the incidence of each crater type on 10 different geological units is documented. It is shown that several crater types are preferentially associated with specific target materials: radial textured craters are found primarily on Tharsis and Elysium lavas, a type of crater here called ‘pancake craters’ on fractured terrain, old lavas, and channel materials. The occurrence of secondary craters is also strongly terrain dependent. Three times as many craters on young lavas have secondary craters as compared to those craters on ridged and cratered plains materials, and 10 times as many have secondary craters when compared to primary craters on ancient terrain materials. The maximum radial extent of fluidized ejecta blankets is demonstrated to be a function of both crater altitude and latitude. The most extensive ejecta units are found at low altitudes and high latitudes, while the least mobile ejecta is located at high elevations and close to the equator. Only pancake craters exhibit any pronounced latitudinal variation in their distribution. These craters are almost exclusively located poleward of latitudes 40°N and 40°S. For the majority of the sample craters (N = 1333), there is no such systematic latitudinal variation in crater occurrence.
Eolian features in the western desert of Egypt and some applications to Mars
Authors: El‐Baz Farouk , Breed C. S. , Grolier M. J. , McCauley J. F.
Published: February 2008

Relations of landform types to wind regimes, bedrock composition, sediment supply, and topography are shown by field studies and satellite photographs of the Western Desert of Egypt. This desert, which lies at the core of the largest hyperarid region on earth, provides analogs of Martian wind‐formed features. These include sand dunes, alternating light and dark streaks, knob ‘shadows,’ and yardangs. Surface particles have been segregated by wind into deposits (dunes, sand sheets, and light streaks) that can be differentiated by their grain size distributions, surface shapes, and colors. Throughgoing sand of mostly fine to medium grain size is migrating southward in longitudinal dune belts and barchan chains whose long axes lie parallel to the prevailing northerly winds, but topographic variations such as scarps and depressions strongly influence the zones of deposition and dune morphology. Sand from the longitudinal dunes on the plains is commonly redistributed into barchans in the depressions. These barchans are generally simple crescents that are morphologically similar to many of the dunes seen on Viking orbiter pictures of the north polar sand sea on mars. Light streaks are depositional features consisting of dune belts and elongate sheets of coarse to medium sand and granules. Intervening dark streaks are erosional features consisting of strips of desert‐varnished bedrock and lag gravel surfaces exposed between the sand deposits. The shape of both light and dark streaks is controlled by wind flow around topographic highs. Dark zones (shadows) in the lee of mountains, hills, and knobs are erosional products from the topographic highs; they change shape only in response to movement of the adjacent lighter‐colored sand deposits. Streamlined yardangs carved in crystalline limestone constitute one of the largest yardang fields on earth. Yardangs occur also in sandstone of the Nubian Series and in lacustrine sediments. The variables that affect the patterns of wind erosion and deposition in the Western Desert are topographic effects on wind velocities and directions, resistance of the bedrock, sand supply, and climatic change with time; vegetation is essentially absent and is not a controlling factor.
Mars south polar spring and summer temperatures: A residual CO2 frost
Authors: Kieffer Hugh H.
Published: February 2008

The Viking infrared thermal mapper (IRTM) has measured reflected and emitted energy over Mars south polar cap throughout the martian spring and summer. During these 1976–1977 observations the polar cap displayed complex spatial, spectral, and temporal variations. The cap recession was accompanied by a bright rim and dark internal collar. High albedos did not directly correspond with low temperatures as would be expected for a simple polar frost model. Both the polar cap and the surrounding terrain brightened erratically during the global dust storms. The polar cap remained approximately symmetrical around the geometric pole until about Ls 237, when the eastern hemisphere (longitudes 180°–360°) darkened and the western hemisphere began to develop spectral contrasts at thermal wavelengths. As the cap shrank to its residual position centered at –87.5°, 30°W, it maintained large differences in brightness temperature between the four IRTM surface‐sensing bands at 7, 9, 11, and 20 μm. Whereas T9 reached 214 K, T20 never exceeded 175 K. No single mechanism explains the observed spectral behavior. The late summer infrared spectral pattern can be matched by a surface consisting of CO2 frost with 20‐μ emissivity of 0.8 and ∼6% dark, warm soil under a dusty atmosphere of moderate infrared opacity and spectral properties similar to those measured for the martian global dust storms. Throughout the summer, the polar frost remained at the temperature of solid CO2. This low temperature, the spectral pattern, the absence of appreciable water vapor in the south polar atmosphere, and the absence of surface warming expected if H2O ice were to become exposed, all imply that the residual south polar cap seen by Viking was covered by solid CO2. Thus Mars appears to have a residual polar cap of CO2 in the south and one of H2O in the north. This difference is due in part to the occurrence of global dust storms during the southern summer. An accumulation of solid CO2 over the location of the residual cap beyond that predicted by radiation models seems required to explain the persistence of CO2 frost in spite of the large apparent energy imbalance during the summer.
Behavior of the Martian north polar cap, 1975–1978
Authors: Iwasaki Kyosuke , Saito Yoshikazu , Akabane Tokuhide
Published: February 2008

In the photographic observations of Mars at the Kwasan Observatory and at the Hida Observatory during the 1977–1978 apparition, the north polar cap was first observed at Ls = 14°, and the latitude of the edge of the cap was about 65°N. This edge of the cap changed little until Mars reached Ls = 50°, and then the cap started to shrink. The edge was observed near 74°N at Ls = 70°. The relatively constant dimension of the north polar cap observed before Ls = 50° appears to be a regular phenomenon in the behavior of the north polar cap. The photographs obtained at the Hida Observatory during the 1975–1976 apparition were examined to study the nature of the north polar cap near Ls = 0°. Red filter photographs taken in the period from Ls = 340°–0° revealed dark surface features of the northern high latitudes, when blue filter photographs show the extensive polar brightening (i.e., the polar hood). The latitude of the northernmost dark feature observed was about 65°N. A wide spread north polar cap, which is predicted by most of the existing models, was not observed in our observations in 1975–1976.
Formation and deposition of volcanic sulfate aerosols on Mars
Authors: Settle Mark
Published: February 2008

Sulfurous gases released at the surface of Mars during episodes of volcanic activity would be naturally transported into the upper levels of the Martian atmosphere (20‐ to 30‐km altitude) owing to the synoptic convergence of lower‐level winds in the Tharsis region of the planet. The circulation of the upper atmosphere would globally disperse such gases over time scales of 25 earth days. The rate limiting step in sulfate aerosol formation on Mars is inferred to be the gas phase oxidation of SO2 which is accomplished via chemical reactions with O, OH, and HO2. Under present‐day atmospheric conditions aerosol formation would occur over periods of several thousand earth days. However atmospheric concentrations of odd hydrogen species (OH, HO2) should increase significantly during periods of persistent surface volcanism. Under these circumstances sulfate aerosol formation could occur on time scales of several hundred earth days. Submicron‐sized aerosol particles would circuit Mars several dozen times before they are removed from the atmosphere by gravitational forces. Such aerosols would be globally dispersed and would be deposited over a wide range of equatorial and mid‐latitudes. Volcanic sulfate aerosols on Mars are inferred to consist of liquid droplets and liquid‐solid slurries containing aqueous solutions of sulfuric acid. These acidic solutions would be chemically reactive and would trigger leaching processes within surface materials upon deposition. Sulfate aerosol deposition is a viable mechanism for transporting sulfur to the Viking lander sites. Atmospheric circulation models indicate that time‐averaged vertical winds over Chryse Planitia and Utopia Planitia are directed toward the surface during most Martian seasons. Aerosol particles settling out of the atmosphere would be expected to be preferentially deposited in these regions. Aerosol deposition on a global or hemispheric scale could account for the similar concentrations of sulfur within surficial soils at the two Viking lander sites.
Shock wave studies in Blair dolomite
Authors: Larson D. B.
Published: February 2008

Two types of shock wave experiments have been conducted on samples of Blair dolomite. The first employed a light‐gas gun to produce uniaxial strain, while the second used a spherical high‐explosive charge to cause radial divergent flow. Comparisons of data taken from these two types of experiments (at strain rates of 106/s and 104/s, respectively) with quasi‐static data (at 10−4/s) show that Blair dolomite is strongly time dependent in its behavior. This time dependence appears over the entire stress interval from 0.24 to 5.33 GPa.
Seismic refraction studies of the Sunda Trench and Forearc Basin
Authors: Kieckhefer R. M. , Shor G. G. , Curray J. R. , Sugiarta W. , Hehuwat F.
Published: February 2008

Six refraction lines were shot parallel to structure, from the Sunda Trench axis to the west coast of Sumatra, near Nias Island. Seaward of the Nias Island ridge, 2.4–3.8 km of low‐velocity sediment (2.0–3.6 km/s) is underlain by a wedge of 4.7‐ to 4.9‐km/s material, probably dewatered sediment and oceanic basement. The wedge thickens from 1.2 km beneath the trench axis to 13.5 km immediately seaward of the ridge. Layer 3, 6.6–7.5 km/s and 3.7–23 km thick, dips 5° landward beneath this wedge. The large variation in layer 3 thickness may be evidence that imbricate thrust faulting, responsible for the thickening which forms the 4.7‐ to 4.9‐km/s wedge, also extends downward into layer 3. The forearc basin, landward of Nias Island, has 3.0 km of low‐velocity sediment overlying 19 km of 6.5‐km/s material and 8.1‐km/s Moho. Near the coast of Sumatra, layers of 2.1, 4.3, 5.3, and 6.0 km/s, whose thicknesses total 8.1 km, are underlain by a large, undetermined thickness of 6.8‐km/s material. This 6.5‐ to 6.8‐km/s layer may be either lower continental (granitic) crust or thickened oceanic layer 3.
Gravimetric model of the Atlantic equatorial fracture zones
Authors: Sibuet Jean‐Claude , Veyrat‐Peinet Bernard
Published: February 2008

A vertical distribution of temperatures in the lithosphere is used to generate a simple gravimetric model which closely matches the observed free‐air anomaly across the Atlantic equatorial fractures zones. Topographic features associated with fracture zones are not compensated in the active transform part but become progressively compensated in the fossil one. At distances corresponding to a time period of 10–20 m.y., compensation is fully achieved. As the fossil fracture zone complex is often as much as 50 km wide, the position of plate boundary cannot be determined on morphological grounds only. Based on correspondance between the foot of the sharp wall of the fracture zone and the inflexion point of the free‐air anomaly curve, a criterion is proposed to define the position of the plate boundary which corresponds to the contact at depth between the lithospheric blocks. Thus using this simple criterion, the fracture zone pattern of an ocean can be better defined, giving more severe constraints on the kinematic evolution of this ocean.