On the upstream mobility scheme for two-phase flow in porous media

When neglecting capillarity, two-phase incompressible flow in porous media is modelled as a scalar nonlinear hyperbolic conservation law. A change in the rock type results in a change of the flux function. Discretising in one dimension with a finite volume method, we investigate two numerical fluxes, an extension of the Godunov flux and the upstream mobility flux, the latter being widely used in hydrogeology and petroleum engineering. Then, in the case of a changing rock type, one can give examples when the upstream mobility flux does not give the right answer.     

Systematic assessment of irregular building–soil interaction using efficient modal analysis

In this paper an efficient methodology applying modal analysis is developed to assess systematically the combined soil–structure interaction and torsional coupling effects on asymmetric buildings. This method is implemented in the frequency domain to accurately incorporate the frequency‐dependent foundation impedance functions. For extensively extracting the soil–structure interaction effects, a diagonal transfer matrix in the modal space is derived. A comprehensive investigation of asymmetric building–soil interaction can then be conveniently conducted by examining various types of response quantities. Results of parametric study show that the increasing height‐to‐base ratio of a structure generally amplifies its translational and torsional responses. Moreover, both the translational and torsional responses are reduced for the case where the two resonant frequencies are well separated and this reduction is enhanced with the decreasing values of the relative soil stiffness and the height‐to‐base ratio. The most noteworthy phenomenon may be the fact that the SSI effects can enlarge the translational response if the structure is slender and the two resonant frequencies are very close. Copyright © 2001 John Wiley & Sons, Ltd.     

Transient analysis of earthquake and explosion arrivals

Summary An electronic sound spectrograph has been used to analyze the transients in complicated earthquake and explosion signals. Transient analysis with a sound spectrograph gives a means for directly obtaining group velocity at each of the spectral frequencies for each of the separate arrival branches, for any type of transient signal. Compared to frequency analysis, it presents the fine spectral structure of the signal as it changes with time, not an average over a time that includes many parts of the seismic signal.Dispersion as well as the body wave spectrum of theP wave has been observed by transient analysis of seismic signals. Dispersion has also possibly been observed in theS wave, and in the various multiply reflectedS waves, which have been found to increase in period from one arrival to the next. The dispersed pattern of arrival of fundamental and higher mode surface waves has been observed for oceanic, continental, and mixed paths. Among these signals is a clear indication of the continental second shear mode. The separation of surface waves for the direct and complementary paths has also been accomplished. Our results compare well with those obtained by standard techniques.The dispersion of the fundamental and higher mode signals from explosive sources in shallow water may be easily studied by making sound spectrograms and amplitude sections of these seismic signals. These shallow water shots show bubble pulses and Airy phases, which are clearly defined on the spectrograms and sections.

---

Zusammenfassung Ein elektronischer Schallspektrograph wurde benutzt, um die nichtstationären Vorgänge in komplizierten Erdbeben- und Explosionswellen zu analysieren. Die Analyse von nichtstationären Vorgängen mittels dieses Schallspektrographen ergibt unmittelbar die Gruppengeschwindigkeit jeder einzelnen Spektralfrequenz für die verschiedenen seismischen Wellenphasen, die ja solche nichtstationären Vorgänge darstellen. Verglichen mit einer gewöhnlichen Frequenzanalyse liefert diese Art von Analyse die Spektralfeinstruktur des zeitlich sich ändernden Signals und nicht ein Mittel über ein Zeitintervall, das einen grösseren Teil des seismischen Schwingungsablaufs umfasst.Sowohl Dispersionserscheinungen in derP-Welle als auch deren diskretes Amplitudenspektrum wurden mit Hilfe dieser Analyse seismischer Signale festgestellt. Dispersion wurde mit ziemlicher Wahrscheinlichkeit auch bei derS-Welle beobachtet, und in den verschiedenen mehrfachreflektiertenS-Wellen zeigt sich in aufeinanderfolgenden Reflexionen eine Periodenzunahme. Das disperse Erscheinungsbild der Oberflächenwellen in ihrer Grundschwingungstype und den zugehörigen Schwingungstypen höherer Ordnung wurde für ozeanischen, kontinentalen und gemischten Weg aufgenommen. Unter diesen Wellentypen findet sich eine klare Andeutung der kontinentalen Scherschwingungsform zweiter Ordnung vom Rayleigh-Typus (Second Shear Mode). Die Aufspaltung von Oberflächenwellen für direkten und antipodalen Weg wurde ebenfalls erreicht. Unsere Ergebnisse zeigen eine gute Übereinstimmung mit den von herkömmlichen Methoden stammenden Resultaten.Die Dispersion von Wellentypen erster und höherer Ordnung, die durch Explosionen im Seichtwasser angeregt werden, kann leicht an Hand der Schallspektrogramme und momentanen Amplitudenspektren ihrer seismischen Signale untersucht werden. Solche Seichtwasserdetonationen zeigen Pulsationen und Airy-Phasen, die sich eindeutig auf den Spektrogrammen und Amplitudenbildern abzeichnen.

---

---

With two plates: Figs. 6 & 17

---

Preliminary results presented at the 30th Annual Meeting of the Eastern Section of the Seismological Society of America, June 13–14, 1958, inSt. Louis, Missouri, U.S.A.-Lamont Geological Observatory Contribution No. 383.     

Dihedral angle measurements and infiltration property of SiO<Subscript>2</Subscript>-rich melts in mantle peridotite assemblages

Petrological and experimental studies demonstrated that nepheline-normative, SiO₂-rich melts can be present in the upper mantle at pressures 1.5 GPa. To evaluate the role of such melts in mantle processes and magma genesis, we carried out two types of experiments: (1) melt distribution experiments to characterize the grain-scale distribution of a small fraction of typical SiO₂-rich mantle melt (SRMM) in polycrystalline olivine (Ol) at 1,180°C, 1.2 GPa; and (2) an infiltration experiment to test the ability of SRMM to impregnate and metasomatise neighbouring non-molten mantle rocks. The median dihedral angles at Ol-Ol-SRMM contacts are equal to 50°, implying that melt should be interconnected at all melt fractions. Complications arise, however, in the investigated system because Ol–liquid interfacial energy is anisotropic, and we estimate that the connectivity threshold in the SRMM–Ol system is 0.3 vol%. Regarding the very low volume fraction of SRMM in peridotites, we conclude that these melts either occur as isolated pockets or form a network of grain edge channels with a low degree of connectivity due to a large number of dry grain edges. Even in the case where an interconnected network exists, their large viscosities should prohibit the extraction of SRMM from peridotite sources. The infiltration experiment also points to a very reduced mobility of SRMM in the upper mantle. In this experiment, a slice of synthetic dunite was immersed into a magma reservoir made of 60 wt% SRMM+40 wt% Ol, and subjected to 1,180°C-1.2 GPa for 113 h: despite this long duration, the SiO₂-rich liquid was unable to infiltrate measurably the dunite. Our experiments do not support the hypothesis that SRMM represent agents of mantle metasomatism.     

River dissolved and solid loads in the Lesser Antilles: New insight into basalt weathering processes

We present here the first available estimations of chemical weathering and associated atmospheric CO₂ consumption rates as well as mechanical erosion rate for the Lesser Antilles. The chemical weathering (100–120 t/km²/year) and CO₂ consumption (1.1–1.4 × 10⁶ mol/km²/year) rates are calculated after subtraction of the atmospheric and hydrothermal inputs in the chemical composition of the river dissolved loads. These rates thus reflect only the low-temperature basalt weathering. Mechanical erosion rates (approx. 800–4000 t/km²/year) are estimated by a geochemical mass balance between the dissolved and solid loads and mean unaltered rock. The calculated chemical weathering rates and associated atmospheric CO₂ consumption rates are among the highest values worldwide but are still lower than those of other tropical volcanic islands and do not fit with the HCO₃⁻ concentration vs. 1/T correlation proposed by Dessert et al. (2001). The thick soils and explosive volcanism context of the Lesser Antilles are the two possible keys to this different weathering behaviour; the development of thick soils limits the chemical weathering and the presence of very porous pyroclastic flows allows an important water infiltration and thus subsurface weathering mechanisms, which are less effective for atmospheric CO₂ consumption.     

Variable resolution techniques for weather prediction

Summary This paper presents a brief overview of a few variable resolution techniques in the context of the horizontal discretization of the meteorological equations. These are the grid refinement method, the static and dynamic coordinate transformation methods and the variable resolution in physical space method. The latter is illustrated by a variable resolution reformulation of the popular C-grid discretization suitable for use in a limited area model.With 5 Figures     

Nitrogen isotopic composition of macromolecular organic matter in interplanetary dust particles

Nitrogen concentrations and isotopic compositions were measured by ion microprobe scanning imaging in two interplanetary dust particles L2021 K1 and L2036 E22, in which imaging of D/H and C/H ratios has previously evidenced the presence of D-rich macromolecular organic components. High nitrogen concentrations of 10-20 wt% and δ¹⁵N values up to +400‰ are observed in these D-rich macromolecular components. The previous study of D/H and C/H ratios has revealed three different D-rich macromolecular phases. The one previously ascribed to macromolecular organic matter akin the insoluble organic matter (IOM) from carbonaceous chondrites is enriched in nitrogen by one order of magnitude compared to the carbonaceous chondrite IOM, although its isotopic composition is still similar to what is known from Renazzo (δ¹⁵N = +208‰).The correlation observed in macromolecular organic material between the D- and ¹⁵N-excesses suggests that the latter originate probably from chemical reactions typical of the cold interstellar medium. These interstellar materials preserved to some extent in IDPs are therefore macromolecular organic components with various aliphaticity and aromaticity. They are heavily N-heterosubstituted as shown by their high nitrogen concentrations >10 wt%. They have high D/H ratios >10⁻³ and δ¹⁵N values ≥ +400‰. In L2021 K1 a mixture is observed at the micron scale between interstellar and chondritic-like organic phases. This indicates that some IDPs contain organic materials processed at various heliocentric distances in a turbulent nebula. Comparison with observation in comets suggests that these molecules may be cometary macromolecules. A correlation is observed between the D/H ratios and δ¹⁵N values of macromolecular organic matter from IDPs, meteorites, the Earth and of major nebular reservoirs. This suggests that most macromolecular organic matter in the inner solar system was probably issued from interstellar precursors and further processed in the protosolar nebula.