Wave propagation in a seven-story reinforced concrete building: I. Theoretical models

For transient, high frequency, and pulse like excitation of structures in the near field of strong earthquakes, the classical design approach based on relative response spectrum and mode superposition may not be conservative. For such excitations, it is more natural to use wave propagation methods. In this paper (Part I), we review several two-dimensional wave propagation models of buildings and show results for theoretical dispersion curves computed for these models. We also estimate the parameters of these models that would correspond to a seven-story reinforced concrete building in Van Nuys, California. Ambient vibration tests data for this building imply vertical shear wave velocity β_z=112 m/s and anisotropy factor β_x/β_z=0.55 for NS vibrations, and β_z=88 m/s and β_x/β_z=1 for EW vibrations. The velocity of shear waves propagating through the slabs is estimated to be about 2000 m/s. In the companion paper (Part II), we estimate phase velocities of vertically and horizontally propagating waves between seven pairs of recording points in the building using recorded response to four earthquakes.     

Primitive island arc and oceanic lavas from the hunter ridge-hunter fracture zone. Evidence from glass,olivine and spinel compositions

Summary At its southernmost end, the main spreading centre of the North Fiji Basin is propagating into arc crust of the poorly-known Hunter Ridge. We define nine magmatic groups from major element glass chemistry and olivine and spinel compositions in samples dredged from twenty six sites in this area by the R/V Academician A. Nesmeyanov in 1990. These include groups of boninites, island arc tholeiites (IAT), mid-ocean ridge basalts (MORB), enriched mid-ocean ridge basalts (E-MORB), olivine porphyritic andesites and basaltic andesite and Na-rhyolites. Primitive lavas containing highly forsteritic olivine phenocrysts are common in all the groups, except for the rhyolites.We report over 100 glass analyses for dredged rocks from this region, and about 300 olivine-spinel pairs for representatives of all the magmatic groups identified, except the Na-rhyolites.The MORB in this region are probably produced at the propagating spreading centre in the southern part of the North Fiji Basin. Juxtaposition of shallow, hot MORB-source diapirs supplying the MORB in this area, and the sub-arc damp, refractory upper mantle beneath the Hunter Ridge, provides suitable petrogenetic conditions to produce a range of magma types, from island arc tholeiites through to high-Ca boninites. The latter were recovered in eleven dredges.The E-MORB lavas recovered from the extreme southern margin of the North Fiji Basin are shown to be essentially identical to those dredged from adjacent older South Fiji Basin crust. It is hypothesized that the former were either scraped off the South Fiji Basin crust during an episode of oblique subduction that may have generated the Hunter Ridge during the last 5 Myr, or alternatively, that slices of the South Fiji Basin crust were trapped and incorporated into the North Fiji Basin as the subduction zones fronting the Vanuatu arc stepped or propagated southward.

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Primitive Inselbogen- und ozeanische Laven von Hunter Rücken und der Hunter BruchZone: die Bedeutung der Zusammensetzung von Glas, Olivin und Spinell

Zusammenfassung Das spreading centre des Nord-Fidschi-Beckens setzt sich an seinem südlichsten Ende in die Inselbogen-Kruste des noch wenig bekannten Hunter-Rückens fort.Wir definieren 9 magmatische Gruppen auf der Basis der Hauptelement-Zusammensetzung von Gläsern und der Zusammensetzung von Olivin und Spinell in Proben die das Forschungsschiff R/V Akademiker A. Nesmeyanov von 26 Stellen im Jahr 1990 aufgesammelt hat. Zu diesen gehören Gruppen von Boniniten, Inselbogentholeiiten (IAT), Basalten zentralozeanischer Rücken (MORB), angereicherte zentralozeanische Rücken (E-MORB), Olivin-porphyritische Andesite und basaltische Andesite, sowie Na-Rhyolite. Primitive Laven mit Olivinkristallen, die reich an Forsterit-Komponenten sind, kommen in allen diesen Gruppen, mit Ausnahme der Rhyolite, vor.Wir legen über 100 Glas-Analysen von Gesteinen aus diesem Gebiet vor und über 300 Olivin-Spinell-Paare für Vertreter aller der hier identifizierten magmatischen Gruppen, mit Ausnahme der Natriumrhyolite.Die MORB in diesem Gebiet sind wahrscheinlich an dem aktiven Spreading Center im Südteil des Nord-Fidschi-Beckens entstanden. Das nebeneinander Vorkommen von seichten heißen MORB-Quellen Diapiren, die MORB in diesem Gebiet erzeugen, und der Sub-Inselbogen, wasserhaltige, refraktäre obere Mantel unter dem Hunter Rücken führen zu geeigneten petrogenetischen Bedingungen für die Entstehung einer Vielfalt von Magmatypen, von Inselbogentholeiiten bis zu sehr Kalziumreichen Boniniten. Die letzteren wurden in 11 Dredge-Proben gefunden.Die E-MORS Laven, die aus dem extremen Südteil des Nord-Fidschi-Beckens entnommen wurden, sind im wesentlichen mit jenen identisch, die aus der benachbarten älteren Kruste des Süd-Fidschi-Beckens stammen. Es wird vermutet, daß die letzteren entweder aus dem Süd-Fidschi-Becken während einer Episode obliger Subduktion, die in den letzten 5 Millionen Jahren zur Entstehung des Hunter Ridge geführt hat, abgeschert wurden, oder auch daß Teile der Kruste des Süd-Fidschi-Beckens in das Nord-Fidschi-Becken inkorporiert wurden als Subduktionszonen gegenüber dem Vanuato-Bogen sich nach Süden fortbewegten.

     

The Magma Feeding System of the Klyuchevskaya Group of Volcanoes (Kamchatka)

Doklady Earth Sciences - Using observations from a large-scale seismic station network, we built a seismic tomography model of velocity anomalies for longitudinal (P-wave) and transverse (S-wave)...     

Age of Detrital Zircons from Sandstones of the Mesozoic Flysch Formation in the South Anyui Suture Zone (Western Chukotka)

The South Anyui fold zone (western Chukotka) is considered a suture zone related to closure of the South Anyui oceanic basin and collision of Eurasia with the Chukotka–Arctic Alaska microcontinent in the Early Cretaceous. The existence of a compensatory sedimentation basin (foredeep) during folding in the terminal Jurassic–initial Cretaceous remains debatable. This work presents first data on age estimates of detrital zircons from Upper Mesozoic terrigenous sequences of the South Anyui suture zone obtained by the fission-track method. The distal flysch of presumably Late Jurassic age and the proximal flysch of probably Late Triassic age were sampled in the Uyamkanda River basin. The fission-track dating showed that sandstones from the flysch sections contain detrital zircons of two different-age populations. Young zircon populations from sandstones of distal turbidites in the upper course of the Uyamkanda River (two samples) are 149 ± 10.2 and 155.4 ± 9.0 Ma old (Late Jurassic), whereas those from coarse-grained proximal turbidites sampled in the lower course of the Uyamkanda River (one sample) is 131.1 ± 7.5 Ma old (Early Cretaceous). The data obtained indicate that the Late Mesozoic folding in the South Anyui suture zone was accompanied by the formation of a marginal sedimentary basin. Sediments accumulated in this basin compose tectonic nappes that constitute a fold–thrust structure with the northern vergence.     

Tuning a physically-based model of the air–sea gas transfer velocity

Air–sea gas transfer velocities are estimated for one year using a 1-D upper-ocean model (GOTM) and a modified version of the NOAA–COARE transfer velocity parameterization. Tuning parameters are evaluated with the aim of bringing the physically based NOAA–COARE parameterization in line with current estimates, based on simple wind-speed dependent models derived from bomb-radiocarbon inventories and deliberate tracer release experiments. We suggest that A = 1.3 and B = 1.0, for the sub-layer scaling parameter and the bubble mediated exchange, respectively, are consistent with the global average CO₂ transfer velocity k. Using these parameters and a simple 2nd order polynomial approximation, with respect to wind speed, we estimate a global annual average k for CO₂ of 16.4 ± 5.6 cm h^?1 when using global mean winds of 6.89 m s^?1 from the NCEP/NCAR Reanalysis 1 1954–2000. The tuned model can be used to predict the transfer velocity of any gas, with appropriate treatment of the dependence on molecular properties including the strong solubility dependence of bubble-mediated transfer. For example, an initial estimate of the global average transfer velocity of DMS (a relatively soluble gas) is only 11.9 cm h^?1 whilst for less soluble methane the estimate is 18.0 cm h^?1.     

Modelling phytoplankton succession on the Bering Sea shelf: role of climate influences and trophic interactions in generating Emiliania huxleyi blooms 1997–2000

Several years of continuous physical and biological anomalies have been affecting the Bering Sea shelf ecosystem starting from 1997. Such anomalies reached their peak in a striking visual phenomenon: the first appearance in the area of bright waters caused by massive blooms of the coccolithophore Emiliania huxleyi (E. huxleyi). This study is intended to provide an insight into the mechanisms of phytoplankton succession in the south-eastern part of the shelf during such years and addresses the causes of E. huxleyi success by means of a 2-layer ecosystem model, field data and satellite-derived information. A number of potential hypotheses are delineated based on observations conducted in the area and on previous knowledge of E. huxleyi general ecology. Some of these hypotheses are then considered as causative factors and explored with the model. The unusual climatic conditions of 1997 resulted most notably in a particularly shallow mixed layer depth and high sea surface temperature (about 4 °C above climatological mean). Despite the fact that the model could not reproduce for E. huxleyi a clear non-bloom to bloom transition (pre- vs. post-1997), several tests suggest that this species was favoured by the shallow mixed layer depth in conjunction with a lack of photoinhibition. A top-down control by microzooplankton selectively grazing phytoplankton other than E. huxleyi appears to be responsible for the long persistence of the blooms. Interestingly, observations reveal that the high N:P ratio hypothesis, regarded as crucial in the formation of blooms of this species in previous studies, does not hold on the Bering Sea shelf.     

Diagnostic of a Solar Flare via Analyses of Emission in Spectral Lines of Highly Ionized Iron

An analysis of the dynamics of the electron temperature of the solar atmosphere in regions where solar flares appear is presented. The temperatures are estimated from the emission in spectral lines of ions with various degrees of ionization. The emission of ionized helium and highly ionized iron was used. Images of preflare states and of flares from the archive of the American SDO spacecraft are analyzed. A solar flare is usually preceded by the registration of a bright glowing structure above the action region, with a temperature exceeding that of the corona. This preflare structure (~10¹⁰ cm) is identified with the development of a system of currents, which, according to numerical simulations, is responsible for the accumulation of energy above the active region before the flare. After several tens of hours of a slow increase in the brightness of the preflare glow in the 94 Å iron (FeXVIII) line, the emission in the 193 Å line of FeXXIV increases sharply, indicating a flare-like growth of the temperature up to at least 20 MK. This growth of the emission coincides with the onset of the solar flare. The observed dynamics of the emission in spectral lines of highly ionized ions is consistent with an electrodynamic model of a solar flare based on the accumulation of magnetic energy in a current sheet above the active region and the explosive release of the stored energy. Studies of mechanisms for solar flares are of special importance in connection with the discovery of solar cosmic rays. Information from the worldwide network of neutron monitors and from the GOES spacecraft has made it possible to firmly state that the source of solar rays is solar flares, not shocks generated by such flares. It cannot be ruled out that a similar mechanism, not shocks, is also responsible for the acceleration of cosmic rays in the Galaxy.     

On features of structure of bottom gravity current frontal zone

The results of qualitative laboratory and numerical experiments on two-dimensional non-linear model are described, aiming at an investigation of the structure of the front of bottom gravity current. Non-coincidence of frontal interfaces in density and velocity fields within the bottom gravity current leading (frontal) part is stated on the base of comparative analysis of numerical and laboratory experiments. This fact is experimentally confirmed by field example of marine water inflow into a brackish lagoon. The density gradient along the stream line is shown to be an additional effective criterion for the localization of the frontal zone.