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51.
52.
C.?Bouvet?de?MaisonneuveEmail author F.?Costa C.?Huber P.?Vonlanthen O.?Bachmann M.?A.?Dungan 《Contributions to Mineralogy and Petrology》2016,171(6):56
Reconciling the diverse records of magmatic events preserved by multiple crystals and minerals in the same sample is often challenging. In the case of basaltic–andesites from Volcán Llaima (Chile), Mg zoning in olivine is always simpler than Ca zoning in plagioclase. A model that explains a number of chemical patterns is that Llaima magmas stall in the upper crust, where they undergo decompression crystallization and form crystal-mush bodies. Frequent magma inputs from deeper reservoirs provide the potential for remobilization and eruption. The records of multiple recharge events in Llaima plagioclase versus an apparent maximum of one such event in coexisting olivine are addressed by using trace element zoning in olivine phenocrysts. We have integrated elements that (1) respond to changes in magma composition due to recharge or mixing (Mg, Fe, Ni, Mn, ±Ca), with (2) elements that are incorporated during rapid, disequilibrium crystal growth (P, Ti, Sc, V, Al). A more complex history is obtained when these elements are evaluated considering their partition coefficients, diffusivities, and crystal growth rates. The olivine archive can then be reconciled with the plagioclase archive of magma reservoir processes. Olivine (and plagioclase) phenocrysts may experience up to three or more recharge events between nucleation and eruption. Diffusion modeling of major and trace element zoning in two dimensions using a new lattice Boltzmann model suggests that recharge events occur on the order of months to a couple of years prior to eruption, whereas crystal residence times are more likely to be on the order of a few years to decades. 相似文献
53.
The consistent estimation of terrestrial reference frames (TRF), celestial reference frames (CRF) and Earth orientation parameters (EOP) is still an open subject and offers a large field of investigations. Until now, source positions resulting from Very Long Baseline Interferometry (VLBI) observations are not routinely combined on the level of normal equations in the same way as it is a common process for station coordinates and EOPs. The combination of source positions based on VLBI observations is now integrated in the IVS combination process. We present the studies carried out to evaluate the benefit of the combination compared to individual solutions. On the level of source time series, improved statistics regarding weighted root mean square have been found for the combination in comparison with the individual contributions. In total, 67 stations and 907 sources (including 291 ICRF2 defining sources) are included in the consistently generated CRF and TRF covering 30 years of VLBI contributions. The rotation angles \(A_1\), \(A_2\) and \(A_3\) relative to ICRF2 are ?12.7, 51.7 and 1.8 \({\upmu }\) as, the drifts \(D_\alpha \) and \(D_\delta \) are ?67.2 and 19.1 \(\upmu \) as/rad and the bias \(B_\delta \) is 26.1 \(\upmu \) as. The comparison of the TRF solution with the IVS routinely combined quarterly TRF solution shows no significant impact on the TRF, when the CRF is estimated consistently with the TRF. The root mean square value of the post-fit station coordinate residuals is 0.9 cm. 相似文献
54.
Controls on magma permeability in the volcanic conduit during the climactic phase of the Kos Plateau Tuff eruption (Aegean Arc) 总被引:1,自引:1,他引:0
X-ray computed microtomography (μCT) was applied to pumices from the largest Quaternary explosive eruption of the active South
Aegean Arc (the Kos Plateau Tuff; KPT) in order to better understand magma permeability within volcanic conduits. Two different
types of pumices (one with highly elongated bubbles, tube pumice; and the other with near spherical bubbles, frothy pumice)
produced synchronously and with identical chemical composition were selected for μCT imaging to obtain porosity, tortuosity,
bubble size and throat size distributions. Tortuosity drops on average from 2.2 in frothy pumice to 1.5 in tube pumice. Bubble
size and throat size distributions provide estimates for mean bubble size (~93–98 μm) and mean throat size (~23–29 μm). Using
a modified Kozeny-Carman equation, variations in porosity, tortuosity, and throat size observed in KPT pumices explain the
spread found in laboratory measurements of the Darcian permeability. Measured difference in inertial permeability between tube and frothy pumices can also be partly explained by the same variables but require an additional
parameter related to the internal roughness of the porous medium (friction factor f
0
). Constitutive equations for both types of permeability allow the quantification of laminar and turbulent gas escape during
ascent of rhyolitic magma in volcanic conduits. 相似文献
55.
Allowing structures to uplift modifies their seismic response; uplifting works as a mechanical fuse and limits the forces transmitted to the superstructure. However, engineers are generally reluctant to construct an unanchored structure because the system could overturn due to lacking redundancy. Using a safety factor for the design of a flat rocking foundation, ie, designing it wider, goes against the main idea of this seismic modification method as the force demand for the structure increases. We propose to extend the flat base of a rocking block with curved extensions to better protect the block from overturning, yet not prevent its uplifting. After investigating the seismic response of such rocking blocks, we extend the study to investigate the seismic response of rolling and rocking frames comprising columns with curved base extensions. The equations of motion are derived, time history analyses are performed, and rocking spectra are constructed. We draw two important conclusions: (a) the response of a class of rocking oscillators with curved base extensions is equivalent to the response of a flat-base rocking oscillators of the same slenderness, yet larger size; (b) the rotation demand on two negative stiffness rocking and rolling oscillators with the same uplifting acceleration and the same size is roughly the same as long as the rocking oscillators are not close to overturning. The above findings can serve as a basis for the rational seismic design of structures supported on rocking columns with curved bases, a system that has been used since the 1960s. 相似文献
56.
J. A. Bachmann M. Strand M. F. Vassiliou M. Broccardo B. Stojadinović 《地震工程与结构动力学》2018,47(2):535-552
An argument of engineers and researchers against the use of rocking as a seismic response modification technique is that the rocking motion of a structure is chaotic and the existing models are incapable of predicting it well. This argument is supported by the documented inability of rocking models to predict the motion of a specimen excited by a single ground motion. A statistical comparison of the experimental and the numerical responses of a rigid rocking oscillator not to a specific ground motion, but to ensembles of ground motions that have the same statistical properties, is presented. It is shown that the simple analytical model proposed by Housner in 1963 is capable of predicting the statistics of seismic response of a rigid rocking oscillator. 相似文献
57.
Rahmatulla M. Igamberdiev Goerres Grenzdoerffer Ralf Bill Hendrik Schubert Martin Bachmann Bernd Lennartz 《International Journal of Applied Earth Observation and Geoinformation》2011
This study presents an approach for chlorophyll content determination of small shallow water bodies (kettle holes) from hyperspectral airborne ROSIS and HyMap data (acquired on 15 May and 29 July 2008 respectively). Investigated field and airborne spectra for almost all kettle holes do not correspond to each other due to differences in ground sampling distance. Field spectra were collected from the height of 30–35 cm (i.e. area of 0.01–0.015 m2). Airborne pixels of ROSIS and HyMap imageries cover an area of 4 m2 and 16 m2 respectively and their spectra are highly influenced by algae or bottom properties of the kettle holes. Analysis of airborne spectra revealed that chlorophyll absorption near 677 nm is the same for both datasets. In order to enhance absorption properties, both airborne hyperspectral datasets were normalized by the continuum removal approach. Linear regression algorithms for ROSIS and HyMap datasets were derived using normalized average chlorophyll absorption spectra for each kettle hole. Overall accuracy of biomass mapping for ROSIS data was 71%, and for HyMap 64%. Biomass mapping results showed that, depending on the type of kettle hole, algae distribution, the ‘packaging effect’ and bottom reflection lead to miscalculations of the chlorophyll content using hyperspectral airborne data. 相似文献
58.
Celine Longchamp C. Bonadonna O. Bachmann A. Skopelitis 《Bulletin of Volcanology》2011,73(9):1337-1352
Explosive eruptions associated with tephra deposits that are only exposed in proximal areas are difficult to characterize.
In fact, the determination of physical parameters such as column height, mass eruption rate, erupted volume, and eruption
duration is mainly based on empirical models and is therefore very sensitive to the quality of the field data collected. We
have applied and compared different modeling approaches for the characterization of the two main tephra deposits, the Lower
Pumice (LP) and Upper Pumice (UP) of Nisyros volcano, Greece, which are exposed only within 5 km of the probable vent. Isopach
and isopleth maps were compiled for two possible vent locations (on the north and on the south rim of the caldera), and different
models were applied to calculate the column height, the erupted volume, and the mass eruption rate. We found a column height
of about 15 km above sea level and a mass eruption rate of about 2 × 107 kg/s for both eruptions regardless of the vent location considered. In contrast, the associated wind velocity for both UP
and LP varied between 0 and 20 m/s for the north and south vent, respectively. The derived erupted volume for the south vent
(considered as the best vent location) ranges between 2 and 27 × 108 m3 for the LP and between 1 and 5 × 108 m3 for the UP based on the application of four different methods (integration of exponential fit based on one isopach line,
integration of exponential and power-law fit based on two isopach lines, and an inversion technique combined with an advection–diffusion
model). The eruption that produced the UP could be classified as subplinian. Discrepancies associated with different vent
locations are smaller than the discrepancies associated with the use of different models for the determination of erupted
mass, plume height, and mass eruption rate. Proximal outcrops are predominantly coarse grained with ≥90 wt% of the clasts
ranging between −6ϕ and 0ϕ. The associated total grainsize distribution is considered to result from a combination of turbulent
fallout from both the plume margins and the umbrella region, and as a result, it is fines-depleted. Given that primary deposit
thickness observed on Nisyros for both LP and UP is between 1 and 8 m, if an event of similar scale were to happen again,
it would have a significant impact on the entire island with major damage to infrastructure, agriculture, and tourism. Neighboring
islands and the continent could also be significantly affected. 相似文献
59.
Ohne Zusammenfassung 相似文献
60.
An adaptive spectral technique for ground clutter and noise suppression in weather radar echoes is presented. This technique detects weak echoes that are masked by the residuals from ground clutter. The technique is demonstrated on two clear air cases observed with Doppler weather radar. After adaptive suppression of ground clutter and its residue, features appear over the Oklahoma City urban area where otherwise none could be seen. These are interpreted as birds' corridors between two lakes and along a river. 相似文献