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  • Xanthium canadense  (4)
  • 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones  (3)
  • 1
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    Natural and Experimental Evidence of Melt Lubrication of Faults During Earthquakes (2007)
    NPG
    Details
    Publication Date: 2017-04-04
    Description: Melt produced by friction during earthquakes may act either as a coseismic fault lubricant or as a viscous brake. Here we estimate the dynamic shear resistance (tf) in the presence of frictioninduced melts from both exhumed faults and high-velocity (1.28 meters per second) frictional experiments. Exhumed faults within granitoids (tonalites) indicate low tf at 10 kilometers in depth. Friction experiments on tonalite samples show that tf depends weakly on normal stress. Extrapolation of experimental data yields tf values consistent with the field estimates and well below the Byerlee strength. We conclude that friction-induced melts can lubricate faults at intermediate crustal depths.
    Description: Published
    Description: 647-649
    Description: JCR Journal
    Description: reserved
    Keywords: Melt Lubrication ; Faults ; Earthquakes ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Low- to high-velocity frictional properties of the clay-rich gouges from the slipping zone of the 1963 Vaiont slide, northern Italy (2012)
    Details
    Publication Date: 2017-04-04
    Description: The final slip of about 450 m at about 30 m/s of the 1963 Vaiont landslide (Italy) was preceded by 〉3 year long creeping phase which was localized in centimeter-thick clay-rich layers (60–70% smectites, 20–30% calcite and quartz). Here we investigate the frictional properties of the clay-rich layers under similar deformation conditions as during the landslide: 1–5 MPa normal stress, 2 × 10−7 to 1.31 m/s slip rate and displacements up to 34 m. Experiments were performed at room humidity and wet conditions with biaxial, torsion and rotary shear apparatus. The clay-rich gouge was velocity-independent to velocity-weakening in both room humidity and wet conditions. In room humidity experiments, the coefficient of friction decreased from 0.47 at v 〈 5.0 × 10−5 m/s to 0.12 at 1.31 m/s. Microstructural and mineralogical analyses of the gouge after experiments indicate that the dramatic weakening results from thermo-chemical pressurization of pore fluids (smectite decomposition to illite-type clays) and powder lubrication. In wet experiments, the coefficient of friction decreased from 0.17 at v 〈 1.0 × 10−4 m/s to 0.0 at v 〉 0.70 m/s: full lubrication results from the formation of a continuous water film in the gouge. The Vaiont landslide occurred under wet to saturated conditions. The unstable behavior of the landslide is explained by the velocity-weakening behavior of the Vaiont clay-rich gouges. The formation of a continuous film of liquid water in the slipping zone reduced the coefficient of friction to almost zero, even without invoking the activation of thermal pressurization. This explains the extraordinary high velocity achieved by the slide during the final collapse.
    Description: Published
    Description: B09208
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: friction ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 3
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    Fault lubrication during earthquakes (2012)
    Details
    Publication Date: 2017-04-04
    Description: The determination of rock friction at seismic slip rates (about 1 m s(-1)) is of paramount importance in earthquake mechanics, as fault friction controls the stress drop, the mechanical work and the frictional heat generated during slip(1). Given the difficulty in determining friction by seismological methods(1), elucidating constraints are derived from experimental studies(2-9). Here we review a large set of published and unpublished experiments (similar to 300) performed in rotary shear apparatus at slip rates of 0.1-2.6 ms(-1). The experiments indicate a significant decrease in friction (of up to one order of magnitude), which we term fault lubrication, both for cohesive (silicate-built(4-6), quartz-built(3) and carbonate-built(7,8)) rocks and non-cohesive rocks (clay-rich(9), anhydrite, gypsum and dolomite(10) gouges) typical of crustal seismogenic sources. The available mechanical work and the associated temperature rise in the slipping zone trigger(11,12) a number of physicochemical processes (gelification, decarbonation and dehydration reactions, melting and so on) whose products are responsible for fault lubrication. The similarity between (1) experimental and natural fault products and (2) mechanical work measures resulting from these laboratory experiments and seismological estimates(13,14) suggests that it is reasonable to extrapolate experimental data to conditions typical of earthquake nucleation depths (7-15 km). It seems that faults are lubricated during earthquakes, irrespective of the fault rock composition and of the specific weakening mechanism involved.
    Description: European Research Counsel
    Description: Published
    Description: 494-498
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: friction ; faults ; lubrication ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 4
    Electronic Resource
    Electronic Resource
    Leaf nitrogen distribution in relation to leaf age and photon flux density in dominant and subordinate plants in dense stands of a dicotyledonous herb (1998)
    Springer
    Oecologia 113 (1998), S. 314-324 
    Details
    ISSN: 1432-1939
    Keywords: Key words Leaf age ; Leaf mass per area ; Nitrogen content ; Photon flux density ; Xanthium canadense
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We studied the effects of photon flux density (PFD) and leaf position, a measure of developmental age, on the distribution of nitrogen content per unit leaf area (N area) in plants of different heights, in dense stands grown at two nitrogen availabilities and in solitary plants of the erect dicotyledonous herb Xanthium canadense. Taller more dominant plants received higher PFD levels and experienced a larger difference in relative PFD between their youngest and oldest leaves than shorter subordinate plants in the stands. Differences in PFD between leaves of solitary plants were assumed to be minimal and differences in leaf traits, found for these plants, could thus be mainly attributed to an effect of leaf position. In the solitary plants, N area decreased with leaf position while in the plants from the stands it decreased with decreasing relative PFD, indicating both factors to be important in determining the distribution of N area. Due to the effect of leaf position on N area, leaves of subordinate plants had a higher N area than older leaves of dominant plants which were at the same height or slightly higher in the canopy. Consequently, the N area distribution patterns of individual plants plotted as a function of relative PFD were steeper, and probably closer to the optimal distribution which maximizes photosynthesis, than the average distribution in the stand. Leaves of subordinate plants had a lower mass per unit area (LMA) than those of dominant plants. In the dominant plants, LMA decreased with decreasing relative PFD (and with leaf position) while in the subordinate plants it increased. This surprising result for the subordinate plants can be explained by the fact that, during the course of a growing season, these plants became increasingly shaded and newer leaves were thus formed at progressively lower light availability. This indicates that LMA was strongly determined by the relative PFD at leaf formation and to a lesser extent by the current PFD. Leaf N content per unit mass (N mass) was strongly determined by leaf position independent of relative PFD. This indicates that N mass is strongly ontogenetically related to the leaf-aging process while changes in N area, in response to PFD, were regulated through changes in LMA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050382
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of shift in flowering time on the reproductive output of Xanthium canadense in a seasonal environment (1998)
    Springer
    Oecologia 114 (1998), S. 361-367 
    Details
    ISSN: 1432-1939
    Keywords: Key words Cost of reproduction ; Optimal flowering ; Photoperiodic manipulation ; Seasonal environment ; Xanthium canadense
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We studied the effects of a change in flowering date on the reproductive output of a short-day annual plant, Xanthium canadense. The flowering date was changed by photoperiodic manipulation to 1 month earlier or later than the natural flowering date. Plants with the natural flowering date attained the highest reproductive output. For those flowering 1 month earlier or later, the reproductive output was decreased by 42% or 23%, respectively. The reproductive output was analyzed as the product of the biomass production during the reproductive period and its allocation to the reproductive organs. Although delay in flowering increased biomass production, it decreased its fractional allocation to the reproductive organs. The highest reproductive output in the natural flowering plants resulted from a compromise between these two effects of flowering. Plants flowering earlier had higher translocation rates to the reproductive organs and accelerated plant senescence. Later flowering caused a reduction in biomass translocation to the reproductive organs and thus extended the reproductive period. These experimental results are discussed in relation to the cost of reproduction and the optimal time for flowering that maximizes the final reproductive output. It is suggested that the natural flowering time maximized the reproductive output while minimizing the cost of reproduction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00008818
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  • 6
    Electronic Resource
    Electronic Resource
    Timing of seed germination and the reproductive effort in Xanthium canadense (1993)
    Springer
    Oecologia 95 (1993), S. 334-339 
    Details
    ISSN: 1432-1939
    Keywords: Flowering ; Germination ; Model ; Reproductive effort ; Xanthium canadense
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of different dates of germination on the timing of flowering and the final reproductive yield was examined in a short-day annual plant Xanthium canadense (cocklebur). Delays in germination of 30 and 60 days deferred flower initiation by 2 and 9 days, respectively. Although plants that germinated later were smaller because of the shorter growing period, the reproductive yields did not show as much reduction as the vegetative biomass. The reproductive effort (RE, defined as the ratio of final reproductive yield to the vegetative biomass at the end of the growing season) increased 1.5 and 2.5 times with delays in germination of 30 and 60 days, respectively. A simple model of plant growth was used to analyse the factors involved in the control of RE, which depends only on the dry mass productivity and its partitioning in the reproductive phase, and is independent of the productivity and partitioning in the vegetative phase. Since relative allocation of dry mass to the reproductive part in the reproductive phase was similar for plants with different germination dates, the different REs could be ascribed mainly to differences in productivity of the vegetative parts in the reproductive period. The dependence of RE on plant size is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00320985
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  • 7
    Electronic Resource
    Electronic Resource
    Growth schedule of Xanthium canadense: Does it optimize the timing of reproduction? (1991)
    Springer
    Oecologia 88 (1991), S. 55-60 
    Details
    ISSN: 1432-1939
    Keywords: Annual plant ; Nutrition ; Optimization ; Reproductive allocation ; Xanthium canadense
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The effects of nutrition on the timing of reproductive initiation of a short-day annual plant Xanthium canadense (cocklebur) were examined with the following hypotheses in mind: If the plant always follows an optimal growth schedule, low-nutrient plants will initiate reproductive growth earlier than high-nutrient plants. On the other hand, if the plant flowers in response to photoperiodic stimuli, both plants will initiate reproductive growth on the same day. The sand-culture experiment showed that high-nutrient plants flowered earlier than the low-nutrient plants, leading to rejection of the first hypothesis. The predicted optimal flowering time is 2 days later than the actual flowering time in high-nutrient plants and 10 days earlier in low-nutrient plants. These deviations from the optimal times reduced the reproductive yield by 0.1% and 2.3%, respectively. The ratio of the final reproductive yield to the vegetative mass at flower initiation was 1.10 in high-nutrient plants and 0.63 in low-nutrient plants. Since the expected ratio for the optimal growth schedule is 1.0, high-nutrient plants followed the opitmal growth schedule more closely than the low-nutrient plants. Cocklebur is a fast-growing annual which is common in relatively nutrient-rich environments. This study suggests that cocklebur adapts itself to such environments through its photoperiodic response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328403
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