Numerical modelling study on the flexural uplift of the Transantarctic Mountains

In this study, based on a 2-D thermomechanical finite element model, the uplift of the Transantarctic Mountains (TAM) is discussed in relation to the flexural uplift of a rheologically layered lithosphere, which is described by Vening-Meinesz's cantilever kinematics. The general model behaviour shows that the thickness of the crust and the geothermal gradient in the lithosphere are the principal factors in controlling the effective elastic thickness ( T _e). Although T _e is also significantly dependent on the magnitude of the uplift and the wet or dry rheological condition of rocks, these two factors do not have a dominant influence on the half-wavelength of the TAM. The model with a plausible crustal structure beneath Antarctica shows that the thermal structure beneath East Antarctica is the critical factor, controlling the half-wavelength of the TAM. If there is a significant radiogenic heat source in the Antarctic lithosphere, T _e beneath East Antarctica is estimated to be 50 km, at most, and the lithosphere has no potential to explain an exceptionally large-scale half-wavelength of the TAM. Even for the model without a heat source, if East Antarctica is significantly thermally influenced by West Antarctica, T _e is estimated to be about 60 km, and it is difficult to reproduce the half-wavelength of the TAM. Contrarily, when a radiogenic heat source is absent and the thermal structure beneath East Antarctica is not significantly affected by that beneath West Antarctica, the rheological structure beneath East Antarctica has the potential to reproduce the half-wavelength of the TAM ( T _e∼ 100 km). Thus, the presence of a radiogenic heat source in the crust and mantle and the thermal influence of West Antarctica on East Antarctica are crucial factors in the reproduction of the half-wavelength found in the TAM.     

Field experiments on remediation of coastal sediments using granulated coal ash

Field experiments were carried out to evaluate the effect of Granulated Coal Ash (GCA) on remediation of coastal sediments in terms of removing phosphates and hydrogen sulfide. Phosphate concentrations in the sediment were kept below 0.2 mg/l after the application of GCA, whereas those in the control sites increased up to 1.0 mg/l. The concentration of hydrogen sulfide in the sediment was maintained at almost zero in the experimental sites (GCA application sites) for over one year, whereas it ranged 0.1–2.4 mg S L⁻¹ in control sites. Meanwhile, individual number of benthos increased in the experimental sites by several orders of magnitude compared to the control sites. The major process involved in hydrogen sulfide removal by GCA was thought to be the increase in pH, which suppresses hydrogen sulfide formation. From our findings, we concluded that GCA is an effective material for remediating organically enriched coastal sediment.     

Effect of helix bending deflection on load settlement behaviour of screw pile

A screw pile has higher end bearing capacity than any other straight pipe piles due to its larger helix with respect to central shaft. However, larger helices are not frequently used as it will bend and may reduce the actual bearing capacity of the ground. In the present study, the effect of helix bending deflection on the load settlement behaviour and ultimate bearing capacity is investigated. To achieve the objectives, model scale pile load tests were conducted. The effect of helix bending on the load settlement behaviour at higher stress level was also investigated in this research. The helices with different helix-to-shaft-diameter ratios and thicknesses were used, so that clear difference of deformed and non-deformed screw piles in the load settlement behaviour can be observed. Dry Toyoura sand in dense state was used as a model ground. It is observed from test results that the helix bending deflection starts affecting the load settlement behaviour of the ground if it is more than the critical helix bending deflection. The ratio of critical helix bending deflection to outstand length decreases with increase in helix-to-shaft-diameter ratio, and its relationship is presented in this study. It is also observed that the Roark’s formula for flat circular plate having uniform load over a very small circular area with fixed outer edges showed good agreement with the measured helix bending deflection. In order to estimate the optimum helix thickness, the well-agreed equation is also modified with respect to critical helix bending deflection.

     

Expansion of the disturbing function for high eccentricity and large amplitude of libration

Following some ideas, developed by Woltjer (1928), Message (1989), Yokoyama (1988, 1989) and Duriez (1990) an expansion of the disturbing function is given for high values of the eccentricity and large amplitude of libration. The classical expansion can be obtained as a particular case of the present model. Several asteroids with high eccentricity and large amplitude of libration are tested and the results are much better than those obtained from the classical theory.     

Geologic evidence for late Quaternary repetitive surface faulting on the Isurugi fault along the northwestern margin of the Tonami Plain,north‐central Japan

Our detailed field investigation, paleoseismic trenching, and airborne light detection and ranging (LiDAR)‐derived topographic data provides the first direct evidence for late Quaternary repetitive surface faulting on the northeast‐striking Isurugi fault along the northwestern margin of the Tonami Plain in the Hokuriku region of north‐central Japan. This fault has been interpreted previously by different researchers as both inactive and active, owing to a lack of geologic evidence and a failure to identify fault‐related geomorphic features. Our mapping of LiDAR topography revealed a series of northeast‐trending warped fluvial terraces, about 1.5 km long and 170 m wide, with an age of ≤ 29 ka. We interpreted these geomorphologic features to represent an active pop‐up structure bounded to the southeast by the northwest‐dipping main thrust of the Isurugi fault and to the northwest by a southeast‐dipping backthrust that splays off the main thrust in the shallow subsurface. Paleoseismic trenching across the northwestern part of an elongate terrace exposed a series of southeast‐dipping backthrusts and associated northwest‐verging monoclines. The deformation and depositional age of the strata provide evidence for repetitive surface rupturing on the backthrusts since the latest Pleistocene; the latest of these events occurred in the Holocene between about 4.0 and 0.9 ka. Despite the poor preservation of the surface expression of the Isurugi fault, repetitive scarp‐forming faulting in the late Quaternary and the proximity of the Oyabe River and its tributaries to the fault trace suggest that there may be an extension of the Isurugi fault to the northeast and southwest beneath the Tonami Plain that makes the fault long enough to generate a large earthquake (Mw ≥ 6.8) accompanied by surface rupture.     

Characteristics of isolated hybrid tremor (HBT) during a calm activity period at Aso Volcano

Isolated-type tremors having two events with different dominant frequencies are characteristic seismological phenomena observed during the fumarolic activity stage at Aso Volcano. These isolated tremors are called hybrid tremors (HBT) and comprise two parts: an initial part named the “HF-part” with a dominant frequency in the high-frequency region (approximately 10 Hz) and the following part named the “LF-part” with a dominant frequency in the low-frequency region (approximately 2 Hz). The LF-part is observed after the HF-part, and the HBT is accompanied by a long-period tremor (LPT). Hypocenters and source parameters are estimated using seismograms recorded at 64 stations around Nakadake crater. The amplitude distributions of all HF-parts have almost similar trends. Similarly, the amplitude distributions of all LF-parts have almost similar trends. However, the amplitude distributions of HF- and LF-parts are not similar. From these results, we proposed that the hypocenters and source parameters of HF- and LF-parts are not common, but each of them have common hypocenters and source parameters. The hypocenter region of HF-parts was estimated to be just beneath the fumarole region south of the 1st crater: the volume fluctuation is the major source factor. The hypocenter region of LF-parts is estimated to be at a depth of approximately 300 m beneath the first crater: the strike–slip component is the major source parameter. The hypocentral depth of LF-parts is located at the upper end of the crack estimated to be the source of the LPTs. The LPTs and HBTs are observed almost simultaneously. We consider that volcanic fluid is involved in the source mechanisms of both HBT and LPT.     

Color measurements of volcanic ash deposits from three different styles of summit activity at Sakurajima volcano,Japan: Conduit processes recorded in color of volcanic ash

We measured quantitatively colors of volcanic ash deposits erupted from three different styles of summit activity (Strombolian activity, Vulcanian explosions and continuous ash venting activity) at Sakurajima volcano from 1974 to 1985. Colors of Strombolian ash samples have larger yellow components of their visible spectra (b^? values) than those of explosion and continuous venting ash samples. Colors of explosion ash samples show larger variation in both red and yellow components of their visible spectra (a^? and b^? values, respectively), while colors of continuous venting ash samples are in the narrow ranges within colors of explosion ash samples. Colors of components with lower densities than 3.1 g/cm³ (groundmass and phenocrystic plagioclase) obtained by magnetic and heavy liquid separation methods are similar to the unseparated bulk ash samples. This result suggests that the color variations of ash deposits are mainly originated from the particles composed of groundmass. The particles can be classified into three different types of particles with different vesicularity and crystallinity (vesicular particle [VP], dense particle with vesicles [DPV] and dense particle without vesicles [DP]). Analytical results of component proportions, chemical compositions of groundmass glasses, ferrous iron contents and surface ferric materials show that (1) VP has larger yellow components of the visible spectrum (b^? values) and high ferrous iron content, and is less crystallized than the DP and DPV, (2) DP has larger red and yellow components of its visible spectrum (a^? and b^? values, respectively) and involves ferric materials on the surfaces produced by oxidation process, and (3) DPV has smaller red and yellow components of its visible spectrum (a^? and b^? values, respectively) and involves less ferric materials on the ash surfaces. Color differences of ash deposits from three different activity styles can be explained by the different mixing ratios of VP, DPV and DP. During the Strombolian activity, the VP is a main component in the ash, which is formed from relatively less degassed and crystallized magma. In the Vulcanian explosion and continuous ash venting activity, the proportions of DPV and DP in ash are larger than that in the Strombolian activity. The highly crystallized DP may correspond to a vent cap, and DPV to a magma below the cap. The color measurements of ash deposits provide information on the pre-eruptive processes at the shallower levels of a conduit.     

Relations between Light Hydrocarbon, Carbon Monoxide, and Carbon Dioxide Concentrations in the Plume from the Combustion of Plant Material in a Furnace

To systematically explain relations between light hydrocarbons, CO, and CO₂ concentrations/emissions of biomassburning, we measured concentrations/emissions of carbon gases – CO,CO₂, light hydrocarbons (CH₄, C₂H₆,C₂H₄, C₂H₂, C₃H₈, C₃H₆,n-C₄H₁₀, i-C₄H₁₀, n-C₅H₁₂,i-C₅H₁₂), and THC (total hydrocarbon) – in the burning of dead plant material, mainly Imperata grass, byclosed-chamber experiments and by time-series analyses of gas concentrations in combustion plumes in relatively efficient and inefficient combustion situations. Concentrations of hydrocarbons measured were well correlated to [CO] although [C₂H₂] was exceptionally well correlated to[CO₂]. The phase diagrams (relation between [CO]/ [CO₂] and [hydrocarbon]/ [CO₂]) obtained by the time-seriesexperiments well illustrated the variation in the overall emission rates of the closed-chamber experiments. The higher rates of decrease in hydrocarbon concentration with increasing carbon number in the efficient case compared with the inefficient case probably reflected the rate of oxidation and the amount of radicals. The overall concentrations (or emissions) of C₂H₄ and C₃H₆ were higher thanthose of C₂H₆ and C₃H₈, suggesting a linkage to mechanisms in whichthe predominant path of hydrocarbon oxidation is through the degradation of alkyl radicals, which can be immediately converted into or formed from alkenes. For C₃ and C₄ species, normal-chain species hadhigher emissions than iso-chain species under lower combustion efficiency. This may be attributable to the presence of tertiary C–H bonds in iso-species,which show more reactivity in the abstraction of H than secondary C–H bonds unless the carbon number is large.     

Local high relief at the southern margin of the Andean plateau by 9 Ma: evidence from ignimbritic valley fills and river incision

A valley‐filling ignimbrite re‐exposed through subsequent river incision at the southern margin of the Andean (Puna) plateau preserves pristine geological evidence of pre‐late Miocene palaeotopography in the north western Argentine Andes. Our new ⁴⁰Ar/³⁹Ar dating of the Las Papas Ignimbrites yields a plateau age of 9.24 ± 0.03 Ma, indicating valley‐relief and orographic‐barrier conditions comparable to the present‐day. A later infill of Plio–Pleistocene coarse conglomerates has been linked to wetter conditions, but resulted in no additional net incision of the Las Papas valley, considering that the base of the ignimbrite remains unexposed in the valley bottom. Our observations indicate that at least 550 m of local plateau margin relief (and likely >2 km) existed by 9 Ma at the southern Puna margin, which likely aided the efficiency of the orographic barrier to rainfall along the eastern and south eastern flanks of the Puna and causes aridity in the plateau interior.     

Trace element concentrations in silicate spherules from oceanic sediments

The possible existence of meteoritic spherules was investigated among several silicate spherules separated from oceanic sediments and analyzed by means of INAA (instrumental neutron activation analysis).A 0.72 mg glassy spherule was found to have uniform enrichment of 4 ~ 5 for the refractory REE (rare earth elements) and Sc with substantial depletion of Ce relative to chondritic abundances. This implies that this spherule is meteoritic in origin and that the enrichment of refractory elements was established by high temperature heating in a high O/H environment, possibly at the time of entering the Earth's atmosphere.The other three analyzed spherules showed major and trace element abundances that are consistent with an origin in the oceanic environment.