Satoru Honda

Both Comprehensive and Brief Self-Administered Diet History Questionnaires Satisfactorily Rank Nutrient Intakes in Japanese Adults

Background A comprehensive self-administered diet history questionnaire (DHQ: 150-item semi-quantitative questionnaire) and a brief self-administered DHQ (BDHQ: 58-item fixed-portion–type questionnaire) were developed for assessing Japanese diets. We compared the relative validity of nutrient intake derived from DHQ with that from the BDHQ, using semi-weighed 16-day dietary records (DRs) as reference. Methods Ninety-two Japanese women aged 31 to 69 years and 92 Japanese men aged 32 to 76 years completed a 4-nonconsecutive-day DR, a DHQ, and a BDHQ 4 times each (once per season) in 3 areas of Japan (Osaka, Nagano, and Tottori). Results No significant differences were seen in estimates of energy-adjusted intakes of 42 selected nutrients (based on the residual method) between the 16-day DRs and the first DHQ (DHQ1) or between the DR and the first BDHQ (BDHQ1) for 18 (43%) and 14 (33%) nutrients, respectively, among women and for 4 (10%) and 21 (50%) nutrients among men. The median (interquartile range) Pearson correlation coefficients with the DR for energy-adjusted intakes of the 42 nutrients were 0.57 (0.50 to 0.64) for the DHQ1 and 0.54 (0.45 to 0.61) for the BDHQ1 in women; in men, the respective values were 0.50 (0.42 to 0.59) and 0.56 (0.41 to 0.63). Similar results were observed for the means of the 4 DHQs and BDHQs. Conclusions The DHQ and BDHQ had satisfactory ranking ability for the energy-adjusted intakes of many nutrients among the present Japanese population, although these instruments were satisfactory in estimating mean values for only a small number of nutrients.

Thermal structure beneath Tohoku, northeast japan

Combined with geophysical observations and petrological considerations, we have studied the thermal models of the Tohoku (northeast Japan) subduction zone. The temperature of the deeper part of the mantle wedge is constrained by the petrological requirements that demand a high-temperature region (> 1400°C) beneath the volcanic zone. To satisfy this condition, namely to explain the arc volcanism in the Tohoku subduction zone, a high-temperature upper mantle beneath the Japan Sea (possibly 1400°C at the depth shallower than 100 km) is required. Heat flow distribution, which constrains the temperature structure at shallower depth, shows that low heat-flow values ranging from 20 to 50 mW/m2 are distributed between the trench and aseismic front and consistently high heat flow values (80–120 mW/m2) prevail in the area landward of the volcanic front including the Japan Sea. Recent heat flow measurements indicate that the transition from low to high heat flow occurs between the aseismic front and volcanic front. This heat flow distribution restricts the form of the flow in the mantle wedge and shear stress acting at the plate boundary. A rigid (non-moving) triangular region bounded by the subducting slab and the vertical plane beneath the aseismic front is necessary to explain the low-heat-flow zone between the trench and aseismic front. Shear stress of about 500 to 1000 bar is supposed to act at the interface between the subducting slab and rigid triangular mantle. We also suggest that, to explain the peak of heat flow near the volcanic front (> 120 mW/m2), magma migration rate of about 0.05 cm3 cm−2 year−1 is necessary. A comparison of the thermal structure of the Tohoku subduction zone with that of the central South America, which was preliminary calculated by the similar scheme, shows that the temperature in the mantle wedge of the central South America is probably lower than that of the Tohoku subduction zone. This difference may result in that of the nature of volcanic rocks.

Small-scale convection under the back-arc occurring in the low viscosity wedge

Abstract Water released from subducting slabs through a dehydration reaction may lower the viscosity of the mantle significantly. Thus, we may expect a low viscosity wedge (LVW) above the subducting slabs. The LVW coupled with a large-scale flow induced by the subducting slabs may allow the existence of roll-like small-scale convection whose axis is normal to the strike of the plate boundary. Such a roll structure may explain the origin of along-arc variations of mantle temperature proposed recently in northeast Japan. We study this possibility using both 2D and 3D models with/without pressure- and temperature-dependent viscosity. 2D models without pressure and temperature dependence of viscosity show that, with a reasonable geometry of the LVW and subduction speed, small-scale convection is likely to occur when the viscosity of the LVW is less than 10 19 Pa s. Corresponding 3D model studies reveal that the wavelength of rolls depends on the depth of the LVW. The inclusion of temperature-dependent viscosity requires the existence of further low viscosity in the LVW, since temperature dependence suppresses the instability of the cold thermal boundary layer. Pressure (i.e. depth) dependence coupled with temperature dependence of the viscosity promotes short wavelength instabilities. The model, which shows a relatively moderate viscosity decrease in the LVW (most of the LVW viscosity is 10 18 ∼10 19 Pa s) and a wavelength of roll ∼80 km, has a rather small activation energy and volume (∼130 kJ/mol and ∼4 cm 3 /mol) of the viscosity. This small activation energy and volume may be possible, if we regard them as an effective viscosity of non-linear rheology.

Multiple phase transitions and the style of mantle convection

Abstract Multiple phase transitions, based on experimental and theoretical results, have been incorporated into an extended Boussinesq model of mantle convection. A formulation is used which facilitates the numerical computations of convection with multiple phase transitions and a triple point near the 670 km discontinuity. The propensity for layered convection is enhanced by including the additional phase transitions. The location of the triple point of the spinel to perovskite phase transitions plays an important role in controlling the fate of the ascending hot plumes. A plume with a core temperature above this triple point temperature T c tends to pass easily through the phase boundary at 670 km. Plumes with a core temperature lower than T c are blocked by the multiple phase transitions. Both depth-dependent thermal expansivity and internal heating increase the tendency of the convective system to layering. The dynamical time-scales in the transition zone are much shorter than those of the top and bottom boundary layers. Simulations with increasing Rayleigh number (Ra) from 10 6 to 5 × 10 7 show unambiguously the increased tendency toward layering with larger Ra. In the early Earth, when Ra was higher and internal heating was several times stronger, layered convection might have been the preferred mode of mantle convection. With time, as both Ra and radioactive heating decreased, the style of mantle convection would have become less layered.

Three-dimensional dynamics of hydrous thermal-chemical plumes in oceanic subduction zones

Hydration and partial melting along subducting slabs can trigger Rayleigh-Taylor-like instabilities. We use 3-D petrological-thermomechanical numerical simulations to investigate small-scale convection and hydrous, partially molten, cold plumes formed in the mantle wedge in response to slab dehydration. The simulations were carried out with the I3ELVIS code, which is based on a multigrid approach combined with marker-in-cell methods and conservative finite difference schemes. Our numerical simulations show that three types of plumes occur above the slab-mantle interface: (1) finger-like plumes that form sheet-like structure parallel to the trench, (2) ridge-like structures perpendicular to the trench, and (3) flattened wave-like instabilities propagating upward along the upper surface of the slab and forming zigzag patterns parallel to the trench. The viscosity of the plume material is the main factor controlling the geometry of the plumes. Our results show that lower viscosity of the partially molten rocks facilitates the Rayleigh-Taylor-like instabilities with small wavelengths. In particular, in low-viscosity models (1018–1019 Pa s) the typical spacing of finger-like plumes is about 30–45 km, while in high-viscosity models (1020–1021 Pa s) plumes become rather sheet-like, and the spacing between them increases to 70–100 km. Water released from the slab forms a low-viscosity wedge with complex 3-D geometries. The computed spatial and temporal pattern of melt generation intensity above the slab is compared to the distribution and ages of volcanoes in the northeast Japan. Based on the similarity of the patterns we suggest that specific clustering of volcanic activity in this region could be potentially related to the activity of thermal-chemical plumes.

Broadband seismic observation at the Sakurajima Volcano, Japan

We installed a portable broadband seismometer (Streckeisen STS-2) at the Sakurajima volcano, which has been very active in the recent years. The recorded seismograms show a wide variety (both in temporal and spectral contents) of seismic events, from explosions to tremors, and exhibit the importance of such broadband seismometry at volcanos. We present examples of seismograms to show the potential of broadband seismic observation in monitoring volcanic activities.

Fractal analysis of fault systems in Japan and the Philippines

Complexity of fault systems in Japan and the Philippines is quantitatively measured using fractal dimension. The areas studied are the Median Tectonic Line, Izu, Unzen on the Japanese Islands, and the fault system yielded by the Philippine earthquake which occurred on July 16, 1990. Results are summarized as follows: Fractal dimensions along the Median Tectonic Line vary between 1 and 1.3. The Unzen area gives the highest fractal dimension (1.4) of all the areas studied, which implies that the fault system there is the most complex. Fractal dimension of the fault system associated with the Philippine earthquake is smaller than 1. It can be interpreted that this fault system is almost one-dimensional, with truncated by numerous gaps of various sizes.

Evolution of late Cenozoic magmatism and the crust–mantle structure in the NE Japan Arc

Abstract We review the evolution of late Cenozoic magmatism in the NE Japan arc, and examine the relationship between the magmatism and the crust–mantle structure. Recent studies reveal secular changes in the mode of magmatic activity, the magma plumbing system, erupted volumes and magmatic composition associated with the evolution of crust–mantle structures related to the tectonic evolution of the arc. The evolution of Cenozoic magmatism in the arc can be divided into three periods: the continental margin (66–21 Ma), the back-arc basin (21–13.5 Ma) and the island-arc period (13.5–0 Ma). Magmatic evolution in the back-arc basin and the island-arc periods appears to be related to the 2D to 3D change in the convection pattern of the mantle wedge related to the asthenosphere upwelling and subsequent cooling of the mantle. Geodynamic changes in the mantle caused back-arc basin basalt eruptions during the back-arc basin opening (basalt phase) followed by crustal heating and re-melting, which generated many felsic plutons and calderas (rhyolite/granite phase) in the early stage of the island-arc period. This was followed by crustal cooling and strong compression, which ensured vent connections and mixing between deeper mafic and shallower felsic magmas, erupting large volumes of Quaternary andesites (andesite phase).

The timescales of plume generation caused by continental aggregation

Abstract To understand the thermal evolution of the mantle following the aggregation of non-subductable thick continental lithosphere, we study a numerical model in which a supercontinent, simulated by high viscosity raft, HVR, covers a part of the top surface of a convection layer. We model infinite Prandtl number convection either in a three-dimensional (3D) spherical shell, 3D rectangular box (aspect ratios: 8 and 4) or two-dimensional (2D) rectangular box (aspect ratio: 8) and except for the HVR, we specify a constant viscosity. The HVR, which has a viscosity higher than that of its surrounding, is instantaneously placed on the top surface of a well-developed convection layer and its position is fixed. Our results from 3D spherical shell cases with and without phase transitions show the emergence of a large plume characterized by a long wavelength thermal anomaly (a degree one pattern) for a Pangea-like geometry. We analyze the volume averaged temperature under the HVR (=〈 T C 〉) the remaining (oceanic) area (=〈 T O 〉) and total area (=〈 T M 〉) to determine the timescale of plume generation. The difference between 〈 T C 〉 and 〈 T O 〉(=Δ T CO ) and 〈 T M 〉 show the existence of two characteristic timescales.Δ T CO exhibits an initial rapid increase and may become constant or continue to gradually increase. Meanwhile, 〈 T M 〉 shows a similar behavior but with a longer timescale. We find that these timescales associated with the increase of Δ T CO and 〈 T M 〉 can be attributed to the formation of large scale flow (i.e. plume) and response of the whole system to the emplacement of the HVR, respectively. For 3D spherical cases, we find that the timescale of plume generation is 1–2 Gyr, if the Rayleigh number is 10 6 . To determine the effects of the viscosity of the HVR, 2D versus 3D modeling and the effects of the internal heating, we have also studied 2D and 3D rectangular box cases. A factor of about two variation exists in the timescale of plume generation. It appears that the timescale becomes greater for a smaller amount of internal heating. This may be attributed to the time-dependent flow caused by the internal heating. For 2D cases, we find that the timescale of the high Rayleigh number (10 7 ) case is shortened by a factor of three to five when compared to the Ra=10 6 case, which is consistent with the simple boundary layer theory. This may imply that well-developed plumes may arise with the timescale of 0.2 to 0.4 Gyr (for Ra=10 7 ).

The interaction of plumes with the transition zone under continents and oceans

Abstract The dynamics of mantle flow with phase transitions can be influenced by the presence of a thick continental lithosphere, especially for the 400 km phase transition. We have studied the effects of the continental lithosphere on the mantle convection with the two major phase transitions at 400 km and 660 km. A 2-D model with an aspect-ratio 8 box was used in which the surface was divided into two domains: “oceanic” and “continental”. The “continental” lithosphere is modeled by a highly viscous, 200 km thick lid which is 100 times stiffer than the “oceanic” part. We also consider the consequences of plate reconfiguration by switching instantaneously the underlying rheological structure of the “oceanic” and “continental” domains. A depth-dependent viscosity with an additional jump at 660 km depth was employed. Other depth-dependent properties employed are the thermal expansivity and the thermal diffusivity. Both internal and basal heating configurations were studied. Our results show that there are distinct differences in the mode of interaction of plumes with the transition zone under continents and oceans. Much larger stationary plumes are developed in the lower mantle under continents, and erupt from time to time into the upper mantle, creating a very hot continental upper mantle. Plumes under oceans are weaker but produce fast horizontal jets, when the plumes impinge upon the surface. Very large plumes are formed in the internally heated cases because of the presence of depth-dependent properties in the lower mantle, creating a thick bottom boundary layer. This thick thermal boundary layer is swept upward under the continents by a large-scale flow in the lower mantle. These results can be important for the interpretation of seismic tomography under Africa and the central Pacific.