We present Early Cretaceous partial melting recorded by pelitic gneiss from the Nagasaki Metamorphic Complex, western Kyushu, Japan. The existence of the partially melted rock in the complex may ...imply initiation of long-lived high-T metamorphism in proto-southwest Japan at Cretaceous eastern margin of Eurasia. The gneisses are composed of three garnet-bearing layers and one felsic lens, and they show mylonitic foliation. Application of Zr-in-rutile geothermometer and quartz-in-garnet Raman geobarometer for inclusion rutile and quartz in garnet provided prograde condition of 670-692°C and 1.01-1.26 GPa and peak condition of 755-769°C and 1.17-1.38 GPa. These conditions correspond to those of lower crustal depths between volcanic arc and forearc where thermal advection by wedge mantle corner flow occurs. Presence of the felsic lens whose mineral assemblage can undergo partial melting under the peak condition and presence of a crystallized melt inclusion in garnet suggest that distinct partial melting occurred during the metamorphism. The concordant U-Pb ages of metamorphic zircon rims are ranging from 131.5 ± 4.3 to 120.1 ± 3.9 Ma. The mean square weighted deviation (MSWD) of the metamorphic age was as large as 6.4, implying a significant duration of high-T condition for growth of metamorphic zircon. The obtained ages are within the period of the magmatic hiatus that has previously proposed around southwest Japan and Korean Peninsula (ca. 160-120 Ma) that is due to stop of wedge mantle corner flow by flatting of subducting slab. Our results suggest that high-T metamorphism associated with partial melting at lower crustal depths along Early Cretaceous proto-southwest Japan has already been initiated at the late stage of the hiatus (ca. 130 Ma). This may be due to slab rollback and trench retreat at eastern margin of Eurasia.
These townhouse models from the Siebold collection constitute an invaluable piece of historical material through which the structure of modern era townhouse can be examined in detail. However, it was ...unknown at first which town or region in Japan had inspired the architectural style used in the models. By singling out “town headmen residence” from other townhouse models, further examination has also revealed that this particular model was built to the image of the official housing of “machi otona” from town house of Nagasaki. In addition, the other machiya models also model the town house of Nagasaki.
SUMMARY
Unzen volcano, located on Shimabara Peninsula, Nagasaki, Japan, is an active volcano that has been intensively monitored since 1989, one year before the most recent eruption in 1990–1995. ...Previous earthquake and surface deformation studies have revealed that magma is transported obliquely from a magma reservoir beneath Tachibana Bay, to the west of Shimabara Peninsula. Here, we conduct broad-band magnetotelluric (MT) surveys at 99 sites around Shimabara Peninsula to investigate the crustal structure beneath Unzen volcano that is related to magma migration. A 3-D resistivity model that is constructed from 25 broad-band MT sites and 45 telluric sites shows a broad high-resistivity zone beneath Shimabara Peninsula and low-resistivity zones to the west and east of the peninsula. An unexpected observation is the spatial alignment of the high-resistivity zone with a seismic low-velocity zone (LVZ) at 3–15 km depth. Quantitative analysis indicates this high-resistivity zone contains < 0.7 per cent melt under the assumption that the melt is stored in a good porosity network, while < 11 per cent melt in relatively poor pore network. We infer this high-resistivity, LVZ to be a highly crystallized mush zone (HCMZ) with low permeability. The hypocentres and pressure sources of the 1990–1995 eruption are distributed along the boundary between the high- and low-resistivity zones beneath the western part of the peninsula. We therefore conclude that the magma migrated along a structural boundary that possessed a relatively high permeability. Previous studies have suggested that eruptible magma is usually transported vertically upward through the centre of the mush zone, whereas the present results reveal that magma can be transported along the upper boundary of an HCMZ.
Large sets of radiocarbon dates are increasingly used as proxies for inferring past population dynamics and the last few years, in particular, saw an increase in the development of new statistical ...techniques to overcome some of the key challenges imposed by this kind of data. These include: 1) null hypothesis significance testing approaches based on Monte-Carlo simulations or mark permutations; 2) non-parametric Bayesian modelling approaches, and 3) the use of more traditional techniques such as correlation, regression, and AIC-based model comparison directly on the summed probability distribution of radiocarbon dates (SPD). While the range of opportunities offered by these solutions is unquestionably appealing, they often do not consider the uncertainty and the biases arising from calibration effects or sampling error. Here we introduce a novel Bayesian approach and nimbleCarbon, an R package that offers model fitting and comparison for population growth models based on the temporal frequency data of radiocarbon dates. We evaluate the robustness of the proposed approach on a range of simulated scenarios and illustrate its application on a case study focused on the demographic impact of the introduction of wet-rice farming in prehistoric Japan during the 1st millennium BCE.
The frequent occurrence of landslide tsunami has aroused great social concern, hence an efficient approach for modeling the phenomena is required urgently. Herein, we present and supplement a ...meshless numerical model named ‘Tsunami Squares’ (TS). TS simulates both the landslide and its generated wave using an updated numerical scheme that has enhanced computational efficiency. TS also provides an artful way of approximating linear dispersive wave propagation and non-linear wave inundation that makes it quite capable of simulating real-scale events. A well-designed test that compares TS output with an analytical formula for a tsunami propagation calculation provides firm validation of the approach. We then applied the ‘Tsunami Squares’ to simulate the 1792 Unzen-Mayuyama mega slide and generated tsunami. This event remains the largest volcanic disaster in the history of Japan. Landslide dynamics simulated by TS coincide with historical reports and the known geometry of landslide deposits. The model output of tsunami runup heights well match the observed values recorded by the locations of historical ‘Tsunami Stones’. This well documented and data-rich case further validates the ‘Tsunami Squares’ model and the excellent reproduction of the 1792 event provides new insights for better understanding of landslide tsunami hazards.
•Development of a new model for linear and non-linear wave propagation and inundation•Model validation with an analytical formula of a Gaussian water pile propagation•Model application to the data-rich 1792 Unzen-Mayuyama landslide tsunami•Features of energy dissipation in landslide and its generated tsunami dynamics
We document the pressure–temperature structure of a mylonitized metamorphic pile in the Nagasaki Metamorphic Complex (NMC), western Kyushu, Japan, and we discuss the role of advection of the lower ...crust in the formation of this metamorphic pile. The NMC consists of upper and lower units. The upper unit is a mylonitized metamorphic pile that consists of metamorphic rocks of amphibolite to granulite facies. The lower unit consists of metamorphic rocks of the epidote–blueschist subfacies. The upper unit was extruded onto the lower unit. Peak metamorphic temperatures of the upper unit show continuous increase from 600 to 780°C from the unit boundary towards upper structural levels, although peak metamorphic pressures within the upper unit are almost constant around 1.1GPa. The upper part of the upper unit is associated with migmatitic rocks that formed around 113.7±1.6Ma, and the pressure-temperature conditions are consistent with those of partial melting of mafic gneiss. The upper unit underwent high-T mylonitization in the lower crust, and was finally juxtaposed against the lower unit, also at depths of the lower crust. Thermal-advection models of a subduction zone show that the pressure and temperature conditions of the upper unit were reached underneath the region from the volcanic arc to the forearc; for the lower unit, the conditions were reached near the corner of corner flow of the shallow asthenosphere. The models also indicate that horizontal advection of the lower crust was activated by the corner flow, and that this process provides a satisfactory explanation for the formation of the mylonitized pile in the NMC.
► We describe P–T structure of mylonitized metamorphic pile. ► The mylonitized pile shows abnormal high thermal gradient. ► The mylonitized pile was formed at depths of lower crust. ► Numerical models suggest that the pile was formed underneath volcanic arc to forearc. ► We conclude that the horizontal advection is crucial to formation of the pile.
Objective: The present study aims to investigate the factors related to self-rated ikigai (purpose in life) among older residents participating in hillside residential community-based activities in ...Nagasaki City.Methods: A self-administered anonymous questionnaire survey was carried out with older residents participating in two hillside residential community-based activities in Nagasaki City, Japan. The questionnaire included questions on sociodemographic information (age, sex, family structure, education, and self-rated economic satisfaction), self-rated health, mental health status measured using Geriatric Depression Scale-15 (GDS-15), and self-rated ikigai score that was estimated using a visual analog scale.Results: A total of 32 older residents (7 males, 25 females) participated in the questionnaire survey. Although self-rated ikigai score was not associated with sociodemographic factors, there were associations between the score, self-rated health (P=0.001), and mental health (GDS-15) (P=0.015). Statistically significant correlations between self-rated ikigai score and social participation (ρ=0.426, P=0.017), self-rated health (ρ=−0.485, P=0.007), and mental health (GDS-15) (ρ=−0.523, P=0.007) were observed.Conclusion: Increasing social participation may increase individual ikigai, preventing poor self-rated health and low mental health status in older people. Maintaining their social participation in the community might be effective for the health promotion of older residents in hillside residential areas of Nagasaki City.
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