H2O-undersaturated melting experiments of synthesized basalt (SiO2 = 50.7 wt.%, MgO = 8.3 wt.%, Mg# = 60) were conducted at fO2 corresponding to NNO+1 and NNO−1 to clarify the effects of pressure (2–7 kbar) and H2O on fractional crystallization in island arcs. H2O content was ranged from nominally anhydrous to 4.4 wt.%. Differentiation trends, namely the liquid lines of descent, change
sensitively according to pressure-H2O relations. Tholeiitic differentiation trends are reproduced with H2O ≤ ∼2 wt.% in primary magma. With such quantities of H2O, fractional crystallization is controlled by olivine + plagioclase at 2 kbar. Increasing the pressure from 2 to ≥4 kbar
induces early crystallization of orthopyroxene instead of olivine and therefore SiO2 enrichment in the residual melts is suppressed. Increasing H2O (≥ ∼2 wt.% in primary magma) stabilizes clinopyroxene relative to orthopyroxene and/or magnetite. Although the phase relations
and proportions strongly depend on fO2 and H2O content, differentiation trends are always calc-alkaline. 相似文献
Concern has grown regarding how public and private sectors should make effective use of local groundwater to alleviate negative impacts of water-supply cutoff following an earthquake event, which can be regarded as an emergency groundwater governance problem. Existing literature on groundwater governance, however, is based on the tacit assumption of groundwater utilization under normal social conditions, and scant consideration has been given to the role of groundwater following occurrence of a natural disaster. This study conducted questionnaire surveys to reveal how groundwater was used in three cities (Kumamoto, Sapporo, and Sendai) in Japan struck by large earthquakes between 2010 and 2020. Results revealed substantial differences between these cities in terms of groundwater utilization following earthquake occurrence. The time between the restoration of the electricity supply and restoration of the waterworks, and the social capital accumulated by local governments, are indicated as possible reasons for such differences. Analysis also identified policy challenges for improved groundwater governance in an emergency: (1) establishment of a strategy for emergency water supply through combined use of groundwater and other water sources, (2) enhancement of methods for timely inspection of groundwater quality following occurrence of a disaster, (3) maintenance of records of the number of registered disaster emergency wells (DEWs), (4) creation of methods for publicizing locational information on DEWs with adequate regard for the privacy of well owners, and (5) recognition of the importance of making DEWs part of overall disaster preparedness.
The first sign of magma accumulating beneath Miyakejima, an island volcano in the northern Izu islands, Japan, came at around 18:00 on 26 June 2000, when a swarm of earthquakes was detected by a volcano seismic network on the island. Earthquakes occurred initially beneath the southwest flank near the summit and gradually migrated west of the island, where a submarine eruption occurred the next morning. Earthquakes then migrated further to the northwest between Miyakejima and Kozushima, another volcanic island and developed to the most intense earthquake swarm ever observed in and around Japanese archipelago. To better image how the initial magma intrusion occurred, we relocated hypocenters by using a station-correction method and a double-difference method. The relocated epicenters are generally concentrated near the upper bound of dyke intrusions inferred from geodetic studies throughout the initial stages of the 2000 eruption at Miyakejima from 26 to 27 June 2000. As for seismic activity westward off Miyakejima in the morning on 27 June, hypocenters from both a nationwide seismic network that were relocated by the double-difference method, and those from the volcano seismic network relocated by the station-correction method, formed a very shallow cluster that ascended slowly with time as it propagated northwestward from Miyakejima. This suggests that the dykes have both a radial and upward component of movement.Editorial responsibility: S. Nakada, T. Druitt 相似文献
Permanent ground displacement as induced by seismic liquefaction was measured in the area which was recently hit by an earthquake. The measurement was carried out by comparing two aerophotographs of the area which were taken before and after the tremor. Using the measured data an empirical equation was derived which can calculate the magnitude of the displacement briefly. Furthermore, a finite-element technique was developed in order to predict the magnitude and the direction of the displacement in more precise manners. 相似文献
Different geoenvironmental site investigation techniques to assess contamination from a municipal solid waste disposal site
in Brazil are presented here. Superficial geophysical investigation (geoelectrical survey), resistivity piezocone penetration
tests (RCPTU), soil samples collected with direct-push samplers and water samples collected from monitoring wells were applied
in this study. The application of the geoelectrical method was indispensable to identify the presence and flow direction of
contamination plumes (leachate) as well as to indicate the most suitable locations for RCPTU tests and soil and water sampling.
Chemical analyses of groundwater samples contributed to a better understanding of the flow of the contaminated plume. The
piezocone presented some limitations for tropical soils, since the groundwater level is sometimes deeper than the layer which
is impenetrable to the cone, and the soil genesis and unsaturated conditions affect soil behavior. The combined interpretation
of geoelectrical measurements and soil and water samplings underpinned the interpretation of RCPTU tests. The interpretation
of all the test results indicates that the contamination plume has already overreached the landfill’s west-northwest borders.
Geoenvironmental laboratory test results suggest that contamination from the solid waste disposal site has been developing
gradually, indicating the need for continuous monitoring of the groundwater. 相似文献
A large devastating earthquake with a magnitude of 7.6 struck in Kashmir on Oct. 8, 2005. The largest city influenced by the
earthquake was Muzaffarabad. Balakot town was the nearest settlement to the epicenter, and it was the most heavily damaged.
The earthquake caused extensive damage to housing and structures founded on loose deposits or weathered/sheared rock masses.
Furthermore, extensive slope failures occurred along Neelum and Jhelum valleys, which obstructed both river flow and roadways.
In this article, failures of natural and cut slopes as well as other ground failures induced by the earthquake and their geotechnical
evaluation are presented, and their implications on civil infrastructures and site selection for reconstruction and rehabilitation
are discussed. It is suggested that if housing and constructions on soil slopes containing boulders as observed in Balakot
and Muzaffarabad are allowed, there should be a safety zone between the slope crest and allowable construction boundary. 相似文献
Synthetic melilites on the join Ca2MgSi2O7 (åkermanite: Ak)-Ca2Fe3+AlSiO7 (ferrialuminium gehlenite: FAGeh) were studied using X-ray powder diffraction and 57Fe Mössbauer spectroscopic methods to determine the distribution of Fe3+ between two different tetrahedral sites (T1 and T2), and the relationship between ionic substitution and incommensurate (IC) structure. Melilites were synthesized from starting materials with compositions of Ak100, Ak80FAGeh20, Ak70FAGeh30 and Ak50FAGeh50 by sintering at 1,170–1,350 °C and 1 atm. The average chemical compositions and end-member components, Ak, FAGeh and Geh (Ca2Al2SiO7), of the synthetic melilites were Ca2.015Mg1.023Si1.981O7 (Ak100), Ca2.017Mg0.788Fe0.1873+Al0.221Si1.791O7 (Ak78FAGeh19Geh3), Ca1.995Mg0.695Fe0.2583+Al0.318Si1.723O7 (Ak69FAGeh25Geh6) and Ca1.982Mg0.495Fe0.4493+Al0.519Si1.535O7 (Ak49FAGeh44Geh7), respectively. Rietveld refinements using X-ray powder diffraction data measured using CuKα-radiation at room temperature converged successfully with goodness-of-fits of 1.15–1.26. The refined Fe occupancies at the T1 and T2 sites and the Mg and Si contents determined by electron microprobe analysis gave the site populations of [0.788Mg + 0.082Fe3+ + 0.130Al]T1[0.104Fe3+ + 0.104Al + 1.792Si]T2 for Ak78FAGeh19Geh3, [0.695Mg + 0.127Fe3+ + 0.178Al]T1[0.132Fe3+ + 0.144Al + 1.724Si]T2 for Ak69FAGeh25Geh6 and [0.495Mg + 0.202Fe3+ + 0.303Al]T1[0.248Fe3+ + 0.216Al + 1.536Si]T2 for Ak49FAGeh44Geh7 (apfu: atoms per formula unit), respectively. The results indicate that Fe3+ is distributed at both the T1 and the T2 sites. The mean T1–O distance decreases with the substitution of Fe3+ + Al3+ for Mg2+ at the T1 site, whereas the mean T2–O distance increases with substitution of Fe3+ + Al3+ for Si4+ at the T2 site, causing decrease in the a dimension and increase in the c dimension. However, in spite of the successful Rietveld refinements for the X-ray powder diffraction data measured using CuKα-radiation at room temperature, each Bragg reflection measured using CuKα1-radiation at room temperature showed weak shoulders, which were not observed in those measured at 200 °C. The Mössbauer spectra of the melilites measured at room temperature consist of two doublets assigned to Fe3+ at the T1 site and two or three doublets to Fe3+ at the T2 site, implying the existence of multiple T1 and T2 sites with different site distortions. These facts can be interpreted in terms of the IC structure in all synthetic melilites at room temperature, respectively. The results of Mössbauer analysis indicate that the IC structure in melilite is caused by not only known multiple T1 site, but also multiple T2 site at room temperature. 相似文献
The density and the undrained shear strength (su) of bed sediments at either side of the Isahaya Bay dike in the Ariake Sea, Japan, were investigated using nuclear density cone penetration tests (ND-CPTs). The nuclear density cone penetrometer (ND-CP) was operated from a boat, conducting 71 ND-CPTs. Furthermore, 26 undisturbed samples were obtained for soil density and su measurements to calibrate the ND-CPT data. The results show that the density and su obtained from in situ with the ND-CPTs agree well with those from the laboratory tests on undisturbed samples, and the obtained density profiles show good repeatability. The vertical variation in density and su of the bed sediment can be obtained from the ND-CPT results. The relations between the density and su show that su increases with an increase in density, but that this relation is site specific. The values of su show an exponentially growing trend and the values of log su show a linearly increasing trend with density. The vertical distribution of the bed sediments can be described using the density values obtained with the ND-CPT. 相似文献