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41.
42.
We developed an objective method to define the aftershock areas of large earthquakes as a function of time after the main shock. The definition is based upon the amount of energy released by aftershocks, the spatial distribution of the energy release is first determined and is contoured. The 1-day aftershock area is defined by a contour line corresponding to the energy release level of 1015.6 ergs/(100 km2 · day). The 10-day, 100-day and 1-y aftershock areas are similarly defined by contour lines corresponding to 1014.8, 1014.0, and 1013.5 ergs/(100 km2 · day), respectively. We also define the expansion ratios at time t by the ratio of the aftershock area at t to that at 1 day.Using this method we study the aftershock area expansion patterns of 44 large (Ms ? 7.5) and five moderate shallow earthquakes which occurred from 1963 to 1980. Each aftershock sequence is examined at four different times, i.e., 1 day, 10 days, 100 days, and 1 y after the main event. We define the aftershock area expansion ratios η and ηe by , respectively: here S(t) and L(t) are the area and the length of the aftershock area, respectively, at time t. Our study suggests that a distinct regional variation of aftershock area expansion patterns is present; it is strongly correlated with the tectonic environment. In general, the subduction zones of the “Mariana” type have large expansion ratios, and those of the “Chilean” type have small expansion ratios. Some earthquakes that occurred in the areas of complex bathymetry such as aseismic ridges tend to have large expansion ratios.These results can be explained in terms of an asperity model of fault zones in which a fault plane is represented by a distribution of strong spots, called the asperities, and weak zones surrounding the asperities. The rupture immediately after the main shock mostly involves asperities. After the main rupture is completed, the stress change caused by the main shock gradually propagates outward into the surrounding weak zones. This stress propagation manifests itself as expansion of aftershock activity. In this simple picture, if the fault zone is represented by relatively large asperities separated by small weak zones (“Chilean” type), then little expansion of aftershock activity would be expected. On the other hand, if relatively small asperities are sparsely distributed (“Mariana” type), significant expansion occurs. The actual distribution of asperities is likely to be more complex than the two cases described above. However, we would expect that the expansion ratio is in general proportional to the spatial ratio of the total asperity area to the fault area. 相似文献
43.
Hiroo Mizuno 《Journal of Geodesy》1994,68(3):137-150
A simple statistical approach has been applied to the repeated electro-optical distance measurements (EDM) of 1,358 lines in the Tohoku district of Japan to obtain knowledge about the precision of EDM and the possible accumulation of strain. The average time interval between measurements is about seven or eight years. It is shown that the whole data of the difference between distance measurements repeated over a given lineD are interpreted in terms of EDM errors comprising distance proportional systematic errors and standard errors expressed by the usual form
. The rate of horizontal deformation must therefore be much smaller than the strain rates of about 0.7 0.8 ppm over 7 to 8 years which have been hitherto expected. 相似文献
44.
45.
This paper presents an investigation based on the testimonies of ethnic Bamar or Burman women migrant workers in the ethnically diverse 'borderland' town of Tachilek, Myanmar and interviews with their relatives in the home village in the central Burman heartlands. We examine how the concept of relational places, here involving a village in the central Mandalay Division and a town in the Myanmar–Thailand borderland, is related to differential power relations affecting the women migrants. We focus on the ways that gender identity and social position are limited by the relational places of community elders and the migrant women themselves, and suggest that the relational places of migrants in Myanmar are constructed through the nexus of varied forms of state control in both the central Burman heartlands and the multiethnic borderlands of the country. 相似文献
46.
Ionospheric detection of gravity waves induced by tsunamis 总被引:1,自引:0,他引:1
47.
Representations of the radiated energy in earthquakes 总被引:7,自引:0,他引:7
48.
M. Kusakabe Y. Komoda B. Takano T. Abiko 《Journal of Volcanology and Geothermal Research》2000,97(1-4)
Sulfur isotope effects during the SO2 disproportionation reaction to form elemental sulfur (3SO2+3H2O→2HSO4−+S+2H+) at 200–330°C and saturated water vapor pressures were experimentally determined. Initially, a large kinetic isotopic fractionation takes place between HSO4− and S, followed by a slow approach to equilibrium. The equilibrium fractionation factors, estimated from the longest run results, are expressed by 1000 ln αHSO4−–S=6.21×106/T2+3.62. The rates at which the initial kinetic fractionation factors approach the equilibrium ones were evaluated at the experimental conditions.δ34S values of HSO4− and elemental sulfur were examined for active crater lakes including Noboribetsu and Niseko, (Hokkaido, Japan), Khloridnoe, Bannoe and Maly Semiachik (Kamchatka), Poás (Costa Rica), Ruapehu (New Zealand) and Kawah Ijen and Keli Mutu (Indonesia). ΔHSO4−–S values are 28‰ for Keli Mutu, 26‰ for Kawah Ijen, 24‰ for Ruapehu, 23‰ for Poás, 22‰ for Maly Semiachik, 21‰ for Yugama, 13‰ for Bannoe, 9‰ for Niseko, 4‰ for Khloridonoe, and 0‰ for Noboribetsu, in the decreasing order. The SO2 disproportionation reaction in the magmatic hydrothermal system below crater lakes where magmatic gases condense is responsible for high ΔHSO4−–S values, whereas contribution of HSO4− produced through bacterial oxidation of reduced sulfur becomes progressively dominant for lakes with lower ΔHSO4−–S values. Currently, Noboribetsu crater lake contains no HSO4− of magmatic origin. A 40-year period observation of δ34SHSO4− and δ34SS values at Yugama indicated that the isotopic variations reflect changes in the supply rate of SO2 to the magmatic hydrothermal system. This implies a possibility of volcano monitoring by continuous observation of δ34SHSO4− values. The δ18O values of HSO4− and lake water from the studied lakes covary, indicating oxygen isotopic equilibration between them. The covariance gives strong evidence that lake water circulates through the sublimnic zone at temperatures of 140±30°C. 相似文献
49.
Atsushi Kamei Masaaki Owada Takuji Hamamoto Yasuhito Osanai Masaki Yuhara and Hiroo Kagami 《Island Arc》2000,9(1):97-112
Abstract Miyanohara tonalite occurs in the middle part of the Higo metamorphic belt in the central Kyushu, Southwest Japan. This tonalite intrudes into early Permian Ryuhozan metamorphic rocks in the south and is intruded by Cretaceous Shiraishino granodiorite in the north. The Miyanohara tonalite yielded three mineral ages: (i) 110–100 Ma for Sm–Nd and Rb–Sr internal isochrons and for K–Ar hornblende; (ii) 183 Ma for Sm–Nd internal isochron; and (iii) 211 Ma for Sm–Nd internal isochron. The ages of 110–100 Ma may indicate cooling age due to the thermal effect of the Shiraishino granodiorite intrusion. The ages of 183 Ma and 211 Ma are consistent with timing of intrusion of the Miyanohara tonalite based on geologic constraints. The hornblende in the sample which gave 183 Ma shows discontinuous zoning under microscope, whereas the one which gave 211 Ma does not show zonal structure. These mineralogical features suggest that the 183 Ma sample has suffered severely from later tectonothermal effect compared with the 211 Ma sample. Therefore, the age of 211 Ma is regarded as near crystallization age for the Miyanohara tonalite. The magmatic process, geochronology and initial Sr and Nd isotope ratios for the Miyanohara tonalite are similar to those of early Jurassic granites from the Outer Plutonic Zone of the Hida belt that constitutes a marginal part of east Asia before the opening of the Japan Sea. Intrusion of the Miyanohara tonalite is considered to have taken place in the active continental margin during the late Triassic. 相似文献
50.
Late Miocene (7–9 Ma) basaltic rocks from the Monbetsu‐Kamishihoro graben in northeast Hokkaido have chemical affinities to certain back‐arc basin basalts (referred to herein as Hokkaido BABB). Pb‐, Nd‐ and Sr‐isotopic compositions of the Hokkaido BABB and arc‐type volcanic rocks (11–13 Ma and 4–4.5 Ma) from the nearby region indicate mixing between the depleted mantle and an EM II‐like enriched component (e.g. subducted pelagic sediment) in the magma generation. At a given 87Sr/86Sr, Hokkaido BABB have slightly lower 143Nd/144Nd and slightly less radiogenic 206Pb/204Pb compared with associated arc‐type lavas, but both these suites are difficult to distinguish solely on the basis of isotopic compositions. These isotopic data indicate that while generation of the Hokkaido BABB involves smaller amounts of the EM II‐like enriched component than do associated arc lavas, Hokkaido BABB are isotopically distinct from basalts produced at normal back‐arc basin spreading centers. Instead, northeast Hokkaido BABB are more similar to basalts erupted during the initial rifting stage of back‐arc basins. The Monbetsu‐Kamishihoro graben may have developed in association with extension that formed the Kurile Basin, suggesting that opening of the basin continued until late Miocene (7–9 Ma). 相似文献