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Temporal behavior of the background seismicity rate in central Japan, 1998 to mid-2003 总被引：1，自引：0，他引：1
We studied the temporal behavior of the background shallow seismicity rate in 700 circular areas across inland Japan. To search for and test the significance of the possible rate changes in background seismicity, we developed an efficient computational method that applies the space–time ETAS model proposed by Ogata in 1998 to the areas. Also, we conducted Monte Carlo tests using a simulated catalog to validate the model we applied. Our first finding was that the activation anomalies were found so frequently that the constant background seismicity hypothesis may not be appropriate and/or the triggered event model with constraints on the parameters may not adequately describe the observed seismicity. However, quiescence occasionally occurs merely by chance. Another outcome of our study was that we could automatically find several anomalous background seismicity rate changes associated with the occurrence of large earthquakes. Very significant seismic activation was found before the M6.1 Mt. Iwate earthquake of 1998. Also, possible seismic quiescence was found in an area 150 km southwest of the focal region of the M7.3 Western Tottori earthquake of 2000. The seismicity rate in the area recovered after the mainshock. 相似文献
2.
Hajime Fukushima Akiko Higurashi Yasushi Mitomi Teruyuki Nakajima Toshimitsu Noguchi Toshio Tanaka Mitsuhiro Toratani 《Journal of Oceanography》1998,54(5):417-430
This paper first describes the atmospheric correction algorithm for OCTS visible band data used at NASDA/EOC. Sharing a basic
structure with Gordon and Wang’s Sea WiFS algorithm, it uses 10 candidate aerosol models including the “Asian dust model”
introduced in consideration of the unique feature of aerosols over the east Asian waters. Based on the observations at 670
and 865 nm bands, the algorithm selects a pair of aerosol models that account best for the observed spectral reflectances,
and synthesizes the aerosol reflectance used for the atmospheric correction. Two different schemes for determining the value
of the parameter for the aerosol model selection are presented and their anticipated estimation error is analyzed in terms
of retrieved water reflectance at 443 nm. The results of our numerical simulation show that the standard deviation of the
estimation error of the “weighted average” scheme is mostly within the permissible level of ±0.002, reducing the error by
18% on average compared to the “simple average” scheme. The paper further discusses the expected error under the old CZCS-type
atmospheric correction, which assumes constant aerosol optical properties throughout the given image. Although our algorithm
has a better performance than the CZCS algorithm, further analysis shows that the error induced by the assumption taken in
the algorithm that the water-leaving radiance at 670 nm band is negligibly small may be large in high pigment concentration
waters, indicating the necessity for future improvements. 相似文献
3.
Akio Yoshida Kohji Hososno Toshimitsu Tsukakoshi Akio Kobayashi Hiromi Takayama Stefan Wiemer 《Tectonophysics》2006,417(1-2):17
We investigate the relationship between changes in seismicity and crustal deformations in the Tokai region. We describe how seismicity in the subducted slab increased remarkably in the fall of 2000 and decreased in the fall of 2001, while in contrast, the crust seismicity decreased in the fall of 2000 and increased in the fall of 2001. We note that the trend of horizontal displacement at GPS stations changed coincidentally and we propose interpreting the increase and decrease in seismic activities and the changes in crustal deformations in a unified way based on changes in the state of the interplate coupling, i.e., the back-slip rate was reduced in the fall of 2000 and was partially restored in the fall of 2001. We explain why reduction of the back-slip rate increases seismogenic stress in the slab and decreases stress in the crust. We also describe the substantial positive dilatation observed in the region around Mt. Fuji in the fall of 2000 and suggest that the remarkable increase of low-frequency earthquakes beneath Mt. Fuji in October 2000 may have been caused by deceleration of the converging motion of the Izu micro-plate with the Eurasian plate. The decrease of the subduction velocity of the Izu micro-plate on the Suruga Trough in late 2000 would also have contributed to weakening of the interplate coupling beneath the Tokai region, since reduction of the relative velocity between overriding and subducting plates produces the same effect on the plate interface as a diminishing back-slip rate. However, subduction of the Izu micro-plate on the Suruga Trough was accelerated in early 2003, which may have caused increases in both slab and crust seismicities in that period. 相似文献
4.
To clarify the beneficial roles of naturally occurring organic ligands on the growth of phytoplankton in newly upwelled water,
phytoplankton culture experiments using disphotic zone water were conducted to discriminate between the effects of EDTA in
the detoxification of certain toxic metal ions and increasing the availability of essential metals. Culture media were prepared
by adding EDTA and Chelex-100, separately or in combination, to disphotic zone water samples. Our proposed working hypothesis
is that phytoplankton growth can be enhanced by removing toxic metal ions from culture media by Chelex-100 and by detoxification
of toxic metal ions or increasing the availability of essential metals by EDTA. A shortening of the lag period and an increase
of the specific population growth rate were clearly observed after the addition of Chelex-100; nd EDTA. The effects of EDTA
were more considerable than those of Chelex-100; a 17 to 44% in shortening the lag period and a 35 to 56% increase in the
growth rate, when comparing the effects of Chelex-100 with those of EDTA. The similar effects of removing toxic metal ion
by Chelex-100 as those of detoxification by EDTA suggested that EDTA has a role not only of detoxification but also of increasing
the availability of essential metals. The present study suggests that the low productivity in newly upwelled water observed
by Barber and Ryther (1969) can be ascribed to both toxic metal ions and a lack of available forms of essential metals because
of their low contents of free natural organic ligands. 相似文献
5.
Yasuhiro Kuwayama Toshimitsu Sawai Kei Hirose Nagayoshi Sata Yasuo Ohishi 《Physics and Chemistry of Minerals》2009,36(9):511-518
The phase relations of Fe-6.4 wt% Si and Fe-9.9 wt% Si have been investigated up to 130 GPa and 2,600 K based on in situ synchrotron
X-ray diffraction measurements in a laser-heated diamond-anvil cell along with chemical analysis of the quenched samples using
a field-emission electron probe microanalyzer. We found that the maximum solubility of silicon in solid hcp-iron increases
with increasing pressure. Linear extrapolation of the phase boundary between hcp + B2 and hcp phases for Fe-9.9 wt% Si suggests
that the solid hcp-iron can include more than 9.9 wt% Si at the Earth’s inner-core conditions. If silicon is a major light
element in the outer core, a substantial amount of silicon may be incorporated into the inner core during inner-core solidification. 相似文献
6.
A three-dimensional numerical model of hydrodynamics and water quality in Hakata Bay 总被引：1，自引：0，他引：1
The hydrodynamics and water quality in Hakata Bay, Japan, are strongly affected by the seasonal variations in both the gravitational circulation and the stratification in the bay. The three-dimensional hydrodynamics and water quality model has been developed to simulate the long-term transport and fate of pollutants in the system. The model is unique in that it completely integrates the refined modelling of the hydrodynamics, biochemical reactions and the ecosystem in the coastal areas. It is a 3-dimensional segmented model which is capable of resolving mean daily variations in all the parameters relevant to pollution control. It predicts daily fluctuations in the oxygen content at different depths in water throughout the year. It takes into account transport and settling of pollutant particles. It predicts light penetration from computed turbidity variations. It includes interactions between the ecosystem and water quality, through nutrient cycling and photosynthesis. The model has been calibrated well against the data set of historical water quality observations in Hakata Bay. 相似文献
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