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51.
A seismicity gap was observed in the early stage of the activity of the earthquake swarm which has been taken place in the northern part of the Aso caldera during January 1975. In the following stage, small earthquakes began to occur, until at last the largest earthquake occured within the seismicity gap. The b-value appreciably increased after the largest earthquake. The above-mentioned characteristics of this earthquake swarm may be a typical example of the fracturing phenomena in relatively heterogeneous rocks. From the estimation of the ultimate strain energy that can be stored up in the seismicity gap, it may be concluded that the above-mentioned largest earthquake took place by the release of ultimate strain energy stored within the seismicity gap. 相似文献
52.
Toshio Fukushima 《Journal of Geodesy》2006,79(12):689-693
By using Halley’s third-order formula to find the root of a non-linear equation, we develop a new iterative procedure to solve an irrational form of the “latitude equation”, the equation to determine the geodetic latitude for given Cartesian coordinates. With a limit to one iteration, starting from zero height, and minimizing the number of divisions by means of the rational form representation of Halley’s formula, we obtain a new non-iterative method to transform Cartesian coordinates to geodetic ones. The new method is sufficiently precise in the sense that the maximum error of the latitude and the relative height is less than 6 micro-arcseconds for the range of height, −10 km ≤ h ≤ 30,000 km. The new method is around 50% faster than our previous method, roughly twice as fast as the well-known Bowring’s method, and much faster than the recently developed methods of Borkowski, Laskowski, Lin and Wang, Jones, Pollard, and Vermeille. 相似文献
53.
Toshio Nozaka 《Island Arc》1999,8(2):154-167
Blueschist tectonic blocks occur in serpentinites at Mochimaru, Hiroshima Prefecture, Southwest Japan. They contain alkali amphibole coexisting with pumpellyite and chlorite, with or without calcic amphibole. Textural and chemical analyses reveal that the blueschists, together with other mafic schists, have similar metamorphic history. After their capture by serpentinites and before the emplacement of the serpentinites into the present geological position, the tectonic blocks were subjected to high P/T metamorphism around the boundary between the blueschist and pumpellyite–actinolite facies. The amphiboles formed by this metamorphism change from tremolite through glaucophane to ferroglaucophane with increasing FeO/MgO of whole rock compositions. The P–T conditions are estimated to be within 200–350°C and 5–7 kbar. These are higher P/T conditions than those of the regional metamorphism of Southwest Japan. The difference in the P–T conditions implies differences in tectonic situation and timing of metamorphism between the blocks and regional metamorphic rocks. In addition, the high P/T metamorphism of the tectonic blocks probably occurred in more reducing environments than the regional metamorphism. Because the ferric/ferrous iron ratios of the tectonic blocks are within a narrow range, it is stressed that oxygen fugacity was externally buffered during the high P/T metamorphism by the serpentinization process of the host ultramafic rocks. The reducing effect of serpentinization is common throughout the high P/T metamorphic terranes of Southwest Japan. 相似文献
54.
55.
Temporal variations of the net Kuroshio transport and its relation to atmospheric variations 总被引:1,自引:0,他引:1
Shusaku Sugimoto Kimio Hanawa Kumiko Narikiyo Megumi Fujimori Toshio Suga 《Journal of Oceanography》2010,66(5):611-619
Temporal variations of the net Kuroshio transport are investigated using long-term hydrographic data from repeat section of
the 137°E meridian from the south of Japan (34°N) to New Guinea (1°S) conducted by the Japan Meteorological Agency. In this
study, boundaries of the Kuroshio and the Kuroshio Counter Current (KCC) are defined based on the sea surface dynamic height
distribution. Westward flows associated with the KCC and cold-core eddy north of the Kuroshio are removed from the eastward
flow associated with the Kuroshio in order to estimate the net Kuroshio transport strictly. The net Kuroshio transport reveals
low-frequency variations: significant signals on a decadal (about 10-year) timescale. The variations of net Kuroshio transport
are predominantly caused by changes in the magnitude of oceanic current speed fields associated with a vertical movement of
the main pycnocline depth around the southern boundary of the Kuroshio: deepening of the main pycnocline around the southern
boundary of the Kuroshio forms a sharp northern upward-tilting slope of the isopycnal surfaces at the Kuroshio region, and
eventually the net Kuroshio transport increases together with the Kuroshio eastward transport. By using a wind-driven hindcast
model, it is found that the main pycnocline depth variation results from the first-mode baroclinic Rossby waves attributable
to two types of Aleutian Low (AL) changes: a change in the magnitude of AL and meridional movement of AL. 相似文献
56.
Characteristics of coastal trapped waves along the southern and eastern coasts of Australia 总被引:1,自引:0,他引:1
The spatial structures and propagation characteristics of coastal trapped waves (CTWs) along the southern and eastern coasts
of Australia are investigated using observed daily mean sea level data and results from a high-resolution ocean general circulation
model (OGCM), and by conducting sensitivity studies with idealized numerical models. The results obtained from the sea level
observations show that shortterm variations, with a typical period of 1 to 2 weeks, dominate the sea level variability in
the southern half of Australia. The signal propagates anticlockwise around Australia with a propagation speed of 4.5 m/s or
faster in the western and southern coasts and 2.1 to 3.6 m/s in the eastern coast. Strong seasonality of the wave activity,
with large amplitude during austral winter, is also observed. It turns out that the waves are mainly generated by synoptic
weather disturbances in the southwestern and southeastern regions. The numerical experiment with idealized wind forcing and
realistic topography confirms that the propagating signals have characteristics of the CTW both in the southern and eastern
coasts. Sensitivity experiments demonstrate that the difference in the phase speed between the coasts and reduction of the
amplitude of the waves in the eastern coast are attributed to the different shape of the continental shelf in each region.
The structures and the propagation characteristics of the CTWs around Australia are well reproduced in OFES (OGCM for the
Earth Simulator) with dominant contribution from the first mode, although meso-scale eddies may modify the structure of the
CTWs in the eastern coast. It is also found that generation or reinforcement of the waves by the wind forcing in the southern
part of the eastern coast is necessary to obtain realistically large amplitude of the CTWs in the eastern coast. 相似文献
57.
Yuko Soma Yukinori Tani Mitsuyuki Soma Hideo Mitake Ryo Kurihara Shinya Hashomoto Takahiro Watanabe Toshio Nakamura 《Journal of Paleolimnology》2007,37(2):163-175
Detailed depth profiles of photosynthetic pigments in a sediment core (G-12) collected at the BDP93 site, the Buguldeika saddle,
of south Lake Baikal, along with depth profiles of total organic carbon (TOC) and biogenic silica, were studied to elucidate
the temporal changes of phytoplankton assemblages in the lake during the past 28 kyr. In addition to the quantification of
carotenoids by high-performance liquid chromatography with photodiode-array detection (HPLC-PDA), steryl chlorin esters (SCEs)
were analyzed by HPLC-PDA, HPLC-mass spectrometry (LC-MS) and sterols in SCEs by gas chromatography–mass spectrometry (GC–MS)
to enrich the taxonomical information on the phytoplankton composition. Allochthonous input of organic matter from the Selenga
River resulted in the higher TOC contents in core G-12 than in a previously reported core (G-6) collected at another site
from the southern basin. The poorer correlation in core G-12 than in G-6 between TOC and chlorophyll-a-originating pigments, which are indicative of autochthonous production, also indicated a significant allochthonous input
at the site. The abundance of lutein among the carotenoids detected, and the good correlation of total chlorophyll a and b shows that green algae represented a significant portion of the phytoplankton, accompanying the diatoms at the G-12 site,
after the last glacial period. The presence of cryptomonads and cyanobacteria were confirmed from marker carotenoids in the
sediment core. GC–MS analysis of sterols in SCEs detected marker sterols of diatoms, green algae, chrysophytes and dinoflagellates.
The depth profiles of the measured indicators gave consistent features for temporal changes in phytoplankton assemblage at
the G-12 site of Lake Baikal after the last glacial maximum.
Notably, the profile of a chrysophyte-specific sterol in SCEs was consistent with the reported distribution of chrysophyte
cysts during the Holocene. The presence of phytoplankton, such as green algae, diatoms and chrysophytes, in Lake Baikal during
the late last glacial period was indicated by the analysis of sterols in SCEs.
Sedimentary carotenoids and sterols in SCEs were found to give complementary information about phytoplankton composition.
These molecular indicators allow us to reconstruct past lake phytoplankton assemblages responding to environmental changes
with a time resolution as high as age–depth relationship in sediments attainable at present. 相似文献
58.
藏北高原土壤温度的变化特征 总被引:10,自引:0,他引:10
通过GAME -Tibet野外工作前期所得到的土壤温度资料 ,初步分析了藏北高原不同地点不同深度土壤温度随时间的变化特征 ,并探讨了这种特征形成的原因。认为这可能与降雪、反照率、长波辐射、凝结潜热等的反馈过程及土壤湿度有关。由于土壤湿度等的影响 ,较潮湿的地方下层土壤从开始冻结到完全冻结需要一个较长的时间过程。 相似文献
59.
60.
Netrananda Sahu Swadhin K. Behera J. V. Ratnam Roberto Valmir Da Silva Pradipta Parhi Weili Duan Kaoru Takara R. B. Singh Toshio Yamagata 《Climate Dynamics》2014,42(5-6):1509-1516
Extremely-low discharge events of the Paranaíba River basin during the austral summer season (December–February, DJF), are found to be associated with the Pacific sea surface temperature anomalies resembling the recently identified El Niño Modoki phenomenon. Extreme discharge events are identified based on their persistent flow for 7 days and more after taking retention time into consideration. Ninety percent of the extremely low discharge events during peak streamflow seasons of DJF, are found to occur during the El Niño Modoki years. A diagnostics study of atmospheric anomalies has shown a clear connection between the modified Walker circulation, associated with the El Niño Modoki, and the precipitation anomalies over the Paranaíba River basin. The climate variations have direct relationship with the rainfall. Streamflow variations are considered as the surrogates to rainfalls. Thus, El Niño Modoki phase is important component to understand and predict the streamflow variations in the Paranaíba River basin. 相似文献