Source characteristics of the 1992 Nicaragua tsunami earthquake inferred from teleseismic body waves     

Masayuki Kikuchi  Hiroo Kanamori 《Pure and Applied Geophysics》1995,144(3-4):441-453

We analyzed the broadband body waves of the 1992 Nicaragua earthquake to determine the nature of rupture. The rupture propagation was represented by the distribution of point sources with moment-rate functions at 9 grid points with uniform spacing of 20 km along the fault strike. The moment-rate functions were then parameterized, and the parameters were determined with the least squares method with some constraints. The centroid times of the individual moment-rate functions indicate slow and smooth rupture propagation at a velocity of 1.5 km/s toward NW and 1.0 km/s toward SE. Including a small initial break which precedes the main rupture by about 10 s, we obtained a total source duration of 110 s. The total seismic moment isM _o =3.4×10²⁰ Nm, which is consistent with the value determined from long-period surface waves,M _o =3.7×10²⁰ Nm. The average rise time of dislocation is determined to be 10 s. The major moment release occurred along a fault length of 160 km. With the assumption of a fault widthW=50 km, we obtained the dislocationD=1.3 m. From andD the dislocation velocity isD=D/0.1 m/s, significantly smaller than the typical value for ordinary earthquakes. The stress drop =1.1 MPa is also less than the typical value for subduction zone earthquakes by a factor of 2–3. On the other hand, the apparent stress defined by 2E _s /M _o , where andE _s are respectively the rigidity and the seismic wave energy, is 0.037 MPa, more than an order of magnitude smaller than . The Nicaragua tsunami earthquake is characterized by the following three properties: 1) slow rupture propagation; 2) smooth rupture; 3) slow dislocation motion.  相似文献   

Reproductive ecology of the dominant dinoflagellate, <Emphasis Type="Italic">Ceratium fusus</Emphasis>, in coastal area of Sagami Bay,Japan     

Seung Ho Baek  Shinji Shimode  Tomohiko Kikuchi 《Journal of Oceanography》2007,63(1):35-45

The seasonal abundance of the dominant dinoflagellate, Ceratium fusus, was investigated from January 2000 to December 2003 in a coastal region of Sagami Bay, Japan. The growth of this species was also examined under laboratory conditions. In Sagami Bay, C. fusus increased significantly from April to September, and decreased from November to February, though it was found at all times through out the observation period. C. fusus increased markedly in September 2001 and August 2003 after heavy rainfalls that produced pycnoclines. Rapid growth was observed over a salinity range of 24 to 30, with the highest specific rate of 0.59 d⁻¹ measured under the following conditions: salinity 27, temperature 24°C, photon irradiance 600 μmol m⁻²s⁻¹. The growth rate of C. fusus increased with increasing irradiance from 58 to 216 μmol m⁻²s⁻¹, plateauing between 216 and 796 μmol m⁻²s⁻¹ under all temperature and salinity treatments (except at a temperature of 12°C). Both field and laboratory experiments indicated that C. fusus has the ability to grow under wide ranges of water temperatures (14–28°C), salinities (20–34), and photon irradiance (50–800 μmol m⁻²s⁻¹); it is also able to grow at low nutrient concentrations. This physiological flexibility ensures that populations persist when bloom conditions come to an end.  相似文献   

The Kyucho in the Bungo Channel,Japan —Periodic intrusion of oceanic warm water     

Hidetaka Takeoka  Hideki Akiyama  Takahiro Kikuchi 《Journal of Oceanography》1993,49(4):369-382

Kyucho is a sudden and swift current which is usually accompanied by rise of water temperature. Several features of the Kyucho in the Bungo Channel, Japan, are presented through field observations. The Kyucho in the Bungo Channel is an intrusion of warm water from the Pacific Ocean into the eastern half of the Bungo Channel, being driven gravitationally and advancing along the eastern coast of the channel. The Kyucho occurs usually in summer and seldom occurs in winter. It occurs at neap tides showing the prominent spring-neap periodicity. The modulation of the vertical mixing intensity associated with the variations of tidal current, wind and surface heating etc. is supposed to be a main cause of springneap and seasonal periodicities.  相似文献   

Evidence of a phase shift to Epizoanthus gabrieli Carlgreen, 1951 (Order Zoanthidea) and loss of coral cover on reefs in the Southwest Atlantic          下载免费PDF全文

Igor C. S. Cruz  Ruy K. P. de Kikuchi  Leila L. Longo  Joel C. Creed 《Marine Ecology》2015,36(3):318-325

There is at present a ‘coral reef crisis’; one of the more drastic consequences of this is a phase shift, in which reef‐building corals are replaced by non‐reef building benthos such as macroalgae and soft corals. Previous studies have principally focused on the shift to macroalgae. Our goal was to investigate whether the dominance of the zoanthid Epizoanthus gabrieli on some reefs of Todos os Santos Bay, Brazil, represented a non‐algal phase shift. In 2003, we identified a high cover of this species on two reefs (52% and 70%), but only in 2007 was it possible to confirm a reduction in coral cover. This dominance has persisted for over 9 years, characterizing a true phase shift. This loss of coral cover may be a result of anthropogenic disturbances within the bay; however, given the large number of human impacts, further studies are needed to identify specific causes of this shift. Although there are some reports of phase shift involving species pertaining to the Class Anthozoa, this is the first report of this phenomenon involving the order Zoanthidea.  相似文献   

The degree of Cl-loss for the particulate matter (PM) and fog water sampled at the same air mass at the Hachimantai mountain range in northern Japan     

Ryoei Kikuchi  Makoto Takada  Keita Hifumi  Keiji Yoshimura  Toru Ozeki  Takashi Kimoto  Masahiro Kajikawa  Nobuaki Ogawa   《Atmospheric Research》2009,94(3):501-509

It is well known that sea-salt aerosols in particulate matter (PM) react with acids such as H₂SO₄ and HNO₃ during transportation and thereby lose chloride ions (Cl-loss). The PM and fog were sampled concurrently at different altitudes in the Hachimantai mountain range, northern Japan. The PM and fog sampled at different altitudes had nearly identical properties for the ion components. However, the PM was in a Cl-depleted state (more than 80% of all samples), but the fog water was not in so Cl-depleted state (less than 29%). As a result, it could be explained that this phenomenon caused because the fog droplets took up the gaseous state HCl other than sea-salt PM. After all Cl^- in the fog water recovered and was rather rich compared with the sea-salt or the PM by the uptake of the gaseous state HCl. Moreover, it was found that for PM_coarse(2.5 < D < 10), 86% of the acid (H₂SO₄ and HNO₃) was consumed for Cl-loss reactions and/or for dissolution of Ca and Mg in soil particles.  相似文献   

Multi-scale climate variability of the South China Sea monsoon: A review   总被引：10，自引：0，他引：10  

Bin Wang  Fei Huang  Zhiwei Wu  Jing Yang  Xiouhua Fu  Kazuyoshi Kikuchi 《Dynamics of Atmospheres and Oceans》2009,47(1-3):15-37

This review recapitulates climate variations of the South China Sea (SCS) monsoon and our current understanding of the important physical processes responsible for the SCS summer monsoon's intraseasonal to interannual variations. We demonstrate that the 850 hPa meridional shear vorticity index (SCSMI) can conveniently measure and monitor SCS monsoon variations on a timescale ranging from intraseasonal to interdecadal. Analyses with this multi-scale index reveal that the two principal modes of intraseasonal variation, the quasi-biweekly and 30–60-day modes, have different source regions and lifecycles, and both may be potentially predicted at a lead time longer than one-half of their corresponding lifecycles. The leading mode of interannual variation is seasonally dependent: the seasonal precipitation anomaly suddenly reverses the sign from summer to fall, and the reversed anomaly then persists through the next summer. Since the late 1970s, the relationship between the SCS summer monsoon and El Niño-Southern Oscillation (ENSO) has significantly strengthened. Before the late 1970s, the SCS summer monsoon was primarily influenced by ENSO development, while after the late 1970s, it has been affected mainly in the decaying phase of ENSO. The year of 1993 marked a sudden interdecadal change in precipitation and circulation in the SCS and its surrounding region. Over the past 60 years, the SCS summer monsoon's strength shows no significant trend, but the SCS winter monsoon displays a significant strengthening tendency (mainly in its easterly component and its total wind speed). A number of outstanding issues are raised for future studies.  相似文献   

Formation and geochemical significance of micrometallic aggregates including fissiogenic platinum group elements in the Oklo natural reactor, Gabon     

Makiko Kikuchi  François Gauthier-Lafaye 《Geochimica et cosmochimica acta》2010,74(16):4709-165

Metallic aggregates with a size of a few tens μm and consisting mainly of Ru, Rh, Pd, Te, Pb, As, Sb, S and Bi were found in the acid residue of SD37-S2/CD uraninite taken from Oklo natural reactor zone (RZ) 13. Quantitative analyses of major elements using an electron probe microanalyzer and in situ isotopic analyses of Zr, Mo, Ru, Pb and U using a sensitive high-resolution ion microprobe were performed on the metallic aggregates to determine the geochemical behaviors of fission products and actinides and to ascertain the processes of formation of the aggregates in the RZs. The chemical compositions of the aggregates investigated in this study are significantly different from those reported previously, showing lower Pb content and no correlation between the contents of Pb and S in the individual grains. The ²³⁵U/²³⁸U ratios in metallic aggregates vary significantly from 0.00478 to 0.01466, indicating chemical fractionation between U and Pu during the formation of the aggregates. The Pb isotopic data indicate that most of the Pb in the aggregates decayed from 2.05 Ga-old uraninite that existed in the RZ originally and that there was chemical fractionation between U and Pb in some aggregates. The Zr and Mo isotopic ratios, ⁹⁰Zr/⁹¹Zr and ⁹⁵Mo/⁹⁷Mo, for most of the aggregates had small variations, which can be simply explained by constant separate mixing of fissiogenic and nonfissiogenic components. On the other hand, a large variation in the ⁹⁹Ru/¹⁰¹Ru ratio (0.324-1.73) cannot be explained only by a two component mixing theory; thus, chemical fractionation between Tc and Ru during the reactor criticality is suggested. The large variations in the ²³⁵U/²³⁸U and ⁹⁹Ru/¹⁰¹Ru isotopic ratios suggest that the aggregates formed under various redox conditions owing to the radiolysis of water.  相似文献   

Shock-induced phase change in BaZnGeO4 crystals     

H. Takei  Y. Syono  T. Goto  M. Kikuchi 《Physics and Chemistry of Minerals》1983,10(1):16-20

Shock-loading experiments are performed on single-crystal specimens of BaZnGeO₄ (BZG) between 13 and 51 GPa using a propellant gun and a two-stage light gas gun. Observation by an optical microscope reveals that all the shocked specimens are made of fragmented blocks of 10 ～ 100 μm in size. X-ray analyses indicate that the samples shocked to pressures above 41 GPa became a polycrystalline state of BZG with a weakly textured structure. A small amount of dissociation products of BaGeO₃ (pyroxene type) and ZnO (wurtzite type) are detected in this pressure range. Between 27 and 19 GPa, a new phase which is thought to be produced by considerable deformations in the ring structure consisting of ZnO₄ and GeO₄ tetrahedra is observed. Below 19 GPa, shocked specimens are brought into a well aligned mosaic structure, but no significant change in the crystal structure is detected.  相似文献   

Boreal summer quasi-monthly oscillation in the global tropics   总被引：1，自引：0，他引：1  

Bin Wang  Peter Webster  Kazuyoshi Kikuchi  Tetsuzo Yasunari  Yanjun Qi 《Climate Dynamics》2006,27(7-8):661-675

The boreal summer intraseasonal oscillation (ISO) in the global tropics is documented here using a 7-year suite (1998–2004) of satellite measurements. A composite scenario was made of 28 selected events with reference to the oscillation in the eastern equatorial Indian Ocean (EIO), where the oscillation is most regular and its intensity is indicative of the strength of the subsequent northward propagation. The average oscillation period is about 32 days, and this quasi-monthly oscillation (QMO) is primarily confined to the tropical Indian and Pacific Oceans. Topics that were investigated are the partition of convective versus stratiform clouds, the vertical structure of precipitation rates, and the evolution of cloud types during the initial organization and the development of intraseasonal convective anomalies in the central Indian Ocean. During the initiation of the convective anomalies, the stratiform and convective rains have comparable rates; the prevailing cloud type experiences a trimodal evolution from shallow to deep convection, and finally to anvil and extended stratiform clouds. A major northwest/southeast-slanted rainband forms as the equatorial rainfall anomalies reach Sumatra, and the rainband subsequently propagates northeastward into the west Pacific Ocean. The enhanced precipitation in the west Pacific then rapidly traverses the Pacific along the Intertropical Convergence Zone, meanwhile migrating northward to the Philippine Sea. A seesaw teleconnection in rainfall anomalies is found between the southern Bay of Bengal (5–15°N, 80–100°E) and the eastern Pacific (5–15°N, 85–105°W). Local sea-surface temperature (SST)-rainfall anomalies display a negative simultaneous correlation in the off-equatorial regions but a zero correlation (quadrature phase relationship) near the equator. We propose that atmosphere–ocean interaction and the vertical monsoon easterly shear are important contributors to the northeastward propagation component of the intraseasonal rainband. The observed evidence presented here provides critical information for validating the numerical models, and it supports the self-induction mechanism theory for maintenance of the boreal summer ISO.  相似文献   

Body waveform inversion for the source process of the February 3, 1996 Lijiang, Yunnan earthquake     

Yang Xu  Masayuki Kikuchi  You-Jin Su 《地震学报(英文版)》1998,11(2):135-140

The source process of February 3, 1996 Lijiang earthquake in Yunnan was studied by body waveform inversion using teleseismic data from IRIS. Two normal double-couple subevents with different strikes were obtained. The difference of the onset time between these two subevents, which are 15 km apart in space, is 7 s. The total seismic moment is 3.81 × 10¹⁸ Nm (M _w=6.3). The total fault area S is about 720 km² from the aftershock data and the average dislocation is about ū=0.18 m. Considering both the result of inversion and tectonic environment around the source, the first rupture might result from the extension along the NNW directed Zhongdian-Yongsheng fault belt where an earthquake of M=6.4 occurred in 1966. Then, the second started along the NE directed the eastern foot of Snow Mountain fault where rupture seemed to be able to propagate more easily.  相似文献