Surface-wave ray tracing equations and Fermat's principle in an anisotropic earth     

Toshiro Tanimoto 《Geophysical Journal International》1987,88(1):231-240

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Global instability of thin stellar discs     

Takao Fujiwara  Shunsuke Hozumi 《Astrophysics and Space Science》1986,119(1):199-200

We have determined the dominant global modes of stellar discs by integrating the linearized collisionless Boltzmann equation. The models examined are the Kuzmin discs with two types of the distribution function. It is found that the growth rate correlates well with the central value ofQ.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.  相似文献   

Strong ground motions from the 2011 off-the Pacific-Coast-of-Tohoku, Japan (Mw?=?9.0) earthquake obtained from a dense nationwide seismic network     

Takashi Furumura  Shunsuke Takemura  Shinako Noguchi  Teito Takemoto  Takuto Maeda  Kazuhisa Iwai  Simanchal Padhy 《Landslides》2011,8(3):333-338

The dense recordings of the K-NET and KiK-net nationwide strong motion network of 1,189 accelerometers show clearly the radiation and propagation properties of the strong ground motions associated with the 2011 off-the-Pacific Coast-of-Tohoku, Japan (Mw = 9.0) earthquake. The snapshots of seismic wave propagation reveal strong ground motions from this earthquake that originate from three large slips; the first two slips occurred over the plate interface of off-Miyagi at the southwest and the east of the hypocenter, and the third one just beneath the northern end of Ibaraki over the plate interface or in the crust. Such multiple shocks of this event caused large accelerations (maximum 1–2 G) and prolonged ground shaking lasting several minutes with dominant high-frequency (T < 1 s) signals over the entire area of northern Japan. On the other hand, ground motions of relatively longer–period band (T = 1–2 s), which caused significant damage to wooden-frame houses, were about 1/2–1/3 of those observed near the source area of the destructive 1995 Kobe, Japan (M = 7.3) earthquake. Also, the long-period (T = 6–8 s) ground motion in the Kanto (Tokyo) sedimentary basin was at an almost comparable level of those observed during the recent Mw = 7 inland earthquakes, but not as large as that from the former M = 8 earthquakes. Therefore, the impact of the strong ground motion from the present M = 9 earthquake was not as large as expected from the previously M = 7–8 earthquakes and caused strong motion damage only to short-scale construction and according to instruments inside the buildings, both have a shorter (T < 1 s) natural period.  相似文献   

Aerodynamic Parameters of Urban Building Arrays with Random Geometries   总被引：5，自引：5，他引：0  

Sheikh Ahmad Zaki  Aya Hagishima  Jun Tanimoto  Naoki Ikegaya 《Boundary-Layer Meteorology》2011,138(1):99-120

It is difficult to describe the flow characteristics within and above urban canopies using only geometrical parameters such as plan area index (λ _p ) and frontal area index (λ _f ) because urban surfaces comprise buildings with random layouts, shapes, and heights. Furthermore, two types of ‘randomness’ are associated with the geometry of building arrays: the randomness of element heights (vertical) and that of the rotation angles of each block (horizontal). In this study, wind-tunnel experiments were conducted on seven types of urban building arrays with various roughness packing densities to measure the bulk drag coefficient (C _d ) and mean wind profile; aerodynamic parameters such as roughness length (z _o ) and displacement height (d) were also estimated. The results are compared with previous results from regular arrays having neither ‘vertical’ nor ‘horizontal’ randomness. In vertical random arrays, the plot of C _d and z _o versus λ _f exhibited a monotonic increase, and z _o increased by a factor of almost two for λ _f = 48–70%. C _d was strongly influenced by the standard deviation of the height of blocks (σ) when λ _p ≥ 17%, whereas C _d was independent of σ when λ _p = 7%. In the case of horizontal random arrays, the plot of the estimated C _d against λ _f showed a peak. The effect of both vertical and horizontal randomness of the layout on aerodynamic parameters can be explained by the structure of the vortices around the blocks; the aspect ratio of the block is an appropriate index for the estimation of such features.  相似文献   

Oceanic Rossby waves induced by the meridional shift of the ITCZ in association with ENSO events   总被引：1，自引：0，他引：1  

Hiroto Abe  Youichi Tanimoto  Takuya Hasegawa  Naoto Ebuchi  Kimio Hanawa 《Journal of Oceanography》2014,70(2):165-174

This study investigated the eastern Pacific Intertropical Convergence Zone (ITCZ) as an atmospheric forcing to the ocean by using various observed and reanalysis data sets over 29 years. Climatologically, a zonal band of positive wind stress curl (WSC) with a 10° meridional width was exhibited along the ITCZ. A southward shift of the positive WSC band during the El Niño phase induced a negative (positive) WSC anomaly along the northern (southern) portion of the ITCZ, and vice versa during the La Niña phase. This meridional dipole accounted for more than 25 % of interannual variances of the WSC anomalies (WSCAs), based on analysis of the period 1993–2008. The negative (positive) WSCA in the northern portion of the ITCZ during the El Niño (La Niña) phase was collocated with a positive (negative) sea surface height anomaly (SSHA) that propagated westward as a Rossby wave all the way to the western North Pacific. This finding indicates that this off-equatorial Rossby wave is induced by the WSCA around the ITCZ. Our analysis of a 1.5-layer reduced gravity model revealed that the Rossby waves are mostly explained by wind stress forcing, rather than by reflection of an equatorial Kelvin wave on the eastern coastal boundary. The off-equatorial Rossby wave had the same SSHA polarity as the equatorial Kelvin wave, and generation of a phase-preserving Rossby wave without the Kelvin wave reflection was explained by meridional movement of the ITCZ. Thus, the ITCZ acts as an atmospheric bridge that connects the equatorial and off-equatorial oceanic waves.  相似文献   

Suspended particles near the bottom in Osaka Bay     

Kichiichiro Kawana  Terumi Tanimoto 《Journal of Oceanography》1979,35(2):75-81

The vertical distributions of suspended particles in Osaka Bay were measured by using anin situ beam attenuation meter. The concentration of suspended particles near the bottom increases rapidly toward the bottom where size of sediment is in a range of silt. The settling velocity of suspended particles near the bottom was measured with the use of a settling tower in the laboratory. The settling velocity of the suspended particles with diameter from 10 to 100m is 2×10^–3cm s^–1 to 5×10^–2cm s^–1. The density of the particles ranges from 2.0 to 1.1 and decreases with increasing particle diameter.  相似文献   

The oceanic excitation hypothesis for the continuous oscillations of the Earth   总被引：4，自引：0，他引：4  

T. Tanimoto 《Geophysical Journal International》2005,160(1):276-288

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Ultrahigh-temperature metamorphism in the Achankovil Zone: Implications for the correlation of crustal blocks in southern India   总被引：1，自引：3，他引：1  

Shunsuke Ishii  Toshiaki Tsunogae  M. Santosh 《Gondwana Research》2006,10(1-2):99

The Achankovil Zone of southern India, a NW–SE trending lineament of 8–10 km in width and > 100 km length, is a kinematically debated crustal feature, considered to mark the boundary between the Madurai Granulite Block in the north and the Trivandrum Granulite Block in the south. Both these crustal blocks show evidence for ultrahigh-temperature metamorphism during the Pan-African orogeny, although the exhumation styles are markedly different. The Achankovil Zone is characterized by discontinuous strands of cordierite-bearing gneiss with an assemblage of cordierite + garnet + quartz + plagioclase + spinel + ilmenite + magnetite ± orthopyroxene ± biotite ± K-feldspar ± sillimanite. The lithology preserves several peak and post-peak metamorphic assemblages including: (1) orthopyroxene + garnet, (2) perthite and/or anti-perthite, (3) cordierite ± orthopyroxene corona around garnet, and (4) cordierite + quartz symplectite after garnet. We estimate the peak metamorphic conditions of these rocks using orthopyroxene-bearing geothermobarometers and feldspar solvus which yield 8.5–9.5 kbar and 940–1040 °C, the highest P–T conditions so far recorded from the Achankovil Zone. The retrograde conditions were obtained from cordierite-bearing geothermobarometers at 3.5–4.5 kbar and 720 ± 60 °C. From orthopyroxene chemistry, we record a multistage exhumation history for these rocks, which is closely comparable with those reported in recent studies from the Madurai Granulite Block, but different from those documented from the Trivandrum Granulite Block. An evaluation of the petrologic and geochronologic data, together with the nature of exhumation paths leads us to propose that the Achankovil Zone is probably the southern flank of the Madurai Granulite Block, and not a unit of the Trivandrum Granulite Block as presently believed. Post-tectonic alkali granites that form an array of “suturing plutons” along the margin of the Madurai Granulite Block and within the Achankovil Zone, but are absent in the Trivandrum Granulite Block, suggest that the boundary between the Madurai Granulite Block and the Trivandrum Granulite Block might lie along the Tenmalai shear zone at the southern extremity of the Achankovil Zone.  相似文献   

Dynamic tensile cracking in slopes possibly induced by Rayleigh surface waves     

Koji Uenishi  Shunsuke Sakurai 《Geomechanics and Geoengineering》2015,10(3):212-222

The 1978 Miyagi-ken-oki earthquake generated crack openings in fill slopes in Sendai, Japan. Although the slopes were reinforced with steel pipe piles after this event, tensile cracking was induced again in the same slopes by the 2011 off the Pacific coast of Tohoku earthquake. This clearly indicates conventional countermeasures against dynamic slope failures, usually based on body wave interaction with slopes, are not always effective. Considering that similar open cracks in the top surfaces of slopes were also found in New Zealand and California, we may need to clarify the generation mechanism of such cracks with some new insights. Recently, it has been indicated that the effect of Rayleigh surface wave propagation on dynamic slope stability may become significant. In this contribution, therefore, by performing two-dimensional elastodynamic analyses of Rayleigh/body wave interaction with a geometrically simple model slope, we show Rayleigh waves may play a more dominant role than body waves in generating the open cracks, and emphasise the importance of taking into account the dynamic slope failures induced by Rayleigh waves. Surface waves may be produced also by nearby blasting, etc., and therefore, the results obtained here may be of crucial importance in comprehending the dynamic stability of slopes in general.  相似文献   

Waveform inversion of mantle Love waves:the Born seismogram approach     

Toshiro Tanimoto 《Geophysical Journal International》1984,78(3):641-660

Summary. Normal mode theory, extended to the slightly laterally heterogeneous earth by the first-order Born approximation, is applied to the waveform inversion of mantle Love wave (200–500 s) for the Earth's lateral heterogeneity at l = 2 and a spherically symmétric anelasticity ( Q _μ) structure. The data are from the Global Digital Seismograph Network (GDSN). The l =2 pattern is very similar to the results of other studies that used either different méthods, such as phase velocity measurements and multiplet location measurements, or a different data set, such as mantle Rayleigh waves from different instruments. The results are carefully analysed for variance reduction and are most naturally explained by heterogeneity in the upper 420 km. Because of the poor resolution of the data set for the deep interior, however, a fairly large heterogeneity in the transition zones, of the order of up to 3.5 per cent in shear wave velocity, is allowed. It is noteworthy that Love waves of this period range cannot constrain the structure below 420 km and thus any model presented by similar studies below this depth are likely to be constrained by Rayleigh waves (spheroidal modes) only.
The calculated modal Q values for the obtained Q _μ model fall within the error bars of the observations. The result demonstrates the discrepancy of Rayleigh wave Q and Love wave Q and indicates that care must be taken when both Rayleigh and Love wave data, including amplitude information, are inverted simultaneously.
Anomalous amplitude inversions of G2 and G3, for example, are observed for some source-receiver pairs. This is due to multipathing effects. One example near the epicentral region, which is modelled by the obtained l = 2 heterogeneity, is shown.  相似文献