基于地震折射剖面的菲律宾海板块15～20°N九州—帕劳海岭的地壳结构变化     

A.Nishizawa  K.Kaneda  Y.Katagiri  J.Kasahara  张洁 《世界地震译丛》2011,(3)

得到了菲律宾海板块15～20°N之间4条垂直于九州—帕劳海岭(KPR)剖面的重合广角和多道地震反射数据。九州—帕劳海岭为晚始新世时期形成的残余岛弧,其下的地壳厚度沿走向由8km变至20km,并且总是大于西侧西菲律宾海盆和东侧帕里西维拉海盆的相邻洋壳厚度。4条剖面中地壳最厚的区域位于九州—帕劳海岭与冲之鸟礁接壤处,初步推断可能是下地壳增厚的缘故。没有明显的证据能证明,在伊豆—小笠原—马里亚纳岛弧共轭断裂对应部分之下有推测出的P波速度为6.0～6.5km/s的厚(>5km)中地壳层。我们的结果表明,15～20°N的九州—帕劳海岭之下的地壳,相对于报道有P波速度6.0km/s的中地壳层的更北部海岭地区而言,属于不太成熟的岛弧地壳。  相似文献   

Sub-Moho seismic profile in the Mariana Basin — Ocean bottom seismograph long-range explosion experiment     

S. Nagumo  T. Ouchi  J. Kasahara  S. Koresawa  Y. Tomoda  K. Kobayashi  A.S. Furumoto  M.E. Odegard  G.H. Sutton 《Earth and Planetary Science Letters》1981,53(1):93-102

Ocean bottom seismograph (OBS) long-range explosion experiments were carried out in the Mariana Basin in 1973 and 1976. Seven large shots (8.5–1.5 ton) as well as several tens of small shots were fired. The maximum range of observation was about 1900 km. As many as 25 OBS stations were deployed in an array of about 800 km. It is found that the sub-Moho P-wave velocity structure is of stratified nature, being composed of alternating high- and low-velocity layers. High-velocity layers with apparent velocities of 8.1, 8.2, 8.4, 8.6 and 8.7 km/s are identified. Low-velocity layers, sandwiched between the high-velocity layers of 8.4, 8.6 and 8.7 km/s, are very prominent. The sub-Moho high-velocity lid with an apparent velocity of 8.4 km/s is very thin. Thinning of this lid, thickening of the low-velocity layer, and the presence under it of another high-velocity layer (8.6 km/s) appear to characterize the uppermost mantle structure beneath the Mariana Basin.  相似文献   

Preliminary analysis of deformation at the Eurasia–Pacific–North America plate junction from GPS data     

E. I. Gordeev  A. A. Gusev  V. E. Levin  V. F. Bakhtiarov  V. M. Pavlov  V. N. Chebrov  M. Kasahara 《Geophysical Journal International》2001,147(1):189-198

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Ocean bottom seismograph development at Hawaii Institute of Geophysics     

George H. Sutton  Junzo Kasahara  William N. Ichinose  David A. Byrne 《Marine Geophysical Researches》1977,3(2):153-177

Three distinct ocean bottom seismograph (OBS) systems have been developed at the Hawaii Institute of Geophysics to satisfy the different requirements for short-range refraction and anisotropy experiments, long-range refraction experiments, and short-term and semi-permanent monitoring for earthquakes. One system, originally designed for semi-permanent use in conjunction with a monster buoy of the IDOE North Pacific Experiment has been modified for emplacement off Oahu. It contains 3-component 1 Hz seismometers and a hydrophone and obtains power and transmits data via tow conductor cable. Two additional systems were designed for short-term use: a 2 Hz telemetering system (TOBS); and 4.5 Hz free-fall pop-up system (POBS). The TOBS contains 3-component seismometers and a hydrophone and transmits data to the ship via light-weight single-conductor electromechanical cable and an HF-VHF radio link from a surface buoy. The bottom package also includes a backup tape recorder. This system exhibits the advantages of real-time data acquisition (e.g. precise timing, rapid appraisal of data quality, optimum use of explosives, and common recording with other data) and the complexities and difficulties associated with a deep-sea mooring. However, use of cable with near neutral bouyancy permits the design of a deep-water system with low weights and stress levels. The POBS is a self-contained package containing a vertical and single horizontal seismometer, hydrophone, cassette tape recorder, and pre-set timed release. This system is relatively simple and inexpensive. Total weight of 150 kg in air (before launch) permits emplacement and retrieval from a ship with no special equipment by two (strong) persons. Experience to data suggests that the optimum deployment scheme for many studies is a combination of TOBS's and POBS's.Hawaii Institute of Geophysics Contribution 835.  相似文献   

Size of the hard X-ray source in the Crab Nebula     

Y. Fukada  S. Hayakawa  I. Kasahara  F. Makino  Y. Tanaka  H. Akiyama  M. Matsuoka  J. Nishimura  M. Oda  M. Nakagawa  H. Sakurai  V. S. Iyenger  P. K. Kunte  R. K. Manchanda  B. V. Sreekantan 《Astrophysics and Space Science》1976,42(1):245-248

The size of the hard X-ray source in the Crab Nebula was observed with scintillation counters on board two balloons at a lunar occulatation on 24 January, 1975. The Gaussian width of the source is 34 (+17, –14) and the center thereof is offset from the pulsar by 6±4 at position angle 102°. The observed time profile can also be fitted to an alternative model of two line sources whose intensities are 48% at 11 and 25.5% at 7 on both sides of the pulsar.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.  相似文献   

Aseismic faulting following the 1973 Nemuro-Oki earthquake,Hokkaido, Japan (a possibility)     

Keichi Kasahara 《Pure and Applied Geophysics》1975,113(1):127-139

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Aseismic faulting following the 1973 Nemuro-oki earthquake,Hokkaido, Japan (a retrospective study)     

Keichi Kasahara  Teruyuki Kato 《Pure and Applied Geophysics》1980,119(2):392-403

Tidal records at Hanasaki, southeastern Hokkaido, are analysed to clarify the post-seismic crustal vertical movement in the 1973 Nemuro-oki, Japan, earthquake. The result shows that the post-seismic uplift, as speculated byKasahara (1975), terminated in late 1975 and reverted to the previous rate of rapid subsidence of about 1 cm/yr. Ceasing of the post-seismic uplift, which occurred much earlier than previously speculated, could be explained by supplementary mechanisms, such as frictional resistance against creeping at the fault surface. This unexpected mode of movement, however, raises a new question about the accumulation of tectonic movements in this district. Since the subsidence rate extrapolated from geomorphological data for the past several thousand years is almost one order of magnitude lower than the recent rate as mentioned above, we have to provide some alternative explanation for the discrepancy between the two rates. In other words, simple repetition of co-, post- and inter-seismic movements in seismic cycles due to plate subduction, must be modified in this district. Several possible modifications to the subduction process are suggested, and a brief discussion of vertical movements expected in each case is given.  相似文献   

Multidisciplinary geophysical measurements on the ocean floor usingdecommissioned submarine cables: VENUS project     

Kasahara  J. Shirasaki  Y. Momma  H. 《Oceanic Engineering, IEEE Journal of》2000,25(1):111-120

To perform geophysical and multidisciplinary real-time measurements on the ocean floor, it has been attempted to reuse decommissioned submarine cables. The VENUS project reuses the TPC-2, which is one of these systems and runs across the entire Philippine Sea Plate between Guam Island and Okinawa Island. The VENUS system comprises an ocean floor observatory, a submarine cable, and a land system. The major components of the ocean floor observatory are geophysical instruments and a telemetry system. There are seven scientific instrument units including broadband seismometers and a hydrophone array. Digital telemetry using the old analog telephone cable obtains high data accuracy and real-time accessibility to data from a laboratory on land. The bottom-telemetry system and a part of sensor units were installed at a depth of 2157 m on the landward slope of the Ryukyu (Nansei-Syoto) Trench on August 29, 1999. The data from the hydrophone array and tsunami gauge have been correctly transmitted to the data center. The rest of the scientific instruments will be deployed by deep-tow equipment and a remotely operated vehicle. Using a decommissioned submarine cable will greatly reduce construction costs compared to using a new cable system  相似文献   

Nonhydrostatic Atmospheric Normal Modes on Beta-Planes   总被引：1，自引：0，他引：1  

J.-H. Qian  A. Kasahara 《Pure and Applied Geophysics》2003,160(7):1315-1358

--To facilitate the understanding of nonhydrostatic effect in global and regional nonhydrostatic models, the normal modes of a nonhydrostatic, stratified, and compressible atmosphere are studied using Cartesian coordinates on midlatitude and equatorial #-planes. The dynamical equations without forcing and dissipation are linearized around the basic state at rest, and solved by using the method of separation of variables. An eigenvalue-eigenfunction problem is formulated, consisting of the horizontal and vertical structure equations with suitable boundary conditions. The wave frequency and the separation parameter, referred to as "equivalent height," appear in both the horizontal and vertical characteristic equations as a coupled problem, unlike the hydrostatic case. Therefore, the nonhydrostatic equivalent height depends not only on the vertical modal scale, as in the hydrostatic case, but also on the zonal and meridional modal scales. Numerical resu lts on the dispersion relations are presented for an isothermal atmosphere. Three kinds of normal modes, namely acoustic, gravity, and Rossby modes, are solved and compared with the corresponding global solutions. Nonhydrostatic effects are studied in terms of normal modes in a wide range of wavelengths from small to planetary scales. It is demonstrated that Rossby modes are hardly affected by nonhydrostatic effects regardless of wavelengths. However, nonhydrostatic effects on gravity modes become significant for smaller horizontal and deeper vertical scales of motion. The equivalent height plays a particularly important role in evaluating nonhydrostatic effects of normal modes on the equatorial #-plane, because the equivalent height appears in the scaling of meridional distance variable of the eigenfunctions. The implementation of nonhydrostatic normal mode analysis on high-resolution numerical modeling is also discussed.  相似文献   

Simultaneous hard X-ray and optical observations of Sco X-1 and a model of semi-opaque X-ray sources     

Izumi Kasahara 《Astrophysics and Space Science》1974,29(1):191-210

Simultaneous observations of hard X-ray and optical emission from Sco X-1 were carried out at Hyderabad, India, on April 16 and 19, 1972. During the first and the second observations Sco X-1 was on the average in a bright phase ofB=12.5 mag. and a slightly darker phase ofB=12.7 mag. respectively. During the first observation the X-ray intensity in the energy range 20–40 keV measured with balloon borne scintillation counters showed an enhancement of a factor of about two in coincidence with an optical flare ofB0.2 mag., whereas the apparent temperature derived from the X-ray spectrum observed in the energy range 20–35 keV showed no appreciable change. Both the X-ray intensity and the apparent temperature observed on April 19 are considerably lower than those observed on April 16. Taking into account the effect of radiative transfer in a hot plasma, the electron density and the optical depth for electron scattering of the plasma cloud are derived asn _e 3×10¹⁶ cm^–3 and _es 10 for the quiescent bright phase. The flare is explained by an increase of the plasma mass by about 30% and an increase of _es by _es 1 without appreciable change of the plasma temperature. The results on April 19 is interpreted as indicating that the quiescent dark phase may be characterized by a decrease of the plasma mass, its contraction and lower temperature.  相似文献