Three-dimensional Mapping of Magma Source and Transport Regions from Seismic Data: The Mantle Wedge beneath Northeastern Japan     

H. Sato  K. Muro  A. Hasegawa 《Pure and Applied Geophysics》1998,153(2-4):377-398

—We investigate the distribution of partial melt in island arc using the seismic velocity structure of the mantle wedge beneath northeastern Japan. The comparison of the seismic tomography with laboratory velocity data on a partially-molten mantle rock yields estimates of melting zones in three dimensions. We employ experimental data on the degree of partial melt in hydrous peridotite to give constraints on the melt fraction and temperature. Melting and magma-rich zones derived from the velocity structure coincide with observed low Q zones. The results of the three-dimensional mapping indicate that the source of magma in island arc is diapir-like melting patches localized within the low velocity zones of the mantle wedge. Extensive volcanic activity along the volcanic front is due to the presence of vast magma-rich zones just beneath the Moho. Those melting zones in the uppermost mantle may, in turn, cause melting of lower crustal materials and produce felsic magma. Melt appears to stay at and beneath the Moho, where crystallization fractionation may proceed. Melt exists at greater depths in the back-arc region, which may correlate with across-arc variations of chemical compositions of the volcanic rocks observed in northeastern Japan. We suggest that magma migration in the ductile lower crust may cause low-frequency microearthquakes, and magma penetration into the brittle upper crust may produce mid-crustal S-wave reflectors.  相似文献   

Crustal structure and accurate hypocenter determination along the Longmenshan fault zone     

赵珠  范军  郑斯华  长谷川昭  内茂木 《地震学报(英文版)》1997,10(6):761-768

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The method for consecutive subtraction of selected anomalies: the estimated crustal velocity structure in the 1996 Onikobe (M= 5.9) earthquake area, northeastern Japan     

T. A. Smaglichenko  A. V. Nikolaev  S. Horiuchi  A. Hasegawa 《Geophysical Journal International》2003,153(3):627-644

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Characteristics of an atypical large-meander path of the Kuroshio current south of Japan formed in September 2017     

Nagano  Akira  Yamashita  Yusuke  Hasegawa  Takuya  Ariyoshi  Keisuke  Matsumoto  Hiroyuki  Shinohara  Masanao 《Marine Geophysical Researches》2019,40(4):525-539

Since September 2017, the Kuroshio has taken a large-meander (LM) path in the region south of Japan. We examined characteristics of the 2017–present LM path in comparison with previous LM paths, using tide gauge, altimetric sea surface height, and bottom pressure data. The 2017–present LM path was formed from a path passing through a channel south of Hachijo-jima Island, while a typical LM path originated from a path through a channel north of Miyake-jima Island. The meander trough of this atypical path was found to be shifted far to the east and to vary on a timescale of months. These characteristics are different from those of a typical LM path but they are similar to those of the 1981–1984 LM path. Therefore, we identified two types of LM path; a stable and unstable LM paths. The 2017–present unstable type large meander has a zonal scale greater than that of the 2004–2005 stable type large meander and protrudes from the eastern boundary of the Shikoku Basin, i.e., Izu-Ogasawara Ridge. No significant bottom pressure depression was observed, associated with the formation of the 2017–present LM path, indicating that baroclinic instability was not important in the formation of this LM path. Due to no significant bottom steering, even during the 2017–present LM period, a mesoscale current path disturbance occurred southeast of Kyushu, propagated eastward, and amplified the offshore displacement of the Kuroshio.

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El Niño-related sea surface elevation and ocean bottom pressure enhancement associated with the retreat of the Oyashio southeast of Hokkaido,Japan     

Hasegawa  Takuya  Nagano  Akira  Matsumoto  Hiroyuki  Ariyoshi  Keisuke  Wakita  Masahide 《Marine Geophysical Researches》2019,40(4):505-512

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Comparative energetics analysis of CCM2 with different horizontal resolutions     

A. Hasegawa  H. L. Tanaka  H. Hirakuchi  S. Taguchi 《Climate Dynamics》1997,13(7-8):521-532

 Comprehensive global energetics analysis is carried out for the NCAR CCM2 with different horizontal resolutions of R15, T42, T63, and T106 to assess the effect of various model truncations on the global energetics characteristics in climate models. Both the energy levels and energy transformations are examined over the zonal wave number domain during a northern winter and summer. In addition to the simulated atmosphere, the ECMWF global analysis during 1986 to 1990 is analyzed for comparison using the same diagnostic scheme. Previous studies have revealed that zonal kinetic energy is supplied by synoptic disturbances in terms of the zonal-wave interactions of kinetic energy. According to our result, however, such an energy flow from eddies to zonal motions is valid only for zonal wave numbers up to about 30. We find that the zonal-wave interactions of kinetic energy change sign beyond wave number 30 where the energy is transformed from zonal to eddies for both the ECMWF and CCM2-T106. The large-scale zonal motions are diffusive against the short waves beyond wave number 30, which may well be parameterized by various forms of the diffusion schemes. We suggest from this result that the atmospheric disturbances with wave numbers lower than 30 are necessary to represent accurately the two-way interactions between zonal and eddy motions, because these waves can actively influence the behavior of the zonal motions. Based on this finding, we suggest that the model resolution of R15 is inadequate for climate studies from the energetics point of view, and that resolution of T42 is the minimum requirement to represent the general circulation adequately. Some other discrepancies are discussed in detail for the coarse resolution climate models. Received: 15 July 1996/Accepted: 3 January 1997  相似文献   

Viscosity Distribution within the Earth     

Hitoshi Takeuchi  Yosaku Hasegawa 《Geophysical Journal International》1965,9(5):503-508

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Effects of frozen soil and snow cover on cold‐season soil water dynamics in Tokachi,Japan     

Yukiyoshi Iwata  Tomoyoshi Hirota  Masaki Hayashi  Shinji Suzuki  Shuichi Hasegawa 《水文研究》2010,24(13):1755-1765

Despite the potential impact of winter soil water movements in cold regions, relatively few field studies have investigated cold‐season hydrological processes that occur before spring‐onset of snowmelt infiltration. The contribution of soil water fluxes in winter to the annual water balance was evaluated over 5 years of field observations at an agricultural field in Tokachi, Hokkaido, Japan. In two of the winters, soil frost reached a maximum depth of 0·2 m (‘frozen’ winters), whereas soil frost was mostly absent during the remaining three winters (‘unfrozen’ winters). Significant infiltration of winter snowmelt water, to a depth exceeding 1·0 m, occurred during both frozen and unfrozen winters. Such infiltration ranged between 126 and 255 mm, representing 28–51% of total annual soil water fluxes. During frozen winters, a substantial quantity of water (ca 40 mm) was drawn from deeper layers into the 0–0·2 m topsoil layer when this froze. Under such conditions, the progression and regression of the freezing front, regulated by the thickness of snow cover, controlled the quantity of soil water flux below the frozen layer. During unfrozen winters, 13–62 mm of water infiltrated to a depth of 0·2 m, before the spring snowmelt. These results indicate the importance of correctly evaluating winter soil water movement in cold regions. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

The detectability of shallow slow earthquakes by the Dense Oceanfloor Network system for Earthquakes and Tsunamis (DONET) in Tonankai district,Japan     

Keisuke Ariyoshi  Ryoko Nakata  Toru Matsuzawa  Ryota Hino  Takane Hori  Akira Hasegawa  Yoshiyuki Kaneda 《Marine Geophysical Researches》2014,35(3):295-310

In order to understand the characteristics of shallow very low-frequency (VLF) events as revealed by recent ocean-floor observation studies, we perform a trial simulation of earthquake cycles in the Tonankai district by taking the characteristics of the 1944 Tonankai earthquake and assuming that slow earthquakes occur on numerous small asperities. Our simulation results show that the increase of moment release rate of shallower VLF events in the pre-seismic stage of a megathrust earthquake is higher than that of deeper VLF events. This increase may make leveling change due to VLF swarms detectable at Dense Oceanfloor Network system for Earthquakes and Tsunamis (DONET). We also introduce the time series of hydraulic pressure data at DONET, comparing with the leveling change expected from our numerical simulation. Since leveling change due to shallower VLF swarms is so local as to be incoherent, removal of the moving-averaged data from the data stacked by four nearby observation points in the same node may be useful to detect the short-term local leveling change.  相似文献   

Orbit of periodic comet 153P/Ikeya–Zhang     

Ichiro Hasegawa  Syuichi Nakano 《Monthly notices of the Royal Astronomical Society》2003,345(3):883-888

The orbit of Comet C/2002C1 (Ikeya–Zhang) has a similarity to that of Comet C/1661C1 (Hevelius), and the numerical integration of the motion of C/2002C1 backward shows a possible linkage of those two comets. Thus, 153P/Ikeya–Zhang was designated a periodic comet. Historical records of comets in 877 and 1273 are also identified with Comet 153P/Ikeya–Zhang. The integrated orbital elements during 77 and 2362, and historical records of the comet are also presented and discussed.  相似文献