Strain and stress changes in the Tokai region of central Japan expected from a 3D subduction model     

Hidekuni Kuroki  Hidemi M ItoAkio Yoshida 《Physics of the Earth and Planetary Interiors》2003,135(4):231-252

Using a 3D simulation model with a rate- and state-dependent friction law, Kuroki et al. (2002) discussed a process of a hypothetical great earthquake in the Tokai region, where the Philippine Sea plate subducts beneath the Eurasian plate. One of the main concerns was characteristic changes in volumetric strain and displacement on the ground surface which are caused by the evolution of the coupling between the two plates, i.e. evolution of a strongly coupled region between the plates which results in a preslip of the earthquake.In the present paper we discuss other observable phenomena which might help us to identify the stage of the coupling. The preslip of the earthquake could be more effectively detected by using full information about the change of strain rather than volumetric strain alone; the change in rotation angle of principal strain axes should amount to several tens of degrees while the order of the change in volumetric strain is 10⁻⁸ to 10⁻⁷ for 1 day before the earthquake. The spatial pattern of the displacement field on the ground surface provides us with information on the intermediate-term precursory changes in the plate coupling. Information given by micro-earthquakes is less direct. The seismicity should change considerably when a highly shear-stressed ring on the plate interface passes nearby, and ups and downs of seismicity rate will be estimated by Coulomb failure stress. On the other hand, focal mechanisms are rather insensitive to the progress of plate subduction. The changes may be not significant even at the time of the preslip. The interplate coupling yields a stress field that should produce reverse fault type mechanisms, but the stress field is modulated by a curved shape of the plate interface. Superposition of a regional tectonic stress to this field explains observed spatial distribution of focal mechanisms in the Tokai region which involve large strike-slip components.  相似文献   

Experimental verification of torsional response control of asymmetric buildings using MR dampers     

Osamu Yoshida  Shirley J. Dyke  Luca M. Giacosa  Kevin Z. Truman 《地震工程与结构动力学》2003,32(13):2085-2105

This paper proposes a semiactive control system to reduce the coupled lateral and torsional motions in asymmetric buildings subjected to horizontal seismic excitations. Magnetorheological (MR) dampers are applied as semiactive control devices and the control input determination is based on a clipped‐optimal control algorithm which uses absolute acceleration feedback. The performance of this method is studied experimentally using a 2‐story building model with an asymmetric stiffness distribution. An automated system identification methodology is implemented to develop a control‐oriented model which has the natural frequencies observed in the experimental system. The parameters for the MR damper model are identified using experimental data to develop an integrated model of the structure and MR dampers. To demonstrate the performance of this control system on the experimental structure, a shake table is used to reproduce an El Centro 1940 N–S earthquake as well as a random white noise excitation. The responses for the proposed control system are compared to those of passive control cases in which a constant voltage is applied to the MR damper. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Concentrations of 222 Rn, Its Short-Lived Daughters And 212 Pb And Their Ratios Under Complex Atmospheric Conditions And Topography     

Toshio Kataoka  Eiji Yunoki  Mitsuo Shimizu  Tadashige Mori  Osamu Tsukamoto  Satoshi Takahashi  Hironori Fudeyasu  Yukitaka Ohashi  Ken Sahashi  Toshihiko Maitani  Koh'ichi Miyashita  Toru Iwata  Takayuki Sasaki  Yoko Fujikawa  Akira Kudo  Roger H. Shaw 《Boundary-Layer Meteorology》2003,107(1):219-249

Atmospheric activity concentrations of ²¹²Pb and short-lived ²²²Rndaughters, together with meteorological elements, have been observed continuously atthree sites at Kamisaibara Village in Japan. In addition, atmospheric activity concentrationof ²²²Rn, equilibrium-equivalent concentration of ²²²Rn and conditionsof the lower atmosphere were observed for three intensive observation periods at Akawase,one of the three sites in Kamisaibara Village. The equilibrium-equivalent concentration of²²²Rn is almost the same as the atmospheric activity concentration of short-lived²²²Rn daughters.The activity concentrations of ²¹²Pb and the short-lived ²²²Rn daughtersand their ratio were low in the daytime owing to convective mixing, and high at nightowing to the surface-based inversion during periods of no precipitation. Their variationshave several patterns corresponding to the scale of the drainage wind or weak mixing.Mechanical mixing due to strong winds through both day and night during the first andsecond observation periods made the atmospheric activity concentrations of ²¹²Pb and the short-lived ²²²Rn daughters continuously low. However, their ratios werecontinuously high during the first period yet continuously low during the second period.This difference can be explained by the effect ofextraction of ²²⁰Rn and ²²²Rndue to strong winds and snow cover. There were also cases in which the ratio of theatmospheric activity concentration of ²¹²Pb to that of the short-lived ²²²Rndaughters at night was equal to or less than the ratio in the daytime. Thisinverse trend, asin the periods of no precipitation mentioned above, is considered to be due to near-neutralconditions on these nights.We find a difference in the ratio of the equilibrium-equivalent concentration of²²²Rn (the activity concentration of short-lived ²²²Rn daughters) tothe activity concentration of ²²²Rn during the first observation period and thatduring the second. The difference can be explained by snow cover on the ground. Wealso find differences among the ratios of the activity concentration of the short-lived²²²Rn daughters to that of ²²²Rn during the three observation periods.These differences can be explained by the submergence of paddy fields.  相似文献   

Fourth Nepal Geological Congress     

Masaru Yoshida  Takeshi Imayama  Ranjan K. Dahal 《Gondwana Research》2004,7(4):1249-1251

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Fracture-zone conditions on a recently active fault: insights from mineralogical and geochemical analyses of the Hirabayashi NIED drill core on the Nojima fault, southwest Japan, which ruptured in the 1995 Kobe earthquake     

Tatsuo Matsuda  Kentaro Omura  Ryuji Ikeda  Takashi Arai  Kenta Kobayashi  Koji Shimada  Hidemi Tanaka  Tomoaki Tomita  Satoshi Hirano   《Tectonophysics》2004,378(3-4):143

An 1800-m-deep borehole into the Nojima fault zone was drilled at Nojima-Hirabayashi, Japan, after the 1995 Hyogo-ken Nanbu (Kobe) earthquake. Three possible fracture zones were detected at depths of about 1140, 1300, and 1800 m. To assess these fracture zones in this recently active fault, we analyzed the distributions of fault rocks, minerals, and chemical elements in these zones. The central fault plane in the shallowest fracture zone was identified by foliated blue-gray gouge at a depth of 1140 m. The degree of fracturing was evidently greater in the hanging wall than in the footwall. Minerals detected in this zone were quartz, orthoclase, plagioclase, and biotite, as in the parent rock (granodiorite), and also kaolinite, smectite, laumontite, stilbite, calcite, ankerite, and siderite, which are related to hydrothermal alteration. Biotite was absent in both the hanging wall and footwall across the central fault plane, but it was absent over a greater distance from the central fault plane in the hanging wall than in the footwall. Major element compositions across this zone suggested that hydrothermal alteration minerals such as kaolinite and smectite occurred across the central fault plane for a greater distance in the hanging wall than in the footwall. Similarly, H₂O+ and CO₂ had higher concentrations in the hanging wall than in the footwall. This asymmetrical distribution pattern is probably due to the greater degree of wall–rock fracturing and associated alteration in the hanging wall. We attributed the characteristics of this zone to fault activity and fluid–rock interactions. We analyzed the other fracture zones along this fault in the same way. In the fracture zone at about 1300 m depth, we detected the same kinds of hydrothermal alteration minerals as in the shallower zone, but they were in fewer samples. We detected relatively little H₂O+ and CO₂, and little evidence for movement of the major chemical elements, indicating little past fluid–rock interaction. In the fracture zone at about 1800 m depth, H₂O+ and CO₂ were very enriched throughout the interval, as in the fracture zone at about 1140 m depth. However, smectite was absent and chlorite was present, indicating the occurrence of chloritization, which requires a temperature of more than 200 °C. Only smectite can form under the present conditions in these fracture zones. The chloritization probably occurred in the past when the fracture zone was deeper than it is now. These observations suggest that among the three fracture zones, that at about 1140 m depth was the most activated at the time of the 1995 Hyogo-ken Nanbu (Kobe) earthquake.  相似文献   

Changing distribution of gender in the Extended Bangkok Region under globalization     

Satoshi Nakagawa 《GeoJournal》2004,61(3):255-262

This study examines recent changes in the structure of migration and population by gender in the Extended Bangkok Region (EBR) taking the influences of economic globalization into consideration. The EBR is understood here to consist of three concentric zones, namely the Bangkok Metropolis (BM), the Vicinity and the Extended Urban Region (EUR). The spatial policy of the Thai government has encouraged investors to build manufacturing factories outside the BM. Consequently the industrial structure of the BM has turned strongly into service-dominated while the Vicinity and the EUR have attracted factories mainly owned by foreign capitals. Light industries and electronics industries, both of which set up relatively earlier, concentrated on the Vicinity, the adjacent provinces to the BM, while heavy and petrochemical industries are recently have developed in the outer regions, the EUR. Service sectors and light industries as well as electronics industries prefer females to males to employ as workers. As a consequence the population structures of the BM and the Vicinity became female-dominant while male workers were likely to gather in the EUR attracted by heavy and petrochemical industries. The gender imbalance in the population in the areas in concern may have been one of the consequences of the economic globalization of Thailand. The Thai government supported the economic globalization through its investment promotion policy, but it seems that the government did not assume the policy resulted in such gender imbalance. It can be suggested that in the future this gender imbalance may cause changes in family formation behaviors of the Thai population. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The Central Africa Copperbelt in Southeastern Democratic Republic of Congo: IGCP-450 Field Workshop on Proterozoic Sediment-hosted Base Metal Deposits of West Gondwana     

M. Yoshida  J. Kokonyangi  J. Batumike 《Gondwana Research》2004,7(2):640-643

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The Central Granites-Gneiss-Migmatite Belt (CGGMB) of Madagascar: the Eastern Neoproterozoic Suture of the East African Orogen   总被引：1，自引：0，他引：1  

R.A. Rambeloson  M. Yoshida  V. Ramasiarinoro  L. Le Duc  B. Ralison 《Gondwana Research》2003,6(4):641-651

The northeastern part of Madagascar is characterized by Archaean to early Proterozoic rocks composed principally of Archaean granite and greenstone/amphibolite as well as reworked migmatite with subordinate Proterozoic paragneisses. The southern part is mostly occupied by Proterozoic rocks, composed mostly of Meso to Neo-Proterozoic and less metamorphic metasediments (Itremo Group) in the northwest, para- and ortho-gneisses in most other areas, with minor granitic gneisses with some Archaean components in the southeast. The north-northwest trending Central Granite-Gneiss-Migmatite Belt (CGGMB) is situated at the western margin of the Archaean-early Proterozoic terrain. The CGGMB is composed of granite, gneiss and migmatite with distinct lithologies and structures. They are: i) many types of granites including alkaline to mildly alkaline granites, and calc-alkaline granites; ii) batholitic granites, migmatitic granites and granite dyke swarm, iii) eclogite, and iv) the Ankazobe-Antananarivo-Fianarantsoa Virgation.

The CGGMB was formed by the collision of the palaeo-Dharwar Craton to the east and the East African Orogen to the west at ca. 820-720 Ma and suffered indentation by a part of the western part of the East African Orogen at ca. 530 Ma that produced the Ankazobe-Antananarivo-Fianarantsoa Virgation at the centre of the CGGMB. Thus, the CGGMB is proposed to be the continuation of the eastern suture between the palaeo Dharwar Craton and the East African Orogen, and carries the main feature of the Pan-African collisional event in Madagascar.  相似文献   

On the Solar Origins of Intense Geomagnetic Storms Observed During 6–11 March 1993     

Srivastava  Nandita  Gonzalez  Walter D.  Gonzalez  Alicia L.C.  Masuda  Satoshi 《Solar physics》1998,183(2):419-434

Intense geomagnetic storms with DST index -100 nT were recorded on 9 March and 11 March 1993 associated with solar activity on 6 March and 9-10 March, respectively. In this paper, we discuss the characteristic features of the solar origins of the two events that gave rise to coronal and interplanetary disturbances and as a consequence produced strong geomagnetic activity at the Earth. The source of the activity in one case is attributed to a major 3M7.0 flare that occurred on 6 March 1993 and in the other case, to two large filament disruptions on the disk during 9-10 March, 1993. Both these sources were found to be located near changing or varying low-latitude coronal holes. They were also located close to the heliospheric currents sheets. Distinct X-ray activity was observed for both the events as observed by the Yohkoh SXT telescope. The detailed evolution and a comparison of these events on the basis of Yohkoh soft X-ray observations are presented here.  相似文献   

A Report of IGCP-368 Activities and its Future Programs     

Masaru Yoshida 《Gondwana Research》1998,1(3-4):421-423

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