Non-hypersingular boundary integral equations for two-dimensional non-planar crack analysis     

Taku Tada  Teruo Yamashita 《Geophysical Journal International》1997,130(2):269-282

We derive a set of non-hypersingular boundary integral equations, both elastodynamic and elastostatic, for the analysis of arbitrarily shaped 2-D anti-plane and in-plane cracks located in an infinite homogeneous isotropic medium, rendered in a unified nomenclature for all cases. The hypersingularities that appear in the usual formulations for the dynamic cases, existent both at the source point and at the wavefront, are removed by way of a regularization technique based on integration by parts. The equations for the in-plane cases are presented in terms of a local Cartesian coordinate system, one of the axes of which is always held locally tangential to the crack trace. The expressions for the elastic field at any point on the model plane are also given.
Our formulations are shown to yield accurate numerical results, as long as appropriate stabilization measures are taken in the numerical scheme. The numerical applicability of our method to non-planar crack problems is illustrated by simulations of dynamic growth of a hackly crack which has small off-plane side-branches. The results imply that the branching of a crack brings about a significant decrease in the crack-tip stress concentration level and consequently may play an essential role in the arrest of earthquake rupturing.  相似文献   

Crustal structure and tectonics of the Hidaka Collision Zone, Hokkaido (Japan), revealed by vibroseis seismic reflection and gravity surveys     

Kazunori Arita  Takashi Ikawa  Tanio Ito  Akihiko Yamamoto  Matsuhiko Saito  Yasunori Nishida  Hideyuki Satoh  Gaku Kimura  Teruo Watanabe  Takeshi Ikawa  Toru Kuroda 《Tectonophysics》1998,290(3-4):197-210

This study is the first integrated geological and geophysical investigation of the Hidaka Collision Zone in southern Central Hokkaido, Japan, which shows complex collision tectonics with a westward vergence. The Hidaka Collision Zone consists of the Idon'nappu Belt (IB), the Poroshiri Ophiolite Belt (POB) and the Hidaka Metamorphic Belt (HMB) with the Hidaka Belt from west to east. The POB (metamorphosed ophiolites) is overthrust by the HMB (steeply eastward-dipping palaeo-arc crust) along the Hidaka Main Thrust (HMT), and in turn, thrusts over the Idon'nappu Belt (melanges) along the Hidaka Western Thrust (HWT). Seismic reflection and gravity surveys along a 20-km-long traverse across the southern Hidaka Mountains revealed hitherto unknown crustal structures of the collision zone such as listric thrusts, back thrusts, frontal thrust-and-fold structures, and duplex structures. The main findings are as follows. (1) The HMT, which dips steeply at the surface, is a listric fault dipping gently at a depth of 7 km beneath the eastern end of the HMB, and cutting across the lithological boundaries and schistosity of the Hidaka metamorphic rocks. (2) A second reflector is detected 1 km below the HMT reflector. The intervening part between these two reflectors is inferred to be the POB, which is only little exposed at the surface. This inference is supported by the high positive Bouguer anomalies along the Hidaka Mountains. (3) The shallow portion of the IB at the front of the collision zone has a number of NNE-dipping reflectors, indicative of imbricated fold-and-thrust structures. (4) Subhorizontal reflectors at a depth of 14 km are recognized intermittently at both sides of the seismic profile. These reflectors may correspond to the velocity boundary (5.9–6.6 km/s) previously obtained from seismic refraction profiling in the northern Hidaka Mountains. (5) These crustal structures as well as the back thrust found in the eastern end of the traverse represent characteristics of collisional tectonics resulting from the two collisional events since the Early Tertiary.  相似文献   

Brightness distribution of diffuse soft X-rays     

H. Iwanami  H. Kunieda  F. Nagase  K. Yamashita  T. Murakami 《Astrophysics and Space Science》1979,61(1):217-227

The brightness distribution of diffuse soft X-rays in the pulse height range 0.15–0.3 keV (L-band) and 0.5–0.8 keV (M-band) are obtained over a quarter of the sky centered at the galactic anticenter with 1.5 m polypropylene window proportional counters on board a sounding rocket. In theL-band three enhanced regions are noticed on the map. They coincide with the northern and southern Hi holes and the inner part of the galactic radio Loop II.In the northern Hi hole theN _H dependence of theL-band flux and the hardness ratioM/L can be fitted with a local hot plasma model with the absorption by a low velocity neutral hydrogen gas (|V|<25 km s^–1) along the line of sight. The X-ray feature of Loop II is similar to that of Loop I. In the lowN _H region (<3×10²⁰ H atoms cm^–2) theM/L value is lower than 0.3, whereas it varies in the range 0.1–0.4 at low latitudes (|b|<30⁰). This fact seems to be interpreted in terms of a model that a number of hot plasma clouds contribute to X-ray emission.  相似文献   

Ecophysiology of juvenile flatfish in nursery grounds     

Yoh Yamashita  Masaru Tanaka  John M. Miller 《Journal of Sea Research》2001,45(3-4)

Relationships between biotic and abiotic factors and the ecological performance of late larval and juvenile flatfish in nursery grounds are examined from ecophysiological viewpoints. The first events in the nursery are metamorphosis and settlement. Development of organs, osmoregulation and behavioural changes during metamorphosis, and size at metamorphosis are regulated by environmental factors. Various hormones play critical roles in this regulation. Effects of environmental conditions on individual growth in the nursery grounds are described on the basis of Fry's five environmental factors: limiting, controlling, masking, directive and lethal factors. The main limiting factors are food and dissolved oxygen; controlling factors are temperature and body size; masking factors are salinity and pollutants; lethal factors are extreme environments; and directive factors are food, predators and dissolved oxygen. In addition to temperature, it has been indicated that dissolved oxygen seems to be relatively important for flatfish of the eastern US and northern European countries, while food abundance appears to be more critical for Japanese flounder. The feasibility is discussed of ecophysiological modelling to predict individual growth and subpopulation production based on the assessment of the role of environmental variability using the above classification, which organises and integrates environmental effects.  相似文献   

SR isotope geochemistry of voluminous rhyolite of the Tamagawa Welded Tuffs, related rocks and andesite of the young volcanics, in Hachimantai geothermal area, Northeast Japan     

Shigeko Togashi  Teruo Shirahase  Shiro Tamanyu 《Journal of Volcanology and Geothermal Research》1985,24(3-4)

The volcanic rocks from the Hachimantai geothermal area, Northeast Japan, are divided into the following five groups: (1) rhyolite of the Tamagawa Welded Tuffs (about 500 km³, 2.0–1.4 Ma); (2) andesite related to the Tamagawa Welded Tuffs (about 10 km³, 1.5 Ma); (3) andesite of the Matsukawa Andesite (about 100 km³, 1.8-1.2 Ma); (4) dacite of the Kashinai Formation (about 100 km³, 1.1 Ma); and (5) andesite of the Young Volcanics (about 300 km³, younger than 1 Ma). ratios of less-altered samples of the five groups range from 0.7038 to 0.7046. There is no significant difference in ratios among the five groups in spite of differences in age and chemical composition. Therefore, fusion of or contamination by old acidic crust can be ruled out for the genesis of the voluminous acidic magma which produced the rhyolite of the Tamagawa Welded Tuffs and the dacite of the Kashinai Formation.The low ratios and the chemistry suggest two possibilities for the genesis of the acidic rocks. One is a low degree of partial melting of the basic crust, which has a low ratio, under high temperature. Another is a high degree of fractional crystallization from basic magma derived from the mantle.  相似文献   

Shortwave radiation climatonomy of the urban atmosphere in Toronto     

Dr. S. Yamashita 《Theoretical and Applied Climatology》1979,27(2-3):193-203

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Geophysical characteristics of dacite volcanism — the 1977–1978 eruption of Usu volcano     

I. Yokoyama  H. Yamashita  H. Watanabe  Hm. Okada 《Journal of Volcanology and Geothermal Research》1981,9(4):335-358

The 1977–1978 eruption of Usu volcano is discussed from the geophysical standpoint as a classic example of dacite volcanism. The activities of dacitic volcanoes are characterized by persistent earthquake swarms and remarkable crustal deformations due to the high viscosity of the magmas; the former include shocks felt near the volcanoes and the latter accompany formation of lava domes or cryptodomes.The hypocenters of the earthquakes occurring beneath Usu volcano have been located precisely. Their distribution defines an earthquake-free zone which underlies the area of doming within the summit crater. This zone is regarded as occupied by viscous magma. The domings within the summit crater forming the cryptodomes have amounted to about 160 m. In addition to uplift they showed thrusting towards the northeast. As a result, the northeastern foot of the volcano has contracted by about 150 m. The relation between crustal deformation and earthquake occurrence is examined, and it is found that the abrupt domings are accompanied by the larger earthquakes (M = 3–4.3). Both the seismic activity and the ground deformation are shown to have a unique and common energy source.The energy of activities of Usu volcano consists of the explosive type, the deformation type and the seismic type; the second and the third are in parallel with each other in discharges, and both energies are complementary to the explosive energy. The explosive energy and the seismic energy have been calculated for an explosion sequence, and it is concluded that the deformation energy is about 10 times greater than the seismic energy. The discharge rate of the seismic energy and the upheaval rates of the cryptodomes have continued to decrease since the outburst of the eruption, except for a small increase at the end of January 1978. Eruptions are governed not only by the supply of the energies but also by the depth of the magma, which has gradually approached the surface. The last eruption occurred in October 1978; however, the crustal deformations and the earthquake swarms are still proceeding as of January 1980, albeit at a lower rate of activity.  相似文献   

Mechanisms of crustal uplift and subsidence at the Yellowstone caldera,Wyoming     

Daniel Dzurisin  Kenneth M. Yamashita  Jack W. Kleinman 《Bulletin of Volcanology》1994,56(4):261-270

Leveling surveys in 1923, 1976, and each year from 1983 to 1993 have shown that the east-central part of the Yellowstone caldera, near the base of the Sour Creek resurgent dome, rose at an average rate of 14±1 mm/year from 1923 to 1976 and 22±1 mm/year from 1976 to 1984. In contrast, no detectable movement occurred in the same area from 1984 to 1985 (-2±5 mm/year), and from 1985 to 1993 the area subsided at an average rate of 19±1 mm/year. We conclude that uplift from 1923 to 1984 was caused by: (1) pressurization of the deep hydrothermal system by fluids released from a crystallizing body of rhyolite magma beneath the caldera, then trapped beneath a self-sealed zone near the base of the hydrothermal system; and (2) aseismic intrusions of magma into the lower part of the sub-caldera magma body. Subsidence since 1985 is attributed to: (1) depressurization and fluid loss from the deep hydrothermal system, and (2) sagging of the caldera floor in response to regional crustal extension. Future intrusions might trigger renewed eruptive activity at Yellowstone, but most intrusions at large silicic calderas seem to be accommodated without eruptions. Overpressurization of the deep hydrothermal system could conceivably result in a phreatic or phreatomagmatic eruption, but this hazard is mitigated by episodic rupturing of the self-sealed zone during shallow earthquake swarms. Historical ground movements, although rapid by most geologic standards, seem to be typical of inter-eruption periods at large, mature, silicic magma systems like Yellowstone. The greatest short-term hazards posed by continuing unrest in the Yellowstone region are: (1) moderate to large earthquakes (magnitude 5.5–7.5), with a recurrence interval of a few decdes; and (2) small hydrothermal explosions, most of which affect only a small area (<0.01 km²), with a recurrence interval of a few years.  相似文献   

The international at-sea intercomparison of fCO₂ systems during the R/V Meteor Cruise 36/1 in the North Atlantic Ocean     

Arne Krtzinger  Ludger Mintrop  Douglas W. R. Wallace  Kenneth M. Johnson  Craig Neill  Bronte Tilbrook  Philip Towler  Hisayuki Y. Inoue  Masao Ishii  Gary Shaffer  Rodrigo F. Torres Saavedra  Eiji Ohtaki  Eiji Yamashita  Alain Poisson  Christian Brunet  Bernard Schauer  Catherine Goyet  Greg Eischeid 《Marine Chemistry》2000,72(2-4)

The ‘International Intercomparison Exercise of fCO₂ Systems’ was carried out in 1996 during the R/V Meteor Cruise 36/1 from Bermuda/UK to Gran Canaria/Spain. Nine groups from six countries (Australia, Denmark, France, Germany, Japan, USA) participated in this exercise, bringing together 15 participants with seven underway fugacity of carbon dioxide (fCO₂) systems, one discrete fCO₂ system, and two underway pH systems, as well as systems for discrete measurement of total alkalinity and total dissolved inorganic carbon. Here, we compare surface seawater fCO₂ measured synchronously by all participating instruments. A common infrastructure (seawater and calibration gas supply), different quality checks (performance of calibration procedures for CO₂, temperature measurements) and a common procedure for calculation of final fCO₂ were provided to reduce the largest possible amount of controllable sources of error. The results show that under such conditions underway measurements of the fCO₂ in surface seawater and overlying air can be made to a high degree of agreement (±1 μatm) with a variety of possible equilibrator and system designs. Also, discrete fCO₂ measurements can be made in good agreement (±3 μatm) with underway fCO₂ data sets. However, even well-designed systems, which are operated without any obvious sign of malfunction, can show significant differences of the order of 10 μatm. Based on our results, no “best choice” for the type of the equilibrator nor specifics on its dimensions and flow rates of seawater and air can be made in regard to the achievable accuracy of the fCO₂ system. Measurements of equilibrator temperature do not seem to be made with the required accuracy resulting in significant errors in fCO₂ results. Calculation of fCO₂ from high-quality total dissolved inorganic carbon (C_T) and total alkalinity (A_T) measurements does not yield results comparable in accuracy and precision to fCO₂ measurements.  相似文献   

Bathymetric imaging of protothrust zone along the Nankai Trough          下载免费PDF全文

Mikiya Yamashita  Seiichi Miura  Gregory F. Moore  Ayako Nakanishi  Shuichi Kodaira  Yoshiyuki Kaneda 《Island Arc》2018,27(2)

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