Tokaido — megalopolis of Japan

The Tokaido east coast road has been the main road of Japan since Mediaeval times, and the journey from Tokyo at one end to Kyoto or Osaka at the other, which used to take a fortnight, can now be completed in about three hours by bullet train, and an even faster linear-motor car is likely to be in operation in the near future.Already during the 18. cent., Edo (Tokyo) was the largest city in the world, with a population over a million, and the rapid urbanization of Japan's population since Meiji times, and particularly during the post-WW II period, has been quite unprecendented. In 1950, the median size of place was 13,000 and by 1975 it was 140,000. About 60 million lived in the Tokaido zone.The Kanto, Nobi and Osaka plains, adjacent to the good harbours of Tokyo, Ise and Osaka bays, enjoying the relatively mild climate of the Pacific coast, and being within 600 km of each other, have been the focii of urban and industrial development in Japan. The emergence of Tokaido megalopolis was boosted by capital investment in this zone, and was contingent upon the industriousness and high level of education of the people.The concept of megalopolis in Japan is popularly associated with rapid urbanization, poly-nuclear and linear form, and concentration of population, capital and information, all of which elements are typified by the Tokaido zone. The linear megalopolis pattern has been postulated as a more efficient growth form for high-dense society than the radial metropolitan pattern. It has even been suggested that megalopolis is a concept perceived by the intellect, its physical structure determined by information networks, metropolis being perceived by the eye and its physical structure being determined by transport and energy networks.Quite irrespective of the concept of megalopolis, there can be no denying that Japan's society is a high-dense society. In 1975, 57% of the population lived in Densely Inhabited Districts (DIDs) at minimum densities of 40 persons per hectare, and these DIDs covered only 2.2% of the land area of Japan. The current trend is for more and more people to live in DIDs, but for overall DID densities to decrease. During the past 25 years, there has been a huge influx of population into the Tokaido zone, and while until 1960 the greatest increases were in the three main metropolitan centres, as these became saturated, rapid urbanization spread into the neighbouring prefectures. Since the mid-sixties, the central metropolitan wards have begun to lose residents, but the daytime population has continued to increase, giving rise to increasingly complex commuting patterns. To give an example, the commuting field of Yokohama includes almost all the prefectures of Tokaido megalopolis.Like the image of megalopolis itself, life in Tokaido megalopolis has its good and bad aspects. Although per capita space in dwellings is increasing somewhat, housing is extremely expensive and people commute long distances. Incomes are high but environmental problems persist. There is a U-turn phenomenon, but metropolitan suburbs remain a popular choice of residence.Central management functions and knowledge and information oriented occupations are predominantly concentrated in Tokyo and Osaka, the two main nodes of Tokaido megalopolis. In the intermediate cities, new employment opportunities are stimulated by the expansion of second-level managerial functions. The transport and communications networks of Tokaido are becoming congested as mobility and information flow increase.Planning in the eighties will be affected by the switch from industries dependent on raw materials to knowledge intensive industries; from investment in production to investment in public facilities and pollution control. Within Tokaido megalopolis, there is room for local governments to expand efforts to improve the existing situation, and at its fringes to avert some of the less desirable consequences of rapid urbanization.     

模糊数学方法在分析日本东海地区地震前兆中的应用

本文把模糊模式识别的直接方法用于检测日本东海地区地震活动性、体积应变、地下水位、地下水氡含量、地倾斜和潮位中的前兆变化。此方法可消除诸如降雨和气温变化等干扰,使我们能更清晰地识别出地震前兆。此外,还把模糊相似方法和模糊聚类方法应用于识别地震空区及检验地震活动随时间变化的相似性。上述方法在日本其他地区同样有效,即将编入日本气象研究所板内地震预报计划中的计算机系统内。     

Depth distribution of radiolarians from the Chukchi and Beaufort Seas, western Arctic

The depth distributions of the radiolarian fauna in the Chukchi and Beaufort Seas, marginal seas of the western Arctic Ocean, were examined quantitatively in depth-stratified plankton tows from 4 or 5 intervals above 500 m and in surface sediments from various depths between 163 and 2907 m. The radiolarian assemblage from the water column in September 2000 was dominated by Amphimelissa setosa and followed by the Actinomma boreale/leptoderma group, Pseudodictyophimus gracilipes and Spongotrochus glacialis. These species are related to the Arctic Surface Water shallower than 150 m. This assemblage is similar to that in the Greenland Sea relating to the ice edge, but did not contain typical Pacific radiolarians in spite of the flow of water of Pacific origin in this region. The living depth of Ceratocyrtis historicosa was restricted to the relatively warm water between 300 and 500 m corresponding to the upper Arctic Intermediate Water (AIW) originating from the Atlantic Ocean. Radiolarian assemblages in the surface sediments are similar to those in the plankton tows, except for common Cycladophora davisiana in sediment samples below 500 m. C. davisiana is probably a deep-water species adapted to the lower AIW or the Canadian Basin Deep Water ventilated from the shelves.     

Monitoring of fault healing after the 1999 Kocaeli, Turkey, earthquake

The North Anatolian fault zone that ruptured during the mainshock of theM 7.4 Kocaeli (Izmit) earthquake of 17 August 1999 has beenmonitored using S wave splitting, in order to test a hypothesisproposed by Tadokoro et al. (1999). This idea is based on the observationof the M 7.2 1995 Hyogo-ken Nanbu (Kobe) earthquake, Japan.After the Hyogo-ken Nanbu earthquake, a temporal change was detectedin the direction of faster shear wave polarization in 2–3 years after the mainshock (Tadokoro, 1999). Four seismic stations were installed within andnear the fault zone at Kizanlik where the fault offset was 1.5 m, about80 km to the east of the epicenter of the Kocaeli earthquake. Theobservation period was from August 30 to October 27, 1999. Preliminaryresult shows that the average directions of faster shear wave polarization attwo stations were roughly parallel to the fault strike. We expect that thedirection of faster shear wave polarization will change to the same directionas the regional tectonic stress reflecting fault healing process. We havealready carried out a repeated aftershock observation at the same site in2000 for monitoring the fault healing process.     

Geometry of the Nojima Fault at Nojima-Hirabayashi, Japan – II. Microstructures and their Implications for Permeability and Strength

Samples of damage-zone granodiorite and fault core from two drillholes into the active, strike-slip Nojima fault zone display microstructures and alteration features that explain their measured present-day strengths and permeabilities and provide insight on the evolution of these properties in the fault zone. The least deformed damage-zone rocks contain two sets of nearly perpendicular (60–90° angles), roughly vertical fractures that are concentrated in quartz-rich areas, with one set typically dominating over the other. With increasing intensity of deformation, which corresponds generally to increasing proximity to the core, zones of heavily fragmented rock, termed microbreccia zones, develop between prominent fractures of both sets. Granodiorite adjoining intersecting microbreccia zones in the active fault strands has been repeatedly fractured and locally brecciated, accompanied by the generation of millimeter-scale voids that are partly filled with secondary minerals. Minor shear bands overprint some of the heavily deformed areas, and small-scale shear zones form from the pairing of closely spaced shear bands. Strength and permeability measurements were made on core collected from the fault within a year after a major (Kobe) earthquake. Measured strengths of the samples decrease regularly with increasing fracturing and fragmentation, such that the gouge of the fault core and completely brecciated samples from the damage zone are the weakest. Permeability increases with increasing disruption, generally reaching a peak in heavily fractured but still more or less cohesive rock at the scale of the laboratory samples. Complete loss of cohesion, as in the gouge or the interiors of large microbreccia zones, is accompanied by a reduction of permeability by 1-2 orders of magnitude below the peak values. The core samples show abundant evidence of hydrothermal alteration and mineral precipitation. Permeability is thus expected to decrease and strength to increase somewhat in active fault strands between earthquakes, as mineral deposits progressively seal fractures and fill pore spaces.     

Spin rates of fast-rotating asteroids and fragments in impact disruption

We present a new experimental result of fragment spin-rate in impact disruption, using a thin glass plate. A cylindrical projectile impacts on a side (edge) of the plate. Dispersed fragments are observed using a high-speed camera and the spin rates of fragments are measured. We find that the measured fragment spin-rate decreases with increasing size. Assuming that the rotational energy of fragments is supplied from the residual stress, the spin rate ω decreases with increasing fragment size r as ω∼r−1, which explains the above experimental results. This size-dependence is similar to that of the observed spin rates of small fast-rotating asteroids. Our results suggest that spin rates of fragments of small asteroids immediately after disruption may have a similar size-dependence, and can provide constraints on the subsequent spin-state evolution of small asteroids due to thermal torques.     

Holocene climate reconstructions from tandem trace-element and stable-isotope composition of ostracodes from Coldwater Lake, North Dakota, U.S.A.

The geochemistry of ostracode shells and bulk carbonates in a 19-meter sediment core documents at century-scale resolution the evolution of water chemistry in Coldwater Lake, North Dakota, providing a continuous paleohydrologic record of Holocene climate change in the northern Great Plains. A combination of ¹⁸O, ¹³C, Mg/Ca and Sr/Ca in ostracode calcite aided by Sr/Ca in bulk carbonates are used to constrain the paleoclimatic reconstructions. A fresh-water phase in the early Holocene, indicated by the absence of Candona rawsoni and low concentrations of Sr/Ca in bulk carbonate, was followed by a sharp increase in salinity between 10800 and 8900 yr B.P. The climate was predominately dry during the late part of the early Holocene and most of the middle Holocene (8900–5000 yr B.P.), when the lake was very sensitive and recorded a series of dry and wet oscillations. Maximum salinity occurred around 5500 yr B.P. and was followed by a gradual decrease between 5000 and 2400 yr B.P. From 2400 yr B.P. the ¹⁸O, Mg/Ca, and Sr/Ca in the ostracodes indicate generally wet conditions interrupted by a series of lesser salinity and temperature oscillations lasting until 600 yr B.P. Ostracode geochemistry indicates that a warm and dry climate returned at about the time of the Little Ice Age (600–150 yr B.P.). Ostracode ¹³C shows a ong-term increasing trend during the Holocene, which suggests that lake productivity and atmospheric CO₂ exchange made greater contributions to the hypolimnetic carbon pool as the lake became shallower with time.     

Crustal structure in and around the region of the 1995 Kobe Earthquake deduced from a wide-angle and refraction seismic exploration

Abstract The 1995 Kobe (Hyogo-ken Nanbu) earthquake (M_JMA 7.2, M_w 6.9) occurred on Jan. 17, 1995, at a depth of 17 km, beneath the areas of southern part of Hyogo prefecture and Awaji Island. To investigate P-wave velocity distribution and seismological characteristics in the aftershock area of this great earthquake, a wide-angle and refraction seismic exploration was carried out by the Research Group for Explosion Seismology (RGES) . The profile including 6 shot points and 205 observations was 135 km in length, extending from Keihoku, Northern Kyoto prefecture, through Kobe, to Seidan on Awaji Island. The charge of each shot was 350–700 kg. The P-wave velocity structure model showed a complicated sedimentary layer which is shallower than 2.5 km, a 2.5 km-thick basement layer whose velocity is 5.5 km/s, overlying the crystalline upper crust, and the boundary between the upper and lower crust.
Almost all aftershock hypocenters were located in the upper crust. However, the structure model suggests that the hypocenters of the main shock and some aftershock clusters were situated deeper than the boundary between the upper and lower crust. We found that the P-velocity in the upper crust beneath the northern part of Awaji Island is 5.64 km/s which is 3% lower than that of the surrounding area. The low-velocity zone coincides with the region where the high stress moment release was observed.     

The inner solar system cratering record and the evolution of impactor populations

We review previously published and newly obtained crater size-frequency distributions in the inner solar system. These data indicate that the Moon and the terrestrial planets have been bombarded by two populations of objects. Population 1,dominating at early times, had nearly the same size distribution as the present-day asteroid belt, and produced heavily cratered surfaces with a complex, multi-sloped crater size-frequency distribution. Population 2, dominating since about 3.8–3.7 Gyr,had the same size distribution as near-Earth objects(NEOs) and a much lower impact flux, and produced a crater size distribution characterized by a differential –3single-slope power law in the crater diameter range 0.02 km to 100 km. Taken together with the results from a large body of work on age-dating of lunar and meteorite samples and theoretical work in solar system dynamics, a plausible interpretation of these data is as follows. The NEO population is the source of Population 2 and it has been in near-steady state over the past ～ 3.7–3.8 Gyr; these objects are derived from the main asteroid belt by size-dependent non-gravitational effects that favor the ejection of smaller asteroids. However, Population 1 was composed of main belt asteroids ejected from their source region in a size-independent manner, possibly by means of gravitational resonance sweeping during orbit migration of giant planets;this caused the so-called Late Heavy Bombardment(LHB). The LHB began some time before ～3.9 Gyr, peaked and declined rapidly over the next ～ 100 to 300 Myr,and possibly more slowly from about 3.8–3.7 Gyr to ～2 Gyr. A third crater population(Population S) consisted of secondary impact craters that can dominate the cratering record at small diameters.