A channelised long run-out debris slide triggered by the Noto Hanto Earthquake in 2007, Japan   总被引：2，自引：1，他引：1  

Yasuhiko Okada  Hirotaka Ochiai  Ushio Kurokawa  Yasuhiro Ogawa  Shiho Asano 《Landslides》2008,5(2):235-239

A strong earthquake (M _J 6.9, M _W 6.6–6.7) at about 11 km depth hit the western shore of the Noto Peninsula on Honshu, Japan, at about 00:42 coordinated universal time (9:42 a.m. local time) on 25 March 2007 (the Noto Hanto Earthquake in 2007). The earthquake triggered only 61 landslides, with most traveling short distances. It caused one long run-out landslide in the Nakanoya district of Monzen town, Wajima city, Ishikawa Prefecture, when a portion of a deep-seated landslide transformed into a moderate debris slide down a channel. The rock slide occurred on a south-facing convex-shaped slope on a small spur where earthquake ground shaking likely was strongly amplified by topography. A portion of the rock slide reached a small channel floored by materials containing abundant groundwater. Constant-volume box-shear tests on normally consolidated saturated specimens revealed that the apparent angle of internal friction of the channel-floor material was 33–36° at 10-mm shear displacement and did not show much decrease in effective normal stress during shearing. In situ rock-sliding testing on the exposed channel materials showed a low kinetic-friction angle of about 21°. We suggest that an unsaturated portion of the rock slide slid down the channel, with sliding between the rock-slide mass and the channel floor. Because the slope angle of the travel path nearly equaled the kinetic-friction angle, the unsaturated rock slide mass may have traveled at a moderately slow speed, or it might have decelerated and accelerated. Slow speed is supported by accounts from local residents that suggest movement of debris continued for 3 days after the main shock.  相似文献   

Seasonal and annual variation in the primary production regime in the central part of Sagami Bay     

Jota Kanda  Shiho FujiwaraHiroshi Kitazato  Yoshihiro Okada 《Progress in Oceanography》2003,57(1):17-29

Seasonal variations in the primary production regime in the upper water column were assessed by shipboard observations using hydrocasts and natural fluorescence profiling at a fixed station in the central part of Sagami Bay, Japan. The observations were conducted as a part of ‘Project Sagami’ dedicated to the interdisciplinary study of seasonality in bathyal benthic populations and its coupling with water column processes. Based on the time-series observations at intervals of about 1 to 2 months, primary productivity in terms of chlorophyll abundance appeared to be elevated during the spring of 1997, but the observed peaks of biomass were much less significant in the spring of 1998. Meanwhile, the organic matter flux, as indicated by sediment trap data and benthic observations, had a significant peak in the spring of 1998 as well, and its magnitude was comparable to that in 1997. Satellite images of ocean color obtained during the spring of 1997 indicate the importance of events with time scales much shorter than a month, and suggest qualitative differences in the phytoplankton community in the euphotic zone for each bloom event during this period. The possible mechanisms that could yield the spring maximum of material input to the benthic community are discussed.  相似文献   

Study on the manganese nodule V. Thermal studies of the iron-manganese phase     

Akihiko Okada  Tadayuki Minakuchi  Makoto Shima 《Journal of Oceanography》1972,28(2):39-47

The thermal phase transformation of the iron-manganese phase of the Pacific Ocean manganese nodules were studied by the differential thermal and X-ray diffraction methods. X-ray powder patterns of the heated samples at the temperature of 600°C to 1000°C show the occurrence of hematite, bixbyite and cubic and tetragonal (Fe, Mn)₃O₄. Bixbyite produced by the heat treatment of the iron-manganese phase gives an abnormal X-ray pattern in comparison with the standard sample of bixbyite. Cubic (Fe, Mn)₃O₄ is produced not only by the reaction of bixbyite with hematite over 900°C, but also at the lower temperature, such as 600°C. While, tetragonal (Fe, Mn)₃O₄ is a reaction product of cubic (Fe, Mn)₃O₄ with bixbyite over 900°C in the case of manganese rich nodules. The species and quantities of the products after the heat treatment are assumed to be mostly influenced by the relative contents of iron and manganese in the manganese nodule.  相似文献   

Deep convection seesaw controlled by freshwater transport through the Denmark Strait   总被引：1，自引：0，他引：1  

Akira Oka  Hiroyasu Hasumi  Naosuke Okada  Takashi T. Sakamoto  Tatsuo Suzuki 《Ocean Modelling》2006,15(3-4):157

Observations of deep ocean temperature and salinity in the Labrador and Greenland Seas indicate that there is negative correlation between the activities of deep convection in these two sites. A previous study suggests that this negative correlation is controlled by the North Atlantic Oscillation (NAO). In this study, we discuss this deep convection seesaw by using a coupled atmosphere and ocean general circulation model. In this simulation, the deep convection is realistically simulated in both the Labrador and Greenland Seas and their negative correlation is also recognized. Regression of sea level pressure to wintertime mixed layer depth in the Labrador Sea reveals strong correlation between the convection and the NAO as previous studies suggest, but a significant portion of their variability is not correlated. On the other hand, the convection in the Greenland Sea is not directly related to the NAO, and its variability is in phase with changes in the freshwater budget in the GIN Seas. The deep convection seesaw found in the model is controlled by freshwater transport through the Denmark Strait. When this transport is larger, more freshwater flows to the Labrador Sea and less to the Greenland Sea. This leads to lower upper-ocean surface salinity in the Labrador Sea and higher salinity in the Greenland Sea, which produces negative correlation between these two deep convective activities. The deep convection seesaw observed in the recent decades could be interpreted as induced by the changes in the freshwater transport through the Denmark Strait, whose role has not been discussed so far.  相似文献   

Consideration of natural hazards in the design and risk management of industrial facilities   总被引：1，自引：0，他引：1  

Ana Maria Cruz  Norio Okada 《Natural Hazards》2008,44(2):213-227

Recent chemical accidents precipitated by natural disasters have prompted governments in the United States, Japan, and Europe, among other countries, to re-evaluate current practices in the design and risk management of industrial facilities. This paper presents an overview of natural hazard design considerations and external events risk management requirements in the industrial sector, with particular emphasis on industrial practices in the United States, Japan, and Europe. The analysis shows that although regulations exist to ensure industrial plant structures are built to resist natural hazards (up to the design level), there are few laws to address the performance of non-structural elements and safety and emergency response measures during a natural disaster. Laws usually also refer to natural hazards only indirectly, and provisions to prevent or respond to simultaneous disasters from single or multiple sources concurrent with the natural disaster are usually not present.

Ana Maria CruzEmail:

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The eastern and western ends of Nankai Trough: results of Box 5 and Box 7 Kaiko survey     

X. Le Pichon  T. Iiyama  H. Chamley  J. Charvet  M. Faure  H. Fujimoto  T. Furuta  Y. Ida  H. Kagami  S. Lallemant  J. Leggett  A. Murata  H. Okada  C. Rangin  V. Renard  A. Taira  H. Tokuyama 《Earth and Planetary Science Letters》1987,83(1-4)

Seabeam mapping and detailed geophysical surveying have been conducted over the Nankai Trough where the fossil Shikoku Ridge is subducted below southwest Japan. The geometry of the oceanic lithosphere bending under the margin as well as the three-dimensional structure of the accretionary prism have thus been determined in detail. Three 350° trending, probably transform faults have been identified in the area of the survey. They do not extend further south and appear to be limited to the last phase of spreading within the Shikoku Basin, probably between 15 and 12 Ma; this last phase of spreading would then have been accompanied by a sharp change in spreading direction from east-west to N 350°. The two eastern transform faults limit a zone of reduced Nankai trench fill of turbidites opposite to the Tosa Bae Embayment. This observation suggests that the Tosa Bae Embayment actually results from this reduced supply of trench fill to the imbricate thrusting process. The accretionary prism can be divided into three different tectonic provinces separated by continuous mappable thrusts, the Lower and Upper Main Thrusts. Surface shortening is limited to the lower accretionary prism south of the Upper Main Thrust (UMT) whereas uplift with possible extension characterizes the prism above the UMT. Deformation, due to the relative plate motion, mostly affects the lower accretionary prism south of the UMT.  相似文献   

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   

The measurement of incident and azimuthal angles and the polarization of whistlers at low latitudes     

T. Okada  A. Iwai  M. Hayakawa 《Planetary and Space Science》1977,25(3):233-241

In order to estimate the path latitude of low-latitude whistlers, the measurement of the direction of arrival (bearing and elevation) and the polarization has been successfully carried out a low-latitude station at Takayama (geomag. lat. 26°), by using our newly developed electronic devices. Our system of using two crossed loops and a vertical monopole is, in principle, based on Crary's method and is effective for elliptically polarized waves. The measurements were made at a specific frequency of 4.5 kHz.The main results of our preliminary experiments are (i) the exit points of observed whistlers are located several tens of kilometers approximately north-north-east of the observing site and (ii) although a few whistlers have shown the polarization very close to circular, the polarization of most whistlers are generally elliptical, indicating the effect of multi-rays propagating in the Earth- ionosphere waveguide.  相似文献   

A complex earth slide–earth flow induction by the heavy rainfall in July 2006, Okaya City, Nagano Prefecture, Japan     

Yasuhiko Okada  Hirotaka Ochiai  Takashi Okamoto  Kyoji Sassa  Hiroshi Fukuoka  Ogbonnaya Igwe 《Landslides》2007,4(2):197-203

A seasonal rain front (Baiu front) accompanied a long-term accumulation of precipitation propagated over the wide areas of the main island of Japan during 15–24 July 2006. In Okaya City, Nagano Prefecture, several flow-type landslides occurred in the early morning of 19 July 2006, claiming eight lives. Among these landslides, a most peculiar complex earth slide–earth flow occurred on a north gentle slope of the upstream portion of the Motosawagawa River. In the source area, volcanoclastic soils overlying tuffaceous rocks at about 4-m depth slid due to the prolonged precipitation that raised the water table level in the soil. Along with the travel path, the failed materials fluidized causing the liquefaction of the volcanoclastic soils underlain by volcanic black ash soils. The resulting flow spread over a wide area up to the final deposition. Constant volume box-shear tests on undisturbed volcanoclastic soil specimens taken from the source area showed effective normal stress tended to decrease during shearing. The ring shear tests on saturated disturbed specimens produced the large loss of shear resistance, which may explain the fluidized motion of the complex landslide.  相似文献   

Channel bed adjustments following major aggradation in a steep headwater setting: findings from Oyabu Creek, Kyushu, Japan   总被引：1，自引：0，他引：1  

Mio Kasai  Tomomi Marutani  Gary Brierley 《Geomorphology》2004,62(3-4):199-215

A typhoon in 1993 induced major aggradation along Oyabu Creek, a steep, gravel bed mountain stream in Kyushu, Japan. Processes of sediment reworking are inferred from a 7-year monitoring program that measured adjustments to channel cross-sections, the longitudinal profile, and the extent/distribution of bedrock outcrops along a 3-km study reach. Over time, the reach adopted a riffle and pool structure, with notable increase in the area of exposed bedrock on the bed. This adjustment process was characterised by progressive reduction in sediment storage change per unit flow. The relaxation pathway following disturbance induced by the typhoon was shaped by the magnitude and frequency of subsequent rainfall events, the capacity of these events to transport available sediments, and physical linkages between reaches. Adjacent subreaches demonstrated differing relaxation pathways in response to these influences, induced by spatial and temporal variability in threshold conditions along the channel. Longer-term evidence indicates that responses to major disturbance, such as the 1993 typhoon, occur as ‘cycles’ of around 20-year duration. A relaxation period of 7 years is required to attain a quasi-equilibrium bed configuration and rate of sediment flux. The timeframe of cycles is considered to reflect changes to hillslope–channel bed coupling, marking the period required to generate sufficient sediment stores to reactivate phases of aggradation and subsequent degradation.  相似文献