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Research about Japan

Source-linked reports with geographic coverage including Japan.

At least 109 records · Page 6Linked to original sources
USGS2001

Inferring rate and state friction parameters from a rupture model of the 1995 Hyogo-ken Nanbu (Kobe) Japan earthquake

We consider the applicability of laboratory-derived rate-and state-variable friction laws to the dynamic rupture of the 1995 Kobe earthquake. We analyze the shear stress and slip evolution of Ide and Takeo's [1997] dislocation model, fitting the inferred stress change time histories by calculating the dynamic load and the instantaneous friction at a series of points within the rupture area. For points exhibiting a fast-weakening behavior, the Dieterich-Ruina friction law, with values of d c = 0.01–0.05 m for critical slip, fits the stress change time series well. This range of d c is 10–20 times smaller than the slip distance over which the stress is released, D c , which previous studies have equated with the slip-weakening distance. The limited resolution and low-pass character of the strong motion inversion degrades the resolution of the frictional parameters and suggests that the actual d c is less than this value. Stress time series at points characterized by a slow-weakening behavior are well fitted by the Dieterich-Ruina friction law with values of d c ≥0.01–0.05 m. The apparent fracture energy G c can be estimated from waveform inversions more stably than the other friction parameters. We obtain a G c ≈ 1.5×l0 6 J m −2 for the 1995 Kobe earthquake, in agreement with estimates for previous earthquakes. From this estimate and a plausible upper bound for the local rock strength we infer a lower bound for D c of about 0.008 m.

Kobe, Osaka↗
USGS2001

Updip limit of the seismogenic zone beneath the accretionary prism of southwest Japan: An effect of diagenetic to low-grade metamorphic processes and increasing effective stress

Off southwest Japan the seaward limit of coseismic displacement (or updip limit of the seismogenic zone) of the 1946 M w 8.3 thrust earthquake reaches to 4 km depth and ∼40 km landward of the trench. This limit coincides with the estimated location of the 150 °C isotherm, and has been linked to changes in physical properties associated with the smectite to illite clay-mineral transition. Here we show that this limit correlates with a suite of diagenetic to low-grade metamorphic processes characterized by (1) declining fluid production and decreasing fluid pressure ratio (λ * ) and (2) active clay, carbonate, and zeolite cementation and the transition to pressure solution and quartz cementation. These diagenetic to low-grade metamorphic changes cause the onset of velocity weakening during thrust faulting, an increase in effective stress, and strengthening of the hanging wall, which together combine to produce recordable earthquakes.

Geology↗
USGS1998

Use of fault striations and dislocation models to infer tectonic shear stress during the 1995 Hyogo-Ken Nanbu (Kobe) earthquake

Dislocation models of the 1995 Hyogo-ken Nanbu (Kobe) earthquake derived by Yoshida et al. (1996) show substantial changes in direction of slip with time at specific points on the Nojima and Rokko fault systems, as do striations we observed on exposures of the Nojima fault surface on Awaji Island. Spudich (1992) showed that the initial stress, that is, the shear traction on the fault before the earthquake origin time, can be derived at points on the fault where the slip rake rotates with time if slip velocity and stress change are known at these points. From Yoshida's slip model, we calculated dynamic stress changes on the ruptured fault surfaces. To estimate errors, we compared the slip velocities and dynamic stress changes of several published models of the earthquake. The differences between these models had an exponential distribution, not gaussian. We developed a Bayesian method to estimate the probability density function (PDF) of initial stress from the striations and from Yoshida's slip model. Striations near Toshima and Hirabayashi give initial stresses of about 13 and 7 MPa, respectively. We obtained initial stresses of about 7 to 17 MPa at depths of 2 to 10 km on a subset of points on the Nojima and Rokko fault systems. Our initial stresses and coseismic stress changes agree well with postearthquake stresses measured by hydrofracturing in deep boreholes near Hirabayashi and Ogura on Awaji Island. Our results indicate that the Nojima fault slipped at very low shear stress, and fractional stress drop was complete near the surface and about 32% below depths of 2 km. Our results at depth depend on the accuracy of the rake rotations in Yoshida's model, which are probably correct on the Nojima fault but debatable on the Rokko fault. Our results imply that curved or cross-cutting fault striations can be formed in a single earthquake, contradicting a common assumption of structural geology.

Bulletin of the Seismological Society of America↗
USGS1996

Application of a feedforward neural network in the search for kuroko deposits in the Hokuroku District, Japan

A feedforward neural network with one hidden layer and five neurons was trained to recognize the distance to kuroko mineral deposits. Average amounts per hole of pyrite, sericite, and gypsum plus anhydrite as measured by X-rays in 69 drillholes were used to train the net. Drillholes near and between the Fukazawa, Furutobe, and Shakanai mines were used. The training data were selected carefully to represent well-explored areas where some confidence of the distance to ore was assured. A logarithmic transform was applied to remove the skewness of distance and each variable was scaled and centered by subtracting the median and dividing by the interquartile range. The learning algorithm of annealing plus conjugate gradients was used to minimize the mean squared error of the scaled distance to ore. The trained network then was applied to all of the 152 drillholes that had measured gypsum, sericite, and pyrite. A contour plot of the neural net predicted distance to ore shows fairly wide areas of 1 km or less to ore; each of the known deposit groups is within the 1 km contour. The high and low distances on the margins of the contoured distance plot are in part the result of boundary effects of the contouring algorithm. For example, the short distances to ore predicted west of the Shakanai (Hanaoka) deposits are in basement. However, the short distances to ore predicted northeast of Furotobe, just off the figure, coincide with the location of the Nurukawa kuroko deposit and the Omaki deposit, south of the Shakanai-Hanaoka deposits, seems to be on an extension of short distance to ore contour, but is beyond the 3 km limit from drillholes. Also of interest are some areas only a few kilometers from the Fukazawa and Shakanai groups of deposits that are estimated to be many kilometers from ore, apparently reflecting the network's recognition of the extreme local variability of the geology near some deposits.

Mathematical Geology↗
USGS1996

Seismology, geology, and geotechnical issues

The Hyogoken-Nanbu (Kobe) earthquake of January 17, 1995 (5:46:52 JST) occurred in an area of complex faulting located near Awaji Island and the Hanshin area of Japan (34.607 N, 135.043 E, depth 14.3 km; Japan Meteorological Agency, JMA). The area which is near the urban centers of Kobe City and Osaka is located about 250 km from the Nankai trough, which forms the boundary between the Philippine Sea and Eurasian plates (Figure 2.1.1). The earthquake of magnitude 7.2 (JMA) is the most severe earthquake to affect the region this century. The largest previous earthquake near Kobe City was a magnitude 6.1 which occurred in 1916 on or near the same fault. Other large but distant earthquakes occurred in 1944 and 1946 along the plate boundary (Figure 2.1.1). Numerous faults known to be active in the Quaternary extend throughout the affected region (Figure 2.1.2). However, prior to January 17, 1995 the area was characterized by relatively low seismicity compared with areas near the plate boundaries (Figure 2.1.1). This 1995 earthquake having occurred at considerable distance from the plate margin, can be considered an intraplate event.

Hanshin↗
USGS1995

The Hanshin-Awaji Earthquake of January 17, 1995: Performance of lifelines

This report describes the damage to lifelines caused by the 1995 Hanshin-Awaji (Kobe) earthquake in Japan. It begins with a summary of the earthquake's seismological characteristics which is followed by separate chapters that focus on the performance of lifelines in the affected region. In order of presentation, individual chapters discuss the damage to: 1) electric power networks; 2) gas delivery systems; 3) hospitals (considered as a system composed of building/architectural components, as well as communication and support systems); 4) telecommunication systems; 5) transportation systems; and 6) water supply systems and wastewater systems. The transportation section includes three subsections: airport facilities, highways and bridges, and underground rapid transit systems. For each lifeline, an overview of the system is given, indicating the owner/operator, the location and extent of the service area, the number of households and industrial/commercial customers served. In addition to descriptions of the individual system, design criteria for the physical components of the individual systems are provided, including a comparison of the differences between the US and Japanese systems. The performance of each lifeline system is discussed with reference to seismic damage, emergency response, service interruption and restoration.

Hanshin↗
USGS1995

Seismological and engineering aspects of the 1995 Hyogoken-Nanbu (Kobe) earthquake

Immediately following the Jan. 17, 1995, Kobe earthquake, a reconnaissance team was organized under the auspices of the Earthquake Hazard Mitigation Program of the Engineering Directorate of the National Science Foundation. The mission of the team was to provide a timely, first-hand overview of the type and extent of the damage, and to provide the necessary background information for future research and for U.S.-Japan cooperation in earthquake engineering. Additional information was gathered through participation in U.S.-Japan seminars and workshops, and through collaboration with researchers and practicing engineers in Japan. The research team has focused its efforts on seismology, strong ground motion, geotechnical engineering, and structural engineering. This report provides summaries of the findings in these subject areas.

Hanshin↗
USGS1994

Mobilization of beryllium in the sedimentary column at convergent margins

Studies of Be distributions in subduction zone sediments will help to understand questions regarding the enrichments of cosmogenic Be-10 in arc volcanic rocks. Analyses of Be-10 and Be-9 in sediments of Ocean Drilling Program Site 808, Nankai Trough and Be-9 in porewaters of Site 808 and Sites 671 and 672, Barbados ridge complex, show significant decreases in solid phase Be-10 and large increases of porewater Be-9 at the location of the décollement zone and below or at potential flow conduits. These data imply the potential mobilization of Be during pore fluid expulsion upon sediment burial. Experiments involving reaction between a décollement sediment and a synthetic NaCl-CaCl 2 solution at elevated pressure and temperatures were conducted in an attempt to mimic early subduction zone processes. The results demonstrate that Be is mobilized under elevated pressure and temperature with a strong pH dependence. The Be mobilization provides an explanation of Be-10 enrichment in arc volcanic rocks and supports the argument of the importance of the fluid processes in subduction zones at convergent margins.

Nankai Trough, Pacific Ocean↗
USGS1994

Postbreeding dispersal and drift-net mortality of endangered Japanese Murrelets

The incidental catch of seabirds in high-seas drift nets was recorded in 1990-1991 by scientific observers on commercial squid and large-mesh fishery vessels operating in the North Pacific Transitional Zone. Twenty-six Synthliboramphus murrelet deaths were recorded in the months of August through December. All but one were from the Korean squid fishery in a small area bounded by 38°-44°N and 142°-157°E. Five specimens of the dead birds were collected and later identified as Japanese Murrelets ( S. wumizusume ). As fishing effort was widely distributed over a large area east of Japan, these data suggest that postbreeding Japanese Murrelets migrate north to winter in a relatively small area southeast of Hokkaido, where persistent eddies form at the confluence of the Oyashio and Kuroshio currents. Fronts between cold Oyashio water and Kuroshio warm-core eddies promote the aggregation of zooplankton and pelagic fishes, which in turn may attract murrelets during the nonbreeding season. The estimated total mortality of Japanese Murrelets in high-seas drift-net fisheries represents a significant proportion of the total world population of this rare and endangered species.

North Pacific Transitional Zone↗
USGS1994

Magnetic and gravity constraints on forearc upper crustal structure and composition, offshore northeast Japan

Marine magnetic and gravity data from the northeast Japan forearc offer insight to the subsurface structure, density and magnetization from which geologic interpretations and tectonic reconstructions can be made. Positive marine magnetic anomalies, on-land geology, drill hole data, and 2-1/2-dimensional models reveal that Kitakami plutons and possibly their associated volcanic rocks constitute part of the modern forearc basement and lie 100-150 km further east than previously thought. A method to create magnetization and density contrast maps was employed to produce a three-dimensional picture of the forearc basement rock properties averaged over a 14-km thickness. -Author

Pacific Ocean↗
USGS1991

Mortality of seabirds in the Japanese land-based gillnet fishery for salmon

Mortality rates of seabirds in the Japanese land-based drift gillnet fishery for salmon were assessed from 413 gillnet sets made by Japanese research vessels in offshore areas used by the commercial fleet. Sixteen species of seabirds were recorded in nets. Shearwaters, primarily Short-tailed Shearwaters ( Puffinus tenuirostris ), and to a lesser extent Sooty Shearwaters ( P. griseus ), predominated in the catches, followed by lesser numbers of Tufted Puffins ( Fratercula cirrhata ) and Thick-billed Murres ( Uria lomvia ). Catch-rates of seabirds varied by oceanographic zone, with most being caught in oceanic waters north of the Subarctic Front. Approximately 151,000 seabirds were killed in the offshore component of the land-based fishery in 1977. Mortality was reduced to about 57,000 seabirds in 1987 because of a reduction in fishing effort. No estimates are available of seabird mortality in the nearshore component of the fishery. Mortality of seabirds in the land-based fishery is discussed with respect to other major drift gillnet fisheries in the North Pacific.

The Condor↗
USGS1990

Threat of an earthquake right under the capital in Japan

Tokyo, Japan's capital, has been enjoying a seismically quiet period following the 1923 Kanto earthquake of magnitude 7.9 that killed more than 140,000 people. Such a quiet period seems likely to be a repetition of the 80-year quiescence after the great 1703 Genroku earthquake of magntidue 8.2 that occurred in an epicentral area adjacent to that of the 1923 Kanto earthquake. In 1784, seismic activity immediately under the capital area revived with occasional occurrence of magnitude 6 to 7 shocks. Earthquakes of this class tended to occur more frequently as time went on and they eventually culminated in the 1923 Kanto earthquake. As more than 60 years have passed since the Kanto earthquake, we may well expect another revival of activity immediately under the capital area.

Tokyo area↗
USGS1989

Tectonic erosion at the front of the Japan trench convergent margin

The imaging of a multichannel seismic record was improved by reprocessing using pre-stack techniques. The reprocessed record shows structures that indicate tectonic erosion and gravity collapse at the front of the Japan trench margin. Much of the lower slope appears to be underlain by a detached, coherent block of continental crust. The lower slope has failed by mass wasting and the resulting apron of slump debris at the base of the slope has become involved in thrust faulting at the front of the subduction zone. Slumping continues as long as debris is removed from the front of the margin by subduction, and the apron cannot build up sufficiently to stabilize the failing lower slope. Truncated beds at the base of the upper plate indicate subcrustal erosion as well, this probably being the main cause of massive subsidence of the margin. Subsidence was the cause of oversteepening, destabilization and subsequent gravity collapse of the leading edge of the upper plate.

Tectonophysics↗
USGS1989

Subduction of the Daiichi Kashima Seamount in the Japan trench

In 1984-1985, the Kaiko consortium collected Seabeam, single-channel seismic and submersible sampling data in the vicinity of the Daiichi-Kashima seamount and the southern Japan trench. We performed a prestack migration of a Shell multichannel seismic profile, that crosses this area, and examined it in the light of this unusually diverse Kaiko dataset. Unlike the frontal structure of the northern Japan trench, where mass-wasting appears to be the dominant tectonic process, the margin in front of the Daiichi-Kashima shows indentation, imbrication, uplift and erosion. Emplacement of the front one-third of the seamount beneath the margin front occurs without accretion. We conclude that the Daiichi-Kashima seamount exemplifies an intermediate stage between the initial collision and subduction of a seamount at a continental margin.

Daiichi Kashima↗
USGS1988

Integrating spatial and frequency information in the search for kuroko deposits of the Hokuroku District, Japan

A new method (FINDER) that uses the area of influence and Bayesian statistics to aid in selection of target areas on the basis of one or more variables and multiple observations was tested with drill hole data. A previously defined bimodal distribution of Na 2 O with the low sodium group confined to a 1.5 X 3.0-km zone beneath the cluster of deposits at Fukazawa was used as a control area for one test of FINDER. Using the Na 2 O means and standard deviations for the control area and minimum Na 2 O values from 174 drill holes, a probability map of centers of sodium depletion is produced for the Hokuroku district. High probability areas correspond to the known deposits that should have been rediscovered and to several areas without known deposits.Use of X-ray data from 165 drill holes, some of which also have chemical analyses, led to the identification of two additional variables, sericite and gypsum plus anhydrite, that allow more drill holes to be used and that expand the areas of influence around drill holes. Sericite is enriched up to 2.15 km and gypsum plus anhydrite up to 3.5 km from the centroid of the control area Fukazawa deposits. For the deposit groups with X-ray data nearby, Fukazawa, Shakanai, and Furutobe, a pattern of sericite enrichment, kuroko deposits, and gypsum plus anhydrite enrichment over 4 or 5 km is shown.With sodium, sericite, and gypsum plus anhydrite, FINDER's high probability areas include each of the four groups of kuroko deposits that should have been rediscovered and only one known deposit that is much smaller than Fukazawa is missed. Several large areas that are favorable centers of undiscovered deposits and other areas that are unlikely centers of deposits are also identified.

Hokuroku District↗
USGS1988

Earthquake warning system for Japan Railways’ bullet train; implications for disaster prevention in California

In Japan, the level of public awareness of the dangers of earthquakes is high. The 1923 Kanto earthquake killed about 120,000 people out of a total Japanese population of about 50 million; an equivalent disaster in the U.S would involve 600,000 deaths. Today, Japanese society is well aware of the prediction of the Tokai earthquake. It is estimated by the Tokyo earthquake. It is estimated by the Tokyo muncipal government that this predicted earthquake could kill 30,000 people. (this estimate is viewed by many as conservative; other Japanese government agencies have made estimates but they have not been published.) Reduction in the number deaths from 120,000 to 30,000 between the Kanto earthquake and the predicted Tokai earthquake is due in large part to the reduction in the proportion of wooden construction (houses).

Earthquakes & Volcanoes (USGS)↗