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1.
Tsuneji Rikitake 《Tectonophysics》1974,23(3):225-236
Earthquake prediction studies in Japan have made progress since a national program was officially launched in 1965. A sum of 18 million dollars has been allocated for the program in addition to expenses for salaries, construction of observatories and other supporting routines. As a result, 17 crustal deformation observatories, 19 microearthquake observatories and 1 magnetic observatory, all equipped with modern instruments have been completed. It has also become possible to repeat the first-order levelling surveys along levelling routes of 20,000 km in length with an interval of five years.The program has been tested during the 1965—1966 Matsushiro activity of swarm earthquakes. Judging from the fact that long-term predictions could be issued to the public from time to time during the active period, the program would seem to be directed in the right direction. An anomalous land deformation has been found in an area south of Tokyo in 1969. An operation to investigate the anomaly has been carried out intensively over the area concerned with special emphasis on detecting the possibilities of a large earthquake occurring there.Intensification of the program orientated towards actual prediction is now under consideration. A more extensive program including a nation-wide network of geodimeter surveys, real-time monitoring of microearthquakes, real-time observations by oceanbottom seismographs and other disciplines is going to be planned. 相似文献
2.
A research team called the “C.A. (conductivity anomaly) Group” has been active since the early 1960's in Japan. A number of organized observations of geomagnetic variation anomaly have been carried out by the group. As a result, the overall distribution of Parkinson vectors for short-period variation over Japan has become clear. It seems likely that the anomalously large vertical component as observed in central Japan can be accounted for by assuming a depression of the highly conducting mantle layer beneath Japan, although effects of the sea surrounding Japan on geomagnetic variations are also seen. Such a model seems to harmonize with observations of heat flow, seismic wave velocities and attenuation. Use of the transfer function technique has recently become popular and consequently frequency characteristics of geomagnetic variation anomaly will be thoroughly examined in coming years.Intensive observations of island and peninsula effects on geomagnetic variation have been conducted, sometimes in cooperation with the University of Hawaii. Beautiful reversal of the sign of the vertical component at the northern and southern observation points on an island has often been reported.Numerical work on electromagnetic induction in two-dimensional conductors, thin sheets and so on has also been intensively advanced. It is particularly important to estimate the frequency response of an underground model which is believed to account for the geomagnetic variation anomaly in central Japan. 相似文献
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T. Rikitake Dr. 《GeoJournal》1980,4(2):145-152
Present status of earthquake prediction and warning is reviewed with special emphasis on the Large-Scale Earthquake Countermeasures Act in Japan. Following possible regionalization of occurrences of a great earthquake by means of historical data analysis and crustal strain monitoring, statistics of earthquake precursors are presented along with the nature of precursors of various disciplines.The precursor time of the first-kind precursor depends on the magnitude of the main shock. The larger the magnitude is, the longer is the precursor time. The precursor of the second kind has a precursor time amounting to about a few hours, while that for the third kind ranges from a few to several ten days. A practical approach to actual prediction is suggested on the basis of the analysis of precursors. Difficulties in converting a prediction to a warning is briefly pointed out as well. 相似文献
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Tsuneji Rikitake 《Tectonophysics》1975,26(1-2)
Statistics of ultimate strain are improved by adding new data to the previous ones. The critical value for horizontal strain seems somewhat larger than that for vertical strain, although parameters of a Weibull distribution, which is customarily used for quality-control research and which fits in very well with the present statistics, are calculated for the whole set of data making no distinction between the two subsets because of their scantiness.On the basis of the parameters thus determined and strain rates obtained from geodetic data, probabilities of earthquake occurrence in a few regions in Japan and the U.S. are estimated. Probability of having an earthquake in an area southwest of Tokyo, where we had the 1923 earthquake (magnitude 7.9), at this time amounts to 20%, a value almost the same as that obtained in the previous papers. The probability will reach some 50 and 90% by 2000 and 2050, respectively. In the North Izu district, where an earthquake of magnitude 7.0 occurred in 1930, a shearing crustal motion is going on to an extent for which we have a probability for an earthquake recurring there in these 40 years amounting to 40%. By the end of this century, it will become as high as 85%.Similar estimates of such cumulative probabilities are made for the San Francisco and Fort Tejon regions, where great earthquakes occurred respectively in 1906 and 1857, yielding values of 30 and 80% at present. These probabilities are tentative because of possible errors in evaluating geodetic measurements and uncertainty of the ultimate crustal strain assigned to the San Andreas fault. 相似文献
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Tsuneji Rikitake 《Surveys in Geophysics》1972,1(1):4-26
A long-term research program on earthquake prediction in Japan, officially launched in 1965, has made progress. Many of the developments achieved in recent years in various disciplines are outlined. Some of the important findings include: detection of land-deformation by intensified levelling and geodimeter surveys, empirical relations between the extent of a premonitory land-deformation and the magnitude and occurrence-time, and the growth and decay of earthquake swarms accompanied by occurrences of large-scale earthquakes. Operations research on selection of survey areas for levelling and the location of crustal deformation observatories has been made.To process data for earthquake predictions, three centers for different disciplines were set up: in the Geographical Survey Institute, the Japan Meteorological Agency, and the Earthquake Research Institute (University of Tokyo). A newly established committee, called the Coordinating Committee for Earthquake Prediction, which consists of about 30 specialists, analyzes the data flowing into these three channels. The committee issues a warning of earthquake danger, whenever possible.A tentative strategy for achieving earthquake prediction is proposed. An attempt is made to evaluate ratings of earthquake threats on the basis of probability theory.An anomalous land-deformation was found in the South Kanto district, an area south of Tokyo, in 1969. following the strategy, an intensive effort, called Operation South Kanto, aiming at a possible prediction of large earthquakes is now under way. Judging from the results of various earthquake prediction elements, the probability of having an earthquake of magnitude 7 or there-abouts within a period of about 10 yr can not be low if anomalous land-deformation is related to the probability of earthquake occurrence. 相似文献
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Anomaly of Geomagnetic Variations in Japan 总被引：1，自引：0，他引：1
T. Rikitake 《Geophysical Journal International》1959,2(4):276-287
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Dr. Tsuneji Rikitake 《Pure and Applied Geophysics》1953,26(1):30-40
Summary A general theory of a time-dependent magnetic dipole in the earth is discussed. On the basis of the weastward drift of the «equatorial» dipole in the two eccentric dipoles model due toH. G. Macht, the impossibility of the origin of geomagnetic secular variation being in a deep interior of the earth's core is established from the standpoints of the shielding effect and the motions in the core. But the westward drift of the core's top layer relative to the mantle seems to be quite reasonable, even if we take into account the shielding effect of the mantle. 相似文献
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Dr. Tsuneji Rikitake 《Pure and Applied Geophysics》1952,22(1-2):37-41
Summary From the standpoint of the electrical state of the earth's interior as inferred from both geophysical and physical researches, the possibility ofElsasser-Bullard's theory is discussed. The electromagnetic shielding within the earth's mantle is also taken into account. It is of interest that the theory seems to well harmonize with the electrical state considered. 相似文献