- 著者
- Takane Hori
- 出版者
- The Seismological Society of Japan, The Volcanological Society of Japan , The Geodetic Society of Japan
- 雑誌
- Journal of Physics of the Earth (ISSN:00223743)
- 巻号頁・発行日
- vol.44, no.4, pp.349-356, 1996 (Released:2009-04-30)
- 参考文献数
- 18
- 被引用文献数
- 10 13

To evaluate the temporal variation of seismicity in the Inner Zone of Southwest Japan before and after the Nankai trough events, we introduced a statistical model and estimated the value of the model parameters. We used the data of disastrous earthquakes to estimate them. Because of the lack of spatially sufficient data, we used data from the 9th century in the case of the northern Kinki region, and in the case of the whole Inner Zone of Southwest Japan only data after the 17th century. The results show that for the northern Kinki region the seismicity has a peak before the Nankai trough events, although there is no significant change before them in the whole Inner Zone of Southwest Japan. The seismicity in the Inner Zone of Southwest Japan increases just after the Nankai trough events. We compared the obtained intensity functions with the recent JMA data from 1885 to 1995. The seismicity seems to have increased in the last 30 years. Using data from this period, we estimated the occurrence time of the next Nankai trough event. Our results show that it will occur in the 2030'S.

- 著者
- George E. Williams
- 出版者
- The Seismological Society of Japan, The Volcanological Society of Japan , The Geodetic Society of Japan
- 雑誌
- Journal of Physics of the Earth (ISSN:00223743)
- 巻号頁・発行日
- vol.38, no.6, pp.475-491, 1990 (Released:2009-04-30)
- 参考文献数
- 40
- 被引用文献数
- 18 23

The recent recognition of cyclically laminated tidal rhythmites provides a new approach to tracing the dynamic history of the Earth-Moon system. Late Proterozoic (-5650 Ma) elastic rhythmites in South Australia represent an unsurpassed palaeotidal record of -560 years' duration that provides numerous palaeorotational parameters. At -5650 Ma there were 13.1+-0.1 lunar months/year, 400+-7 solar days/year, and 30.5+-0.5 solar days/lunar month. The lunar apsides and lunar nodal cycles were then 9.7+-0.1 years and 19.5+-0.5 years, respectively. The indicated mean Earth-Moon distance of 58.28+-0.30 Earth radii at -5650 Ma gives a mean rate of lunar retreat of 1.95+-0.29 cm/year since that time, about half the present rate of lunar retreat of 3.7+-0.2 cm/year obtained by lunar laser ranging. The rhythmite data imply a substantial obliquity of the ecliptic at -5650 Ma, and indicate virtually no overall change in the Earth's moment of inertia, which militates against significant Earth expansion since -5650 Ma. Early Proterozoic (-52, 500 Ma) cyclic banded iron-formation in Western Australia, that may record submarine fumarolic activity triggered by earth tides, suggests -514.5+-0.5 lunar months/year and a mean Earth-Moon distance of -554.6 Earth radii at -52, 500 Ma. The combined rhythmite data suggest a mean rate of lunar retreat of -51.27 cm/year during the Proterozoic (-52, 500-650 Ma); the indicated increasing mean rate of lunar retreat since -52, 500 Ma is consistent with increasing oceanic tidal dissipation as the Earth's rotation slows. A close approach of the Moon during earlier time is uncertain. Continued study of tidal rhythmites promises to further illuminate the evolving dynamics of the Earth-Moon system.

- 著者
- Toshihiko HASHIDA Kunihiko SHIMAZAKI
- 出版者
- The Seismological Society of Japan, The Volcanological Society of Japan , The Geodetic Society of Japan
- 雑誌
- Journal of Physics of the Earth (ISSN:00223743)
- 巻号頁・発行日
- vol.32, no.4, pp.299-316, 1984 (Released:2009-04-30)
- 参考文献数
- 21
- 被引用文献数
- 18 19 31

Seismic intensity data, which measure the degree of ground shaking, contain information on attenuation along the path from the source to the station and earthquake source strength. With some reasonable assumptions about the seismic intensity data, a properly formulated damped least squares estimation procedure can be used to determine simultaneously both three-dimensional attenuation structure and source strength. By means of this method, sufficiently distributed earthquakes with a large amount of seismic intensity data may provide information on the crust and upper mantle Q structure in a region where a spatial variation of attenuation is large enough to affect the distribution of seismic intensity. To check the validity of the method, numerical experiments were undertaken for artificial data including errors comparable to those expected from using seismic intensity. The results obtained for a two-dimensional island arc structure model show the method to be practical. The reliability of the obtained solution for Q structure can be measured by the corresponding diagonal element of the resolution matrix. By using a large number of seismic intensity data up to about one thousand and selecting solutions with high resolution, a Q structure with an accuracy of 1.5×10-3 in 1/Q and a source strength with an accuracy of 0.1 in magnitude scale can be obtained. This method is extendable to many regions including island arcs and continents because large amounts of intensity data are easily attainable.

- 著者
- Yoshiko Yamanaka Kunihiko Shimazaki
- 出版者
- 雑誌
- Journal of Physics of the Earth (ISSN:00223743)
- 巻号頁・発行日
- vol.38, no.4, pp.305-324, 1990 (Released:2009-04-30)
- 参考文献数
- 40
- 被引用文献数
- 39 46

The logarithmic number of aftershocks which occur within one month after a large shallow earthquake in Japan is found to be proportional to the logarithm of the seismic moment of the main shock. The proportional constants for interplate and intraplate earthquakes are different, but it turns out to reflect a similar difference in scaling relations of the fault area to the seismic moment between interplate and intraplate earthquakes. Thus we can derive the fundamental relationship that the aftershock number is proportional to the fault area of the main shock. This is consistent with the hypothesis that aftershocks are generated by unbroken strong patches on the main-shack fault, if the patch density is constant. Combining this new result with the results of previous studies on aftershocks, we propose that a rate of aftershock occurrence is given by where n(t) indicates the number of aftershocks which occur t days after the main shock, S indicates the fault area of the main shock in km2, Mth is the threshold magnitude, b is the b-value of the. Gutenberg-Richter relationship, and c and p are the c- and p-values, respectively, of the modified Omori formula. The constant k amounts to 13.4 for an interplate earthquake and to 31.7-63.5 for an intraplate earthquake depending on the assumption on its fault width. Apparently the areal density of aftershocks on the fault plane is higher for an intraplate earthquake than for an interplate earthquake. Further examination of the results suggests that the areal density of the aftershocks of a continental intraplate earthquake may be systematically higher than that of an oceanic intraplate earthquake. These differences may indicate some intrinsic difference in rupturing process among a continental intraplate, an oceanic intraplate, and an interplate events.

- 著者
- Kiyoji SHIONO
- 出版者
- 雑誌
- Journal of Physics of the Earth (ISSN:00223743)
- 巻号頁・発行日
- vol.25, no.1, pp.1-26, 1977 (Released:2009-04-30)
- 参考文献数
- 53
- 被引用文献数
- 35 39

Focal mechanisms are investigated for 56 major earthquakes with magnitudes around 6.0 and greater that have occurred in southwest Japan since 1920's in order to clarify the relationship between seismic activity and the underthrusting of the Philippine Sea plate along the Nankai trough and the Ryukyu trench.Focal mechanisms of large earthquakes along the Nankai trough and in the Hyuganada are similar to one another, indicating a low-angled thrusting. This feature can be explained in terms of elastic rebound of the continental block which is dragged down by the underthrusting Philippine Sea plate.For very shallow inland earthquakes except those located around the Izu peninsula and in the Kyushu region, the P-axes tend to be oriented in the eastwest direction. This seismological evidence, together with geologic evidence, indicates that the E-W tectonic compression has prevailed in the crust of southwest Japan for one or two million years up to the present. The E-W compression has been interpreted to arise mainly from the subduction of the Pacific plate.Focal mechanisms of subcrustal earthquakes are characterized by systematic alignments of the T-axes. In the region from Iyonada to the southern Chubu district where the Philippine Sea plate does not penetrate into the asthenosphere but remains in the continental plate, the T-axes are parallel to the leading edge of the underthrusting plate (parallel extension). Under the Kyushu island and the northern Ryukyu arc, on the other hand, the T-axes dip westwards and are approximately parallel to the dip of the inclined seismic zone extending down to 150-200 km, suggesting down-dip extension characteristic of the intermediate-depth seismic zones. From these facts, the following tectonic model can be derived: While the leading edge of the underthrusting oceanic plate remains within the continental plate, subcrustal earthquakes with T-axes parallel to the leading edge occur as a result of interaction between the oceanic and the continental plates. As soon as the oceanic plate begins to penetrate down into the asthenosphere, subcrustal earthquakes with down-dip extension occur in the underthrusting plate by the gravitational pull.

- 著者
- Dan McKenzie Mike J. Bickle
- 出版者
- 雑誌
- Journal of Physics of the Earth (ISSN:00223743)
- 巻号頁・発行日
- vol.38, no.6, pp.511-515, 1990 (Released:2009-04-30)
- 参考文献数
- 3
- 被引用文献数
- 3 5 6

In an earlier paper the variation of melt fraction with temperature near the solidus of a rock with the composition of a garnet peridotite was parameterized as a continuous function of temperature. A number of people have suggested that eutectic melting is a better description of the behaviour near the solidus. Therefore a 'eutectic' parameterization is used here, and requires a finite melt fraction to be produced at the solidus before the temperature can increase further. The resulting changes in melt volumes and compositions are small, and are of similar magnitude to the likely errors in the earlier calculations.

- 著者
- Mitsuhiro MATSU'URA Takaya IWASAKI Yasunori SUZUKI Ryosuke SATO
- 出版者
- 雑誌
- Journal of Physics of the Earth (ISSN:00223743)
- 巻号頁・発行日
- vol.28, no.2, pp.119-143, 1980 (Released:2009-04-30)
- 参考文献数
- 28
- 被引用文献数
- 30 35

An inverse method to find optimum fault parameters from geodetic data with random errors is extended so as to be applicable to a case of the data including a systematic error caused by movements of reference points in triangulation. Application of the new inverse method to static displacement data associated with the Kanto earthquake of 1923 yields a dislocation source model which adequately explains both the seismological and the geodetic data.From the geodetic data, it is found that the fault motion of the Kanto earthquake is a reverse, right-lateral slip of 4.8m with a slip-angle of 140° on a plane which dips 25° towards N24°E, where the slip-angle is measured counterclockwise from a strike on the fault plane. The fault length, width, and the depth to the upper fault margin are determined as 95km, 54km, and 1.5km respectively. The seismic moment and stress drop of this earthquake are estimated to be 8.4×1027 dyne·cm and 45 bars, respectively.Taking the static fault solution as the basic model, the dynamic process of the fracture is investigated on the basis of the long-period seismograms recorded at Hongo, Tokyo. The result shows that the rupture starts from a relocated hypocenter, 35.41°N, 139.22°E and 13.5km (depth), and extends outwards on the fault plane with a propagating velocity of the rupture front of 2.0km/sec. The rise time of the source time function is assumed to be 5.0sec. The maximum amplitude of acceleration for a frequency range of 0.0-3.3Hz at Tokyo is estimated to be about 280gal for the horizontal component and to be 60gal for the vertical component, by applying an empirical formula to the calculated ground displacements.

- 著者
- ANDO Masataka
- 出版者
- 雑誌
- Journal of Physics of the Earth (ISSN:00223743)
- 巻号頁・発行日
- vol.22, no.2, pp.263-277, 1974
- 被引用文献数
- 48

Kanto earthquake of 1923 was associated with various sorts of seismic and tectonic effects such as surface displacements, seismic damages, tsunamis and volcanism. The writer previously proposed a fault-origin model of the earthquake from a geodetic viewpoint. The present paper is to develop the geodetic model on the idea that the various sorts of the associated effects in 1923 can be interpreted with a simple fault-origin model, equally well. The geodetic model is slightly revised to fit the effects. Thus it is found out that the fault model can be much simplified except for the area immediately adjacent to the fault. The fault is tectonically interpreted as one of the transform faults along the northeastern boundary of the Philippine-Sea plate with the Asian plate.

- 著者
- H. HONDA
- 出版者
- 雑誌
- Journal of Physics of the Earth (ISSN:00223743)
- 巻号頁・発行日
- vol.10, no.2, pp.1-97, 1962 (Released:2009-04-30)
- 参考文献数
- 265
- 被引用文献数
- 33 43

- 著者
- Tokuji UTSU
- 出版者
- 雑誌
- Journal of Physics of the Earth (ISSN:00223743)
- 巻号頁・発行日
- vol.14, no.2, pp.37-40, 1966 (Released:2009-04-30)
- 参考文献数
- 6
- 被引用文献数
- 68 83

The probability density function for the value of b in the formula logn(M)=a-bM estimated by the author's method has been obtained in an exact form. This function leads to a simple method to test the statistical significance of the difference between two b-values. Application of this method to SUYEHIRO'S data on foreshocks and aftershocks of the great Chilean earthquake of 1960 indicates a significant difference in b-value between the foreshocks and the aftershocks at the 98% confidence level.

- 著者
- H. S. VIRK S. L. KOUL
- 出版者
- 雑誌
- Journal of Physics of the Earth (ISSN:00223743)
- 巻号頁・発行日
- vol.25, no.2, pp.177-186, 1977 (Released:2009-04-30)
- 参考文献数
- 17
- 被引用文献数
- 12 12 12

The fossil fission track technique has been used for dating Himalayan muscovites of Kathmandu Valley, Nepal. The mean ages obtained for different locations range from 2.5±0.6m.y. to 23±3.3m.y. The uranium concentration has been estimated to be 10-10 atom/atom. The experimental results confirm that the Himalayan orogeny belongs to the Tertiary era.

- 著者
- Masanori SAITO
- 出版者
- 雑誌
- Journal of Physics of the Earth (ISSN:00223743)
- 巻号頁・発行日
- vol.22, no.3, pp.313-324, 1974 (Released:2009-04-30)
- 参考文献数
- 2
- 被引用文献数
- 4 5

The use of Hilbert transform is essential when we are dealing with bandwidth limited signals and causal functions. However, the Hilbert transform is originally defined for functions of continuous arguments and is not of immediate use for discrete (sampled) functions which are the common form of data today. In this paper we propose two kinds of 'discrete Hilbert transforms'; one is defined on the discrete time domain and the other on the frequency domain of sampled functions. It will be shown that the essential properties of the conventional Hilbert transform are conserved in the new definitions.