著者

野澤 貴 武村 雅之

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.50, no.1, pp.11-20, 1997-05-28 (Released:2010-03-11)

参考文献数

12

被引用文献数

1

---

Records observed at the Takada observatory by an Imamura's type strong motion seismograph are useful in Japan to investigate a source process of the 1923 Kanto earthquake (M=7.9). Ground motion in the vertical component is completely recorded to the end. Those in horizontal components are also recorded to the end, though the amplitudes of them are saturated in the midst of the records. The instrumental response of the seismograph has been already clarified by TAKEMURA and NOZAWA (1996), and many records from the recent earthquakes occurring near the focal region of the Kanto earthquake are also obtained at the same site with modern instruments. First, a crustal structure model from the source to the station is established so as to explain the dispersion characteristics of Love-waves observed for the recent earthquakes, and their records are simulated by the normal mode theory using the obtained structure to confirm its validity. Secondly, the records from the Kanto earthquake are reproduced using the same structure model. NOZAWA et al. (1995) proposed the two possible source models for the Kanto earthquake through the simulation of the records at the Gifu observatory. Two big subevents with a time interval of about 12s are assumed on the fault plane in both the models, while the focal mechanism and the focal depth of the second subevent are different between these models. It is found that these models similarly explain the records at the Takada observatory from the Kanto earthquake. The maximum displacements of the reproduced horizontal ground motions are estimated about 20cm in NS component. and about 10cm in EW component. These results are consistent with the fact that the amplitudes of the records in NS component are strongly saturated compared with those in EW component.

著者

小山 順二 武村 雅之

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.36, no.2, pp.255-257, 1983-06-25 (Released:2010-03-11)

参考文献数

10

著者

小山 順二 武村 雅之 鈴木 次郎

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.33, no.2, pp.187-198, 1980-06-25 (Released:2010-03-11)

参考文献数

21

---

A simple method is developed to determine seismic moments of earthquakes by using tabulated data in usual seismological bulletins. The method is qualified through the criteria such as simplicity of calculations, coverage of wide magnitude range, and insensitivity of the instrumental response: At first, characteristic period Tc of each earthquake is defined as the average value of apparent periods of wavelets which give maximum amplitudes of ground displacement at epicentral distances between 200 and 700km. Secondly, amplitude information is taken into consideration, making a product of maximum amplitude, its period and epicentral distance. Seismic-moment factor Me for a given earthquake is defined at the characteristic period Tc as the average value of those products evaluated from horizontal components at stations within epicentral distance range from 200 to 400km. The narrow range of epicentral distance in evaluating Me is taken so as to reduce the uncertainty due to seismic-energy attenuation into a permissible range and to be able to obtain equal number of observations for small earthquakes to that for large ones. The relation between the seismic-moment factors and characteristic periods for 163 intraplate earthquakes in Japan from 1926 to 1977 clearly demonstrates that Me is proportional to the cube of Tc. A scaling model of earthquakes that satisfies the empirical relations among surface-wave magnitude, JMA magnitude, and body-wave magnitude facilitates the estimate of static seismic-moments from calculated Me's. The seismic moments of 16 earthquakes determined by conventional analyses from near- and/or far-field observations are consistent with static seismic-moments thus estimated. This shows the potential in practice of the present method especially in routine processing of seismic data.

著者

羽鳥 徳太郎

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.42, no.4, pp.467-473, 1989-12-24 (Released:2010-03-11)

参考文献数

33

被引用文献数

3

---

The Pacific coast of Japan has often suffered severe damage by distant tsunamis propagated from the circum Pacific regions (Chile-Peru, Kurile-Kamchatka and Aleutian-Alaska). Based on the historical documents or tide-gauge records observed in Japan during the period of about 400 years, 1586-1988, the geographic distribution of cumulative tsunami energy, ∑H2 for each 150km segment along the coast is investigated. The energy distribution for the distant tsunamis is compared with that of the near tsunamis which were generated in the vicinity of Japan. The obtained results are as follows:1) The amount of cumulative energy, ∑H2=51m2 from the Chile-Peru tsunamis is largest at the Sanriku region, northeastern Japan.2) The tsunami energy from the Kurile-Kamchatka reaching East Hokkaido and Sanriku regions is large, but the amount of energy is about one-third of that of the Chile-Peru tsunamis.3) The energy from the Aleutian-Alaska and Philippine-Indonesia tsunamis is relatively small because of the effect of directivity.4) The pattern of energy distribution for the distant tsunamis is different from that for the near tsunamis generated around Japan. Percentage of the energy from the distant tsunamis reaching SW. Hokkaido, Fukushima, Ibaraki and Okinawa is about 50% of the total tsunamigenic energy.

著者

羽鳥 徳太郎

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.55, no.1, pp.51-57, 2002-07-25 (Released:2010-03-11)

参考文献数

27

著者

羽鳥 徳太郎

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.43, no.4, pp.493-498, 1990-12-24 (Released:2010-03-11)

参考文献数

16

被引用文献数

3

---

Based on tide-gauge records observed at the Hokkaido and Sakhalin coasts facing the Okhotsk Sea, the characteristics of seven Kurile tsunamis (1918-1978) passing through the straits are investigated. The ratio of wave-heights at the Okhotsk Sea coast to Hanasaki located at the Pacific side was about one-half for tsunamis generating off the Urup Island, and the ratio has a tendency of decrease when the tsunami source moves to western direction toward Hokkaido. It suggests the effective tsunami energy passes into the Iturup Straits than other straits or channels. The travel time at Hanasaki becomes long when the tsunami source moves to the east direction, but that of the Hokkaido-Sakhalin region in the Okhotsk Sea is usually unchanged: For example, travel times of the Kurile tsunamis were mostly about 1.5 hours at Abashiri and 3 hours at Wakkanai. We found through the refraction diagrams that the unchanged travel times were caused by sea-bottom topography in the Okhotsk Sea. The wave rays emitted from the Iturup Straits concentrate in Sakhalin, while those from the Kunashiri Channel concentrate in Hokkaido. For future tsunamis coming-into the Okhotsk Sea, it is indispensable to take into considerations of the effect of tidal currents.

著者

束田 進也 卜部 卓

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.47, no.3, pp.341-344, 1994-10-14 (Released:2010-03-11)

参考文献数

4

著者

小田 仁

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.42, no.3, pp.333-339, 1989-09-24 (Released:2010-03-11)

参考文献数

21

---

We have reexamined whether the velocity decrease of the seismic waves due to dilatancy can be detected or not. A numerical investigation was made to see the change of travel times by using synthetic seismograms of P-waves traveling through a dilatant region. In synthesizing the seismograms, the Brune's source model was used, and the P-wave velocity was assumed to increase with increasing frequency and to approach asymptotically an intrinsic velocity. This relation between P-wave velocity and frequency is based on the experimental result obtained by uniaxial compression test of a granitic rock sample; the velocity decrease is larger at low frequencies than at high frequencies. The dispersion curve is characterized by crack density ε, crack width 2a and intrinsic velocity α. A characteristic frequency fM=5α/πa, above which no velocity decrease is found, is defined. We investigated the change of the P-arrival times in the synthetic seismograms, changing both crack density and crack width. When the P-wave forms of earthquakes with the same magnitudes are recorded without off scale, the travel time anomaly can be detected in the case of fc<<fM, where fc is the corner frequency of seismic source spectrum. Therefore, for detecting the travel time anomaly, it is necessary to observe earthquakes in low frequency range of f<<fM, where the significant velocity decrease is expected. For this purpose, group arrival times of the P-wave at low frequencies may also be useful.

著者

武村 雅之

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.51, no.2, pp.211-228, 1998-10-15 (Released:2010-03-11)

参考文献数

31

被引用文献数

3 22

---

According to SHIMAZAKI (1986), the large and small Japanese intraplate earthquakes obey the different scaling laws: M0∝L3 for small events but M0∝L2 for large events, where L and M0 are fault length and seismic moment, respectively. This is caused by the fact that the fault widths W for the large events are bounded by the thickness of the seismogenic layer in the crust. We examined the relations among source parameters for 33 Japanese intraplate earthquakes from 1885 to 1995 and confirmed the validity of the results obtained by SHIMAZAKI (1986) for the events of M=5 to 8, where M is the magnitude in the scale of the Japan Meteorological Agency (JMA). Relations between source parameters and JMA magnitude M were also derived from the relations among source parameters, using the M0-M relation by TAKEMURA (1990).SHIMAZAKI (1986) also indicated the offset of the L-M0 relation at the transition between small and large earthquakes, and suggested that the offset appeared to be due to the difference in boundary conditions between buried and surface faults. We found an offset from 6.5 to 6.8 in the JMA magnitude M, as well as the offsets of a factor of about 2 in D and M0, but no offset in L and W, where D is the average slip of the fault. Also we found that almost all events with M≥6.8 accompanied the surface faults, while most of the events with M≤6.5 did not accompany any surface fault. These results strongly supported that the offsets in D, M0, and M were caused by the surface fault breaks for the large earthquakes. Furthermore, we examined the relation between the damages from the Japanese intraplate earthquake and its JMA magnitude M. The damages suddenly increased from M=6.5 to M=6.8. The scaling law obtained above gave the large earthquake a strip fault whose location was very shallow. Because of these conditions, the intraplate earthquakes with M≥6.8 bring about strong ground motions in the wide area.

著者

纐纈 一起

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.44, no.3, pp.165-176, 1991-09-24 (Released:2010-03-11)

参考文献数

23

被引用文献数

2

---

We present a new ‘bending’ formulation of three-dimensional ray tracing in a spherical Earth. This is suitable for computer programming, and we have already corrected some errors in previously published formulations. By using this formulation we calculate a seismic ray traveling in a velocity model for the subduction zone around the Japan islands. The result is compared with those by appoximate ray-tracing methods, such as Ray Initializer, Circular Ray Tracer and Pseudo-Bending. The model includes the Conrad and Moho discontinuities, and the upper boundary of the subducting Pacific plate. To evaluate the effect of the discontinuities we also calculate exact rays for continuous models derived from the Lagrange or spline interpolation of the discontinuous model. The comparison shows that appoximate ray-tracing methods and smoothed continuous models may lead detailed seismic tomography of the subduction zone to a wrong result. In particular, the discontinuities should be taken into calculations to obtain precise trajectories of rays traveling through a subducting slab.

著者

坪井 誠司 纐纈 一起 鷹野 澄 宮武 隆 阿部 勝征 萩原 幸男

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.42, no.3, pp.277-284, 1989-09-24 (Released:2010-03-11)

参考文献数

14

被引用文献数

2

---

The Earthquake Prediction Data Center (EPDC) of the Earthquake Research Institute, University of Tokyo, has been receiving the hypocentral parameters and arrival time data acquired through the University Information System for Earthquake Prediction Research, which is operated by Japanese national universities under the national program for earthquake prediction. Through the cooperation of these universities, the data and hypocenters were compiled and stored in the database system of the EPDC. There are two types of database; one is the real-time database and the other is the revised database which is sent by magnetic tapes from each regional center. EPDC has prepared to open these database for every seismologists to use and now the real-time database can be used by the real-time monitoring system and the revised database is open to be public as the Japan University Network Earthquake Catalog. The hypocentral coordinates and orgin times listed in the catalog are redetermined by EPDC using the arrival time data of the revised database. Although, the minimun magnitude of the earthquakes listed in the catalog is 2.0, the earthquakes listed in the catalog covers the microearthquake activities in Japan. In the present paper, we discuss the hypocenter determination procedure of the catalog and also the characteristics of the hypocenters listed in the catalog.

著者

古村 孝志 纐纈 一起 坂上 実 山中 佳子 高橋 正義

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.54, no.2, pp.299-308, 2001-09-20 (Released:2010-03-11)

参考文献数

12

---

Seismic intensity at Shikine-jima during the earthquake swarm of Izu-Islands in 2000 is usually one or two ranks higher than that at neighbor island, though epicentral distances to these islands are almost similar. In order to investigate the cause of anomalous large seismic intensity, three portable strong motion instruments have been installed at the island.The spectral ratios of observed S waveforms at sedimentary stations at Shikine-jima demonstrate severe site amplification of 2 to 10 within a wide frequency range between 1 to 10Hz relative to rock site. The experiments based on a GA inversion indicate unusual subsurface structure with very low (VS=31-427m/s) and high attenuation (QS=15-148) superficial layer overlying a bedrock (VS=1000m/s, QS=200) with large contrast at the interface is a main cause of high seismic intensities.The influence of nonlinearity was also found near a coast of Shikine-jima when the ground acceleration level exceeds 300cm/s2. The nonlinear ground response yielded a considerable reduction of the ground motions, so that the observed peak accelerations during the severe earthquakes were only about 50% of that predicted by linear ground response.

著者

纐纈 一起

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.42, no.3, pp.325-331, 1989-09-24 (Released:2010-03-11)

参考文献数

16

被引用文献数

2

---

Some techniques used in statistics, such as the variable change method, the penalty function method and the gradient projection method, are introduced to determine the location of a hypocenter with a definitely non-negative depth. Numerical simulations are carried out to compare the efficiency of them by using synthetic arrival time data for a four-station seismic array. They demonstrate that the penalty function method with a proper weight is the most efficient. However, if we take an improper weight, it may lead to a negative depth or an invalid solution. Since the variable change method and the gradient projection method do not have such arbitrariness, those can be implemented more easily into hypocenter determination processes operated routinely. The demonstration with real arrival time data shows that the variable change method as z=h2 has practical efficiency.

著者

纐纈 一起 竹中 博士

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.42, no.3, pp.391-403, 1989-09-24 (Released:2010-03-11)

参考文献数

96

被引用文献数

1 4

---

We review recent theoretical studies on wave propagation in the near field of seismic sources. These include theories for horizontally layered media as well as those for irregularly layered media. Ray theory and its extensions are easily applied to arbitrarily inhomogeneous media, but they include serious approximations. The finite difference method is also flexible, but requires extensive computation. Except for these methods, we should note that all the methods currently available for irregularly layered media belong to the category of the method of weighted residuals.

著者

纐纈 一起 古村 孝志

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.55, no.2, pp.97-105, 2002-10-31 (Released:2010-11-17)

参考文献数

20

---

The significant attenuation of seismic motion in the west of the 2001 Geiyo earthquake is inferred from strong motion distributions, observed seismograms and their spectra. Since this attenuation is identified even in the distribution of borehole motions, that is assumed to arise in a deeper part like the mantle wedge. If we assume a low-Q zone in the mantle wedge, a strong motion simulation with Qs = 20-30 can reproduce the observations. This zone may be related to dehydration of the Philippine sea plate.

著者

尾池 和夫

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.28, no.3, pp.331-346, 1975-10-10 (Released:2010-03-11)

参考文献数

17

被引用文献数

1 3

---

Five stations of the Tottori Microearthquake Observatory have supplied an amount of records of microearthquakes since June, 1965. They are very useful to investigate the characteristics of spatial and temporal distribution of microearthquakes. Using data from three stations MZT, OYT and IZT, a seismological bulletin has been compiled. It contains P, P-S and P-F times and directions of initial motions at three stations, the coordinates of foci calculated from data of three stations and magnitude of each shock determined from total duration (P-F time).From June, 1965 to December, 1973, 7346 earthquake foci have been determined. Their epicenters have been plotted on seismicity maps. One of significant results from them is that the close relation between active faults and alignments of epicenters has been recognized.Computed results of epicenters from data of the three stations have good accuracy comparing with those from five stations. Errors of hypocenters near to the network are less than 2km. Those of distant foci whose P-S times are larger than 10 seconds are less than 10km. Because of the important purpose to know the temporal distribution of microearthquakes, almost all data containing some reading values which do not have so good accuracy have been used for calculation.Frequency distribution of magnitudes shows the normal activity in this region. It also shows that distant shocks whose magnitude are larger than 2.0 and epicentral distances are about 150km, are detected by this network of three stations. Hypocenters whose magnitudes are larger than 1.0 have been detected in the near region around the network.

著者

尾池 和夫

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.38, no.3, pp.459-461, 1985-09-25 (Released:2010-03-11)

参考文献数

1

著者

野田 弘 尾池 和夫

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.39, no.4, pp.635-643, 1986-12-25 (Released:2010-03-11)

参考文献数

8

---

Variations of the level of ground water were observed at four stations near the epicenter of the shallow earthquake (M4.6) which occurred in the southern part of the Lake Biwa which has been recently a low seismicity region.About ten days before the occurrence of the earthquake anomalous changes of the water level were observed. Considering the relation between the variation of water level and rainfall in the ordinary period these anomalous changes were precursors of the earthquake.Co-seismic steps of the water level were observed at two stations. One of them was a sudden ascent which was observed at the region where initial P motions were compressional. At another station which was in the dilatational P region sudden descents were recorded.Such characteristic variations of the ground water level are detectable by using deep wells when an earthquake occur conspicuously in the low seismicity region, even if its magnitude is small.

著者

尾池 和夫 三雲 健

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.21, no.1, pp.54-66, 1968-05-30 (Released:2010-03-11)

参考文献数

6

---

A multipartite seismometer array with a span of about 1km has been set up at one of the temporary stations for the observation of microearthquakes in Wakayama region, to examine the effects of local underground structure.The apparent velocity and direction of wave approach for about 200 microearthquakes were determined by means of least squares from arrival times of P waves at 5 recording sites, as well as from the conventional tripartite technique. Parameters computed from 4 selected tripartite nets show systematic deviations from the results of least squares in relation to the azimuth. A possible explanation for the azimuthal dependence and for average travel-time residuals for each of the recording sites would be that there exists an upward-warping interface in the shallow portion of the crust. Several kinds of later phases can be identified on seismograms between the initial P and S waves. Their apparent velocities and travel-times appear to be consistent with the interpretation that these phases may be SV waves converted from incident P waves or vice versa at the above interface.

著者

尾池 和夫 志知 竜一 浅田 敏

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.28, no.1, pp.75-94, 1975-04-10 (Released:2010-03-11)

参考文献数

4