著者

神田 克久 武村 雅之 宇佐美 龍夫

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.56, no.1, pp.39-57, 2003-06-02 (Released:2010-03-11)

参考文献数

30

被引用文献数

6

---

The method of the inversion analysis to evaluate the distribution of seismic energy radiated from an earthquake fault plane based on seismic intensity distribution data has been developed. The fault plane is divided into small sub-faults. The optimized seismic energy distribution of each sub-fault is calculated using the least square method to minimize the error between evaluated and observed seismic intensities.The energy distribution of a seismic fault is related to seismic intensity using the attenuation formula with equivalent hypocentral distance. The parameters of the attenuation formula are obtained from a regression analysis with measured seismic intensity data of recent moderate earthquakes.The forward analyses using an assumed model are performed to verify the accuracy of the inversion analysis and to evaluate the effect of factors such as the standard deviation of seismic intensity, constraint condition of inversion analysis and configuration of observation stations.Finally, the method is applied to the Showa Tonankai earthquake in 1944 and the Showa Nankai earthquake in 1946 and the result is compared with the tsunami and strong motion waveform inversion results to confirm the efficiency and applicability of the method.

著者

宇佐美 竜夫 狩野 京一 佐藤 泰夫

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.15, no.4, pp.261-269, 1962-12-25 (Released:2010-03-11)

参考文献数

1

---

It is known that the equation of motion for isotropic and homogeneous elastic medium has 8 solutions having different expressions which satisfy the condition Δ=0. Six of these solutions are found to be expressed by the linear combination of the other two which can be considered as the most basic ones. Some other revisions are made on the former paper (Zisin; vol. 14 (1961), pp. 18-28).

著者

佐藤 泰夫 宇佐美 竜夫

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.17, no.3, pp.167-169, 1964-09-25 (Released:2010-03-11)

参考文献数

1

著者

梶川 昌三 山田 功夫 深尾 良夫

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.46, no.3, pp.229-235, 1993-12-14 (Released:2010-03-11)

参考文献数

5

---

One of the largest different conditions between the nature and laboratory experiment of rock fracturing is strain rate. Conventional experiment at a constant strain rate may not simulate the precursory stage of seismic fracture, where strain rate is so low that any anomalous crustal deformation may occur by consuming the strain energy that has already accumulated rather than one newly supplied from the exterior. In order to simulate such a preseismic stage of the crust, we conducted a “zero strain-rate experiment” using Westary granite as a sample. The granite specimen is loaded at a constant strain-rate mode until stress reaches a level about 90% of the fracture stress. The bulk axial strainis then kept constant by servo-control to observe the time-variations of axial stress, local strains, dilatant strain and AE-activity.Initially the axial stress decays exponentially and then linearly until the sample is finally broken. Axial surface strain shows a different behavior at different locality; strain concentration occurs in the area near the final fault and strain relaxation in the area far from it. Very anomalous behaviors are observed in both the areas just prior to the final break. Some implications of these results are discussed in conjunction with the field observations of crustal deformation before earthquake occurrence.

著者

松澤 暢

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.525-536, 1989-12-24 (Released:2010-03-11)

参考文献数

68

---

Many later phases such as ScSp, PS, SP and SS converted or reflected at the upper boundary of a descending oceanic plate are frequently observed in a subduction zone. The location of the upper boundary has been estimated to be just above the deep seismic zone by the use of these phases. Moreover, from the analyses of the later phases such as PS and channel waves, it has been found that a low velocity layer exists on the surface of the plate. The most probable interpretation of the low velocity layer, at least in the shallow depths, is the descending oceanic crust.

著者

山下 哲央 岡田 知己 松澤 暢 長谷川 昭

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.56, no.4, pp.457-469, 2004-03-25 (Released:2010-03-11)

参考文献数

38

被引用文献数

2

---

We estimated the scaling relation, i. e. MO (seismic moment)-fC (corner frequency) relation, of small to moderate-sized earthquakes east off northeastern Japan. We used spectral ratio method to accurately estimate fC from observed spectra of earthquakes. We calculated spectral ratios of all the event pairs with spatial separations less than the hypocenter location errors, and estimated fC values by fitting them with theoretical spectral ratios. Seismic moments were estimated from the JMA (Japan Meteorological Agency) magnitudes. We also estimated spatial variation of the scaling relation along the plate boundary of the subduction zone. Obtained scaling relation was compared with the scaling law derived by Nadeau and Johnson (1998) in which seismic coupling coefficient was assumed to be 100%. Obtained MO-fC samples are somewhat scattered and the distribution range corresponds to seismic coupling coefficients of 1 to 100%. The range corresponds to stress drops of 0.1 to 10MPa. Regional variations of stress drops are also observed. In particular, lower stress drops are estimated in and around the fault area of the 1896 Sanriku tsunami earthquake. Higher stress drops are obtained for the deeper portion (deep thrust zone) of the plate boundary. This tendency of higher stress drops for deeper events can be explained by the difference in physical properties (i. e., rigidity) which depend on depth. The MO-fC relation also varies along the arc. Areas with higher stress drops are distributed in and around the asperities of some large earthquakes. These events with higher stress drops might occur off the plate boundary and/or on the plate boundary in and around the asperities.

著者

松澤 暢

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.Supplement, pp.145-158, 1991-07-24 (Released:2010-03-11)

参考文献数

133

---

Three-dimensional velocity structure beneath island arcs, especially beneath Japan arc, has been investigated in detail by many studies in the last dacade. The low-velocity zone beneath active volcanoes and the high-velocity slab have been delineated by using the block inversion technique. The location of the upper boundary of the descending slab has been estimated precisely by the use of some kinds of converted or reflected waves; the boundary has been located just above the deep seismic zone. In some regions, an oblique thin low-velocity layer has been found on the descending high-velocity slab.

著者

有吉 慶介 松澤 暢 矢部 康男 長谷川 昭 加藤 尚之

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.59, no.4, pp.309-324, 2007-03-25 (Released:2013-08-05)

参考文献数

48

---

A two-dimensional (2D) numerical simulation of seismic cycles on the plate boundary in a subduction zone is performed based on a rate- and state-dependent friction law to obtain insight into complicated cycle of interplate earthquakes off Miyagi Prefecture and to investigate possible precursory sliding behavior. Assuming that the complexity of seismic cycle such as the off Miyagi Prefecture Earthquake is mainly due to the heterogeneity of frictional properties, we divide the plate boundary into five segments along dip direction: three frictionally stable segments and two (shallower and deeper) seismogenic segments are placed alternately. From many trial simulation results, we find that the frictional parameters (b-a)and dc in the deeper seismogenic segment should be smaller than those in the shallower segment in order to generate earthquakes in the deeper segment more frequently than in the shallower segment. The simulation results show that preseismic, coseismic, and postseismic slip in a seismogenic segment tends to become larger when it occurs just after the earthquake in the other seismogenic segment, because the previous earthquake in the other seismogenic segment keeps on forward slip through the intermediate aseismic segment. We also find that the stress rate in the down-dip direction in the vicinity of the lower edge of the deeper seismogenic segment is compressional for the period of about one year prior to the occurrence of the earthquake in the segment while it is tensional prior to the event in the shallower segment. This result suggests that seismic activity change in a slab can be a clue to the intermediate-term prediction of large interplate earthquakes.

著者

海野 徳仁 河野 俊夫 岡田 知己 中島 淳一 松澤 暢 内田 直希 長谷川 昭 田村 良明 青木 元

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.59, no.4, pp.325-337, 2007-03-25 (Released:2013-08-05)

参考文献数

21

被引用文献数

1 5

---

Hypocenters of the main shocks and aftershocks of the 1933 Mjma 7.1, 1936 Mjma 7.4, 1937 Mjma 7.1, 1939 Mjma 6.9, 1978 Mjma 7.4, and 1981 Mjma 7.0 Miyagi-oki, NE Japan, earthquakes are relocated by using S-P times reported in the Seismological Bulletin of the Japan Meteorological Agency (JMA) and those re-read from original smoked-paper seismograms observed at Mizusawa station of National Astronomical Observatory of Japan (NAOJ) and at Mukaiyama station of Tohoku University. In order to avoid large errors caused by inaccuracies in the arrival times of P- and S-waves and the limited number of observation stations, we determined hypocenters by using a grid search method based on the assumption that these events occurred at the boundary between the subducting Pacific plate and the overriding plate. The main shock epicenters of the 1933, 1936, 1937, and 1978 earthquakes are determined close to each other, and distributions of their aftershocks show that aftershock areas of 1933, 1936, and 1937 events partly overlap with that of the 1978 event and occupy its easternmost, central, and westernmost portions, respectively. It is likely that the 1933, 1936, and 1937 events possibly ruptured a part of the source area of the 1978 event, that is the eastern, central, and western portions, respectively. Locations of the main shock and aftershock area of the 1939 event are adjacent to the eastern edge of the source area of 1978 event. After the 1978 event, the 1981 earthquake had occurred there following the slip on the asperities in the presumed Miyagi-oki earthquake source area.

著者

内田 直希 松澤 暢 三浦 哲 平原 聡 長谷川 昭

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.59, no.4, pp.287-295, 2007-03-25 (Released:2013-08-05)

参考文献数

26

被引用文献数

4

---

Spatio-temporal distribution of quasi-static slip on the plate boundary east off Miyagi and Fukushima prefectures, NE Honshu, Japan is estimated by using small repeating earthquake data. The analysis of small repeating earthquakes has advantages of relatively high spatial resolution, especially near the trench, and the availability of long-term data (22 years) compared to GPS data. The results show that the repeating earthquakes are distributed outside the coseismic slip areas (asperities) of large earthquakes, showing that fault creep is dominant outside the asperities. The cumulative slip (slip histories) of small repeating earthquake groups reveal the existence of many non-steady aseismic slip events. Most of the episodic quasi-static slip events are associated with M≥ 6 earthquakes and they are frequently seen in the areas near the Japan trench in particular. Minor afterslip (∼15cm) of the 2005 Miyagi-oki earthquake (M7.2) is also estimated in the area which encompasses the coseismic slip area of the 2005 earthquake.

著者

堀内 茂木 松澤 暢 長谷川 昭

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.52, no.2, pp.241-254, 1999-10-20 (Released:2010-03-11)

参考文献数

22

被引用文献数

2

---

Many earthquakes occur after a destructive shallow earthquake or before a volcanic eruption. It is very important to determine accurate hypocenters as early as possible at a time of such a huge seismic activity, since seismicity data are essential for the understanding of the crustal activity. We developed an automatic data processing system of seismic waves which has a swarm mode processing and can locate accurate hypocenters even for a huge seismicity. The main difference between the swarm and ordinary modes is that the former assumes hypocenters for all events to be in a small area. Event detection is made by estimating approximate origin times calculated from each picked arrival time of P and S waves for several low noise stations close to the swarm area and each theoretical travel time from the swarm area to these stations. We assume events having similar origin times to be seismic events. The system picks P and S wave arrival times not only for these stations but also for all stations by setting time windows at their arrivals which are calculated from the approximate origin time. The application of swarm mode to waveform data at a huge seismicity after the 1996 Onikobe earthquake sequence showed that the new system is very effective and can determine more precise hypocenters rather than manual pickings.

著者

勝俣 啓 卜部 卓 森谷 正義 中村 正夫 瀬戸 憲彦 中村 功 溝上 恵

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.499-511, 1990-12-24 (Released:2010-03-11)

参考文献数

4

---

Explosion seismic refraction experiments were carried out in 1988 for the investigation of the shallow crustal structure in the volcanic island of Nii-jima, northern part of Izu-Bonin island arc, Japan. One hundred and eight seismograms were obtained at 54 temporary stations aligned on the three profiles arranged like a triangle on the island. The main features of the shallow crustal velocity structure revealed by the travel time analysis are as follows:1) Surfaces of high velocity layers are raised beneath volcanos in the island of Nii-jima.2) The structure mostly consists of three layers with P-wave velocities of 1.9km/s, 2.8km/s and 4.5km/s, respectively.3) A layer with a velocity of 1.5km/s exists over the 1.9km/s layer at two explosion sites in shore.4) There is no 1.9km/s layer beneath Mt. Acchi volcano in the northern part of the island.5) The top of the 2.8km/s layer is much shallower beneath Mt. Mineji volcano in the central part of the island and beneath Ajiaiso beach in the northwestern part of the island.6) Both top of the 2.8km/s layer and that of the 4.5km/s layer are much shallower beneath Mt. Acchi volcano in the northern part of the island.7) The 1.9km/s layer is thicker beneath the small plain in the central part of the inland, beneath the place between Mt. Mineji and Ajiaiso beach, and beneath Wakago village in the northern part of the island.

著者

河村 将 工藤 健 山岡 耕春 古本 宗充

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.63, no.3, pp.123-137, 2011-02-25 (Released:2012-03-26)

参考文献数

16

被引用文献数

1

---

We developed a comprehensive statistical validation system of crustal activities with which to easily address spatially and temporally sufficient range of a database of geophysical measures. The system involves carrying out the following four processes: (1) creating the database of geophysical measures with spatially and temporally gridded and other convenient formats, (2) comparing any two geophysical measures, at least one of which is time-variable, (3) classifying the spatiotemporal relationship of these geophysical measures into some types by defining a statistical index, and (4) evaluating and validating the relationships between classification results and the occurrence of target physical events such as large inland earthquakes. With the system, we aim for making a statistical model, or an appropriate rule for monitoring of crustal activities. Formulation of the rule is, in turn, expected to lead to comprehensive understanding of crustal activities. Here, we focused on the relations of seismicity and strain rate to introduce the conception and algorithm of the system. The system requires input of the database and other parameters and leads to output of various spatiotemporal distributions, 2-by-2 contingency tables, and probability gains for prediction and alarm rates for target physical events.

著者

宇津 徳治

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.10, no.1, pp.35-45, 1957-08-25 (Released:2010-03-11)

被引用文献数

45

著者

渡部 豪 田部井 隆雄

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.57, no.1, pp.1-10, 2004-08-25 (Released:2010-03-11)

参考文献数

23

被引用文献数

1 4

---

The Ryukyu Arc is a NE-SW trending island arc that connects southwest Japan and Taiwan. The Philippine Sea plate subducts at the Ryukyu Trench, the southeastern boundary of the Ryukyu Arc. While the plate model predicts a rather high subduction rate (60-80mm/yr), plate coupling has been estimated so small from the earthquake data. Another factor characterizing tectonic features of the region is an active backarc opening at the Okinawa Trough that forms the northwestern boundary of the region. Japanese nationwide continuous GPS array has illustrated a trenchward motion of the Ryukyu Arc. However, it is difficult to quantify the effects of the subduction and the backarc opening because there is little deployment of the GPS network in the direction perpendicular to the strikes of those two boundaries. To model tectonic movement of the region, at first we divide the region into four crustal blocks based on horizontal GPS velocities and geological conditions. As the first approximation, plate coupling is neglected. Crustal velocities predicted from the block motions are in good agreement with the observed ones with an average discrepancy of about 3mm/yr. Next, we introduce moment tensor data of shallow earthquakes to calculate crustal strain rates in several segments and further estimate spatial variation of the plate coupling. The results show that the estimated plate coupling is smaller than 10% in most segments except 50% in the northernmost part. We interpret that the plate coupling at the Ryukyu Trench is so small and the trench can behave as a free boundary. Thus if a backarc opening occurs at the Okinawa Trough, the Ryukyu Arc can easily move trenchward without significant internal deformation. However, detailed mechanism of the backarc opening remains still unknown and is an important problem to be resolved in the future.

著者

山田 功夫

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.53, no.3, pp.259-262, 2001-03-25 (Released:2010-03-11)

参考文献数

2

被引用文献数

1 2

著者

石橋 克彦 太田 陽子 松田 時彦

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.35, no.2, pp.195-212, 1982-06-25 (Released:2010-03-11)

参考文献数

19

被引用文献数

1 1

---

Uplifted Holocene marine terraces of Hatsu-shima Island (0.44km2) in the western part of Sagami Bay on the Pacific coast of central Japan have been investigated with special reference to the late Quaternary seismic crustal movement of the island. Hatsu-shima Island, which is located at the top of the western steep scarp of the northernmost part of the Sagami trough, was uplifted almost uniformly by around 2m at the time of the 1923 Kanto earthquake (Ms=8.2).The whole surface of the island consists of a flight of marine terraces developed on Pliocene volcanics. These terraces are clearly classified into three groups; I, II, and III. Terrace I, the highest (about 50m asl), is distributed only in the southeastern small part of the island. Terrace II, 25-40m asl, is the widest in the island and tilting, generally, northwestward. Terraces I and II have been correlated to Obaradai Terrace of about 80, 000yrs B. P. in age and to Misaki Terrace of about 60, 000yrs B. P. in age, respectively, by SUGIHARA (1980) based on marker tephras covering the terraces.Terraces III, rather narrow but well defined especially in the northern and western parts of the island, is distributed along the present shoreline at the foot of a former sea cliff as high as about 20m surrounding Terrace II (or I in the southeastern part). In this paper they are subdivided into three; IIIa, IIIb, and IIIc. Terrace IIIa, the highest and widest among group III, is rather flat with about 10m asl inner margin. Planned excavation at three localities on this terrace has revealed that terrace deposits composed of marine gravel and sand of 1.5-2m thickness rest unconformably on rather weathered bed rock. Fossil shells that were obtained at the base of terrace deposits at Excavation B, which are judged to be in situ and to represent the terrace's age, have been dated at 6, 730±190 14C yrs B. P. (GaK-9080). From this 14C date, as well as from the topographical features, Terrace IIIa can be interpreted as the highest Holocene terrace formed about 6, 000 years ago (so-called Numa Terrace). The height of former shoreline is estimated at around 9m asl. Terraces IIIb and IIIc are narrow emergent shingle beach, whose inner margins are 6-7m asl and about 4m asl, respectively. IIIc includes the emergent beach of 1923 in its lowest part. Although the topographical separation between IIIb and IIIc is not necessarily clear, they can be distinguished from each other as IIIb surface is covered by dense vegetation including many pine trees which have been growing since before the 1923 coseismic uplift, whereas IIIc surface has no vegetation. Therefore, it is almost certain that at least two times of intermittent emergence had occurred between the formation of Terrace IIIa and the 1923 coseismic uplift. However, the dates of emergence have remained undefined, because 14C dates of fossil shells which were collected from Terraces IIIb and IIIc are so much scattered implying that the materials are not in situ. In the northern part of the island there is a prominent flat surface higher than Terrace IIIa, 10-15m asl, where Hatsu-shima village is situated. In this paper it is named IIIa' Surface and considered a secondary surface modified from Terrace IIIa by landslides of a back scarp and artificial alteration based on its sedimentological features, surrounding topographical features, and rather young 14C dates of materials obtained from this surface.

著者

今村 文彦 首藤 伸夫 後藤 智明

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.3, pp.389-402, 1990-09-24 (Released:2010-03-09)

参考文献数

14

被引用文献数

15

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The linear Boussinesq equation should be used in numerical simulations for distant tsunamis in the Pacific Ocean, because the dispersion effect is not negligible. Its difference equation which can not be expressed by an explicit scheme requires a long CPU time. One of the present authors has introduced a new technique, in which the first term of discretization error in the difference equation of the linear long wave theory was used and controlled to replace the physical dispersion term. This method is applied in the present study. The effect of ocean current on the tsunami propagation is confirmed to be negligible in wave direction and wave height. The 1960 Chilean tsunami is simulated. The Coriolis force has not only the effect on the propagation direction but also the dispersion effect, which is examined by comparing with the computed result without the Coriolis force. Effect of the sea bottom topography is examined in detail in terms of wave energy. About 40% of initial wave energy remains on the continental shelf in the neighborhood of Chile, and the rest is radiated to the Ocean. After scattered and trapped by islands and sea mounts, about 25% of the total energy arrives at Japan. The computed results shows a fairly good agreement with tide records after making correction of the effect of the water depth. For further discussions of the tsunami in shallow seas, simulations should be performed using the shallow-water theory and detailed topography.

著者

山川 宜男

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.8, no.2, pp.84-98, 1955-10-20 (Released:2010-03-11)

参考文献数

7

被引用文献数

18

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Japanese seismologists succeeded in explaining the push-pull distribution of the initial motion of earthquakes by assuming two types stress distribution on the sphere which covers the hypocenter. Type A is the combination of hydrostatic pressure and pressure with distribution expressed in spherical harmonic P2(cosθ). Type B is the distribution of pressure expressed in P21(cosθ)cosφ. Generally the polar axis of these spherical harmonics does not coincide with vertical axis. On this point, Y. Sato obtained the formulae which express the transformation of the spherical harmonics by the rotation of coordinate system. According to his result, P2(cosθ0)=P2(cosθ)(1/4+3/4cos2χ)+P21(cosθ)cos(φ-φ)(1/2sin2χ)+P22(cosθ)cos2(φ-φ)(1/8-1/8cos2χ)P21(cosθ0)cosφ0=[sinφA21-cosφB21]where A21=P21(cosθ)sin(φ-φ)cosχ+P22(cosθ)sin2(φ-φ)(1/2sinχ)B21=P2(cosθ)(3/2sin2χ)-P21(cosθ)cos(φ-φ)cos2χ-P22(cosθ)cos2(φ-φ)(1/4sin2χ)where (φ, φ, χ) is Euler angles which express the rotation of the coordinate.In this paper, we calculated the strain produced in a semi-infinite elastic solid when hydrostatic pressure and pressure with distribution expressed in spherical harmonics P2(cosθ), P21(cosθ)cosφ, P22(cosθ)cos2φ were applied at the interior spherical cavity.The deformations expressed in cylindrical coordinate (R, φ, z) at the surface of semiinfinite elastic solid are as follows:—(1) The case in which hydrostatic pressure -P is appliedUR=3a3P/4μR/(f2+R2)3/2, Uφ=0, Uz=-3a3P/4μf/(f2+R2)3/2(2) The case of -PP2(cosθ)UR=3a3P/46μ[-5P/(f+R23/2)+18f2R/(f2+R2)5/2], Uφ=0, Uz=-3a3P/46μ[-5f/(f2+R23/2)+18f3/(f2+R2)5/2](3) The case of -PP21(cosθ)cosφUR=54a3P/23μcosφ[-f((f2+R2)3/2+f3(f2+R2)5/2], Uφ45a5P/184μsinφf(R2+f2)5/2, Uz=45a5P/184μsinφf(R2+f2)5/2(4) The case of -PP22(cosθ)cos2φUR=9a3P/23μcos2φ[4f/R3-4f2/R3(R2+f2)1/2+5R(f2+R2)3/2-2f2/R(R2+f2)3/2-6f2R

著者

宇津 徳治

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.22, no.1, pp.41-53, 1969-05-30 (Released:2010-03-11)

参考文献数

16

被引用文献数

4

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Arrival times of P and S waves at Japanese stations from 33 intermediate and deep earthquakes in and near Japan are plotted in the form of S-P vs. P plots. Most of the plotted points for each earthquake (except one which occurred in Kyushu) fit a straight line with a slope of about 0.77. This means that the velocity ratio of P to S waves is about 1.77 and Poisson's ratio is about 0.265 for the portion of the upper mantle concerned. It should be emphasized that the ratio does not differ significantly between the two distinctive portions of the upper mantle, i. e., the inclined deep seismic layer of high-Q and high-V and the overlying wedge-shaped region of low-Q and low-V. For certain deep earthquakes, plotted points in ranges of larger S-P deviate systematically from the straight lines fitted to points in ranges of smaller S-P. From this deviation it is suggested that a portion of the upper mantle under the deep seismic layer has a comparatively large Poisson's ratio.