著者
小林 励司
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.73, pp.225-249, 2021-01-29 (Released:2021-03-30)
参考文献数
38

A large earthquake (M7.1) occurred during the 1914 eruption of Sakurajima volcano in Kagoshima prefecture, Japan. I estimated seismic intensities in the present Japan Meteorological Agency (JMA) scale for the 1914 Sakurajima earthquake in Kagoshima city. Previous studies on seismic intensities in Kagoshima city are used their own unique methods to estimated seismic intensities from data of damaged houses and stonewalls. I used a method of estimating seismic intensities from data of damaged houses, which has been commonly used. Previous studies using this method have assumed that each household owns one house, but the numbers of damaged houses in some towns are significantly larger than those of households in the case of the 1914 Sakurajima earthquake. I, therefore, made two assumptions A and B. The assumption A is that each household owns one house. The assumption B is that the ratio of houses to households in each town equal to the maximum ratio of total damaged houses to households. As a result, the maximum seismic intensities for the assumptions A and B are 6 upper and 6 lower, respectively. The areas with higher seismic intensity than 6 lower are consistent with the previous studies on the 1914 Sakurajima earthquake, but the areas with lower seismic intensities than 5 upper are inconsistent because I did not take stonewall damages into consideration, which the previous studies did. I compared our results with distributions of seismic intensities predicted by an attenuation relation between intensity and distance with two different sets of source parameters. One set of source parameters showed seismic intensities of 6 lower and 6 upper in Kagoshima city, and the other set showed those of 5 lower and 5 upper. The observed seismic intensities are on average lower than the predicted ones, probably suggesting that large coseismic slip area is distributed further than epicenter, that Kagoshima city is located in the opposite direction of the rupture propagation and its directivity effect make the amplitudes smaller, or that amplitudes at frequencies which affect seismic intensities are smaller than those expected from the magnitude. The observed seismic intensity distributions are also rougher than the predicted ones and could be affected by local soil conditions.
著者
松本 拓己 伊藤 喜宏 松林 弘智
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.58, no.4, pp.427-443, 2006-03-31 (Released:2010-03-11)
参考文献数
17
被引用文献数
1 1

The 2004 Mid Niigata Prefecture earthquake (MJ6.8) that occurred on October 23, 2004 is the 2nd largest intra-plate earthquake after F-net, the broadband seismograph network of the National Research Institute for Earth Science and Disaster Prevention (NIED) was established with a dense and homogeneous distribution all over Japan. We determined moment tensor solutions of the main shock, aftershocks, and earthquakes occurred around mid Niigata prefecture from January 1997 to October 22, 2004, using a surface wave with an extended method of the NIED F-net routine processing. The horizontal distance to the station is rounded to the nearest interval of 1km, and the variance reduction approach is applied to a focal depth from 2km with an interval of 1km. We obtain the moment tensors of 117 events with MJ exceeding 2.8 and spatial distribution of these moment tensors. The focal mechanism of main shock, aftershocks, earthquakes before main shock, is mainly of the reverse fault type with P axes trending WNW-ESE. But the focal mechanism of 15 percent aftershocks is the strike-slip type. There are high dip angle reverse faults, in deep part, and low dip angle reverse faults in shallow part.
著者
山中 浩明 瀬尾 和大 佐間野 隆憲
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.1, pp.9-20, 1991-03-24 (Released:2010-03-11)
参考文献数
15
被引用文献数
1

The seismic refraction survey was conducted in the southwestern part of the Tokyo Metropolitan area to make clear the deep sedimentary structure. Two explosions were made at Daikoku and Maioka in Yokohama city in 1988, and the resultant seismic waves were observed at 83 temporary observation sites along four surveying lines:a) Yumenoshima to Enoshima, b) Daikoku to Nagatsuta, c) Nagatsuta to Kanazawa, andd) around Takatsu.The travel time analysis for the above data and additional data from previous explosions in the area for reference has been made.The followings were our conclusions:1) The subsurface structure consists of five layers characterized by P-wave velocities of 1.8, 2.3, 2.9, 4.7 and 5.5km/s. The top layer with a P-wave velocity of 1.8km/s disappears around Enoshima. The layer with a P-wave velocity of 5.5km/s could not be confirmed for the southwestward area.2) The topography of the layer with a P-wave velocity of 4.7km/s forms a synclined structure having its maximum depth of more than 4km between the Maioka and Daikoku explosion sites. The depth to this layer becomes drastically shallower toward Enoshima.3) The step-like topography of the layer with a P-wave velocity of 5.5km/s, which has been found in the previous study, could not be confirmed, because of low S/N ratios of the observed seismograms.
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.49, no.4, pp.461-466, 1997-03-14 (Released:2010-03-11)
参考文献数
8

A small tsunami accompanied with the Hyogoken-Nanbu earthquake on January 17, 1995 (epicenter: 34°36′N, 135°03′E, d=14km, M=7.2, JMA), was observed at many tidal stations around the source area. The maximum double amplitude at Ei, Awaji Island, reached 68cm, and those at most Stations were 10-20cm or less with the wave period of 10-20min. By judging from the diagram of the attenuation of wave-height with distance, tsunami magnitude on the Imamura-Iida scale was determined to be m=-2, which is smaller by two grades (amplitude: 1/5 less) than those generated by earthquakes of the same magnitudes, because the seismic faults lay on land. The size of the source area estimated by means of an inverse refraction diagram is 70×13km2 extending NE-SW direction from the Hanshin region to the western area of Awaji Island. The tsunami source comprehends the aftershock area. Considering the distribution of the initial motions of tsunami observed by tidegauges, it suggests that the sea-bottom on the east side of the northern tsunami source (the northern part of Osaka Bay) was uplifted and that on the west side (Harima-Nada Sea) was subsided.
著者
松村 正三
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.49, no.1, pp.85-88, 1996-05-24 (Released:2010-03-11)
参考文献数
15
被引用文献数
1
著者
八木原 寛 角田 寿喜 後藤 和彦 清水 洋
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.1, pp.53-61, 1994-06-14 (Released:2010-03-11)
参考文献数
30

On January 30, 1992, a shallow earthquake of magnitude 4.9 followed by about 300 aftershocks occurred in a northern area of the Koshiki channel, north-western Kagoshima Prefecture. We located seismic events observed at two stations of NOEV (Nansei-toko Observatory for Earthquakes and Volcanoes) and four stations of SEVO (Shimabara Earthquake and Volcano Observatory), using Joint hypocenter determination (JHD). Hypocenters of the mainshock and its aftershocks were nearly vertically distributed at depths from 5km to 13km in a small area.Initial motions at the seismic stations of NOEV, SEVO and FMO (Fukuoka Meteorological Observatory) suggest a focal mechanism of strike slip fault type with a T-axis of NNW-SSE direction: the mechanism is very similar to those reported for the earthquakes in and around the area. The nodal plane striking in NE-SW agrees with trends of the fault system in the channel and the other WNW-ESE plane is parallel to the earthquake alignment along Amakusanada-Izumi-Kakuto areas. Hypocenters of the event and aftershocks nearly vertically distributing are, however, not consistent with any of the planes.In March of 1991, about 10 months before the M 4.9 event, an earthquake swarm (Mmax 2.9) occurred at depths around 5km almost within the same epicentral area. Namely, two different types of earthquake sequence occurred at different depths in the same area: the swarm occupied a shallower zone than the focal zone of the M 4.9 event. Although some volcanic process may be inferred from hypocenters vertically aligning, it is probably difficult to explain the fact that the earthquake swarm at shallow depths occurred about 10 months before the M 4.9 event at a deeper depth without accompanying any notable foreshocks.
著者
深畑 幸俊
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.61, no.Supplement, pp.103-113, 2009-07-31 (Released:2013-11-21)
参考文献数
64
被引用文献数
2 7

Inversion analyses play a central role in solid earth sciences, since observable quantities are very limited for the earth’s interior. Classical least squares method does not work well in these fields, since observed data are commonly inaccurate and/or insufficient. Least squares methods with additional conditions, such as damping or smoothing, have been widely used, but the weight of damping or smoothing have to be manually adjusted, if we do not take in a probabilistic point of view. In 1980, H. Akaike proposed a Bayesian Information Criterion (ABIC), where smoothness constraint is regarded as prior information that is combined with information from observed data by Bayes’ rule, and then the optimal weight between the information from observed data and prior constraint is objectively determined by minimizing ABIC. ABIC had been introduced to geophysics by several studies. Among them, Yabuki and Matsu’urea (1992) has been the most influential. The inverse method developed by them has been widely applied to various problems in seismology and geodesy. Recently, it has become clear that the inverse method must be further developed beyond the framework given by Yabuki and Matsu’ura (1992). Generalization has been performed in dealing with prior constraints, hyperparameters, and observed data.
著者
弘瀬 冬樹 中島 淳一 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.60, no.3, pp.123-138, 2008-02-15 (Released:2013-08-20)
参考文献数
46
被引用文献数
5 17

We estimated three-dimensional seismic velocity structure in and around the Philippine Sea plate subducting beneath the Kanto district in Japan by applying the double-difference tomography method to arrival time data of earthquakes obtained by the dense nationwide seismic network (Kiban-network). A low S-wave velocity and high Vp/Vs layer with several-km thick, which is shallowly inclined toward the subducting direction of the slab, has been clearly imaged. Comparison with the location of the upper surface of the Philippine Sea slab estimated from seismic refraction surveys, hypocenter distribution of relocated earthquakes, and focal mechanisms shows that this low S-wave velocity and high Vp/Vs layer corresponds to the crust of the Philippine Sea slab. Based on the presently obtained location of the low S-wave velocity and high Vp/Vs layer, hypocenter distribution, and focal mechanisms, we estimated the configuration of the upper surface of the Philippine Sea slab in the Kanto district. Presently estimated configuration of the Philippine Sea slab shows that the slab bends concavely and the depression is located eastward compared with those of the previous studies. Most of the earthquakes associated with the Philippine Sea slab occur along the plate boundary and/ or around the slab Moho. Prominent low S-wave velocity and high Vp/Vs layer was detected at depth of 30 km beneath the region along the latitude of 35.8 degrees, suggesting the serpentinization of the forearc mantle wedge due to dehydration of subducting slab.
著者
上田 誠也
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.391-405, 1991-07-24 (Released:2010-03-11)
参考文献数
38
被引用文献数
4

In Greece, astonishing success has reportedly been achieved in predicting earthquakes by monitoring the geoelectric potential changes. The method, called the VAN-method taking the initials of Varotsos, Alexopoulos and Nomikos, claims that earthquakes with magnitude greater than ca. 5 occurring in Greece can be predicted within the errors of 100km in epicenter and 0.7 in magnitude. The lead time is between several hours and ca. 20 days. The actual success rate and alarm rate for the recent one year are both estimated to be about 60%. Some technical aspects and the outline of suggested physical mechanism of the method are reviewed. A brief introduction of our attempt to apply the method in Japan is also given.
著者
佃 為成
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.11-20, 2003-06-02 (Released:2010-03-11)
参考文献数
7
被引用文献数
2 1

A new probability process model for earthquake forecast is presented based on Bayesian treatment. The prior probability at the beginning of this process is estimated from long-term data from earthquake history and active fault activities in a target area. The posterior probability is deduced from Bayes' theorem in terms of the prior probability and two conditional probabilities: “alarm rate” and “null alarm rate”. The former is defined to be the probability that a precursory anomaly is detected on condition that an earthquake is accompanied, and the latter to be that on condition that no earthquake is accompanied. These probabilities are estimated mainly by statistical tests of previously accumulated observation data. The test consists of trials of detecting anomaly during each assigned detecting period and of registering earthquake events during the corresponding hypothetical forecasting period. Regarding the estimated posterior probability as the prior probability for the next step of the Bayesian process, we will obtain a new posterior probability when data from another anomaly event is input into the process. Successive application of this procedure continues to renew the posterior probability until a dicision is made to issue an earthquake warning. The final posterior probability pN for N independent anomaly observations with alarm rate qi and null alarm rate si for i=1, 2, …N is given byPN=x1x2…xN/x1x2…xN+a1-p0x1x2…xN, where p0 is the first prior probability, a1=(1-p0)/p0, xi=qi/si and the approximation (-) is valid if pN<<1. The well known terms, “secular probability” and “success rate” are interpreted in the above framework to be a prior probability and the induced posterior probability, respectively. The ratio of alarm rate to null alarm rate, i. e., xi in the above formula, for each precursory anomaly observation is a key factor for reliability on earthquake prediction. The probability gain, i. e., the ratio of the posterior probability to the prior probability, is approximated to be the product of the above ratios.
著者
相田 勇
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.4, pp.449-460, 1975-12-10 (Released:2010-03-11)
参考文献数
13
被引用文献数
1 3

On May 21, 1792, a gigantic collapse of Mt. Mayuyama in Shimabara Peninsula, Kyushu, occurred. Following this event, a severe tsunami of about 10 meters in height was generated by the landslide and attacked the coast of Ariake-kai, killing more than 14, 500 persons. Many historical documents tell us the phenomena of this tsunami in fair details, so that we attempted to reconstruct a numerical model of the tsunami consistent with the historical data. In the numerical computation, a finite difference method with a leap-frog system is adapted, and two kinds of source input are tried; one is the prescrived water mass transport normal to shore line and the other the vertical displacement of sea bottom. When the transport of 18, 000m3/min (current speed-20m/sec) per unit length of shore on the center line of landslide area is assumed to be continued during 2 to 4 min, the computed waves agree fairly well with the real tsunami behaviors, the height of tsunami in various places along the coast and the order of the maximum crest in the sequence of a wave train. Therefore, it seems probable that the extraordinary flow of water normal to the shore occurred by some physical mechanisms of the mountain collapse.The energy of this tsunami is estimated to be about 5×1019erg, and this is about 1/100-1/1000 of the available potential energy of the slided material due to the collapse of the mountain. It is significant that the tsunami energy is several times larger than that of the 1968 Hyuganada Earthquake (M=7.5). The wave spreaded over a wide area and gave distructive damages to the coast more than 120km on both side of Ariake-kai.
著者
村上 亮 小沢 慎三郎
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.57, no.2, pp.209-231, 2004-12-27 (Released:2010-03-11)
参考文献数
43
被引用文献数
1 6

To evaluate a reliability of GPS vertical data we mapped vertical crustal deformation field of Japan using continuous GPS measurements with a nationwide dense network (GEONET) of the Geographical Survey Institute during the period from 1996 to 2003. We confirmed that the GPS vertical deformation field reasonably agrees with those derived from leveling, tidal record and geomorphologic analysis. The conformity with the other data sets suggests a dependability of the GPS vertical results. The GPS data illustrate details of a spatial pattern of the vertical deformation field and manifest their usefulness when applied to constrain tectonic models. A subsidence along the pacific coast of the southeastern Hokkaido propounds a possibility of a downdip extension of a plate coupling reaching to the depth of about 80km. Uplift around Hidaka mountains in the central Hokkaido suggests a present-day mountain building process at least during the interseismic period. An apparent subsidence found in the central mountainous region of the central Honshu island contrasts sharply with the presumed uplift through Quaternary inferred from geomorphologic analyses. Vertical deformations along the Nankai trough in the southwestern Japan can be attributed to an elastic deformation due to a dragging of the subducting Philippine Sea plate. The GPS result confirms a coupling of plates and a resultant strain accumulation in the Tokai region. Those results demonstrate the usefulness of the GPS vertical data and encourage us in further applications in the studies to understand ongoing tectonic processes in Japan.
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.44, no.4, pp.297-303, 1991-12-24 (Released:2010-03-11)
参考文献数
13

Based on an epicentral distance dependence of tsunami amplitude observed at tide stations, the tsunami magnitudes were obtained to be m=-2 and m=-1 for the Oshima-Kinkai tsunami of Feb. 20, 1990 and the Tokaido-Oki tsunami of Sept. 24, 1990, respectively. The locality on magnitudes of the tsunamis generated along the Izu-Mariana Island-Arc since 1900 are discussed in relation to earthauake magnitude. According to the statistical relation, the magnitude values (Imamura-Iida scale) of the tsunamis generated near the trench triple junction off Boso Peninsula are one to two grades larger than the average tsunami magnitude. Such tsunamis were mostly caused by low-frequency earthquake with the high-angle dip-slip fault. While, the magnitudes of the tsunamis generated off the west side of Oshima Is. are one grade less than the average value, with caused by earthquakes of the strike-slip type. The magnitudes of a few tsunamis generated on the ridge were larger than the average value. Especially, the 1984 Torishima-Kinkai tsunami had an abnormal magnitude. The regional difference of seismic mechanisms were found by the deviation of tsunami magnitudes.
著者
寒川 旭
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.40, no.2, pp.235-245, 1987-06-25 (Released:2010-03-11)
参考文献数
18
被引用文献数
2 3

In the morning of September 27, 1611, a strong earthquake hit the Aizu Basin and its surroundings. The damage and its location are thoroughly described in old documents. Landslides occurred in many places on the upthrown side of the Aizu active fault system, which borders the western fringe of the basin. The earthquake fault occurred along the active fault system and dammed up the Nippashi (Ohkawa) River, forming a small lake. The altitude of the lake is inferred to have been 174.5-175m above sea level and depth about 2-3m. The lake is assumed to have been 2-2.5km wide and 4km long, which coincides with the description of old documents. Some villages were submerged and moved outside of the lake. Some part of the ancient Echigo Highway was also submerged and were rebuilt about 4km southward. The earthquake is believed to be caused by the Aizu active fault system. The magnitude of the earthquake is calculated at about M7.3, based on the vertical displacement (2.5m) of the earthquake fault.
著者
笠原 順三 大野 一郎 飯田 汲事
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.3, pp.201-209, 1969-11-30 (Released:2010-03-11)
参考文献数
7

When a crystal structure of ammonium fluoride, NH4F, reversibly transforms from Wurtzite structure to NaCl structure at ca. 4kb, a number of small elastic shocks are accompanied with the volume change by the rapid phase transition for polycrystalline specimen. These shocks are also generated during the lowering pressure run, where NaCl structure transforms to Wurtzite structure. If we assume that each of the shocks corresponds to a phase transition in a small volume in the specimen, the amount of the reactant is given by the accumulated number of shocks. Fitting the bulk rate of the phase transition by the equation of the rate theory; dX/dt=K(1-X)p, where X is the mole fraction of the reactant at the time t, we obtain p≈1 and K≈10-1sec-1. The present result shows that the phase transition is the first order reaction and the bulk rate of the phase transition is in the order of 10-1sec-1, although the process of the phase transition is not continuous but is the superposition of very rapid ones with elastic wave radiation.
著者
垣見 俊弘 松田 時彦 相田 勇 衣笠 善博
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.4, pp.389-406, 2003-03-15 (Released:2010-03-09)
参考文献数
49
被引用文献数
9

A new seismotectonic province map of the Japanese Islands and the adjacent areas, which carries maximum magnitudes of earthquake (Mmax) expected for the individual provinces, has been prepared as a revised edition of Kakimi et al. (1994). The major part of the mapped region constitutes an island arc-trench system, which is surrounded by Northwest Pacific Basin (1), Shikoku Basin (2), Philippine Basin (3), Kurile Basin (4), Japan Sea Basins (5), and Korean Peninsula and Tonhai Continental Shelf (6). All of the peripheral provinces have too low seismicity to be given Mmax. The island arc-trench system is subdivided into the following constituent arcs: Kurile Arc (7), Northeast Honshu Arc (8), Izu-Bonin Arc (9), Southwest Honshu Arc (10), Ryukyu Arc (11), Sakhalin Arc (12), and the Tectonic Belt along the Eastern Margin of Japan Sea (13). While the constituent arcs 7 to 11 are divided into three tectonic belts, which remarkably differ from each other in tectonic, seismic, and volcanic activities, from the trench to the inland: Continental Slope on the Trench Side (A), Non-volcanic Outer Belt (B), and Volcanic Inner Belt (C), the constituent arc 10 alone has additionally the Continental Slope on the Marginal Sea Side (D). Province 12 started developing in Late Mesozoic and functioned as a collision belt between the North American Plate (NA) and the Eurasian Plate (EUR) in Late Cenozoic, whereas province 13 is considered to form a current collision belt between NA and EUR plates. Province 11X, Okinawa Trough, is defined as a current rift zone developing between the Tonhai Continental Shelf and the Ryukyu Arc. Some of the provinces are further divided into subprovinces in response to local differences in active faults, seismicity, Mmax etc.All the active faults on land are grouped into seismogenic faults (Matsuda, 1990), which are considered to generate characteristic earthquakes. The magnitudes of earthquake expected for the seismogenic faults (MLmax) are estimated by the equation: log L=0.6ML-2.9 (Matsuda, 1975), where L is the length of the faults in kilometers. The maximum magnitude of earthquake expected for seismogenic faults (MLmax) and the maximum one for historical shallow earthquakes (Mhmax) are compared in each province to choose the larger one as the expected maximum earthquake magnitude (Mmax) for the province. Since no method to decide a seismogenic unit from offshore active faults has been established, Mhmax is tentatively adopted as the Mmax representing the province. Extraordinarily long faults found in inland provinces, which are called the designated faults (Matsuda, 1990), are excluded from estimation of the Mmax. None of the magnitudes of earthquake expected for the designated faults is shown here, because they should be individually estimated. All of the information, such as tectonic geomorphology and geology, characteristics of active (seismogenic) faults, historical earthquakes, modern seismicity, and other, is put into a table to facilitate the identification of a seismotectonic province and the determination of the Mmax and the designated faults. The details of the boundaries between seismotectonic provinces are shown in another table.