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.20, no.1, pp.54-56, 1967-06-25 (Released:2010-03-11)

参考文献数

3

被引用文献数

2

著者

都司 嘉宣

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.2, pp.277-287, 1986-06-25 (Released:2010-03-11)

参考文献数

21

被引用文献数

1

---

The Tenmei Odawara Earthquake outbroke in early morning of 23th August, 1782, and damages of building and houses took place at the castle town of Odawara and its vicinity, 80km SW of Tokyo. USAMI et al. (1984) had newly found out several kind of old documents and had made clear that intensity V or more was felt within the circle with the radius of 45km around Odawara. No reliable record of tsunami had been found out, and it had been considered that no tsunami was accompanied. But in the recent few years two old documents with tsunami disaster records at the fishery harbor of Ajiro in Atami City, 100km SW of Tokyo, were newly found out, inundation height was surveyed as 4 meters, and tsunami magnitude was estimated as m=1. The magnitude of the earthquake was judged by comparison of magnitude of tsunami, and areas of intensities III-IV, V, and VI with the 1982 Urakawa-Oki Earthquake-Tsunami (M=7.1, tsunami magnitude m=0), and was estimated as M=7.2. The Location of the epicenter was suggested to be situated at (35.1°N, 139.2°E), about 10km in the offing of Atami City.

著者

日野 貴之 都司 嘉宣

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.27-38, 1996-05-24 (Released:2010-03-11)

参考文献数

12

---

The Tonankai earthquake of December 7, 1944 occurred on the upper plane of the subducted slab located at the boundary between the Philippine Sea plate and the Eurasian plate. Recently it was pointed out that in the Kumano-coast region, the southeast part of the Kii Peninsula, the direction of the strike of the subducting Philippine Sea plate runs from southwest to northeast, while in the Ensyu-coast region, which is located between Nagoya and Shizuoka, the direction runs from east to west. We assumed that the dislocation of seismic faulting took place on the determined plate boundary and the dislocation is equal on each fault plane. As the plate boundary discontinues beneath the Ise Bay, two different fault planes were considered in our fault model: the one is located along the Kumano-coast on which the amount of slip is 200cm and its direction is N50°E, and the other is along the Ensyu-coast on which the amount of slip is 50cm and its direction is N50°E. We checked that the crustal movement calculated by our model is similar to the observed pattern. We carried out a numerical simulation of the tsunami based on our model. It was found that the sea level changes calculated by our model agreed well with the tide gauge records at four stations on the coast of the Ise Bay.

著者

都司 嘉宣

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.1, pp.35-51, 1982-03-25 (Released:2010-03-11)

参考文献数

10

---

In the evening of November 7, 1855, a large earthquake occurred beneath the sea off the southern coast of the Tokai district, central part of the Honshu Island. Recently more than fifty kind of historical documents were discovered, and we obtained much amount of knowledge about it. Most serious damages occurred in several villages on the coast in the vicinity of Hamamatsu City, where destruction of houses and gushing of sand were reported. Shock of intensity IV (in JMA scale) was experienced in the western part of Shizuoka Prefecture and at several cities on the east coast of the Kii Peninsula. After the occurrence of the earthquake, a small tsunami was generated, and was observed at the Shimoda Port near the tip of the Izu Peninsula, and at three ports on the east coast of the Kii Peninsula, where inundation height was one to two meters. The coast was upheaved near the mouth of the lake of Hamana where it had been subsided with the occurrence of the Ansei Tokai Earthquake of December 23, 1854. In contrast to that, the coast near the cape of Omaezaki was subsided with this earthquake, which had been upheaved with the Ansei Tokai Earthquake.The estimations of the location of the epicenter and the magnitude were made by adapting least mean square method to the formulae which give the relationship between the magnitude and the area of intensities IV, V, and VI. The location of the epicenter and the magnitude are estimated 34.5°N, 137.8°E and M=7.1, respectively.

著者

村瀬 圭

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.11-18, 2002-07-25 (Released:2010-03-11)

参考文献数

28

被引用文献数

1

---

The author investigated fractal structure of hypocentral distributions before the 2000 Tottoriken Seibu earthquake (MJ=7.3), by estimating temporal changes in the spatial fractal dimension D of the hypocenter distributions, and comparing these results with the seismic activity in and around the focal region. The correlation integral method and the running time-window technique were applied to the D-value calculation for the JMA Earthquake Catalogue data during the period of January 1983 -February 2001. The results obtained are summarized as follows; (1) The D-value decreased drastically prior to the main shock in and around the focal region. The precursory durations are estimated as 1-3 years, which may be different with different sizes of the time-window. (2) The D-value decrease must be caused by hypocenter clusterings, or unusual seismic activity, which occurred over the wide area in and around the focal region. (3) Consequently, temporal variations in the D-values associated with a large earthquake may be effective as a precursor to the earthquake.

著者

三浦 大助 幡谷 竜太 阿部 信太郎 宮腰 勝義 井上 大榮 二階堂 学 橘 徹 高瀬 信一

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.33-45, 2002-07-25 (Released:2010-03-11)

参考文献数

26

被引用文献数

3

---

Co-seismic faulting activity during the last three hundred thousands years of the Ichinose fault group, in the southern part of the 150km long Itoigawa-Shizuoka Tectonic Line active fault system, central Japan, was appraised. The Ichinose fault group consists of the mainly two distinct arcuate reverse fault traces bulged toward the east (frontal) and west (behind) directions. We conducted a trench excavation at the Nakano site across the behind fault, where the detailed geological and chronological information for the last ten thousands years was absent. The excavation resulted in evidences for the latest, at least two surface-rupturing events. The events were present sometimes between 665 and 1275 cal.y.B.P. and between 3355 and 4810 cal.y.B.P. The timing of the penultimate event is coincident with the previously estimated latest event on the frontal fault (3, 990-6, 270 cal.y.B.P.). The recurrence time and slip rate between these two events is approximately estimated as 3, 200 years and 0.9-1.8mm/yr in dip-slip, respectively. In comparison with a slip rate estimated from the geomorphological characteristics, the dip-slip rate from our excavation result is coincident well.A reappraisal of geomorphological reference deposits and a result of the seismic investigation study suggest that the total deformation rate of the Ichinose fault group is 3.5-3.7mm/yr (possibly up to 5.0mm/yr) and it becomes to increase in recent several ten thousands years. While the deformation rate suggests that the co-seismic faulting activity at the Ichinose fault group as a whole is ranked as the one of most active faults in Japan, however, it is smaller than that of 6.3-8.3mm/yr estimated previously from the gravimetric and numerical analyses.

著者

遠田 晋次 三浦 大助 宮腰 勝義 井上 大栄

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.4, pp.445-468, 2000-03-25 (Released:2010-03-11)

参考文献数

39

被引用文献数

1 3

---

The Itoigawa-Shizuoka Tectonic Line (ISTL) in central Japan is a complex 150km-long fault system consisting of north-trending east-dipping reverse, northwest-trending left-lateral strike-slip, and north-trending west-dipping reverse faults. To help to resolve segmentation and to estimate the magnitude of future shocks on the ISTL, we conducted four trench excavations across the Hakushu fault, the Shimotsuburai fault, and the Ichinose fault group in the southern part of the ISTL, where no paleoseismological data for the surface faulting had been available. On the trench walls at the Hakushu fault, we found the evidence for the most recent surface-rupturing event occurring sometime between 6, 650 and 7, 000cal. y. B. P. (BC 4700-BC 5050) with approximately one meter of coseismic slip. On the Shimotsuburai fault, we exposed evidence for three events at two trench sites. The low-angle thrust faults and associated sediments record the most recent and the penultimate events occurring between 1, 370 and 2, 500cal. y. B. P. (AD 580-BC 550), and between 7, 940 and 8, 430cal. y. B. P. (BC 5990-BC 6480), respectively. Vertically offset terrace gravels indicate the dip-slip rate of the Shimotsuburai fault to be about 0.5mm/yr during the past 22, 000 years. We also found evidence for the most recent two surface-faulting events on the scarp of the frontal fault of the Ichinose fault group. The most recent event, which accompanied a coseismic slip of 1.8-2.2m, is inferred to have occurred sometime between 3, 990 and 6, 270cal. y. B. P. (BC 2040-BC 4320). The penultimate event, which appears to have a coseismic slip of 2.1-3.0m, is constrained to have occurred between 9, 520cal. y. B. P. (BC 7570) and 10, 930y. B. P. The recurrence time and slip rate are roughly estimated as 5, 000 years and 0.5mm/yr, respectively. Regarding the long elapsed time since the most recent events, the Hakushu fault and the Ichinose fault group have accumulated enough strain to produce surface-rupturing earthquakes today. Based on such long recurrence times and lower slip rates on the southern ISTL relative to the central ISTL, we suggest that multiple segment ruptures of the central and southern ISTL are unlikely to have occurred during the past 10, 000years. However, partial synchronization of rupture timings for the central and southern ISTL might have occurred around 7, 000y. B. P. though. To evaluate the fault activity in the southern ISTL more precisely and to consider fault interaction with central ISTL, we still need to investigate other fault strands of the southern ISTL, and to gather more paleoseismic evidence.

著者

宮岡 一樹 横田 崇

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.65, no.2, pp.205-218, 2012-12-10 (Released:2013-02-05)

参考文献数

28

被引用文献数

1 6

---

The Japan Meteorological Agency has deployed strain-meters in Shizuoka, Aichi, and Nagano Prefectures, aiming to detect a slow slip phenomenon that is expected to occur just before the anticipated great earthquake of M8 class at the plate boundary. In this paper we propose a stacking method in which data at different stations are added according to the following procedure. First, the observed waveform at each station is normalized by the noise level. Then, the normalized wave form is stacked one by one in the order of the magnitude of the signal to noise ratio, by reversing the polarity considering an assumed source location, if necessary, so as the signal to be all positive. This stacking procedure is stopped when the synthesized signal to noise ratio of the stacked waveform becomes the maximum. Members in the optimum data set that gives the largest signal to noise ratio become different if the location of the assumed source is different. It is shown that the signal to noise ratio of the stacked waveform obtained by this method is enhanced 2.3 times of that of the most favorable individual data. A slow slip event as small as Mw 5.0 would be detected if it occurs within the source area of the anticipated Tokai earthquake. We think the stacking method is applicable not only to the strain-meter data, but also to the GNSS and tilt-meter data and such an extension of the method may be effective to detect rising of magma beneath volcanoes.

著者

伊藤 潔 渡辺 邦彦

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.30, no.1, pp.43-54, 1977-04-05 (Released:2010-03-11)

参考文献数

10

被引用文献数

1 3

---

Focal mechanisms of very shallow earthquakes on the west and the southwest of Lake Biwa have been determined by smoothing the first-motion radiation pattern and by individual solutions. Published focal mechanism solutions are also used to examine the tectonic stress which generates earthquakes in the north Kinki district. Along the west coast and the east coast of Lake Biwa seismic active regions of very shallow earthquakes occur and in Lake Biwa seismic activity is very low. Most of mechanism solutions in these active regions are reverse faultings with the maximum pressure axes in the direction of nearly east-west or southeast-northwest. In other regions of north Kinki district and west Chubu district dominant type of faulting is strike-slip with the same pressure direction. These types of faulting from earthquake focal mechanism solutions agree well with those of tectonic active faults developed in this area. The reverse faulting as well as the high seismicity on the both coasts of Lake Biwa is consistent with the subsedence of Lake Biwa which has been continued throuth the Quaternary.

著者

吉田 明夫 古屋 逸夫

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.45, no.1, pp.71-82, 1992-03-24 (Released:2010-03-11)

参考文献数

24

被引用文献数

1 1

---

Pattern of occurrence of precursory phenomena differs significantly in various respects for each earthquake. It is not the same even for earthquakes occurring in adjacent areas. Amplitude of precursory change is not necessarily large at nearer sites, and that it is very often larger than that of coseismic change. These features suggest that precursors occur locally at weak points or stress concentrating sites. It seems that desrimination of earthquake precursors from noises which are not directly related to the occurrence of earthquake is intrinsically difficult. Whether some observed change is a precursor or not may be expressed in a probabilistic way. When various kinds of anomalous change are observed at the same time, the possibility that they are true precursors will be increased. It is important to elucidate the occurrence mechanism of precursors in relation with structure and its change of seismogenic field.

著者

細野 耕司 西 政樹 吉田 明夫

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.59, no.1, pp.29-37, 2006-08-31 (Released:2013-08-05)

参考文献数

22

---

We investigated changes in the depth distribution of aftershocks of three large inland earthquakes in Japan, the 2000 western Tottori Prefecture Earthquake of M 7.3, the 2003 northern Miyagi Prefecture earthquake of M 6.4, and the 2004 mid Niigata Prefecture earthquake of M 6.8. For all of them we found that the seismogenic layer extended to the deeper and shallower zones after occurrence of the main shock. The shallow and deep activities decayed faster than the activity in the intermediate depth. This suggests that when stress is built up very fast, brittle fractures can occur in the zone where increase of stress is usually relaxed through a ductile process. Our results also show that a fault motion could extend to the outside of the seismogenic zone estimated from the background seismicity, which should be taken into consideration in the hazard assessment.

著者

多田 堯 橋本 学

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.41, no.2, pp.259-262, 1988-06-25 (Released:2010-03-11)

参考文献数

13

---

A fault of the 1918 Omachi earthquake (M=6.5) have been estimated based on the vertical crustal movement associated with the earthquake. The 1918 Omachi earthquake was the largest earthquake which had ever occurred near the northern part of the Itoigawa-Shizuoka Tectonic Line (ISTL). The estimated fault is a high dip angle reverse fault with left lateral strike slip component. The fault plane strikes to the N-S and dips to the east. The fault model suggests a possibility that the Chikuma Mountains (Northeastern Japan) thrust against the Matsumoto Basin (Southwestern Japan).

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.49, no.1, pp.55-63, 1996-05-24 (Released:2010-03-11)

参考文献数

14

---

Edo (now Tokyo) area suffered serious damage from a great earthquake in 1855, Ansei era. The earthquake is conceived to be essencially an inland earthquake, although the crustal movement might be extended to the bottom of Tokyo Bay. Whether or not a tsunami was generated by the earthquake is investigated basing on historical documents. Although, no tsunami damage was reported, it seems likely that some phenomena associated with a tsunami, which was too small to be observed obviously, took place. Numerical experiments on three fault models, that are supposed on the upper surface of the subducted Philippine sea plate, are made in order to see possible tsunami generation in Tokyo Bay. Maximum double amplitudes of computed tsunamis amount to 10 to 20cm which are in harmony with historical documents. It may be one of the reasonable interpretations for the source model of the earthquake, therefore, that the Ansei Edo earthquake occurred on the plate boundary. Water oscillations induced by the seismic acceleration in a tank or a pool are numerically investigated. It becomes apparent that such water oscillation is largely controlled by the resonance in the reservoir.

著者

石橋 克彦

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.36, no.2, pp.169-176, 1983-06-25 (Released:2010-03-11)

参考文献数

17

被引用文献数

3

---

TOKYO ASTRONOMICAL OBSERVATORY (1981) and USAMI (1975) are listing a historical destructive earthquake of magnitude 6.7 that occurred in the Aizu province in northeast Japan on November 7, 1433. However, the only basis of the earthquake is the total collapse of the Todera-Hachimangu Shrine due to violent earthquake motion which is described in an old book named “Todera-Hachimangu Ryakki Nagacho”. In this paper reliability of the description has been examined and unreality of the earthquake has been concluded.“Todera-Hachimangu Ryakki Nagacho” is a compiled material written more than 150 years after 1433 and, so, the reliability of its description on older times is generally low. On the other hand, there is another historical document concerning the Todera-Hachimangu Shrine called “Todera-Hachimangu Nagacho”, which is a yearly record mainly on the shrine's ceremony and local happenings written year by year. Its original copy covering most part of the period between 1350 and 1635 is preserved in the shrine. This is the most reliable and basic material concerning the Todera-Hachimangu Shrine and its vicinity for the 14th to the 16th centuries.In “Todera-Hachimangu Nagacho” there is no record about the collapse of the shrine in 1433. On the contrary, it contains a few reliable descriptions which conflict with seismic disaster in the province at that time. Thus, the collapse of the shrine due to an earthquake in 1433 has proved to be not an actual fact. Therefore, the 1433 Aizu earthquake of magnitude 6.7 should be deleted from Japanese historical earthquake catalogs.

著者

島津 康男

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.7, no.3, pp.195-196, 1954-10-30 (Released:2010-03-11)

著者

湯村 哲男 広野 卓蔵 和達 清夫

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.23, no.2, pp.99-121, 1970-06-28 (Released:2010-03-11)

参考文献数

18

---

Spatial distribution of earthquake foci for the period from 1926 to 1968 in and near Japan were expressed in 16 maps each for a layer of 20-40km in thickness lying between 0 to 600km in depth. The maps show definitely the boundary lines and centers of local activities distinguishable in seismicity from each other. We named them seismic blocks. The centers of the shallow seismic blocks which crowd in a zone along the west side of the Japan trench can be traced down to 600km in depth. At first such centers move with increasing depth toward two junction areas of the island arcs of Kuril, NE-Japan and Izu-Bonin, that is, the Hokkaido and the Kwanto districts. From there they continue sinking to north for Hokkaido and to west for Kwanto making a dipping angle of 30°. Then their directions change abruptly by 90° at a depth of about 300km. From North Hokkaido one branch of the locus of the center goes into the Okhotsk Sea and the other into the Japan Sea along the coast of Primorye. On the other hand, the locus of the block center moving toward the west Kwanto turns to the south at that depth under Gifu Pref. for the Shikoku Basin, although a shorter branch goes northward into the Japan Sea. It is notable that few deep shocks occur in the middle of the Japan Sea. Considering the other geophysical and geological phenomena such as (1) the negative zone of isostatic anomaly of gravity lying along the Japan trench branches out to the junction areas in land, (2) the movement of the triangulation stations for the last 60 years or so amounts to about 3m to the north at Aomori Pref. in comparison with the Kui Peninsula, showing that two forces are acting in the respective areas in opposite directions, (3) the axis of mountain ranges made of metamorphic rocks which encounter the locus of the block center in Hokkaido and Central Honshu underwent severer bending, we conclude that the locus of the seismic block center expresses the location of the mantle current coming from the Pacific. itself.

著者

和達 清夫 高橋 末雄

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.27, no.1, pp.42-56, 1974-03-30 (Released:2010-03-11)

参考文献数

23

---

In the present paper the underground structure peculiar to Japan and its neighborhood is dealt with, based on the seismic activity in Japan and neighborhood, especially taking account of the fact that each of the seismic activity area and the seismic inactivity area shows in the subterranean space its respective space, and adding the authors' investigational result to the fruits of researches hitherto.Main results of the present paper are:(1) The seismic activity area was divided into 3 zones: the shallow earthquake zone (particularly the existence of “a thick shallow earthquake zone”), the joint earthquake zone and the deep earthquake zone.(2) A concept that the seismic activity zone can be regarded as “the crust” has been proposed.(3) From the discussion of the travel time residual and the area of abnormal distribution of seismic intensities, the values of Low V and Low Q of the seismic inactivity area were obtained, and in particular the stronger point of that property was found at a comparatively small depth in the underground on the continental side along the volcanic front.(4) The mantle flow in Japan and neighborhood is assumed to be composed of its main flow (along the deep earthquake zone) which flows descending from the Pacific side to the continental side and from east to west, of a weak flow northward in the offing of Tosa and in Enshu-nada, and of flows eastward and southward from the direction of the Sea of Japan.(5) In general, where the mantle flow ascends, there exist Low V and Low Q and the area is related to volcanic activities, and where the flow descends, the area is related to the seismic activity area.(6) The joint earthquake zone is an area of the strongest seismic activity, and is closely related with large-scale earthquakes.

著者

村内 必典

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.5, no.4, pp.157-163, 1953-03-30 (Released:2010-03-11)

参考文献数

3

---

A new volcanic isle near the Bayonnaise Rocks, 450km south of Tokyo was discovered by the crew of a Japanese fishing boat, the No. 11 Myojin Maru, on Sept. 17, 1952. The exact location of the new volcanic isle was given by the stuff of oceanography, Tokyo Fisheries University, at 31°56′. 8N. and 139°59′. 5E. and it belongs to Fuji volcanic belt. According to newspapers, the pyroxysmal eruption as well as lava effusion were observed and the radius of the newly-extruded lava isle was 100-150 meters. Also it was reported that since Sept. 21, intermittent severe explosions were observed. On Sept. 23, by the courtesy of Tokyo Fisheries University we could approach the isle and observed explosios five times in one day on board the Shin' yo Maru, a 230-ton training ship of the University. The newly-formed isle had already disappeared under the sea but we could find the position of the undersea crater because the sea water, there, was remarkably yellowish. On the following day, Sept. 24, the No. 5 Kaiyo Maru, a 211-ton oceanographical survey boat of the Maritime Safety Board was missing near the new undersea volcano and all 31 on the ship, including a crew of 22 and nine experts on geology and oceanography were believed to have met tragic end. It was reported afterwards by a survey ship of MSB that a volcanic isle, 300-400m width, was pushed up again and steamed white vapour. The newly-ejectd pumice is quartz-andesitic. The energy of one explosion, occurred on Sept. 23, was estimated to be about 1018 erg. by the writer.

著者

島崎 邦彦 竹内 均

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.23, no.1, pp.41-48, 1970-04-28 (Released:2010-03-11)

参考文献数

9

---

The Chandler wobble can be considered to be a succession of free damped nutations of the earth excited by some unknown causes. Bearing this in mind, we apply a linear filtering theory of multichannel time series to the analysis of polar motions. Designing a 2-channel prediction error operator, we calculate the prediction error time series y1(t) and y2(t) corresponding to the x1(t) and x2(t) terms in polar motions. The occurrence of large earthquakes is well correlative with abrupt changes of the prediction error. To clarify this relation, prediction error changes D(t)=[{y1(t)-y1(t-1)}2+{y2(t)-y2(t-1)2}]1/2 are calculated and shown in Fig. 3. It is suggested that Earthquakes excite the Chandler wobble. In order to confirm this, we must calculate the excitation function from the occurrence mechanism of each earthquake. It will be the subject for a future study.

著者

島崎 邦彦

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.25, no.1, pp.16-23, 1972-07-30 (Released:2010-03-09)

参考文献数

5

---

A statistical method of detecting unusual seismic activities has been developed. Stationary and random earthquake occurrence is assumed throughout the present study. The probability for earthquakes of which the number is larger (smaller) than m to occur during a time-interval S when n earthquakes occurred during a preceding interval T is calculated. It turns out that such a probability is expressed by a negative binomial distribution. When this probability is smaller than a given significance level, the occurrence of more (less) than m earthquakes during S can be recognized to be unusual.The number of observed micro-earthquakes at the Shiraki Microearthquake Observatory, having the same S-P interval, is analysed. An unusual seismic activity is detected 20 days before the occurrence of the Mivoshi Earthauake Swarm of 1970.