著者

武村 雅之 池浦 友則 工藤 一嘉 大沼 啓人

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.2, pp.193-200, 1994-08-14 (Released:2010-03-11)

参考文献数

15

被引用文献数

4

著者

武村 雅之 池浦 友則

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.4, pp.351-364, 1995-01-24 (Released:2010-03-11)

参考文献数

28

被引用文献数

2

---

Source process of the 1923 Kanto earthquake is investigated from descriptions of about 200 personal experiences near the focal region. The experiences of the strong shaking without a preliminary tremor in and around Odawara city and of the second strong vertical-shaking in the Miura Peninsula suggest that two major subevents occurred during the Kanto earthquake. We infer that the first subevent occurred under Odawara city and the second under the Miura Peninsula. The time interval between the two subevents is estimated to be about ten second from the interval between two prominent phases on an old strong-motion vertical record at Gifu observatory (Δ=226km), which was observed by a seismograph with a natural period of about 1sec. The above result of the two subevents can also explain the best documented account on the earthquake ground motion by Prof. Imamura at the Imperial University of Tokyo.

著者

武村 雅之 池浦 友則 野澤 貴

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.425-444, 2000-03-25 (Released:2010-03-11)

参考文献数

55

被引用文献数

1

---

Magnitudes for the 1923 Kanto earthquake and its major aftershocks were determined in JMA (Japan Meteorological Agency) scale. The original definition of the JMA magnitude is a magnitude that is calculated by the Tsuboi's formula from the maximum amplitudes in horizontal components of seismograms obtained by the regional observation network of JMA. The used seismograms were recorded by standard seismographs, which were the displacement type with the natural period of about 5s and damping ratio of about 8. However, the seismometers had not been yet standardized before 1925 and various types had been used whose instrumental responses were quite different from those of the standard seismographs. The purpose of the present study was that the JMA magnitudes of the 1923 Kanto earthquake and its major 3 aftershocks were determined in consideration of the difference of the instrumental responses. Fortunately, unsaturated seismograms by the Imamura's type strong motion seismographs (displacement type) have been preserved at 7 stations of JMA. The natural period and damping ratio of each seismograph have been evaluated from the free oscillation records preserved at each station. The records for the main shock and aftershocks were digitized and corrected in the instrumental responses to calculate the seismograms with the instrumental response of the standard seismograph of JMA. After that, the maximum amplitudes were measured on the corrected records and the magnitude was determined for each earthquake following the definition of the JMA magnitude. The determined JMA magnitude was 8.1±0.2 for the main shock. All the results were consistent within the difference of 0.2 with the customary results, which were determined from the uncorrected amplitude and seismic intensity data. The standard deviations were smaller than 0.2 for all the events, which shows higher reliability of the present results, comparing with the past ones.

著者

武村 雅之 野澤 貴 池浦 友則

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.317-333, 1999-10-20 (Released:2010-03-11)

参考文献数

30

被引用文献数

2

---

Nozawa et al. (1995) proposed a source model with two big subevents of the same seismic moment for the 1923 Kanto earthquake (M=7.9), through the simulation of the records by the Imamura-type strong motion seismograph (displacementmeter) at Gifu observatory. This model was named Model I in the present study. The first subevent of Model I is located under the Odawara city, having a fault plane with the strike of N290°E and the rake angle of 162°. This fault has much strike slip component, which is consistent with the focal mechanism solution by KANAMORI (1971). However, the direction of the strike is not compatible with the trench axis of the Sagami trough. The second subevent occurring 12s after the first subevent is located under the Miura Peninsula. The fault of the second subevent, having much dip slip component, well explains the geodetic data. Recently, the seismograms by the Imamura-type strong motion seismographs at Sendai (Mukaiyama) observatory and Yamagata observatory were examined and the instrumental responses of the seismographs were revealed. Crustal structure from source to stations was estimated in the present study so as to explain the observed Love and Rayleigh waves at Sendai (JMA) and Yamagata observatories from the recent events occurring near the focal region of the 1923 Kanto earthquake. However, Model I failed to explain the records of the 1923 Kanto earthquake at Sendai (Mukaiyama) and Yamagata observatories, using the obtained crustal structure. Then, we revised Model I to explain these records, in consideration of the newly determined focal mechanism solution by Lallemant et al.. (1996) and iso-depth contour of the upper boundary of the Philippine Sea plate by Ishida (1992). The first subevent of the revised model (Model R) has a fault plane with the strike of N321°E and the rake angle of 128°, and the twice of seismic moment of the second subevent. The direction of the fault strike of the first subevent is parallel to the trench axis of the Sagami trough, while the fault plane of the second subevent is the same as Model I. Model R succeeded in explaining not only the records at Sendai (Mukaiyama) and Yamagata observatories but also those at Gifu observatory in the period range from 2 to 20s. This shows the fault model, being in agreement with the geometry of subduction zone along the Sagami trough, is better to explain the seismic records observed in Japan.

著者

野澤 貴 武村 雅之 池浦 友則 山中 浩明

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.48, no.3, pp.331-340, 1995-11-25 (Released:2010-03-11)

参考文献数

30

被引用文献数

1

---

Records observed at Gifu observatory by an Imamura's type strong motion seismograph are one of the most useful records in Japan to investigate a source process of the 1923 Kanto earthquake (M=7.9). It is because amplitudes of the records are not saturated in EW and UD components, instrumental response of the seismograph has been clarified, and many records due to recent events occurred near the focal region of the Kanto earthquake have been obtained by more accurate seismographs at the same site. In the present study, a source process of the 1923 Kanto earthquake is elucidated through a simulation of the records using the normal mode theory in the period range from 2 to 20s. First, a crustal structure from the source to the station is estimated so as to explain dispersive characteristics of Love waves observed at Gifu observatory for the recent events, and their records are simulated to confirm a validity of the estimated crustal structure. Secondly, the records from the Kanto earthquake are simulated using the obtained crustal structure to deduce the source process of this event. According to KANAMORI (1971), a macroscopic faulting is a reverse right-lateral fault on a plane dipping 34° towards N20°E, whose slip has much strike component. If two big subevents with the same focal mechanism obtained by KANAMORI (1971) and with a time interval of about 12s are assumed on the fault plane, the observed records can be well explained. The first subevent is located under the Odawara city and the second one under the Miura Peninsula. The focal depth of the second event is 15 to 35km being deeper than that of the first event, which is 5 to 25km in depth. The seismic moments and the rise time are assumed 2.5×1027 dyne-cm and 5s for both the events respectively. On the other hand, if the focal mechanism of the second event is dip slip type, the observed records can be also explained well, even though the focal depth of the second subevent is the same as that of the first one. This model is consistent with a slip distribution on the fault plane obtained from geodetic data.

著者

丹羽 正徳 山中 浩明 武村 雅之 池浦 友則

出版者

一般社団法人日本建築学会

雑誌

学術講演梗概集. B, 構造I (ISSN:09150129)

巻号頁・発行日

vol.1993, pp.175-176, 1993-07-25