著者

神田 克久 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.58, no.3, pp.177-198, 2005-12-25 (Released:2010-03-11)

参考文献数

41

被引用文献数

2

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The inversion analysis using seismic intensity data is carried out to investigate the source characteristics of major damage earthquakes that have occurred in the sea off Miyagi Prefecture since 1861. It can evaluate short-period seismic wave radiation zones (SPRZ) on an earthquake fault plane. Comparison of the result of the inversion analysis for the May 26, 2003 Off-Miyagi earthquake with the source region deduced from reported aftershock activity verified sufficient accuracy of the present method. We compared the location of SPRZ among analyzed earthquakes and identified the kinds of earthquakes. The SPRZ of the June 12, 1978 earthquake was located near the seacoast of Miyagi Prefecture, adjacent to the large slip area obtained from the waveform inversion by Yamanaka and Kikuchi (2004). The SPRZ of the November 3, 1936 and July 27, 1937 earthquakes were located on the south of that of the 1978 earthquake, which may indicate that the rupture area of the 1936 and 1937 earthquakes were different from that of the 1978 earthquake. On the contrary, location of the SPRZ of the February 20, 1897 earthquake was similar to that of the 1978 earthquake. The SPRZ of the August 5, 1897 earthquake was located near the Japan Trench, while that of the April 23, 1898 earthquake was just beneath the coast of northern Miyagi Prefecture, suggesting that it was an intermediate-depth intraslab earthquake the same as the May 26, 2003 event. The location of the SPRZ of the 21 October, 1861 earthquake was mostly consistent with that of the 1978 earthquake. We consider that the 1861 earthquake should have occurred on the upper boundary of the subducting Pacific plate, not in the inland of northern Miyagi Prefecture.

著者

神田 克久 武村 雅之

出版者

公益社団法人 日本地震工学会

雑誌

日本地震工学会論文集 (ISSN:18846246)

巻号頁・発行日

vol.7, no.2, pp.68-79, 2007 (Released:2010-08-12)

参考文献数

20

被引用文献数

6 6

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最近、高密度の地点で多くの地震のデータが得られるようになった計測震度をデータベース化して、短周期地震動に関する距離減衰特性や地点による揺れやすさの分析を行った。関東平野では、揺れやすさの尺度である相対震度についてマグニチュード (M) 依存性がみられ、埼玉東部などの低地ではM が大きくなると相対震度が大きくなり、千葉県南部などの丘陵地では逆の傾向が見られた。得られた震度の距離減衰特性や相対震度を用いて、1923 年大正関東地震と1703 年元禄地震の震度インバージョン解析を行い、短周期地震波発生域を求めた。大正関東地震は三浦半島を挟んで2 箇所に短周期地震波発生域があり、その重心は別に求められているアスペリティ (すべりの大きな領域) の終端部にあたる。元禄地震の短周期地震波発生域は、神奈川県から房総半島南部までは大正関東地震に類似し、加えて房総半島南東沖に広がっていることが分かった。

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.57, no.2, pp.153-170, 2004-12-27 (Released:2010-03-11)

参考文献数

36

被引用文献数

4

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An inversion analysis has been developed to evaluate short-period seismic wave radiation zones on an earthquake fault plane using seismic intensity data. It is a useful method for historical earthquakes, for which neither strong motion nor tsunami data have been observed by instruments. Since the accuracy of the present method is verified by using ground motion waveforms synthesized by the stochastic Green's function method, it is concluded that the effects of directivity of the fault rupture process and the radiation pattern on seismic intensity distribution can be neglected in the frequency range that is effective for seismic intensity. The present method is applied to great earthquakes that have occurred since 300 years ago in the Nankai Trough seismogenic zone in southwestern Japan, where the Philippine Sea plate is subducting beneath the Eurasian plate. The reliability of their solutions is discussed based on a sensitivity analysis. It is noted that short-period seismic wave radiation zones are often adjacent to large slip areas, termed asperities, but don't always overlap them. Furthermore, they are sometimes located where fault rupture has stopped. Short-period seismic waves are not always radiated from the same zone. For example, fault zones in the Enshu-Nada Sea, the Kumano-Nada Sea, the Kii Channel and the Kochi seacoast have radiated short-period seismic waves at every event, but whether or not short-period seismic waves were radiated in the interior of Suruga Bay, off the Shiono Cape and off the Muroto Cape varied with the events. It is also concluded that crustal structures such as subducted seamounts and subducted ridges take an important role of radiation of short-period seismic waves.

著者

髙橋 利昌 浅野 彰洋 大内 泰志 川崎 真治 武村 雅之 神田 克久 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.60, no.3, pp.193-217, 2008-02-15 (Released:2013-08-20)

参考文献数

40

被引用文献数

1 1

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The major earthquakes of M=7 class, so-called Geiyo earthquake, have occurred in the subducted slab of the Philippine Sea plate under Aki-nada and Iyo-nada sea. The upper surface of the Philippine Sea plate is located in the depth from 40-45km in this region. Five Geiyo earthquakes can be found in 1649, 1686, 1857, 1905, and 2001 since 17th century. Magnitudes M of the older 4 events were larger than 7, while that of the last one is 6.7 in JMA (Japan Meteorological Agency) scale. Magnitudes and locations of focal regions of them were redetermined from seismic intensity data by the method of an attenuation curve fitting and of the seismic intensity inversion. Optimal magnitudes of old events were obtained between 6.7 to 6.9. This results show the old 4 events have almost the same magnitude as the 2001 event. One of the possible reasons why the former values were overestimated is that the empirical relation between magnitude and isoseismal area from inland shallow earthquakes was applied to determine the magnitude of the historical intraslab events such as Geiyo earthquakes.

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

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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.