著者

岩田 貴樹

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.133-141, 2009-07-31 (Released:2013-11-21)

参考文献数

70

被引用文献数

3

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In recent years, many researchers in seismicity analysis have focused on earthquake triggering or fault interactions.To evaluate these phenomena quantitatively, models for the spatio-temporal distribution of seismic activity have been constructed. This review paper introduces two important models : the ETAS (epidemic-type aftershock sequence) model developed by Y. Ogata and a seismicity model based on rate- and state-dependent friction law by J. Dieterich. The former is a pure statistical model, while the latter includes some physical parameters in its derivation.These two models now play separate role in probabilistic earthquake forecasting. For further achievement in the probabilistic earthquake forecasting, the integration of the two contrasting models should be considered. Further development of models would give new insights into earthquake occurrence.

著者

岩田 貴樹 吉田 圭佑 深畑 幸俊

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.128, no.5, pp.797-811, 2019-10-25 (Released:2019-11-15)

参考文献数

49

被引用文献数

10

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In order to understand crustal dynamics, including the occurrence of earthquakes and the development of mountain ranges, it is important to estimate the stress state in the Earth's crust from observed data. This paper reviews stress tensor inversion techniques using seismological data. The techniques were originally applied to a dataset of slip orientations taken from focal mechanisms. Subsequently, other techniques, which use P wave first-motion polarities or centroid moment tensor (CMT) solutions, were developed. This paper clarifies the principles and basic hypotheses, on which each technique is built. In the techniques using focal mechanisms and P wave first-motion data, the Wallace–Bott hypothesis that a fault slips in the direction of maximum resolved shear stress plays the principal role; basically, we search for a stress state that satisfies observed data on the basis of the Wallace–Bott hypothesis. On the other hand, the stress inversion technique using CMT data is not based on the Wallace–Bott hypothesis; instead, it is assumed that stress released by earthquakes is proportional to the stress tensor in the region surrounding the hypocenter. The characteristics and advantages of these techniques are also compared from physical and pragmatic viewpoints. It would be valuable to further improve these techniques, as well as to compare their performance using synthetic and actual data to clarify the differences and advantages of their characteristics in more detail.

著者

岩田 貴樹 中西 一郎

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.51, no.1, pp.51-59, 1998-07-03 (Released:2010-03-11)

参考文献数

29

被引用文献数

1

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We investigate the correlation between the occurrence of earthquake and the earth tide by analyzing the tail of the Matsushiro earthquake swarm that is recorded by the Matsushiro Seismic Array System during the period of November 1984 to December 1994. The seismic activity of the tail exhibits many bursts of earthquakes. We remove the bursts, because they affect our aim to investigate whether the correlation exists or not. We use the tidal strain data recorded by EW- and NS-component extensometers located in Matsushiro Seismological Observatory, Japan Meteorological Agency. We apply Schuster's test to the Matsushiro earthquake swarm. The hypothesis that the earthquakes in the swarm take place randomly is tested and is rejected for the EW-component. The earthquakes tend to occur when the tidal strain of the EW-component is in a compressional state. This state is consistent with the stress field at Matsushiro obtained by using focal mechanisms or in situ stress measurements.We also investigate the spatial variation of the correlation. A significant correlation is seen in the northwestern part of Matsushiro. The largest earthquake with magnitude of 5.2 occurred on 30 December 1986 near the region. We further investigate the temporal variation of the correlation in this region. The correlation becomes high right after the occurrence of the largest earthquake, whereas the correlation is low before the occurrence of it. This suggests that the strain changes caused by the largest earthquake make the correlation high in this region.