地震 第2輯
Online ISSN : 1883-9029
Print ISSN : 0037-1114
アスペリティの破壊に伴うb値の変化
東北日本太平洋下のb値の時空間分布
弘瀬 冬樹中村 綾子長谷川 昭
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2002 年 55 巻 3 号 p. 249-260

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We found a clear b-value variation associated with the rupture of asperities based on investigations of spatial and temporal distributions of frequency-magnitude relation for earthquakes in the northeastern (NE) Japan subduction zone. We used the Tohoku-University earthquake catalogue in the period from January 1, 1981 to October 3, 2001 after correcting artificial magnitude shift and removing artificial events. Spatial distribution of b-value is compared with the locations of asperities estimated on the plate boundary east off NE Japan. Estimated b-value decreases with increasing depth. Anomalously high b-values are observed in two areas off-Iwate and off-Fukushima regions, and asperities do not intrude into them. Temporal variation of b-value for presently analysed six asperities shows a remarkable increase in b-value after the rupture of each asperity. Then the b-value decreases gradually. These observations suggest that b-value reflects the stress change occurring in the vicinity of the asperities.

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