2003年宁河地震序列特征的分析

Analysis on the characteristics of Ninghe earthquake sequence occurred in 2003

2003年4月天津宁河地震序列的发生,使天津市大部分地区明显有感,震中烈度Ⅴ度。分析结果表明,宁河地震序列从空间、时间、强度分布等方面均具有震群性质的基本特征,但余震贫乏、序列的频度和强度衰减快,不同于传统意义的震群;宁河地震序列发生的位置靠近唐山余震区的西南端,又具有相对独立的空间特征;3次4级左右地震的震源机制解不一致,可能与震源区构造复杂有关,是震源区调整让位的一种表现形式,说明震源区应力仍在调整中。

Ninghe earthquake sequence occurred in April of 2003 was clearly felt by the majority area of Tianjin municipality and the epicentral intensity is V. The analytical results indicate that Ninghe earthquake sequence has the basic characteristics of earthquake swarm in the distribution of space, time and intensity. However, it is different from the traditional earthquake swarm because it had only a few aftershocks and its frequency and intensity attenuated rapidly. Although Ninghe earthquake sequence occurred at the southwestern end of Tangshan aftershock zone, it has the spatial characteristics of its own. The focal-mechanism solutions of three M≈4 earthquakes are not consistent, which might be related to the complicated tectonics in the focal region. It is a kind of manifestation of the stress adjustment and variation in the focal region, indicating that the stress in the focal region is still being adjusted.