2007年云南泞洱M_S6.4地震前滇西南地区震源动力学参数时空变化特征

本文根据在近震源条件下,利用Brune模式,由昆明数字遥测地震台网观测到的波形资料,测定了2005年1月至2007年5月期间滇西南地区98次ML≥2.5地震的震源动力学参数,分析了在2007年6月3日云南泞洱MS6.4地震前视应力和拐角频率的时空变化特征。泞洱MS6.4地震前,较高视应力(2.5×105 Pa以上)主要分布在红河断裂与无量山断裂之间,较低视应力(2.5×105 Pa以下)在空间的分布则显得较为分散、随机。较低的拐角频率(1.5Hz以下)集中分布在泞洱地震震中东北部的红河断裂与无量山断裂之间,随着频率的增大,分布范围逐渐向西南扩展,直到整个区域,较高的拐角频率(3.5Hz以上)则集中分布在泞洱地震震中西南部的区域内。从视应力和拐角频率的时间变化曲线看,泞洱MS6.4地震前滇西南地区视应力表现出了明显的升高变化过程;含ML3.6以上地震的拐角频率随时间的变化呈下降—上升—下降的复杂过程,ML<3.6地震的拐角频率呈趋势下降过程。

Temporal and Spatial Variation of Focal Dynamic Parameters in Southwest Yunnan before the 2007 M_S6.4 Ning′er Earthquake

On the condition of near-source,the Brune model is employed to determine the focal dynamic parameters of 98 ML≥2.5 earthquakes occurred in southwest Yunnan during January 2005 to May 2007 with seismic waveform data recorded by the Kunming Digital Seismic Network.Space-time variation characteristics of apparent and corner frequency before 2007 Ning′er MS6.4 earthquake in Yunnan Province on June 4,2007 are analyzed.The results show that before Ning′er MS6.4 earthquake,high apparent stress(higher than 2.5×105 Pa) mainly concentrated in the area from Honghe fault to Wuliangshan fault,distribution of low apparent stress(higher than 2.5×105 Pa) was random and dispersed.Small corner frequency(smaller than 1.5 Hz) mainly concentrated in the area from Honghe fault to Wuliangshan fault,the range of distribution enlarged continuously with the frequency increase until the entire area was covered.And big corner frequency(bigger than 1.5 Hz) mainly concentrated in the southwest of the epicenter area.The apparent stress showed an obvious increase process and the corner frequency including ML≥3.6 earthquakes showed a decrease-increase-decrease process,but the corner frequency for ML≤3.6 earthquakes showed a trend of decrease.