Delay times of surface wave for different station pairs in Yunnan region have been calculated by ambient noise method, using continuous waveform records of 46 stations in Yunnan network from Jan. , 2008 to Jan. , 2010. Then, surface wave velocity distribution of different times in the same window length is obtained by tomography method.According to experiment, we apply window length of three months as the stack days to obtain noise cross-correlation function with stable signal-to-noise ratio (SNR). The results show that the wave velocity structure changes obviously in different times. These changes include ① the wave velocity in Chenghai fault increases due to energy accumulation after the Wenchuan Ms8.0 earthquake in 2008; ② Panzhihua region is located on the boundary of velocity rising and dropping before the Panzhihua Ms6.1 earthquake in 2008; ③ Wave velocity increases in the hypocentral area before the Yaoan Ms6.0 earthquake in 2009, and reduces after the shock. Comparing with conventional time-dependent seismic tomography, ambient noise method using the fixed rays in different times can reduce the error caused by uneven distribution and hypocenter location errors.%本文利用2008年1月至2010年1月云南地震台网46个台站的连续波形资料,采用背景噪声方法计算云南地区不同台站对之间的面波延迟时间,通过层析成像方法反演得到不同时间段相同时间窗长的面波波速分布.根据试验,将三个月的时间窗长作为云南地区得到稳定信噪比的延迟时间的叠加天数.结果表明,不同时间段得到的波速结构具有明显的变化.这些变化表明:①2008年汶川8.0级地震后,程海断裂带波速增加,能量积累加剧;②2008年攀枝花6.1级地震前攀枝花地区处于速度升高和速度降低的分界带上;③2009年姚安6.0级地震前震中所在区域面波波速升高,而震后出现降低.与传统的动态成像相比,背景噪声方法由于采用固定的台站对,不同时间段的射线固定,这样可以减小由于不同时段地震分布不均一和震源定位而引起的误差,使动态反演结果更加可靠.
展开▼
