利用地震噪声准实时监测短周期面波波速变化

Near realtime monitoring the change of group velocity of short-period surface wave via seismic noise analysis

依据由噪声信号提取面波格林函数的原理,利用福建省地震台网25个宽频带台站2007年7月2日—8月29日的脉动观测资料,得到了瑞雷波群速度在福建地区的分布,并将该结果作为下一步相对变化动态成像的背景速度分布.分布结果表明,福建地区周期为3—5s的瑞雷波群速度大致在2.9—3.1km/s之间,平均速度为3.0km/s,瑞雷波群速度分布呈北高南低的现象,这与福建地区北部多山、南部多平原盆地的地理环境有很好的吻合.而且,该群速度分布图在漳州盆地地区表现出一个非常明显的低速,这主要是因为受到盆地沉积层的影响.通过滑动窗(窗长为20d,步长1d)技术得到了观测区内周期约为3—5s的瑞雷波波速分布变化的连续图像;再利用扣除背景影响的技术,得到了2007年8月14日—2008年7月1日福建地区瑞雷波波速的相对变化时空动态图像.通过分析相对变化时空动态图像与该时间范围内发生的地震的对应关系,表明福建地区瑞雷波波速在多次网内中等强度的地震或震群(ML>3.0)中均表现出震前波速升高,震后下降恢复的变化趋势.初步分析认为,这可能与震前整个地区受到的应力增大震后应力得到释放所导致的介质变化有关.

Based on the method of extracting surface wave Green function from seismic background noise,the distribution of group velocity of Rayleigh waves in Fujian province is obtained with the seismic background noise data recorded by 25 broadband stations of Fujian digital seismic station network from July 2 2007 to August 29 2008,and it can also be used as the background velocity distribution for calculating the relative change of velocity dynamic imaging.The results imply that the group velocity of Rayleigh waves in Fujian province is between 2.9 km/s and 3.1 km/s with average velocity 3.0 km/s,and its distribution shows that the velocity is higher in the north and lower in the south,this is coincident with the topography of Fujian province where there are many mountains distributed in the north while many plains and basins in the south.From the group velocity distribution image,an obvious low velocity area can be found in the area of Zhangzhou basin,it must be affected by the sedimentary d...更多eposit in this basin.The evolution of continuous images of the group velocity of Rayleigh waves whose period is about 3—5 s are obtained through the technology of sliding-window （the length of time window is 20 days while the step size is 1 day）,in the meantime the relative change temporal-spatial dynamic images of group velocity of Rayleigh waves from August 14,2007 to July 1,2008 in Fujian area are also obtained with the technology of background correction.Through the analysis of the relation between the evolution of dynamic images and the seismic activity during this period,it can be concluded that the group velocity of Rayleigh waves in Fujian area become higher before earthquake while lower after earthquake in many times moderate earthquakes or earthquake swarm （ML〉3.0） happened within our seismic network,and it may relate to the change of medium which is caused by the increment of stress before earthquake while release after earthquake through the preliminary analysis.