长白山天池火山地区的尾波Q值估计

Coda Q Estimates in the Mt. Changbai Tianchi Volcanic Region,East China

对1999～2005年间长白山天池火山观测站所有数字化波形记录中震级ML≥0.6的94个火山地震事件,利用频率在1.0～16.0Hz范围内的记录,依据S波单次反散射模型测算了长白山天池火山区的尾波Q值,获得尾波Q值与频率的关系为QC=(47±2)f(0.74±0.01)。假定衰减完全由散射损失造成,则估计得到长白山天池火山区的最小平均自由程为17km,且与所用的频率无关,表明天池火山区下方散射体分布密度较大。

On the basis of near-field data recorded by the Mt.Changbai Tianchi volcanic station,94 digital local events with ML≥0.6 during 1999～2005 are selected.Then coda QC in the Mt.Changbai Tianchi volcanic region,East China has been determined according to dispersion theory of coda from the decay of the amplitudes of coda wave on narrow band-pass-filtered seismograms of local microearthquakes in a range from 1.0Hz to 16Hz.It has a frequency dependence of the form QC=（47±2）f（0.74±0.01）,which shows that Mt.Changbai Tianchi volcanic region belongs to unstable tectonic environment.For each frequency band,the coda QC values,averaged over all earthquakes.Considering a model incorporating both scattering and intrinsic attenuation,and assuming that the attenuation is entirely due to the scattering loss,a frequency-independent minimum mean free path of about 17km have been obtained,so the density of scatters is large under the Mt.Changbai Tianchi volcanic region.