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用布龙园位错模式测定道孚地区1974～1983年间发生的42次M_L在2.5至3.6的小震震源参数,结果表明道孚6.9级地震前2年多时间小震应力降明显增大,这些小震主要集中在道孚地震破裂带的西北侧附近,相应于小震活动和形变测量确定的断裂带“闭锁段”端部应力集中的部位,这说明高应力降可能与构造应力的状态有关。同时研究了对等时段滑动采样对P波谱参数的影响,统计结果表明,改变采样部位不影响拐角频率fo的数值;在震中距Δ=120公里时,采样区间向后移动2秒,谱的零频值Ω_o会降低16%左右。从频谱曲线上得到拐角频率fo的不确定数是1.31,地震矩M_o的不确定数是1.43。采用平均的方法,可将应力降Δσ的不确定数由2.4降到1.6。
42 samples of small earthquakes with M_L 2.5-2.6 occurred in Daofu area during 1974-1983 were measured by the Braun Park dislocation model. The results show that the stress drop of the small earthquakes occurred more than two years before the Daofang M 6.9 Earth Mover, These small earthquakes mainly focus on the northwestern side of the Daofu earthquake rupture zone and correspond to the locations of stress concentration at the ends of the “latching section” of the fault zone, which are determined by the small earthquakes and deformation measurements. This shows that the high stress drop may be related to the state of tectonic stress related. At the same time, the influence of sliding sampling in the same period on P-wave parameters is studied. The statistical results show that changing sampling points does not affect the value of corner frequency fo. When the epicentral distance is 120 km, the sampling interval moves backward for 2 seconds, Frequency Ω_o will be reduced by about 16%. The uncertainty of the corner frequency fo from the spectral curve is 1.31 and the uncertainty of the seismic moment M_o is 1.43. Using an averaging method, the uncertainty of the stress drop Δσ can be reduced from 2.4 to 1.6.