一种降低微震定位误差的偏振分析方法

目前微地震监测技术已成为地球物理界的热门技术之一。对于微地震震源定位,主流的初至时差分析方法由于方程组局部极值、初至拾取困难以及波速恒定假设等问题,极易产生超定或欠定的误差,而且未考虑有效数据不足的情况。为此,利用所测量的检波器姿态信息,计算出参考校正角,并将垂直、径向和切向分量数据校正为标准的三分量数据,以此提取同型波来计算偏振角,所获取的偏振角数据一方面可进行定位求解,另一方面也可对三分量数据进行进一步的校正,以提高时差分析中初至拾取的准确性;综合偏振角极化分析与初至时差分析两种方法建立了最小误差优化模型,实现了更为复杂地质条件下的联合定位,降低了定位误差。最后对数值模拟实验和野外实验结果进行了统计分析,结果表明:最优化联合定位方法能够大大降低定位误差且在有效数据不足的情况下仍能保证较好的定位效果,有效数据在9组以上时的定位误差小于7 m。

A polarization analysis method for reducing the errors of microseismic location

At present, microseismic monitoring is one of the hot technologies in the field of geophysics. As for the predominant first arrival moveout analysis method, overdetermined or underdetermined errors tend to occur in microseismic source location because of the local extremum of equation sets, first arrival pickup difficulty and constant wave velocity assumption and the valid data are insufficient. In view of this, firstly, the reference correction angles were calculated by using the measured attitude information of geophones, and the vertical, radial and tangential components were corrected to be standard three-component data, so that the homologous waves were extracted for polarization angle calculation. And based on the calculated polarization angles, location resolution could be performed and three-component data could be further corrected, so that the first arrival pickup of moveout analysis could be more accurate. Secondly, a minimum error optimization model was established by combining the polarization angle polarization analysis method with the first arrival moveout analysis method, so that combined location could be realized in more complex geologic conditions and the location errors reduced. And finally, statistic analysis was conducted on numerical simulation experiments and field test results. It is shown that optimized combined location method can decrease location errors greatly and realize better location even without sufficient valid data, with location error less than 7 m when there are more than 9 sets of valid data.