缓倾地层微震定位算法探讨及其数值验证

Microseismic location algorithm for gently inclined strata and its numerical verification

倾斜层状地层中速度模型对于震源精确定位具有重要意义。基于水平层状地层两点间的快速射线追踪法,分析了应力波在倾斜地层中的传播路径及规律。结合网格搜索法,提出了针对倾斜地层的微震定位算法,并与传统的基于单一速度模型的定位算法进行对比分析;探索性地采用了颗粒流理论构建地层数值模型,通过颗粒间的相互作用模拟应力波传播进行定位算法有效性验证。研究结果表明:(1)对于倾斜地层,基于简化弹性波等速传播规律的定位算法精度较差,单一速度模型不能满足复杂介质的定位要求;(2)采用倾斜分层速度模型并改进应力波传播路径的计算方法能有效提高倾斜地层的震源定位精度,同时分析了地层倾角以及地层数对算法精度的影响,表明定位误差与倾角、地层数成正比;(3)通过减小网格搜索法的网格尺寸可在一定程度上提高定位精度,合理的尺寸大小和搜索策略有助于网格搜索法在实际工程中的应用。建立的倾斜地层震源定位及其验证方法可为进一步研究复杂地层定位监测技术提供重要的理论和技术支撑。

The velocity model is significant for precisely locating the earthquake source in inclined strata. This study analyzed the propagation path and propagation regularity of stress waves in inclined strata, according to the fast ray-tracing technique between two points in horizontal layered media. Microseismic location algorithm was developed for inclined strata using grid searching method, which was also compared with traditional location methods based on single velocity model. The particle flow theory was exploratively used to establish the stratum numerical model. Subsequently, the validity of the proposed algorithm was verified by simulating the stress wave propagation through the interaction of particles. Results show that the traditional location algorithm, based on simplified elastic wave propagation at a constant velocity, is imprecise for inclined strata, indicating that the single velocity model cannot satisfy the locating demand for complex media., On the basis of the inclined layered velocity model and a modified computational method for stress wave propagation path, the seismic sources can be located much more accurately. Meanwhile, the location deviation was found to be proportional to the dip angle and stratum number. In addition, the location precision can be also increased by reducing the grid size in the grid searching method, suggesting that reasonable sizes and searching strategies can facilitate the application of grid searching method in practical engineering. The microseismic location method and the proposed verification process can provide important theoretical and technical support for further studies on the positioning and monitoring technology in the complex strata.