非穿透体和起伏地表模型的FMM走时计算

FMM-based travel time calculation in complex model including non-penetrating abnormal body and irregular ground surface

在隧道或巷道工程地震超前探测中较常用偏移成像技术,计算地震射线走时是该技术的核心部分。由于在近似地下全空间区域内成像,隧道或巷道、空洞、采空区等非穿透体对地震波走时计算有较大影响。为此,文中发展了基于FMM(fast marching method)的含非穿透体的走时算法。该算法采用非穿透体区域标记法,当FMM窄带区在计算到非穿透体时会自动避开或绕过,使得波前推进更加符合实际传播情况。这种算法也适用于起伏地表模型,只需要将起伏地表以上区域也作为非穿透体来对待。因而,新算法可以同时处理含有起伏地表的模型。改进的算法与常规算法相比只是增加了标记点,保持了FMM的计算精度和效率。理论模型试验表明,改进的算法能够较准确地计算走时,对复杂异常体的适应性较强,而且有很好的稳定性。

Migration imaging technique is commonly used in reconnaissance beyond tunnel or roadway, of which the important part is the travel time calculation. Because the imaging area approximates the whole underground space, such non-penetrating bodies as tunnels or roadways, holes, and mine goaves have a great influence on the travel time of seismic wave.Therefore, based on Fast Marching method （FMM） , the authors developed a new algorithm to calculate the travel time of seismic waves for those complex models including the non-penetrating bodies.In this algorithm, a labeling technique is adopted for non-penetrating bodies, and the ray will automatically avoid and bypass the non-penetrating bodies in narrow band of FMM when a ray approaches them, making the seismic wavefront propagation more realistic.Also,this new algorithm can be applicable to the model for irregular ground surface if the above surface area is regarded as a non-penetrating body.Therefore ,the new algorithm can deal with the model with non-penetratlng bodies and irregular ground surface simultaneously. Compared with the conventional algorithm, the marked point is the only change of the developed algorithm, which main- tains the accuracy and efficiency of FMM.The numerical test results show that the improved algorithm can calculate the travel time accu- rately, and has strong adaptability and good stability to complex model.