Application of First Arrival Tomography Inversion Technique in the Investigation of Urban Geological Active Fault
王安国1
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作者信息
1. 北京市地质调查研究所,北京 102206
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摘要
利用回折波法建立初始模型,通过菲涅耳带层析成像方法进行迭代.假设初至波在水平地表和垂向连续介质中以回折波的方式传播,使用勒让德多项式拟合初至曲线,利用 Gauss-Legendre 积分公式计算回折波的回折点深度和速度.初至层析反演成像处理在城市地质活动断裂调查中有两个主要目的:层析反演的静校正应用于叠加成像,清晰显示活动断裂的特征;提供准确的表层速度模型,确定活动断裂上下盘的速度异常带位置.只有同时实现这两个目的,初至层析反演技术才能被确认为适用的解决方案.利用城市地质地震勘探数据进行初至层析反演成像,获取 0～200 m 深度的地层结构,反演结果较清晰地反映了表层速度结构的横向变化和异常体的分布情况,叠加成像剖面能够准确识别断层位置,反演的结果明确揭示出多个断层的位置和走向,为城市规划和地下空间建设提供了参考依据.应用实例表明,初至层析反演技术是一种应用于城市地质活动断裂调查中的可靠技术手段,具有广阔的应用前景.
Abstract
The study establishes initial model with folding wave method,and iterates with Fresnel band tomography method.Assuming that the first arrival wave propagates as a recurve wave in horizontal surface and vertical continuum,the first arrival curve is fitted by Legendre polynomial,and the recurve point depth and velocity are calculated by Gauss-Legendre integral formula.There are two main purposes of the first arrival tomography inversion imaging in the investigation of urban geological active faults:the static correction of tomography inversion is applied to superposition imaging to clearly show the characteristics of active faults;an accurate surface velocity model is provided,and the velocity anomaly zone location of the upper and lower plates of active faults is determined.The first arrival tomography inversion imaging is performed with the urban geological seismic survey data to obtain the formation structure at a depth of 0～200 m.The inversion results clearly reflect the lateral changes of the surface velocity structure and the distribution of anomalous bodies.The superposed imaging profile can accurately identify the location of faults.The inversion results clearly reveal the location and trend of multiple faults,which provides reference for urban planning and underground space construction.The application examples show that the first arrival tomography inversion technique is a reliable technique for the investigation of urban geological active faults,with a broad application prospect.
关键词
初至波/层析反演/速度模型/活动断裂/叠加成像
Key words
First arrival wave/Chromatographic inversion/Velocity model/Active fault/Superimposed imaging
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