横向变速起伏介质走时反演

Traveltime inversion in the medium in which velocity varies laterally.

本文实现了横向变速起伏介质情形下同时估计速度和深度的走时反演。备层介质由不等宽度的网格组成,在网格节点间的速度由线性函数表示,反射界面由光滑三次样条函数构成,理论走时由快速射线追踪方法获取.更演算法采用迭代阻尼最小二乘法,并采用自适应修改阻尼因子来提高迭代效果,采用区间约束和点约束提高解的唯一性。理论模型及实际资料试算结果表明,本反演算法具有迭代效果好、精度高、稳定性强的特点,适用于任意起伏构造及横向速度梯度变化的介质。

We achieve a traveltime inversion technique for simultaneously estimating velocity and depth in the undulate medium in which velocity varies laterally. The inversion technique involves the following essentials. ·The medium is divided into layers which are represented by different-size nets; ·Velocity between net points is expressed by linear function; ·Reflector consists of smooth cubic spline function; ·Theoretical traveltime is calculated using fast ray tracing; ·Inversion algorithm is based on an iterative damping least square method; ·Self-adaptively revised damping factor is used to improve iteration effect; ·Regional and point restrictions are applied to achieving sole solution. Theoretical and practical estimations show that this inversion brings good iteration effect, high accuracy and stable operation, and hence applies to any undulate medium where velocity shows laterally gradient variation.