玉溪盆地三维速度结构建模

3-D modeling of velocity structure for the Yuxi basin

本文以玉溪盆地为例,提出了一种包含数据预处理、模型建立、模型修正和模型检验的建模方法.基于各类数据间不同的可信度,给出了消除各类数据间速度偏差的折减函数.为避免以往模型修正过程中对地震波形数据的依赖以及对地脉动H/V谱进行模拟等复杂问题,本文提出了一种改进的模型修正方法,即根据基阶瑞雷波H/V谱与实测地脉动H/V谱形状变化相似的原则,对模型进行修正.修正依据为:在玉溪盆地中,单个地脉动测点所在位置处的地下速度结构中各沉积层面的深度均增加约15m时,由该点的地下速度结构得到的基阶瑞雷波H/V谱的波峰周期和波谷周期均增加约0.1s,且二者分别由盆地内沉积层的深层和浅层的速度结构所控制.由于地脉动数据的获取较方便,因此该模型修正方法具有广泛的适用性,由该方法修正后的玉溪盆地三维速度结构模型经检验具有较高的准确度.

To achieve ground motion prediction,it is necessary to build a 3-D velocity structure model of sedimentary basin.Taking the Yuxi basin as an example,we provide a modeling procedure,including data preprocessing,model building,model updating and model testing.Based on the different credibility of various data,we propose a function that can eliminate the velocity deviation among various data.In this paper,an improved model updating method is proposed in order to avoid the dependence on the seismic waveform data and the simulation of the microtremors spectral ratio of horizontal to vertical component（H/Vspectra）.We apply the theory that the H/Vspectral shape of the fundamental-mode Rayleigh,including its peak and trough periods,is similar to that of the microtremors to update the 3-D velocity structure model.When the depth of each sedimentary layer in the velocity structure under a single microtremors measuring point is increased by about 15 m,the H/Vspectral peak and trough periods of the fundamental-mode Rayleigh wave will both increase about 0.1 s,moreover,the two periods are controlled by deep or shallow velocity structures of the sedimentary layers in basin respectively.Because of the convenient acquisition of the microtremors data,the model updating method has extensive applicability.The 3-D velocity structure model of the Yuxi basin modified by the model updating method has been confirmed a high accuracy after inspection.