利用高采样率数采实现地震波速变化高精度测量

摘要

Physical properties of the medium as well as its stress status change are the main factors that causes seismic velocity change, thus variations in the medium can be speculated by monitoring velocity change. However, precision of the measurement is usually affected by sample rate, SNR of the instruments and time triggered precision. With the purpose of realize high precision measurement, we designed a set of monitoring system, which includes a highpowered rare-earth giant magnetostrictive source and a general data-acquisition system with high sample rate. We used stacking to increase SNR, and enhanced the trigger precision by increasing the sample rate. Meanwhile, we used the near-field data for correction, so as to eliminate the instrument effects on seismic velocity change. The practical observation suggests that our system can obviously decrease time error, and realize high precision measurement of seismic velocity.%介质物理性质与应力状态的改变是导致地震波速变化的主要因素,通过高精度波速变化测量可推测地下介质发生的变化.然而,高精度波速变化测量对测量仪器提出了较高要求,波速变化的测量精度常常受到仪器的采样率、信噪比以及时间触发精度的影响.为实现高精度测量,设计一套由大功率稀土超磁致可重复震源和高采样率通用数采组成的观测系统,通过叠加的办法提高信噪比,利用增加采样率的方法提高时间触发精度.同时,使用近场数据进行校正,以消除仪器响应对波速变化的影响.实际观测表明,该系统能够明显减小走时测量误差,实现地震波速变化高精度测量.