近震震源深度测定精度的理论误差分析

The analysis of the theoretical error of the accuracy of measuring the focal depth of near earthquake

震源深度是地震学中最难准确测定的参数之一,各种方法对于震源深度的估计都具相当程度的不确定性,影响着人们对震源过程的认识。各种因素对震源深度的影响是非线性的,本文从近震走时公式入手,分析了震中距、到时残差和速度模型(地壳模型)对震源深度的影响。当地震波传播速度一定时,震源深度的误差随着震中距或台站距离的增大和走时残差的增大而增大。走时残差一定时,震源深度误差随着震中距的增大和地震波速度的增大而增大。研究也表明,当速度已知,走时残差一定时,越浅的地震,定位误差可能越大。定位精度产生的水平误差随着震中距、走时误差和地震波速度的增大而增大,震源深度误差也将增大。另外,震源深度的误差会导致发震时刻的变化,随之而来的结果都会因此而改变。

Focal depth is one of the most difficult seismic parameters to determinate accurately in seismology. The focal depth estimated with various methods can not be uncertain to a considerable degree,which affects the understanding of the source process. The influence of the various factors on focal depth is non-linear. The paper analyzes the influence of epicentral distance,the arrival time residuals and velocity model （crust model） on focal depth on the basis of travel time formula of near earthquake. When the velocity of wave propagation is certain,the error of focal depth increases with the epicentral distance or the location of the station and the travel time residual. When the travel time residual is certain,the error of focal depth increases with the epicentral distance and the velocity of seismic wave. The study also shows that the location error perhaps becomes bigger for shallower earthquake when the velocity is known and the travel time residual is certain. The horizontal error caused by location accuracy increases with the epicentral distance,the travel time residual and the velocity of seismic wave,and the error of focal depth increases with these factors. On the other hand,the errors of focal depth can lead to the changes of origin time,and the results that follow will change,too.