首都圈平均波速比分析

Analysis on Average Velocity Rations in the Capital Area,China

摘要:

首都圈数字地震台网覆盖京、津和河北中部,其中自2002年5月-2003年12新记录1级以上地震1186个,台站记录的纵、横波到时差约 2～25 s.选取被5个以上台站所记录到的地震,震中位于网内或者网缘附近,计算其平均波速比.分析认为:(1)通过HYPODD修订震源位置,绝大多数震源深度在8～10 km,平均波速比所反映的是地壳上层的状态.(2)无论是从较长的时间尺度还是从较大的空间范围来看,平均波速比值都是非常稳定的.(3)平均波速比的可靠性有赖于较多的台站数目,以满足拟合精度的要求.少数台站的测定结果往往伴随较大的误差,单一地震的平均波速比值大幅度的涨落,不宜表征地壳介质性质的改变.

Abstract:

The Capital Digital Seismic Network, covering Beijing, Tianjin and central Hebei province,has recorded 1186 new earthquakes with M≥1. 0 during May 2002 to Dec. 2003, in which the arrival time differences between longitudinal wave and transverse wave are 2-25 s. Choosing the earthquakes recorded by 5 or above 5 stations, and demanding the epicenters are located in the network or near its edge, we calculate the average velocity ratios in this area. It is thought on the analysis that： （1） The majority of earthquakes are at depth of 8-10 km, after relocating the focus by HYPODD, so the average velocity ratio we obtained can only reflect the state in the upper crust. （2） The average velocity ratios are very steady, whatever in the long time scale or large spatial scale. （3） The reliability of average velocity ratios relies on the number of stations to satisfy the fitting precision. The results from fewer stations are always accompanied by larger errors, and single earthquake with big amplitude of change in average velocity ratio is not suitable to represent the property change of crustal media.