本文通过对发生在日本及其周围5～7级地震的宽频带地震图的分析,发展通过初至P波波形确定矩震级的技术。理论上我们把在宽频带地震仪记录的P波段位移作为一个近似的源时间函数,并对其积分,得到在每个台站的标量矩。我们的结果表明,对多道记录的组合,能在没有进行震源机制校正的情况下给出一个好的矩震级估计值。这个技术相当简单和稳健。因此,它将有效地对大地震可能引起的海啸进行快速评定。 Based on the analysis of wideband seismograms of earthquakes of magnitude 5-7 in and around Japan, this paper develops a technique for determining moment magnitude through the first-arrival P waveforms. In theory, we consider the P-band displacement recorded in a broadband seismometer as an approximate source-time function and integrate it to obtain the scalar moment at each station. Our results show that a good moment magnitude estimate can be given without the correction of focal mechanisms for many combinations of records. This technique is fairly simple and robust. Therefore, it will effectively assess the potential tsunami caused by the earthquake.