大地震震级测定及速报

DETERMINATION OF MAGNITUDE OF STRONG EARTHQUAKES FOR QUICK REPORT

为了研究在强烈地震发生时,记录图最大振幅出格,如何决速测定强震震级这一实用化很强的问题,在用面波持续时间及测定体波震级方法的基础上。本文用云南1988年11月发生在澜沧、耿马地区的两次M_S≥7.0的地震资料(由全国基准台网SK仪器记录的地震图),进一步研究用这两种方法快速测定大地震震级作为速报方法的可能性。研究结果表明,用归算的面波持续时间测定M_S作为大震速报,一般需要等待从地震图初至后延10—20分钟的时间,而用体波测定震级m_B作为大震速报仅需要等待从初至后延数秒至5分钟左右。因此,是最为实用的大震速报方法。其优点在于图上最先到达的总是体波,对于M_S≥7.0的地震,体波振幅往往不限幅,这种特征满足强震测定和大震速报的需要。本文用澜沧、耿马两次大震的资料,对这两种方法作了较好的比较和检验。用收集到的约1500多个中强地震的面波震级和体波震级数据,经验统计给出两者之间的线性关系为M_S=1.55mg-3.47。

It is a practical problem how to quickly determine the magnitude of a strong earthquake when the maximum amplitude on the seismogram was out of scale.The magnitudes of the Lancang and Gengma great earthquakes(M_s=7.2, M_S=7.6)were first determined with two methods: the coda wave duration method and the body wave method, the data recorded by SK instruments at stations of the national standard network.The results indicate that the duration time, which is the time from the wave onset to the end of coda waves is usually about 10—20 minutes, but the duration is only several seconds to 5 minutes for body waves.So it is quite clear that with the coda wave duration method, the time of magnitude determination is much longer than that needed with the body wave method.Then, using data of more than 1500 earthquakes (M_S>5.0)for studying the surface-and body-wave magnitudes, a statistical relation between Ms and m_B is found as. M_S=1.55m_B-3.47.