震级新国标实施前后中强浅源地震速报震级差异的分析对比

目前震级新国标拟在中国地震震级测定中开始使用。 为系统评估震级新国标对中强浅源地震的速报震级影响, 基于2001—2017年中国大陆发布的5级以上浅源地震速报目录, 本文系统分析了新国标宽频带面波震级与原速报震级的差异, 并与国外面波震级结果以及国、 内外矩震级的结果进行了对比研究。 结果表明: 采用新国标, 国内、 外面波震级对6级以上地震测定结果基本一致, 但5、 6级以上地震的频次分别为原来的80%、 60%左右, 而6.5级以上地震频次差异不大。 国内、 外矩震级测定结果比较一致, 由于国际上目前采用矩震级发布, 而矩震级与面波震级之间存在系统偏差, 因此, 为保持与国际结果一致, 应加快矩震级在地震速报中的应用, 这可能会导致6、 7级地震频次进一步降低。 由于速报震级在实际工作中既有可能采用面波震级, 也有可能采用矩震级, 或两者的结合; 因此, 速报震级仅用于地震信息发布、 地震应急、 科普宣传等社会应用, 如果使用震级进行科学研究、 地震活动性统计等专业应用研究, 最好统一使用一种标度, 即面波震级或矩震级。

Differences of Rapid Report Magnitude for Moderate-Strong Shallow Earthquakes before and after the Implementation of the New National Standard

The New National Standard (NNS) of earthquake magnitude have been used in the determination of earthquake magnitude. To estimate the magnitude impact of the NNS on the moderate-strong shallow earthquakes in quick report, the differences between the magnitudes of broad band surface wave (M_S(BB)) and the magnitudes of old rapid determination are systematically analyzed based on the rapid report catalogue of M≥5.0 earthquakes in China mainland from 2001 to 2017. In addition, we make a comparative analysis on the M_S(BB) , M_S(NEIC), M_W(CENC) and M_W(GCMT). The results show that the NNS magnitudes are basically consistent with that of the NEIC for M≥6. The frequencies of earthquakes with M≥5 and M≥6 decrease to about 60% and 80% of the original data, but difference is little when M≥6.5. The moment magnitudes estimated by China mainland are consistent with the international results. Because the earthquake magnitude is released using the moment magnitude in world and there is systematical difference between the moment magnitude and surface wave magnitude. Thus, we should take the moment magnitude as the rapid determination result in China to consistent with the international results. It may further decrease the frequency of M6 and M7 earthquakes.