Analysis of the Completeness Magnitude and Seismic Network Coverage of Japan
Analysis of the Completeness Magnitude and Seismic Network Coverage of Japan
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DOI：
10.1785/0120100077
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发表时间：
2010-12-01
影响因子：
3
通讯作者：
Hirata, N.
中科院分区：
文献类型：
--
作者：
Nanjo, K. Z.;Ishibe, T.;Hirata, N.
完整震级 M-c 的可靠估计对于地震活动相关研究至关重要，高于该震级的所有地震都被认为是由地震网络检测到的。我们对日本的MC进行全面分析。我们使用日本气象厅 (JMA) 维护的目录以及向 JMA 报告的地震台的可用信息。为了计算 M-c，我们采用基于古腾堡-里希特频率幅度定律的常用方法。目前，M-c = 1. 0 在大陆可能是典型的，但要获得完整的目录，需要使用震级为 1.9 级或更大的地震。与南加州地震台网（SCSN）的比较表明，大陆近期事件的可探测性总体上表现出与南加州地震台网权威区域相似的完整性水平。我们认为，日本目前的 M-c 是由于网络现代化随着时间的推移而取得的成功。特别是，我们表明 M-c 的时空变化与 Hi-net 钻孔台的增加以提高地震台密度密切相关；它于 1997 年 10 月在日本西南部开始，一直持续到日本东北部，直到 2002 年。根据此匹配，我们确认 M-c 与台站密度成反比。此外，我们发现，无论 1997 年之后网络如何变化，这种相关性在时间上都没有变化，这表明站点密度以外的因素对 M-c 的影响不会随时间变化。与阿拉斯加和加利福尼亚相反（Wiemer 和 Wyss，2000），我们的结果并没有将这些因素简单地归因于人为噪音。因为这是由于钻孔站减少了环境噪声，所以我们得出结论，在日本，人为噪声对 M-c 的影响微不足道。
Areliable estimate of completeness magnitude, M-c, above which all earthquakes are considered to be detected by a seismic network, is vital for seismicity-related studies. We show a comprehensive analysis of Mc in Japan. We use the catalog maintained by the Japan Meteorological Agency (JMA) and also available information on seismic stations that report to JMA. For computing M-c, we adopt a commonly used method based on the Gutenberg-Richter frequency-magnitude law. Presently, M-c = 1. 0 might be typical in the mainland, but to have a complete catalog, one needs to use earthquakes with magnitudes of 1.9 or larger. Comparison with the Southern California Seismic Network (SCSN) suggests that the recent event detectability in the mainland generally shows similar completeness levels to that in the authoritative region of SCSN. We argue that the current M-c of Japan is due to the success of network modernization over time. Particularly, we show that the spatiotemporal change of M-c closely matches the addition of the Hi-net borehole stations to enhancing seismic-station density; it started in October 1997 in southwestern Japan, continuing to northeastern Japan until 2002. As suggested from this matching, we confirm that M-c inversely correlates with station density. Further, we find that irrespective of the network change after 1997, this correlation is unchanged in time, demonstrating that the influence on M-c from factors beyond station density does not vary in time. Contrary to Alaska and California (Wiemer and Wyss, 2000), our results do not attribute such factors simply to anthropogenic noise. Because this is due to the borehole stations that reduce ambient noise, we conclude that in Japan the anthropogenic noise has an insignificant effect on M-c.