基于地震目录估计完备震级方法的数值实验

本文将5种估计完备震级(magnitude of completeness,简记为Mc)的方法运用在三个不同模型产生的理论地震目录上,进而对比它们的优缺点.我们发现分段斜率中值分析法MBASS(The Median-based analysis of the segment slope)适用于不完备部分台网探测地震能力随震级变化快及监测能力在时间上存在不均匀性(heterogeneity)的目录中,但是要求目录包含大量的地震事件,而b值稳定法MBS(The Mcby b-value stability approach)则适合用于台网探测地震能力随震级减小衰减慢地震目录,但是比较费时.最大曲率法MAXC(The Maximum Curvature technique)和拟合优度测试法GFT(The Goodness-of-Fit Test)在使用时都低估Mc,需要加调整量.完整性震级范围法EMR(Mcfrom Entire Magnitude Range)则一般给出比较稳定、适中的Mc估计值.这种方法适用在地震数目少,且对地震丢失容忍度比较高的情况.在实践中针对不同性质的地震目录,我们希望这项研究能帮助研究者选择最合适估计完备震级Mc的方法,并指出了一些估计完备震级中应当避免的问题.

Numerical tests on catalog-based methods to estimate magnitude of completeness

This study compares five methods for estimating the completeness magnitude threshold of earthquake catalogs through applying them to synthetic catalogs generated from 3 different models. We have found that the Median-based analysis of the segment slope (MBASS) method is suitable for catalogs recorded by networks whose detection ability improves rapidly with magnitude and for those with temporal heterogeneity if the amount of earthquakes is large enough. The M_c by b-value stability approach (MBS) is optimal in dealing with catalogs recorded by networks whose detection ability improves slowly with magnitude, but it is time-consuming. The Maximum Curvature technique (MAXC)& The Goodness-of-Fit Test (GFT) method underestimate M_c and need an M_c criterion. The M_c from Entire Magnitude Range (EMR) method gives a moderate and stable M_c estimation. It is recommended when the amount of events is not large and the tolerance of missing events is relatively high.This study helps us to choose the optimal M_c estimation method in practice to cope with different earthquake catalogs and points out some potential problems caused by these methods.