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The M-D scale in Northern Morocco: A comparative study of two empirical approaches

机译：摩洛哥北部的M-D量表：两种经验方法的比较研究

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摘要

We have derived, evaluated, and compared two empirical methods for computing duration magnitude M-D from 25 short-period vertical component stations of the Northern Morocco Seismic Network (NMSN). M-D has been scaled to IGN (Insituto Geograpfico National, Spain) body-wave magnitude (mb(IGN)), using a set of 479 shallow (less than 30 km) earthquakes recorded from March 1992 to February 2001, with 2.5 <= mb(IGN) <= 5.4. In the first approach: Individual Network Calibration, we determined an individual M-D formula for each station. In the second approach: Global Network Calibration, we used a single relationship to compute M-Dij (from the jth observation for the i-th earthquake) magnitudes at 25 selected stations as: M-Dij = - 0.14 +1.63 log(10) (tau(ij))+0.031(Delta ij)+cSta(j). Residuals (M-Dij - mb(IGN)) for both techniques were thereafter deduced. Comparison between the two approaches provided the principal results: (1) The mean correlation between estimated magnitude; M-Dij and reference magnitude; mb(IGN) is about 89.9% for the individual calibration method, and near 95% for global calibration method in which station corrections cSta(j) were introduced, (2) Residuals (M-Dij - mb(IGN)) are relatively large, and are ranging between - 0.60 and 0.60 magnitude units, for the individual calibration method, whereas they vary in the range - 0.38 to 0.40, for the global calibration method with corrections; cSta(j). (3) A random distribution of residuals (M-Dij - mb(IGN)) is observed for each station in the case of the individual approach. Thus, the resulting average of these residuals is almost equal to zero. Using a global calibration without corrections results in negative residuals for a group stations and positive residuals for another an group indicating respectively that sites corresponding to these groups have a tendency to underestimate, or overestimate observed magnitude values.
机译：我们已经得出，评估和比较了两种经验方法，用于从北摩洛哥地震台网（NMSN）的25个短周期垂直分量站计算持续时间震级M-D。 MD已使用1992年3月至2001年2月记录的479次浅层地震（小于30 km）地震定标为IGN（西班牙国家地理研究所）体波震级（mb（IGN）），其中2.5 <= mb （IGN）<= 5.4。在第一种方法：单独网络校准中，我们为每个站点确定了单独的M-D公式。在第二种方法：全球网络校准中，我们使用单个关系来计算25个选定站点的M-Dij（从第i次地震的第j个观测值）震级为：M-Dij =-0.14 +1.63 log（10） （τ（ij））+ 0.031（Δij）+ cSta（j）。此后推导这两种技术的残差（M-Dij-mb（IGN））。两种方法的比较提供了主要结果：（1）估计震级之间的平均相关性; M-Dij和参考幅度;单个校准方法的mb（IGN）约为89.9％，而引入站校正cSta（j）的全局校准方法的mb（IGN）则接近95％，（2）残留量（M-Dij-mb（IGN））相对较大对于单个校准方法，，其范围在-0.60到0.60幅度单位之间，而对于带有校正的全局校准方法，它们在-0.38到0.40范围内变化; cSta（j）。 （3）在个别进场的情况下，观察到每个站的残差的随机分布（M-Dij-mb（IGN））。因此，这些残差的所得平均值几乎等于零。使用不进行校正的全局校准会导致一组站的负残差，而导致另一组的正残差，分别表明与这些组相对应的站点倾向于低估或高估观测到的幅度值。

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