Changes of Reporting Rates in the Southern California Earthquake Catalog, Introduced by a New Definition of ML
Changes of Reporting Rates in the Southern California Earthquake Catalog, Introduced by a New Definition of ML
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ML 的新定义引入了南加州地震目录中报告率的变化
DOI：
10.1785/0120090124
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发表时间：
2010
影响因子：
3
通讯作者：
E. Hauksson
中科院分区：
文献类型：
--
作者：
T. Tormann;S. Wiemer;E. Hauksson
从2008年1月开始，加州南部的当地震级M_L由一个新的校准确定，提供了各种改进确定小地震M_L。前几年的星等正在重新计算，星表也在不断更新，第一年的重叠数据现在可以提供。重新校准震级标度可能会导致报告同质性的中断，并经常在目录统计中产生可能影响大范围地震活动性研究的人为因素。为了寻找这样一个间断，我们比较了2007年的老M_L星表和新M_L星表。结果表明：（1）96%的M_L事件的两个震级值不一致，人工测定的震级也被修正：（2）震级差是不规则的，从最大1.5个单位到最大2.3个单位不等，平均变化为-0.13个单位;（3）M1.8级以上的事件数减少了32%，（4）完整性震级从1.6级明显下降到1.3级，下降了0.3个单位;（5）b值减少了大约0.2个单位，从1.16下降到0.95;（6）新的幅度校准产生更稳定的b值估计，因此可以被认为是更好的缩放。
我们选择的例子，如何在震级校准的变化可能会影响地震活动性和灾害相关的分析，是基于南加州地震台网（SCSN）目录。特别是b值从~1.1变化到~0.9，对危险相关应用具有潜在的重大影响。
Starting January 2008, local magnitudes M_L for southern California are determined by a new calibration that provides various improvements for determining M_L for small earthquakes. Magnitudes for the previous years are being recalculated and the catalog continuously updated, with the first year of overlapping data now being available. Recalibrating a magnitude scale can cause a break in homogeneity of reporting and often produces artifacts in the catalog statistics that can influence a wide range of seismicity studies. To search for such a break, we compare the old M_L and the new M_L catalogs for 2007. We find (1) the two magnitude values differ for 96% of the M_L events, and hand-determined magnitudes are also revised; (2) the magnitude differences are irregular from magnitude increases of up to 1.5 units to reductions by as much as 2.3 units, with an average change of -0.13 units; (3) the number of events above M 1.8 decreases by 32% for the new magnitude scale; (4) the completeness magnitude apparently drops by 0.3 units from 1.6 to 1.3; (5) the b-value reduces by approximately 0.2 units, dropping from 1.16 to 0.95; (6) the new magnitude calibration produces a more stable b-value estimate and can therefore be regarded as the better scaling.
We document selected examples of how the change in magnitude calibration may affect seismicity- and hazard-related analyses that are based on the Southern California Seismic Network (SCSN) catalog. Especially the change of the b-value from ~1.1 to ~0.9 has potentially major implications for hazard related applications.