The 19 September 2017 M 7.1 Puebla‐Morelos Earthquake: Spectral Ratios Confirm Mexico City Zoning
The 19 September 2017 M 7.1 Puebla‐Morelos Earthquake: Spectral Ratios Confirm Mexico City Zoning
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2017 年 9 月 19 日 M 7.1 普埃布拉-莫雷洛斯地震：频谱比确认墨西哥城分区
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发表时间：
2018
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通讯作者：
L. Quintanar
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作者：
M. Çelebi;V. Sahakian;D. Melgar;L. Quintanar
了解盆地对强烈震动的响应的一个重要因素是频谱比分析，它可以提供有关特定位置地震动主频率的信息。根据 2017 年 9 月 19 日普埃布拉-莫雷洛斯州 M 7.1 地震主震期间墨西哥城强震台记录的加速度计算出的谱比揭示了与 2004 年墨西哥地震设计规范中绘制的主要周期一致的周期。此外，通过记录 1985 年 9 月 19 日米却肯州 M 8.1 地震的少数强震台的主震和余震记录，计算出的主要周期验证了这些研究。尽管每个区域（I区、II区、IIIa区、b区、c区和d区）中的电台数量不相同，但仍然可以确认属于特定区（特别是IIIa区、b区、c区和d区）的站点频率（周期）。频谱比通过两种不同的方法计算：(1) 台站 X 方向上的水平信道的平滑幅度频谱相对于参考硬土（或岩石）台站相同 X 方向上的水平信道的平滑幅度频谱的水平与水平 (H/H) 比率；(2) 两者的水平与垂直 (H/V) 比率（或也称为 Nakamura 方法） 同一站的水平（H）和垂直（V）频道。我们对两种方法得出的识别频率（周期）进行了比较，发现它们非常相似，并且与 2004 年抗震设计规范中墨西哥城分区图中所示的频率非常一致。
One important element of understanding basin response to strong shaking is the analysis of spectral ratios, which may provide information about the dominant frequency of ground motion at specific locations. Spectral ratios computed from accelerations recorded by strong-motion stations in Mexico City during the mainshock of the 19 September 2017 M 7.1 Puebla-Morelos earthquake reveal predominate periods consistent with those mapped in the 2004 Mexican seismic design code. Furthermore, the predominant periods thus computed validate those studies using mainshock and aftershock recordings of the handful strong-motion stations that recorded the 19 September 1985M 8.1 Michoacán earthquake. Even though the number of stations in each of the zones (zones I, II, IIIa, b, c, and d) is not the same, they still allow confirmation of site frequencies (periods) attributable to the specific zones (particularly those in zones IIIa, b, c, and d). Spectral ratios are computed with two different methods: (1) horizontal to horizontal (H/H) ratio of smoothed amplitude spectrum of a horizontal channel in direction X of a station with respect to the smoothed amplitude spectrum of the horizontal channel in the same X direction of a reference stiff soil (or rock) station and (2) horizontal to vertical (H/V) ratio (or also known as the Nakamura method) of both horizontal (H) and vertical (V) channels of the same station. We show a comparison of the identified frequencies (periods) derived by both methods and find they are very similar and in good agreement with those indicated in the zoning maps of Mexico City in the 2004 seismic design code.