A Method for Rapid Determination of Moment Magnitude Mw for Moderate to Large Earthquakes from the Near-Field Spectra of Strong-Motion Records (MWSYNTH)
A Method for Rapid Determination of Moment Magnitude Mw for Moderate to Large Earthquakes from the Near-Field Spectra of Strong-Motion Records (MWSYNTH)
复制标题
一种根据强震记录近场谱快速确定中大地震矩震级Mw的方法(MWSYNTH)
DOI：
10.1785/0120080234
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发表时间：
2009
影响因子：
3
通讯作者：
M. Vallée
中科院分区：
文献类型：
--
作者：
B. Delouis;J. Charléty;M. Vallée
地震矩和相应的矩震级Mw是从远场体波的频谱中经典地获得的。近场记录通常不用于此目的，特别是在大地震的情况下，因为不同类型的波同时到达，阻止了地震矩和频谱之间的简单关系的定义。我们发展了一种从近场记录的位移谱确定Mw的原始方法。将从真实的记录中获得的低频谱振幅与用Mw标度的运动学破裂模型计算的合成记录进行了比较。计算了不同断层方位和震中距1 ~ 100 km的合成记录并取平均值。受加速度记录中基线偏移影响的频谱的初始部分通过高通滤波自动识别和去除，高通滤波使用适合于每个站的截止频率。作为矩震级、震中距离和滤波的函数的合成谱值仅计算一次并存储在表中。真实的记录的光谱振幅被简单地内插在合成数据表中，从而允许快速确定Mw。用22个震级在3.9 ~ 7.7级之间的浅源地震（深度< 50 km）验证了该方法的有效性。我们发现，80秒的信号窗口后，地震的起源时间提供了强大的值Mw在这里考虑的整个震级范围。可以使用较短的时间窗口，但对于大型事件，Mw被低估。该方法非常适合于近实时快速测定Mw。
Seismic moment and the corresponding moment magnitude Mw are clas- sically obtained from the spectrum of far-field body waves. Near-field records are generally not used for that purpose, particularly in the case of large earthquakes be- cause different types of wave arrive simultaneously, preventing the definition of a simple relation between the seismic moment and the spectrum. We developed an orig- inal method to determine Mw from the displacement spectra of near-field records. The spectral amplitude at low frequency obtained from the real records is compared to that of synthetic records computed using kinematic rupture models scaled with Mw. Syn- thetic records are computed and averaged for various fault orientations and for epi- central distances ranging from 1 to 100 km. The initial portion of the spectrum affected by baseline shift in the acceleration records is automatically identified and removed by high-pass filtering using a cutoff frequency adapted to each station. The synthetic spectral values as a function of moment magnitude, epicentral distance, and filtering are computed only once and stored in tables. The spectral amplitudes of the real records are simply interpolated in the tables of synthetic data, allowing a fast determination of Mw. The method has been validated using 22 shallow earthquakes (depth < 50 km) with magnitude ranging from 3.9 to 7.7. We show that a window of 80 sec of signal after the earthquake origin time provides robust values of Mw for the whole magnitude range considered here. Shorter time windows may be used but with Mw underestimated for large events. The method is well suited for near real-time fast determination of Mw.