Modified frequency-wavenumber algorithm for regional seismograms using Filon's quadrature: modelling of Lg waves in eastern North America
Modified frequency-wavenumber algorithm for regional seismograms using Filon's quadrature: modelling of Lg waves in eastern North America
复制标题
使用菲隆求积法修正区域地震图频率波数算法：北美东部 Lg 波建模
DOI：
10.1111/j.1365-246x.1994.tb04680.x
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发表时间：
1994
影响因子：
2.8
通讯作者：
C. K. Saikia
中科院分区：
文献类型：
--
作者：
C. K. Saikia
总结
本研究的主要重点是开发一种有效的频率-波数编码，以合成由大量地壳层组成的介质中的高频（例如，10 Hz）区域地震图（距离超过1000 km），并研究区域波导对Lg波的影响。在这个新开发的代码中，频率波数响应的评估通过使用Filon的正交在高频和Bessei的函数（实施梯形积分）在低频的多项式近似。与梯形积分所需的时间相比，这将计算时间减少了数倍。利用该算法，成功地模拟了哈佛的宽带地震图和1988年11月25日萨格奈地震的短周期ECTN（Eastern Canadian Telemetered Network）地震图。使用了5.9的力矩大小。最初，平均波导被校准以成功地激发HRV处的区域Pnl和Snl波，其近表面结构受匹配所记录的频率内容的约束。壳幔过渡带的约束建模的强度的宽带Snl波，包括Sn，sSmSnSmSSmS，和sSmSSmS阶段，相对于初始Pnl波。对模型进行了修改，使其由具有交替的高低速分布的薄层组成，以匹配从300至600公里外观测到的高频ECTN Lg波。此外，还通过将其响应与区域Lg地震图进行卷积，研究了近地表不规则接收器结构对Lg波持续时间的影响。初步研究表明，这种方法是可行的建模整个Lg波，包括尾波。数值研究表明，Lg地震图的形状和峰值振幅比Pnl地震图更强烈地依赖于震源深度、滞弹性和地壳波导。
SUMMARY
The main focus of this study is to develop an efficient frequency-wavenumber code to synthesize high-frequency (say, 10 Hz) regional seismograms (up to a distance of more than 1000 km) in a medium consisting of a large number of crustal layers, and investigate effects of regional waveguides on Lg waves. In this newly developed code, the frequency-wavenumber response is evaluated by using the Filon's quadrature at high frequency and the polynomial approximation of Bessei's functions (implementing trapezoidal integration) at low frequency. This has reduced the computation time by several folds compared to the time needed for the trapezoidal integration. Using this algorithm, both broad-band seismograms at Harvard and short-period ECTN (Eastern Canadian Telemetered Network) seismograms from 1988 November 25 Saguenay earthquake were successfully modelled. A moment magnitude of 5.9 was used. Initially an average waveguide was calibrated to successfully excite the regional Pnl and Snl waves at HRV, its near-surface structure constrained by matching the recorded frequency content. The crust-mantle transition zone was constrained by modelling the strength of the broad-band Snl waves, consisting of Sn, sSmSnSmSSmS, and sSmSSmS phases, relative to the initial Pnl waves. The model was modified to consist of thin layers with an alternating high-and low-velocity distribution to match the high-frequency ECTN Lg waves observed from 300 to 600 km away. In addition, the effect of a near-surface irregular receiver structure on the duration of Lg waves was also investigated by convolving its response with the regional Lg seismograms. Initial study suggests this method as viable for modelling the entire Lg waves including the coda. Numerical studies suggest that the shapes and peak amplitudes on Lg seismograms depend more strongly on the source depth, anelasticity and crustal waveguide than do the Pnl seismograms.