Multimode multioffset phase analysis of surface waves, a new approach to extend MOPA to higher modes
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Abstract:
SUMMARY Multioffset phase analysis (MOPA) is a fairly recent technique for evaluating seismic surface wave dispersion and estimating the presence of lateral variations. The main limitation of MOPA is that it is based on the assumption of one predominant mode, usually the fundamental mode, in the wave propagation. However, MOPA can be extended (at least) to the two-mode case: this new technique will be called multimode MOPA (MMMOPA). The method employs both amplitude and phase spectral information. The analysis is performed for each frequency independently. The presence of two modes causes the amplitude to have an oscillating behaviour as a function of offset (beats): the spatial period of the oscillating amplitude is identified, amplitude maxima and minima are extracted, and the local wavenumber is computed via linear regression. The resulting multimodal dispersion curve is consequently derived. Model uncertainties can be estimated by propagating the experimental phase and amplitude error variances through the different steps of the analysis all the way to the final phase velocities. An algorithm running the process in an automatic way has been implemented and tested on both synthetic and real data, with success. This is the base for future developments that, in the MOPA framework, can take into account rapid lateral velocity variations within the same acquisition window and estimate the modal absorption, for the estimation of the damping ratio, even in the presence of multimode surface wave propagation.Keywords:
Maxima and minima
Wavenumber
毛状、毛状严肃的波浪拥有一个随机的人物，和他们的斜坡 wavenumber 系列能被用来关于可变性的空间规模代表波浪精力的吝啬的分布。但是斜坡 wavenumber 系列的简单、实际的模型到目前为止没被提出。在这篇文章，我们探讨毛状的水表面和毛状严肃的波浪的斜坡 wavenumber 系列的精确定义。由联合存在斜坡 wavenumber 模型并且使用水表面波浪的分散关系，我们导出毛状、毛状严肃的波浪的斜坡 wavenumber 光谱模型。同时，由使用斜坡， wavenumber 当模特儿，风速度上的斜坡 wavenumber 光谱的依赖用在在一辆实验室风波浪坦克被执行的一个实验获得的数据被分析。一般来说，斜坡 wavenumber 系列被风速度在水表面上面深刻地影响。有风的斜坡 wavenumber 光谱增加显然加速并且不为不同的风速度穿过对方。但是为一样的风速度，斜坡 wavenumber 系列是实质上相同的，尽管毛状、毛状严肃的波浪在不同时间和地点是激动的。而且，从模型获得的斜坡 wavenumber 系列关于价值和曲线的形状与试验性的结果同意相当好。关键词毛状、毛状严肃的波浪 - 斜坡 wavenumber 光谱模型 - 风速度依赖由中国(号码 60372077 ) 的国家自然科学基础支持了。
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