Ambient noise tomography has become a popular method in the past two decades to image the crust and uppermost mantle structure. To date, broadband Rayleigh wave signals can be obtained from ambient noise, which can be utilized to study the earth's interior structure from the surface down to ∼200–300 km depths. However, it is hard to extract intermediate- and long-period (>50 s) Love wave signals from ambient noise using conventional data processing techniques for ambient noise. Array-based data processing techniques can enhance weak signals. In this study, we adopt a modified algorithm of the double-beamforming method to extract broadband Love wave signals from ambient noise. We validate the accuracy of the dispersion curves measured from our method by comparing them to those measured from the conventional method. Then, we use a finite frequency ambient noise tomography method to construct broadband Love wave phase velocity maps across the contiguous USA. These phase velocity maps are consistent with those obtained from conventional methods at short periods (<40 s). Finally, we analyze the resolution of our double-beamforming method based on checkerboard tests and find that the resolution of phase velocity maps based on our method is close to the aperture of the subarrays used in our double-beamforming method.

中文翻译：

---

基于环境噪声互相关改进双波束形成的宽带Love波相速度图

在过去的二十年中，环境噪声断层扫描已成为对地壳和最上地幔结构进行成像的流行方法。迄今为止，宽带瑞利波信号可以从环境噪声中获得，可用于研究从表面到约200-300公里深度的地球内部结构。然而，利用传统的环境噪声数据处理技术很难从环境噪声中提取中长周期（>50 s）乐福波信号。基于阵列的数据处理技术可以增强微弱信号。在本研究中，我们采用双波束形成方法的改进算法从环境噪声中提取宽带洛夫波信号。我们通过将我们的方法测量的色散曲线与传统方法测量的色散曲线进行比较来验证其准确性。然后，我们使用有限频率环境噪声断层扫描方法来构建美国本土的宽带洛夫波相速度图。这些相速度图与传统方法在短周期（<40 秒）内获得的相速度图一致。最后，我们通过棋盘测试分析了双波束形成方法的分辨率，发现基于我们的方法的相速度图的分辨率接近于双波束形成方法中使用的子阵的孔径。