Improving the vertical and horizontal resolution of seismic anisotropy and heterogeneity using surface waves

地震和海浪产生的地震波沿着地球表面传播，但其振动能穿透几十到几百公里进入固体内部。这些波的速度是我们测量构造板块（岩石圈）和底层对流地幔（软流圈）结构的主要手段之一。测量速度的最佳方法之一是在陆地或海底设置地震台站阵列，但由于地震到台站的传播路径多种多样，以及海浪源分布不均匀，测量变得更加困难。在这个项目中，我们将开发新的技术来克服这些困难，以改进我们对地震表面波速度的测量，从而提高我们对岩石圈和软流圈结构的认识。新测量的一个主要目标是测试海洋岩石圈的变形是否与软流圈有根本不同，这是一个有争议的假设，但最近的许多研究都支持这一假设。对太平洋海底地震仪阵列中的洛夫波和瑞利波频散的分析将检验海洋岩石圈内的径向各向异性与软流圈内的径向各向异性明显不同的假设。几组研究人员从全球层析研究中报告说，与软流圈具有强各向异性的SHSV相比，上层岩石圈的径向各向异性较小或以SVSH为特征。这种对比被解释为表明岩石圈的深度范围或枯竭层的深度范围，但与早期的研究结果不一致，该研究表明SHSV随着深度的增加而逐渐减小。为了提高深度分辨率，解决岩石圈径向各向异性程度和软流圈各向异性强度的模糊问题，我们将：(1)将Love波频散的测量扩展到更短的周期，(2)增加Love波和Rayleigh波的高模相速度测量，(3)利用环境噪声相关将高模态分析扩展到短周期，以填补浅层岩石圈SV灵敏度的空白。

Earthquakes and ocean waves generate seismic waves that travel along the surface of the earth, but with vibrations that penetrate tens to hundreds of kilometers into the solid interior. The velocities of these waves are one of our primary means of measuring the structure of the tectonic plates (lithosphere) and the underlying convecting mantle (asthenosphere). One of the best ways to measure the velocity is with arrays of seismic stations, either on land or on the sea floor, but the measurements are made more difficult due to multiple propagation paths from the earthquakes to the stations and by uneven distribution of ocean wave sources. In this project, we will develop new techniques to overcome these difficulties to improve our measurements of seismic surface wave velocity and therefore our knowledge of the structure of the lithosphere and asthenosphere. One primary goal of the new measurements is to test whether deformation of the oceanic lithosphere is fundamentally different than the asthenosphere, a controversial hypothesis that a number of recent studies have supported.The analysis of Love and Rayleigh wave dispersion within ocean-bottom-seismometer arrays in the Pacific will test the hypothesis that radial anisotropy within the oceanic lithosphere is distinctly different than within the asthenosphere. Several groups of investigators have reported from global tomographic studies that radial anisotropy in the upper lithosphere is either small or characterized by SVSH in contrast to the strong anisotropy in the asthenosphere with SHSV. This contrast has been interpreted as indicating either the depth extent of the lithosphere or the depth extent of a depleted layer, but is in disagreement with earlier studies that showed SHSV decreasing gradually with increasing depth. To improve the depth resolution and resolve the ambiguity about the extent of lithospheric radial anisotropy and strength of asthenospheric anisotropy, we will: (1) extend the measurement of fundamental mode Love wave dispersion to shorter periods, (2) add measurements of higher mode phase velocity for Love and Rayleigh waves, and (3) extend higher mode analysis to short periods using ambient noise correlation to fill in the gap in sensitivity to SV in the shallow lithosphere.