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

利用面波提高地震各向异性和非均质性的垂直和水平分辨率

• 批准号: 1547368
• 负责人: Donald Forsyth
• 金额: $ 10.77万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-12-15 至 2019-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1547368&HistoricalAwards=false
• 关键词: Improving; vertical; horizontal; resolution; seismic

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.

地震和海浪产生的地震波沿着地球表面传播，但其振动会穿透数十至数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）和下面的对流地幔（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部署地震台站阵列，但由于地震到台站的多条传播路径以及海洋波源的不均匀分布，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，以提高我们的地震面波速度的测量，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的不同，这是一个有争议的假设，最近的一些研究已经支持了太平洋海底地震仪阵列内的Love和Rayleigh波色散的分析将测试海洋岩石圈内的径向各向异性明显不同于软流圈内的假设。 几组研究人员从全球层析成像研究报告，径向各向异性在上部岩石圈是小的或特征的SVSH与强各向异性在软流圈与SHSV。 这种对比被解释为指示岩石圈的深度范围或耗尽层的深度范围，但与早期的研究表明SHSV随着深度的增加而逐渐减小的结果不一致。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性，我们将：（1）将基模Love波频散的测量扩展到较短的周期，（2）增加Love波和Rayleigh波的较高模相速度的测量，（3）利用环境噪声相关性将高阶模态分析扩展到短周期，填补了岩石圈浅层SV敏感性的差距。