Interferometric Imaging of Deep Mantle Reflectors Beneath the Western United States

美国西部下方深部地幔反射器的干涉成像

• 批准号: 0952187
• 负责人: Michael Thorne
• 金额: $ 15.44万
• 依托单位: University of Utah
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-05-15 至 2012-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0952187&HistoricalAwards=false
• 关键词: Interferometric; Imaging; Deep; Mantle; Reflectors

Recent seismological investigations of the upper-mantle located directly beneath the western United States have resolved a remarkable degree of structure and heterogeneity. These efforts have revealed previously unknown structures, such as large-scale mantle drips. How these upper-mantle structures are related to structure and processes in the mid- and lower-mantle is currently unresolved. A key step in deciphering this interaction between upper-mantle structures with deeper mantle layers is to use high resolution mapping of seismic discontinuities. In particular, discontinuities located approximately 400 to 700 km in depth (the mantle transition zone) are expected to be strongly affected by their interaction with upper mantle structures and are key target areas being investigated in this study.This work has developed a new technique based on seismic interferometry to investigate the nature of seismic reflectors in the upper- to mid-mantle region. Seismic processing using an interferometry approach has been extensively utilized in small-scale oil exploration efforts in the last decade, yet has not been applied to deeper targets as techniques of this kind require dense spacing of seismic recorders. Prior to the significant increase in seismic instruments made possible by the USArray project, this technique would not have been possible to adapt.Past efforts for looking at mantle discontinuity structure have been focused on studying seismic wave reflections off of the underside of seismic discontinuities. Many of these efforts have used underside reflections from the seismic phase SS (termed SS-precursors). However, using SS-precursors presents challenges in determining discontinuity depth, as knowledge of the seismic wave velocity on both the source- and receiver-side of the SS path is needed. The technique used in this study applies cross-correlation interferometry to migrate the SS-precursor data with the direct S-wave arrival passing through the discontinuity. This eliminates the need for detailed velocity structure on both source- and receiver-paths and is not dependent on any prior knowledge of where the seismic source is located. This technique provides better spatial resolution on mantle discontinuity structure and is elucidating the link between upper- and lower-mantle processes.

最近对美国西部正下方的上地幔进行的地震学调查已经解决了相当程度的结构和不均匀性。 这些努力揭示了以前未知的结构，如大规模的地幔滴。 这些上地幔结构如何与中、下地幔的结构和过程相关，目前还没有解决。 解释上地幔结构与更深地幔层之间的这种相互作用的关键步骤是使用地震不连续面的高分辨率映射。 特别是，位于深度约400至700公里（地幔过渡带）的不连续性预计将受到强烈的影响，他们与上地幔结构的相互作用，是在这项研究中正在调查的关键目标areas.这项工作已经开发出一种新的技术，地震干涉测量的基础上，调查的性质，在上中地幔区域的地震反射。 在过去十年中，使用干涉测量法的地震处理已广泛用于小规模石油勘探工作，但尚未应用于更深的目标，因为这种技术需要密集的地震记录器间距。 在USAray项目使地震仪器显著增加之前，这种技术不可能适应。过去研究地幔不连续结构的努力一直集中在研究地震波反射的地震不连续面的底面。 这些努力中的许多已经使用来自地震相SS（称为SS-前兆）的底面反射。 然而，使用SS前兆在确定不连续深度方面存在挑战，因为需要了解SS路径的震源侧和接收器侧的地震波速度。 本文采用互相关干涉法对直达横波通过不连续面的SS前兆数据进行偏移。 这消除了对源路径和接收器路径上的详细速度结构的需要，并且不依赖于震源位于何处的任何先验知识。 这项技术提供了更好的空间分辨率地幔不连续结构，并阐明上地幔和下地幔过程之间的联系。