Collaborative Research: Mapping Crustal Tectonic Structure Using Seismic Anisotropy

合作研究：利用地震各向异性绘制地壳构造结构图

• 批准号: 0337340
• 负责人: David Okaya
• 金额: $ 12.64万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-01-15 至 2006-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0337340&HistoricalAwards=false
• 关键词: Collaborative; Research; Mapping; Crustal; Tectonic

MAPPING CRUSTAL TECTONIC STRUCTURE USING SEISMIC ANISOTROPY Seismic anisotropy has been observed to correlate with aligned cracks in the shallow crust and inferred to be related to lattice-preferred orientation (LPO) of olivine due to mantle flow. However, anisotropic behavior due to structural layering or inherent foliation of crustal material is not as well studied even though metamorphism and deformation are fundamental expressions of plate convergence and have the potential to pervasively structure the crust and influence wave propagation at regional scales. Regional foliations and compositional alignments are produced by deformation and metamorphism associated with tectonic processes and should result in "anisotropic terranes" detectable by seismic methods. Thus the identification and mapping of anisotropy within the crust can serve as a proxy for the presence and spatial extent of tectonic deformation. We examine a three-dimensional exhumed regionally-foliated antiformal structure located at Nanga Parbat, Pakistan, to test our hypothesis that regional deformation and metamorphism result in crustal anisotropy and that this anisotropy can be observed in the recorded seismic wavefield and used as a proxy to map subsurface rock fabric. For our study we use an existing data set collected by the NSF-Continental Dynamics Nanga Parbat project (NSF EAR-9418849). We have identified 365 high-quality local earthquakes which were recorded within a temporary 56 short-period/broadband array. The combination of local earthquakes/stations provides internal illumination of the Nanga Parbat antiform. Using this data set, our research objectives are to: (1) quantify the observations of seismic anisotropy in the seismic data, (2) develop techniques to systematically analyze the anisotropic signatures recorded in the seismic wavefields (interpretive tomography), (3) calibrate these observations using petrophysical properties directly measured from Nanga Parbat rock samples, (4) use Christoffel anisotropy theory and synthetic seismograms computed by 3D anisotropy wave propagation code for verification of our analyses, (5) develop a set of tools that can be used to help design field experiments to measure the anisotropic wave field through complex 3-D structures, and (6) determine Vp, Vs, and Vp/Vs ratios to better constrain geodynamic modeling of crustal deformation. These objectives allow us to understand the relationship between seismic anisotropy and crustal tectonic deformation.

已经观察到使用地震震荡的地震各向异性的映射地壳构造结构与浅层地壳中的对齐裂纹相关，并推断出与橄榄石的晶状体脱落方向（LPO）相关。然而，即使变质和变形是板收敛的基本表达，也没有对地壳材料的结构分层或固有的叶面引起的各向异性行为，并且有可能在区域尺度上泛滥地结构地壳并影响波浪传播。区域叶子和组成比对是通过与构造过程相关的变形和变质性产生的，应通过地震方法检测到可检测到的“各向异性地层”。因此，在地壳内的各向异性的鉴定和映射可以作为构造变形的存在和空间范围的代理。 我们检查了位于巴基斯坦Nanga Parbat的三维区域散布的抗形结构，以检验我们的假设，即区域变形和变质性会导致地壳各向异性，并且可以在记录的地震波场中观察到这种各向异性，并用作proxy to proxy to proxy绘制地下岩石面料。 在我们的研究中，我们使用了NSF-汤型动力学Nanga Parbat项目（NSF EAR-9418849）收集的现有数据集。 我们已经确定了365个高质量的当地地震，这些地震记录在临时的56个短期/宽带阵列中。 局部地震/站点的结合提供了Nanga Parbat Antiform的内部照明。 Using this data set, our research objectives are to: (1) quantify the observations of seismic anisotropy in the seismic data, (2) develop techniques to systematically analyze the anisotropic signatures recorded in the seismic wavefields (interpretive tomography), (3) calibrate these observations using petrophysical properties directly measured from Nanga Parbat rock samples, (4) use Christoffel anisotropy theory and synthetic seismograms computed by 3D anisotropy wave propagation code for verification of our analyses, (5) develop a set of tools that can be used to help design field experiments to measure the anisotropic wave field through complex 3-D structures, and (6) determine Vp, Vs, and Vp/Vs ratios to better constrain geodynamic modeling of crustal deformation. 这些目标使我们能够了解地震各向异性和地壳构造变形之间的关系。