Collaborative Research: Understanding free-surface scattering in an anisotropic medium with active and passive seismic methods at the Homestake Mine, South Dakota

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项目编号	1525229
	Collaborative Research: Understanding free-surface scattering in an anisotropic medium with active and passive seismic methods at the Homestake Mine, South Dakota
	Victor Tsai
主持机构	California Institute of Technology
项目开始年	2015
	2015-08-15
项目结束日期	2017-07-31
资助机构	US-NSF
项目类别	Standard Grant
项目经费	15878(USD)
国家	美国
语种	英语
英文摘要	Seismologists and exploration geophysicists utilize what are commonly called seismic waves to image the Earth?s interior. In fact, the major tool used for oil and gas exploration today is the seismic method, which use seismic waves comparable to sound waves to image the earth. How seismic waves propagate is also of fundamental importance to understanding of how earthquakes work. The standard models used to describe seismic wave propagation in both the academic world of seismology and the oil and gas industry make two simplifying assumptions that will be tested in this project: (1) the Earth?s surface acts like a mirror when seismic waves interact with it, and (2) material properties are isotropic meaning physical properties that control seismic wave propagation are not dependent upon the direction a wave is propagating. Both assumptions are known to be frequently wrong, but unraveling the when and how has proven experimentally difficult. This is an experimental proposal to address some of the shortcomings in previous data. The experiment is possible only because of the availability of a unique facility that has become accessible in the past few years called the Sanford Underground Laboratory in Lead, South Dakota, that is located within the Homestake Mine. Homestake was once the deepest gold mine in North America, but has now been converted to a facility for underground science. The project builds on an existing collaboration between physicists at the University of Minnesota and geophysicists at the California Institute of Technology and Indiana University. That group is currently operating a unique three-dimensional passive seismic array with sensors in the underground and on the surface. This project extends that project by adding a component of ?active source? data acquisition. That is, the current array is much like a passive sonar array listening for transients (earthquakes and mining explosions) and measuring background noise fields. This project centers on the use of controlled, manmade sources to supplement the listening mode. The active source data will provide strong added constraints on the physics of the process not possible with the listening mode alone. In this project the reseachers will collect three types of active source experimental data. (1) A novel experimental geometry called Horizontal Seismic Profile (HSP). This is a variant of a method commonly used in oil and gas exploration with vertical boreholes, but in this case the borehole is human sized and approximately horizontal. (2) an upside down reflection survey. This is much like reflection profiling using in the oil and gas industry, but the data will be collected in a mine drift to study how waves are reflected by the free surface. (3) Is a surface active source experiment where they will use an accelerated weight drop source to put a controlled pulse into the ground to be recorded by the operational passive array instruments. Analysis of these data will center on addressing two fundamental questions about the nature of seismic wave propagation. (1) How are seismic waves scattered by Earth?s free surface and the related complexity exploration geophysicists commonly call the weathered layer? (2) How good are existing theoretical models of anisotropic wave propagation and related models for how heterogeneity at scales smaller than a wavelength yield anisotropic behavior? The weathered layer problem will be addressed directly by the upside down reflection survey and HSP experiments and indirectly by analysis of passive array particle motions. The active source data will be modeling using a Kirchhoff integration forward modeling method using high resolution topography and a 3D geologic model under development by Sanford Underground Laboratory. The combined active and passive data will yield what is likely the most comprehensive data set per unit volume ever assembled to understand the scale dependence of anisotropy. A critical reason is the outstanding control provided by the observations collected by the mine and now being assembled for the research community by the Sanford Underground Laboratory. The HSP data will provide clean signals isolated from the free surface effect. Anisotropic parameters from these data will be measured using phase velocity measurements for P and the split S modes qS1, and qS2. Particle motion methods will provide an independent measure of S wave splitting. The surface source data will provide a dense volume sampling of azimuth dependence of propagation speeds. These data will be used to test if the entire rock volume of Homestake can be described as a uniform anisotropic medium or needs to be treated as a heterogeneous, anisotropic medium.
来源学科分类	Geosciences - Earth Sciences
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/68414
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Victor Tsai.Collaborative Research: Understanding free-surface scattering in an anisotropic medium with active and passive seismic methods at the Homestake Mine, South Dakota.2015.