Collaborative Research: Multiscale Aspects for Wave Propagation Inverse Problems

协作研究：波传播反问题的多尺度方面

• 批准号: 0714159
• 负责人: Susan Minkoff
• 金额: $ 12万
• 依托单位: University of Maryland Baltimore County
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-09-01 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0714159&HistoricalAwards=false
• 关键词: Collaborative; Research; Multiscale; Aspects; Wave

Many natural materials exhibit structural heterogeneity across a wide range of scales. Examples of such media with microstructure include virtually every part of the Earth's crust, and manufactured composite materials such as concrete. These materials also support wave motion, and various technologies have evolved which use propagating waves for nondestructive interogation of material structure. In their present state, these technologies (reflection seismology, ultrasonic nondestructive evaluation, etc) are for the most part based on theoretical understanding and computational methods developed for waves in homogeneous (or near-homogeneous) materials. This divide between theoretical basis and application context is bridged to some extent by effective medium theories which attempt to express at macroscopic scales the effect of microscopic heterogeneities. However rigorous justification of the effective medium approach is largely limited to periodic material models, which do not resemble disordered materials such as sedimentary rock. This study will attempt to leverage recent advances in the simulation of acoustic and elastic waves in media with microstructure to assess the feasibility of explaining simulated experimental data by means of simpler models without microstructure. These models may exhibit physical characteristics not present on the microscopic scale, for instance viscous loss or anisotropic response. Our approach combines various numerial simulation methods, including numerical upscaling, for computing waves in highly heterogeneous models, with inversion or parameter estimation to determine macroscopic models. The proposed work will rely upon a previously developed computational framework for inversion.For scientists to be able to produce oil and gas, to predict earthquakes and other tectonic events such as tsunamis, to safely remediate contaminants, and to bury excess greenhouse gases underground, they must first be able to image the earth's subsurface. Rock layers, fluids, and faults need to be mapped and their depths and lateral extent understood. To create an image of the subsurface, energy is sent into the ground which generates a wave. The heterogeneous nature of the subsurface causes a portion of these waves to be sent back to the surface where seismometers (microphones) record the waves as they pass. From these signals scientists try to infer the structure of the subsurface. This inference is enormously complicated by the very complex mechanical nature of rock, which is composed of microscopic grain particles in a porous lattice. The physical characteristics of these tiny constituents and the fluids within the pores combine in a complex and poorly understood way to yield the observable response of the Earth. In our previous work, we havedevised methods to simulate propagation of waves through complex microscopically structured material, and also procedures to determine the macroscopic material descriptions from observable data. This proposal envisions the fusion of these two lines of work and could shed light on which aspects of subsurface structure can, or can't, be inferred from seismic recordings.

许多天然材料在广泛的尺度上表现出结构性异质性。具有微观结构的此类介质的例子包括地球地壳的每个部分以及制成的复合材料（例如混凝土）。这些材料还支持波动，并且各种技术已经进化，这些技术利用传播波来无损材料结构。在目前的状态下，这些技术（反思地震学，超声波无损评估等）大部分是基于理论理解和针对均匀（或近乎同质）材料的波浪开发的理论理解和计算方法。在某种程度上，试图以宏观尺度表达微观异质性的效果的有效培养基理论在一定程度上弥合了理论基础和应用环境之间的这种鸿沟。无论有效的培养基方法的严格理由在很大程度上仅限于周期性材料模型，这些模型与无序材料（如沉积岩石）不类似。这项研究将试图利用具有微观结构的媒体模拟声波和弹性波的最新进展，以评估通过没有微观结构的简单模型来解释模拟实验数据的可行性。这些模型可能表现出微观量表不存在的物理特征，例如粘性损失或各向异性反应。我们的方法结合了各种数字仿真方法，包括数值升级，用于计算高度异质模型中的波，以及倒置或参数估计以确定宏观模型。拟议的工作将依赖于以前开发的计算框架。要使科学家能够产生石油和天然气，预测地震和其他构造事件，例如海啸，安全地弥补污染物，并在地下掩埋多余的温室气体，他们必须首先能够形象地球的地下图像。需要绘制岩石层，流体和断层，并理解它们的深度和横向范围。为了创建地下的图像，将能量发送到产生波浪的地面。地下的异质性使这些波的一部分被发送回表面，在该表面，地震仪（麦克风）记录了波浪时的波动。从这些信号中，科学家试图推断地下的结构。岩石的非常复杂的机械性质极为复杂，岩石由多孔晶格中的微观晶粒颗粒组成。这些微小成分的物理特征和毛孔中的流体以复杂且知之甚少的方式结合在一起，以产生地球的可观察反应。在我们先前的工作中，我们介绍了通过复杂的显微镜结构材料模拟波传播的方法，以及从可观察到的数据中确定宏观材料描述的程序。该建议设想了这两种工作的融合，并可能阐明地下结构的哪些方面可以从地震记录中推断出来或不能推断出来。