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.

许多天然材料在很宽的尺度范围内表现出结构异质性。这种具有微观结构的介质的例子几乎包括地壳的每一部分，以及制造的复合材料，如混凝土。这些材料也支持波动，并且已经发展了各种技术，这些技术使用传播波对材料结构进行无损检测。目前，这些技术（反射地震学、超声波无损评价等）大部分是基于对均匀（或近均匀）材料中波的理论理解和计算方法。有效介质理论试图在宏观尺度上表达微观非均匀性的影响，在一定程度上弥合了理论基础和应用背景之间的鸿沟。然而，有效介质方法的严格论证在很大程度上限于周期性材料模型，它不像沉积岩等无序材料。本研究将试图利用最近的进展，在介质中的微观结构的声波和弹性波的模拟，以评估解释模拟实验数据的可行性，通过更简单的模型没有微观结构。这些模型可能表现出微观尺度上不存在的物理特性，例如粘性损失或各向异性响应。我们的方法结合了各种数值模拟方法，包括数值放大，计算波在高度异构的模型，反演或参数估计，以确定宏观模型。科学家要想生产石油和天然气、预测地震和海啸等其他地质构造事件、安全地修复污染物以及将多余的温室气体埋在地下，他们必须首先能够对地球的地下进行成像。需要绘制岩层、流体和断层图，并了解它们的深度和横向范围。为了创建地下的图像，能量被发送到地面，产生波。地下的不均匀性导致这些波的一部分被发送回地面，地震仪（麦克风）在波通过时记录波。科学家们试图从这些信号推断地下的结构。岩石是由多孔晶格中的微观颗粒组成的，其非常复杂的力学性质使这一推论变得非常复杂。这些微小成分的物理特性和孔隙内的流体联合收割机以一种复杂而又知之甚少的方式结合在一起，产生了地球的可观测响应。在我们以前的工作中，我们已经设计了方法来模拟波通过复杂的微观结构的材料的传播，以及从可观察到的数据来确定宏观材料描述的程序。这项提议设想了这两条工作线的融合，并可以阐明地下结构的哪些方面可以或不能从地震记录中推断出来。