The Dependence of Surface Deformation on Rheology Throughout the Seismic Cycle

整个地震周期中表面变形对流变的依赖性

• 批准号: 1045372
• 负责人: Eric Hetland
• 金额: $ 24.97万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-01-15 至 2014-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1045372&HistoricalAwards=false
• 关键词: Dependence; Surface; Deformation; Rheology; Throughout

A fundamental question in lithospheric dynamics is if the lower crust is stronger or weaker than the upper-most mantle. This question is not only of importance to understanding the physical state of the lithosphere, but is also essential to being able to describe the earthquake cycle on major faults (i.e., the repeated cycle of stress build-up on faults during a period of hundreds to thousands of years, and then the eventual release of that stress during an earthquake).Observations of the earthquake cycle are largely composed of measurements of the deformation of Earth?s surface at times during the earthquake cycle. In order to translate those observations of surface deformation to stresses in the seismogenic crust, we require mechanical models that accurately describe the mechanical properties (i.e., rheologies) of the lithosphere. Whether the lower crust is stronger or weaker than the upper-most mantle has strong implications for the evolution of stresses on faults during the earthquake cycle. As the earthquake cycle is significantly longer than the era of modern measurements of Earth deformation, we do not have a complete record of observations throughout an earthquake cycle. Without complete observations, it is not always possible to uniquely validate mechanical models directly from observations. Furthermore, models of the earthquake cycle with significant rheologic complexity are often computationally expensive, and thus not suited to explore the full range of permissible model parameters that are consistent with observations.Mechanical models of the earthquake cycle most often only contain Maxwell viscoelasticity, and do not consider either a robust depth- dependence of material properties or localized shear zones within the lower crust or mantle. However, the rheology of the lithosphere is likely more complicated than Maxwell viscoelasticity and material properties of the lithosphere are expected to be depth-dependent. Rheologic complexities that likely have significant impact on deformation of the lithosphere throughout the earthquake cycle include depth-dependent viscosity, power-law creep, Burgers viscoelasticity, and localized creep at depth. In this project we will: (1) Quantify the sensitivity of surface deformation throughout the earthquake cycle to rheologies at various depths.; (2) Determine if Burgers viscoelasticity and power-law creep have the same affect in models of the earthquake cycle.; (3) Systematically test the similarity of interseismic surface deformation due to localized or distributed creep at depth.; (4) Establish the time-dependent correspondence between surface deformation in idealized models and deformation in models with depth dependent viscosity, power-law creep, transient viscoelasticity, or localized creep at depth. The last point will contribute to an understanding of the non-uniquenesses inherent in trying to validate models of the earthquake cycle from observations of surface deformation. Additionally, by knowing the correspondences between idealized models and classes of more complicated models, one will be able to constrain computationally efficient idealized models to geodetic data, and then determine the range of the more complicated models directly from the idealized model inferences.

岩石圈动力学的一个基本问题是下地壳是否比最上地幔更强或更弱。这个问题不仅对于理解岩石圈的物理状态很重要，而且对于能够描述主要断层上的地震周期也至关重要（即，断层上应力累积的重复周期在数百至数千年，然后在地震期间最终释放该应力）。地震周期的观测主要由地震周期期间地球表面变形的测量组成。为了将表面变形的观察结果转化为发震地壳中的应力，我们需要能够准确描述岩石圈力学特性（即流变学）的力学模型。下地壳是否比最上地幔更强或更弱，对于地震周期期间断层上的应力演化具有重要意义。由于地震周期明显长于现代地球变形测量的时代，因此我们没有整个地震周期的完整观测记录。如果没有完整的观察，并不总是能够直接从观察中唯一地验证力学模型。此外，具有显着流变复杂性的地震周期模型通常计算成本较高，因此不适合探索与观测结果一致的全部允许模型参数。地震周期的力学模型通常仅包含麦克斯韦粘弹性，并且不适合探索与观测结果一致的全部允许模型参数。不考虑材料特性的强烈深度依赖性或下地壳或地幔内的局部剪切带。然而，岩石圈的流变学可能比麦克斯韦粘弹性更复杂，并且岩石圈的材料特性预计与深度相关。流变复杂性可能对整个地震周期中岩石圈的变形产生重大影响，包括深度相关的粘度、幂律蠕变、伯格粘弹性和深度局部蠕变。在这个项目中，我们将：（1）量化整个地震周期中地表变形对不同深度流变的敏感性。 (2) 确定伯格斯粘弹性和幂律蠕变在地震周期模型中是否具有相同的影响； (3) 系统测试深部局部或分布蠕变引起的震间地表变形的相似性； (4) 建立理想化模型中的表面变形与具有深度相关粘度、幂律蠕变、瞬态粘弹性或深度局部蠕变的模型中的变形之间的时间相关对应关系。最后一点将有助于理解通过表面变形观测来验证地震周期模型所固有的非唯一性。此外，通过了解理想化模型与更复杂模型类别之间的对应关系，我们将能够将计算效率高的理想化模型约束到大地测量数据，然后直接从理想化模型推论确定更复杂模型的范围。