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.

岩石圈动力学中的一个基本问题是，下壳是否比最高地幔更强或弱。这个问题不仅对于理解岩石圈的物理状态至关重要，而且对于能够描述主要断层的地震周期（即，在数百至数千年内的压力重复循环中重复累积的地震周期，然后在地震周期中释放这种压力的次数）。地震周期。为了将表面变形的观察转换为地震壳中的应力，我们需要机械模型，以准确描述岩石圈的机械性能（即流变学）。下层地壳是否比最高地幔更强或弱，对地震周期中断层的应力演变具有很大的影响。由于地震周期明显长于地球变形的现代测量时代，我们在整个地震周期中都没有完整的观测记录。没有完整的观察，并非总是可以直接从观察结果直接验证机械模型。此外，具有显着流变学复杂性的地震循环模型通常在计算上很昂贵，因此不适合探索与观察结果一致的全部允许模型参数。地震循环的机械模型通常仅包含Maxwell粘弹性，并且不包含Maxwell visco弹性，并且不考虑强大的深度依赖性物质的依赖性或较低的材料依赖性或替代品的依赖性或替代品。但是，岩石圈的流变学可能比麦克斯韦粘弹性更为复杂，岩石圈的材料特性预计将是深度依赖性的。在整个地震循环中可能对岩石圈变形有重大影响的流变复杂性包括深度依赖性粘度，幂律蠕变，汉堡粘弹性和深度的局部蠕变。在这个项目中，我们将：（1）量化整个地震周期表面变形的灵敏度对各个深度的流变。 （2）确定汉堡粘弹性和幂律蠕变是否在地震周期的模型中具有相同的影响。 （3）系统测试由于深度处局部或分布的蠕变而导致的经济震动表面变形的相似性。 （4）在理想化模型中的表面变形与具有深度依赖性粘度，幂律蠕变，瞬态粘弹性或深度处的局部蠕变的模型中建立时间相关的对应关系。最后一点将有助于理解试图从表面变形的观察结果验证地震循环模型所固有的非唯一性。此外，通过了解理想化的模型与更复杂模型的类别之间的对应关系，人们将能够将计算有效的理想化模型限制为地球数据，然后直接从理想化的模型推断中确定更复杂模型的范围。