Collaborative Research: Geodetic Constraints on Moment Deficit and Physics-based Earthquake Cycle Models in the Source Region of the M 9 Tohoku, Japan Earthquake

合作研究：日本东北9级地震震源区矩差的大地测量约束和基于物理的地震周期模型

• 批准号: 1141832
• 负责人: Kaj Johnson
• 金额: $ 9.34万
• 依托单位: Indiana University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-07-01 至 2014-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1141832&HistoricalAwards=false
• 关键词: Collaborative; Research; Geodetic; Constraints; Moment

The Mw 9 March 11, 2011 Tohoku earthquake, resulting in 25,000 fatalities, was the largestearthquake to strike Japan in modern times. The failure of long-term forecasts to anticipate anevent of this magnitude is leading to a reevaluation of our scienti c understanding of subductionzone fault dynamics. At the same time, the enormous Japanese investment in seismic andgeodetic monitoring provides an unprecedented opportunity to study processes leading to giantearthquakes. The investigators will focus here on two aspects of the quake that raise central issues for our abilityto forecast future hazards globally: 1) the constraints that geodetic strain accumulation placeon the seismic moment budget, and 2) how the distribution of mechanical properties on theplate interface control seismic versus aseismic slip.Forecasts of seismic hazard rely primarily on the historical record, paleoseismology, andgeodetic strain accumulation. While a strict time-predictable model has proven inconsistentwith geodetic data in some areas, the rate of strain accumulation must strongly inuence the recurrence rate and/or size of large earthquakes. Previous analyses of the extensive JapaneseGPS data set regularize the underdetermined inverse problem; the inferred plate coupling isthus conditional on the choice of regularizing functional. In addition, most assumed no coupling at the trench, an area that effectively lies in the model null-space. The researchers propose rather to estimate rigorous bounds on the moment deficit rate, independent of any regularizing functional. They also propose to systematically explore the effects of time-dependent viscoelastic effects on estimates of slip deficit.The Tohoku earthquake also raises profound questions about the frictional properties ofthe subducting plate interface. Mw 7 events along the Japan-Kurile trench have repeatedin nearly the same locations. Substantial afterslip following these events suggested that thefault surrounding these seismic `asperities' have different frictional properties, e.g., velocityweakening `asperities' surrounded by velocity strengthening regions. The fact that the March11 earthquake seems to have ruptured through both areas raises important questions. Is theasperity paradigm fundamentally flawed? Or did the M 9 activate other weakening mechanisms(thermal pressurization?) that allowed it to rupture through velocity strengthening regions?To distinguish between competing hypotheses the researchers will use a combination of GPS data basedhypothesis testing and physics based fault modeling. They will test whether or not post-seismicGPS data can be fit with afterslip only in regions that have not experienced seismic slip inthe last several decades. They will test alternative physical models that could accountfor the observed behavior, by extending our numerical codes that couple rate-state friction,thermal pressurization, and dilatant strengthening to three dimensions. This will allow them totest for example whether dilatancy could stabilize slip in otherwise velocity weakening regions,or thermal pressurization could allow ruptures to extend into velocity strengthening areas.

2011年3月11日发生的东北地震造成25，000人死亡，是日本近代发生的最大地震。长期预测未能预测到这种规模的事件，导致我们重新评估对俯冲带断层动力学的科学理解。与此同时，日本在地震和大地测量监测方面的巨大投资为研究导致大地震的过程提供了前所未有的机会。研究人员将集中在地震的两个方面，这两个方面为我们预测全球未来灾害的能力提出了核心问题：1）大地应变积累对地震矩预算的约束，以及2）板块界面上的力学性质分布如何控制地震与地震滑动。地震灾害的预测主要依赖于历史记录、古地震学和大地应变积累。虽然严格的时间可预测模型已被证明与某些地区的大地测量数据不一致，但应变累积速率必须强烈影响大地震的复发率和/或规模。以前的分析广泛的JapaneseGPS数据集正则化欠定逆问题，推断板耦合isthus正则化功能的选择条件。此外，大多数假设没有耦合在沟槽，一个区域，有效地位于模型零空间。研究人员建议，而不是估计严格的界限的时刻赤字率，独立于任何正规化功能。他们还建议系统地探索随时间变化的粘弹性效应对滑动亏损估计的影响。东北地震也提出了关于俯冲板块界面摩擦特性的深刻问题。沿日本-千岛海沟沿着的MW 7地震在几乎相同的位置重复发生。这些事件之后的大量后滑表明，围绕这些地震“粗糙体”的断层具有不同的摩擦特性，例如，被速度强化区域包围的速度弱化“粗糙体”。事实上，3月11日的地震似乎已经破裂，通过这两个地区提出了重要的问题。粗糙范式是否存在根本性缺陷？还是M9启动了其他削弱机制（热增压？）使其能够在速度强化区破裂为了区分相互竞争的假设，研究人员将使用基于GPS数据的假设检验和基于物理的故障建模相结合.他们将测试地震后的GPS数据是否只适用于在过去几十年中没有经历地震滑动的地区。他们将测试替代的物理模型，可以解释观察到的行为，通过扩展我们的数值代码，耦合率状态摩擦，热加压，和增强到三维。这将使他们能够测试，例如，在其他速度减弱的区域中，双折射是否可以稳定滑动，或者热加压是否可以允许破裂延伸到速度加强区域。