Investigation of source spectral models and scaling for slow slip processes in subduction zones

该奖项是根据2009年美国恢复和再投资法案（公法111 - 5）资助的。最近，在全球许多俯冲带发现了一种新的变形和弱地震辐射耦合模式。缓慢的滑动和微弱的震颤以准规则的间隔从大型逆冲断层界面的锁定部分间歇性地向下倾斜，并被称为间歇性震颤和滑动（ETS）。ETS与俯冲带的锁定和危险部分可能的相互作用要求更好地理解这一有趣的现象。研究人员将开发适当的模型，将这些缓慢滑动过程的不同大小和持续时间联系起来。这些模型将有助于比较这些过程的不同实例，以及比较各种频率范围的现有数据。这是一条了解慢滑过程物理学与更好理解的地震物理学有何不同的途径。更广泛的影响包括促进一名或多名研究生的教育，可能还有本科生。这项工作将阐明一种新的断层滑动模式，并可能对地震学、大地测量学、摩擦学和岩石力学的研究产生变革性的影响。更好地了解俯冲带中较小和较大的慢滑事件之间的关系可能有助于预测那里大地震的发生，因此可能与地震危险性直接相关。 此外，间歇性震颤和滑动事件提供了一个宝贵的机会，以提高公众对区域地震危险的认识。目前，我们对ETS源过程的性质和基本物理学缺乏基本的了解。我们也不明白最近对慢滑过程的观测越来越多，其中包括微小的低频地震，稍大的极低频地震，慢滑事件，偶发性震颤和滑动，以及大型无声地震之间的关系。这些慢滑过程的特点是紧急开始，弱振幅，和长的持续时间。与具有相似时刻的常规地震相比，它们的频谱在高频能量上有所损耗。地震学家了解常规地震的一种方法是通过震源谱模型，如Ω平方模型。对于规则地震，震源谱模型代表了我们对地震的理解，即地震是一个尺度不变的过程，在很大的地震矩范围内是自相似的。这样一个统一的模型是缺乏慢滑现象。我建议开发适当的源缩放模型的慢滑过程，并与现有的数据在不同的频率范围内进行比较，以限制可能的模型的慢滑事件的源谱。构建这样的模型涉及到确定光谱斜率、拐角频率、应力降和传播速度之间的关系和约束条件，对俯冲带（特别是卡斯卡迪亚和日本）慢滑过程的观测数量迅速增加，这是一个及时的建议。一个合适的谱模型将有助于比较来自不同俯冲带、频带和ETS事件量级的数据。在某些情况下，这些数据应进行比较的绝对力矩率谱。在其他情况下，只能进行相对比较，但这仍然可能对潜在源光谱模型造成很大的限制。而定期地震有一个大致恒定的破裂速度支撑其自相似的性质，对于慢滑事件有证据表明，破裂传播速度是大小相关的。同样，应力降，虽然在一个非常大的范围内的大小的定期地震恒定，可能是规模依赖于缓慢的滑动过程。约束有效的源谱模型将揭示重要的物理性质之间的关系，如应力降，破裂速度，和moment.The建议的源谱模型的建设和比较与各种类型的数据将解决许多关键问题的慢滑过程，并进一步阐明ETS过程的物理。了解慢滑过程是否以及如何随着尺寸而扩展将代表一个根本性的进步，因此有可能成为真正的变革。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)Recently, a new mode of coupled deformation and weak seismic radiation has been discovered in numerous subduction zones globally. Slow slip and weak tremor occur episodically down-dip from the locked portion of the megathrust interface at quasi-regular intervals and have been termed Episodic Tremor and Slip (ETS). The likely interaction of ETS with the locked and hazardous portions of subduction zones mandate better understanding of this intriguing phenomenon.The researcher will develop appropriate models to relate the different sizes and durations of these slow slip processes. The models will facilitate comparison of different instances of these processes, as well as comparisons of available data at various frequency ranges. This is an avenue to understanding how the physics of slow slip processes differs from the better-understood physics of earthquakes.Broader impacts include furthering the education of one or more graduate students, and possibly undergraduates. This work will elucidate a new mode of fault slip, and could have a transformative impact on studies in seismology, geodesy, friction and rock mechanics. A better understanding of the relationship between smaller and larger slow slip events in subduction zones may help forecast the occurrence of large earthquakes there, and thus could be directly relevant to seismic hazard. As well, episodic tremor and slip events provide a valuable opportunity to advance public awareness of the regional seismic hazard. At present we lack a fundamental understanding of the nature and basic physics of the ETS source process. Nor do we understand the relationship between the growing menagerie of recent observations of slow slip processes, which include tiny low frequency earthquakes, somewhat larger very low frequency earthquakes, slow slip events, episodic tremor and slip, and large silent earthquakes. These slow slip processes are characterized by emergent beginnings, weak amplitudes, and long durations. Their spectra are depleted in high-frequency energy compared with regular earthquakes of similar moment.One way in which seismologists understand regular earthquakes is through models of the source spectrum such as the omega-squared model. For regular earthquakes, a source spectral model represents our understanding of earthquakes as a scale-invariant process that is self-similar over a very large range of seismic moments. Such a unifying model is lacking for slow slip phenomena. I propose to develop appropriate source scaling models for slow slip processes and compare with available data at various frequency ranges to constrain possible models of the source spectrum of slow slip events. Constructing such models involves determining relations among and constraints on spectral slope, corner frequency, stress drop, and propagation velocity.Burgeoning numbers of observations of slow slip processes from subduction zones, particularly Cascadia and Japan render this a timely proposal. An appropriate spectral model will facilitate comparison of data from different subduction zones, frequency bands, and magnitudes of ETS events. In some cases these data should be compared in terms of absolute moment rate spectra. In other cases only a relative comparison can be made, but that may still place strong constraints on potential source spectral models. Whereas regular earthquakes have a roughly constant rupture velocity underpinning their self-similar nature, for slow slip events there is evidence that rupture propagation velocity is size-dependent. Similarly, stress drop, although constant over a very large range of sizes of regular earthquakes, may be size-dependent for slow slip processes. Constraining valid source spectral models will reveal relationships between important physical properties such as stress drop, rupture velocity, and moment.The proposed source spectral model construction and comparison with various types of data will address many key questions about slow slip processes and further elucidate the physics of the ETS process. Understanding whether and how slow slip processes scale with size would represent a fundamental advance, and as such has the potential to be truly transformative.