Do slickenfibers record episodic tremor and slow slip?

光滑纤维是否记录阵发性震颤和慢滑？

• 批准号: 2051565
• 负责人: Randolph Williams
• 金额: $ 15.71万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-05-01 至 2023-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2051565&HistoricalAwards=false
• 关键词: Do; slickenfibers; record; episodic; tremor

The earthquake cycle encompasses a variety of seismic processes that are only partially understood by geologists. For example, many large, earthquake-producing faults around the world also exhibit persistent episodes of seismic tremor (shaking that is only perceptible with modern instruments) accompanying slow slip (at rates of millimeters per year rather than the meters per second rates typical of earthquakes). This process, known as “episodic tremor and slow slip”, has been proposed to be a potential precursory phenomenon that may forecast larger earthquake ruptures. Leveraging this forecasting potential, however, requires determining the physical mechanisms underlying episodic tremor and slow slip, which is hindered by the lack of a definitive geologic record. This research will test the validity of a recently proposed geologic record of episodic tremor and slow slip: quartz veins that form incrementally following micro-slip events in earthquake-producing faults. This work will quantify the time scales of vein formation via hydrothermal experiments and assess their compatibility with those of the recurrence of episodic tremor and slow slip observed in active faults.Although much of the formation of incrementally developed quartz slickenfibers is consistent with seismological observations of episodic tremor and slow slip (depth, presence of fluids, stress drops, etc), a critical question remains unanswered: are the time scales of slickenfiber formation compatible with seismologically observed repeat times? For this to be true, quartz cements delineating microslip increments in slickenfibers must precipitate over time scales from 3 months to ~2 years depending on tectonic setting. Given typical fracture opening increments observed in slickenfibers, this conceptual model implies quartz precipitation rates of more than 10 μm / year. These rates are several orders of magnitude faster than those predicted by current kinetic-rate models. Recent work has argued that coseismic decreases in pore-fluid pressure may stimulate transient increases in quartz growth rates, allowing slickenfiber formation over time scales consistent with the recurrence of episodic tremor and slow slip. To test this hypothesis, this research will utilize a novel approach that allows accurate detection of precipitation rates as small as ~3 μm / year in hydrothermal experiments simulating large coseismic decreases in fluid pressure. Critically, these experiments will be conducted at temperature and pressure conditions consistent with the crustal depths where episodic tremor and slow slip occurs. Thus, the proposed work will be able to unequivocally determine if the time scales of slickenfiber formation are compatible with those of episodic tremor and slow slip, regardless of how much quartz is grown over the course of the experiments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

地震周期包括地质学家仅部分了解的各种地震过程。例如，世界各地许多大型地震发震断层也表现出持续的地震震动(只有用现代仪器才能察觉到的震动)，并伴随着缓慢的滑动(以每年毫米的速度，而不是地震的典型速度每秒米)。这一过程被称为“幕式震颤和缓慢滑动”，被认为是一种潜在的前兆现象，可能预示着更大的地震破裂。然而，利用这种预测潜力需要确定幕式震颤和缓慢滑动背后的物理机制，而缺乏明确的地质记录阻碍了这一点。这项研究将检验最近提出的一项关于幕式地震和慢滑的地质记录的有效性：在发震断层中，随着微滑移事件，逐渐形成的石英脉。这项工作将通过热液实验来量化脉脉形成的时间尺度，并评估它们与在活动断裂中观察到的幕式震颤和慢滑重复的时间尺度的兼容性。尽管逐渐发育的石英滑石纤维的形成与对幕式地震和慢滑(深度、流体的存在、应力降等)的地震学观察一致，但一个关键的问题仍然没有答案：滑石纤维形成的时间尺度是否与地震观测的重复时间兼容？要做到这一点，描述滑石纤维中微滑移增量的石英胶结物必须在3个月到~2年的时间尺度上沉淀下来，这取决于构造环境。考虑到在滑石纤维中观察到的典型的裂缝张开增量，这个概念模型意味着石英的沉淀速率超过10μm/年。这些速度比目前的动力学速度模型预测的速度快了几个数量级。最近的工作认为，孔隙流体压力的同震降低可能会刺激石英生长速率的瞬时增加，从而允许随着时间尺度的推移形成滑移纤维，这与周期性地震和缓慢滑动的复发相一致。为了验证这一假设，这项研究将利用一种新的方法，在模拟流体压力大幅同震下降的热液实验中，准确检测到低至~3μm/年的降雨率。关键是，这些实验将在与地壳深度一致的温度和压力条件下进行，在那里发生阵发性地震和缓慢滑动。因此，这项拟议的工作将能够毫不含糊地确定光滑纤维形成的时间尺度是否与阵发性震动和缓慢滑动的时间尺度兼容，无论在实验过程中生长了多少石英。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Are Low‐Frequency Earthquake Moments Area‐ or Slip‐Limited? A Rock Record Examination

低频地震矩区域或滑动区域是否有限？

• DOI: 10.1029/2021gl095759
• 发表时间: 2022
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Williams, Randolph T.;Kirkpatrick, James D.
• 通讯作者: Kirkpatrick, James D.