Physical Modeling of Long Period Events in a Controlled-Source Condition

受控源条件下长周期事件的物理建模

• 批准号: 2021768
• 负责人: Roohollah Askari
• 金额: $ 45.21万
• 依托单位: Michigan Technological University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2021768&HistoricalAwards=false
• 关键词: Physical; Modeling; Long; Period; Events

Pressure changes in rock cavities filled with fluids produce specific seismic signals. These signals are abundant in volcano "plumbing systems". They are called long-period (LP) events because of their duration. LP seismicity is an important precursor for volcanic eruptions because it is triggered by magma transport preceding the eruptions. Yet, the source mechanism of LP events is still poorly understood. A theoretical model developed in the 1980s, The Chouet’s model, has been widely used to describe this mechanism. The model has been thoroughly explored with numerical simulations but not tested experimentally. This is because producing LP signals in the laboratory is challenging. Here, the researchers are developing a new apparatus to artificially generate LP signals. The apparatus consists of a crack filled with fluid and embedded within a large concrete slab. The slab is 6-meter long (~20 ft) and instrumented. Pressure in the fluid is varied while sensors record the produced signals. Analysis of the signal allow unveiling the source mechanism of LP events. The project outcomes have strong implications for volcanic eruption hazard assessment. They also find applications in other disciplines, such as glaciology where LP events are triggered by water-filled cracks or the geothermal energy sector. The project provides support for an early career scientist and a graduate student at Michigan Technological University. It also provides training for undergraduate students, notably from groups underrepresented in Science, as well as outreach to K-12 students. It is funded by both the Geophysics and the Petrology and Geochemistry programs.The goal of the researcher is to quantitively characterize LP signals with respect to the fundamental parameters that influence LP seismicity. These critical parameters include crack stiffness (rheology contrasts of the materials), fluid viscosity, triggering location, source frequency, crack orientation, and mass transport. The new apparatus is 6m x 6m wide and 22-cm thick. The concrete slab is equipped with controlled piezoelectric sources which generate pressure pulses from different locations/orientations with respect to the crack. It is also equipped with transducer and strain sensors to analyze the slab response and the produced signals. The cracks can be filled with water or ethanol. In addition to providing constraints for computational modeling, this research explores regions of the parameter space which cannot be easily probed numerically. It, thus, bridges a critical gap between theoretical models and the LP signals observed at active volcanoes.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.

充满流体的岩石洞穴中的压力变化产生特定的地震信号。这些信号在火山“管道系统”中非常丰富。它们被称为长周期（LP）事件，因为它们的持续时间。LP地震活动是火山喷发的重要前兆，因为它是由喷发前的岩浆输送触发的。然而，LP事件的源机制仍然知之甚少。 在20世纪80年代发展起来的理论模型，Chouet模型，已被广泛用于描述这种机制。该模型已被彻底探讨了数值模拟，但没有实验测试。这是因为在实验室中产生LP信号具有挑战性。在这里，研究人员正在开发一种新的装置来人工产生LP信号。该装置由一个充满流体的裂缝组成，并嵌入一个大的混凝土板中。该板长6米（约20英尺），装有仪器。流体中的压力变化，同时传感器记录产生的信号。信号分析揭示了LP事件的震源机制。该项目的成果对火山喷发危险性评估具有重要意义。它们还在其他学科中找到应用，例如冰川学（LP事件由充满水的裂缝或地热能部门触发）。该项目为密歇根理工大学的一名早期职业科学家和一名研究生提供支持。它还为本科生提供培训，特别是来自科学领域代表性不足的群体，以及对K-12学生的宣传。 该项目由地球物理学、岩石学和地球化学项目资助，研究人员的目标是定量描述LP信号与影响LP地震活动性的基本参数之间的关系。这些关键参数包括裂纹刚度（材料的流变学对比），流体粘度，触发位置，源频率，裂纹方向和质量输运。新仪器宽6米x 6米，厚22厘米。混凝土板配备有受控压电源，其从相对于裂缝的不同位置/取向产生压力脉冲。它还配备了传感器和应变传感器来分析板的响应和产生的信号。可以用水或乙醇填充裂缝。除了提供计算建模的限制，本研究探讨了区域的参数空间，不能很容易地探测数值。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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

Laboratory Measurements of the Impact of Fracture and Fluid Properties on the Propagation of Krauklis Waves

裂缝和流体性质对克劳克利斯波传播影响的实验室测量

• DOI: 10.1029/2020jb021593
• 发表时间: 2021
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Cao, Haitao;Nakagawa, Seiji;Askari, Roohollah
• 通讯作者: Askari, Roohollah