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

在充满流体的岩洞中，压力的变化会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。由于其持续时间长，因此被称为长周期事件。低压地震活动性是火山喷发的重要前兆，因为它是由火山喷发前的岩浆运移引发的。然而，LP事件的源机制仍然知之甚少。一个在20世纪80年代发展起来的理论模型，the Chouet’s model，被广泛用于描述这一机制。该模型已通过数值模拟进行了深入的研究，但尚未进行实验验证。这是因为在实验室中产生LP信号是具有挑战性的。在这里，研究人员正在开发一种人工产生LP信号的新设备。该装置由一个充满流体的裂缝组成，并嵌入在一个大混凝土板中。平板长6米（约20英尺），配有仪器。当传感器记录产生的信号时，流体中的压力会发生变化。对信号的分析可以揭示LP事件的源机制。项目成果对火山喷发危险性评价具有重要意义。他们也在其他学科中找到了应用，比如冰川学，在冰川学中，LP事件是由充满水的裂缝或地热能源部门引发的。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，并向K-12学生提供推广。它是由地球物理学、岩石学和地球化学项目共同资助的。研究人员的目标是根据影响低震源地震活动性的基本参数对低震源信号进行定量表征。这些关键参数包括裂纹刚度（材料的流变对比）、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，厚22厘米。混凝土板上装有可控的压电源，可以从裂缝的不同位置/方向产生压力脉冲。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。裂缝可以用水或乙醇填充。除了为计算建模提供约束外，本研究还探索了参数空间中不易用数值方法探测的区域。因此，它弥合了理论模型和在活火山观测到的LP信号之间的关键差距。该奖项反映了美国国家科学基金会的法定使命，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。

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.