Analysis of the Seismicity Associated with the 1986 Eruptionof Mt. St. Augustine, Alaska: Relationship to Shallow Crustal Magmatic Processes

我们建议使用地震活动的时空行为来获得圣奥古斯丁火山管道系统的改进模型，并推断与1986年火山喷发相关的岩浆迁移过程。通过使用a)火山地震速度结构的真实二维模型和b)火山地震台站记录的地震波的传播时间和振幅数据，可以准确地确定震源参数。利用1976年一次火山喷发资料的初步结果表明，基于高斯束法的正演模拟振幅数据可能提供一种有效的限制震源深度的手段。这种方法在火山地震学上的潜力需要详细的勘探，我们建议在这次调查中进行。岩浆沿中央层状火山的导管向上运动，由于裂缝扩展、岩脉侵位、寄主岩石角化和最终的喷口开挖而产生微地震活动。喷发前地震前兆的精确位置（尤其是深度）可以为最终喷发的岩浆库的物理/化学不稳定性的演变提供重要线索。如果我们成功地开发出一种对震源深度高度敏感的地震定位方案，它将在火山喷发预测中具有重要的应用价值。

We propose to use space-time behavior of seismicity to obtain an improved model of Mt. St. Augustine's plumbing sytem and to infer the magma migration processes associated with its 1986 eruption. The ability to accurately determine hypocentral parameters would be achieved by using a) a realistic two- dimensional model of the volcano's seismic velocity structure and b) both travel time and amplitude data of seismic waves recorded at seismic stations on the volcano. Preliminary results using data from an eruption in 1976 indicate that amplitude data from forward modeling based on the Gaussian beam method might provide a powerful means of constraining focal depth. The potential of that method for volcano seismology requires detailed exploration, which we propose to conduct in this investigation. Magma movement up the conduit of a central stratovolcano always produces microearthquake activity due to fracture propagation, dike emplacement, brecciation of host rocks and eventually vent excavation. Precise location (especially of depth) of precursor earthquakes prior to eruptions can give important clues about the evolution of the physical/chemical instability in the magma reservoir that eventually erupts. If we succeed in developing an earthquake location scheme that is highly sensitive to depth of focus it could have an important application for eruption prediction.