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

我们建议利用地震活动的时空行为来获得一个改进的Mt.圣奥古斯丁的管道系统，并推断与1986年喷发有关的岩浆迁移过程。准确确定震源参数的能力将通过使用a)火山地震速度结构的真实二维模型和b)火山地震台记录的地震波的旅行时间和幅度数据来实现。使用1976年一次喷发的数据的初步结果表明，基于高斯光束方法的正演模拟的幅度数据可能提供一种强有力的手段来约束震源深度。这种方法用于火山地震学的潜力需要进行详细的勘探，我们在这次调查中建议进行这种探索。岩浆沿着中央层状火山的管道向上运动，由于裂缝扩展、岩脉侵位、围岩角砾化以及最终的喷口开挖，总是会产生微震活动。前兆地震在喷发前的准确位置(特别是深度)可以为最终喷发的岩浆储集层中物理/化学不稳定的演化提供重要线索。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，它可能会在喷发预测方面有重要的应用。

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.