Broadband Seismic Studies of Dome Growth at Merapi Volcano, Indonesia

EAR-0001199Voight, Barry 1998 年在默拉皮火山（印度尼西亚爪哇）山顶部署了为期一个月的宽带地震仪，产生了与活跃的安山质穹顶生长相关的火山地震的重要数据集。 这些地震传统上称为多相 (MP) 事件，通常以短周期台站上的 3-4 Hz 地面运动为特征。 然而，在圆顶数百米范围内收集的数据显示，MP 波形上叠加了相对高幅度、独特的、非常长周期（4 秒）的水平地面运动，在许多事件中，同一站点的波形几乎相同。 在更远距离的宽带站上观察不到极长周期脉冲。 水平地面运动的主导、脉冲幅度随距离的衰减、熔岩穹顶附近的台站的紧密距离以及现代宽带地震仪的特征都表明，这些变形脉冲是由于活跃生长的默拉皮穹顶的熔岩挤出过程引起的动态近场倾斜造成的。 拟议开展一个为期两年的项目，利用数值方法分析这些数据，计算合成位移和旋转场，并在两个项目中进行为期一个月的宽带地震仪 PASSCAL/RAMP 部署，并结合高数据速率倾斜测量，以便在默拉皮预期的持续活动期间收集更多数据。 这项研究的结果将对解释与火山过程相关的宽带信号产生重要影响，并可能导致对与活动火山穹顶生长相关的地震过程的全新理解。

EAR-0001199Voight, Barry A month-long deployment of broadband seismographs at the summit of Merapi volcano (Java, Indonesia) in 1998 has yield a remarkable data set of volcanic earthquakes associated with active andesitic dome growth. These earthquakes, traditionally termed multiphase (MP) events, are usually characterized by 3-4 Hz ground motions on short-period stations. However, data collected within a few hundred meters of the dome showed relatively high-amplitude, distinctive, very-long-period (4 sec) horizontal ground motions superposed on the MP waveforms, with nearly identical waveforms at the same stations over many events. Very-long-period pulses are not observed at broadband stations at greater distance. Dominance of horizontal ground motions, pulse amplitude decay with distance, the close proximity of stations near lava dome, and character of modern broadband seismographs all suggest that these deformational pulses are due to dynamic, near-field tilts caused by lava extrusion processes at the actively growing Merapi dome. A two year-project is proposed to analyze these data using numerical methods to compute synthetic displacement and rotation fields and two conduct a one-month long PASSCAL/RAMP deployment of broadband seismographs, in conjunction with high-data-rate tiltmetry, to collect more data during expected sustained actiity at Merapi. The results of this study will have important implications in interpreting broadband signals associated with volcanic processes, and may lead to fundamentally new understanding of seismic processes associated with active volcanic dome growth.