Presenter: Maria R.P. Sudibyo
Date: 2015/11/05
Abstract
Mount Erebus is the most active volcano in Antarctica, an uncommon volcano in terms of its unusual phonolitic lava, its persistent Strombolian activity and its longlived convecting summit lava lake. During the monitoring in 1994 to 1998, several activities including short-period explosions, very long-period events, acoustic explosions, and volcanic tremor have been observed. Short period explosions show similar waveforms characteristic, which persists for tens of seconds into event codas at frequency up to several Hz, implying small range variation of source location, which is compatible with the small size (50 m diameter) of the lava lake. The explosion size distribution follows an approximately power distribution with a b-value of 7. Broadband observations report a very long-period signals with strong spectral peaks near 20,12, and 7 s, that precede lava lake surface explosion by 1.5 s and persists for up to 150 s. Particle motions suggest that an initial depth of VLP source residing between 300 to 800 m below the lava lake, although this depth can be exaggerated by nearradial tilt. The seismic/acoustic ratio show sharp trend of smaller explosions, implying\ that smaller and shallower events experience more seismic attenuation compared to the larger events, or that the shallower part of magma column is seismically isolated, which is not impacted by the smallest explosions due to the sharp impedance contrast across distinct layer. The synthetic acoustic signals are obtain using Green's function by varying delay times and amplitudes ratio. From the result obtained, they conclude that multi-pulse acoustic signals arise from two or more individual sources. Vulcanic tremor exhibit both monochromatic and polychromatic spectra.
Reference