A phreatic explosion model inferred from a very long period seismic event at Mayon Volcano, Philippines

• Published in: Journal of geophysical research. Solid earth 2015-01, Vol.120 (1), p.226-242
• Main Authors: Maeda, Yuta, Kumagai, Hiroyuki, Lacson Jr, Rudy, Figueroa II, Melquiades S., Yamashina, Tadashi, Ohkura, Takahiro, Baloloy, Alejo V.
• Format: Article
• Language: English
• Subjects: Approximation; Atmospheric precipitations; Bandpass filters; Boiling; Clay; Clay minerals; crack sealing; Cracks; Craters; Deposits; Discharge; Earthquake prediction; Explosions; Fragmentation; Geophysics; Inflation; Inversions; Mathematical models; Mayon Volcano; Meteorological data; Minerals; Peak frequency; Philippines; Phreatic explosion; Precipitation; Precursors; Sealing; Seismic activity; source time function; Thermography; Time functions; Vertical forces; very long period event; Volcanoes; Water vapor; Water vapour; waveform inversion; Waveforms
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1002/2014JB011440

During a phreatic explosion at Mayon Volcano, Philippines, on 7 May 2013, a very long period seismic event with a peak frequency of 0.4 Hz was observed. Our frequency‐domain waveform inversion solution of the event in the frequency range 0.1–0.6 Hz is consistent with a subhorizontal tensile crack and a vertical single force at a shallow location beneath the summit crater. The source time functions obtained by the waveform inversion are band‐passed forms. We estimated the deconvolved forms of the source time functions (DSTFs), which are source time functions corrected for the effects of the band‐pass filter. The DSTF of the crack can be approximated by an impulse‐type function composed of inflation followed by deflation, whereas the DSTF of the single force can be approximated by a downward impulse. The inflation of the crack may be attributed to boiling of underground water and its deflation can be attributed to discharge of water vapor, whereas the downward force may be understood as the counterforce of the explosion. Our results suggest that only a portion of the crack wall was destroyed by the explosion. We could not find clear precursors in seismic, thermography, geothermal, geodetic, and meteorological data. We present a model of repeated explosions in which an explosion can occur once the fragmented portion of the crack is sealed by precipitation of clay minerals or hydrothermal secondary deposits. This model may explain the absence of clear precursory signals before the 2013 explosion. Key Points A VLP event took place during a phreatic explosion at Mayon in 2013 Crack inflation‐deflation and a downward force were estimated as the source We develop a model of repeated explosions caused by sealing of the crack