Initial phases of explosion earthquakes accompanying Vulcanian eruptions at Lokon-Empung volcano, Indonesia

Taishi Yamada, Hiroshi Aoyama, Takeshi Nishimura, Hiroshi Yakiwara, Haruhisa Nakamichi, Jun Oikawa, Masato Iguchi, Muhamad Hendrasto, Yasa Suparman

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

We examine the initial phases of explosion earthquakes accompanying Vulcanian eruptions at Lokon-Empung volcano in Indonesia to reveal the triggering process of explosive eruptions. In 2012–2013, 56 Vulcanian eruptions at Lokon-Empung were observed by our temporary observation network being comprised of four broadband seismometers and two infrasound microphones at 1.6–6.8 km from the active vent. The seismic records of each explosion earthquake share almost the same waveform characteristics of initial phases, consisting of a small compressional onset (P phase) and a subsequent large dilatational phase (D phase). Particle orbits of both phases show straight motion from beneath the active vent, which suggests that these phases are composed of a longitudinal body wave. For each explosion, the origin times of the P phase precedes 0.8–2.5 s before the occurrence of an explosion at the vent that are detected by infrasound data. Since the signal-to-noise ratio of the P phase is insufficient for a quantitative analysis, we analyze the D phase dominating the initial phases. Our analysis for the signals of 0.2–1.0 Hz shows the D phase are well explained by a cylindrical contraction source with a half-cosine shaped time function located at 1.0–1.3 km depth beneath the active vent. We also recognize that some explosions are followed by a prominent tremor that coincides with continuous ash emission (ET). The seismic amplitudes and intensity of the D phase of events in ET are larger than the explosions without accompanying tremor (EX). The frequency distribution of the time interval from the previous eruption is also different in the events in ET and EX. The implosion source in the initial phases of explosion earthquakes at several km beneath the active vent has been reported at Sakurajima volcano. Since our result shows considerable agreement with the previous works at Sakurajima, both Lokon-Empung and Sakurajima may share similar initial processes of Vulcanian eruptions.

Original languageEnglish
Pages (from-to)310-321
Number of pages12
JournalJournal of Volcanology and Geothermal Research
Volume327
DOIs
Publication statusPublished - 2016 Nov 15

Keywords

  • Explosion earthquakes
  • Implosion source
  • Lokon-Empung
  • Vulcanian eruptions

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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