Journal
JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH
Volume 261, Issue -, Pages 171-192Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.jvolgeores.2013.03.014
Keywords
Volcano-seismology; Long-period seismicity; Complex frequency evolution; Fluids and gas; Eruption triggering; VLP waveform inversion; Merapi
Categories
Funding
- European MIAVITA project
- European Commission
- NZ Core funded research
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The link between seismicity and degassing is investigated during the VEI 4 eruptions of Merapi volcano (Indonesia) in October and in early November 2010. Seismicity comprised a large number and variety of earthquakes including Volcano-Tectonic events, a sustained period of Long Period Seismicity (LPS), i.e., Long-Period events (LP), Very Long Period events (VLP) and tremor. LPS seismicity is ascribed to the excitation of fluid-filled cavity resonance and inertial displacement of fluids and magma. We investigate here LPS that occurred between 17 October and 4 November 2010 to obtain insights into the volcano eruption processes which preceded the paroxysmal phase of the eruption on 4-5 November. We proceed to the moment tensor inversion of a well-recorded large VLP event during the intrusion phase on 17 October 2010, i.e., before the first explosion on 26 October. By using two simplified models (crack and pipe), we find a shallow source for this VLP event at about 1 km to the south of the summit and less than 1 km below the surface. We analyze more than 90 LP events that occurred during the multi-phase eruption (29 October-4 November). We show that most of them have a dominant frequency in the range 0.2-4 Hz. We could locate 48 of those LP events; at least 3 dusters of LP events occurred successively. We interpret these observations as generated by different fluid-filled containers in the summit area that were excited while magma rose. We also observe significant variations of the complex frequency during the course of the eruption. We discuss these changes in terms of a variable ratio of fluid to solid densities and/or by possible conduit geometry change and/or permeability of the conduit or the edifice and/or by resonance of different fluid-containers during the release of more than 0.4 Tg of SO2 and large but unknown masses of other volcanic gases. Finally, we also discuss how the major explosions of the eruption were possibly triggered by passing waves resulting from regional tectonic earthquakes on 3 and 4 November. (C) 2013 Elsevier B.V. All rights reserved.
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