[S-VC28] International Volcanology

[SVC28-05] The eruption dynamics of Sinabung, Indonesia, as inferred from seismic multi-parameters from 2010 to 2015

*Vico Luthfi Ipmawan^1,2,4, Masato Iguchi², Takahiro Ohkura³, Takeshi Tameguri¹ (1.Earth and Planetary Science Division, Graduate School of Science, Kyoto University, 2.Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University, 3.Aso Volcanological Laboratory, Institute for Geothermal Sciences, Graduate School of Science, Kyoto University, 4.Physics Department, Institut Teknologi Sumatera)

Keywords:dome growth, earthquakes family, source parameter, hypocenter migration, phylogenetic tree method

Sinabung volcano is located in North Sumatera Province, Sumatera, Indonesia. Sinabung started to erupt in August 2010. The eruptive activity lasts until 2021. There are at least 7 eruption phases that Sinabung has shown, namely, 1) phreatic phase (mostly August - September 2010 and September 2013); 2) the first phase of dome growth and collapse with pyroclastic density currents (PDC) (18 December 2013 - 10 January 2014); 3) lava-flow and collapse phase (10 January 2014 - mid-September 2014); 4) second phase of dome growth and collapse with PDC (mid-September 2014 - July 2015); 5) dominancy of Vulcanian phase with PDC (August 2015 - December 2017); 6) paroxysmal event (February 19, 2018); 7) recurrence of eruption with PDC (August 2020). In this study, we analyzed Sinabung's seismic data from August 2010 to December 2015. The seismicity shows a variety of waveforms and types: Low Frequency (LF), Hybrid, Volcano-tectonic (VT), Rockfall, Gas Emissions, and PDC events. The migration of the VT hypocenter that began in July 2011 is considered as a magma intrusion. In June 2013, VT seismicity increased significantly and its hypocenter became shallower indicating magma intrusion is getting closer to summit, making this a precursor to the highest magmatic activity in January-February 2014. This intrusion also resulted in a VT swarm that occurred near the pressure source in northeast (NE) of summit. During this period, 10 VT earthquake families were detected based on the cross-correlation-based phylogenetical tree method. The epicenter distribution of these families show a linear form that may be generated by fault activity triggered by the inflation process of the pressure source in the NE of the summit (Hotta et al, 2019). In November 2013, the LF earthquake appeared, suggesting that magma approaching the surface causes the release of gas. This leakage of gas may make the viscosity of the magma increase followed by lava dome growth associated with an increase in Hybrid earthquakes. In this episode of predominantly Hybrid seismic activity, we had identified two families of Hybrid earthquakes, that occurred before and after the appearance of the lava dome at the top of the crater. The later family showed a decrease in rupture length, seismic moment, and stress drop. This decrease in Hybrid source parameters is interpreted as a result of pressure release due to lava dome extrusion. In January and February 2014, magmatic activity was highest, characterized by high rockfall and PDC events activity. The period from February to September 2014 was marked by lava flow activity and collapse accompanied by an increase in real-time seismic amplitude (RSAM) in the frequency of <5 Hz related to the process of magma transport and lava extrusion. The volume of lava dome growth in the second phase (September 2014) was less than that in the first phase. This smaller volume was accompanied by a decrease in Hybrid's seismic moment and stress drop compared to the first one. It can be considered that the magma supply rate in the first lava dome period was higher, resulting in the formation of plugs with higher density and higher rigidity. The formation of plugs allows higher pressures to accumulate underneath the plugs.