Episode of domes formation at Merapi volcano observed by a small aperture seismic array in the period 2018-2022

<p>Following the explosive eruption of 2010, Merapi volcano experienced a 4-year rest period, followed by a period of phreatic activity between 2014 and 2018. A first magmatic eruption occurred in 2018-2019, and a second one started in 2020 and is still ongoing. The first eruption formed a dome in the center of the crater (in the same location as the 2010 lava dome), and the maximum volume reached 700.000 m³. The second eruption is very original, characterized by the formation of two domes almost simultaneously. The first dome appeared in January 2021 on the southwest flank; the latter is located inside the crater (west of the 2018-2019 dome). The two domes are about 200m apart, separated by the southwest wall of the crater.</p> <p>&#160;</p> <p>Our objective in this work is to follow the magmatic activity through the seismicity generated over five years, including the period of these two magmatic eruptions. For this purpose, we use a seismic array that has been operating continuously since 2013 and throughout this period. This seismic array has a 300m aperture on the northeast Merapi flank (Pasar Bubar site), consisting of 5 mid-band stations (Guralp 6TD). We estimated the slowness vector over a sliding window of 20 seconds by inverting the time delays calculated between each pair of stations using the inter-spectral method in the 1-5 Hz frequency band. This robust approach gives us the back-azimuth and apparent velocity for the dominant wavefield. The analysis carried out during the period from the beginning of 2018 to the end of 2022 shows variations of the slowness vector related to intrusive processes and deformation of the crater's northern part, which will be presented in this work.</p>