The 26th June 2018 eruption at Sierra Negra volcano, Galapagos archipelago: early results on seismic tremor and low frequency seismicity from a temporary network

This presentation gives early results on the analysis of seismic character of data collected by a temporary network of 14 seismic stations installed at Sierra Negra volcano, Galapagos during the 26th June 2018 eruption. Sierra Negra volcano is one of the most active volcanoes on the Galapagos Islands, approximately 1000 km west of continental Ecuador. The Galapagos Islands are the manifestation of a mantle hot spot under the eastward-moving Nazca plate. Active volcanism is concentrated on the island of Isabela, where Sierra Negra volcano is located. Since March 2017, an increase of seismicity was recorded at one of the permanent seismic stations in the network of the Instituto Geofísico of the Escuela Politécnica Nacional in Ecuador. The increase ended with a magnitude 5.5 earthquake on 26th June 2018. A short-lived aftershock sequence followed the main event. After 8 hours of relatively "quiet" period, the seismicity increased again with an accelerating rate in the next 3 hours. A pre-eruptive tremor begun after a drop in the earthquake rate, followed by the onset of the eruption. Fissures were opened in the north of the caldera. This sequence of events was recorded by a temporary network of 14 broadband seismic stations installed before the eruption. Three of them were located inside the caldera to record near-field effects of the seismic waves. In this presentation we will provide preliminary results on the analysis of data recorded by the temporary network, with a focus on the characterization of pre-eruptive long-period earthquakes and tremor. The temporal and spatial evolution of the events will be presented and its relationship to the dynamics of the volcano will be discussed.