Pre-Eruptive Time-Lapse Velocity Changes Prior to the 2018 Eruption of Sierra Negra Volcano, Galapagos Island Observed with Seismic Coda Wave Interferometry on Seismic Multiplets.

Changes in external stress state and fluid content alter the mechanical properties of an elastic medium. Hence, variations in seismic wave velocity and (crack induced) seismic anisotropy can be used as proxies for changes in stress and possible fluid ingression.

In this study, we use the Coda Wave Interferometry (CWI) technique to measure time-lapse changes in seismic velocity prior to the 2018 eruption of Sierra Negra Volcano. Sierra Negra volcano is one of the most active volcanoes on the Galapagos Islands, about 1000 km west of continental Ecuador. On 26th June 2018 at 09:15 UTC, a magnitude 5.3 earthquake occurred near the south-west caldera rim and an intense seismic swarm started around 17:15 UTC. Seismic tremor dominated at about 19:45 UTC, which marked the onset of the eruption. Both prior to and during the eruption period several families of repeating earthquake s have been identified in a very large seismicity sequence. The events are identified using the Fingerprint and Similarity Thresholding (FAST) method (Yoon et al. 2015). High detection sensitivity, computational efficiency, and scalability to massive data volumes are big advantages of the FAST method over competing approaches.

Our aim is to understand whether changes in seismic velocity measured with CWI method provide new insight into the physical processes related to the eruption and if they match the same information seen in time-lapse velocity changes estimated using seismic noise