Susan L. Beck

Monitoring variations in seismic velocities surrounding active volcanoes provides insights into crustal deformation caused by eruptions and earthquakes. Turrialba volcano in Costa Rica has been erupting sporadically since 2010 and experienced a local seismic swarm in 2016, including the Mw 5.5 Capellades earthquake. It is thus an ideal natural laboratory to study crustal velocity changes associated with a seismic event at an active volcano. We use seismic noise-generated surface waves to characterize emergent upper crustal velocity variations following the earthquake sequence off the flank of the volcano. Our study highlights a rapid velocity drop immediately following the earthquake implying widespread damage and/or a readjustment of local stress. From the frequency dependence of surface waves, we find that the depth over which the velocities vary is localized to the upper ∼2.5 km of the crust, coinciding with the depth extent of the Capellades earthquake aftershock sequence as well as the shallow magma chamber feeding the Turrialban eruption. From the areal extent of the velocity decrease, crustal variations are likely tied to both damage following the seismic sequence and the evolution of the shallow magma reservoir feeding Turrialba.