Tracking the temporal evolution of seismic attenuation at a volcano by using remote seismicity occurring in a seismic nest. Case: Nevado del Ruiz volcano and Bucaramanga seismic nest, Colombia

A seismic study was conducted on the attenuation of seismic waves in the Nevado del Ruiz Volcano (NRV) for the period January 2017-December 2024, based on remote earthquakes generated in the Bucaramanga Seismic Nest (BSN), located 320 km away at northeast of the volcano and recorded in one seismic station deployed at NRV. It was possible to observe a temporal variation in the attenuation in the NRV related to changes in its activity, due to the movement of fluids inside the volcano. An increase in attenuation was detected between 2017 and 2018 and subsequently a new, larger increase between 2022 and 2024. These changes coincide with significant variations in degassing inside the volcano detected with other instruments and techniques. A negative relationship was observed between seismic attenuation and the SO ₂ flux to the atmosphere for some periods, while a positive relationship with the radiated seismic energy of seismicity associated with fluid dynamics inside the volcano was observed as well. This behavior may indicate circulating of fluids inside the NRV which accumulate inside the volcano generating higher seismic attenuation. Some of these fluids are subsequently released into the atmosphere such as SO ₂ , producing a decrease in the attenuation of seismic waves at NRV. This process seems to repeat itself over time. This study suggests that seismic attenuation measured in repetitive remote earthquakes located in the NSB can be used as a new tool for volcanic seismic monitoring in Colombia.