Tracking changes in the tremor sources associated with a Gorely Volcano degassing episode in 2013

Gorely, one of the most active volcanoes in Kamchatka, experienced a long period of degassing from 2010 to 2013. This degassing has been accompanied by intense seismovolcanic activity in form of nearly continuous tremors that were recorded by a temporary network of seismographs. To better understand the relationship between the volcanic degassing and seismic signals, we analyze here three months of continuous seismic data of 15 stations operated in 2013 using the network covariance matrix approach. We identified a high-coherence seismovolcanic tremor in the 0.5–5 Hz frequency band and examined its temporal variations by analyzing the spectral width of the covariance matrix. Tremor sources were located and clustered based on the first eigenvectors of the covariance matrix. We identified three sequential tremor source clusters active throughout the observation period. Most of tremor sources were located beneath Gorely within the volcanic edifice, above 1 km depth. A small group of sources located at depths up to 3 km below sea level is aligned along a nearly vertical conduit-like structure. When the seismic activity switched from cluster 1 to cluster 3 in mid-October 2013, the tremor sources were slightly shifted toward northeast. During the period of cluster 1 (before October 15, 2013) the peaks of low tremor coherence coincided with the precipitation. Based on the frequency distribution of high-coherence signals, source locations and volcanological observations, we suggest that the tremor activity is controlled by complex gas dynamics within the volcano and its interaction with infiltrating meteoric fluids in Gorely's conduit system.