Abstract
The Udina complex, consisting of two stratovolcanoes—Bolshaya and Malaya Udinas—is located at the southeastern edge of the Klyuchevskoy volcano group (KGV) in Kamchatka. Prior to 2017, it was considered to be extinct; however, since late 2017, continuing seismic activity beneath Bolshaya Udina has been recorded, which may indicate the possible awakening of this volcano complex. To perform a detailed investigation of this seismic process, we installed four temporary seismic stations in the vicinity of the Udinas0 volcanoes and operated them for two months—from May to July 2018. Using the data obtained from this network, we detected and localized 559 local events in the area of the Udina volcanoes. Furthermore, we performed a tomographic inversion to improve the locations of the sources. The tomography unexpectedly resulted in a stable model, which was carefully verified via a series of different tests. We found that the seismicity formed an elliptical cluster oriented in the north-northeast–south-southwest direction. Beneath the volcano, the seismicity occurred at depths of greater than 5 km from the surface. In the tomography model, we observed an anomaly of a high Vp, low Vs, and high Vp/Vs ratio located directly beneath Bolshaya Udina. These seismic properties may indicate the presence of magma intrusions with a high content of melts and fluids, which may justify changing the current status of this volcano from “extinct” to “active.” We also observed that the seismicity cluster connects Bolshaya Udina with the Tolud zone, where continuous seismicity has been observed at depths of approximately 10–20 km in previous years. This zone is considered to be a magma storage in the lower crust that contributed to feeding the fissure eruptions in the Tolbachinsky Dol. Based on the results of this study, we conclude that during 2018, the Tolud magma source appeared to have built another pathway to Bolshaya Udina.
•Increased seismicity beneath the Udina volcano since December 2017 may indicate possible awakening.•We used 4 stations of temporary network to localize the events and estimate seismic velocity structure.•Synthetic tests show that despite a small number of stations, tomography provides reliable results.