The search for pre-eruptive observables that can be used for short-term volcanic early warning remains a scientific challenge. Pre-eruptive patterns in seismic data are usually identified by analyzing seismic catalogues (e.g., the number and types of recorded seismic events), the evolution of seismic energy, or changes in the tensional state of the volcanic medium as a consequence of changes in the volume of the volcano. However, although successful volcanic predictions have been achieved, there is still no generally valid model suitable for a large range of eruptive scenarios. In this study, we evaluate the potential successful use of Shannon entropy as short-term volcanic eruption forecasting extracted from seismic signals at five well studied volcanoes (Etna, Mount St. Helens, Kilauea, Augustine, and Bezymianny). We identified temporal patterns that can be used as short-term eruptive precursors. We quantified how the Shannon entropy drops several hours before the eruptions analyzed, between 4 days and 12 h before. When Shannon entropy is combined with the temporal evolution of other features (i.e., energy, kurtosis, and the frequency index) and complementary information on types of seismic sources, the meaning of physical changes in the volcanic system could be obtained. Our results show that pre-eruptive variation in Shannon entropy offers is a confident short-term volcanic eruption forecasting tool.

The Canadian Beaufort Sea continental margin of northwestern Canada is a Cenozoic convergent margin, potentially representing a rare case of incipient subduction. Here, we produce P- and S-wave seismic velocity models of the crust and the uppermost mantle using recordings from regional earthquakes. Our models reveal a northwest-dipping very low-velocity anomaly within the crust (δV up to -15%) beneath the Romanzof Uplift. We interpret this low-velocity feature to correspond to a weaker and thicker crust due to shortening and stacking of igneous and sedimentary rocks. The co-location of the thickened crust and lack of present-day seismicity indicates that north-south compression is accommodated by slow, aseismic deformation in the narrow margin beneath the Romanzof Uplift or more broadly offshore. Neither interpretation requires a subduction initiation process.

Okmok volcano located on the northeastern part of the Umnak Island is one of the most active volcanoes in the Aleutian Arc. It was initially built as a large shield volcano, but was strongly destroyed by two caldera-forming eruptions 12,000 and 2,040 years ago. The post-caldera eruptions occur mostly along the inner perimeter of the caldera from a series of distinct cones. Here, we perform seismic tomography to explore the deep sources of magmatic activity beneath Okmok. We use the local earthquake data of the Alaska Volcano Observatory (AVO) in the time period from 2003 to 2017 to build a model with the 3D distributions of the P and S wave velocities and Vp/Vs ratio. At depths of more than 10 km, we observe a vertically aligned anomaly of high Vp/Vs ratio representing a steady conduit likely responsible for the volcano evolution since its origin. Above this conduit, we reveal a large anomaly of high Vp/Vs ratio representing the main magma reservoir providing the material for all recent eruptions in the caldera. It appears to be connected with another large shallow reservoir located below the Cone A that was the source of most of Okmok’s historical eruptions. The most recent eruption in 2008 took place right above the deep conduit. To reach the surface, the magma for this eruption passed through the shallow ductile zone, where it was saturated by silicic components. This interpretation is consistent with the petrology studies and modeling of ground deformations.

Klyuchevskoy and surrounding volcanoes in central Kamchatka form the Northern Group of Volcanoes (NGV), which is an area of the particularly diverse and intensive Pleistocene-Holocene volcanism. In this study, we present a new seismic tomographic model of the crust and uppermost mantle beneath NGV based on local earthquake data recorded by several permanent and temporary seismic networks including a large-scale KISS experiment that was conducted in 2015-2016 by an international scientific consortium. The new model has for Kamchatka an unprecedented resolution and reveals many features associated with the present and past volcanic activity within the NGV. In the upper crust, we found several prominent high-velocity anomalies interpreted as traces of large basaltic shield volcanoes, which were hidden by more recent volcanic structures and sediments. For the mantle structures, we found that the entire system of NGV was fed by an asthenospheric flow arriving through a slab window located below the Kamchatka-Aleutian junction. The interaction of the hot asthenospheric material with fluids released from the slab determines the particular volcanic activity within the NVG. We argue that the eastern branch of the Central Kamchatka Depression, which is associated with a prominent low-velocity anomaly in the uppermost mantle, was formed as a recent rift zone separating the NGV from the Kamchatka Eastern Ranges.

Akutan Island hosts a volcano considered as one of most active in the Aleutians Arc. Besides the regular eruption activity, Akutan in 1996 experienced a remarkable seismic unrest with earthquakes reaching the magnitude of M 5.3. We build a new tomography model including the 3D distributions of the , and ratio based on arrival time data from more than 4000 local earthquakes. In this model, we reveal a columnar anomaly of high ratio with the top boundary at a depth of 5-6 km below surface, which represents a steady conduit feeding the Akutan volcano. At a depth of ~4 km, the deep conduit is split in two branches, one of which ascend to the summit area and another one directs to a fumarole field at the flank of the volcano. This structure explains distinct geochemical features of emitted gases in these two areas. In the upper part of the velocity model, the highly heterogeneous structures are associated with interactions of shallow magmatic sources, meteoric and magmatic fluids, as well as degassing. Besides the prominent anomaly associated with the shallow magma reservoir beneath the caldera and the active cone, we observe several areas with high ratio, some of which are interpreted as shallow magma storages, and some as zones of meteoric water penetration. We propose a scenario of abrupt fluid ejection from the deep magma conduit that led to the seismic unrest and strong ground deformations in the Akutan area in 1996.