Anomalous seismic structure beneath the Klyuchevskoy Group, Kamchatka

Abstract

The Klyuchevskoy Group is among the most active volcanic features on Earth, yet its position within the Kamchatka subduction zone is hard to explain with a simple tectonic mechanism. The geochemistry of Klyuchevskoy Group lavas is typical for volcanic products resulting from flux melting in the mantle wedge, yet the depth to the subducting Pacific plate beneath it is much larger than the average depth of volatile release in subduction zones. We present new seismological constraints on the upper mantle structure beneath the Klyuchevskoy Group and identify a planar dipping seismic feature in the mantle wedge which is ∼100 km deep and appears to be sharply bounded. We hypothesize that this upper mantle structure may be the true source of melts erupting at the Klyuchevskoy Group, and that the presence of this feature may explain both the extraordinary productivity of the Klyuchevskoy Group and its unusual location.

Magmatic and Sedimentary Structure beneath the Klyuchevskoy Volcanic Group, Kamchatka, From Ambient Noise Tomography

“…A further implication of back‐arc spreading is that a crustal thinning signature would be expected within the depression. Assuming isostatic compensation, an isostatic balance can be constructed between the CKD and the approximately 35 km thick crust (Iwasaki et al, ; Levin et al, ; Nikulin et al, ) on the CKD shoulders. Using continental crust density of 2.7 g/cm 3 , mantle density of 3.4/cm 3 , sediment density of 2.2/cm 3 (for the 5 km thick Layer S2), and unconsolidated sediment density of 1.6/cm 3 (for the 3 km thick Layer S1), the thinned crustal thickness within the CKD would be expected to be approximately 18 km.…”

“…During eruptions, continuous tremor signals can be located (Droznin et al, ), tracked (Soubestre et al, ), and associated with a volcanic source based on their characteristic network‐based tremor fingerprint (Soubestre et al, ). Long‐period seismicity (Shapiro et al, ) occurs both at shallow depths, less than 5 km, and also at around 30 km depth, the inferred location of a gradational crust–mantle transition (Nikulin et al, ). The deep long period seismicity is more active during repose periods and surges in deep seismicity transfer into elevated shallow activity, which immediately precedes eruptions (Fedotov & Zharinov, ; Senyukov et al, ; Shapiro, Droznin, et al, ).…”

Multiscale Seismic Tomography Imaging of Volcanic Complexes

“…Active seismic clusters were observed within this high Vp/Vs anomaly only above ~30-35 km in depth. These depths correspond to the lowermost parts of the crust, whose thickness reaches the values of about 30-35 km, based on the results of receiver function analysis (Nikulin et al, 2010). We propose that these earthquakes in the lowermost crust, which fit to high values of Vp/Vs, mark the first level of magma storage between 25 and 30 km in depth.…”

Network‐Based Detection and Classification of Seismovolcanic Tremors: Example From the Klyuchevskoy Volcanic Group in Kamchatka

“…In addition, two other very active volcanoes, Shiveluch and Kizimen, are respectively located north and south of KVG (Figure ). The volcano earthquakes together with tectonic regional and teleseismic events were used to study the internal structure of the KVG with the seismic tomography (e.g., Balesta et al, ; Gorbatov et al, ; Gontovaya et al, ; Ivanov et al, ; Koulakov et al, , , ; Lees et al, ; Slavina et al, , ) and with receiver functions (Levin et al, ; Nikulin et al, ). The sustained volcanic activity of the KVG and closely located volcanoes requires permanent monitoring and makes this region particularly suitable for testing volcanic monitoring methods.…”