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

Abstract

The Klyuchevskoy Volcanic Group is a cluster of the world's most active subduction volcanoes, situated on the Kamchatka Peninsula, Russia. The volcanoes lie in an unusual off‐arc position within the Central Kamchatka Depression (CKD), a large sedimentary basin whose origin is not fully understood. Many gaps also remain in the knowledge of the crustal magmatic plumbing system of these volcanoes. We conducted an ambient noise surface wave tomography, to image the 3‐D shear wave velocity structure of the Klyuchevskoy Volcanic Group and CKD within the surrounding region. Vertical component cross correlations of the continuous seismic noise are used to measure interstation Rayleigh wave group and phase traveltimes. We perform a two‐step surface wave tomography to model the 3‐D Vsv velocity structure. For each inversion stage we use a transdimensional Bayesian Monte Carlo approach, with coupled uncertainty propagation. This ensures that our model provides a reliable 3‐D velocity image of the upper 15 km of the crust, as well as a robust assessment of the uncertainty in the observed structure. Beneath the active volcanoes, we image small slow velocity anomalies at depths of 2–5 km but find no evidence for magma storage regions deeper than 5 km—noting the 15 km depth limit of the model. We also map two clearly defined sedimentary layers within the CKD, revealing an extensive 8 km deep sedimentary accumulation. This volume of sediments is consistent with the possibility that the CKD was formed as an Eocene‐Pliocene fore‐arc regime, rather than by recent (<2 Ma) back‐arc extension.

Mantle and Crustal Sources of Magmatic Activity of Klyuchevskoy and Surrounding Volcanoes in Kamchatka Inferred From Earthquake Tomography

“…In the crust, the model is generally consistent with the previous study by Koulakov et al (2017), because at shallow depths, the tomography is mostly controlled by the same subsets as used in the previous case. We also observe some correspondence with the new results of the ambient noise tomography (Green et al, 2020, and especially with Egorushkin et al, 2020).…”

“…It is unlikely that such amount of subsidence occurred merely due to isostatic compensation caused by the volcanic mass growing, as proposed by Melekestsev (1980). Green et al (2020) proposed that the CKD subsidence and accumulation of sediments occurred in two stages. The first stage was related to relatively slow formation of the fore‐arc basin during Eocene‐Pliocene, when Sredinny Range acted as the main volcanic arc (Avdeiko et al, 2007; Portnyagin et al, 2005).…”

“…The temporary network included 30 sensors Trillium Compact (period of up to 120 s), six Guralp CMG‐6T (30 s period), eight Guralp‐CNG‐6TD (30 s period), nine CME‐4111 (30 s period), and 30 Mark L‐4C‐3D with the nominal period of 1 s, which can be extended up to 20 s. All stations recorded three‐component seismograms with the sample rate of 100 Hz. More details on the network are described in Green et al (2020). The network operated until July 2016.…”

Anatomy of the Bezymianny volcano merely before an explosive eruption on 20.12.2017

“…Based on the data of permanent seismic stations operated by the KBGS and several temporary seismic networks installed in the vicinity of Bezymianny and its neighboring volcanoes of the KGV, previous studies [29][30][31][32][33][34][35] revealed multilevel magma storages in the crust and the uppermost mantle: the shallow-most level being located at circa 8 km depth. Multiple petrological studies 36,37 revealed consistent storage conditions of magmas for Bezymianny, but they could not yet characterize the lateral complexity and dimensions of potential reservoirs.…”

Mantle and crustal sources of magmatic activity of Klyuchevskoy and surrounding volcanoes in Kamchatka inferred from earthquake tomography

“…The temporary network included 30 sensors Trillium Compact (period of up to 120 s), six Guralp CMG-6T (30 s period), eight Guralp-CNG-6TD (30 s period), nine CME-4111 (30 s period), and 30 Mark L-4C-3D with the nominal period of 1 s, which can be extended up to 20 s. All stations recorded three-component seismograms with the sample rate of 100 Hz. More details on the network are described in Green et al (2020). The network operated until July 2016.…”