Abstract
AbstractThe 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.
Highlights
Through a cross validation of the two methods, we found that phase weighted stacking (PWS) provides reliable Rayleigh wave dispersion measurements, very similar to those obtained through linear stacking for paths with large signal‐to‐noise ratio (SNR), but enables the analysis of low SNR pairs
A 1‐D depth‐dependent average is made as a reference of the entire volume, excluding grid nodes to the west of x = −100 km, where extreme high velocities correlate with poor fit (Figure 10), and large standard deviations at shallow depths (Figures S7–S10)
A more complete depth range is presented in Figures S7–S10, and further vertical cross sections are shown in Figures S12 and S13
Summary
The Klyuchevskoy Volcanic Group (KVG) lies on the Kamchatka peninsula in Russia at the intersection of the Kuril‐Kamchatka arc and the transcurrent western end of the Aleutian arc (Figure 1a). The extraordinary productivity can be related to the unique tectonic setting of the group (Figure 1a), situated on the northwestern cusp of the subducting Pacific plate and just where the Hawaiian‐Emperor seamount chain subducts beneath Kamchatka. Competing geodynamical models exist to explain the elevated volcanism, including mantle flow around the edge of the subducting slab, melting of the slab (Yogodzinski et al, 2001), enhanced fluid release from the thick highly hydrated seamount crust (Dorendorf et al, 2000), and slab detachment (Levin et al, 2002)
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