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Abstract We develop a 3‐D isotropic shear velocity model for the Alaska subduction zone using data from seafloor and land‐based seismographs to investigate along‐strike variations in structure. By applying ambient noise and teleseismic Helmholtz tomography, we derive Rayleigh wave group and phase velocity dispersion maps, then invert them for shear velocity structure using a Bayesian Monte Carlo algorithm. For land‐based stations, we perform a joint inversion of receiver functions and dispersion curves. The forearc crust is relatively thick (35–42 km) and has reduced lower crustal velocities beneath the Kodiak and Semidi segments, which may promote higher seismic coupling. Bristol Bay Basin crust is relatively thin and has a high‐velocity lower layer, suggesting a dense mafic lower crust emplaced by the rifting processes. The incoming plate shows low uppermost mantle velocities, indicating serpentinization. This hydration is more pronounced in the Shumagin segment, with greater velocity reduction extending to 18 ± 3 km depth, compared to the Semidi segment, showing smaller reductions extending to 14 ± 3 km depth. Our estimates of percent serpentinization from VSreduction and VP/VSare larger than those determined using VPreduction in prior studies, likely due to water in cracks affecting VSmore than VP. Revised estimates of serpentinization show that more water subducts than previous studies, and that twice as much mantle water is subducted in the Shumagin segment compared to the Semidi segment. Together with estimates from other subduction zones, the results indicate a wide variation in subducted mantle water between different subduction segments.
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High‐Resolution Characterization of the Firn Layer Near the West Antarctic Ice Sheet Divide Camp With Active and Passive Seismic Data
Abstract We construct a high‐resolution shear‐wave velocity (VS) model for the uppermost 100 m using ambient noise tomography near the West Antarctic Ice Sheet Divide camp. This is achieved via joint inversion of Rayleigh wave phase velocity and H/V ratio, whose signal‐to‐noise ratios are boosted by three‐station interferometry and phase‐matched filtering, respectively. The VSshows a steep increase (0.04–0.9 km/s) in the top 5 m, with sharp interfaces at ∼8–12 m, followed by a gradual increase (1.2–1.8 km/s) between 10 and 45 m depth, and to 2 km/s at ∼65 m. The compressional‐wave velocity and empirically‐obtained density profile compares well with the results from Herglotz–Wiechert inversion of diving waves in active‐source shot experiments and ice core analysis. Our approach offers a tool to characterize high‐resolution properties of the firn and shallow ice column, which helps to infer the physical properties of deeper ice sheets, thereby contributes to improved understanding of Earth's cryosphere.
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- Award ID(s):
- 1739027
- PAR ID:
- 10614130
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 51
- Issue:
- 12
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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