TY - JOUR T1 - Plate Age and Uppermost Mantle Structure Across the Juan de Fuca and Gorda Plates JF - Journal of Geophysical Research: Solid Earth Y1 - 2023 A1 - Wu, Mengyu A1 - Wang, Hongda A1 - Zhang, Shane A1 - Ritzwoller, Michael H. KW - asthenosphere KW - Juan de Fuca KW - Lithosphere KW - plate age KW - thermal structure KW - Vs model AB - To test the relationship between plate age and uppermost mantle structure for the Juan de Fuca and Gorda plates, as well as the mode of lithospheric cooling, we produce a new 3D oceanic shear wave speed (VS) model. This model is constructed using a new high-quality Rayleigh wave phase speed data set across the plates and is based on a novel thermo-seismic hybrid parameterization. In the lithosphere, we find that the VS structure is primarily (68% of study area) governed by conductive cooling. Exceptions are observed, suggesting advective heat influx along ridges and hydrothermal circulation through cracks near the subduction trench and transform faults. In the asthenosphere of the Juan de Fuca plate, no simple monotonic relationship between seismic structure and plate age exists, but instead there is a non-monotonic slow-fast-slow VS pattern from west to east. The two slow asthenospheric VS anomalies indicate the presence of partial melt beneath both the mid-ocean ridge and the subduction trench. The partial melt beneath the trench is enigmatic. VL - 128 UR - https://onlinelibrary.wiley.com/doi/abs/10.1029/2023JB026494 N1 - _eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2023JB026494 ER - TY - JOUR T1 - Isotropic and azimuthally anisotropic Rayleigh wave dispersion across the Juan de Fuca and Gorda plates and U.S. Cascadia from earthquake data and ambient noise two- and three-station interferometry JF - Geophysical Journal International Y1 - 2021 A1 - Zhang, Shane A1 - Wang, Hongda A1 - Wu, Mengyu A1 - Ritzwoller, Michael H AB - We use data from the Cascadia Initiative (CI) amphibious array and the USArray Transportable Array to construct and compare Rayleigh wave isotropic and azimuthally anisotropic phase speed maps across the Juan de Fuca and Gorda Plates extending onto the continental northwestern United States. Results from both earthquakes (28–80 s) as well as ambient noise two- and three-station interferometry (10–40 s) are produced. Compared with two-station interferometry, three-station direct wave interferometry provides >50 per cent improvement in the signal-to-noise ratio and the number of dispersion measurements obtained, particularly in the noisier oceanic environment. Earthquake and ambient noise results are complementary in bandwidth and azimuthal coverage, and agree within about twice the estimated uncertainties of each method. We, therefore, combine measurements from the different methods to produce composite results that provide an improved data set in accuracy, resolution and spatial and azimuthal coverage over each individual method. A great variety of both isotropic and azimuthally anisotropic structures are resolved. Across the oceanic plate, fast directions of anisotropy with 180° periodicity (2ψ) generally align with palaeo-spreading directions while 2ψ amplitudes mostly increase with lithospheric age, both displaying substantial variations with depth and age. Strong (>3 per cent) apparent anisotropy with 360° periodicity (1ψ) is observed at long periods (>50 s) surrounding the Cascade Range, probably caused by backscattering from heterogeneous isotropic structures. VL - 226 UR - https://doi.org/10.1093/gji/ggab142 ER -