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 VS reduction and VP/VS are larger than those determined using VP reduction in prior studies, likely due to water in cracks affecting VS more 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.

Accurately determining the seismic structure of the deep crust of continents is crucial for understanding the geological record and continental dynamics. However, traditional surface wave methods often face challenges in solving the trade-offs between elastic parameters and discontinuities. In this work, we present a new approach that combines two established inversion techniques, receiver function H-ᵰ5; stacking and joint inversion of surface wave dispersion and receiver function waveforms, within a Bayesian Monte Carlo (MC) framework to address these challenges. As demonstrated by the synthetic test, the new method greatly reduces trade-offs between critical parameters, such as the deep crustal Vs, Moho depth, and crustal Vp/Vs ratio. This eliminates the need for assumptions regarding crustal Vp/Vs ratios in joint inversion, leading to a more accurate outcome. Furthermore, it improves the precision of the upper mantle velocity structure by reducing its trade-off with Moho depth. Additional notes on the sources of bias in the results are also included. Application of the new approach to USArray stations in the Northwestern US reveals consistency with previous studies and also identifies new features. Notably, we find elevated Vp/Vs ratios in the crystalline crust of regions such as coastal Oregon, suggesting potential mafic composition or fluid presence. Shallower Moho depth in the Basin and Range indicates reduced crustal support to the topography. The uppermost mantle Vs, averaging 5 km below Moho, aligns well with the Pn-derived Moho temperature map, offering the potential of using Vs as an additional constraint to Moho temperature and crustal thermal properties.

The location and origin of Neoproterozoic-Cambrian sutures provide keys to understand the formation and evolution of the supercontinent Gondwana. The Larsemann Hills is located near a major Neoproterozoic-Cambrian suture zone in the Prydz Belt, but has not been examined locally by comprehensive geophysical studies. In this study, we analyzed data collected from a 1-D joint seismic-MT array deployed during the 36th Chinese National Antarctic Research Expedition. We found that a sharp Moho discontinuity offset of 6-8 km shows up in the stacked image of teleseismic P-wave receiver function analysis; coinciding with the abrupt Moho offset, a near-vertical channel with (1) low resistivity extending to the uppermost mantle depths, and (2) a high crustal Poisson’s ratio in the crust is identified. These findings provide evidence for the determination of the location and collisional nature of the Prydz belt or a portion of it.

To advance the understanding of the tectonic processes shaping the African continent, we construct the first continental-scale shear-wave velocity (Vs) model of the crust and uppermost mantle from joint analysis of ambient seismic noise and earthquake data recorded by ~1529 broadband seismic stations located in Africa, Arabia, and Europe from 1987 to 2018. We apply the widely used ambient noise cross-correlation and earthquake two-station methods to retrieve the fundamental-mode Rayleigh-wave group and phase velocity dispersions in the period range of 5 – 50 s which are jointly inverted using the neighbourhood algorithm to build a new three-dimensional Vs model with associated uncertainties. The inclusion of relatively short-period dispersion data from ambient seismic noise allows us to achieve better resolution at shallow depth and obtain a more accurate model than previous global and continental-scale studies, revealing lithospheric structures that correlate well with known tectonic features. In sparsely instrumented regions of north-central Africa, our model provides seismic evidence for the existence of cratonic remnants beneath thick sediments within the poorly imaged Sahara Metacraton and reveals unique mantle upwelling beneath hotspots, suggesting that they may be fed by unconnected plumes. The estimated crustal thickness varies among and within tectonic provinces and shows no clear evidence for the secular variation in crustal genesis. Our new model has the potential to serve as a preliminary reference velocity model for Africa and is useful for practical applications, including monitoring of the Comprehensive Nuclear-Test-Ban Treaty, geodynamic modeling as well as seismic hazard analysis.