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- Title
A New Shear‐Velocity Model of Continental Australia Based on Multi‐Scale Surface‐Wave Tomography.
- Authors
Magrini, Fabrizio; Kästle, Emanuel; Pilia, Simone; Rawlinson, Nicholas; De Siena, Luca
- Abstract
The Australian Seismological Reference Model (AuSREM) represents a state‐of‐the‐art geophysical synthesis of the Australian continent. To date, its shear‐wave component has limited resolution at lower‐crustal to uppermost‐mantle depths, where it is mainly constrained by sparse measurements collected at the local scale. In this study, we compile a large data set of surface‐wave phase velocities based on seismic ambient noise and teleseismic earthquakes, to produce Rayleigh and Love phase‐velocity maps of continental Australia in a broad period range (4–200 s). Via transdimensional Bayesian inversion, we translate the phase‐velocity maps into a 3‐D shear‐wave velocity model extending to 300 km depth. Owing to the unprecedented seismic coverage and to the joint use of ambient‐noise and teleseismic data, the retrieved model fills a tomographic gap in the known shear‐wave velocity structure of the continent, comprising lower‐crustal to uppermost mantle depths. Consistent with AuSREM, strong velocity heterogeneities in our model highlight the (faster) cratonic blocks and the (slower) sedimentary basins at upper‐crustal depths. At mantle depths, the most prominent feature of the continent is a large‐scale eastward decrease in shear‐wave velocity. We interpret our observations in light of the relevant literature, and produce depth maps of the Moho and lithosphere‐asthenosphere boundary (LAB). Notably, our LAB proxy features a stripe of thicker lithosphere extending to the east coast, which is not visible in the AuSREM LAB model. This observation supports the idea that lateral variations in lithospheric thickness control both the composition and volume of surface volcanism in eastern Australia. Plain Language Summary: The current seismological reference model of Australia (AuSREM) provides spatial variations in compressional‐ and shear‐wave velocity, but has limited resolution at lower‐crustal to uppermost‐mantle depths. In this study, we measure surface‐wave (Rayleigh and Love) phase velocities across Australia using both seismic ambient noise (continuous background noise largely generated by oceans) and teleseismic (distant) earthquakes. We use the compiled data set to produce a 3‐D shear‐wave velocity model of Australia, characterized by unprecedented resolution throughout the crust and extending to 300 km depth. Consistent with AuSREM, our model allows the (faster) cratonic blocks to be clearly discriminated from the (slower) sedimentary basins at upper‐crustal depths. The upper mantle beneath Australia is characterized by a large‐scale pattern of shear‐wave velocity decreasing eastward. Through our 3‐D shear‐wave velocity model, we also provide estimates of crustal and lithospheric thickness. The lateral variations of the latter support the hypothesis that lithospheric thickness controls both the composition and volume of surface volcanism in eastern Australia. Key Points: 3‐D shear‐velocity model of Australia extending to 300 km depth, derived from Rayleigh and Love phase velocities in the period range 4–200 sContinent‐wide estimate of Moho, and good illumination of structural continuity between lower crust and upper mantleLithosphere‐asthenosphere boundary proxy supports lithospheric thickness controlling the composition and volume of surface volcanism in eastern Australia
- Subjects
AUSTRALIA; SEDIMENTARY basins; PHASE velocity; MICROSEISMS; TOMOGRAPHY; SEISMIC wave velocity
- Publication
Journal of Geophysical Research. Solid Earth, 2023, Vol 128, Issue 7, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2023JB026688