Sn-wave velocity structure of the uppermost mantle beneath the Australian continent

Abstract

We have extracted a data set of more than 5000 Sn traveltimes for source-station pairs within continental Australia, with 3-D source relocation using Pn arrivals to improve data consistency. We conduct tomographic inversion for S-wave-speed structure down to 100 km using the Fast Marching Tomography (FMTOMO) method for the whole Australian continent. We obtain a 3-D model with potential resolution of 3.0 o × 3.0 o. The new S-wave-speed model provides strong constraints on structure in a zone that was previously poorly characterized. The S velocities in the uppermost mantle are rather fast, with patterns of variation generally corresponding to those for Pn. We find strong heterogeneities of S wave speed in the uppermost mantle across the entire continent of Australia with a close relation to crustal geological features. For instance, the cratons in the western Australia usually have high S velocities (>4.70 km s −1), while the volcanic regions on the eastern margin of Australia are characterized by low S velocities (<4.40 km s −1). Exploiting an equivalent Pn inversion, we also determine the V p /V s ratios across the whole continent. We find that most of the uppermost mantle has V p /V s between 1.65 and 1.85, but with patches in central Australia and in the east with much higher V p /V s ratios. Distinctive local anomalies on the eastern margin may indicate the positions of remnants of mantle plumes.

The Lithospheric Architecture of Australia From Seismic Receiver Functions

“…Most components of these cratons were formed by roughly 1.8 Ga and were sutured together by the Neoproterozoic as part of the supercontinent Rodinia (Betts et al., 2002; Cawood & Korsch, 2008). The amalgamation of these cratons can be observed seismically throughout central Australia as lower wave speeds above 80 km, and anomalously strong radial anisotropy (Sun & Kennett, 2016; Wei et al., 2018; Yoshizawa, 2014; Yoshizawa & Kennett, 2015). In general, these cratons are thicker, colder, denser, and more depleted than the Phanerozoic east, with a gradational seismic LAB and MLDs at depths between 70 and 90 km (Debayle & Kennett, 2000; Fichtner et al., 2010; Fishwick & Rawlinson, 2012; Fishwick & Reading, 2008; Fishwick et al., 2005; Ford et al., 2010; Tesauro et al., 2020; Yoshizawa, 2014; Yoshizawa & Kennett, 2015).…”

“…Following the breakup of Rodinia, successive orogenic events accreted new lithosphere onto the cratonic core over a roughly 500 million‐year time span (Betts et al., 2002). During the Cenozoic, Australia drifted north‐northeast over a potential mantle plume, resulting in volcanic chains along the eastern margin that can be observed as lower seismic velocities and a shallower seismic LAB (Davies et al., 2015; Ford et al., 2010; Rawlinson et al., 2016; Wei et al., 2018). In contrast to most of the Precambrian west, eastern Australia has thinner, warmer lithosphere increasing stepwise to the west with a well‐defined LAB between 70 and 100 km (Demidjuk et al., 2007; Fishwick & Reading, 2008; Ford et al., 2010).…”

Variations in Seismic Wave Speed and VP/VS Ratio in the North American Lithosphere

“…(Fang et al, 2016, 2019) develop tomographic models of V P / V S at a smaller scale within Southern California, but they rely on local earthquake data and their technique cannot yet be transferred to continental scales due to computational restrictions. Studies that do report V P / V S over larger areas (Hejrani et al, 2015; Schmandt & Humphreys, 2010; Tesoniero et al, 2015; Wei et al, 2018) derive these estimates from separate models of V P and V S , which may introduce bias from different ray coverage, smoothing, and other regularization strategies that have been applied (Kennett et al, 1998).…”

Structure of the crust and upper mantle beneath Bass Strait, southeast Australia, from teleseismic body wave tomography

“…In another study, Rawlinson et al (2017) suggest that an interaction between this passing plume and preexisting Edge Driven Convection (EDC) (King and Anderson, 1998) and Shear Driven Upwelling (SDU) (King and Ritsema, 2000) (caused by a huge central cavity in the lithosphere, which corresponds to the central low velocity zone north of the NVP in our model) was responsible for the NVP volcanism. A more recent study by Wei et al (2018) using 3-D S n traveltime tomography finds strong heterogeneities in S wave speed in the upper mantle across the entire Australian continent. They also include Pn data to determine the uppermost mantle Vp/Vs ratio across the whole continent.…”