Anisotropic Rayleigh wave phase velocity maps of eastern China

Abstract

We explore the variations of Rayleigh wave phase velocity beneath eastern China in a broad period range (20-200 s). Rayleigh wave dispersion curves are measured by the two-station technique for a total of 734 interstation paths using vertical component broadband waveforms at 39 seismic stations in eastern China from 466 global earthquakes. In addition, 599 waveform inversion interstation measurements were added to this data set. The interstation dispersion curves are then inverted for high-resolution isotropic and azimuthally anisotropic phase velocity maps at periods between 20 and 200 s. At shorter periods sampling the crustal depth range, phase velocities are higher in the southeastern part of the region, reflecting the thinner crust there. The Jiangnan Belt separates Cathaysia from the Yangtze Craton, the latter with thicker crust and a deep, high-velocity cratonic root. The eastern part of Yangtze Craton, however, east of 115-116• E, does not display a deep root and has a thin lithosphere. Azimuthal anisotropy at long periods (>120 s) shows fast propagation directions broadly similar to that of the absolute plate motion. Beneath Cathaysia and eastern Yangtze Craton, anisotropy in the asthenosphere is strong and suggests coast-perpendicular flow. Asthenospheric flow from beneath China's thick continental lithosphere toward the thinner lithosphere of the margin and the resulting decompression melting may be the fundamental causes of the intraplate basaltic volcanism along the eastern coast of China.

Layered anisotropy within the crust and lithospheric mantle beneath the Sea of Japan

“…Shorter periods (30 s, sampling the deep crust) display fast velocities beneath Korea, consistent with previous surface-wave tomographic imaging by Cho et al (2007) and ambient noise cross-correlation study by Kang and Shin (2006). At 30-40 s, the fast velocities are also in good agreement with tomographic studies at larger scale (Friederich, 2003;Lebedev and Nolet, 2003;Gao et al, 2011;Legendre et al, 2015b), and are consistent with previous observations and crustal models of mainland China (Zheng et al, 2008;Sun et al, 2010;Zhou et al, 2012), receiver function analyses (Yoo et al, 2007;Chen et al, 2010), gravity measurements (Xu, 2007), and surface-wave analysis of the East China Sea and Korean Peninsula (Legendre et al, 2014b).…”

Seismic anisotropy of Precambrian lithosphere: Insights from Rayleigh wave tomography of the eastern Superior Craton

“…Individual dispersion curves measured between pairs of seismic stations describe the average medium properties between the two stations, which can be affected by the presence of strong lateral heterogeneity. Measuring the dispersion curves from multiple events from opposite directions enables the detection of such heterogeneities and improves the measurement quality [Legendre et al, 2014]. Laterally heterogeneous media also generate seismic wave diffraction, introducing nonplane wave energy.…”

“…Since the model grid used in this kind of tomography is based on a triangular geometry, instead of the classic Cartesian framework [e.g., Nolet , ; Pawlak et al , ; Boyce et al , ], the anomaly shapes in Figure are in fact the closest to a “standard” checkerboard. This type of synthetic test was successfully used in previous models [e.g., Deschamps et al , ; Darbyshire and Lebedev , ; Legendre et al , ]. The width of the negative anomalies that we test for ranges from 200 to 400 km.…”

Limited southward underthrusting of the Asian lithosphere and material extrusion beneath the northeastern margin of Tibet, inferred from teleseismic Rayleigh wave tomography

“…Direct observational evidence may come from a high‐resolution upper mantle structure image over the complete interaction belt among Northeastern Tibet, the North China Craton, and the Yangtze Craton. Surface wave tomography with a reasonable station coverage for this whole region is thus a good proxy to fulfill this target, as many previous studies have demonstrated [ Bourjot and Romanowicz , ; Friederich , ; Priestley et al , ; Yao et al , ; Pandey et al , ; Legendre et al , , , ].…”