Japan Geoscience Union Meeting 2018

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Tectonophysics

[S-IT20] Structure and Dynamics of Earth and Planetary Mantles

Mon. May 21, 2018 9:00 AM - 10:30 AM A05 (Tokyo Bay Makuhari Hall)

convener:Takashi Yoshino(Institute for Planetary Materials, Okayama University), Dapeng Zhao(Department of Geophysics, Tohoku University), Takashi Nakagawa(海洋研究開発機構数理科学・先端技術研究分野), Chairperson:Zhao Dapeng(Tohoku University), Kubo Tomoaki

9:45 AM - 10:00 AM

[SIT20-04] Quantify chemical stratification in the mantle transition zone using USArray data

Kai Deng1, *Teh-Ru Alex Song1 (1.Seismological Laboratory, Department of Earth Sciences, University College London)

Keywords:transition zone, USArray, forward and backward scattering waves, long-term subduction, chemical stratification

Plate tectonic processes operating over much of the Earth’s history induce long-term mantle mixing of chemical heterogeneities, recycling of volatiles into the mantle and regulate basalt geochemistry. Fundamental questions relevant to the mantle transition zone concern the nature of phase transition, the distribution of chemical heterogeneities (e.g., harzburgite, basalt), the temperature gradient, as well as the degree and extent of hydration and melting. One particularly important question is how the slab stagnation may be influenced by hydration or/and basalt enrichment in the mantle transition zone. To help answer these questions, we aim to detail upper mantle seismic discontinuity properties, including the shear velocity contrast, the density contrast, the transition sharpness and the gradient using high-quality receiver functions using broadband data.

We collect USArray seismic data and calculate receiver functions up to 350 s after the P arrival. Stacked receiver function record sections show robust detection of forward converted waves and backward scattering of top-side reflections between 0.1 Hz and 0.5 Hz. Timings of the forward/backward scattering waves are migrated to obtain the topography of the 410 and 660. Frequency-dependent amplitudes of forward and backward scattering waves are analyzed to estimate the shear velocity and density jump, as well as the transition width and local velocity and density gradient near the 410 and 660 beneath the US continent. To examine the impact of long-term subduction on the thermochemical state of the transition zone, we will compare features of TZSDs in the tectonically active western US and stable eastern US, while contrasting them against the result previously obtained in the east Asia beneath the Chinese continent and South Korea.