Seismic triplication used to reveal slab subduction that had disappeared in the late Mesozoic beneath the northeastern South China Sea

Seismic triplication used to reveal slab subduction that had disappeared in the late Mesozoic... We provided a new study of the seismic velocity structure of the mantle transition zone (MTZ) beneath the northeastern South China Sea using P-wave triplications from two earthquakes at the central Philippines recorded by the Chinese Digital Seismic Network. Through fitting the observed and theoretical triplications modeled by the dynamic ray tracing method for traveltimes, and the reflectivity method for synthetic waveforms using grid-searching method, best-fit velocity models based on IASP91 were obtained to constrain the P-wave velocity structure of the MTZ. The models show that a high-velocity anomaly (HVA) resides at the bottom of MTZ. The HVA is 215km to 225km thick, with a P-wave velocity increment of 1.0% between 450km and 665km or 675km transition and increase by 2.5–3.5% at 665km or 675km depth. The P-wave velocity increment ranges from approximately 0.3% to 0.8% below the 665km or 675km. We proposed that the HVA in the MTZ was caused by the broken fragments of a diving oceanic plate falling into the MTZ at a high angle, and/or by unstable thick continental lithosphere dropping into the MTZ sequentially or almost simultaneously. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Tectonophysics Elsevier

Seismic triplication used to reveal slab subduction that had disappeared in the late Mesozoic beneath the northeastern South China Sea

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Publisher
Elsevier
Copyright
Copyright © 2018 Elsevier B.V.
ISSN
0040-1951
eISSN
1879-3266
D.O.I.
10.1016/j.tecto.2017.12.030
Publisher site
See Article on Publisher Site

Abstract

We provided a new study of the seismic velocity structure of the mantle transition zone (MTZ) beneath the northeastern South China Sea using P-wave triplications from two earthquakes at the central Philippines recorded by the Chinese Digital Seismic Network. Through fitting the observed and theoretical triplications modeled by the dynamic ray tracing method for traveltimes, and the reflectivity method for synthetic waveforms using grid-searching method, best-fit velocity models based on IASP91 were obtained to constrain the P-wave velocity structure of the MTZ. The models show that a high-velocity anomaly (HVA) resides at the bottom of MTZ. The HVA is 215km to 225km thick, with a P-wave velocity increment of 1.0% between 450km and 665km or 675km transition and increase by 2.5–3.5% at 665km or 675km depth. The P-wave velocity increment ranges from approximately 0.3% to 0.8% below the 665km or 675km. We proposed that the HVA in the MTZ was caused by the broken fragments of a diving oceanic plate falling into the MTZ at a high angle, and/or by unstable thick continental lithosphere dropping into the MTZ sequentially or almost simultaneously.

Journal

TectonophysicsElsevier

Published: Mar 15, 2018

References

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