Research

  • 3-D imaging of mantle transition zone beneath continental US with receiver functions

    • The mantle transition zone has been widely studied by multiple sub-fields in geosciences including seismology, mineral physics and geodynamics. Due to the relatively high water storage capacity of olivine polymorphs (wadsleyite and ringwoodite) inside the transition zone, it is proposed to be a potential water reservoir that may contain a bulk amount water up to several ocean masses. However, there is an ongoing debate about the hydration level of those minerals and how it varies from place to place. Considering the fact that dehydration melting, which may happen during phase transitions between hydrated olivine polymorphs, may be seismically detectable, large-scale seismic imaging of heterogeneous scatters at that depth range will contribute to the debate. Therefore, in order to obtain an accurate image with relatively large spatial coverage, more than 100,000 P to S receiver functions from USArray will be used for imaging structures in depth range of 300 km to 800 km beneath the continental US with an improved 3-D Kirchhoff pre-stacking migration method. [Link]

  • Distortion on seismic waves induced by undulated interface

    • Several studies have indicated that the focus/defocus effects from the topography of a discontinuity may reshape not only the traveltime but also the amplitude of seismic waves. Therefore, the 3-D topography structures of an interface could be constrained by modeling the distortion on seismic phases. We combined the representation theorem and geometric ray theory to develope a method to calculated S to P conversions with 3-D topography. Synthetic tests indicated the focus/defocus due to discontinuity topography substantially alters the amplitudes of converted phases (60% to 300% based on our examples). Then by modeling the s410P phase from a deep earthquake beneath South America, an elevated 410 km discontinuity was found to match our observations best. [PDF]


Publications

    2019
  • Zhang, H., & Schmandt, B. 2019. Application of Ps Scattering Kernels to Imaging the Mantle Transition Zone with Receiver Functions. Journal of Geophysical Research: Solid Earth. [Link]

    • 2017
  • Qian, Y., Ni, S., Wei, S., Almeida, R. and Zhang, H. 2017. The effects of core-reflected waves on finite fault inversions with teleseismic body wave data. Geophysical Journal International. [Link]
  • Zhang, H., Ni, S., Chu, R. and Schmandt, B. 2017. An algorithm for computing synthetic body waves due to underside conversion on an undulating interface and application to the 410 km discontinuity. Geophysical Journal International. [PDF]