TY - JOUR
T1 - Intermittent and lateral varying ULVZ structure at the northeastern margin of the Pacific LLSVP
AU - Zhao, Chunpeng
AU - Garnero, Edward
AU - Li, Mingming
AU - McNamara, Allen
AU - Yu, Shule
N1 - Funding Information:
We thank the Incorporated Research Institutions for Seismology, EarthScope's USArray, and the Canadian National Seismograph Network for providing freely available high-quality broadband data. The data for this paper are available by contacting the corresponding author at czhao6@asu.edu. This research was supported by NSF grants EAR1401270 and EAR1161038.
Publisher Copyright:
©2017. American Geophysical Union. All Rights Reserved.
PY - 2017/2/1
Y1 - 2017/2/1
N2 - Thin patches with ultralow velocities have been proposed to exist at the core-mantle boundary (CMB). The detection and mapping of ultralow velocity zones (ULVZs) are difficult, in part, because of limited source-receiver geometries of seismic phases used in ULVZ modeling. Here we develop a new approach that simultaneously utilizes ScS precursor and postcursor energies to investigate the CMB region for ULVZ structure. We stacked source-deconvolved ScS waveforms within 1.5° geographic bins to extract ScS precursor and postcursor energies, if present, with ScS effectively removed from waveforms. We investigate the CMB beneath the central Pacific Ocean, and evidence for ULVZs is clearly apparent. Geographic bin stacks possessing similar ScS precursor-plus-postcursor behavior are grouped by using cluster analysis to produce more robust waveforms by enhancing the signal-to-noise ratios. Synthetic seismograms that demonstrate the amplitude and timing of the ULVZ arrivals are sensitive to ULVZ thickness and internal velocities. To pursue local ULVZ properties we processed 13,850 1-D synthetic models with various ULVZ thicknesses and internal properties, using the identical ScS-stripping method as with the data. A best fitting model was found for each geographical bin cluster by using an amplitude-sensitive cross-correlation algorithm. While limitations exist due to 1-D modeling, strong lateral variations are clearly apparent in ULVZ thickness and properties across the large low shear velocity province (LLSVP) margin in our study area. Inside hypothesized LLSVP edges, ULVZs appear to distribute unevenly, suggesting 3-D variations of convection currents.
AB - Thin patches with ultralow velocities have been proposed to exist at the core-mantle boundary (CMB). The detection and mapping of ultralow velocity zones (ULVZs) are difficult, in part, because of limited source-receiver geometries of seismic phases used in ULVZ modeling. Here we develop a new approach that simultaneously utilizes ScS precursor and postcursor energies to investigate the CMB region for ULVZ structure. We stacked source-deconvolved ScS waveforms within 1.5° geographic bins to extract ScS precursor and postcursor energies, if present, with ScS effectively removed from waveforms. We investigate the CMB beneath the central Pacific Ocean, and evidence for ULVZs is clearly apparent. Geographic bin stacks possessing similar ScS precursor-plus-postcursor behavior are grouped by using cluster analysis to produce more robust waveforms by enhancing the signal-to-noise ratios. Synthetic seismograms that demonstrate the amplitude and timing of the ULVZ arrivals are sensitive to ULVZ thickness and internal velocities. To pursue local ULVZ properties we processed 13,850 1-D synthetic models with various ULVZ thicknesses and internal properties, using the identical ScS-stripping method as with the data. A best fitting model was found for each geographical bin cluster by using an amplitude-sensitive cross-correlation algorithm. While limitations exist due to 1-D modeling, strong lateral variations are clearly apparent in ULVZ thickness and properties across the large low shear velocity province (LLSVP) margin in our study area. Inside hypothesized LLSVP edges, ULVZs appear to distribute unevenly, suggesting 3-D variations of convection currents.
KW - LLSVP
KW - ScS
KW - ULVZ
KW - core-mantle boundary
KW - seismology
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U2 - 10.1002/2016JB013449
DO - 10.1002/2016JB013449
M3 - Article
AN - SCOPUS:85013168600
SN - 2169-9313
VL - 122
SP - 1198
EP - 1220
JO - Journal of Geophysical Research: Solid Earth
JF - Journal of Geophysical Research: Solid Earth
IS - 2
ER -