Abstract
The thermal structure of the lower mantle plays a key role in understanding the dynamic processes of the Earth's evolution and mantle convection. Because intrinsic attenuation in the lower mantle is highly sensitive to temperature, determining of the attenuation of the lower mantle could help us determine its thermal state. We attempted to constrain the attenuation of the lower mantle by measuring the amplitude ratios of p to ScP on the vertical component and s to ScS on the tangential component at short epicentral distances for seismic wave data from deep earthquakes in Northeast China. We calculated the theoretical amplitude ratios of p to ScP and s to ScS by using ray theory and the axial-symmetric spectral element method AxiSEM, as well as by considering the effects of radiation patterns, geometrical spreading, and ScP reflection coefficients. By comparing the observed amplitude ratios with the synthetic results, we constrained the quality factors as Qα ≈ 3,000 and Qβ ≈ 1,300 in the lower mantle beneath Northeast China, which are much larger than those in the preliminary reference Earth model (PREM) model of Qα ~800 and Qβ ~312. We propose that the lower mantle beneath Northeast China is relatively colder than the average mantle, resulting in weaker intrinsic attenuation and higher velocity. We estimated the temperature of the lower mantle beneath Northeast China as approximately 300–700 K colder than the global average value.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.