Scattering coefficients in the mantle revealed from the seismogram envelope analysis based on the multiple isotropic scattering model |
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| Institution: | 1. Engineering Laboratory for Deep Resources Equipment and Technology, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China;3. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China;4. College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;5. Faculty of Architecture, Civil and Transportation Engineering, Beijing University of Technology, Beijing, China;6. College of Control Science and Engineering, Bohai University, Jinzhou, Liaoning Province, China;1. School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, United States;2. Applied Physics Laboratory, The Johns Hopkins University, Laurel, MD 20723, United States;3. Planetary Geodynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States;1. Institute of Geophysics, ETH Zurich, Zurich, Switzerland;2. Swiss Seismological Service, ETH Zurich, Zurich, Switzerland;3. Department of Electrical and Electronic Engineering, Imperial College London, London, UK;4. School of Earth Sciences, University of Bristol, Bristol, UK;5. Université de Paris, Institut de Physique du Globe de Paris, CNRS, Paris, France;6. Institute of Theoretical Physics, University of Zurich, Zurich, Switzerland;7. Institut Supérieur de l''Aéronautique et de l''Espace SUPAERO, Toulouse, France;8. Max Planck Institute for Solar System Research, Göttingen, Germany;9. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA;10. Laboratoire de Météorologie Dynamique, Sorbonne University, Paris, France;11. Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY, USA;12. Laboratoire de Planétologie et Géodynamique, Univ. Nantes, Univ. Angers, CNRS, Nantes, France;13. Institut Universitaire de France, Paris, France;14. Johns Hopkins Applied Physics Laboratory, Laurel, MD, USA;15. Institute of Earth Sciences Jaume Almera of the Spanish Scientific Research Council (ICTJA-CSIC), Barcelona, Spain |
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| Abstract: | At longer periods, scattered ScS waves sometimes dominate over coda waves at large lapse times. Examining recordings of seismic envelopes at 9 IRIS seismic stations of regional earthquakes with focal depths deeper than 150 km in periods from 1 to 20 s for a wide lapse time range up to 2000 s, we found significant frequency dependence. The coda decay gradient at short periods is steeper than that at longer periods; however, the change of coda gradient associated with the ScS arrival becomes distinct as the period becomes longer. In particular, a clear offset of coda amplitude appears in central Asia for 10 and 15 s period bands. The multiple isotropic scattering process of S-waves in the heterogeneous mantle can be simply simulated by using the Monte Carlo simulation method based on the radiative transfer theory in scattering media. Assuming a two-plane-layer attenuation structure and smoothed velocity model of the PREM, we estimated the average total scattering coefficients of S-waves such as 7.52 × 10? 4～1.32 × 10? 3 km? 1 and 2.08 × 10? 4～6.23 × 10? 4 km? 1 at 4 s, and 4.51 × 10? 4～7.37 × 10? 4 km? 1 and 2.80 × 10? 5～2.71 × 10? 4 km? 1 at 10 s, for the lithosphere and the upper mantle and for the lower mantle, respectively. Our results indicate that scattering occurs mostly in the lithosphere and the upper mantle and support that medium heterogeneity spreads over the whole mantle though its scattering power is small. Strong scattering occurs beneath central Asia and Papua New Guinea, whereas the scattering beneath Italy and regions of east Russia is much weaker. The numerical calculation enables us to confirm that much stronger scattering than intrinsic attenuation causes the offset behavior with coda decay gradient change after the ScS arrival for 4 and 10 s period bands in some regions. |
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