Abstract
Important information about small-scale heterogeneities is hardly accessible by the traditional deterministic seismic tomography. Fluctuations of the phase and the logarithmic amplitude of direct teleseismic plane P waves can be used to characterize small-scale heterogeneities. Seismic data recorded by the Hi-CLIMB array are used to analyze the average power spectrum of the small-scale velocity heterogeneities under Tibet. Coherence functions of the logarithmic amplitude and the phase fluctuations due to different earthquakes from different back azimuths show consistent characteristics, indicating that fluctuations are due to heterogeneities under the stations. Assuming that the heterogeneities are statistically stationary and distributed within a layer, we invert for the average heterogeneity spectrum by fitting both the logarithmic amplitude and the phase coherence data. Multiscale nature of the heterogeneity is evident. The inverted power spectrum is “red” at the large-scale end, meaning that the power spectrum decreases as the length scale decreases. Such a decreasing trend stops at smaller scales ∼20–50 km and 10 km. This may indicate that mantle convection is not effective in destroying smaller heterogeneities.
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References
Aki K (1973). Scattering of P waves under the Montana Lasa. J Geophys Res78(8): 1 334–1 346.
Bataille K D and Flatté S M (1988). Inhomogeneities near the core-mantle boundary inferred from short-period scattered PKP waves recorded at the Global Digital Seismograph Network. J Geophys Res93(B12): 15 057–15 064.
Bercovici D (2007). Mantle dynamics past, present, and future: An introduction and overview. In: Gerald S ed. Treatise on Geophysics. Elsevier, Amsterdam, 1–30.
Berteussen K A, Husebye E S, Mereu R F and Ram A (1977). Quantitative assessment of the crust-upper mantle heterogeneities beneath the Gauribidanur seismic array in southern India. Earth Planet Sci Lett37(2): 326–332.
Buland R and Chapman C H (1983). The computation of seismic travel times. Bull Seismol Soc Am73(5): 1 271–1 302.
Capon J (1974). Characterization of crust and upper mantle structure under LASA as a random medium. Bull Seismol Soc Am64(1): 235–266.
Capon J and Berteussen K A (1974). A random medium analysis of crust and upper mantle structure under NORSAR. Geophys Res Lett1(7): 327–328.
Chen X and Aki K (1991). General coherence functions for amplitude and phase fluctuations in a randomly heterogeneous medium. Geophys J Int105(1): 155–162.
Chernov L A (1960). Wave Propagation in a Random Medium. McGraw-Hill, New York, 168pp.
Chevrot S, Montagner J P and Snieder R (1998). The spectrum of tomographic earth models. Geophys J Int133(3): 783–788.
Constable S C, Parker R L and Constable C G (1987). Occam’s inversion: A practical algorithm for generating smooth models from electromagnetic sounding data. Geophysics52(3): 289–300.
Dziewonski A M (2005). The robust aspects of global seismic tomography. Geological Society of America Special Papers388: 147–154.
Efron B and Tibshirani R J (1993). An Introduction to the Bootstrap. Chapman & Hall/CRC, New York, 456pp.
Flatté S M and Wu R S (1988). Small-scale structure in the lithosphere and asthenosphere deduced from arrival time and amplitude fluctuations at NORSAR. J Geophys Res93(B6): 6 601–6 614.
Grand S P, van der Hilst R D and Widiyantoro S (1997). Global seismic tomography: a snapshot of convection in the Earth. GSA Today7(4): 1–7.
Kennett B L N and Engdahl E R (1991). Traveltimes for global earthquake location and phase identification. Geophys J Int105(2): 429–465.
Maceira M, Larmat C, Rowe C A, Allen R M and Obrebski M J (2011). Validating seismic imaging methods and 3D seismic velocity models. Eos Trans AGU92: S41A–2182.
Nábělek J, Hetényi G, Vergne J, Sapkota S, Kafle B, Jiang M, Su H, Chen J, Huang B S and the Hi-CILMB Team (2009). Underplating in the Himalaya-Tibet collision zone revealed by the Hi-CLIMB experiment. Science325(5946): 1 371–1 374.
Sato H and Fehler M (1998). Seismic Wave Propagation and Scattering in the Heterogeneous Earth. Springer-Verlag, New York, 308pp.
Wu R S and Flatté S M (1990). Transmission fluctuations across an array and heterogeneities in the crust and upper mantle. Pure Appl Geophys132(1–2): 175–196.
Wu R S and Xie X B (1991). Numerical tests of stochastic tomography. Phys Earth Planet Inter67: 180–193.
Zheng Y and Wu R S (2008). Theory of transmission fluctuations in a depth-dependent background medium. In: Sato H and Fehler M eds. Earth Heterogeneity and Scattering Effects on Seismic Waves. Academic Press, Amsterdam, 21–41.
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Zheng, Y. Scale lengths of heterogeneities under Tibet. Earthq Sci 25, 409–414 (2012). https://doi.org/10.1007/s11589-012-0866-y
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DOI: https://doi.org/10.1007/s11589-012-0866-y