A new catalogue of normal-mode splitting function measurements up to 10 mHz

The splitting of the Earth's free-oscillation spectra places important constraints on the wave speed and density structure of the Earth's mantle and core. We present a new set of 164 self-coupled and 32 cross-coupled splitting functions. They are derived from modal spectra up to 10 mHz for 91 events with Mw ≥ 7.4 from the last 34 yr (1976–2010). Our data include the 2001 June 23 Peru event (Mw = 8.4), the Sumatra events of 2004 (Mw = 9.0) and 2005 (Mw = 8.6), the 2008 Wenchuan, China event (Mw = 7.9) and the 2010 Chile event (Mw = 8.8). The new events provide significant improvement of data coverage particularly in continental areas. Almost half of the splitting functions have never been measured before. In particular, we measured 33 new modes sensitive to mantle compressional wave velocity, 10 new inner-core sensitive modes and 22 new cross-coupled splitting functions. These provide new constraints on the large-scale compressional structure of the mantle and the odd-degree structure of the mantle and inner core and can be used in future inversions of heterogeneous Earth structure. Our new splitting function coefficient data set will be available online.

[1]  G. Masters,et al.  Observably split multiplets—data analysis and interpretation in terms of large-scale aspherical structure , 1992 .

[2]  B. Kennett,et al.  Normal-mode representations of multiple-ray reflections in a spherical earth , 1978 .

[3]  F. Dahlen.  The Normal Modes of a Rotating, Elliptical Earth—II Near-Resonance Multiplet Coupling , 1969 .

[4]  H. Hamaguchi,et al.  Degree one heterogeneity and hemispherical variation of anisotropy in the inner core from PKP(BC)–PKP(DF) times , 1997 .

[5]  D. Giardini,et al.  Splitting Functions of Long-Period Normal Modes of the Earth , 1988 .

[6]  Jeannot Trampert,et al.  Robust Normal Mode Constraints on Inner-Core Anisotropy from Model Space Search , 2003, Science.

[7]  L. Wen,et al.  Hemispherical variations in seismic velocity at the top of the Earth's inner core , 2001, Nature.

[8]  Joseph S. Resovsky,et al.  Improved normal mode constraints on lower mantle vp from generalized spectral fitting , 2003 .

[9]  Gabi Laske,et al.  CRUST 5.1: A global crustal model at 5° × 5° , 1998 .

[10]  Gabi Laske,et al.  The Relative Behavior of Shear Velocity, Bulk Sound Speed, and Compressional Velocity in the Mantle: Implications for Chemical and Thermal Structure , 2013 .

[11]  J. Woodhouse,et al.  Regional Variation of Inner Core Anisotropy from Seismic Normal Mode Observations , 2010, Science.

[12]  Joseph S. Resovsky,et al.  New and refined constraints on three‐dimensional Earth structure from normal modes below 3 mHz , 1998 .

[13]  J. Tromp,et al.  Normal-mode and free-Air gravity constraints on lateral variations in velocity and density of Earth's mantle , 1999, Science.

[14]  F. A. Dahlen,et al.  The Effect of A General Aspherical Perturbation on the Free Oscillations of the Earth , 1978 .

[15]  B. Romanowicz.  Can we resolve 3D density heterogeneity in the lower mantle? , 2001 .

[16]  Andrea Morelli,et al.  Anisotropy of the inner core inferred from PKIKP travel times , 1986 .

[17]  Joseph S. Resovsky,et al.  A degree 8 mantle shear velocity model from normal mode observations below 3 mHz , 1999 .

[18]  C. Kuo,et al.  On the resolution of density anomalies in the Earth's mantle using spectral fitting of normal‐mode data , 2002 .

[19]  J. Woodhouse,et al.  Normal mode coupling due to hemispherical anisotropic structure in Earth's inner core , 2009 .

[20]  D. Giardini,et al.  Three-dimensional structure of the Earth from splitting in free-oscillation spectra , 1987, Nature.

[21]  A. Deuss,et al.  Hemispherical structure in inner core velocity anisotropy , 2011 .

[22]  B. Romanowicz,et al.  Inner core anisotropy inferred by direct inversion of normal mode spectra , 1999 .

[23]  Jeroen Tromp,et al.  Support for anisotropy of the Earth's inner core from free oscillations , 1993, Nature.

[24]  F. Dahlen.  The Normal Modes of a Rotating, Elliptical Earth , 1968 .

[25]  A. Deuss,et al.  Splitting function measurements for Earth's longest period normal modes using recent large earthquakes , 2011 .

[26]  J. Tromp.  Normal-mode splitting due to inner-core anisotropy , 1995 .

[27]  Domenico Giardini,et al.  Evidence for inner core anisotropy from free oscillations , 1986 .

[28]  A. Tarantola,et al.  Generalized Nonlinear Inverse Problems Solved Using the Least Squares Criterion (Paper 1R1855) , 1982 .

[29]  D. Giardini,et al.  Large‐scale three‐dimensional even‐degree structure of the Earth from splitting of long‐period normal modes , 1991 .

[30]  D. L. Anderson,et al.  Preliminary reference earth model , 1981 .

[31]  Jeannot Trampert,et al.  Using probabilistic seismic tomography to test mantle velocity–density relationships , 2003 .

[32]  G. Masters,et al.  Observations of anomalous splitting and their interpretation in terms of aspherical structure , 1986 .

[33]  Jeroen Tromp,et al.  Normal-mode constraints on the structure of the Earth , 1996 .

[34]  John H. Woodhouse,et al.  Theoretical free-oscillation spectra: the importance of wide band coupling , 2001 .

[35]  Joseph S. Resovsky,et al.  Regularization uncertainty in density models estimated from normal mode data , 1999 .

[36]  G. Masters,et al.  Constraining aspherical structure with low-degree interaction coefficients: Application to uncoupled multiplets , 1988 .

[37]  J. Woodhouse.  The coupling and attenuation of nearly resonant multiplets in the Earth's free oscillation spectrum , 1980 .

[38]  J. Woodhouse,et al.  Complex Shear Wave Velocity Structure Imaged Beneath Africa and Iceland. , 1999, Science.

[39]  J. Tromp,et al.  Theoretical Global Seismology , 1998 .

[40]  G. Masters,et al.  Matrix autoregressive analysis of free‐oscillation coupling and splitting , 2000 .

[41]  A. Deuss.  Normal mode constraints on shear and compressional wave velocity of the Earth's inner core , 2007 .

[42]  K. Creager.  Large-scale variations in inner core anisotropy , 1999 .

[43]  F. Dahlen.  The effect of data windows on the estimation of free oscillation parameters , 1982 .

[44]  Joseph S. Resovsky,et al.  Probabilistic Tomography Maps Chemical Heterogeneities Throughout the Lower Mantle , 2004, Science.

[45]  John H. Woodhouse,et al.  S40RTS: A degree-40 shear-velocity model for the mantle from new Rayleigh wave dispersion, teleseismic traveltime and normal-mode splitting function measurements , 2011 .