Subduction zone guided waves and the heterogeneity structure of the subducted plate: Intensity anomalies in northern Japan

[1] The subducting Pacific plate acts an efficient waveguide for high-frequency signals and often produces anomalously large intensity on the eastern seaboard of northern Japan during deep earthquakes. The waveform records in the region of high intensity show a low-frequency (f 2 Hz) later arrivals with a long coda. This behavior is not explained by a simple subduction zone model comprising a high-velocity plate with low attenuation. From the analysis of observed broadband waveforms and numerical simulation of seismic wave propagation in the Pacific subduction zone we demonstrate that the high-frequency guided waves traveling in the subducting plate arise from the scattering of seismic waves by heterogeneity in plate structure. Our preferred model of the heterogeneity has elongated scatterers parallel to the plate margin described by a von Karmann function with a downdip correlation length of about 10 km and much shorter correlation length of about 0.5 km in thickness. The standard deviation of wave speed fluctuations from the averaged background model is about 2%. This new heterogeneous plate model generates significant scattering of seismic waves with wavelengths shorter than correlation distance in thickness, but low-frequency waves, with long wavelengths, can easy tunnel through such lamina structure. The result is frequency-selective propagation characteristics with a faster low-frequency phase followed by large and high-frequency signals with very long coda. A low-wave speed channel effect from the former oceanic crust at the top of the subducting slab is not necessary to explain the observed dispersed signals and the very long high-frequency coda. Three-dimensional simulations, using the Earth simulator supercomputer for modeling of high-frequency seismic wave propagation in the Pacific subduction zone including plate heterogeneity, clearly demonstrate the scattering waveguide effects for high-frequency seismic waves traveling in the plate. The region of large intensity for the heterogeneous model migrates away from the hypocenter into northern Japan with an elongated zone along the Pacific coast, almost comparable to the observations from deep events in the Pacific plate.

[1]  B. Isacks,et al.  Propagation of high‐frequency seismic waves inside the subducted lithosphere from intermediate‐depth earthquakes recorded in the Vanuatu Arc , 1985 .

[2]  T. Wallace,et al.  Subduction and collision processes in the Central Andes constrained by converted seismic phases , 2000, Nature.

[3]  Takashi Furumura,et al.  Parallel PSM/FDM Hybrid Simulation of Ground Motions from the 1999 Chi-Chi, Taiwan, Earthquake , 2002 .

[4]  K. Fuchs,et al.  Tunneling of low-frequency waves through the subcrustal lithosphere , 1976 .

[5]  Robert W. Clayton,et al.  A finite-difference simulation of wave propagation in two-dimensional random media , 1984 .

[6]  Joakim O. Blanch,et al.  Viscoelastic finite-difference modeling , 1994 .

[7]  The origin of teleseismic Pn waves: Multiple crustal scattering of upper mantle whispering gallery phases , 2003 .

[8]  D. Gubbins,et al.  Anomalous high‐frequency wave propagation from the Tonga–Kermadec seismic zone to New Zealand , 1986 .

[9]  D. Walker.  High‐frequency Pn and Sn phases recorded in the western Pacific , 1977 .

[10]  T. Utsu.  Regional Differences in Absorption of Seismic Waves in the Upper Mantle as Inferred from Abnomal Distributions of Seismic Intensities , 1966 .

[11]  T. Utsu,et al.  Anomalies in Seismic Wave Velocity and Attenuation Associated with a Deep Earthquake Zone(2) , 1967 .

[12]  T. Ouchi.  Spectral structure of high frequency P and S phases observed by OBS's in the Mariana Basin. , 1981 .

[13]  K. Fuchs.  Seismic anisotropy of the subcrustal lithosphere as evidence for dynamical processes in the upper mantle , 1977 .

[14]  M. Tittgemeyer,et al.  Scales of Heterogeneities in the Continental Crust and Upper Mantle , 1999 .

[15]  Naoto Wada,et al.  Newly imaged shape of the deep seismic zone within the subducting Pacific plate beneath the Hokkaido corner, Japan-Kurile arc-arc junction , 2003 .

[16]  E. Morozova,et al.  Heterogeneity of the uppermost mantle beneath Russian Eurasia from the ultra‐long‐range profile quartz , 1999 .

[17]  Moshe Reshef,et al.  A nonreflecting boundary condition for discrete acoustic and elastic wave equations , 1985 .

[18]  G. Abers.  Hydrated subducted crust at 100–250 km depth , 2000 .

[19]  Hiromitsu Nakamura,et al.  An Approximate Expression of Slip Velocity Time Function for Simulation of Near-field Strong Ground Motion , 2002 .

[20]  A. Levander,et al.  Origin of upper-mantle seismic scattering – evidence from Russian peaceful nuclear explosion data , 2003 .

[21]  V. Formisano,et al.  Ion acoustic wave forms generated by ion‐ion streams at the Earth's bow shock , 1982 .

[22]  J. Oliver,et al.  Propagation of seismic waves through and beneath the lithosphere that descends under the Tonga Island Arc , 1972 .

[23]  C. Haberland,et al.  Guided waves propagating in subducted oceanic crust , 2003 .

[24]  D. Walker.  High‐frequency Pn,Sn velocities: Some comparisons for the western, central, and South Pacific , 1981 .

[25]  Arthur Frankel,et al.  A review of numerical experiments on seismic wave scattering , 1989 .

[26]  N. Umino,et al.  Estimation of thickness of a low-velocity layer at the surface of the descending oceanic plate beneath the Northeastern Japan Arc by using synthesized PS-wave , 1987 .

[27]  K. Aki,et al.  Origin of coda waves: Source, attenuation, and scattering effects , 1975 .

[28]  High‐frequency precursors to P wave arrivals in New Zealand: Implications for slab structure , 1996 .

[29]  B. Isacks,et al.  High Frequency Shear Waves Guided by a Continuous Lithosphere Descending beneath western South America , 1973 .

[30]  A. Hasegawa,et al.  P wave tomographic imaging of the crust and upper mantle beneath the Japan Islands , 1993 .

[31]  Iwao Tsuchiya.  On the Variation of General Circulation in 1901-1940 , 1959 .

[32]  G. Abers,et al.  High resolution image of the subducted Pacific (?) plate beneath central Alaska, 50–150 km depth , 2003 .

[33]  G. Abers,et al.  The wet Nicaraguan slab , 2003 .

[34]  B. Kennett.  Observational and theoretical constraints on crustal and upper mantle heterogeneity , 1987 .

[35]  Hiroshi Takenaka,et al.  Parallel 3-D pseudospectral simulation of seismic wave propagation , 1998 .

[36]  Y. Fukao,et al.  A seismological constraint on the depth of basalt–eclogite transition in a subducting oceanic crust , 1983, Nature.

[37]  Kunihiro Ryoki.  Three-Dimensional Depth Structure of the Crust and Uppermost Mantle beneath Southwestern Japan and Its Regional Gravity Anomalies , 1999 .

[38]  和達 清夫.  Shallow and deep earthquakes , 1932 .

[39]  F. Yamazaki,et al.  Configuration of subducted Philippine Sea plate beneath the Chubu district, central Japan , 1985 .

[40]  Takeshi Tanaka,et al.  Subducting oceanic crust on the Philippine Sea plate in Southwest Japan , 1990 .

[41]  M. Tittgemeyer,et al.  Finite difference modelling of P-wave scattering in the upper mantle , 2000 .

[42]  J. A. Snoke,et al.  A model not requiring continuous lithosphere for anomalous high-frequency arrivals from deep-focus South American earthquakes , 1974 .

[43]  B. Kennett.  On regional S , 1985 .

[44]  T. Furumura,et al.  Large Scale Parallel Simulation and Visualization of 3D Seismic Wavefield \\ Using the Earth Simulator , 2004 .

[45]  Dispersion of P waves in subducted lithosphere: Evidence for an eclogite layer , 1991 .

[46]  Kim B. Olsen,et al.  On the implementation of perfectly matched layers in a three‐dimensional fourth‐order velocity‐stress finite difference scheme , 2003 .

[47]  A. Hasegawa,et al.  Attenuation structure beneath the volcanic front in northeastern Japan from broad-band seismograms , 2000 .

[48]  A. Hasegawa,et al.  Three-dimensional attenuation structure beneath the northeastern Japan arc estimated from spectra of small earthquakes , 2000 .

[49]  E. R. Engdahl,et al.  Constraints on seismic velocities in the Earth from traveltimes , 1995 .

[50]  Y. Fukao,et al.  Seismic detection of the untransformed ‘basaltic’ oceanic crust subducting into the mantle , 1985 .

[51]  L. T. Ikelle,et al.  2-D random media with ellipsoidal autocorrelation functions , 1993 .