Approximation of surface wave mode conversion at a passive continental margin by a mode-matching technique

Meier, Thomas; Malischewsky, Peter G.

doi:10.1046/j.1365-246x.2000.00040.x

Cited by 13 publications

(10 citation statements)

References 45 publications

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“…The validity of the approximation of independent propagation of the individual modes of the seismogram has been explored theoretically (Kennett & Nolet 1990;Kennett 1995;Meier & Malischewsky 2000) and been found to be subject to certain frequency limitations, to which we adhere. The validity of the approximation of independent propagation of the individual modes of the seismogram has been explored theoretically (Kennett & Nolet 1990;Kennett 1995;Meier & Malischewsky 2000) and been found to be subject to certain frequency limitations, to which we adhere.…”

Section: Introductionmentioning

confidence: 99%

Multimode Rayleigh wave inversion for heterogeneity and azimuthal anisotropy of the Australian upper mantle

Simons¹,

Hilst²,

Montagner

et al. 2002

Geophysical Journal International

178

166

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Summary We present an azimuthally anisotropic 3‐D shear‐wave speed model of the Australian upper mantle obtained from the dispersion of fundamental and higher modes of Rayleigh waves. We compare two tomographic techniques to map path‐average earth models into a 3‐D model for heterogeneity and azimuthal anisotropy. Method I uses a rectangular surface cell parametrization and depth basis functions that represent independently constrained estimates of radial earth structure. It performs an iterative inversion with norm damping and gradient regularization. Method II uses a direct inversion of individual depth layers constrained by Bayesian assumptions about the model covariance. We recall that Bayesian inversions and discrete regularization approaches are theoretically equivalent, and with a synthetic example we show that they can give similar results. The model we present here uses the discrete regularized inversion of independent path constraints of Method I, on an equal‐area grid. With the exception of westernmost Australia, we can retrieve structure on length scales of about 250 km laterally and 50 km in the radial direction, to within 0.8 per cent for the velocity, 20 per cent for the anisotropic magnitude and 20° for its direction. On length scales of 1000 km and longer, down to about 200 km, there is a good correlation between velocity heterogeneity and geologic age. At shorter length scales and at depths below 200 km, however, this relationship breaks down. The observed magnitude and direction of maximum anisotropy do not, in general, appear to be correlated to surface geology. The pattern of anisotropy appears to be rather complex in the upper 150 km, whereas a smoother pattern of fast axes is obtained at larger depth. If some of the deeper directions of anisotropy are aligned with the approximately N–S direction of absolute plate motion, this correspondence is not everywhere obvious, despite the fast (7 cm yr−1) northward motion of the Australian plate. More research is needed to interpret our observations in terms of continental deformation. Predictions of SKS splitting times and directions, an integrated measure of anisotropy, are poorly matched by observations of shear‐wave birefringence.

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Section: Introductionmentioning

confidence: 99%

Multimode Rayleigh wave inversion for heterogeneity and azimuthal anisotropy of the Australian upper mantle

Simons¹,

Hilst²,

Montagner

et al. 2002

Geophysical Journal International

178

166

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“…Our interpretation of the phase splitting as a Moiré pattern explains well the observed features of the short‐period wavefield of T = 20 to 50 s. Since Moiré patterns appear as a result of the interference of two plane waves, this feature is expected to be caused by medium heterogeneity at the far‐field rather than by medium heterogeneity just beneath Japan. Scattering by mountains [ Ji et al , 2005; Stich and Morelli , 2007] or seamounts [ Obara and Matsumura , 2010], by continental margin [ Capon , 1970; Meier and Malischewsky , 2000], or by medium heterogeneity [ Maeda et al , 2006; Sato and Nohechi , 2001] between the epicenter and Japan could be the cause of these multipath effects.…”

Section: Discussionmentioning

confidence: 99%

Interference of long-period seismic wavefield observed by the dense Hi-net array in Japan

et al. 2011

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[1] In order to recover small signals of long-period ground motions recorded by a short-period seismometer, we designed a time domain recursive filter that simulates seismic waves recorded with broadband seismometers. We applied the time domain filter to seismograms recorded by the dense Hi-net array, which consists of 800 stations at intervals of approximately 20 km. The effectiveness of the time domain filter is demonstrated through the comparison of broadband waveforms obtained by the filter and STS-2 true broadband seismograms from the F-net at the same site. Good agreement is observed between filtered and true broadband waveforms with high correlation coefficients for periods of up to 100 s for waveforms from the 2007 Sumatra earthquake (M7.9), which occurred approximately 5000-5800 km away from Japan. The applicability of the time domain filter to the recovery of long-period signals from the record of a short-period seismometer depends on the signal-to-noise ratio. As a result, a limited bandwidth of broadband signal is recovered for smaller earthquake. From the spatiotemporal variation of the long-period (T = 20-100 s) wavefield obtained by the time domain filter, we newly found an anomalous phase pattern of splitting of polarity along the wavefront, particularly for the relatively short period band of from 20-50 s. Array analysis of the dense broadband waveforms revealed multipathing of the Rayleigh waves, which propagated toward central Japan from two directions with slightly different slowness vectors. The interference of two Rayleigh waves caused such splitting of wavefield.Citation: Maeda, T., K. Obara, T. Furumura, and T. Saito (2011), Interference of long-period seismic wavefield observed by the dense Hi-net array in Japan,

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“…There are several possible factors that will influence the accuracy of the inversion results; for example, the errors in the source parameters (Zielhuis & Nolet 1994) and the uncertainty of the boundary locations (Meier & Malischewsky 2000). In general, we should use events with a reliable focal mechanism, and delimit the regions based on the local geological settings.…”

Section: Discussionmentioning

confidence: 99%

“…Although a number of methods for the computation of the coupling coefficient have been suggested recently (e.g. Vaccari et al 1989; Romanelli et al 1996; Meier & Malischewsky 2000), it can only be determined analytically for a very few cases. Recently, by considering a passive continental margin, Meier & Malischewsky (2000) have studied, in some detail, a case of vertical discontinuity, and associated mode conversion of surface waves.…”

Section: Representation Of Surface Waves In Vertical Welded Stratifiementioning

confidence: 99%

“…If the sharp heterogeneity is approximated by a vertical discontinuity, the wavefield can be expressed in terms of incident, reflected and transmitted waves. Recently, analytic methods, which, although approximate, enable the simple computation of the coupling coefficients among incident, reflected and transmitted waves, were made available by Vaccari et al (1989); Romanelli et al (1996) and Meier et al (1997) for a flat Earth geometry, and by Meier & Malischewsky (2000) for a spherical Earth geometry, using the mode‐matching approaches of Alsop (1966), Gregersen & Alsop (1976), Gregersen (1978) and Malischewsky (1987).…”

Section: Introductionmentioning

confidence: 99%

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Waveform inversion for lateral heterogeneities using multimode surface waves

Zou¹

2002

Geophysical Journal International

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Summary We propose a waveform inversion scheme that can be used to invert strong structural heterogeneities. The method is based on a ray approximation for surface waves. Strong structural lateral variations are modelled by vertical discontinuities. Therefore, a geologically heterogeneous region is partitioned into a number of lateral homogeneous subregions. Synthetic seismograms are calculated by modal summation over incident and transmitted modes. With this method the complete waveforms of surface waves, including mode cross‐branch coupling, multipathing and scattering, are considered in the inversion. We test the method with several geophysically realistic structural models. An example of waveform inversion for real data—a wave path across the Iberian peninsula and the oceanic structure off the French coast owing to the Gibraltar earthquake (Ms= 5.7)—is presented. The method allows us to obtain the information represented by different set of structures along the same source–receiver minor arc through which the waves have propagated. The method is applicable to different models of lateral heterogeneity. In its present development, it is most appropriate for inverting structures around tectonic scenarios such as continental margins, grabens and discontinuities between major plates.

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Approximation of surface wave mode conversion at a passive continental margin by a mode-matching technique

Cited by 13 publications

References 45 publications

Multimode Rayleigh wave inversion for heterogeneity and azimuthal anisotropy of the Australian upper mantle

Multimode Rayleigh wave inversion for heterogeneity and azimuthal anisotropy of the Australian upper mantle

Interference of long-period seismic wavefield observed by the dense Hi-net array in Japan

Waveform inversion for lateral heterogeneities using multimode surface waves

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