Validity of surface-wave ray theory on a laterally heterogeneous earth

Wang, Zheng; Dahlen, F. A.

doi:10.1111/j.1365-246x.1995.tb06888.x

Cited by 62 publications

(52 citation statements)

References 24 publications

(23 reference statements)

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“…First, we ignore the deviation of the raypaths from the great circle. For smooth models this eect has been shown to be small when the data are phase-or groupdispersion curves (WANG and DAHLEN, 1995;WANG et al, 1998). The assumption of a``smooth model'' is more questionable for the maps in this study with the largest amplitude anomalies (the shortest period models).…”

Section: Introductionmentioning

confidence: 69%

Global Models of Surface Wave Group Velocity

Larson¹,

Ekström²

2001

Pure appl. geophys.

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Ð Measurements of group velocity are derived from phase-velocity dispersion curves and modeled with global laterally-varying isotropic structure. Maps for both Love and Rayleigh waves are created in the period range 35 s to 175 s. The data set of group-velocity measurements includes over 50,000 minor-arc observations and 5,000 major-arc observations. The errors in the measurements are estimated by an empirical method of comparing pairwise-similar paths, resulting in uncertainties which are 20% to 40% of the size of the typical measurement. The models are determined by least-squares inversion for spherical harmonic maps expanded up to degree 40. This parameterization allows for resolution of structures as small as 500 km. The models explain 70±98% of the variance relative to the Preliminary Reference Earth Model (PREM). For the area of Eurasia, the group-velocity maps from this study are compared with those of RITZWOLLER and LEVSHIN (1998). The results of the two studies are in very good agreement, particularly in terms of spatial correlation. The models also agree in amplitude at wavelengths longer than 30 degrees. For shorter wavelengths, the agreement is good only for models at short periods. The global maps are useful for prediction of group arrival times, for revealing tectonic structures, for determination of seismic event locations and source parameters, and as a basis for regional group-velocity studies.

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Section: Introductionmentioning

confidence: 69%

Global Models of Surface Wave Group Velocity

Larson¹,

Ekström²

2001

Pure appl. geophys.

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“…One particular consequence of the very strong deviations at short period is that it may be so large that taking into account finite frequency effects based on kernels or Fresnel zones (e.g. Wang & Dahlen 1995;Ritzwoller et al 2002;Yoshizawa & Kennett 2002;Zhou et al 2004) around the great-circle may be inadequate. The data from the present study should allow better quantifying and possibly fostering tools to correct for these effects.…”

Section: O N C L U S I O N S a N D Discussionmentioning

confidence: 99%

Arrival angle anomalies of Rayleigh waves observed at a broadband array: a systematic study based on earthquake data, full waveform simulations and noise correlations

et al. 2015

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S U M M A R YDeviation of seismic surface waves from the great-circle between source and receiver is illustrated by the anomalies in the arrival angle, that is the difference between the observed backazimuth of the incident waves and the great-circle. Such arrival angle anomalies have been known for decades, but observations remain scattered. We present a systematic study of arrival angle anomalies of fundamental mode Rayleigh waves (20-100 s period interval) from 289 earthquakes and recorded by a broadband network LAPNET, located in northern Finland. These observations are compared with those of full waveform synthetic seismograms for the same events, calculated in a 3-D Earth and also compared with those of seismograms obtained by ambient noise correlation. The arrival angle anomalies for individual events are complex, and have significant variations with period. On average, the mean absolute deviation decreases from ∼9 • at 20 s period to ∼3 • at 100 s period. The synthetic seismograms show the same evolution, albeit with somewhat smaller deviations. While the arrival angle anomalies are fairly well simulated at long periods, the deviations at short periods are very poorly modelled, demonstrating the importance of the continuous improvement of global crustal models. At 20-30 s period, both event data and numerical simulations have strong multipathing, and relative amplitude changes between different waves will induced differences in deviations between very closely located events. The source mechanism has only limited influence on the deviations, demonstrating that they are directly linked to propagation effects, including near-field effects in the source area. This observation is confirmed by the comparison with seismic noise correlation records, that is where the surface waves correspond to those emitted by a point source at the surface, as the two types of observations are remarkably similar in the cases where earthquakes are located close to seismic stations. This agreement additionally confirms that the noise correlations capture the complex surface wave propagation.

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“…This method has beenused in several studies of earth structure e.g., Levshin et al, 2001;Shapiro et al, 2002. Ray-theory is a high frequency approximation, however, which is not justi ed in the presence of heterogeneities whose length-scale is comparable to the wavelength of the wave e.g., Woodhouse, 1974;Wang & Dahlen, 1995. For the ray approximation to be valid, the rst Fresnel zone must be smaller than the scale-length of the heterogeneity, which places limitations on the lateral resolution of seismic models based on ray-theory. The Born or Rytov approximation for surface wave scattering e.g., Woodhouse & Girnius, 1982;Yomogida & Aki, 1987;Snieder & Romanowicz, 1988;Bostock & Kennett, 1992;Friederich et al, 1993, Friederich 1999Meier et al, 1997;Spetzler et al, 2001Spetzler et al, , 2002Yoshizawa & Kennett, 2002;Snieder, 2002 models the nite width of the surface wave sensitivity zone.…”

Section: Introductionmentioning

confidence: 99%

Minor-arc and major-arc global surface wave diffraction tomography

Levshin¹,

Barmin²,

Ritzwoller³

et al. 2005

Physics of the Earth and Planetary Interiors

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We discuss extending global surface wave di raction tomography to accommodate major-arc dispersion measurements. The introduction of major-arc surface wave dispersion measurements improves path density and resolution in regions poorly covered by minor-arc measurements alone, as occurs in much of the southern hemisphere. The addition of major-arc measurements to the inversion for dispersion maps does not appreciably degrade the t to the minor-arc measurements but signi cantly improves the t to the major-arc measurements. For these reasons, we conclude that the addition of major-arc measurements is worthwhile in the interim until the broad-band network of ocean bottom or Antarctic stations is improved in the future.

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Validity of surface-wave ray theory on a laterally heterogeneous earth

Cited by 62 publications

References 24 publications

Global Models of Surface Wave Group Velocity

Global Models of Surface Wave Group Velocity

Arrival angle anomalies of Rayleigh waves observed at a broadband array: a systematic study based on earthquake data, full waveform simulations and noise correlations

Minor-arc and major-arc global surface wave diffraction tomography

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