Apparent initial phase of a source of Rayleigh waves

Knopoff, L.; Schwab, Fred

doi:10.1029/jb073i002p00755

Cited by 62 publications

(26 citation statements)

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“…We assume that each wave path is along the great circle from the source to the receiver and that the source group time shift for the periods and path length considered is negligible (KNOPOFF and SCHWAB, 1968;PANZA et al, 1973;LEVSHIN et al, 1999).…”

Section: Tomographymentioning

confidence: 99%

Group Velocity Tomography in the Subantarctic Scotia Sea Region

Vuan

Russi

Panza

2000

Pure appl. geophys.

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More than 150 events, recently recorded by seven seismic broadband stations (OGS-IAA, IRIS, GSETT3-IDC), have been collected and processed to obtain an overview of the crust and upper mantle shear wave velocities.Group velocities of the fundamental mode Rayleigh and Love waves, in the period range from 15 s to 50 s, are used to obtain tomographic maps of the Scotia Sea region, the tip of Antarctic Peninsula, and the tip of South America. Errors in the measurements, estimated on clusters, are larger for Love waves than for Rayleigh waves and their averages are 0.060 -0.080 km/s and 0.030 -0.040 km/s, respectively.From the regionalisation of the dispersion measurements, we obtain smoothed local dispersion curves in correspondence with the main geological and tectonic features, and from their nonlinear inversion, the shear wave velocity versus depth profiles.The correlation length of the heterogeneity, which can be resolved by Rayleigh waves, varies between 200 and 400 km in most parts of the studied area, but becomes greater near the periphery of the maps. The spatial resolution of Love waves (400 -600 km) is poorer than that of Rayleigh waves, due to the deteriorated path coverage and to the larger errors in the group velocity measurements.Models of the shear wave velocity in the crust and upper mantle for the tip of South America, the Falkland Plateau, the Scotia Sea, the South Sandwich oceanic spreading ridge, the South Sandwich trench, the South Scotia ridge, the tip of Antarctic Peninsula, the Bransfield Strait and the Drake Passage are presented.Our regional models and the existing large-scale models (e.g., CRUST5.1), help to define a 3-D velocity model of the Scotia Sea region to be further investigated by waveform inversion.

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Section: Tomographymentioning

confidence: 99%

Group Velocity Tomography in the Subantarctic Scotia Sea Region

Vuan

Russi

Panza

2000

Pure appl. geophys.

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“…This technique can be used either with a single epicentre-receiver pair to determine the ' average ' structure over the propagation path, or with several different epicentres and receivers, where some form of the crossing-path technique (Sant8 1961) is used to regionalize the area under investigation. In either case, one must know the apparent initial phase Y (Knopoff & Schwab 1968), to obtain accurate phase velocity results. The quantity Y enters the problem when the average phase velocity for a given epicentre-receiver path is computed from …”

Section: Introductionmentioning

confidence: 99%

Structural Dependence of the Apparent Initial Phase of Rayleigh Wave

Frez

Schwab

1976

Geophysical Journal International

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Summary For Rayleigh waves generated by buried point sources, we investigate the effect of incomplete knowledge of the structure beneath the epicentre on the apparent initial phase. The effect is described in terms of a critical distance between epicentre and receiver, beyond which we expect an overall error in phase velocity which does not exceed 0.04 km s−1. A quarter of this error is due to uncertainty in the subepicentral structure. The main classes of focal mechanisms are treated explicitly. For the common classes of shallow‐crustal continental, and crustal oceanic sources, the effect is unimportant. The main, deep‐crustal continental mechanisms require critical distances of 1600–2200 km, with avoidance of a 30‐s period range. The results for the common, shallow‐subcrustal mechanisms show strong effects due to structural uncertainty. For an oceanic source depth of 34 km, one must accept large critical distances of 5100–6900 km if only a 40‐s period range is to be avoided; for the smaller critical distances of 2600–2100 km, the period ranges to be avoided become quite large—up to 100 s in extent. Of the common classes of sources at depths of about 72 km, only vertical dip slip in an oceanic structure gives fairly good results. Other combinations of source class and environment result in critical distances of up to 11000 km, as well as some excessively large period ranges to be avoided. The results for the deeper, vertical dip‐slip mechanisms are better: maximum critical distances of 4600 and 2000 km for source depths of about 150 and 300 km, respectively.

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“…We have performed a group velocity study for three reasons. First, measurements of group velocities are much less sensitive to source effects than phase velocities [e.g., Knopoff and Schwab, 1968;Muyzert and $nieder, 1996] since they derive from measurements of the wave packet envelopes rather than the constituent phases. This is particularly true at shorter periods and longer ranges.…”

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confidence: 99%