Multimode Surface Waves for Selected Focal Mechanisms I. Dip-Slip Sources on a Vertical Fault Plane

Panza, G. F.; Schwab, Fred; Knopoff, L.

doi:10.1111/j.1365-246x.1973.tb02396.x

Cited by 53 publications

(20 citation statements)

References 9 publications

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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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“…By the same method it is, at present, not possible to make reliable phase velocity measurements since they require a good knowledge of the apparent Pure appl. geophys., Figure 1 Main plate tectonic setting as evidenced by CMT solutions for earthquakes located in the Scotia Sea region from 1977 to 1996. initial phase that is source mechanism dependent (PANZA et al, 1973). However, the effect of the initial phase of the source is not so severe when the source receiver distance is below 2000 km and the period of the measurements ranges between 10 and 30 -40 s; this effect for a fixed period decreases with distance.…”

Section: Datamentioning

confidence: 98%

S -wave Velocity Models in the Scotia Sea Region, Antarctica, from Nonlinear Inversion of Rayleigh Waves Dispersion

Vuan¹,

Cazzaro²,

Costa³

et al. 1999

Pure and Applied Geophysics

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More than 60 events recorded by four recently deployed seismic broadband stations around Scotia Sea, Antarctica, have been collected and processed to obtain a general overview of the crust and upper mantle seismic velocities.Group velocity of the fundamental mode of Rayleigh waves in the period between 10 s to 30 -40 s is used to obtain the S-wave velocity versus depth along ten different paths crossing the Scotia Sea region. Data recorded by two IRIS (Incorporated Research Institutions for Seismology) stations (PMSA, EFI) and the two stations of the OGS-IAA (Osservatorio Geofisico Sperimentale -Instituto Antarctico Argentino) network (ESPZ, USHU) are used.The Frequency-Time Analysis (FTAN) technique is applied to the data set to measure the dispersion properties. A nonlinear inversion procedure, ''Hedgehog,'' is performed to retrieve the S-wave velocity models consistent with the dispersion data.The average Moho depth variation on a section North to South is consistent with the topography, geological observations and Scotia Sea tectonic models.North Scotia Ridge and South Scotia Ridge models are characterised by similar S-wave velocities ranging between 2.0 km/s at the surface to 3.2 km/s to depths of 8 km/s. In the lower crust the S-wave velocity increases slowly to reach a value of 3.8 km/s. The average Moho depth is estimated between 17 km to 20 km and 16 km to 19 km, respectively, for the North Scotia Ridge and South Scotia Ridge, while the Scotia Sea, bounded by the two ridges, has a faster and thinner crust, with an average Moho depth between 9 km and 12 km.On other paths crossing from east to west the southern part of the Scotia plate and the Antarctic plate south of South Scotia Ridge, we observe an average Moho depth between 14 km and 18 km and a very fast upper crust, compared to that of the ridge. The S-wave velocity ranges between 3.0 and 3.6 km/s in the thin (9-13 km) and fast crust of the Drake Passage channel. In contrast the models for the tip of the Antarctic Peninsula consist of two layers with a large velocity gradient (2.3 -3.0 km/s) in the upper crust (6-km thick) and a small velocity gradient (3.0 -4.0) in the lower crust (14-km thick).

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“…From surface waves theory, the displacement of the fundamental mode dominates the earthquake ground motion at long period, T ≥ 5 s (Panza et al, 1973(Panza et al, , 1975a(Panza et al, , 1975b, therefore, the separation of the propagation from the source contribution to earthquake ground motion, commonly, but incorrectly, assumed in GMPE, is possible without relevant violation of the tensor nature of earthquake ground motion. The prediction of ground motion at long period is a crucial requirement by displacement-based design techniques.…”

Section: Discussionmentioning

confidence: 99%

Broadband NDSHA computations and earthquake ground motion observations for the Italian territory

Magrin

Gusev

Romanelli

et al. 2016

IJEIE

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Abstract:The aim of this work is two-fold: 1) to compare the results of national scale NDSHA modelling for the Italian region at 10 Hz cut-off, based on the relevant available knowledge, with observations (e.g., peak ground motion values) and existing empirical attenuation relations; 2) to update the scaling law for source spectra (SLSS) to be used for the selected area. The new set of source spectra, defined along the lines suggested by the comparison with empirical attenuation relations, produces acceptable results in terms of PGV and spectral acceleration at long periods. Synthetic PGA and SA at short periods show a faster attenuation with respect to the observed ones and, therefore, the effect of complex attenuation factors should be explored in future ad hoc studies.

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Multimode Surface Waves for Selected Focal Mechanisms I. Dip-Slip Sources on a Vertical Fault Plane

Cited by 53 publications

References 9 publications

Group Velocity Tomography in the Subantarctic Scotia Sea Region

Group Velocity Tomography in the Subantarctic Scotia Sea Region

S -wave Velocity Models in the Scotia Sea Region, Antarctica, from Nonlinear Inversion of Rayleigh Waves Dispersion

Broadband NDSHA computations and earthquake ground motion observations for the Italian territory

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