Shear-wave velocity in the south-eastern Brazilian continental shelf

Souza, Jorge Luis de

doi:10.1111/j.1365-246x.1995.tb07020.x

Cited by 5 publications

(6 citation statements)

References 24 publications

(15 reference statements)

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“…These results agree well with those obtained in previous studies (James et al. , 1993.; De Souza, 1995; Snoke and James, 1997).…”

Section: Resultssupporting

confidence: 94%

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Shear‐wave velocity structure of South America from Rayleigh‐wave analysis

Corchete

2011

Terra Nova

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Terra Nova, 24, 87–104, 2012 Abstract The elastic structure beneath South America is shown by means of S‐velocity maps for depths ranging from zero to 400 km, determined by the regionalization and inversion of Rayleigh‐wave dispersion. The traces of 128 earthquakes, occurring from 1990 to 2009, have been used to obtain Rayleigh‐wave dispersion data. These earthquakes were registered by 71 seismic station located in South America. The dispersion curves were obtained for periods between 5 and 250 s, by digital filtering with a combination of Multiple Filter Technique and Time Variable Filtering techniques. Later, all seismic events (and some stations) were grouped to obtain a dispersion curve for each source‐station path. These dispersion curves were regionalized and inverted according to the generalized inversion theory, to obtain shear‐wave velocity models for rectangular blocks 4° × 4° in size. The shear‐velocity structure obtained through this procedure is shown in the S‐velocity maps plotted for several depths. These results agree well with the geology and other geophysical results previously obtained. The obtained S‐velocity models suggest the existence of lateral and vertical heterogeneity. The zones with consolidated and old structures (such as shields, cratons and massifs) present greater S‐velocity values than the other zones, although this difference can be very little or negligible in some case. Nevertheless, in the depth range of 15–65 km, the different Moho depths present in the study area generate the principal variation of S‐velocity. Finally, a very interesting feature found in this study is the existence of a low S‐velocity channel beneath South America, from 180 to 280 km of depth, in which the S‐velocity decreases with depth.

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“…These results agree well with those obtained in previous studies (James et al. , 1993.; De Souza, 1995; Snoke and James, 1997).…”

Section: Resultssupporting

confidence: 94%

“…Also, in other studies developed in SE Brazil (James et al. , 1993.; De Souza, 1995), S‐velocities similar to those shown in Fig. 8 are obtained.…”

Section: Resultssupporting

confidence: 86%

Shear‐wave velocity structure of South America from Rayleigh‐wave analysis

Corchete

2011

Terra Nova

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“…Most of the data were acquired from the IRIS-DMC and the Geoscope Data Center (G. Roult). All maps were generated with the Generic Mapping Tools (GMT) data processing and display software package (Wessel & Smith 1991, 1995. Aspects of this research were supported by AFOSR contract F49620-95-1-0139 and NSF O¤ce of Polar Programs grant NSF-OPP-9615139.…”

Section: Acknowledgmentsmentioning

confidence: 99%

Group-velocity tomography of South America and the surrounding oceans

Vdovin¹,

Rial

Levshin³

et al. 1999

Geophysical Journal International

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Summary This paper presents the results of a study of the dispersion characteristics of broad‐band fundamental‐mode surface waves propagating across South America and the surrounding oceans. Broad‐band waveform data from about 765 events from 1977 to 1996 recorded at 48 individual stations have produced 7000 Rayleigh‐wave and 4800 Love‐wave dispersion curves. We present group‐velocity maps from 20 to 150 s period for Rayleigh waves and from 20 to 100 s for Love waves. Measurement uncertainties estimated from cluster analyses average about 0.025–0.030 km s− 1, but are larger for the short‐period Love waves. We estimate surface resolving kernels and show that the average resolution across South America is about 6°–8° for Rayleigh waves and 7°–10° for Love waves below 100 s period but degrades at longer periods and near the periphery of the maps. The estimated maps produce a variance reduction relative to the Preliminary Reference Earth Model (PREM) of more than 90 per cent at short periods, more than 80 per cent for Rayleigh and Love waves below about 100 s period, but nearer to about 70 per cent at longer periods. Synthetic experiments are presented to estimate the bias caused by azimuthal anisotropy using the recent global model of Trampert & Woodhouse (1996). This bias, which is worse for Love than for Rayleigh waves, may be substantial (up to 5 per cent in some places), but it is expected to be largely off the continent and is not correlated with the main features of the observed maps. Many known geological and tectonic structures are observed in the group‐velocity maps. Of particular note are the signatures of sedimentary basins (e.g. Maturin‐Llanos Basin, Marañon‐Ucayali‐Madre de Dios complex, Chaco‐Tarija Basin, S. Paraná Basin, the basins in the W. Caribbean and W. Gulf of Mexico), variations in crustal thickness (e.g. Andes, Altiplano, Brazilian Highlands), continental roots (e.g. Guyana and Guaporé shields, Sao Francisco Craton), and the Galapagos thermal anomaly. Comparison of the estimated group‐velocity maps with those predicted by CRUST5.1/S16B30 is qualitatively good, but there are significant differences in detail that provide new information that should help to calibrate future crustal and upper‐mantle models of South America.

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“…1-To get the best solution of the equation system (1), a group-velocity range (Δc) covering a large interval of group-velocities (c n , 1, 2, , n p =  iterations) and a group-velocity step (ζ) are previously defined; 2-The first value of the group-velocity range (i.e., a constant group-velocity value-c 1 ) is then attributed in all cells of the grid (v j values); 3-With the v j values of the previous item, the V i values are then calculated; 4-As the terms U i , d ij and D i are known, then the equation system is solved (for the particular group-velocity c 1 -item 2) and the values of u j are computed via Equation (3). In this step, both resolution and covariance matrices are also computed by using Equations (4) and (5); Figure 1.…”

Section: Two-dimensional Surface Wave Tomography Estimation Of the Ramentioning

confidence: 99%

“…It has been widely used in surface wave dispersion studies worldwide ( [3] [4], [36]- [38]). Both P and S wave velocities, as well as density of Preliminary Reference Earth Model ( [39]) were used as starting parameters in the dispersion inversion procedure.…”

Section: Three-dimensional Image Of Mohorovičić Discontinuity In Nortmentioning

confidence: 99%