Explosion-Generated Short-Period Surface Wave Dispersion and Noise Studies Along Linear Seismic Arrays In Southern Sweden

Abstract

SUMMARY The dispersion of short-period fundamental-mode Rayleigh waves (Rg) was measured along linear arrays on the Baltic Shield. The data used is a selected set of 176 records along three refraction profiles in southern Sweden. The phase velocity, determined in the 0.2-3.5 Hz band, could be grouped into a number of dispersion regions. Each regional dispersion showed a high internal consistency and the slowness as function of frequency was almost linear in the 1-3 Hz band. Linear regression was used to separate the effects of the medium from the experimental uncertainties. Systematic studies of the noise-to-signal ratio showed that the standard deviation of the dispersion, within each region and the above frequency band, essentially reflected the lateral heterogeneities. From the dispersion shear velocity models were inverted down to about 2-3 km, in one case down to 6 km. The S-wave velocity was weakly constrained to a non-decreasing function of depth with decreasing gradient. The P-wave velocity was constrained using recent results on Poisson’s constant ranging from 0.28 to 0.25 in the 0-2 km interval. The density was constrained using geological knowledge of the area. Using these constraints, the S-wave velocity increased rapidly with depth in the first few hundred metres of the crust. The models could be naturally grouped into three sets with similar character, in close agreement with the large-scale surface geology. The highest velocities were found in the east, in the Smiland-Varmland Granitic Belt and the smallest in the northwest, in the Sveconorwegian crust.