Delineation of Crustal Structure at VLC Seismographic Station Using Joint Inversion of Receiver Functions and Dispersion Data

Abstract

Joint inversion of body wave receiver functions and dispersion data was used to model the shear wave velocity distribution of the crust and upper mantle below VLC (44.16° N, 10.39° E), a broadband seismographic station in Italy. Receiver functions are primarily sensitive to the shear wave velocity contrasts and vertical travel times, whereas the surface wave dispersion measurements are sensitive to absolute vertical shear wave velocity averages and changes as function of depth. Each data set has inherent lapses but by jointly inverting both we are able to draw on the capabilities of one to compensate the imperfections of the other and this provides better S-wave velocity constraints than we would obtain by inverting either data set individually. The receiver functions were computed from the teleseismic earthquakes recorded by VLC station between 2005 and 2012, while the dispersion curves at regional scale were determined by the Frequency Time Analysis and have been used to obtain tomography maps, using the two-dimensional tomography algorithm developed by Ditmar and Yanovskaya in 1987. The inversion results include a crust with a sharp gradient near the surface (shear velocity changing from 2.15 to 3.4 kms-1 in 5 km) underlain by a 13-km-thick layer with a shear velocity of and 3.4 kms-1 another 15-km- thick layer with a shear velocity of 3.72 kms-1, and an upper mantle with an average shear velocity of 4.4 kms-1. The crust–mantle transition has a significant gradient, with velocity values varying from 3.72 to 4.4 kms-1 at about 32 km depth. This result is also in agreement with shear wave velocity cross-section of the area obtained from ITA-LSO data sets.