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Quarry blasts recorded along three lines on the central Iberian Meseta are used in an attempt to interpret the crustal structure. The results of the interpretation of the data, together with published surface wave and earthquake data, suggest a layered structure of the crust having the following features: the basement, in some areas covered by up to 4km of sediments, has a P-velocity of 6.1 kms-'; a low-velocity layer, between 7 and 11 km depth, seems to exist on the basis of both P and S interpretation of seismic data; a thick middle crust of 12 km has aP-velocity of 6.4 km s-' and overlies a lower crust with a mean P-velocity of 6.9kms-' and a possible slight negative gradient; the mean up/u, ratio for the crust is about 1.75; the Moho is reached at about 31km depth and consists of a transition zone at least 1.5 km thick. The P-velocity of the upper mantle is close to 8.1 kms-' and the S-velocity about 4.5 kms-', which gives a up/u, ratio of 1.8 for the uppermost mantle. A tentative petrological interpretation of the velocities and composition of the layers is given.

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