SOME ATTRIBUTES OF WAVE-FIELDS SCATTERED FROM IVREA-TYPE LOWER CRUST

The Ivrea Zone in northern Italy is a well studied sliver of extended lower continental crust which was brought to the surface in the course of Alpine lithospheric shortening. Based on two 1:25,000 geological m aps from the central Ivrea Zone and petrophysical parameters of the co rresponding lithologies we have constructed geologically constrained, stochastic seismic models of Ivrea-type lower crust. A stochastic rath er than a deterministic approach is applied due to the limited availab ility of detailed geological maps and the high degree of small-scale s tructural and petrophysical complexity of the Ivrea Zone. The primary characteristic of the resulting model is its ''layered'' self-affine o r fractal structure and its bimodal velocity distribution. While we ar e not suggesting that Ivrea-type structure is universal for extended l ower continental crust, synthetic seismograms may help to constrain so me pertinent quantitative aspects observed in deep seismic reflection data: (1) Ivrea-type lower crust can explain the high observed reflect ion coefficients and bright reflectivity in the lower crust; (2) obser ved lower-crustal Q-factors can be largely explained by scattering los ses and intrinsic Q-factors of reflective lower crust are likely to be larger than 1000, which is incompatible with the presence of free vol atiles; (3) in agreement with recent broad band studies of the lower c rust, Ivrea-type lower crust does not create any tuning effects; and ( 4) for Ivrea-type heterogeneity the lateral correlation of the reflect ed signal is largely independent of the lateral characteristic scale o f the scattering structures, which suggests that multiple scattering m ay be important in the reflective lower crust.