Deep crustal roots beneath the northern Apennines inferred from teleseismic receiver functions

Abstract

Teleseismic waveforms recorded by a regional array crossing the northern Italian peninsula and northern Corsica are analyzed using the receiver function technique, to determine the first order crustal structure. The receiver function approach is used to isolate receiver-side PS conversions generated at the crust-mantle boundary and any major velocity discontinuity beneath the stations. We used the time delay between the direct P wave and the PS wave converted at the Moho discontinuity to infer crustal thickness beneath the stations. The crust-mantle boundary is estimated at 25 ± 1 km of depth in northern Corsica, 20 ± 2 km beneath the Elba island and 20 to 24 ± 2 km beneath Tuscany. In the eastern portion of the array, Moho depth increases from 28 ± 2 km beneath the Adriatic coast to 49 ± 3 km beneath the Apennine chain, in a distance of about 100 km. A double PS conversion produced beneath the Val Tiberina graben, to the west of the Apennines, corresponds to interfaces as deep as 20 ± 2 and 52 ± 2 km. This observation supports the hypothesis of partial overlapping between the shallow Tuscan Moho and the deeper Adriatic Moho. The westward deepening of the Adriatic Moho beneath the northern Apennines can be explained by lithosphere delamination that has dragged downward the Adriatic lower crust. The deep crustal root estimated beneath the northern Apennines indicates that this portion of the chain is isostatically overcompensated.