Dependence of the seismotectonic regime on the thermal state in the northern italian apennines

In order to study the relationships between recent seismotectonic processes and thermal conditions of the lithosphere, we analyzed the lateral variations both in surface heat-flow density and in seismic activity of the northern Italian Apennines. The focal depths have been related to the mechanical properties of the lithosphere. The hypocentre distribution indicates that the thickness of the seismogenic crustal layer increases towards the outer part of the range. Rheological models confirm this result, showing that in the western areas, marked by heat-flow density greater than 60 mW/m2 and by positive gravity anomalies, the depth of the crustal brittle-ductile transition is rather shallow, being about 10 km. In the cold external parts of the chain, this depth increases, ranging from 15 to 25 km; brittle seismogenic levels can be also found in the upper mantle, below an essentially aseismic, ductile crustal layer. The estimated limiting temperatures of the brittle strength zones are about 320°-380°C and 550°-600°C for crustal and upper mantle materials, respectively. © 1993.