Deep structure of the Colli Albani volcanic district (central Italy) from receiver functions analysis

Abstract

The Colli Albani is a Quaternary quiescent volcano, located a few kilometers southeast of Rome (Italy). During the past decade, seismic swarms, ground deformation, and gas emissions occurred in the southwestern part of the volcano, where the last phreatomagmatic eruptions (27 ka) developed, building up several coalescent craters. In the frame of a Dipartimento Protezione Civile – Istituto Nazionale di Geofisica e Vulcanologica project aimed at the definition and mitigation of volcanic hazard, a temporary array of seismic stations has been deployed on the volcano and surrounding areas. We present results obtained using receiver functions analysis for eight stations, located upon and around the volcanic edifice, and revealing how the built of the volcanic edifice influenced the prevolcanic structures. The stations show some common features: the Moho is almost flat and located at 23 km, in agreement with the thinning of the Thyrrenian crust. Also the presence of a shallow limestone layer is a stable feature under every station, with a variable thickness between 4 and 5 km. However, some features change from station to station, indicating a local complexity of the crustal structure: a shallow discontinuity dividing the Plio-Pleistocene sediments by the Meso-Cenozoic limestones, and a localized anisotropic layer, in the central part of the old structure, which points of the deformation of the limestones. Other two strongly anisotropic layers are detected under the stations in lower crust and upper mantle, with symmetry axis directions related to the evolution of the volcano complex.