Integrating controlled-source and ambient noise seismic measures for archaeological prospection: the Scrovegni Chapel case

Abstract

SUMMARY In this paper, we present the results of an analysis of passive seismic noise recorded around the Scrovegni Chapel in Padua (Italy), using a dense 2-D network with nearly 1500 autonomous seismic nodes. Surface wave tomography using the active records allowed the imaging of several structures located at a depth of few metres, while this study focuses on the processing of about 22 hr of continuous passive records. First, the ambient noise is characterized in terms of amplitude, frequency content and azimuthal distribution, in order to ensure the applicability of the interferometric method. Second, a cross-correlation analysis is performed to retrieve virtual source gathers. Third, traveltimes are extracted from virtual source gathers using the same processing sequence applied to active gathers. Fourth, Eikonal tomography is run to retrieve isotropic phase velocity maps and azimuthal anisotropy. We compare and discuss the results obtained from the active and the passive methods, and finally propose a strategy for the integration of passive and active information. The new quasi-3-D shear wave velocity model obtained from the joint active and passive analysis is more accurate at depth, due to the addition of the passive low-frequency information.