Preface to the 'Deep Seismix-2014' special issue

The earliest attempt of seismic characterization of the subsurface using controlled sources date from the mid 1800’s[Mallet, 1852]. This initial experiment, carried out in Ireland, was followed by increasing efforts in the development of the theory of seismic wave propagation through heterogeneous media. In the early 1900’s, the discovery by Andija Mohorovićić(1857-1936) of the seismic velocity discontinuity that bears his name ( Mohorovićic, 1910), interpreted to represent the Crust-Mantle boundary, and the success achieved by controlled-source seismic techniques in hydrocarbon exploration, together represented a turning point in the development of seismic imaging methods. In the ensuing decades, the methods began to be used by the academia to place constraints on the subsurface structure and properties of the Earth's crust, and to explore the inner architecture of geological structures such as orogens, continental margins, and ocean basins. The seismic techniques, in particular the common-mid-point (CMP) imaging, were applied to the characterization of the crystalline crust (Meissner,1967, and Clowes et al., 1968), triggering a rapid development of the normal-incidence deep seismic reflection method for the determination of crustal structure.The Deep Seismix symposium series started at Cornell University in 1984 (Barazangi and Brown, 1986a, 1986b). The aim of that first symposium was to foster discussion and collaboration between researchers working on seismic reflection imaging techniques and to demonstrate the potential of these techniques to produce high-resolution images of the Earth's interior. In particular, seismic reflection imaging has played a key role in providing the knowledge we currently have on the internal architecture and geodynamic evolution of the heterogeneous crust and uppermost mantle. To date, the series has kept the spirit and aims of its inaugural symposium of 1984, but it has progressively incorporated new techniques using both controlled