During the past thirty years various accelerogram data sets recorded by" flee field" strong-motion stations in Greece have been compiled by two institutes that are in charge of running national strong-motion networks. These data sets have been of limited potential use for research because of nonstandard processing, nonhomogeneous earthquake parameters adopted, and a minimum standard of site characterization based only on surface geology. In addition, given an everincreasing cumulative number of accelerograms, a database was required to facilitate data selection by users. To satisfy all these issues we have developed HEAD version 1.0--a unified HEllenic Accelerogram Database--which is briefly presented in the present paper. Homogeneous strong-motion data processing and site characterization based on detailed borehole data or/and Vs profiles allow the data to be used to their full potential. Instrument and housing characteristics are provided for each station, and relocated earthquake hypocenter parameters and moment-magnitude are given for each earthquake.

Understanding the nature of strong ground motion is of crucial importance in reducing seismic risk worldwide. Publication of strong-motion data is essential for development of building codes and design methods for large engineering structures as well as for development of near-field seismology. After realizing the need for organized strong-motion data sets, the scientific community has developed user-friendly databases (among others, Kinoshita, 1998; Steidl and Lee, 2000; Ambraseys et al., 2002; LDEO/NCEER, 2003). In Greece, deployment of a strong-motion network began in the early 1970's under the auspices of the Geodynamic Institute (GEIN) of the National Observatory of Athens; ten years later the Institute of Engineering Seismology and Earthquake Engineering (ITSAK) began an effort to install a new strongmotion network throughout Greece. Prior to 2000 the vast majority of strong-motion instruments of the national network were analog (SMA-1 Kinemetrics). In recent years, ana-