INTRODUCTION In the past, computerized seismological networks used dedicated telephone lines for continuous telemetering of relatively low-dynamic range, narrow bandwidth data to a central recording facility. These networks have served well the purpose of studying the spatial and temporal distribution of seismicity. However, the high data transmission costs, limitations in dynamic range and bandwidth, and the distortion problems associated with long-distance transfer of analog data have limited the possibility of retrieving the earthquake source information carried by the seismic waves. In the 1980s some networks were designed using microor mini-computers for digitization and data decimation at the observation sites. Event detection is performed in the computer at each site and only the detected events are transferred to the center. Partly due to the relatively high investment cost of these systems, the station spacing within the networks is rather large, limiting the routine analysis to origin time estimation, epicenter location, and...