This report describes the seismic activity in and around the Hanford Site during Fiscal year 2003. Hanford Seismic Monitoring provides an uninterrupted collection of high-quality raw and processed seismic data from the Hanford Seismic Network for the U.S. Department of Energy and its contractors. Hanford Seismic Monitoring also locates and identifies sources of seismic activity and monitors changes in the historical pattern of seismic activity at the Hanford Site. The data are compiled, archived, and published for use by the Hanford Site for waste management, Natural Phenomena Hazards assessments, and engineering design and construction. In addition, the seismic monitoring organization works with the Hanford Site Emergency Services Organization to provide assistance in the event of a significant earthquake on the Hanford Site. The Hanford Seismic Network and the Eastern Washington Regional Network consist of 41 individual sensor sites and 15 radio relay sites maintained by the Hanford Seismic Monitoring staff. For the Hanford Seismic Network, there were 1,336 triggers during fiscal year 2003. Of these triggers, 590 were earthquakes. One hundred and one earthquakes of the 590 earthquakes were located in the Hanford Seismic Network area. Stratigraphically 35 (34.6%) occurred in the Columbia River basalt, 29 (28.7%) were earthquakes in …