Strong ground motions have been observed at Tokyo University of Science, Noda campus, in Chiba Prefecture for more than 16 years. A velocity seismograph is installed and low trigger level enabled us to obtain a number of long period ground motions with long duration. This report describes outline of observation system and recorded motions, focusing on the recorded time. Site amplification characteristics of recorded motions are also discussed in terms of site amplification and group delay time. Long duration of the recorded motions is indispensable to evaluate long period characteristics of the ground motions more precisely.
