Abstract
In Niigata-ken Chuetsu Area, the new seismic observation network consisting of 40 stations was established for the study of seismicity around the fault zone of western margin of the Nagaoka plain. The characteristics of the records observed in this network during the 2011 off the Pacific Coast of Tohoku Earthquake were studied. The several significant pulses were recognized in the acceleration records in Miyagi and Fukushima prefecture but there were no significant pulses in acceleration data of the network. The values of PGA were 10-20 cm/s2 in a hill side and 30-40 cm/s2 in the plain side. The acceleration Fourier spectra of the records were poor in higher frequency than 1 Hz. The spectrum amplitude in frequency of 0.1-2 Hz in plain side showed approximately five times larger than those in hill side. The spectrum amplitude in lower frequency than 0.1 Hz was almost the same in both sides. The common spectrum peaks were recognized at 0.04, 0.06 and 0.08 Hz in UD- and EW- component and 0.02 Hz in NS-component. Two clear pulses with period of about 20 seconds were recognized with the interval of about 50 s in the velocity waveforms of EW and UD. The values of PGA and PGV were large in plain side and small in hill side. Spatial distributions of PGA and PGV showed correlation to the topography and relative amplification factor to the reference station showed correlation to AVS30 those were calculated from PS-logging data. The relative amplification factor of the acceleration responses with 5 % damping at period of 5 and 10 seconds showed correlation to the depth of seismic bedrock not to topography. This also suggests that the effects of the thick sedimentary layers in this area on long-period ground motion amplification.
