Hibiki HIGUCHI

Analysis of Earthquake Motion Propagation Characteristics using Earthquake Observation Records

Takaaki IKEDA, Masataka SHIGA

Japan, a country with a high seismic activity, necessitates the implementation of reasonable input ground motions in the seismic design of structures. This is particularly crucial in the absence of seismometers in certain regions, where the estimation of damage mechanisms and the prediction of future damage are challenging.
This study focuses on the Joetsu and Chuetsu region of Niigata Prefecture and the Shinkawa region of Toyama Prefecture, with the aim of evaluating the influence of propagation path characteristics on observed surface ground motions in these areas.
The frequency characteristics of the observed records were analyzed using Fourier spectra. The Fourier spectra were calculated using seismic waveform data observed at 15 sites in the Jōetsu, Chuetsu, and Sado region of Niigata Prefecture, and the adjacent Shinkawa region of Toyama Prefecture from seven earthquakes that occurred around the Noto Peninsula. All 15 observation sites are part of the K-NET strong-motion observation network, operated by the National Research Institute for Earth Science and Disaster Resilience (NIED). The primary objective of this study was to examine the impact of the propagation path on surface ground motion in the frequency domain. To this end, a comparative analysis was conducted of source characteristics and site characteristics derived from subsurface ground properties.
The analysis results indicate that when the seismic bedrock depth offshore from Joetsu is deeper along the propagation path, the amplitude below 1 Hz increases. By comprehending the propagation path characteristics elucidated in this study, it becomes feasible to estimate reasonable ground motions in the target region.
The study's analysis encompassed seven recorded earthquakes at 15 observation sites across the Joetsu, Chuetsu region, and Sado region of Niigata Prefecture, as well as the adjacent Shinkawa region of Toyama Prefecture. To facilitate a more comprehensive analysis of frequency characteristics in future studies, it is imperative to augment the number of earthquakes analyzed, incorporating a range of arrival directions and magnitudes.