大阪平野及びその周辺地域における広周波数帯域・広動帯域地震波観測

Abstract

We started to observe seismic waves from small to large earthquakes at two ground sitesin the plain of Osaka and a rock site around the northern edge of the plain to elucidate andpredict vibrational characteristics for strong ground motion. From comparisons between theseismograms from earthquakes occurring in different source regions, we found that theseismic motions at the ground sites are characterized by strong excitation in the coda partsof S waves. This S-coda excitation shows the following characteristics: it is composed ofdispersive long-period (1 to 4 sec) wave motions; it becomes conspicuous about 10 to 20 seclate for the arrivals of the principal S-parts and is of long duration (for several tens ofseconds); it does not depend on directions of the wave arrivals; it is remarkable even at aepicentral distance where Rayleigh waves generating in the source region do not yet fullygrow.