Abstract
This study tries to clarify the factors and mechanisms affecting the embankment dams that were either damaged (d) or undamaged (u) due to the earthquake on northern Awaji Island.
Multivariate statistical analyses (including 10 or 11 items) were performed on 395 dams (d:112, u: 283) in the Nojima fault area (Nj) and on 1562 dams (d: 348, u: 1214) in the 5 Town area (5T). On the peaks of category score (CS) for main items, there are six angles to the epicenter (Nj: 10, 150, 30, 70, 100 and 130 deg. in the order of CS peak values, 5T: 100, 160, 140, 70, 40 and 10 deg.id.), seven angles to the fault (Nj: 100, 80, 20, 160, 40, 140 and 120deg..id.), one for the distance to epicenter (Nj・5T: 10 km), and two for the distance to the fault (Nj: －150 and 600 m). These results can be explained by the radiation patterns. When they are combined with the relation between the emphasized seismic waves ( P or SV: 45 and 135 deg, and SH: 0 and 90 deg., theoretical emergent angles to fault) and CS peak angles, they support secondary strong motion source As’ as well as the primary As near the epicenter.
