Statistical Research on S-Wave Incident Angle

Abstract

均質な弾性半空間媒質内で点震源を仮定しさらに実体波のみを考慮することにより, 強震動記録からS波入射角を評価する理論式を求めた。アメリカ西部で観測された214個の強震動記録を用いて, S波入射角, 震央距離及び周波数間の統計的関係を求め, S波の平均入射角は震央距離に関係なく約57°となる結果を得た。

In this paper, the following assumptions are made: 1. Seismic source is a point one; 2. The near-field seismic waves are body ones; and 3. The medium of the earth is a half-space which is homogeneous and elastic. According to the above-mentioned assumptions, this paper obtain a theoretical formula to estimate S-wave incident angle by using the record of strong ground motion. During the process of calculations, the paper also presents a method of getting in-plane and anti-plane from the record of strong ground motion. By making use of 214 records of strong ground motion in the western American, this paper gives a statistical relation among S-wave incident angle, epicentral distance and frequency. The results show that the average value of S-wave incident angle is about 570, and has little to do with the epicentral distance.