Magnitude and Distance Scaling of Response Spectral Shapes for Rock Sites with Applications to North American Tectonic Environment

Response spectral shapes (Sa/a) computed from the BLWN (Band Limited White Noise) ground motion model combined with RVT (Random Vibration Theory) compare favorably with shapes computed from WNA (Western North American) earthquakes recorded at rock sites. The comparisons are made at close distances and for moment magnitudes 4 1/2, approximately 5, 6, and 6 1/2. Predicted spectral shapes for the ENA (Eastern North America) show reasonably good agreement with empirical results at frequencies of 1 and 10 Hz and with other random process models at frequencies of 0.5, 1, 2, 5, 10, and 20 Hz. Magnitude dependence of Sa/a is predicted to be significant for periods greater than 0.2 seconds in WNA and for periods greater than 0.1 seconds in ENA and increases with increasing period. Distance scaling appears to be significant only in WNA and at distances exceeding 50 km.