BLIND PREDICTION OF THE SITE EFFECTS AT ASHIGARA VALLEY, JAPAN, AND ITS COMPARISON WITH REALITY

Weak and strong ground motions were numerically predicted for three st ations of the Ashigara Valley test site. The prediction was based on t he records from a rock-outcrop station, one weak-motion record from a surface-sediments station, and the standard geotechnical model. The da ta were provided by the Japanese Working Group on the Effects of Surfa ce Geology as a part of an international experiment. The finite-differ ence method for SH waves in a 2-D linear viscoelastic medium (a causal and model) was employed. Comparison with the real records shows that at two stations the predictions fit better than at the third one. Stra ngely, the two better predictions were for stations situated at larger distances from the reference rock station (one station was on the sur face, the other in a borehole). The strong ground motion (the peak acc eleration of about 200 cm s(-2)) was not predicted qualitatively worse than the weak motion (8 cm s(-2)). A less sophisticated second predic tion (not submitted during the experiment), in which we did not attemp t to fit the available weak-motion record at the sedimentary station, agrees with the reality significantly better.