2016 Volume 16 Issue 9 Pages 9_46-9_66
In this paper, we show the possibility that can be interpreted through the surface layer model for the cause of the earthquake damage at the 1944 Tonankai earthquake.
As modeling the three-dimensional surface layer, we used the 34,600 points of borehole logs, the 499 points of PS logging and the 25,287 grain size analysis database. we classified lithofacies of borehole logs into nine strata. And we interpolated elevation values of stratum boundary.
The lithofacies and N-values of borehole logs were interpolated for each stratum. The modeling procedure is as follows : 1) Depth of the descriptions of lithofacies and N-values in the borehole logs were standardized to obtain regularly aligned datasets for vertical intervals of 1m in the altitudes, 2) The values of lithofacies indexes were converted to grain size distribution (the composition ratio of gravel fraction, sand fraction and fine fraction) based on the grain size analysis database. 3) The irregularly scattered values of grain size distribution and N-values were horizontally interpolated to obtain regularly gridded datasets in each altitude, 4) The datasets were stacked vertically. 5) The values of grain size distribution at every grid were converted to the values of lithofacies indexes. The three-dimensional lithofacies and N-value model was converted to three-dimensional S-wave velocity structure model using empirical conversion formula of S-wave velocity.
Using the three-dimensional surface layer model, strong ground motions and liquefaction were simulated for the hypothetical Tonankai earthquake. The distribution of the simulated seismic intensity in the Nagoya City area shows good agreement with that of observed building damage at the 1944 Tonankai earthquake. Similarly, simulated distribution at "high" liquefaction potential shows good agreement with the liquefaction confirmed area at the 1944 Tonankai earthquake.
