Non-linear site response: a focus of thick sedimentary deposits. Learnings from Japanese strong motion recordings

This contribution presents a statistical analysis of the non-linear behavior that can be detected on strong motionrecordings obtained on thick Japanese sedimentary sites from the KiK-net and K-NET networks, and presents acomparison with other site types, with thinner deposits and/or higher fundamental frequencies. The non-linear effects are quantified by comparing various kinds of site-response characteristics (surface-to-borehole spectral ratios, H/V spectral ratios) for moderate to large motion to their weak motion counterparts. While a non-linear behavior can be detected on thick and thin sites as well, thick sites do not exhibit any peculiar high-frequency reduction. Moreover, from a qualitative viewpoint, the distribution of velocity profiles for sites with very large PGA (above 0.4 g) is similar to the distribution for all strong motion sites in Japan, without any bias towards stiff or shallow sites. The inconsistency of such results with the high frequency decrease predicted by most non-linear simulations warns on the caution to use non-linear degradation curves at large depths, or frequency independent damping.