Nonlinear site response evidence of K-NET and KiK-net records from the 2011 off the Pacific coast of Tohoku Earthquake

Luis Fabian Bonilla (1) , Kenichi Tsuda (2) , Nelson Pulido (3) , Julie Regnier (4) , Aurore Laurendeau (5)

1 IFSTTAR/GERS/SV - Séismes et Vibrations
2 Shimizu Corporation
3 NIED - National Research Institute for Earth Science and Disaster Prevention
4 ERA 6 Risque sismique - Equipe recherche associée au LCPC - ERA 6 Risque sismique
5 ISTerre - Institut des Sciences de la Terre

We analyzed the acceleration time histories recorded by the K-NET and KiK-net stations of the Mw 9 Tohoku Earthquake in order to investigate site response issues related to near-source effects. Time-frequency analysis of K-NET stations in the Miyagi prefecture, closest to the rupture area, show that sites having a Vs30 < 400 m/s present a combination of deamplification at frequencies higher than 5 to 10 Hz and cyclic mobility (high acceleration peaks riding over a low frequency carrier). This suggests strong nonlinear site response at these stations. Furthermore, using KiK-net data we are able to compute borehole transfer functions from the mainshock and events having small PGA values from the local dataset. The ratio between weak-motion and strong-motion borehole transfer functions constitutes an indicator of nonlinear site response. This ratio reveals strong dependence on Vs30 and shows that widespread nonlinear behavior took place during this large earthquake.

Keywords: KiK-net; K-NET; Tohoku Earthquake; Site response; cyclic mobility

Domains: Geomorphology

Luis Fabian Bonilla, Kenichi Tsuda, Nelson Pulido, Julie Regnier, Aurore Laurendeau. Nonlinear site response evidence of K-NET and KiK-net records from the 2011 off the Pacific coast of Tohoku Earthquake. Earth Planets and Space, 2011, 63 (7), pp.785-789. ⟨10.5047/eps.2011.06.012⟩. ⟨insu-00679354⟩