Site characterization at Chilean strong-motion stations: Comparison of downhole and microtremor shear-wave velocity methods

Abstract

A blind comparison of independent invasive (downhole, standard penetration, bender element) and noninvasive microtremor shear-wave velocity (Vs) profiling is presented for 11 strong-motion stations in central and southern Chile that recorded the 2010 M-W 8.8 Maule earthquake. For the majority of stations, site classification based on average V-s in the upper 30 m (V-s30) is consistent irrespective of methodology. For a variety of geological conditions, excellent to good agreement is obtained between invasive and noninvasive V-s structure at five stations over the entire borehole length and in the uppermost layer at three stations. Site classification based on site period is evaluated using earthquake and microtremor recordings. Short site periods are observed at stiff coarse-grained stations whereas longer site periods are observed at soft fine-grained stations. The use of both V-s30 and site period criteria are recommended in future revisions of the Chilean building code for robust earthquake site response characterization.