“…Dynamic reduction of soil moduli and increases in damping with increasing shear strain can substantially modify ground motion amplitudes as a function of frequency (Ishihara, 1996). While there has been evidence of nonlinear soil response in surface strong motion recordings (Field et al, 1997;Cultera et al, 1999), interpretation of these surface records solely in terms of soil nonlinearity is intrinsically non-unique (O 'Connell, 1999a). In contrast, downhole strong motion arrays have provided definitive evidence of soil nonlinearity consistent with laboratory testing of soils (Chang et al, 1991;Wen et al, 1995, Ghayamghamain andKawakami, 1996;Satoh et al, 1995Satoh et al, , 1997Satoh et al, , 2001).…”