TY - JOUR
T1 - Geometrical focusing as a mechanism for significant amplification of ground motion in sedimentary basins
T2 - Analytical and numerical study
AU - Shani-Kadmiel, Shahar
AU - Tsesarsky, Michael
AU - Louie, John N.
AU - Gvirtzman, Zohar
PY - 2014/1/1
Y1 - 2014/1/1
N2 - We study the geometrical and material conditions which lead to focusing of seismic waves traveling across a concave velocity interface representing the boundary of a sedimentary basin within a denser rock. We approximate, using geometrical analysis for plane-waves, the combination of interface eccentricities and velocity ratios for which the seismic rays converge to a near surface region of the basin. 2-D finite difference modeling is used to compute Peak Ground Velocity (PGV) and spectral amplification across the basin. We show that effective geometrical focusing occurs for a narrow set of eccentricities and velocity ratios, where seismic energy is converged to a region of ± 0.5 km from surface. This mechanism leads to significant amplification of PGV at the center of the basin, up to a factor of 3; frequencies of the modeled spectrum are amplified up to the corner frequency of the source. Finally, we suggest a practical method for evaluating the potential for effective geometrical focusing in sedimentary basins.
AB - We study the geometrical and material conditions which lead to focusing of seismic waves traveling across a concave velocity interface representing the boundary of a sedimentary basin within a denser rock. We approximate, using geometrical analysis for plane-waves, the combination of interface eccentricities and velocity ratios for which the seismic rays converge to a near surface region of the basin. 2-D finite difference modeling is used to compute Peak Ground Velocity (PGV) and spectral amplification across the basin. We show that effective geometrical focusing occurs for a narrow set of eccentricities and velocity ratios, where seismic energy is converged to a region of ± 0.5 km from surface. This mechanism leads to significant amplification of PGV at the center of the basin, up to a factor of 3; frequencies of the modeled spectrum are amplified up to the corner frequency of the source. Finally, we suggest a practical method for evaluating the potential for effective geometrical focusing in sedimentary basins.
KW - Alluvial valley response
KW - Geometrical focusing
KW - Ground motion amplification
KW - Sedimentary basin response
KW - Seismic wave propagation
KW - Site response
UR - http://www.scopus.com/inward/record.url?scp=84896045665&partnerID=8YFLogxK
U2 - 10.1007/s10518-013-9526-4
DO - 10.1007/s10518-013-9526-4
M3 - Article
AN - SCOPUS:84896045665
SN - 1570-761X
VL - 12
SP - 607
EP - 625
JO - Bulletin of Earthquake Engineering
JF - Bulletin of Earthquake Engineering
IS - 2
ER -