J Seismol DOI 10.1007/s10950-011-9264-5 ORIGINAL ARTICLE On the effect of topography on surface wave propagation in the ambient noise frequency range Andreas Köhler · Christian Weidle · Valérie Maupin Received: 8 March 2011 / Accepted: 1 December 2011 © Springer Science+Business Media B.V. 2011 Abstract Due to the increasing popularity of ana- lyzing empirical Green’s functions obtained from ambient seismic noise, more and more regional tomographical studies based on short-period sur- face waves are published. Results could poten- tially be biased in mountainous regions where topography is not small compared to the wave- length and penetration depth of the considered waves. We investigate the effect of topography on the propagation of short-period Rayleigh waves empirically by means of synthetic data using a spectral element code and a 3-D model with real topography. We show that topography along a profile through the studied area can result in an underestimation of phase velocities of up to about 0.7% at the shortest investigated period (3 s). Contrary to the expectation that this bias results from the increased surface distance along topog- raphy, we find that this error can be estimated by local topographic contrasts in the vicinity of the A. Köhler (B ) · C. Weidle · V. Maupin Department of Geosciences, University of Oslo, Post Box 1047, 0316 Oslo, Norway e-mail: andreas.kohler@geo.uio.no Present Address: C. Weidle Department of Geosciences, Christian-Albrechts-Universität zu Kiel, Otto-Hahn-Platz 1, 24118 Kiel, Germany receiver alone. We discuss and generalize our re- sults by considering topographic profiles through other mountain ranges and find that southern Norway is a good proxy to assess the topography effect. Nevertheless, topographic bias on phase velocity measurements is in general not large enough to significantly affect recovered velocity variations in the ambient noise frequency range. Keywords Surface waves · Topography · Wave propagation · Phase velocity 1 Introduction The motivation for this study are findings of a surface wave tomography of southern Norway based on ambient seismic noise analysis (Köhler et al. 2011). Low velocity anomalies of about 1– 3% have been found between 3- and 10-s period within the western part of southern Norway, a region characterized by large topographic con- trasts. In this region, elevation reaches 2,000 m a.s.l. and high mountains are cut by fjords with up to 1,000 water depth, summing to vertical con- trasts of up to 3 km on relatively short horizontal distances (Fig. 1). Due to the rather small pene- tration depths and short wavelengths of ambient seismic noise (about 9 km at 3 s), we have to take into consideration that topography may affect the