Topographic Amplification Effects – Ridges

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Susan E. Hough,
Localized damage caused by topographic amplification during the 2010 M7.0 Haiti Earthquake

Local geological conditions, including both near-surface sedimentary layers 1, 2, 3, 4 and topographic features 5, 6, 7, 8, 9, are known to significantly influence ground motions caused by earthquakes. Microzonation maps use local geological conditions to characterize seismic hazard, but commonly incorporate the effect of only sedimentary layers 10, 11, 12. Microzonation does not take into account local topography, because significant topographic amplification is assumed to be rare. Here we show that, although the extent of structural damage in the 2010 Haiti earthquake was primarily due to poor construction, topographic amplification contributed significantly to damage in the district of Petionville, south of central Port-au-Prince. A large number of substantial, relatively well-built structures situated along a foothill ridge in this district sustained serious damage or collapse. Using recordings of aftershocks, we calculate the ground motion response at two seismic stations along the topographic ridge and at two stations in the adjacent valley. Ground motions on the ridge are amplified relative to both sites in the valley and a hard-rock reference site, and thus cannot be explained by sediment-induced amplification. Instead, the amplitude and predominant frequencies of ground motion indicate the amplification of seismic waves by a narrow, steep ridge. We suggest that microzonation maps can potentially be significantly improved by incorporation of topographic effects.

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Author information Affiliations US Geological Survey, Pasadena1. US Geological Survey, 525 S. Wilson Avenue, Pasadena, California 91106, USA Susan E. Hough, Doug Given & Alan Yong Bureau des Mines et de l’Energie, Delmas 19, rue nina 14, Box 2174, Port au Prince, Haiti Jean Robert Altidor, Dieuseul Anglade, M. Guillard Janvier, Bernard Saint-Louis Mildor & Claude Prepetit US Geological Survey, Golden, Colorado 80401, USA J. Zebulon Maharrey & Mark

Meremonte Contributions S.E.H., J.R.A., D.A., D.G., M.G.J., J.Z.M., M.M., B.S-L.M. and C.P. contributed to the planning and execution of the field deployment; S.E.H., J.R.A., D.G. and A.Y. contributed to data processing and analysis. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: Susan E. Hough