Ambient Vibration Techniques Applied to Explain Heavy Damages Caused in Corso (Algeria) by the 2003 Boumerdes Earthquake: Understanding Seismic Amplification Due to Gentle Slopes

Abstract

Damages from earthquakes may be locally increased by spotty seismic wave amplification, generally known as site effects. There are numerous reports of observed localized higher damages from earthquakes related either to seismic wave velocity contrasts at depth, often evidenced by ambient vibration H/V peaks ( e.g. Gueguen et al. 1998, 2000; Panou et al. 2005; Teves-Costa et al. 2007; Theodulidis et al. 2008; Cara et al. 2008; Hellel et al. 2010) or to topographic amplification ( e.g. , Boore 1972; Celebi 1987, 1991; Ashford and Sitar 1994; Athanasopoulos et al. 1999). Numerical studies have been performed, using various methods, to model and quantify topographic amplification effects ( e.g. , Boore 1972; Smith 1975; Sanchez-Sesma et al. 1982; Bard 1982; Chavez-Garcia et al. 1996; Geli et al. 1988; Athanasopoulos et al. 1999; Nguyen and Gatmiri 2007). As pointed out by Geli et al. (1988) and Ashford et al. (1997), most numerical methods consider an isolated two-dimensional ridge on the surface of a homogeneous half-space. Some involve a three-dimensional ridge ( e.g. , Bouchon and Barker 1996; Spudich et al. 1996; LeBrun et al. 1999). Results have consistently shown amplification at the top of the ridge, but these results usually considerably underestimate amplifications observed in the field. Topographic effects, including from small-scale ridges in the 10–25-m range, have also been studied using field observations from earthquakes in various places around the world ( e.g. , Davis and West 1973; Bouchon and Barker 1996; Spudich et al. 1996; Chavez-Garcia et al. 1996; 1997; Zaslavsky and Shapira 2000; Zaslavsky et al. 2000; Toshinawa et al. 2004). The H/V spectral ratio from ambient vibrations (Nakamura 1989) has also been used to quantify …