- © 2012 by the Seismological Society of America
Investigations of geological structures, such as layer thickness, depth to bedrock, and tectonic features, are important tasks for geologists and engineers. Direct investigational methods, such as boreholes and trenches, can provide accurate data. However, these direct methods are usually expensive and time consuming. More often, geophysical methods that are less expensive and faster to implement (e.g., seismic and electric surveys and ground penetrating radar) are used. However, these geophysical methods may be difficult, or even impossible, to implement in some cases, such as regions with steep slopes or those highly urbanized. In contrast, the single‐station horizontal‐to‐vertical spectral‐ratio (HVSR) method (Nogoshi and Igarashi, 1970, 1971; Nakamura, 1989) and/or dense‐array techniques (Aki, 1957; Lacoss et al., 1969) based on ambient vibration recordings have fewer constraints.
The HVSR method has been used extensively to evaluate site effects, seismic microzonation, and basin structure (e.g., Fäh et al., 1997; Guéguen et al., 2000; Alfaro et al., 2001; Duval et al., 2001; Navarro et al., 2001; Panou et al., 2005; Chatelain, Guillier, Parvez, 2008; Bensalem et al., 2010). In such studies, one assumes a 1D soil column. Variations in the fundamental frequency are used to estimate the first‐order geometry of the interface between a sediment layer and the underlying bedrock (e.g., Yamanaka et al., 1994; Ibs‐von Seth and Wohlenberg, 1999; Delgado et al., 2000; Parolai et al., 2002; Oliveto et al., 2004). By imaging the soil–bedrock interface, the HVSR method has the ability to highlight blind faults. For a simple 1D soil column, the shear‐wave velocity VS, the fundamental …