Mustapha Hellel

Experimental Relationship Between Ambient Vibration H/V Peak Amplitude and Shear‐wave Velocity Contrast

Originally proposed by Nogoshi and Igarashi (1970, 1971), the ambient vibration H/V spectral ratio (HVSR) method consists of estimating the ratio between the Fourier amplitude spectra of the horizontal (H) to vertical (V) components of ambient noise vibrations recorded at a single station. This method, widespread by Nakamura (1989, 2000), is now widely used for evaluation of site effects and in seismic micro‐zoning studies (e.g., Gueguen et al. , 2000; Alfaro et al. , 2001; Duval et al. , 2001; Guillier et al. , 2004; Panou et al. , 2005; Chatelain et al. , 2008a; Bensalem et al. , 2010; Hellel et al. , 2010). These studies are based on the HVSR peak‐frequency value and distribution, which reflect both the value and spatial variation of the soft sediment topmost‐layer resonance frequency. The frequency of the HVSR peak is related to the topmost‐layer thickness, while its amplitude is proportional to the shear‐wave velocity contrast between the surficial layer and the underlying seismic bedrock. The shape of the HVSR curve is controlled by the S ‐wave transfer function between the underlying rock and the surface sediments. Theoretical investigations of 1D structure from synthetic noise have shown that the HVSR peak is pronounced around the S ‐wave fundamental frequency when the surficial layer has a sharp shear‐wave velocity contrast with the seismic bedrock (Field and Jacob, 1993; Lachet and Bard, 1994; Lermo and Chavez‐Garcia, 1994; Wakamatsu and Yasui, 1996; Tokeshi and Sugimura, 1998). To our knowledge, no experimental study has yet been completed on this subject. A second peak may appear on HVSR curves, indicating the …

Basement Mapping with Single‐Station and Array Ambient Vibration Data: Delineating Faults under Boumerdes City, Algeria

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., Fah et al. , 1997; Gueguen 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 V S, the fundamental …