A comparison of site response techniques using earthquake data and ambient seismic noise analysis in the large urban areas of Santiago de Chile

Abstract

S U M M A R YSituated in an active tectonic region, Santiago de Chile, the country's capital with more than six million inhabitants, faces tremendous earthquake risk. Macroseismic data for the 1985 Valparaiso event show large variations in the distribution of damage to buildings within short distances, indicating strong effects of local sediments on ground motion. Therefore, a temporary seismic network was installed in the urban area for recording earthquake activity and a study was carried out aiming to estimate site amplification derived from horizontal-tovertical (H/V ) spectral ratios from earthquake data (EHV) and ambient noise (NHV), as well as using the standard spectral ratio (SSR) technique with a nearby reference station located on igneous rock. The results lead to the following conclusions:(1) The analysis of earthquake data shows significant dependence on the local geological structure with respect to amplitude and duration.(2) An amplification of ground motion at frequencies higher than the fundamental one can be found. This amplification would not be found when looking at NHV ratios alone.(3) The analysis of NHV spectral ratios shows that they can only provide a lower bound in amplitude for site amplification.(4) P-wave site responses always show lower amplitudes than those derived by S waves, and sometimes even fail to provide some frequencies of amplification.(5) No variability in terms of time and amplitude is observed in the analysis of the H/V ratio of noise.(6) Due to the geological conditions in some parts of the investigated area, the fundamental resonance frequency of a site is difficult to estimate following standard criteria proposed by the SESAME consortium, suggesting that these are too restrictive under certain circumstances.

Seismic site characterization of the Kastelli (Kissamos) Basin in northwest Crete (Greece): assessments using ambient noise recordings

“…Comparisons between HVSR applied to earthquake and ambient noise and other site effect techniques (e.g SSR, 1D TF and GIT) have shown agreement in the fundamental frequency while fluctuations in the amplification is evident suggesting a lower amplitude of HVSR (e.g Pilz et al 2009;Ameri et al 2011), compatible (e.g Horike et al 2001Rodriguez and Midorikawa 2002;Mucciarelli et al 2003b;Di Giacomo et al 2005) and at few cases higher (Nguyen et al 2004;Teves-Costa et at.1996). A generalized outcome in terms of ground amplitude is that HVSR technique can be considered as a lower bound estimator of the amplification .…”

“…The results allow us to infer that the amplitude quality criteria of A>2 proposed by Sesame might be too restricted since neighboring sites presenting stability in the HVSR shape and frequencies show HVSR peak slightly below and beyond 2.0. Suggestions that the amplitude clarity criteria of A >2 might be too restricted have been also mentioned by Bonnefoy-Claudet et al (2008) and Pilz et al (2009).…”

Efectos de sitio para Ingenieros Geotécnicos, estudio del valle Parkway

“…Chile no está exento de ello por supuesto, y muchos estudios de efectos de sitio han sido publicados, especialmente para Santiago (e.g., Astroza y Monge, 1991; Leyton y Ruiz, 2011;Assimaki et al, 2012). Para este último caso, Pilz et al (2009Pilz et al ( , 2010Pilz et al ( , 2011 presentan tres estudios que siguen la línea mostrada en este trabajo: determinación experimental de efectos de sitio, construcción de un modelo del subsuelo y comparación de simulaciones numéricas del movimiento sísmico con registros para sismos pasados. Sin embargo, esos trabajos están dirigidos a especialistas en el tema, por lo que no se aborda de forma global la estrategia seguida para abordar efectos de sitio, y el énfasis está en los resultados y no en los métodos de análisis, las hipótesis en las que están basados y las incertidumbres asociadas a su aplicación.…”

Effects of Surface Geology on Seismic Ground Motion Deduced from Ambient-Noise Measurements in the Town of Avellino, Irpinia Region (Italy)

“…The HVSR method also appears not able to evaluate the absolute amplification of the seismic motion, as it gives results that generally do not agree with those coming from methods based on earthquake recordings (LACHET et al, 1996;BARD, 1999;HORIKE et al, 2001;SOURIAU et al, 2007;D23.12, SESAME, 2004;PILZ et al, 2009). The main question regarding the HVSR method concerns the theoretical aspects: whether the HVSR can be affected by source effects as well as by site effects, and whether body waves or surface waves constitute most of the ambient noise (FÄ H et al, 2001;HERAK, 2008).…”