Geophysical study and 3D modeling of site effects in Viña del Mar city, Chile

Abstract

The Maule 2010 earthquake (Mw 8.8) produced damage to several buildings throughout the Central Chile. This was particularly the case in the downtown of Viña del Mar city, where an anomalous concentration of structural damage was found in several medium-rise buildings distributed along a narrow area of approximately 1 km of length. These observations suggest the possibility of a localized area of seismic amplification effects. We conducted a geophysical characterization using Surface-Wave based techniques and gravimetry to characterize the main dynamic properties of the soil and the depth of the basin. This data, complemented with several Standard Penetration Test (SPT) measurements, was used to develop a 3D geotechnical characterization of the area. Additionally, the cyclic behavior of predominant materials was characterized experimentally based on remolded samples. To assess complex site amplification effects, we developed a computational 3D model constrained by Surface-Wave geophysics and laboratory results, assuming a homogenous basin infill with increasing stiffness with depth. Results partially agree with damage observations and suggest an explanation related to basement shape in some areas of the modeled region.