Seismic Evaluation of a Profile of Volcanic Ash From the South American Andes

Abstract

Although soils derived from volcanic ash are only a small portion of the soils that cover the world's surface, cities have developed on some of these soils. This makes their study interesting, especially since soils derived from volcanic ash have special characteristics including a high void ratio, liquid limits that can be greater than 100%, and shear wave velocities close to 150 m/s. Cities on these soils in the South American Andes are in areas with frequent and intense seismic activity making an understanding of how earthquakes affect these soils a matter of importance. This paper analyzes site response by the equivalent linear method, taking into account the variability of these soils. The Monte Carlo method was used for degradation of the shear modulus and damping curves. The results of this study show factors that amplify spectral acceleration can cause this measurement to become greater than four. In addition, the authors found that maximum spectral accelerations are functions of high plasticity indexes whose influence increases when shear wave velocities are between 175 and 225m/s.