Soil degradation evolution in Concepción for the El Maule earthquake 2010

Abstract

Dynamic amplification takes decades of study. For example, as a result of the 1960 earthquake, the soil and drift displacement amplification were characterized for Concepción city (Poblete and Dobry, 1968). However, the 2010 El Maule earthquake surprisingly delivered a twopeak spectrum for the site. The peak of high periods is attributed to the site, while for low periods to the source. The study of the displacement records of the Concepción Centro and San Pedro de la Paz stations identifies two pulses for this event (Ruiz and Saragoni, 2012). The characteristics of these pulses and their frequencies are related mainly to Love-type surface waves. The foundation soils of the stations are made up of sands, whose cyclical horizontal deformations allow estimating their rigidity degradation; and theoretically an increase in their vibrating periods. This prediction is validated by examining the shift registers and acceleration spectrograms for the stations. The deformations and periods vary their magnitudes throughout the record. The period of the degraded soil in the strong phase of the earthquake can be related to the period measured by the H/V method. The estimated period with the “Autocorrelogram” technique (Sandoval and Saragoni, 2016) can also be understood as an average of the previous ones. This gives access to evaluation of the period of the soil in different phases or magnitudes of earthquakes, useful in seismic hazard studies.