Seasonality in Site Response: An Example From Two Historical Earthquake in Kazakhstan

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

During the past 150 years, the city of Almaty (formerly Verny) in Kazakhstan has suffered significant damage due to several large earthquakes. The Mw 7.3, 9 June 1887 Verny earthquake, a time when the city mainly consisted of adobe buildings with a population of 30,000, was nearly totally destroyed with 300 deaths. The Mw 7.8-8, 4 January 1911 Kemin earthquake saw 390 deaths, 44 in Verny itself. Remarkably, the earthquake generated in Verny (ca. 50 km from the epicenter) significant soil deformation and ground failure, in particular in the loam sandy soils, with cracks in the ground sometimes reaching 1 m in width and 5 meters in depth.

A crucial step towards preparing for future events, mitigating against earthquake risk and defining optimal engineering designs involves undertaking site response studies. With regard to this, in this study we investigate the possibility that the extreme ground failure observed after the 1911 Kemin earthquake could have been due to the presence of a shallow frozen ground layer that may have inhibited the drainage of pore-pressure excess through the surface, therefore inducing liquefaction at depth. We make use of information collected by two arrays established to measure ambient seismic noise, borehole data, and surface temperature data. From these datasets, we estimated parameters for evaluating the dynamic properties of soil, and characterized the corresponding sediment layers at the site of the observed liquefaction.

Although the estimated soil parameters are not optimally constrained, the dynamic analysis, carried out using selected strong motion recordings expected to be compatible with the 1911 Kemin earthquake, indicated that the extensive ground failure that occurred during the Kemin event (which occurred in winter), was different to that observed during the 1887 event (which occurred at the end of spring), which could be due to the presence of a superficial frozen soil layer. Our results indicate that for this region, possible “seasonal” effects should therefore be considered when undertaking site effect studies.

Presenting Author: Stefano Parolai

Authors