The season that an earthquake occurs could affect the extent of ground failure and destruction that the event brings, according to a new look at two historical earthquakes that occurred about 100 years ago near Almaty, Kazakhstan.

In a paper published in Seismological Research Letters, researchers conclude that the June 1887 magnitude 7.3 Verny earthquake and the nearby January 1911 magnitude 7.8 Kemin earthquake likely produced similar shaking. However, the 1911 earthquake caused significantly more ground failure, probably due to a shallow frozen ground layer that was present during the winter months.

The frozen layer may have inhibited the drainage of pore-pressure excess through the surface during the earthquake, causing liquefaction at depth. In effect, the frozen layer extending about one meter below the surface «was a sealant layer that was not allowing the pore pressure to diffuse,» explained Stefano Parolai, a co-author of the paper at the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale in Italy.

The findings suggest seismologists should incorporate potential seasonal differences in soil characteristics «as they are making probabilistic liquefaction or ground failure assessments,» added co-author Denis Sandron, also at the Istituto Nazionale.

The effect of frozen ground on ground deformation is already calculated for some types of infrastructure such as oil pipelines in Alaska, but Parolai said the Kazakhstan study shows the importance of considering these effects in urban areas as well, especially when it can become a seasonal effect.

The Verny (Verny is the former name of Almaty) earthquake destroyed nearly all of the town’s adobe buildings and killed 300 people in 1887. The Kemin earthquake, which took place about 40 kilometers from Verny, caused a surprising amount of widespread ground failure and destruction and 390 deaths.

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