Field evidence and numerical investigation of the Mw = 7.1 October 23 Van, Tabanli and the Mw>5.7 November Earthquakes of 2011

On Sunday, October 23rd, 2011, the Van province, in the Eastern Turkey, was stricken by a magnitude Mw = 7.2 earthquake. The maximum horizontal peak ground acceleration, i.e. 0.182g, was measured from the seismic station in Muradiye, at about 40km from the epicenter. Several MW > 5.7 strong motion aftershocks were recorded in November 2011. The exceptionally rich sequence of ground motions was due to the dense seismo-tectonic activity of the Eastern Turkey, where many active historical faults exist and newly generated can also be found because of the ongoing continental collision between the Arabian and the Eurasian Plates. The 2011 Van earthquake sequence caused around 700 casualties; the total economic losses are estimated at around 1 billion US dollars. The present paper deals with the seismological and structural damage assessment of two major seismic events and aftershock sequences in Van region; special emphasis is on the findings of the site investigations performed in the aftermath of the major seismic event. The performed investigation has shown that there is substantial field evidence demonstrating that the losses generated to the local social communities were caused by typical structural and non-structural deficiencies that have been surveyed in the past in several moderate-to-major earthquakes worldwide, especially in poor countries. Comprehensive numerical simulations were also carried out to assess the characteristics of the strong motion records and their effects on existing representative building type of structures in the earthquake-affected region. It was found that the local building stock is highly vulnerable and requires urgent major structural interventions for seismic strengthening. A cost-efficient retrofitting scheme is however not straightforward. It should be a trade-off between two competing aspects: the use of innovative materials and technologies on one hand, and the low-quality of the workmanships and lack of adequate quality control during construction phase, which are available in the Van province, on the other hand