Analysis of strong ground motion data from the Van earthquake (Turkey), 2011

Abstract

An earthquake of magnitude 6.6 (ML) and 7.2 (Mw) occurred at 13: 41 p.m. local time on October 23, 2011 in the western of the Erçek Lake and about 20 km away from the city center of Van, Turkey (EQE-KOERI in The October 23, 2011 Van, Turkey earthquake (Mw = 7.2). Technical report. İstanbul, 2011). The earthquake was recorded using by the 22 accelerometers in the stations belong to National Strong Motion Observation Network (DEMP 2011. Republic of Turkey prime ministry disaster and emergency management presidency, Earthquake Department, 23-Oct-2011 Van Earthquake Report). The distance of these stations from the earthquake epicenter varies between 42 and 590 km. The closest station to the earthquake is Van–Muradiye acceleration-meter station and measured higher values of acceleration in N–S component, E–W direction and vertical direction are 178 cm/s², 168.5 cm/s² and 78.5 cm/s², respectively. The highest acceleration value was recorded at the N–S component in Van–Muradiye acceleration-meter station. Seismic intensity values calculated by using these acceleration values and for Van-Merkez earthquake, maximum intensity is predicted as IX whereas the maximum intensity value is predicted as VI for Van-Edremit earthquake. It is understood that the Everek Fault with approximately E–W direction has caused the earthquake. Focal mechanism solutions of Mw: 7.2 earthquakes reveal E–W oriented thrust fault mechanism. Since there were no marker to thrust faulting in the field as fault rupture, morphological indicators, other effects of earthquake like mass movements show that E–W oriented thrust fault named as “Everek Fault” is the primary source of this event. The most important proof of this idea was the aftershocks. Due to the Bitlis station is located the Southwestern edge of the fault and the high accelerations in the E–W component, it is seen that the forward directivity effect in the station records. The time of the earthquake is one of the important parameters determining the structural damage. It is also one of the important parameters of the strong motion earthquakes. The acceleration values greater than 50 gal (cm/s²) in the Van–Muradiye station has continued approximately 16 s. The area has important seismic activities and complex fault systems. The acceleration record in the Van–Muradiye station is very important to seismology of strong ground motion. When records of Muradiye and Van Stations area analyzed in terms of response spectra, both ground motions are below the design spectra defined for 1st degree earthquake zone. Buildings in Van city and Erciş district generally consists of 4–8 storey concrete structures, which is very common in Turkey. Therefore, due to the higher ground acceleration is greater than expected empirical values, the major damages has occurred in buildings.